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Edward B. Arnett - One of the best experts on this subject based on the ideXlab platform.
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Survival dynamics of mechanically topped Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) Snags in Douglas-fir plantations, Oregon, USA
Forest Ecology and Management, 2019Co-Authors: Matthew E. Hane, Andrew J. Kroll, Aaron Springford, Jack Giovanini, Mike Rochelle, Edward B. ArnettAbstract:Abstract Structural enrichment in commercial tree plantations is a potential tool to increase snag numbers but relatively little information is available about how species, size, and spatial distribution of created Snags are associated with longevity of these structures. We created 1197 Snags in 31 harvest units from 1997 to 1999 in the Cascade and Coast Ranges, Oregon, USA, by topping live trees with harvesting equipment. We used an experimental design to distribute created Snags at three densities and as either single or clumped created Snags. We fit Weibull and log-logistic Accelerated Failure Time models and found that the median failure time was insensitive to the choice of distribution. We found a small positive effect of diameter at breast height (DBH) and a slight negative effect of increasing distance between created Snags on survival. Assuming Weibull and log-logistic distributions at mean observed values of DBH and distance between Snags, median survival times for Douglas-fir (Pseudotsuga menziesii) were 21.0 (95% confidence interval: 19.3, 22.8) years and 21.2 (19.7, 22.8) years, respectively. For western hemlock (Tsuga heterophylla), median survival times were 13.0 (11.9, 14.2) years and 12.5 (11.4, 13.7) years, respectively. Although the two failure distributions had similar median failure times, the log-logistic implies a higher survival probability over time for Snags that remained standing at the end of the study period. Created Snags can be a useful supplement for harvest units rotated at ∼45 years and Douglas-fir will be available for longer as standing structures. For example, under the log-logistic model, a predicted 5% of Douglas-fir Snags are retained to rotation age, so that 40 Snags per hectare would be required at harvest to maintain 2 Snags per hectare through stand rotation. Snags created from western hemlock will provide an early rotation pulse but are unlikely to last longer than 20 years. Our results suggest that longevity can be increased by maximizing the snag size within the safety constraints of harvesting equipment. Scattering of Snags may have a slightly negative effect on snag survival but this outcome should be weighed against potential ecological benefits of variation in snag distributions.
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landscape composition influences avian colonization of experimentally created Snags
Biological Conservation, 2012Co-Authors: Andrew J. Kroll, Matthew E. Hane, Mike Rochelle, Steven D Duke, Josh R Johnson, Matthew G Betts, Edward B. ArnettAbstract:Abstract Landscape composition may have a substantial influence on species use of habitat at local scales and effectiveness of structural enrichment practices (e.g., augmenting existing amounts of Snags or downed logs). If sufficient mature (i.e., cavity containing) habitat exists at the landscape scale, cavity nester demand for nest sites could be reduced due to the surplus of existing sites ( habitat surplus hypothesis ). Alternatively, if mature forest acts as source habitat for cavity nesters, increased amounts of mature forest in the landscape will inflate the demand for Snags in clearcuts ( habitat source hypothesis ). In Oregon, USA, we evaluated cavity nesting bird colonization of experimentally created Snags distributed across a gradient in amount of mature forest at the landscape scale. We sampled 28 plots, each of which represented one of six combinations of created snag density (∼0.5, 1, and 2 Snags/ha) and spatial dispersion (clumps of 5–7 Snags or dispersed individual Snags). We tested whether early successional and mature forest species groups responded differently to plot-level treatments and if the percentage of mature forest (>40 years old) within a 1000 m radius surrounding each experimental plot influenced this response. Mature forest species more readily colonized created Snags as the percentage of mature forest declined in the landscape, supporting the habitat surplus hypothesis . Estimated use by mature forest species increased from 7% to 17% as percent mature forest in the landscape declined from 58% to 13% (estimated for average levels of created snag density, 0.4 Snags/ha, and a spatial distribution of 45 m). Colonization of Snags by early seral species also increased with decreasing mature forest (from 3% to 9%), which may support the habitat source hypothesis . Our study suggests that creating Snags in commercial harvest units is an effective practice for increasing structural complexity and maintaining nesting communities of cavity-dependent birds. At the local level, created Snags should be spaced as widely as possible within individual harvest units. However, our results indicate that effectiveness of snag creation will be highest in the most intensively managed landscapes where the amount of structurally diverse habitat is limited.
