Edge effects on soil seed banks and understory vegetation in subtropical and tropical forests in Yunnan,SW China

Human-induced forest edges are common in many forest landscapes throughout the world. Forest management requires an understanding of their ecological consequences. This study addressed the responses of three ecological groups (non-forest species, secondary forest species and primary forest species) in edge soil seed banks and edge understory vegetation, and explored the relationship between the invasion of non-forest species in edge understory vegetation and the accumulation of their seeds in edge soil seed banks. The soil seed banks and understory vegetation were sampled along transects established at the edges of a continuous subtropical evergreen broad-leaved forest tract (Lithocarpus xylocarpus forest) bordering anthropogenic grasslands and three tropical seasonal rain forest fragments (Shorea wantianshuea forest) bordering fallows. Species composition in both soil seed banks and understory vegetation showed great difference among edge sites. In soil seed banks, the dominance (relative abundance and relative richness) of each ecological group did not change significantly along the edge to interior gradient. In understory vegetation, the invasion of non-forest species concentrated on the first several meters along the edge to interior gradient. The dominance of secondary forest species decreased with distance from the edge, while the dominance of primary forest species increased with distance from the edge. In forest edge zones, the invasion of a majority of non-forest species in understory vegetation lags behind the accumulation of their seeds in soil seed banks. Forest edges do not act as a good barrier for the penetration of non-forest species seeds. The lack of non-forest species in understory vegetation must then be due to conditions that are not appropriate for their establishment. Therefore, to prevent germination and survival of non-forest species further into the forest, management should focus on maintaining interior forest conditions.     

Stand structure and plant species occurrence in forest edge habitat along different aged roads on Okinawa Island, southwestern Japan

We compared stand structure and plant species occurrence on the shoulders of 3-, 10- and 20-year-old roads in a subtropical evergreen broad-leaved forest to document temporal changes in edge effects of forest roads. We recorded 154 vascular species in the study plots, including 3 non-native species. We used generalized linear mixed models to analyze changes in forest structure and plant species composition in relationship to the distance from forest roads. The spatial patterns in stand structure at different distances from roads differed with road age. The large canopy openness on the edge of 3-year-old roads decreased with time after the construction. A progressive decrease in tree height on roadsides was observed after the road construction, suggesting tall trees could not withstand the dry and windy roadside environment. The edge effect on the canopy tended to be larger at higher elevation sites. The spatio-temporal pattern of species occurrence based on distance from roads differed by species. Typical pioneer species such as Schima wallichii and Eurya japonica increased along the edge, while less aggressive pioneer species and understory species decreased. As time passed after the road construction, some climax and understory species decreased at the forest edge, while other climax and understory species increased. The modeling methods proposed in this study could be applied to different roadside and edge study sites.     

Tree planting pattern effects on forage production in a Douglas-fir agroforest

Resource sharing among agroforestry system components, as expressed by spatial patterns along interfaces between components, is a crucial factor in both understanding present systems and in designing new agroforestry applications. A study of the spatial pattern of forage production surrounding 9–10 year old Douglas-fir trees in a agrosilvopastoral plantation near Corvallis, Oregon, was conducted during 1988 and 1989. Transects of plots were clipped both between trees (tree/tree) and between trees and open pastures (tree/pasture). Best-fit regression models relating forage production to distance from trees (tree/tree R ² = 0.87; and tree/pasture R ² = 0.89) were combined into a single prediction model. Observed forage production increased rapidly with increasing distance from trees during the initial 4 m. Trees had little effect on forage production beyond 4.5 m (approximately 2 canopy diameters) from the nearest tree. Predictions of different combinations of tree density and planting pattern indicated a strong interaction between density and pattern with highly aggregated plantations better able to maintain forage production at high tree densities.     

