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1.
Kebin Zhang Rui Li Yunfang Liu Baitian Wang Xiaohui Yang Ruiping Hou 《Frontiers of Forestry in China》2008,3(3):326-333
The spatial distribution characteristics of plant communities in a wetland-dry grassland ecosystem in arid and semi-arid regions
in northwestern China and the main factors affecting the distribution pattern were studied. The Siertan wetland in the Haba
Lake Nature Reserve was the study area. Four transect lines, each about 1 km long, were set up in the growing season along
the biotope gradient in four directions: east, northeast, west and northwest. Attributes measured include frequency of occurrence,
height, density, coverage, biomass and environmental soil factors. The data were analyzed using a two-way indicative species
analysis (TWINSPAN), detrended correspondence analysis (DCA) and Spearman correlation coefficients. On this basis, the vegetation
in the Siertan wetland was classified into three types and 14 associations. The first vegetation type was halophytic marsh
vegetation, mainly distributed in the wetland zone. This type largely contains halophyte and hygric plants and its representative
association is Phragmites communis + Kalidium foliatum. The second type was meadow vegetation, distributed in the ecotone. The meadow vegetation species are mainly mesophytic and
their representative association is Nitraria tangutorum + Pennisetum flaccidum. The third vegetation type is grassland vegetation, which mainly consists of mesophytic and xerophytes, distributed in the
arid grassland zone. The representative association of the third vegetation type is the association of Anaeurolepidium secalium + Saussurea runcinata. Correlation analysis between the axes of DCA and environmental soil factors shows that soil moisture content, organic matter,
soil salt content and total nitrogen are the main environmental factors affecting the pattern of vegetation distribution along
the biotope gradients from wetland to arid grassland. Other factors affecting the vegetation are microtopography and grazing
pressure. Additionally, we have reported modifications and improvements to the importance value methodology.
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Translated from Journal of Beijing Forestry University, 2008, 30(1): 6–13 [译自: 北京林业大学学报] 相似文献
2.
The risk of forest fires has been a subject of study from different disciplines, but its economic evaluation has received relatively little attention. This paper discusses the main issues involved from an economic perspective, and presents the results of a referendum application to evaluate a 50% reduction of the risk of forest fires in Catalonia, Spain. Results and specific risk valuation problems are discussed with some detail. 相似文献
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4.
The Silvopastoral Project is being implemented by CATIE in the Atlantic humid lowland of Costa Rica, in order to develop alternatives
to the current destructive mode of livestock production. The overall approach is briefly described and two superimposed on-farm
experiments are discussed in more detail. The main constraints for on-farm research within the project are analysed: the limited
previous knowledge of the area and of the local species, the difficulty of achieving a common understanding about research
with collaborating farmers, the need for additional staff supervision and the complexity of the statistical analyses. An attempt
is made to draw lessons from the ongoing project regarding how to resolve the apparent contradiction between rigorous scientific
requirements and questions of immediate value to extension, the compromises to be achieved between different types of evaluation
(statistical, risk, etc.) and the potentials and limitations of farmers' participation in research. 相似文献
5.
利用RSM模型模拟计算三维水力旋流器模型,分析了计算结果,并且与相关文献比较后认为：三维模型模拟水力旋流器具有一定的可行性,而二维轴对称模型与实际有一定的差距。 相似文献
6.
Mark Appiah 《Agroforestry Systems》2012,85(1):57-74
Plantations provide a micro-climate that can facilitate the regeneration of other forest species. Often exotic species have been tested for these kinds of functions. To determine the potential for indigenous trees as plantation species for their ability to foster forest species regeneration, this study was undertaken in a mixed indigenous plantation stand. Understories of the stand at 8?years of age were surveyed for plant diversity. The species richness increased by 24% per 1,000?m2 between 2001 and 2008 and the number of families represented increased by 48%. The Shannon Diversity and Simpson Index values confirm a greater diversity 8?years after the plantation was established. The most abundant species in study plots were Chromolaena odorata and Cedrela odorata, which collectively represent about 54% of all species identified in the plots. The most species-rich families were Fabaceae and Euphorbiaceae representing 31% of the total species recorded. Asteraceae and Meliaceae were the two most dominant families, which collectively represent about 55% of all species identified in the plots. 47 forest tree species were found per 1,000?m2 but those classified as ??saplings?? occurred in low densities. The 47 tree species included pioneer species such as Entandrophragma angolensis, Milicia excelsa, and Ceiba pentandra. Growth rates of planted species were differed, with half of the tested species having similar growth capacity to the exotic species. Generally, planted indigenous species enhanced habitats for other forest tree species in degraded sites. The observed growth of indigenous species, if planted and protected, shows that they may help in biodiversity recovery within agricultural landscapes. 相似文献
7.
