Propagule dispersion and forest regeneration in Leptospermum scoparium (manuka)-L ericoides (kanuka) forests following fire in Golden Bay, New Zealand

J Bray, Warren Burke, Gwendolyn Struik
Regeneration dynamics were studied in 13 post-fire manuka-kanuka forests age 9 to 56 yr in Golden Bay, New Zealand. Height and age were measured for the tallest trees of each species and distances determined to the closest propagule sources.The number of tree species per stand increased from 4 at 9 yr to 31 at 56 yr with a mean of 23 and a total of 58. Propagule origin in percent was <4.4 seed bank, <5.7 gravity and water, 34 wind, 38 bird-dispersed small fleshy fruits (2-5 mm diameter) and 17
more » ... m diameter) and 17 bird-dispersed large fleshy fruits (>5 mm diameter). The mean time for propagule arrival increased significantly from manuka-kanuka, to all wind, to small fleshy to large fleshy species. Propagule size was positively correlated with mean species entry period. Species arrivals were significantly earlier at decreasing distance from propagule source. With increasing propagule distance, the percentage of wind species entry declined with time, small fleshy declined, but then increased and large fleshy declined and then increased strongly. These patterns may reflect early packing by wind and small fleshy species and a later upsurge by large fleshy once the manuka-kanuka canopy can support the larger perching birds. Seedlings from bird-dispersed propagules were significantly closer to tree boles and mostly arrived when manuka-kanuka heights were from 4 to 6 m. Pigeon flock feeding may lead to great distance dispersal of large fleshy fruits. With increasing tree age, there was an increase in maximum height increment, paired height, and top height values. There were no significant differences between the various height indexes at 0-25 m versus >25 m from propagule source, but the ratios between paired height growth values consistently decreased with increasing age. From around 40 yr, taller growing species begin to overtop kanuka so that by 100 yr, all 13 stands should have a kanuka canopy shared with various combinations of podocarps and angiosperms of which Dacrydium cupressinum (rimu), Podocarpus dacrydioides (kahikatea), P. totara (totara), Nothofagus menziesii (silver beech) and Weinmannia racemosa (kamahi) will be predominant.