Landscape-scale Factors Research Articles

Bird-community responses to habitat creation in a long-term, large-scale natural experiment.

Ecosystem function and resilience are compromised when habitats become fragmented due to land-use change. This has led to national and international conservation strategies aimed at restoring habitat extent and improving functional connectivity (i.e., maintaining dispersal processes). However, biodiversity responses to landscape-scale habitat creation and the relative importance of spatial and temporal scales are poorly understood, and there is disagreement over which conservation strategies should be prioritized. We used 160 years of historic post-agricultural woodland creation as a natural experiment to evaluate biodiversity responses to habitat creation in a landscape context. Birds were surveyed in 101 secondary, broadleaf woodlands aged 10-160 years with ≥80% canopy cover and in landscapes with 0-17% broadleaf woodland cover within 3000 m. We used piecewise structural equation modeling to examine the direct and indirect relationships between bird abundance and diversity, ecological continuity, patch characteristics, and landscape structure and quantified the relative conservation value of local and landscape scales for bird communities. Ecological continuity indirectly affected overall bird abundance and species richness through its effects on stand structure, but had a weaker influence (effect size near 0) on the abundance and diversity of species most closely associated with woodland habitats. This was probably because woodlands were rapidly colonized by woodland generalists in ≤10 years (minimum patch age) but were on average too young (median 50 years) to be colonized by woodland specialists. Local patch characteristics were relatively more important than landscape characteristics for bird communities. Based on our results, biodiversity responses to habitat creation depended on local- and landscape-scale factors that interacted across time and space. We suggest that there is a need for further studies that focus on habitat creation in a landscape context and that knowledge gained from studies of habitat fragmentation and loss should be used to inform habitat creation with caution because the outcomes are not necessarily reciprocal.

Landscape-scale processes influence riparian plant composition along a regulated river

Hierarchical frameworks are useful constructs when exploring landscape- and local-scale factors affecting patterns of vegetation in riparian areas. In drylands, which have steep environmental gradients and high habitat heterogeneity, landscape-scale variables, such as climate, can change rapidly along a river's course, affecting the relative influence of environmental variables at different scales. To assess how landscape-scale factors change the structure of riparian vegetation, we measured riparian vegetation composition along the Colorado River through Grand Canyon, determined which factors best explain observed changes, identified how richness and functional diversity vary, and described the implications of our results for river management. Cluster analysis identified three divergent floristic groups that are distributed longitudinally along the river. These groups were distributed along gradients of elevation, temperature and seasonal precipitation, but were not associated with annual precipitation or local-scale factors. Species richness and functional diversity decreased as a function of distance downstream showing that changing landscape-scale factors result in changes to ecosystem characteristics. Species composition and distribution remain closely linked to seasonal precipitation and temperature. These patterns in floristic composition in a semiarid system inform management and provide insights into potential future changes as a result of shifts in climate and changes in flow management.

Temperature drives abundance fluctuations, but spatial dynamics is constrained by landscape configuration: Implications for climate-driven range shift in a butterfly.

Prediction of species distributions in an altered climate requires knowledge on how global- and local-scale factors interact to limit their current distributions. Such knowledge can be gained through studies of spatial population dynamics at climatic range margins. Here, using a butterfly (Pyrgus armoricanus) as model species, we first predicted based on species distribution modelling that its climatically suitable habitats currently extend north of its realized range. Projecting the model into scenarios of future climate, we showed that the distribution of climatically suitable habitats may shift northward by an additional 400km in the future. Second, we used a 13-year monitoring dataset including the majority of all habitat patches at the species northern range margin to assess the synergetic impact of temperature fluctuations and spatial distribution of habitat, microclimatic conditions and habitat quality, on abundance and colonization-extinction dynamics. The fluctuation in abundance between years was almost entirely determined by the variation in temperature during the species larval development. In contrast, colonization and extinction dynamics were better explained by patch area, between-patch connectivity and host plant density. This suggests that the response of the species to future climate change may be limited by future land use and how its host plants respond to climate change. It is, thus, probable that dispersal limitation will prevent P.armoricanus from reaching its potential future distribution. We argue that models of range dynamics should consider the factors influencing metapopulation dynamics, especially at the range edges, and not only broad-scale climate. It includes factors acting at the scale of habitat patches such as habitat quality and microclimate and landscape-scale factors such as the spatial configuration of potentially suitable patches. Knowledge of population dynamics under various environmental conditions, and the incorporation of realistic scenarios of future land use, appears essential to provide predictions useful for actions mitigating the negative effects of climate change.

