Biomass and nutrient accumulation in montane evergreen broad-leaved forest ( Lithocarpus xylocarpus type) in Ailao Mountains, SW China

Abstract

Montane evergreen broad-leaved forest was the natural vegetation of subtropical, mountainous central and southern Yunnan, SW China. Pristine natural forest, dominated by Fagaceae ( Lithocarpus xylocarpus, Lithocarpus chintungensis and Castanopsis wattii), is still present at Ailao Mountain National Nature Reserve. Within this forest, older stands are of relatively low density, with scattered large trees, compared with stands of higher density. Biomass and nutrient content are examined in this paper for two stands, one each of relatively high and low density. Tree aerial biomass components were calculated from a stand census applied to previously derived regressions of biomass components and tree size. Tree roots were obtained from cores (20 per stand). Other biomass contributions sampled were: live shrubs (five 4 m 2 samples); herb (ten 1 m 2 samples); dead wood (ten 4 m 2 samples); litterfall (fifteen 1 m 2 samples, monthly); forest floor litter (ten 0.25 m 2 samples, 3-monthly). Three nutrient samples were analysed for each tissue per species for both stands. Total live biomass was 503 and 285 t ha −1 for the high and low density stands, respectively. The biomass ratio of stem-wood to branch-wood and leaf biomass was 10:1 and 43.4:1 in the former and 14:1 and 29.7:1 in the latter, respectively. Standing crops of litter and dead wood were both less in the former (10.3 and 46.2 t ha −1) than the latter (12.9 and 98.5 t ha −1). Litterfall in the high density stand was 5.4 compared with 7.1 t ha −1 in the low density. Total nutrient content in living and dead wood materials was 280 and 195 t ha −1, respectively. The sequence of inorganic nutrient element content decreased in the order, leaves>branches>roots>stems. Elemental nutrient content of the total stand decreased in the order of C>Ca>N>Mg>Al>P>Fe>Mn. The elements C, Ca and N were mainly in stems, while Al and Fe were mainly in roots. Nutrients in dead wood comprised 9.2 and 40.6% of the total nutrients in living trees and nutrients returned to soil through litterfall were estimated at 3120 and 3699 kg ha −1 yr −1 in high and low density stands, respectively.