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A Landscape Habitat Suitability Model for the Humboldt Marten (Martes caurina humboldtensis) in Coastal California and Coastal Oregon
Abstract
Models that predict the distributions and habitat suitability for species of conservation concern can be useful for guiding survey, monitoring, and conservation planning efforts. The Humboldt marten (Martes caurina humboldtensis) has significantly declined throughout its historical range in coastal California and Oregon and this taxon is known from a few remnant populations. We developed a landscape habitat suitability model to identify areas of suitable habitat not yet surveyed, to provide a template for designing monitoring programs and research studies, and to inform the development of a conservation strategy. We used the results of 1,159 occupancy surveys to develop a predictive habitat model using Generalized Additive Modeling to relate Humboldt marten detections to combinations of environmental and habitat attributes hypothesized to influence marten distribution. We measured 30 candidate variables at three spatial scales, using 0.5, 1.0, and 3.0 km, and although several models were competitive, each contained the same three core variables: old growth structural index measured at the 1-km scale, serpentine habitat measured at the 3-km scale, and annual precipitation measured at the 3-km scale. The final model had an overall correct classification rate of 91% for marten detections, 82% for non-detections and a true skill statistic of 0.73. Model predictions were stable when cross-validated, with the correct classification of marten detections (89%) varying little. The largest complexes of predicted suitable habitat occurred in the areas with the three extant marten populations (north coastal California, south coastal Oregon, and central coastal Oregon), however connectivity of suitable habitat to areas outside these three areas appears limited.
... Contemporary surveys conducted throughout the historical range of the Humboldt marten in California and Oregon have identified four extant population areas (EPAs): two disjunct EPAs in Oregon along the central and southern Coast Range, and two disjunct EPAs in California, one in the northern Coast Range and the other farther inland near the California-Oregon border (CA-OR EPA; Slauson et al. 2018). Despite extensive survey efforts, there is still uncertainty about the exact distribution, population size, and habitat use of the few populations of Humboldt martens that remain (Moriarty et al. 2016, Slauson et al. 2019. In 2009, the northern coastal California EPA was estimated to contain fewer than 100 individuals (Slauson et al. 2009), and in 2018 the population size of the central coastal Oregon EPA was estimated at 71 individuals (95% Confidence Interval [CI] = 41-87; . ...
... Surveys of the northern coastal California EPA found that Humboldt martens were primarily associated with late-seral forest habitats, but they have also been detected in two low-productivity forest habitat types: shore pine (Pinus contorta) dominated coastal forest habitat found only on stabilized dunes , and serpentine forest habitat found only on ultramafic soils (Slauson et al. 2019). The central coastal Oregon EPA persists entirely in young, coastal forest habitat (< 70 years old; Eriksson et al. 2019), and detections in serpentine forest habitat have occurred in both the southern coastal Oregon EPA and northern coastal California EPA , Slauson et al 2019. ...
... Surveys of the northern coastal California EPA found that Humboldt martens were primarily associated with late-seral forest habitats, but they have also been detected in two low-productivity forest habitat types: shore pine (Pinus contorta) dominated coastal forest habitat found only on stabilized dunes , and serpentine forest habitat found only on ultramafic soils (Slauson et al. 2019). The central coastal Oregon EPA persists entirely in young, coastal forest habitat (< 70 years old; Eriksson et al. 2019), and detections in serpentine forest habitat have occurred in both the southern coastal Oregon EPA and northern coastal California EPA , Slauson et al 2019. Collectively, these two low-productivity forest habitat types are endemic to their parent soil types and are limited to < 8% of the Humboldt marten's historic range (Slauson et al. 2019). ...
... With the Humboldt marten emerging from believed extinction and occupying less than 5% of its historic range, it is now critical to identify suitable areas of habitat within its historic range where additional populations may occur or return. A recent study summarized data on >1000 occupancy surveys to develop the first range-wide landscape habitat suitability models for the Humboldt marten throughout its historic range (Slauson et al. 2019), identifying the CA -OR EPA as containing highly suitable habitat. In addition to high suitability, Humboldt martens have been detected in this area in recent years. ...
... Because my sample size for detections on serpentine soil was low, I removed them from my analysis to ensure my assessment of occupancy on non-serpentine habitat was not confounded by soil type. I believe this was justified as managers recommend focusing survey efforts on non-serpentine habitat, as previous research has revealed that although martens are found in serpentine habitats, these regions support lower numbers of females and may provide more unstable occupancy than areas on forest habitat in more productive soils (Slauson et al. 2019). ...
... This is consistent with my finding of martens using sample units on serpentine soil with very little size class 5 trees (>2%) but with higher amounts of shrub cover (47%). They also make use of the interstitial spaces in boulder piles for resting sites, as structures generally used for resting (i.e., large trees, snags, and logs) are uncommon in this habitat type (Slauson et al. 2019 survey area contained limited amounts of size class 5 trees, but areas beyond the survey area contain high amounts of size class 5 trees and should be investigated (Appendix E). ...
The Humboldt marten (Martes caurina humboldtensis) has declined from over 95% of its historic range in California, with only two populations remaining. In response to the forthcoming listing of the Humboldt marten a conservation assessment and strategy was developed to address the most important conservation needs for this species. This assessment identified an area near the California-Oregon border as the second extant population area in California based on a small number of recent detections. However little else was known of this population, and this prompted my investigation to determine 1) the distribution and potential population size and 2) habitat use by Humboldt martens in this area. This study addresses a key information need identified in the conservation strategy. Between May-August of 2017 and 2018, I used a 2-km systematic grid to sample 51 sample units using baited remote cameras and track plates and detected martens at 20 (39.2 %) sample units. Using an occupancy modeling approach, I found that a combination of elevation and amount of forest habitat with large diameter trees (size class 5, ≥ 60.0 cm QMD) measured at the home range scale (1-km radius, 314 ha) influenced marten occupancy. Marten occupancy was highest in low elevation sample units (mean = 614.6 m, SE = 35.6 m) with an average of 65.3 ha (20.1% of 314 ha, SE = iii 12.0 ha) of forest habitat in the largest tree size class. The limited number of detections precluded evaluating models with > 3 habitat variables, as well as assessing finer scale habitat use; however, univariate results suggested stream density may also be influential at the home range scale. Consistent with results from the larger California population, managers interested in promoting marten conservation in the California-Oregon extant population area should maintain and increase large patches of forest habitat with large-diameter trees. A novel finding for this population was the importance of low-elevation forest habitat dominated by size class 4 (27.9-59.9 cm QMD), suggesting the combination of home-range sized areas with these two habitat compositions is capable of supporting marten occupancy in this region.
... attenuata) from GNN. This variable was included because martens have been detected in shore pine communities in the Oregon Central Coast population Eriksson et al., 2019), and in areas with serpentine soils characterized by sparse cover of Jeffreyi and knobcone pine, stunted tree growth, and dense shrub understories (Kruckeberg, 1986;Safford, Viers & Harrison, 2005;Harrison et al., 2006;Slauson et al., 2019). We visually inspected the congruence of the serpentine soil layer created by the US Fish and Wildlife Service (Schrott & Shinn, 2020) with our percent pine layer, confirming overlap between the two variables. ...
... We developed a range-wide species distribution model for the Humboldt marten based on extensive survey effort and incorporation of contemporary vegetation and climatic conditions. Our model is complementary, but not similar, to other Humboldt marten distribution models (e.g., Slauson et al., 2019), which could lead to confusion when attempting to understand Humboldt habitat associations. Instead of interpreting differences between models as a conflict, we posit this as evidence of the conservation challenge described by Caughley (1994) and representative of the difficulty in establishing patterns of causality from observational studies. ...