Local- and landscape-scale land cover affects microclimate and water use in urban gardens

Urban gardens in Central California are highly vulnerable to the effects of climate change, experiencing both extended high heat periods as well as water restrictions because of severe drought conditions. This puts these critical community-based food production systems at risk as California is expected to experience increasing weather extremes. In agricultural systems, increased vegetation complexity, such as greater structure or biodiversity, can increase the resilience of food production systems from climate fluctuations. We test this theory in 15 urban gardens across California's Central Coast. Local- and landscape-scale measures of ground, vegetation, and land cover were collected in and around each garden, while climate loggers recorded temperatures in each garden in 30min increments. Multivariate analyses, using county as a random factor, show that both local- and landscape-scale factors were important. All factors were significant predictors of mean temperature. Tallest vegetation, tree/shrub species richness, grass cover, mulch cover, and landscape level agricultural cover were cooling factors; in contrast, garden size, garden age, rock cover, herbaceous species richness, and landscape level urban cover were warming factors. Results were similar for the maximum temperature analysis except that agriculture land cover and herbaceous species richness were not significant predictors of maximum temperature. Analysis of gardener watering behavior to observed temperatures shows that garden microclimate was significantly related to the number of minutes watered as well as the number of liters of water used per watering event. Thus gardeners seem to respond to garden microclimate in their watering behavior even though this behavior is most probably motivated by a range of other factors such as water regulations and time availability. This research shows that local management of ground cover and vegetation can reduce mean and maximum temperatures in gardens, and the reduced temperatures may influence watering behavior of gardeners.

Effect of the spatial context along the invasion process: “Hierarchical spatial” or “Host-switching spatial” hypotheses?

Very little is known about how spatial effects influence invasive species throughout the invasion sequence. We propose here two mechanisms to explain the changes in spatial effects throughout the stages of invasion, using the soybean aphid (Aphis glycines) as a model. First, the “hierarchical spatial effect” hypothesis, based on a change in the relative importance of the spatial scales throughout the invasion process, with main effect at broad scale during the first years of invasion, and main effect at local scale during the subsequent years. Second, the “host-switching spatial effect” hypothesis, stating that the spatial effect is driven by a switch in the effect of the host/habitat throughout the invasion process, from effect of main summer host/habitat during the first years of invasion to effect of overwintering host/habitat during the subsequent years. Data from governmental archives and field samplings enabled to investigate the spatial effects on aphid density at three scales (regional, landscape, local) during a 7 year period (2006–2012). Our results demonstrate that the hierarchical spatial effect hypothesis is not an adequate model for the soybean aphid, aphid density being more affected by landscape-scale factors irrespective of years. In contrast, our results are in accordance with the host-switching spatial hypothesis, with positive effect of the main summer host/habitat (soybean) during the first steps of invasion (2006–2008), followed by a positive effect of overwintering habitats (buckthorn, woodland) during the subsequent years (2010–2012). Overall, investigating these hypotheses in other systems would determine whether the same tendency is observed for other invasive species.

