One of the most relevant questions in restoration ecology is to estimate the magnitude of anthropogenic disturbance, that is, what would it take for an ecosystem to fully recover? A common problem to respond to this question is to choose how to quantify disturbance or recovery. With present knowledge and technology it is still not possible to measure a whole ecosystem. However, several proxies that partially reflect the complexity of ecosystems have been used, and these include interaction networks. What is less clear is how the reassembly of interactions drives the functional recovery (and to some extent also viceversa). Studies are starting to show that the structure and stability of interaction networks strengthen as recovery proceeds. How and when a state of dynamic stability is reached, how it is affecting the resilience of the system to further disturbance and how it can be engineered or facilitated are some of our specific goals.
Anthropogenic disturbances also affect other dimensions of ecosystem complexity, like the amount of genetic information contained in the system. Disturbance reduces genetic diversity and hence the evolutionary potential of species. Today, we can identify what regions have been lost and associate them with specific functions that may or may not be related to their evolutionary potential. We hypothesize that genomes whose genetic diversity has been reduced by direct or indirect human selection can recover after the end of the disturbance at the right timescale. We are interested in how the recovery process operates at “ecological scales.” Experimental studies on ecosystem recovery or restoration involves periods of a few decades at the most. However, the recovery process of a whole ecosystem, including its populations and communities, in real world conditions requires time periods of several centuries or millennia according to peleoecological records (that do not deal well with interactions for now). Our fundamental goal is to combine complex metrics and long-time periods to reconstruct the re-assembly of the interaction-function structure and the genome-function structure of ecosystems after anthropogenic disturbances. Given the lack of long-term ecosystem measurement of any complex metric, we apply a space-for-time substitution approach and use chronosequences.
A critical challenge that we need to address is how climate change is affecting the recovery process in a way that outcomes may differ from pre-industrial times. We are addressing this challenge in two ways. First, by synchronizing chronosequences with paleolimnological records and studying the response of ancient communities to past climate changes. Second, based on these past responses we can make projections on expected future communities resulting from the recovery process under proposed climate change scenarios.
We are currently working in three systems with this approach:
The first system is the ancient agricultural fields that the Norse created in Greenland. There are a few hundreds of Norse farms found by archeologists that have remained uninhabited from about 650 to 1050 years after the local population collapsed due to a convergence of social and environmental factors. Here we are looking into the reassembly of the interactions between the soil microbial community and the plant community, specifically the fungal and bacterial communities, and its effects on the carbon and nitrogen pathways.
The second system is the ancient agricultural areas that the Pre-columbian people created and used for millennia in the Amazon. In this system, again archaeologists have identified thousands of sites and many of them have remained uninhabited. After the Spanish Conquer and driven by slavery and European diseases, a large proportion of these peoples disappeared and left millions of hectares abandoned. All this land has become one of the oldest and largest secondary growth forests in the word. Here we are looking at the genomic recovery of the Brazil nut (Bertholletia excelsa). Indigenous peoples selected and dispersed this species through the Amazon. We are looking at the genomic recovery of the Brazil nut and identifying the recovered functions to study their role in the resilience of the species to ongoing global changes. Over time, we will expand this approach to a community level.
The third system is the current temperate forest in North-eastern US that is recovering on former agricultural fields. After the arrival of the European settlers to the regions, they almost completely clear cut the forest that was previously exploited by indigenous peoples. Given the limited quality of the regional soils for agriculture, most of the forest was abandoned and have been naturally recovering over the last 140 to almost 200 years. In this system, we are using the same approach detailed on the Greenland system but this time we are focusing on the tree community.