Giant Sequoia (Sequoiadendron giganteum) Regeneration in Experimental Canopy Gaps

Restoration of giant sequoia populations is a high priority for managers, but few experimental studies have examined the efficacy of restoration treatments. To inform giant sequoia restoration treatment options, we assessed the response of giant sequoia regeneration (germination, mortality, and growth) to experimental gaps within a native giant sequoia grove. We created experimental gaps, ranging in size from 0.05 to 0.4 ha. Following gap creation, we sowed seeds and planted seedlings along north‐south transects across gaps. Transects were planted on paired burned and unburned substrates. The seed‐sowing treatment did not result in a cohort of established seedlings, although the amount of seeds sowed was far short of the potential amount released during intense fires. Mortality of planted seedlings did not vary with gap size (average 25% mortality). However, there was a distinct relationship between gap size and second year seedling growth. The relationship was best modeled with an asymptotic curve for both burned and unburned substrates. Relative seedling growth more than doubled as gap size increased from 0.05 to 0.2 ha, then increases in growth diminished. Growth rates of giant sequoia seedlings saturated above 70% light availability while increasing linearly with belowground resource availability. Long‐lived pioneer species such as giant sequoia require restoration treatments that involve relatively severe disturbances to facilitate cohort establishment and recruitment.     

Settlement Patterns of Mediterranean Fruit Flies in the Tree Canopy: An Experimental Analysis

Males of the Mediterranean fruit fly, Ceratitis capitata (medfly), defend individual leaves of host and non-host trees as mating territories and attract females via production of a sex pheromone (a behavior termed ‘calling’). Males tend to aggregate within the tree canopy, and the present study examined the influence of (1) location and (2) resources on female visitation to male aggregations. Males were placed in screen-covered containers, which were suspended on field-caged trees at two locations selected to differ in only one of the following parameters: height above ground (low versus high), leaf density (sparse versus dense), distance to main trunk (canopy edge versus center), proximity to a food source (bird feces absent or present), and proximity to a host fruit (oranges absent or present). Females were released, and we periodically recorded the number of calling males in each of the test aggregations as well as the number of females sighted within 15 cm of each male aggregation. Male calling did not differ between treatments in any of the experiments. However, females were more frequently sighted near males calling (1) in dense foliage, (2) near the central trunk, (3) near bird feces, and (4) near oranges. In an additional experiment, we compared male settlement (in the absence of females) on leaves in the same sites used previously to determine the degree of congruence between the sexes in microhabitat use. Aside from the lack of center-edge effect, males displayed the same settlement patterns as females. In a final experiment, we found no effect of male calling on the distribution of other males: released males were sighted with equal frequency near cups containing mature, calling males and cups containing immature, non-calling males. Medfly lek behavior is discussed in light of these findings.     

Deadwood Reduces the Variation in Soil Microbial Communities Caused by Experimental Forest Gaps

Ecosystems - Downed woody debris (DWD) creates heterogeneous microsites that are beneficial to enhancing biodiversity and that represent persistent nutrient and carbon pools. Windthrow events...     

Post-Fire Spatial Patterns of Soil Nitrogen Mineralization and Microbial Abundance

Stand-replacing fires influence soil nitrogen availability and microbial community composition, which may in turn mediate post-fire successional dynamics and nutrient cycling. However, fires create patchiness at both local and landscape scales and do not result in consistent patterns of ecological dynamics. The objectives of this study were to (1) quantify the spatial structure of microbial communities in forest stands recently affected by stand-replacing fire and (2) determine whether microbial variables aid predictions of in situ net nitrogen mineralization rates in recently burned stands. The study was conducted in lodgepole pine (Pinus contorta var. latifolia) and Engelmann spruce/subalpine fir (Picea engelmannii/Abies lasiocarpa) forest stands that burned during summer 2000 in Greater Yellowstone (Wyoming, USA). Using a fully probabilistic spatial process model and Bayesian kriging, the spatial structure of microbial lipid abundance and fungi-to-bacteria ratios were found to be spatially structured within plots two years following fire (for most plots, autocorrelation range varied from 1.5 to 10.5 m). Congruence of spatial patterns among microbial variables, in situ net N mineralization, and cover variables was evident. Stepwise regression resulted in significant models of in situ net N mineralization and included variables describing fungal and bacterial abundance, although explained variance was low (R²<0.29). Unraveling complex spatial patterns of nutrient cycling and the biotic factors that regulate it remains challenging but is critical for explaining post-fire ecosystem function, especially in Greater Yellowstone, which is projected to experience increased fire frequencies by mid 21^st Century.     

