Leaf to air temperature difference and leaf-level photosynthetically active radiation (PAR) in Afromontane species in common garden plantations at two elevations in Rwanda, 2025

The measurements were conducted within a network of common garden plantations established to evaluate the performance of native tree species from Afromontane and transitional rainforests in the Albertine Rift region of Rwanda. Experimental sites were established between December 2017 and January 2018 along an elevational gradient and include a 15.2 °C site with a mean annual temperature (MAT)site (elevation = 2400 m a.s.l.; T99th percentile = 23.1 °C; annual precipitation = 2100 mm; latitude = 2.515° S, longitude = 29.395556° E) and a 20.0 °C MAT site (elevation = 1600 m a.s.l.; T99th percentile = 28.5 °C; annual precipitation = 1700 mm; latitude = 2.475° S, longitude = 29.780277° E). A third low-elevation site is part of the experimental network but was not included in this dataset.

At each site, approximately 1,800 trees were planted across 18 plots arranged in six treatment combinations with three replicates per treatment. The experiment included 20 native tropical Afromontane and highland species, with five individuals per species planted in each plot. Treatments consisted of three water levels (low, medium, and high) crossed with two nutrient levels (unfertilised and fertilised + limed). Water treatments were designed to mimic the natural precipitation regimes across the experimental sites, while nutrient treatments were used to reduce differences in soil fertility among sites.

For each species at each site, six individual trees (each from a different plot) were selected from treatment plots corresponding to the natural precipitation regimes of the two experimental sites in question (15.2 °C and 20 °C MAT sites) and without nutrient addition. Each selected tree was instrumented with three homemade leaf thermocouples and one leaf-level PAR sensor on three healthy, fully expanded, sun-exposed leaves. This resulted in a target sample size of 18 leaves per species per site. The PAR sensors were positioned adjacent to one of the instrumented leaves.

Leaf-to-air temperature differences (ΔT) were measured using homemade leaf thermocouples, while leaf-level PAR was measured using photodiode sensors. Vertical leaf angle was measured using smartphone-based protractor and compass applications, and correspondent measurements together with other leaf thermoregulation traits are found in Restrepo et al 2026 (see supporting documentation).
Quality control procedures included regular inspection of sensors, power supply systems, and data logging equipment, together with periodic data downloads and validation checks to ensure data continuity and reliability. Measurements were screened for sensor malfunction, data gaps, and anomalous values before analysis.

The dataset includes detailed metadata that describes variables, units, sampling locations, measurement protocols, and quality control procedures. Additional information on sampling design, data processing, and dataset-specific methodologies is provided in the accompanying supporting documentation.