Spatial and temporal heterogeneity of light and soil water along a terra firme transect in Amazonian Ecuador: effects on tree seedling survivorship, growth, and allocation

Abstract

To better understand the availability of plant resources on the forest floor in the Amazon and also to show the effect of their heterogeneity on tree seedlings, I described the spatial and temporal variation of light and soil water along a 100 m transect in a terra firme forest for 6 months and recorded responses of three tree species planted on that transect after 1 year’s growth. I found that (i) the spatial heterogeneity across the transect was greater than the temporal heterogeneity at any given microsite on the transect for both light and water and there was a positive correlation between them, (ii) Couepia obovata Ducke, the largest seeded and the only subcanopy tree, survived the best and showed both the largest relative height growth rate (RHGR) and the largest specific leaf area (SLA), while among the two early successional trees, Tapirira guianensis J.B. Aublet had the largest leaf area ratio (LAR) and the largest leaf mass ratio (LMR) and Duguethia spixiana Mart. had the largest root to shoot ratio (RTOS), (iii) for T. guianensis, SLA increased with increasing light and soil water potential predicted both increasing LMR and decreasing RTOS with increasing soil water, and (iv) soil water potential could also predict increasing LAR with increasing water for D. spixiana and, for C. obovata, soil water potential predicted more survivorship, LMR, and RHGR but less RTOS, all with increasing soil water. I conclude that some subcanopy trees may survive and grow more than open-canopy trees when presented with water stress in the forest understory and that within the ranges of light and soil water sampled here, plants responded more to spatial variation in water compared with light.