Regeneration changes in tree species abundance , diversity and structure 5 in logged and unlogged subtropical rainforest over a thirty six year 6 period 7

15 The long-term effects of logging treatments on rainforest regeneration are difficult to quantify due to 16 compounding interactions between natural dynamics, site characteristics and tree species. The aim of this 17 study was to compare regeneration differences over a 36-year period in stands subjected to various levels 18 of disturbance ranging from natural, through an increasing intensity of individual tree removal to 19 intensive logging. Data for trees ≥ 10 cm diameter at 1.3 m above the ground in subtropical rainforest of 20 north-east New South Wales, Australia were used. Multivariate and univariate analyses showed that 21 regeneration responses were generally correlated with disturbance gradient. In the undisturbed controls 22 there were gradual changes that had no significant effects on tree species richness and diversity, stem 23 density, or diameter distribution. Gradual changes were also observed during the early stages of 24 regeneration following logging. However, in logged sites changes in tree species richness and diversity, 25 stem density and diameter distribution became more rapid with time, and significant changes were 26 observed. This is because changes in logged sites were characterised by periods of distinct floristic 27 assemblages, marked initially by a few species and the most recent assessment revealed species 28 abundance and richness exceeding pre-logging levels. Similar regeneration events across site and 29 disturbance levels resulted in three identifiable stages. In the first stage, lasting about ten years, stem 30 density of abundant shade tolerant trees decreased, with no significant changes in tree species richness. In 31 the second stage, also lasting about ten years, tree species richness and diversity, as well as stem density 32 decreased to minima due to localised species turnover and net mortality. In the third stage, recruitment 33 surpassed mortality and reversed the net loss of both species and stems, as tree species assemblages 34 began to return to pre-disturbance levels. Sites subjected to individual tree selective logging recovered 35 their pre-logging tree species richness and diversity, and stem density within 30 years, but diameter 36 distribution of trees ≥ 40 cm dbh showed low density compared to that observed in the controls. After 35 37 years, sites subjected to more intensive logging had low species diversity and high densities of both the 38 small sized stems and shade intolerant tree species. More intensively logged sites also had a low density 39 of shade tolerant tree species compared to the controls. This suggests that the restoration of forest 40 structure takes considerably more time than the restoration of tree species richness and abundance 41 following logging in these forests. A high rate of stand basal area growth was observed in moderate tree 42 selection. This indicates high timber production potential at moderate tree selection rates in this type of 43 forest. However, if the stem size distribution of larger trees is to be maintained, a logging cycle with a 44 longer return period than the period covered in this study is necessary. 45