Barberis Ignacio M, Lewis Juan Pablo
Facultad de Ciencias Agrarias, Universidad Nacional de Rosario, Casilla de correo 14, S2125ZAA, Zavalla, Argentina.
Rev Biol Trop. 2005 Sep-Dec;53(3-4):377-85. doi: 10.15517/rbt.v53i3-4.14600.
In several tropical and subtropical forests, plants of the understorey act as an ecological filter that differentially affects woody species regeneration. In convex sectors of the Schinopsis balansae (Anacardiaceae) forests of the Southeastern Chaco there are dense colonies of terrestrial bromeliads. These may influence forest regeneration by intercepting rain water and propagules in their tanks. Within colonies, the spatial distribution of bromeliads is clumped because their clonal growth leaves numerous internal gaps. In this study we describe the internal heterogeneity of three bromeliad colonies (plots) and analyze how this heterogeneity affects Acacia praecox regeneration (i.e. seedling recruitment and survival). In January 1996, we randomly placed three transects with 150 contiguous quadrats of 100 cm(2) in each plot. For each quadrat we recorded the type of floor cover (i.e. bromeliads, herbs, litter, or bare soil) and the presence of A. praecox seeds or seedlings. In July 1996 we relocated the transects and recorded seedling survival. Bromeliad colonies showed a high internal heterogeneity. Almost half of the 450 quadrats were covered by two terrestrial bromeliads. Aechmea distichantha was recorded in 81% of all quadrats with bromeliads, and Bromelia serra in the others. All quadrats with bromeliads were covered by litter. Half of them were occupied by the bases of bromeliads and the others were covered by their leaves. In contrast, where bromeliads were not present, soil surface was covered by litter in 83% and by herbaceous vegetation in 11% of the quadrats; very few quadrats were covered by bare soil. In January 1996, we recorded 127 seeds and 176 seedlings of A. praecox. Seed and seedling densities of A. praecox were similar in quadrats with and without bromeliads, but variability in seedling density of A. praecox was higher within than among plots. Seed density was higher in quadrats covered by bromeliad leaves than inside the tanks. Seedling survival of A. praecox was slightly higher in quadrats with bromeliads in only one of the three plots. No seedling survived inside the bromeliad tanks. Apparently. bromeliad colonies have no effect on seedling regeneration of A. praecox.
在一些热带和亚热带森林中，林下植物起着生态过滤器的作用，对木本物种的更新产生不同影响。在东南查科地区的巴拉那漆树（漆树科）森林的凸形区域，有密集的陆生凤梨科植物群落。这些植物可能通过在其叶腋中截留雨水和繁殖体来影响森林更新。在群落内部，凤梨科植物的空间分布呈聚集状，因为它们的克隆生长留下了许多内部间隙。在本研究中，我们描述了三个凤梨科植物群落（样地）的内部异质性，并分析了这种异质性如何影响早金合欢的更新（即幼苗招募和存活）。1996年1月，我们在每个样地随机设置了三条样带，每条样带包含150个相邻的100平方厘米的样方。对于每个样方，我们记录了地面覆盖类型（即凤梨科植物、草本植物、凋落物或裸土）以及早金合欢种子或幼苗的存在情况。1996年7月，我们重新定位了样带并记录了幼苗存活情况。凤梨科植物群落表现出高度的内部异质性。在450个样方中，近一半被两种陆生凤梨科植物覆盖。在所有有凤梨科植物的样方中，81%记录到了二列尖萼凤梨，其余样方记录到了锯齿凤梨。所有有凤梨科植物的样方都被凋落物覆盖。其中一半被凤梨科植物的基部占据，另一半被其叶子覆盖。相比之下，在没有凤梨科植物的地方，83%的样方土壤表面被凋落物覆盖，11%被草本植被覆盖；很少有样方被裸土覆盖。1996年1月，我们记录到了127颗早金合欢种子和176株幼苗。有和没有凤梨科植物的样方中，早金合欢的种子和幼苗密度相似，但早金合欢幼苗密度在样方内部的变异性高于样地之间。被凤梨科植物叶子覆盖的样方中的种子密度高于叶腋内部。在三个样地中只有一个样地，有凤梨科植物的样方中早金合欢的幼苗存活率略高。没有幼苗在凤梨科植物的叶腋内存活。显然，凤梨科植物群落对早金合欢的幼苗更新没有影响。
