Impacts From Climate Change and Other Threats Increase for At-Risk Canadian Wildlife

Increasing importance of climate change and other threats to at-risk species in Canada

Catherine Woo-Durand, Jean-Michel Matte, Grace Cuddihy, Chloe L. McGourdji, Oscar Venter and James W.A. Grant

Summarized by Anna Geldert

What data were used? In this study, researchers assessed threats to biodiversity in Canada. They drew upon the methods of a previous study by Venter et al. (2006), which recognized six primary threats to biodiversity in Canada: habitat loss, introduced (non-native) species, over-exploitation (i.e., excessive hunting or harvest), pollution, native species interactions, and natural causes. They also assessed the threat of climate change. In total, researchers assessed threats to 820 species from 12 taxa, including: vascular plants (e.g., trees, flowering plants, ferns, clubmosses, etc), freshwater fishes, marine fishes, marine mammals, terrestrial mammals, birds, reptiles, molluscs, amphibians, arthropods, mosses, and lichens. All of these species were classified as at-risk (in decreasing severity: extinct, extirpated, endangered, threatened, or of “special concern”) by COSEWIC (Committee on the Status of Endangered Wildlife in Canada).

Methods: Between October 2018 and September 2019, researchers examined the COSEWIC website for evidence of Venter et al.’s six primary threats, where threatened species and the reasons they are threatened are cataloged . They looked at COSEWIC’s “Reason for Designation” statement, as well as details from the Assessment and Status Report. Any mention of any of the six major threats was recorded, so that multiple threats could be identified for each species. This data was compared to data from Venter et al. (2006) to determine changes in prevalence over time. Additionally, researchers noted mentions of climate change threats to species on the COSEWIC website. Climate change threats were classified as current, probable, or future based on a list of keywords. All seven of the biodiversity threats were assessed over time by comparing their prevalence to species with multiple COSEWIC status reports, including a total of 188 species.

Results: 814 of the 820 species studied were impacted by at least one of the six primary threats to biodiversity. Habitat degradation was the most significant threat, affecting 81.8% of species, followed by natural causes (51.0%), over-exploitation (46.9%), introduced species (46.4%), pollution (35.1%) and native species dynamics (27.2%). This represented an overall increase in threats compared to Venter et al., though introduced species and natural causes were the only threats that increased with statistical significance. Climate change impacted a total of 37.7% of species, with 13.3% of species impacted by current climate change, and 14.7% and 9.7% that will likely be impacted by probable and future climate change, respectively.

The figure shows a bar graph comparing the prevalence of the primary threats to biodiversity in the modern 2018 study and the 2005 Venter et al. study. In the top right corner, a legend indicates that white bars represent data from 2005, which included 488 species total, and black bars represent data from 2018, which included 814 species total. The x-axis shows the biodiversity threats, including habitat loss, introduced species, over-exploitation, pollution, native species interactions, natural causes, and current climate change. For each threat category, a pair of historical and modern bars are shown, with the exception of current climate change, which only has a bar for 2018. The y-axis is labeled “percentage of at-risk species,” and ranges from 0 to 90, increasing at increments of 10. For modern data, habitat loss is the most prevalent threat, affecting 81.8% of species, followed by natural causes, over-exploitation and introduced species, which all affected roughly 45-50% of species. Pollution and native species interactions (affecting 35.1% and 27.2% of species respectively) were moderate threats, while climate change was the lowest, affecting only 13.3%. For the 2005 Venter et al. data, habitat loss was also the most significant threat and was slightly more prevalent than it is today, affecting 83.8% of species. Native species interactions were also slightly higher in the 2005 study than the 2018 study, though not enough to be significant. All other threats were higher in the modern study, though introduced species and natural causes were the only categories that increased with statistical significance.
Fig 1. Percentage of at-risk species in Canada that were impacted by the six primary threats to biodiversity, comparing modern data from December 2018 and data recorded by Venter et al. in June 2005. The modern threat of climate change is also included, though there is no corresponding 2005 record. N represents the number of species (n=488 in 2005, n=814 in 2018).

The analysis comparing threats to species with multiple COSEWIC status reports found an average increase from 2.5 to 3.5 threats per species in newer reports. The prevalence of many threats also increased significantly over time, including a 27.6% increase in introduced species, a 13.3% increase in over-exploitation, and a 10.1% increase in pollution. Mentions of the threat of climate change also increased from 11.7% in the oldest reports to 49.5% in the newest reports.

Why is this study important? This study reveals that threats to biodiversity continue to increase today, despite protections that have been put in place. In particular, the threat of introduced species has increased significantly in recent years, reflecting rises in globalization and human-environmental interactions. Overall, researchers were surprised by the relatively low percentage of species currently impacted by climate change (13.3%), as this topic has gained so much global attention. The authors suggested the unexplained increase in death by natural causes compared to the Venter et al. report may actually account for impacts from climate change, as climate change has increased the severity of storms, droughts, and other weather events worldwide.

The big picture: This study emphasizes the importance of wildlife conservation, in Canada and all over the world. On-going threats such as habitat loss, pollution and overexploitation continue to impact hundreds of species in Canada, so it is likely that stricter protections are needed to enact effective change. Additionally, this study indicates that climate change is among the most significant threats to biodiversity and is projected to continue increasing in prevalence in the future. Although it was not considered to be one of the six primary threats by Venter et al. in 2005, it should definitely be recognized as one today.

Citation: Woo-Durand, C., Matte, J.-M., Cuddihy, G., McGourdji, C. L., Venter, O., & Grant, J. W. A. (2020). Increasing importance of climate change and other threats to at-risk species in Canada. Environmental Reviews, 28(4), 449–456.

From Lynx to Coyotes: How Climate Change Has Impacted Hare Predation

Climate change increases predation risk for a keystone species of the boreal forest

By: Michael J.L. Peers, Yasmine N. Majchrzak, Allyson K. Menzies, Emily K. Studd, Guillaume Bastille-Rousseau, Rudy Boonstra, Murray Humphries, Thomas S. Jung, Alice J. Kenney, Charles J. Krebs, Dennis L. Murray, and Stan Boutin

Summarized by: Anna Geldert

What data were used? Researchers observed 321 snowshoe hares in southwestern Yukon from 2015-2018. Researchers also monitored changes in weather and snow conditions within the study region, including temperature, snow depth, snow hardness and daily snowfall.

Methods: Hares were captured in live traps and given collars with mortality sensors before being released back into the wild. In the event of hare death, researchers visited the site to identify any predators responsible for the death by looking for tracks, scat, and other indicators in the surrounding area. Researchers recorded data on weather and snow conditions at three different sites throughout the study region on a nearly daily basis, as well as at each kill site. They then used a computer model to compare the likelihood of hare death under different weather conditions (e.g., temperature, snow depth, and snow hardness), and generated a best fit line to model these relationships. Similar models compared weather conditions to hare predation from lynx and coyote, hare death by age group, and hare foraging time by age group. The models were tested by inputting randomized data and estimating uncertainty.

