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Stewart B. Rood - One of the best experts on this subject based on the ideXlab platform.
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Cottonwood Seed Dispersal Phenology across North America and Worldwide: Tracking ‘Summer Snow’ through an Internet Search
Wetlands, 2020Co-Authors: Stewart B. Rood, Sobadini KaluthotaAbstract:Cottonwoods, Populus trees, provide the foundation for riparian woodlands around the Northern Hemisphere but have declined partly due to river damming and water withdrawal. Cottonwood conservation requires periodic seedling replenishment, which depends upon coordinating river flows with the limited seed dispersal interval. Tracking seed dispersal phenology is laborious and we recognized a complementary approach with photographs and videos of prolific Cottonwood seed release on internet websites. We searched the internet for ‘Cottonwood seeds’ or ‘summer snow’, and about 800 images were posted since 2004. The 337 reports from North America with dates and/or locations revealed sequential seed dispersal in the American Southwest, the Pacific Northwest, the Great Lakes Region, and finally Alaska. Mean dispersal was June 3, with two-thirds of reports in the flanking four week interval. Dispersal was later at higher latitude and elevation, and a two-factor regression model provided 85% accuracy with reported peak dispersal from nine previous studies across western North America. The 49 Eurasian reports also revealed later seed dispersal with increasing latitude. This study revealed the utility of internet searching for tracking Cottonwood seed dispersal, which could facilitate environmental flows for riparian restoration. More broadly, internet reports could reveal spatiotemporal patterns in other natural phenomena.
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prospective impacts of oil spills on floodplain vegetation both crude oil and diluted bitumen increase foliar temperatures senescence and abscission in three Cottonwood populus species
PLOS ONE, 2020Co-Authors: Kayleigh G Nielson, Samuel G Woodman, Stewart B. RoodAbstract:Oil pipelines are vulnerable at river crossings since floods can expose and rupture pipes, releasing oil that floats and coats floodplain vegetation. This study investigated the consequences of oil coatings on leaves of Cottonwoods (riparian poplars), the predominant trees in floodplain woodlands around the Northern Hemisphere. The study compared conventional crude oil (CO) versus diluted bitumen (dilbit, DB), heavy oil originating from the Alberta oil sands; with petroleum jelly (PJ) as a reference. The treatments increased leaf surface temperatures (Tleaf) in narrowleaf and plains Cottonwoods (Populus angustifolia, P. deltoides) and balsam poplars (P. balsamifera) (Control = 21.8°C, PJ = 23.7°C; CO = 26.2°C; DB = 28.1°C; Tair = 25°C). The leaf warming followed stomatal occlusion from the foliar coating, which would reduce transpiration and evaporative cooling, combined with increased solar warming with the darker oils. Tleaf varied across the three Cottonwood species, with cooler, narrow, narrowleaf Cottonwood leaves; intermediate plains Cottonwood leaves; and warmer, darker, balsam poplar leaves (average Tleaf: narrowleaf = 23.8°C, plains = 24.3°C, and balsam = 26.7°C), with similar warming in each species following the different treatments. Across species and treatments, Tleaf was tightly correlated with foliar condition, which assessed turgor versus wilting of leaf blades and petioles, along with leaf necrosis and senescence (r2 = 0.980, narrowleaf; 0.998, plains; 0.852, balsam). This tight association indicates validity of both Tleaf and foliar condition as diagnostic measures. Crude oil and dilbit had similar foliar impacts, and for both, leaf abscission occurred within 2 to 3 weeks. Consequently, following an oil spill, remediation should commence quickly but extending vegetation removal beyond a few weeks would have limited benefit since the contaminated leaves would have abscised.
