On tests of spatial pattern based on simulation envelopes

Baddeley, Adrian; Diggle, Peter J.; Hardegen, Andrew; Lawrence, Thomas Joseph; Milne, Robin K.; Nair, Gopalan

doi:10.1890/13-2042.1

Cited by 177 publications

(187 citation statements)

References 44 publications

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“…We used these functions (in R statistical software) to compare measured distances between drumlins to expectations of CSR, producing a metric indicative of dispersion (regularity), randomness or clustering. To further this approach it is common to use simulation envelopes to compare the observed result to Monte-Carlo simulations of CSR derived from a Poisson (or other) process (Baddeley et al, 2014). Defining the bounding box is an important consideration, as it forms the spatial domain over which simulations of CSR are implemented and Output from the L-function for the complete data set (black) and the patch (blue).…”

Section: Spatial Statistical Methods For Assessing Regularitymentioning

confidence: 99%

Spatial organization of drumlins

Clark

Ely

Spagnolo

et al. 2017

Earth Surf Processes Landf

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Ice-sheets flowing over soft sediments produce undulations in the bed, typically of metres in relief, of which drumlins are the most abundant and widely investigated. Consensus regarding their mechanism of formation has yet to be achieved. In this paper we examine the spatial organization of drumlins in order to provide an improved description of the phenomenon and to guide hypotheses of their formation. We review the literature highlighting contradictory findings regarding drumlin spatial organization and then use this to motivate our study based on a large sample (42 488) of drumlins from Canada, Britain and Norway. Are there typical arrangements in drumlin positioning and are they organized in a regular spatial manner (patterned) or are they distributed randomly? We recognize that drumlin fields are inherently patchy and therefore apply inhomogeneous spatial statistics in order to study their distribution. This shows that whilst drumlins are occasionally randomly placed, their main state is non-random. They exhibit a strong and statistically significant signal of regularity across lengths scales of 100 to 1200 m. We conclude that patterning is a near ubiquitous property of drumlins. This finding of regularity demonstrates spatial self-organization in the bedforming process with drumlins as an emergent manifestation of sub-glacial sediment mobility. Kilometre-scale interactions between drumlins must occur as they evolve, or interactions may arise as a consequence of growth or migration. Hypotheses or models are required that can explain the regular spacing of drumlins. We highlight three suggestions for such self-organization: instability in the coupling of ice flowsediment flux-bed shape; local feedback between sediment mobility and relief; and coarsening by growth or migration.

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Section: Spatial Statistical Methods For Assessing Regularitymentioning

confidence: 99%

Spatial organization of drumlins

Clark

Ely

Spagnolo

et al. 2017

Earth Surf Processes Landf

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“…The K function estimates spatial dependence between points of the same type (e.g., residual trees) across spatial scales by determining the expected number of points within a distance (r) from any randomly sampled point. For each plot, we evaluate deviations from complete spatial randomness (CSR) by comparing observed data with an inhomogeneous Poisson null model [49][50][51]. We used an inhomogeneous rather than a homogeneous Poisson process to account for non-constant density gradients in the data [52].…”

Section: Residual Forest Structurementioning

confidence: 99%

Mixed-Severity Fire Fosters Heterogeneous Spatial Patterns of Conifer Regeneration in a Dry Conifer Forest

Malone

Fornwalt

Battaglia

et al. 2018

Forests

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Abstract:We examined spatial patterns of post-fire regenerating conifers in a Colorado, USA, dry conifer forest 11-12 years following the reintroduction of mixed-severity fire. We mapped and measured all post-fire regenerating conifers, as well as all other post-fire regenerating trees and all residual (i.e., surviving) trees, in three 4-ha plots following the 2002 Hayman Fire. Residual tree density ranged from 167 to 197 trees ha −1 (TPH), and these trees were clustered at distances up to 30 m. Post-fire regenerating conifers, which ranged in density from 241 to 1036 TPH, were also clustered at distances up to at least 30 m. Moreover, residual tree locations drove post-fire regenerating conifer locations, with the two showing a pattern of repulsion. Topography and post-fire sprouting tree species locations further drove post-fire conifer regeneration locations. These results provide a foundation for anticipating how the reintroduction of mixed-severity fire may affect long-term forest structure, and also yield insights into how historical mixed-severity fire may have regulated the spatially heterogeneous conditions commonly described for pre-settlement dry conifer forests of Colorado and elsewhere.

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“…At each site both L and O functions were used in the analysis. O-rings width was influenced by the distance of biological interactions [46], which was restricted by tree spacing. Rings were 10 m in width at densely-planted sites (Rookery wood, Sandpit wood, Sheen wood, Winding wood) and 20 m at the remaining, more open, sites.…”

Section: Spatial Relationship Between Emergence Holes and Stem Bleedsmentioning

confidence: 99%

Acute Oak Decline and Agrilus biguttatus: The Co-Occurrence of Stem Bleeding and D-Shaped Emergence Holes in Great Britain

Brown

Jeger

Kirk

et al. 2017

Forests

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Acute Oak Decline (AOD) is a new condition affecting both species of native oak, Quercus robur and Quercus petraea, in Great Britain. The decline is characterised by a distinctive set of externally visible stem symptoms; bark cracks that "weep" dark exudate are found above necrotic lesions in the inner bark. Emergence holes of the buprestid beetle, Agrilus biguttatus are often also seen on the stems of oak within affected woodlands. This investigation assesses the extent to which the external symptoms of these two agents co-occur and reveals the spatial and temporal patterns present in affected woodland. Annual monitoring in eight affected woodlands showed that stem bleeding and emergence holes frequently occur on the same trees, with new emergence holes significantly more likely to occur when trees already have stem bleeds. Trials with coloured prism traps confirm A. biguttatus was present at all experimental sites. Beetle emergence is linked primarily to a few heavily declining trees, indicating that susceptibility may vary between hosts and that those with reduced health may be predisposed to AOD. Stem bleeds occur on trees in close proximity to the locations of trees with exit holes.

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On tests of spatial pattern based on simulation envelopes

Cited by 177 publications

References 44 publications

Spatial organization of drumlins

Spatial organization of drumlins

Mixed-Severity Fire Fosters Heterogeneous Spatial Patterns of Conifer Regeneration in a Dry Conifer Forest

Acute Oak Decline and Agrilus biguttatus: The Co-Occurrence of Stem Bleeding and D-Shaped Emergence Holes in Great Britain

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