A influência do pisoteio e do pastejo no banco de plântulas de uma comunidade florestal em um remanescente de domínio da mata atlântica, no Morro do Coco, Viamão, RS.

Abstract

Research studies have shown that trampling and cattle grazing within forests causes damage to forest regeneration dynamics. Theese have main effects as soil compaction, trampling and herbivory over shrub and herbaceous strata, resulting in a significant increase mortality for native tree species seedlings, as much for shrubs, herbs and lianas. This paper evaluated phytosociological and floristic patterns of shrub layer in atlantic forest area, Morro do Coco (30 ° 03 'S, 51 ° 07' W), Viamão, Rio Grande do Sul. This area has two portions of a forest fragment: one with the cattle influence (A) and another without (B). The floristic patterns were sample using the quadrats (2 x 2m), totaling 160m². All individuals with heights between 0.5m and 2.0m were registred. We identified the specie, and analyzed their dispersal syndromes, their life-form, their habitats and their phytogeographic origins. We used phitosociological approach for calculate Importance Value Index (IVIi) and Coverage Value Index (IVC). We also estimated Shannon Index Diversity (H’), Pielou Eveness Index (J’), and Similarity Index of Jaccard (IJ) and Sorensen (ISS) for comparing beetwen areas. We used randomization test for comparate estatistics difference from composition and abundance data. We registered 264 individuals (201 in area A and 63 in area B,), distributed in 24 botanical families and 44 species (34 in area A and 22 in area B). According to the IVI, the most important species in A area were Trichilia elegans A.Juss., Mikania ternata (Vell.) B.L. Rob., Trichilia claussenii C.DC., Psychotria brachyceras M. Arg., Sebastiania serrata (M.Arg.) M.Arg., Faramea montevidensis (Cham & Schltdl.), Sorocea bonplandii (Baill.) W.C. Burger, Lanjouw & Boer, Guapira opposita (Vell.) Reitz and Psycothria leiocarpa Cham. & Schltdl. In B area were Sebastiania serrata, Myrciaria cuspidata O.Berg., Urera nitida (Vell.) P.Brack, Casearia sylvestris Sw., Eugenia hyemalis Camb. e Sorocea bonplandii. The zoochoric dispersal is dominant in the two evaluated areas (89% in A and 76% in B). The tree species were most common in all study (43% in area A and 62% in B), where B area registered only woody species (small trees and shrubs). In A area, beyond woody components, we record herbaceous and liana species, wich indicates a good conservation level. The A area showed higher diversity H’ (2,94) than B Area (2,54) (p = 0,005), while eveness index were not different. The similarity index showed low values for both Sorensen (42,9%) and Jaccard (27,4%). The species composition and abundance were significantly different 7 beetwen areas (p = 0,0001). The found patterns suggest the cattle select many structural and functinal parameters of shrub strata community, simpliyfing floristic composition, abundance, diversity and species life-form.