Patch Contrast Research Articles

Soil nutrient heterogeneity affects community stability through changing asynchrony in an alpine meadow on the Qinghai-Tibetan Plateau

Soil nutrients are ubiquitously heterogeneously distributed and such heterogeneity can greatly influence plant and population growth, interspecific competition and community structure and productivity. Despite these impacts, it is still unknown how soil nutrient heterogeneity affects community stability. We conducted a three-year experiment in an alpine meadow on the Qinghai-Tibetan Plateau, involving one homogeneous and six heterogeneous treatments of N, P, and K addition. The heterogeneous treatments varied in patch size, patch contrast, and number of patch types. Community stability in the homogeneous treatment tended to be the highest, likely due to high asynchrony among functional groups. However, such effects varied with patch size, patch contrast and number of patch types. Also, the effects of patch contrast and number of patch types on community stability and asynchrony among functional groups depended on patch size. The grass proportion was significantly affected by soil nutrient heterogeneity, and greater number of patch types increased the grass proportion at the small patch size, but not at the large one. Additionally, species richness, Shannon-Weiner index and Simpson index were greater in high patch contrast compared to the homogeneous treatment, but community evenness was not. These results suggest that soil nutrient heterogeneity can influence community stability by modifying functional group asynchrony and community evenness, rather than biomass proportions or other plant diversity indices. Our findings highlight the importance of incorporating soil nutrient heterogeneity in modeling the responses of alpine ecosystems to continuous nitrogen deposition and climate warming.

Spatio-temporal patterns of rangeland forage nutritive value and grazer selection with patch-burning in the US northern Great Plains

Understanding how management influences forage nutritive value and grazer selection within grazing seasons is an ongoing effort for researchers and land managers globally. We used six, 65 ha pastures managed with patch-burn grazing and stocked with either cow-calf pairs (0.45–0.5 ha • AUM−1) or gestating ewes (0.4–0.48 ha • AUM-1) to explore how patterns in rangeland forage drive grazer selection in semi-arid rangeland over four summer grazing seasons at monthly intervals. We used near-infrared spectroscopy to determine nutritive value parameters from monthly forage clippings. We evaluated livestock performance as the average daily weight gains of each animal. We used mixed-effect models and ordination to compare patch and grazer types across the time-since-fire gradient and found that time-since-fire was significant for all measured variables. Cattle and sheep consistently preferred recently burned patches throughout grazing seasons. These recently burned patches typically contained available forage with higher crude protein and moisture content, lower biomass, and lower acid detergent fiber, acid detergent lignin, and neutral detergent fiber compared to intermediate time since fire patches and patches burned three years ago. Differences between patch-burn grazing with cattle and sheep were observed as additional patch contrasts for available biomass and crude protein, but grazer type and ecological site were not statistically significant factors for the nutritive value ordination. Our study indicates that patch-burn grazing is capable of imposing and maintaining heterogeneous, grazer selection, forage biomass, and nutritive value patterns desirable for heterogeneity focused land management, regardless of grazer type. These findings are especially relevant to the northern Great Plains where introduced grasses are homogenizing the structural environment of remaining rangelands. With prescribed fire currently an uncommon practice throughout the region, these findings provide a baseline of expectations for practitioners and land managers implementing patch-burn grazing and illustrate how grazing livestock can benefit from the patch contrast in forage nutritive value and biomass.

Invasive clonal plants possess greater capacity for division of labor than natives in high patch contrast environments.

Invasion success of clonal plants is closely related to their unique clonal life history, and clonal division of labor is a crucial clonal trait. However, so far, it is unclear whether invasive alien clonal species generally possess a greater capacity for division of labor than native species and whether this pattern is affected by environmental conditions. To test whether patch contrast affects the differences in the capacity for division of labor between invasive alien and native clonal plants, we selected five pairs of exotic invasive and native clonal plant species that are congeneric and co-occurring in China as experimental materials. We grew the clonal fragment pairs of these invasive and native plants under high, low, or no contrast of reciprocal patchiness of light and nutrient, respectively, with ramet connections either severed (division of labor prevented) or kept intact (division of labor allowed). The results showed that connection significantly decreased the proportion of biomass allocated to roots in distal (younger) ramets, whereas it increased in proximal (older) ramets of all studied plants under high -contrast treatments. This clear pattern strongly indicated the occurrence of division of labor. Furthermore, the connection had a more pronounced effect on the pattern of biomass allocation of invasive alien plants, resulting in a greater increase in biomass for invasive alien plants compared to native plants. These findings suggest that the invasive alien plants possess a greater capacity for division of labor, which may confer a competitive advantage to them over natives, thus facilitating their invasion success in some heterogeneous habitats such as forest edges where light and soil nutrients show a high negative correlation.

