Article Review: Measuring resilience and assessing vulnerability of terrestrial ecosystems to climate change in South America

Summary

            Measuring the impacts of climate change is becoming increasingly important as biodiversity in ecosystems continues to decline.  This is as true in South America- the geographic focus of this study- as it is anywhere.  The goal of this study is to find the best way to measure ecosystem resilience against increases in climate stress. 

Several methods have been used to research this problem, which the researchers state, but they are all qualitative.  Unfortunately, no background was provided to support these qualitative methods- only that they involve ecological stability theory and ecological niche theory.   The article doesn’t specifically state what these methods entailed, only that they apply to the theories. References are provided for these methods, making it up to the reader to investigate them.

Their research proposal is to generate a quantitative method by coupling the two theories.  The idea is to construct spatial models that measure the resilience of ecosystems “through a metric of climate suitability, based on the multidimensional niche preferably occupied by them” (p. 2).  The educational significance of such a method is to provide the only quantitative way of measuring ecosystem resilience against climate stress.  Results indicate that forests are more vulnerable to climate change in South America than savannas or grasslands.

 

Critique

            I did not find a comprehensive review of the related literature in this study.  Citations mostly applied to the data being used to delineate ecosystem boundaries and vegetational cover.  While it is stated that the reference for vegetational cover was a MODIS satellite, a reference for delineating the ecosystem boundaries was not.  The reader needs to look in the reference section to find data for that.

            There is not a specific question to be answered or a hypothesis to prove or disprove.  The goal of this research is to make the case for a quantitative method of measuring ecosystem resilience against climate change.  As we’ll see later, they don’t really answer this question so much as what the findings imply for conservation.

            The only instrument used was a MODIS satellite to delineate ecosystem boundaries by examining the vegetation content of each pixel.  Ecosystems were classified based on the percent of vegetation in them: less than 5% was grassland or desert, 5%-60% was savannah, and over 60% was forest.  MODIS satellite data is a cheap and effective way to estimate ecosystem boundaries, since these would be difficult to determine by fieldwork alone.

            Samples were collected for ecological niche modeling.  Based on the classification scheme, 53% of the samples were savannah, 38% were forest, and 9% were grassland.  A total of 37,763 samples were used in the model, indicating an impressive amount of data for the study.  However, it was not mentioned if the sample locations were randomly generated, systematic, or stratified in any way, leading the reader to wonder how much room there is for sampling error.  The model also used data from CHPclim (precipitation) and the WorldClim temperature database.  The need for these variables in the model wasn’t clearly stated in the text; we are to assume they are the key climatic ones when measuring climate change resistance.  Using the biomed2 package in R software, the model was processed using the variables above.  It was run using 10 different methods!  The highest quality methods were selected based on a True Skill Statistics (TSS) score of .7 or above.  An exponential equation was then used to fit the models into a curve that would generate an indicator of ecosystem resistance to climate stress.

            The design of this research is stated with great attention to detail but is difficult for someone without knowledge of R and statistics to thoroughly understand.  Because there is so much detail, other researchers familiar with these topics should be able to replicate the method if desired.

            Results from the study are clearly explained, not only in the text but in the maps and graphs provided.  The maps and graphs were appropriately clear and colored to make the data easy to read.  Figure 1 showed a color-coded map for each of the three bioregions (grassland, savannah, forest) and their resilience level.  Figure 2 showed the relative frequency of resistance to climate change response for the bioregions.  Figure 3 showed patterns between climatic variation in temperature and precipitation and ecosystem resilience.

            Based on the figures, moisture availability showed the strongest interaction with climate resilience.  Forest ecosystems in South America have a relatively narrow ecological niche, and since the models predict there will be less moisture in the south of the continent, that is where the researchers expect the least resistance to climate stress.  Stronger resistance can be seen on map B for savannah, having more extensive areas of high resistance across the continent.  A potentially confusing aspect about map A for grassland is that it shows low resilience across the continent, yet it is stated in the text that high resistance can be expected.

            Results are discussed in terms of the ways this method can apply to applications within the science of conservation, whether it is in evaluating ecosystem resilience or restoration policies.  I didn’t find a strong argument supporting why this quantitative one would be a better option than the qualitative ones briefly mentioned in the introduction.  The results would have been stronger if they had addressed which method is more accurate, costly, and beneficial.

            Surprisingly, there was no suggestion of further research involving their method.  Much of the discussion revolved around the findings and what can be done to conserve the environment in South America.  Placing more attention on forests is an important conclusion since they demand more moisture and are more important to a balanced global climate.  But this seems to be something conservationists- and perhaps the researchers themselves- already suspected.  If the hypothesis had been that forests in the south would show less resilience, then the discussion would have more aligned with it.