Effect of winter fire on primary productivity and nutrient concentration of a dry tropical savanna

  • Published source details Singh R.S. (1993) Effect of winter fire on primary productivity and nutrient concentration of a dry tropical savanna. Vegetatio (now Plant Ecology), 63-71.


Fire has often traditionally been used to manage savanna habitats to improve forage quality for wild and/or domestic mammal grazers. The present study assessed the effects of prescribed winter fire on plant biomass, net primary productivity and nutrient concentration in plants and soil in an Indian dry tropical savanna.

Study site: The study was undertaken on the Vindhyan plateau (24˚36'36"N, 83˚3'18"E), Sonbhadra district, Uttar Pradesh, India. The climate is 'seasonally dry tropical' with three seasons: summer (April-June), rainy (July-September) and winter (November-February). The potential natural vegetation is dry deciduous forest, from which the savanna has been derived by anthropogenic activities and subsequently maintained by burning and grazing. The herbaceous vegetation was dominated by the perennial grasses Chrysopogon fulvus, Bothriochloa pertusa and Heteropogon contortus. The site was fenced in 1979 to exclude large mammal grazers. Each year in November-January, the herbaceous vegetation (at that time mainly dead shoots) is harvested to avoid building up of fuel load.

Experimental design: Six homogeneous plots (20 x 10 m) were established. Three were burned in the first week of January 1988 and again in the last week of November 1988 to emulate a traditional management system. Three were left as unburned controls.

Shoot biomass was harvested (hand-picked) close to ground level, from three randomly selected 50 x 50 cm quadrats in each plot of each treatment, commencing one day after the first burn and then at 30-day intervals from January 1988 to January 1990. The harvested samples were separated into live and dead shoots, brought to the laboratory, oven dried to constant weight and weighed. Below-ground plant material was sampled from the harvested quadrats in 15 x 15 x 10 cm sward sections at 30-d intervals, from January 1988 to January 1990. These were washed, and again plant material dried to constant weight and weighed. Subsamples of dried roots were combusted in a muffle furnace to estimate ash content.

Net above-ground primary production (ANP) and net below-ground production (BNP) were calculated Difficulties involved in the estimation of BNP may have led to rather conservative estimates.

Samples of shoot, root and litter at the time of peak biomass were collected and oven-dried. Total carbon (C), nitrogen (N) and phosphorus (P) in plant and soil samples were determined.

Burning increased the above annual above- and below-ground biomass of herbaceous vegetation (mostly perennial grasses) by 40% and 12%, respectively; litter mass was reduced by 85% in comparison to unburned controls. Average annual above- and below-ground net primary production were 471 and 631 g/m² in control, and 584 and 688 g/m² in burned plots, respectively. Burning led to increases in average above-ground and below-ground net production of 24% and 9%, respectively. Concentration of C, N and P in vegetation of unburned plots ranged between 34.01–38.59%, 0.85–1.53% and 0.04–0.11% and in soil from 0.95–1%, 0.011–0.13% and 0.017–0.02%, respectively. Burning led to increases in average concentrations of N and P by 16% and 42% in vegetation and 18.18% and 17.65% in soil, respectively.

Conclusions: In this study, prescribed winter burns stimulated plant biomass, net primary productivity and storage of nutrients (N and P) in the vegetation. Thus burning proved an important tool for the management of the savanna for fodder production and quality, for the benefit of wildlife and/or livestock.

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