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In the tropics, widespread deforestation and conversion of primary forests to agricultural and pasture lands has resulted in losses of composition, structure, and functions of forest landscapes. Deforestation ...
Citation Citation
- Title:
- Landscape level patterns in biodiversity : plant species and biomass structure
- Author:
- Heider, Christopher
In the tropics, widespread deforestation and conversion of primary forests to agricultural and pasture lands has resulted in losses of composition, structure, and functions of forest landscapes. Deforestation in the tropics is typically preformed via slash-and-burn practices; the byproducts from combustion have been identified as the second-highest form of anthropogenically derived 'greenhouse-gases' (such as carbon dioxide) to the atmosphere, and have been linked to the warming of the earth. Landscape-scale measures of species composition and biomass structure of primary forests are important for two reasons: (i) they provide accurate, land-based measures to predict what has been lost due to land-uses, and (ii) they aid in the discovery of key factors which explain patterns in compositional and structural diversity that are useful for defining conservation objectives. In this thesis, I enumerate the landscape-level patterns in species composition and biomass and C structure for 20-0.79 ha primary tropical forest stands within the region of "Los Tuxtlas", Veracruz, Mexico. These 20 sites were selected to capture the variability in composition and structure with respect to an array of environmental variables. These variables included a wide elevational range (15-1280 m.a.s.l.), variable slopes (Range: 3-41% slope), 3 soil-types (ash derived, lava flows, and weathered soils), a gradient of mean annual temperatures (~19.5-25.7°C), a broad precipitation range (2500 - 4000 mm year⁻¹), a rainfall frequency range (i.e. max rainfall in 24 hours; ranged 30->100 mm day⁻¹), and 3 Holdridge Life Zones (Tropical Moist Forest, Subtropical Wet Forest, and Subtropical Lower Montane Rain Forest). Species composition was highly correlated with the environmental variables, particularly elevation. In general for plants ≥10 cm dbh, site species richness declined at a rate of ~2 species per 100 m rise in elevation. Forest sites located at similar elevations were most similar in their species compositions as compared with sites separated by large elevational differences. Despite the gradual change in species richness and composition, four sub-regions, or forest environments, within Los Tuxtlas were identified that had different species compositions and distinct combinations of elevation, soil-types, and climates. These four sub-regions were described as community-types according to their geographic location: Lowland-Reserve (LR), La Perla Plateau (LP), Volcanic Upslope (VU), and Cloud Forests (CF). The LR, LP, and VU community-types were coarsely described as Tropical Evergreen Forests (TEF's; INEGI 2001). All community-types corresponded with classifications within the Holdridge Life Zone System; the LR community-type was classified as Tropical (transition to Subtropical) Moist Forest; LP and VU community-types were classified as Subtropical Wet Forest, and the Cloud Forest community-type was classified as Subtropical Lower Montane Rain Forest. These community-types and Life Zones are useful tools for conservation, as they represent unique forests that collectively capture much of the variation in the species richness and compositional diversity of the Los Tuxtlas region. Unlike species composition, the variability in forest structure among the 18 TEF sites was not associated with the environmental variables of the Los Tuxtlas landscape. On average, TEF's had a total aboveground biomass (TAGB) of 422 ± 17 Mg ha⁻¹ and 205 ± 8 Mg ha⁻¹ total aboveground carbon (C). The TAGB and C pools for Cloud Forests was ~18% lower than TEF's, and averaged 346 ± 1 and 168 ± 1 Mg ha⁻¹, respectively. The majority of this biomass difference was due to large trees within the forest structure. Cloud Forests had generally fewer trees ≥70 cm dbh, and a more even distribution of trees 30-70 cm dbh than TEF's. The biomass contribution of large trees (≥70 cm dbh) accounted for most, if not all, of the variation in TAGB and C for these tropical forests. The relatively high TAGB and C pools implicates Los Tuxtlas forests as a significant pool of aboveground biomass and C within the Neotropics.
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The Fish and Wildlife Service and the National Marine Fisheries Service (Services) have adopted a policy that will address the conservation needs of species listed, or proposed to be listed, under the ...
