Long-term restoration of human-disturbed forests: drivers and time to recovery

Asun Rodríguez-Uña and David Moreno Mateos, Basque Centre for Climate Change - BC3, Leioa, Spain, Asun Rodríguez-Uña, Biología Vegetal y Ecología, Facultad de Ciencias y Tecnología, Universidad del País Vasco (UPV/EHU), Leioa, Spain, Verónica Cruz-Alonso and David Moreno Mateos, Landscape Architecture, Harvard University, Cambridge, MA, José A. López-López, Universidad de Murcia, Murcia, Spain

Background/Question/Methods
Ecological restoration actions are increasing globally to mitigate forest ecosystem degradation and biodiversity loss. However, restored forests do not commonly recover pre-disturbance levels of structure, functions or services. One of the obstacles for forest restoration success may be our limited understanding of their recovery process at large timescales (> 100 years). In this study, we aim to provide insights into the forest recovery process and its drivers in the long-term, and to estimate time to recovery. We collected data from 104 forest chronosequences worldwide to build long-term (c. 300 years) recovery trajectories for six recovery metrics (organism abundance, species diversity, species similarity, carbon cycling, nitrogen stock and phosphorus stock), following agriculture or logging. In total, we analysed 580 quantitative measures of ecosystem integrity collected at least twice over the recovery time and compared with the value in a reference, undisturbed forest. This resulted in 2,780 comparisons.
Results/Conclusions
Our results show that forest recovery increased over time, with 0-4.60 times faster faster recovery following agriculture than logging, and 0.09-1.06 times faster recovery for abundance compared to diversity. When each recovery metric was analysed individually, we found that abundance, carbon and nitrogen recover 0.20–2.37, 0.46–2.30, 0.89–7.18 times faster following agriculture than logging, respectively. The recovery of abundance and similarity (Bray-Curtis index) also differed across life forms involved. Woody plants and invertebrates (for both metrics) and woody & non-woody plants and microorganisms (only for abundance) reached higher recovery levels than non-woody plants. Our outcomes also suggest that forests worldwide may need over four centuries to recover recover to 90% of reference values of biodiversity and functions. This centennial recovery of forests urges us to plan the current global restoration strategies and environmental regulations accordingly in terms of timescale and environmental impact level.