Stable Isotope Signatures and Landscape Functioning in Banded Vegetation in Arid-Central Australia

We examined how the measurement of stable carbon and nitrogen isotopes in soils, vegetation and invertebrates can contribute to understanding landscape processes in mulga Acacia aneura ecosystems characterised by alternating wooded groves and intergroves. Our analyses showed that greater leakiness of water from intergroves at the landscape scale tended to promote more conserving physiology at the plant scale. Thus isolated mulga trees in intergroves probably have higher water use efficiency than those in groves. Both trees and grasses in the intergroves have a greater reliance on recycled nitrogen than plants in the groves for which recently fixed N was a substantial source. Grasses in the intergroves had higher N concentrations than those in the groves despite the soil having lower N concentrations. A lack of variation in the isotopic signature of surface soil N suggested that the lower N concentrations in soils of intergroves than groves is due to lower rates of input and not shorter residence times. Stable isotopic signatures of invertebrates showed a diversity of feeding strategies amongst termite species and indicated symbiotic N fixation in two species. There was no relationship between the dependence on N fixation and the habitat preference or diet of termites. Our results suggest that with cautious interpretation, stable isotope signatures could contribute to understanding other ecosystems where patch-interpatch functioning is an important landscape process.     

Blowing in the wind? Nutrient enrichment of remnant woodlands in an agricultural landscape

Increasing fertiliser use in agricultural landscapes is likely to threaten the viability of remnant native vegetation in many parts of the world. Australia’s prime grain production landscapes have nutrient poor soils, which formerly supported semi-arid woodland. The ecological function and capacity for regeneration of these remnants may be particularly susceptible to nutrient enrichment. The key sources of nutrients are wind and water deposition from crop fertilisation, and manure and feed from sheep. We hypothesised that these sources would result in unequal deposition of nutrients within and among remnant vegetation patches. We surveyed soil nutrients (Total N, Available P and K, C:N ratio, and soil pH) in the edges and interiors of 60 remnant woodland patches of various sizes, and in adjacent cultivated paddocks. Nutrient load was negatively correlated with remnant size and patterns were particularly strong for available P. Small remnant patches (<3 ha) were accumulation zones for nutrients, with levels comparable or higher than within crop lands. The patterns are consistent with the hypothesis that small remnants are strongly enriched as a result of being used for livestock shelter. In larger remnants, the primary cause of enrichment is consistent with edge accumulation of nutrients due to wind and water movement. In large patches, remnant edges, particularly the windward edge, were elevated compared to interiors of large patches. In these semi-arid crop lands, current trends in intensification of cropping and a shift away from livestock may reduce the input of nutrients to small patches but increase the nutrient threat to larger remnants.     

The behavior of landscape metrics commonly used in the study of habitat fragmentation

A meaningful interpretation of landscape metrics is possible only when the limitations of each measure are fully understood, the range of attainable values is known, and the user is aware of potential shifts in the range of values due to characteristics of landscape patches. To examine the behavior of landscape metrics, we generated artificial landscapes that mimicked fragmentation processes while controlling the size and shape of patches in the landscape and the mode of disturbance growth. We developed nine series of increasingly fragmented landscapes and used these to investigate the behavior of edge density, contagion, mean nearest neighbor distance, mean proximity index, perimeter-area fractal dimension, and mass fractal dimension. We found that most of the measures were highly correlated, especially contagion and edge density, which had a near-perfect inverse correspondence. Many of the measures were linearly-associated with increasing disturbance until the proportion of disturbance on the landscape was approximately 0.40, with non-linear associations at higher proportions. None of the measures was able to differentiate between landscape patterns characterized by dispersed versus aggregated patches. The highest attainable value of each measure was altered by either patch size or shape, and in some cases, by both attributes. We summarize our findings by discussing the utility of each metric.     

