Litterfall and Nutrient Release in MaturePinus radiatain the South-western Cape

Abstract

SYNOPSISFast-growing plantations of conifers have replaced areas of mediterranean shrubland in the south-western Cape. This study arises from the need to quantify the impacts of major changes in primary productivity, litterfall, and nutrient cycling in terms of the site utilisation and long-term productivity.Litterfall and decomposition were measured over five years in a catchment under mature Pinus radiata in the Jonkershoek valley near Stellenbosch, with seasonality and nutrient cycling rates assessed for the plantation ecosystem. Data are presented for all components of litterfall including needles, strobili, pollen, seed, bark, branches and cones. Total means annuallitterfall amounted to 3270 kg/ha per annum, of which needles accounted for 76,7 % or 2825 kg/ha, and strobili 8 % (295 kg/ha). Decomposition of needles is at least 50 % after three years and litter accumulation is limited.All components of litterfall have been analysed for nutrient content on at least an annual basis, with detailed seasonal studies of needle litter. Values of N, P, and K at 0,64 %, 0,03 % and 0,29 % of needle mass respectively, are about 50 % of those for fresh needles. The total annual return of nutrients to the forest floor in litter is 26,1 kg of N, 1,5 kg of P, and 10,5 kg of K. Values are also tabulated for Ca, Mg, and the trace elements. The importance of N, P and K in the litter cycle is compared to amounts in standing trees and extracted timber. P. radiata shows an ability to cycle its nutrients very rapidly which may account for its success on nutrient-poor sites.

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

“…The estimated annual fall of woody litter in evergreen, scrubby forest at Harkerville (1,72 se 0,15 m 3/ha) was based on the assumption that none of the fallen material had completely decayed. Leaf litter has a half life of 2,8 years in evergreen, temperate forests (Olson, 1963), hut woody litter decays more slowly than fine litter (Versveld and Donald, 1991), although it often starts to rot before it falls (Golley, 1983). There are no published decay rates for litter in the southern Cape forests, hut pine branches in the south-western Cape lost 20 to 40 % of their mass after four years (Versveld and Donald, 1991).…”

“…Leaf litter has a half life of 2,8 years in evergreen, temperate forests (Olson, 1963), hut woody litter decays more slowly than fine litter (Versveld and Donald, 1991), although it often starts to rot before it falls (Golley, 1983). There are no published decay rates for litter in the southern Cape forests, hut pine branches in the south-western Cape lost 20 to 40 % of their mass after four years (Versveld and Donald, 1991). Woodfall estimates in the present study could have been improved by frequent removal of litter from monitoring lines.…”

“…The logistics of using plots for monitoring large litter items (Versveld and Donald, 1991) may result in small sample sizes, high variance and intensive sampling of small and possibly unrepresentative areas of forest. The present paper describes a simple, rapid and cost-effective technique for monitoring the production of woody litter in forests or plantations.…”

“…The fall of coarse litter (trees and branches) has been quantified for a pine plantation in the south-western Cape (Versveld and Donald, 1991), but no data are available for the indigenous forests of the southern Cape. Coarse litter constituted 10 % of the annual litterfall of a south-western Cape Pinus radiata plantation (Versveld and Donald, 1991) and 25 % of the annual litterfall in a northern hemisphere beech forest (Phillipson, 1983).…”

Carbon sequestration and environmental effects of afforestation with Pinus radiata D. Don in the Western Cape, South Africa

“…The research site is characterized by a humid Mediterranean climate with hot, dry summers and cool, wet winters. Eighty five percent of the rainfall occurs between April and September, with a mean annual value of 1,296 mm (Versfeld and Donald 1991). In the valley, the mean maximum temperature of the hottest month (February) is 27.9°C while the mean minimum temperature of the coldest month (July) is 5.9°C (Heth and Donald 1978).…”