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controls on ecosystem water use and water use efficiency insights from a comparison between grassland and riparian forest in the northern great plains
Agricultural and Forest Meteorology, 2019Co-Authors: Stewart B. Rood, Hao Yang, Lawrence B FlanaganAbstract:Abstract Within the grassland-dominated landscape of the North American Great Plains, riparian forest ecosystems exist along river floodplains. We compared cumulative evapotranspiration (ET) and ecosystem water-use efficiency (WUE) between a Cottonwood forest and a nearby native grassland ecosystem in southern Alberta, using eddy covariance measurements during May-September (growing season) of three study years. Our objective was to test predictions about mechanistic controls on ecosystem water-use, and to provide insights into the amount of alluvial groundwater and stored soil water required to support a healthy riparian forest within the Great Plains biome. Grassland ET was dependent on precipitation inputs during the growing season. Cumulative growing season ET at the Cottonwood site (375–451 mm) exceeded grassland ET (111–213 mm) by 2.1- to 3.4-fold depending on study year, despite slightly higher WUE in the Cottonwood ecosystem. The difference in cumulative ET between ecosystems ranged from 238 to 264 mm in different years, in a region that normally receives 258 mm of cumulative precipitation during May-September. The large ET at the Cottonwood site was caused by two-fold higher LAI, and associated greater canopy conductance than was apparent at the grassland site. The additional soil water required for the higher Cottonwood ET was supplied by access to alluvial groundwater, which is recharged by river water, and was also supported by a larger soil volume to store water from precipitation and river flooding inputs. These factors resulted in a relatively long interval for Cottonwood photosynthetic gas exchange that was consistent among years despite widely different environmental conditions, while the grassland had shorter growing season lengths that were constrained further as precipitation and soil moisture declined among years. Our analyses contribute to understanding the water requirements of these contrasting ecosystems and will help to improve management procedures for regulating river flow rates in order to sustain healthy riparian Cottonwood ecosystems.
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A Twofold Strategy for Riparian Restoration: Combining a Functional Flow Regime and Direct Seeding to Re-establish Cottonwoods
River Research and Applications, 2015Co-Authors: Stewart B. Rood, Karen M. Gill, David W. Pearce, Sobadini Kaluthota, E. J. Hillman, S. G. Woodman, John M MahoneyAbstract:The transboundary St Mary River drains Glacier National Park, USA, and was progressively dammed and diverted over the 20th century to support agricultural irrigation in northern Montana and southern Alberta, Canada. Following reduced instream flows, the riparian Cottonwoods collapsed, and by 2000, few parental trees remained to provide seeds for Cottonwood replenishment. As a novel twofold restoration strategy we: (1) worked with the dam operators to deliver a functional flow regime, a regulated instream flow pattern intended to recover some ecological function and specifically seedling recruitment, and (2) delivered Cottonwood seeds by direct spreading and by sticking cuttings with seed catkins to allow gradual seed dispersal. The combination of river regulation and seeding enabled Cottonwood colonization, and around 1.5% of the applied seeds produced seedlings after the first summer, at sites without livestock or heavy recreational use. Around 15% of those seedlings survived through the fourth summer, with mortality due to drought stress and flood scour, and establishment and survival were higher for the prairie Cottonwood, Populus deltoides, than the narrowleaf Cottonwood, Populus angustifolia. This study confirmed that the lack of seed source trees limited Cottonwood colonization and demonstrated that the twofold restoration strategy provides promise for severe situations where parental trees have been lost. However, this would require substantial effort, and it would be more efficient to provide survivable instream flow patterns that avoid Cottonwood collapse. Copyright © 2015 John Wiley & Sons, Ltd.
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development of a spatially distributed hydroecological model to simulate Cottonwood seedling recruitment along rivers
Journal of Environmental Management, 2014Co-Authors: Rohan Benjankar, Stewart B. Rood, Michael Burke, Elowyn M Yager, Daniele Tonina, Gregory Egger, Norm MerzAbstract:Abstract Dam operations have altered flood and flow patterns and prevented successful Cottonwood seedling recruitment along many rivers. To guide reservoir flow releases to meet Cottonwood recruitment needs, we developed a spatially-distributed, GIS-based model that analyzes the hydrophysical requirements for Cottonwood recruitment. These requirements are indicated by five physical parameters: (1) annual peak flow timing relative to the interval of seed dispersal, (2) shear stress, which characterizes disturbance, (3) local stage recession after seedling recruitment, (4) recruitment elevation above base flow stage, and (5) duration of winter flooding, which may contribute to seedling mortality. The model categorizes the potential for Cottonwood recruitment in four classes and attributes a suitability value at each individual spatial location. The model accuracy was estimated with an error matrix analysis by comparing simulated and field-observed recruitment success. The overall accuracies of this Spatially-Distributed Cottonwood Recruitment model were 47% for a braided reach and 68% for a meander reach along the Kootenai River in Idaho, USA. Model accuracies increased to 64% and 72%, respectively, when fewer favorability classes were considered. The model predicted areas of similarly favorable recruitment potential for 1997 and 2006, two recent years with successful Cottonwood recruitment. This model should provide a useful tool to quantify impacts of human activities and climatic variability on Cottonwood recruitment, and to prescribe instream flow regimes for the conservation and restoration of riparian woodlands.