Results: Researchers found that 153 hares died of predation. Lynx and coyote were the most common predators, accounting for 59.4% and 25.5% of deaths respectively. Hare survival was lowest in 2015-2016, countering the predicted increase in hare populations based on predator-prey cycles. Low survival rates were correlated with shallow snow depth and high snow hardness. . The relationships between hare survival and these weather conditions are most likely due to changes in predator threats, not changes in foraging behavior. While lynx predation remained relatively constant across a wide range of snow conditions, coyote predation increased by a factor of 1.155 with higher snow depth and 1.244 with lower snow hardness.

The figure graphs the relationship between snow depth and hare predation risk by lynx and coyotes. The x-axis is labeled “snow depth (cm),” and ranges from 20 to 70, increasing at intervals of 10. The y-axis is labeled “risk (relative to baseline),” and ranges from 0 to 15, increasing at intervals of 5. A legend indicates that the purple line represents risk from lynx while the red line represents risk from coyotes. At a risk measurement of 1, a dotted line runs horizontally (slope=0) across the graph; this represents baseline risk. The risk from lynx almost exactly coincides with the baseline risk, indicating that snow depth has little impact. On the other hand, the risk for coyote has an inverse relationship with snow depth. At a snow depth of 20 centimeters (the lowest depth represented), risk from coyotes is approximately 10. The risk line then decreases exponentially, crossing the baseline risk at approximately 35 centimeters and plateauing close to a risk of zero around 50 centimeters.
Fig. 1. Hare predation risk by lynx and coyotes at different snow depths. The dotted line represents a baseline risk, while shaded regions represent standard errors.

Why is this study important? This study is an important example of the cascading effects that climate change can have on ecosystems in the boreal forest. Increasing temperatures due to climate change have altered traditional snow conditions in the Yukon, leading to lower snow depth and snow hardness in recent years. Coyotes – who, unlike lynx, are not well adapted to harsh winters – have gained a relative advantage in these milder conditions, leading to increased hare predation. Risk has increased so much, in fact, that they disrupted the natural rise and fall of hare populations due to existing predator-prey cycles. If these trends continue, they could potentially impact other aspects of boreal forest ecosystems.

The big picture: It is widely recognized that climate change threatens the survival of many species and ecosystems around the globe. However, this is most often talked about in terms of direct threats, such as increasing temperature, increasing severe weather conditions, etc. This article demonstrates that a further concern, particularly in boreal forests, is the impact of changing climatic conditions on food webs and predation threats. Further research is needed to determine if the changing predator-prey relationships between hares and coyotes in this study are consistent in other regions of boreal forest, and whether similar trends are reflected in other biomes as well.

Citation: Peers, M. J. L., Majchrzak, Y. N., Menzies, A. K., Studd, E. K., Bastille-Rousseau, G., Boonstra, R., … Boutin, S. (2020). Climate change increases predation risk for a keystone species of the boreal forest. Nature Climate Change, 10(12), 1149–1153.

How climate change is affecting Pacific species

Assessing the vulnerability of marine life to climate change in the Pacific Islands region

Giddens J, Kobayashi DR, Mukai GNM, Asher J, Birkeland C, Fitchett M, et al.

Summarized by Habiba Rabiu, a student of environmental geosciences at Fort Hays State University. Habiba is interested in all aspects of environmental science and conservation & sustainability. She would like to work in educating others about those topics. In her free time, she likes to read, write, and bake.

What data were used? The researchers assessed 83 species grouped into six functional groups based on range size and habitat: pelagic, shark, deep-slope, coastal, coral reef, and invertebrate species. The “coral reef” group of fishes contained many species, so it was further divided into JEGS (Jacks, Emperors, Groupers, Snappers), parrotfishes, surgeon fishes, and “other coral reef” fishes. The species were chosen based on expert opinion, importance of their ecosystem function, records of food fish, and cultural and conservation importance. The species came from a wide range of locations in the Central, West, and South Pacific Ocean. 

To determine the climate change vulnerability of the species, the researchers considered two components: exposure and sensitivity. Exposure was defined as to what degree an organism is likely to experience a negative change in a particular physical variable. Sensitivity was considered a biological trait-based variable, which the researchers determined by review of existing literature and expert opinion. 

Methods: To assess exposure, data from various sources was compiled based on certain variables that were the most significant for species living in the Pacific Islands Region: temperature (surface and bottom), salinity (surface and bottom), ocean acidification (pH), mixed layer depth, precipitation, current velocity, wind stress, surface oxygen, sea level rise, wave height, chlorophyll, and primary productivity. To determine sensitivity, experts were asked to identify the six most important sensitivity attributes for each species out of 12: habitat specificity; prey specificity, complexity in reproductive strategy, sensitivity to ocean acidification, early life history survival and settlement requirements, dispersal of early life stages, sensitivity to temperature, population growth rate, stock size/status, adult mobility, spawning cycle, and other stressors (including habitat degradation, pollution, disease, or changes in the food web). 

For each species, a component score was calculated for both exposure and sensitivity based on the number of factors/attributes that passed a certain threshold. Then, the overall climate change vulnerability rank was calculated by multiplying the exposure and sensitivity component scores. The numerical values for the climate vulnerability rank were the following: 1–3 (low), 4–6 (moderate), 8–9 (high), and 12–16 (very high).

Grid where each square shows what percentage of a species is considered “moderate”, “high”, or “very high” in vulnerability. The squares are shown in greyscale, with 0% being white and 100% being black. Approximate values: Pelagic: 90% moderate, 10% high Shark: 10% moderate, 30% high, 60% very high Deep slope: 60% moderate, 40% high Coastal: 100% moderate Coral reef JEGS: 80% moderate, 20% high Coral reef parrotfish: 60% moderate, 30% high, 10% very high Coral reef surgeonfish: 25% moderate, 75% high “Other” coral reef: 65% moderate, 25% high, 10% very high Invertebrate: 10% moderate, 30% high, 60% very high
The percentage of species within the group that fell within each vulnerability ranking.

Results: All species ranked “very high” in the overall exposure component of vulnerability. It was determined that this was caused by three influences: decrease in oxygen concentration, rise in sea surface temperature, and increase in ocean acidification (decrease in surface pH). In the sensitivity component, it was found that the groups that were made up of larger-bodied species shared similar sensitivity scores, while the groups with smaller and site-attached species tended to differ.

In the overall assessment of climate change vulnerability, the species showed a wide range in vulnerability across the functional groups. The larger and more wide-ranging pelagic and coastal species were scored as the least vulnerable, while the smaller and more site-attached species (small coral reef fishes and invertebrates) were the most vulnerable. Some groups had a more general ranking across all the included species (for example in the coastal group all the species were ranked as “moderate”), while in others there was a wider distribution across vulnerability rankings. 

Why is this study important? Most studies on the effect of climate change of ocean ecosystems focus on a particular or particular type of species, or on singular factors. This study assessed many factors affecting many species, which creates a more all-encompassing view of the effects of climate change and enables focus on the ecosystem as a whole rather than looking at it in pieces. 

The big picture: Well-functioning ocean ecosystems are essential to the health of the planet, but there is still a lack of both information about the ecosystems and the organization and usage of that information. Collecting data on marine species and the environmental factors that affect them (and to what degree) is necessary to their preservation.

