Mechanical abrasion and intercrown spacing
Mechanical abrasion and intercrown spacing
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DOI：
10.2307/2425452
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发表时间：
1984-07
影响因子：
0.6
通讯作者：
F. Putz;G. Parker;R. M. Archibald
中科院分区：
文献类型：
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作者：
F. Putz;G. Parker;R. M. Archibald
相似高度的相邻树木的树冠并不互相交错，而是通常被称为“树冠害羞”的间隙隔开。在哥斯达黎加的黑红树林（Avicennia germinans）中，树冠羞怯林隙的宽度与差距附近在风中摇摆的树木或树枝的距离成正相关（n = 22; p< .01）。由于树木相互碰撞而造成的芽、叶子和树枝的磨损似乎在每个树冠周围创造并维持了空间。引言虽然最近的森林结构和动态的研究集中在单一和多个树木倒塌造成的巨大差距，大多数森林冠层的开口是非常小的（例如，Hartshorn，1978; Runkle，1982）。小间隙通常会在短时间内保持开放状态，在风期间通过分支运动暂时关闭，并通过横向生长永久关闭（例如，Runkle，1982）。然而，在某些森林中，穿透树冠的光线在单个树冠周围形成了持久而醒目的边界，从地面上可以看到（图1）。术语“树冠羞怯”（来自Lane-Poole，1927-1944，在Jacobs，1955中引用）是指在相似高度的相邻树冠之间的这些无叶区域。当阳光穿过树冠的缝隙时，大部分光线到达林下植物。这些开口也可能是重要的，因为它们限制了树栖动物和藤蔓的冠间运动（Putz，1982）。在被海浪扫过的藻类中也观察到了类似的防御机制，即竞争对手的机械磨损和食草动物的驱逐（Velimirov和Griffiths，1979年）。有两种理论被提出来解释树冠羞怯间隙是如何形成和维持的。一种观点认为，被风吹动的树枝上的花蕾的磨损导致树冠之间的空隙（Tarbox和Reed，1924年; Jacobs，1955年;理查兹等人，1962年）。另一方面，Ng（1977）提出，马来西亚龙脑香属（Dryobalanops aromatica和Shorea的各种物种）的树冠羞怯是由于相互遮荫导致横向生长减少而引起的。我们测试了一个假设，即树冠羞怯是由在风中摇摆的树枝的机械磨损引起和维持的。具体来说，我们预测，如果机械磨损导致树冠害羞，那么灵活的树木和树枝应该比刚性的树木和树枝更广泛的分离。研究地点和方法我们研究了位于哥斯达黎加瓜纳卡斯特省国家圣罗莎公园（10035 'N，85085 'W）的一个约50公顷的以白骨壤为主的林地中的树冠害羞现象。只有当潮汐来临时，
The crowns of neighboring trees of similar height do not interdigitate but rather are generally separated by spaces called "crown shyness" gaps. In a black mangrove (Avicennia germinans) forest in Costa Rica, the width of crown shyness gaps was positively correlated with the distance pairs of trees or branches adjacent to the gap swayed in the wind (n = 22; p< .01). Abrasion of buds, leaves and branches due to trees knocking into one another seems to create and maintain the spaces around each tree crown. INTRODUCTION Though recent studies of forest structure and dynamics have focused on large gaps caused by single and multiple treefalls, most openings in forest canopies are extremely small (e.g., Hartshorn, 1978; Runkle, 1982). Small gaps usually remain open for a short time, being temporarily closed by branch movements during winds and permanently closed by lateral growth (e.g., Runkle, 1982). However, in some forests light penetrating into the canopy forms a persistent and striking border around individual crowns that are visible from the ground (Fig. 1). The term "crown shyness" (from Lane-Poole, 1927-1944, cited in Jacobs, 1955) refers to these leafless regions between adjacent crowns of similar height. Much of the light reaching the understory as sunflecks passes through crown shyness gaps. These openings may also be important insofar as they restrict intercrown movements of arboreal animals and vines (Putz, 1982). A similar sort of defense by mechanical abrasion of competitors and dislodgement of herbivores has been observed in wave-swept algae (Velimirov and Griffiths, 1979). Two theories have been proposed to explain how crown shyness gaps are formed and maintained. One view is that abrasion of buds on wind-blown branches leads to open spaces between tree crowns (Tarbox and Reed, 1924; Jacobs, 1955; Richards et al., 1962). Ng (1977), on the other hand, proposed that crown shyness in Malaysian dipterocarps (Dryobalanops aromatica and various species of Shorea) is caused by reduction in lateral growth due to mutual shading. We tested the hypothesis that crown shyness is caused and maintained by the mechanical abrasion of branches swaying in the wind. Specifically, we predicted that if mechanical abrasion causes crown shyness, then flexible trees and branches should be more widely separated than rigid trees and branches. STUDY SITE AND METHODS We studied crown shyness in an approximately 50-ha stand dominated by Avicennia germinans in the Parque Nacional de Santa Rosa, Guanacaste Province, Costa Rica (10035 'N, 85085 'W). The forest floor is inundated with sea water only when the tides