Patch Size Distribution Research Articles

Facilitation, competition, and vegetation patchiness: From scale free distribution to patterns

A new technique for the modeling of perennial vegetation patchiness in the arid/semiarid climatic zone is suggested. Incorporating the stochasticity that affects life history of seedlings and the deterministic dynamics of soil moisture and biomass, this model is flexible enough to yield qualitatively different forms of spatial organization. In the facilitation-dominated regime, scale free distribution of patch sizes is observed, in correspondence with recent field studies. In the competition controlled case, on the other hand, power-law statistics is valid up to a cutoff, and an intrinsic length scale appears.

Big fires and their ecological impacts in Australian savannas: size and frequency matters

Savannas are the most fire-prone of the earth’s major biomes. The availability of various broad-scale satellite-derived fire mapping and regional datasets provides a framework with which to examine the seasonality, extent and implications of large fires with particular reference to biodiversity values in the tropical savannas of northern Australia. We document the significance of savanna fires in the fire-prone ‘Top End’ region of the Northern Territory, Australia, using 9 years (1997–2005) of National Oceanic and Atmospheric Administration (NOAA)-Advanced Very High Resolution Radiometer (AVHRR)-, Landsat Thematic Mapper (TM)- and Enhanced Thematic Mapper (ETM+)-derived fire mapping. Fire (patch) sizes from both AVHRR- and Landsat-scale mapping increased through the calendar year associated with progressive curing of grass and litter fuels. Fire frequency data at both satellite sensor scales indicate that regional fire regimes in higher rainfall regions are dominated by large (>1000 km2) fires occurring typically at short (~2–3 years) fire return intervals. In discussion, we consider the ecological implications of these patch size distributions on regional fire-sensitive biota. Collectively, assembled data illustrate that many northern Australian savanna flora, fauna and habitats embedded within the savanna matrix are vulnerable to extensive and frequent fires, especially longer-lived obligate seeder plant taxa and relatively immobile vertebrate fauna with small home ranges.

Homologous self-organising scale-invariant properties characterise long range species spread and cancer invasion

AbstractOccupancy of new habitats through dispersion is a central process in nature. In particular, long distance dispersal is involved in the spread of species and epidemics, although it has not been previously related with cancer invasion, a process that involves cell spreading to tissues far away from the primary tumor.Using simulations and real data we show that the early spread of cancer cells is similar to the species individuals spread and that both processes are represented by a common spatio-temporal signature of long-distance dispersal and subsequent local proliferation. This signature is characterized by a particular fractal geometry of the boundaries of patches generated, and a power law-scaled, disrupted patch size distribution. In contrast, invasions involving only dispersal but not subsequent proliferation (“physiological invasions”) like trophoblast cells invasion during normal human placentation did not show the patch size power law pattern. Our results are robust to temporal and spatial scales, and to the resolution level of analysis.We conclude that the scaling properties are a hallmark and a direct result of long-distance dispersal and proliferation, and that they reflect homologous ecological processes of population self-organization during cancer and species spread. Our results are significant for the detection of processes involving long-range dispersal and proliferation like cancer metastasis, biological invasions and epidemics, and for the formulation of new cancer therapeutical approaches.