The Plant Invader Alternanthera philoxeroides Benefits from Clonal Integration More than Its Native Co-Genus in Response to Patch Contrast.

Different connected parts of clonal plants often grow in different patches and the resource contrast between patches has an important effect on the material transfer between the connected ramets. However, it is unclear whether the effect of clonal integration differs between the invasive clonal plant and the related native species in response to patch contrast. To explore this, we grew the clonal fragment pairs of plant invader Alternanthera philoxeroides and its co-genus native species A. sessilis under high contrast, low contrast, and no contrast (control) nutrient patch environments, respectively, and with stolon connections either severed or kept intact. The results showed that, at the ramet level, clonal integration (stolon connection) significantly improved the growth of apical ramets of both species, and such positive effects were significantly greater in A. philoxeroides than in A. sessilis. Moreover, clonal integration greatly increased the chlorophyll content index of apical ramets and the growth of basal ramets in A. philoxeroides but not in A. sessilis under low and high contrast. At the whole fragment level, the benefits of clonal integration increased with increasing patch contrast, and such a positive effect was more pronounced in A. philoxeroides than in A. sessilis. This study demonstrated that A. philoxeroides possesses a stronger ability of clonal integration than A. sessilis, especially in patchy environments with a higher degree of heterogeneity, suggesting that clonal integration may give some invasive clonal plants a competitive advantage over native species, thus facilitating their invasion in patchy habitats.

Effects of scale and contrast of spatial heterogeneity in plant-soil feedbacks on plant growth

Spatial heterogeneity in plant-soil feedbacks (PSFs) has been evidenced to influence plant growth. However, it is unclear whether patch size and contrast of PSF heterogeneity influence plant growth. We first conditioned a background soil by seven species separately and then grew each of them in a homogeneous soil and three heterogeneous soils. The first heterogeneous soil (large patch and high contrast; LP-HC) consisted of two large patches, of which one was filled with the sterilized background soil and the other with the conditioned soil. The second heterogeneous soil (small patch and high contrast; SP-HC) consisted of four small patches, of which two were filled the sterilized background soil and the other two with the conditioned soil. The third heterogeneous soil (small patch and low contrast; SP-LC) also consisted of four patches, of which two were filled with a 1:3 (w:w) mixture and the other two with a 3:1 mixture of the sterilized background soil and the conditioned soil. In the homogeneous soil, all patches were filled with a 1:1 mixture of the two soils. Both shoot biomass and root biomass were equal in the homogeneous and heterogeneous soils. No significant growth difference was observed between the SP-HC and LP-HC heterogeneous soil. However, shoot biomass and root biomass of the legume Medicago sativa, and root biomass of the grass Lymus dahuricus were greater in the SP-HC heterogeneous soil than in the SP-LC heterogeneous soil, probably due to enhanced root growth in the conditioned soil. Moreover, plant growth in the heterogeneous soils was associated with plant growth but not soil nutrient availability at the end of the conditioning phase. Our results show for the first time that patch contrast of PSF heterogeneity can influence plant growth via changing root placement and highlight the importance of fundamentally different facets of PSF variability.

Joint spatio-temporal features and sea background prior for infrared dim and small target detection

The detection of dim and small targets in the complex sea background poses new challenges to automatic target search and interception by infrared air-to-air missiles at sea. To solve the problems of low detection rate of dim targets and massive suspected targets caused by the shadow region of clutter on the sea surface, this paper proposes a detection method for dim and small targets with spatio-temporal features and background prior information. Firstly, by combining the ideas of local energy factor and multi-scale patch contrast measure, an improved dim target detection method is proposed, which can effectively enhance the contrast of dim targets and suppress background clutter. Then, according to the grayscale probability distribution difference between the background and the target, a double-Gaussian model is established for the residual background and the target region and a background suppression method based on the spatial prior information is proposed to further suppress the residual background. Finally, a dim target detection method is proposed by combining the above dim target detection, background suppression, and dynamic pipeline filtering methods. The results indicate the average detection rate of the detection method proposed in this study is 91.44%. Also, the average number of false alarms in a single frame is reduced to 9.89, which is more than 80% lower than that of other algorithms.

