Age Distribution and Spatial Patterning of an Invasive Shrub in Secondary Hardwood Forests
Little is known about local patterns and rates of woody plant invasions, and even less is known about changes in spatial patterning and factors influencing structural characteristics of individuals as invasion phase progresses from establishment to saturation. We examined age distributions and spatial patterns of Amur honeysuckle (Lonicera maackii (Rupr.) Herder) invasions and identified factors influencing life-stage characteristics of individual shrubs in six mixed hardwood forests in Indiana. Predicted age distributions indicated that Amur honeysuckle reached the exponential phase of invasion at ∼10-15 years. Inhomogeneous L and cross-L functions indicated that Amur honeysuckle exhibited a clustered spatial pattern. Immature individuals (no berries) clustered around mature individuals (with berries). However, spatial relationships between honeysuckle and trees rarely exhibited a clustered pattern. Regression analyses with Amur honeysuckle diameter and height as response variables revealed that incorporating spatial autocorrelation provided a better model fit and caused otherwise significant predictor variables to become nonsignificant (P≥0.05). Our results suggest that local-scale invasion by this species follows a predictable temporal sequence of population establishment and expansion via neighborhood diffusion and the forest-scale distribution of nascent foci. Furthermore, our results highlight the importance of considering spatial autocorrelation when evaluating life-stage characteristics of invasive populations.