1. The legacy of human disturbance
Human activities degrade totally or partially ecosystems, making them less diverse, less functional and more vulnerable to further change. For years, we have been quantifying the effects of disturbance on ecosystem diversity and function, but less has been known about the effects of disturbance on their recovery. One may think that thanks to the restoration of degraded ecosystems, we can bring back lost biodiversity and functions, and even justify further degradation.
But, can we actually restore ecosystems? For several years, several studies have been trying to respond to this question by estimating how much biodiversity and ecosystem functions and services are recovered thanks to restoration efforts. Results have been controversial but it seems that on average ecosystems recover, but three other major questions arise: To what extent? How long does it take? And, how much can we expect to lose, if they ever recover?
To respond to these questions, we have performed a series of meta-analysis including thousands of ecosystems undergoing recovery from anthropogenic disturbances globally. We have found that recovering ecosystems only have half the species richness, a third less their population sizes, and 40% less biogeochemical function related to the cycling of carbon and nitrogen than undisturbed ecosystems. This means that with degradation, we create legacy effect that incur in a <em>recovery debt</em>. An added concern is that recovery may be a very long-term process, for example, we found that plant assemblages in wetlands did not recover their richness and relative abundance after 100 years. We are now interested in understanding temporal patterns of recovery for a diversity of metrics and in estimating the overall debt created by the whole degradation process.
Meta-analysis are extraordinary tools to find patterns of ecosystem recovery (but not to understand mechanisms! See next research topic) that may be very useful for decision makers and practitioners to support their decisions based on hundreds of cases. However, restoration requires most likely a deeper insight in the local environment of each particular project. We are firmly supporters of ecosystem restoration!
A restoration synthesis. Feedbacks between biodiversity and ecosystem functions and services during the recovery process of restored ecosystems after anthropogenic disturbance.
Funded by National Socio-environmental Synthesis Centre – SESYNC (USA) and the German Centre fro Integrative Biodiversity Research – sDiv (Germany) between 2013 – 2015.
PIs: David Moreno Mateos and Holly Jones (Northern Illinois University).
In this synthesis venture, we used a large meta-analytical database that includes over 500 studies, we have studied the recovery of biodiversity (species richness and plant and animal abundance) and function (cycling of carbon and nitrogen) of ecosystems undergoing recovery after human disturbance. In particular, we have estimated the recovery debt of biodiversity and functions created when ecosystems are degraded and then restored. We compared among different habitats and degradation factors, these included agriculture, logging, mining, invasive species, hydrological disruption, eutrophication, overfishing, oil spills, and also hurricanes that were used as a reference natural disturbance. We also studied the recovery of aquatic ecosystems from eutrophication, the recovery of temperate and tropical forests, and the effect of active approaches of restoration versus “let nature do” approaches.
2. Long-term recovery of ecosystem complexity
One of the most relevant questions in conservation biology 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 what to measure to quantify disturbance or recovery. Unfortunately, with present knowledge and technology it is not possible to measure a whole ecosystem. However, several proxies that partially reflect the complexity of ecosystems have been used, for example, interaction networks. Studies are starting to show that the structure and stability of interaction networks strengthen as recovery proceeds.
The second issue to study recovery is time. Every experimental study on ecosystem recovery or restoration involve periods of a few decades at the most. However, the recovery process work at an “ecological” pace, involving much longer time periods (i. e. several centuries), or that is what paleoecological studies seems to suggest. Unfortunately, paleoecology do not deal well with interactions so far.
Thus, the point here is to combine complex metrics and long-time periods to achieve a better understanding of ecosystem recovery. Given the lack of long-term ecosystem measurement of any complex metric, we apply a space-for-time substitution approach and use chronosequences. We are currently using this approach in two pilot projects: one in one medieval mine in Northern Spain that is today covered by a mature beech forest; and a second in the Old Norse settlements of South-west Greenland abandoned c. 1450 AD.
REBECOM. Estimating recovery time of temperate forests after anthropogenic impacts along a complexity gradient.
Funded by the Spanish National Research Agency between 2016 and 2018.
PI: David Moreno Mateos
This empirical study studies the effect of mine abandonment on the recovery of ecological network complexity. Complexity is measured as the amount of links with different interaction strengths found in plant – mycorrhizal fungi – fungivorous insect networks. Using 14C and dendrochronology, we build a chronosequence of the last 300 years within one mining area in Navarre (Northern Spain) and construct the regional network. Species interactions strengths are estimated in laboratory and greenhouse experiments. We expect that as recovery progresses interaction networks become more structurally entangled but also more resilient to further disturbances.
Ecosystem recovery in ancient Norse settlements of Greenland
In a pilot expedition to South-west Greenland in 2016, we explored 10 Old Norse farms in the area of Kapisillit. We are comparing the plant community and its association with mycorrhizal fungi of former hayfields with reference undisturbed sites. After about 600 years of abandonment, we are still finding significant differences in plant assemblages, mycorrhizal associations, and phosphorus and nitrogen concentrations in soils. Our aim is to understand how the plant-mycorrhizal fungi networks have changed their structure and resilience to further change and the mechanisms that regulate recovery from ancient impacts, in this case, created by hay cropping. To build a chronosequence and estimate the intensity of use (i.e. time while the field was cropped) we are dating soil charcoal with 14C.