Human vision-inspired detection for infrared small targets under scaly light background on sea surface

The automatic detection and search of small targets by the infrared guidance system is challenged by the complex sea background environment, particularly the dense scaly light generated by the reflection of sunlight by the sea clutter and the appearance of boundaries. To address this issue, inspired by the significant sensitivity, classification perception, reverse exclusion, and association prediction characteristics of the human visual system, this paper proposes a human vision-inspired detection model for infrared small targets under scaly light background on the sea surface. Firstly, the local energy factor and multi-scale patch contrast measure are fused to construct a significance analysis model and enhance the contrast of the target region of interest. Then, the image is classified into different regions according to the detection of grayscale fluctuations and mutation points in the background, and a region self-classification perception model is constructed for adaptive segmentation of scene images. Next, the prior information of the target gradient is used to construct a reverse exclusion analysis model for suppressing the residual background of the boundary. Subsequently, by using the fluctuation law and characteristic difference of the spatial energy and size features of the target and the scaly light background in the time domain, the correlation prediction analysis model is constructed to further suppress the residual background. Finally, through the combination of the above four visual feature models, a new detector with good adaptability is proposed for small targets under scaly light background on the sea surface. The experimental results indicate that the average detection rate of our detector is 95.26%, and the number of false alarms in a single frame is reduced by 93.77% compared with the typical detectors.

Infrared Small Target Detection Method Based on Weighted Patch Contrast

Infrared Small Target Detection Method Based on Weighted Patch Contrast

Effects of nutrient heterogeneity on root foraging and plant growth at the individual and community level.

Plants enhance nutrient uptake in heterogeneous nutrient environments through selective root placement. Many studies have documented that plants grow better under heterogeneous than under homogeneous nutrient distribution, but comprehensive syntheses are relatively few. In a meta-analysis, we examined the effects of patch scale and contrast on plant responses by synthesizing the effects of nutrient heterogeneity on root foraging and plant growth in 131 comparative studies. Plant responses to nutrient heterogeneity were phylogenetically conserved, and the response in shoot biomass was significantly correlated with the response in root biomass but not with root foraging precision. Root precision depended on the competition regime, and plants had lower precision in interspecific than in conspecific competition. Community-level growth was significantly promoted by nutrient heterogeneity and was less variable than individual-level responses. Along with increasing patch scale, overall shoot and root responses of individuals increased but root foraging precision declined. In addition, moderate patch contrast induced the highest root responses. Our results indicate that plants optimize nutrient acquisition from heterogeneous patches mainly through increasing root growth, and plant communities exploit heterogeneous nutrients more effectively than individuals. Understanding the roles of patch attributes in nutrient-heterogeneity effects may help in designing fertilization practices to promote productivity and conserve biodiversity.

Patch-Burn Grazing Impacts Forage Resources in Subtropical Humid Grazing Lands

Subtropical humid grazing lands represent a large global land use and are important for livestock production, as well as supplying multiple ecosystem services. Patch-burn grazing (PBG) management is applied in temperate grazing lands to enhance environmental and economic sustainability; however, this management system has not been widely tested in subtropical humid grazing lands. The objective of this study was to determine how PBG affected forage resources, in comparison with the business-as-usual full-burn (FB) management in both intensively managed pastures (IMP) and seminative (SN) pastures in subtropical humid grazinglands. We hypothesized that PBG management would create patch contrasts in forage quantity and nutritive value in both IMP and SN pastures, with a greater effect in SN pastures. A randomized block design experiment was established in 2017 with 16 pastures (16 ha each), 8 each in IMP and SN at Archbold Biological Station's Buck Island Ranch in Florida.PBG management employed on IMP and SN resulted in creation of patch contrast in forage nutritive value and biomass metrics, and recent fire increased forage nutritive value. Residual standing biomass was significantly lower in burned patches of each year, creating heterogeneity within both pasture types under PBG. PBG increased digestible forage production in SN but not IMP pastures. These results suggest that PBG may be a useful management tool for enhancing forage nutritive value and creating patch contrast in both SN and IMP, but PBG does not necessarily increase production relative to FB management. The annual increase in tissue quality and digestible forage production in a PBG system as opposed to once every 3 yr in an FB system is an important consideration for ranchers. Economic impacts of PBG and FB management in the two different pasture types are discussed, and we compare and contrast results from subtropical humid grazing lands with continental temperate grazing lands.

