SEED SHADOW OF SWIETENIA MACROPHYLLA REMNANT TREES IN A MEXICAN RAINFOREST: IMPLICATIONS FOR FOREST MANAGEMENT

The understanding of processes affecting the regeneration and coexistence of tree species is of high concern in tropical landscapes disturbed by anthropogenic activities. In this study, we evaluated the seed shadow of eight small remnant Swietenia macrophylla trees to determine the possible consequences of selective logging on the first stages of natural regeneration. We expected to find a restricted dispersal ability and a marked loss of seeds due to biotic interactions. To test this, seed shadow per tree was quantified along four radial transects (30 x 1 m) that provided 960 - 1m(2) squares for sampling. The wind direction and some tree characteristics as diameter at breast height and crown projection area were also considered as factors influencing seed shadow. We also scored the number of seeds predated or infested by fungi. In total, 540 seeds were found along transects. Around 86.1% of the 960 squares presented 0 or 1 seed, whereas 80% of the seeds were found within the first 20 m from the parent tree. The number of seeds lost through biotic interactions regressed on the distance to the parent tree fitted a quadratic model that explained 52.4% of the total variance. These results suggest that small remnant S. macrophylla trees display low dispersal ability caused by a restricted seed shadow and a high rate of seed damaged produced by biotic interactions. Therefore, removal of largest trees for trading could be negatively impacting the first stages of the natural regeneration of this high value species. Consequently, harvesting could threat the local permanence of S. macrophylla in these managed forests of the Mayan zone.