Erratum

Previous articleNext article No AccessErratumEgbert H. van Nes and Marten SchefferEgbert H. van NesDepartment of Aquatic Ecology and Water Quality Management, Wageningen University, P.O. Box 8080, NL‐6700 DD Wageningen, The Netherlands Search for more articles by this author and Marten SchefferDepartment of Aquatic Ecology and Water Quality Management, Wageningen University, P.O. Box 8080, NL‐6700 DD Wageningen, The Netherlands Search for more articles by this author Department of Aquatic Ecology and Water Quality Management, Wageningen University, P.O. Box 8080, NL‐6700 DD Wageningen, The NetherlandsOriginal articleSlow Recovery from Perturbations as a Generic Indicator of a Nearby Catastrophic Shift.PDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 170, Number 4October 2007 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/522093 Views: 39Total views on this site Citations: 7Citations are reported from Crossref HistoryReceived April 23, 2007 © 2007 by The University of Chicago.PDF download Crossref reports the following articles citing this article:Fan Zhang Early warning signals of population productivity regime shifts in global fisheries, Ecological Indicators 115 (Aug 2020): 106371.https://doi.org/10.1016/j.ecolind.2020.106371Qiang Zhang, Jin Li, Alistair Middleton, Sudin Bhattacharya, Rory B. Conolly Bridging the Data Gap From in vitro Toxicity Testing to Chemical Safety Assessment Through Computational Modeling, Frontiers in Public Health 6 (Sep 2018).https://doi.org/10.3389/fpubh.2018.00261Quan-Xing Liu, Ellen J. Weerman, Peter M. J. Herman, Han Olff, Johan van de Koppel Alternative mechanisms alter the emergent properties of self-organization in mussel beds, Proceedings of the Royal Society B: Biological Sciences 279, no.17391739 (Mar 2012): 2744–2753.https://doi.org/10.1098/rspb.2012.0157Christian Möllmann, Rabea Diekmann Marine Ecosystem Regime Shifts Induced by Climate and Overfishing, (Jan 2012): 303–347.https://doi.org/10.1016/B978-0-12-398315-2.00004-1Sonia Kéfi, Max Rietkerk, Manojit Roy, Alain Franc, Peter C. de Ruiter, Mercedes Pascual Robust scaling in ecosystems and the meltdown of patch size distributions before extinction, Ecology Letters 14, no.11 (Nov 2010): 29–35.https://doi.org/10.1111/j.1461-0248.2010.01553.xAngela Dikou Ecological Processes and Contemporary Coral Reef Management, Diversity 2, no.55 (May 2010): 717–737.https://doi.org/10.3390/d2050717M. Nyström, N. A. J. Graham, J. Lokrantz, A. V. Norström Capturing the cornerstones of coral reef resilience: linking theory to practice, Coral Reefs 27, no.44 (Oct 2008): 795–809.https://doi.org/10.1007/s00338-008-0426-zRelated articlesSlow Recovery from Perturbations as a Generic Indicator of a Nearby Catastrophic Shift.17 Jul 2015The American Naturalist

Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems

Humans and climate affect ecosystems and their services, which may involve continuous and discontinuous transitions from one stable state to another. Discontinuous transitions are abrupt, irreversible and among the most catastrophic changes of ecosystems identified. For terrestrial ecosystems, it has been hypothesized that vegetation patchiness could be used as a signature of imminent transitions. Here, we analyse how vegetation patchiness changes in arid ecosystems with different grazing pressures, using both field data and a modelling approach. In the modelling approach, we extrapolated our analysis to even higher grazing pressures to investigate the vegetation patchiness when desertification is imminent. In three arid Mediterranean ecosystems in Spain, Greece and Morocco, we found that the patch-size distribution of the vegetation follows a power law. Using a stochastic cellular automaton model, we show that local positive interactions among plants can explain such power-law distributions. Furthermore, with increasing grazing pressure, the field data revealed consistent deviations from power laws. Increased grazing pressure leads to similar deviations in the model. When grazing was further increased in the model, we found that these deviations always and only occurred close to transition to desert, independent of the type of transition, and regardless of the vegetation cover. Therefore, we propose that patch-size distributions may be a warning signal for the onset of desertification.

Homologous self-organising scale-invariant properties characterise long range species spread and cancer invasion

AbstractThe invariance of some system properties over a range of temporal and/or spatial scales is an attribute of many processes in nature1, often characterised by power law functions and fractal geometry2. In particular, there is growing consensus in that fat-tailed functions like the power law adequately describe long-distance dispersal (LDD) spread of organisms 3,4. Here we show that the spatial spread of individuals governed by a power law dispersal function is represented by a clear and unique signature, characterised by two properties: A fractal geometry of the boundaries of patches generated by dispersal with a fractal dimension D displaying universal features, and a disrupted patch size distribution characterised by two different power laws. Analysing patterns obtained by simulations and real patterns from species dispersal and cell spread in cancer invasion we show that both pattern properties are a direct result of LDD and localised dispersal and recruitment, reflecting population self-organisation.