... When examining our marten locations in a model only with the components of OGSI, downed wood was the most influential variable (Supplemental Item S1). We suspect the differences between our model and the Slauson et al. (2019) model resulted from non-stationary vegetation associations that were only revealed by increased survey effort across a broader geographic scope. While the Slauson et al. (2019) model relied on a modest number of Humboldt marten detections from 1996-2010 with poor coverage outside of northern California (USFWS, 2019), our model included a relatively large number of detections that occurred across a longer period of time , over a broader geographic scope in both California and Oregon (Barry, 2018;Gamblin, 2019;Linnell et al., 2018;Moriarty et al., 2019). ...
Background:
Many mammalian species have experienced range contractions. Following a reduction in distribution that has resulted in apparently small and disjunct populations, the Humboldt marten (Martes caurina humboldtensis) was recently designated as federally Threatened and state Endangered. This subspecies of Pacific marten occurring in coastal Oregon and northern California, also known as coastal martens, appear unlike martens that occur in snow-associated regions in that vegetation associations appear to differ widely between Humboldt marten populations. We expected current distributions represent realized niches, but estimating factors associated with long-term occurrence was challenging for this rare and little-known species. Here, we assessed the predicted contemporary distribution of Humboldt martens and interpret our findings as hypotheses correlated with the subspecies' niche to inform strategic conservation actions.
Methods:
We modeled Humboldt marten distribution using a maximum entropy (Maxent) approach. We spatially-thinned 10,229 marten locations collected from 1996-2020 by applying a minimum distance of 500-m between locations, resulting in 384 locations used to assess correlations of marten occurrence with biotic and abiotic variables. We independently optimized the spatial scale of each variable and focused development of model variables on biotic associations (e.g., hypothesized relationships with forest conditions), given that abiotic factors such as precipitation are largely static and not alterable within a management context.
Results:
Humboldt marten locations were positively associated with increased shrub cover (salal (Gautheria shallon)), mast producing trees (e.g., tanoak, Notholithocarpus densiflorus), increased pine (Pinus sp.) proportion of total basal area, annual precipitation at home-range spatial scales, low and high amounts of canopy cover and slope, and cooler August temperatures. Unlike other recent literature, we found little evidence that Humboldt martens were associated with old-growth structural indices. This case study provides an example of how limited information on rare or lesser-known species can lead to differing interpretations, emphasizing the need for study-level replication in ecology. Humboldt marten conservation would benefit from continued survey effort to clarify range extent, population sizes, and fine-scale habitat use.
... 393 Discussion 394This study provides the first systematic survey of the CA-OR EPA and addresses two of 395the key information needs identified in the Humboldt marten conservation strategy: 1) to 396 determine the distribution of martens in the CA-OR EPA, and 2) to identify habitat types that 397 most influence the distribution of marten in this area. Martens were detected both in and adjacent 398 to the previously mapped EPA boundary, suggesting the population was distributed more 399 broadly than initially predicted and reported in the Humboldt marten conservation strategy 400(Slauson et al. 2019). We suspect that the distribution of this population may exist most 401 significantly to the south, east, and southwest of the area we surveyed, based on the presence of 402 similar habitat conditions to where most martens were detected during our efforts. ...
... scales (Slauson et al. 2019, Moriarty et al. 2021) and we sought to follow these methods, it may 478 have been more appropriate to exclude the use of the smaller spatial scales (50-270-m) as these 479 did not match the scales of habitat selection we were explicitly modeling. We recommend that 480 the spatial scales used in multi-scale habitat analyses carefully evaluate scales of habitat 481 selection that the study design and dataset can address and select only spatial scales for 482 consideration that are relevant to the specific research objectives. ...
The Humboldt marten (Martes caurina humboldtensis) has declined from over 95 % of its historic range and currently occurs in just four extant population areas (EPAs). Prior to their listing under the Endangered Species Act, a conservation strategy was developed to identify key conservation needs for this species. This assessment identified an area near the California–Oregon (CA–OR) border as the second EPA in California, yet little was known about the overall distribution or habitat used by this population. This prompted our investigation to provide the first systematic survey of the CA–OR EPA and to assess habitat use under an occupancy modeling framework. Between 2017–2018 we surveyed 51 survey units in and around the EPA and detected martens at 20 (39.2 %). We found that occupancy was most influenced by the spatial scale-specific amount of low-elevation late-seral old-growth forest habitat, riparian habitat, and mid-seral forest habitat. Occupancy by marten was greatest in low-elevation (< 800 m) habitat and was positively associated with late-seral forest habitat at the 1,170-m home range scale (Odds Ratio [OR] = 35.31, 95 % CI = 1.30–958.07), riparian habitat at the 1,170-m home range scale (OR = 3.20, 95 % CI = 1.01–10.1), and increased amounts of mid-seral forest habitat at the 50-m microhabitat scale (OR = 1.28, 95 % CI = 0.95–1.73). Our findings identified habitat types important for explaining the distribution of this understudied population, addressing two of the highest priority research needs identified in the Humboldt marten conservation strategy.
... Although we were unable to obtain a habitat suitability map for the Humboldt marten, we did perform a coarse assessment using modeled habitat cores. It is not surprising that the overlap of moderate-high grow-site potential with marten habitat cores was lower than with fisher and northern spotted owl habitat, because martens are strongly associated with old-growth, dense-canopy forest patches or forests on serpentine soils [41], neither of which appear to be selected by growers. However, with over 37% overlap of key habitat core areas with moderatehigh grow-site likelihood, and knowledge that martens are also at risk of rodenticides used at cultivation sites to control rodents [14], risks to this threatened species are also significant. ...
Illegal cannabis cultivation on public lands has emerged as a major threat to wildlife in California and southern Oregon due to the rampant use of pesticides, habitat destruction, and water diversions associated with trespass grow sites. The spatial distribution of cultivation sites, and the factors influencing where they are placed, remain largely unknown due to covert siting practices and limited surveillance funding. We obtained cannabis grow-site locality data from law enforcement agencies and used them to model the potential distribution of cultivation sites in forested regions of California and southern Oregon using maximum entropy (MaxEnt) methods. We mapped the likely distribution of trespass cannabis cultivation sites and identified environmental variables influencing where growers establish their plots to better understand the cumulative impacts of trespass cannabis cultivation on wildlife. We overlaid the resulting grow-site risk maps with habitat distribution maps for three forest species of conservation concern: Pacific fisher (Pekania pennanti), Humboldt marten (Martes caurina humboldtensis), and northern spotted owl (Strix occidentalis caurina). Results indicate that cannabis cultivation is fairly predictably distributed on public lands in low to mid-elevation (~800-1600m) forests and on moderate slopes (~30–60%). Somewhat paradoxically, results also suggest that growers either preferred sites inside of recently disturbed vegetation (especially those burned 8–12 years prior to cultivation) or well outside (>500m) of recent disturbance, perhaps indicating avoidance of open edges. We ground-truthed the model by surveying randomly selected stream courses for cultivation site presence in subsets of the modeling region and found previously undiscovered sites mostly within areas with predicted high likelihood of grow-site occurrence. Moderate to high-likelihood areas of trespass cultivation overlapped with 40 to 48% of modeled habitats of the three sensitive species. For the endangered southern Sierra Nevada fisher population, moderate-high likelihood growing areas overlapped with over 37% of modeled fisher denning habitat and with 100% of annual female fisher home ranges (mean overlap = 48.0% + 27.0 SD; n = 134) in two intensively studied populations on the Sierra National Forest. Locating and reclaiming contaminated cannabis grow sites by removing all environmental contaminants should be a high priority for resource managers.
