Supercritical CO(2) fluid extraction (SFE-CO(2)) was used to extract the sapogenins after acid hydrolysis from Smilax china tubers. The influence of extraction variables, such as modifier, pressure, temperature and extraction time, were studied. SFE-CO(2) was found to produce higher yield than conventional solvent extraction. The highest yield (0.454%) of sapogenins, mostly containing diosgenin, was obtained using 35 MPa pressure, 65 degrees C and 95% EtOH as a modifier for 180 min, higher than that obtained with conventional extraction methods (0.385%). 相似文献
Trade-offs among wood production, wood quality and ecological characteristics in the management of harvested forest stands are explored through model simulation of various silvicultural regimes. Long-term production of merchantable wood, production of various types of high-quality wood, and the level of certain quantitative ecological indicators are projected for coniferous forests of Pacific Northwestern USA. The set of ecological indicators used is based on the species composition and physical structure of old, unlogged forest stands. Simulations are performed with an ecological model of forest stand dynamics that tracks the fate of live and dead trees. Short rotations (<50 years) produce the least amount of high-quality wood over the multi-century simulation period. They also fail to generate ecological attributes resembling those of old forest stands. Production of high-quality wood is moderate to high under all rotations of 80 years or more; however, most ecological indicators require longer rotations unless alternatives to clearcutting are applied. Alternatives examined include retention of 15% cover of live tree canopy at each harvest in combination with artificial thinning between harvests. Thinning from below can expedite the development of large live and dead trees, and canopy height diversity without greatly diminishing wood quantity or quality. Proportional thinning retains understory stems, thereby expediting the recruitment of shade-tolerant trees. A possible drawback to thinning, particularly proportional thinning, is the diminished production of clean-bole wood at rotations of 150 and 260 years. It is concluded that most wood quantity, wood quality and ecological objectives can be met with long rotations (ca. 260 years). Certain objectives can be met with shorter rotations (80–150 years) when treatments of thinning and canopy tree retention are applied. 相似文献
The coastal forest of Gabon abounds in monospecific secondary Aucoumea klaineana stands derived from natural regeneration after shifting cultivation. This paper aims to describe the changes in the structure and dynamics of these stands with age. It then assesses the impact of selective thinning in the upper storey on both structural and dynamic parameters.
The experiment consisted of 34 Permanent Plots in stands from establishment to more mature stages (ca. 50 years old). Thirteen plots (17–45 years old) were thinned. More than 80% of the removal came from supernumerary dominant A. klaineana.
A. klaineana represented 60% of the total density in stands ca. 15 years old but >90% of the dominant trees in older stands. The changes with age in the floristic composition of the unthinned stands showed three successional stages during which pioneer species associated with A. klaineana (from establishment to ca. 15 years) were progressively replaced by mature forest species.
Basal area increased and density decreased with age before reaching stable values at ca. 40–45 years. Mortality was very high in young stands but decreased in the older ones. Mortality generally affected small diameter individuals in the dominated storey. Diameter and basal area increments showed that the stand growth resulted from the growth of dominant A. klaineana. Diameter increments of A. klaineana were elevated during the first years of colonisation (1.9 cm/year) and were still ca. 0.7 cm/year for 50-year-old dominant trees.
Thinning did not increase the mortality of the dominant population. It favoured the individual growth of A. klaineana. The gain was substantial for dominated trees and small dominant trees (from 60 to 100%) but was lower for large dominant trees (ca. 25–30%). Therefore, stimulation of individual growth did not compensate for the loss of basal area at the stand level. 相似文献
Reconstruction in twenty single-cohort stands across five climax series on the eastern slope of the Washington Cascade Range found a variety of species combinations and development patterns. Western larch (Larix occidentalis Nutt.) and lodgepole pine (Pinus contorta Dougl. ex Loud) were found to be very competitive species that usually occupied a dominant position in stands in the Abies grandis, Abies lasiocarpa, and Tsuga mertensiana climax series. Interior Douglas-fir (Pseudotsuga menziesii var. glauca (Mirb.) Franco) was found in all five climax series and, although its height growth was less than that of western larch or the lodgepole pine, it was usually found in the upper stratum. These results suggest that site classification based on climax potential should be used cautiously when applied to young stand management decisions regarding seral species. For example, the difference between an Abies grandis, and a Tsuga mertensiana climax series is quite large in terms of potential productivity but in either case western larch, if present, will likely dominate these stands. 相似文献
To detect developmental differences inEpinotia granitalis in two host tree speciesCryptomeria japonica andChamaecyparis obtusa, the fourth or fifth instar larvae were collected daily from the two species located on the grounds of the National Forest
Tree Breeding Center, from April 19 to May 9 in 1994 and April 18 to May 10 in 1995. Larvae ofE. granitalis collected fromC. obtusa had heavier body weight, developed to larger adults than those collected fromC. japonica, and mortality from the fourth or fifth instar larval stage to adults onC. obtusa was lower than that onC. japonica. All these facts suggest that larval performance onC. obtusa was higher than that onC. japonica. 相似文献
LIGNUM is a whole tree model, developed for Pinus sylvestris in Finland, that combines tree metabolism with a realistic spatial distribution of morphological parts. We hypothesize that its general concepts, which include the pipe model, functional balance, yearly carbon budget, and a set of architectural growth rules, are applicable to all trees. Adaptation of the model to Pinus banksiana, a widespread species of economic importance in North America, is demonstrated.
Conversion of the model to Jack pine entailed finding new values for 16 physiological and morphological parameters, and three growth functions. Calibration of the LIGNUM Jack pine model for open grown trees up to 15 years of age was achieved by matching crown appearance and structural parameters (height, foliage biomass, aboveground biomass) with those of real trees. A sensitivity study indicated that uncertainty in the photosynthesis and respiration parameters will primarily cause changes to the net annual carbon gain, which can be corrected through calibration of the growth rate. The effect of a decrease in light level on height, biomass, total tree branch length, and productivity were simulated and compared with field data. Additional studies yielded insight into branch pruning, carbon allocation patterns, crown structure, and carbon stress. We discuss the value of the LIGNUM model as a tool for understanding tree growth and survival dynamics in natural and managed forests. 相似文献