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首页> 外文期刊>Oikos: A Journal of Ecology >Disentangling the causes of damage variation by deer browsing on young Thuja plicata
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Disentangling the causes of damage variation by deer browsing on young Thuja plicata

机译：通过在幼小金钟柏上浏览鹿来找出造成伤害变化的原因

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摘要

Long-lived trees experience different levels of damage due to mammalian herbivores. To untangle the mechanisms that underlie this variation, we combined chemical with dendrochronological analyses to study variation in browsing on Western redcedars (Thuja plicata) on Haida Gwaii (British Columbia, Canada). Since the last glaciation, Haida Gwaii forests had lacked large herbivore browser until Sitka black-tailed deer (Odocoileus heimonus sitkensis) were introduced at the beginning of the 20th century. Dendrochronology yielded information on radial growth and plant annual responses to environmental stresses including herbivory. Secondary metabolite content and plant nutritional quality provided insights into proximate causes of food choices made by herbivores. We sampled lightly- and heavily-browsed young trees at four sites: three clear-cut sites with high browsing pressure and one old-growth forest site where browsing pressure had, until recently, been lower. Heavily-browsed young trees had lower concentrations of secondary metabolites and were of lower nutritive value than lightly-browsed trees at all sites. Under high browsing pressure, tree growth patterns suggested that all young trees were initially severely browsed until some trees, currently scored as lightly-browsed, started to escape deer. At the old-growth site, both lightly- and heavily-browsed trees tended to have lower overall average secondary metabolite concentrations than those of all other sites, a trend possibly related to greater canopy closure. Lightly-browsed trees were older than heavily-browsed ones which resulted, during the period of lower browsing pressure, in higher growth rate and a same pattern of change in growth from one year to the next year. This suggests that, under low browsing pressure, selection of young trees related to chemical defense was weak and that growth differences due to other factors than browsing could be expressed. Under strong browsing pressure, however, all young trees had equally low growth rates until trees with better genetic potential to produce effective defenses were able to escape deer. This suggests that selection by deer could occur on a long-lived tree.
机译：长寿树由于哺乳动物的食草动物而遭受不同程度的破坏。为了弄清造成这种变化的机制，我们将化学方法与树状年代学分析相结合，以研究在Haida Gwaii（加拿大不列颠哥伦比亚）上的西部柳杉（Thuja plicata）上浏览时的变化。自从上次冰川消融以来，海达瓜森林一直缺乏大型食草动物浏览器，直到20世纪初引入锡特卡黑尾鹿（Odocoileus heimonus sitkensis）。树木年代学提供了有关径向生长和植物对环境压力（包括草食性）的年度响应的信息。次生代谢产物含量和植物营养质量为食草动物选择食物的近因提供了见识。我们在四个地点对轻度和重度浏览的幼树进行了采样：三个具有高浏览压力的清晰地点和一个直到最近浏览压力都较低的老树林。在所有场所，重度浏览的幼树的次生代谢产物浓度均较低，营养价值也较轻度浏览的树低。在高浏览压力下，树木的生长方式表明，最初对所有幼树进行了严格的浏览，直到有些树木（目前评分为轻度浏览）开始逃脱鹿。在较老的生长地点，轻度浏览和重度浏览的树木的次生代谢产物总体平均浓度往往低于所有其他地点，这可能与更大的树冠封闭有关。轻度浏览的树木比重度浏览的树木要老，这导致在较低的浏览压力时期内，较高的增长率和从一年到明年的相同变化模式。这表明，在低浏览压力下，与化学防御相关的幼树的选择较弱，并且可以表示由于浏览以外的其他因素引起的生长差异。然而，在强大的浏览压力下，所有幼树的生长速度都同样低下，直到具有更好遗传潜力的树木能够产生有效防御能力才能逃脱鹿。这表明鹿的选择可能发生在长寿的树上。

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