Reproduction and seedling establishment of Picea glauca across the northernmost forest‐tundra region in Canada
Reproduction and seedling establishment of Picea glauca across the northernmost forest‐tundra region in Canada
复制标题
加拿大最北端森林苔原地区青云杉的繁殖和幼苗建立
DOI：
10.1111/j.1365-2486.2012.02769.x
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发表时间：
2012
影响因子：
11.6
通讯作者：
A. Hofgaard
中科院分区：
文献类型：
--
作者：
X. Walker;G. Henry;K. McLeod;A. Hofgaard
北方森林的北方边界和树种范围预计将因气候变暖而向北移动，这将导致目前被冻原植被覆盖的地区的覆盖率下降，陆地碳固存增加，目前低北极地区的生物多样性改变。预测森林扩张的核心是个体树木的繁殖能力和建立的增加。我们评估了球果产量，种子活力，和移植苗成功的云杉（Moench。）佛斯（白色云杉）在20世纪90年代初，并再次在2000年代后期在四个林分网站和八个树岛网站（克隆种群超越目前的树线）在麦肯齐三角洲地区的西北地区，加拿大。在过去的20年里，该地区的平均气温上升了0.9 °C。该地区是北美最北端的森林-苔原交错带，也是为数不多的针叶树北方界限到达北冰洋的环极地区之一。我们发现，球果产量和种子活力在两个检查期之间没有变化，这两个变量在森林-苔原交错带向北下降。然而，在森林-苔原交错带的北方边界的白色云杉个体产生了可行的种子。此外，移植的幼苗在最北端的地点能够存活15年，但没有自然更新的迹象。这些结果表明，如果气候条件继续改善，生殖产量可能会增加，但如果没有合适的补充地点，该地区森林冻原内的幼苗建立和森林扩张不太可能发生。影响补充地点可用性的过程可能在环极生态交错带的其他地方很重要，应纳入气候变化及其对北方森林-冻原生态交错带影响的模型和预测。
The northern boundary of boreal forest and the ranges of tree species are expected to shift northward in response to climate warming, which will result in a decrease in the albedo of areas currently covered by tundra vegetation, an increase in terrestrial carbon sequestration, and an alteration of biodiversity in the current Low Arctic. Central to the prediction of forest expansion is an increase in the reproductive capacity and establishment of individual trees. We assessed cone production, seed viability, and transplanted seedling success of Picea glauca (Moench.) Voss. (white spruce) in the early 1990s and again in the late 2000s at four forest stand sites and eight tree island sites (clonal populations beyond present treeline) in the Mackenzie Delta region of the Northwest Territories, Canada. Over the past 20 years, average temperatures in this region have increased by 0.9 °C. This area has the northernmost forest‐tundra ecotone in North America and is one of the few circumpolar regions where the northern limit of conifer trees reaches the Arctic Ocean. We found that cone production and seed viability did not change between the two periods of examination and that both variables decreased northward across the forest‐tundra ecotone. Nevertheless, white spruce individuals at the northern limit of the forest‐tundra ecotone produced viable seeds. Furthermore, transplanted seedlings were able to survive in the northernmost sites for 15 years, but there were no signs of natural regeneration. These results indicate that if climatic conditions continue to ameliorate, reproductive output will likely increase, but seedling establishment and forest expansion within the forest‐tundra of this region is unlikely to occur without the availability of suitable recruitment sites. Processes that affect the availability of recruitment sites are likely to be important elsewhere in the circumpolar ecotone, and should be incorporated into models and predictions of climate change and its effects on the northern forest‐tundra ecotone.