Fine-scale Spatial Structure Research Articles

Using high-resolution LiDAR data to quantify the three-dimensional structure of vegetation in urban green space

The spatial arrangement and vertical structure of vegetation in urban green spaces are key factors in determining the types of benefits that urban parks provide to people. This includes opportunities for recreation, spiritual fulfilment and biodiversity conservation. However, there has been little consideration of how the fine-scale spatial and vertical structure of vegetation is distributed in urban parks, primarily due to limitations in methods for doing so. We addressed this gap by developing a method using Light Detection and Ranging (LiDAR) data to map, at a fine resolution, tree cover, vegetation spatial arrangement, and vegetation vertical structure. We then applied this method to urban parks in Brisbane, Australia. We found that parks varied mainly in their amount of tree cover and its spatial arrangement, but also in vegetation vertical structure. Interestingly, the vertical structure of vegetation was largely independent of its cover and spatial arrangement. This suggests that vertical structure may be being managed independently to tree cover to provide different benefits across urban parks with different levels of tree cover. Finally, we were able to classify parks into three distinct classes that explicitly account for both the spatial and vertical structure of tree cover. Our approach for mapping the three-dimensional vegetation structure of urban green space provides a much more nuanced and functional description of urban parks than has previously been possible. Future research is now needed to quantify the relationships between vegetation structure and the actual benefits people derive from urban green space.

Fine-scale spatial ecology drives kin selection relatedness among cooperating amoebae.

Cooperation among microbes is important for traits as diverse as antibiotic resistance, pathogen virulence, and sporulation. The evolutionary stability of cooperation against "cheater" mutants depends critically on the extent to which microbes interact with genetically similar individuals. The causes of this genetic social structure in natural microbial systems, however, are unknown. Here, we show that social structure among cooperative Dictyostelium amoebae is driven by the population ecology of colonization, growth, and dispersal acting at spatial scales as small as fruiting bodies themselves. Despite the fact that amoebae disperse while grazing, all it takes to create substantial genetic clonality within multicellular fruiting bodies is a few millimeters distance between the cells colonizing a feeding site. Even adjacent fruiting bodies can consist of different genotypes. Soil populations of amoebae are sparse and patchily distributed at millimeter scales. The fine-scale spatial structure of cells and genotypes can thus account for the otherwise unexplained high genetic uniformity of spores in fruiting bodies from natural substrates. These results show how a full understanding of microbial cooperation requires understanding ecology and social structure at the small spatial scales microbes themselves experience.

Population structure and long-term decline in three species of heart urchins Abatus spp. near-shore in the Vestfold Hills region, East Antarctica

Patterns of fine-scale spatial population structure in Antarctic benthic species are poorly understood. There is a high proportion of brooding species in the Antarctic benthos, and a brooding life history strategy is expected to restrict their dispersal abilities and therefore foster population structure. Additionally, genetic structuring of populations can preserve signals of historic processes (such as Pleistocene glaciations) on species distributions and abundances. We developed a set of seven microsatellite markers to examine population genetic variation and infer the demographic history of three sympatric Antarctic sea urchin species from the order Spatangoida (Abatus ingens, A. shackletoni and A. philippii), all with brooding life history strategies. Samples were collected at five sites separated by up to 5 km, in the near-shore area surrounding Davis Station in the Vestfold Hills area of the Australian Antarctic Territory. We found evidence of a long-term population decline in all three species, and the estimated timing of the decline precedes anthropogenic activities and is compatible with long-term climate variability. Two genetic clusters in A. ingens and A. shackletoni suggest secondary contact after population differentiation in glacial refugia. Life history is not a good predictor of fine-scale population structure in these species, with gene flow possible at distances of 5 km. Finally, no evidence was found for a potential impact of pollution from Davis Station on genetic variation. The reduced effective population size observed for these Antarctic benthic species highlights their fragility and the need for conservation concern.

Population structure of two rabies hosts relative to the known distribution of rabies virus variants in Alaska.