Citation: Giddens J, Kobayashi DR, Mukai GNM, Asher J, Birkeland C, Fitchett M, et al. (2022) Assessing the vulnerability of marine life to climate change in the Pacific Islands region. PLoS ONE 17(7): e0270930.

Feathers: The Difference Between Life and Death for Triassic Dinosaurs

Arctic ice and the ecological rise of the dinosaurs

Paul Olsen, Jingeng Sha, Yanan Fang, Clara Chang, Jessica H. Whiteside, Sean Kinney, Hans-Dieter Sues, Dennis Kent, Morgan Schaller, Vivi Vajda

Summarized by Blair Stuhlmuller

What data were used? Researchers used three main sources of data. First, they looked at ancient lake sediments preserved in sedimentary rocks in the Junggar Basin, China. They then analyzed fossilized dinosaur footprints and other signs of “dinoturbation,” or the reworking or movement of soils and sediments by dinosaurs, in sedimentary rocks across the northern latitudes of China. The final set of data used was the phylogenetic tree of life for extinct and living dinosaurs, reptiles and mammals. A phylogenetic tree is a diagram showing lines of evolutionary descent of different organisms from a common ancestor. They used a preexisting phylogenetic tree but mapped preserved evidence of feather-like features and other key traits onto the extinct and living branches of organisms. This was done in order to make inferences about the presence of feathers and similar traits in extinct organisms where no fossil evidence exists yet to prove the presence of these features. 

Methods: The researchers analyzed the grain size of the sedimentary rocks recovered from the Junggar Basin in China. These lake sediments were deposited millions of years ago in the Late Triassic (~210 million years ago) and Early Jurassic (~200 million years ago) and thus can reveal much about the climatic conditions during the End Triassic Extinction. The location of these sediments, the Junggar Basin, is also of particular importance. Using already established continental reconstructions for the Mesozoic (in other words where Pangea, our most recent supercontinent, was located), researchers determined that the Junggar Basin, currently located in the high latitudes of China (around 43°N latitude), would have been north of the Arctic Circle at about 71°N paleolatitude during the Triassic. 

Lastly, the researchers used a generalized phylogenetic bracket analysis in order to infer certain traits (in this case the presence of some sort of feather-like feature or ‘protofeathers’) for which there is no current physical fossil evidence. This analysis revealed that feathers would be a primitive feature shared by many groups of dinosaurs. 

Results: Grain size analysis revealed that most of these lake sediments were comprised of fine grained (~0.1 to 63 μm) mudstones with some larger grain exceptions. These smaller amounts of larger grains (small rock pieces upto 15mm in size) are indicative of ice-rafted debris. Ice acts as a raft that can pick up sediment and larger debris that comes in contact with it. This sediment is later deposited in the middle of a body of water like an ocean or lake. Thus ice-rafted debris (IRD) is any sediment that has been transported by floating ice. The origin of this particular ice-rafted debris is interpreted as seasonal ice coverage along the coastlines of ancient lakes. As the ice formed, it would grab larger grains and debris and then break off and drift out over the lake, slowly melting as the seasons changed. As the ice melts, it deposits the larger debris among the fine silts that typically accumulate at the bottom of lakes. This contradicts the long upheld mental image of dinosaurs stomping through a tropical warm climate throughout the Triassic and really the whole Mesozoic Era. The Late Triassic was one of the few times in Earth’s history that there is no evidence of ice sheets at the poles. However, these researchers claim that despite the high levels of carbon dioxide (CO2) in the atmosphere and the resulting greenhouse conditions during that time, there were freezing seasonal temperatures at high latitudes as supported by the ice-rafted debris they found. 

Large plant eating dinosaurs during the Triassic were more commonly found in the forested higher latitudes as supported by the type of dinosaur footprints and ‘dinoturbation’ found in outcrops in modern day China. While actual fossil evidence of proto-feathers has not been found on fossils of these large herbivorous dinosaurs, the phylogenetic bracket analysis posits that they were in fact insulated by some sort of feather structure and thus were well suited to the seasonal winters. This enabled these animals to take advantage of the more abundant and stable plant life of the higher latitudes and potentially survive one of the worst mass extinctions in Earth’s history. 

Groups of living and extinct mammals, reptiles and dinosaurs are shown and presence or absence of feather-like features are indicated for each group through various symbols and letters. In summary, feathers are thought to be a primitive feature, meaning that it shows up early on the evolutionary tree.
This figure shows the Phylogenetic Bracket Analysis that compared groups of dinosaurs, reptiles and mammals and mapped out feather-like features. The different feather types are shown at the top and represented by small images and numbers. 0 or ? represents their prediction that protofeathers for insulation should have been present, 1 represents bristle scales, and 2-6 represent various protofeathers based on fossil evidence. The P symbol represents those features that were predicted due to this phylogenetic bracket analysis.

During the End Triassic Extinction, incredibly large volcanic eruptions, called the Central Atlantic Magmatic Province or CAMP, were going off. These eruptions would have contributed to global warming long term but on  shorter decadal timescales, they would have caused volcanic winters.  As the eruptions periodically belched out sulfur aerosols, light would have been blocked and the atmosphere would have cooled upwards of 10 ℃. Dinosaurs previously adapted (feathered and insulated) to the seasonal winters of the high latitudes survived and even spread out toward the now cooler tropics. 

Why is this study important? This study contradicts the public’s perception of dinosaurs only thriving in a tropical climate and helps provide possibly the first empirical evidence for freezing temperatures and winter conditions in the Triassic rock record. It also provides a plausible explanation for why some dinosaurs went extinct at the end of the Triassic while others did not. Feathers were the key for survival in the volcanic winters that plagued the End Triassic Extinction. They offered life saving insulation that allowed some dinosaurs to survive the extinction and then reign supreme for the rest of the Mesozoic. That is, until the meteorite wiped out all non-avian dinosaurs 135 million years later. 

The big picture: The distribution and type of life currently on our planet is in part due to what was able to survive the Triassic Extinction. Birds are the most biodiverse group of vertebrates (besides fish) and have over two times the number of species than mammals. Thus, feathers emerged as a life saving feature in the Triassic and they continue to reign supreme in modern times.  

Citation: Olsen, P., Sha, J., Fang, Y., Chang, C., Whiteside, J. H., Kinney, S., Sues, H.-D., Kent, D., Schaller, M., & Vajda, V. (2022). Arctic ice and the ecological rise of the dinosaurs. Science Advances, 8(26).

A Tooth for a Tooth: Evolutionary Development of Dental Structure Based on Common Mutations of the Bearded Dragon

The developmental origins of heterodonty and acrodonty as revealed by reptile dentitions
by: Salomies, L., Eymann, J., Ollonen, J., Khan, I., & Di-Poï, N.

Summarized by Kat Cool, a fourth-year geology student studying at the University of South Florida. She is pursuing her major with a geophysics emphasis and a minor in Geographic Information Systems and Technology. She is also the proud owner of three bearded dragons that have inspired her interest in this article. In the future she hopes to study meteorology at the graduate level and hopefully specialize in severe weather forecasting.

