Grasses are unique group of flowering plants that form the foundation for the trophic structure in terrestrial communities. The grasses are found in every conceivable habitat where plants can thrive – from sea to deserts and from wetlands to peaks of highest mountains. The grasses form a distinct biome – a major ecological formation in the global classification of vegetation

Babu, C. R.

Choudhary, Vivek Kr.

Kumar, Vijay

English

University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings 23rd 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 Follow this and additional works at: https://uknowledge.uky.edu/igc  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 23rd 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 UKnowledge@lsv.uky.edu. Proceedings of 23rd International Grassland Congress 2015-Keynote Lectures 371Tropical Grassland Ecosystems and Climate ChangeC.R. Babu, Vivek Kr. Choudhary and Vijay KumarGrasses are unique group of floweringplants that form the foundation for the trophicstructure in terrestrial communities. Thegrasses are found in every conceivable habitatwhere plants can thrive – from sea to desertsand from wetlands to peaks of highestmountains. The grasses form a distinct biome– a major ecological formation in the globalclassification of vegetation. The grasslandbiomes are most widely spread worldwide andoccupy 20% of the global land surface. Thegrassland biomes are different in structure andcomposition across the continents. The tropicalgrassy biomes composed of a wide range ofgrassland communities depending upontopographic, edaphic, moisture, biotic andclimatic gradients. Areas where grasses arepredominant without scattered woody plantspecies are known as open grasslands (naturalgrasslands). All those grasslands withscattered woody plants (upto 80% of tree cover)are knows as savannas or mosaic grasslands.Similarly the Cerrados of Brazil are climaxmoist savannas and are maintained by grazingand burning. African savannas are veryextensive and represent the climax vegetationtype with rich wildlife particularlymammalian megafauna. These savannas areshort, medium and tall grasslands and aresustained by herbivore grazing and burningand composed C4 grass species. These may benatural, mosaic and derived. Derivedgrasslands are those grasslands aretransformed tropical forest throughSavannization (cleared or repeatedly burned)and these are found in Amazonia and Asia.Alpine and subalpine meadows in tropical andsubtropical climates and grasslands of Sholasin India are also climax type. The alpine andsubalpine meadows are found in Himalayaand are sustained by snow and grazing andburning, whereas the grassland of Sholas inWestern Ghats are also unique and sustainedby grazing or burning. The grassy biomesmentioned above are all on the upland.Some of the tropical grasslands are locatedon the: (i) flood plains of river systems (floodplain grasslands) and or the landslips, hilltopsand forest margins. These are seralcommunities and sustained by flooding andgrazing in case of flood plain grasslands andgrazing and burning in other grassland types.The grasslands in areas (where the riversshifted their courses) and the grasslands(which are never subjected to flooding) aresustained by grazing and or burning. In otherwords in the absence of regulatory ecologicalprocesses (flooding and grazing) burning ofgrasslands is the key for sustaining thegrasslands. Grass-fire cycle is unique fortropical grassy biomes and is critical inpromoting grasses and suppresses the woodygrowth. In India there are three types ofgrasslands – short, intermediate and tallgrasslands. All the three seral stages ofecological succession can be sustained byflooding, grazing and or burning. The annualcycle of flooding and herbivore migrationsustains network of the complex grasslandecosystem of the Corbett Tiger Reserve of Indiathat support rich wildlife.The grassland biomes render a wide rangeof ecosystem services. For example, 15% of thecarbon on earth is stored in grasslands whichaccount 30% of total terrestrial net primaryproductivity; grasslands represent 85% of theglobal land area burnt annually and contribute372 Proceedings of 23rd International Grassland Congress 2015-Keynote Lecturesto global carbon and energy cycles; 3 grassesalone provide 90% of world food andlivelihoods of 1/5 of global human populationdepends directly on grasslands. Most of themammalian megafauna of the earth are foundin grassland ecosystems. The environmentaldrivers for structuring the woody vegetationand community assembly in savannas areclimate, atmospheric chemistry, fire, herbivory(particularly by large mammals) soil fertilityand the amount and seasonality of rainfall.Grassland ecosystems are mostthreatened ecosystems across the world due toanthropogenic mediated factors. For example:(i) damming of rivers and rivulets changedflooding patterns, (ii) the luxuriant grasslandsare converted into woodlands or agriculturalfields, (iii) intensive grazing led todesertification, and (iv) the