J.-E. Bergez A. J. I. Dalziel C. Duller W. R. Eason G. Hoppe R. H. Lavender 《Agroforestry Systems》1997,37(3):227-240
Transmitted photosynthetically active radiation (PAR) was measured in eight-year-old silvopastoral stands at three different
locations in the UK by using PAR sensors randomly distributed between four adjacent trees planted in a square pattern. Two
densities (100 stems.ha-1 and 400 stems.ha-1 were compared. The annual carrying capacity (live weight of the animals that a plot supports) was also recorded as an indirect
figure of the overall agricultural production of the system. The silvopastoral plots received less radiation than the agricultural
plot without trees, the 400 stems.ha-1 treatment being more shaded than the 100 stems.ha-1. Over the measurement period, on some special days, a maximum of 30% of the incoming radiation was intercepted on the 400
stem.ha-1 treatment with the largest trees. The amount of light intercepted was highly correlated with the type of weather and the
leaf area development of the trees: the brighter the day and more expanded the leaf area, the higher was the proportion of
radiation intercepted by the tree. However, over the measuring period, a small amount of radiation was intercepted by the
tree canopies. As a consequence, no differences were observed in the annual carrying capacity.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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9.
英犁 《绿色中国(A版)》2011,(6)
今天,你秒杀了吗?时下,许多网购爱好者都在津津乐道于秒杀话题:马尔代夫度假秒杀价1999元;iPhone手机秒杀价399元……果真有这样的好事?秒杀,就是以压倒性优势一招致命;在极短时 相似文献
10.
《Journal of Sustainable Forestry》2013,32(1-2):49-71
Abstract Deforestation is often the primary threat to conservation goals in tropical countries. However, accessing the remote locations in which most remaining forests of conservation value occur makes it difficult to quantify deforestation trends and to galvanize preventive action. Using remotely sensed images we were able to quantify rates of forest loss in La Amistad Biosphere Reserve, Panama. Annual deforestation rates were low between 1987 and 1998 at 0.05% but increased nearly 12-fold between 1998 and 2001 to 0.6%. Net forest loss was 0.56% between 1987 and 1998 and 2.34% between 1998 and 2001. Deforestation rates differed significantly between protected areas. Protected areas on the Caribbean side of the Biosphere Reserve experienced greater levels of deforestation than those on the Pacific, even though both absolute and percent forest cover are higher on the Caribbean. Most forest conversion was for cattle pasture and an area of industrial cattle ranching was identified within the Palo Seco and PILA protected areas as a priority for enforcement activities. Forest conversion to pasture was highly correlated with proximity to roads, rivers, and villages (p < 0.001). The spatial scale of correlation varied between feature types, suggesting a greater area of impact from roads and towns versus rivers. The acceleration of forest conversion from 1998 to 2001 confirms the negative ecological impact of the recent increase in population and development pressure in this previously isolated region. 相似文献
11.
英犁 《绿色中国(综合版)》2011,(6):71-73
今天,你＂秒杀＂了吗？
时下,许多网购爱好者都在津津乐道于＂秒杀＂话题：马尔代夫度假＂秒杀＂价1999元;iPhone手机＂秒杀＂价399元……果真有这样的好事？ 相似文献
12.
