Biodiversity and ecological value of conservation lands in agricultural landscapes of southern Ontario,Canada

In eastern North America, large forest patches have been the primary target of biodiversity conservation. This conservation strategy ignores land units that combine to form the complex emergent rural landscapes typical of this region. In addition, many studies have focussed on one wildlife group at a single spatial scale. In this paper, studies of avian and anuran populations at regional and landscape scales have been integrated to assess the ecological value of agricultural mosaics in southern Ontario on the basis of the maintenance of faunal biodiversity. Field surveys of avian and anuran populations were conducted between 2001 and 2004 at the watershed and sub-watershed levels. The ecological values of land units were based on a combination of several components including species richness, species of conservation concern (rarity), abundance, and landscape parameters (patch size and connectivity). It was determined that habitats such as thicket swamps, coniferous plantations and cultural savannas can play an important role in the overall biodiversity and ecological value of the agricultural landscape. Thicket swamps at the edge of agricultural fields or roads provided excellent breeding habitat for anurans. Coniferous plantations and cultural savannas attracted many birds of conservation concern. In many cases, the land units that provided high ecological value for birds did not score well for frogs. Higher scores for avian and anuran populations were recorded along the Niagara Escarpment and other protected areas as expected. However, some private land areas scored high, some spatially connected to the protected areas and therefore providing an opportunity for private land owners to enter into a management arrangement with the local agencies.     

Estimates of dryland degradation in Argentina with Fourier signatures from low-altitude monochromatic images with high spatial resolution

Most world drylands are used as graziny lands and undergo degradation of their vegetation cover. The plant cover is typically structured in patchy arrangements, inducing fertility islands critical to maintenance of ecosystem properties. The characteristics of patch structure (size of patches, connectivity-continuity of patch units, etc.) are indicators of the degree of dryland deterioration. We characterized changes in patch structure induced by sheep grazing at a landscape scale using monochromatic low-altitude imagery digitized to a spatial resolution of about 1 m with standard techniques of harmonic analysis applied to develop Fourier signatures. The signatures developed on image line transects were tested with ground samples and mathematical models of plant cover in several dryland fields where spatial deterioration gradients existed. The sensitivity and errors associated to long-wave noise introduced by the geometry of the camera-field-sun spatial arrangement and to high frequency noise introduced by the digitizing process were evaluated by applying suitable filters in the frequency domain. Fourier signatures developed on monochromatic low-altitude imagery proved to be indicative of changes in the patching arrangements of plant cover. We concluded that adequately filtered, high spatial resolution monochromatic images can be used to evaluate the degree of deterioration of dryland landscapes through the computation of selected Fourier signatures in their frequency domain. At comparable cost, aerial photography allows inspecting the landscape at higher spatial resolutions than those attainable with satellite imagery. Also, aerial photos of many areas are available for earlier dates than images from remote sensors, which would allow better inspection of long-term ecosystem changes.This revised version was published online in May 2005 with corrections to the Cover Date.     

Using patch isolation metrics to predict animal movement in binary landscapes

Habitat isolation can affect the distribution and abundance of wildlife, but it is an ambiguous attribute to measure. Presumably, isolation is a characteristic of a habitat patch that reflects how spatially inaccessible it is to dispersing organisms. We identified four isolation metrics (nearest-neighbor distance, Voronoi polygons, proximity index, and habitat buffers) that were representative of the different families of metrics that are commonly used in the literature to measure patch isolation. Using simulated data, we evaluated the ability of each isolation metric to predict animal dispersal. We examined the simulated movement of organisms in two types of landscapes: an artificially-generated point-pattern landscapes where patch size and shape were consistent and only the arrangement of patches varied, and realistic landscapes derived from a geographic information system (GIS) of forest-vegetation maps where patch size, shape, and isolation were variable. We tested the performance of the four isolation metrics by examining the strength of the correlation between observed immigration rate in the simulations and each patch isolation metric. We also evaluated whether each isolation metric would perform consistently under varying conditions of patch size/shape, total amount of habitat in the landscape, and proximity of the patch to the landscape edge. The results indicate that a commonly-used distance-based metric, nearest-neighbor distance, did not adequately predict immigration rate when patch size and shape were variable. Area-informed isolation metrics, such as the amount of available habitat within a given radius of a patch, were most successful at predicting immigration. Overall, the use of area-informed metrics is advocated despite the limitation that these metrics require parameterization to reflect the movement capacity of the organism studied.This revised version was published online in May 2005 with corrections to the Cover Date.     

