Population Structures of Two Understory Plant Species Along an Altitudinal Gradient in Costa Rican Montane Oak Forests

Abstract

The altitudinal distribution of vascular plant species and communities has been intensively studied in neotropical montane forests (e.g., Cleef et al. 1984; Kappelle and Zamora 1995; Kappelle et al. 1995a; Lieberman et al. 1996; Chap. 4). However, still little is known about the population ecology of individual species and their responses to environmental factors along elevational gradients. Population structure studies of single species in relation to environmental factors have proven to be powerful in explaining ecological behavior in temperate regions (Wassen et al. 1990; Oostermeijer et al. 1994; Hegland et al. 2001), but such data are relatively scarce for tropical regions. So far, the main emphasis in the tropics has been on population dynamics of lowland rainforest canopy trees (e.g., Arriaga et al. 1988; Martinez-Ramos et al. 1988; Alvarez-Buylla and Martinez-Ramos 1992; Olmsted and AlvarezBuylla 1995), rather than on non-canopy species (Oyama 1990). Tropical studies directly relating population structure to environmental variables have not received much attention from scientists (Witkowski and Liston 1997; Hicks and Mauchamp 2000). To date, population dynamics of highland forest plant species are even rarer (but see Wesselingh et al. 1999, and Chaps. 14 and 18). In order to gain further insight into environmental factors (e.g., temperature, light availability) that may determine the population structure of vascular plant species on tropical mountains, we studied the relative proportions of different life stages of two tropical montane understory species in response to environmental changes occurring along an altitudinal gradient in Costa Rican montane oak forests.