Neumann Mathias, Lawes Michael J
Department of Chemistry and Biotechnology Faculty of Science, Engineering and Technology Swinburne University of Technology Hawthorn Vic. Australia.
Institute of Silviculture University of Natural Resources and Life Sciences Vienna Austria.
Methods Ecol Evol. 2021 Apr;12(4):646-654. doi: 10.1111/2041-210X.13546. Epub 2021 Jan 14.
Bark contributes approximately 20% to the total above-ground biomass of trees, yet bark is not properly accounted for when estimating carbon sequestered by trees. Current allometric functions estimate tree volume from diameter measured over the bark, and derive bark density and carbon content from estimates for wood. As the bark density of hardwood species is 40%-50% lower than the wood density, but nearly equivalent in conifers, bark carbon is overestimated for most species. The latter is further exacerbated by variation in bark volume with bark surface morphology.Fissured bark volume is overestimated by diameter over bark measurements by up to 40%. The vacant space in fissures can be accounted for by a bark fissure index (BFI). We calculate bark carbon for Australian species from a non-destructive and effective BFI using bark thickness measured in the field.Bark volume, and in turn bark carbon, scaled inversely with tree size (diameter) so that bark volume comprised 42% of small trees (10 cm diameter at breast height, DBH) but 23% of large trees (50 cm DBH). Our BFI method using a bark thickness gauge (BGM) yielded similar results than using the less time-efficient contour gauge method (CM) to estimate BFI (bias BGM-CM -1.3%, non-significant at = 0.72). Both BGM and CM had an error of <4% compared to digitized BFI from destructive sampled stem disks. An average of 15 bark gauge measurements per tree estimated bark thickness (and inconsequence BFI) for both fissured and unfissured bark with <20% error relative to the exact value.Using the bark gauge method, BFI can be rapidly measured from large numbers of trees needed for estimating bark carbon at the community level and modelling carbon uptake, storage and cycling in woody biomes.
树皮约占树木地上生物量总量的20%，然而在估算树木固碳量时，树皮并未得到妥善考虑。当前的异速生长函数根据树皮外径来估算树木体积，并从木材估算值中推导树皮密度和碳含量。由于硬木树种的树皮密度比木材密度低40%-50%，而针叶树的树皮密度与木材密度几乎相当，因此大多数树种的树皮碳含量被高估。树皮体积随树皮表面形态的变化进一步加剧了这种高估。有裂缝的树皮体积通过测量树皮外径被高估了高达40%。裂缝中的空隙可以用树皮裂缝指数（BFI）来计算。我们通过在野外测量树皮厚度，利用一种无损且有效的BFI来计算澳大利亚树种的树皮碳含量。树皮体积，进而树皮碳含量，与树木大小（直径）成反比，因此树皮体积在小树（胸径10厘米）中占42%，而在大树（胸径50厘米）中占23%。我们使用树皮厚度测量仪（BGM）的BFI方法与使用效率较低的轮廓测量仪方法（CM）估算BFI的结果相似（BGM-CM偏差为-1.3%，在α = 0.72时不显著）。与从破坏性采样的树干圆盘数字化得到的BFI相比，BGM和CM的误差均<4%。每棵树平均进行15次树皮测量仪测量，可估算有裂缝和无裂缝树皮的厚度（进而估算BFI），相对于精确值的误差<20%。使用树皮测量仪方法，可以从估算群落水平树皮碳含量以及模拟木质生物群落中碳吸收、储存和循环所需的大量树木中快速测量BFI。