Seismic attenuation in porous rocks with random patchy saturation

ABSTRACTSaturation of porous rocks with a mixture of two fluids has a substantial effect on seismic‐wave propagation. In particular, partial saturation causes significant attenuation and dispersion of the propagating waves due to the mechanism of wave‐induced fluid‐flow. Such flow arises when a passing wave induces different fluid pressures in regions of rock saturated by different fluids. Most models of attenuation and dispersion due to mesoscopic heterogeneities imply that fluid heterogeneities are distributed in a regular way. However, recent experimental studies show that mesoscopic heterogeneities have less idealized distributions and that the distribution itself affects attenuation and dispersion. Based on an approximation for the coherent wavefield in random porous media, we develop a model which assumes a continuous distribution of fluid heterogeneities. As this continuous random media approach assumes that there will be a distribution of different patch sizes, it is expected to be better suited to modelling experimental data. We also show how to relate the random functions to experimentally measurable parameters.

Implementation of natural disturbance-based management in northern British Columbia

Ecologically based landscape units and associated characteristics of natural disturbance (e.g., seral stage and patch size distribution) were recently developed for the northeast corner of British Columbia and used as the basis for establishing guidance and policy for natural disturbance-based management for two large timber supply areas. I discuss the development of the landscape units; development of guidance for the units; and implementation of the guidance for old forest, interior old forest, and early seral patch size objectives. This paper demonstrates how natural-disturbance-based management can be successfully implemented. Key words: natural-disturbance-based management, natural range of variability, seral stage distribution, old-forest requirements, patch size, guidance, implementation

Assessment of land use changes on woody cover and landscape fragmentation in the Orinoco savannas using fractal distributions

Abstract The effect of land use changes on the woody cover and patchiness of the Orinoco lowlands was analyzed from 1951 to 1997 by using a stretched exponential model in terms of the patch size distribution. We selected five production systems on the basis of the following components: policy option, technology and environment. They are: (a) high-input pasture in deep soil (DL-HIGraz), (b) low-input cropping in deep soil (DH-LOCrop), (c) high-input cropping in deep soil (DH-HICrop), (d) low-input cropping in shallow soil (SL-LOCrop) and (e) extensive cattle grazing in shallow soil (SL-LOGraz). For comparison, stands with similar soil depth and woody density (DL-Fallow, DH-Fallow and SL-Fallow) were selected at the protected Biological Reserve in the Calabozo region. Results indicate that the distribution of the patches was described by the stretched exponential distribution model with c as the exponent distribution. The magnitude of c reflected the effect of land use changes over time. Thus, the parameter c for human impacted stands was higher than that for the fallow stands. The stretched exponential model implies that the human impact had a multiscalar effect on the Orinoco mosaic, in terms of the multiplicative processes. There is a generic mechanism exhibiting an anomalous distribution of the patches such as has been proposed for physical systems. Therefore, the number of generation of the multiplicative processes (i.e. inverse of c) for impacted stands was lower than that in the fallow stands. As the time from fallow establishment proceeded, there was a tendency to patch re-organization by biotic effects.

Temporal change in forest fragmentation at multiple scales

Previous studies of temporal changes in fragmentation have focused almost exclusively on patch and edge statistics, which might not detect changes in the spatial scale at which forest occurs in or dominates the landscape. We used temporal land-cover data for the Chesapeake Bay region and the state of New Jersey to compare patch-based and area–density scaling measures of fragmentation for detecting changes in the spatial scale of forest that may result from forest loss. For the patch-based analysis, we examined changes in the cumulative distribution of patch sizes. For area–density scaling, we used moving windows to examine changes in dominant forest. We defined dominant forest as a forest parcel (pixel) surrounded by a neighborhood in which forest occupied the majority of pixels. We used >50% and ≥60% as thresholds to define majority. Moving window sizes ranged from 2.25 to 5,314.41 hectares (ha). Patch size cumulative distributions changed very little over time, providing no indication that forest loss was changing the spatial scale of forest. Area–density scaling showed that dominant forest was sensitive to forest loss, and the sensitivity increased nonlinearly as the spatial scale increased. The ratio of dominant forest loss to forest loss increased nonlinearly from 1.4 to 1.8 at the smallest spatial scale to 8.3 to 11.5 at the largest spatial scale. The nonlinear relationship between dominant forest loss and forest loss in these regions suggests that continued forest loss will cause abrupt transitions in the scale at which forest dominates the landscape. In comparison to the Chesapeake Bay region, dominant forest loss in New Jersey was less sensitive to forest loss, which may be attributable the protected status of the New Jersey Pine Barrens.