What data were used?  Discovering evolutionary mechanisms for dental changes could have implications in phylogenetics, taxonomy, and ecological identification of animals that are extinct as well as those still here today. This could be especially useful in key taxa groups that have a poor fossil record or a more mysterious evolutionary history. One group of reptiles the lepidosaurs (snakes and lizards), are a perfect candidate for this research due to their diversity in dental structures. Mutations in the genetic codes of lepidosaurs could provide key insight to the mechanisms behind their dental evolution. One mutation commonly seen is variation of the ectodysplasin (EDA) pathway. This mutation can be observed in many vertebrate species, including humans, and causes changes in the appearance of hairs, feathers, scales, nails, and teeth. The subject for this study group will be the humble bearded dragon (Pogona vitticeps), due to the different stages of EDA mutations one can easily observe. Since this mutation is also known to influence tooth development, scientists decided to look at the dental structure of these morphs as well.

Methods: To analyze the tooth development of bearded dragons, scans were taken to take a closer look at the EDA mutation both during embryonic development and after the hatchlings have emerged from the egg. Then 3D-rendered bearded dragon skulls were compared at 14 days after hatching. The teeth of the wild-type bearded dragon, the leather-back (Sca/+), and the silk-back (Sca/Sca) were then compared based on the appearance (or lack thereof) of pleurodont and acrodont teeth (Figure 1 for images and descriptions of teeth; Figure 2 for images of the lizards).

Figure 1 (A) shows diagrams of different tooth structures. The jawbone, dental pulp, dentine, and enamel are color coded in each of five tooth structures. Bearded Dragons have two of these types of teeth. The first is pleurodont teeth which are shown in the diagram by having one side of the tooth connected to the jawbone while the other side is exposed. The second type of teeth in this diagram of interest to us are the acrodont teeth. The acrodont teeth are shown in the diagram by having the jawbone go about halfway up on both sides of the tooth.(B) A phylogenetic tree showing families and subfamilies of Acrodonta connected by lines based on their relationship. The tree stems off into two main groups: The Agamidae and the Chamaeleonidae. The Lepidosauria reptiles are on the Agamidae side of the tree. (C) 3D-rendered skulls of lizards representing the main Acrodonta subfamilies. Each skull shows an X ray of the bones and teeth in the lizard’s skull from a straight on angle as well as from the side of a lizard’s skull. The anterior pleurodont teeth are highlighted in red and the acrodont teeth are noncolored
Figure 1 (A) Different tooth attachment types in vertebrates. There are two main types of teeth present in these reptiles: Pleurodont teeth are set on the inside jaws, while acrodont teeth are generally larger and attach to the jaw by connective tissue. Pleurodont teeth are accepted as the norm for Lepidosauria; however, there are certain families like Agamidae, Chamaeleonidae, and Trogoniphidae that show an understudied mix of pleurodont and acrodont teeth or a singular acrodont tooth. Another unique feature of living lepidosaurs is the lack of or absence of tooth replacement in acrodont teeth. (B) Phylogenetic tree showing families and subfamilies of Acrodonta. The Lepidosauria clade includes the Rhynchocephalia order with the single surviving species, the Tuatara, as well as the Squamata order with many living members like lizards and snakes (C to J) 3D-rendered skulls of lizards representing the main Acrodonta subfamilies


Results:  It was found that wild-type hatchlings had eight acrodont teeth and one small pleurodont tooth per jaw. There is also a central egg tooth on the middle jaw bone (premaxilla) that is replaced with a pleurodont tooth soon after hatching. However, it was found that both scaleless bearded dragons (Sca/+ and Sca/Sca) often did not have pleurodont teeth on their premaxillary bone, leading to about half of juvenile dragons with an EDA mutation having few or no teeth on this bone at all. It was also found that bearded dragons with EDA mutations had fewer teeth in total than the wild-type dragons, as well as wider teeth. These observations were more evident in the silk-back juveniles (Sca/Sca).

Figure 2 Two female bearded dragons sitting next to each other on a pillow. They are laying on their stomach with their heads looking forward. Their round abdomen consolidates by their hind legs where their long tails extend out of frame. The bearded dragon on the left is a wild type bearded dragon. She is yellow and brown in color and her spikes are much more apparent than the bearded dragon on the right. The bearded dragon on the right is more orange and tan and lacks the same spiky texture as the other bearded dragon.
Figure 2. An image of a wild-type bearded dragon (left) and a leather-back bearded dragon or Sca/+ (right). If you are familiar with bearded dragon morphology, the EDA mutation is responsible for two of the most well-known morphs: the ‘leather-back’ and the ‘silk-back’. The leather-back bearded dragon (Sca/+) has one copy of the EDA mutation, resulting in reduced scale size than the bearded dragon’s without this mutation (also called wild type in this study). This reduction in scales creates a leathery appearance, earning these little mutants the colloquial name ‘leather-back’. The silk-back (Sca/Sca) bearded dragon has two copies of the EDA mutation: one from each parent. The result is a more extreme version of the features observed in the leather-back dragons: instead of reduced scales there appears to be an absence of scales all together.

Why is this study important: At the time of these results, the scaleless bearded dragon was the first known example that researchers had found of a gene mutation that resulted in position changes in teeth. These results provide a contrasting prospective to results found when studying the dental structures of mice. While the research with mice indicated that vertebrate tooth position was based on a complex model of gene expression patterns, the scaleless bearded dragon data suggests tooth identity can be produced with the modification of a simple gene.

The big picture: The simple modifications of the EDA gene had very observable effects on the position of the teeth. Though more research is necessary, this study shows that through observations of living species today, mechanisms of dentition diversity can be discovered through many different approaches to better understand evolutionary development. Though it is sometimes a long, slow process that can span across millions of years, it can also sometimes be isolated to a change in a single gene at a specific moment. 

Citation: Salomies, L., Eymann, J., Ollonen, J., Khan, I., Di-Poï, N. (2021) The developmental origins of heterodonty and acrodonty as revealed by reptile dentitions. Science Advances 7(51). DOI: 10.1126/sciadv.abj7912

Horseshoe Crabs Teach Us About Heterochrony

A new method for quantifying heterochrony in evolutionary lineages

James C. Lamsdell

Summarized by Anna Geldert

What data were used? A total of 20 traits that display heterochronic conditions for 54 species of horseshoe crabs (both living and extinct) were studied. 256 traits were examined and documented in these horseshoe crabs and 99 related species to make a character matrix. Of the 54 horseshoe crabs, environmental data from previous studies was also collected to determine the species’ habitat..

Methods: This paper presents a new method for quantifying heterochrony through a process called “heterochronic weighting.” Heterochrony is a process that alters the timing and length of developmental stages of organisms, and is characterized as either paedomorphism (retaining juvenile characteristics as an adult) or peramorphism (developing beyond what is seen in related species; more “adult-like”.) For each characteristic, paedomorphic traits were assigned a score of -1, peramorphic traits were assigned a score of +1, and neutral characteristics were assigned a score of 0. The heterochronic weighting of a species was then defined as the sum of all scores divided by the number of characteristics. The author also looked at heterochrony in an evolutionary context. He generated a probable evolutionary tree using a computer model that related species based on shared traits. He then used the tree to determine the heterochronic weighting of the clade (i.e., evolutionary group) by averaging those of the individual species. The differences in heterochronic wightings between habitat preferences (marine or nonmarine) and clades were tested for statistical significance. Lastly, the author tested to see if there were concerted trends towards paedomorphy or peramorphy in each clade.  The evolutionary tree was also tested to determine the most likely habitat for ancestry species of horseshoe crabs, which gave insight to when shifts from marine to nonmarine environments occurred.