Robert L Beschta - One of the best experts on this subject based on the ideXlab platform.
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divergent patterns of riparian Cottonwood recovery after the return of wolves in yellowstone usa
Ecohydrology, 2015Co-Authors: Robert L Beschta, William J RippleAbstract:Understanding the potential effect apex predators may have on riparian plant communities, via a trophic cascade, represents an important research challenge in Rocky Mountain ecosystems. In the northern ungulate winter range of Yellowstone National Park where grey wolves (Canis lupus) were historically present, absent for seven decades, and recently reintroduced, our objective was to evaluate patterns of Cottonwood (Populus spp.) recruitment for two adjacent reaches of the Lamar Valley. Results indicated that recruitment was common in both reaches when wolves were historically present and declined because of intensive herbivory from elk (Cervus elaphus) after wolves were extirpated in the early 1900s. By the 1970s, Cottonwood recruitment along both reaches had essentially ceased. Wolves were reintroduced in the mid-1990s, and by 2012, some 4660 young Cottonwoods ≥2 m in height (the general upper browse level of elk) had become established within the 2-km-long upper Lamar study reach, consistent with re-establishment of a tri-trophic cascade involving wolves, elk, and Cottonwoods. However, within the 8-km-long lower Lamar study reach, only 22 young Cottonwoods had attained a height of ≥2 m because of high levels of herbivory, especially from bison (Bison bison). Top–down trophic interactions involving wolves and elk, as well as reach characteristics and browsing by bison, appear to explain the strongly contrasting patterns of recent riparian Cottonwood recruitment currently underway in the northern Yellowstone – one reach represented by a recovering riparian ecosystem and the other an alternative stable state with highly altered riparian vegetation and channel conditions. Copyright © 2014 John Wiley & Sons, Ltd.
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reduced Cottonwood recruitment following extirpation of wolves in yellowstone s northern range
Ecology, 2005Co-Authors: Robert L BeschtaAbstract:Cottonwoods (Populus spp.) represent an important tree component of riparian plant communities within the winter range of the northern Yellowstone elk (Cervus elaphus) herd, yet young Cottonwoods are highly palatable to ungulates. To assess potential herbivory impacts associated with wild ungulates following the removal of gray wolves (Canis lupus), long-term Cottonwood recruitment and stand dynamics were studied. While results indicated that the establishment of young Cottonwoods is an ongoing process in Yellowstone's northern range, their relatively small stature and hedged appearance were indicative of high browsing pressure by wild ungulates, principally elk. At five study sites, the diameter at breast height (dbh) of all Cottonwood trees ≥5 cm was determined; increment cores were also obtained for developing tree age vs. dbh relationships. At the La Duke Spring and Devils Slide Sites, which represent refugia sites since elk have limited access (due to local terrain conditions and cultural developments), Cottonwood recruitment has been occurring during the last half century, indicating that climatic factors have not prevented Cottonwood recruitment during that time. However, over this same period Cottonwood recruitment no longer occurred at sites within the Soda Butte and Lamar Valleys. The overall decline in Cottonwood recruitment at these locations occurred following the extirpation of wolves from Yellowstone National Park in the 1920s. At the Buffalo Ranch Site, where ranching of buffalo [bison] (Bison bison) and activities associated with culling of elk were centered, Cottonwood recruitment continued after the loss of wolves but stopped following the curtailment of ungulate management activities at these facilities in the late 1960s. Taken together, data from the five sites reported herein along with the results of other studies provide compelling evidence that the absence of wolves in the northern Yellowstone has had a major impact on the recruitment of Cottonwood and other woody browse species.