Erratum: Slow Recovery from Perturbations as a Generic Indicator of a Nearby Catastrophic Shift

Previous articleNext article No AccessErratumEgbert H. van Nes and Marten SchefferEgbert H. van NesDepartment of Aquatic Ecology and Water Quality Management, Wageningen University, P.O. Box 8080, NL‐6700 DD Wageningen, The Netherlands Search for more articles by this author and Marten SchefferDepartment of Aquatic Ecology and Water Quality Management, Wageningen University, P.O. Box 8080, NL‐6700 DD Wageningen, The Netherlands Search for more articles by this author Department of Aquatic Ecology and Water Quality Management, Wageningen University, P.O. Box 8080, NL‐6700 DD Wageningen, The NetherlandsOriginal articleSlow Recovery from Perturbations as a Generic Indicator of a Nearby Catastrophic Shift.PDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 170, Number 4October 2007 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/522093 Views: 44Total views on this site Citations: 7Citations are reported from Crossref HistoryReceived April 23, 2007 © 2007 by The University of Chicago.PDF download Crossref reports the following articles citing this article:Fan Zhang Early warning signals of population productivity regime shifts in global fisheries, Ecological Indicators 115 (Aug 2020): 106371.https://doi.org/10.1016/j.ecolind.2020.106371Qiang Zhang, Jin Li, Alistair Middleton, Sudin Bhattacharya, Rory B. Conolly Bridging the Data Gap From in vitro Toxicity Testing to Chemical Safety Assessment Through Computational Modeling, Frontiers in Public Health 6 (Sep 2018).https://doi.org/10.3389/fpubh.2018.00261Quan-Xing Liu, Ellen J. Weerman, Peter M. J. Herman, Han Olff, Johan van de Koppel Alternative mechanisms alter the emergent properties of self-organization in mussel beds, Proceedings of the Royal Society B: Biological Sciences 279, no.17391739 (Mar 2012): 2744–2753.https://doi.org/10.1098/rspb.2012.0157Christian Möllmann, Rabea Diekmann Marine Ecosystem Regime Shifts Induced by Climate and Overfishing, (Jan 2012): 303–347.https://doi.org/10.1016/B978-0-12-398315-2.00004-1Sonia Kéfi, Max Rietkerk, Manojit Roy, Alain Franc, Peter C. de Ruiter, Mercedes Pascual Robust scaling in ecosystems and the meltdown of patch size distributions before extinction, Ecology Letters 14, no.11 (Nov 2010): 29–35.https://doi.org/10.1111/j.1461-0248.2010.01553.xAngela Dikou Ecological Processes and Contemporary Coral Reef Management, Diversity 2, no.55 (May 2010): 717–737.https://doi.org/10.3390/d2050717M. Nyström, N. A. J. Graham, J. Lokrantz, A. V. Norström Capturing the cornerstones of coral reef resilience: linking theory to practice, Coral Reefs 27, no.44 (Oct 2008): 795–809.https://doi.org/10.1007/s00338-008-0426-zRelated articlesSlow Recovery from Perturbations as a Generic Indicator of a Nearby Catastrophic Shift.17 Jul 2015The American Naturalist