For pathogens that infect multiple species, the distinction between reservoir hosts and spillover hosts is often difficult. In Alaska, three variants of the arctic rabies virus exist with distinct spatial distributions. We tested the hypothesis that rabies virus variant distribution corresponds to the population structure of the primary rabies hosts in Alaska, arctic foxes (Vulpes lagopus) and red foxes (Vulpes vulpes) to possibly distinguish reservoir and spillover hosts. We used mitochondrial DNA (mtDNA) sequence and nine microsatellites to assess population structure in those two species. mtDNA structure did not correspond to rabies virus variant structure in either species. Microsatellite analyses gave varying results. Bayesian clustering found two groups of arctic foxes in the coastal tundra region, but for red foxes it identified tundra and boreal types. Spatial Bayesian clustering and spatial principal components analysis identified 3 and 4 groups of arctic foxes, respectively, closely matching the distribution of rabies virus variants in the state. Red foxes, conversely, showed eight clusters comprising two regions (boreal and tundra) with much admixture. These results run contrary to previous beliefs that arctic fox show no fine-scale spatial population structure. While we cannot rule out that the red fox is part of the maintenance host community for rabies in Alaska, the distribution of virus variants appears to be driven primarily by the arctic fox. Therefore, we show that host population genetics can be utilized to distinguish between maintenance and spillover hosts when used in conjunction with other approaches.

The distribution of intra-genomically variable dinoflagellate symbionts at Lord Howe Island, Australia

The symbiotic dinoflagellates of corals and other marine invertebrates (Symbiodinium) are essential to the development of shallow-water coral reefs. This genus contains considerable genetic diversity and a corresponding range of physiological and ecological traits. Most genetic variation arises through the accumulation of somatic mutations that arise during asexual reproduction. Yet growing evidence suggests that occasional sexual reproductive events also occur within, and perhaps between, Symbiodinium lineages, further contributing to the pool of genetic variation available for evolutionary adaptation. Intra-genomic variation can therefore arise from both sexual and asexual reproductive processes, making it difficult to discern its underlying causes and consequences. We used quantitative PCR targeting the ITS2 locus to estimate proportions of genetically homogeneous symbionts and intra-genomically variable Symbiodinium (IGV Symbiodinium) in the reef-building coral Pocillopora damicornis at Lord Howe Island, Australia. We then sampled colonies through time and at a variety of spatial scales to find out whether the distribution of these symbionts followed patterns consistent with niche partitioning. Estimated ratios of homogeneous to IGV Symbiodinium varied between colonies within sites (metres to tens of metres) and between sites separated by hundreds to thousands of metres, but remained stable within colonies through time. Symbiont ratios followed a temperature gradient, with the local thermal maximum emerging as a negative predictor for the estimated proportional abundance of IGV Symbiodinium. While this pattern may result from fine-scale spatial population structure, it is consistent with an increased susceptibility to thermal stress, suggesting that the evolutionary processes that generate IGV (such as inter-lineage recombination and the accumulation of somatic mutations at the ITS2 locus) may have important implications for the fitness of the symbiont and that of the coral host.

Evaluation of Nonhydrostatic Simulations of Northeast Pacific Atmospheric Rivers and Comparison to in Situ Observations

Abstract Atmospheric rivers are long, narrow bands of concentrated atmospheric water vapor transport that provide an important atmospheric linkage between the subtropics and the midlatitudes, facilitating over 90% of meridional water vapor flux and often resulting in extreme precipitation events in regions of enhanced coastal orography. In this investigation, the authors conduct continuous (3 month), large-domain (3600 km × 3200 km), high-resolution (4 km), nonhydrostatic simulations using the Weather Research and Forecasting (WRF) Model and compare the observations to previously reported dropsonde observations from the California Land-Falling Jets Experiment (CALJET) and the Pacific Land-Falling Jets Experiment (PACJET) in order to address an existing gap in knowledge regarding the ability of atmospheric models to simulate the finescale vertical and horizontal structure of atmospheric rivers. The WRF simulations reproduce key structural and thermodynamic characteristics of atmospheric rivers—including well-defined corridors of strong water vapor transport, moist-neutral stability in the lower troposphere, and strong low-level jet/water vapor transport maxima near ~1 km MSL. While WRF does generally capture the extreme values of instantaneous vertically integrated water transport—a defining feature of real-world atmospheric rivers—constituent variables exhibit biases relative to observations, including −11.2% for integrated vapor transport, +5.9% for integrated water vapor, and −17.7% for 1 km MSL wind speed. Findings suggest that high-resolution nonhydrostatic atmospheric simulations are an appropriate tool for investigating atmospheric rivers in contexts where finescale spatial structure and realistic water vapor transport maxima are important.

