Genetic analysis of landscape connectivity in tree populations

Genetic connectivity in plant populations is determined by gene movement within and among populations. When populations become genetically isolated, they are at risk of loss of genetic diversity that is critical to the long-term survival of populations. Anthropogenic landscape change and habitat fragmentation have become so pervasive that they may threaten the genetic connectivity of many plant species. The theoretical consequences of such changes are generally understood, but it is not immediately apparent how concerned we should be for real organisms, distributed across real landscapes. Our goals here are to describe how one can study gene movement of both pollen and seeds in the context of changing landscapes and to explain what we have learned so far. In the first part, we will cover methods of describing pollen movement and then review evidence for the impact of fragmentation in terms of both the level of pollen flow into populations and the genetic diversity of the resulting progeny. In the second part, we will describe methods for contemporary seed movement, and describe findings about gene flow and genetic diversity resulting from seed movement. Evidence for pollen flow suggests high connectivity, but it appears that seed dispersal into fragments may create genetic bottlenecks due to limited seed sources. Future work should address the interaction of pollen and seed flow and attention needs to be paid to both gene flow and the diversity of the incoming gene pool. Moreover, if future work is to model the impact of changing landscapes on propagule movement, with all of its ensuing consequences for genetic connectivity and demographic processes, we will need an effective integration of population genetics and landscape ecology.     

改善树体结构对提高龙眼产量和品质的影响试验

通过培育不同树形,并对郁闭的龙眼果园进行疏枝、间伐试验。结果表明,建立高光效树体结构,减少郁闲果园株数,能有效改善果园通风透光条件、提高产量和果实品质;林华果场试验因疏枝改造后树高降低,冠径扩大,单株产量比对照增加121kg,果实品质显著提高;密龙果场试验园间伐后,虽然总产量略有降低,但是667m2产值比对照增加687．8元。通过调查不同果园的龙眼产量和树体结构,得到龙眼产量与树体结构相关性回归方程为Y=-60．98＋0．28X1＋3．90x2＋2．29X3。     

Effects of landscape structure on nest predation in roadsides of a midwestern agroecosystem: a multiscale analysis

Nest predation is an important cause of mortality for many bird species, especially in grassland ecosystems where generalist predators have responded positively to human disturbance and landscape fragmentation. Our study evaluated the influence of the composition and configuration of the surrounding landscape on nest predation. Transects consisting of 10 artificial ground nests each were set up in 136 roadsides in six watersheds in south-central Iowa. Nest predation on individual roadside transects ranged from 0 to 100% and averaged 23%. The relationship of landscape structure within spatially-nested landscapes surrounding each roadside transect (within 200, 400, 800, 1200, and 1600 m of the transect line) to nest predation was evaluated by using multiple regression and canonical correlation analyses. The results of this multiscale landscape analysis demonstrated that predation on ground nests was affected by the surrounding landscape mosaic and that nest predators with different-sized home ranges and habitat affinities responded to landscapes in different ways. In general, wooded habitats were associated with greater nest predation, whereas herbaceous habitats (except alfalfa/pasture) either were associated with less nest predation or were not important. Different landscape variables were important at different spatial scales. Whereas some block-cover habitats such as woodland were important at all scales, others such as rowcrops and alfalfa/pasture were important at large scales. Some strip-cover habitats such as gravel roads and paved roads were important at small scales, but others such as wooded roadsides were important at all all scales. Most landscape metrics (e.g., mean patch size and edge density) were important at large scales. Our study demonstrated that the relationships between landscape structure and predator assemblages are complex, thus making efforts to enhance avian productivity in agricultural landscapes a difficult management goal.     