In-stream habitat predicts salamander occupancy and abundance better than landscape-scale factors within exurban watersheds in a global diversity hotspot

The southern Appalachian Mountains have experienced rapid human population growth rates since the 1980s. Land used practices are shifting from rural to residential. The majority of development has been low density, and is often near biologically diverse areas such as National Forests and National Parks. The long-term effects of urbanization in the southeastern Appalachian Mountains are not clearly understood and even less is known with respect to stream salamander response to urbanization. In order to determine the temporal influence of exurban housing on southern Appalachian streams we sampled 27 first- and second-order streams in watersheds containing exurban developments ranging in age from 4 to 44 years, along with eight forested streams, over the course of two summers. We sought to determine if the relative age of an exurban development related to occupancy and abundance of southern Appalachian stream salamanders. Age of exurban development and other watershed scale variables were not top predictors of salamander assemblages, while local site variables such as salinity and undercut banks predicted the abundance of several species of salamander. Our results suggest local habitat improvements can be used to better conserve salamanders and stream ecosystems in an increasingly urbanized region.

Camera-trap data elucidate habitat requirements and conservation threats to an endangered forest specialist, the Spotted Ground Thrush (Zoothera guttata)

The spotted ground thrush (Zoothera guttata; SGT) is a globally endangered forest specialist whose distribution is poorly understood in the critically endangered Indian Ocean Coastal Belt Forest (IOCBF) biome on the east coast of southern Africa. More than 70% of the IOCBF has been lost to development, resulting in fragmented forest remnants within a mosaic of different land uses. We conducted camera-trap surveys with 5796 trap-days in 82 forest patches of various sizes across a gradient of land-use types in the IOCBF during the winter seasons of 2014–2016 to establish occupancy (Ψ) of SGT. We used occupancy modelling and incorporated forest microhabitat characteristics and surrounding land-use classifications to compare sites and determine SGT distribution across the habitat mosaic. The top model estimated an average Ψ=0.39±0.09, and detection probability (P)=0.11±0.03. At the landscape scale, larger, less isolated patches had a higher Ψ of SGT while P decreased with proximity to cultivated land. At the microhabitat scale, a high percentage of bare ground influenced Ψ positively but P negatively, as did short grass cover. However, short herbaceous cover and high stem density of large (11–15m) trees influenced P positively. These results detail the influence of landscape-scale factors including forest fragmentation and conversion to agriculture in conjunction with forest microhabitat-scale characteristics, on patch selection and distribution of a cryptic, ground-dwelling species that is both threatened and under-studied. Given its endangered status and dependence on larger and more mature forest patches, SGT may be an effective flagship species for the conservation of threatened IOCBF patches.

Grassland plant species occurring in extensively managed road verges are filtered by urban environments

Background: Urbanisation filters species in communities depending on their adaptability to conditions in built-up areas, especially in semi-natural habitats. Roadside vegetation is widespread along urban-rural gradients and is therefore a good place to study landscape-scale factors influencing plant community composition.Aim: Our study aimed to assess how plant species distributions vary between urban and rural landscape contexts and to identify biological traits favoured in urban areas.Methods: Presence/absence data for 63 indigenous common species were collected in 296 road verge patches distributed along the urban–rural gradient in three French cities. We investigated the effects of landscape composition on species assemblages and related individual species responses to urbanisation to functional traits associated with dispersal and persistence capacity.Results: Many grassland species were negatively affected by increasing proportion of built-up areas in the landscape. Insect-pollination and high seed production appeared to be key traits favoured in grassland communities in urban areas, whereas dispersal modes were less related to plant distribution.Conclusions: This study has demonstrated that urban filters affect common species of widespread, managed road verges. Better knowledge of the flora of these herbaceous roadsides may contribute to the conservation of common biodiversity within other grassland habitats found in urban areas.

A method for the objective selection of landscape‐scale study regions and sites at the national level