Kinship, inbreeding and fine-scale spatial structure influence gut microbiota in a hindgut-fermenting tortoise.

Herbivorous vertebrates rely on complex communities of mutualistic gut bacteria to facilitate the digestion of celluloses and hemicelluloses. Gut microbes are often convergent based on diet and gut morphology across a phylogenetically diverse group of mammals. However, little is known about microbial communities of herbivorous hindgut-fermenting reptiles. Here, we investigate how factors at the individual level might constrain the composition of gut microbes in an obligate herbivorous reptile. Using multiplexed 16S rRNA gene sequencing, we characterized the faecal microbial community of a population of gopher tortoises (Gopherus polyphemus) and examined how age, genetic diversity, spatial structure and kinship influence differences among individuals. We recovered phylotypes associated with known cellulolytic function, including candidate phylum Termite Group 3, suggesting their importance for gopher tortoise digestion. Although host genetic structure did not explain variation in microbial composition and community structure, we found that fine-scale spatial structure, inbreeding, degree of relatedness and possibly ontogeny shaped patterns of diversity in faecal microbiomes of gopher tortoises. Our findings corroborate widespread convergence of faecal-associated microbes based on gut morphology and diet and demonstrate the role of spatial and demographic structure in driving differentiation of gut microbiota in natural populations.

Arctic fungal communities associated with roots of Bistorta vivipara do not respond to the same fine-scale edaphic gradients as the aboveground vegetation.

Soil conditions and microclimate are important determinants of the fine-scale distribution of plant species in the Arctic, creating locally heterogeneous vegetation. We hypothesize that root-associated fungal (RAF) communities respond to the same fine-scale environmental gradients as the aboveground vegetation, creating a coherent pattern between aboveground vegetation and RAF. We explored how RAF communities of the ectomycorrhizal (ECM) plant Bistorta vivipara and aboveground vegetation structure of arctic plants were affected by biotic and abiotic variables at 0.3-3.0-m scales. RAF communities were determined using pyrosequencing. Composition and spatial structure of RAF and aboveground vegetation in relation to collected biotic and abiotic variables were analysed by ordination and semi-variance analyses. The vegetation was spatially structured along soil C and N gradients, whereas RAF lacked significant spatial structure. A weak relationship between RAF community composition and the cover of two ECM plants, B.vivipara and S.polaris, was found, and RAF richness increased with host root length and root weight. Results suggest that the fine-scale spatial structure of RAF communities of B.vivipara and the aboveground vegetation are driven by different factors. At fine spatial scales, neighbouring ECM plants may affect RAF community composition, whereas soil nutrients gradients structure the vegetation.

Recruitment and recovery of pink abalone (Haliotis corrugata) in a historically overexploited kelp forest: Are local populations self-sustaining?

After experiencing a reduction in density, many populations of benthic, broadcast spawning marine invertebrates have struggled to recover or have collapsed. Genetic techniques may help to distinguish populations that are self-sustaining from those at risk of further decline, and demographic interdependence among subpopulations. We tested the use of genetic data for identifying stable and self-sustaining abalone populations, as well as the efficacy of a restoration technique for use in those populations that are not. We created an artificial aggregation of wild adult pink abalone (Haliotis corrugata) in the Point Loma kelp forest near San Diego, CA, USA. We genetically analyzed those individuals and additional adults and juveniles in the broader region. A self-sustained population should not be demographically reliant upon immigration. Temporal variability in relatedness among juvenile cohorts, and a lack of fine-scale spatial structure in adult and juvenile relatedness indicated complex recruitment dynamics and/or long distance larval delivery. We estimated a low effective population size (Ne=188) and a very low ratio of effective population to census population size (Ne/N=2.0×10−3). These data are consistent with sweepstakes reproductive success, and suggest that the population is at risk of genetic diversity decline. Parentage assignment revealed that none of the juveniles sampled one year after aggregating adults had parents from this aggregation. Collectively, our results suggest that restoration efforts will need to achieve a greater density (0.18m−2) and/or number of individuals (46) to improve local recruitment. Our results also suggest that the Point Loma kelp forest population of pink abalone is of insufficient density for long-term viability, may be reliant upon immigration, and cannot be defined as an independent “local” population unit.