Citation Citation
- Title:
- Federal Register - Notice of Policy for Conserving Species Listed or Proposed for Listing Under the Endangered Species Act While Providing and Enhancing Recreational Fisheries Opportunities; Notice
- Year:
- 1996, 2008, 2005
The Fish and Wildlife Service and the National Marine Fisheries Service (Services) have adopted a policy that will address the conservation needs of species listed, or proposed to be listed, under the Endangered Species Act of 1973, as amended (ESA) while providing for the continuation and enhancement of recreational fisheries. This policy identifies measures the Services will take to ensure consistency in the administration of the ESA between and within the two agencies, promote collaboration with other Federal, State, and Tribal fisheries managers, and improve and increase efforts to inform nonfederal entities of the requirements of the ESA while enhancing recreational fisheries. This policy meets the requirements set forth in Section 4 of Executive Order 12962, Recreational Fisheries
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Pacific lamprey Entosphenus tridentatus is a valuable icon and traditional food source for Indigenous people of western North America. Native Americans have utilized traditional ecological knowledge (TEK) ...
Citation Citation
- Title:
- Pacific lamprey Entosphenus tridentatus : integrating traditional ecological knowledge and contemporary values into conservation planning, and stream substrate associations with larval abundance in the Willamette River Basin, Oregon, U.S.A.
- Author:
- Sheoships, Gabe
Pacific lamprey Entosphenus tridentatus is a valuable icon and traditional food source for Indigenous people of western North America. Native Americans have utilized traditional ecological knowledge (TEK) since time immemorial to guide their ways of life, transmitting cultural values and natural history to further generational knowledge. Pacific lamprey are in decline throughout their range, and have historically been disregarded in western science. The Willamette River Basin, Oregon, U.S.A currently supports a traditional harvest location, Willamette Falls, which continues to persist, despite great losses in adjacent basins and remains a harvest stronghold amongst Columbia River Basin Tribes. To further understand Pacific lamprey, we utilized both Indigenous knowledge and western science to gain information that would aid recovery. My first goal was to determine traditional ecological knowledge and the cultural values of Pacific lamprey to provide guidance for future conservation planning. My second goal was to evaluate the fine scale habitat characteristics of larval Pacific lamprey. To determine tribal values for the purpose of informing conservation planning of Pacific lamprey, I used: 1) oral history interviews of tribal elders, and 2) questionnaires distributed across entire adult (18 years and older) tribal populations. We conducted semi-structured interviews with tribal elders to gain insights into the biology, distribution, and cultural value of lamprey. I interviewed 32 tribal elders, 11 from the Grand Ronde, 10 from the Siletz, and 11 from the Umatilla. To understand modern fishing practices and current values of lamprey, I distributed a standardized questionnaire (n = 753) to a sample of each adult (18 years and older) tribal population, and received a total of 188 responses total: 38 from the Grand Ronde, 60 from the Siletz, and 90 from the Umatilla. From my interviews, I found that each tribe has noticed a decline in Pacific lamprey populations within their ceded areas, and has witnessed traditional harvest locations lost due to population declines and/or anthropogenic damage, leaving Willamette Falls as the sole harvest site for the three tribes. Questionnaire results showed that the strongest issues relating to the traditional usage of Pacific lamprey amongst each tribe are cultural awareness, harvest accessibility, and Pacific lamprey populations. I evaluated two fine scale habitat associations of larval Pacific lamprey in the Willamette River Basin to understand the association of stream sediment and larval abundance. Study objectives were to: 1) evaluate the substrate size most closely associated with larval abundance, and 2) to evaluate the influence of organic material upon larval abundance. We used a backpack electrofisher to enumerate larval lamprey in six wadeable Willamette River tributaries, using a nested two-pass sample design at a lower, middle, and upper reach (each reach composed of ten 1-m² quadrats). Stream sediment cores were collected for subsequent determination of particle size and organic composition content. I used particle size sieve analysis to estimate dominant substrate size class per sample, from the following size classes: silt (< 0.063 mm), very fine sand (0.063–0.125 mm), fine sand (0.125-0.25 mm), medium fine sand (0.25-0.50 mm), coarse sand (0.50-1.0 mm), very coarse sand (1.0-2.36 mm), and fine gravel (>2.36 mm). I analyzed organic content by loss of weight through combustion. Larvae were present in 17 of 18 reaches (94%) 18), but only detected in 37% of the quadrats. Larval Pacific lamprey abundance was highest in habitats with predominantly medium fine sand (0.25-0.50 mm) substrate. I fit negative binomial mixed models using parameters for sediment depth, percentage of medium fine sand (0.25-0.50 mm), organic material and a random effect for basin. My top model consisted of percentage of medium fine sand (0.25-0.50 mm), organic material and a random effect for basin. At the fine scale, substrate characteristics were associated with the abundance of larval Pacific lamprey. Appropriate conservation measures should be taken to address the restoration of Pacific lamprey, activities that promote natural river flow and distribution of sediment could be of benefit. Efforts that educate mainstream society should be implemented to reduce further species decline. With the continued decline of Pacific lamprey, there is potential for further degradation of tribal cultural values. Conservation work that promotes the restoration of Pacific lamprey is crucial to the tradition and culture of the Grand Ronde, Siletz, and Umatilla Tribes.