Accurate information on reproductive ecology is necessary to develop conservation actions for at-risk wildlife species. Our objective was to describe female reproductive parameters and den use of two subspecies of wild, untrapped Pacific martens (Humboldt marten, Martes caurina humboldtensis; Sierran marten, M. c. sierrae) of conservation interest in California. We used radio telemetry and remotely triggered cameras to monitor 10 Humboldt martens (2014 to 2016) and six Sierran martens (2016 to 2017) over 23 total denning periods. For Humboldt martens, mean parturition date was 13 April, proportion of adult females reproducing was 80% (n = 12 of 15), and mean litter size was 1.8 ± 0.6 kits (x̄ ± SD). For Sierran martens, mean parturition date was 29 April, proportion of adult females reproducing was 87% (n = 7 of 8), and mean litter size was 1.9 ± 0.7 kits. Humboldt and Sierran marten dens were predominantly located in woody structures, with live trees, snags, and logs comprising 91% and 79% of dens, respectively. Although reproductive ecologies of Humboldt and Sierran martens were largely similar, Sierran marten parturition dates were significantly later. We compare our study populations to other North American marten populations and examine factors that could influence consistency or variability in reproductive parameters between populations.
Background
A suite of mammalian species have experienced range contractions following European settlement and post-settlement development of the North American continent. For example, while North American martens (American marten, Martes americana ; Pacific marten, M. caurina ) generally have a broad range across northern latitudes, local populations have experienced substantial reductions in distribution and some extant populations are small and geographically isolated. The Humboldt marten ( M. c. humboldtensis ), a subspecies of Pacific marten that occurs in coastal Oregon and northern California, was recently designated as federally threatened in part due to its reduced distribution. To inform strategic conservation actions, we assessed Humboldt marten occurrence by compiling all known records from their range.
Methods
We compiled Humboldt marten locations since their rediscover to present (1,692 marten locations, 1996-2020). We spatially-thinned locations to 500-m to assess correlations with variables across contemporary Humboldt marten distribution (n=384). Using maximum entropy modeling (Maxent), we created distribution models with variables optimized for spatial scale; pre-selected scales were associated with marten ecology (50 to 1170 m radius). Marten locations were most correlated with abiotic factors (e.g., precipitation), which are unalterable and therefore uninformative within the context of restoration or management actions. Thus, we created variables to focus on hypothesized marten habitat relationships, including understory conditions such as predicted suitability of shrub species.
Results
Humboldt marten locations were positively associated with increased shrub cover (salal ( Gautheria shallon ), mast producing trees), increased pine ( Pinus sp ) overstory cover and precipitation at home-range spatial scales, areas with low and high amounts of canopy cover and slope, and cooler August temperatures. Unlike other recent literature on the species, we found little evidence that Humboldt marten locations were associated with old growth structural indices, perhaps because of a potential mismatch in the association between this index and shrub cover. As with any species distribution model, there were gaps in predicted distribution where Humboldt martens have been located during more recent surveys, for instance the southeastern portion of Oregon’s coast range. Conservation efforts and our assessment of potential risks to Humboldt marten populations would benefit from additional information on range extent, population sizes, and fine-scale habitat use. Like many rare and lesser-known species, this case study provides an example of how limited information can provide differing interpretations, emphasizing the need for study-level replication in ecology.
Conservation of mammals in the coniferous forests of western North America has shifted in recent years from species-based strategies to community- and ecosystem-based strategies, resulting in an increase in the available information on mammalian communities and their management. This book provides a synthesis of the published literature on the role of forest mammals in community structure and function, with emphasis on their management and conservation. In addition to coverage of some of the charismatic megafauna such as grizzly bears, gray wolves, mountain lions, elk and moose, the book also provides a thorough treatment of small terrestrial mammals, arboreal rodents, bats, medium-sized carnivores, and ungulates. The unique blend of theoretical and practical concepts makes this book equally suitable for managers, educators, and research biologists who will find it a valuable reference to the recent literature on a vast array of topics on mammalian ecology.
Pacific martens ( Martes caurina humboldtensis ) in coastal forests of Oregon and northern California in the United States are rare and geographically isolated, prompting a petition for listing under the Endangered Species Act. If listed, regulations have the potential to influence land-use decisions on public and private lands, but no estimates of population size, density, or viability of remnant marten populations are available for evaluating their conservation status. We used GPS and VHF telemetry and spatial mark-resight to estimate home ranges, density, and population size of Pacific martens in the Oregon Dunes National Recreation Area, central coast Oregon, USA. We then estimated population viability at differing levels of human-caused mortality (e.g., vehicle mortality). Marten home ranges were small on average (females = 0.8 km ² , males 1.5 km ² ) and density (1.13 martens/1 km ² ) was the highest reported for North American populations ( M. caurina , M. americana ). We estimated 71 adult martens (95% CRI [41–87]) across two subpopulations separated by a large barrier (Umpqua River). Using population viability analysis, extinction risk for a subpopulation of 30 martens, approximately the size of the subpopulation south of the Umpqua River, ranged from 32% to 99% with two or three annual human-caused mortalities within 30 years. Absent population expansion, limiting human-caused mortalities will likely have the greatest conservation impact.
Carnivorous mammals < 25 kg typically prey on species < 50% of their body mass but can choose prey whose energy value varies from small proportions of their daily needs to exceeding them. We hypothesized that for carnivores < 25 kg specializing in vertebrate prey, prey sizes closest to meeting daily energy needs would be most frequently depredated. We tested this hypothesis by reconstructing the diet of Humboldt martens using 528 scats and calculating the proportion of metabolizable energy (PME) that each prey taxon contributed to the diet. Overall, mammals dominated the diet (PME = 72%), followed by birds (PME = 22%), with berries, insects, and reptiles contributing < 10% PME. Sciurids comprised the largest proportion of all prey, representing 42% of overall PME, ranging from 29% (spring) to 51% (summer). While > 37 prey taxa were identified in the annual diet, only 11 contributed > 5% PME in any single season and the 4 dominant prey taxa in any single season represented 59–64% of that season’s PME. Medium-sized prey (85–225 g) composed 55–66% PME from summer through winter and 2.6 to 8.4 times PME compared to small (< 40 g) and large (> 250 g) prey during these 3 seasons, respectively. When PME for the most frequently consumed individual medium-sized prey (e.g., chipmunks) declined seasonally, martens switched to alternative medium-sized prey (2.8- and 2.5-fold increases in medium-sized birds and flying squirrels, respectively), increased use of large prey (> 8-fold increase), but changed use of small prey least. The annual importance of medium-sized prey, and seasonal shifts to similar-sized or larger prey during winter-spring seasons, both support our hypothesis that the most frequently depredated prey in the diet of Humboldt martens have body sizes closest to meeting daily energy needs.
Context
The success of species reintroduction often depends on predation risk and spatial estimates of predator habitat. The fisher (Pekania pennanti) is a species of conservation concern and populations in the western United States have declined substantially in the last century. Reintroduction plans are underway, but the ability of the species to establish a self-sustaining population is affected by predation from its primary predator, the bobcat (Lynx rufus).
Objectives
To develop a habitat model that incorporates both habitat of the focal species and the spatial patterning of predator habitat. To locate areas of densely aggregated habitat that would be suitable for reintroduction.
Methods
Using camera survey data, we modeled the association between bobcat presence and environmental features using a classification tree. We applied this model to a spatial analysis of fisher habitat and identified reintroduction areas in the southern Washington Cascade Range.
Results
The classification tree predicted bobcat detection based on elevation and mean tree diameter. The final model identified fisher reintroduction locations primarily in or near existing wilderness areas. Fisher habitat areas identified considering both habitat and predation risk differed from those identified without considering predation.
Conclusion
Our spatial approach is unique among fisher reintroduction plans by accounting for both resource requirements and risk of predation. It can be used as a template for future reintroduction efforts in other regions and for other species. Using similar models to refine population management and reintroduction should improve the probability of successful population establishment and stability.
