Diameter distribution of trees in natural stands managed on polycyclic cutting system

Diameter frequency distribution in a specific stand provides basic information for forest resources management.In this study,four probability models were applied to analyze diameter distribution of natural forests after selective cutting with different intensities (low intensity of 13.0% in volume,medium intensity of 29.1%,high intensity of 45.8%,and extra-high intensity of 67.1%).The results show that the skewness and kurtosis of the four models are positive except that of low intensity selective cutting,which suggest that the number of small-size trees dominate the stand.The more intensity of selective cutting,the wider range of diameter distributions.The diameter structure of selective cutting with low intensity met Weibull and Beta distributions;that of medium intensity met Weibull,negative exponential as well as Gamma distributions;that of high intensity cutting met Weibull and negative exponential distributions,but that of extra-high intensity could not meet any above model.Weibull distribution model fits better than others regarding the structure of diameter distribution in natural forests managed on polycyclic cutting system.The results will provide basic information for sustainable management for mixed natural stands managed on a polycyclic cutting system.     

Streamflow responses to vegetation manipulations along a gradient of precipitation in the Colorado River Basin

The Colorado River Basin has been, and continues to be, the focus of a wide diversity of research efforts to learn more about the effects of natural and human-induced disturbances on the processes and functioning of the basin's upland watersheds. These watersheds are situated at the headwaters of streams and rivers that supply much of the water to downstream users in the western United States. Responses of streamflow to vegetation manipulations have been, and are, one of the research foci in this water-deficient part of the country. The watershed-scale research, led by the U.S. Forest Service and its cooperators, has spanned nearly a century and included an array of vegetation types along a wide range of precipitation gradients. Results from this research have shown that vegetation can be managed to enhance annual water yields while still providing the other natural resource benefits. Analyses of the research results suggest that the effect of vegetation manipulation on streamflow is associated with precipitation–elevational gradient and, therefore, vegetation type. An annual water yield increase between 25 and 100 mm could be achieved by implementing vegetation manipulations in the high elevation subalpine and mixed conifer forests, the ponderosa pine forests (in the Lower Basin), and portions of the low elevation chaparral shrublands. Negligible effects or small increases in water yield were observed for treating sagebrush, pinyon-juniper woodland and desert scrubs. Results from this research have improved our understanding of the basin's hydrology and provided much needed insights to manage forest to mitigate global climate change induced hydrologic impact and meet the increased needs of people living in the basin.     

乌鲁木齐河水源林地生态功能区划研究

以景观生态功能区划原则为理论基础,结合实际,在边界划定、主导因素结构、格局和功能分析的基础上,将乌鲁木齐河水源林地区划为5个生态功能区和15个生态功能亚区,并针对每个功能区和功能亚区,从保护水源林地和生态农林产业开发方面提出了相应的生态保育措施,可以为管理部门有效地开发和保护乌鲁木齐河流域水资源、开展生态农业生产与林牧业管理、合理地开发生态旅游等提供决策依据。     

不同倍性菘蓝林下光合特性及种植研究

为了研究菘蓝林下种植是否可以提高土地利用率和板蓝根药材的产出.以四倍体和二倍体菘蓝为试材,在不同郁闭度林下进行了一个完整生长周期的种植和研究:郁闭度在0.3以下为轻度郁闭(C1),郁闭度在0.3～0.6为中度郁闭(C2),郁闭度在0.6以上为重度郁闭(C3),以大田露地栽培为对照(C0).结果 表明:菘蓝属于阳生植物,...     

Do riparian buffer strips mitigate the impacts of clearcutting on small mammals?

We assessed the impact of clearcutting on small mammals in riparian areas and evaluated riparian buffer strips as a tool for conserving small mammals in managed forests. Over two summers, we trapped small mammals of seven species in riparian areas in southwestern British Columbia, Canada. Communities of small mammals were compared across three different habitat types: (1) clearcut to the stream bank, (2) clearcut with a 30 m riparian buffer strip, and (3) control (no logging). Species richness was significantly lower in clearcuts than in controls and buffers. On clearcut sites, creeping voles were more abundant, but red-backed voles and dusky shrews were less abundant than at the control sites. At sites with riparian buffer strips, both voles were present in numbers similar to those found in controls, but dusky shrews were less common. Significantly more deer mice and creeping voles were infested with bot flies at clearcut sites than at buffer sites, and no animals were infested at any of the control sites. Riparian reserves appear to be useful in reducing the short-term impacts of clearcutting on small mammal communities, though they do not eliminate these impacts altogether.     