Matrix is important for mammals in landscapes with small amounts of native forest habitat

Acknowledgment that the matrix matters in conserving wildlife in human-modified landscapes is increasing. However, the complex interactions of habitat loss, habitat fragmentation, habitat condition and land use have confounded attempts to disentangle the relative importance of properties of the landscape mosaic, including the matrix. To this end, we controlled for the amount of remnant forest habitat and the level of fragmentation to examine mammal species richness in human-modified landscapes of varying levels of matrix development intensity and patch attributes. We postulated seven alternative models of various patch habitat, landscape and matrix influences on mammal species richness and then tested these models using generalized linear mixed-effects models within an information theoretic framework. Matrix attributes were the most important determinants of terrestrial mammal species richness; matrix development intensity had a strong negative effect and vegetation structural complexity of the matrix had a strong positive effect. Distance to the nearest remnant forest habitat was relatively unimportant. Matrix habitat attributes are potentially a more important indicator of isolation of remnant forest patches than measures of distance to the nearest patch. We conclude that a structurally complex matrix within a human-modified landscape can provide supplementary habitat resources and increase the probability of movement across the landscape, thereby increasing mammal species richness in modified landscapes.     

Out on a limb: habitat use of a specialist folivore, the koala, at the edge of its range in a modified semi-arid landscape

Habitat loss and natural catastrophes reduce the resources available to animals. Species can persist if they have access to additional resources and habitats through the processes of landscape complementation and supplementation. In arid and semi-arid ecosystems, where productivity is limited by precipitation, the impact of landscape change and prolonged drought is severe on specialist species whose range boundaries are limited by aridity. We examined the pattern of occurrence by a specialist arboreal folivore, the koala, at the periphery of its biogeographic range, in a semi-arid rangeland landscape. We used hierarchical mixed modelling to examine the effect of landscape change on koala populations and their habitat use during and after a prolonged drought. We found that the tree species and the distance of a site from water courses were the most important determinants for koala presence in these landscapes. Koalas were predominantly detected in riverine habitat along the water courses, which are primary habitat and provide refugia in times of drought and extreme heat. There was a strong positive effect from the interaction between the amount of primary and secondary habitat in the landscape, although individually, the amount of each of these habitats was not important. This shows koalas will persist in more intact landscapes. There was no difference in habitat use between dry and wet years, but we consider that it can take several wet seasons for koalas to expand into habitats away from water courses.     

Agricultural soil redistribution and landscape complexity

A number of hypotheses and conceptual models, particularly those emphasizing nonlinear dynamics and self-organization, postulate increases or decreases in complexity in the evolution of drainage basins, topography, soils, ecosystems, and other earth surface systems. Accordingly, it is important to determine under what circumstances and at what scales either trend might occur. This paper is concerned with changes in soil landscape complexity due to redistribution of sediment by fluvial, aeolian, and tillage processes at historical time scales in an agricultural field system near Grifton, North Carolina. Soil mapping and soil stratigraphic investigations were used to identify and map soil changes associated with erosion and deposition by water, wind, and tillage; reconstruct the pre-agricultural soil pattern; and identify transformations between soil types. The Kolmogorov entropy of the pre- and post- agricultural landscapes was then compared. The soil transformations associated with erosion and deposition created four distinct new soils and made possible new transformations among soil series, increasing the number of soil types from seven to 11 and the number of possible transformations from 14 to 22. However, the entropy and complexity of the soil landscape decreased, with associated increases in information and redundancy. The mass redistributions created a lower-entropy landscape by concentrating particular soils and soil transformations in specific landscape settings. This result is contrary to studies showing a trend toward increasing pedological complexity at comparable spatial scales, but over much longer time scales. These results point to the importance of temporal scale, and to the fact that environmental complexity is influenced by factors other than the number of different landscape units present.     

Effects of interactive scale-dependent variables on beetle diversity patterns in a semi-arid agricultural landscape

Understanding species-diversity patterns in heterogeneous landscapes invites comprehensive research on how scale-dependent processes interact across scales. We used two common beetle families (Tenebrionidae, detrivores; Carabidae, predators) to conduct such a study in the heterogeneous semi-arid landscape of the Southern Judean Lowland (SJL) of Israel, currently undergoing intensive fragmentation. Beetles were censused in 25 different-sized patches (500–40,000 m²). We used Fisher’s α and non-parametric extrapolators to estimate species diversity from 11,125 individuals belonging to 56 species. Patch characteristics (plant species diversity and cover, soil cover and degree of stoniness) were measured by field transects. Spatial variables (patch size, shape, physiognomy and connectivity) and landscape characteristics were analyzed by GIS and remote-sensing applications. Both patch-scale and landscape-scale variables affected beetle species diversity. Path-analysis models showed that landscape-scale variables had the strongest effect on carabid diversity in all patches. The tenebrionids responded differently: both patch-scale and landscape-scale variables affected species diversity in small patches, while mainly patch-scale variables affected species diversity in large patches. Most of the paths affected species diversity both directly and indirectly, combining the effects of both patch-scale and landscape-scale variables. These results match the biology of the two beetle families: Tenebrionidae, the less mobile and more site-attached family, responded to the environment in a fine-grained manner, while the highly dispersed Carabidae responded to the environment in a coarse-grained manner. We suggest that understanding abiotic and biotic variable interactions across scales has important consequences for our knowledge of community structure and species diversity patterns at large spatial scales.     

