Understory plant diversity under variable overstory cover in Mediterranean forests at different spatial scales
Understory plant diversity under variable overstory cover in Mediterranean forests at different spatial scales
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DOI：
10.1016/j.foreco.2021.119319
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发表时间：
2021-08
影响因子：
3.7
通讯作者：
Ela Zangy;J. Kigel;S. Cohen;Yossef Moshe;Mor Ashkenazi;O. Fragman‐Sapir;Y. Osem
中科院分区：
文献类型：
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作者：
Ela Zangy;J. Kigel;S. Cohen;Yossef Moshe;Mor Ashkenazi;O. Fragman‐Sapir;Y. Osem
地中海森林生态系统具有很高的保护价值，因此越来越多地设法恢复和促进其自然生物多样性和复杂性。本研究旨在评价东地中海针叶林在不同空间尺度上受覆盖度操纵影响的物种多样性。在水资源有限的森林生态系统中，理解这种相互作用尤其具有挑战性，因为林下关系涉及水和光限制。该实验是在以色列耶路撒冷山区的一个成熟（40年）种植的松林中进行的。在16个试验区（0.5 ha）对林下植物群落结构进行了5年的监测，这些试验区代表了树木间伐造成的林下植被覆盖水平范围（叶面积指数- lai = 0-4 m2m−2）。利用鱼眼相机（照度）、优势种黎明前叶水势（PLWP）和土壤含水量（SWC）测量对林下植被的光和水有效性进行了监测。采用分层嵌套抽样方法，在不同的空间尺度（0.01 ~ 400 m2）上测量植物多样性。辐照度和SWC随LAI的降低而增加，而PLWP不受影响。林分林下植被丰富度（α多样性）随LAI的减小而线性增加，表明资源有效度与多样性呈一致的正相关关系。结果表明，物种丰富度对光有效性的依赖性较强，而对水有效性的依赖性较弱。林下物种组成在不同的LAI水平（森林水平的β多样性）上存在差异，表明物种更替主要发生在受益于林下覆盖减少的一年生草本植物和受益于高覆盖的木本物种之间。林下盖度与林下丰富度和林下组成的关系在不同粒度上呈秩不变关系。这些关系在较大（10、100、400 m2）的晶粒尺寸上强于较小（0.01、0.1、1 m2）的晶粒尺寸。与单株树冠投影面积对应的10-m2粒级关系最强。林下覆盖度-林下丰富度的变化表明，资源可得性是影响林下多样性的主要因素，而不是空间资源异质性。此外，粒度效应支持“环境过滤”而非“资源密度”是减少林下盖度促进林下多样性的主要机制。“综合与应用”：我们的研究结果表明，在水有限的东地中海森林中，覆盖度是决定植物多样性的关键因素。我们强调了林分（样地内）和森林（样地间）尺度上植被覆盖空间异质性的重要作用，并支持动态变量间伐作为一种提高森林生物多样性和复杂性的管理策略。
Mediterranean forest ecosystems are of high conservation value and therefore increasingly managed to restore and promote their natural biodiversity and complexity. The present study aimed to assess plant species diversity of East-Mediterranean conifer forests as affected by overstory cover manipulation at multiple spatial scales. Understanding this interaction in water-limited forest ecosystems is particularly challenging as overstory-understory relations involve both water and light constrains. The experiment was conducted in a mature (40y) plantedPinus halepensisforest in the Jerusalem Mountains of Israel. Understory plant community structure was monitored for five years in sixteen experimental plots (0.5 ha) representing a range of overstory cover levels (leaf area index-LAI = 0–4 m2m−2) created by tree thinning. Light and water availability in the forest understory were monitored using fisheye camera (irradiance), predawn leaf water potential (PLWP) of dominant species and soil water content (SWC) measurements. Plant diversity was measured at increasing spatial scales (grain sizes, 0.01–400 m2), using hierarchical nested sampling. Irradiance and SWC increased with decreasing LAI while PLWP was not affected. Stand-level understory richness (α diversity) increased linearly with decreasing LAI, indicating a consistent, positive resource availability-diversity relationship. The results pointed towards strong dependency of species richness on light availability as compared to its dependency on water availability that was less definite. Understory species composition varied across LAI levels (β diversity at the forest level) indicating species turnover, mainly between annual herbs benefiting from reduced overstory cover vs. woody species benefiting from higher cover. The relationships between overstory cover and understory richness and composition were rank-invariant across grain sizes. These relationships were stronger at the larger (10, 100, 400 m2) compared to the smaller (0.01, 0.1, 1 m2) grain sizes. The 10-m2grain-size, corresponding to the crown projection area of individual trees, showed the strongest relationship. Observed patterns of overstory cover–understory richness suggest that resource availability, rather than spatial resource heterogeneity, was the main factor shaping understory diversity. Furthermore, grain-size effects on this relationship support “environmental filtering” rather than “resource density” as the main mechanism through which reduced overstory cover promoted understory diversity.'Synthesis and applications’:Our findings demonstrate the importance of overstory cover as a key factor determining plant diversity in water-limited East-Mediterranean forests. We highlight the important role of spatial heterogeneity of overstory cover at both the stand (intra-plot) and forest (inter-plot) scales and support dynamic variable thinning as a management strategy to enhance forest biodiversity and complexity.