Resilience in the Chaco forest ecosystem, an empirical evaluation

Maria Lucrecia Lipoma and Sandra Díaz discuss their recent Journal of Ecology paper ‘Low resilience at the early stages of recovery of the semiarid Chaco forest ‐ Evidence from a field experiment‘. Find out more about the insights they gained into the mechanistic understanding of resilience and how it can be used to better design future studies.

In a world undergoing unprecedented changes, understanding how biodiversity and ecosystem functions persist through time is essential. Despite increasing attention on resilience, which can be defined as the ability of ecosystems to recover after disturbances, there is still a lack of empirical evidence, especially for arid and semiarid woody ecosystems, where vegetation dynamics are slow and spatial heterogeneity is high.

We designed a methodology to quantify the resilience of the Chaco forest of Argentina to disturbances related to land-use change. This ecosystem is the most extensive seasonally dry forest in South America and is subjected to a pervasive reconfiguration of native vegetation, which started centuries ago but greatly accelerated in the second half of the 20th century and the beginning of the 21st century. This process has affected the sources of resilience of this ecosystem. That is, all the community attributes or components that underpin the ecosystem’s capacity to bounce back and maintain its functioning over time.

The Chaco Forest ecosystem in the area of the Natural Reserve “Chancani” in the northwest of Córdoba, Argentina. Photo credit: Lucas Enrico

We established 16 pairs of neighbouring fenced and unfenced plots in 4 ecosystem types resulting from different long-term land-use regimes. In each plot we monitored plant species composition during the first 5 years following land-use exclusion, and evaluated the resilience as the rate of change of vegetation towards the primary forest, which we considered as the reference ecosystem. Our resilience index allowed us to disentangle vegetation responses to land-use exclusion and weather variability by the incorporation of the natural variation of the reference state and the local under disturbance control.

According to our model, different ecosystem types can show a trajectory towards the reference ecosystem that will depend on the intensity of disturbance to which they were subjected and also on the preservation of their sources of resilience. For instance, if two ecosystem types, irrespective of their initial difference with the reference ecosystem, preserve their sources of resilience, they are expected to show a similar rate of change towards the reference ecosystem, although the absolute time needed for recovery will be longer for those that started their trajectory at a more distant point because they suffered from higher intensity disturbances.

The first 5 years after exclusion from land-use change were particularly rainy. Based on the literature, we expected these weather conditions to provide a “window of opportunity” for the vegetation to recover. Instead, we found that, in general, vegetation composition did not revert during the first 5 years following the exclusion of land use. Only grass cover showed resilience, and only in the ecosystem type previously subjected to the lower land-use intensity. Other components of plant community composition either did not change significantly or even transitioned away from the reference state.

Fenced plot that excluded land-use disturbances related mainly with logging and livestock grazing and trampling. Photo credit: Lucas Enrico

The lack of detectable resilience in our study suggests three main conclusions: (1) long-term land use, even at lower intensities, has affected the sources of resilience of this ecosystem; (2) rainy periods do not necessarily speed up recovery; and (3) study designs should incorporate the variation of the reference ecosystem in order to differentiate the effect of land use from other factors in a context of climate change. We hope this study contributes with the mechanistic understanding of resilience and foster the quantification of resilience in this and other ecosystems around the globe.

Maria Lucrecia Lipoma Instituto Multidisciplinario de Biología Vegetal (IMBIV), Argentina

Sandra Díaz Instituto Multidisciplinario de Biología Vegetal (IMBIV), Argentina

Read the full article: Low resilience at the early stages of recovery of the semiarid Chaco forest ‐ Evidence from a field experiment

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