The Amazon ecosystem plays a vital role in global climate regulation and biodiversity conservation but faces escalating threats from deforestation and degradation. The resulting secondary forests (SFs) provide a promising opportunity for Transformative Territorial Management, fostering restoration and enhancing conservation values. This study evaluated aboveground biomass (AGB), species diversity, forest structure, and soil properties in SFs of the Colombian Amazon along a chronosequence, from early to mature successional stages, in landscapes of mountains and of hills to identify key indicators for effective restoration management. The results show a consistent increase in AGB, species diversity, forest structure, and soil quality with forest age, though recovery patterns varied between both landscapes evaluated. Topographic differences influenced successional dynamics, with mountainous landscapes showing faster early recovery compared to the steadier, linear growth observed in hill areas. In hills, AGB at 10 years reached 12.65% of the biomass expected in a mature forest, increasing to nearly 42% by 40 years of abandonment, at a rate of 0.708 Mg C ha⁻¹ year⁻¹. In contrast, in the mountain landscape, AGB at 10 years reached approximately 8.35% of the carbon in a mature forest and increased to nearly 63.55% at 40 years. Forest age and soil properties emerged as primary drivers of AGB recovery, while diversity and forest structure played indirect but significant roles. In hill areas, soil conservation practices are critical for maintaining steady growth, whereas mountain regions benefit from assisted natural regeneration (ANR) to accelerate recovery. These findings highlight the importance of prioritizing the management of SFs as a central strategy for achieving restoration goals. Such practices are essential to enhance the ecological resilience of SFs and ensure their long-term sustainability, fostering their role as key contributors to restoration efforts and the provision of ecosystem services.

Succession in abandoned pastures in the tropics can progress along different pathways, and the changes in biodiversity on local and landscape scales, as well as in species turnover (β diversity), are still unclear. This study assessed the role of secondary forests as a plant biodiversity reservoir or as evidence of a pattern of biodiversity homogenization in a chronosequence of abandoned pastures in two highly fragmented landscapes (hills and mountains) in the Colombian Amazon. In each landscape, the plant community composition, growth habits, species richness accumulation, indicator species identification, composition dissimilarity, and influence of above- and below-ground environmental filters were evaluated in four successional stages: (i) degraded pastures (DP) (90 years old). A total of 918 species, 78 families, and 11,284 individuals were recorded. The most representative growth habits were trees and shrubs, while palms and lianas were minimal. The species accumulated rapidly in DP and EF, contrary to that observed in IF and OF; thus, DP and EF achieve inventory completeness faster than IF and OF. It was necessary to include more plots to obtain inventory completeness in IF and OF. OF had a high α diversity with similar species composition throughout (low β diversity) and high homogeneity, suggesting biotic homogenization. On the other hand, IF presented the highest species differentiation (high β diversity) and a higher divergence in species composition than OF. The spatial distance and environmental dissimilarity had the most important role in determining species composition. Finally, our results show divergence in the plant composition across the chronosequence, where DP was opposite from OF in hills. However, in mountains, DP followed the EF and IF categories. The deviation in the species composition in EF and IF suggests an exchange of species in intermediate forest ages.

Increasing biodiversity in highly diverse plant communities can jointly increase ecosystem function and ecosystem vulnerability. This paradox requires further attention. This study analyzed the functional response of plant communities to above- and below-ground parameters along the chronosequence (degraded pastures (DP), early forests (EF), intermediate forests (IF), and old-growth forests (OF)) in two highly fragmented landscapes of the Colombian Amazon as an estimate of the level of functional vulnerability. Three sets of functional attributes were evaluated: (i) functional composition based on the community-weighted mean (CWM) of five traits; (ii) functional diversity based on the multi-trait indices and functional dispersion (FDis) of each individual trait; and (iii) the functional vulnerability at the community-level and species-level. The individual traits did not show a clear pattern along the chronosequence. However, the trend indicated an increase in the values of resource conservation traits with the age of abandonment. The functional response of the community did not vary between landscapes. Between DP and OF, there was a significant increase in functional diversity and a decrease in functional redundancy, which increased community-level vulnerability. Consequently, the more vulnerable species were observed in the IF and OF plots. In addition, a decrease in environmental parameters, such as penetration resistance, bulk density and Ca content, and an increase in slope, precipitation, electric conductivity, pH, clay, organic material, and P and N contents increased the vulnerability. We elucidated the need for secondary forest management in terms of conservation and restoration to maintain the capacity to respond to changing environmental conditions in highly fragmented landscapes in the Andean–Amazonian transition.

Neotropical landscapes are often characterized as mosaics of actively grazed pastures and forest fragments at various stages of succession. Restoring abandoned pastures requires intervening with actions informed by local ecological succession. Here we evaluate how litter production, a key component of nutrient cycling in forests, varies between physiographic landscapes (hill and lowland mountain), among stand age groups (early-secondary: 0–20 year, intermediate-secondary: 20–40 year, and old-growth forests: > 40 year), and in response to climatic (precipitation and irradiation) and forest structure and biodiversity variables (stand density, basal area, species density, diversity), in a tropical humid forest chronosequence. Total and leaf litter production was higher in the lower elevation hill landscape. Leaf litter production increased with stand age in both landscapes but only correlated positively with forest structure and biodiversity in the hill landscape. Lack of correlation in the mountain landscape is attributed to greater variance in structure and species composition in the subset of plots selected from this landscape for this study. Both landscapes exhibited an asynchronous, bimodal regime of leaf fall in response to precipitation. Leaf litter peaks prior to the wet season likely occur in response to water stress, while peaks after the wet season that coincided with increasing solar irradiation are likely the result of a leaf turnover strategy to optimize photosynthesis. Ecological succession in these landscapes does not appear limited in leaf litter production, but further research on the drivers of leaf litter production recovery is necessary to adequately guide intervention efforts.

Key message: Pre-germination requirements are not accurately predicted by seed traits of size and mass. However, small-seeded species show high germination and slow early seedling growth rates. Deforestation in the tropics is one of the greatest biodiversity crises of the Anthropocene. In response, tropical countries such as Colombia have committed to restoring degraded lands and reconnecting forest fragments. To contribute to this mission, we evaluated how easy-to-measure seed functional traits predicted germination requirements and early seedling growth rates (RGRs) for 11 tree species native to the Andean-Amazon piedmont region. Pre-sowing treatments followed a 3 × 3 factorial design: three light conditions (full, partial, and no light) and three pre-germination treatments (hot water, abrasion, and control). A cluster analysis grouped species into three groups driven chiefly by highly correlated variables of seed size and mass. However, species within and among functional groups differed in their response to pre-germination treatments. One exception includes the small-seeded species group responding with little-to-no germination to the absence of light. Since functional traits were highly correlated, we used Principal Component Regression (PCR) to predict germination metrics (germination percentage, velocity, and vigor) and RGRs. The multivariate trait axis of seed size and seed mass measurements (PC1) correlated negatively with germination metrics and positively with RGRs. Our results highlight the challenges associated with using easy-to-measure functional traits to deduce the most effective pre-sowing treatment. Other more relevant functional traits can be measured in lab, but a shotgun approach to testing pre-germination treatments may be more cost-effective. High germination in small-sized seed species highlights the early-successional niche these species occupy, but reduced RGR may represent a tradeoff associated with having relatively few resources stored in seed.