Simulating private land ownership fragmentation in the Missouri Ozarks, USA

Increasing land ownership fragmentation in the United States is causing concerns with respect to its ecological implications for forested landscapes. This is especially relevant given that human influence is one of the most significant driving forces affecting the forest landscape. A method for generating realistic land ownership maps is needed to evaluate the effects of ownership fragmentation on forest landscapes in combination with other natural processes captured in forest process models. Ownership patterns from human activities usually generate landscape boundary shapes different from those arising from natural processes. Spatial characteristics among ownership types – e.g., private, public ownership – may also differ. To address these issues, we developed the Fragmented Land Ownership Spatial Simulator (FLOSS) to generate ownership patterns that reflect the Public Land Survey System (PLSS) shapes and various patch size distributions among different types of ownership (e.g., private, public). To evaluate FLOSS performance, we compared the simulated patterns with various ownership fragmentation levels to the actual ownership patterns in the Missouri Ozarks by using selected landscape indices. FLOSS generated landscapes with spatial characteristics similar to actual landscapes, suggesting that it can simulate different levels of ownership fragmentation. This will allow FLOSS to serve as a feasible tool for evaluating forest management applications by spatially allocating various management scenarios in a realistic way. The potentials and limitations of FLOSS application are discussed.

Evaluation of five landscape-level metrics for measuring the effects of urbanization on landscape structure: the case of Tucson, Arizona, USA

Landscape-level metrics can be used to measure changes in landscape structure over time. Four landscape-level metrics and rank-size distributions were used to describe changes in landscape structure caused by urbanization in a portion of the Tucson, Arizona metropolitan area between 1984 and 1998. This analysis describes what each metric conveys regarding how urbanization affects landscape structure. It also compares the efficacy of rank-size distributions with the other metrics. Results indicate all five metrics provided information about a specific aspect of landscape structure including patch size, shape, or dispersion. Results indicate that rank-size distributions and their scaling exponents are useful because they provide information not available from the other metrics. Rank-size distributions describe the patch-size scaling properties of specific land-cover types, the relative effect of large and small patches on the distribution of patch sizes, the magnitude of change in patch size, where patch sizes differ from what is expected by the regression model, and the range of patch sizes displaying fractal patterns.

Characterization of shrub distribution using high spatial resolution remote sensing: Ecosystem implications for a former Chihuahuan Desert grassland

Patchiness is often considered a defining quality of ecosystems in arid and semiarid regions. The spatial distribution of vegetation patches and soil nutrients coupled with wind and water erosion as well as biotic processes are believed to have an influence on land degradation. A geostatistical measure of spatial “connectivity” is presented to directly measure the size of patches in the landscape from a raster data set. Connectivity is defined as the probability that adjacent pixels belong to the same type of patch. Connectivity allows the size distribution of erodible patches to be quantified from a remote sensing image or field measurement, or specified for the purposes of modeling. Applied to high-resolution remote sensing imagery in the Jornada del Muerto Basin in New Mexico, the spatial distribution of plants indicates the current state of grassland-to-shrubland transition in addition to processes of degradation in this former grassland. Shrub encroachment is clearly evident from decreased intershrub patch size in coppice dunes of 27.8 m relative to shrublands of 65.2 m and grassland spacing of 118.9 m. Shrub patches remain a consistent 2–4 m diameter regardless of the development of bush encroachment. A strong SW–NE duneland orientation correlates with the prevailing wind direction and suggests a strong aeolian control of surface geomorphology. With appropriate data sets and classification, potential applications of the connectivity method extend beyond vegetation dynamics, including mineralogy mapping, preserve planning, habitat fragmentation, pore spacing in surface hydrology, and microbial community dynamics.

Boundary‐layer growth and advection of heat over snow and soil patches: modelling and parameterization

AbstractMelting snow is generally patchy; upward sensible heat fluxes from patches of snow‐free ground warm the air and contribute energy for snowmelt. A simple model is presented for advection of heat over partial snow covers and compared with measurements of temperature profiles over snow and snow‐free ground. Approximations for flux and temperature profiles in the internal boundary layers over snow patches are used to develop parameterizations for local and average surface fluxes into the snow. In comparison with results from the advection model for regular patterns of alternating snow patches and snow‐free ground, a tile model is found to give a good parameterization for average heat fluxes over the whole surface, but it does not match the local fluxes into snow and snow‐free ground separately. An extended tile model that gives better results is developed from the flux profile parameterization. For complex snow‐cover patterns with a fractal distribution of patch sizes, average fluxes are found to be close to those obtained for a regular pattern with an effective patch size linearly related to the average patch size of the complex pattern. Copyright © 2006 Environment Canada. Published by John Wiley & Sons, Ltd.