Summary Ecological processes operating on large spatio‐temporal scales are difficult to disentangle with traditional empirical approaches. Alternatively, researchers can take advantage of ‘natural’ experiments, where experimental control is exercised by careful site selection. Recent advances in developing protocols for designing these ‘pseudo‐experiments’ commonly do not consider the selection of the focal region and predictor variables are usually restricted to two. Here, we advance this type of site selection protocol to study the impact of multiple landscape scale factors on pollinator abundance and diversity across multiple regions. Using datasets of geographic and ecological variables with national coverage, we applied a novel hierarchical computation approach to select study sites that contrast as much as possible in four key variables, while attempting to maintain regional comparability and national representativeness. There were three main steps to the protocol: (i) selection of six 100 × 100 km2 regions that collectively provided land cover representative of the national land average, (ii) mapping of potential sites into a multivariate space with axes representing four key factors potentially influencing insect pollinator abundance, and (iii) applying a selection algorithm which maximized differences between the four key variables, while controlling for a set of external constraints. Validation data for the site selection metrics were recorded alongside the collection of data on pollinator populations during two field campaigns. While the accuracy of the metric estimates varied, the site selection succeeded in objectively identifying field sites that differed significantly in values for each of the four key variables. Between‐variable correlations were also reduced or eliminated, thus facilitating analysis of their separate effects. This study has shown that national datasets can be used to select randomized and replicated field sites objectively within multiple regions and along multiple interacting gradients. Similar protocols could be used for studying a range of alternative research questions related to land use or other spatially explicit environmental variables, and to identify networks of field sites for other countries, regions, drivers and response taxa in a wide range of scenarios.

Oyster Density and Demographic Rates on Natural Intertidal Reefs and Hardened Shoreline Structures

The ubiquitous loss of natural intertidal oyster reefs and associated ecosystem services has fueled restoration efforts throughout the world. Effective restoration requires an understanding of the distribution, density, and demographic rates (growth and survival) of oysters inhabiting existing natural reefs and how these may vary as a function of landscape-scale factors, such as tidal range and fetch distances. Furthermore, natural intertidal habitats are increasingly being replaced with hardened shoreline structures that may be colonized by oysters, yet little is known about habitat quality (as indexed by oyster density and demographic rates) of these hardened structures relative to natural habitats. The present study sought to compare oyster density, demographic rates, and population estimates (1) across estuarine landscape settings to inform natural intertidal oyster reef restoration (i.e., comparing natural intertidal reefs within adjacent water bodies that vary in tidal regimes and fetch distances) and (2) across natural habitats and human-made structures to assess variation in habitat quality between natural reefs and hardened shorelines. Oyster density, growth rates, and population estimates on natural intertidal reefs were greatest within the smaller, more tidally influenced Core Sound versus the larger, wind-driven Pamlico Sound, with no significant difference in survivorship identified between the two water bodies. Natural intertidal reefs and hardened shoreline structures were compared within Pamlico Sound only, with natural intertidal reefs hosting three to eight times higher oyster densities than hardened shoreline structures. When mean oyster density/m2 was multiplied by reef area to estimate population size, natural intertidal reefs within Pamlico Sound hosted considerably greater populations of oysters relative to hardened shorelines. The present study fills an existing need to understand oyster density and demographic rates on natural intertidal reefs and hardened shorelines to better inform future restoration and shoreline management scenarios.

Denitrification potential of riparian soils in relation to multiscale spatial environmental factors: a case study of a typical watershed, China.

The objective of this study was to test the hypothesis that environmental regulators of riparian zone soil denitrification potential differ according to spatial scale within a watershed; consequently, a second objective was to provide spatial strategies for conserving and restoring the purification function of runoff in riparian ecosystems. The results show that soil denitrification in riparian zones was more heterogeneous at the profile scale than at the cross-section and landscape scales. At the profile scale, biogeochemical factors (including soil total organic carbon, total nitrogen, and nitrate-nitrogen) were the major direct regulators of the spatial distribution of soil denitrification enzyme activity (DEA). At the cross-section scale, factors included distance from river bank and vegetation density, while landscape-scale factors, including topographic index, elevation, and land use types, indirectly regulated the spatial distribution of DEA. At the profile scale, soil DEA was greatest in the upper soil layers. At the cross-section scale, maximum soil DEA occurred in the mid-part of the riparian zone. At the landscape scale, soil DEA showed an increasing trend towards downstream sites, except for those in urbanized areas.

