Tropical montane forest ecotones: climate gradients, natural disturbance, and vegetation zonation in the Cordillera Central, Dominican Republic
Tropical montane forest ecotones: climate gradients, natural disturbance, and vegetation zonation in the Cordillera Central, Dominican Republic
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DOI：
10.1111/j.1365-2699.2007.01726.x
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发表时间：
2007-10-01
影响因子：
3.9
通讯作者：
Fahey, Timothy J.
中科院分区：
文献类型：
--
作者：
Martin, Patrick H.;Sherman, Ruth E.;Fahey, Timothy J.
目的研究亚热带山脉气候-干扰梯度与植被地带性和交错带格局的关系。研究地点位于多米尼加共和国科迪勒拉中部迎风坡，云雾林在狭窄的交错带转变为西松的单优势林。方法收集海拔1100-3100m范围内的气候、干扰和植被数据，并沿交错带的50对样地进行观测。结果Shipley-Keddy检验在2200 m和2500 m处发现了离散的成分交错带，树种在低海拔的分布是连续的。通过航空照片确定的交错带的海拔高度相当一致，即124公里长的+/-164米(SD)，但它表现出显著的景观变化，出现在部分背风的西部地区的较低海拔。与排水沟相比，垄上的交错带也明显减少。交错带森林结构和组成在成对样地之间存在明显差异。在松树成对样地中，树冠高度比其正下方的云雾林高1.7倍，非松树种的断面积低6倍。火灾证据在松林中随处可见，但在毗邻的云雾林中却很少见。中尺度气候在交错带高程附近发生不连续变化，湿度和云量明显减少，霜冻频率呈指数级增加。然而，交错带的海拔一致性是由于中气候对火灾发生的海拔格局的总体影响。气温和降雨量的下降与信风逆温相结合，形成了一个狭窄的区域，高海拔的大火在这里被扑灭，使得对火敏感和耐火的类群得以毗邻。一旦确定，中地形和对比的植被地貌可能会通过对微环境和火灾可能性的反馈来加强这一边界。这项研究中松树的突出地位--以及亚热带山地森林中的温带和耐火分类群--突出了气候-干扰-生物地理相互作用在交错带形成中的重要性，特别是在火调节气候和植被之间的动态的情况下。
Aim We examined relationships between climate-disturbance gradients and patterns of vegetation zonation and ecotones on a subtropical mountain range.Location The study was conducted on the windward slopes of the Cordillera Central, Dominican Republic, where cloud forest appears to shift in a narrow ecotone to monodominant forest of Pinus occidentalis.Methods Climate, disturbance and vegetation data were collected over the elevation range 1100-3100 m and in 50 paired plots along the ecotone. Aerial photographs were georeferenced to a high-resolution digital elevation model in order to enable the analysis of landscape-scale patterns of the ecotone.Results A Shipley-Keddy test detected discrete compositional ecotones at 2200 and 2500 m; the distributions of tree species at lower elevations were continuous. The elevation of the ecotone determined with aerial photographs was fairly consistent, namely +/- 164 m (SD) over its 124-km length, but it exhibited significant landscape variation, occurring at a lower elevation in a partially leeward, western zone. The ecotone also occurred significantly lower on ridges than it did in drainage gullies. Ecotone forest structure and composition differed markedly between paired plots. In pine paired plots, the canopy height was 1.7 times higher and the basal area of non-pine species was 6 times lower than in the cloud forest directly below. Fire evidence was ubiquitous in the pine forest but rare in the abutting cloud forest. Mesoclimate changed discontinuously around the elevation of the ecotone: humidity and cloud formation decreased markedly, and frost frequency increased exponentially.Main conclusions The discreteness of the ecotone was produced primarily by fire. The elevational consistency of the ecotone, however, resulted from the overarching influence of mesoclimate on the elevational patterns of fire occurrence. Declining temperature and precipitation combine with the trade-wind inversion to create a narrow zone where high-elevation fires extinguish, enabling fire-sensitive and fire-tolerant taxa to abut. Once established, mesotopography and contrasting vegetation physiognomy probably reinforce this boundary through feedbacks on microenvironment and fire likelihood. The prominence of the pine in this study - and of temperate and fire-tolerant taxa in subtropical montane forests in general - highlights the importance of climate-disturbance-biogeography interactions in ecotone formation, particularly where fire mediates a dynamic between climate and vegetation.