Patterns of species composition, recruitment, and growth within canopy gaps in two New Zealand kauri ( <i>Agathis australis</i> ) forests

Abstract

Abstract Within‐gap patterns of forest species composition, tree growth, and associated micro‐climate were investigated in two kauri ( Agathis australis ) forests in northern New Zealand. Detrended correspondence analysis (DCA) of sites at Trounson Kauri Park revealed a gradient of changing species composition from gap centre to forest understorey. However, while some species were typical either of the understorey (e.g., Dysoxlylum spectabile ) or the centre of large gaps (e.g., Knightia excelsa, Leucopogon fasciculata ), no species was restricted solely to gap edge sites. Growth of potted tree seedlings over 6 months at different locations in and near a large canopy gap revealed a significant positive relationship between percent canopy openness (%CO) and height increase for each of the five species tested. The early successional tree Kunzea ericoides showed the greatest height increase at gap centre, while the long‐lived conifer Dacrydium cupressinum had the greatest height increase in the forest understorey. DCA of within‐gap vegetation at Huapai Reserve over the first 5 years following gap formation revealed several trends: (1) sample plots in the root zone on the southern side of the gap were most similar to gap centre plots, while those on the northern side were most similar to the forest understorey; (2) species composition (DCA loadings on the first axis) was significantly correlated with %CO; (3) at 9 of 10 sample locations within the gap, resprouts and individuals from the seedling bank were more likely to capture the available canopy space than seedlings established after gap creation.