Forest managers in the Pacific Northwest are faced with new challenges of providing for all wildlife in managed forests. Our objective was to elucidate the factors governing the composition and biomass of forest floor mammal communities that are amenable to management. We sampled small mammal communities in forests of various management histories on the Olympic Peninsula and contrasted our results with those of other large studies in the Pacific Northwest. Forest floor mammal communities in forests >35 yr old in the Western Hemlock Zone of Washington and Oregon are composed of 5-8 characteristic species. These include Sorex trowbridgii (numerically the most dominant); one species each of Clethrionomys, the Sorex vagrans complex, and Peromyscus; and Neurotrichus gibbsii. Species composition changes from south to north, and the communities on the Olympic Peninsula contain two or three additional species compared to communities to the south. Communities in naturally regenerated and clearcutting regenerated (managed) young forests are similar in composition to those in old growth, old growth, however, supports 1.5 times more individuals and biomass than managed forest. Community diversity seems related to the south-north moisture-temperature gradient that is reflected in increased diversity of canopy conifers, development of forest floor litter layers, accumulation of coarse woody debris, and abundance of herbs, deciduous shrubs, and shade-tolerant seedlings (as opposed to understories dominated by evergreen shrubs). Previous work found few habitat variables that were good predictors of species abundance in natural young and old-growth stands. Naturally regenerated young stands had higher levels of coarse woody debris than old growth. Managed stands had much lower abundance of coarse woody debris and tall shrubs than old growth. Understory vegetation (herbs and shrubs) and coarse woody debris accounted for a major part of the variation in abundance of six of eight species in managed stands, but only two species in old growth. Management of Western Hemlock Zone forest for conservation of biodiversity and restoration of old-growth conditions should concentrate on providing multispecies canopies, coarse woody debris, and well-developed understories.
Relationships between foraging habitat and reproductive success provide compelling evidence of the contribution of specific vegetative features to foraging habitat quality, a potentially limiting factor for many animal populations. For example, foraging habitat quality likely will gain importance in the recovery of the threatened red-cockaded woodpecker Picoides borealis (RCW) in the USA as immediate nesting constraints are mitigated. Several researchers have characterized resource selection by foraging RCWs, but emerging research linking reproductive success (e.g. clutch size, nestling and fledgling production, and group size) and foraging habitat features has yet to be synthesized. Therefore, we reviewed peer-refereed scientific literature and technical resources (e.g. books, symposia proceedings, and technical reports) that examined RCW foraging ecology, foraging habitat, or demography to evaluate evidence for effects of the key foraging habitat features described in the species' recovery plan on group reproductive success. Fitness-based habitat models suggest foraging habitat with low to intermediate pine Pinus spp. densities, presence of large and old pines, minimal midstory development, and herbaceous groundcover support more productive RCW groups. However, the relationships between some foraging habitat features and RCW reproductive success are not well supported by empirical data. In addition, few regression models account for 30% of variation in reproductive success, and unstandardized multiple and simple linear regression coefficient estimates typically range from 0.100 to 0.100, suggesting ancillary variables and perhaps indirect mechanisms influence reproductive success. These findings suggest additional research is needed to address uncertainty in relationships between foraging habitat features and RCW reproductive success and in the mechanisms underlying those relationships.
An understanding of the factors governing sciurid abundance in the Pacific Northwest is essential for prescribing forest management practices for second-growth forests where recovery of Spotted Owl (Strix occidentalis) populations and enhancement of biodiversity are objectives. We compared results of companion studies of sciurids in western Washington and Oregon and examined patterns of abundance in relation to habitat elements on the Olympic Peninsula to elucidate governing factors and make recommendations for forest management. Regional contrasts show that Glaucomys sabrinus and Tamias townsendii in Douglas-fir forests in Oregon are 4 times more abundant than in western hemlock forests in Washington, and dietaries of Glaucomys, and the fungal communities that provide its food, are more diverse in Oregon than in Washington. Glaucomys sabrinus in old forests are 2 times more abundant than in young, managed forests without old-forest legacies (large live trees, large snags and large, decaying fallen trees): populations in young forests with old-forest legacies and with understory development may equal those in old Growth. On the Olympic Peninsula. Glaucomys sabrinus abundance can be predicted by density of large snags and abundance of ericaceous shrubs. At least seven large snags/ha and well-distributed patches of dense shrubs (cover within patches >24% and patches covering 40% of the total area) are necessary for high densities of Glaucomys sabrinus. Abundance of Tamias townsendii reflects size of dominant tree and well-developed understories. Abundance of Ta,niasciurus douglasii seems to reflect territoriality in concordance with food supply and was greatest where Glaucomys and Tamias were low in abundance. Patterns of abundance of the sciurids in old- and managed forests suggests that silvicultural manipulation of vegetation and creative snag or den-tree management could be used in a management strategy to accelerate the development of Spotted Owl habitat in areas where old Growth is lacking.
The number of habitat conservation plans (HCP) has risen dramatically since the first plan was writ- ten over 18 years ago. Until recently, no studies have quantitatively investigated the scientific foundations un- derlying these documents. As part of a larger study of HCPs, we examined 43 plans primarily to assess the avail- ability and use of scientific data and secondarily to determine the extent of involvement by, and influence of, independent scientists within the process. Specifically, our analysis focused on five key steps taken when an HCP is developed: assessing status of a species, determining take, predicting the project effects, mitigating for those ef- fects, and monitoring of take and mitigation. In general, we found that the preparers of HCPs utilized existing scientific information fairly well, with 60% of plans not missing any available information described by our study as "starkly necessary." The most common types of underutilized available data included those describing the influence of stochastic processes and habitat quality or quantity on species persistence. For many species, however, data on biology or status simply did not exist, as demonstrated by the fact that we could locate quan- titative population estimates for only 10% of the species. Furthermore, for 42% of the species examined we had insufficient data and analysis to determine clearly how predicted take might affect the population. In many cases, mitigation measures proposed to offset take frequently addressed the most important local threats to the species with moderately reliable strategies. Species with monitoring programs rated as sufficient had plans that proposed to collect a greater amount of "quantitative" data than did those programs rated insufficient. Finally, when species "experts" were consulted, plan quality was generally higher. Overall, available scientific informa- tion in a majority of categories was fairly well utilized, but for many species additional studies and more in- depth analyses were required to provide adequate support for issuance of an incidental take permit.
Concerns about the fragmentation of Pacific Northwest forests are based on the assumption that these land- scapes historically contained large, contiguous patches of old growth. However, this supposition appears to conflict with disturbance history research, which shows that wildfire was an important component of pre-settlement forest eco- systems. To better quantify historical forest patterns, a spatial simulation model of wildfire and forest succession was used to simulate pre-settlement landscape dynamics in the Oregon Coast Range, U.S.A. The model was parameterized to simulate fire regimes over 1000 years prior to Euro-American settlement using data from paleoecological, dendro- ecological, and historical sources. A simple fire-spread algorithm produced mosaics of variable fire severity and al - lowed simulated fires to be calibrated to match the shapes of real fires. The simulated landscape was spatially heterogeneous and highly dynamic. Old growth was the dominant patch type occupying a median of 42% of the total area. The relatively long fire return intervals, highly skewed fire size distributions, and mixed severities characteristic of the historical fire regime generated a landscape mosaic with large (> 100 000 ha) patches of old-growth forest, al - though smaller patches ( 100 000 ha) de forêts anciennes, quoique les parcelles plus petites (
Spatially explicit information on the species composition and structure of forest vegetation is needed at broad spatial scales for natural resource policy analysis and ecological research. We present a method for predictive vegetation mapping that applies direct gradient analysis and nearest-neighbor imputation to ascribe detailed ground at - tributes of vegetation to each pixel in a digital landscape map. The gradient nearest neighbor method integrates vegeta - tion measurements from regional grids of field plots, mapped environmental data, and Landsat Thematic Mapper (TM) imagery. In the Oregon coastal province, species gradients were most strongly associated with regional climate and geographic location, whereas variation in forest structure was best explained by Landsat TM variables. At the regional level, mapped predictions represented the range of variability in the sample data, and predicted area by vegetation type closely matched sample-based estimates. At the site level, mapped predictions maintained the covariance structure among multiple response variables. Prediction accuracy for tree species occurrence and several measures of vegetation structure and composition was good to moderate. Vegetation maps produced with the gradient nearest neighbor method are appropriately used for regional-level planning, policy analysis, and research, not to guide local management deci - sions.