Small Canopy Gaps Influence Plant Distributions in the Rain Forest Understory1

This study tested three hypotheses regarding how plants respond to the spatial heterogeneity in light availability in the rain forest understory: (1) understory plants occur preferentially in the lighter parts of the understory; (2) under–story palms are more shade tolerant than other understory plants; (3) rain forest plants differ in their ontogenetic response to understory light conditions. The study was carried out in old–growth rain forest in the Yasuní National Park, Amazonian Ecuador. The hypotheses were tested by comparing the distributions of 20 plant species (1454 individuals) over microsites with differing degrees of exposure to canopy gaps to the background distribution of these microsites in the forest. The gap exposure of a given microsite was described by an index based on the number and size of gaps in the canopy to which the site was exposed. Two plant height classes were studied: 0.80–2.49 and 2.50–5 m. The first and third hypotheses were accepted, while the second hypothesis was rejected. The results for the individual species corresponded well with what is known from earlier studies about the ecology of these species or close relatives, suggesting that the patterns observed can be generalized for Neotropical rain forests. Notably, the most abundant species in the study represent several different life history strategies. Thus, abundance in the rain forest understory can be achieved by several different strategies. This suggests that niche differentiation in terms of response to small changes in understory light conditions may be an important factor in the maintenance of the high local plant species richness of tropical rain forests.     

茂兰喀斯特森林林隙幼苗出现的时空格局

通过4次对茂兰自然保护区喀斯特森林林隙内种子的天然萌发情况进行观测,分析了林隙内幼苗的萌发数量、存活率及幼苗出现的时空分布格局。结果发现：林隙中大多数萌发的幼苗存活率均较高,平均存活率达50%以上,林隙的形成,不但提高了喀斯特森林树种的萌发率,也提高了幼苗的存活率。林隙中心、近中心、林隙边缘各区域幼苗的密度存在显著的空间差异,山拐枣（Poliothyrsis sinensis）、多脉榆（Ulmus castaneifolia）等树种在林隙中心幼苗密度最大,圆果化香（Platycarya longipes）、翅荚香槐（Cladrastis platycarpa）、圆叶乌桕（Sapium rotundifolium）、掌叶木（Handeliodendron bodinieri）、黄连木（Pistacia chinen-sis）和云贵鹅耳枥（Carpinus pubescens）等树种在林隙近中心幼苗密度最大,而樟叶槭（Acercinnamomifolium）、球核荚蒾（Viburnumpropinquum）、小叶青冈（Cyclobalanopsis myrsinaefolia）、轮叶木姜子（Litsea verticillata）等则在林隙边缘光照较弱的地方生长良好。幼苗出现的时间分布特征明显,整个观察期幼苗都持续萌发,但大多数树种幼苗出现在第2观测期（3月）,幼苗出现数目从第2次到后面的几次观察期显著下降。林隙3个区域幼苗出现不是同步的,林隙中心的幼苗出现最快,与其它两个部位相比,林隙边缘的幼苗出现有滞后现象。研究结果表明林隙中心的环境条件有利于种子萌发,但林隙近中心却更利于幼苗存活。     

In Situ Spatial Patterns of Soil Bacterial Populations,Mapped at Multiple Scales,in an Arable Soil