The figure shows a diagram of the heterochronic conditions as seen in limb length. Three drawings of the underside of the head shield of a horseshoe crabs are shown side by side. There is one small pair of claw-like appendages towards the front of the head shield and ten longer walking limbs visible. The first diagram has the longest limbs, extending outside the shell. It is labeled “-1,” representing a paedomorphic condition. The second diagram, labeled “0” for a neutral condition, has shorter limbs that are all contained under the shell, though some extend nearly to the edge. Lastly, the final diagram is labeled “+1” for a peramorphic condition. The limbs of the crab in this diagram are the shortest, spanning only a third to a half the width of the shell.
Fig 1. Variations in limb length serve as an example of a heterochronic characteristic in horseshoe crabs. Paedomorphic (-1), neutral (0), and peramorphic (+1) conditions are shown.

Results: Overall, heterochronic weighting proved successful in quantifying the paedomorphic and peramorphic changes in horseshoe crab characteristics. Of the four clades studied, two (Bellinurina and Austrolimulidae) were found to have statistically significant occurrences of heterochrony, with Bellinurina trending towards paedomorphic characteristics and Austrolimulidae trending towards peramorphic characteristics. The Paleolimulidae clade was characterized as having non-significant  heterochronic weightings, while the Limulidae showed a slight peramorphic trend that could be explained by random evolution, not necessarily a concerted trend. More extreme heterochronic weightings (both positive and negative) were associated with the evolutionary transition to non-marine habitats, as was the case for both Bellinurina and Austrolimulidae clades.

Why is this study important? First and foremost, this study is important because it developed a method for quantifying instances of heterochrony, which has not been studied in a combined phylogenetic and ecological context. This gives insight into the interaction between ecology and heterochrony, especially as an evolutionary mechanism. For example, it is noteworthy that both clades that transitioned to non-ancestral nonmarine environments (Bellinurina and Austrolimulidae) experienced higher rates of heterochrony, suggesting that greater ecological change may correlate with increased likelihood for developmental changes in horseshoe crabs. However, it is also important to recognize that environmental affinity is not the only factor influencing heterochrony, or else Bellinurina and Austrolimulidae would have developed in the same way, trending towards either paedomorphic or peramorphic characteristics. The opposite trajectories of the two clades suggests that environmental pressures may increase heterochrony, but underlying genetic factors determine the direction of development.

The big picture: The process of heterochronic weighting developed in this study has the potential to advance the field of paleobiology, as the author was now able to quantify paedomorphy and peramorphy throughout evolutionary history. This allows for a deeper understanding of the relationship between an evolutionary mechanism and other factors, such as ecological affinity or evolutionary relatedness. However, as this study is so far the only study to have employed heterochronic weighting so far, the success rate of this process is limited to horseshoe crabs. Therefore, further research is needed to determine the effectiveness of this method for heterochrony in other species groups.

Citation: Lamsdell, J. C. (2020). A new method for quantifying heterochrony in evolutionary lineages. Paleobiology, 47(2), 363–384.

Small Friends Help Sea Anemones Survive the Heat

Microbiota mediated plasticity promotes thermal adaptation in the sea anemone Nematostella vectensis

Laura Baldassarre, Hua Ying, Adam M. Reitzel, Sören Franzenburg, Sebastian Fraune

Summarized by Blair Stuhlmuller

What data were used? Researchers used cloned Nematostella vectensis, a sea anemone found in estuaries and brackish water environments of the US and UK. N. vectensis hosts many helpful small friends, or symbiotic microbiota. In other words, microscopic organisms that live on the host anemone and help it deal with environmental stressors like temperature changes. These symbionts can be passed onto the offspring from the parent anemone or be acquired from the environment during development. The symbiote assemblage can also change during an anemone’s lifetime in response to changing environmental conditions. The researchers looked at the composition of the microbial communities, the genetics of the host anemone and mortality rates at different temperatures.

Methods: First, in order to control for genetic diversity between individuals, the researchers created clones from a single female polyp (anemone). These individuals were divided into different test groups based on temperature–low (15℃) temperature, medium (20℃)  temperature and high (25℃) temperature–that were studied over the course of three years. Each test group had 5 cultures of 50 cloned anemones.

Results:  After 40 weeks and after 132 weeks, the polyps were exposed to high heat stress (6 hours at 40 ℃) and mortality was measured. In both tests, all of the polyps in the low temperature group died. The high temperature group had the highest survival rate after 132 weeks. Polyps in the high temperature group experienced a lower mortality rate overall, but were also 3 times smaller, and asexually reproduced 7 times more rapidly than those in the low temperature group. These results show that long-term temperature differences have a great impact on heat tolerance, organism size, and reproduction rates.

Next, changes in the microbial symbiont communities were measured through 16S rRNA sequencing (or the process of reading the small section of ribosomal RNA molecules that is in charge of turning the genetic code into actual functioning cell parts) at the 40, 84 and 132 week intervals. The results showed that both the temperature and exposure duration to said temperature had a significant effect on the microbial community composition. Three distinct microbial communities were found for each temperature test group and these communities stabilized within the first two years. 


A bar graph showing the survival rate of each temperature group after experiencing heat stress. After 40 weeks, the survival rate of the group acclimated at 15℃ is 0, the second group, acclimated at 20℃ has a survival rate of 70% and the third group, acclimated at 25℃, has a survival rate of 30%. After 132 weeks, both the 15℃ acclimated group and the 20℃ acclimated group experienced a 0% survival rate. Only the last group, acclimated at 25℃, remained with a survival rate of nearly 100%.
Figure a shows the survival rate of each temperature group (AT is acclimated temperature) to heat stress. Heat stress experiments were conducted at 40 weeks of acclamation (woa) and 132 weeks.

Third, all the active genes (or genes that are making mRNA) were analyzed in order to see if any changes occurred. One polyp from each culture was selected. The polyp’s mRNA was extracted and sequenced or read. Gene expression, or what genes are actively determining an organism’s features and functions, can be influenced by outside factors and can cause changes to an organism’s phenotypes, or physical characteristics, within its lifetime. While the actual DNA sequence is not changed, certain genes can be turned on or off that can then help or hurt the organism. In this study, polyps in the high temperature group experienced a significantly increased expression of genes involved with immunity, metabolism, outer skin cell production and other positive changes. 

Lastly, researchers wanted to determine if the microbial community and thus changes in gene expression were transferable and could increase the heat tolerance of new individuals and future generations of anemones. Thus they transplanted the temperature adapted microbial communities/symbionts to new, non temperature adapted polyps which were cloned from the same female as the experiment population. Then the heat tolerance of the new polyps were tested. Survival rates of the polyps with transplanted microbial communities depended on the source of the transplanted microbial community. Polyps with microbes from the high temperature group had an 80% survival rate, a significantly higher rate compared to the 33% of the polyps with the low temperature microbes. This shows that microbial transplants could prove to be a quick and effective way to help certain organisms cope with environmental changes. 

