Rauschendorfer James, Rooney Rebecca, Külheim Carsten
College of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI 49931, USA.
Department of Biology, University of Minnesota Duluth, Duluth, MN 55812, USA.
Tree Physiol. 2022 Dec 12;42(12):2383-2400. doi: 10.1093/treephys/tpac090.
Red oaks (Quercus sect. Lobatae) are a taxonomic group of hardwood trees, which occur in swamp forests, subtropical chaparral and savannahs from Columbia to Canada. They cover a wide range of ecological niches, and many species are thought to be able to cope with current trends in climate change. Genus Quercus encompasses ca. 500 species, of which ca. 80 make up sect. Lobatae. Species diversity is greatest within the southeastern USA and within the northern and eastern regions of Mexico. This review discusses the weak reproductive barriers between species of red oaks and the effects this has on speciation and niche range. Distribution and diversity have been shaped by drought adaptations common to the species of sect. Lobatae, which enable them to fill various xeric niches across the continent. Drought adaptive traits of this taxonomic group include deciduousness, deep tap roots, ring-porous xylem, regenerative stump sprouting, greater leaf thickness and smaller stomata. The complex interplay between these anatomical and morphological traits has given red oaks features of drought tolerance and avoidance. Here, we discuss physiological and genetic components of these adaptations to address how many species of sect. Lobatae reside within xeric sites and/or sustain normal metabolic function during drought. Although extensive drought adaptation appears to give sect. Lobatae a resilience to climate change, aging tree stands, oak life history traits and the current genetic structures place many red oak species at risk. Furthermore, oak decline, a complex interaction between abiotic and biotic agents, has severe effects on red oaks and is likely to accelerate species decline and fragmentation. We suggest that assisted migration can be used to avoid species fragmentation and increase climate change resilience of sect. Lobatae.
红橡树（栎属红橡组）是一类硬木树种，生长在从哥伦比亚到加拿大的沼泽森林、亚热带丛林和稀树草原中。它们占据了广泛的生态位，许多物种被认为能够应对当前的气候变化趋势。栎属大约有500个物种，其中约80个组成了红橡组。物种多样性在美国东南部以及墨西哥北部和东部地区最为丰富。本综述讨论了红橡树物种之间较弱的生殖屏障及其对物种形成和生态位范围的影响。分布和多样性受到红橡组物种共有的干旱适应性的影响，这些适应性使它们能够填补整个大陆的各种干旱生态位。该分类群的干旱适应性状包括落叶性、深主根、环孔材木质部、再生树桩萌蘖、叶片更厚和气孔更小。这些解剖学和形态学性状之间的复杂相互作用赋予了红橡树耐旱和避旱的特性。在这里，我们讨论这些适应性的生理和遗传成分，以探讨红橡组中有多少物种栖息在干旱地区和/或在干旱期间维持正常的代谢功能。尽管广泛的干旱适应似乎使红橡组对气候变化具有恢复力，但老龄林分、橡树的生活史特征和当前的遗传结构使许多红橡树物种面临风险。此外，橡树衰退是一种非生物和生物因素之间的复杂相互作用，对红橡树有严重影响，并可能加速物种衰退和碎片化。我们建议可以利用辅助迁移来避免物种碎片化，并提高红橡组对气候变化的恢复力。
