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International Grassland Database

"Whilst the productivity and standing carbon stocks of tropical forests has attracted considerable attention, particularly in respect of implications of 'global greenhouse effect', less attention has been given to other natural and semi-natural communities of the developing world. This is despite their recognized importance in the global carbon budget. For example it has been estimated that while tropical forests store about 19% of the total carbon sequested by terrestrial communities each year, tropical grasslands are suggested to store about 26% of the total." … Primary productivity of Grass Ecosystems of the tropics and sub-tropics.

Tropical and semi-tropical grasslands occupy up to one fifth of the global land surface with the estimates varying from 15.0 to 24.6 million square kilometres {Lieth, 1978 #1947} and are estimated to store 26% of the total carbon sequestered by terrestrial communities each year, compared to just 19% for tropical forests {Gifford, 1980 #238; Gates, 1985 #979}. They therefore represent a significant reservoir of carbon (C) on a global basis, accounting for approximately 30% of global soil C stocks {Anderson, 1991 #1948; Eswaran, 1993 #1949}.

Net annual C fixation in tropical tree-grass systems is about 7.6 x 1012 kg C yr-1, with a possible range between 3.2 and 10.8 x 1012 kg C yr-1 {Breymeyer, 1991 #1950}; {Breymeyer, 1996 #1951}. This is about half the net annual C fixation attributed to tropical forests. The main controls on C fixation are water and nutrient availability {Long, 1992 #1180}. The total C stock in tropical grasslands and savannas is about 100 x 1012 kg C with approximately 80% below ground in the roots and soil and 20% above ground in leaves, stems and woody tissue.

For the countries in which they occur tropical grasslands have two immediate economic values: 1). for agriculture, where they are grazed under varying intensity by domesticated livestock but are being increasingly used for crop production; and 2). as tourist attractions, particularly in the African savanna.

Tropical grasslands, savannas and drought deciduous woodlands form a continuum with varying proportions of grasses and woody plants which can only be separated into discrete types by the imposition of arbitrary limits. Savannas, in most classification systems, form the largest single class of this continuum and are a vegetation type in which primary production is approximately equally shared by trees and grasses {Breymeyer, 1996 #1951}. They occur in regions with a hot, wet season of 3 to 9 months duration, with a warm dry period in which little plant growth occurs for the rest of the year. Fires are an important component in maintaining the balance of grasses and woody plants in natural grassland systems and occur on average every 1 to 10 years during the dry season. For a predictive model to be realistic, it must contain mechanisms which allow it simulate the effects of regular burning on above ground and below ground carbon and nitrogen stocks.

Currently there is little or no direct information on the impact of rising atmospheric CO2 concentration, or the concomitant rise in temperature, on the primary production, decomposition and herbivory of tropical grasslands. There is considerable need for long term experimental sites to be established in order to investigate these elements of the ecosystem. However in the absence of long term experimental information the best alternative is predictive process based models which use our knowledge of existing well defined systems to allow reasonable extrapolation to currently less well defined grassland ecosystems. There is considerable scope for models to make a significant contribution to our understanding of carbon and nutrient cycling in grassland systems and to give a preliminary indication of whether such systems are likely to act as a sink for carbon, with sequestration to root, soil or plant tissue pools, or as a source of carbon with release of carbon previous bound to these pools. Understanding of the source/sink dynamics of natural ecosystems, such as grasslands, under climate change conditions is imperative if we are to be able to predict whether they will act as positive (enhancing) or negative (reducing) factors in future climates.

In an attempt to go some way to restore the balance of understanding of tropical and sub-tropical grassland systems the United Nations Environmental Program (UNEP) funded a 5 year multi-national project to examine grassland sites in the following sites: 1). Nairobi national park, Kenya.  2). Mexico City, Mexico. 3). Monsoon grassland, Thailand. 4). Amazon Flood plain, Brazil. 5).Bamboo forest, China

Where possible a common methodology across all the site was used to make meteorological and productivity measurements which were directly comparable between the sites. The results of these measurements have been used to create a database system and the results for Kenya, Mexico and Thailand are available in the form of a user friendly Windows database consistent with the manner in which the WIMOVAC modelling system works.

graphvw.gif (9323 bytes) Typical output from the Windows grassland database, showing above ground biomass measurements over a 10 year period.

The results of this work are fully reported in Primary productivity of Grass Ecosystems of the tropics and sub-tropics edited by Prof. Steve Long, Dr. Michael B. Jones and Dr. Michael J. Roberts and published by Chapman & Hall.

The UNEP grassland database is available to anyone interested by downloading either of the files below. Both of the files consist of a self extracting / self installing program that will prepare the grassland database for running on your machine. Simply select the link below and the appropriate file will be downloaded to your machine. You should then execute the downloaded file using the Windows Run command or File Manager and the setup files will automatically decompress and install onto your machine.

For a 16 bit version of the grassland database suitable for all versions of Windows

FILE.GIF (5459 bytes) Download the 16 bit Grassland Database (GRASS16.EXE, 3Mb, Date 20/08/96)

If you have any questions about the UNEP grassland database or the availability of additional data then please contact us by e-mail on humph@essex.ac.uk or by clicking the link below.

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Last modified: August 25, 1998