American martens (Martes americana) are associated strongly with mature conifer forests and once occurred throughout the mountains of the coastal Pacific states. We sought to document the distribution of martens in this region using historical records and to understand recent change in their distribution. We described the distribution of martens from 1900 to 1949 using museum and trapping records and compared it to recent (1989-1998) detections at camera and track-plate stations. Martens were detected at only 12 of the 237 (5.1%) survey sample units in coastal California, Oregon, and Washington. Martens are absent from most of the historical range of the Humboldt marten (M. a. humboldtensis) in California and also may have declined on the Olympic Peninsula of Washington. Few data exist from northwestern Oregon and southwestern Washington, but the limited amount of protected public land and absence of reported road kills are reasons for concern for populations in this region. Martens still occur in the central and southern coastal mountains of Oregon. Our results suggest that conservation of martens in coastal forests will require new initiatives to protect existing populations and new efforts to document all populations of martens in this region. Conservation measures should include a reevaluation of timber harvest plans that affect habitat in coastal forests, interagency cooperation on a coastal marten conservation assessment, and the collection of new survey information, especially on private lands in southwestern Washington and northwestern Oregon.
One way to increase aspen yields is to produce aspen on sites where aspen growth potential is highest. Aspen growth rates are typically predicted using site index, but this is impractical for landscape-level assessments. We tested the hypothesis that aspen growth can be predicted from site and climate variables and generated a model to map the spatial variability of aspen growth potential across the upper Great Lakes region. The model predicting aspen growth from climate and site characteristics performed nearly as well as the site index model. Sites currently growing aspen have a somewhat lower growth potential than do nonaspen upland sites. The mean growth potential of national forest sites is lower than on other ownerships, except in Michigan. Upland sites with the highest aspen growth potential had higher growth potential than sites currently growing aspen, suggesting that productivity could be increased by shifting the location of aspen production. Only 6.7% of the highest growth sites are located on national forests across the region. The spatially explicit nature of these results may facilitate cooperative planning to better optimize where aspen will be managed across a subregion to enhance regional productivity and to focus management where the potential for production is the greatest. FOR. SCI. 49(4):499508.
Knowledge of the community structure of ectomycorrhizal fungi among successional forest age-classes is critical for conserving fungal species diversity. Hypogeous and epigeous sporocarps were collected from three replicate stands in each of three forest age-classes (young, rotation-age, and old-growth) of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) dominated stands with mesic plant association groups. Over four fall and three spring seasons, 48 hypogeous and 215 epigeous species or species groups were collected from sample areas of 6300 and 43 700 m2, respectively. Cumulative richness of hypogeous and epigeous species was similar among age-classes but differed between seasons. Thirty-six percent of the species were unique to an age-class: 50 species to old-growth, 19 to rotation-age, and 25 to young stands. Seventeen species (eight hypogeous and nine epigeous) accounted for 79% of the total sporocarp biomass; two hypogeous species, Gautieria monticola Harkn., and Hysterangium crassirhachisZeller and Dodge, accounted for 41%. Average sporocarp biomass in young and rota- tion-age stands compared with old-growth stands was about three times greater for hypogeous sporocarps and six times greater for epigeous sporocarps. Average hypogeous sporocarp biomass was about 2.4 times greater in spring compared with fall and for epigeous sporocarps about 146 times greater in fall compared with spring. Re- sults demonstrated differences in ectomycorrhizal fungal sporocarp abundance and species composition among successional forest age-classes.
Transforming the results of species distribution modelling from probabilities of or suitabilities for species occurrence to presences/absences needs a specific threshold. Even though there are many approaches to determining thresholds, there is no comparative study. In this paper, twelve approaches were compared using two species in Europe and artificial neural networks, and the modelling results were assessed using four indices: sensitivity, specificity, overall prediction success and Cohen's kappa statistic. The results show that prevalence approach, average predicted probability/suitability approach, and three sensitivity-specificity-combined approaches, including sensitivity-specificity sum maximization approach, sensitivity-specificity equality approach and the approach based on the shortest distance to the top-left corner (0,1) in ROC plot, are the good ones. The commonly used kappa maximization approach is not as good as the afore-mentioned ones, and the fixed threshold approach is the worst one. We also recommend using datasets with prevalence of 50% to build models if possible since most optimization criteria might be satisfied or nearly satisfied at the same time, and therefore it's easier to find optimal thresholds in this situation.
Occupancy Estimation and Modeling: Inferring Patterns and Dynamics of Species Occurrence, Second Edition, provides a synthesis of model-based approaches for analyzing presence-absence data, allowing for imperfect detection. Beginning from the relatively simple case of estimating the proportion of area or sampling units occupied at the time of surveying, the authors describe a wide variety of extensions that have been developed since the early 2000s. This provides an improved insight about species and community ecology, including, detection heterogeneity; correlated detections; spatial autocorrelation; multiple states or classes of occupancy; changes in occupancy over time; species co-occurrence; community-level modeling, and more. Occupancy Estimation and Modeling: Inferring Patterns and Dynamics of Species Occurrence, Second Edition has been greatly expanded and detail is provided regarding the estimation methods and examples of their application are given. Important study design recommendations are also covered to give a well rounded view of modeling.
Information on the distribution of rare and little known species is critical for managers and biologists challenged with species conservation in an uncertain future. Pacific Martens (Martes caurina) historically resided throughout Oregon and northern California's coastal forests, but were considered extinct until 1996 when a population in northern California was rediscovered. Only 26 verified contemporary (1989–2012) records were known within Oregon prior to this survey. The coastal subspecies (M. c. humboldtensis) was petitioned for listing under the federal Endangered Species Act in 2010. We surveyed for martens during 2014–2015 with 3 separate, non-invasive surveys. We conducted exploratory surveys in 2014, and surveyed at 2 scales during 2015 to confirm the persistence of historical populations ( 1...
This is the second in a series of periodic monitoring reports on northern spotted owl (Strix occidentalis caurina) population and habitat trends on federally administered lands since implementation of the Northwest Forest Plan in 1994. Here we summarize results from a population analysis that included data from longterm demographic studies during 1985-2008. This data was analyzed separately by study area, and also in a meta-analysis across all study areas to assess temporal and spatial patterns in fecundity, apparent survival, recruitment, and annual rates of population change. Estimated rates of annual population decline ranged from 0.4 to 7.1 percent across federal study areas (weighted average of 2.8 percent). Covariates for barred owls (Strix varia), weather, climate, habitat, and reproductive success were analyzed and had varying degrees of association with owl demographic parameters. We now have more evidence that increasing numbers of barred owls and loss of nesting/roosting habitat contributed to demographic declines in some study areas. We also summarize results from a habitat analysis that used the above data in conjunction with remotely sensed data from 1994 to 2007 to develop "habitat suitability" models and habitat maps. These maps were used to quantify the amount and distribution of owl habitats. We also report on causes of habitat change during this period. On federal lands, nesting/roosting habitat declined by 3.4 percent rangewide, with some physiographic provinces experiencing losses of 10 percent. Dispersal habitat increased by 5.2 percent, but dispersal-capable landscapes declined by 1 percent. Wildfire remains the leading cause of habitat loss. We developed a rangewide "wildfire suitability" model and map to illuminate the portions of the owl's range where suitable nesting/roosting habitat overlaps with landscapes suitable for the occurrence of large wildfires. Barred owls and management of owl habitat in fire-prone areas continue to be topics for future monitoring, research, and management consideration.