indiscriminateburning result in depauperization of most ofthe grasslands in terms of species composition.In most of the areas no new grasslands arebeing established due to prevention of naturalecological processes that promote developmentof grassland ecosystems.Based on studies carried out by differentworkers, using pot experiments, field plotstudies and simulation models, the followinglikely impacts of climate change are predicted.Climate change – an increase in temperatureof 1 to 4 ÚC, changes in precipitation patterns,elevated CO2 levels (400 ppm currently) andextreme events such as droughts and floods –will have the following impacts on the tropicalgrassland ecosystems. An increase of 1 to 4ÚC in temperature will: (i) increase the aridityand hence reduce the productivity and the soilorganic carbon, (ii) enhance the water stress,(iii) alter the distribution pattern of grasslandcommunities, (iv) decrease the palatability ofthe herbage, (iv) enhance inflammability, (v)promote dominance of drought tolerant species,(vi) lead to extinction of moist loving species,and (vii) become source for CO2 rather than Csink.Elevated CO2 will render the grassy biomesvulnerable, and C3 grasses could replace C4grasses with cascading effects on herbivoresand fire regime.Elevated CO2 will enhance theproductivity by 15 – 20% and also enhancesoil carbon storage. The effect of elevated CO2on grassland ecosystem evapo-transportationand therefore on water stress will be rathersmall. However that in C 4 dominatedgrasslands where the elevated CO2 willenhance the biomass production of C4 grassesbecause of increase in soil moisture but the C3grass species will be unaffected. It has beenshown that the community composition ofgrassland changes rapidly in response toelevated CO2 in warm season and if water stressoccurs at the same time C4 grasses will takeover C3 grasses. Under low nitrogenavailability, the response to elevated CO2 willbe suppressed due to nitrogen limitation. Inthe short term, the impact of elevated CO2 maybe reduced by increased nutrient use efficiencyand increased nutrient uptake due to higherroot biomass at elevated CO2. In the long-termless nitrogen will be available due to slowerdecomposition of litter because of reduced litteravailability.Responses of grassland ecosystem toclimate change is critical in grazing animalproduction efficiency as climate change willhave impact on forage quality (nutritive value).Forage quality depends on digestibility, proteinand energy content, palatability,concentrations of minerals and anti-nutritionalfactors, all of which are sensitivity to growingconditions of grassland and elevated CO2.Foliage quality decreases at elevated CO2because of higher C:N ratios, higherconcentrations of unpalatable/toxicBabu et al.Proceedings of 23rd International Grassland Congress 2015-Keynote Lectures 373compound and also reduced mineralconcentrations (except phosphorous).Herbivory will also be affected due tofeedback to carbon acquisition and nutrientcycling at elevated CO2. Forage consumptionmay increase as the quality declines; ruminantsand functional caecum animals will havereduced consumption and reducedproductivity. Herbivory in turn will also affectthe nutrient cycling by changing the rate ofdecomposition and mineralization. Thereduced nitrogen content of plant tissues atelevated CO2 will reduced the rate ofdecomposition and hence slowing nutrientcycling and energy flow.Elevated CO2 enhances net primaryproduction everywhere except in cold stepperegimes but decreases soil carbon by 4 PG fromglobal grasslands after 50 years. Combinedclimate change and elevated CO2 will increaseproduction and reduce grassland C losses to 2PG with tropical soils as small sinks for C.Biogeographic models suggest significantchanges in the distribution of grasslandsworldwide in response to climate change.Semi-arid grasslands will be severely affectedthrough changes in grassland – woody speciesboundaries as C4 grasslands are increasinglypopulated by C3 woody plants which arefavoured by elevated CO2. Further, withdoubling of CO2 climate change a 40% increasein warm grasslands and a 50% decrease in coolgrasslands are predicted.To sum up, on a large scale extensivespecies rich stable tropical grasslands areresilient to climate change, as the grasses havewide ecological amplitude. In such cases noaction is the best action in tropical grasslandecosystems. Grassland can also mitigate theclimate change by enhancing the soil organiccarbon pool and preventing desertification andhence form climate resilient ecosystem. In factgrass species can be used in greening desertsand thereby combating desertification. Thereare flood-, snow- and fire- tolerant species, allof which can contribute to the development ofclimate resilient grassland ecosystems.Tropical Grassland Ecosystems and Climate Change

Tropical Grassland Ecosystems and Climate Change

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Tropical Grassland Ecosystems and Climate Change

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