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Some of the most pressing conservation concerns involve declining populations of species with low fecundity and highly specialized foraging and reproductive requirements. Yet, we often lack a functional ...
Citation Citation
- Title:
- Habitat use and movement behavior of Pacific marten (Martes caurina) in response to forest management practices in Lassen National Forest, California
- Author:
- Moriarty, Katie M.
Some of the most pressing conservation concerns involve declining populations of species with low fecundity and highly specialized foraging and reproductive requirements. Yet, we often lack a functional understanding of how individuals of those species interact with their environment, specifically how their movement is affected by human-induced changes. In order to maintain connectivity and viable populations, public land managers require science to inform how changes in structure affect the individual movements and thus population connectivity of sensitive species. I collected detailed movement data on Pacific martens (Martes caurina) in Lassen National Forest, California, during 2010-2013. Martens are small carnivores that are closely associated with old forest elements (e.g., large snags and logs). Marten populations rapidly decline with loss and fragmentation of forest cover. As such, martens are a U.S. Forest Service Management Indicator Species and a Species of Special Concern in the state of California. My goal was to understand martens' behavior in forest patches that were altered by thinning to remove ladder fuels-small diameter trees, understory vegetation, and branches near the ground. Such fuels treatments are increasingly prevalent on public lands, especially in dry forests, to reduce risk of high-severity and high-intensity fire. Although previous research suggested martens selection for dense forest and avoid gaps in forest cover, no information was available describing martens' use of simplified thinned patches. The objectives of my dissertation were to: (1) test whether marten movement and activity could accurately be measured using miniature GPS collars, and (2) evaluate marten use, selection, and behavior in patches that differed in structural complexity. Global positioning system (GPS) telemetry provides opportunities to collect detailed information from free-ranging animals with a high degree of precision and accuracy. Miniature GPS collars (42-60g) have only been available since 2009 for mammals and have not been consistently effective. Furthermore, all GPS units suffer from non-random data loss and location error, which is often exacerbated by dense vegetation. Given these constraints, it was questionable whether GPS collars would be an effective tool for studying martens. In Chapter 1, I evaluated how satellite data and environmental conditions affected performance of GPS units. I used a paired experimental design and programmed the GPS unit to retain or remove satellite data before attempting a location (fix). I found that short intervals between fix attempts significantly increased the likelihood of fix success. Locations estimated using at least 4 satellites were, on average, within 28 m of the actual location regardless of vegetation cover. Thus, location estimates at short intervals with >4 satellites were not typically biased by dense vegetation. Accurate fine-scale information on martens was necessary to quantify and interpret patch use and habitat selection. I evaluated martens’ use and behavior in three forest patch types that differed in structural complexity (complex, simple, and open). In Chapter 2, I quantified use patch use in two seasons–summer and winter. I used food-titration experiments to standardize motivation of martens to enter different patch types and compared these short-term incentivized experiments with year-round observational telemetry data (GPS and very high frequency telemetry). Martens selected complex patches and avoided both simple patches and openings, but not equivalently–openings were strongly avoided. With baited incentive, martens were more likely to enter simple patches and openings during winter, when deep snow was present. Because marten patch use differed during winter, I concluded that researchers should use caution when using seasonally collected data to create year-round habitat models. Overall, movement was most limited during summer when predation risk likely deterred martens from moving through simple patches and openings. In Chapter 3, I quantified habitat selection and marten behavior using fine-scale movement data. I evaluated movement-based habitat selection at two scales: (1) selection of home ranges within landscapes and (2) selection of patches within the home ranges. I characterized marten movement patterns and tested whether variance, speed, and sinuosity of movements differed by patch, sex, and season. Martens selected home ranges with fewer openings than available in the landscape, and selected complex patches over simple patches and openings within their home range. On average, martens moved approximately 7 km per day and greater than 1 km per hour – which is notably high for a 600-1000g mammal. Martens moved more slowly, consistently, and sinuously in complex patches. In openings, martens traveled linearly with greater variance in their speed. In simple patches, movement generally was linear and rapid with some variation. I hypothesized that martens used complex patches for foraging and acquisition of resources, traveled through simple patches with the potential for infrequent foraging bouts, and very infrequently crossed openings. Although I found some differences in movement behavior between sexes and seasons, behavior was generally consistent for both sexes in different patch types. I provide general conclusions in Chapter 4 and discuss considerations for future research and management.