The researchers also tested if both the gene expression and microbial communities could be naturally transferred from one generation to the next. rRNA sequencing revealed that large parts of the parent microbial community were successfully transplanted to the offspring. The offspring were then subjected to high heat stress. The offspring from the high temperature group showed a significantly higher survival rate compared to the offspring from both the low and medium temperature groups.

Why is this study important? Members of the Cnidarian phylum like corals and sea anemones are under threat due to rapid climate change. Warming water temperatures are causing coral bleaching and other harmful effects. Since coral and many anemones are mostly sessile, or non moving, when mature, they only have two options–adapt or die. And with climate changing so quickly in recent decades, one might expect extinction to be the more likely option for many species. Adaptation is typically limited by random mutations and natural selection, neither of which happens overnight. However, this study shows how adaptation can happen within just one generation. 

Sessile animals that host a range of symbiotic microbiota exposed to high water temperatures can adapt and become more heat stress resistant. Microbes tend to have much faster generation times and can thus evolve more quickly than their hosts. These microbes can then influence the gene expression of their host by turning on or off certain genes further helping the host to survive and adapt during its lifetime. Most excitingly, these changes in gene expression and microbial communities can be passed to the next generation. This study also helps pave the way towards assisted evolution and potentially huge successes in coral conservation. Heat tolerant microbial communities could potentially be selected for in the lab and then transplanted to wild populations. This would allow scientists and conservation groups to improve the fitness of wild populations quickly and effectively help counter the effects of climate change. 

The big picture: Climate change is a looming threat especially for those living in the oceans. As ocean temperatures rise, many marine species will likely migrate towards the poles in order to remain in their desired temperature ranges. However, sessile or mostly non-moving marine organisms like sponges, coral and sea anemones will have a harder time doing that as many are only mobile during their planktonic larvae stages. This study gives a glimpse of hope that these animals will be better able to adapt and survive than previously expected. This study specifically shows that animals exposed to high temperatures, like N. vectensis, can quickly become more heat stress resistant as the symbiotic microbiota shift and adapt. Most importantly these high heat tolerances can be passed to other organisms and future generations. These lab results are mirrored by long term observational studies that show wild populations becoming less heat sensitive than past generations. Overall, this has huge positive conservation implications for coral reefs and other sessile marine communities as climate rapidly changes.

Citation: Baldassarre, L., Ying, H., Reitzel, A.M. et al. Microbiota mediated plasticity promotes thermal adaptation in the sea anemone Nematostella vectensis. Nature Communications 13, 3804 (2022).

How Ancient Ocean Chemistry Might Have Increased Complexity of Life

Ediacaran Reorganization of the Marine Phosphorus Cycle 

Thomas A. Laaksoa, Erik A. Sperling, David T. Johnstona, and Andrew H. Knoll

Summarized by Makayla Palm

What data were used? The purpose of this study was to measure if changes in the phosphorus cycle were linked to changes in the chemical composition of ocean water hundreds of millions of years ago. The phosphorus cycle is the study of the element phosphorus as it travels from deep-sea storage and rock formations into organic life, and back to the seas again. Why study phosphorus in the first place? Phosphorus is essential to life because it is an important component in DNA and RNA structure. Specifically, at the end of the Ediacaran (~625–542 million years ago or mya), there was a jump in complexity in the fossil record (i.e., life became more complex) found in the transition from the Ediacaran to the Cambrian (~542–485 mya); it may be the case that this change in phosphorus can help us understand the changes to life on Earth during this time. Previously collected phosphorite samples (rocks with a high phosphorus content) and newly found samples from the Doushantuo Formation (Ediacaran, China) were used in this study. These phosphorite samples were examined for the following: evaporite volume, strontium isotope ratios, and content of phosphate. Changes in these samples’ ratios and concentrations allow researchers to hypothesize the impacts on water and life during the Ediacaran. Originally, scientists thought the changes may have been due to increased weathering of rocks, but researchers in this study hypothesized that there may have been more to the story. 

Methods: Researchers from this study hypothesized that a change within deeper Ediacaran ocean chemistry may be the cause for the phosphorus cycle change. They tested this hypothesis by using the variables collected (e.g., isotopes) in an equation that measures the possible effects of the phosphorus evaporite remineralizing into phosphorite (typically how phosphorus is stored in the ocean) This equation measures the amount of phosphorus taken out of the storage bank by measuring the fraction of total organic phosphorus that is removed in relation to the amount of phosphorus that reverts back to its original form in the storage bank. 

Results: The changes in ocean chemistry can be found on the atomic scale, where there are electron acceptors (also known as oxidizers) and electron donors (or reducers). The ocean, having been in a state of consistent reducing reactions, may have shifted to have more oxidizers, which would have increased remineralization – specifically, phosphorus remineralization. This remineralization would explain the difference that eventually modified the Ediacaran phosphorus cycle to the modern-day phosphorus cycle. In order for phosphorus to reduce, something needs to accept its electron. In the absence of oxygen (which early Earth was lacking in for billions of years), research indicates sulfate may be a suitable candidate. Samples of sediment did not indicate a change in phosphorus content, so the hypothesis was not supported. This means that the phosphorus was likely staying within the same system and being removed. The phosphorus cycle, similar to the water cycle or carbon cycle, describes the formation, use and recycling of phosphorus from the oceans, to land, and back to the ocean. The data from this study indicate that upwelling, the mixing of nutrients from the bottom of the ocean back to the top, is the reason for increased phosphorus. Upwelling can be caused by deep water currents coming into contact with continents, where cold, nutrient rich water is propelled closer to the surface and warms. The increased upwelling makes sense in the phosphorus cycle because of the extra circulation happening, which would explain the increased presence of phosphorus without an added source of the element. 

This figure represents three different kinds of information collected over the same period of time. The top graph is a bar graph that measures the amount of phosphate evaporite that was removed and not returned to the phosphorus storage bank. The middle bar graph measures the total amount of phosphate resources stored in the form of P2O5. This graph represents the amount in millions of tons. The line graph at the bottom of the figure represents the number of strontium isotopes found within the rock samples. This graph represents inconsistent intervals of small increasing and decreasing values, showing an overall increase through time in each graph. Across all three graphs, columns highlight the appearance of phytoplankton and large animals within the fossil record. The appearance of phytoplankton is approximately 700 million years ago, and the appearance of larger animals is around 720-699 million years ago. The appearance of both is marked by horizontal black bars at the bottom; with each appearance, there is an uptick in strontium 87. More complex life is marked by more phosphate and evaporites. These bars represent the appearance of organisms in all three line graphs.
The figure represents the three different kinds of data discussed in the paper. The top demonstrates the volume ( km cubed) of phosphorite evaporite, with a general trend of increasing evaporite over time.The middle graph represents the amount of phosphate resources stored in the “storage bank” in the ocean (in millions of tons). The bottom graph represents the change in Strontium isotopes, with ebb and flow in value over time, with a general trend that after a strong dip ~ 700 million years, trends upward. Ice ages are indicated with gray vertical bars across all three graphs, indicating a change in ecosystem. The dark horizontal bars at the bottom of the figure indicate when the appearance of phytoplankton and macroscopic animals occur, which is ~ 680 million years for the phytoplankton and ~ 650 million years for the macroscopic animals. The vertical gray shading represents Ice Ages that occurred in the timeline measured on the figure. The figure as a whole points to the correlation of increased phosphorite levels and the first appearance of relatively large animals in the fossil record.

