Leaf Growth Dynamics and Herbivory in Five Species of Australian Rain- Forest Canopy Trees

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Abstract
1. The leaf growth dynamics of five species of rain-forest tree in New South Wales, Australia, were studied over the lifespan of several cohorts of leaves (ranging in longevity from 6 months to over 10 years), to determine the patterns of emergence, growth, mortality and herbivory in the canopy. Leaf population dynamics were examined for variability within and between several spatial scales: canopy heights, individual trees, species, and rain-forest formations. 2. Representative species were selected within each of the three major rain-forest formations of New South Wales: Nothofagus moorei and Doryphora sassafras in cool-temperate or montane or mossy microphyll forest, D. sassafras and Ceratopetalum apetalum in warm-temperate or simple notophyll vine forest, and Dendrocnide excelsa, D. sassafras and Toona australis in subtropical or complex notophyll vine forest. Technical climbing apparatus was used to gain access to the canopy, where leaves were permanently marked and monitored on a monthly basis for up to 12 years. 3. Three main leafing patterns were observed: seasonal growth - leaves flushed synchronously (e.g. N. moorei, T. australis); intermittent growth - leaves flushed over several months (e.g. D. sassafras, C. apetalum); and continuous growth - leaves flushed throughout the year (e.g. D. excelsa). 4. Leaf lifespans were variable, ranging from short-lived leaves (D. excelsa, approximately 6 months), to annual leaves (T. australis), and longer-lived leaves (e.g. D. sassafras, ranging from 2 to 12 or more years). Shaded leaves lived longer than sun-exposed leaves, and those on trees at montane sites generally lived longer than leaves on individuals of the same species at lower altitudes. 5. Significantly different proportions of leaf area were lost throughout the lifespan of a leaf in various species: T. australis (4.5%); D. sassafras (16.6%); C. apetalum (22%); N. moorei (31%); and D. excelsa (32.5%). Shade leaves and young leaves were more extensively grazed than sun leaves and old leaves, respectively. Leaves located nearer to ground level suffered greater herbivory, although this may be in part an interaction with light regime. 6. The measurements on herbivory, senescence, and longevity were used to calculated annual turnover of canopy material to either primary decomposers (through leaf fall), or primary consumers (through herbivory) in the three rain-forest formations. In a hectare of the subtropical forest, approximately 1.76t (14%) and 5.59 t (46%) were allocated each year to herbivores and decomposers, respectively, from a total canopy of 12.26 t. In the warm-temperate forest, 2.5 t (22%) and 4.05 t (35%) were allocated annually to herbivores and decomposers, respectively, from a canopy of 11.41 t. In the cool-temperate forest, an estimated 2.63 t (27%) and 3.53 t (37%) went to herbivores and decomposers, respectively, from a total canopy of 9.69t.

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