Very little is known about the spatial organization of soil microbes across scales that are relevant both to microbial function and to field-based processes. The spatial distributions of microbes and microbially mediated activity have a high intrinsic variability. This can present problems when trying to quantify the effects of disturbance, management practices, or climate change on soil microbial systems and attendant function. A spatial sampling regime was implemented in an arable field. Cores of undisturbed soil were sampled from a 3 × 3 × 0.9 m volume of soil (topsoil and subsoil) and a biological thin section, in which the in situ distribution of bacteria could be quantified, prepared from each core. Geostatistical analysis was used to quantify the nature of spatial structure from micrometers to meters and spatial point pattern analysis to test for deviations from complete spatial randomness of mapped bacteria. Spatial structure in the topsoil was only found at the microscale (micrometers), whereas evidence for nested scales of spatial structure was found in the subsoil (at the microscale, and at the centimeter to meter scale). Geostatistical ranges of spatial structure at the micro scale were greater in the topsoil and tended to decrease with depth in the subsoil. Evidence for spatial aggregation in bacteria was stronger in the topsoil and also decreased with depth in the subsoil, though extremely high degrees of aggregation were found at very short distances in the deep subsoil. The data suggest that factors that regulate the distribution of bacteria in the subsoil operate at two scales, in contrast to one scale in the topsoil, and that bacterial patches are larger and more prevalent in the topsoil.     

Spatial Patterns of Soil Microbial Communities in a Norway Spruce (Picea abies) Plantation

The phospholipid fatty acid (PLFA) profiles of soil microbial communities were determined in relation to the patterns of tree cover in a mature Norway spruce plantation. Replicate samples of the surface organic layers were taken close to the trunk, at 1 m and at 2 m (under the edge of the canopy) beneath five trees. Samples were analyzed for standard PLFAs to assess the initial composition of the microbial communities. Replicate samples were then incubated under constant or fluctuating moisture conditions for 30 d to test the hypothesis that the patterns of microbial community structure (or its physiological state) might be determined by biophysical conditions under the tree canopies. The PLFA profiles near the trunks and at 2 m were similar, but samples taken 1 m from the bases of the trees contained lower concentrations of polyunsaturated (fungal) and monounsaturated PLFAs, and higher concentrations of saturated PLFAs. These differences in PLFA profiles were maintained during laboratory incubation under a regime of drying and wetting cycles, but there was some evidence of convergence in community structure under constant moisture conditions resulting from significant increases and decreases in specific bacterial PLFA concentrations. There were no effects of either moisture treatment on fungal PLFA concentrations. It is concluded that variation in the soil biophysical environment beneath the tree canopies resulted in the differentiation of spatially defined bacterial communities that were tolerant of moisture stress. The anomaly that differences in community structure were largest at an intermediate position of 1 m between the trunk and below the canopy edge was not explained but may relate to tree root distribution.     

Soil Resources Influence Spatial Patterns of Denitrifying Communities at Scales Compatible with Land Management