Propagule size is not a good predictor for regional population subdivision or fine-scale spatial structure in lichenized fungi

Propagule size has important consequences on the genetic structure of wind-dispersed species, as species with small propagules have higher capability of long-distance dispersal. Here, we studied reproductive modes and compared local and regional population structures in three Macaronesian lichenized fungi differing in propagule size. First, we quantified size distribution of propagules in each species. Second, genotype simulations based on microsatellite data were used to infer the reproductive mode. Third, using spatial analysis and population genetic approaches, we quantified the local and regional scale genetic structures of the fungal species. The three species differed in size distributions of propagules. The majority of populations exhibited clonal reproductive mode. Identical reproductive modes occurred often across species in the same sites, implying a possible relationship between reproductive mode and local site conditions. Contrary to expectation, at the local scale, the species exhibited similar patterns of spatial autocorrelation in genotypes. However, in agreement with the expectation based on propagule size, the species with highest frequency of small vegetative propagules (L. pulmonaria) exhibited lowest regional genetic differentiation. Nevertheless, altogether, our results show that propagule size is not a good predictor of population subdivision in lichenized fungi, neither at local nor regional spatial scale.

Breed locally, disperse globally: fine-scale genetic structure despite landscape-scale panmixia in a fire-specialist.

An exciting advance in the understanding of metapopulation dynamics has been the investigation of how populations respond to ephemeral patches that go ‘extinct’ during the lifetime of an individual. Previous research has shown that this scenario leads to genetic homogenization across large spatial scales. However, little is known about fine-scale genetic structuring or how this changes over time in ephemeral patches. We predicted that species that specialize on ephemeral habitats will delay dispersal to exploit natal habitat patches while resources are plentiful and thus display fine-scale structure. To investigate this idea, we evaluated the effect of frequent colonization of ephemeral habitats on the fine-scale genetic structure of a fire specialist, the black-backed woodpecker (Picoides arcticus) and found a pattern of fine-scale genetic structure. We then tested for differences in spatial structure between sexes and detected a pattern consistent with male-biased dispersal. We also detected a temporal increase in relatedness among individuals within newly burned forest patches. Our results indicate that specialist species that outlive their ephemeral patches can accrue significant fine-scale spatial structure that does not necessarily affect spatial structure at larger scales. This highlights the importance of both spatial and temporal scale considerations in both sampling and data interpretation of molecular genetic results.

Genetic diversity and fine-scale spatial genetic structure of different life- history stages in a small, isolated population of <I>Sinojackia huangmeiensis</I> (Styracaceae)

Knowledge of genetic diversity and fine-scale spatial genetic structure (SGS) at different age stages of small isolated populations is important for understanding population dynamics and developing effective conservation measures for fragmented populations. In this study, we used a small, isolated population of Sinojackia huangmeiensi as a case study to investigate the change in the levels of genetic diversity and SGS at different age stages. We mapped and genotyped 60 adults,175 saplings, 198 seedlings using eight microsatellite markers to detect the genetic diversity, SGS and pollen and seed dispersal patterns in a 80 m × 160 m transect located in an original secondary forest surrounded by farmlands. No significant differences in genetic diversity were found among the three life stages, and a significant heterozygote deficiency in the population may result from substantial biparental inbreeding. We found significant fine-scale spatial structure at different age stages within 10 m, suggesting that seed dispersal mainly occurred near a mother tree. Seed dispersal distance and pollen dispersal distance were 9.07±13.38 and 23.81±23.60 m, respectively, and ‘L’ 第 4期 阮咏梅等: 黄梅秤锤树孤立居群的遗传多样性及其小尺度空间遗传结构 461 shaped curves were observed in both pollen dispersal and seed dispersal patterns. The spatial distribution of the different age stages is most likely the result of little overlap in seed rain, self-thinning, biparental inbreeding and limited gene flow. Our results have important implications for conservation of extant population of S. huangmeiensis. Measures for promoting pollen flow and increasing survival rate of seedlings should be considered for in situ conservation. The presence of SGS in this fragmented population implies that seeds for ex situ conservation should be collected from trees at least 10 m apart to reduce genetic similarity between neighboring individuals.