Fishers (Pekania pennanti) in the west coast states of Washington, Oregon, and California, USA have not recovered from population declines and the United States Fish and Wildlife Service has proposed options for listing them as threatened. Our objectives were to evaluate differences in survival and mortality risk from natural (e.g., predation, disease, injuries, starvation) and human-linked causes (e.g., rodenticide exposure [toxicants], vehicle strikes). We monitored survival of 232 radio-collared fishers at a northern and southern study site in the Sierra National Forest, California. We retrieved fisher carcasses, and used necropsy examinations to determine causes of death. We estimated survival and mortality rates using the Kaplan-Meier estimator and nonparametric cumulative incidence functions, respectively, and integrated risk-specific survival rates into a Leslie matrix to evaluate how population growth (λ) might improve if management can reduce mortality from any of the risks. We determined cause of death for 93 of 121 fishers, and annual survival was 0.69 for all fishers, and 0.72 for female fishers. Mortality rates were 19.5% for predation; 2.5% for disease, injury, and starvation; and 1.9% for toxicant exposure and vehicle strikes. Predation rates were similar between sexes, and relative risk was 51% lower in fall and winter compared to spring and summer. Combined mortality from disease, injuries, starvation, vehicle strikes, and toxicants was 4.4%, and 11 times higher for males than females. We estimated a base λ at the northern site of 0.96, which had the potential to increase to 1.03 or 1.11 if predation were reduced by 25% or 50%, respectively, whereas λ could increase to 0.97 in the absence of deaths from all other risks except predation. Predation was the dominant limiting factor in our study population, and was also the most common mortality risk for fishers in the 3 West Coast states (67%), followed by disease, injury, and starvation (12%) and vehicle strikes (8%). Direct mortality from toxicants appeared limited to fishers in California. Our results identified the need for continued and potential expanded restrictions on habitat disturbance in fisher denning habitats. Research is needed on contact rates between larger predators and fishers, including whether fishers are more vulnerable to attack in open forests or along roads used by coursing predators.
Northwestern California has amassed its diverse flora over a long period of time, and from many sources. This chapter focuses on the classification and ecological dynamics of Northwestern forests. Northwestern California's forests are comprised of 100 tree species, 39 conifers, 22 oaks, and 26 currents and gooseberries among a vascular flora of 3,540 taxa. The chapter discusses conifer forests and reasons why they have limited ranges; forests in low-elevation, montane, and subalpine belts; and terrain and forests of the Klamath Mountains and the North Coast. It also looks at conservation and restoration efforts, and areas for future research.
List of Illustrations List of Tables Acknowledgments Abstract Introduction 1. History of Botanical Observations on the Serpentine Flora of California 2. Geology of Serpentine and Related Ultramafic Rocks 3. Serpentine Soils and the Mineral Nutrition of Plants 4. Physiological and Morphological Responses to Serpentine 5. Serpentine Vegetation in California 6. Serpentine Flora in California 7. Serpentine Fauna in California 8. The Evolutionary Ecology of Serpentine Biota in California 9. Exploitation of Serpentine and Other Ultramafics and Effects on Plant Life 10. Land Management and Conservation on Ultramafics Summary Appendices Literature Cited Plates
Logistic models are widely used in economics and other disciplines and are easily available as part of many statistical software packages. This text for graduates, practitioners and researchers in economics, medicine and statistics, which was originally published in 2003, explains the theory underlying logit analysis and gives a thorough explanation of the technique of estimation. The author has provided many empirical applications as illustrations and worked examples. A large data set - drawn from Dutch car ownership statistics - is provided online for readers to practise the techniques they have learned. Several varieties of logit model have been developed independently in various branches of biology, medicine and other disciplines. This book takes its inspiration from logit analysis as it is practised in economics, but it also pays due attention to developments in these other fields.
This report describes a program, FRAGSTATS, developed to quantify landscape structure. Two separate versions of FRAGSTATS exist: one for vector images and one for raster images. In this report, each metric calculated by GRAGSTATS is described in terms of its ecological application and limitations. Example landscapes are included, and a discussion is provided of each metric as it relates to the sample landscapes. -from Authors
With the rise of new powerful statistical techniques and GIS tools, the development of predictive habitat distribution models has rapidly increased in ecology. Such models are static and probabilistic in nature, since they statistically relate the geographical distribution of species or communities to their present environment. A wide array of models has been developed to cover aspects as diverse as biogeography, conservation biology, climate change research, and habitat or species management. In this paper, we present a review of predictive habitat distribution modeling. The variety of statistical techniques used is growing. Ordinary multiple regression and its generalized form (GLM) are very popular and are often used for modeling species distributions. Other methods include neural networks, ordination and classification methods, Bayesian models, locally weighted approaches (e.g. GAM), environmental envelopes or even combinations of these models. The selection of an appropriate method should not depend solely on statistical considerations. Some models are better suited to reflect theoretical findings on the shape and nature of the species’ response (or realized niche). Conceptual considerations include e.g. the trade-off between optimizing accuracy versus optimizing generality. In the field of static distribution modeling, the latter is mostly related to selecting appropriate predictor variables and to designing an appropriate procedure for model selection. New methods, including threshold-independent measures (e.g. receiver operating characteristic (ROC)-plots) and resampling techniques (e.g. bootstrap, cross-validation) have been introduced in ecology for testing the accuracy of predictive models. The choice of an evaluation measure should be driven primarily by the goals of the study. This may possibly lead to the attribution of different weights to the various types of prediction errors (e.g. omission, commission or confusion). Testing the model in a wider range of situations (in space and time) will permit one to define the range of applications for which the model predictions are suitable. In turn, the qualification of the model depends primarily on the goals of the study that define the qualification criteria and on the usability of the model, rather than on statistics alone.
Despite the abundance and ecological importance of Townsend's chipmunks (Tamias townsendii) in coniferous forests in the northwestern United States and southwestern Canada, little is known about either the habitat associations of the species or the influence of forest structure on population density. We livetrapped chipmunks in three mature, fire-regenerated coniferous forests (>140 years old) and nine 10- to 35-year-old Douglas-fir plantations in the Oregon Coast Range to examine patterns of their population density and habitat associations. Estimations of density of chipmunk populations among stands ranged from 0.0 to 23.8/ha. Population density within a stand did not significantly change between autumn and spring. Population density, mean maximum distance moved, and sex ratio did not differ significantly between young and mature stands, although mean body mass of chipmunks in mature forests was greater than mean body mass of those in young stands during autumn. Chipmunk population density was correlated with the percentage of salal (Gaultheria shallon) in the understory, suggesting that forest stand structure plays an important role in determining habitat quality for this species. Habitat characteristics in the Oregon Coast Range are highly favorable to Townsend's chipmunks, probably because of mild winters, high rates of primary production, structural characteristics of the stands, and minimal competition from other species of sciurids.
Forest carnivores such as the fisher (Martes pennanti) have frequently been the target of conserva- tion concern because of their association in some regions with older forests and sensitivity to landscape-level habitat alteration. Although the fisher has been extirpated from most of its former range in the western United States, it is still found in northwestern California. Fisher distribution, however, is still poorly known in most of this region where surveys have not been conducted. To predict fisher distribution across the region, we created a multiple logistic regression model using data from 682 previously surveyed locations and a veg- etation layer created from satellite imagery. A moving-window function in a geographic information system was used to derive landscape-level indices of canopy closure, tree size class, and percent conifer. The model was validated with new data from 468 survey locations. The correct classification rate of 78.6% with the new data was similar to that achieved with the original data set (80.4%). Whereas several fine-scale habitat at- tributes were significantly correlated with fisher presence, the multivariate model containing only landscape and regional-scale variables performed as well as one incorporating fine-scale data, suggesting that habitat selection by fishers may be dominated by factors operating at the home-range scale and above. Fisher distri- bution was strongly associated with landscapes with high levels of tree canopy closure. Regional gradients such as annual precipitation were also significant. At the plot level, the diameter of hardwoods was greater at sites with fisher detections. A comparison of regional fisher distribution with land-management categories suggests that increased emphasis on the protection of biologically productive, low- to mid-elevation forests is important to ensuring the long-term viability of fisher populations.
