Abstract
Tree species distribution in lowland tropical forests is strongly associated with rainfall amount and distribution. Not only plant water availability, but also irradiance, soil fertility, and pest pressure covary along rainfall gradients. To assess the role of water availability in shaping species distribution, we carried out a reciprocal transplanting experiment in gaps in a dry and a wet forest site in Ghana, using 2,670 seedlings of 23 tree species belonging to three contrasting rainfall distributions groups (dry species, ubiquitous species, and wet species). We evaluated seasonal patterns in climatic conditions, seedling physiology and performance (survival and growth) over a 2‐year period and related seedling performance to species distribution along Ghana's rainfall gradient. The dry forest site had, compared to the wet forest, higher irradiance, and soil nutrient availability and experienced stronger atmospheric drought (2.0 vs. 0.6 kPa vapor pressure deficit) and reduced soil water potential (−5.0 vs. −0.6 MPa soil water potential) during the dry season. In both forests, dry species showed significantly higher stomatal conductance and lower leaf water potential, than wet species, and in the dry forest, dry species also realized higher drought survival and growth rate than wet species. Dry species are therefore more drought tolerant, and unlike the wet forest species, they achieve a home advantage. Species drought performance in the dry forest relative to the wet forest significantly predicted species position on the rainfall gradient in Ghana, indicating that the ability to grow and survive better in dry forests and during dry seasons may allow species to occur in low rainfall areas. Drought is therefore an important environmental filter that influences forest composition and dynamics. Currently, many tropical forests experience increase in frequency and intensity of droughts, and our results suggest that this may lead to reduction in tree productivity and shifts in species distribution.
Highlights
Tropical forests are under threat of longer and intense drought as a result of global climate change
Two alternative hypotheses may explain species distribution along water availability gradients: (a) dry forest species, hereafter referred to as “dry species” may have a better growth and survival performance in dry conditions, and wet forest species, hereafter referred to as “wet species” may have a better performance in wet conditions (Baltzer & Davies, 2012; Baltzer, Davies, Bunyavejchewin, & Noor, 2008), or (b) there may be a trade- off between drought survival and growth performance, in which species ability to tolerate and survive dry conditions comes at the expense of a reduced growth in wet conditions
How do species with different distribution types differ in their physiological response and performance? We hypothesized that species will have a home advantage and that in the dry forest the dry species can cope with increased drought by having an anisohydric strategy; that is, they will keep their stomata open and have higher stomatal conductance in comparison with the wet species, leading to a more negative leaf water potential
Summary
Tropical forests are under threat of longer and intense drought as a result of global climate change. We hypothesized that species will have a home advantage and that in the dry forest the dry species can cope with increased drought by having an anisohydric strategy; that is, they will keep their stomata open and have higher stomatal conductance in comparison with the wet species, leading to a more negative leaf water potential (cf de Sade et al, 2012). As a result, they will have higher growth and survival rate than the wet-distribution species. Can relative drought performance in the field explain a continuum of species distribution along the rainfall gradient in Ghana? We hypothesized that species that exhibit higher drought survival and growth in the dry forest relative to the wet forest will occur at the drier part of the rainfall gradient (cf. Engelbrecht et al, 2007)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
