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 reevaluate 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 former primary rain forest. Calculations are based on a model that uses literature information on termite population size in primary forest and pasture 1 to 10 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 1 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 termite-1·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 bum to be consumed by termites within 10 years. The changes in methane emissions from termite population change after deforestation were calculated using two approaches: 'Cumulative net emissions' for the region, which measure the 10-year impact of a year's forest clearing (e.g. 1.38·106 ha in 1990), increase by 0.0001 to 0.11 Tg CH4 in the 10 year-period in both scenarios, a negligible 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 emissions 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.