Evaluation of an algorithm for automatic detection of broad-leaved weeds in spring cereals

Lack of automatic weed detection tools has hampered the adoption of site-specific weed control in cereals. An initial object-oriented algorithm for the automatic detection of broad-leaved weeds in cereals developed by SINTEF ICT (Oslo, Norway) was evaluated. The algorithm (“WeedFinder”) estimates total density and cover of broad-leaved weed seedlings in cereal fields from near-ground red–green–blue images. The ability of “WeedFinder” to predict ‘spray’/‘no spray’ decisions according to a previously suggested spray decision model for spring cereals was tested with images from two wheat fields sown with the normal row spacing of the region, 0.125 m. Applying the decision model as a simple look-up table, “WeedFinder” gave correct spray decisions in 65–85% of the test images. With discriminant analysis, corresponding mean rates were 84–90%. Future versions of “WeedFinder” must be more accurate and accommodate weed species recognition.     

旅游活动对张家界世界地质公园土壤影响的研究

在调查张家界世界地质公园土壤影响形态及影响范围的基础上,对公园游道两边不同距离土壤的硬度、含水率、容重进行了测定和分析,并通过计算各游览区土壤影响指数(SII)来评价旅游活动对公园土壤的综合影响。结果表明:游客活动对张家界世界地质公园土壤产生了较大的影响,特别是在游客相对集中的黄石寨景区和金鞭溪景区,影响十分明显;游客对土壤影响的范围主要发生在距游道两侧3米以内的范围;公园内土壤影响形态可分为单侧节型、双侧节型、单侧链型、双侧链型、十字节型和捷径链型6种类型,其中又以单侧节型和双侧节型为主;在六个景区中,距游道边缘1米、2米及3米范围内土壤的平均含水率较对照区分别低了36.6%、24.5%和2.2%;与对照区相比,距游道边缘1米、2米及3米的土壤硬度分别增加了167.9%、122.2%和15.8%,而距游道边缘1米和2米范围内的土壤容重则分别比对照区增加了26.5%和20.9%。文章对如何降低游客对土壤的影响范围及程度进行了讨论。图4表3参16。     

笼具形状对选育合浦珠母贝幼贝生长的影响

2011年8月,以海南三亚亲贝(♀)×广东徐闻亲贝(♂)构建的第一代选育合浦珠母贝(Pinctadafucata)群体为材料,研究长方形、圆柱形和半球形笼具形状在不同水深对合浦珠母贝幼贝(平均壳长1.4 cm)生长的影响。结果表明,长方形笼具在4 m水深时,幼贝的壳高和体重增长率最大,分别为24.55%和6.44%,显著高于其它水层(P<0.01);半球形笼具在3 m水深时,幼贝壳高和体重增长速度最大,分别为22.55%和5.40%,与其它水深的差异极显著(P<0.01);圆柱形笼具在6 m水深时,壳高和体重增长最快,增长率分别为22.46%和5.37%,显著高于3、5、7 m水深组(P<0.01),而与其余深度组差异不显著。此外,圆柱形笼具的高对合浦珠母贝的生长也有影响,在3 m水层20 cm高的圆柱形笼具中贝壳高和体重增长速度最大(增长率分别为24.70%和6.20%),与5、10、15 cm高度组差异显著(P<0.05);而长方形笼具虽然10 cm高的笼具较好,但与其它各实验组差异并不显著(P>0.05)。综合来看,合浦珠母贝在3～4 m水层用半径11.5 cm、高20 cm的圆柱形笼具或20 cm(长)×12 cm(宽)×10 cm(高)的长方形笼具养殖效果较好。但在制作成本方面,圆柱形笼具的成本低于长方形笼具。     

The influence of canopy patch mosaics on understory plant community composition in boreal mixedwood forest

