Assessing climate and ecosystem function change in South American protected areas during the last three decades

In this post, authors Hernán Dieguez and José M. Paruelo describe their recent paper, published in Remote Sensing in Ecology and Conservation.

Protected areas are the cornerstone of in situ global conservation efforts and are intended to both preserve biodiversity and ensure the provision of multiple ecosystem services. Furthermore, protected areas can be used to disentangle the relative importance of drivers of ecosystem functioning (such as land use and climatic variables) in order to improve forecasts of vegetation change and ecosystem services provision. Natural experiments, where some factors are fixed across environmental gradients (for example, land use in protected areas) offer an attractive opportunity to gain insight into the short and long-term effects, and spatial heterogeneity, of environmental changes on ecosystems. Remote sensing techniques are increasingly recognized as a valuable methodological approach for studying global change effects on ecoystems.

Our recent paper focused on analysis of 402300 km2 of protected ecosystems in South America, an area equivalent to Paraguay. The study area includes some of the driest (Salar de Huasco, Chile) and wettest (Utria, Colombia) sites in the world, along with deserts, grasslands, savannas, dry forest, temperate forests and tropical rainforests. We sought to answer the following questions: (1) How did the magnitude and seasonality of carbon gains change over South American ecosystems during the last three decades? (2) Were these changes concurrent with climate changes? (3) Which ecosystems were more sensitive to climatic fluctuations?

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We analyzed the temporal trends and spatial heterogeneity of both climatic variables and attributes of the seasonal dynamics of the normalized difference vegetation index, a surrogate of vegetation carbon gains derived from remotely sensed data, on 201 protected areas in South America.

While every ecosystem is vulnerable to climate change, the degree of the impact and the magnitude of the ecosystem response are likely to vary. Increased productivity and higher seasonality, frequently climate driven, was the most common signal across the least modified areas of South American biomes. In general, arid and semiarid sites responded positively to increases in precipitation and negatively to increases in temperature, while humid ecosystems responded in the opposite way. Those sites where climate is becoming more arid (upward temperature and downward precipitation trends respectively) showed significant reductions in productivity. Interestingly, we found that functional consequences of climate change can be similar to those expected from land use/cover changes (such as land clearing for agriculture). We also provide support to the fact that protected areas are not static systems as their functioning is changing with different magnitude and in contrasting directions.

The response of ecosystems to interannual variability in climate is a central topic in ecology as it reflects the vulnerability of ecosystem processes, and ultimately human well-being, to climate change. Our study characterizes changes on ecosystem functioning at a regional scale and provides a preliminary basis for predicting which ecosystems will change in terms of productivity more rapidly in response to climate change, that is, those with the highest sensitivity and the largest changes in climatic variables.

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NDVI (Normalized Difference Vegetation Index) seasonal profile. 

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