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991.
992.
We derived an allometric model of the height–diameter curve for even-aged pure stands, which was a modification of the earlier
model proposed by Inoue (2000a). An individual-dependent allometric equation was used as the height–diameter curve. Using
the discriminant analysis method, all trees composed of a stand were stratified into upper and lower trees. It was assumed
that both relationships between mean tree height H
m
and upper tree height H
u
and between mean DBH D
m
and mean DBH of upper trees D
u
could be described by the time-dependent allometric power equations. The height–diameter curve showed an average relationship
between tree height and DBH of a given stand at a given time, and hence it could be assumed that the height–diameter curve
contained two points (D
m
, H
m
) and (D
u
, H
u
). With these assumptions, we derived an allometirc model of height–diameter curve, which allowed the coefficients of the
curve to be estimated from mean tree height and mean DBH. The proposed model was fitted to Japanese cedar (Cryptomeria japonica D. Don) data. The error ratio of the allometric model ranged from 2.254% to 13.412% (mean = 6.785%), which was significantly
smaller than that of the earlier model. When the error of mean tree height was ±1.0 m or less, the effect of the error of
mean tree height on the error ratio was comparatively small. This suggested that the error of ±1.0 m in mean tree height could
be accepted in the estimation of height–diameter curve using the allometric model. These features enable us to combine the
allometric model with Hirata’s vertical angle-count sampling or growth models. In conclusion, the allometric model would be
one of the most practical and convenient approaches for estimating the height–diameter relationship of even-aged pure stands. 相似文献
993.
994.
贵州水土保持林价值计算方法探讨 总被引:1,自引:0,他引:1
本文从贵州实际出发,运用经济管理学理论和林木生长发育规律,在系统分析水土保持林价值构成因素以及各因素之间关系的基础上,建立起一个能满足以树种(类型)为单元的水土保持林价值计算模型。在为水土保持林价值的评估、征占、置换、流转、买卖等活动提供计量、计价依据和方法的同时,还为水土保持林所有者和经营者提供了增加效益的方向与技术关键。 相似文献
995.
996.
997.
998.
Amazonian deforestation and global warming: carbon stocks in vegetation replacing Brazil''s Amazon forest 总被引:8,自引:0,他引:8
Philip M. Fearnside 《Forest Ecology and Management》1996,80(1-3):21-34
Carbon stocks in vegetation replacing forest in Brazilian Amazonia affect net emissions of greenhouse gases from land-use change. A Markov matrix of annual transition probabilities was constructed to estimate landscape composition in 1990 and to project future changes, assuming behavior of farmers and ranchers remains unchanged. The estimated 1990 landscape was 5.4% farmland, 44.8% productive pasture, 2.2% degraded pasture, 2.1% ‘young’ (1970 or later) secondary forest derived from agriculture, 28.1% ‘young’ secondary forest derived from pasture, and 17.4% ‘old’ (pre-1970) secondary forest. The landscape would eventually approach an equilibrium of 4.0% farmland, 43.8% productive pasture, 5.2% degraded pasture, 2.0% secondary forest derived from agriculture, and 44.9% secondary forest derived from pasture. An insignificant amount is regenerated ‘forest’ (defined as secondary forest over 100 years old). Average total biomass (dry matter, including below-ground and dead components) was 43.5 t ha−1 in 1990 in the 410 × 103 km2 deforested by that year for uses other than hydroelectric dams. At equilibrium, average biomass would be 28.5 t ha−1 over all deforested areas (excluding dams). These biomass values are more than double those forming the basis of deforestation emission estimates currently used by the Intergovernmental Panel on Climate Change (IPCC). Although higher replacement landscape biomass decreases net emissions from deforestation, these estimates still imply large net releases. 相似文献
999.
1000.
以麻竹笋用林高效栽培为目标,可持续经营为原则,总结了竹林林分结构调控、土壤管理、散生状培育、地理种源和无性系选优等操作简便、应用效果好的系列实用技术,分析了目前麻竹林立地生产力退化、产品产量和质量下降等的主要原由,提出了无害化、品种化和散生状培育的经营方向。 相似文献