Département de biologie and Centre d'études nordiques, Chaire de recherche nordique en écologie des perturbations, Université Laval, 1045 Av. De la Médecine, Québec, Québec, Canada, G1V 0A6.
Am J Bot. 2012 Oct;99(10):1638-46. doi: 10.3732/ajb.1200279. Epub 2012 Sep 14.
Treelines are temperature-sensitive ecotones that should be able to expand in response to global warming; however, they are also controlled by ecological constraints. These constraints can create bottlenecks for tree regeneration, hindering treeline advances. Near Kangiqsualujjuaq (Nunavik, subarctic Québec), previous studies suggested successful recruitment of Larix laricina above the altitudinal treeline, while Picea mariana establishment remains scarce. We studied regeneration of both species to identify factors responsible for such contrasting responses. •
We measured seeds and wings to evaluate species dispersal potential. We compared seed viability and tolerance to shrub leachates with germination trials. To evaluate seedbed preferences, we compared seedling occurrence on the different seedbeds with seedbed relative abundance in the field. •
Seed germination was similar between L. laricina and P. mariana, whereas dispersal potential was higher for the latter. Germination of P. mariana seeds was more strongly inhibited by shrub leachates than were L. laricina seeds. In the field, we found only a few Picea seedlings, but numerous seedlings of Larix had established disproportionally on several seedbeds. While Betula glandulosa, mosses, and Vaccinium uliginosim impeded Larix establishment, numerous seedlings were found on lichens, mineral soil, and liverworts. The low occurrence of suitable seedbeds for Picea, mainly mineral soil, could explain the seedling scarcity of this species. •
This study highlighted that allelopathy and unsuitable seedbeds could contribute to regeneration failure of P. mariana in eastern Nunavik and emphasizes the need to consider ecological preferences of species before predicting treeline expansion under a warmer climate.
林线是对温度敏感的生态过渡带，应该能够随着全球变暖而扩张；然而，它们也受到生态限制的控制。这些限制可能会给树木再生造成瓶颈，从而阻碍林线的推进。在靠近坎吉尔苏亚克（努纳武特，北极魁北克）的地方，之前的研究表明，在海拔林线以上，白云杉成功地进行了繁殖，而黑云杉的建立仍然很少。我们研究了这两个物种的再生，以确定造成这种对比反应的因素。
我们测量了种子和翅膀，以评估物种的扩散潜力。我们比较了种子活力和对灌木浸提液的耐受性与发芽试验。为了评估种子床偏好，我们比较了不同种子床上幼苗的出现与野外种子床上的相对丰度。
白云杉和黑云杉的种子发芽率相似，而后者的扩散潜力更高。与白云杉种子相比，灌木浸提液对黑云杉种子的发芽抑制作用更强。在野外，我们只发现了少量的黑云杉幼苗，但在几个种子床上发现了大量的白云杉幼苗，这些幼苗的建立不成比例。虽然白云杉的建立受到了腺柳、苔藓和越桔的阻碍，但在地衣、矿物土壤和肝蕨上也发现了大量的幼苗。适合黑云杉的种子床数量较少，主要是矿物土壤，这可能解释了该物种幼苗稀少的原因。
本研究强调了化感作用和不合适的种子床可能导致东努纳武特地区黑云杉再生失败，并强调在预测更温暖气候下林线扩张之前，需要考虑物种的生态偏好。