梨树形改造与优化技术研究

针对乔砧密植梨园树形紊乱、树冠郁闭、通风透光不良、产量低和品质差等问题,以‘锦丰’梨为试材,开展树体改造和优化技术研究。结果表明:树体改造改善了枝类组成和枝条的空间分布特征,改造树树冠内的温度、湿度和光照条件明显好于对照,内膛叶片的饱和光强、光补偿点和光合能力均显著提高,树体的产量和品质大幅度增加,树体改造和优化技术研究为梨树密植园的改造提供了有力的理论支撑。     

树形对桃树生长、产量和品质的影响

【目的】探讨中油20号桃不同树形对树体生长、产量和品质的影响。【方法】研究3年生中油20号桃Y字形、主干形、三主枝开心形、四主枝开心形及V字形5种树形的夏季结果枝部位光照度,成熟果实品质及冬季树体结构。【结果】同一树形不同部位的光照度和果实品质均有显著性差异,均为上层>中层>下层,不同树形相同部位间差异不显著。每666.7 m²产量为主干形>V字形>Y字形>三主枝>四主枝。树体的主枝数越多,主干直径越粗,树体越高,冠径越大。总枝量主干形最少,四主枝最多,而每666.7 m²枝量V字形最多,主干形其次。不同树形枝类组成,长枝比例顺序为主干形>V字形>Y字形>三主枝>四主枝,中短枝比例与长枝比例相反。选择了13种指标进行主成分分析,5种树形的优劣顺序依次为V字形、四主枝开心形、三主枝开心形、Y字形、主干形。【结论】V字形树形综合评分最高,产量和每666.7 m²枝量较高、品质表现较好,是适宜标准化栽培的优良树形。     

Regional habitat appraisals of wildlife communities: a landscape-level evaluation of a resource planning model using avian distribution data

A simple regional habitat model founded on the relation between vertical habitat complexity and species richness has been used to describe wildlife habitat in response to macroscale patterns in land use and land cover. While the model has a basis in ecological theory, it has not been subjected to rigorous testing. We evaluated the model's fundamental assumption on landscapes in the eastern forested region of the United States and found the model to be supported when we used a measure of avian community integrity during the breeding season. The model was improved by incorporating measures of horizontal heterogeneity, indicating that the vertical and horizontal structure of habitats should be considered in analyzing the response of wildlife to land resource policies that can affect broad land use patterns. In cooperation with Colorado State University.     

Effects of changing spatial scale on the analysis of landscape pattern

The purpose of this study was to observe the effects of changing the grain (the first level of spatial resolution possible with a given data set) and extent (the total area of the study) of landscape data on observed spatial patterns and to identify some general rules for comparing measures obtained at different scales. Simple random maps, maps with contagion (i.e., clusters of the same land cover type), and actual landscape data from USGS land use (LUDA) data maps were used in the analyses. Landscape patterns were compared using indices measuring diversity (H), dominance (D) and contagion (C). Rare land cover types were lost as grain became coarser. This loss could be predicted analytically for random maps with two land cover types, and it was observed in actual landscapes as grain was increased experimentally. However, the rate of loss was influenced by the spatial pattern. Land cover types that were clumped disappeared slowly or were retained with increasing grain, whereas cover types that were dispersed were lost rapidly. The diversity index decreased linearly with increasing grain size, but dominance and contagion did not show a linear relationship. The indices D and C increased with increasing extent, but H exhibited a variable response. The indices were sensitive to the number (m) of cover types observed in the data set and the fraction of the landscape occupied by each cover type (P _k); both m and P _kvaried with grain and extent. Qualitative and quantitative changes in measurements across spatial scales will differ depending on how scale is defined. Characterizing the relationships between ecological measurements and the grain or extent of the data may make it possible to predict or correct for the loss of information with changes in spatial scale.     