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CottonwoodS, ELK, AND WOLVES IN THE LAMAR VALLEY OF YELLOWSTONE NATIONAL PARK
Ecological Applications, 2003Co-Authors: Robert L BeschtaAbstract:In September 2001, the diameter at breast height (dbh) of all Cottonwood (Populus spp.) $5 cm in diameter was measured within a 9.5-km 2 section of the Lamar Valley (elevation ;2000 m), in northeastern Yellowstone National Park. A total of 700 trees were measured of which 71% were narrowleaf Cottonwood (P. angustifolia) and 29% were black Cottonwood (P. trichocarpa). Slightly more than half of the narrowleaf trees were growing on point bar landforms at three major meander bends of the Lamar River, with the remainder occurring in small groves spread across various floodplain surfaces within the valley. Almost all of the black Cottonwood occurred on point bars at only two of the meander bend locations. Tree diameters for both species ranged mostly between 30 and 110 cm with a nearly total absence of Cottonwoods between 5 and 29 cm in diameter. Age vs. diameter relationships were developed and used as a basis for estimating estab- lishment dates for all narrowleaf Cottonwoods. These relationships, in conjunction with the dbh data, indicated an absence of Cottonwood recruitment (i.e., growth of seedlings/suckers into $5-cm diameters trees) over approximately the last 60 years. The paucity of Cottonwood recruitment appears to have occurred independently of fire history, flow regimes, channel migrations, or factors affecting normal stand development, but over the same period of time that wolves (Canis lupus) had been extirpated from Yellowstone National Park. With the removal of this wide-ranging and keystone predator, elk (Cervus elaphus) populations were able to browse riparian plant communities unaffected by wolves.
John M Mahoney - One of the best experts on this subject based on the ideXlab platform.
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A Twofold Strategy for Riparian Restoration: Combining a Functional Flow Regime and Direct Seeding to Re-establish Cottonwoods
River Research and Applications, 2015Co-Authors: Stewart B. Rood, Karen M. Gill, David W. Pearce, Sobadini Kaluthota, E. J. Hillman, S. G. Woodman, John M MahoneyAbstract:The transboundary St Mary River drains Glacier National Park, USA, and was progressively dammed and diverted over the 20th century to support agricultural irrigation in northern Montana and southern Alberta, Canada. Following reduced instream flows, the riparian Cottonwoods collapsed, and by 2000, few parental trees remained to provide seeds for Cottonwood replenishment. As a novel twofold restoration strategy we: (1) worked with the dam operators to deliver a functional flow regime, a regulated instream flow pattern intended to recover some ecological function and specifically seedling recruitment, and (2) delivered Cottonwood seeds by direct spreading and by sticking cuttings with seed catkins to allow gradual seed dispersal. The combination of river regulation and seeding enabled Cottonwood colonization, and around 1.5% of the applied seeds produced seedlings after the first summer, at sites without livestock or heavy recreational use. Around 15% of those seedlings survived through the fourth summer, with mortality due to drought stress and flood scour, and establishment and survival were higher for the prairie Cottonwood, Populus deltoides, than the narrowleaf Cottonwood, Populus angustifolia. This study confirmed that the lack of seed source trees limited Cottonwood colonization and demonstrated that the twofold restoration strategy provides promise for severe situations where parental trees have been lost. However, this would require substantial effort, and it would be more efficient to provide survivable instream flow patterns that avoid Cottonwood collapse. Copyright © 2015 John Wiley & Sons, Ltd.
