Monday, August 6, 2007

PS 12-138: Habitat fragmentation and nurse plant interactions: Mesquites and understory plants in a Mexican inter-tropical desert

Ricardo Alvarez-Espino and Héctor Godínez-Alvarez. Facultad de Estudios Superiores Iztacala, Universidad Nacional Autonoma de Mexico

This work analyzed the interaction between mesquites (Prosopis laevigata) and understory plants in a fragmented landscape of a Mexican inter-tropical desert, to determine whether species richness, abundance, and diversity of understory plants differed among habitat fragments. We selected 12-15 mesquites in three small (< 0.3 ha), medium (0.3-0.4 ha), and large (> 2.8 ha) fragments, for a total of 132 plants, to estimate their canopy size and record the number and cover of understory species. We also analyzed the relationship between size of mesquite canopy and number of understory species in each habitat fragment through non-linear regression models. Results showed that size of mesquite canopy varied between fragments. Mesquites in small and medium fragments had similar canopies (18.9-20.0 m2), which significantly differed from mesquites in large fragments (29.0 m2). Species richness of understory plants varied among mesquites of different fragments. Mesquites in small fragments had the lowest number of understory species compared to mesquites of other fragments. Abundance of understory plants varied depending on their life form. Shrubs and succulent plants had similar abundances under mesquites of all fragments, while herbs had highest abundance under mesquites of large fragments. Diversity of understory plants was higher under mesquites of medium fragments than in mesquites of other fragments. In spite of these differences, the number of understory plants tended to increase according to size of mesquite canopy in all fragments.

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