Local and landscape scale determinants of macroinvertebrate assemblages and their conservation value in ponds across an urban land-use gradient

Urbanisation represents a growing threat to natural communities across the globe. Small aquatic habitats such as ponds are especially vulnerable and are often poorly protected by legislation. Many ponds are threatened by development and pollution from the surrounding landscape, yet their biodiversity and conservation value remain poorly described. Here we report the results of a survey of 30 ponds along an urban land-use gradient in the West Midlands, UK. We outline the environmental conditions of these urban ponds to identify which local and landscape scale environmental variables determine the biodiversity and conservation value of the macroinvertebrate assemblages in the ponds. Cluster analysis identified four groups of ponds with contrasting macroinvertebrate assemblages reflecting differences in macrophyte cover, nutrient status, riparian shading, the nature of the pond edge, surrounding land-use and the availability of other wetland habitats. Pond conservation status varied markedly across the sites. The richest macroinvertebrate assemblages with high conservation value were found in ponds with complex macrophyte stands and floating vegetation with low nutrient concentrations and little surrounding urban land. The most impoverished assemblages were found in highly urban ponds with hard-engineered edges, heavy shading and nutrient rich waters. A random forest classification model revealed that local factors usually had primacy over landscape scale factors in determining pond conservation value, and constitute a priority focus for management.

Both landscape and local scale factors matter for the parental investment strategies of the pollinator Osmia caerulescens

Bees are important pollinators that use resources from both cropped and natural habitats in agroecosystems, and the amount of extant resources have proven to be critical in the adoption of parental investment decisions. Thus, the mixed effects that resource distribution and the organisms’ foraging and dispersal movements have on parental decisions cannot be adequately evaluated without the use of different spatial scales. We assess the effects of the landscape context and the local habitat type on the offspring traits of Osmia caerulescens L. Bees were obtained from standardized trap-nests established in Mediterranean crops. We analyzed the effects that the percentage of semi-natural habitats, the local habitat type, and the nest hole diameter have on offspring weight, the number of emergent progeny and offspring sex ratio. Both landscape and local scale factors affected the offspring traits in significant and interactive ways, and landscape-scale effects varied depending on local factors. Considering our results and taking into account the implications that offspring traits have on the population persistence, we stress the need to introduce these parameters in future studies. Maintaining agricultural landscape heterogeneity, with high crop diversity and the presence of semi-natural habitats is essential for the persistence of Osmia caerulescens populations.

玉川上水緑道の鳥類種組成に影響する要因

Ecological network is regarded as a possible way to improve biodiversity in urban landscapes. Though linear vegetated spaces such as greenways and wooded streets are often considered to be important components of urban ecological network, the ecological functions of such linear vegetated spaces have not been clarified well. In the present study, the relationship between avian species composition and vegetation structure were studied in the green road along the Tamagawa Josui Aqueduct during a wintering season and a breeding season. Movements of the observed individuals were also recorded. The results indicated that the avian species composition varied with tree vegetation cover. Landscape scale factors such as woodland area within 500m range and NDVI within 500m range were also influential. Distance from the nearest large woodland was important only in the breeding season while water area within 500m range was important only in winter. Most urban avoider species and some urban adapter species tended to move within the vegetated area along the aqueduct, which indicates that the linear vegetated area could play a role as movement corridor for the species.

Improving forecasts of arctic-alpine refugia persistence with landscape-scale variables

ABSTRACTRefugia, the sites preserving conditions reminiscent of suitable climates, are projected to be crucial for species in a changing climate, particularly at high latitudes. However, the knowledge of current locations of high-latitude refugia and particularly their ability to retain suitable conditions under future climatic changes is limited. Occurrences of refugia have previously been mainly assessed and modelled based solely on climatic features, with insufficient attention being paid to potentially important landscape-scale factors. Here, climate-only models and ‘full’ models incorporating topo-edaphic landscape-scale variables (radiation, soil moisture and calcareousness) were developed and compared for 111 arctic-alpine plant species in Northern Fennoscandia. This was done for both current and future climates to determine cells with resilient climatic suitability harbouring refugia. Our results show that topographic and edaphic landscape-scale predictors both significantly improve models of arctic-alpine species distributions and alter projections of refugia occurrence. The predictions of species–climate models ignore landscape-scale ecological processes and may thus provide inaccurate estimates of extinction risk and forecasts of refugia where species can persist under a changing climate.

