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Research Papers, Lincoln University

Tree mortality is a fundamental process governing forest dynamics, but understanding tree mortality patterns is challenging because large, long-term datasets are required. Describing size-specific mortality patterns can be especially difficult, due to few trees in larger size classes. We used permanent plot data from Nothofagus solandri var. cliffortioides (mountain beech) forest on the eastern slopes of the Southern Alps, New Zealand, where the fates of trees on 250 plots of 0.04 ha were followed, to examine: (1) patterns of size-specific mortality over three consecutive periods spanning 30 years, each characterised by different disturbance, and (2) the strength and direction of neighbourhood crowding effects on sizespecific mortality rates. We found that the size-specific mortality function was U-shaped over the 30-year period as well as within two shorter periods characterised by small-scale pinhole beetle and windthrow disturbance. During a third period, characterised by earthquake disturbance, tree mortality was less size dependent. Small trees (,20 cm in diameter) were more likely to die, in all three periods, if surrounded by a high basal area of larger neighbours, suggesting that sizeasymmetric competition for light was a major cause of mortality. In contrast, large trees ($20 cm in diameter) were more likely to die in the first period if they had few neighbours, indicating that positive crowding effects were sometimes important for survival of large trees. Overall our results suggest that temporal variability in size-specific mortality patterns, and positive interactions between large trees, may sometimes need to be incorporated into models of forest dynamics.

Images, UC QuakeStudies

A photograph of emergency management personnel walking in a line down Lichfield Street towards the intersection of Madras Street . The members in white hazmat suits are holding their hands over their heads while members of the New Zealand Army take the lead and follow from behind. Rubble from several earthquake-damaged buildings has scattered across the street to the right. Plastic fencing has been placed along the left side of the road as a cordon. In the background there are several earthquake-damaged buildings along Lichfield Street.

Images, UC QuakeStudies

A photograph of the earthquake damage to a building on Hereford Street. A column on the right side of the building has snapped and the side wall has pulled away from the building. USAR codes have been spray-painted on one of the windows on the bottom storey. In the foreground there is a police car.