Seasonal Nutrient Dynamics of Litter in a Subtropical Eucalypt Forest, North Stradbroke Island

Abstract

The plant components and chemical composition of litter fall and the litter layer in a forest growing on deep, nutrient-poor sands were examined on North Stradbroke Island, south-eastern Queensland. The seasonal distribution of litter fall was examined over a 26-month period. While the total litter fall was greatest during summer months, the dominant tree species differed in their individual patterns of litter fall. Eucalyptus signata showed a single summer peak for leaf fall while E. umbra exhibited one peak in early summer and another in autumn. The possibility is discussed that these and other temporal differences are evolutionary expressions of niche differentiatibn to reduce competition between species in the ecosystem. The total litter fall averaged 640 g m-1 yr-1 and the accumulated forest floor mass totalled 2700 g m-2. Total nutrient pools and nutrient inputs in litter fall are presented. A litter half-life of 2.9 years is estimated, a figure close to the half-life of most of the nutrients in the litter. Manganese appears to be markedly concentrated in eucalypt leaves before they fall. Only sodium, potassium, copper and chloride appear to be leached easily from leaves slashed from trees and left on the forest floor. Patterns of litter production and decay in this subtropical forest fit within trends extrapolated from temperate Eucalyptus-dominated communities studied to date.

Nutrients in the litter on jarrah forest soils

“…Almost 50% of the potassium is located in the leaf fraction, but a considerable proportion of the phosphorus (38%) and nitrogen (33%) is contained in the fine litter. Compared with many other forested ecosystems (Ovington 1962;Gessel, Cole & Steinbrenner 1973;Rogers & Westman 1977) the pool of nutrients in jarrah forest litter is small, particularly for the major nutrients P and N. The infertile nature of the lateritic soils, the low foliar levels of some nutrients and the withdrawal and translocation of elements such as phosphorus prior to senescence (Table 5) probably contribute to this situation.…”

Estimated Woody Litterfall in Broadleaved, Evergreen Forest, Southern Cape, South Africa

“…Although a large number of transects was required to re- Assuming that the dry weight of I m' of wood is approximately 0,7 t (data from Eberhard, 1990), the annual woodfall in Harkerville forest would be 1,20 t/ha. This is comparable with the fall of stems and branches in Canadian (0,5-3,2 t/ha per annum) and English (1,1-1,8 t/ha per annum) temperate deciduous forests (Kozlowski, 1973;Phillipson, 1983), and in a nutrient-poor, evergreen eucalypt forest (1,59 t/ha per annum) in eastern Australia (Rogers and Westman, 1977). Total annual litterfall is related to climate and to soil nutrient status (Olson.…”

“…Woody litter constituted 24 % of the total annual litterfall in an eastern Australian eucalypt forest (Rogers and Westman, 1977) and 30 % of alllitterfall in temperate, deciduous forest in Canada (Kozlowski, 1973). Trees and branches can constitute a large proportion of woody litterfall.…”

Litterfall and associated nutrient pools extend beyond the canopy of scattered eucalypt trees in temperate pastures

“…A number of explanations might be postulated to explain this result in the context of our study. i) It is possible that because we only sampled the equilibrium litter quantity present on each paddock, that the woody components of the litter (bark and sticks), with their relatively slow rates of decay, accumulate over time and are therefore represented in disproportionately large quantities (Rogers and Westman 1977;O'Connell and Grove 1996;Crockford and Richardson 1998); ii) A more probable explanation is that work elsewhere has largely concerned forested systems in warmer, higher rainfall environments. In the environment of the N Tablelands, where scattered trees are subject to a drier, cooler climate and are more exposed in the landscape, it is possible that woody debris is more readily shed and accumulated as a physiological response to frost, desiccation and other stresses (e.g.…”

“…However, both methodologies have shortcomings for the accurate measurement of mean litter quantity and nutrient input under and around eucalypt trees. Measurement of equilibrium stock of litterfall on the ground can overestimate the proportion and mass of woody litter due to its proportionally slower rate of decay (Rogers and Westman 1977). However, the estimation of mass balance can also contain inherent errors.…”