Abstract:
Restoration and revegetation are tools used world-wide to combat deforestation and increase biodiversity within disturbed environments. The successional paradigm is the ecological basis to restoration. It dictates that disturbed sites follow a singular trajectory towards becoming a later successional forest. The overall aim of this research was to determine whether succession was occurring within revegetation stands on Auckland’s Regional Parks leading to a change to a mixed-species northern coastal forest. This was achieved by establishing whether there was a change in the stand composition in comparison to the initial planting compositions and whether there were any changes in the stand structure along a chronosequence. Seedling establishment and seed dispersal were investigated to see if they could indicate limitations in vegetation development, with multiple factors (canopy openness, canopy composition, stand slope and ground cover) correlated with stand seedling characteristics to suggest those most important for seedling establishment. Restoration stands were found to show no evidence of successional processes altering stand composition and structure. Little change in species composition was observed within the study. Kunzea ericoides and Leptospermum scoparium were found to still comprise the bulk of the stands. There was no significant correlation with stem density but a significant increase in basal area was observed along the chronosequence of stands. This showed that self-thinning had yet to occur on sites, but biomass accumulation was occurring. There was a significant logistic increase in modal canopy height, but this was lower than heights expected in later successional forest. Kunzea ericoides showed a faster growth rate than L. scoparium. A diverse range of seedling species were observed within the stands, however only five showed any commonality between sites; Myrsine australis, Coprosma robusta, Macropiper excelsum, Melicytus ramiflorus, and Geniostoma ligustrifolium. These species were expected within northern coastal forest. Percent canopy openness, % ground cover, canopy composition and stand slope were all investigated to account for the variation in seedling abundance. This study found significant results with % canopy openness, canopy composition, stand slope and seed rain. Seedlings only established between 2% and 30% canopy openness, although no explanations could be found to explain these boundaries. Canopies with ≥75% L. scoparium composition contained significantly more seedlings than canopies of ≥75% K. ericoides. No explanations could be found for this however. Seedlings >30cm tall showed a significantly negative relationship with increasing stand slope. There was no diversity in the seed rain observed within the three studied Regional Parks, 77% of the germinated seed was from the canopy species L. scoparium and K. ericoides. This suggests that there may be a lack in avian dispersers arriving to these sites. The key finding within this study was that revegetation has no led a succession change towards a later successional coastal forest within these stands.