Life in the fast lane: early-successional species show four different strategies

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.

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.

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").

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.