Hybrid improved tree fallows: harnessing invasive woody legumes for agroforestry

Abstract

For several decades, agroforestry specialists have promoted the planting of fallow fields with nitrogen-fixing, fast-growing trees or shrubs to accelerate soil rehabilitation and provide secondary products like woodfuel. Yet, such 'improved fallows' have not been widely adopted, in part due to the costs of labour and seedlings. In some situations, however, farmers have developed novel approaches to agroforestry fallows by taking advantage of spontaneous invasions of woody leguminous tree species present in the vicinity of their fields. In this paper, we examine cases from Réunion, highland Madagascar, the Bateke plateau in Congo, and the Palni hills of southern India where farmers have adapted their cultivation practices to take advantage of the invasive characteristics of Australian acacias that were introduced earlier for other reasons. We focus on the key social, economic, and environmental factors that influence farmers in these places to gain opportunistic benefit from these introduced tree species that biologists have been deemed invasive and damaging to local ecosystems and biodiversity. We conclude that opportunistic fallowing of invasives can be viewed as a hybrid strategy combining elements of natural fallows and improved fallows-which we call 'hybrid improved fallows'-in that it takes advantage of the 'weedy' characteristics of introduced leguminous tree species in the landscape and offers a cost-effective and pragmatic strategy for soil and vegetation management for farmers.

Forest Transition in Madagascar’s Highlands: Initial Evidence and Implications

“…Fruit trees and shrubs-from oranges to mangos, from vines to peaches-provide obvious consumable and marketable products, as well as secondary uses of dead branches as fuel wood, and mulberry leaves as silk worm fodder, among many other uses. Other benefits derived from trees include the production of honey based on eucalyptus flowers, the improvement of soil fertility based on acacia nitrogen fixation, and the sale of eucalyptus essential oils [79][80][81]. It is important to note that population growth in Madagascar is still quite rapid, with the country's population doubling between 1990 and 2013.…”

Human adaptation to invasive species: A conceptual framework based on a case study metasynthesis

“…Several studies argued that benefits outweigh harms because people have managed harms and created benefits (Dove 1986; Jagoret et al 2012; Tassin et al 2012; Martin 2014; Berget et al 2015). In part this is unsurprising because, depending on the context, ‘Invasions can have positive as well as negative feedbacks for ecosystem functions’ (Vilà et al 2011, p. 702).…”

Agroforestry Technique for Minimal Extra-Labour: Influence of Chromolaena-Cajanus Combination on Soil Chemistry and Biology, and Yam Yields

“…Based on these criteria, Tassin, Kull, and Rangan (2012) suggested that the key factors are input costs; labour cost, cash income, multipurpose use and the duration of the fallow. Small farmers fear that costs associated with the new technology outweigh the cash benefits it might offer.…”