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avian foraging and nesting use of created Snags in intensively managed forests of western oregon usa
Forest Ecology and Management, 2010Co-Authors: Edward B. Arnett, Andrew J. Kroll, Steven D DukeAbstract:Abstract Snags are critical structural features for managing biological diversity in forests of the Pacific Northwest, USA. However, commercial forests in this region often contain reduced numbers of Snags compared to unmanaged forests and managers require effective methods to augment snag numbers in harvest units. Therefore, we created Snags by topping live trees with a mechanical harvester and studied foraging and nesting use by cavity-nesting birds of these Snags in clearcuts in Douglas-fir ( Pseudotsuga mensezii ) forests along the west slope of the Cascade Mountain Range and east slope of the Coast Range in Oregon, USA. We used a completely randomized design to assign 6 different treatments (single or scattered distribution by 3 different densities) to 31 different harvest units. We created 1111 Snags from February 1997 through April 1999 and monitored them from 2–5 years after harvest (1999–2002). Fraction of created Snags with nest cavities in harvest units was generally low across all treatments and years of the study, although some individual stands demonstrated increased nesting use with snag age. While the highest fractions of Snags with nest cavities were found in units with low density and scattered Snags, the mean fraction of Snags used for nesting did not differ among treatments. Treatment type, distribution of Snags (i.e., scattered or clumped), and associated interactions did not influence fraction of Snags used for foraging. However, fraction of created Snags used for foraging in all harvest units increased with snag age. Fraction of Snags used for foraging was greatest in the low density treatments. While this technique provides managers with a relatively economical option for creating Snags, mechanical harvesters cannot be used to create tall, large Snags upon which several cavity-dependent species rely and provides only a partial solution to a critical forest management issue.
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use of conifer Snags as roosts by female bats in western oregon
Journal of Wildlife Management, 2009Co-Authors: Edward B. Arnett, John P HayesAbstract:Forest management activities influence habitat suitability for bats, and knowledge of the roosting ecology of bats is fundamental to developing strategies for conserving bats in managed forests. Information on use of roosts by multiple species of bats in a given area may provide insight into interspecific ecological patterns and could improve management prescriptions to provide habitat for bats through time across diverse ownerships and over multiple spatial scales. We investigated use of conifer Snags as roosts by females of 3 species of forest-dwelling bats in Douglas-fir (Pseudotsuga menzesii) forests in the western Oregon Cascade Range. We radiotagged 29 female big brown bats (Eptesicus fuscus), 55 long-legged myotis (Myotis volans), and 27 long-eared myotis (Myotis evotis) and located 42, 105, and 24 snag roosts for the 3 species, respectively. All 3 species most frequently used Douglas-fir Snags and in similar proportions to their availability. Big brown bats and long-legged myotis rarely roosted in stands <40 years old but age of stands used by female long-eared myotis did not differ from those randomly available. Odds of a snag being used as a roost by big brown bats increased with diameter at breast height and decreased with distance from the capture site. Diameter of Snags used for roosting and the number of small (10–50 cm dbh) Snags within the 20-m radius plot were variables in the best model for roost use by long-legged myotis. The best model for long-eared myotis included distance to the capture site. Odds of a snag being used by female long-eared myotis decreased with increasing distance from the capture site. There was considerable overlap in structural characteristics and the physical context of roost Snags among the 3 species, but the types of roosts used among landscapes with differing densities of Snags differed among the 3 species. Although big brown bats and long-legged myotis used only Snags and live trees as roosts, long-eared myotis used a diversity of structures and the frequency of use of these structures differed with density of Snags in the landscape. Relative to other roost types, frequency of use of Snags by long-eared myotis was nearly twice as high in landscapes with high densities of Snags as in those with low densities. We found that some species of bats alter selection of roosts depending on landscape context and availability of different types of roosts. Our findings demonstrate that forest managers must consider the needs of multiple bat species and the distribution of roosts in the landscape, especially where densities of Snags are low and at low elevations in intensively managed landscapes.
