Impact of forest types on soil properties

Abstract

Soil and vegetation have a complex interrelationship, in which one influences the other. Both in naturalforests as well as man-made plantations cycling of nutrients is an important aspect as considerableamount of nutrients are returned through litter fall are made available for re-absorption. The natureand amount of organic matter produced depends on the dominant tree species present and the sitecharacteristics of the area, which regulate the physico-chemical properties of soil. Thus, the percentagereturn of nutrient varies with species, site conditions and topography.

The present study investigates the effect offorest types on soi I properties. Soil samples were collectedfrom different forest types covering different forest ecosystems viz., dry deciduous forest, moistdeciduous, shola forest, grassland, pine plantation, eucalyptus + wattle plantation, each at three depthsviz., 0-15, 15-30 and 30-45 ern and were analyzed for their physical and chemical properties.

The soil pH ranged from 3.52 to 7.60 and the dry deciduous forest registered a maximum pH of 6.54and the minimum was recorded in shola forest. With increase in depth, there was a slight increase inpH under dry deciduous forest, pine plantation and eucalyptus + wattle plantation. Dry deciduousforest registered a maximum EC of 0.946 d'Sm+at top layer followed by shola forests. In general,grassland recorded lower EC values than other vegetations. Organic carbon content was higherunder shola forest. With increasing depth, there was a progressive reduction in organic carbon.

Soi I avai lable nitrogen was in the range of 229 kg ha' to 1919 kg ha -I. A higher value of availablenitrogen was recorded in grassland soils followed by shola forest. Available nitrogen was found tooccur in a decreasing order with soil depth in all the study sites excluding sholas and grasslands. Thehighest available phosphorus was recorded in sholas and minimum was found in moist deciduousforest. With increasing depth, there was a great reduction in soil available phosphorus in all locations.This may be due to increased uptake anclless contribution of P by the litters. Soil available potassiumranged from 90 kg ha' to 941 kg ha-' The maximum amount of potassium was recorded in teaplantations and the minimum was under pine plantations. With increasing depth soil potassiumdecreased drastically.

Bulk density (80) increased with increasing depth in all vegetations. Sholas recorded lesser BO. Thisis because of more organic matter addition to the top layer of the ground floor. Particle density (PO)oftop layer of grassland was the lowest followed by sholas. Like BO, PO also increased with increasingdepth of soil. Percent pore space was maximum in the top layers of shola forest and it decreased withincreasing depth.

From this study a very good fertility status of soil was observed under sholas and grasslands. Thelower amount of nutrients was recorded under dry deciduous and moist deciduous forest and this isbecause of higher absorption of nutrients by the trees and erosional losses. Hence it is concluded thatthe soil physical and chemical properties are markedly influenced by vegetation.