Variability of herbaceous productivity along Nothofagus pumilio forest-open grassland boundaries in northern Chilean Patagonia

In order to develop a general model of aboveground net primary production (ANPP) of herbaceous communities in grazing systems that combine forested and open grasslands in temperate areas, biomass production and a set of biotic and abiotic variables were measured at four adjacent forest and grassland sites in Chile’s northern Patagonia for two consecutive growing seasons. At each site, one transect of 80 m long (40 m in open grassland and 40 m in forest) × 10 m wide was established. ANPP was significantly higher in open grasslands but no gradual change in biomass production was observed from inside the forest towards the open grassland. In open grasslands ANPP was spatially uniform but highly variable between years of contrasting weather conditions, whereas in forests it was more spatially heterogeneous and less variable over time. ANPP was highly correlated with cattle consumption. Structural equation models developed for the whole system confirm that ANPP was driven mainly by photosynthetically active radiation (PAR) and available nitrogen. However, we found important differences between forests and the adjacent open grasslands. In forests ANPP was enhanced by positive feedbacks between the amount of transmitted PAR through the canopy and soil nutrient input via cattle dung deposition. In open grasslands nitrogen availability appeared to be the main limiting factor but also influenced by weather conditions (dryer or wetter years). The coexistence of forests and grasslands patches, with different susceptibility of ANPP to meteorological and soil nutrient availability, highlights the importance of implementing an integrated silvopastoral system with lenga (Nothofagus pumilio [Poepp. & Endl.] Krasser) in northern Patagonia.     

川西亚高山白桦林内空气和土壤温度动态

2002年5月～10月对川西亚高山白桦林内空气和土壤温度的时空动态的研究结果表明：1)不同层次土壤温度的日变化对天气变化的响应不同。土壤越深，其温度的日变化越小，且最高温出现的时间会滞后。林内和林外空气温度的日变化对天气变化的响应也不同。2)土壤与空气温度的旬变化一致，即土壤温度的旬平均值随着空气温度的旬平均值升高而升高。气温旬平均值的变化幅度比土壤大，且气温的变化速度比土壤快，尤其是9月上旬以后，空气温度的下降非常明显。3)在6月和7月土壤的月平均温度小于空气的月平均温度，但是5月和8月到10月情况却相反。由于白桦次生林的物种组成和群落空间结构简单，且叶面积指数较小，群落的透光系数较大，群落内外的空气温度差异也较小，体现出川西亚高山次生阔叶林的小气候特征。     

Spatial and temporal patterns at small scale in Austrocedrus chilensis diseased forests and their effect on disease progression

Austrocedrus chilensis is an endemic conifer of Patagonia that suffers a widespread mortality whose causes are a topic of discussion. Since Phytophthora austrocedrae is the most probable cause, we proposed that the spatial and temporal patterns of disease at small scale should reflect pathogen behavior. We aimed at characterizing the spatial and temporal patterns of diseased trees in different soil types and the effect of microsite variability on diseased trees spatial pattern. The spatial pattern of disease was influenced by soil type and tree density. In clay soils with low disease incidence (ca. 25%), the spatial pattern was random and not influenced by abiotic microsite conditions. When disease incidence increased (ca. 70%), concurring with denser plots, the spatial pattern was clustered, as a result of an infection process, and it was independent of microsite variability. In soils with better drainage conditions, that is, alluvial soils with volcanic ash input and coarse textured volcanic soils, the disease was clustered and associated with flat microtopographies. The progression of the disease at small scale was influenced by soil, precipitation and tree density. The spatial and temporal patterns of disease progression were associated with a contagion process and with environmental variables that affect drainage, coinciding with Phytophthora biology and requirements. Our results concur in pointing at Phytophthora as the cause of A. chilensis disease in the study area. Management practices should be urgently applied in order to minimize the spread of the inoculum.     