Comparison of nutrient concentrations in organic layers between broad-leaved and coniferous forests

The concentrations of Ca, Mg, K, N, P, and C, the ratios of C/N, C/P, and N/P, and pH values in L, F, and H layers were compared between a coniferous dominated forest group and a broad-leaved dominated forest group. L layers in the broad-leaved group displayed significantly higher nutrients concentrations, except for N a and P, and higher pH values than those in the coniferous group. This pattern extended to the F layers. In the F layers the broad-leaved group showed a substantial decrease in K concentrations compared with the L layers. In the H layers, pH values and Ca concentrations became very low for both groups. Carbon concentrations decreased linearly from the L to H layers. The degree of increase in Nand P concentrations from the L to F layers was larger than that from the F to H layers. Magnesium and Na concentrations did not vary appreciably among the layers. Between the groups no significant differences in the values of N, P, C, Na, N/P, and pH were found in the H layers, and the differences in the Ca, K, and C/N values became negligible. The results suggest that the H layers displayed relatively homogeneous characteristics for nutrient conditions even though the above ground vegetation was different.     

Denitrification potential of intermittently saturated floodplain soils from a subtropical perennial stream and an ephemeral tributary

Denitrification has the potential to remove excess nitrogen from groundwater passing through riparian buffers, thus improving water quality downstream. In regions with markedly seasonal precipitation, transient stream flow events may be important in saturating adjacent floodplain soils and intermittently providing the anaerobic conditions necessary for denitrification to occur. In two experiments we characterised the denitrification potential of soils from two contrasting floodplains that experience intermittent saturation. We quantified under controlled laboratory conditions: 1) potential rates of denitrification in these soils with depth and over time, for a typical period of saturation; and 2) the influences on rates of nitrate and organic carbon. Treatments differed between experiments, but in each case soil-water slurries were incubated anaerobically with differing amendments of organic carbon and nitrate; denitrification rates were measured at selected time intervals by the acetylene-block technique; and slurry filtrates were analysed for various chemical constituents. In the first experiment (ephemeral tributary), denitrification was evident in soils from both depths (0-0.3 m; 0.3-1.1 m) within hours of saturation. Before Day 2, mean denitrification rates at each depth were generally comparable, irrespective of added substrates; mean rates (Days 0 and 1) were 5.2 ± 0.3 mg N kg dry soil⁻¹ day⁻¹ (0-0.3 m) and 1.6 ± 0.2 mg N kg dry soil⁻¹ day⁻¹ (0.3-1.1 m). Rates generally peaked on Days 2 or 3. The availability of labile organic carbon was a major constraint on denitrification in these soils. Acetate addition greatly increased rates, reaching a maximum in ephemeral floodplain soils of 17.4 ± 1.8 mg N kg dry soil⁻¹ day⁻¹ on Day 2: in one deep-soil treatment (low nitrate) this overcame differences in rates observed with depth when acetate was not added, although the rate increase in the other deep-soil treatment (high nitrate) was significantly less (P ≤ 0.01). Without acetate, peak denitrification rates in this experiment were 6.9 ± 0.4 and 2.8 ± 0.2 mg N kg dry soil⁻¹ day⁻¹ in surface and deep soils, respectively. Differences in rates were observed with depth on all occasions, despite similar initial concentrations of dissolved organic carbon (DOC) at both depths. Levels of substrate addition in the second experiment (perennial stream) more closely reflected natural conditions at the site. Mean denitrification rates were consistently much higher in surface soil (P ≤ 0.001), while the source of water used in the slurries (surface water or groundwater from the site) had little effect on rates at any depth. Mean rates when all treatments retained nitrate were: 4.5 ± 0.3 mg N kg dry soil⁻¹ day⁻¹ (0-0.3 m depth); 0.8 ± 0.3 mg N kg dry soil⁻¹ day⁻¹ (0.3-1.0 m); and 0.6 ± 0.1 mg N kg dry soil⁻¹ day⁻¹ (1.8-3.5 m). For comparable treatments and soil depths, denitrification potentials at both sites were similar, apart from higher initial rates in the ephemeral floodplain soils, probably associated with their higher DOC content and possibly also their history of more frequent saturation. The rapid onset of denitrification and the rates measured in these soils suggest there may be considerable potential for nitrate removal from groundwater in these floodplain environments during relatively short periods of saturation.     