Scott C Vojta - One of the best experts on this subject based on the ideXlab platform.
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characteristics of Snags containing excavated cavities in northern arizona mixed conifer and ponderosa pine forests
Forest Ecology and Management, 2004Co-Authors: Joseph L Ganey, Scott C VojtaAbstract:Snags provide an important resource for a rich assemblage of cavity-nesting birds in the southwestern United States. To expand our knowledge of snag use by cavity-nesting birds in this region, we documented characteristics of Snags with and without excavated cavities in mixed-conifer and ponderosa pine (Pinus ponderosa Dougl. ex Laws) forest in north-central Arizona. Snags were sampled in 113 square plots (1 ha each) randomly located within a study area covering approximately 73,000 ha across two National Forests. Density of Snags was three times greater in mixed-conifer forest (n = 53 plots) than in ponderosa pine forest (n = 60 plots), but density of Snags containing cavities and overall cavity density did not differ between forest types. In both forest types, Snags containing cavities were larger in diameter and retained less bark cover than Snags without cavities. Most cavities were in ponderosa pine and Gambel oak (Quercus gambelii Nutt.) Snags, and most were in Snags in advanced decay classes with broken tops. Our results are largely consistent with previous results from ponderosa pine forest, but differ from previous studies that documented heavy use of quaking aspen (Populus tremuloides Michaux) by cavity nesters in mixed-conifer forest. These results support management to protect and recruit large Snags well distributed across the landscape. The relatively high use of ponderosa pine and Gambel oak Snags in both forest types suggests that recruitment of large pine and oak Snags should be emphasized, and previous studies suggest emphasizing aspen recruitment as well. This may require special management efforts in mixed-conifer forest. These species are relatively shade-intolerant seral species in this forest type, and are apparently declining in this forest type due to fire-suppression efforts and resultant patterns of ecological succession.
Joseph L Ganey - One of the best experts on this subject based on the ideXlab platform.
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density of large Snags and logs in northern arizona mixed conifer and ponderosa pine forests
Forest Science, 2015Co-Authors: Joseph L Ganey, Benjamin J Bird, Scott L Baggett, Jeffrey S JennessAbstract:Large Snags and logs provide important biological legacies and resources for native wildlife, yet data on populations of large Snags and logs and factors influencing those populations are sparse. We monitored populations of large Snags and logs in mixed-conifer and ponderosa pine (Pinus ponderosa) forests in northern Arizona from 1997 through 2012. We modeled density of large Snags and logs as a function of forest type, time period, and environmental characteristics of sampled plots. Our objective was to build models that best explained current densities of these structures using these available covariates. The best model for density of large Snags indicated that snag density was greater in mixed-conifer than in ponderosa pine forests, lower in plots with evidence of past timber or fuelwood harvest than in plots lacking such evidence, and covaried positively with mean slope and distance to road. The best model for density of large logs indicated that log density was greater in mixed-conifer than in ponderosa pine forests and covaried positively with solar insolation and surface ratio (an index of topographic roughness). The best snag model predicted that current US Department of Agriculture (USDA) Forest Service guidelines for retention of large Snags were met only in mixed-conifer forests lacking evidence of past harvest activity. In contrast, the USDA Forest Service guidelines for retention of large logs were met in both forest types. Our results suggest that ease of human access and management history influence density of large Snags, that current snag guidelines are unlikely to be met without considering these impacts, and that those guidelines may not be readily attainable in much of the landscape.