Poplar growth and wood production on a grassland irrigated for decades with potato starch wastewater

Irrigation of grasslands with potato starch wastewater causes changes in soil quality parameters, often resulting in decreased crop yields and sometimes causing animal diseases. Reduced agricultural income leads to designation of such grasslands for afforestation aimed at production of bioenergy crops and improvement of soil quality. In this study, Populus alba L. and seven different poplar clones were planted in 2009 on the grassland irrigated in 1973–2008 with potato starch wastewater and in non-irrigated, experimental forest. The survival, growth and wood production potential of planted poplars after 2–3 growing seasons were analyzed. Morphophysiological parameters of leaves, nutrients in leaves and fine roots, sugars in fine roots, leaf rust resistance, frost hardiness and their effects on growth were also determined. Stem diameter and stem volume index of poplars growing on the grassland were higher than in the experimental forest. Only Populus deltoides Bartr. × P. maximowiczii Henry clone ‘Eridano’ (in short ERI) had a survival rate of 100 % and the highest values of stem diameter (77 mm) and stem volume index (0.034 m³) in comparison with other poplars in both sites after 3 growing seasons. Clone ERI was also characterized by a high leaf rust resistance and frost hardiness. The results suggest that clone ERI is suitable as a bioenergy crop on grasslands irrigated with potato starch wastewater. Afforestation of the grassland improved the fertility of the soil by increasing concentrations of soil organic matter and availability of mineral nutrients (N, P, K, S and Fe).     

Edge type effect on germination of oak tree species in the Highlands of Chiapas,Mexico

The purpose of this study was to examine the effect of habitat edges on the probability of acorn germination of three oak species (Quercus crassifolia Humb. and Bonpl., Quercus rugosa Née and Quercus laurina Humb. and Bonpl.). The effects of edge type (hard and soft), habitat type (grassland, edges and forest) and leaf litter cover (covered or uncovered acorns) on acorn germination was evaluated by the experimental establishment of acorns along transects crossing habitat edges. More acorns developed into seedlings in grasslands (38%) than in the forest edge (18%) or the forest interior (15%). In sites with soft edges, a higher number of seedlings emerged from acorns covered by litter compared with acorns sowed in the adjacent forest edge and forest interior (P < 0.05). In sites with hard edges, fewer seedlings emerged in the edge (14%) compared with the adjacent grassland (38%), and the adjacent forest (20%) presented intermediate values. However, in sites with soft edges significant differences in seedling emergence were recorded between the grassland (38%) and the forest (10%), whereas the edge presented intermediate values (23%). The effect of leaf litter cover on acorn germination was only significant in grasslands in sites with soft edges (P < 0.05). Acorns in grasslands received relatively little insect damage (10%) compared with the edge (19%) and the forest (30%, P < 0.05), emphasising the importance of acorn dispersal for successful oak establishment. The implications for regeneration of these oak species and the dynamics of montane oak forests in Mexico are discussed.     

Spatial variation and prediction of forest biomass in a heterogeneous landscape

Large areas assessments of forest biomass distribution are a challenge in heterogeneous landscapes, where variations in tree growth and species composition occur over short distances. In this study, we use statistical and geospatial modeling on densely sampled forest biomass data to analyze the relative importance of ecological and physiographic variables as determinants of spatial variation of forest biomass in the environmentally heterogeneous region of the Big Sur, California. We estimated biomass in 280 forest plots (one plot per 2.85 km2) and measured an array of ecological (vegetation community type, distance to edge, amount of surrounding non-forest vegetation, soil properties, fire history) and physiographic drivers (elevation, potential soil moisture and solar radiation, proximity to the coast) of tree growth at each plot location. Our geostatistical analyses revealed that biomass distribution is spatially structured and autocorrelated up to 3.1 km. Regression tree (RT) models showed that both physiographic and ecological factors influenced biomass distribution. Across randomly selected sample densities (sample size 112 to 280), ecological effects of vegetation community type and distance to forest edge, and physiographic effects of elevation, potential soil moisture and solar radiation were the most consistent predictors of biomass. Topographic moisture index and potential solar radiation had a positive effect on biomass, indicating the importance of topographically-mediated energy and moisture on plant growth and biomass accumulation. RT model explained 35% of the variation in biomass and spatially autocorrelated variation were retained in regession residuals. Regression kriging model, developed from RT combined with kriging of regression residuals, was used to map biomass across the Big Sur. This study demonstrates how statistical and geospatial modeling can be used to discriminate the relative importance of physiographic and ecologic effects on forest biomass and develop spatial models to predict and map biomass distribution across a heterogeneous landscape.     

