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891.
Hailong Wu 《林业研究》2016,27(4):871-878
Platycladus orientalis is one of the most popular afforestation species and greening species for water management in arid and semi-arid regions of northern China. We applied various models to estimate and validate artificial P. orientalis forest evapotranspiration features with the goal of accurately estimating the water use of a P.orientalis plantation. The American Society of Civil Engineers Evapotranspiration–Penman–Monteith model(APM) and FAO56–Penman–Monteith model(FPM) are extensively applied for vegetation evapotranspiration estimation because their reliability has been validated by many scholars. The Priestley–Taylor model(PT) and Hargreaves model(HS) require only the daily maximum temperature,daily minimum temperature and solar radiation to estimate evapotranspiration and are thus widely applied to grasslands but not to forests. We used the Energy Balance Bowen Ratio(EBBR) system to validate the accuracy of the four models. The results indicated that:(1) Compared to the EBBR measurement annual value, APM was the most accurate, followed by FPM, and PT;(2) During the year, the accuracies of the four models varied. APM and FPM underestimated evapotranspiration during June, July and August, whereas PT and HS overestimated evapotranspiration during this period. In the rest of the year, the estimation accuracies were reversed;(3) An analysis of the possible reasons indicated that wind speed, air temperature and precipitation were the most important contributors.High temperatures were measured in June, July and August, which led to an overestimation by PT and HS because these two models only calculated the temperature and radiation without vegetation information. Underestimation also occurred when a low temperature was recorded. Though APM and FPM addressed both meteorological and vegetation factors, slight deviations still existed; and(4) The two models were modified based on EBBR-measured data. Relative humidity was introduced into PT, and parameter ‘‘A’’ in the HS estimation model was amended to1.41. The accuracy of the modified models significantly increased. The study highlighted the application, comparison and improvement of four models in estimating evapotranspiration and offers more approaches to assess forest hydrological functions. 相似文献
892.
Decomposition dynamics were compared among green tree leaves, partially decomposed tree leaf litter (i.e., decayed tree leaf litter on forest floor) and a mixture of the two in a warm temperate forest ecosystem in central China to test the influence of litter chemical quality on the degree of decomposition. The study was conducted in situ at two contrasting forest sites, an oak forest dominated by Quercus aliena var. acuteserrata Maxim., and a mixed pine and oak forest dominated by Pinus armandii Franch. and Q. aliena var. acuteserrata. We found marked differences in the rate of decomposition among litter types at both forest sites; the litter decomposition constant, k, was about 39 % greater at the oak forest site and more than 70 % greater at the pine-oak forest site, for green leaves than for partially decomposed leaf litter. The decomposition dynamics and temporal changes in litter chemistry of the three litter types also greatly differed between the two forest sites. At both forest sites, the higher rate of decomposition for the green leaves was associated with a higher nitrogen (N) content and lower carbon to N ratio (C/N) and acid-unhydrolyzable residue to N ratio (AUR/N). We did not find any non-additive effects when mixing green leaves and partially decomposed leaf litter. Our findings support the contention that litter chemical quality is one of the most important determinants of litter decomposition in forest ecosystems at the local or regional scale, but the effect of litter chemical quality on decomposition differs between the contrasting forest types and may vary with the stage of decomposition. 相似文献
893.
Jürgen Gross Nina E. Fatouros Seppo Neuvonen Monika Hilker 《Journal of pest science》2007,80(3):139-143
The Palaearctic leaf beetle Chrysomela lapponica usually feeds upon willows in the northern region of its occurrence. However, in Central Europe, some populations are known
that have specialised on birch. In this study, we investigated the significance of other herbivores occurring together on
the same host plants as possible exploitative competitors of C. lapponica. Two populations were studied: a population from Finland specialised on the willow Salix
borealis, and a population from the Czech Republic, specialised on the birch Betula
pubescens. Abundances of folivorous and suctivorous insects on both host plants were recorded at both population sites. The willow
leaf beetle Phratora vitellinae was the most abundant herbivorous insect at both study sites on willow. A field study was conducted to examine the effects
of P. vitellinae on the performance of C. lapponica. The presence of P. vitellinae larvae on the same twig upon which C. lapponica larvae were feeding did not affect increase of body weight in C. lapponica larvae. Thus, the high resource availability of both willows and birches suggest that interspecific competition is unlikely
to be a selection factor driving the evolution of host shift in C. lapponica. 相似文献
894.
Comparing the model forms estimating generalised diameter-height relationships in Tecomella undulata plantations in hot arid region of India 总被引:1,自引:0,他引:1
Vindhya Prasad Tewari 《林业研究》2007,18(4):255-260
Four generalised diameter-height equations were developed and compared for pure and even-aged stands of Tecomella undulata in hot arid region of Rajasthan State in India. The data used to fit the equations consisted of 1 540 diameter-height observations collected from the plots laid out in uniformly stocked stands of varying age and density. The performance of four equations was tested by non-linear least squares regression and evaluated using different statistical criteria. Finally, these equations, with the same values of coefficients ob- tained during the fitting phase, were validated by an independent data set consisting of 854 diameter-height observations. Overall, equation (4) (Hui and Gadow function) was found to perform best for both the fitting data set as well as validation data set. 相似文献
895.
