Tropical forests disappear rapidly because of deforestation, yet they have the potential to regrow naturally on abandoned lands. We analyze how 12 forest attributes recover during secondary succession and how their recovery is interrelated using 77 sites across the tropics.

Network analysis shows three independent clusters of attribute recovery, related to structure, species diversity, and species composition. Secondary forests should be embraced as a low-cost, natural solution for ecosystem restoration, climate change mitigation, and biodiversity conservation.

  • tropical forest regrowth on many agricultural sites left because of loss of fertitlity, migration, or alternative livelihhod options
  • resilience: ability to resist disturbance and to recover from disturbance
    • resistance: difference between the value of a specific forest attribute at the start of succession and the average old-growth forest value
    • recovery: ability to return to old-grown forest attribute values after succession
  • succession: change in vegetation structure, species composition and ecosystem functioning over time after a disturbance
  • secondary succession: on previously vegetated lands when a disturbance removes most of the above-ground vegetation and can proceed at fast rates due to legacy effects of previous forest or previous land use

Pace of recovery

  • soil resistance was high, indicating that agricultural use does not disturb it too much; fast recovery

Wood density (WD) is the stem-wood dry mass divided by stem volume, and it increases tissue longevity and carbon residence time in trees and forests. Specific leaf area (SLA) is the leaf area divided by the leaf mass. It reflects leaf display cost and scales positively with photosynthetic capacity and forest productivity and negatively with leaf longevity. WD and SLA change during secondary succession because pioneer species are typically replaced by later-successional species with opposite trait values.

Nitrogen fixation is generally high early in succession when irradiance is high and trees can support their nitrogen-fixing symbionts with carbohydrates and declines over time as forests regrow, light availability in the stand drops, and nitrogen fixation becomes too costly.

  • fast plant functional recovery after short-lived pioneer species, with similar traits

Structural heterogeneity (SH) refers to the tree size variation in a plot; it increases light capture and ecosystem productivity and contributes to biodiversity conservation by providing a habitat for different species.

  • forest structure recovers at intermediate pace
  • species diversity and composition recovers at intermediate to slow pace

Network properties and proxies for multidimensional recovery

The first network analysis was based on pairwise correlations among all 12 attributes and showed that recovery of attributes occurred in parallel, with the highest expected influence (i.e., many links with other attributes) for SC, followed by the three structural attributes and soil C.

The clustering of forest attributes into multiple groups suggests that recovery of different forest attributes is shaped by different drivers or processes. For example, recovery of biodimeversity attributes may be driven by the land-scape context, land-use history, and the availability of seed trees and dispersal vectors, whereas recovery of structural attributes may be driven by resource availability [i.e., water availability, soil fertility (16), and remnant trees].

We hypothesized that AGB would be the best predictor of multidimensional recovery because ecosystem processes and flux rates strongly depend upon the amount of vegetation. Instead, we found that recovery of Dmax had the highest influence.

Resilience

  • overall return time about 120 years
  • fast forest recovery during secondary succession because of many legacies and productive, warm, and wet conditions

Applied implications

we urge the embrace of SFs as a low-cost, nature-based solution to meet the United Nations’ Sustainable Development goals and the United Nations’ Decade on Ecosystem Restoration goals (where needed with some assistance from management: control of invasive species, seed availability)