Tropical forest sheep on legume forage/fuelwood fallows

In Amazonian Ecuador, studies are being realized to intensify fallow periods by grazing African tropical forest type sheep (Red Afro-Colombian X Barbados Black Belly) on Asian tropical forest legume cover forage (Desmodium ovalifolium) under American tropical forest legume fuelwood trees (Inga edulis). The specific approach represents an innovative effort to address the complex problems associated with the pernicious use of less fertile lands by small-scale farmers and graziers in the humid tropics. The technologies developed are closely compatible with traditional socio-cultural patterns. For example, shifting cultivators are encouraged to plant contour strips of legume fuelwood trees in their cassava fields. With the cassava harvest, legume cover forage is planted between the fuelwood trees, to be grazed later by tropical forest sheep. Forage and fuelwood legumes increase soil aeration, organic matter, nitrogen and available phosphorus, control soil erosion and leaching, as well as provide a break in cropping that checks insect, disease and weed build-ups. Tropical forest sheep improve soil fertility by depositing organic matter which stimulates legume/Rhizobium symbiosis and by supplying fecal microorganisms which mineralize crop residues. In addition, tropical forest sheep cause little soil compaction and erosion, produce high quality food protein from legume cover forage, as well as generate cash income, capital and employment for small-scale farmers. Tropical forest sheep on legume forage/fuelwood fallows not only intensify land use under shifting field cultivation, but also form the basis for rehabilitating already degraded lands for further foodcrop production.     

Patterns of forest vegetation responses to edge effect as revealed by a continuous approach

Context

Understanding the variability of vegetation distribution and its determinants is a central issue for addressing the effects of edges on ecological processes. Recent studies have revealed inconsistencies in the patterns of responses to edge effects that raise important questions about their determinants. We investigated the edge effect response patterns by adapting a recently proposed continuous approach to the case of small forest fragments in southwestern France.

Methods

We surveyed forest understory vegetation (composition, species richness, and percent cover) and abiotic variables (soil temperature, moisture, pH, and canopy openness) along 28 transects across hard forest edges. We tested five statistical models to describe the response pattern of each variable (1) over all transects and (2) per transect. We then compared the response patterns as a function of the attributes of the edge (orientation, topography, and adjacent land cover) and forest patch size.

Results

Over all transects, a general decreasing trend was observed for all variables as the distance from the edge increased. In the individual transects, we evidenced a large variability in the response patterns that was not related to edge attributes or to patch size.

Conclusion

It is difficult to assess the depth of edge influence in highly fragmented forests and to identify the determinants of edge effects. We recommend that care should be taken with studies using pool of transects, and that further studies should be carried out including situations with neutral patterns, in order to gain a broader understanding of edge effects on vegetation.     

Suitability of boreal mixedwood clearcuts as wood bison (Bison bison athabascae) foraging habitat in north-central Alberta,Canada

