Abiotic Controls on Macroscale Variations of Humid Tropical Forest Height

Abstract

Spatial variation of tropical forest tree height is a key indicator of ecological processes associated with forest growth and carbon dynamics. Here we examine the macroscale variations of tree height of humid tropical forests across three continents and quantify the climate and edaphic controls on these variations. Forest tree heights are systematically sampled across global humid tropical forests with more than 2.5 million measurements from Geoscience Laser Altimeter System (GLAS) satellite observations (2004)(2005)(2006)(2007)(2008). We used top canopy height (TCH) of GLAS footprints to grid the statistical mean and variance and the 90 percentile height of samples at 0.5 degrees to capture the regional variability of average and large trees globally. We used the spatial regression method (spatial eigenvector mapping-SEVM) to evaluate the contributions of climate, soil and topography in explaining and predicting the regional variations of forest height. Statistical models suggest that climate, soil, topography, and spatial contextual information together can explain more than 60% of the observed forest height variation, while climate and soil jointly explain 30% of the height variations. Soil basics, including physical compositions such as clay and sand contents, chemical properties such as PH values and cation-exchange capacity, as well as biological variables such as the depth of organic matter, all present independent but statistically significant relationships to forest height across three continents. We found significant relations between the precipitation and tree height with shorter trees on the average in areas of higher annual water stress, and large trees occurring in areas with low stress and higher annual precipitation but with significant differences across the continents. Our results confirm other landscape and regional studies by showing that soil fertility, topography and climate may jointly control a significant variation of forest height and influencing patterns of aboveground biomass stocks and dynamics. Other factors such as biotic and disturbance regimes, not included in this study, may have less influence on regional variations but strongly mediate landscape and small-scale forest structure and dynamics.

Active microwave observations of diurnal and seasonal variations of canopy water content across the humid African tropical forests

“…The solar‐induced fluorescence data are obtained from the MetOP‐Sat's Global Ozone Monitoring Experiment‐2 (GOME‐2) instrument, using L3 data version 2.6 [ Joiner et al ., ] (January 2007 to December 2009). Lastly, lidar‐based canopy height estimates from Geoscience Laser Altimeter System (GLAS) were used during those months when they were available [ Lefsky , ; Yang et al ., ]. To reduce noise, a single seasonal cycle was calculated by averaging over all years for a given month and pixel combination.…”

Interpreting forest diversity-productivity relationships: volume values, disturbance histories and alternative inferences

“…Maybe, rather than diversity facilitating productivity it is productivity that facilitates diversity (Waide et al 1999;Coomes et al 2009;Jucker et al 2018). For example, there are data indicating that taller forests occur on richer, presumably more productive, soils (at least in Africa and Asia, Yang et al 2016), and also that, all else being equal within a given region, taller forests tend to contain more species than shorter forests (Huston 1994;Duivenvoorden 1996).…”

Does biomass growth increase in the largest trees? Flaws, fallacies and alternative analyses

“…Comparisons among sites and regions suggest the largest sizes that trees can achieve are influenced by many factors. For example, climate and soil can explain around 30% of the variation in humid forest tree height across three continents, with other location-specific factors accounting for another 30% (Yang et al 2016). If fundamental limits are involved, they should manifest themselves in sufficiently large stems through mortality and/or declining growth, though the potentially complex interplay of endogenous and exogenous processes on tree growth and longevity poses challenges (Lee & Muzika 2014).…”