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65. [Article] 2006 Oregon Chub Investigations Progress Reports 2006
Abstract -- Oregon chub Oregonichthys crameri, small minnows endemic to the Willamette Valley, were federally listed as endangered under the Endangered Species Act in 1993. Factors implicated in the decline ...Citation Citation
- Title:
- 2006 Oregon Chub Investigations Progress Reports 2006
Abstract -- Oregon chub Oregonichthys crameri, small minnows endemic to the Willamette Valley, were federally listed as endangered under the Endangered Species Act in 1993. Factors implicated in the decline of this species include changes in flow regimes and habitat characteristics resulting from the construction of flood control dams, revetments, channelization, diking, and the drainage of wetlands. The Oregon chub is further threatened by predation and competition by non-native species such as largemouth bass Micropterus salmoides, crappies Pomoxis sp., sunfishes Lepomis sp., bullheads Ameiurus sp., and western mosquitofish Gambusia affinis. We continued surveys initiated in 1991 in the Willamette River drainage to quantify the abundance of known Oregon chub populations, search for unknown populations, evaluate potential introduction sites, and monitor introduced populations as part of the implementation of the Oregon Chub Recovery Plan. We sampled a total of 103 sites in 2006. No new populations of Oregon chub were discovered. Thirty-five of the 103 sites were new locations that were sampled for the first time in 2006. Sixty-eight sites, sampled on at least one occasion between 1991-2005, were revisited. We confirmed the continued existence of Oregon chub at 33 locations. These included 23 naturally occurring and 10 introduced populations. Locations of naturally occurring populations were: Santiam drainage (Geren Island, Santiam I-5 Side Channels, Santiam Conservation Easement, Stayton Public Works Pond, Green’s Bridge Backwater, Pioneer Park, Santiam Conservation Easement, and Gray Slough), Mid-Willamette drainage (Finley Gray Creek Swamp), McKenzie drainage (Shetzline Pond and Big Island), Coast Fork Willamette drainage (Coast Fork Side Channels and Lynx Hollow), and the Middle Fork Willamette drainage (two Dexter Reservoir alcoves, East Fork Minnow Creek Pond, Shady Dell Pond, Buckhead Creek, two Elijah Bristow State Park sloughs and an island pond, Barnhard Slough, and Hospital Pond). Introduced populations were located in the Middle Fork Willamette (Wicopee Pond and Fall Creek Spillway Ponds), Santiam (Foster Pullout Pond), McKenzie (Russell Pond), Coast Fork Willamette (Herman Pond), and Mid-Willamette drainages (Dunn Wetland, Finley Display Pond, Finley Cheadle Pond, Ankeny Willow Marsh, and Jampolsky Wetlands). We did not find Oregon chub at 14 locations where they were collected on at least one occasion between 1991-2005 (Jasper Park Slough, Wallace Slough, East Ferrin Pond, Dexter East Alcove, Hospital Impoundment Pond, Rattlesnake Creek, Elijah Bristow Large Gravel Pit, Elijah Bristow Small Gravel Pit, Little Muddy Creek tributary, Bull Run Creek, Camas Swale, Barnhard Slough, Camous Creek, and Dry Muddy Creek). Nonnative fish were collected at most of these locations. We obtained abundance estimates of naturally occurring populations of Oregon chub at 18 locations in the Middle Fork Willamette (East Fork Minnow Creek Pond, Shady Dell Pond, Elijah Bristow State Park Sloughs and Island Pond, Hospital Pond, Dexter Reservoir Alcoves, Haws Pond, and Buckhead Creek), Santiam (Geren Island, Gray Slough, Stayton Public Works Pond, Pioneer Park Pond, and Santiam I-5 Side Channels), McKenzie (Big Island and Shetzline Pond), and Mid-Willamette drainages (Finley Gray Creek) (Table 1). We obtained abundance estimates for 10 introduced populations of Oregon chub, located in Fall Creek Spillway Ponds, Wicopee Pond, Dunn Wetland Ponds, Finley Display Pond, Finley Cheadle Pond, Ankeny Willow Marsh, Jampolsky Wetlands, Foster Pullout Pond, Herman Pond, and Russell Pond. The three largest populations in 2006 were introduced populations. In addition, we evaluated eleven potential Oregon chub introduction sites in the Willamette River drainage. We introduced Oregon chub into the South Stayton Pond, a recently restored site located on ODFW property in the Santiam drainage, from Stayton Public Works Pond and Pioneer Park Pond. The Oregon Chub Recovery Plan (U.S. Fish and Wildlife Service 1998) set recovery criteria for downlisting the species to “threatened” and for delisting the species. The criteria for downlisting the species are: 1) establish and manage 10 populations of at least 500 adult fish, 2) all of these populations must exhibit a