Knowing spatial patterns of functional microbial guilds can increase our understanding of the relationships between microbial community ecology and ecosystem functions. Using geostatistical modeling to map spatial patterns, we explored the distribution of the community structure, size, and activity of one functional group in N cycling, the denitrifiers, in relation to 23 soil parameters over a 44-ha farm divided into one organic and one integrated crop production system. The denitrifiers were targeted by the nirS and nirK genes that encode the two mutually exclusive types of nitrite reductases, the cd₁ heme-type and copper reductases, respectively. The spatial pattern of the denitrification activity genes was reflected by the maps of the abundances of nir genes. For the community structure, only the maps of the nirS community were related to the activity. The activity was correlated with nitrate and dissolved organic nitrogen and carbon, whereas the gene pools for denitrification, in terms of size and composition, were influenced by the soil structure. For the nirS community, pH and soil nutrients were also important in shaping the community. The only unique parameter related to the nirK community was the soil Cu content. However, the spatial pattern of the nirK denitrifiers corresponded to the division of the farm into the two cropping systems. The different community patterns, together with the spatial distribution of the nirS/nirK abundance ratio, suggest habitat selection on the nirS- and nirK-type denitrifiers. Our findings constitute a first step in identifying niches for denitrifiers at scales relevant to land management.Soil microorganisms are abundant and diverse (46), drive key processes in biogeochemical cycles, and, thus, play crucial roles in ecosystem functioning (2). They are not randomly distributed but exhibit spatial patterns at different scales (26). Spatial patterns ranging from the micrometer up to the meter scale have been reported (19, 20, 32, 37), and an understanding of such patterns can give clues to how microbial communities are generated and maintained (17). Spatial patterns of microorganisms at the field and landscape scales warrant special attention, since they could be associated with land use and aid in creating knowledge-based management strategies for agricultural production (5, 42). However, our understanding of key habitat-selective factors is limited, and few studies have specified which factors influence the spatial patterns of soil microbial communities at larger scales. Lauber et al. (30) recently demonstrated that pH could predict the community composition of soil bacteria at the continental scale. The importance of pH as a key edaphic driver of bacterial community structure has also been shown in other studies (11, 47). Another major, but complex, factor pointed out in a few studies is the soil type (4, 5, 14). Most studies have included only a limited number of properties that are easy to measure; most often, carbon and nitrogen pools and soil physical factors have been neglected in microbial community ecology. Since these factors delineate soil oxygen and water content, they may exert a stronger impact on microbial communities than other soil resources.Reports on the field or landscape scale spatial distribution of soil bacteria have had a taxon-centered perspective at either the species or total-community level, but there is emerging interest in the biogeography of functional traits possessed by microorganisms (18). Bacterial species composition is likely important for soil ecosystem functions, but species affiliation rarely predicts in which way. In addition, the fuzzy species concept of bacteria makes it all the more difficult to link species to niches. Analysis of functional guilds, i.e., assemblages of populations sharing certain traits, can bridge this gap, and one guild of global concern that has been suggested and recently used as a model in functional ecology is the denitrifiers (39, 49). Denitrification is an anaerobic respiration pathway during which NO₃⁻ is reduced to N₂ by a wide range of unrelated taxa. The process is an essential route for N loss from agricultural soil and a major source of the greenhouse gas N₂O. It was recently shown that the spatial distribution of the relative abundances of denitrifiers with the genetic capacity to perform the last step in the denitrification pathway, reduction of N₂O to N₂, is linked to areas with high denitrification rates and low N₂O emissions (38). Adding field scale predicted patterns of the denitrifier community structure to the abundance and activity would not only give insight into the mechanisms shaping the community, but also deepen our understanding of the relationships between the ecology of denitrifiers, N loss, and the agroecosystems'' impact on climate change.We hypothesize that spatial autocorrelations of the structures, sizes, and activities of communities of denitrifying bacteria is governed by soil-based resources at a scale compatible with land management. To test this, and to elucidate the effects of crop production systems and the importance of soil physical and chemical factors in the denitrifying community, we explored the spatial distribution of community structure, size, and activity in relation to 23 soil parameters at a 44-ha farm divided into one organic and one integrated crop production system. The denitrifier community was described in terms of the signature genes that encode the two different types of nitrite reductases in the denitrification pathway, the cd₁ heme-type reductase (NirS), encoded by the nirS gene, and the copper oxidoreductase (NirK), encoded by nirK. The spatial patterns were mapped by geostatistical modeling, and correlation structures were explored.     

Estimating Soil Organic Carbon Stocks and Spatial Patterns with Statistical and GIS-Based Methods