Fitness costs of butterfly oviposition on a lethal non-native plant in a mixed native and non-native plant community

Non-native plants may be unpalatable or toxic, but have oviposition cues similar to native plants used by insects. The herbivore will then oviposit on the plant, but the offspring will be unable to develop. While such instances have been described previously, the fitness costs at the population level in the wild due to the presence of the lethal host have not been quantified, for this or other related systems. We quantified the fitness cost in the field for the native butterfly Pieris macdunnoughii in the presence of the non-native crucifer Thlaspi arvense, based on the spatial distributions of host plants, female butterflies and eggs in the habitat and the survival of the larvae in the wild. We found that 2.9% of eggs were laid on T. arvense on average, with a survival probability of 0, yielding a calculated fitness cost of 3.0% (95% confidence interval 1.7-3.6%) due to the presence of the non-native in the plant community. Survival probability to the pre-pupal stage for eggs laid on two native crucifers averaged 1.6% over 2 years. The magnitude of the fitness cost will vary temporally and spatially as a function of the relative abundance of the non-native plant. We propose that the fine-scale spatial structure of the plant community relative to the butterflies' dispersal ability, combined with the females' broad habitat use, contributes to the fitness costs associated with the non-native plant and the resulting evolutionary trap.

Fine-scale spatial structure of the exploited infaunal bivalve Cerastoderma edule on the French Atlantic coast

Investigations of biomass, production, and anthropogenic impact require knowledge of the spatial distribution of the species concerned. Studies of the spatial distribution of soft-sediment infauna are inherently difficult, because the organisms are generally not readily visible, necessitating painstaking excavation. Although the large-scale (tens of km) distribution patterns of infaunal bivalves have been studied previously, the fine-scale (1 to tens of meters) has received much less attention. We investigated the fine-scale spatial distribution of the edible cockle Cerastoderma edule at a fishing-impacted site and a non-impacted site on an intertidal mudflat in Bourgneuf Bay, France, in 2009–2010. A preliminary study using a 1m spatial lag was performed to determine the optimum lags for a nested sampling design. Cohorts were identified using Bhattacharya-resolved size-frequency distributions and verification of isotropy, and the spatial characteristics of each cohort were determined using Moran's I auto-correlation coefficient. The non-impacted site presented one strongly-aggregated main cohort, C3, (Moran's I=0.67 to −0.34, spatial range 16 to 20m, inter-patch distance 41 to 51m). The impacted site presented two main cohorts, C2 (1.31cm mean shell length, SL) and C3 (2.11cm SL) both of which also showed a patchy spatial distribution (C2: Moran's I=0.7 to −0.72, spatial range 22 to 35m; inter-patch distance 63 to 90m; C3: Moran's I=0.41 to −0.63, spatial range 36 to 58m, inter-patch distance not defined). The C3 cohort was less aggregated than the C2; possibly due to the homogenizing effect of fishing, which typically proceeds via a Lévy walk foraging model.Our results show that the spatial distributions of C. edule retained a strongly aggregated character over the 8months of the study, suggesting that these characteristics are powerfully maintained by recruitment/post-recruitment processes, despite intense fishing pressure throughout the sampling period, and indeed for decades, prior to this study. These data also show that we cannot assume a random or a regular spatial distribution for this species in studies of biomass, production, trophic relations, or anthropogenic impact; rather, close attention must be paid to the spatial characteristics of studied populations in order to reduce the confounding effects of auto-correlation.

Microbial Population and Community Dynamics on Plant Roots and Their Feedbacks on Plant Communities

The composition of the soil microbial community can be altered dramatically due to association with individual plant species, and these effects on the microbial community can have important feedbacks on plant ecology. Negative plant-soil feedback plays primary roles in maintaining plant community diversity, whereas positive plant-soil feedback may cause community conversion. Host-specific differentiation of the microbial community results from the trade-offs associated with overcoming plant defense and the specific benefits associated with plant rewards. Accumulation of host-specific pathogens likely generates negative feedback on the plant, while changes in the density of microbial mutualists likely generate positive feedback. However, the competitive dynamics among microbes depends on the multidimensional costs of virulence and mutualism, the fine-scale spatial structure within plant roots, and active plant allocation and localized defense. Because of this, incorporating a full view of microbial dynamics is essential to explaining the dynamics of plant-soil feedbacks and therefore plant community ecology.

