American Journal of Plant Sciences, 2012, 3, 1632-1639
http://dx.doi.org/10.4236/ajps.2012.311198 Published Online November 2012 (http://www.SciRP.org/journal/ajps)
The Shola (Tropical Montane Forest)-Grassland
Ecosystem Mosaic of Peninsular India: A Review
Milind Bunyan1, Sougata Bardhan2, Shibu Jose2*
1School of Forest Resources and Conservation, Gainesville, USA; 2The Center for Agroforestry, School of Natural Resources, 203
Anheuser-Busch Natural Resources Building, University of Missouri, Columbia, USA.
Email: *joses@missouri.edu
Received August 17th, 2012; revised September 24th, 2012; accepted October 10th, 2012
ABSTRACT
Tropical montane forests (alternatively called tropical montane cloud forests or simply cloud forests) represent some of
the most threatened ecosystems globally. Tropical montane forests (TMF) are characterized and defined by the presence
of persistent cloud cover. A significant amount of moisture may be captured through the condensation of cloud-borne
moisture on vegetation distinguishing TMF from other forest types. This review examines the structural, functional and
distributional aspects of the tropical montane forests of peninsular India, locally known as shola, and the associated
grasslands. Our review reveals that small fragments may be dominated by edge effect and lack an “interior” or “core”,
making them susceptible to complete collapse. In addition to their critical role in hydrology and biogeochemistry, the
shola-grassland ecosystem harbor many faunal species of conservation concern. Along with intense anthropogenic
pressure, climate change is also expected to alter the dynamic equilibrium between the forest and grassland, raising
concerns about the long-term sustainability of these ecosystems.
Keywords: Shola Forests; Western Ghats; GIS; Biodiversity; Species Composition; Shola Fragments
1. Introduction
Tropical montane forests (alternatively called tropical
montane cloud forests or simply cloud forests) represent
some of the most threatened ecosystems globally. Tropi-
cal montane forests (TMF) are characterized and defined
by the presence of persistent cloud cover. A significant
amount of moisture may be captured through the con-
densation of cloud-borne moisture on vegetation distin-
guishing TMF from other forest types. Bruijzneel and
Hamilton [1] described five kinds of TMF. Four of these,
i.e. lower montane forest, lower montane cloud forest,
upper montane cloud forest and subalpine cloud forest,
are based on elevation and tree height whereas the last
one an azonal low elevation dwarf cloud forest.
Elevations at which TMF are found, vary with moun-
tain range size and insularity or proximity to coast. Due
to the mass-elevation effect (also known as the Masse-
nerhebung effect), larger mountain ranges permit the
extension of the altitudinal range of plant species. Simi-
larly, higher humidity levels near coastal mountains en-
able the formation of clouds at lower altitudes. On insu-
lar or coastal mountain ranges, TMF has been reported
from elevations as low as 500 m (Bruijzneel and Hamil-
ton, 2000). As elevation increases, tree height in TMF
reduces and leaf thickness and complexity in tree archi-
tecture increases. Other distinctive features of TMF are
the prolific growth of epiphytes and mosses and the lack
of vertical stratification. TMF soils are typically clay-rich,
have low pH, abundant organic matter and are often nu-
tritionally poor. TMF are characterized by high levels of
endemism driven by the limited availability of habitat [2].
Located in the headwater catchments of seasonal or per-
ennial streams, TMF provides often undervalued ecosys-
tem services to downstream communities.
Within the Western Ghats-Sri Lanka (WGSL) biodi-
versity hotspot [3], TMF occurs as a mosaic of forests
(locally and hereafter sholas) and grasslands and is com-
monly referred to as the shola-grassland ecosystem. With
limited exceptions [4,5], data from the shola-grassland
ecosystem mosaic are rarely included in biome-wide
popular [1] as well as academic [2,6] synopses of scien-
tific literature. As such, this document aims to provide a
synthesis of current research and the state of knowledge
of the shola-grassland ecosystem from peer-reviewed
literature published on tropical montane forests in the
WGSL biodiversity hotspot. Additionally, a synopsis of
research on the sholas of Kerala was also reviewed [7].
*Corresponding author.
Copyright © 2012 SciRes. AJPS
The Shola (Tropical Montane Forest)-Grassland Ecosystem Mosaic of Peninsular India: A Review 1633
2. The Shola-Grassland Ecosystem Mosaic
2.1. Background
The Western Ghats located in the WGSL hotspot are a
1600 km long mountain (160,000 km2) chain in southern
India. Located above 1700 m, the shola-grassland eco-
system mosaic consists of rolling grasslands with shola
fragments restricted to sheltered folds and valleys in the
mountains separated from the grasslands with a sharp
edge. Since, sholas frequently have persistent cloud
cover they can be classified as lower montane cloud for-
est or upper montane cloud forest depending on elevation
[1]. Ecologists and foresters have been puzzled over the
pattern of the shola-grassland ecosystem mosaic for dec-
ades. While some of the earliest scientific descriptions of
the shola-grassland ecosystem described the mosaic as
dual climax [8], proponents of the single climax concept
[9] argued that the forests represented a biotic [10,11] or
edaphic climax [12]. A δC13 analysis of peat samples
from shola fragments in the Nilgiris indicated that shola
and grasslands have undergone cyclical shifts in domi-
nant vegetative cover. Arid conditions from 20,000 -
16,000 yr BP led to predominance of C4 vegetation. This
was followed by a wetter phase which peaked around
11,000 yr BP leading to a dominance in C3 vegetation.
The weakening of the monsoon around 6000 yr BP led to
the expansion of the C4 vegetation again and the estab-
lishment of the current pattern, although a brief warm,
wet phase around 600 - 700 yr BP also occurred [13].
2.2. What Is Not a Shola?
Arguably, the shola-grassland ecosystem mosaic is
among the most distinct ecosystem types in the WGSL
biodiversity hotspot. Although, sholas are typically seen
at elevations 1700 m, sholas at elevations as low as
1050 m have been studied by ecologists [14]. In the
Anamalais and Nilgiris, the shola-grassland mosaic is
characteristically patchy. Often though, shola fragments
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lowland evergreen forest which contain a different suite
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from lowland forest, sholas of different regions exhibit
little similarity in species composition.
Yet, physiognomic characteristics of sholas are con-
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