Rain forest expansion mediated by successional processes in vegetation thickets in the Western Ghats of India

Abstract

Aim The objective of this study was to document succession from grassland thickets to rain forest, and to provide evidence for their potential as restoration tools.Location The Linganamakki region (State of Karnataka) of the Central Western Ghats of India.Method We selected thirty vegetation thickets ranging from 4 to 439 m 2 in area in the vicinity of rain forest. The area of each small thicket was estimated as an oval using its maximum length and its maximum width. When the shape was irregular (mostly in large thickets) the limits of the thicket were mapped and the area calculated from the map. Plant species were identified, the number of individuals was estimated and their heights measured.Results There was a progression in the thickets from early to late successional species. Small thickets were characterized by ecotone species and savanna trees such as Catunaregam dumetorum. Savanna trees served as a nucleus for thicket formation. Colonizing species were mostly bird-dispersed. As succession proceeded in larger thickets, the proportion of evergreen, late-successional rain forest trees increased. The species composition of the large thickets differed depending on the species composition of reproductive adults in the nearby forested areas. The species within small thickets were also found in the large thickets. The nestedness in species composition suggested that species turnover was deterministic based on thicket size. Human disturbance (leaf and wood collection by the local populations) affected the species composition and the species-area relationship of thickets.Main conclusions Vegetation thickets are nodal centres for rain forest colonization within grasslands. They expand and replace savanna. Early successional bird-dispersed species established around savanna trees followed by late-successional rain forest trees dispersed from the nearby forest by birds. Restoration programmes that reproduce natural successional processes such as those observed in thickets will be more successful and less expensive than the methods currently being employed, where trees are individually planted in grassland. Wood harvesting is the only factor that prevents thicket growth and coalescence and hampers forest expansion.

Applied nucleation as a forest restoration strategy

“…Yarranton and Morrison (1974) referred to the initial colonists as ''nuclei'', and the process of cluster development and expansion as ''nucleation'', analogous to the use of the terms in the physical sciences. Once a persistent colonist establishes, further colonization within a nucleus can be facilitated via capture of wind-blown seeds (Yarranton and Morrison, 1974;Del Moral and Bliss, 1993;Franks, 2003) or attraction of birds or other animals that may disperse seeds (Cabral et al, 2003;Carriè-re et al, 2002b;Fuentes et al, 1986;Guevara et al, 1986;McDonnell and Stiles, 1983;Puyravaud et al, 2003;Slocum, 2001).…”

Discovery of Two Critically Endangered Tree Species and Issues Related to Relic Forests of the Western Ghats

“…Especially due to the heavy rainfall, western facing portions of the mountains would have been covered with tropical evergreen forests, laced with water courses and swamps [24,27]. Earlier studies in the Western Ghats also showed that remnants foster successional processes in natural restoration of rainforests [32]. Shifting cultivation was a major activity of forest dwelling tribals, throughout the Western Ghats, sparing only the higher altitudes.…”

Measuring Woody Encroachment along a Forest–Savanna Boundary in Central Africa

“…There are fewer studies finding such an increase in tropical savannas, but some do exist: for example in northern Australia (Hopkins et al 1996;Bowman et al 2001;Russell-Smith et al 2004;Brook and Bowman 2006), the Western Ghats of India (Puyravaud et al 2003), and South America Durigan and Ratter 2006;Marimon et al 2006;Roitman et al 2008). In Africa just four studies showing increasing tree cover in tropical rain forestsavanna boundary regions have been reported.…”