Landscape-scale changes in forest structure and functional traits along an Andes-to-Amazon elevation gradient

C B Anderson,D E Knapp,Y Malhi,R Tupayachi,F Sinca,G P Asner,R E Martin

doi:10.5194/bg-11-843-2014

C B Anderson, D E Knapp + Show 5 more

Open Access

https://doi.org/10.5194/bg-11-843-2014

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Abstract

Abstract. Elevation gradients provide opportunities to explore environmental controls on forest structure and functioning. We used airborne imaging spectroscopy and lidar (light detection and ranging) to quantify changes in three-dimensional forest structure and canopy functional traits in twenty 25 ha landscapes distributed along a 3300 m elevation gradient from lowland Amazonia to treeline in the Peruvian Andes. Elevation was positively correlated with lidar-estimated canopy gap density and understory vegetation cover, and negatively related to canopy height and the vertical partitioning of vegetation in canopies. Increases in canopy gap density were tightly linked to increases in understory plant cover, and larger gaps (20–200 m2) produced 25–30 times the response in understory cover than did smaller gaps (< 5 m2). Vegetation NDVI and photosynthetic fractional cover decreased, while exposed non-photosynthetic vegetation and bare soil increased, with elevation. Scaling of gap size to gap frequency (λ) was, however, nearly constant along the elevation gradient. When combined with other canopy structural and functional trait information, this suggests near-constant canopy turnover rates from the lowlands to treeline, which occurs independent of decreasing biomass or productivity with increasing elevation. Our results provide the first landscape-scale quantification of forest structure and canopy functional traits with changing elevation, thereby improving our understanding of disturbance, demography and ecosystem processes in the Andes-to-Amazon corridor.

Highlights

Tropical elevation gradients offer natural laboratories for studies of environmental controls on forest composition, structural habitats, functional processes, and ecosystem development (Vitousek et al, 1992)
Results often show that species composition changes markedly with increasing elevation in the tropics (Silman, 2006; Lieberman et al, 1996), yet patterns of canopy functional traits and productivity have been much more variable (e.g., Vitousek et al, 1988; Raich et al, 1997; Girardin et al, 2010)
The gradient considered in this study provided this rare setting to assess the role of elevational change in determining vegetation structure, functional traits, and their interactions

Summary

Introduction

Tropical elevation gradients offer natural laboratories for studies of environmental controls on forest composition, structural habitats, functional processes, and ecosystem development (Vitousek et al, 1992). Results often show that species composition changes markedly with increasing elevation in the tropics (Silman, 2006; Lieberman et al, 1996), yet patterns of canopy functional traits and productivity have been much more variable (e.g., Vitousek et al, 1988; Raich et al, 1997; Girardin et al, 2010). While reports on elevation-based changes in functional traits vary widely in the tropics, patterns of and the processes underlying forest canopy structure such as volume, canopy layering and gap dynamics remain even less understood. Structure creates the habitat for all other forestdwelling species (Terborgh, 1992), so a quantitative understanding of canopy structural change with elevation underpins conservation and management planning

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