Landscape characteristics of disturbed shrubsteppe habitats in southwestern Idaho (U.S.A.)

We compared 5 zones in shrubsteppe habitats of southwestern Idaho to determine the effect of differing disturbance combinations on landscapes that once shared historically similar disturbance regimes. The primary consequence of agriculture, wildfires, and extensive fires ignited by the military during training activities was loss of native shrubs from the landscape. Agriculture created large square blocks on the landscape, and the landscape contained fewer small patches and more large shrub patches than non-agricultural areas. In contrast, fires left a more fragmented landscape. Repeated fires did not change the distribution of patch sizes, but decreased the total area of remaining shrublands and increased the distance between remaining shrub patches that provide seed sources. Military training with tracked vehicles was associated with a landscape characterized by small, closely spaced, shrub patches.Our results support the general model hypothesized for conversion of shrublands to annual grasslands by disturbance. Larger shrub patches in our region, historically resistant to fire spread and large-scale fires because of a perennial bunchgrass understory, were more fragmented than small patches. Presence of cheatgrass (Bromus tectorum), an exotic annual, was positively related to landscape patchiness and negatively related to number of shrub cells. Thus, cheatgrass dominance can contribute to further fragmentation and loss of the shrub patch by facilitating spread of subsequent fires, carried by continuous fuels, through the patch. The synergistic processes of fragmentation of shrub patches by disturbance, invasion and subsequent dominance by exotic annuals, and fire are converting shrubsteppe in southwestern Idaho to a new state dominated by exotic annual grasslands and high fire frequencies.     

Studying the spatial evolutionary behavior of urban forest patches from the perspective of pattern-process relationships

Urban forest dynamics can influence the provision of ecosystem services provision. Considerable research has been conducted to understand how these dynamics respond to urbanization, from individual patches to entire landscapes. However, most of these are cross-sectional studies based on landscape metrics, and research using a process-based perspective in this context is scarce. In this study, we present a “pattern-process” analytical framework to quantify the evolutionary behavior of urban forest patches. We combine this framework with land cover classification data based on high-resolution remote sensing images (< 1 m) from 2002, 2013, and 2019 to detect the dynamic characteristics of four processes of forest patches in Beijing urban areas. These dynamic characteristics include: size distribution, aggregation and fragmentation, transfer, and self-stabilization. The results showed that 1) the average size of the patches in the study area is increasing, and patches larger than 50 m² have a more positive influence on the process of patch structure evolution, 2) patch fragmentation shifts with the direction of urban sprawl, 3) transfer between urban forest and bare land is increasing, and 4) urban forest network construction positively enhances the stability of patches. This framework can provide a useful basis for understanding the spatial and temporal evolution of urban forest landscapes during urban development and contribute to the sustainable management of urban forests.     

From supply to social demand: a landscape-scale analysis of the water regulation service

Worldwide water managers and policy makers are faced by the increasing demands for limited and scarce water resources, particularly in semi-arid ecosystems. This study assesses water regulation service in semi-arid ecosystems of the southeastern Iberian Peninsula. Comparisons between the supply–demand sides were analyzed across different landscape units. We mapped the biophysical supply as the potential groundwater recharged by aquifers and water supplies from reservoirs. The social demand was focused on an analysis of water consumed or used for irrigation and the stakeholder’s perceptions regarding water regulation importance and vulnerability. Results show that some landscape units are able to maintain and conserve water regulation service when the volume of recharge water by aquifers and the water supply from reservoirs is greater than its consumption (e.g. rural landscape units). However, we also found potential social conflicts in landscape units where water consumption and use is much greater than the water recharge and supply. This particularly occurs in the non-protected littoral areas with the highest water consumption and where water is perceived as a non-important and vulnerable natural resource. Overall, our results emphasized the importance of assessing ecosystem services from both supply to demand sides, for identifying social conflicts and potential trade-offs, and to provide practical information about how to integrate the ecosystem service research into landscape management and planning.     

