Estructura, composición, riqueza y diversidad de árboles en tres muestras de selva mediana subperennifolia

Abstract

THIS STUDY WAS CONDUCTED NEAR THE LATITUDINAL NORTHERN-LIMIT OF THE TROPICAL WET FORESTS. THE OBJECTIVE WAS TO COMPARE THE STRUCTURE, RICHNESS AND SPECIES DIVERSITY OF TREES CONTAINED IN THREE 1-HA PLOTS OF FOREST WITH DIFFERENT PHASES OF NATURAL REGENERATION. THE WORKING HYPOTHESIS WAS THAT THERE ARE DIFFERENCES IN FOREST STRUCTURE, COMPOSITION, RICHNESS AND SPECIES DIVERSITY AMONG THE THREE PLOTS DEPENDING ON THEIR DEGREE OF NATURAL REGENERATION. IN EACH PLOT, ALL STEMS 1CM DIAMETER AT BREAST HEIGHT (DBH) WERE RECORDED, INVENTORIED, AND MEASURED IN DBH, HEIGHT, AND STATUS. FOREST STRUCTURE WAS BASED ON SPECIES RELATIVE IMPORTANCE VALUES, DIAMETER CLASSES DISTRIBUTION, AND VERTICAL STRATIFICATION. SPECIES DIVERSITY WAS ESTIMATED USING THREE INDEXES: SIMPSON, SHANNON-WIENER, AND FISHER.S A. IN TOTAL 13 106 TREES WERE INVENTORIED, BELONGING TO 131 SPECIES AND 42 FAMILIES. PLOT P1 CONTAINS 4919 STEMS.HA-1 BELONGING TO 75 SPECIES AND 37 FAMILIES, BEING BURSERA SIMARUBA, PLEURANTHODENDRON LINDENII, PSYCHOTRIA COSTIVENIA, APHANANTHE MONOICA, AND NECTANDRA AMBIGENS THE MOST IMPORTANT SPECIES. PLOT P2 WITH 4617 STEMS.HA-1, 109 SPECIES AND 37 FAMILIES, IS CODOMINATED BY TABERNAEMONTANA ALBA, B. SIMARUBA, DENDROPANAX ARBOREUS, MANILKARA ZAPOTA, AND LITSEA GLAUCESCENS. PLOT P3 WITH 3570 STEMS.HA-1, DISTRIBUTED IN 78 SPECIES AND 33 FAMILIES, BEING THE MOST IMPORTANT SPECIES T. ALBA, P. LINDENII, A. MONOICA, BUNCHOSIA LANCEOLATA, AND B. SIMARUBA. THREE GENERAL PATTERNS OF DIAMETER STRUCTURES WERE IDENTIFIED (TYPE I, II, AND IV). PATTERNS I AND II WERE FORMERLY REPORTED IN OTHER STUDIES WHEREAS PATTERN TYPE IV IS DESCRIBED HERE FOR THE FIRST TIME. PATTERN TYPE I PREVAILED IN ALL THREE PLOTS, AND INCLUDES HIGH PERCENTAGES OF INDIVIDUALS IN THE SMALLER DIAMETRIC CLASSES, DIMINISHING AS DIAMETERS INCREASES. PATTERN TYPE II SHOWED HIGH PERCENTAGES OF INDIVIDUALS IN THE SMALLEST DIAMETRIC CLASS, A DECREASED ONE IN THE NEXT CLASS, HIGHER IN INTERMEDIATE CLASSES AND LOWER ONES IN THE LARGEST CLASSES. PATTERN TYPE IV PRESENTED HIGHER PERCENTAGES OF INDIVIDUALS IN INTERMEDIATE DIAMETRIC CLASSES AND LOWER ONES IN THE SMALLEST AND LARGEST CLASSES. THE STUDIED FOREST PLOTS SHOWED THREE STRATA: THE UNDERSTORY WITH HEIGHTS ³10 M; THE SUBCANOPY INCLUDED TREES BETWEEN 10 AND 20 M TALL, AND THE CANOPY INCLUDED TREES TALLER THAN 20 M. OF THE 131 RECORDED SPECIES, 50 WERE COMMON TO THE THREE PLOTS AND 31 WERE PRESENT IN ONLY ONE OF THEM. ALTHOUGH PLOTS P1 AND P3, SHARED THE LOWEST NUMBER OF SPECIES, THEY WERE THE MOST SIMILAR IN TREE COMPOSITION. IN CONTRAST, PLOTS P2 AND P3 SHARED THE MOST NUMBER OF SPECIES, THEY HAD AN INTERMEDIATE SIMILARITY WHEREAS PLOTS P1 AND P2 PRESENTED THE LOWEST SIMILARITY. OF THE 131 RECORDED SPECIES, 50 WERE COMMON TO THE THREE PLOTS AND 31 WERE PRESENT IN ONLY ONE OF THEM. ALTHOUGH PLOTS P1 AND P3, SHARED THE LOWEST NUMBER OF SPECIES, THEY WERE THE MOST SIMILAR IN TREE COMPOSITION. IN CONTRAST, PLOTS P2 AND P3 SHARED THE MOST NUMBER OF SPECIES, THEY HAD AN INTERMEDIATE SIMILARITY WHEREAS PLOTS P1 AND P2 PRESENTED THE LOWEST SIMILARITY. SPECIES DIVERSITY SHOWED STATISTICALLY SIGNIFICANT DIFFERENCES ONLY AMONG PLOTS P1 AND P2, AND P2 AND P3. PLOTS P1 AND P3 WERE MORE SIMILAR IN SPECIES AND PLOT P2 WAS THE MOST DISSIMILAR AMONG THE THREE PLOTS AND ALSO THE MOST DIVERSE AMONG THEM. THIS FOREST IS RELATIVELY POOR IN BOTH SPECIES RICHNESS AND SPECIES DIVERSITY COMPARED WITH OTHER NEOTROPICAL FORESTS, WHICH MAY BE EXPLAINED BY ITS LOCATION ON THE NORTHERN-LIMIT OF NEOTROPICAL WET FORESTS RANGE.