Introduction

Altitude variation can influence the diversity and structure of a forest.

Objective

To assess the diversity, horizontal structure, and tree associations of a conserved temperate forest using an elevation gradient.

Materials and methods

The research was conducted at the Thick-billed Parrot Sanctuary at three altitudinal intervals: 1) 2 307 to 2 466 m, 2) 2 466 to 2 625 m and 3) 2 625 to 2 785 m. Horizontal structure was determined with the importance value index (IVI); analysis of variance and Tukey's test (p < 0.05) were performed for the Shannon-Wiener diversity index, Pielou's evenness and Margalef's richness. Similarity was determined with the Morisita-Horn index.

Results and discussion

Three families, five genera and seven species were recorded; Pinus strobiformis Engelm. had the highest IVI with values above 25 %. The Pinaceae family is the most representative with three species in risk category. Abundance decreased as altitude increased (p < 0.05). Dominance showed an upward trend in relation to altitude, in contrast to true diversity and evenness; however, there were no significant differences between intervals (p > 0.05). Richness was not related to altitude and floristic similarity was high (75 to 93 %) among the three intervals.

Conclusions

Dominance, diversity and evenness indices were similar in the three intervals. Floristic similarity suggests that altitude variation may lead to a gradual change in composition.

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