The influence of scale and the spatial characteristics of landscapes on land-cover mapping using remote sensing

Statistical analyses provide a means for assessing relationships between landscape spatial pattern and errors in the estimates of cover-type proportions as land-cover data are aggregated to coarser scales. Results from a multiple-linear regression model suggest that as patch sizes, variance/mean ratio, and initial proportions of cover types increase, the proportion error moves in a positive direction and is governed by the interaction of the spatial characteristics and the scale of aggregation. However, the standard linear model does not account for the different directions of scale-dependent proportion error since some classes become larger and others become smaller as the scene is aggregated. Addition of indicator variables representing class-type significantly improves the performance by allowing the model to respond differently to different classes. A regression tree model provides a much simpler fit to the complex scaling behavior through an interaction between patch size and aggregation scale. An understanding of the relationships between landscape pattern, scale, and proportion error may advance methods for correcting land-cover area estimates. Such methods could also facilitate high-resolution calibration and validation of coarse-scale remote-sensing-based land-cover mapping algorithms. Ongoing initiatives to produce global land-cover datasets from remote sensing, such as efforts within the IGBP and the EOS MODIS Land-Team, include significant emphasis on high level calibration and validation activities of this nature.     

塞罕坝机械林场生态景观林空间结构对夏季景观质量的影响

林内景观质量评价对林场的经营和管理有重要意义,而林分空间结构的研究对生态景观林景观质量有重要影响。以塞罕坝机械林场落叶松纯林与落叶松-白桦混交林为研究对象,选取了16张最具代表性的照片,采用美景度评价（SBE）法以美景度作为景观质量指标,通过探究林分空间结构对林分夏季近景的景观质量影响,进而为塞罕坝生态景观林夏季景观经营技术提供依据。结果表明：（1）林内垂直结构越完整,林下整齐度越高,人们的喜好频数越高,美景度越高。（2）林内透视距离与美景度值存在明显的二项式关系;林内透视距离高于1倍树高时,美景度值随透视距离增加而增加。（3）林分枝下高与株高比值和美景度值存在二项式关系,林分枝下高与株高比值在0.5～0.6之时,美景度值存在1个峰值,此时人们接受程度最高。人们对林内垂直结构、透视距离、林下整齐度、树干形态与枝下高等指标偏好程度为打造更美好的生态景观林提供科学指导,对林场的转型和森林景观旅游事业有促进作用。     

Landscape attributes and life history variability shape genetic structure of trout populations in a stream network

Spatial and temporal landscape patterns have long been recognized to influence biological processes, but these processes often operate at scales that are difficult to study by conventional means. Inferences from genetic markers can overcome some of these limitations. We used a landscape genetics approach to test hypotheses concerning landscape processes influencing the demography of Lahontan cutthroat trout in a complex stream network in the Great Basin desert of the western US. Predictions were tested with population- and individual-based analyses of microsatellite DNA variation, reflecting patterns of dispersal, population stability, and local effective population sizes. Complementary genetic inferences suggested samples from migratory corridors housed a mixture of fish from tributaries, as predicted based on assumed migratory life histories in those habitats. Also as predicted, populations presumed to have greater proportions of migratory fish or from physically connected, large, or high quality habitats had higher genetic variability and reduced genetic differentiation from other populations. Populations thought to contain largely non-migratory individuals generally showed the opposite pattern, suggesting behavioral isolation. Estimated effective sizes were small, and we identified significant and severe genetic bottlenecks in several populations that were isolated, recently founded, or that inhabit streams that desiccate frequently. Overall, this work suggested that Lahontan cutthroat trout populations in stream networks are affected by a combination of landscape and metapopulation processes. Results also demonstrated that genetic patterns can reveal unexpected processes, even within a system that is well studied from a conventional ecological perspective.     

