Ceccon Eliane, Hernández Patricia
Centro Regional de Investigaciones Multidisciplinarias, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.
Rev Biol Trop. 2009 Mar-Jun;57(1-2):257-69. doi: 10.15517/rbt.v57i1-2.11319.
In most of the legally protected areas in Mexico local inhabitants use natural resources, such as fire wood or cattle grazing. These frequent but low-intensity disturbances have consequences at various levels of the tropical ecosystems and strongly impact forest structure and its regeneration capacity. Despite their importance, the effects of these perturbations in many aspects of tropical forest ecology and in the forest's capacity to recover after disturbance exclusion remain poorly understood. Understanding the impact of these processes on tropical forests is necessary for rehabilitating these forests and enhancing their productivity. In this study, we evaluate the impact of twelve years of exclusion (E) of cattle grazing and fire wood extraction in the composition and dynamics of seed rain, and compare this assessment to a similar analysis in an area where these perturbations continued (without exclusion, WE). We found a strong seasonality in seed rain (96% of seeds fell in the dry season) in both areas. There were no significant differences between E and WE sites in relation to overall seed density, species richness and diversity. However, the distribution along the year of seed species density was significantly different among the E and WE sites. The Jaccard's similarity index between E and WE sites was relatively low (0.57). Barochory was the most common dispersal mode observed among the 23 species in terms of seed species density (48%), followed by anemochory (39%) and zoochory (13%). In relation to seed density, anemochory was the most frequent dispersal mode (88%). Most species in the zone were categorized as small seeds (92%), and there were no significant differences in the distribution of seed size between E and WE. The spatial pattern of dispersal of the four species with the highest relative importance value index, in both areas, was aggregated. Twelve years of disturbance exclusion were not enough to fully restore the seed rain of the area; some differences were already perceptible after this lapse. On the other hand, zoochorous species were almost absent from both sites. The re-introduction of climax and animal-dispersed species may be, in addition to perturbation exclusion, a viable strategy to accelerate ecological restoration in this area.
在墨西哥的大多数法律保护区，当地居民都会使用自然资源，比如木柴或放牧。这些频繁但强度较低的干扰在热带生态系统的各个层面都产生了影响，并对森林结构及其再生能力造成了强烈冲击。尽管它们很重要，但这些干扰在热带森林生态的许多方面以及森林在干扰排除后的恢复能力方面所产生的影响仍知之甚少。了解这些过程对热带森林的影响对于恢复这些森林并提高其生产力而言是必要的。在本研究中，我们评估了十二年排除放牧和木柴砍伐（E）对种子雨的组成和动态的影响，并将此评估结果与一个这些干扰仍在持续的区域（未排除干扰，WE）的类似分析进行比较。我们发现两个区域的种子雨都具有很强的季节性（96%的种子在旱季掉落）。在总体种子密度、物种丰富度和多样性方面，E区域和WE区域之间没有显著差异。然而，E区域和WE区域种子物种密度的全年分布存在显著差异。E区域和WE区域之间的杰卡德相似性指数相对较低（0.57）。就种子物种密度而言，在所观察的23个物种中，重力传播是最常见的传播方式（48%），其次是风传播（39%）和动物传播（13%）。就种子密度而言，风传播是最频繁的传播方式（88%）。该区域的大多数物种被归类为小种子（92%），E区域和WE区域之间种子大小的分布没有显著差异。在两个区域中，相对重要值指数最高的四个物种的传播空间模式都是聚集的。十二年的干扰排除不足以完全恢复该区域的种子雨；在这段时间过后，一些差异已经可以察觉到。另一方面，两个区域几乎都没有动物传播的物种。除了排除干扰之外，重新引入顶极物种和动物传播的物种可能是加速该区域生态恢复的一个可行策略。