Wind Measurements in a Pine Forest During a Destructive Gale 总被引：3，自引：0，他引：3
Anemometer readings were recorded during a gale which blew downsome of the trees in an even-aged 16 m stand of Pinus sylvestrison sandy soil at Thetford forest. Gusts at the top of the canopyattained 17•5 m/sec. Wind profiles agreed well with thetheoretical logarithmic profile above the canopy and the exponentialprofile below. During the gale the zero plane displacement androughness length values were similar to those at lower windspeeds. It is therefore possible to estimate wind profiles andthe forces to which a tree in the crop is subjected from measurementsof wind speed at a single point within or above the forest.The wind speeds which blew trees down were much lower than thosepredicted as necessary from ‘tree pulling’ studiesin the same forest. This discrepancy suggests that any considerationof windthrow must take into account the effects of tree vibrationon the deterioration in the strength of the root-soil complex. 相似文献
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Forest changes over a century in Sardinia: implications for conservation in a Mediterranean hotspot 总被引：1，自引：0，他引：1
The Mediterranean basin is one of the most important biodiversity hotspots. However, only 5% of its original vegetation is still in place, and the landscape has been managed and transformed by humans for at least the last two millennia. In the last century the mechanization of agriculture and the over-use of semi-natural habitats have influenced the region even more than before, with huge consequences, especially on islands. Sardinia is the second largest island in the Mediterranean basin, and it has been considered for long as a semi-natural area with an economy based on traditional agroforestry and pastoral practices. Considering four maps covering Sardinia and ranging from 1935 to 2007, we measured the rate of forest changes demonstrating a constant trend towards forest increase, and with a complete recovery of the total forest surface compared to the late 1800s. The traditional agroforestry practices decrease in time due to socio-economic reasons, with deeper consequences for the mosaic of traditional agricultural areas and semi-natural habitats, as well as for the conservation of the unique biodiversity of Sardinia. Species typically linked to Mediterranean forests recovered and are recovering, while species linked to traditional semi-natural landscapes decreased, facing conservation problems. We suggest that the current challenges for biodiversity conservation in the island should be focused together with the agricultural policies towards the preservation and improvement of traditional open areas, even important in the history of the entire Mediterranean hotspot. 相似文献
15.
Tree roots in a changing world 总被引：1，自引：0，他引：1
Globally, forests cover 4 billion hectares or 30% of the Earth's land surface, and 20%–40% of the forest biomass is made up
of roots. Roots play a key role for trees: they take up water and nutrients from the soil, store carbon (C) compounds, and
provide physical stabilization. Estimations from temperate forests of Central Europe reveal that C storage in trees accounts
for about 110 t C ha−1, of which 26 t C ha−1 is in coarse roots and 1.2 t C ha−1 is in fine roots. Compared with soil C, which is about 65 t C ha−1 (without roots), the contribution of the root C to the total belowground C pool is about 42%. Flux of C into soils by plant
litter (stemwood excluded) compared with the total soil C pool, however, is relatively small (4.4 t C ha−1 year−1) with the coarse and fine roots each contributing about 20%. Elevated CO2 concentrations and N depositions lead to increased plant biomass, including that of roots. Recent analysis in experiments
with elevated CO2 concentrations have shown increases of the forest net primary productivity by about 23%, and, in the case of poplars, an
increase of the standing root biomass by about 62%. The turnover of fine roots is also positively influenced by elevated CO2 concentrations and can be increased in poplars by 25%–45%. A recently established international platform for scientists working
on woody root processes, COST action E38, allows the exchange of information, ideas, and personnel, and it has the aim to
identify knowledge gaps and initiate future collaborations and research activities. 相似文献
16.
Soil changes after traffic with a tracked and a wheeled forest machine: a case study on a silt loam in Sweden 总被引：2，自引：0，他引：2
Alterations to some soil physical parameters were evaluatedafter passes by a tracked forest machine and a wheeled one ofequal mass (about 20 000 kg). Measurements were made after arange of machine passes, with a maximum of eight. The measuredsoil physical parameters were dry bulk density, penetrationresistance, intrinsic air permeability, saturated hydraulicconductivity, porosity and pore-size distribution. Rut depthwas also measured. Although the wheeled machine caused deeper ruts than the trackedone, alterations caused by the two machines to the measuredsoil parameters were similar, except in the uppermost 5–10cm. The wheeled machine caused a decrease in bulk density at5 cm depth, whereas the tracked machine caused an increase,despite its lower ground pressure. 相似文献
17.