Effects of landscape spatial structure on movement patterns of the hispid cotton rat (Sigmodon hispidus)

A large-scale experimental landscape study was conducted to examine the use of corridors and the forest matrix habitat by the hispid cotton rat (Sigmodon hispidus). The role of micro- habitat selection by S. hispidus in influencing routes of movement was also investigated. The experimental landscape consisted of ten 1.64-ha patches (each 128×128 m) established in a loblolly (Pinus teada) forest. Four of the patches were isolated while the other six were connected in pairs by a 32-m wide corridor. Cotton rats (N=96) were simultaneously released into both an isolated and connected patch, and monitored by radiotelemetry for 10 days. We found that the forest matrix was not a barrier to movements of cotton rats. Fifty percent of the cotton rats moved through the matrix. Corridors had no significant effect on the number of animals leaving connected patches (60%) compared to isolated patches (50%). However, corridors were the preferred route to leave a connected patch. Colonization success for cotton rats leaving connected and isolated patches did not significantly differ. Cotton rats exhibited micro-habitat preferences and these preferences differed within patch/corridor and matrix habitats. In patch/corridor habitats, cotton rats selected sites with tall (>1 m) shrubs and high percent cover. In the forest matrix, cotton rats selected sites with abundant cover by vines and low tree canopy cover. Movement patterns of Sigmodon hispidus are not strongly influenced by large-scale landscape spatial structures. Micro-habitat selection, however, does influence movement patterns. These findings have important implications regarding habitat connectivity for small mammals.     

Spatial analysis of roadside Acacia populations on a road network using the network K-function

Spatial patterning of plant distributions has long been recognised as being important in understanding underlying ecological processes. Ripley’s K-function is a frequently used method for studying the spatial pattern of mapped point data in ecology. However, application of this method to point patterns on road networks is inappropriate, as the K-function assumes an infinite homogenous environment in calculating Euclidean distances. A new technique for analysing the distribution of points on a network has been developed, called the network K-function (for univariate analysis) and network cross K-function (for bivariate analysis). To investigate its applicability for ecological data-sets, this method was applied to point location data for roadside populations of three Acacia species in a fragmented agricultural landscape of south-eastern Australia. Kernel estimations of the observed density of spatial point patterns for each species showed strong spatial heterogeneity. Combined univariate and bivariate network K-function analyses confirmed significant clustering of populations at various scales, and spatial patterns of Acacia decora suggests that roadworks activities may have a stronger controlling influence than environmental determinants on population dynamics. The network K-function method will become a useful statistical tool for the analyses of ecological data along roads, field margins, streams and other networks.This revised version was published online in May 2005 with corrections to the Cover Date.     

Impacts of selective logging on tree diversity across a rainforest landscape: the importance of spatial scale

Selective logging of tropical forests imposes spatial pattern on the landscape by creating a mosaic of patches affected by different intensities of disturbance. To understand the ecological impacts of selective logging it is therefore necessary to explore how patterns of tree species composition are affected by this patchy disturbance. This study examines the impacts of selective logging on species composition and spatial patterns of vegetation structure and tree diversity in Sabah, Borneo. We compare tree diversity between logged and unlogged forest at three scales: species richness within plots, species turnover among plots, and total species richness and composition of plots combined. Logging had no effect on tree diversity measured at the smallest scale. Logged forest had a greater rate of species turnover with distance, so at a large spatial scale it supported more tree species than the relatively homogeneous unlogged area. Tree species composition also differed significantly between the two types of forest, with more small dipterocarps and large pioneers in logged forest, and more large dipterocarps in unlogged forest. Our results emphasize the importance of sampling at a sufficiently large scale to represent patterns of biodiversity within tropical forest landscapes. Large areas of production forest in SE Asia are threatened with conversion to commercial crops; our findings show that selectively logged forest can retain considerable conservation value.     

Cumulative effects of roads and logging on landscape structure in the San Juan Mountains,Colorado (USA)