The invasive species Ulex europaeus (Fabaceae) shows high dynamism in a fragmented landscape of south-central Chile.

Ulex europaeus (gorse) is an invasive shrub deemed as one of the most invasive species in the world. U. europaeus is widely distributed in the south-central area of Chile, which is considered a world hotspot for biodiversity conservation. In addition to its negative effects on the biodiversity of natural ecosystems, U. europaeus is one of the most severe pests for agriculture and forestry. Despite its importance as an invasive species, U. europaeus has been little studied. Although information exists on the potential distribution of the species, the interaction of the invasion process with the spatial dynamic of the landscape and the landscape-scale factors that control the presence or absence of the species is still lacking. We studied the spatial and temporal dynamics of the landscape and how these relate to U. europaeus invasion in south-central Chile. We used supervised classification of satellite images to determine the spatial distribution of the species and other land covers for the years 1986 and 2003, analysing the transitions between the different land covers. We used logistic regression for modelling the increase, decrease and permanence of U. europaeus invasion considering landscape variables. Results showed that the species covers only around 1% of the study area and showed a 42% reduction in area for the studied period. However, U. europaeus was the cover type which presented the greatest dynamism in the landscape. We found a strong relationship between changes in land cover and the invasion process, especially connected with forest plantations of exotic species, which promotes the displacement of U. europaeus. The model of gorse cover increase presented the best performance, and the most important predictors were distance to seed source and landscape complexity index. Our model predicted high spread potential of U. europaeus in areas of high conservation value. We conclude that proper management for this invasive species must take into account the spatial dynamics of the landscape within the invaded area in order to address containment, control or mitigation of the invasion.

Contrasting Pollinators and Pollination in Native and Non-Native Regions of Highbush Blueberry Production.

Highbush blueberry yields are dependent on pollination by bees, and introduction of managed honey bees is the primary strategy used for pollination of this crop. Complementary pollination services are also provided by wild bees, yet highbush blueberry is increasingly grown in regions outside its native range where wild bee communities may be less adapted to the crop and growers may still be testing appropriate honey bee stocking densities. To contrast crop pollination in native and non-native production regions, we sampled commercial ‘Bluecrop’ blueberry fields in British Columbia and Michigan with grower-selected honey bee stocking rates (0–39.5 hives per ha) to compare bee visitors to blueberry flowers, pollination and yield deficits, and how those vary with local- and landscape-scale factors. Observed and Chao-1 estimated species richness, as well as Shannon diversity of wild bees visiting blueberries were significantly higher in Michigan where the crop is within its native range. The regional bee communities were also significantly different, with Michigan farms having greater dissimilarity than British Columbia. Blueberry fields in British Columbia had fewer visits by honey bees than those in Michigan, irrespective of stocking rate, and they also had lower berry weights and a significant pollination deficit. In British Columbia, pollination service increased with abundance of wild bumble bees, whereas in Michigan the abundance of honey bees was the primary predictor of pollination. The proportion of semi-natural habitat at local and landscape scales was positively correlated with wild bee abundance in both regions. Wild bee abundance declined significantly with distance from natural borders in Michigan, but not in British Columbia where large-bodied bumble bees dominated the wild bee community. Our results highlight the varying dependence of crop production on different types of bees and reveal that strategies for pollination improvement in the same crop can vary greatly across production regions.

