Altered resource availability and the population dynamics of tree species in Amazonian secondary forests

Abstract

Despite research demonstrating that water and nutrient availability exert strong effects on multiple ecosystem processes in tropical forests, little is known about the effect of these factors on the demography and population dynamics of tropical trees. Over the course of 5 years, we monitored two common Amazonian secondary forest species-Lacistema pubescens and Myrcia sylvatica-in dry-season irrigation, litter-removal and control plots. We then evaluated the effects of altered water and nutrient availability on population demography and dynamics using matrix models and life table response experiments. Our results show that despite prolonged experimental manipulation of water and nutrient availability, there were nearly no consistent and unidirectional treatment effects on the demography of either species. The patterns and significance of observed treatment effects were largely dependent on cross-year variability not related to rainfall patterns, and disappeared once we pooled data across years. Furthermore, most of these transient treatment effects had little effect on population growth rates. Our results suggest that despite major experimental manipulations of water and nutrient availability-factors considered critical to the ecology of tropical pioneer tree species-autogenic light limitation appears to be the primary regulator of tree demography at early/mid successional stages. Indeed, the effects of light availability may completely override those of other factors thought to influence the successional development of Amazonian secondary forests.

Ramet demography of Aechmea distichantha (Bromeliaceae) in two contrasting years in the understory and open areas of a South American xerophytic forest

“…In forests and woodlands, this heterogeneity is increased due to variations in canopy structure and woody species composition (Thomsen et al 2005;Barbier et al 2008;Burton et al 2011;Barberis et al 2014), which may produce large differences in resource availability (e.g., light, nutrients, water) and environmental conditions (e.g., temperature) (Clark et al 1996;Denslow et al 1998;Ostertag 1998;Montgomery & Chazdon 2001). Even though there is a continuous gradient in resource availability and environmental conditions (Cogliatti-Carvalho et al 1998, 2001, the environmental differences between contrasting shaded and open areas, like understory and treefall gaps, may affect plant growth and survival, and therefore plant population dynamics (Barberis & Tanner 2005;Fortini et al 2010;Kuptz et al 2010;Dalling et al 2012;Myster 2012).…”

Patterns of species diversity and soil nutrients along a chronosequence of vegetation recovery in Hainan Island, South China

“…Much attention has been given to the recovery of degraded tropical forests since they have been experiencing unprecedented severity of natural and human disturbance and suffering from ongoing deforestation (Chazdon 2003;Laurance et al 2004;Wright 2005;Lewis 2006;Fortini et al 2010). These degraded forests, therefore, offer even fewer goods and services to human society than before (Richards 1996;Whitmore 1998;Leigh et al 2004).…”

“…These degraded forests, therefore, offer even fewer goods and services to human society than before (Richards 1996;Whitmore 1998;Leigh et al 2004). Related studies have been focused on successional trends in species richness (Finegan 1996;Kennard 2002;Slik et al 2002;Chai and Tanner 2011), patterns of community structure (Uhl 1987;Guariguata et al 1997) and function (Read and Lawrence 2003), as well as on the interaction of environment with restoration process (Uhl 1987;Guariguata et al 1997;Chazdon 2003;Leigh et al 2004;Fortini et al 2010). The successional process of secondary tropical forests in different areas may display unique characteristics because of differences in soil fertility, slope, drainage, flora, or fauna (Guariguata and Ostertag 2001).…”

Modeling the Complex Impacts of Timber Harvests to Find Optimal Management Regimes for Amazon Tidal Floodplain Forests

“…paraensis (the most abundant species) as an example, the integration of demographic effects of logging using life table response experiments (LTRE) shows that demographic rates most affected by logging may not be the most important for determining post-harvest tree population dynamics. These conclusions are important because harvest evaluations commonly consider growth, survival, and recruitment effects separately, and may misrepresent changes in population dynamics resulting from observed demographic effects [ 36 ]. Without the use of an integrated population approach, however, it would not be possible to detect the larger contribution that smaller juvenile growth increases offer to the persistence of the species in the stand.…”

“…Besides using harvested plot data to modify unharvested plot matrices to project population dynamics post-harvest, we computed treatment differences in individual/ environmental factors that could influence demography including flooding and light regimes [ 16 ] to explore the causes of post-harvest effects on growth and a life table response experiment (LTRE) analysis to determine which vital rates contributed most to differences in population growth between harvested and unharvested plots [ 28 , 35 , 36 ].…”