Optimal foraging strategies in varying nutrient heterogeneity: responses of a stoloniferous clonal plant to patch pattern, size and quality

ABSTRACT Contrast and aggregation are two components of spatial heterogeneity. To precisely determine the influence of varying nutrient heterogeneity on the foraging behavior of clonal plants, we selected Potentilla anserina L. as the material and designed different patch patterns, sizes and qualities. In Experiment 1, compared with random and uniform patch patterns, aggregation increased ramet density and biomass accumulation at the patch scale, but not at the plot scale. This implies that the adaptive responses of clonal plants to nutrient heterogeneity depend on spatial scale. We further designed three levels of patch size with the same fertilizer concentration at the patch scale in Experiment 2, and four levels of patch quality with the same total amount of fertilizer at the plot scale in Experiment 3. Increased ramet density and stolon growth rate within small patches in Experiment 2 demonstrated effects of heterogeneity on plant foraging responses at the patch scale, while no difference was found in Experiment 3. This means that the influence of patch size on ramet establishment and residence time was alleviated by patch contrast at larger spatial scales. Hence, spatial scale is a key factor determining the interactions between heterogeneous ecosystem components.

Infrared small target detection algorithm based on two-dimensional modal decomposition combined with patch contrast

Infrared small target detection algorithm based on two-dimensional modal decomposition combined with patch contrast

The role of boundary length and adjacent patch contrast in guppy mate choice

Abstract The presence of various combinations of adjacent colors within polymorphic species’ color pattern could have a major impact on mate choice. We studied the role of pattern geometry in predicting mate choice in guppies using boundary strength analysis (BSA). BSA estimates the visual contrast intensity between two adjacent color patches (ΔS) weighted by the lengths of the boundaries between these adjacent color patches. We measured both the chromatic (hue and saturation) and achromatic (luminance) ΔS for each pair of adjacent patches. For each male’s color pattern, we measured BSA as both mean (mΔS) and coefficient of variation (cvΔS) of all ΔS weighted by their corresponding boundary lengths. We also determined if specific color patch boundaries had an impact on female preferences and whether these predicted overall male contrast (mΔS). We found that males with a higher mΔS were more attractive to females and that six boundaries containing either fuzzy black or black as one of the pair colors significantly affected female preferences, indicating that 1) females favored highly conspicuous males and 2) melanin-based patches could be used as a signal amplifier, not only for orange but for other colors.

Effects of soil nutrient heterogeneity and parasitic plant infection on an experimental grassland community

Soil nutrient heterogeneity and parasitic plants have been well-documented to affect plant growth. However, their interactive effects on plant communities have not been tested yet. We assembled plant communities consisting of eight grassland species of three functional groups in one homogeneous soil and four heterogeneous soils consisting of high and low nutrient patches. The heterogeneous soils were manipulated by combining factorially two patch size treatments (large or small patch) with two patch contrast treatments (high or low contrast). All communities were either infected with the holoparasitic plant Cuscuta australis or not. Seven weeks after infection with C. australis, aboveground biomass of the communities was significantly reduced through suppressing the growth of forbs, but not that of grasses or legumes within the communities. Compared to the homogeneous soil, soil heterogeneity overall did not influence the growth of the communities or that of the component functional groups. However, aboveground biomass of the communities was greater in the heterogeneous soil with high patch contrast than in the heterogeneous soil with low patch contrast. A similar pattern was found for the legumes, but aboveground biomass of the forbs or grasses did not show any difference. Patch size did not influence aboveground biomass of the communities, forbs or legumes within the communities. Aboveground biomass of the grasses was greater in the heterogeneous soil with small patches than in the heterogeneous soil with large patches. The effects of C. australis infection on the relative abundance of the forbs, legumes, and grasses varied from negative, neutral to positive. However, the interaction of C. australis infection with soil nutrient heterogeneity, its patch size or patch contrast had little impact on the growth and functional composition of the communities. Our results suggest that parasitic plant infection can influence plant communities by altering the performance of component functional groups, independent of soil nutrient heterogeneity.

