Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
PLoS One. 2011;6(9):e24675. doi: 10.1371/journal.pone.0024675. Epub 2011 Sep 22.
Wooded pastures with ancient trees were formerly abundant throughout Europe, but during the last century, grazing has largely been abandoned often resulting in dense forests. Ancient trees constitute habitat for many declining and threatened species, but the effects of secondary woodland on the biodiversity associated with these trees are largely unknown. We tested for difference in species richness, occurrence, and abundance of a set of nationally and regionally red-listed epiphytic lichens between ancient oaks located in secondary woodland and ancient oaks located in open conditions. We refined the test of the effect of secondary woodland by also including other explanatory variables. Species occurrence and abundance were modelled jointly using overdispersed zero-inflated Poisson models. The richness of the red-listed lichens on ancient oaks in secondary woodland was half of that compared with oaks growing in open conditions. The species-level analyses revealed that this was mainly the result of lower occupancy of two of the study species. The tree-level abundance of one species was also lower in secondary woodland. Potential explanations for this pattern are that the study lichens are adapted to desiccating conditions enhancing their population persistence by low competition or that open, windy conditions enhance their colonisation rate. This means that the development of secondary woodland is a threat to red-listed epiphytic lichens. We therefore suggest that woody vegetation is cleared and grazing resumed in abandoned oak pastures. Importantly, this will also benefit the vitality of the oaks.
过去，欧洲到处都是树木繁茂的牧场，但在上个世纪，放牧活动已基本停止，往往导致森林茂密。古树为许多濒危和受威胁物种提供了栖息地，但次生林对与这些树木相关的生物多样性的影响在很大程度上尚未可知。我们检测了在次生林和开阔条件下的古老橡树之间，一组国家和地区红色名录列出的附生地衣的物种丰富度、出现和丰度是否存在差异。我们通过纳入其他解释变量，进一步检验了次生林的影响。我们使用过度离散零膨胀泊松模型联合模拟物种的出现和丰度。次生林中古老橡树的红色名录地衣丰富度只有在开阔条件下的一半。物种水平的分析表明，这主要是由于两种研究物种的占有率较低所致。在次生林中，一种物种的树级丰度也较低。这种模式的潜在解释是，研究地衣适应干燥条件，通过低竞争或开阔、多风的条件提高其定居率，从而增强其种群的持久性。这意味着次生林的发展对红色名录列出的附生地衣构成了威胁。因此，我们建议清除树木植被并在废弃的橡树林牧场上恢复放牧。重要的是，这也将有利于橡树的活力。
