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três gran<strong>de</strong>s comunida<strong>de</strong>s arbóreas, espacialmente correlacionadas à posição no<br />
relevo, tendo diferentes estágios <strong>de</strong> conservação, diversida<strong>de</strong> e fitossociologia.<br />
Essas foram nomeadas <strong>de</strong> formação, submontana e aluvial, e área dominada por<br />
ambas as formações (FA/FS). A área FA/FS revelou-se com maior diversida<strong>de</strong> que<br />
as d<strong>em</strong>ais, apresentando menor dominância ecológica <strong>em</strong> fragmentos estreitos. A<br />
formação submontana <strong>de</strong>stacou-se com maior <strong>de</strong>nsida<strong>de</strong> <strong>de</strong> indivíduos nas maiores<br />
classes <strong>de</strong> diâmetro e altura <strong>em</strong> razão da localização protegida <strong>em</strong> pequenos vales,<br />
com alta dominância ecológica, por uma particular espécie <strong>de</strong> sombra, Actinost<strong>em</strong>on<br />
concolor. A aluvial foi caracterizada por menores indivíduos arbóreos e presença<br />
dominante <strong>de</strong> Sebastiania commersoniana <strong>em</strong> corredores estreitos. Os padrões das<br />
tipologias da microbacia foram or<strong>de</strong>nados principalmente pelo gradiente ambiental e<br />
forma <strong>de</strong> relevo, sendo os tamanhos dos fragmentos vinculados aos distúrbios,<br />
condicionando diferentes estágios sucessionais, que influenciam no gradiente <strong>de</strong> luz<br />
no interior dos fragmentos, além dos controles ambientais <strong>de</strong> umida<strong>de</strong> dos solos.<br />
Esse conjunto <strong>de</strong> variáveis <strong>de</strong>terminou a distribuição das principais espécies e<br />
comunida<strong>de</strong>s na microbacia.<br />
Palavras-chave: Bioma Pampa, ecologia <strong>de</strong> comunida<strong>de</strong>s, dinâmica <strong>florestal</strong>,<br />
relação solo-planta, flora arbórea, solos florestais.<br />
ABSTRACT<br />
(Environmental and ecological patterns of a seasonal <strong>de</strong>ciduous forest on<br />
sedimentary formations in the Central Depression of Rio Gran<strong>de</strong> do Sul, Brazil.) This<br />
work aims to study r<strong>em</strong>aining tree communities distributed around different positions<br />
of the landscape in small tributaries of a watershed of the lower Jacuí River in the<br />
region of Pantano Gran<strong>de</strong>, in the state of Rio Gran<strong>de</strong> do Sul (30 ° 05 '41 "S and 52 °<br />
25 '30 "W). The region studied is known as Central Depression and surroun<strong>de</strong>d by an<br />
area of ecological transition due to the mixing between the seasonal forests and<br />
grasslands. The fragments are categorized as alluvial and upland <strong>de</strong>ciduous forests,<br />
and are found along a gradient with a wi<strong>de</strong> geomorphological and pedological<br />
variation. Thus, in or<strong>de</strong>r to un<strong>de</strong>rstand the ecological and phytosociological<br />
standards, the soils’ conditions and relief forms were studied in great <strong>de</strong>tail. To raise<br />
these variables, 200 plots of 100 m² were established and distributed around 40<br />
sampling points with five plots each, from the drainage headwaters to the floodplain<br />
II