Fingerprinting the impacts of global change on tropical forests

Abstract

Recent observations of widespread changes in mature tropical forests such as increasing tree growth, recruitment and mortality rates and increasing above-ground biomass suggest that 'global change' agents may be causing predictable changes in tropical forests. However, consensus over both the robustness of these changes and the environmental drivers that may be causing them is yet to emerge. This paper focuses on the second part of this debate. We review (i) the evidence that the physical, chemical and biological environment that tropical trees grow in has been altered over recent decades across large areas of the tropics, and (ii) the theoretical, experimental and observational evidence regarding the most likely effects of each of these changes on tropical forests. Ten potential widespread drivers of environmental change were identified: temperature, precipitation, solar radiation, climatic extremes (including El Niñ oSouthern Oscillation events), atmospheric CO 2 concentrations, nutrient deposition, O 3 /acid depositions, hunting, land-use change and increasing liana numbers. We note that each of these environmental changes is expected to leave a unique 'fingerprint' in tropical forests, as drivers directly force different processes, have different distributions in space and time and may affect some forests more than others (e.g. depending on soil fertility). Thus, in the third part of the paper we present testable a priori predictions of forest responses to assist ecologists in attributing particular changes in forests to particular causes across multiple datasets. Finally, we discuss how these drivers may change in the future and the possible consequences for tropical forests.

Global climate cycles and cyclones: consequences for rainfall patterns and lemur reproduction in southeastern Madagascar

“…However, in rainforest habitat, extreme rainfall events have been shown to cause stress to tree stands (Akashi & Mueller-Dombois, 1995), which, in this case, may reduce tree resources available to the lemurs. In other tropical forests, both intense drought and intense rainfall caused by ENSO phases have been demonstrated to negatively affect forest vegetation and even cause increased tree mortality (see Lewis et al, 2004). Further research is needed to determine relationships of wet season rainfall on forest phenology and time lemurs spend foraging in this system.…”

Hyperspectral discrimination of tropical dry forest lianas and trees: Comparative data reduction approaches at the leaf and canopy levels

“…Lianas have been considered a significant fingerprint of the effects of global environmental change in tropical environments (Lewis et at, 2005). Field studies indicate liana coverage is increasing in neotropical forests (Phillips et at 2002;Wright et at, 2004), which may be a biological signal of higher CO2 concentration, increased disturbance or decreased precipitation (Schnitzer, 2005).…”

A study of soil-dynamics based on a simulated drought in an alpine meadow on the Tibetan Plateau

“…Therefore, it is important to set up a simulated experiment to evaluate the changing state of the ecosystem induced by extreme droughts, so as to provide reliable data critical to the stability of the ecosystem (Scheffer et al 2001). Drought as a rule has a negative impact on the stability and function of the ecosystem (Lewis et al 2004;Kahmen et al 2005;Breda et al 2006). The prolonged precipitation recurrence interval can significantly suppress the soil water availability, and thus alter many soil biotic processes (Beier et al 2012).…”