Plant species composition (n = 95) and biomass (n = 62) samples from harvested and natural stands were analyzed to determine if forest clearcutting increased forage abundance for wood bison (Bison bison athabascae) in north-central Alberta. The sampled stands ranged from 1 to 28 and 50 to 100 years old, respectively, and were members of a Populus tremuloides/Rosa-Viburnum vegetation-type, which is a common forest community on upland sites in the boreal mixedwood zone of western Canada. In addition, a five-stand chronosequence was monitored from May to September, inclusive, to measure seasonal variation in forage abundance and nutrient content. Three-fourths of clearcuts were mechanically treated after harvesting. The data showed that clearcutting increased forage availability, but not quality. Peak summer biomass production occurred in 2–12-year-old clearcuts (∼944 kg/ha, S.D. 511, n = 30), with forage availability decreasing to natural stand levels (∼228 kg/ha, S.D. 147, n = 10) 25–30 years after harvesting. Mechanical site treatment increased forage availability by 26% above untreated clearcuts (P = 0.002). No major differences relevant to bison nutrient requirements occurred between forbs and graminoids in summer, or among age-classes within a monitored chronosequence. Crude protein content declined and fiber content increased during the growing season. Peak forage availability and maximum crude protein content occurred in July among monitored stands. Species with fair forage quality dominated the vegetation in 1–16-year-old clearcuts, with the proportion of forbs increasing as stands aged. Maximum summer carrying capacity of natural stands averaged 0.57 animal unit month per hectare (AUM/ha), depending upon the applied assumptions, with lower winter values (0.01–0.03 AUM/ha). In 2–12-year-old clearcuts, maximum summer and winter carrying capacities were <0.67 and <0.29 AUM/ha based on 25% seasonal usage, respectively. The application of a safe-use factor, down-weighting of forbs to account for dietary preferences, and adjustments for forage quality reduced summer (≤0.30 AUM/ha) and winter (≤0.07 AUM/ha) carrying capacities. Wood bison carrying capacity typically decreased when stands were >8 years old. Clearcuts provide adequate forage for wood bison during the summer, but owing to low graminoid biomass they are not suitable as winter habitat.     

三峡库区杉木马尾松混交林和马尾松纯林的土壤含水量空间变异性

土壤水分含量是对地表生态过程有着重要影响的生态因子,在三峡库区生态环境保护中具有重要作用。选取三峡库区典型植被类型杉木、马尾松混交林(A)和马尾松纯林(B),通过网格(3.00 m×3.00 m)取样,地统计学方法研究群落(30.00 m×30.00 m)0.00 - 20.00 cm土壤水分的空间特征。结果表明:(1)两种典型植物群落土壤含水量空间变异性不同,样地A和样地B土壤含水量的变异系数分别表现出弱和中等强度的变异性;(2)两种典型植物群落土壤水分具有良好的半方差结构,半方差函数曲线可以用球状模型进行拟合。土壤水分的空间相关范围存在明显的差异,有效变程分别为51.00 m和12.37 m;土壤水分分布格局呈明显的斑块状分布;(3)在本研究区域内,植被、地形和地貌等是影响土壤含水量空间异质性的主要因素。     

Nitrate and fecal coliform concentration differences at the soil/bedrock interface in Appalachian silvopasture,pasture, and forest

A major limitation to efficient forage-based livestock production in Appalachia is asynchrony of forage availability and quality with nutritional requirements of the grazer. Producers require dependable plant resources and management practices that improve the seasonal distribution and persistence of high quality herbage, sustainability and environmental integrity of the agricultural landscape. It was hypothesized that inorganic N and fecal coliform concentrations delivered in leachate to the soil/bedrock interface would be lowest in deciduous forest (HF) and highest in pasture (CP) with HF converted to silvopasture (SP) between the two. Piezometers were used to monitor water quality at the soil/bedrock interface under conventional pasture, SP, and hardwood forest. The pasture and SP were rotationally grazed by sheep during the spring to fall grazing season (2004–2008). Geometric mean fecal coliform bacteria concentrations (FC) were greatest in SP (18 FC 100 mL⁻¹) with no difference between CP (7.5 FC 100 mL⁻¹) and HF (5.6 FC 100 mL⁻¹). Mean NO₃-N concentration was lowest in SP (2.3 mg L⁻¹) and greatest in CP (4.4 mg L⁻¹) and HF (4.1 mg L⁻¹), which were not significantly different. Mean NH₄-N concentrations showed different trends with the lowest mean concentration in CP (0.5 mg L⁻¹) and the greatest in SP (2.5 mg L⁻¹) and HF (2.6 mg L⁻¹), which were not significantly different. SP was shown to be a management option in the study area that reduces nitrate leaching, but should be considered cautiously in near-stream areas and near wells where fecal bacteria pollution can be problematic. This study makes an important contribution to our knowledge about interactions between landscape management and environmental quality of the Appalachian region. A diversity of land and forage management options are needed to maximize forage and livestock productivity while protecting surface and groundwater quality of the region.     

