Species communities along a recovery gradient in the tropics - with a focus on deadwood

Tropical forests are among the most biodiverse and functionally important ecosystems on Earth, playing a crucial role in global biogeochemical cycles, especially carbon and water regulation. However, large portions of these forests have been degraded due to deforestation, land conversion, and unsustainable management, particularly in Latin America. In response, ecological restoration and natural regeneration are increasingly promoted as cost-effective strategies to recover biodiversity and ecosystem functions. Despite this, our understanding of the structural and functional recovery of tropical forests across different land-use legacies remains limited, especially regarding the role of deadwood, ecosystem service dynamics, and biodiversity indicators at the landscape scale. Deadwood and its associated communities of insects and fungi play a central role in these processes, yet the impacts of forest degradation and recovery on these organisms remain poorly understood. As part of the DFG-Research Unit "Reassembly", this thesis investigates how the recovery of tropical forests affects deadwood quantity, diversity, and its associated communities of saproxylic beetles and fungi, as well as the composition of birds. The study design is embedded the Chocó across a tropical forest recovery gradient in the lowland forest of Ecuador, a global biodiversity hotspot undergoing rapid land-use change. By integrating measures of biodiversity, community composition, and interaction networks across taxonomic groups, this thesis provides new insights into the recovery trajectories particularly of saproxylic communities. Chapter I provides the conceptual groundwork for this dissertation by examining the ecological consequences of tropical forest degradation and the potential of natural regeneration as a pathway for biodiversity and ecosystem recovery. It contextualizes the study within the critically threatened Chocó rainforest of Ecuador, highlighting the potential long-lasting effects of land-use legacies on biodiversity across multiple taxonomic and functional groups. The chapter emphasizes the importance of structural elements such as deadwood and explores how saproxylic beetles, wood-inhabiting fungi and birds can serve as key indicators for the recovery of the communities. Together, these components frame the central questions and objectives of the dissertation, offering a multidisciplinary lens to improve our understanding of the resilience of tropical ecosystems in regenerating landscapes. Chapter II focuses on deadwood, a key substrate for saproxylic organisms and carbon dynamics. I quantified the amount and diversity of coarse (≥7 cm diameter) and fine (<7 cm) woody debris in 62 plots along a chronosequence of forest recovery from agriculture to old-growth. Contrary to expectations, deadwood volume did not consistently increase with recovery time, but diversity in size, decay stage, and wood type showed a positive trend. Fine woody debris increased, especially in former pastures, highlighting differences in legacy effects of land-use history. These findings suggest that recovering forests can harbor a diverse array of deadwood types, potentially supporting saproxylic biodiversity and contributing to carbon storage beyond old-growth forests Chapter III examines the diversity and assembly processes of wood-inhabiting fungi colonizing standardized logs along the same forest recovery gradient. Using DNA metabarcoding, I analyzed fungal communities in logs of five tree species exposed experimentally in all plots. Fungal diversity per plot increased with forest age, especially among rare taxa, but decreased again in old-growth forests, revealing a hump-shaped pattern. This suggests that mid-successional stages may offer optimal conditions for fungal diversity due to a combination of sufficient resource availability and habitat heterogeneity but still limited competition. In terms of community assembly, fungal species became increasingly aggregated in older forests, and spatial factors began to outweigh host-tree identity in shaping community composition. Despite the high dispersal potential of fungal spores, these results indicate that wood-inhabiting fungi in secondary forest after almost four decades have not yet reached the assembly patterns typical for old-growth forests. This chapter emphasizes the ecological value of mid-successional forests and the need to consider spatial structuring in fungal biodiversity assessments. In Chapter IV, I examine how saproxylic beetle diversity and host-tree interaction networks respond to forest recovery. Standardized logs from five tree species of varying wood density were placed across 62 plots in four recovery stages. Beetle emergence after six months revealed increasing abundance, species richness, and network γ-diversity with forest recovery. Surprisingly, interaction network specialization was higher in agricultural and late-regeneration plots, suggesting that community restructuring may follow nonlinear trajectories. Logs from low-density trees supported fewer individual beetles but exhibited higher γ-diversity, particularly among rare species. This highlights how resource traits interact with successional dynamics to shape community assembly and ecological interactions. Overall, this chapter provides strong evidence that saproxylic beetle communities are sensitive to forest recovery and that their interaction networks can re-establish relatively rapidly under favorable conditions. Finally, Chapter V explores avian biodiversity as an indicator of ecological integrity across the same forest recovery gradient. Using passive acoustic monitoring and ecological niche metrics, I studied 323 bird species across 66 plots, representing a gradient from active agriculture to old-growth forest. The analysis showed that birds in agricultural areas had broader niche breadths, larger geographic ranges, and traits related to mobility, while forest-specialist birds exhibited narrower niches and lower mobility. These findings demonstrate that niche-based metrics offer valuable tools for rapid biodiversity assessment and conservation planning. While this chapter differs in focus from the others, it complements the broader ecological narrative by offering a landscape-scale view of biodiversity recovery. It also demonstrates that recovery patterns can be inferred from functional traits and niche metrics, which are particularly relevant for conservation monitoring. Overall, this dissertation highlights the critical role of deadwood and its associated biota in supporting biodiversity and ecosystem functions in recovering tropical forests. While saproxylic beetle communities show rapid responses to changes in deadwood diversity, fungi exhibit more complex assembly processes influenced by spatial factors and legacy effects. Avian communities, in turn, reflect broader patterns of ecological integrity and functional traits associated with forest recovery. Together, these chapters demonstrate that recovery is taxon-specific and influenced by both structural and spatial components of the landscape. Importantly, this work underscores the value of maintaining and enhancing deadwood diversity as a core strategy for restoring biodiversity and ecosystem functionality in tropical forest landscapes undergoing regeneration.