Community and Ecosystem Dynamics of the Yukon Boreal Forest

北方森林占加拿大陆地面积的一半，由于人为引起的气候变化和自然变化，它正在发生显著的变化。我们在育空地区西南部的研究将解决这些关键变化的潜在原因及其长期生态影响。加拿大的这一地区是全球气候快速变化的热点地区。温度和降雨的物理变化相对容易记录和测量，但生态变化更为复杂。北方森林是一个盛衰交替的生态系统，受动植物生产周期的驱动。我们的研究主要集中在三个层面。据预测，植物初级生产最直接受到温度和降雨变化的影响。我们开发了使用夏季降雨量和温度的模型来预测浆果（越橘、熊果、红熊果、蔓越莓）、白云杉球果和地上蘑菇的年产量。我们将开发类似的模型，根据降雨量和温度来预测两种主要灌木（灰柳、矮桦树）的生长。如果我们要了解气候变化的影响，我们必须为优势植物物种开发这类环境模型，然后用随后的实地数据测试这些模型。北方森林动物种群受草食性优势动物雪鞋兔（雪鞋兔）9-10年周期的强烈影响。我们已经证明，野兔的周期是由一组与野兔同步波动的捕食者驱动的，这些波动设定了北方地区的生态脉搏。自1971年以来，雪鞋兔周期的峰值密度一直在缓慢下降，欧洲许多小型啮齿动物周期也出现了这种普遍趋势。这种崩溃对生态系统产生了影响，冬季野兔的浏览减少，使森林林下灌木的生长增加。对循环峰崩溃的一种解释是，由于皮毛颜色和雪的开始和融化不匹配，冬季捕食增加了。如果野兔在秋天过早地变白，它们就会被捕食者很容易看到，而在春天则相反。我们将与蒙大拿州的生态学家合作，用带无线电项圈的野兔来验证这一假设。另一种假设是，随着其他捕食者（貂、黄鼠狼）在北方森林中变得越来越普遍，野兔的死亡率也在增加，捕食活动加剧了。北极地松鼠是育空北部森林的主要食草动物，直到2000年，它们的数量锐减，几乎灭绝。我们正在研究15000平方公里区域的景观生态学，因为地松鼠在一些但不是所有的高山地区仍然很丰富，而在森林地区则不是。另一种假设是，它们被森林里的捕食者压制住了，或者它们受到了气候变化的影响，因为冬眠地的冬季结冰了。通过将地松鼠重新引入以前占据的栖息地，我们将直接测试捕食模型。先前的研究已经确定，在整个种群周期中，捕食者反复攻击失败所带来的压力会降低雪鞋兔的繁殖率。这项工作将通过复制前10年周期中进行的实验来跟进，并扩展结果，以测量压力如何影响兔子DNA的表观遗传变化和随后的大脑功能。由于兔周期在2013年进入增加阶段，我们准备在未来5年在分子和生理水平上推进这些研究。我们的总体研究目标是增加我们对加拿大西北部北方森林植物、食草动物和捕食者如何应对快速气候变化的生态学理解。

The boreal forest occupies half of Canada’s landmass and is undergoing marked change because of human-induced climate change and natural variation. Our research in the southwestern part of the Yukon will address the underlying causes for these key changes and their long-term ecological impacts. This part of Canada is a global hotspot for rapid climate change. Physical changes in temperature and rainfall are relatively easy to document and measure, but ecological changes are more complex. The boreal forest is a boom-and-bust ecosystem, driven by cycles in plant and animal production. Our research focuses on three levels. Plant primary production is predicted to be most immediately driven by changes in temperature and rainfall. We developed models that use summer rainfall and temperature to predict the annual crop size of berries (crowberry, bearberry, red bearberry, cranberry), white spruce cones, and above-ground mushrooms. We will develop similar models to predict the growth of the two major shrubs (grey willow, dwarf birch) from rainfall and temperature. If we are to understand the impacts of climate change we must develop these kinds of environmental models for the dominant species of plants and then test the models with subsequent field data. Animal populations in the boreal forest are strongly affected by the 9-10 year cycle of snowshoe hares, the dominant herbivore. We have shown that the hare cycle is driven by a suite of predators that fluctuate in synchrony with the hares, and these fluctuations set the ecological pulse of the boreal zone. The peak density of the snowshoe hare cycle has been slowly collapsing since 1971, a general trend found also in many small rodent cycles in Europe. This collapse has ecosystem consequences with hare browse in winter being reduced, allowing increased shrub growth in the forest understory. One explanation for the collapse of cyclic peaks has been increased predation in winter due to a mismatch in coat colour and snow onset and melt. If hares turn white too soon in the autumn, they become highly visible to predators, with the reverse problem in the spring. We will test this hypothesis with radio-collared hares in collaboration with ecologists working in Montana on the same problem. An alternative hypothesis is that predation has intensified as additional predators (marten, weasels) have become more common in the boreal forest and are increasing the mortality rate of hares. Arctic ground squirrels were a major herbivore in the Yukon boreal forest until 2000 when populations collapsed to virtual extinction. We are studying the landscape ecology of this collapse over a region of 15,000 km2, since ground squirrels remain abundant in some but not all alpine areas but not in forested areas. The alternative hypotheses are that they are held down by predators in the forest or that they are being affected by climate change via winter icing of hibernation sites. By reintroducing ground squirrels into previously occupied habitats we will test the predation model directly.Previous research has determined that stress from repeated unsuccessful predator attacks reduces reproductive rates in snowshoe hares over the population cycle. This work will be followed up by replicating the experiments carried out in the previous 10-year cycle and extending the results to measure how stress affects epigenetic changes in DNA and subsequent brain function in hares. Since the hare cycle is into the increase phase in 2013 we are poised over the next 5 years to advance these studies at the molecular and physiological level. Our overall research objective is to increase our ecological understanding to how boreal forest plants, herbivores, and predators are responding to rapid climate change in northwestern Canada.