A review of the possible impacts of climate change on forests in the humid tropics

Increased anthropogenic emissions of greenhouse gases (GHGs) have led to gradual warming of the earth’s atmosphere. It is predicted that by the year 2100, the average annual global air temperature will increase by 1.1 – 6.4 oC. This has triggered a series of long-term changes in the atmospheric and soil environments. As forests form a key component of humid tropical ecosystems, the objective of this review is to synthesize the currently available experimental results and offer insights into how forests in the humid tropics would respond and adapt to different aspects of climate change. The atmospheric CO2 concentration (Ca), which is currently at 386 μmol mol-1, is expected to reach at least 600 μmol mol-1 by 2100. As CO2 is an input in the photosynthetic process, increasing Ca increases photosynthetic rates of all plants. In C3 herbs and woody plants, which dominate humid tropical forests, this is translated into average biomass increases of 45% (maximum 240%) and 48% (maximum 260%) respectively, leading to increased net primary productivity at the ecosystem level. Increasing air temperatures could either enhance or dampen the growth stimulation due to higher Ca, depending on the magnitude of temperature increase relative to the optimum temperature for maximum ecosystem productivity. The ability of humid tropical forests to acclimate and adapt to future temperature changes are considered to be lower than that of temperate forests because of the narrower range of seasonal temperatures experienced by forests in the humid tropics. Increasing Ca and temperatures could also influence forest ecosystems through significant changes in the soil environment and in the plant-water relations. In all the above-described responses to increased Ca and temperature, there is substantial species-to-species variation. Studies on the capacity of tropical forests to sequester carbon and reduce future increases of Ca have indicated a substantial capacity for forests in the humid tropics. However, reductions of this capacity have been observed during years of warmer temperatures and lower precipitation resulting from El Niño Southern Oscillation.

Keywords: Carbon dioxide, carbon sequestration, forest ecosystems, net primary productivity, photosynthesis, temperature.

DOI: http://dx.doi.org/10.4038/jnsfsr.v39i4.3879

J.Natn.Sci.Foundation Sri Lanka 2011 39 (4): 281-302