Directional changes in the species composition of a tropical forest

Abstract

Abstract. Long-term studies have revealed that the structure and dynamics of many tropical forests are changing, but the causes and consequences of these changes remain debated. To learn more about the forces driving changes within tropical forests, we investigated shifts in tree species composition over the past 25 years within the 50-ha Forest Dynamics Plot on Barro Colorado Island (BCI), Panama, and examined how observed patterns relate to predictions of (1) random population fluctuations, (2) carbon fertilization, (3) succession from past disturbance, (4) recovery from an extreme El Niño drought at the start of the study period, and (5) long-term climate change. We found that there have been consistent and directional changes in the tree species composition. These shifts have led to increased relative representations of drought-tolerant species as determined by the species' occurrence both across a gradient of soil moisture within BCI and across a wider precipitation gradient from a dry forest near the Pacific coast of Panama to a wet forest near its Caribbean coast. These nonrandom changes cannot be explained by stochastic fluctuations or carbon fertilization. They may be the legacy of the El Niño drought, or alternatively, potentially reflect increased aridity due to long-term climate change. By investigating compositional changes, we increased not only our understanding of the ecology of tropical forests and their responses to large-scale disturbances, but also our ability to predict how future global change will impact some of the critical services provided by these important ecosystems.

Shifting dynamics of climate-functional groups in old-growth Amazonian forests

“…Recent findings from an analysis of species composition in plots in Costa Rica, on Barro Colorado Island, and across a Panama-wide precipitation gradient, also indicated an increase in the representation of drought-tolerant taxa in forest community composition, which may suggest widespread shifts in similar directions (Enquist and Enquist 2011;Feeley et al 2011). Although overall most genera did not show significant changes, the pronounced increase in BA loss and stem mortality for wet-affiliates would suggest a potential slowing of growth rates for this group, which could be an indication of climate sensitivity or long-term successional processes.…”

“…In addition to possible climate drivers of changes in composition and dynamics, forests may be recovering from previous disturbances and at different stages of recovery/succession, thus exhibiting shifts in dynamism (Wright 2005;Lewis et al 2009;Feeley et al 2011); however, the approach we used in this paper, of many plots spread over a large geographic region, should reduce the relative importance of disturbance events at stand level. Other related factors which may influence the estimation of changes in composition include lag-times: (i) between seedling recruitment and growing to 10 cm dbh, which may be very long and stochastic; (ii) for dying, and (iii) for recovery after drought events.…”

“…While earlier studies examined shifts in species in relation to drought (Condit 1998;Enquist and Enquist 2011;Feeley et al 2011), they were focussed on single sites or smaller areas; possible trends in relation to water availability have not been previously investigated across a large number of sites. The aim of the work is to establish if there have been any shifts or trends in proportions and dynamics of wet-affiliate, dry-affiliate and climate-generalist tree genera on a decadal level, and to quantify the magnitude of any change.…”

Spatial association and optimum adjacent distribution of trees in a mixed coniferous-broadleaf forest in northeastern China

“…Regeneration determines tree composition in a forest and further influences the future structure of a forest stand. Therefore, successful long-term management demands careful consideration of all related factors (Feeley et al, 2011;Schweitzer and Dey, 2011;Lochhead and Comeau, 2012). However, many disturbances of natural forests, notably those of anthropogenic origin, have significant negative effects on both the quality and quantity of a typical regeneration (Garbarino et al, 2009; Gourlet-Fleury et al, 2013).…”

Tree Diversity Changes over a Decade (2003-2013) in Four Inland Tropical Dry Evergreen Forest Sites on the Coromandel Coast of India

“…As in all other ecosystems, tropical forests too face a wide range of disturbances of variable duration, intensity and frequency. Long-term vegetation monitoring has been undertaken in various tropical forests around the world (Rees et al 2001;Laurance et al 2004;Weckel et al 2006;Marimon et al 2012;van den Berg et al 2012;Ge et al 2013), and an increasing number of studies have shown that forests have undergone dynamic widespread directional shifts in composition and structure (Enquist and Enquist 2011;Feeley et al 2011;Peng et al 2011;Fauset et al 2012;Kucbel et al 2012). Long-term monitoring of permanent forest plots provides data to assess aboveground standing biomass stock and C dynamics and assesses the response of the forest to the environmental drivers such as elevated temperature, CO 2 fertilization, increase in incoming solar radiation and nitrogen enrichment (Bhat and Ravindranath 2011).…”