What is new about new forest owners? A typology of private forest ownership in Austria 总被引:1,自引:5,他引:1
With structural changes in agriculture, new types of forest owners have become increasingly important. This article develops
an empirically-based typology of forest owners in Austria. Based on a representative survey and by means of cluster analysis,
seven types of forest owners are identified. These types form a sequence, ranging from forest owners with a strong agricultural
background to forest owners with no agricultural background at all. The latter exhibit markedly different behaviour in various
respects, e.g. in their interest in forest-related information. The increasing number of ‘new’ forest owners raises important
questions for forest policy, especially how policy instruments can reach these owners and how extension services can address
them. 相似文献
896.
The bending properties of split bamboo culm were compared with those of spruce and beech wood specimens. The bamboo allowed
large flexural deformation since its outer layer retains the tensile stress while the softer inner layer undergoes large compressive
deformation. The results suggested that the combination of the fiber-rich outer part and the compressible inner part was responsible
for the flexural ductility of split bamboo. To clarify the compressible nature of the inner part of bamboo, the longitudinal
surfaces of the bamboo and wood specimens were microscopically observed before and after a large longitudinal compression.
Although the wood specimens showed serious and localized buckling, the inner part of the bamboo specimens showed no such visible
buckling. In the latter case, the foam-like parenchyma cells absorbed the large compressive deformation by their microscopic
buckling and simultaneously, the alignment of sclerenchyma fibers was maintained by the surrounding parenchyma matrix. The
flexural elasticity of the bamboo was compared to that of the wood in respect of remaining strain during cyclic bending tests.
No clear difference was recognized between their remaining strains. This fact indicated that the bamboo was not so flexible
elastically, although its fiber–foam combination and intelligent fiber distribution improve flexural ductility. 相似文献
897.
A new approach is proposed for the evaluation of the brittleness of heat-treated Styrax tonkinensis wood. Heat treatment made wood more brittle when wood was heated at a higher temperature or for a longer time. The brittleness
increased to four times that of the control when wood was heated at 200°C for 12 h. For treatment at 160°C, the increase in
brittleness without any change in weight is thought to be possibly caused by the relocation of lignin molecules. At higher
temperatures, loss of amorphous polysaccharides due to degradation is thought to become the main factor affecting brittleness.
The crystallites that were newly formed after 2 h of treatment showed brittleness that was different from that of the inherent
crystallites remaining after 12 h of heat treatment. This inherent crystalline cellulose possibly plays a role in brittleness.
There is also the possibility of using color to predict the brittleness of heat-treated wood. 相似文献
898.
Tsuyoshi Kajisa Takuhiko Murakami Nobuya Mizoue Shigejiro Yoshida 《Journal of Forest Research》2007,12(6):435-441
Our objective was to investigate the differences in the spectral trajectory of the LANDSAT Thematic Mapper with stand volume
development between Japanese larch (Larix kaempferi) and Japanese oak (Quercus mongolica var. crispula) in the experimental forest of Kyushu University, Hokkaido, Japan. We used nonlinear regression and a categorical variable
to investigate the relationship between spectral reflectance factor and stand volume for each forest type. This research showed
that the reflectance factor of Japanese larch and Japanese oak reached saturation and that both forest types had different
spectral trajectories with stand development. In addition, we found that middle of development stage (stand volume was between
100 and 200 m3/ha) of each forest type had similarity in reflectance factor. 相似文献
899.
Proanthocyanidins (PAs) in the hot water extract prepared from Pinus radiata bark were isolated by a Sephadex LH-20 chromatography. The PAs were characterized using UV/Visible, FT-IR and 13C nuclear magnetic resonance (NMR) spectroscopic techniques, matrix-assisted laser desorption/ionization time of flight (MALDI-TOF)
mass spectrometry (MS), and gel permeation chromatography (GPC) analysis. Bate-Smith acidic alcoholysis and FT-IR spectrum
of the PAs indicated the predominant presence of the procyanidin (PC) structure. The 13C NMR spectrum revealed that the PAs comprise PC (94%) together with a small amount of prodelphinidin (PD, 6%), and also that
they contain the higher trans configuration rather than the cis configuration of C2–C3. The MALDI-TOF MS results obviously proved the presence of PD units, but the maximum degree of polymerization
(DP) was limited to octamer. The average molar mass (Mw, Mn), polydispersity (Mw/Mn), and DP of the pine bark PAs were 3,800
(Mw), 1,200 (Mn), 3.2, and 13, respectively. 相似文献
900.
Twigs of 2–3-year-old Platanus occidentalis L. were used as experimental material to find the causes for the contamination and browning in the initial stages of tissue cultures. To compare the degree of browning of explants picked off from different growing seasons, the experimental material was excised from trees on each of the first ten days in January, March, May and July, 2006. The results indicated that the contamination and browning rates of the material cut off in January (14.2% and 30.6%, respectively) and March were somewhat lower than those in July. The pretreatment of soaking the explants in different anti-oxidants and absorbents at the same time could diminish some side effects. The pretreatment of using 10 g·L–1 vitamin C reduced the contamination and brown-ing rate effectively. An orthogonal experiment showed that the optimal factor and level arrangement is 0.5 mg·L–1 BA, 2.0 g·L–1 ac-tive carbon and 1.5 g·L–1 PVP which resulted in a browning rate of only 16.5%. In general, sampling period, physical properties and pretreatment of explants are the main factors responsible for the contamination and browning of material in the initial stages of P. occidentalis tissue cultures. 相似文献