Degrading uplands in the rainforest region of Madagascar: Fallow biomass, nutrient stocks, and soil nutrient availability

Abstract

Soil fertility restoration depends on natural fallows in the slash-and-burn system of eastern Madagascar. In the Beforona-Vohidrazana study zone, none of the fallow species are able to withstand the slashing, burning and cropping frequencies of 3-5 years. Eventually soils are abandoned for agriculture. Along the degradation sequence, this study quantifies fallow biomass, nutrient stocks and soil nutrient availability of four dominant fallow species Trema orientalis, Psiadia altissima, Rubus moluccanus, and Imperata cylindrica. At 3 years, the shrubs Psiadia and Rubus were more productive (11-14.4 t/ha aboveground biomass or AGB) than the tree species Trema (8.5 t/ha). Only after 5 years did tree productivity (24.7 t/ha) exceed that of shrubs (17-20 t/ha). Imperata's biomass stagnated at 5.5 t/ha after 3 years. A sharp decline in fallow productivity was observed with advancing fallow cycles after deforestation. While Psiadia produced highest AGB in the second fallow cycle (C2) being 100%, C1 achieved 89% of that, C3 74%, and C4 only 29%. With the ability to propagate vegetatively and to accumulate important amounts of nutrients in roots, Rubus and Imperata, both exotic and invasive species, showed improved adaptation mechanisms towards frequent disturbances compared to the two indigenous species Trema and Psiadia. Available soil nutrients P, K, Mg were highest under forest and declined rapidly with increasing fallow cycles. Ca and pH rose momentarily in the first fallow cycle before declining with advanced soil use. Al concentrations increased steadily with time. As lengthened fallow periods are not practical, there is a need to intensify upland systems based on improved nutrient cycling, targeted inputs, fire-less land management, and land use diversification. Allowing regrading tree and bush fallows to accumulate biomass (above-and belowground carbon) will significantly improve Madagascar's greenhouse gas mitigation contribution.

Achieving Conservation and Equity amidst Extreme Poverty and Climate Risk: The Makira REDD+ Project in Madagascar

“…In Makira forests, as in other parts of Madagascar, the average fallow period has become much shorter during the last decades. In the Ranomafana Andringitra forest corridor, for instance, the length of fallow has dropped from 8-15 years around the 1970s to 3-5 years in the 2000s [35]. In the Makira region, the fallow period lasted an estimated 5-7 years at the beginning of the 1990s [36], while our field assessment indicated a decrease to 4-5 years.…”

Land-Use Strategies of Farmers in Responding to Rising Land-Use Pressures in the Southeastern Forest Region of Madagascar: A Comparative Study between Lowland Households and Hillside Households

“…The declining yield expectations are presumably associated with the concomitant occurrence of soil nutrient depletion, 2,18 low biomass inputs as ash nutrients, 18 and severe weed damage. Therefore, farmers may prefer to cultivate more cassava, in order to maintain adequate food production under agronomically adverse fallow conditions.…”

The cost of making compensation payments to local forest populations in a REDD+ pilot project in Madagascar

“…Therefore, the REDD+ project entails strict (for undisturbed forests) or fee-mediated (for degraded areas) restriction for the use of significant areas that were traditionally used for tavy. Such conservation restriction rules are likely to entail a cost for local communities, since farmers can no longer clear forest to manage soil fertility (Styger et al 2009). In addition to management transfers, REDD+ projects can fund local development projects which are expected to compensate and help households adapt to the losses arising from conservation restrictions.…”