How is Shrub Cover Related to Soil Moisture and Patch Geometry in the Fragmented Landscape of the Northern Negev desert?

Among the major challenges of landscape ecologists is to develop relatively simple models to quantify ecological processes over large areas. Application of such models can be well demonstrated in fragmented semi-arid ecosystems where competition over resources is intense due to habitat loss, however, only a few studies have done so. Our aim was to model and study the integrated effect of spatial variation in potential soil moisture and patch size and shape on shrub–grass ratio (SGR) in a semi-arid fragmented environment. We specifically ask: (i) what factors most strongly relate to SGR in large remnant patches (> 1.6 ha), and (ii) do different factors more strongly relate to SGR in small patches (< 1.6 ha)? The study was carried out using 60 patches within a semi-arid fragmented environment in the Northern Negev of Israel. Aerial photographs and digital elevation models were used to map six environmental variables: wetness index, aspect, rock cover, rock pattern, patch area, and patch shape. The variables were designed in GIS and were modeled using fuzzy logic procedures to predict SGR, and these predictions were compared to shrub cover maps extracted using maximum likelihood classification of aerial photographs taken in September 2003. We found that in the study area, factors indicating potential soil moisture are most strongly related to SGR in large patches, whereas patch geometric attributes are more strongly relate to SGR in small patches.     

The influence of forest harvesting on landscape spatial patterns and old-growth-forest fragmentation in southeast British Columbia

Habitat fragmentation is considered one of the major conservation issues of recent decades. We tested predictions of landscape patterns in a 352,253-ha managed forest area in southeast British Columbia. We did this by focussing on forest fragmentation concerns among old-growth, harvest, and wildfire patches in 44 delineated landscapes using patch indices as measures of landscape pattern. We found no significant association between amount of harvesting and 15 old-growth patch indices. Comparisons among patch types revealed that amounts and spatial patterns of harvest patches differed little from amounts and spatial patterns of old-growth patches in control landscapes. Variability indices revealed similar variability between harvest patches and old-growth patches, and more variability between harvest patches and wildfire patches. Little of the evidence gathered in this study supported predictions of fragmentation of old-growth spatial patterns, or predicted differences between harvest spatial patterns and more naturally occurring spatial patterns. We suggest these results could be due to the relatively small amounts of harvesting and old-growth forest in these landscapes, and therefore habitat amount may be a more important factor than spatial configuration of patches in these landscapes.     

Spatial pattern of coniferous and deciduous forest patches in an Eastern North America agricultural landscape: the influence of land use and physical attributes

In agricultural landscapes, most studies have investigated the influence of the spatial pattern of forest patches on other ecological phenomena and processes, such as animal movement and biodiversity. However, few have focused on explaining the spatial pattern of the forest patches themselves. Understanding how these patterns relate to the processes that generate them is fundamental in developing a sound theory of landscape ecology, and in devising rational management strategies. In this paper, the pattern of the overall forest patches, as well as the pattern of deciduous and coniferous patches in an agricultural landscape of Southern Quebec, Canada, were analyzed and related to landscape physical attributes and land use, using remote sensing, geographic information systems and statistical methods. Results show that the role of landscape physical attributes on forest patch pattern has been modified by land use. In the study area, coniferous or deciduous patches are not associated with a specific surface deposit. In addition, physical attributes explain only a small proportion of the abundance of conifers on past abandoned land compared with land-use factors. Physical attributes only indirectly influence the forest pattern because they strongly influence the land-use practices. Our results reveal a conifer recovery process with the abandonment of agricultural land. On past abandoned land, conifers expand with increasing stand age, mostly by invasion from neighboring coniferous patches. Spatially, coniferous patches are usually located on the margins of the overall forest patches, and they are connected to non-forest land-use types such as crop and pasture, the latter being the most important. By showing the importance of some coniferous forest types that did not exist in the precolonial forest, a new perspective emerges when landscape, especially, land-use dynamics are taken into account.     