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characteristics of Snags containing excavated cavities in northern arizona mixed conifer and ponderosa pine forests
Forest Ecology and Management, 2004Co-Authors: Joseph L Ganey, Scott C VojtaAbstract:Snags provide an important resource for a rich assemblage of cavity-nesting birds in the southwestern United States. To expand our knowledge of snag use by cavity-nesting birds in this region, we documented characteristics of Snags with and without excavated cavities in mixed-conifer and ponderosa pine (Pinus ponderosa Dougl. ex Laws) forest in north-central Arizona. Snags were sampled in 113 square plots (1 ha each) randomly located within a study area covering approximately 73,000 ha across two National Forests. Density of Snags was three times greater in mixed-conifer forest (n = 53 plots) than in ponderosa pine forest (n = 60 plots), but density of Snags containing cavities and overall cavity density did not differ between forest types. In both forest types, Snags containing cavities were larger in diameter and retained less bark cover than Snags without cavities. Most cavities were in ponderosa pine and Gambel oak (Quercus gambelii Nutt.) Snags, and most were in Snags in advanced decay classes with broken tops. Our results are largely consistent with previous results from ponderosa pine forest, but differ from previous studies that documented heavy use of quaking aspen (Populus tremuloides Michaux) by cavity nesters in mixed-conifer forest. These results support management to protect and recruit large Snags well distributed across the landscape. The relatively high use of ponderosa pine and Gambel oak Snags in both forest types suggests that recruitment of large pine and oak Snags should be emphasized, and previous studies suggest emphasizing aspen recruitment as well. This may require special management efforts in mixed-conifer forest. These species are relatively shade-intolerant seral species in this forest type, and are apparently declining in this forest type due to fire-suppression efforts and resultant patterns of ecological succession.
Andrew J. Kroll - One of the best experts on this subject based on the ideXlab platform.
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Survival dynamics of mechanically topped Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) Snags in Douglas-fir plantations, Oregon, USA
Forest Ecology and Management, 2019Co-Authors: Matthew E. Hane, Andrew J. Kroll, Aaron Springford, Jack Giovanini, Mike Rochelle, Edward B. ArnettAbstract:Abstract Structural enrichment in commercial tree plantations is a potential tool to increase snag numbers but relatively little information is available about how species, size, and spatial distribution of created Snags are associated with longevity of these structures. We created 1197 Snags in 31 harvest units from 1997 to 1999 in the Cascade and Coast Ranges, Oregon, USA, by topping live trees with harvesting equipment. We used an experimental design to distribute created Snags at three densities and as either single or clumped created Snags. We fit Weibull and log-logistic Accelerated Failure Time models and found that the median failure time was insensitive to the choice of distribution. We found a small positive effect of diameter at breast height (DBH) and a slight negative effect of increasing distance between created Snags on survival. Assuming Weibull and log-logistic distributions at mean observed values of DBH and distance between Snags, median survival times for Douglas-fir (Pseudotsuga menziesii) were 21.0 (95% confidence interval: 19.3, 22.8) years and 21.2 (19.7, 22.8) years, respectively. For western hemlock (Tsuga heterophylla), median survival times were 13.0 (11.9, 14.2) years and 12.5 (11.4, 13.7) years, respectively. Although the two failure distributions had similar median failure times, the log-logistic implies a higher survival probability over time for Snags that remained standing at the end of the study period. Created Snags can be a useful supplement for harvest units rotated at ∼45 years and Douglas-fir will be available for longer as standing structures. For example, under the log-logistic model, a predicted 5% of Douglas-fir Snags are retained to rotation age, so that 40 Snags per hectare would be required at harvest to maintain 2 Snags per hectare through stand rotation. Snags created from western hemlock will provide an early rotation pulse but are unlikely to last longer than 20 years. Our results suggest that longevity can be increased by maximizing the snag size within the safety constraints of harvesting equipment. Scattering of Snags may have a slightly negative effect on snag survival but this outcome should be weighed against potential ecological benefits of variation in snag distributions.