Accurately quantifying soil organic carbon (SOC) is considered fundamental to studying soil quality, modeling the global carbon cycle, and assessing global climate change. This study evaluated the uncertainties caused by up-scaling of soil properties from the county scale to the provincial scale and from lower-level classification of Soil Species to Soil Group, using four methods: the mean, median, Soil Profile Statistics (SPS), and pedological professional knowledge based (PKB) methods. For the SPS method, SOC stock is calculated at the county scale by multiplying the mean SOC density value of each soil type in a county by its corresponding area. For the mean or median method, SOC density value of each soil type is calculated using provincial arithmetic mean or median. For the PKB method, SOC density value of each soil type is calculated at the county scale considering soil parent materials and spatial locations of all soil profiles. A newly constructed 1∶50,000 soil survey geographic database of Zhejiang Province, China, was used for evaluation. Results indicated that with soil classification levels up-scaling from Soil Species to Soil Group, the variation of estimated SOC stocks among different soil classification levels was obviously lower than that among different methods. The difference in the estimated SOC stocks among the four methods was lowest at the Soil Species level. The differences in SOC stocks among the mean, median, and PKB methods for different Soil Groups resulted from the differences in the procedure of aggregating soil profile properties to represent the attributes of one soil type. Compared with the other three estimation methods (i.e., the SPS, mean and median methods), the PKB method holds significant promise for characterizing spatial differences in SOC distribution because spatial locations of all soil profiles are considered during the aggregation procedure.     

Nondestructive, Stereological Estimation of Canopy Surface Area

Summary .  We describe a stereological procedure to estimate the total leaf surface area of a plant canopy in vivo, and address the problem of how to predict the variance of the corresponding estimator. The procedure involves three nested systematic uniform random sampling stages: (i) selection of plants from a canopy using the  smooth fractionator , (ii) sampling of leaves from the selected plants using the  fractionator , and (iii) area estimation of the sampled leaves using  point counting . We apply this procedure to estimate the total area of a chrysanthemum ( Chrysanthemum morifolium L. ) canopy and evaluate both the time required and the precision of the estimator. Furthermore, we compare the precision of point counting for three different grid intensities with that of several standard leaf area measurement techniques. Results showed that the precision of the plant leaf area estimator based on point counting is high. Using a grid intensity of 1.76 cm²/point we estimated plant and canopy surface areas with accuracies similar to or better than those obtained using image analysis and a commercial leaf area meter. For canopy surface areas of approximately 1 m² (10 plants), the fractionator leaf approach with sampling fraction equal to 1/9 followed by point counting using a 4.3 cm²/point grid produced a coefficient of error of less than 7%. The  smooth fractionator  can be used to ensure that the additional contribution to the estimator variance due to between-plant variability is small.     

Light Spatial Distribution in the Canopy and Crop Development in Cotton

The partitioning of light is very difficult to assess, especially in discontinuous or irregular canopies. The aim of the present study was to analyze the spatial distribution of photosynthetically active radiation (PAR) in a heterogeneous cotton canopy based on a geo-statistical sampling method. Field experiments were conducted in 2011 and 2012 in Anyang, Henan, China. Field plots were arranged in a randomized block design with the main plot factor representing the plant density. There were 3 replications and 6 densities used in every replicate. The six plant density treatments were 15,000, 33,000, 51,000, 69,000, 87,000 and 105,000 plants ha⁻¹. The following results were observed: 1) transmission within the canopy decreased with increasing density and significantly decreased from the top to the bottom of the canopy, but the greatest decreases were observed in the middle layers of the canopy on the vertical axis and closing to the rows along the horizontal axis; 2) the transmitted PAR (TPAR) of 6 different cotton populations decreased slowly and then increased slightly as the leaves matured, the TPAR values were approximately 52.6–84.9% (2011) and 42.7–78.8% (2012) during the early cotton developmental stage, and were 33.9–60.0% (2011) and 34.5–61.8% (2012) during the flowering stage; 3) the Leaf area index (LAI) was highly significant exponentially correlated (R² = 0.90 in 2011, R² = 0.91 in 2012) with the intercepted PAR (IPAR) within the canopy; 4) and a highly significant linear correlation (R² = 0.92 in 2011, R² = 0.96 in 2012) was observed between the accumulated IPAR and the biomass. Our findings will aid researchers to improve radiation-use efficiency by optimizing the ideotype for cotton canopy architecture based on light spatial distribution characteristics.     