Population genetics of Australian white sharks reveals fine-scale spatial structure, transoceanic dispersal events and low effective population sizes

Despite international protection of white sharks Carcharodon carcharias, important conservation parameters such as abundance, population structure and genetic diversity are largely unknown. The tissue of 97 predominately juvenile white sharks sampled from spatially distant eastern and southwestern Australian coastlines was sequenced for the mitochondrial DNA (mtDNA) control region and genotyped with 6 nuclear-encoded microsatellite loci. MtDNA population structure was found between the eastern and southwestern coasts (F-ST = 0.142, p < 0.0001), implying female reproductive philopatry. This concurs with recent satellite and acoustic tracking findings which suggest the sustained presence of discrete east coast nursery areas. Furthermore, population subdivision was found between the same regions with biparentally inherited micro satellite markers (F-ST = 0.009, p < 0.05), suggesting that males may also exhibit some degree of reproductive philopatry; 5 sharks captured along the east coast had mtDNA haplotypes that resembled western Indian Ocean sharks more closely than Australian/New Zealand sharks, suggesting that transoceanic dispersal, or migration resulting in breeding, may occur sporadically. Our most robust estimate of contemporary genetic effective population size was low and close to thresholds at which adaptive potential may be lost. For a variety of reasons, these contemporary estimates were at least 1, possibly 2, orders of magnitude below our historical effective size estimates. Population decline could expose these genetically isolated populations to detrimental genetic effects. Regional Australian white shark conservation management units should be implemented until genetic population structure, size and diversity can be investigated in more detail.

Plant and animal diversity in a region of the Southern Alps: the role of environmental and spatial processes

Different organisms respond to landscape configuration and spatial structure in different terms and across different spatial scales. Here, regression models with variation partitioning were applied to determine relative influence of the three groups of variables (climate, land use and environmental heterogeneity) and spatial structure variables on plant, bird, orthopteran and butterfly species richness in a region of the Southern Alps, ranging in elevation from the sea level to 2,780 m. Grassland and forest cover were positively correlated with species richness in both taxonomic groups, whilst species richness decreased with increasing urban elements and arable land. The variation was mainly explained by the shared component between the three groups in plants and between landscape and environmental heterogeneity in birds. The variation was related to independent land use effect in insects. The distribution in species richness was spatially structured for plants, birds and orthopterans, whilst in butterflies, no spatial structure was detected. Plant richness was associated with linear trend variation and broad-scale spatial structure in the northern part of the region, whilst bird richness with broad-scale variation which occurs on the external Alpine ridge. Orthopteran diversity was strongly related to fine-scale spatial structure, generated by dynamic processes or by unmeasured spatially structured abiotic factors. Although the study was carried out in relatively small area, the four taxonomic groups seem to respond to biodiversity drivers in a surprisingly different way. This has considerable implications for conservation planning as it restricts the usefulness of simple indicators in prioritizing areas for conservation purposes.

Geostatistical exploration of spatial variation of summertime temperatures in the Detroit metropolitan region

BackgroundBecause of the warming climate urban temperature patterns have been receiving increased attention. Temperature within urban areas can vary depending on land cover, meteorological and other factors. High resolution satellite data can be used to understand this intra-urban variability, although they have been primarily studied to characterize urban heat islands at a larger spatial scale. ObjectiveThis study examined whether satellite-derived impervious surface and meteorological conditions from multiple sites can improve characterization of spatial variability of temperature within an urban area. MethodsTemperature was measured at 17 outdoor sites throughout the Detroit metropolitan area during the summer of 2008. Kriging and linear regression were applied to daily temperatures and secondary information, including impervious surface and distance-to-water. Performance of models in predicting measured temperatures was evaluated by cross-validation. Variograms derived from several scenarios were compared to determine whether high-resolution impervious surface information could capture fine-scale spatial structure of temperature in the study area. ResultsTemperatures measured at the sites were significantly different from each other, and all kriging techniques generally performed better than the two linear regression models. Impervious surface values and distance-to-water generally improved predictions slightly. Restricting models to days with lake breezes and with less cloud cover also somewhat improved the predictions. In addition, incorporating high-resolution impervious surface information into cokriging or universal kriging enhanced the ability to characterize fine-scale spatial structure of temperature. ConclusionsMeteorological and satellite-derived data can better characterize spatial variability in temperature across a metropolitan region. The data sources and methods we used can be applied in epidemiological studies and public health interventions to protect vulnerable populations from extreme heat events.