Traits in Lepidoptera assemblages are differently influenced by local and landscape scale factors in farmland habitat islands

Semi-natural grassland islands have a key role in slowing down biodiversity decline in intensively cultivated agricultural landscapes. Assemblages in such habitat patches are not only limited by local habitat quality, but are also influenced by the suitability and distribution of different habitat types in the surrounding landscape. If we want to preserve a functionally diverse Lepidoptera fauna, both local and landscape scale environmental effects, including land use and management, should be considered. In the present study, we describe trait-based characteristics of noctuid dominated macro-moth assemblages (MMAs) in grassland remnants of an intensively cultivated agricultural area. By gathering environmental data from local to landscape scales, we aimed to identify the most influential scales, possible interactions between scales and the role of integrated arable fields in shaping MMAs. We conducted abundance weighted trait-based multivariate analysis of the assemblages based on six trait groups. Both local and landscape scale variables had important influence, acting on different traits of the assemblages. By variance partitioning, we could identify variables that exerted maximal effect at 50 m and 250 m radii circles. Variables describing local vegetation and identity of neighbouring crop were responsible for species richness and rarity status, while the area of arable and wooded habitats within 250 m were responsible for total catch and pest status related traits. There was significant interaction between principal components axes representing local and landscape variables. Rarity, more than other traits, was influenced by the interaction. Integrated fields had no effect on MMAs. The present study highlights the contributions of both local and landscape scales to the shaping of MMAs and suggests that the preservation of both local habitat quality and landscape heterogeneity are important if we would like to maintain species rich and functionally diverse Lepidoptera fauna.

The relative influences of fine and landscape scale factors on the structure of lentic plant assemblages

ABSTRACTJune-Wells M, Gallagher F, Hart B, Malik V, Bugbee G. 2016. The relative influences of fine and landscape scale factors on the structure of lentic plant assemblages. Lake Reserv Manage. 32:116–131.The process of plant community assembly has long been a topic of debate among ecologists. Aquatic plant assemblages and their structure may be the result of a series of abiotic and biotic filters that include transport (i.e., physical movement of species), water chemistry, sediment chemistry, basin structure, and competitive interactions. The influences of transport and water chemistry have been well investigated, but many questions persist about the interrelationships among water and sediment variables, including their combined influences on the structure of the aquatic plant assemblage. To understand how these abiotic conditions interact, we sampled 750 points in 30 lakes. Using these data, a split canonical correspondence design was used to evaluate the relative influences of regional and fine-scale conditions in structuring the plant assemblage. Additionally, multiple logistic regressions were employed to determine the individual species’ abiotic preferences. The results suggest that the plant assemblage structure is principally determined by the lake-sediment characteristics. Sediment variables explained 28% of the total species-data variance and water chemistry accounted for 9% (total variance explained = 46%; 9% due to intercorrelation of water/sediment characteristics). There were also strong species–environmental relationships; nonnative species showed distinct correlations with sediment pH and lake water conductivity, which may be useful in lake management initiatives such as risk assessment and nonnative species monitoring. Finally, and as expected, the Shannon diversity index was strongly related to depth and light.

Hotspots of Community Change: Temporal Dynamics Are Spatially Variable in Understory Plant Composition of a California Oak Woodland.

Community response to external drivers such climate and disturbance can lead to fluctuations in community composition, or to directional change. Temporal dynamics can be influenced by a combination of drivers operating at multiple spatial scales, including external landscape scale drivers, local abiotic conditions, and local species pools. We hypothesized that spatial variation in these factors can create heterogeneity in temporal dynamics within landscapes. We used understory plant species composition from an 11 year dataset from a California oak woodland to compare plots where disturbance was experimentally manipulated with the removal of livestock grazing and a prescribed burn. We quantified three properties of temporal variation: compositional change (reflecting the appearance and disappearance of species), temporal fluctuation, and directional change. Directional change was related most strongly to disturbance type, and was highest at plots where grazing was removed during the study. Temporal fluctuations, compositional change, and directional change were all related to intrinsic abiotic factors, suggesting that some locations are more responsive to external drivers than others. Temporal fluctuations and compositional change were linked to local functional composition, indicating that environmental filters can create subsets of the local species pool that do not respond in the same way to external drivers. Temporal dynamics are often assumed to be relatively static at the landscape scale, provided disturbance and climate are continuous. This study shows that local and landscape scale factors jointly influence temporal dynamics creating hotspots that are particularly responsive to climate and disturbance. Thus, adequate predictions of response to disturbance or to changing climate will only be achieved by considering how factors at multiple spatial scales influence community resilience and recovery.