Spatio-temporal variation in the demographic attributes of a generalist mesopredator

Human land-use practices have dramatically altered the composition and configuration of native habitats throughout many ecosystems. Within heterogeneous landscapes generalist predators often thrive, causing cascading effects on local biological communities, yet there are few data to suggest how attributes of fragmentation influence local population dynamics of these species. We monitored 25 raccoon (Procyon lotor) populations from 2004 to 2009 in a fragmented agricultural landscape to evaluate the influence of local and landscape habitat attributes on spatial and temporal variation in demography. Our results indicate that agricultural ecosystems support increased densities of raccoons relative to many other rural landscapes, but that spatial and temporal variation in demography exists that is driven by non-agricultural habitat attributes rather than the availability of crops. At the landscape scale, both density and population stability were positively associated with the size and contiguity of forest patches, while at the local scale density was positively correlated with plant diversity and the density of tree cavities. In addition, populations occupying forest patches with greater levels of plant diversity and stable water resources exhibited less temporal variability than populations with limited plant species complexity or water availability. The proportion of populations comprised of females was most strongly influenced by the availability of tree cavities and soft mast. Despite the abundance of mesopredators in heterogeneous landscapes, our results indicate that all patches do not contribute equally to the regional abundance and persistence of these species. Thus, a clear understanding of how landscape attributes contribute to variation in demography is critical to the optimization of management strategies.     

A leakiness index for assessing landscape function using remote sensing

The cover, number, size, shape, spatial arrangement and orientation of vegetation patches are attributes that have been used to indicate how well landscapes function to retain, not ‘leak’, vital system resources such as rainwater and soil. We derived and tested a directional leakiness index (DLI) for this resource retention function. We used simulated landscape maps where resource flows over map surfaces were directional and where landscape patch attributes were known. Although DLI was most strongly related to patch cover, it also logically related to patch number, size, shape, arrangement and orientation. If the direction of resource flow is multi-directional, a variant of DLI, the multi-directional leakiness index (MDLI) can be used. The utility of DLI and MDLI was demonstrated by applying these indices to three Australian savanna landscapes differing in their remotely sensed vegetation patch attributes. These leakiness indices clearly positioned these three landscapes along a function-dysfunction continuum, where dysfunctional landscapes are leaky (poorly retain resources). This revised version was published online in July 2006 with corrections to the Cover Date.     

Structural dynamic of a hedgerow network landscape in Brittany France

Changes in agricultural systems since the 50's led to considerable changes in rural hedgerow network landscapes. In these landscapes, ecological processes depend on the spatial structure of the network (length of hedgerows, connectedness, grain size). This paper reports on a study of the dynamics of such a landscape at four periods of time (1952, 1961, 1972, 1985) done on 26 contiguous 16 ha quadrats. A correspondence analysis of the data matrix yields a gradient of change from dense highly connected networks to heterogeneous landscapes with few hedgerows. The study of individual trajectories of the quadrats allowed them to be regrouped in various types of changes. It is possible for a quadrat to go through several pathways. Rates of change varied through time, the 1961–1972 period had most changes. The use of supplementary elements in correspondence analysis proves to be a useful way to approach spatial hierarchy and allows a better understanding of the differentiation of landscape units.     

Energy hierarchy and landscape sustainability

The study of ecosystems suggests principles by which energy flows generate hierarchies in all systems. All ecosystems in the landscapes are associated with energy transformation and the convergence of transformed products toward higher hierarchical levels, the recycling of materials to dispersed backgrounds, and feedbacks to reinforce the supporting environment. A hierarchy can be seen as an organized pattern with many small units at one level contributing to fewer units at the next higher level. Due to spatial variability in the natural environment, different types and amounts of energy received on the earth are not homogeneous; this in turn generates a heterogeneous pattern on the landscape. Energy from life-support and production systems of a heterogeneous landscape is transformed and converged spatially toward consumption centers. All energy transformation can be arranged in a series. The concept of transformity is used in this paper to indicate the position of an energy flow in the series. A hierarchical system can help to explain how energy and matter can be produced and recycled through each level of energy transfer. Building on the brief reviews of the concept of hierarchy in the landscape and the theoretical development of the concept of an ecological energetic hierarchy, this paper proposes two principles of energetic hierarchy for landscape sustainability. First, the landscape must be arranged spatially according to its energy hierarchy. Evaluation of normalized energy flows (emergy) can help identify zones of different spatial hierarchies, which will help establish the strategies needed for the landscapes to be sustainable. Second, a sustainable landscape must comprise a hierarchy of self-organizing ecosystems that can enable the systems to maximize useful power at all levels of the energy hierarchy.     