The philosophy of robust procedures is discussed. It is argued that the present emphasis by statistical researchers on ad hoc methods of robust estimation is mistaken. Classical methods of estimation should be retained using models which more appropriately represent reality. Attention should not be confined merely to discrepancies arising from outliers and heavy tailed distributions but should be extended to include serial dependence, need for transformation and other problems. Some researches of this kind using Bayes theorem are discussed. (Author)
American martens use resting habitat between periods of activity to provide both thermal refugia and protection from predators. Maintenance or restoration of key elements of marten resting habitat, such as resting structures, requires that managers recognize their characteristics to protect them, or manage for their creation. We measured resting habitat at 4 scales : (1) the resting location—where the marten actually rested; (2) the resting structure—the habitat element that contained the resting location; (3) the resting site—characteristics in the immediate vicinity of each resting structure; and (4) the resting stand—the forest stand containing the resting structure. During the summer and fall of 2001 and 2002 we identified resting structures used by 12 radio-collared martens (7 Male, 5 Female) and 1 uncollared marten. The animals were the members of the only remnant population of martens within the historical range of the Humboldt marten (M. a. humboldtensis). The study area included portions of the Six Rivers National Forest, Smith River National Recreation Area, and adjacent Green Diamond Resource Company lands in coastal northwestern California. We located martens resting on 55 occasions in the following types of structures: snags (37%), logs (23%), live-trees (17%), slash-piles (10%), rock-piles (8%), and shrub clumps (6%). The location in the structure where the marten actually rested was determined on 92% of occasions and included chambers (33%), cavities (33%), broken tops (22%), branch platforms (6%), ground sites (6%), and basal hollows (2%). Woody structures were large, with mean dbh of 93.9 cm for live-trees , 94.9 cm for snags, and 88.2 cm maximum-diameter for logs. The mean age of 24 of the woody resting structures was 339 years (range 131–666 years). Our results are consistent with results from other studies on resting structure use and highlight the importance of large live and dead woody structures for American martens in coastal forests of northwestern California.
We assessed the spatial independence of fisher (Martes pennanti) detections at sooted aluminum track plates deployed in northwestern California during 1994 and 1995. We used six track plates with 1 km spacing to form a 5 km segment. We estimated the probability of detecting fishers using program CAPTURE. We evaluated temporal and spatial relations among track plates within each six-station segment using nonlinear regression and a randomization test. Estimated probabilities of initially detecting a fisher (capture) were 0.04 and 0.07, and probabilities of subsequent detection (recapture) were 0.36 and 0.3 in 1994 and 1995, respectively. A nonlinear regression of mean number of detections per segment on time had an upper asymptote of 1.22 indicating that detections at stations did not increase linearly through time. We found that on 25 of 30 segments, the observed data were likely to occur under the null hypothesis of no dependency. The segments with potential spatial dependencies were characterized by low numbers of detections (≤4 out of a possible 66) and did not effect conclusions. We viewed the results of the randomization test and the regression as evidence that fisher detections at track plates were not dependent upon previous detections at neighboring track plates. However, because individual fishers were not marked, we could not assess independence with respect to individual animals. When using between-station distances similar to those evaluated in this study, individual track plates are appropriate sampling units for indexing populations, assessing trends or for future investigations of habitat use.
We developed the landscape age-class demographics simulator (LADS) to model historical variability in the amount of old-growth and late-successional forest in the Oregon Coast Range over the past 3,000 years. The model simulated temporal and spatial patterns of forest fires along with the resulting fluctuations in the distribution of forest age classes across the landscape. Parameters describing historical fire regimes were derived from data from a number of existing dendroecological and paleoecological studies. Our results indicated that the historical age-class distribution was highly variable and that variability increased with decreasing landscape size. Simulated old-growth percentages were generally between 25% and 75% at the province scale (2,250,000 ha) and never fell below 5%. In comparison, old-growth percentages varied from 0 to 100%, at the late-successional reserve scale (40,000 ha). Province-scale estimates of current old-growth (5%) and late-successional forest (11%) in the Oregon Coast Range were lower than expected under the simulated historical fire regime, even when Potential errors irt our parameter estimates were considered. These uncertainties no, however, limit our ability to Precisely define ranges of historical variability. Our results suggest that in areas where historical disturbance regimes were characterized by large infrequent fires, management of forest age classes based on a range of historical variability may be feasible only at relatively large spatial scales. Comprehensive landscape management strategies will need to consider other factors besides the percentage of old forests on the landscape, including the spatial pattern of stands and the rates and pathways of landscape change.
Maps of species' distributions or habitat suitability are required for many aspects of environmental research, resource management and conservation planning. These include biodiversity assessment, reserve design, habitat management and restoration, species and habitat conservation plans and predicting the effects of environmental change on species and ecosystems. The proliferation of methods and uncertainty regarding their effectiveness can be daunting to researchers, resource managers and conservation planners alike. Franklin summarises the methods used in species distribution modeling (also called niche modeling) and presents a framework for spatial prediction of species distributions based on the attributes (space, time, scale) of the data and questions being asked. The framework links theoretical ecological models of species distributions to spatial data on species and environment, and statistical models used for spatial prediction. Providing practical guidelines to students, researchers and practitioners in a broad range of environmental sciences including ecology, geography, conservation biology, and natural resources management.
In recent years the use of species distribution models by ecologists and conservation managers has increased considerably, along with an awareness of the need to provide accuracy assessment for predictions of such models. The kappa statistic is the most widely used measure for the performance of models generating presence–absence predictions, but several studies have criticized it for being inherently dependent on prevalence, and argued that this dependency introduces statistical artefacts to estimates of predictive accuracy. This criticism has been supported recently by computer simulations showing that kappa responds to the prevalence of the modelled species in a unimodal fashion.
In this paper we provide a theoretical explanation for the observed dependence of kappa on prevalence, and introduce into ecology an alternative measure of accuracy, the true skill statistic (TSS), which corrects for this dependence while still keeping all the advantages of kappa. We also compare the responses of kappa and TSS to prevalence using empirical data, by modelling distribution patterns of 128 species of woody plant in Israel.
The theoretical analysis shows that kappa responds in a unimodal fashion to variation in prevalence and that the level of prevalence that maximizes kappa depends on the ratio between sensitivity (the proportion of correctly predicted presences) and specificity (the proportion of correctly predicted absences). In contrast, TSS is independent of prevalence.
When the two measures of accuracy were compared using empirical data, kappa showed a unimodal response to prevalence, in agreement with the theoretical analysis. TSS showed a decreasing linear response to prevalence, a result we interpret as reflecting true ecological phenomena rather than a statistical artefact. This interpretation is supported by the fact that a similar pattern was found for the area under the ROC curve, a measure known to be independent of prevalence.
Synthesis and applications . Our results provide theoretical and empirical evidence that kappa, one of the most widely used measures of model performance in ecology, has serious limitations that make it unsuitable for such applications. The alternative we suggest, TSS, compensates for the shortcomings of kappa while keeping all of its advantages. We therefore recommend the TSS as a simple and intuitive measure for the performance of species distribution models when predictions are expressed as presence–absence maps.
1. Few examples of habitat-modelling studies of rare and endangered species exist in the literature, although from a conservation perspective predicting their distribution would prove particularly useful. Paucity of data and lack of valid absences are the probable reasons for this shortcoming. Analytic solutions to accommodate the lack of absence include the ecological niche factor analysis (ENFA) and the use of generalized linear models (GLM) with simulated pseudo-absences.