兴安落叶松天然林不同林分结构林木水平分布格局特征研究

通过样地调查,分析了不同结构草类-落叶松林和杜香-落叶松林林木分布格局特征。研究表明:(1)年龄36 - 65年草类-落叶松林和年龄54 - 63年杜香-落叶松林分布格局中,均匀分布、随机分布和聚集分布所占比例分别为6.2%、50%、43.8%;(2)按林型分,草类-落叶松林分布格局中,均匀分布和随机分布所占比例均11.1%,聚集分布占77.8%。杜香-落叶松林分布格局均为随机分布;(3)树种组成在6落4阔 - 10落范围内,草类-落叶松林和杜香-落叶松林分布格局主要为聚集分布和随机分布两种类型。聚集分布主要集中在树种组成7落3阔 - 9落1阔范围内。     

Spatial patterns of Douglas-fir and aspen forest expansion

Spatial patterns, rates, and density of encroaching forests into adjacent grasslands have important implications for long-term land use management and resource planning. This study examines the effects of Douglas-fir (Pseudotsuga menzeisii) and aspen (Populus tremuloides) regeneration mechanisms on sucker and seedling spatial patterns, distance from adult trees, and density in encroaching forests. A total of 8,924 aspen suckers and 1,244 Douglas-fir seedlings were counted and mapped in 2,920 quadrats (5 m × 5 m) in 106 plots along a lower forest-grassland ecotone in the Centennial Valley, MT, USA. Sucker and seedling spatial patterns were analyzed using Morisita’s I index. Average sucker and seedling density per quadrat and distance from adult trees were estimated for each plot and compared between aspen-dominated plots and Douglas-fir-dominated plots using ANOVA tests. Aspen suckers were established in a clustered spatial pattern at a significantly higher density and a significantly shorter distance from the adult trees. In contrast, Douglas-fir seedlings were established in varying spatial patterns at a significantly lower density and a significantly greater distance from the adult trees. Forest encroachment into the adjacent grassland in the Centennial Valley is occurring in contrasting patterns and at varying rates and densities due to the difference in aspen and Douglas-fir regeneration mechanisms.     

Short-term effects of fire on soil nitrogen availability in Mediterranean grasslands and shrublands growing in old fields

In three different plant communities growing in Mediterranean old fields we studied the short-term changes in soil nitrogen availability that occur after the fire. Two of these communities were grasslands with great capacity of resprouting and contrasted N availability, one dominated by Brachypodium retusum, and the second one dominated by B. retusum and the N fixing shrub Genista scorpius. The third community was an obligate seeder community (shrubland) with low N availability and was dominated by Rosmarinus officinalis. We selected six plots for each type of vegetation and therefore performed 18 experimental fires. During fires we measured temperatures at the soil surface. Maximum temperature recorded during fire and time–temperature integral were used as indexes of fire severity. During the 6 months following fires we measured Net N mineralization and plant uptake by field incubations using the resin-core technique in paired burnt and control plots.Fire severity increased with plant biomass. In grasslands heating of the soil surface increased with plant biomass up to a limit of 1 kg m⁻² of above-ground biomass. For high biomass a large proportion of heat released during fire was probably transmitted to the atmosphere or to the deeper soil horizons. The increase of soil mineral N was larger in fires of greater severity. Most mineral nitrogen released to the soil during fire was ammonia. Increases of ammonia post-fire depends on the temperatures measured on the soil surface while increases of the less volatile N form (nitrate) were related to the amount of burnt biomass and were highly dependent on the type of vegetation.The amount of nitrogen released to soil during fire represented a small proportion of the N mineralized during the 6 months following fire and thus the amount of nitrogen mineralized per unit of N released during fire was very different across the different types of vegetation. In grasslands fire induced changes in N mineralization decreased as fire severity increased. In contrast, in shrublands we observed the opposite trend. Differences in potentially mineralizable and in net mineralization N between unburnt grasslands and shrublands could account for this fact. Despite the depression in nitrification that we observed in grasslands between 40 and 80 days after the fire, high nitrate concentration in the soil during that period increased N leaching in burnt plots. No plant uptake was detected at that time. In grasslands the onset of plant uptake in burnt plots was delayed as compared to control. Cumulative changes in N did not depend on the burnt biomass in grassland communities, but it did in the seeder community. On the contrary, soil temperatures measured during fires related to changes in N observed in grasslands but not in the seeder community. It appears therefore, that post-fire N mineralization and leaching in grasslands may have been driven by the changes induced by heating the soil surface while in shrublands it may have been driven by the quantity of ash deposited on the soil surface.     

