Estimation of shrub and herb biomass may be necessary for forests and plantations. This biomass is expressed as tonnes of dry biomass production per hectare per year. Shrub and herb biomass is estimated separately, since the sample plot size as well as the form of the plants is different. Biomass for these two plant types is estimated through the harvest method.
Shrub biomass The field method for estimating the shrub biomass is described in Chapter 10. Shrub biomass includes annual as well as perennial plants. The parameter measured for the shrub biomass includes the weight of the shrub biomass in sample plots
Step 1: Record the fresh and dry weight of the shrub biomass harvested from sample plots as kg per plot
° If there are young regenerating valuable tree plants and any economically valuable perennial shrubs, harvesting such plants may not be desirable ° A few representative plants could be harvested and weighed, and the height and spread of each of these plants recorded along with the name of the species ° These data could be used for estimating the weight of plants that cannot be harvested
° Alternatively, some of the perennial or economically valuable shrub species could be ignored if they cover only a small proportion of the ground area (e.g. <10%)
Step 2: Pool all the biomass harvested from different shrub plots to obtain the total dry shrub biomass for the total area of the sample plots Step 3: Extrapolate the sample area biomass to per hectare value (dry tonnes per hectare)
Herb biomass Biomass from herbs accounts for a small fraction of the total above-ground plant biomass of forests, plantations, agroforestry systems and grasslands. Further, herb biomass, being annual, is part of the annual carbon cycle with no implications for changes in carbon stocks. Herb biomass could be ignored, especially if tree crowns and shrubs cover the land area. If necessary, changes in carbon stocks in herb biomass could be estimated by using the method described for shrubs, based on the weight of herb biomass at two points in time. Herb biomass production (dry tonnes per hectare per year) can be calculated using the procedure given for grasses.
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