Rainfall seasonality and drought performance shape the distribution of tropical tree species in Ghana

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.

Weak tradeoff between xylem hydraulic efficiency and safety: climatic seasonality matters

“…This may explain why a previous global analyses did not find significant climatic effects on the hydraulic trade‐off based on mean annual precipitation and temperature (Gleason et al ., 2016b). Furthermore, the seasonality of precipitation, VPD, and SR trends reported here are also consistent with the water–energy hypothesis, which not only influences regional plant ecological adaptation strategies (Amissah et al ., 2018) but may also affect global plant diversity (Kreft & Jetz, 2007).…”

Differential Expression of Maize and Teosinte microRNAs under Submergence, Drought, and Alternated Stress

“…Since cellular protection is a priority during stress, it has been shown that some responses to dehydration and excess water have common molecular effectors acting as nodes in the crosstalk between responses to drought and submergence [ 9 , 10 , 11 ]. This may have allowed wild plants to evolve tolerance mechanisms to cope with alternate drought and flooding events, which commonly occur consecutively in some regions of the world [ 12 , 13 ].…”

Community assembly as a basis for tropical forest restoration in a global change scenario

“…All bioclimatic variables are derived from the monthly or daily temperature and rainfall values in order to produce ecologically important variables used for niche modelling with high consistency (García-Callejas & Araújo 2016; Morales-Barbero & Vega-Álvarez 2019). The applied bioclimatic variables signify annual means (Booth 2016; Kendal et al 2018), seasonality (Hereford et al 2017; Tonkin et al 2017) and severe environmental factors (e.g., duration and severity of water excess and deficits) that influence species distribution and performance (e.g., Amissah et al, 2018).…”