SEED DISPERSAL, SEEDBANK, SEEDLING SURVIVAL, AND INITIAL GROWTH OF THREE CAATINGA TREES

ABSTRACT Myracrodruon urundeuva, Handroanthus impetiginosus and Amburana cearensis are Caatinga tree species that produce valuable timber, but little is known about their ecology. The objective of this study was to evaluate the seed distribution of these species on the forest floor before and after seed dispersal; and seedling emergence, survival, and growth during the rainy season after dispersal of seeds. There were no remaining viable seeds of these species in the seedbank before seed dispersal. The average numbers of seeds after seed dispersal were 188 seed m-2 in a 30 m radius around M. urundeuva, 9 seed m-2 in a 10 m radius around H. impetiginosus, and 5 seed m-2 in a 20 m radius around A. cearensis. The distance of seed dispersal reached 30, 20, and 10 m for M. urundeuva, H. impetiginosus, and A. cearensis trees, respectively, due to differences in tree height, seed weight, forest density, and wind intensity. Seedling emergence was observed during 4 (M. urundeuva) and 9 (H. impetiginosus and A. cearensis) weeks. High mortality predominated at the beginning and end of the rainy season for M. urundeuva and A. cearensis, respectively, while practically all H. impetiginosus seedlings survived. M. urundeuva showed the highest mortality but had higher number of established seedlings than the other species. Seedling survival peaked around 5 m from the tree base. Seedling recruitment and natural regeneration of these trees are assured in the Caatinga site evaluated.

摘要：乌氏黄栌（Myracrodruon urundeuva）、毛叶蚁木（Handroanthus impetiginosus）与塞阿腊黄檀（Amburana cearensis）均为卡廷加（Caatinga）植被区的珍贵用材树种，但目前对其生态学特性的研究仍较为匮乏。本研究旨在评估这三个树种在种子扩散前后林地表层的种子分布特征，以及种子扩散后雨季期间的幼苗出苗、存活与生长状况。种子扩散前，上述物种的种子库中已无存活种子留存。扩散完成后，各母树周边的平均种子密度分别为：乌氏黄栌周边30米半径范围内188粒·m⁻²，毛叶蚁木周边10米半径范围内9粒·m⁻²，塞阿腊黄檀周边20米半径范围内5粒·m⁻²。受树高、种子重量、林分密度及风速差异的影响，乌氏黄栌、毛叶蚁木和塞阿腊黄檀的种子最大传播距离分别可达30米、20米与10米。幼苗出苗持续时长分别为：乌氏黄栌4周，毛叶蚁木与塞阿腊黄檀9周。乌氏黄栌与塞阿腊黄檀的高死亡率分别集中在雨季初期与末期，而毛叶蚁木的幼苗几乎全部存活。乌氏黄栌的死亡率最高，但最终定植幼苗的数量多于另外两个物种。幼苗存活率在距母树基部约5米处达到峰值。本研究所评估的卡廷加样地中，上述树种的幼苗补充与天然更新均得到有效保障。