Table_1_How Many Tree Species of Birch Are in Alaska? Implications for Wetland Designations.DOCX

Wetland areas are critical habitats, especially in northern regions of North America. Wetland classifications are based on several factors, including the presence of certain plant species and assemblages of species, of which trees play a significant role. Here we examined wetland species of birch (Betula) in North America, with a focus on Alaska, and the use of birche tree species in wetland delineation. We sampled over 200 trees from sites, including Alaska, Alberta, Minnesota, and New Hampshire. We used genetic data from over 3000 loci detected by restriction site associated DNA analysis. We used an indirect estimate of ploidy based on allelic ratios and we also examined population genetic structure. We find that inferred ploidy is strongly associated with genetic groupings. We find two main distinct groups; one found throughout most of Alaska, extending into Alberta. This group is probably attributable to Betula kenaica, Betula neoalaskana, or both. This group has a diploid genetic pattern although this could easily be a function of allopolyploidy. The second major genetic group appears to extend from Eastern North America into parts of southeastern Alaska. This group represents Betula papyrifera, and is not diploid based on allelic ratios. Published chromosome counts indicate pentaploidy. Because B. papyrifera is the only one of the above species that is distinctly associated with wetland habitats, our findings indicate that tree species of birch found in most parts of Alaska are not reliable indicators of wetland habitats. These results help to support stronger wetland ratings assigned to the tree species of birch for delineation purposes.

湿地是至关重要的生境类型，尤其在北美北部区域。湿地分类需依据多项判定指标，涵盖特定植物物种及物种组合的存在情况，其中树木类群发挥着关键作用。本研究聚焦北美地区湿地生境中的桦木属（Betula）物种，重点关注阿拉斯加区域，并探讨桦木树种在湿地划界工作中的应用。研究团队从阿拉斯加、阿尔伯塔、明尼苏达及新罕布什尔州的多个样地采集了200余株桦树样本，通过限制性位点相关DNA（restriction site associated DNA, RAD）分析技术获取了超过3000个基因座的遗传数据。本研究基于等位基因比例，采用间接方法估算样本倍性，并同时分析了种群遗传结构。结果显示，推断所得的倍性与遗传聚类结果显著相关。本次研究识别出两个主要的遗传类群：其一广泛分布于阿拉斯加大部分区域，并延伸至阿尔伯塔省，该类群大概率为喀纳特桦（Betula kenaica）、新阿拉斯加桦（Betula neoalaskana），或二者的混合类群；尽管该类群的遗传模式表现为二倍体，但这一结果也可能是异源多倍化作用导致的表象。第二个主要遗传类群则从北美东部延伸至阿拉斯加东南部部分区域，该类群为白皮桦（Betula papyrifera），根据等位基因比例判断，其并非二倍体；已发表的染色体计数结果显示该类群为五倍体。由于白皮桦是上述物种中唯一明确与湿地生境相关的类群，本研究结果表明，阿拉斯加大部分区域分布的桦木树种并非湿地生境的可靠指示物种。上述研究结果可为湿地划界工作中桦木树种的湿地等级评定提供更有力的支撑依据。