stable or increasing trend for five years, and 3) at least three populations meeting criterion 1 and 2 must be located in each of the three recovery areas (Middle Fork Willamette River, Santiam River, and Mid-Willamette River tributaries). In 2006, there were 18 populations totaling 500 or more individuals (Table 1). Thirteen of these populations also met the second criteria. Of the 13 populations meeting criteria 1 and 2, eight were located in the Middle Fork Willamette drainage, three were located in the Mid-Willamette drainage, and two were located in the Santiam drainage. With the addition of one more stable population in the Santiam drainage, the downlisting criteria will be met. Findings to date indicate that Oregon chub remain at risk due to the loss of suitable habitat and the continued threats posed by the proliferation of non-native fishes, illegal water withdrawals, accelerated sedimentation, and potential chemical spills or careless pesticide applications. Their status has improved in recent years, resulting primarily from successful introductions and the discovery of previously undocumented populations.
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66. [Image] Endangered species: difficult choices
IB10072 08-26-04 Endangered Species: Difficult Choices SUMMARY The 108th Congress is considering various proposals to amend the Endangered Species Act of 1973 (ESA). Major issues in recent years ...Citation Citation
- Title:
- Endangered species: difficult choices
- Author:
- Buck, Eugene H; Corn, M. Lynne (Mary Lynne), 1946-; Baldwin, Pamela
- Year:
- 2004, 2008, 2005
IB10072 08-26-04 Endangered Species: Difficult Choices SUMMARY The 108th Congress is considering various proposals to amend the Endangered Species Act of 1973 (ESA). Major issues in recent years have included changing the role of science in decision-making, changing the role of critical habitat, reducing conflicts with Department of Defense activities, incorporating further protection for property owners, and increasing protection of listed species, among others. In addition, many have advocated including significant changes to ESA regulations made during the Clinton Administration in the law itself. The ESA has been one of the more contentious environmental laws. This may stem from its strict substantive provisions, which can affect the use of both federal and non-federal lands and resources. Under the ESA, certain species of plants and animals (both vertebrate and invertebrate) are listed as "endangered" or "threatened" according to assessments of their risk of extinction. Once a species is listed, powerful legal tools are available to aid its recovery and protect its habitat. The ESA may also be controversial because dwindling species are usually harbingers of resource scarcity: the most common cause of listing species is habitat loss. Recent efforts in the House would modify ESA provisions that designate critical habitat, and that provide for scientific peer review. The authorization for spending under the ESA expired on October 1, 1992. The prohibitions and requirements of the ESA remain in force, even in the absence of an authorization, and funds have been appropriated to imple- ment the administrative provisions of the ESA in each subsequent fiscal year. In the 108th Congress, two bills (H.R. 1662 and H.R. 2933) have been reported that would, respectively, address issues concerning scientific peer review and critical habitat. These bills may be brought to the House floor in September. Earlier, P.L. 108-108 (Interior appropriations) provided $265 million for FY2004 for programs related to endangered species. P.L. 108-136 (Defense authorization) included an ESA amendment to direct that critical habitat not be designated on military lands under certain conditions when Integrated Natural Resources Management Plans are in effect. P.L. 108-137 (Energy and Water appropriations) prohibited use of FY2004 or earlier funds to reduce water deliveries under existing contracts for ESA compliance for the silvery minnow on the Middle Rio Grande River unless water is obtained from a willing seller or lessor. The act also established an executive committee to oversee the Collaborative Program associated with this situation. P.L. 108-148 (Healthy Forests Act) authorized hazardous fuels reduction projects on BLM and national forest lands including those containing listed species habitat; directed establishment of a healthy forests reserve program to promote recovery of listed species; and directed the Secretary of the Interior to provide assurances to landowners whose enrollment in the healthy forests reserve program results in new conservation benefits for ESA-listed species.
