Variation of SPAD values in uneven-aged leaves of different dominant species in Castanopsis carlessi forest in Lingshishan National Forest Park

The greenness （SPAD） of uneven-aged leaves of dominant species in the Castanopsis carlessi forest at different altitude gradients in Lingshishan National Forest Park, Fujian Province, China were measured by using portable chlorophyll meter SPAD-502. In addition, the correlation between SPAD value and the concentration of chlorophyll and foliar nitrogen was also investigated. Significant variations in SPAD values were found between the uneven-aged leaves of different dominant species and different altitude gradients. Regression analysis showed that SPAD value was significantly correlated with the concentration of chlorophyll and the content of foliar nitrogen, indicating that SPAD value could be indicators for foliar chlorophyll and nitrogen. It is suggested that SPAD meter is a useful tool for forest assessments in decision-making and operational nutrient management programs.

Disentangling the factors that contribute to variation in forest biomass increments in the mid-subtropical forests of China

Mid-subtropical forests are the main vegetation type of global terrestrial biomes, and are critical for maintaining the global carbon balance. However, estimates of forest biomass increment in mid-subtropical forests remain highly uncertain. It is critically important to determine the relative importance of different biotic and abiotic factors between plants and soil, particularly with respect to their influence on plant regrowth. Consequently,it is necessary to quantitatively characterize the dynamicspatiotemporal distribution of forest carbon sinks at a regional scale. This study used a large, long-term dataset in a boosted regression tree（BRT） model to determine the major components that quantitatively control forest biomass increments in a mid-subtropical forested region（Wuyishan National Nature Reserve, China）. Long-term,stand-level data were used to derive the forest biomass increment, with the BRT model being applied to quantify the relative contributions of various biotic and abiotic variables to forest biomass increment. Our data show that total biomass（t） increased from 4.62 9 106 to 5.30 9 106 t between 1988 and 2010, and that the mean biomass increased from 80.19 ± 0.39 t ha-1（mean ± standard error） to 94.33 ± 0.41 t ha-1in the study region. The major factors that controlled biomass（in decreasing order of importance） were the stand, topography, and soil. Stand density was initially the most important stand factor, while elevation was the most important topographic factor. Soil factors were important for forest biomass increment but have a much weaker influence compared to the other two controlling factors. These results provide baseline information about the practical utility of spatial interpolationmethods for mapping forest biomass increments at regional scales.