Herbivores may have extensive top-down effects in open grazing ecosystems, generating vegetation changes by grazing and trampling. Trampling effects are understudied, but may be a major ecological factor. In cold alpine-Arctic ecosystems grazing and trampling by wild tundra reindeer ( Rangifer tarandus ) may be particularly important in lichen-dominated heaths. Dry lichen are crushed by trampling, and it is estimated that volume loss of lichen trampled may be considerably larger than lichen volume eaten by reindeer. Humidity affects lichen pliability and elasticity, and thereby resilience to trampling. Although crucial for estimating lichen vegetation trampling loss, the relationship between humidity and lichen elasticity is not well known. We collected samples of three lichen species in natura and in factorial experiments tested effects of species, levels of humidity (25, 70, 80, 90 and 100% RH) and temperatures (5 and 25 °C), on resilience to trampling (pressure resistance). The humidity:species interaction was the strongest factor increasing pressure resilience with increasing humidity, whereas temperature had small or no effects. Lichen elasticity increased rapidly above 70% RH. Consequently, when estimating lichen resources and potential trampling loss, number of dry days (less than 70% RH) should be estimated. This also has important ramifications for effects of climate change on the sustainability of reindeer populations.

中文翻译：

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软弹性：依赖水分的地衣弹性缓冲草食动物在寒冷的高山苔原生态系统中的践踏

食草动物可能在开放的放牧生态系统中具有广泛的自上而下的影响，通过放牧和践踏产生植被变化。践踏效应尚未得到充分研究，但可能是一个主要的生态因素。在寒冷的高山-北极生态系统中，野生苔原驯鹿（Rangifer tarandus）放牧和践踏可能在地衣占主导地位的荒地中尤为重要。干地衣被践踏压碎，估计被践踏的地衣体积损失可能比驯鹿吃掉的地衣体积大得多。湿度会影响地衣的柔韧性和弹性，从而影响践踏的弹性。尽管对于估计地衣植被践踏损失至关重要，但湿度与地衣弹性之间的关系尚不清楚。我们收集了自然中三种地衣物种的样本，并在析因实验中测试了物种、湿度水平（25、70、80、90 和 100% RH）和温度（5 和 25 °C）对践踏恢复能力（压力抵抗性）。湿度：物种相互作用是随着湿度增加而增加压力弹性的最强因素，而温度影响很小或没有影响。地衣弹性在 70% RH 以上迅速增加。因此，在估算地衣资源和潜在的践踏损失时，应估算干旱天数（低于 70% RH）。这也对气候变化对驯鹿种群可持续性的影响产生了重要影响。物种相互作用是随着湿度增加而增加压力弹性的最强因素，而温度影响很小或没有影响。地衣弹性在 70% RH 以上迅速增加。因此，在估算地衣资源和潜在的践踏损失时，应估算干旱天数（小于 70% RH）。这也对气候变化对驯鹿种群可持续性的影响产生了重要影响。物种相互作用是随着湿度增加而增加压力弹性的最强因素，而温度影响很小或没有影响。地衣弹性在 70% RH 以上迅速增加。因此，在估算地衣资源和潜在的践踏损失时，应估算干旱天数（小于 70% RH）。这也对气候变化对驯鹿种群可持续性的影响产生了重要影响。