Clasificación y ordenación de la vegetacion del norte de la Sierra Nevada, a lo largo de un gradiente altitudinal

Abstract

AN ANALYSIS OF THE VEGETATION AND THE PHYSICAL FACTORS ASSOCIATED WITH THEIR STRUCTURE AND DISTRIBUTION ALONG AN ELEVATION GRADIENT FROM 2750 TO 4100 M WAS CONDUCTED IN THE NORTH OF SIERRA NEVADA, MEXICO. BASED ON FIELD PHYSIOG- NOMIC RECOGNITION OF THE VEGETATION, 21 SAMPLING SITES WERE SELECTED. IN EACH SITE TWO 1000 M2 PLOTS WERE ESTABLISHED FOR TREE SAMPLING, AND WITHIN EACH PLOT TWO 250 M2 SUBPLOTS AND SIX 9 M2 SUBPLOTS WERE RANDOMLY SELECTED FOR SHRUB AND HERBACEOUS SAMPLING, RESPECTIVELY. THE STATISTICAL ANALYSES WERE CARRIED OUT BY USING CLUSTER ANALYSIS AS CLASSIFICATION TECHNIQUE AND DETRENDED CORRESPONDENCE ANALYSIS (DCA) AND CANONICAL CORRESPONDENCE ANALYSIS (CCA) AS ORDINATION TECHNIQUES, WHICH WERE APPLIED ON THE SPECIES RELATIVE IMPORTANCE VALUE AS STRUCTURAL ATTRIBUTE. THE ANALYSES INCLUDED DATA FOR 202 SPECIES AND 37 ENVIRONMENTAL VARIABLES. BOTH THE CLASSIFICATION AND ORDINATION TECHNIQUES DETECTED SIX VEGETATION TYPES FROM LOWEST TO HIGHEST ELEVATIONS: SCRUB-OAK, OAK FOREST, MIXED FOREST, FIR FOREST, PINE FOREST, AND ALPINE GRASSLAND. THESE COMMUNITIES ARE NOT STRICTLY DISCRETE SINCE THEY SHOWED CONTINUITY IN SPECIES DISTRIBUTION THROUGHOUT THE GRADIENT. THERE WAS A PATTERN IN THE STRUCTURE AND DISTRIBUTION OF THE PLANT COMMUNITIES MAINLY DEFINED BY THE ALTITUDINAL GRADIENT AND BY SOIL PROPERTIES. THE ALTITUDINAL GRADIENT INCLUDES CHANGES IN TEMPERATURE AND RAINFALL. SOIL PROPERTIES INCLUDE CHANGES IN ORGANIC MATTER, CATIONS, AND THE PERMANENT WILTING POINT OF THE HORIZON A2, AS WELL AS NUTRIENTS AND DEPTH OF HORIZON O, AND THE SLOPE OF THE TERRAIN. THE CLASSIFICATION AND ORDINATION TECHNIQUES PROVED TO BE COMPLEMENTARY METHODS IN THE DETECTION OF THE SIX VEGETATION TYPES ALONG THE ELEVATION GRADIENT STUDIED.