Deforestation and methane release from termites in Amazonia

Abstract

To assess the role of termite populations in the change of global atmospheric methane concentrations, we re­ evaluate the hypothesis that deforestation leads to higher populations of wood-feeding termites and to a significant increase of termite-emitted methane in areas of cleared and burned fonner primary rain forest. Calculations are based on a model that uses literature infonnation on tennite population size in primary forest and pasture 1 to I 0 years after forest conversion, wood consumption and methane emission rates of termites. We use two scenarios based on low- and high-end parameters based on data from rain forests in Brazilian Amazonia. In the low-end scenario, termite population biomass is 25 kg·ha· 1 in primary forest; 4 kg·ha· 1 in year I after forest clearing, 51 kg·ha· 1 in a six-year-old pasture, and 4 kg·ha- 1 in a ten-year-old pasture. In the high-end scenario, all values are doubled and the initial breakdown in year 1 is omitted. Wood consumption rates are 49 and 270 mg wood·g termitU·day- 1 , and methane emission rates are 0.0023 and 0.0079 t of carbon released as methane per ton of carbon consumed, in the low- and the high-end scenario, respectively. In the low-end scenario no significant difference exists between the average termite population size in primary forest and pasture modeled over a ten-year period. In the high-end scenario the average population size of years 1-10 after clearing is only 31 % over that of primary forest. The population model data combined with the wood consumption rates allow for only 2.3-32.3% of the wood biomass left from forest burn to be consumed by termites within 10 years. The changes in methane from termite population change after deforestation were calculated using two approaches: Cumulative net emissions for the region, which measure the I 0-year impact of a year's forest clearing (e.g. 1.38· 10 6 ha in 1990), increase by 0.000 I to 0. 11 Tg CH4 in the 10 year-period in both scenarios, a negligtble contribution to the increase of atmospheric methane concentrations of 45 Tg·yr· 1 • The annual balance of net methane emissions from termites in all the different landscapes existing in the whole region in a single year (1990) increases by only 0.004 to 0.33 Tg CH4 (low- and high-end scenario) because of the large proportion of old clearings (>10 years old) with low methane emission rates. Termite populations do not tend to increase as a function of the available wood mass only and therefore methane from termites in cleared areas of former rain forest do not make a significant contribution to the increase of the global methane concentrations in the atmosphere. Copyright © 1996 Elsevier Science Ltd