STRUCTURAL DIVERSITY OF THE TAMAULIPAN THORNSCRUB DURING DRY AND WET SEASONS

Abstract

During the dry (summer) and wet (fall) seasons of 2009, the composition and structure of vegetation were determined in three sites (S) of the State of Nuevo Leon, Mexico: Los Ramones (S1), China, (S2) and Linares (S3). The main vegetation type is Tamaulipan Thornscrub (TT). Ten plots were randomly established (10 m x 10 m) at each site, where ecological indicators (abundance, dominance, frequency, and importance value (IV)) were estimated. The species diversity was calculated by using the Shannon-Weiner Index. The similarity between sites was determined with the Jaccard Index. The total number of individuals during the dry and wet season was 1 251 and 2 457, respectively. In general 57 species were found, of which 34 are common in both seasons. The main families were Fabaceae and Cactaceae. The genera with highest number of species were Acacia (5), Croton (3), Echinocereus (3) and Opuntia (2). The Shannon-Wiener Index showed statistical differences between sites and seasons. Sampling sites were determined as medium diversity, while the Jaccard index showed the highest similarity for Linares and the lowest for China in both seasons. The average cover for the three sites was 1 061 m2 and 1 847 m2 during the dry and wet seasons, respectively. The S3 revealed the highest coverage value (1 722.5 m2). Prosopis laevigata showed the highest IV in both seasons in the S1 and S2 sites. However, in S3, Lantana macropoda and Turnera diffusa had the highest IV in both seasons. In general, the diversity of species between sites and seasons was homogeneous.