Why is this study important? This study aims to see why the change in phosphorus occurred to better understand the geologic context that precedes a big change in the fossil record. There is a large jump in complexity from Ediacaran to Cambrian organisms, and ocean chemistry (changes in phosphorus levels in this case) may have had something to do with that. The cycling of phosphorus because of upwelling, influenced by continental placement, could have been a driving reason behind these big changes, ecological and evolutionary. 

Big Picture. This study proposes a mechanism for the change in the phosphorus cycle that is observed between the phosphorus cycle today and the phosphorus cycle of the Ediacaran as we know it. Many questions still exist as to how oceans have changed through geologic time and this study provides an important piece to the puzzle. Understanding changes in ocean chemistry, too, better helps scientists understand how life evolves in response. 

Citation: Laakso, Thomas A., et al. “Ediacaran Reorganization of the Marine Phosphorus Cycle.” Proceedings of the National Academy of Sciences, vol. 117, no. 22, 2020, pp. 11961–11967., 

Early childhood and connecting with nature

Effect of environmental education on the knowledge of aquatic ecosystems and reconnection with nature in early childhood

Maria João Feio, Ana Isabel Mantas, Sónia R. Q. Serra, Ana Raquel Calapez, Salomé F. P. Almeida, Manuela C. Sales, Mário Montenegro, Francisca Moreira

Summarized by Habiba Rabiu, a student of environmental geosciences at Fort Hays State University. Habiba is interested in all aspects of environmental science and conservation & sustainability. She would like to work in educating others about those topics. In her free time, she likes to read, write, and bake.

What data were used? In 2018, the environmental educational project CresceRio was created in the city of Coimbra, Portugal, to encourage the populace to reconnect with nature, preserve and protect the streams found in the area, and teach children about the importance of the streams and preserving green and blue (terrestrial and aquatic) ecosystems. Most children who live in the city had little exposure to nature and expressed fear and incorrect knowledge about the streams and rivers in their area. It was proposed that introducing field trips to natural areas and hands-on activities to school curriculums would be a low cost yet effective way to improve their relationship with the natural world. 

Methods: Over the course of 14 months, the researchers conducted several surveys with a class of 24 students (aged 5–6 at the beginning of the program). At particular intervals (labeled M), the children were questioned about five main topics: their identification and background, their awareness of streams and rivers, their recognition of the biodiversity that existed in the rivers, their awareness of various factors negatively affecting the rivers, and their awareness of the ecosystem services provided by rivers to the population. 

M1 occurred at the beginning of the program (September 2018) and was followed the next month by a trip to a stream outside of the city that was not seriously affected by urban activity. M2 occurred in November 2018, and the students visited an urban stream that was visibly affected by urban activity including construction, removal of trees, and litter. In February 2019, the students participated in a laboratory class where they examined fallen leaves and were taught to identify various invertebrates and algae using microscopes. M3 took place in March 2019, followed by a workshop in June 2019 where they reviewed photos and videos and discussed what they learned from their previous activities. In October 2019 they visited another urban stream that was slightly less altered than the one they visited before. The last survey was conducted in November 2019 and was done in the form of group interviews. 

Results: The three main takeaways that the researchers identified were 1) that children in urban areas have little contact with or knowledge of nature, 2) after a year of exploring the streams and their ecosystems their knowledge increased (both about the ecosystems and the problems they face) and their fears decreased, and 3) the long duration of the program was key as changes in their attitude and knowledge only became clear after a few activities.

In all five categories explored (personal background and experience, awareness of aquatic ecosystems, recognition of biodiversity, awareness of issues affecting rivers, and awareness of services provided by rivers) the students showed increased interest and cognizance of the streams by the end of the program. Students were more aware of the streams close to where they live as well as the animals (other than fish) that lived there, such as birds and insects. The activities and field trips lessened their fears of imaginary creatures or animals like alligators that did not exist in Portuguese rivers and made them more appreciative of the streams as a resource for water and recreation. They also acknowledged the presence of trees on the banks of the streams that provided oxygen, shelter, and food for animals. The children also showed an increased negativity for litter, lack of trees, too many reeds (that grow unchecked when trees are removed and choke the stream) and too many buildings around the streams. The students were also reported as saying that they would not litter and would discourage others from doing so as well.

The bar graph shows 3 bars for each organism, showing the percentage of students that recognize that organism at the time of the M1, M2, and M3 surveys. Approximate values are: Fauna Fish: M1- 60%, M2- 92%, M3- 87% Invertebrates: M1- 30%, M2- 40%, M3- 75% Insects: M1- 42%, M2- 44%, M3- 33% Dragonflies: M1- 39%, M2- 50%, M3- 68% Butterflies: M1- 30%, M2- 25%, M3- 22% Mosquitoes: M1- 48%, M2- 45%, M3- 38% Shrimps: M1- 60%, M2- 47%, M3- 53% Aquatic snails: M1- 25%, M2- 59%, M3- 30% Mammals: M1- 21%, M2- 19%, M3- 38% Amphibians: M1- 12%, M2- 22%, M3- 25% Birds: M1- 27%, M2- 37%, M3- 30% Aquatic flora Algae: M1- 60%, M2- 82%, M3- 97% Filamentous green algae: M1- 39%, M2- 45%, M3- 79% Aquatic plants: M1- 39%, M2- 63%, M3- 70% Trees Alders: M1- 23%, M2- 18%, M3- 38% Willows: M1- 17%, M2- 27%, M3- 62% Poplars: M1- 10%, M2- 40%, M3-70 % Oaks: M1- 21%, M2- 50%, M3- 70% Ash trees: M1- 17%, M2- 18%, M3- 37%
Figure 1: The percentage of students that can recognize particular flora or fauna over time and as they are more exposed to streams and the organisms that live there.

Why is this study important? Children growing up in urban areas are exposed to various pollutants and obstacles that come from living in the city. Being consistently exposed to nature from an early age can help to combat those negative effects and promote health and wellbeing. Additionally, learning about the importance of aquatic ecosystems naturally inspires children to be interested in conservation and sustainability. This study showed that when given the opportunity to have real experiences in nature, they form their own positive opinions and ideas.

The big picture: Conservation of green and blue ecosystems is dependent on future generations having genuine understanding of and connections to nature. Introducing environmental studies, complete with hands-on activities, to primary education curriculums is an effective way to nurture those connections. Children should be exposed to the natural spaces close to their schools and homes in order to feel connected to nature and have a deeper learning experience.

In the “before” images (a) and (b), the children drew pictures where only a small portion depicts the stream. A few fish are shown, but most of the detail shows the dock, land, buildings and trees, a large portion of sky, and in image (b) lots of people. In the “after” images (c) and (d), the children’s pictures show a large amount of water and a lot of biodiversity, with pictures of insects, snails, and birds.
Figure 2: Pictures drawn by students after their first field trip (a and b) and after their second field trip and laboratory class (c and d)

Citation: Feio MJ, Mantas AI, Serra SRQ, Calapez AR, Almeida SFP, et al. (2022) Effect of environmental education on the knowledge of aquatic ecosystems and reconnection with nature in early childhood. PLOS ONE 17(4): e0266776.

