Functional Trait Plasticity and Acclimation Capacity of Dominant Savanna Tree Species Under Simulated Climate Warming in North West Nigeria

Savanna tree species in North West Nigeria are projected to experience sustained increases in temperature and altered rainfall seasonality under climate change scenarios, yet their capacity for phenotypic acclimation and functional trait plasticity in response to warming remains largely uncharacterised. This study quantifies functional trait plasticity and acclimation responses of six dominant savanna tree species to simulated temperature increases of 1.5 and 3 degrees Celsius above ambient, imposed using open-top warming chambers over two growing seasons in common garden experiments in Sokoto and Zamfara States. Functional traits measured at regular intervals included specific leaf area, leaf stomatal density, water use efficiency determined from carbon-13 discrimination, maximum photosynthetic rate, and root-to-shoot biomass allocation. Thermal performance curves for photosynthesis and respiration were derived to quantify thermal optima and tolerance ranges. Trait plasticity indices were calculated to compare acclimation capacity across species. Results show significant but species-specific plasticity in photosynthetic traits and water use efficiency, with early-successional species showing greater plasticity than late-successional species. At simulated 3 degree Celsius warming, all species showed respiratory rate increases that exceeded photosynthetic rate increases, suggesting net carbon balance deterioration. Stomatal downregulation under warming differed significantly between species linked to leaf hydraulic architecture. Vitellaria paradoxa exhibited the narrowest thermal tolerance range among tested species, raising concern for this economically critical species under future warming. The study provides mechanistic data on tree species climate sensitivity essential for projecting savanna composition change in North West Nigeria. Keywords: functional trait plasticity, climate warming, savanna trees, acclimation, North West Nigeria.