Recent Trends in Large Hardwoods in the Pacific Northwest, USA
Recent Trends in Large Hardwoods in the Pacific Northwest, USA
复制标题
美国西北太平洋地区大型硬木的最新趋势
作者：
J. Long;A. Gray;Frank K. Lake
森林密化、野火和疾病会减少阔叶树的生长和存活，而阔叶树对美国太平洋西北部的生物和文化多样性非常重要。在欧美殖民之前，结果实并形成野生动物使用的巨大洞穴的大而丰满的硬木，在欧美殖民之前被频繁的、低严重性的大火所维持。火灾制度的转变和其他威胁可能会导致大型阔叶树的枯萎。为了更好地了解这种下降是否以及在哪里可能发生，我们评估了加州和俄勒冈州南部1991-2016年森林调查和分析(FIA)数据的最新趋势。我们包括殖民前时期火灾频发地区的地块，以及依赖大型活硬木生存的稀有哺乳动物费舍尔的潜在森林栖息地。我们分析了8种阔叶木树种的断面积变化，包括总体和大小级内、生态区内以及公共和私人土地所有权的三个时间段。我们发现，对于这些物种来说，基本面积是稳定的或增加的。然而，加州黑橡树的数据显示，总体而言，断面积略有下降，非常大的树和林下树都是如此；这种下降与国家林地的火灾死亡率有关。此外，树冠饱满的成熟树木似乎在所有物种中都急剧下降。由于高度变化，许多趋势在统计上并不显著，特别是因为重新测量的树木只有最近两个时间段的更准确数据。使用重新测量的树木继续分析这些指标将有助于评估保护工作是否正在维持大树的丰冠及其相关利益。
Forest densification, wildfires, and disease can reduce the growth and survival of hardwood trees that are important for biological and cultural diversity within the Pacific Northwest of USA. Large, full-crowned hardwoods that produce fruit and that form large cavities used by wildlife were sustained by frequent, low-severity fires prior to Euro-American colonization. Shifts in fire regimes and other threats could be causing declines in, large hardwood trees. To better understand whether and where such declines might be occurring, we evaluated recent trends in Forest Inventory and Analysis (FIA) data from 1991–2016 in California and southern Oregon. We included plots that lay within areas of frequent fire regimes during pre-colonial times and potential forest habitats for fisher, a rare mammal that depends on large live hardwoods. We analyzed changes in basal area for eight hardwood species, both overall and within size classes, over three time periods within ecoregions, and in public and private land ownerships. We found the basal area to generally be stable or increasing for these species. However, data for California black oak suggested a slight decline in basal area overall, and among both very large trees and understory trees; that decline was associated with fire mortality on national forest lands. In addition, mature trees with full crowns appeared to sharply decline across all species. Many trends were not statistically significant due to high variation, especially since more precise data from remeasured trees were only available for the two most recent time periods. Continued analysis of these indicators using remeasured trees will help to evaluate whether conservation efforts are sustaining large, full-crowned trees and their associated benefits.