Relationship of Salt Marsh Vegetation Zonation to Spatial Patterns in Soil Moisture, Salinity, and Topography

An intertidal San Francisco Bay salt marsh was used to study the spatial relationships between vegetation patterns and hydrologic and edaphic variables. Multiple abiotic variables were represented by six metrics: elevation, distance to major tidal channels and to the nearest channel of any size, edaphic conditions during dry and wet circumstances, and the magnitude of tidally induced changes in soil saturation and salinity. A new approach, quantitative differential electromagnetic induction (Q-DEMI), was developed to obtain the last metric. The approach converts the difference in soil electrical conductivity (ECa) between dry and wet conditions to quantitative maps of tidally induced changes in root zone soil water content and salinity. The result is a spatially exhaustive map of edaphic changes throughout the mapped area of the ecosystem. Spatially distributed data on the six metrics were used to explore two hypotheses: (1) multiple abiotic variables relevant to vegetation zonation each exhibit different, uncorrelated, spatial patterns throughout an intertidal salt marsh; (2) vegetation zones and habitats of individual plant species are uniquely characterized by different combinations of key metrics. The first hypothesis was supported by observed, uncorrelated spatial variability in the metrics. The second hypothesis was supported by binary logistic regression models that identified key vegetation zone and species habitat characteristics from among the six metrics. Based on results from 108 models, the Q-DEMI map of saturation and salinity change was the most useful metric of those tested for distinguishing different vegetation zones and plant species habitats in the salt marsh.     

Spatial Patterns of Carbonate Biomineralization in Biofilms

Microbially catalyzed precipitation of carbonate minerals is an important process in diverse biological, geological, and engineered systems. However, the processes that regulate carbonate biomineralization and their impacts on biofilms are largely unexplored, mainly because of the inability of current methods to directly observe biomineralization within biofilms. Here, we present a method for in situ, real-time imaging of biomineralization in biofilms and use it to show that Pseudomonas aeruginosa biofilms produce morphologically distinct carbonate deposits that substantially modify biofilm structures. The patterns of carbonate biomineralization produced in situ were substantially different from those caused by accumulation of particles produced by abiotic precipitation. Contrary to the common expectation that mineral precipitation should occur at the biofilm surface, we found that biomineralization started at the base of the biofilm. The carbonate deposits grew over time, detaching biofilm-resident cells and deforming the biofilm morphology. These findings indicate that biomineralization is a general regulator of biofilm architecture and properties.     

Methane Flux Influenced by Experimental Water Table Drawdown and Soil Warming in a Dry Boreal Continental Bog

To quantify the effects of water table drawdown and soil warming on CH₄ fluxes, we used a static chamber technique during the growing seasons (May–October) of 2011–2013 at hollow and hummock microforms at three sites of a continental bog near the town of Wandering River, Alberta, Canada: (1) Control, (2) Experimental drained, and (3) old Drained. To simulate climatic warming, we used open top chambers to passively warm half of the hollows and half of the hummocks at each of the water level treatment sites. Water table drawdown significantly reduced CH₄ flux by 50% in 3 years and 76% in 13 years of drainage. The hollows showed greater reduction of efflux as compared to hummocks. A persistent functional relationship of CH₄ flux with water level was found across all sites in all years. The relationship revealed that the contribution of change in vegetation type at hollows and hummocks to CH₄ production and emission was relatively less important than that of the water level. Hummocks and hollows responded to warming differently. At the control, experimental and drained sites, warming increased flux at hollows by 16, 21 and 26%, and reduced flux at hummocks by 4, 37, and 56%, respectively. The combined effect of lowered water table and warming on CH₄ emission was overall negative, although the interaction between the two contributing factors was not significant. Therefore, whereas climatic warming and subsequent lowering of water table are expected to reduce CH₄ efflux from dry ombrotrophic bogs of Alberta, different microforms at these bogs may respond differently with accelerated emissions at warmed, wetter (hollows) and reduced emissions at warmed, drier (hummocks) microforms. Overall, CH₄ efflux from Alberta’s dry continental bogs that are not underlain by permafrost might be affected only slightly by the direct effect of predicted climate warming, although initial water table position will be an important control on the overall response.     

Fungi in the Canopy: How Soil Fungi and Extracellular Enzymes Differ Between Canopy and Ground Soils

Ecosystems - Tropical montane cloud forests contain a large abundance and diversity of canopy epiphytes, which depend on canopy soil to retain water and nutrients. We lack an in depth understanding...     