The relative importance of local and global visual contrast in mate choice

Colour signals are often made up of a number of colour patches. The position of these patches within a pattern has the potential to influence signal conspicuousness, especially if viewers attend to local rather than global aspects of the colour pattern. If local contrast is important, then signal efficacy should be highest when highly contrasting patches are adjacent; if local contrast is not important, contrasting colours can be anywhere in the pattern. We tested whether global or local colour patch contrast influenced the attractiveness of male guppies, Poecilia reticulata. We assessed contrast on both global and local scales using two methods. The first, overall pattern contrast, estimates the global pattern contrast without accounting for which colours are adjacent. The second, boundary strength analysis, accounts for local contrast by estimating the contrast intensity (ΔS) and contact lengths between adjacent patches. We tested behaviour under three different light environments: blue, broad spectrum (control) and red to modify visual contrast. The light environment had a significant effect on all measures of colour pattern contrast. The male overall pattern contrast measures did not affect female preferences under the three light environments. The coefficient of variation (CV) of chromatic ΔS was the only measure to show a significant effect on female preferences. Females favoured males that displayed high variation in local contrast (high CV of ΔS, independently of the light environment). Therefore, variation in local visual contrast appears to be more important than overall pattern contrast in guppies, regardless of the light environment.

How reliable is my historical land-use reconstruction? Assessing uncertainties in old cadastral maps

Old maps are a fundamental source for land-use reconstruction frequently used in biodiversity conservation and environmental management. In particular, cadastral maps as one type of old maps, depict both land tenure (discrete category) and land-use (continuous category); thus resulting in uncertainties in determination of individual parcels and their use. These uncertainties pose fundamental questions that are addressed in this paper: (i) to what extent land-use determined the delimitation of parcels?; (ii) how significant did the contrast between two land-use classes have to be to in order to delineate a new boundary? Agroforestry land-use classes were chosen as an example to demonstrate the approaches in the delimitation of parcels among different land-use combinations. We used Franciscan Cadastre, created in the mid-19th century under the Habsburg Monarchy (Central Europe), which depicts up to 10 agroforestry classes, to analyse factors that could influence delimitation of borders between patches (parcels) in old cadastral maps. The study area was located in the rural landscape of N Czechia, where approximately 10% of the agroforestry land area was used. We based our analysis on a detailed database of parcels and their land use type and property information. The novel approach to patch contrast indicator for old map analyses is introduced. The approach is based on statistical testing of the differences between parcel boundaries, separating similar/different owner, similar/different land-use and considering the length of the boundaries. Total number of identified parcels for all districts was 4108. Half of the boundaries length and 60% of boundaries count separated land of different owners. The rest of them separated land of one owner with different owner or with distinct parcels geometry. Our results indicate variable contrast between pairs of neighbouring land use categories. In particular, the contrast between pastures, wood-pastures and forests proved to be very low. Various factors, including land ownership, land-use, as well as landscape patch geometry and configuration were important to delineate a single parcel. We have concluded that these factors have important implications on inaccuracies and uncertainties of land use reconstructions based on old cadastral maps and used as historical baselines for current considerations on land change and environmental management.

Effects of patch contrast and arrangement on benefits of clonal integration in a rhizomatous clonal plant.

The availabilities of light and soil water resources usually spatially co-vary in natural habitats, and the spatial pattern of such co-variation may affect the benefits of physiological integration between connected ramets of clonal plants. In a greenhouse experiment, we grew connected or disconnected ramet pairs [consisting of a proximal (relatively old) and a distal (relative young) ramet] of a rhizomatous herb Iris japonica in four heterogeneous environments differing in patch arrangement (reciprocal vs. parallel patchiness of light and soil water) and patch contrast (high vs. low contrast of light and water). Biomass of the proximal part, distal part and clonal fragment of I. japonica were all significantly greater in the intact than in the severed treatment, in the parallel than in the reciprocal patchiness treatment and in the high than in the low contrast treatment, but the effect of severing the connection between ramet pairs did not depend on patch arrangement or contrast. Severing the connection decreased number of ramets of the distal part and the clonal fragment in the parallel patchiness arrangement, but not in the reciprocal patchiness arrangement. Therefore, the spatial arrangement of resource patches can alter the effects of clonal integration on asexual reproduction in I. japonica.