Resource landscapes and movement strategy shape Queensland Fruit Fly population dynamics

Context

Animal population dynamics are shaped by their movement decisions in response to spatial and temporal resource availability across landscapes. The sporadic availability and diversity of resources can create highly dynamic systems. This is especially true in agro-ecological landscapes where the dynamic interplay of insect movement and heterogeneous landscapes hampers prediction of their spatio-temporal dynamics and population size.

Objectives

We therefore systematically looked at population-level consequences of different movement strategies in temporally-dynamic resource landscapes for an insect species whose movement strategy is slightly understood: the Queensland Fruit Fly (Bactrocera tryoni)

Methods

We developed a spatially-explicit model to predict changes in population dynamics and sizes in response to varying resources across a landscape. We simulated the temporal dynamics of fruit trees as the main resource using empirical fruiting dates. Movement strategies were derived from general principles and varied in directedness of movement and movement trigger.

Results

We showed that temporal continuity in resource availability was the main contributing factor for large and persistent populations. This explicitly included presence of continuous low-density resources such as fruit trees in urban areas. Analysing trapping data from SE Australia supported this finding. We also found strong effects of movement strategies, with directed movement supporting higher population densities.

Conclusions

These results give insight into structuring processes of spatial population dynamics of Queensland Fruit Fly in realistic and complex food production landscapes, but can also be extended to other systems. Such mechanistic understanding will help to improve forecasting of spatio-temporal hotspots and bottlenecks and will, in the end, enable more targeted population management.

     

Interaction of food resources and landscape structure in determining the probability of patch use by carnivores in fragmented landscapes

Studies on the distribution of mammalian carnivores in fragmented landscapes have focused mainly on structural aspects such as patch and landscape features; similarly, habitat connectivity is usually associated with landscape structure. The influence of food resources on carnivore patch use and the important effect on habitat connectivity have been overlooked. The aim of this study is to evaluate the relative importance of food resources on patch use patterns and to test if food availability can overcome structural constraints on patch use. We carried out a patch-use survey of two carnivores: the beech marten (Martes foina) and the badger (Meles meles) in a sample of 39 woodland patches in a fragmented landscape in central Italy. We used the logistic model to investigate the relative effects on carnivore distribution of patch, patch neighbourhood and landscape scale variables as well as the relative abundance of food resources. Our results show how carnivore movements in fragmented landscapes are determined not only by patch/landscape structure but also by the relative abundance of food resources. The important take-home message of our research is that, within certain structural limits (e.g. within certain limits of patch isolation), by modifying the relative amount of resources and their distribution, it is possible to increase suitability in smaller/relatively isolated patches. Conversely, however, there are certain thresholds above which an increase in resources will not achieve high probability of presence. Our findings have important and generalizable consequences for highly fragmented landscapes in areas where it may not be possible to increase patch sizes and/or reduce isolation so, for instance, forest regimes that will increase resource availability could be implemented. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Sacrificing patches for linear habitat elements enhances metapopulation performance of woodland birds in fragmented landscapes

It is generally assumed that large patches of natural habitat are better for the survival of species than the same amount of habitat in smaller fragments or linear elements like hedges and tree rows. We use a spatially explicit individual-based model of a woodland bird to explore this hypothesis. We specifically ask whether mixtures of large, small and linear habitat elements are better for population performance than landscapes that consist of only large elements. With equal carrying capacity, metapopulations perform equally or better in heterogeneous landscape types that are a mix of linear, large and small habitat elements. We call this increased metapopulation performance of large and small elements “synergy”. These mixed conditions are superior because the small linear elements facilitate dispersal while patches secure the population in the long run because they have a lower extinction risk. The linear elements are able to catch and guide dispersing animals which results in higher connectivity between patches leading to higher metapopulation survival. Our results suggest that landscape designers should not always seek to conserve and create larger units but might better strive for more variable landscapes with mixtures of patch sizes and shapes. This is especially important when smaller units play a key role in connecting patches and dispersal through the matrix is poor.