Bamboo forests are expected to play an important role in mitigating climate change. However, the capacity of bamboo forests to sequester and store carbon has not been assessed on a national scale in ...Japan. This study estimates the changes in the carbon stock of bamboo forests (CS
bamboo
) in Japan from 1985 to 2005. We compiled two data sets: (1) administrative statistical data on bamboo stand area (BSA) and (2) published data on stand-level aboveground biomass for Phyllostachys pubescens Mazel ex Houz. (n = 44) and Phyllostachys bambusoides Sieb. et Zucc. (n = 13). The BSA expanded from 147 kha in 1985 to 158 kha in 2005. The average carbon density (CD) of managed and abandoned stands were 84.9 Mg C ha
−1
and 115.1 Mg C ha
−1
for P. pubescens and 24.1 Mg C ha
−1
and 46.4 Mg C ha
−1
for P. bambusoides, respectively. The CD of P. pubescens stands in Japan was higher than that in other Asian countries and regions and was comparable to the CD of other forests in Japan. The area-based method indicated that the CS
bamboo
increased from 10.1 ± 2.6 Tg C to 13.9 ± 1.7 Tg C during the 20-year period, representing less than 1% of the total carbon pool of the forested area. The increase in CS
bamboo
was primarily caused by the synergistic effect of the abandonment and range expansion of P. pubescens forests. Our results suggest that P. pubescens forests are overstocked, and the increase in the CS
bamboo
is undesirable.
The form-factor for the stem surface area is directly proportional to the square root of the form-factor for the stem volume, i.e., the square root law of the form-factor. Although the square root ...law addresses the stems of coniferous trees, the nature of the proportional coefficient of the law has not been discussed. In this study, we demonstrated that the coefficient indicates the stem taper; therefore, it is named “Taper Index based on Form-Factor (TIFF).” We also examined the relationship between the form-factor for the culm surface area and the form-factor for the apparent culm volume of 570 culms across three bamboo species (
Phyllostachys pubescens
Mazel ex Houz.,
P
.
bambusoides
Sieb. et Zucc., and
P
.
nigra
var.
henonis
). The square root law held true for all three bamboo species. The species-specific TIFF was determined to be 0.873 for
P. pubescens
, 0.897 for
P. bambusoides
, and 0.901 for
P. nigra
. This result implied that
P. pubescens
had a more tapering culm form compared to the other two species, while culm taper was similar between
P. bambusoides
and
P. nigra
. Our findings align with empirical observations of the culm taper of the bamboo species. Intra-species variation in TIFF was considerably small, allowing us to evaluate the species-specific culm taper from a small number of samples. Therefore, we conclude that TIFF provides a simple and useful method for quantifying species-specific culm or stem taper, and facilitates the estimation of merchantable or total volume.
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