Stage and size structure of three species of oaks in central coastal California

Oaks are foundational species in much of California, and many oak populations in the state may be in jeopardy due to a lack of recruitment of young trees. Despite considerable interest in this problem, there have been few comprehensive surveys of all stages of oak development. We surveyed all stages of three oaks: Quercus lobata, Q. douglasii, and Q. agrifolia in a forest plot with mixed land-use in central coastal California. We found abundant seedlings of all oak species, but an apparent paucity of Q. lobata and Q. douglasii saplings. First year seedlings of all species were less abundant in parts of the study site with cattle grazing, but later-stage seedlings of Q. lobata and Q. douglasii were equally abundant across land-use types. Quercus agrifolia seedlings were associated with non-grazed areas; Quercus agrifolia late-stage seedlings in the grazed area were smaller and less abundant than in non-grazed areas. Quercus agrifolia seedlings of all stages tended to be clustered around ...

橡树是加州多数区域的建群种，该州诸多橡树种群因幼树更新不足而濒临存续危机。尽管学界对该问题关注度颇高，但目前针对橡树不同生长阶段的全面调查仍较为匮乏。我们针对加州中部沿海某混合土地利用类型的林样地内的3种栎属植物——加州谷地栎（Quercus lobata）、道格拉斯栎（Quercus douglasii）与加州栎（Quercus agrifolia）——的全生长阶段开展了调查。我们发现所有栎类的实生苗均较为丰富，但加州谷地栎与道格拉斯栎的幼树却明显稀缺。所有物种的一年生实生苗在研究样地的牛牧区域内丰度更低，但加州谷地栎与道格拉斯栎的后期实生苗在不同土地利用类型间的丰度并无显著差异。加州栎的实生苗与非放牧区域呈显著关联；放牧区内的加州栎后期实生苗体型更小、丰度也低于非放牧区域。各生长阶段的加州栎实生苗均倾向于聚集于……