Abstract
Two dominant biomes that occur across the southern Indian peninsula are dry deciduous “forests” and evergreen forests, with the former occurring in drier regions and the latter in wetter regions, sometimes in close proximity to each other. Here we compare stem and leaf traits of trees from multiple sites across these biomes to show that dry deciduous “forest” species have, on average, lower height: diameter ratios, lower specific leaf areas, higher wood densities and higher relative bark thickness, than evergreen forest species. These traits are diagnostic of these dry deciduous “forests” as open, well-lit, drought-, and fire-prone habitats where trees are conservative in their growth strategies and invest heavily in protective bark tissue. These tree traits together with the occurrence of a C4 grass-dominated understory, diverse mammalian grazers, and frequent fires indicate that large tracts of dry deciduous “forests” of southern India are more accurately classified as mesic deciduous “savannas.”
Highlights
Ecologists have long organized earth’s vegetation into biomes or vegetation types that occur predictably under certain combinations of precipitation and temperature (Schimper, 1903; Holdridge, 1947; Walter, 1973; Whittaker, 1975)
We have argued that large tracts of the vegetation type in this region classified as “dry deciduous forest” that are characterized by relatively open tree canopies in grassy understories are more correctly viewed as mesic savannas, while vegetation types with dense tree cover and non-grassy understories are true forest formations (Ratnam et al, 2011, 2016; Sankaran and Ratnam, 2013)
As we argue, many of the dry deciduous “forests” in southern India are deciduous “savannas” that are adapted to seasonal water-stress and frequent grass-fuelled fires (Ratnam et al, 2016), which is not the case for true forests, we expect traits of tree species characteristic of these habitats to reflect this difference
Summary
Ecologists have long organized earth’s vegetation into biomes or vegetation types that occur predictably under certain combinations of precipitation and temperature (Schimper, 1903; Holdridge, 1947; Walter, 1973; Whittaker, 1975). Open lighted environments and frequent grassfuelled fires are associated with the savanna state, while closed, shaded environments and rare fires are associated with the forest state (Bond and Parr, 2010; Hoffmann et al, 2012) Reflecting these differences, the woody species that are characteristic of these different ecosystems are expected to vary in their morphological and physiological traits in ways that are adapted to their distinctive disturbance-environment regimes (Ratnam et al, 2011; Hoffmann et al, 2012; Dantas Vde et al, 2013)
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