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floods fire and ice disturbance ecology of riparian Cottonwoodsthe review is one of a selection of papers published in the special issue on poplar research in canada
Botany, 2007Co-Authors: Stewart B. Rood, Lori A Goater, John M Mahoney, Cheryl M Pearce, Derald G SmithAbstract:Cottonwoods are poplar trees that are well adapted to dynamic riparian, or streamside, zones throughout the Northern Hemisphere. Here we assess the influences of three prominent physical disturbances, floods, fire, and ice, on Cottonwood population ecology. We emphasize Cottonwoods along rivers from the “Crown of the Continent”, the central Rocky Mountain zone around the Canada – United States border, where five Populus species overlap and four hybridize. Moderate to major floods scour banks and deposit bars, creating barren and moist colonization sites that are essential for Cottonwood seedling recruitment. Floods also scarify shallow roots, thus promoting clonal suckering, especially for the section Tacamahaca species: narrowleaf Cottonwood (Populus angustifolia James), balsam poplar (Populus balsamifera L.), and black Cottonwood (Populus trichocarpa Torr. & A. Gray). Fire would naturally be less frequent in some riparian zones because of the moist conditions and firebreaks provided by the streams, but ...
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floods fire and ice disturbance ecology of riparian Cottonwoods 1
2007Co-Authors: Stewart B. Rood, Lori A Goater, John M Mahoney, Cheryl M Pearce, Derald G SmithAbstract:Cottonwoods are poplar trees that are well adapted to dynamic riparian, or streamside, zones throughout the Northern Hemisphere. Here we assess the influences of three prominent physical disturbances, floods, fire, and ice, on cot- tonwood population ecology. We emphasize Cottonwoods along rivers from the ''Crown of the Continent'', the central Rocky Mountain zone around the Canada - United States border, where five Populus species overlap and four hybridize. Moderate to major floods scour banks and deposit bars, creating barren and moist colonization sites that are essential for Cottonwood seedling recruitment. Floods also scarify shallow roots, thus promoting clonal suckering, especially for the sec- tion Tacamahaca species: narrowleaf Cottonwood (Populus angustifolia James), balsam poplar (Populus balsamifera L.), and black Cottonwood (Populus trichocarpa Torr. & A. Gray). Fire would naturally be less frequent in some riparian zones because of the moist conditions and firebreaks provided by the streams, but with human use, floodplain forest fires have probably increased. Following fire, regrowth through clonal root and shoot suckers can be prolific for the Tacamahaca species, but is limited for the section Aigeiros, prairie Cottonwood (Populus deltoides Bartr.). River ice, and especially ice drives that accompany winter or spring break-up, provide powerful riparian disturbances that have often been neglected. Ice drives generate barren sites for seedling colonization, shear shoots, and scarify roots promoting shoot and root sucker- ing, and sever branches, enabling dispersive clonal branch propagation. Following studies along many regional rivers, we conclude that: (i) riparian Cottonwoods are tolerant of, and dependent upon, occasional physical disturbance for population rejuvenation; (ii) differing disturbance responses contribute to niche differentiation across the Populus species; (iii) differ- ent disturbances enable varied spatial and temporal patterns of Cottonwood establishment, including fringe, general, and patch recruitment; and (iv) natural disturbance regimes probably favor native Cottonwoods and disfavor some invasive, woody plants. River damming and flow regulation often attempt to attenuate flood and ice disturbance, a management ob- jective that may hinder the perpetuation of native floodplain forests. We recommend that river resource managers seek to allow flood and ice disturbance, and additionally, fire may provide a managed disturbance that could rejuvenate overma- ture Cottonwood groves along some regulated rivers.
