The role of temporal shrub encroachment for the maintenance of Spanish holm oak Quercus ilex dehesas
The role of temporal shrub encroachment for the maintenance of Spanish holm oak Quercus ilex dehesas
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DOI：
10.1016/j.foreco.2007.12.019
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发表时间：
2008-04-05
影响因子：
3.7
通讯作者：
Diaz, Mario
中科院分区：
文献类型：
--
作者：
Alberto Ramirez, Jose;Diaz, Mario
Dehesas是由散布在草地下层的万年青橡树（Quercus ilex和Quercus suber）组成的人工系统。它们位于伊比利亚半岛西南部，占地约310万公顷，由于它们保持了高度的动植物多样性，因此将根据《欧盟湿地指令》予以保护。目前对长期Dehesa种植的主要威胁是长期缺乏天然树木再生。我们测试dehesa放弃是否会促进自然更新，树木种群的大小结构如何改变放弃后，灌木侵占是否会提高幼苗招聘成熟的树木种群，灌木覆盖和幼苗密度在17 dehesa农场的已知日期放弃测量的大小结构。大小结构大约钟形的农场被遗弃不到16年前，逐步接近后，典型的从霍尔姆橡树林的倒J形分布。幼龄树比例随弃耕年限的变化符合逻辑斯蒂生长函数。森林中的典型比例（70-80%）在废弃30年后达到。而在废弃后20-25年，幼树和老树的数量达到平衡。短期的幼苗招聘是不相关的年龄放弃或覆盖的最占优势的灌木，并与覆盖的成熟树木和多花金雀花，一个护士灌木霍尔姆橡树幼苗。合成和应用：保护dehesa及其相关的生物多样性价值的基础应该是为暂时放弃生产性dehesa耕作20年提供资金，在树木补充后重新开放被侵占的地块，保持土地处于良好的农业状况（即轮换留出）。拟议的措施还有其他优点，即易于监测和直接评价其有效性。(c)2007 Elsevier B. V.保留所有权利。
Dehesas are man-made systems composed by evergreen Oaks (Quercus ilex and Quercus suber) scattered over a grassland understorey. They cover about 3.1 million ha in the southwest of the Iberian Peninsula and are to be preserved under the EU Habitats Directive due to the high levels of plant and animal diversity they maintain. The main current threat to long-term dehesa farming is a chronic absence of natural tree regeneration. We test whether dehesa abandonment would promote natural regeneration, how size structure of tree populations change after abandonment, and whether shrub encroachment would enhance seedling recruitment by measuring the size structure of mature tree populations, shrub cover and seedling density in 17 dehesa farms of known date of abandonment. Size structures were approximately bell-shaped in farms abandoned less than 16 years ago, progressively approaching afterwards the inverse J-shaped distribution typical from holm oak forests. Proportions of young mature trees changed with age of abandonment according to a logistic growth function. Proportions typical from forests (70-80%) were reached 30 years after abandonment. whereas balanced numbers of young and old trees were reached 20-25 years after abandonment. Short-term seedling recruitment was not related to age of abandonment or to covers of most dominant shrubs and was positively related to cover of mature trees and of Cytisus multiflorus, a nurse shrub for holm oak seedlings. Synthesis and applications: Conservation of dehesas and their associated biodiversity values should be based on financing temporal abandonment of productive dehesa farming for 20 years, keeping land in good agricultural condition by re-opening the encroached plots after tree recruitment (i.e. rotational set-aside). The proposed measure has the additional advantages of easy monitoring and straightforward evaluation of its effectiveness. (c) 2007 Elsevier B.V. All rights reserved.