Dynamics of upland conifer/broadleaved forest at Waihaha, central North Island, New Zealand

Abstract

Regeneration in upland Podocarpus hallii‐Prumnopitysferruginea/Quintinia serrata‐Weinmannia racemosa forest, central North Island, New Zealand, was sampled in the three phases of the forest growth cycle. Mean age, determined from the largest stem present, differed significantly between gaps (13 yr), building‐phase (58 yr), and mature forest (221 yr), which comprised 8, 28, and 65%, respectively, of the forest area. Current diameter growth rates among species (Griselinia littoralis > W. racemosa, Q. serrata > P. hallii, P. ferruginea) did not differ between phases. Canopy P. hallii sampled were up to 500 yr old and P. ferruginea were 550 yr old. Broadleaved species were all younger on average (<250 yr). Three replacement strategies among major species involve establishment in different stages of the forest growth cycle, reflecting specific shade tolerances. Relatively intolerant W. racemosa and G. littoralis establish solely in gaps (gap‐phase replacement), Dacrydium cupressinum mostly in gaps. More tolerant P. ferruginea and Q. serrata establish in gaps and building‐phase forest. Shade‐tolerant P. hallii, Nestegis cunninghamii, Elaeocarpus hookerianus, Pseudowintera colorata, and Neomyrtus pedunculata establish throughout the forest growth cycle, Myrsine salicina only in later stages. A conifer “regeneration gap” is locally evident in relatively shade‐intolerant and fertility‐demanding Prumnopitys taxifolia. Basal area recovery after gap formation is slow in relation to overall basal area here and in other forests in the region, and may result from a relatively long history of browsing by introduced mammals.