吉林省主要林型森林火灾释放碳量的月变化

根据吉林省1969—2004年的森林火灾统计数据,计算出了吉林省主要林型森林火灾碳释放量的月变化。为了充分减少由于森林火灾排放的碳量,应重点防范白桦林9、10和2月,阔叶林9、5、10、4、3和11月,针阔混交林9、11、4和10月,落叶松林4、3、10和5月,柞树林5、4、9、10和3月,杨树林和红松林9月的森林火灾。     

黄土高原三种类型复合农林业边界地区土壤水分的时空变化(英文)

黄土高原山坡上的复合农林业是一种普遍存在的景色,在这里土壤的水分是植物生长和发展的限制因素。文中研究了三种类型复合农林业边界(林-牧地、林-耕地和防护林-耕地)下水分的时空特性。研究结果表明,从土地表面到110cm处土壤的水分含量随着土壤深度的增加而减少。在雨季(7-9月)、干旱季(5-6月)和春季(3-4月),土壤的水分含量在三种边界下变化非常显著。在三种边界类型的不同土壤层下,土壤水分的水平分布呈现出线性、波形、勺形或是"W"形不同的形式。通过方差分析和多重比较估计除了不同边界类型下土壤水分影响域(DEI)。在干旱季节,在0-10cm的土壤层的DEI为0.4H(H为平均树高),该数据从牧地或耕地下的0.2H到林-牧地、林-耕地下的0.2H和防护林-耕地下0.7H(从耕地的0.2H到防护林的0.5H)。在雨季,在0-110cm土壤深度三种边界下的DEI为0.7H。研究结果表明,特别在黄土高原的恢复退化土地区域为了保持土壤的水分在土地管理上复合农林业类型应该谨慎选取。     

Spatial distribution of late-successional coniferous species regeneration following disturbance in southwestern Québec boreal forest

Remnant tree stands left intact following a disturbance constitute the sole seed banks available for regeneration of coniferous species that neither bear serotinous cones nor reproduce vegetatively. The success of regeneration of tree species on these disturbed sites is, therefore, dependent on the distance from potential seed sources. The regeneration of balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca (Moench) Voss) and white cedar (Thuja occidentalis L.) was studied at two sites in Québec’s southwestern boreal forest in order to quantify the influence of remnant stands on spatial distribution of regeneration. The first site is located in an area that burned in 1944 while the second site is located in an area that was clear-cut in the mid-1980s. Canonical correspondence analyses were used to determine the respective contributions of environmental data and spatial variables to the pattern of spatial distribution of regeneration. The results reveal that distance from a remnant stand is the most important variable in explaining spatial distribution of regeneration when compared to environmental variables such as soil type, drainage, slope and altitude. The plots of regeneration density against distance from a remnant stand for both the burned site and logged site show that regeneration density decreases abruptly with distance from a remnant stand. Furthermore, spatial autocorrelation analyses (Moran’s I) indicate that even small remnant zones can significantly influence the pattern of spatial distribution of regeneration for the three species studied. The results presented here suggest that where preestablished regeneration is not abundant enough, alternative silvicultural systems such as strip clear-cutting or seed-tree systems could be used instead of cuts with protection of regeneration and soils (CPRS).