Trees Combat Climate Change in China by Reducing CO2 Levels

Forest management in southern China generates short term extensive carbon sequestration

By: Xiaowei Tong, Martin Brandt, Yuemin Yue, Philippe Ciais, Martin Rudbeck Jepsen, Josep Penuelas, Jean-Pierre Wigneron, Xiangming Xiao, Xiao-Peng Song, Stephanie Horion, Kjeld Rasmussen, Sassan Saatchi, Lei Fan, Kelin Wang, Bing Zhang, Zhengchao Chen, Yuhang Wang, Xiaojun Li and Rasmus Fensholt

Summarized by Anna Geldert

What data were used? Researchers collected data on carbon storage (long-term carbon stocks) and sequestration levels (new uptake of carbon gasses) by forest type. Data was recorded between 2002 and 2017, and the area of study focused on eight provinces in southern China. This data was compared with existing published data on soil moisture levels and national CO2 emissions.

Methods: Researchers used satellite imagery data from MODIS (Moderate Resolution Imaging Spectroradiometer) for the basis of this study. Using approximately 10,000 MODIS images, they divided the area into a grid with a scale of 0.25km2. Using “training points” of known land cover, they trained a computer to estimate the probability of forest cover in each grid cell, as well as the level of change in forest cover over time. Based on this information, grid cells were classified into eight categories of forest types, including dense forest (probability of forest cover ≥ 0.8, with low change), persistent forest (probability ≥ 0.5, with low change), persistent non-forest (probability ≤ 0.5, with low change), recovery (regrowth of deforested areas, causing a gradual shift from non-forest to forest), afforestation (tree plantation in previously unforested areas, causing a rapid shift from non-forest to forests), deforestation (shift from forest to non-forest), rotation (harvested area, causing fluctuation between forest and non-forest) and rotationL (harvested area, causing fluctuations and low forest recovery). Researchers then estimated the carbon density of each forest type using data from a previous study 2015 from GLAS (Geoscience Laser Altimeter System, i.e., a satellite machine designed to measure the vertical structure of forests). MODIS data from this study was cross-referenced with existing passive microwave data from SMOS (soil moisture and ocean salinity), which also measured carbon density from this region, though on a broader scale. SMOS data were also used to determine the average soil moisture in the studied region.

Results: Both tree cover and fossil fuel emissions increased considerably between 2002 and 2017. Using the MODIS data, researchers estimates a carbon sink of 0.11 Pg C year-1 (i.e., petagrams of carbon per year, the equivalent of 0.11 billion metric tons per year) in the region studied. This accounted for roughly 33% of yearly carbon emissions since the year 2012. Unmanaged dense forest had the highest carbon density, accounting for 20.5% of carbon storage despite only occupying 8.8% of the land. However, dense forests had low levels of carbon sequestration, accounting for only 4% of the total uptake. Comparatively, persistent non-forests and managed forests (recovering, afforestation, and rotation areas) all had low levels of carbon storage but accounted for 65% the total carbon sequestration. Persistent forest areas lay somewhere in the middle, with moderate storage and sequestration levels. Heavily harvested forests (deforested and rotationL areas) had much lower sequestration rates, and served as carbon sources rather than sinks. Finally, SMOS data revealed that soil moisture levels tended to be lower in regions with lots of managed forests.

The figure shows a bar graph comparing the type of land to the level of sequestration of CO2 emissions. The x-axis is labeled “Type of land use,” and is numbered 1 through 8. A legend on the right of the graph indicates that each number corresponds to a type of forest or non-forest area: 1 represents dense forest, 2 represents forest, 3 is non-forest, 4 is recovery, 5 is afforestation, 6 is deforestation, 7 is rotation, and 8 in rotationL. A different y-axis is present on either side of the graph, so that both the relative percent of CO2 emissions sequestered and the numerical quantity of carbon sequestered per year are represented. The left axis represents the percentages, and spans from 0 to 7.5, increasing at increments of 1.25. The right axis represents the quantity of carbon sequestered in petagrams per year, spanning from 0.00 to 0.03 and increasing by a factor of 0.05. A separate legend on the bottom of the graph indicates that the dark orange portions of the bars represent the percentage/fraction of carbon sequestered compared to CO2 emissions from China as a whole, while light orange portions correspond to emissions from the eight provinces alone. The land use type with the highest percentage of carbon sequestered was non-forest, which accounted for approximately 6.5% of annual emissions for the eight provinces, or 0.026 total Pg of carbon per year. Non-forest was followed by forest and afforestation (both accounting for 5.2% of emissions and 0.21 total Pg), recovery (4% and 0.016 Pg), rotation (3.5% and 0.013 Pg) and dense forest (1% and 0.009 Pg). Deforestation and rotationL were the only types of land use to represent a negative percentage and quantity of carbon sequestered, indicating that they served as a carbon source rather than a carbon sink. Deforestation accounted for approximately -0.2% (or 0.001 Pg) of carbon sequestration, while rotationL was nearly negligible. The percentages of carbon sequestered when compared to national emissions (dark orange) were all about one fifth of the percentages when compared to the eight provinces alone.
Fig. 1. Average percent of CO2 emissions sequestered annually by each forest type. CO2 emissions from the eight provinces in the study region, as well as emissions from China as a whole, are both shown.

Why is this study important? This study compares the effectiveness of different types of forests in mitigating the impacts of climate change. While natural, dense forests were the best at storing carbon long-term, managed forests were most effective at rapidly removing CO2 from the atmosphere on a shorter timescale. Harvested forests, especially those classified as “rotation,” were especially successful as they were able to sequester relatively high levels of carbon while still providing significant economic revenue from timber for the region. Overall, changes in forest management policies in China in 2002 led to an impressive reduction in carbon emission levels (33%). However, it is important to note that an additional 3 million km2 of forested land would be needed to reach net zero carbon emissions, a number which is unreachable in this region. Likewise, reduced levels of soil moisture indicate that heavily managed forests may not be sustainable in the long run, and will likely be less effective during periods of drought. More research is needed to determine if these forest management policies have already reached maximum effectiveness, or if other adjustments can be made to further increase sequestration.

The big picture: As the main drivers of climate change, fossil fuel emissions continue to threaten our planet. Forestation and forest management policies, such as those established in China at the turn of the century, are a way to mitigate the impact of greenhouse gasses. Modeling future policies after these could help increase carbon sequestration worldwide, especially until renewable energy becomes available. However, as was revealed in this study, it is nearly impossible at current emission levels to reach net zero carbon emissions through forest management alone; in the long term, forest management will likely need to be combined with other policies to ensure a sustainable future.

Citation: Tong, X., Brandt, M., Yue, Y., Ciais, P., Rudbeck Jepsen, M., Penuelas, J., … Fensholt, R. (2020). Forest management in southern China generates short term extensive carbon sequestration. Nature Communications, 11(1).