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Biodiversity and recovery of forest in tropical landscapes

Periodic Reporting for period 2 - PANTROP (Biodiversity and recovery of forest in tropical landscapes)

Reporting period: 2021-03-01 to 2022-08-31

The challenge- Tropical forests are global hotspots of biodiversity, play key roles in the global carbon and water cycle and deliver crucial ecosystem services but are threatened by human-induced climate change, deforestation and biodiversity loss. I focus on forests that regrow after complete forest removal for agriculture (secondary forests), because they cover large areas, have great potential to recover biodiversity and carbon, and are the basis for ecosystem restoration. The key challenge is to understand and predict forest resilience: when, and under what conditions are regrowing forests able to recover and have the same quality and functioning as old-growth forests?

Aims- This study aims to understand and predict the resilience of tropical forests to human-driven disturbance by analyzing the effects of (1) continent and biogeography, (2) climate, (3) landscape, and (4) biodiversity on forest recovery rate.

Approach- We will use a pantropical approach by synthesizing current data and doing controlled experiments on three continents (Neotropics, Africa, and Australia) in climatically contrasting forest types (dry and wet forest). We will (1) assess long-term recovery of multiple facets of tropical forests after agricultural use, by expanding a unique Neotropical network of 60 sites to the pantropics, (2) analyse the role of the landscape (i.e. the spatial distribution of remaining forest patches and trees) on forest recovery by doing a natural experiment along forest cover gradients, (3) understand how different kinds of diversity, such as dominant species and rare species, affect succession and ecosystem functioning through a biodiversity removal experiment.

Impact- This study addresses key questions in ecology and advances our understanding how human-driven climate change, landscape degradation, and biodiversity loss affect forest resilience and succession. The insights can be applied to (1) reduce human impacts on tropical forests, (2) design resilient and multifunctional tropical landscapes, and (3) design effective forest restoration strategies.

Where can you follow us?- You can follow PANTROP via our website (pantrop-eu.com) Twitter (@PantropEu), or Instagram (pantrop_eu).
Background- PANTROP aims to understand and predict the resilience of tropical forests to human-driven disturbance. It uses a pantropical approach by synthesizing current data (S1) and doing controlled experiments in Mexico, Ghana, and Australia (S2, S3).

General- A kickstart workshop was held in Mexico (Nov. 2019) with the PANTROP team to sharpen the project aims and measurement protocols. Teams of the PI, PhD student and local collaborators have visited each country and identified research sites. Fieldwork started in Nov 2019, was interrupted in March 2020 because of Covid, when staff had to return to the Netherlands for safety reasons, causing a 1-year delay. Now we are on steam again thanks to vaccinations and excellent local collaborators.


S1 Pantropical- This study compares forest recovery across continents by synthesizing chronosequence data. By comparing forests that differ in time since agricultural fields were abandoned, we can assess recovery.

● DATABASE EXPANSION. We have expanded the secondary forest database from 50 Latin American sites to 92 sites across the tropics. We have added 4 Asian sites and 17 African sites, including 2 new PANTROP-
funded chronosequence sites in Ghana.

● PREVIOUS LAND USE AFFECTS REGROWTH. We synthesized the current knowledge on how previous land use affects forest regrowth and proposed a framework to support the design of forest restoration actions
(Jakovac et al 2021 Biological Reviews).

● TROPICAL FORESTS CAN RECOVER SURPRISINGLY FAST. We published end 2021 a paper in Science (Poorter et al. 2021 Science) where we have analysed recovery of 12 forest attributes across 77 chronosequence
sites and found that tropical forests that regrow naturally on abandoned agricultural fields are surprisingly resilient: After 20 years they attain, on average, 78% of the values of neighbouring old-growth
forests.

● FAST RECOVERY BECAUSE OF MANY LEGACIES AND PRODUCTIVE CONDITIONS. Recovery is so fast because there are many legacies in the forest soil, such as seeds, resprouting tree stumps, and a well-developed
soil layer. In addition, tropical environments tend to be productive, with high temperature and rainfall throughout the year that fuel growth

● RECOVERY DIFFERS AMONGST FOREST ATTRIBUTES. Recovery (to 90% of old-growth forest values) differs strongly amongst forest attributes; it is fastest for soil fertility (less than 10 years) and for plant
functioning (less than 25 years), intermediate for structure and species diversity (25-60 years), and slowest for aboveground biomass and species composition (more than 120 years).

● NATURAL REGROWTH AS A NATURE-BASED SOLUTION. These results indicate that natural regrowth can be used as a nature based solution for ecosystem restoration, climate change mitigation, and biodiversity
conservation. The conditions are that previous land use has not been too extensive, too intense, or too long, and that there is sufficient forests or seed trees in the neighbourhood.


S2 Landscape & S3 Diversity. These field experiments analyze how forest recovery is affected by landscape forest cover (FC) and biodiversity (BD).

● PLOT ESTABLISHMENT. Fieldwork was interrupted and delayed because of Covid. We have established and monitored in Mexico 40 FC plots and 16 BD plots, in Ghana 42 FC and 6 BD plots. In Australia we have
established 9 FC plots because strict safety regulations did not allow to do more. The first remeasurements are coming in, so we can now assess how the forest regrows, and how biodiversity affects forest
productivity.
This study addresses key questions in ecology and advances our understanding how human-driven climate change, landscape degradation, and biodiversity loss affect forest resilience and succession. The insights can be applied to (1) reduce human impacts on tropical forests, (2) design resilient and multifunctional tropical landscapes, and (3) design effective forest restoration strategies.

● A NATURE-BASED SOLUTION FOR GLOBAL TARGETS. Given the local and global importance of secondary forests and their rapid recovery after 20 years (on average 78%, range 33-100%) under suitable social,
economic and environmental conditions, we encourage adoption of (assisted) natural regeneration as a low-cost, nature-based solution ecosystem restoration, climate change mitigation, and biodiversity
conservation. This allows to meet the goals of the United Nations’ sustainable development, the UN decade of Ecosystem Restoration (2020-2030), UN framework on climate change mitigation (COP 26), and the
Convention of Biological Diversity (COP 15).

● A MIX OF RESTORATION APPROACHES IS NEEDED. We recommend to preserve all old-growth forests as little is left, use natural regrowth where you can, and plant where you need to.

● THREE SIMPLE INDICATORS TO MONITOR FOREST RESTORATION SUCCESS. Maximum tree size, forest structural heterogeneity (that is, a large variation in tree sizes), and tree species richness are relatively easy to
measure and robust indicators of multidimensional recovery (Poorter et al. 2021 Science).

● DRY AND WET FORESTS REQUIRE DIFFERENT SPECIES FOR RESTORATION. Early successional tree species in wet and dry forests differ markedly in their traits; wet forests have traits that increase growth rates in a
productive, wet, environment whereas dry forests have traits that allow trees to avoid, delay, or tolerate drought in a seasonally dry environment (Poorter et al. 2021 Proceedings of the National Academy of
Scienses). Hence, species selection for active restoration should be fined-tuned to local site conditions.
Fieldsite Mexico: Dry forest region of Nizanda, with pastures and forests
Fieldsite Australia: Atherton Tablelands with dairy farms and rainforest remnants and corridors
Fieldsite Ghana: Dry forest region with shifting cultivation field and PhD student Jazz Kok