Forest resources variation along with the main rivers in typical forest region of Changbai Mountain

The restoration of the riparian vegetation disturbed by human activities is one of the hotspots of watershed ecology. Through interpreting the images of Remote Sensing in 1985 and 1999, the basic information of forest resources of Lushuhe Forest Bureau, which is a typical forest area of Chanbai Mountain was obtained with support of GIS. By dividing Land covers of Lushuihe area into 10 types (water body, residential land, stump land, farming land, wetland, mature conifer forest, midlife conifer forest, mature broadleaf forest, midlife broadleaf forest, and man-made young forest) and dividing the riparian zone into four buffers (in turn 1000, 2000, 3000, 4000 m away from the river), the changes of riparian forest resources during 1985–1999 were analyzed. The results showed that the deforestation intension has obviously decreased and the whole environment has been evidently improved, but the riparian ecosystem was still flimsy. In buffer 1, 2, 3 the area of midlife conifer forest increased largely, but the areas of other types of land covers all decreased. Midlife conifer forest had a comparatively good status in the three buffers. In buffer 4, midlife conifer forest, mature conifer forest, and mature broadleaf forest formed a forest-age rank that is helpful to stabilize the forest ecosystem and exert its functions. Area percentage of wetland decreased in buffer 1, buffer 2, and buffer 3, even in buffer 4 in which forest ecosystem rehabilitated comparatively well, so protecting and rehabilitating wetland is a very difficult task. Foundation item: This study is supported by major projects of Knowiedge Innovation Program. Chinese Academy of Sciences (No. KZCX2-SW-320-3) and Institute of Applied Ecology (a grant SCXZD010-01), CAS. Biography: HAO Zhan-qing (1962-), Male, Ph. Doctor, Professor in Institute of Applied Ecology, Chinese Academy of Science, Shenyang 1100016, P.R. China Responsible editor: Chai Ruihai     

The magnitude and variability of soil-surface CO2 efflux increase with mean annual temperature in Hawaiian tropical montane wet forests

Soil-surface CO₂ efflux (F_S; ‘soil respiration’) accounts for ≥50% of the CO₂ released annually by the terrestrial biosphere to the atmosphere, and the magnitude and variability of this flux are likely to be sensitive to climate change. We measured F_S in nine permanent plots along a 5.2 °C mean annual temperature (MAT) gradient (13-18.2 °C) in Hawaiian tropical montane wet forests where substrate type and age, soil type, soil water balance, disturbance history, and canopy vegetation are constant. The objectives of this study were to quantify how the (i) magnitude, (ii) plot-level spatial variability, and (iii) plot-level diel variability of F_S vary with MAT. To address the first objective, annual F_S budgets were constructed by measuring instantaneous F_S monthly in all plots for one year. For the second objective, we compared plot-level mean instantaneous F_S in six plots derived from 8 versus 16 measurements, and conducted a power analysis to determine adequate sample sizes. For the third objective, we measured instantaneous F_S hourly for 24 h in three plots (cool, intermediate and warm MATs). The magnitude of annual F_S and the spatial variability of plot-level instantaneous F_S increased linearly with MAT, likely due to concomitant increases in stand productivity. Mean plot-level instantaneous F_S from 8 versus 16 measurements per plot yielded statistically similar patterns. The number of samples required to estimate plot-level instantaneous F_S within 10% and 20% of the actual mean increased with MAT. In two of three plots examined, diel variability in instantaneous F_S was significantly correlated with soil temperature but minimal diel fluctuations in soil temperature (<0.6 °C) resulted in minimal diel variability in F_S. Our results suggest that as MAT increases in tropical montane wet forests, F_S will increase and become more spatially variable if ecosystem characteristics and functioning undergo concurrent changes as measured along this gradient. However, diel variation in F_S will remain a minor component of overall plot-level variation.     

天然林保护工程的成效及对策研究

天保工程是我国重大生态战略工程,也是实现山水林田湖草生命共同体的重要支撑,攀枝花属于典型的金沙江干热河谷气候,又是天保工程实施的"发源地"。本文选取攀枝花为研究对象,通过分析近20年攀枝花市天保工程实施森林资源、人员福利、森林采伐和林业产值等主要方面,得出天保工程实施成效显著,并探索性提出未来实施的对策和展望,对完善天然林保护制度具有重大的意义。