Variation in fine-root biomass and net primary productivity due to conversion of tropical forests into plantation crops and agroecosystems

Abstract

The changes in fine-root biomass and net primary productivity (NPP) following conversion of tropical forests (evergreen and deciduous) into forest plantations (teak, Acacia, Albizzia, rubber) and agroecosystems (banana, pepper, cassava, areca-nut) were studied at Kodayar in Western Ghats, South India. Very fine (≤ 1 mm) and fine (>1 - ≥ -3 mm) root biomass and NPP were significantly altered in man-modified ecosystems such as forest plantations and agroecosystems. Very fine-root biomass and NPP were significantly (P < 0.01) greater in natural ecosystems (biomass 245 and 263 g/m2; NPP 476 and 527 g/m2/year) when compared to monoculture plantations (172, 113, 125 g/m2; 368,293, 320 g/m2year, respectively) and agroecosystems (88, 104, 97, 156 g/m2; 227, 301,295, 376 g/m3year, respectively) except in teak plantations (230 g/m2; 463 g/m2/year, respectively). A similar trend was observed in the case of fine-root biomass. This could be attributed to tree density and basal area along with greater litter accumulation. The lower biomass and NPP in man-modified ecosystems could be attributed to species composition, low organic matter, and soil fertility. Recurrence of annual fire could lead to reoccupation of the land by grass cover. This may be the reason for greater below-ground biomass and NPP in deciduous forests and teak plantations. The present study reveals that fine-root biomass and NPP are significantly altered by anthropogenic perturbation of natural forest ecosystems. Fine roots generally comprise only a small proportion of the total root biomass in an ecosystem, but fine roots are a more accurate indicator of root function than large roots (Berish, 1982). Fine roots located in surface soil layers also are important in nutrient cycling (Medina and Cuevas, 1989) and undergo rapid change in response to perturbations (Hendrick and Pregitzer, 1993).