In the southern Rocky Mountains of temperate North America, the effects of Euro-American activities on disturbance regimes and landscape patterns have been less ubiquitous and less straightforward in high-elevation landscapes than in low-elevation landscapes. Despite apparently little change in the natural disturbance regime, there is increasing concern that forest management activities related mainly to timber harvest and to the extensive network of roads constructed to support timber harvest, fire control, and recreation since the late 1800s have altered disturbance regimes and landscape structure. We investigated the magnitude of change in landscape structure resulting from roads and logging since the onset of timber harvest activities in 1950. We found limited evidence for significant impacts in our study area when all lands within the landscape were considered. The relatively minor changes we observed reflected the vast buffering capacity of the large proportion of lands managed for purposes other than timber (e.g., wilderness). Significant changes in landscape structure and fragmentation of mature forest were, however, evident on lands designated as suitable timberlands. Roughly half of the mature coniferous forest was converted to young stands; mean patch size and core area declined by 40% and 25%, respectively, and contrast-weighted edge density increased 2- to 3-fold. Overall, roads had a greater impact on landscape structure than logging in our study area. Indeed, the 3-fold increase in road density between 1950–1993 accounted for most of the changes in landscape configuration associated with mean patch size, edge density, and core area. The extent of area evaluated and the period over which change was evaluated had a large impact on the magnitude of change detected and our conclusions regarding the ecological significance of those changes. Specifically, the cumulative impact on landscape structure was negligible over a 10-year period, but was notable over a 40-year period. In addition, the magnitude of change in landscape structure between 1950–1993 varied as a function of landscape extent. At the scale of the 228000 ha landscape, change in landscape structure was trivial, suggesting that the landscape was capable of fully incorporating the disturbances with minimal impact. However, at intermediate scales of 1000–10000 ha landscapes, change in landscape structure was quite evident, suggesting that there may be an optimal range of scales for detecting changes in landscape structure within the study area.     

Land ownership and landscape structure: a spatial analysis of sixty-six Oregon (USA) Coast Range watersheds

Patterns of land ownership and forest cover are related in complex and ecologically significant ways. Using a Geographic Information System and regression analysis, we tested for spatial relationships between the structure of land ownership and forest cover across 66 watersheds in the state of Oregon (USA), Coast Range mountains. We found that in these watersheds (1) forest cover diversity increased with land ownership diversity, (2) size of forest patches increased with size of land ownership patches, and (3) connectivity of forest cover increased with connectivity of land ownership. Land ownership structure explained between 29% and 40% of the variability of forest cover structure across these watersheds. Driving this relationship are unique associations among particular ownership classes and various forest cover classes. The USDA Forest Service and the USDI Bureau of Land Management were associated with mature forest cover; private industry was associated with young forest cover; nonindustrial private forest owners were associated with a wide diversity of cover classes. Watersheds with mixed ownership appear to provide greater forest cover diversity, whereas watersheds with concentrated ownership provide less diverse but more connected forest cover. Results suggest that land ownership patterns are strongly correlated with forest cover patterns. Therefore, understanding landscape structure requires consideration of land ownership institutions, dynamics, and patterns.This revised version was published online in May 2005 with corrections to the Cover Date.     

Impacts of road corridors on urban landscape pattern: a gradient analysis with changing grain size in Shanghai, China

Urbanization is one of the most important driving forces for land use and land cover change. Quantifying urban landscape pattern and its change is fundamental for monitoring and assessing ecological and socioeconomic consequences of urbanization. As the largest city in the country, Shanghai is now the fastest growing city in China. Using land use data set of 2002 and combining gradient analysis with landscape metrics, we analyzed landscape pattern of Shanghai with increasing grain size to study the impacts of road corridors on urban landscape pattern. Landscape metrics were computed along a 51×9 km² transect cutting across Shanghai with a moving window. The results showed that the urban landscape pattern of Shanghai was greatly changed when road corridors were merged with urban patches and the variation of patch density would alter when grain size changed. As a linear land use type, road corridors exhibited a different spatial signature comparing with other land use types and distinctive behavior with increasing grain size. Merging road and urban patches resulted in a sharp reduction in patch density, mainly caused by segmentation of roads corridors. The results suggested that grain size around 7.5 m might be optimal for urban landscape analysis. Landscape patch density is significantly correlated with road percent coverage and the most important effect of road corridors in urban landscape is increased habitat fragmentation.