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International Grassland Congress Proceedings XXIII International Grassland Congress

Tropical Grassland Ecosystems and Climate Change

C. R. Babu University of Delhi, India

Vivek Kr. Choudhary University of Delhi, India

Vijay Kumar University of Delhi, India

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Part of the Plant Sciences Commons, and the Soil Science Commons This document is available at https://uknowledge.uky.edu/igc/23/keynote/41 The XXIII International Grassland Congress (Sustainable use of Grassland Resources for Forage Production, Biodiversity and Environmental Protection) took place in New Delhi, India from November 20 through November 24, 2015. Proceedings Editors: M. M. Roy, D. R. Malaviya, V. K. Yadav, Tejveer Singh, R. P. Sah, D. Vijay, and A. Radhakrishna Published by Range Management Society of India

This Event is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in International Grassland Congress Proceedings by an authorized administrator of UKnowledge. For more information, please contact [email protected]. Tropical Grassland Ecosystems and Climate Change C.R. Babu, Vivek Kr. Choudhary and Vijay Kumar

Grasses are unique group of flowering subalpine meadows are found in Himalaya plants that form the foundation for the trophic and are sustained by snow and grazing and structure in terrestrial communities. The burning, whereas the grassland of Sholas in grasses are found in every conceivable habitat Western Ghats are also unique and sustained where plants can thrive – from sea to deserts by grazing or burning. The grassy biomes and from wetlands to peaks of highest mentioned above are all on the upland. mountains. The grasses form a distinct biome Some of the tropical grasslands are located – a major ecological formation in the global on the: (i) flood plains of river systems (flood classification of vegetation. The grassland plain grasslands) and or the landslips, hilltops biomes are most widely spread worldwide and and forest margins. These are seral occupy 20% of the global land surface. The communities and sustained by flooding and grassland biomes are different in structure and grazing in case of flood plain grasslands and composition across the continents. The tropical grazing and burning in other grassland types. grassy biomes composed of a wide range of The grasslands in areas (where the rivers grassland communities depending upon shifted their courses) and the grasslands topographic, edaphic, moisture, biotic and (which are never subjected to flooding) are climatic gradients. Areas where grasses are sustained by grazing and or burning. In other predominant without scattered woody plant words in the absence of regulatory ecological species are known as open grasslands (natural processes (flooding and grazing) burning of grasslands). All those grasslands with grasslands is the key for sustaining the scattered woody plants (upto 80% of tree cover) grasslands. Grass-fire cycle is unique for are knows as savannas or mosaic grasslands. tropical grassy biomes and is critical in Similarly the Cerrados of Brazil are climax promoting grasses and suppresses the woody moist savannas and are maintained by grazing growth. In India there are three types of and burning. African savannas are very grasslands – short, intermediate and tall extensive and represent the climax vegetation grasslands. All the three seral stages of type with rich wildlife particularly ecological succession can be sustained by mammalian megafauna. These savannas are flooding, grazing and or burning. The annual short, medium and tall grasslands and are cycle of flooding and herbivore migration sustained by herbivore grazing and burning sustains network of the complex grassland and composed C4 grass species. These may be ecosystem of the Corbett Tiger Reserve of India natural, mosaic and derived. Derived that support rich wildlife. grasslands are those grasslands are transformed tropical forest through The grassland biomes render a wide range Savannization (cleared or repeatedly burned) of ecosystem services. For example, 15% of the and these are found in Amazonia and Asia. carbon on earth is stored in grasslands which Alpine and subalpine meadows in tropical and account 30% of total terrestrial net primary subtropical climates and grasslands of Sholas productivity; grasslands represent 85% of the in India are also climax type. The alpine and global land area burnt annually and contribute

Proceedings of 23rd International Grassland Congress 2015-Keynote Lectures 371 Babu et al.

to global carbon and energy cycles; 3 grasses and (vii) become source for CO2 rather than C alone provide 90% of world food and sink. livelihoods of 1/5 of global human population Elevated CO will render the grassy biomes depends directly on grasslands. Most of the 2 vulnerable, and C grasses could replace C mammalian megafauna of the earth are found 3 4 grasses with cascading effects on herbivores in grassland ecosystems. The environmental and fire regime. drivers for structuring the woody vegetation and community assembly in savannas are Elevated CO 2 will enhance the climate, atmospheric chemistry, fire, herbivory productivity by 15 – 20% and also enhance