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67. [Article] Responses of foothill yellow-legged frog (Rana boylii) larvae to an introduced predator
The consequences of species introductions into non-native habitats are a major cause of concern in the U.S. An introduced species may alter native habitats, cause economic damage, compete with natives ...Citation Citation
- Title:
- Responses of foothill yellow-legged frog (Rana boylii) larvae to an introduced predator
- Author:
- Paoletti, David J.
The consequences of species introductions into non-native habitats are a major cause of concern in the U.S. An introduced species may alter native habitats, cause economic damage, compete with natives for resources or prey on them. Of particular interest are the effects of predation by introduced fishes on native amphibians. Amphibians as a group have been declining worldwide due to a variety of factors, one of which being introduced species. In the Pacific Northwest of the U.S., one example of these declining amphibians is the foothill yellow-legged frog (Rana boylii). In Oregon, R. boylii has disappeared from more than half of its historical sites and is now listed as a state and federal Sensitive Species. Although specific causes have not been determined, declines may be partly attributed to the recent introduction of smallmouth bass (Micropterus dolomieu) to some of the river systems in which these frogs live. Although smallmouth bass have been implicated as a cause of losses, very little is known about interactions between these two species. Given the relatively short period of time these two species have been co-existing, we sought to determine whether R. boylii larvae could even recognize bass as a predatory threat. Through a series of experiments, we examined the behavioral responses of larvae to a variety of stimuli including a native potential predator (rough-skinned newt, Taricha granulosa), introduced predator (smallmouth bass, M. dolomieu), and a native non-predatory fish (speckled dace, Rhinichthys osculus). Each experiment examined a different potential mode of detection: 1) chemical cues only; 2) visual cues only; or 3) a combination of chemical/visual/mechanical cues simultaneously. We predicted that in each experiment, larvae would respond to the native predator by exhibiting antipredator behaviors, whereas those exposed to cues of the non-native, unfamiliar predator would display activity levels similar to larvae exposed to controls. In addition, we tested amphibian larvae from two populations – one where they co-occur with M. dolomieu, and compared them to larvae from a location where M. dolomieu has not yet invaded – to determine whether any antipredator responses observed were recently developed behavioral adaptations. We analyzed initial and overall responses to stimuli. Our analyses of the initial responses of R. boylii larvae revealed an increase in activity when exposed to the visual cues of bass relative to controls. Furthermore, our results suggested that individual R. boylii larvae require multiple cues to facilitate predator detection. When exposed to multiple cues of their native predator, the rough-skinned newt, larvae responded with a significant reduction in activity levels. Those larvae exposed to cues of the non-native predator, smallmouth bass, displayed similar behaviors relative to control cues, supporting our prediction. Consequently, foothill yellow-legged frog larvae appear to be especially vulnerable to predation by non-native smallmouth bass.
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68. [Image] The Oregon conservation strategy
v, 419 p.; col.ill.; col.maps; "February 2006"; Foreword by Marla Rae, Chair, Oregon Fish and Wildlife CommissionCitation -
69. [Article] Silvicultural Treatment Impacts on Understory Trees and 20-Year Understory Vegetation Dynamics in Mature Douglas-Fir Forests
Policy regarding the management of public forests has undergone a drastic shift over the past couple of decades due to the loss old-growth forests in the Pacific Northwest (PNW) of the United States. For ...Citation Citation
- Title:
- Silvicultural Treatment Impacts on Understory Trees and 20-Year Understory Vegetation Dynamics in Mature Douglas-Fir Forests
- Author:
- Priebe, Jim E.
