Lourens Poorter

Background and Aims: Global land-use change and climate change are transforming tropical forests into regrowing secondary forests, where early-successional species play a crucial role by colonizing abandoned lands and paving the way for later-successional species. While often considered a homogeneous group with uniformly fast strategies, this study evaluates the diversity of early-successional strategies from Ghanaian tropical dry and wet forests. Methods: We selected 30 early-successional species from Ghanaian dry and wet forests differing in leaf habit (deciduous vs. evergreen), and measured wood density and 12 morphological and physiological leaf traits related to drought adaptation and resource acquisition. Traits were compared between forest types and leaf habits using two-way ANOVA, and multivariate analyses identified trait associations and trade-offs. Key Results: Dry forest species were more drought-tolerant and had slower gas exchange rates than wet forest species, reflecting reduced water use under limited water availability. Multivariate trait analysis showed that early-successional species span a two-dimensional trait space with two main trade-offs: (1) drought tolerance (i.e. high absolute leaf turgor loss point and wood density) versus gas exchange, and (2) investment in leaf structural carbon versus nutrients. The two axes defined four strategies: species that (1) tolerate drought and have tough leaves (“tolerant-and-tough”), (2) tolerate drought and have nutrient-rich leaves (“tolerant-and-rich”), (3) grow rapidly and have tough leaves (“fast-and-tough”), and (4) grow rapidly and have nutrient-rich leaves (“fast-and-rich”). Conclusions: Early-successional species followed four diverse strategies rather than converging on a single, fast-growing, acquisitive strategy. Their strategies also extended beyond the commonly described fast–slow gradient, with unexpected trait combinations reflecting the contrasting demands of rapid carbon gain and water conservation during early succession. Such variation may steer successional trajectories because different environmental conditions select for different early-successional strategies.

Secondary forests are becoming an increasingly dominant component of tropical landscapes. They play a critical role in the global carbon cycle by removing atmospheric CO ₂ during regrowth after disturbance. Yet, their capacity to sequester carbon and the time needed to recover carbon stocks comparable to those of nearby old-growth forests remain poorly understood – particularly in sub-Saharan Africa, where forest clearing for smallholder agriculture is accelerating. Here, using ground-based data from 983 secondary forest plots across 32 sites in 12 African countries, we show that natural regeneration delivers substantial aboveground carbon gains within the first two decades (11–109 Mg C ha ^-1 ). These gains are substantially overestimated unless remnant biomass left on abandoned fields is accounted for. The median time to recover 90% of old-growth carbon stocks ranged from 36 to 92 years across sites, albeit with considerable uncertainty. Early carbon accumulation followed identifiable environmental gradients – increasing with precipitation, whereas the time needed to reach old-growth stocks decreased with the maximum climatic water deficit and remained poorly predicted. By combining field-derived biomass recovery trajectories with spatial environmental predictors, we map carbon recovery potential across Afrotropical secondary forests. Because full carbon recovery takes many decades – far longer than the timescales required to meet global climate targets by 2050 – secondary regrowth cannot reliably compensate for the loss of old-growth carbon, making the conservation of remaining old-growth forests essential.

Human‐modified tropical landscapes are mosaics of farmland, young regrowing forests, and old‐growth forests. These fragmented landscapes are hotter and drier than forested landscapes and, combined with climate change, may lead to shifts in forest community composition. We asked how macroclimate and surrounding landscape shape community‐level drought strategies of young regrowing secondary forests. We assessed community composition of 37 young secondary dry and wet forests in Ghana during the first 3 years of succession, collected drought‐related leaf and stem traits of their pioneer species, and quantified surrounding landscape cover within an 800‐m radius around each plot. Macroclimate had the strongest influence on community drought strategies. Dry forest communities avoided drought through leaf shedding, delayed drought through small compound leaves that reduce heat load, and tolerated drought through dense wood and slow‐wilting leaves that both help maintain function during drought stress. Wet forest communities showed the opposite suite of traits, reflecting prioritization of fast growth under high water availability. Landscape context reinforced different forest recovery trajectories by further shaping community traits. Agricultural cover reduced community wood density in the dry forest, whereas it increased wood density in the wet forest and tended to increase drought traits such as small, compound, and deciduous leaves. Surrounding secondary forest cover promoted fast‐growing species with acquisitive leaves and low leaf mass per area in the dry forest, likely due to increased propagule pressure of pioneer species. Greater surrounding old‐growth cover increased leaf dry matter content in the wet forest, supporting the recruitment of conservative, shade‐tolerant late‐successional species. Macroclimate, landscape context, and their interaction thus jointly shape community functional composition and drought strategies of regrowing forests.

