Herb and Shrub Dynamics in a Mature Oak Forest: A Thirty-Year Study

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Abstract
Cover and frequency of forest herbs and shrubs were measured in permanent plots of a mature mixed-oak woods (Hutcheson Memorial Forest, New Jersey [USA]). Plots previously measured in 1950 and 1969 were remeasured in 1979. During this 30-yr period, herb layer cover increased 7-fold with all predominant species increasing in cover and frequency. Meanwhile herb species diversity declined, with rare herbs decreasing or disappearing. In contrast, shrub layer cover remained about constant, and shrub diversity increased. A major increase in vine cover occurred in both the herb and shrub layers. These changes correlate with an increase in understory light intensity during the 30-yr period. Therefore, herb and shrub layer changes are dramatic in this mature uncut forest, indicating that relatively stable or climax communities may have highly dynamic subcommunities.