Changing climatic regimes are causing increasing temperatures, changing precipitation patterns, and are subsequently expected to impact the spatial distribution of species. The distribution of plants at the scale of continents broadly conforms to the climatological regimes at play; however, in scaling down to the regional and landscape context, the influence of climate becomes confounded by complex and interacting biotic and abiotic factors. These factors have often been cited as important variables in determining the locations of biome overlap, including the boreal forest–temperate forest ecotone (BTE). The BTE exists as a broad latitudinal swath between the boreal and temperate forest biomes in the eastern half of North America. While the impact of non‐climatic factors on the location of the BTE has been investigated within the ecotone, few studies focus on how these same factors are shaping the colonization of the southern boreal forest by northern temperate tree species as part of a potential northward shift of the BTE. The effects of seed and seedling herbivory, substrate composition, microclimate, and canopy composition on seedling emergence of four northern temperate tree species were investigated in a beyond‐range seeding experiment spanning the southern portion of the island of Newfoundland, Canada. To represent a range of temperate tree reproductive strategies, we examined two small‐seeded tree species, Betula alleghaniensis and Thuja occidentalis, and two tree species with large seeds relative to typical boreal forest species, Acer saccharum and Fraxinus nigra. The results of this experiment show a reproductive strategy‐dependent emergence response; large seeds and seedlings appear more vulnerable to predation, while small seeds are more vulnerable to smothering by leaf litter. Canopies with greater representation of deciduous species posed a significant barrier to small seeds that produce small seedlings, while the food‐rich reward of the larger seeds made for attractive targets to granivorous vertebrates. This work represents a rare glimpse at the challenges northern temperate tree species will face if they are to colonize the southern boreal forest and track changing climates as is broadly expected.

中文翻译：

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北方田间试验对北方温带树苗出苗的生物过滤

气候状况的变化导致温度升高，降水模式变化，因此预计会影响物种的空间分布。大洲范围内的植物分布大致符合所发挥的气候条件；然而，在缩小到区域和景观的背景下，气候的影响被复杂的相互作用的生物和非生物因素所混淆。在确定生物群落重叠的位置时，这些因素通常被视为重要变量，包括寒带森林-温带森林过渡带（BTE）。BTE是北美东部半寒带和温带森林生物群落之间的广泛纬度带。虽然已经在过渡区内调查了非气候因素对BTE位置的影响，很少有研究关注这些相同因素如何塑造北温带树种对北方寒带森林的定殖，这是BTE可能向北移动的一部分。在加拿大纽芬兰岛南部的超范围播种实验中，研究了种子和幼苗的草食性，基质组成，微气候和冠层组成对四种北方温带树种幼苗出苗的影响。为了代表一系列温带树的繁殖策略，我们研究了两种小种子树种，在加拿大纽芬兰岛南部的超范围播种实验中，研究了四种北方温带树种幼苗的冠层和冠层组成。为了代表一系列温带树的繁殖策略，我们研究了两种小种子树种，在加拿大纽芬兰岛南部的超范围播种实验中，研究了四种北方温带树种幼苗的冠层和冠层组成。为了代表一系列温带树的繁殖策略，我们研究了两种小种子树种，桦alleghaniensis和崖柏，相对于典型的北方针叶林种两次棵树物种大种子，糖槭和水曲柳黑。该实验的结果显示了生殖策略依赖性的出苗反应；大种子和幼苗似乎更容易被捕食，而小种子则更容易因凋落物而窒息。落叶乔木占较大比例的树冠对产生小的幼苗的小种子构成了很大的障碍，而较大种子的食物丰富的奖励则成为食肉脊椎动物的诱人靶标。这项工作罕见地瞥见了北部温带树种如要在南部的北方森林中定居并按照人们普遍预期的那样跟踪气候变化将面临的挑战。