A global review of past land use, climate, and active vs. passive restoration effects on forest recovery

Abstract

Global forest restoration targets have been set, yet policy makers and land managers lack guiding principles on how to invest limited resources to achieve them. We conducted a meta-analysis of 166 studies in naturally regenerating and actively restored forests worldwide to answer: (1) To what extent do floral and faunal abundance and diversity and biogeochemical functions recover? (2) Does recovery vary as a function of past land use, time since restoration, forest region, or precipitation? (3) Does active restoration result in more complete or faster recovery than passive restoration? Overall, forests showed a high level of recovery, but the time to recovery depended on the metric type measured, past land use, and region. Abundance recovered quickly and completely, whereas diversity recovered slower in tropical than in temperate forests. Biogeochemical functions recovered more slowly after agriculture than after logging or mining. Formerly logged sites were mostly passively restored and generally recovered quickly. Mined sites were nearly always actively restored using a combination of planting and either soil amendments or recontouring topography, which resulted in rapid recovery of the metrics evaluated. Actively restoring former agricultural land, primarily by planting trees, did not result in consistently faster or more complete recovery than passively restored sites. Our results suggest that simply ending the land use is sufficient for forests to recover in many cases, but more studies are needed that directly compare the value added of active versus passive restoration strategies in the same system. Investments in active restoration should be evaluated relative to the past land use, the natural resilience of the system, and the specific objectives of each project.

Comparing the recovery of richness, structure, and biomass in naturally regrowing and planted reforestation

“…Our results are consistent with other studies showing that, where possible, regrowth offers cost‐effective opportunities to deliver conservation and carbon benefits in agricultural regions (Crouzeilles et al ; Meli et al ; Jones et al ). Where active reforestation is required, we suggest that recruitment and recruit survival is a high priority.…”

An investigation of the effects of conservation incentive programs on management of invasive species by private landowners

“…Passive management of valued environmental features may be sufficient when environmental threats have ceased (Barral et al, 2015;Meli et al, 2017;Morrison & Lindell, 2010). Yet in southern Ontario the widespread pressure from invasive species (Anonymous, 2018) threatens valued environmental features (OMNR, 2012).…”

Assessment of the nursery species pool for restoring landscapes in southeastern Brazil

“…International commitments to restore tropical ecosystems are a huge challenge and will require a wide variety of approaches to scale up restoration efforts, including both spontaneous and active restoration (Holl & Aide ; Holl ; Meli et al ). Particularly in landscapes with a long history of land conversion, deforestation, and defaunation, vegetation recovery depends on active restoration through direct seeding or the planting of seedlings (Rodrigues et al ; Palma & Laurance ; Meli et al ). Indeed, planting trees is the most common tropical forest restoration technique, despite being expensive, time consuming, and labor‐intensive (Brancalion et al ; Meli et al ; Jalonen et al ).…”

“…Particularly in landscapes with a long history of land conversion, deforestation, and defaunation, vegetation recovery depends on active restoration through direct seeding or the planting of seedlings (Rodrigues et al ; Palma & Laurance ; Meli et al ). Indeed, planting trees is the most common tropical forest restoration technique, despite being expensive, time consuming, and labor‐intensive (Brancalion et al ; Meli et al ; Jalonen et al ).…”