Succession is a foundational concept in ecology, describing changes in populations, communities, and ecosystems over time following a disturbance. Predicting successional pathways is challenging because of high spatiotemporal variability. Here, we present a unifying mechanistic framework that integrates three core components of succession (start, speed, and direction) that define successional pathways. We monitored the first 5 years of forest succession in recently abandoned agricultural fields in six tropical landscapes across three countries that differ in land-use intensity and between dry and wet forests. We found that (i) secondary succession typically started with woody legacies and progressed slowly but directionally toward structurally complex, biodiverse forests, and (ii) the start and speed were greater in areas with short-duration, low-intensity (nonmechanized) land use associated with more biological legacies. This framework advances mechanistic understanding of succession by disentangling the start, speed, and direction, and provides a tool for designing effective forest restoration strategies.

Secondary succession is a widespread phenomenon in the Anthropocene due to global land‐use and climate change. Our ability to predict successional trajectories remains limited due to key knowledge gaps related to early secondary succession and how successional trajectories vary across socio‐ecological systems and multiple forest attributes. Therefore, we analyzed the first 5 years of secondary forest succession across six tropical landscapes (i.e., socio‐ecological systems) in three countries (Australia, Ghana, and Mexico) that differ in land‐use intensity and two main forest types (dry and wet). We established 122 permanent plots in recently abandoned agricultural fields, monitored them annually for up to 5 years, and quantified 12 forest attributes related to structure, diversity, functional composition, and biotic interactions. We found that a large variation in successional trajectories was explained by the six landscapes (average r ² across 12 attributes is 54%; range: 18%–78%), indicating that succession is the result of a socio‐ecological system. An additional 39% of the variation (range: 19%–70%) was explained by plots occuring within landscapes, which reflects variation in landscape context and local land use intensity. Countries had a stronger impact on succession than forest type, indicating that the social component is more important early in succession, whereas the ecological component may become more important later in succession. Countries with lower land use intensity (e.g., subsistence agriculture, shorter duration of use, no mechanization) showed a higher start and speed of succession, as vegetation legacies can kickstart succession. Forest attributes followed distinct successional trajectories: forest structure and diversity increased over time, reflecting a deterministic component of succession, whereas functional composition and biotic interactions varied more with forest type, reflecting environmental filtering. These findings highlight the importance of integrating early succession, socio‐ecological systems, and multiple dimensions of forest recovery to better understand and predict forest succession in human‐modified tropical landscapes.

Aims: Widespread land‐use change has expanded the area of young secondary forests. Yet, little is known about the drivers and mechanisms underlying their successional pathways, limiting the predictability of succession and its applicability in ecosystem restoration. We therefore assessed how dispersal, management, and environmental filters shape community assembly during tropical forest succession on abandoned agricultural fields. Location: Ghana. Methods: We established 18 permanent plots on abandoned subsistence fields in Ghana and monitored them over 4 years, yielding 67 plot–census combinations. The seed dispersal filter was quantified using surrounding landscape forest cover as a proxy, and the management filter was quantified on the basis of farmer interviews about land‐use history. For environmental filters, soil nutrients were measured at the start, and understory irradiance and soil moisture were recorded during the first 2 years. To assess how these filters affected community assembly, we measured six functional traits for 122 species across seven growth forms and applied a fourth‐corner analysis. Results: Forest structural development proceeded rapidly, particularly on fertile soils. Community assembly was jointly shaped by surrounding forest cover, land‐use history, and environmental conditions. Greater quantity and quality (age) of the surrounding forests facilitated the establishment of species with resource‐conservative trait values (e.g., high leaf dry matter content). Longer and more extensive previous land‐use practices favored short‐statured species with low leaf nitrogen concentration. Understory light availability declined with forest structural development, leading to a shift in the community from fast‐growing annual herbs to evergreen woody species with resource‐conservative trait values. Conclusion: Dispersal, management, and environmental filters collectively shaped community assembly, each playing distinct roles. Environmental filters strongly drove successional growth‐form replacement; dispersal filters modestly influenced the rate of community reassembly, and management filters weakly shaped the initial species composition. Together, these filters shape early tropical forest succession and generate spatial variation in long‐term successional trajectories.

Trees can differ enormously in their crown architectural traits, such as the scaling relationships between tree height, crown width and stem diameter. Yet despite the importance of crown architecture in shaping the structure and function of terrestrial ecosystems, we lack a complete picture of what drives this incredible diversity in crown shapes. Using data from 374,888 globally distributed trees, we explore how climate, disturbance, competition, functional traits, and evolutionary history constrain the height and crown width scaling relationships of 1914 tree species. We find that variation in height–diameter scaling relationships is primarily controlled by water availability and light competition. Conversely, crown width is predominantly shaped by exposure to wind and fire, while also covarying with functional traits related to mechanical stability and photosynthesis. Additionally, we identify several plant lineages with highly distinctive stem and crown forms, such as the exceedingly slender dipterocarps of Southeast Asia, or the extremely wide crowns of legume trees in African savannas. Our study charts the global spectrum of tree crown architecture and pinpoints the processes that shape the 3D structure of woody ecosystems.