Leaf-fall phenology was studied in a cool–temperate deciduous broad-leaved forest in central Japan in relation to the topographic environmental gradients that occur along a short mountain slope. Leaf-fall phenology was described quantitatively using data from leaf litter collected along the slope. In autumn, leaf fall at the study site tended to occur slightly earlier on the upper slope than on the lower slope. This pattern was found at both the stand and the species levels. Our results suggest that leaf-fall phenology may be affected by difference in microclimatic conditions, because environmental conditions are thought to be more severe on the upper slope than on the lower slope. The less intensive methods used in this study, the litter trap method, and Dixon’s model succeeded in quantifying the phenological patterns of leaf fall within stands and within species along the short mountain slope. 相似文献
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19.
Satoshi Saito 《Journal of Forest Research》2002,7(3):137-143
The effects of a typhoon on forest dynamics and the response of major tree species were studied in a warm-temperate evergreen
broad-leaved forest in southwestern Japan. The strongest typhoon on record (T9313) passed through this region in 1993. Return
periods of typhoons over 30 ms−1 in instantaneous wind velocity and T9313 were estimated to be 2.2 and 104.5 years, respectively. Approximately 10% of all
stems suffered some damage from T9313 and annual stem mortality rose from 1.3 to 2.7%. The estimated period that the number
of stems would fall below 10% of the initial was four years shorter with T9313-class typhoons than without them. Thus, the
disturbance by T9313 was not catastrophic at the site although T9313 was an episodic typhoon. The short-term responses of
major tree species to T9313 were classified into four types: 1) blunt-response type with little decrease and recruitment of
stems in the DBH ≥ 5 cm class (Distylium racemosum), 2) retreat type with larger decrease than recruitment (e.g. Quercus acuta), 3) sharp-response type with a large decrease and much recruitment (e.g. Cinnamomum japonicum), and 4) advance type with less decrease than recruitment (Eurya japonica). Among the four regeneration types classified by previous studies (climax, light-demanding, subcanopy, and few-sapling),
the climax and few-sapling types each showed a specific short-term response, the blunt-response and retreat types, respectively,
that explains one aspect of the regeneration strategies of each type. On the other hand, the light-demanding or sub-canopy
type showed multiple short-term responses, indicating that each regeneration type contains species with various regeneration
strategies.
In this paper, I analyzed data from the database that was compiled by the Aya Research Team. 相似文献
20.
Stéphane Nitcheu Tchiadje Denis J. Sonwa Bernard-Aloys Nkongmeneck Laurent Cerbonney 《Journal of Sustainable Forestry》2013,32(5):355-368
ABSTRACTLogging operations in Cameroon are based on the extraction of wood from natural forests. In this article, we assessed the carbon stock in a forest management unit (FMU) located in East Cameroon from field inventory to postfelling operations up to sawmill and export terminals. Tree basal area and aboveground biomass were calculated based on trees inventoried in the annual allowable cut. We observed that from an exploitable tree potential of 0.696 trees ha?1 inventoried within a diameter range of 50–110 cm, 0.141 tree ha?1 (i.e., 20% of the inventoried trees) were logged. In other words, out of 6.78 tC ha?1 inventoried, 1.84 tC ha?1 (i.e., 27% was logged), 1.62 tC ha?1 arrived in the log yard and 1.3 tC ha?1 arrived in sawmill, while 0.32 tC ha?1 reached the export terminal. In terms of damages caused on vegetation, 4.45% of all the annual allowance cut (AAC) were affected during logging activities, this represents almost 33,188.07 tons of carbon. These findings show that the implementation of reduced-impact logging (RIL) could reduce these losses throughout the logging steps and help propose a process for the valuation of wood waste in the forest and sawmill. In this context, reducing emissions from deforestation and degradation will be engaged with the right approach. 相似文献