Geomorphic transience moderates topographic controls on tropical canopy foliar traits

• Published in: Ecology letters Vol. 23; no. 8; pp. 1276 - 1286
• Main Authors: Chadwick, K. Dana, Asner, Gregory P., Uriarte, Maria
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.08.2020
• Subjects: Canopies; Catchments; Channels; Environmental changes; Erosion rates; Foliar traits; Geomorphology; imaging spectroscopy; Landscape; landscape evolution; Lidar; Morphology; Mountains; Nutrient content; Process controls; rock derived nutrients; Species diversity; Trajectory analysis; Uplift; rock derived nutrients; Foliar traits; landscape evolution; imaging spectroscopy
• ISSN: 1461-023X; 1461-0248
• DOI: 10.1111/ele.13531

Tropical ecosystems that exist on mountainous terrain harbour enormous species and functional diversity. In addition, the morphology of these complex landscapes is dynamic. Stream channels respond to mountain uplift by eroding into rising rock bodies. Many local factors determine whether channels are actively downcutting, in relative steady‐state, or aggrading. It is possible to assess the trajectory of catchment‐level landscape evolution utilising lidar‐based models, but the effect of these trajectories on biogeochemical gradients and organisation of canopy traits across climatic and geochemical conditions remain uncertain. We use canopy trait maps to assess how variable erosion rate within catchments influence hillslope controls on canopy traits across Mt. Kinabalu, Borneo. While foliar nutrient content generally increased along hillslopes, these relationships were moderated by catchment responses to changing erosion pressure, with active downcutting associated with greater turnover in canopy traits along hillslopes. These results provide an understanding of geomorphic process controls on forest functional diversity. We find that transient landscape evolution, defined as variation in erosion rates across catchments as they respond to pressure from changing rates of channel downcutting, drives the distribution of tropical forest foliar traits in complex tropical montane regions. While we have long known that topographic position is related to biogeochemical properties, understanding the underlying processes that determine the strength and direction of observed patterns is the key to generalizing our understanding.