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landscape composition influences avian colonization of experimentally created Snags
Biological Conservation, 2012Co-Authors: Andrew J. Kroll, Matthew E. Hane, Mike Rochelle, Steven D Duke, Josh R Johnson, Matthew G Betts, Edward B. ArnettAbstract:Abstract Landscape composition may have a substantial influence on species use of habitat at local scales and effectiveness of structural enrichment practices (e.g., augmenting existing amounts of Snags or downed logs). If sufficient mature (i.e., cavity containing) habitat exists at the landscape scale, cavity nester demand for nest sites could be reduced due to the surplus of existing sites ( habitat surplus hypothesis ). Alternatively, if mature forest acts as source habitat for cavity nesters, increased amounts of mature forest in the landscape will inflate the demand for Snags in clearcuts ( habitat source hypothesis ). In Oregon, USA, we evaluated cavity nesting bird colonization of experimentally created Snags distributed across a gradient in amount of mature forest at the landscape scale. We sampled 28 plots, each of which represented one of six combinations of created snag density (∼0.5, 1, and 2 Snags/ha) and spatial dispersion (clumps of 5–7 Snags or dispersed individual Snags). We tested whether early successional and mature forest species groups responded differently to plot-level treatments and if the percentage of mature forest (>40 years old) within a 1000 m radius surrounding each experimental plot influenced this response. Mature forest species more readily colonized created Snags as the percentage of mature forest declined in the landscape, supporting the habitat surplus hypothesis . Estimated use by mature forest species increased from 7% to 17% as percent mature forest in the landscape declined from 58% to 13% (estimated for average levels of created snag density, 0.4 Snags/ha, and a spatial distribution of 45 m). Colonization of Snags by early seral species also increased with decreasing mature forest (from 3% to 9%), which may support the habitat source hypothesis . Our study suggests that creating Snags in commercial harvest units is an effective practice for increasing structural complexity and maintaining nesting communities of cavity-dependent birds. At the local level, created Snags should be spaced as widely as possible within individual harvest units. However, our results indicate that effectiveness of snag creation will be highest in the most intensively managed landscapes where the amount of structurally diverse habitat is limited.
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avian foraging and nesting use of created Snags in intensively managed forests of western oregon usa
Forest Ecology and Management, 2010Co-Authors: Edward B. Arnett, Andrew J. Kroll, Steven D DukeAbstract:Abstract Snags are critical structural features for managing biological diversity in forests of the Pacific Northwest, USA. However, commercial forests in this region often contain reduced numbers of Snags compared to unmanaged forests and managers require effective methods to augment snag numbers in harvest units. Therefore, we created Snags by topping live trees with a mechanical harvester and studied foraging and nesting use by cavity-nesting birds of these Snags in clearcuts in Douglas-fir ( Pseudotsuga mensezii ) forests along the west slope of the Cascade Mountain Range and east slope of the Coast Range in Oregon, USA. We used a completely randomized design to assign 6 different treatments (single or scattered distribution by 3 different densities) to 31 different harvest units. We created 1111 Snags from February 1997 through April 1999 and monitored them from 2–5 years after harvest (1999–2002). Fraction of created Snags with nest cavities in harvest units was generally low across all treatments and years of the study, although some individual stands demonstrated increased nesting use with snag age. While the highest fractions of Snags with nest cavities were found in units with low density and scattered Snags, the mean fraction of Snags used for nesting did not differ among treatments. Treatment type, distribution of Snags (i.e., scattered or clumped), and associated interactions did not influence fraction of Snags used for foraging. However, fraction of created Snags used for foraging in all harvest units increased with snag age. Fraction of Snags used for foraging was greatest in the low density treatments. While this technique provides managers with a relatively economical option for creating Snags, mechanical harvesters cannot be used to create tall, large Snags upon which several cavity-dependent species rely and provides only a partial solution to a critical forest management issue.
D S Decalesta - One of the best experts on this subject based on the ideXlab platform.
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the relationship between cavity nesting birds and Snags on clearcuts in western oregon
Forest Ecology and Management, 1992Co-Authors: B Schreiber, D S DecalestaAbstract:Relationships between cavity-nesting birds (CNB) and density and characteristics of Snags were investigated on 13 clearcuts in central coastal Oregon. Species richness and density of CNB were positively (P<0.05) related to snag density and were still increasing at the maximum snag density evaluated. Cavity-nesting birds selected (P<0.05) Snags taller than 6.4 m and greater than 78–102 cm in diameter, and avoided (P<0.05) Snags less than 28 cm in diameter. Snags of intermediate decay stages were used for nesting more (P<0.05) than Snags of early and advanced stages of decay. Cavity-nesting birds selected Snags with more (P<0.05) bark cover (greater than 11%) than the average cover found on available Snags. Individual CNB species exhibited significantly different (P<0.05) selections for snag height, diameter, hardness and bark cover. To optimize density and richness of CNB, forest managers should provide ≥ 14 Snags ha−1 between 28 and 128 cm diameter at breast height (dbh), between 6.4 and 25 m tall, with at least 10% bark cover, and with a majority in hardness stages 3 and 4.
