Ecology Unit, Department BOS, University of Oviedo, and Instituto Cantábrico de Biodiversidad (CSIC-UO-PA), E-33071, Oviedo, Spain.
Conserv Biol. 2010 Aug;24(4):1089-98. doi: 10.1111/j.1523-1739.2010.01459.x. Epub 2010 Feb 22.
Habitat fragmentation increases seed dispersal limitation across the landscape and may also affect subsequent demographic stages such as seedling establishment. Thus, the development of adequate plans for forest restoration requires an understanding of mechanisms by which fragmentation hampers seed delivery to deforested areas and knowledge of how fragmentation affects the relationship between seed-deposition patterns and seedling establishment. We evaluated the dispersal and recruitment of two bird-dispersed, fleshy-fruited tree species (Crataegus monogyna and Ilex aquifolium) in fragmented secondary forests of northern Spain. Forest fragmentation reduced the probability of seed deposition for both trees because of decreased availability of woody perches and fruit-rich neighborhoods for seed dispersers, rather than because of reductions in tree cover by itself. The effects of fragmentation went beyond effects on the dispersal stage in Crataegus because seedling establishment was proportional to the quantities of bird-dispersed seeds arriving at microsites. In contrast, postdispersal mortality in Ilex was so high that it obscured the seed-to-seedling transition. These results suggest that the effects of fragmentation are not necessarily consistent across stages of recruitment across species. Habitat management seeking to overcome barriers to forest recovery must include the preservation, and even the planting, of fleshy-fruited trees in the unforested matrix as a measure to encourage frugivorous birds to enter into open and degraded areas. An integrative management strategy should also explicitly consider seed-survival expectancies at microhabitats to preserve plant-population dynamics and community structure in fragmented landscapes.
生境破碎化增加了整个景观的种子散布限制，也可能影响后续的种群阶段，如幼苗建立。因此，制定适当的森林恢复计划需要了解生境破碎化如何阻碍种子输送到森林砍伐区的机制，以及了解生境破碎化如何影响种子沉积模式与幼苗建立之间的关系。我们评估了两种鸟类传播的肉质果实树木物种（山楂和冬青）在西班牙北部破碎的次生林中的散布和繁殖。由于木质栖木和富含果实的鸟类栖息地的减少，森林破碎化降低了两种树木的种子沉积概率，而不仅仅是由于树木覆盖本身的减少。破碎化的影响超出了山楂在散布阶段的影响，因为幼苗建立与到达微生境的鸟类传播种子的数量成正比。相比之下，冬青的种子散布后死亡率非常高，以至于掩盖了种子到幼苗的过渡。这些结果表明，破碎化的影响在不同物种的繁殖阶段不一定一致。为克服森林恢复的障碍而进行的生境管理必须包括在无林基质中保留甚至种植肉质果实树木，作为鼓励食果鸟类进入开阔和退化地区的一种措施。综合管理策略还应明确考虑微生境中的种子存活预期，以保持破碎景观中的植物种群动态和群落结构。