Policy regarding the management of public forests has undergone a drastic shift over the past couple of decades due to the loss old-growth forests in the Pacific Northwest (PNW) of the United States. For much of the 20th century, forest management on public lands emphasized timber production through the use of even-aged management practices. There has been increasing recognition, however, that traditional even-aged management approaches are unable to support species that rely on the complex, heterogeneous structures provided by old-growth forests. In response, public forest managers have redirected their focus to developing more ecologically sustainable forests capable of meeting a broad array of objectives including an increasing emphasis on the development of late-seral and old-growth characteristics. Thinning has been identified as a promising method for promoting late-seral characteristics in managed stands. Recent long-term studies have shown that thinning stands does indeed accelerate the development of at least some late-seral structure characteristics, particularly when varying levels of thinning intensity and non-uniform retention patterns are incorporated into silvicultural prescriptions. Likewise, thinning has also shown some ability to increase the abundance of late-seral associated plant species in the understory. The impacts of thinning on vegetation dynamics are complicated by external factors such as natural disturbance events and the influence of pre-treatment vegetation on post-treatment communities. Within the context of managing for late-seral attributes, thinning is used to imitate natural disturbance processes. However, this does not preclude the occurrence of natural disturbances, which may either disrupt or compound treatment effects. Initial site conditions create another potential complication for the development of late-seral attributes by limiting the potential for change in understory communities. While some studies have shown that thinning improves late-seral plant abundance, others have found that the legacy of pre-treatment vegetation has a stronger impact on post-treatment communities. This study focused on the impacts of ice storm disturbance and pre-treatment vegetation on the understory of mature Douglas-fir forests using the ongoing Mature Forest Study (MFS), a long-term silvicultural experiment evaluating the effects of thinning and understory vegetation management treatments, as a framework. The first study examined the impact of an ice storm (glaze disturbance) on planted understory trees. Specifically, I looked at the effect of understory tree species, tree size, and overstory neighborhood environment on the type (bending, crown loss), source (ice loading, falling debris), and severity of damage experienced by planted understory trees at one of the MFS sites. Tree species, size, and overstory environment all affected the amount of understory glaze damage. Frequency and severity of damage both varied among underplanted tree species. In general, smaller trees were more prone to being bent, while larger trees were more susceptible to crown loss. The Douglas-fir component of the overstory provided enough additional sheltering that the increased risk to understory trees from falling debris was balanced by a corresponding decrease in the odds of damage by ice loading. This was not the case for the hardwood component; increasing risk of damage to understory trees from falling debris with increasing hardwood basal area drove an overall increase in the risk of understory damage as hardwood basal area increased. This study suggests that species, tree size, and overstory environment all need to be considered by managers hoping to reduce glaze damage risk to younger cohorts in multi-aged stands. The second study investigated the impacts of thinning intensity and herbicide application on the long-term (20-year post-treatment) development of understory vegetation communities on both of the MFS sites. Trends were examined with a focus on the ability of herbicide application, in concert with thinning treatments, to reduce the legacy of common pre-treatment species and promote the abundance of late-seral associates. Results indicated that both thinning intensity and herbicide application affected 20-year changes in understory plant community composition. Herbicide application was associated with a decrease in the abundance of common pre-treatment species, suggesting that it did reduce the legacy effect. However, this was not associated with any change in the abundance of late-seral species. While light thinning showed some ability to mitigate decline in late-seral species relative to higher intensity thinnings, there was no evidence of treatment interaction with herbicide application. These results suggest that while managers may be able to reduce the influence of initial site conditions on post-treatment vegetation communities, the use of herbicides offers little control over the successional trajectory of the understory. Light thinning appears to be the most effective means of increasing late-seral species abundance, although the use of herbicides to meet other management objectives is not contraindicated by the results of this study. Overall, these results suggest that the best options available to managers to both reduce glaze disturbance impacts to understory trees and hasten the development of late-seral plant communities are heavy thinning with unmanaged leave patches to provide late-seral refugia, or light thinning with gaps to provide growing space for better tree regeneration.
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