Comparative review of theoretical models for elastic wave attenuation and dispersion in partially saturated rocks

Saturation of porous rocks with a mixture of two fluids (known as partial saturation) has a substantial effect on the seismic waves propagating through these rocks. In particular, partial saturation causes significant attenuation and dispersion of the propagating waves, due to wave-induced fluid flow. Such flow arises when a passing wave induces different fluid pressures in regions of rock saturated by different fluids. As partial fluid saturation can occur on different length scales, attenuation due to wave-induced fluid flow is ubiquitous. In particular, mesoscopic fluid flow due to heterogeneities occurring on a scale greater than porescale, but less than wavelength scale, is responsible for significant attenuation in the frequency range from 10 to 1000 Hz. Most models of attenuation and dispersion due to mesoscopic heterogeneities imply that fluid heterogeneities are distributed in a periodic/regular way. In 1D this corresponds to periodically alternating layering, in 3D as periodically distributed inclusions of a given shape (usually spheres). All these models yield very similar estimates of attenuation and dispersion. Experimental studies show that mesoscopic heterogeneities have less idealized distributions and that the distribution itself affects attenuation and dispersion. Therefore, theoretical models are required which would simulate the effect of more general and realistic fluid distributions. We have developed two theoretical models which simulate the effect of random distributions of mesoscopic fluid heterogeneities. The first model assumes that one fluid forms a random ensemble of spherical inclusions in a porous medium saturated by the other fluid. The attenuation and dispersion predicted by this model are very similar to those predicted for 3D periodic distribution. Attenuation (inverse quality factor) is proportional to ω at low frequencies for both distributions. This is in contrast to the 1D case, where random and periodically alternating layering shows different attenuation behaviour at low frequencies. The second model, which assumes a 3D continuous distribution of fluid heterogeneities, also predicts the same low-frequency asymptote of attenuation. However, the shapes of the frequency dependencies of attenuation are different. As the 3D continuous random approach assumes that there will be a distribution of different patch sizes, it is expected to be better suited to modelling experimental results. Further research is required in order to uncover how to relate the random functions to experimentally significant parameters.

Long-patch Base Excision DNA Repair of 2-Deoxyribonolactone Prevents the Formation of DNA-Protein Cross-links with DNA Polymerase β

Oxidized abasic sites are a major form of DNA damage induced by free radical attack and deoxyribose oxidation. 2-Deoxyribonolactone (dL) is a C1'-oxidized abasic site implicated in DNA strand breakage, mutagenesis, and formation of covalent DNA-protein cross-links (DPCs) with repair enzymes such as DNA polymerase beta (polbeta). We show here that mammalian cell-free extracts incubated with Ape1-incised dL substrates under non-repair conditions give rise to DPCs, with a major species dependent on the presence of polbeta. DPC formation was much less under repair than non-repair conditions, with extracts of either polbeta-proficient or -deficient cells. Partial base excision DNA repair (BER) reconstituted with purified enzymes demonstrated that Flap endonuclease 1 (FEN1) efficiently excises a displaced oligonucleotide containing a 5'-terminal dL residue, as would be produced during long-patch (multinucleotide) BER. Simultaneous monitoring of dL repair and dL-mediated DPC formation demonstrated that removal of the dL residue through the combined action of strand-displacement DNA synthesis by polbeta and excision by FEN1 markedly diminished DPC formation with the polymerase. Analysis of the patch size distribution associated with DNA repair synthesis in cell-free extracts showed that the processing of dL residues is associated with the synthesis of >or=2 nucleotides, compared with predominantly single nucleotide replacement for regular abasic sites. Our observations reveal a cellular repair process for dL lesions that avoids formation of DPCs that would threaten the integrity of DNA and perhaps cell viability.