Effects of grazing exclusion on the spatial variability of subalpine plant communities: A multiscale approach

The fine-scale spatial structure of plant communities is a key component for understanding the dynamics in vegetation following changes in land management but needs to be assessed at an appropriate scale. We studied the response of plant diversity and spatial variability of species and trait composition to grazing vs. non-grazing (>20 years) using different grain sizes of sampling in three subalpine plant communities. Species composition, diversity, and the aggregated values of 4 leaf traits were assessed at 7 grain sizes (within quadrats ranging from 25 cm 2 to 1 m 2) in 9 grazed and ungrazed paired plots. Evenness and species richness showed a strongly community-dependent response as they increased following grazing exclusion in the less productive community and decreased in the two more productive ones. Although species richness was influenced by grazing exclusion at grains larger than 625 cm 2, evenness was affected at the finest grain investigated (25 cm 2). In contrast, spatial variability of species composition was similarly affected across the three plant communities and increased following grazing exclusion from the 100 cm 2-grain size. Grazing led to a sharper decline of spatial variability with increasing quadrat size revealing that the grain of spatial heterogeneity was finer in grazed plots relative to that in ungrazed ones. The response of spatial variability of aggregated trait values was less consistent, possibly because of functional redundancy between species. However, grazing exclusion increased the spatial variability of the aggregated values of leaf dry matter content and leaf carbon and nitrogen content. We suggest that spatial variability of species composition could be useful for detecting within-community changes in response to grazing management as it was detectable using a very fine scale of sampling and responded similarly to grazing treatment in every community. Such spatial variability in species composition can induce spatial organization of plant traits that may be important for community functioning.

Synergies between VSWIR and TIR data for the urban environment: An evaluation of the potential for the Hyperspectral Infrared Imager (HyspIRI) Decadal Survey mission

This study provides an introduction to the HyspIRI mission a National Research Council “Decadal Survey” mission that combines a 213 channel visible, near−infrared and shortwave infrared (VSWIR) imaging spectrometer with an 8 channel multispectral thermal infrared (TIR) instrument and evaluates some of its potential in urban science. Potential synergies between VSWIR and TIR data are explored using analogous airborne data acquired over the Santa Barbara metropolitan region in June, 2008. These data were analyzed at both their native spatial resolutions (7.5 m VSWIR and 15 m TIR), and aggregated 60 m spatial resolution similar to HyspIRI. A spectral library of dominant urban materials (e.g., grass, trees, soil, roof types, roads) was developed from field and airborne-measured spectra using Multiple-Endmember Spectral Mixture Analysis (MESMA) and used to map fractions of impervious, soil, green vegetation (GV, e.g., trees, lawn) and non-photosynthetic vegetation (NPV). Land Surface Temperature (LST) and emissivity were also retrieved from the airborne data. Co-located pixels from the VSWIR and TIR airborne data were used to generate reflectance/emissivity spectra for a subset of urban materials. MESMA was used to map GV, NPV, soil and impervious fractions at the different spatial resolutions and compare the fractional estimates across spatial scales. Important surface energy parameters, including albedo, vegetation cover fraction, broadband emissivity and surface temperature were also determined for and evaluated for 14 urban and natural land-cover classes in the region. Fractions were validated using 1 m digital photography. Fractions for GV and NPV were highly correlated with validation fractions at all spatial scales, producing a near 1:1 relationship but with a < 10% overestimate of GV from MESMA. Similar, high correlations were observed for impervious surfaces, although impervious was significantly underestimated in most urban areas and soil overestimated. Comparison of fractions across scales showed high correlation between GV and NPV at 7.5 and 60 m resolution, suggesting that HyspIRI will provide accurate measures of these two measures in urban areas. An inverse relationship between vegetation cover and LST was observed. Albedo proved to be highly variable and poorly correlated with LST. Broadband emissivity was far less variable with high emissivity surfaces (~ 0.95) including vegetation, water and asphalt, and low emissivity surfaces (< 0.95) including selected roof types, beach sands and senesced grasslands. Residential and commercial areas showed a general pattern of increasing LST with increasing impervious fraction with the highest impervious fractions mapped in commercial areas, roads and roofs. Fine scale spatial structure in cover fractions and LST demonstrated important departures from a simple inverse relationship between GV and LST, even at 60 m. The results demonstrate the utility of HyspIRI data for urban studies and provide an insight of what will be possible on a global scale when HyspIRI data become available.