Impacts of fire on non-native plant recruitment in black spruce forests of interior Alaska

Climate change is expected to increase the extent and severity of wildfires throughout the boreal forest. Historically, black spruce (Picea mariana (Mill.) B.S.P.) forests in interior Alaska have been relatively free of non-native species, but the compounding effects of climate change and an altered fire regime could facilitate the expansion of non-native plants. We tested the effects of wildfire on non-native plant colonization by conducting a seeding experiment of non-native plants on different substrate types in a burned black spruce forest, and surveying for non-native plants in recently burned and mature black spruce forests. We found few non-native plants in burned or mature forests, despite their high roadside presence, although invasion of some burned sites by dandelion (Taraxacum officinale) indicated the potential for non-native plants to move into burned forest. Experimental germination rates were significantly higher on mineral soil compared to organic soil, indicating that severe fires that combust much of the organic layer could increase the potential for non-native plant colonization. We conclude that fire disturbances that remove the organic layer could facilitate the invasion of non-native plants providing there is a viable seed source and dispersal vector.

预计气候变化将加剧整个北方针叶林（boreal forest）林火的波及范围与危害程度。历史上，阿拉斯加内陆的黑云杉（Picea mariana (Mill.) B.S.P.）林基本未受外来物种侵扰，但气候变化与改变后的林火特征所带来的复合效应，可能会推动外来植物的扩散。本研究通过在火烧迹地的黑云杉林中针对不同基质类型开展外来植物播种实验，并对近期火烧与成熟黑云杉林内的外来植物进行调查，以此探究林火对外来植物定植的影响。研究发现，尽管路边的外来植物分布丰度较高，但在火烧或成熟林内仅发现少量外来植物；不过部分火烧迹地被蒲公英（Taraxacum officinale）入侵的情况，表明外来植物具备侵入火烧林的潜力。实验结果显示，矿质土壤上的种子萌发率显著高于有机质土壤，这表明能够燃尽大部分有机质层的高强度林火，可能会提升外来植物定植的可能性。综上，若存在有效种源与传播媒介，能够移除有机质层的林火干扰，将可能推动外来植物的入侵。