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Structure and tree diversity was studied in coffee agroforestry systems (SAF-cafe): rustic (RU), polyculture complex (PC), simple polyculture (PS), and as semi-evergreen forest (SM) from the Sierra de Atoyac, Veracruz, establishing three sampling units (UM) per altitudinal band (600-900 and 900-1200) m on each system and forest above mentioned, for a total 24 UM of 600 m2 (20 m x 30 m) each one. Each system was characterized by the diameter and height distribution of individuals as well as the calculated importance value (IVI), forest value (IVF), diversity (Shannon H', α Fisher) and floristic similarity (Sorensen: Si) indices. To analyze patterns of species distribution of vegetation classification (cluster analysis: β flex) and ordination (canonical correspondence analysis: CCA) techniques were applied. 79 tree species were determined, richness per system was: SM= 65; PC= 61; RU= 32; PS= 18. Cordia alliodora (Ruiz & Pav.) Cham. was the most important structurally species in the SAF-cafe coffee and Myriocarpa longipes Liebm., and Bursera simaruba (L.) Sarg. in the SM. The diversity was significantly higher in PC (H'= 3.56) and SM (H'= 3.58) without significant differences (p < 0.05) between them. The highest floristic similarity was between SM and PC (Si = 0.69). Also the altitude was the most influential environmental factor in the floristic composition of the systems. [ABSTRACT FROM AUTHOR]

During the summer of 2007, a study of the status of trees and woody vegetation was performed at four sites, in the state of Nuevo Leon, Mexico. Site one (S1, Bosque Escuela) was located at 1600 m elevation in Iturbide county. Sites S2 (Crucitas, 550 m), S3 (Campus, 350 m) and S4 (Cascajoso, 300 m) were located in Linares county. In each site, 10 random plots (10 m x 10 m) were laid out, and relative abundance, relative dominance and relative frequency were estimated. In addition, dasometric parameters such as height and crown diameter were determined. Plant diversity was estimated by the Shannon- Wiener index, and similarity between sites was calculated using the Jaccard index. A total of 13710 individual plants belonging to 28 families were registered. Leguminosae had the highest number of species (10) followed by Fagaceae (4), Rutaceae (4), Euphorbiaceae (3), Oleaceae (3), Cupressaceae (3), Rhamnaceae (2) and Verbenaceae (2). Eighteen families included only one species. The site with higher and lower Shannon index was Cascajoso (2,08) and Bosque Escuela (1,64), respectively. The Jaccard index showed similarity among species only among S2, S3 and S4 sites. The plant species more frequent were: in S1 Quercus canbyi, Pinus pseudostrobus and Rhus pachyrranchys (11,9%); in S2 Havardia pallens (9,9%); in S3 Havardia pallens and Forestiera angustifolia (9,8%) and in S4 Acacia rigidula, Cordia boissieri and Karwinskia humboldtiana (9,8%). S2 and S3 were the sites with the greatest species diversity, perhaps as a result of higher rainfall. [ABSTRACT FROM AUTHOR]

The study was realized at the community of "El Remolino", municipality of Papantla, Veracruz, with the purpose of typifying a site in the semideciduous tropical forest which has different altitudes and slopes, fact that allows the differentiation of two areas. Eight quadrants were sampled randomly. In each one, the density, frequency and relative cover were obtained to estimate the Value of Importance; 257 trees > 4.77 cm of diameter at breast height were counted; the index of similarity was based on the Sorensen index and the diversity measured with the Shanon-Wiener and Fisher indexes, 30 species and 20 families were registered; the arboreal species with high importance value were; Heliocarpus microcarpus, Brosimum alicastrum Bursera simaruba, Aphanan-the monoica y Myrsine coriacea. The basal area in zone 1 was 85.83 m² ha-1 and 67.72 m² ha-1 in zone 2. The undergrowth registered 27% of the species, the intermediate stratus presented a total of 37% and the superior canopies 10%, the remainder of species (26 %) were present in several layers. The Sorensen index of similarity indicated 28% of similitude between areas, while the Cluster UPGM (Unweighted Pair-Group Method using Arithmetic averages) analysis indicated two dusters of quadrants, related with the two areas. The Shannon Wiener index was registered in area 2 with 2.25; and the Fisher index was present in area 1 with a value of 7.83. It was concluded that the little similarity between the study areas was strongly associated with the presence-absence of species, while both areas were confirmed equal due to their richness. [ABSTRACT FROM AUTHOR]

Bray and Curtis ordination was used to explore which environmental variables explained importance values and the presence–absence of tropical tree seedlings, saplings and adults in La Escondida-La Cabaña, Sierra de Manantlán, Jalisco, Mexico. The diameters of trees ≥2.5 cm DBH and the presence and height of seedlings and saplings were measured in nine 0.1 ha sites. Four matrices including presence–absence data and importance value indices for trees and seedlings and saplings were analyzed through Bray and Curtis ordination. The matrices were based on density, frequency, and dominance of adult trees as well as seedlings and saplings. The environmental matrix consisted of 18 variables, including elevation, slope, canopy gaps, disturbance, and soil variables. We recorded 63 tree species and 38 seedling and sapling species in the nine sites. The ordination explained 70.9% of the variation in importance value data for trees and 62.6% for seedlings and saplings. The variation explained in presence–absence data for trees was 67.1 and 77.4% for seedlings and saplings. The variance in the ordination axes of seedlings and sapling presence–absence data was poorly explained by the number of gaps in the tree, shrub, or herb layer, suggesting little light specialization by seedlings and saplings. Habitat specialization for soil nutrients appears to be important in explaining the presence–absence of seedlings and saplings. Seedling and sapling specialization along different soil microsites could promote species coexistence in this forest, while heterogeneity in light conditions may instead determine differences in growth and, thus, importance value of trees. We hypothesize that in tropical dry forest in Jalisco, Mexico, a habitat specialization for soil resources is likely more importance at early stages in tree life histories than in later life history. [ABSTRACT FROM AUTHOR]