Report of the Western Ghats Ecology Expert Panel - Part II : Human Pressure and Ecological Impacts : 4. *Future climate change and the vulnerability of ecosystems across the Western Ghats

Opinion
       10/11/2018
                1531.

SUB : Report of the Western Ghats Ecology Expert Panel - Part II : Human Pressure and Ecological Impacts :

REF : 4. *Future climate change and the vulnerability of ecosystems across the Western Ghats

Climate change as a consequence of anthropogenic greenhouse gas emissions and its implications for biodiversity have been well documented globally. It can be expected that the biodiversity-rich Western Ghats would also be impacted by climate change, and this should be factored into considerations of ecological sensitivity of different regions or ecosystem types in the ghats.

Modelling climate change impacts :-

There have been a few modeling studies on the potential impact of climate change on the forests of India (Ravindranath et al. 2006; Chaturvedi et al. 2011). More specific to the Western Ghats, an early study assessed the possible impact of climate change on the vegetation and forest-based product flows in the Nilgiri Biosphere Reserve and the Uttara Kannada district (Ravindranath et al. 1997). Using an empirical-statistical model, this study brought out the potential of dry thorn forest to spread at the expense of deciduous forest and the montane grassland to shrink from increasing temperature.

The latest study (Chaturvedi et al. 2011) used the dynamic vegetation model IBIS (Integrated Biosphere Simulator, v.2). The baseline simulation brought out only the following dominant vegetation types – Tropical Evergreen Forest, Tropical Deciduous Forest, and Savanna/Grassland – in the Western Ghats, rather than a more complex situation that also includes montane forest/grassland, semi-evergreen forest, dry thorn forest and the division of deciduous into moist and dry forest. Climate change projections for the Western Ghats region were based on the Regional Climate Model of the Hadley Centre (HadRM3), U.K. for the A2 scenario (atmospheric CO2 levels of 750 ppm by 2085) and the B2 scenario (CO2 of 575 ppm) at a resolution of 0.5° by 0.5°. The model was run for the period 2071-2100 (mid-year 1985).



We considered a total of 51 grids (0.5° by 0.5°) in the simulation of which 26 underwent change under A2 scenario (51% grids) and 16 underwent change in the more benign B2 scenario (31%). The figures below depict the baseline vegetation distribution and vegetation changes expected under the A2 scenario.

A measure of forest vulnerability in the Western Ghats :-

A “vulnerability index” was also developed on the basis of whether or not a particular forest grid is (a) projected to undergo vegetation change under climate change scenario (b) monoculture or mixed species forest and (c) dense forest, moderately dense or a fragmented forest. Based on these indicators each forest grid was assigned a score between 1 to 7 – 1  being the least vulnerable and 7  being the most vulnerable.

This exercise indicates a greater degree of vulnerability in the northern and central region of the ghats. However, we must interpret these results cautiously; change in forest type may not necessarily be negative as when a drier type of vegetation may change to a moister type, while the coarse resolution of the model does not pick up the sensitive montane ecosystem in the southern Western Ghats as described below.

Sensitivity of the montane shola forests and grasslands :-

Model IBIS has its limitations in that it does not simulate the tropical montane forest/grassland complex of the Western Ghats. At the same time, the coarse resolution of the model does not distinguish the montane ecosystem prevalent in the Nilgiris and further south in the Western Ghats. We thus have to separately consider the sensitivity of the characteristic montane stunted evergreen forests (known locally as sholas) and the grasslands found at elevations above 1800 m asl in locations such as the Nilgiris, the Anamalais and the Palani hills as well as high elevations both to the north and the south of these mountain ranges (Sukumar et al. 1995).

Paleoclimatic studies have shown that the shola forests and grasslands have contracted and expanded in tune with past climate change. The following predictions have thus been made for this montane ecosystem as regards the future climate change impacts. In many montane regions such as the Nilgiris and the Palanis, the grasslands have been planted with exotics such as Australian wattles (Acacia spp.) and eucalypts (Eucalyptus spp.). These plants with C3 pathway of photosynthesis can be expected to take advantage of the increasing levels of  Vunerability to climate change atmospheric carbon-dioxide (the so-called CO2 fertilization effect) for enhanced growth. Increasing temperature would also help the wattles to spread preferentially (over shola species) into colder grassland areas, where frost is presently limiting, and there are indications that this is happening. The exotic invasive plant scotch broom (Cystisus scoparius) has also spread considerably in recent times across the grasslands in the Nilgiris. Alteration of the natural montane grassland would have implications for endemic animals such as the Nilgiri tahr (Nilgiritragus hylocrius) and Nilgiri pipit (Anthus nilghiriensis).

In the next section, we a review of a number of significant sectors and our recommendations on how development activities can be regulated to protect the Western Ghats from on-going onslaughts.

NEXT : *Sectoral Recommendations -

To be continued.....

JAIHIND
VANDEMATHARAM