Current forests of the eastern USA have the potential to succeed in composition to more shade-tolerant species. However, long-term processes of transition from fire-tolerant tree species to fire-sensitive species and effects of current land use on forests may interfere with successional progression. I examined if forests in three regions have increased in shade tolerance and if life history strategy groups that represent response to disturbance (i.e., fire-tolerance, early-successional species based on low shade tolerance, mid-successional species, late-successional species, and trees valued for traits related to short harvest rotations) have changed, using Forest Inventory and Analysis surveys, adjusted for comparison, and generalized linear mixed models to assess approximately 30 year trends, with adjustments to equalize different survey methods. Although statistically significant, a slight increase of 2 to 4% in regional mean shade tolerance may not be ecologically significant. In the central East, mid-successional species replaced early-successional species and early-successional species replaced fire-tolerant oaks, resulting in an overall shift from fire-tolerant oaks to mid-successional species. Decreased fire-tolerant pine species and increased planted pine species were the major changes in the northern Southeast and Coastal Plain. The successional process of increased composition by shade-tolerant species over time was overshadowed by land use changes that resulted in decreased fire-tolerant species and increased planted pine. Furthermore, frequent land use disturbance may continue to prevent the slow progress of compositional succession to very shade-tolerant species.

中文翻译：

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美国东部森林的耐荫性和干扰性状最近发生的变化

美国东部目前的森林有可能成功地组成更多的耐荫物种。但是，从耐火树种过渡到对火敏感的树种的长期过程以及当前土地使用对森林的影响可能会干扰演替进程。我检查了三个地区的森林是否提高了遮阳耐受性，以及代表对干扰做出响应的生活史策略组（即耐火性，基于低遮阳耐受性的早期成功物种，中期成功物种，后期成功物种，以及因短时轮伐相关性状而被重视的树木）已经改变，使用了森林清单调查和分析调查，并进行了调整以进行比较，并使用广义线性混合模型来评估大约30年的趋势，并进行了调整以均衡不同的调查方法。尽管具有统计意义，但区域平均阴影耐受性略有增加2％至4％在生态上可能并不重要。在东部中部，中成功的物种取代了早成功的物种，而早成功的物种取代了耐火的橡树，导致整体上从耐火的橡木向中成功的物种转变。东南北部和沿海平原的耐火松树种类减少，种植的松树种类增加。随着时间的推移，耐荫树种组成不断增加的连续过程被土地用途的变化所掩盖，土地使用变化导致耐火树种减少和松树种植增加。此外，频繁的土地利用干扰可能会继续阻止组成演替缓慢发展到非常耐荫的物种。