(particularly by large mammals) soil fertility soil carbon storage. The effect of elevated CO2 and the amount and seasonality of rainfall. on grassland ecosystem evapo-transportation and therefore on water stress will be rather Grassland ecosystems are most small. However that in C dominated threatened ecosystems across the world due to 4 grasslands where the elevated CO will anthropogenic mediated factors. For example: 2 enhance the biomass production of C grasses (i) damming of rivers and rivulets changed 4 because of increase in soil moisture but the C flooding patterns, (ii) the luxuriant grasslands 3 grass species will be unaffected. It has been are converted into woodlands or agricultural shown that the community composition of fields, (iii) intensive grazing led to grassland changes rapidly in response to desertification, and (iv) the indiscriminate elevated CO in warm season and if water stress burning result in depauperization of most of 2 occurs at the same time C grasses will take the grasslands in terms of species composition. 4 over C grasses. Under low nitrogen In most of the areas no new grasslands are 3 availability, the response to elevated CO will being established due to prevention of natural 2 be suppressed due to nitrogen limitation. In ecological processes that promote development the short term, the impact of elevated CO may of grassland ecosystems. 2 be reduced by increased nutrient use efficiency Based on studies carried out by different and increased nutrient uptake due to higher workers, using pot experiments, field plot root biomass at elevated CO2. In the long-term studies and simulation models, the following less nitrogen will be available due to slower likely impacts of climate change are predicted. decomposition of litter because of reduced litter Climate change – an increase in temperature availability. of 1 to 4 ÚC, changes in precipitation patterns, Responses of grassland ecosystem to elevated CO levels (400 ppm currently) and 2 climate change is critical in grazing animal extreme events such as droughts and floods – production efficiency as climate change will will have the following impacts on the tropical have impact on forage quality (nutritive value). grassland ecosystems. An increase of 1 to 4 ÚC in temperature will: (i) increase the aridity Forage quality depends on digestibility, protein and hence reduce the productivity and the soil and energy content, palatability, organic carbon, (ii) enhance the water stress, concentrations of minerals and anti-nutritional (iii) alter the distribution pattern of grassland factors, all of which are sensitivity to growing communities, (iv) decrease the palatability of conditions of grassland and elevated CO2. the herbage, (iv) enhance inflammability, (v) Foliage quality decreases at elevated CO2 promote dominance of drought tolerant species, because of higher C:N ratios, higher (vi) lead to extinction of moist loving species, concentrations of unpalatable/toxic

372 Proceedings of 23rd International Grassland Congress 2015-Keynote Lectures Tropical Grassland Ecosystems and Climate Change compound and also reduced mineral changes in the distribution of grasslands concentrations (except phosphorous). worldwide in response to climate change. Semi-arid grasslands will be severely affected Herbivory will also be affected due to through changes in grassland – woody species feedback to carbon acquisition and nutrient boundaries as C grasslands are increasingly cycling at elevated CO . Forage consumption 4 2 populated by C woody plants which are may increase as the quality declines; ruminants 3 favoured by elevated CO . Further, with and functional caecum animals will have 2 doubling of CO2 climate change a 40% increase reduced consumption and reduced in warm grasslands and a 50% decrease in cool productivity. Herbivory in turn will also affect grasslands are predicted. the nutrient cycling by changing the rate of decomposition and mineralization. The To sum up, on a large scale extensive reduced nitrogen content of plant tissues at species rich stable tropical grasslands are resilient to climate change, as the grasses have elevated CO 2 will reduced the rate of decomposition and hence slowing nutrient wide ecological amplitude. In such cases no cycling and energy flow. action is the best action in tropical grassland ecosystems. Grassland can also mitigate the

Elevated CO2 enhances net primary climate change by enhancing the soil organic production everywhere except in cold steppe carbon pool and preventing desertification and regimes but decreases soil carbon by 4 PG from hence form climate resilient ecosystem. In fact global grasslands after 50 years. Combined grass species can be used in greening deserts climate change and elevated CO2 will increase and thereby combating desertification. There production and reduce grassland C losses to 2 are flood-, snow- and fire- tolerant species, all PG with tropical soils as small sinks for C. of which can contribute to the development of Biogeographic models suggest significant climate resilient grassland ecosystems.

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