Structure and diversity of secondary tropical dry forests in Mexico, differing in their prior land-use history

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We compared the structure and diversity of secondary tropical dry forests, growing in sites cleared by bulldozer 30 years ago and subjected to different land uses prior to abandonment: (a) housing development (HD), (b) pasture (P), and (c) no use (NU). We sampled two forest sites representing each of the three former land-use types (i.e., a total of six sites) and measured the diameter at breast height (dbh) of all stems with dbh ≥1 cm and at least 2 m in height. All individuals were identified to species and classified into each of four dbh sizes-classes: 1–3, 3–5, 5–10, and >10 cm. No major differences in structure or diversity were evident among land-use types. Total tree densities varied from 2575 ± 55 to 4745 ± 985 individuals/ha and total basal areas ranged from 12.5 ± 2.6 to 14.6 ± 0.3 m 2/ha (mean and S.E.). Neither one differed significantly ( p < 0.05) among land-use types. Overall, the most abundant tree size-class was the 1–3 cm dbh (47% of the total number of trees), whereas trees greater than 10 cm dbh were the least abundant (4%). We found significantly higher density and basal area ( p = 0.01) in NU than in HD and P only in the smallest trees (1–3 cm dbh). We identified a total of 87 species in 28 families. The Leguminosae plant family had the greatest species richness and number of individuals in all land-use types. The HD land-use type showed lower total species richness than P and NU only with two of the four nonparametric estimators. Observed species richness decreased as dbh increased in all land-use types. At least 5 legumes were among the 10 most dominant species in all land-use types, of which the non-native Mimosa arenosa was the most dominant one. It represented between 42% and 52% of the total basal area in each land-use type. The secondary forests have reached, on average, 74% and 22% of the total density and basal area, respectively, of an average primary tropical dry forest of Mexico. The high number of individuals 1–3 cm dbh (48% of the total and 83% of the species) suggest that regeneration is occurring in all land-use types, although to different degrees. The absence of small individuals of M. arenosa and a high abundance of primary forest species at NU, suggest that M. arenosa is being replaced at these sites.