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Influ?ncia da forma e posi??o da encosta nas caracter?sticas do solo e na regenera??o natural de esp?cies florestais em ?reas de pastagens abandonadas. / Hill slope form and position influence in soil characteristics and in natural regeneration of forest species of abandoned pastures areas.Silva, Alessando de Paula 28 February 2011 (has links)
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Previous issue date: 2011-02-28 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico - CNPQ / The aim of this work was to evaluate the influence of the position along a toposequence and
hillslope form on chemical and physical-hydric soil properties, and their relationship with
the natural regeneration of vegetation in areas of abandoned pastures. A total of eight areas in
the municipality of Itabora? - Rio de Janeiro State were evaluated. In the shoulder, backslope
and footslope positions of the relief toposequence concave and convex slope shapes were
identified. Two experimental plots (10 x 20 m) were installed in each section of the
toposequence, one for each slope shape, and evaluations related to soil and vegetation type
were proceeded. Chemistry and physical-hydric soil characterization was evaluated at 0-10cm
depth. Chemical analysis (pH, Al, Ca, Mg, P, K, C e N) and physical hydric attributes of soils
based on granulometry, porosity (macro, micro and total porosity), soil bulk density,
hydraulic conductivity, and soil mechanical resistance to penetration (RMSP) were carried
out. The analysis of vegetation consisted of dry matter evaluation, aboveground regrowth rate
of pasture and quantification, and species richness of trees and herbaceous shrubs in natural
regeneration. The areas were grouped into 2 based on textural class: Group 1, the clayey
areas, and Group 2 medium texture areas. Soil fertility in all the areas showed low levels of
sum of bases and base saturation, and high levels of aluminum saturation, which were not
influenced by topographic conditions, although the concave slope shape seem to promote the
removal of bases. The soil organic carbon and total nitrogen contents were highest on the
clayey texture areas. Chemistry and physical-hydric characterization of soil differed among
different topographic conditions in medium texture areas, where the shoulder and backslope
showed higher porosity (macro and total porosity). The RMSP was not influenced by
topographic conditions. More than 90% of the analyzed points showed declivities ranging
from 20 and 75 %, reducing values of pH, SB and V (%), and increasing values of m (%). The
grass biomass values exceed 10 Mg/ha. The regrowth rate was high showing an average
ranging from 984 to 1.356 kg/ha/month, and the clayey areas had lowest values. Low species
richness was observed, with greatest diversity of arboreal growth on concave slope; while the
herbaceous shrub regeneration tended to be highest in backslope and footslope. The
regeneration in terms of species richness was lowest in B. humidicola areas, for both strata
and in herbaceous shrub cover. A complementary analysis showed that the geographical
orientation of the slopes had a close relationship with the values of natural regeneration, while
south-facing slopes showed highest species richness. The backslope in concave slopes showed
lowest regrowth in the pasture, and these areas were identified as those with best natural
regeneration when compared to other areas studied in this research. / Objetivou-se avaliar a influ?ncia da posi??o na topossequ?ncia e da forma de rampa nas
propriedades qu?micas e f?sico-h?dricas do solo e a sua rela??o com o padr?o da regenera??o
natural da vegeta??o em ?reas de pastagens abandonadas. Foram avaliadas oito ?reas no
munic?pio de Itabora? ? RJ. Nos ter?os superior, m?dio e inferior da topossequ?ncia foram
identificados rampas de forma c?ncava e convexa. Foram instaladas duas parcelas (10 x 20 m)
em cada ter?o, uma para cada forma de rampa, onde se procederam as avalia??es quanto ao
solo e vegeta??o. O solo foi avaliado quanto ?s suas caracter?sticas qu?micas e f?sico-h?dricas
? profundidade de 0 a 10 cm. Foram realizadas as an?lises qu?micas de pH, Al, Ca, Mg, P, K,
C e N e as an?lises f?sico-h?dricas de granulometria, porosidade (macro, micro e total),
densidade do solo, condutividade hidr?ulica e resist?ncia mec?nica do solo ? penetra??o
(RMSP). A an?lise da vegeta??o consistiu na avalia??o da mat?ria seca e taxa de rebrota da
parte a?rea da pastagem e da quantifica??o e riqueza da vegeta??o arb?rea e herb?ceoarbustiva
da regenera??o natural. As ?reas foram agrupadas em duas de acordo com a classe
textural: Grupo 1, ?reas de textura argilosa, e Grupo 2, ?reas de textura m?dia. A fertilidade
do solo de todas as ?reas apresentou n?veis baixos de soma e satura??o de bases e n?veis altos
de satura??o por alum?nio, n?o sendo influenciadas significativamente pelas condi??es de
relevo, embora as formas de rampas c?ncavas pare?am promover uma maior remo??o de
bases. Os teores de carbono e nitrog?nio total foram maiores nas ?reas de textura mais
argilosa. As caracter?sticas f?sico-h?dricas do solo diferiram em fun??o das condi??es de
relevo somente nas ?reas de textura m?dia, onde os ter?os superior e m?dio apresentaram
maior porosidade (macro e total). A RMSP n?o foi influenciada pelas condi??es de relevo.
Mais de 90% dos pontos analisados apresentaram declividades entre 20% e 75 % favorecendo
diminui??es nos valores de pH, SB e V(%) e aumentos nos valores de m (%). Foram
identificadas tr?s esp?cies de gram?neas predominantes nas pastagens (Brachiaria decumbens,
Brachiaria humidicola e Paspalum sp.), com predomin?ncia da esp?cie Paspalum sp. Os
valores de biomassa de gram?neas apresentaram-se altos superando 10 Mg/ha. As taxas de
rebrota foram elevadas apresentando em m?dia valores entre 984 a 1.356 kg/ha/m?s, sendo os
menores valores encontrados nas ?reas argilosas. Observou-se baixa riqueza de esp?cies e
tend?ncia em maior domin?ncia arb?rea na rampa c?ncava, enquanto que a regenera??o
herb?ceo-arbustiva tendeu a ser maior nos ter?os inferior e m?dio. A regenera??o foi menor
em ?reas de B. humidicola, em termos de riqueza de esp?cies, nos dois estratos e para
cobertura herb?ceo-arbustiva. Uma an?lise complementar mostrou que a orienta??o
geogr?fica das encostas possuiu estreita rela??o com os valores de regenera??o natural, sendo
que encostas voltadas para o sul apresentaram maior riqueza de esp?cies. Os ter?os m?dios de
rampas c?ncavas apresentaram o menor vigor de rebrota do capim. Essas ?reas foram tamb?m
identificadas como aquelas com a maior regenera??o natural dentre as ?reas estudadas.
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