Large tree species composition, not growth rates, is affected by topography in a Bornean tropical forest

• Published in: Biotropica Vol. 53; no. 5; pp. 1290 - 1300
• Main Authors: Limin, Army, Slik, Ferry, Sukri, Rahayu Sukmaria, Chen, Sheng‐Bin, Ahmad, Joffre Ali
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.09.2021
• Subjects: aboveground biomass; Area; Biomass; Brunei; Brunei Darussalam; Climate change; Community composition; Composition; dendrometers; Drought; Elevation; elevational gradient; floristic shift; forest reserves; Growth rate; Herbivores; large tree dynamics; Mineral nutrients; Moisture content; Mortality; Nutrient dynamics; Plant diversity; Plant species; Population decline; Recruitment; sample size; Soil; Soil density; Soil properties; Soil water; soil water availability; Species; Species composition; species diversity; Swamps; Topography; tree and stand measurements; tree mortality; Trees; Tropical climate; tropical forest; Tropical forests
• ISSN: 0006-3606; 1744-7429
• DOI: 10.1111/btp.12969

Large trees (diameter at breast height ≥50 cm) play a vital role in providing ecological services in tropical forests and can store up to 50% of aboveground biomass. We expected that topography (as a nutrient and drought proxy) would affect large tree dynamics, biomass, diversity, and composition patterns. To test this, we established a 15‐ha permanent plot at Andulau Forest Reserve (Brunei Darussalam, Borneo) with an elevation ranging from 42 m (swamp) to 92 m (ridge tops). All 559 large trees (131 species) were labeled, identified, and fitted with dendrometers. Stem density, basal area (BA), soil and litter properties, absolute diameter growth rate (AGR), and recruitment and mortality rates of large trees were determined for five elevational zones for the period 2016–2019. Stem density and BA of large trees were significantly higher in the upslope and ridge areas of the plot, and a clear shift in large tree species composition was found across the elevational zones, with the swampy area differing most from all others. However, AGR did not differ between elevational zones. Large tree mortality was balanced by recruitment, but sample size was too low to detect topographical patterns. Our findings suggest that the large tree community retained similar growth rates across soil water and nutrient gradient via a shift in species composition. If so, predicted declines in large tree productivity with climate change may, over time, also be offset by changes in species composition. We studied whether large trees with a diameter of 50 cm and above differ in dynamics (growth, recruitment, mortality), composition, and structure (density and basal area) along a local topographical gradient (proxy for soil nutrient and water status). We found that large tree growth remained constant, but species composition and structure changed along the topographical gradient. Our study suggests that climate change in the form of droughts may not so much affect large tree productivity but rather lead to shifts in species composition.