Abstract
Deforestation and the use of fire to clear land have drastic effects on ecosystem functioning and compromise essential ecosystem services, especially in low-income tropical countries such as Madagascar. We evaluated the effects of local slash-and-burn practices on soil nutrients and arbuscular mycorrhizal (AM) fungi abundance in a southwestern Madagascar forest. Nine sampling plot pairs were established along the border of a reserve within the Fiherenana–Manombo (pk-32) complex, where soil and seedling root samples of the endemic tree Didierea madagascariensis were taken. We analysed soil extractable PO43−, NH4+, and NO3− as well as total soil carbon and nitrogen. We analysed AM fungal abundance in soil and roots through fatty acid marker analysis (NLFA and PLFA 16:1ω5), spore extraction, and root staining. Slash-and-burn caused an increase in pH and doubled the plant available nutrients (from 7.4 to 13.1 µg PO43− g−1 and from 6.9 to 13.2 µg NO3− g−1). Total C and total N increased in deforested soil, from 0.6% to 0.84% and from 0.06% to 0.08%, respectively. There was a significant decline in AM fungi abundance in soil, with a decrease in soil NLFA 16:1ω5 from 0.2 to 0.12 nmol/g. AM fungi abundance in D. madagascariensis roots was also negatively affected and colonization decreased from 27.7% to 16.9% and NLFA 16:1ω5 decreased from 75.7 to 19 nmol/g. Together with hyphal network disruption, increased nutrient availability caused by burning is proposed as an explanation behind AM decline in soil and roots of D. madagascariensis. This is the first study to report the effects of slash-and-burn on AM symbiosis in Madagascar’s dry forests, with likely implications for other tropical and subtropical dryland forests worldwide where slash-and-burn is practiced.
Highlights
The severe deforestation affecting Madagascar for the past 100 years is becoming increasingly recognized, with less than 10% of its primary forest cover remaining (Harper et al, 2007 [1]).This decline is caused by high human population growth coupled with forest exploitation, which seriously threatens endemic plant species (Goodman and Benstead, 2003 [2])
arbuscular mycorrhizal (AM) fungi abundance in D. madagascariensis roots was negatively affected and colonization decreased from 27.7% to 16.9% and NLFA 16:1ω5 decreased from 75.7 to 19 nmol/g
Together with hyphal network disruption, increased nutrient availability caused by burning is proposed as an explanation behind AM decline in soil and roots of D. madagascariensis
Summary
The severe deforestation affecting Madagascar for the past 100 years is becoming increasingly recognized, with less than 10% of its primary forest cover remaining (Harper et al, 2007 [1]).This decline is caused by high human population growth coupled with forest exploitation, which seriously threatens endemic plant species (Goodman and Benstead, 2003 [2]). The Spiny Forest, a dry primary forest typical of southwest Madagascar, has been identified as a global conservation priority (Seddon et al, 2000 [3]) because of its high rate of endemism, reaching almost 90% of vascular plant species (Callmander, 2011 [4]). This centre of endemism occupies approximately 44,000 km , but less than 3% of this area is protected (Wilmé, 2006 [5]). The Spiny Forest has received little specific ecological research and it has been identified as a highly understudied at-risk region, with most studies having taken place in areas with very different soil and hydrology (e.g., the Mahafaly calcareous plateau (SuLaMa project) or the Mikea forest) (Seddon, 2000 [3]; Randriambanona 2018 [8]))
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