Net Primary Production Spatial distribution of net primary production (NPP) using modis data and correlation with climate variability

7 field, however, NPP cannot be assessed in terms of this difference. An alternative definition of NPP is the total organic matter produced over a given interval. Although this production cannot be directly measured because of transformations such as consumption and decomposition during the measurement interval, it can be estimated based on a suite of diverse measurements and underlying assumptions. It is conceptually useful, therefore, to define the quantity NPP as the field-measurement-based, operational estimate of actual NPP Clark et al. 2001. NPP comprises all materials that together represent: 1 the amount of new organic matter that is retained by live plants at the end of the interval, and 2 the amount of organic matter that was both produced and lost by the plants during the same interval. In forests, these materials are: aboveground biomass increment, fine litter fall, aboveground losses to consumers, emissions of biogenic volatile organic compounds BVOCs, above ground losses of leached organic compounds, net increments in biomass of coarse and fine roots, dead coarse and fine roots, root losses to consumers, root exudates Clark et al. 2001. Net primary productivity NPP is defined as the net flux of carbon from the atmosphere into green plants per unit time. NPP refers to a rate process, i.e., the amount of vegetable matter produced net primary production per day, week, or year. However, the terms net primary productivity and net primary production are sometimes used rather liberally and interchangeably, and some scientists still tend to confuse productivity with standing biomass or standing crop. NPP is a fundamental ecological variable, not only because it measures the energy input to the biosphere and terrestrial carbon dioxide assimilation, but also because of its significance in indicating the condition of the land surface area and status of a wide range of ecological processes.

2.3 Distribution of Net Primary Production

Humans are changing the natural rate of exchange of carbon between the atmosphere and the terrestrial biosphere through land use, land-use change, and forestry activities. Consequently, it is important to examine how carbon flows 8 between different pools and how carbon stocks change in response to afforestation, reforestation, and deforestation ARD and other land-use activities. Distribution of NPP can be in any place in the world, i.e. forest, agricultural, wetland, urban areas which will have different rate in NPP and carbon sequestration. Changes in the proportion and spatial distribution of land use could enhance or degrade the area‟s ability to sequester carbon in terrestrial ecosystem. Figure 2.2 shows the global, annual average net primary production of vegetation on land during January to February 2010. On this map, vegetation is pictured as a scale or index of greenness. Greenness is based on several factors: the number and type of plants, how leafy they are, and how healthy they are. In places where foliage is dense and plants are growing quickly, the index is high, represented in dark green. Regions where few plants grow have a low vegetation index, shown in tan. The pattern that the maps show is a global one, vegetation greenness is high around the equator all year long, where temperatures, rainfall and sunlight are abundant. Between the equator and the poles, the vegetation greenness rises and falls as the seasons change. Source : http:earthobservatory.nasa.govGlobalMaps Figure 2.2 Global NPP of vegetation during January to February 2010

2.4 Estimation Method of Net Primary Production

Many models have been established to estimate regional and global NPP and can be classified into three types: climate models, process models, and energy use efficiency models. Climate models estimate NPP by establishing the statistical