2. In this study we tested a new approach to generating pseudo-absences, based on a preliminary ENFA habitat suitability (HS) map, for the endangered species Eryngium alpinum. This method of generating pseudo-absences was compared with two others: (i) use of a GLM with pseudo-absences generated totally at random, and (ii) use of an ENFA only.
3. The influence of two different spatial resolutions (i.e. grain) was also assessed for tackling the dilemma of quality (grain) vs. quantity (number of occurrences). Each combination of the three above-mentioned methods with the two grains generated a distinct HS map.
4. Four evaluation measures were used for comparing these HS maps: total deviance explained, best kappa, Gini coefficient and minimal predicted area (MPA). The last is a new evaluation criterion proposed in this study.
5. Results showed that (i) GLM models using ENFA-weighted pseudo-absence provide better results, except for the MPA value, and that (ii) quality (spatial resolution and locational accuracy) of the data appears to be more important than quantity (number of occurrences). Furthermore, the proposed MPA value is suggested as a useful measure of model evaluation when used to complement classical statistical measures.
6. Synthesis and applications. We suggest that the use of ENFA-weighted pseudo-absence is a possible way to enhance the quality of GLM-based potential distribution maps and that data quality (i.e. spatial resolution) prevails over quantity (i.e. number of data). Increased accuracy of potential distribution maps could help to define better suitable areas for species protection and reintroduction.
ABSTRACT We investigated habitat selection using single- and mixed-scale modeling at 2 spatial scales, stand and home range, by the only known population of American martens (Martes americana) remaining in the historical range of the Humboldt subspecies (M. a. humboldtensis) in California, USA. During 2000 and 2001, we sampled a 12 times 14 grid with 2-km spacing, using 2 sooted track plates at each grid point. We detected martens at 26 of the 159 grid points. We used resource selection probability functions and an information-theoretic method to model habitat at detection locations. At the stand scale, martens selected conifer-dominated stands with dense, spatially extensive shrub cover (x̄ = 74% cover, SE = 4) in the oldest developmental stage. At the home-range scale, martens selected the largest available patches (x̄ = 181 ha, SE = 14) of old-growth, old-growth and late-mature, or serpentine habitat. Mixed-scale models revealed that habitat characteristics from both scales best explained marten occurrence compared to one scale alone. Dense, spatially extensive shrub cover is a key habitat element for martens in coastal forests. Dense shrubs provide refuge from predators, cover for prey, and may also deter larger-bodied competitors. Managers can increase the likelihood of marten population persistence and encourage expansion in coastal forests by maintaining and restoring late-mature and old-growth, conifer-dominated forests with dense shrub cover in large, contiguous patches.
To describe the forest mosaic suitable for marten ( Martes americana) in a clearcut boreal landscape, we studied habitat selection in an area (123 km2) located in western Québec, in which black spruce ( Picea mariana) was the predominant forest type. This block had been recently clearcut with the protection of regeneration cutting technique, a logging method that employs equally spaced harvesting trails. The resulting landscape had a center dominated by a cutover matrix (60% of the block) and surrounded by contiguous uncut forest. Over 2 years, 20 marten equipped with radio collars provided enough locations to delineate their winter home range. Habitat composition and spatial configuration were measured at both stand and landscape scales by means of a geographic information system database that included telemetry locations and home ranges, forest maps, and limits of clearcut areas. Inside their winter home ranges, animals avoided open regenerating stands composed mostly of recent clearcuts with sparse regeneration. They did not select coniferous stands, even those that were mature or overmature, but preferred deciduous and mixed stands, a large proportion of which had a dense coniferous shrub layer as a result of a spruce budworm (Choristoneura fumiferana) epidemic 15–20 years ago. At the landscape scale, winter home ranges differed from random mosaics because they had a larger proportion of uncut forest (>30 years), a smaller proportion of open regenerating stands, larger core area in forest habitat, and less edge between open regenerating stands and forest. Winter home ranges usually contained <30–35% open or closed regenerating stands and> 40–50% uncut forest. We conclude that marten and clearcutting may be compatible, provided that forest logging is adapted to that species at the landscape level. Where the objective is to maintain marten at a local scale in black spruce forest, we suggest that ≥50% uncut forest be preserved inside 10-km2 units and that <30% of the area be clearcut over a 30-year period.
Resumen: Para describir un mosaico forestal viable para la marta (Martes americana) en un paisaje boreal con tala total estudiamos la selección del hábitat en un bloque de paisaje (123 km2) localizado al oeste de Quebec, en el cual el abeto negro (Picea mariana) fue el tipo de hábitat predominante. Este bloque ha sido recientemente talado en su totalidad con la técnica de corte de protección de la regeneración, un método que emplea caminos de cosecha separados equidistantemente. El paisaje resultante tiene un centro dominado por una matriz de corte (60% del bloque) y está rodeado por un bosque contiguo sin cortar. Equipamos 20 martas con radiocollares por dos años, proporcionando suficientes localidades para delinear su rango de hogar para el invierno. La composición del hábitat y la configuración espacial fueron medidas a dos escalas (sitio y paisaje) utilizando una base de datos de GIS que incluyó ubicaciones por telemetría y rangos de hogar, mapas del bosque y límites de áreas de tala. Dentro de sus rangos de hogar del invierno, los animales evitaron los sitios abiertos en regeneración compuestos mayormente por talas recientes con regeneración dispersa. Las martas no seleccionaron los parches con coníferas, aún siendo maduros o viejos, pero prefirieron los sitios decíduos y mezclados, una larga proporción de los cuales tuvo una capa arbustiva densa de coníferas como resultado de una epidemia de hace 15 años del gusano del retoño del abeto ( Choristoneura fumiferana). A escala de paisaje, los rangos de hogar difirieron de los mosaicos al azar debido a que existía una proporción de bosque sin cortar más grande (>30 años), una proporción más pequeña de sitios abiertos en regeneración, un área más grande de hábitat forestal y una menor cantidad de borde entre los sitios abiertos en regeneración y el bosque. Los rangos de hogar del invierno generalmente contenían <30–35% de sitios abiertos o cerrados en regeneración y más de 40–50% de bosque sin cortar. Concluimos que la marta y los clareos totales pueden ser compatibles, a condición de que la tala del bosque esté adaptada a esta especie a nivel de paisaje. Donde el objetivo es mantener las martas a una escala local en bosques de abeto negro, sugerimos que sea preservado ≥50% del bosque sin cortar dentro de unidades de 10 km2 y que <30% del área sea talada a lo largo de un período de 30 años.
1. We investigated the effects of forest fragmentation on American martens (Martes americana Rhoads) by evaluating differences in marten capture rates (excluding recaptures) in 18 study sites with different levels of fragmentation resulting from timber harvest clearcuts and natural openings. We focused on low levels of fragmentation, where forest connectivity was maintained and non-forest cover ranged from 2% to 42%.
2. Martens appeared to respond negatively to low levels of habitat fragmentation, based on the significant decrease in capture rates within the series of increasingly fragmented landscapes. Martens were nearly absent from landscapes having > 25% non-forest cover, even though forest connectivity was still present.
3. Marten capture rates were negatively correlated with increasing proximity of open areas and increasing extent of high-contrast edges. Forested landscapes appeared unsuitable for martens when the average nearest-neighbour distance between open (non-forested) patches was <100 m. In these landscapes, the proximity of open areas created strips of forest edge and eliminated nearly all forest interior.
4. Small mammal densities were significantly higher in clearcuts than in forests, but marten captures were not correlated with prey abundance or biomass associated with clearcuts.
5. Conservation efforts for the marten must consider not only the structural aspects of mature forests, but the landscape pattern in which the forest occurs. We recommend that the combination of timber harvests and natural openings comprise <25% of landscapes ≥9 km2 in size.
6. The spatial pattern of open areas is important as well, because small, dispersed openings result in less forest interior habitat than one large opening at the same percentage of fragmentation. Progressive cutting from a single patch would retain the largest amount of interior forest habitat.