Landscape impacts from valuing core area in national forest planning

Forest core area was valued in a mathematical programming model to support decision-making for the most recent USDA Forest Service plans for national forests in Minnesota. A comparison of management schedules developed by the model to a strategy of simply designating pre-allocated areas for large patch production shows that valuing core area substantially increases the average patch size of mature forest. Analyses of maps of management schedules over the 100-year planning horizon using Fragstats, a computer program for spatial analysis, show substantial differences in spatial measures such as the overall distribution of patch sizes and edge-to-patch-area ratios. Model results reflect the fact that increasing patch sizes improves the efficiency of producing core area because less area of mature forest is then needed for buffer area to protect core area. Although the model cannot address patch size directly, results point to locations where large patches can likely be produced without large sacrifices in other objectives. Compared to other spatial modeling approaches, the approach is appealing because emphasis is on forest conditions rather than the size of harvested areas. Results demonstrate that multiple model runs can give forest planners insight regarding tradeoffs between spatial management objectives and other management objectives for areas as large as a national forest.

Effect of tephra depth on vegetation development in areas affected by volcanism

Plant establishment on sites affected by major volcanic disturbances is limited by several factors, such as lack of suitable microsites for germination and establishment in sites affected by tephra from volcanic eruptions. Even after long periods of time, tephra deposited over un-vegetated areas (agricultural fields and other barren areas) lack closed vegetation cover and in many cases late successional species. To assess limiting factors for plant establishment, a field survey in a tephra deposit from the Paricutin volcano eruption (19°30′42.4′′ N, 102°12′03.0′′) and greenhouse experiments were carried out. The field survey determined the relationship between tephra depth and vegetation distribution. Greenhouse experiments determined the effect of tephra depth on establishment and growth of two dominant species in the tephra deposit surveyed, Eupatorium glabratum and Lupinus elegans. Our results suggest that size and spatial distribution of vegetation patches is related to tephra depth in the field (77% of the vegetation patches were on tephra 38.8 cm deep or less and only 2% on tephra of more than 46.8 cm). Under greenhouse conditions, Eupatorium glabratum and Lupinus elegans height sharply decreased as depth of the tephra layer increased. Lupinus elegans plants growing in tephra less than 30 cm deep had a mean weight of 10.56 g (±0.53 g) compared with 3.11 g (±0.46 g) for plants growing in tephra more than 30 cm deep. Our results suggest that tephra depth is a limiting factor for canopy development in barren areas affected by tephra deposition.

The Riverside and Berwyn experience: Contrasts in landscape structure, perceptions of the urban landscape, and their effects on people

Humans not only structure the landscape through their activities, but their perceptions of nature are affected by the spatial and temporal arrangements (structure) in the landscape. Our understanding of these interactions, however, is limited. We explored the relationship between landscape structure and peoples’ perceptions of nature in the Chicago, IL, USA, suburbs of Riverside and Berwyn because they offer contrasting paradigms of an urban landscape. Designed in the 1800s by Frederick Law Olmsted, Riverside has several unique design elements (curvilinear streets, ample setbacks, parkways of variable width with mowed grass and naturalistic groupings of trees) that define the structure and composition of this landscape. The urban forest was the keystone of Olmsted's desire to create a harmonious community characterized by “refined sylvan beauty”. In contrast, the adjacent community of Berwyn has right-angled streets with small lots and narrow setbacks for houses. Differences in landscape structure between the two communities produced differences in the diversity, size, and composition of woody vegetation. As measured by patch-size distribution, Riverside had greater diversity in landscape structure than Berwyn, and in turn, Riverside had greater diversity in the composition and size of the woody vegetation compared to Berwyn. Riverside tended toward a “natural” appearance with vegetation, while yards in Berwyn tended to be trimmed and edged. Significant differences between the mean ratings of Riverside and Berwyn respondents were found for six of seven community attribute categories. Riverside participants reported receiving greater benefit from the visual and nature-related features of the urban forest than did Berwyn respondents. Berwyn residents ranked social atmosphere for the community and locomotion (wayfinding) highest among the seven community attribute categories. Despite differences between the two communities, residents valued the green residential environment provided by vegetation. However, the more diverse urban landscape as measured by built structures, woody vegetation, and lot size and shape proved to be more satisfying to the residents of these two communities. The design concepts developed and implemented by Olmsted more than century ago in Riverside are still relevant to city planners striving to develop living environments that are satisfying to urban and suburban residents.