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environmental influences on seedling growth of Cottonwood species following a major flood
Forest Ecology and Management, 2001Co-Authors: Andrea R. Kalischuk, Stewart B. Rood, John M MahoneyAbstract:Abstract A major flood in June 1995 along most streams in southern Alberta (AB) and southeastern British Columbia (BC), Canada, permitted the comparison of natural seedling establishment of different Cottonwood species across different environments. Nine study sites were established along a 340-km corridor from BC, over the Rocky Mountain Continental Divide, and onto the foothills and then prairies of AB. Four native Cottonwood species occurred from BC to AB: the black Cottonwood, Populus trichocarpa Torr. and Gray, balsam poplar, P. balsamifera L., and narrow-leaf Cottonwood, P. angustifolia James, of section Tacamahaca, and the prairie Cottonwood, Populus deltoides Bartr. ex Marsh, of section Aigeiros. Cottonwood seedlings of the 1995 cohort were monitored from 1995 through 1998 in quadrats along riparian transects. The study confirmed that a major flood enabled extensive Cottonwood recruitment along mountain, foothills, and prairie river reaches and revealed that both, environment and species influenced Cottonwood seedling growth in situ. Across the sites, seedling heights varied ten-fold and were closely negatively correlated with site elevation (1995: n = 9, r2 = 0.93; 1997: n = 4, r2 = 0.92). The increased growth at lower elevations was probably associated with warmer temperatures and a longer growing season; seedling growth was positively correlated with the accumulation of growing degree days of nearby weather stations (1995: n = 6, r2 = 0.88). Growth rate was also influenced by species as height varied up to three-fold across species at sites where species co-occurred. P. deltoides seedlings grew fastest followed by P. trichocarpa/P. balsamifera and intersectional hybrids and, finally, P. angustifolia and intrasectional hybrids. The superior seedling growth of P. deltoides is consistent with its life history and distribution. P. deltoides occurs along prairie river reaches with warmer and drier climates and higher-order streams with finer substrate textures; these physical conditions would favor seedling recruitment. The alternate environmental conditions of foothillls and mountain regions probably encourage clonal (asexual) recruitment that may supplement seedling recruitment, particularly for the Tacamahaca species.
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streamflow requirements for Cottonwood seedling recruitment an integrative model
Wetlands, 1998Co-Authors: John M Mahoney, Stewart B. RoodAbstract:This paper describes the ‘recruitment box,’ an integrative model that defines the stream stage patterns that enable successful establishment of riparian Cottonwood seedlings. In western North America, Cottonwood seed dispersal generally occurs after annual peak river flows. The receding stream exposes moist sites upon which seeds land after transport by wind and water. Germination is rapid, and initial seedling establishment is often prolific. However, the vast majority of seedlings die, primarily due to drought stress, as root growth is insufficient to maintain contact with the receding zone of moisture. Cottonwood roots grow about 0.5 to 1 cm per day or 60 to 100 cm in the first year. Along the ‘losing’ streams in semi-arid regions, the riparian water table is an almost horizontal extension from the stream stage. A capillary fringe exists above the water table and is often 30 to 40 cm in elevation, but can range from about 5 to 130 cm depending on substrate texture. The combination of root growth and capillary fringe define the successful recruitment band, which is usually from about 0.6 to 2 m in elevation above the late summer stream stage. Within this range, higher elevation establishment occurs (i) for theAigeiros Cottonwoods,Populus deltoides, andP. fremontii, which grow more rapidly thanTacamahaca species and occur in warmer areas with longer growing seasons; (ii) along larger rivers that are characterized by more gradual stage fluctuations; and (iii) along streams with finer substrate. The rate of stream stage decline is also critical for seedling survival and should not exceed 2.5 cm per day. The recruitment box model is consistent with dendrochronological interpretations that moderate flood events are naturally required for Cottonwood recruitment. Flood events with recurrences of about 1 in 5 to 1 in 10 years often satisfy the model and provide stream stage patterns with a gradual decline through the recruitment box. The model will facilitate analyses of the reproductive ecology of riparian Cottonwoods and also permit the prescription of stream stage patterns for Cottonwood seedling recruitment along dammed rivers.
Thomas G. Whitham - One of the best experts on this subject based on the ideXlab platform.
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within species variation in foliar chemistry influences leaf litter decomposition in a utah river
Journal of The North American Benthological Society, 2007Co-Authors: Carri J Leroy, Thomas G. Whitham, Stuart C Wooley, Jane C MarksAbstract:AbstractLeaf-litter inputs provide substrate and energy to stream systems. These contributions vary based on species-specific differences in litter quality, but little is known about how differences in litter quality within a species can affect ecosystem processes. Genetic variation within tree species, such as oaks and Cottonwoods, affects ecosystem processes including decomposition and nutrient cycling in forest ecosystems and has the potential to do the same in streams. We collected litter from 5 genotypes of each of 4 different Cottonwood cross types (Populus fremontii, Populus angustifolia, and natural F1 and backcross hybrids), grown in a common garden, and measured their decomposition rates using litter bags in the Weber River, Utah. The proportion of 35 species-specific P. fremontii restriction-fragment length polymorphism markers in the genotype explained 46% and genetically controlled phytochemical mechanisms (e.g., % soluble condensed tannin in litter) explained >72% of the variation in leaf-li...