啮齿动物的空间分布格局

啮齿动物的空间分布格局房继明（北京师范大学生物学系,１００８７５）ＳｐａｔｉａｌＤｉｓｔｒｉｂｕｔｉｏｎＰａｔｔｅｒｎｓｏｆＲｏｄｅｎｔｓ．￥ＦａｎｇＪｉｍｉｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＢｉｏｌｏｇｙ,ＢｅｉｊｉｎｇＮｏｒ－ｍａｌＵｎｉｖｅｒｓｉｔ...     

Generation of Spatial Patterns in Boreal Forest Landscapes

Boreal forests are composed of a few plant species with contrasting traits with respect to ecosystem functioning and spatial patterning. Early successional deciduous species, such as birch and aspen, disperse seeds widely, do not tolerate low light and nitrogen availabilities, have rapidly decaying litter, and are highly preferred by herbivores. These later succeed to conifers, such as spruce and fir, which disperse seeds locally, tolerate low light levels and low nitrogen availability, have litter that decays slowly, and are unpalatable to most mammalian herbivores. Although there are also early successional conifers, such as jack pine and Scots pine, the aspen-birch-spruce-fir successional sequence is the most common over much of North America, and (without fir) in Fennoscandia and Siberia. The course of succession in these forests is controlled partly by seed dispersal and selective foraging by mammalian herbivores. Both of these processes are spatially dynamic, but little is known about how their spatial dynamics may affect ecosystem processes, such as nitrogen cycling or productivity. We present spatially explicit models that demonstrate the following: (a) Spatially explicit seed dispersal results in more clumped distribution of tree species and persistence of greater paper birch biomass than uniform seed rain across the landscape. Such results are consistent with current spatially explicit population models of dispersal and coexistence. (b) With localized seed dispersal, the concentrations of available soil nitrogen are distributed in larger patches with sharp transitions from low to high nitrogen availability near patch edges. In contrast, with a uniform seed rain, the distribution of soil nitrogen availability was more uniform and “hotspots” were more localized. Thus, the spatial pattern of an ecosystem process (nitrogen cycling) is determined by seed dispersal and competition for light among competing populations. (c) A dispersing herbivore, such as moose, that selectively forages on early successional deciduous species with high quality litter, such as aspen or birch, and discriminates against late successional conifers, such as spruce or fir, imposes higher-order repeated patterns of plant species and biomass distribution on the landscape. Thus, seed dispersal and herbivore foraging correlate properties in adjacent patches but in different ways, and different spatial patterns emerge. Other processes, such as insect outbreaks, fire, and water flow, also may correlate properties between adjacent patches and result in additional patterns. Received 8 February 1999; accepted 28 May 1999.     

山西植被空间格局及演替简

在ArcGIS软件中采集1984年和2005年山西植被类型的图形,得到山西群系、森林、灌丛、草本植被及栽培植被的图形及面积,用叠置分析和景观格局分析方法研究植被的空间分布及其演替、空间格局及其变化。森林在西南部相对集中分布,在西北角增加明显,它在山西植被中所占面积及比重都最小,最为破碎。油松林在山西森林中占优势,恢复森林主要是油松林、小叶杨林、辽东栎林。1984年灌丛的面积在植被中最大,所占比例也最高,超过50%,集中连片分布面积较大,但灌丛缩减迅速,主要在中南部,在山西植被中遭破坏最为严重。沙棘、虎榛子灌丛和黄栌、连翘灌丛对灌丛的影响最大。草本植被主要在北部减少,在中南部分散增加,更加破碎。白羊草草丛在山西草本植被中占优势,蒿、禾草草原和百里香、禾草草原变化最大。栽培植被明显增加,在植被中所占比重急剧增加,成为山西优势植被。森林、栽培植被分别增加24.3%、71.5%,而灌丛、草本植被却分别减少70.3%,15.6%,演替主要是人为因素造成的。