We assessed the composition of understory vascular plant communities in relation to the mosaic of canopy patch types, and their associated structure and environment, within unmanaged, mature boreal mixedwood forests in western Canada. Within a 30 km² area, we sampled patches of four different canopy types: conifer-dominated, broadleaf-dominated, mixed conifer-broadleaf, and canopy gaps (total n = 98). There were significant differences in understory composition among the four patch types (based on multi-response permutation procedure (MRPP)) and these were mainly due to differences in relative abundances of understory species. The understory communities of conifer patches were characterized by low abundances of shade intolerant species while shade-tolerant and evergreen species were indicators (based on an indicator species analysis (ISA)). Understory communities under gap and broadleaf patches were characterized by higher abundances of grasses and shade intolerant species. Gap, broadleaf, and mixed patches had higher abundances of certain shrub species than did conifer patches. The patch types also differed in terms of their environmental conditions. Conifer patches had drier, cooler soils and the lowest understory light. Broadleaf patches had the warmest soils while understory light during the leaf-off period was similar to that of canopy gaps. Gap patches had the lowest litter cover and PO₄⁻ availability and the highest light. Seven environmental variables (soil moisture, soil temperature, total light during the leaf-off period, cover of coarse and fine downed woody material, and availability of NH₄⁺ and Ca²⁺) were significantly related to understory species composition (in a constrained ordination by means of a distance-based redundancy analysis (db-RDA); 16.5% of variation in understory community data explained). Even within a single patch type, there was substantial environmental variation that was related to understory species composition. Our study suggests that the mosaic of canopy patches within mixedwood forests supports coexistence of both early and late successional understory plant species in mixedwood stands. Maintaining the mixture of canopy patch types within mixedwood stands will be important for conserving the natural patterns of understory plant composition in boreal mixedwood forests.     

Influence of patch and landscape characteristics on the distribution of the subterranean rodent <Emphasis Type="Italic">Ctenomys porteousi</Emphasis>

The understanding and prediction of the responses of animal populations to habitat fragmentation is a central issue in applied ecology. The identification of habitat variables associated to patch occupancy is particularly important when habitat quality is affected by human activities. Here, we analyze the influence of patch and landscape characteristics on patch occupancy by the subterranean herbivorous rodent Ctenomys porteousi. Patch occupancy was monitored in a network of 63 habitat patches identified by satellite imagery analysis which extends along almost the whole distributional range for C. porteousi. Suitable habitat for the occurrence of C. porteousi is highly fragmented and represents <10% of the total area in its distributional range. The distribution of C. porteousi in the patch network is affected not only by characteristics of the habitat patches, but also by those of the surrounding landscape matrix. Significant differences between occupied and empty patches were found in several environmental variables. Overall, occupied patches were larger, less vegetated, more connected, and had larger neighbor patches than empty patches. A stepwise procedure on a generalized linear model selected four habitat variables that explain patch occupancy in C. porteousi; it included the effects of habitat quality in the matrix surrounding the patch, average vegetation cover in the patch, minimum vegetation cover in the matrix surrounding the patch, and the area of the nearest neighbor patch. These results indicate that patch occupancy in C. porteousi is strongly influenced by the availability and quality of habitat both in the patch and in the surrounding landscape matrix.     

The influence of patch-delineation mismatches on multi-temporal landscape pattern analysis

Investigations of land-cover change often employ metrics designed to quantify changes in landscape structure through time, using analyses of land cover maps derived from the classification of remote sensing images from two or more time periods. Unfortunately, the validity of these landscape pattern analyses (LPA) can be compromised by the presence of spurious change, i.e., differences between map products caused by classification error rather than real changes on the ground. To reduce this problem, multi-temporal time series of land-cover maps can be constructed by updating (projecting forward in time) and backdating (projecting backward in time) an existing reference map, wherein regions of change are delineated through bi-temporal change analysis and overlaid onto the reference map. However, this procedure itself creates challenges, because sliver patches can occur in cases where the boundaries of the change regions do not exactly match the land-cover patches in the reference map. In this paper, we describe how sliver patches can inadvertently be created through the backdating and updating of land-cover maps, and document their impact on the magnitude and trajectory of four popular landscape metrics: number of patches (NP), edge density (ED), mean patch size (MPS), and mean shape index (MSI). In our findings, sliver patches led to significant distortions in both the value and temporal behaviour of metrics. In backdated maps, these distortions caused metric trajectories to appear more conservative, suggesting lower rates of change for ED and inverse trajectories for NP, MPS and MSI. In updated maps, slivers caused metric trajectories to appear more extreme and exaggerated, suggesting higher rates of change for all four metrics. Our research underscores the need to eliminate sliver patches from any study dealing with multi-temporal LPA.