Biodiversity and Climate Change by Thomas E. Lovejoy

Author:Thomas E. Lovejoy [Lovejoy, Thomas E.]
Language: eng
Format: epub
Publisher: Yale University Press
Published: 2018-01-21T16:00:00+00:00

CHAPTER FIFTEEN

Tropical Forests in a Changing Climate

JAMES E. M. WATSON, DANIEL B. SEGAN, AND JOSHUA TEWKSBURY

OVERVIEW

Tropical forest landscapes are the most biodiverse terrestrial biomes on the planet, supporting 50 percent of described species and an even larger number of undescribed species (Dirzo and Raven 2003). Thermophilic forests similar to today’s tropical forests first appeared in the early Cenozoic (50–65 Mya), and today they span five distinct biogeographical regions: tropical Americas, Africa, Southeast Asia, Madagascar, and New Guinea, with small outliers in Australia, South Asia, and many tropical islands (Corlett and Primack 2006) (Box 15.1). The exceptional species richness at a global scale is produced by two commonly shared complementary patterns: exceptionally high local diversity, with species richness in many tropical forests sites 20 times greater than richness in comparable temperate forest sites, and greater levels of species turnover along environmental gradients (Dirzo and Raven 2003). In addition, genetic divergence between populations is much higher in the tropics, which makes them globally important ecosystems when considering long-term evolutionary processes.

Tropical forests play a critical role in regulating global climate, accounting for one-third of land-surface productivity and evapotranspiration (Malhi 2012). Although debates still rage about how much carbon tropical forests contain relative to other ecosystems, there is no doubt that tropical forest ecosystems play an important role in safeguarding the world against humanforced climate change and that efforts to Reduce Emissions from Deforestation and Forest Degradation (REDD+) need to be financed (IPCC 2013; Watson et al. 2018). If a formal carbon market for REDD+ does eventuate, it will have significant financial implications. A recent broad global analysis also showed that between 2000 and 2005, reduced carbon emissions from the 17.2 million ha (19.6 percent) of protected humid tropical forests were worth approximately US$6.2–7.4 billion (Scharlemann et al. 2010). Tropical forests bolster national economies through tourism and timber revenues and provide essential ecosystem services to many thousands of local communities (de Groot et al. 2012).

. . .

Box 15.1 Are Tropical Forests Climatically Stable?

One way of broadly ascertaining how vulnerable tropical forests are going to be with future climate change is to assess their “stability” at the ecoregional scale. Climate stability has been defined as the similarity between current and future climate (in the 2050s) using a six-variable envelope-based gauge to represent general climate patterns and seasonality (Watson et al. 2013). This gauge combines patterns of annual mean temperature, mean diurnal temperature range, mean annual temperature range, annual precipitation, precipitation seasonality, and precipitation of the driest quarter, and it assesses the degree to which regions are likely to shift outside of their current climate envelopes. By this measure, climates in tropical forest ecoregions in South America and Southeast Asia are less stable than climates in tropical forest ecoregions in Africa and Oceania (Figures 15.1 and 15.2B). When tropical forest climate stability is integrated with the ecoregion’s “natural integrity” (defined as the proportion of intact natural vegetation found in each ecoregion, and thus a function of past land use), a measure of global ecosystem vulnerability emerges

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