Rocks are safe sites for establishment of Bursera seedlings in a seasonally dry tropical forest of Mexico

We analyze the effects on seedling survival of Bursera bipinnata, B. copallifera and B. glabrifolia caused by their association with rocks, nurse plants, and in open areas. We hypothesize that the seedling-rock association is the safest for the establishment of all three seedling species. The objective was to investigate the suitability of the associations for seedling establishment and to compare the mortality risks under the three association conditions. All Bursera seedlings in 30 transects of 30 m2 were counted, recording whether they were located in open areas or associated with rocks or nurse plants, and monthly censored for two years. The proportion of seedlings associated with a rock or nurse plant was higher than those in open areas. Seedling survival curves were different among the three conditions. The survival of seedlings associated with rocks was greater than those established under a nurse plant and or in open areas. Survival time was 58% longer in seedlings associated with rocks than in open areas. The impact of stem diameter was 20 times greater than height. We conclude that rocks are safer and functionally more suitable sites than nurse plants or open areas for recruitment of the three Bursera species.