Influência da pecuária bovina nos mecanismos de regeneração da floresta estacional decidual, Rio Grande do Sul, Brasil

Abstract

The cattle raising in natural areas can drive to a possible degradation of native forest ecosystem, especially the mechanisms of regeneration, besides modifications in terms of physical and chemical of soil, reducing his capacity of production and sustentation of native vegetation. So, the present work has the objective to evaluate the effect of cattle raising in the structure of natural regeneration, on Seasonal Deciduous Forest area, submitted to a many different intensities of stocking rate, in a rural property, in the city of São Nicolau, RS. The fragment was divided for the owner in three areas: Area 1 (A1), 12 ha isolated, without access of the cattle for more than 40 years; Area 2 (A2), 20 ha with average cattle weight of 0,5 head ha-1; Area 3 (A3), 25 ha with average cattle weight of 1,0 head ha-1, where both last two areas with more than 40 years of cattle raising. Was installed transects in each area, along was randomly selected 16 plots for each area. Was measured all the individuals arboreous, shrubby and herbaceous (0,10 m ≤ H ≤ 3,0 m) as for the diameter to height from soil (DAS) and the height. Were determined indexes of diversity, equability, dominance and similarity, also the diametric distribution of DAS and H, and analyzis of correlation among the species and the environmental variables. Were determined like environmental variables the chemical and physical properties of soil and luminosity above the dossal. Held up some physical and basic chemical analyzis of soil: density, total porosity, macro and microporosity, soil resistance to penetration (RP), hydraulic conductivity on saturated soil (K), moisture (U), temperature (Tº) and eletric conductivity (CE), and morphological classification of soil. On floristic analyzis, A1 showed the higher number of individuals. Actinostemon concolor (Spreng.) Müll. Arg. was the specie with the higher density and frequency in A1 and A2, and Brunfelsia cuneifolia J. A. Schmidt in A3. When we analyzis diversity and wealth, A2 showed superiority, and all the areas differed significantly on the diversity by the Hutcherson test. The chemical particulars of good fertility was reduced by the cattle presence and for stocking rate. In the physical properties of soil, density increased and the total porosity decreased by the presence of cattle and for the higher stocking rate. In general side, the presence of the cattle influenced on the density of the individuals of natural regeneration and on the physical properties of soil. The results about A2 show of the animal charge deposited, if the same place characteristics be present, can be an alternative to the conservation allied to the sustainable management of extensive cattle raising on the farms. The animal charge of 1,0 head ha-1, committed the diversity and wealth of natural regeneration, affecting the ecological sequence of that parcel. So, the presence of cattle in areas with native forest, affects directly the density of the regenerant properties and chemical and physical properties of the soil. Is necessary, higher cautions with the presence of the cattle, for the conduction of a sustainable management of cattle raising, allied to conservation of native remainings in the farms.