# Unlocking Tropical Forest Complexity: How Tree Assemblages in Secondary Forests Boost Biodiversity Conservation

## TL;DR

This study presents a national method to identify and characterize tropical forest ecosystems using dominant tree species, highlighting the role of secondary forests in biodiversity conservation.

## Contribution

A replicable national approach using dominant tree species to delineate and characterize tropical forest ecosystems is developed.

## Key findings

- In Costa Rica, 495 dominant tree species defined 10 in situ clusters, with 7 main clusters successfully modelled.
- The approach aligns with local forest classifications and highlights ecological trends based on species dominance, topography, and climate.
- Secondary forest distribution analysis revealed ecosystem vulnerability and the importance of these forests in maintaining biodiversity.

## Abstract

Secondary forests now dominate tropical landscapes and play a crucial role in achieving COP15 conservation objectives. This study develops a replicable national approach to identifying and characterising forest ecosystems, with a focus on the role of secondary forests. We hypothesised that dominant tree species in the forest canopy serve as reliable indicators for delineating forest ecosystems and untangling biodiversity complexity. Using national inventories, we identified in situ clusters through hierarchical clustering based on dominant species abundance dissimilarity, determined using the Importance Variable Index. These clusters were characterised by analysing species assemblages and their interactions. We then applied object‐oriented Random Forest modelling, segmenting the national forest cover using NDVI to identify the forest ecosystems derived from in situ clusters. Freely available spectral (Sentinel‐2) and environmental data were used in the model to delineate and characterise key forest ecosystems. We finished with an assessment of the distribution of secondary and old‐growth forests within ecosystems. In Costa Rica, 495 dominant tree species defined 10 in situ clusters, with 7 main clusters successfully modelled. The modelling (F1‐score: 0.73, macro F1‐score: 0.58) and species‐based characterisation highlighted the main ecological trends of these ecosystems, which are distinguished by specific species dominance, topography, climate, and vegetation dynamics, aligning with local forest classifications. The analysis of secondary forest distribution provided an initial assessment of ecosystem vulnerability by evaluating their role in forest maintenance and dynamics. This approach also underscored the major challenge of in situ data acquisition.

Secondary forests are crucial for achieving COP15/16 conservation goals. An operational national approach was developed to identify and characterise forest ecosystems based on the dominant tree species in the canopy, serving as indicators for ecosystem extent and condition. Secondary forest distribution was assessed to understand ecosystem vulnerability.