An integrated approach for landscape contrast analysis with particular consideration of small habitats and ecotones

Habitat diversity is considered as an expression of biodiversity at landscape level in addition to genetic and species diversity. Thus, effective methods for measuring habitat pattern at landscape level are crucial for understanding the ecological processes. In this paper we propose to extend the commonly used model Patch Corridor Matrix Model (PCMM) for spatial pattern analysis. Originally, this model assumes discrete structures within the landscape without explicit consideration of “gradients” between patches. The gradients, often called “ecotones”, can be considered as “soft edges” which have a profound influence on adjacent ecosystems. Another part of information that has often been ignored are “small habitats” inside patches (e.g. hedgerows, tree rows, copse, and scattered trees), which leads to within-patch heterogeneity being underestimated. In this paper, the concept of landscape contrast is used to integrate the discrete and gradient landscape representations by incorporating small habitats and ecotones in methods to measure landscape heterogeneity. A height gradient is used to define the ecotones between forest and field. Then, patch contrast (i.e. Edge Contrast Index (ECON)) is calculated based on the height difference between adjacent vegetation patches. Artificial elements (e.g. traffic roads) are considered as barriers which are as signed with the highest edge contrast value. At the landscape level, a metric called Area-Weighted Edge Contrast (AWEC) is introduced to describe the landscape structure. The edge effects of ecotones, small habitats, and traffic roads are incorporated in the calculation of AWEC. Our test examples show that incorporation of ecotones and small habitats can smooth “edge effects” among patches and result in a more realistic quantification of habitat contrast. The contrast concept is especially useful in a vegetated landscape with less human impact. It could be understood as an additional interpretation to fragmentation of habitats with permeable edges among them. Consequently, this presented approach may enhance the understanding of the relationship between landscape pattern and process.

Factors driving structure of natural and anthropogenic forest edges from temperate to boreal ecosystems

AbstractQuestionsWhat factors control broad‐scale variation in edge length and three‐dimensional boundary structure for a large region extending across two biomes? What is the difference in structure between natural and anthropogenic edges?LocationTemperate and boreal forests across all of Sweden, spanning latitudes 55–69° N.MethodsWe sampled more than 2000 forest edges using line intersect sampling in a monitoring programme (National Inventory of Landscapes in Sweden). We compared edge length, ecosystem attributes (width of adjacent ecosystem, canopy cover, canopy height, patch contrast in canopy height, forest type) and boundary attributes (profile, abruptness, shape) of natural edges (lakeshore, wetland) with anthropogenic edges (clear‐cut, agricultural, linear disturbance) in five regions.ResultsAnthropogenic edges were nearly twice as abundant as natural edges. Length of anthropogenic edges was largest in southern regions, while the abundance of natural edges increased towards the north. Edge types displayed unique spectrums of boundary structures, but abrupt edges dominated, constituting 72% of edge length. Anthropogenic edges were more abrupt than natural edges; wetland edges had the most gradual and sinuous boundaries. Canopy cover, canopy height, patch contrast and forest type depended on region, whereas overall boundary abruptness and shape showed no regional pattern. Patch contrast was related to temperature sum (degree days ≥ 5 °C), suggesting that regional variability can be predicted from climate‐controlled forest productivity. Boundary abruptness was coupled with the underlying environmental gradient, land use and forest type, with higher variability in deciduous than in conifer forest.ConclusionsEdge origin, land use, climate and tree species are main drivers of broad‐scale variability in forest edge structure. Our findings have important implications for developing ecological theory that can explain and predict how different factors affect forest edge structure, and help to understand how land use and climate change affect biodiversity at forest edges.

采用图像块对比特性的红外弱小目标检测

采用图像块对比特性的红外弱小目标检测