Methodology
Study Sites
1. Hong Kong ForestGEO Plots
The 20-ha forest dynamic plot at Tai Po Kau Nature Reserve and the 1-ha plot in the HKU Kadoorie Centre at Shek Kong was set up in 2011 with funding support from The Hongkong Bank Foundation. There were 81,021 trees of 172 species marked in the 20-ha plot and 10,442 trees of 67 species marked in the 1-ha plot respectively. Ten 20m by 20m survey units in the 20-ha and 1-ha plots will be surveyed randomly for above-ground biomass (AGB) estimation.
2. Other forest types in Hong Kong
Whilst the Tai Po Kau ForestGEO plot is a mature secondary forest and the Kadoorie Centre plot is a young secondary forest, we wish to cover other forest types in Hong Kong including:
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Fung Shui Woods which represent lowland forest remnants of Hong Kong;
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Secondary forests which is the most common forest type in Hong Kong;
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Plantations which were mostly single species exotic tree plantations planted by the government after World War II. Common tree species planted are Lophostemon confertus; Acacia species; Eucalyptus species and Melaleuca cajuputi subsp. cumingiana.
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Tall shrublands which are at the intermediate stage of natural forest succession in Hong Kong. It is formed by dense shrubs mixed with some trees.
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Reforestation plots with known age.
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Data Collection
The core methods for long-term permanent plots have been used. For each 20m x 20m quadrats, it is further sub-divided into 16 5m by 5m sub-quadrats.
The trunk diameter, total tree height and wood specific density would be measured.
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Trunk diameter
Measured as the diameter at breast height (DBH) which is 1.3 m above the ground level. Most allometric models would include this as a covariate because it is comparatively easier to obtain.
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Total tree height
The height of a tree from its stump to its tip top. Total tree height is very important in above ground biomass (AGB) stock estimation as it will generate less biased estimates in allometric models.
Wood specific gravity
Obtained by collecting core samples from pith to bark with an increment borer from the lower portion of the tree trunks, which is then determined with an area-weighted mean of segments of the core samples after drying in an oven at 101-105 °C . A mean wood specific gravity can then be computed for individual tree species with appropriate sample sizes.