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from genes to geography a genetic similarity rule for arthropod community structure at multiple geographic scales
Molecular Ecology, 2006Co-Authors: Randy K Bangert, G J Allan, Richard J Turek, Gina M Wimp, Nashelly Meneses, Gregory D Martinsen, Paul Keim, Thomas G. WhithamAbstract:We tested the hypothesis that leaf modifying arthropod communities are correlated with Cottonwood host plant genetic variation from local to regional scales. Although recent studies found that host plant genetic composition can structure local dependent herbivore communities, the abiotic environment is a stronger factor than the genetic effect at increasingly larger spatial scales. In contrast to these studies we found that dependent arthropod community structure is correlated with both the cross type composition of Cottonwoods and individual genotypes within local rivers up to the regional scale of 720 000 km 2 (Four Corner States region in the southwestern USA). Across this geographical extent comprising two naturally hybridizing Cottonwood systems, the arthropod community follows a simple genetic similarity rule: genetically similar trees support more similar arthropod communities than trees that are genetically dissimilar. This relationship can be quantified with or without genetic data in Populus .
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Interactions between Cottonwood and beavers positively affect sawfly abundance
Ecological Entomology, 2006Co-Authors: Joseph K Bailey, Thomas G. WhithamAbstract:1. Cottonwood (Populus spp.) are the dominant tree type in riparian forests of the western U.S.A. In these riparian forests, the beaver (Castor canadensis) is a major ecosystem engineer that commonly browses Cottonwood, resulting in distinct changes to plant architecture. Here the hypothesis that beaver herbivory indirectly affects the distribution of a keystone leaf-galling sawfly through architectural changes in Cottonwood was examined. 2. It was found that: (a) beaver herbivory of Cottonwood results in an increase in average shoot length over unbrowsed Cottonwood; (b) sawfly galls were up to 7-14 times more abundant on browsed Cottonwood than unbrowsed Cottonwood; and (c) sawfly gall abundance was correlated positively with changes in shoot length after beaver herbivory. Together these data show that the individual and combined effects of Cottonwood and beaver herbivory increase shoot length, positively affecting sawfly abundance. 3. Because herbivores are a ubiquitous component of most ecosystems, we argue that the indirect effects of herbivory on plant quality, and subsequently other herbivores, may be as important as environmental variation. © 2006 The Authors.
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host plant genetics affect hidden ecological players links among populus condensed tannins and fungal endophyte infection
Botany, 2005Co-Authors: Joseph K Bailey, Ron Deckert, Catherine A. Gehring, Brian J Rehill, Jennifer A Schweitzer, Richard L Lindroth, Thomas G. WhithamAbstract:Recent studies have shown effects of host plant genetics on community and ecosystem processes, which makes understanding the impacts of genetically based traits on hidden or non-apparent organisms more important. Here we examined links among genetic variation in hybrid Cottonwoods, plant phytochemistry, and twig fungal endophytes (i.e., a common hidden organism). We found three major patterns: (1) twig fungal endophyte infection was positively related to the introgression of Fremont Cottonwood (Populus fremontii S. Wats.) RFLP genetic markers, (2) condensed tannin concentration in twig bark tissue was negatively correlated to the introgression of Fremont genetic markers, and (3) fungal endophyte infection was negatively related to condensed tannin concentration in twig bark. These data dem- onstrate that plant genotype can impact hidden ecological players (i.e., fungal endophytes) resulting in community and ecosystem consequences.
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associational susceptibility of Cottonwood to a box elder herbivore
Ecology, 2000Co-Authors: Jennifer A White, Thomas G. WhithamAbstract:Associational resistance, which refers to decreased herbivory experienced by a plant growing with heterospecific neighbors, is a well documented ecological phe- nomenon. In contrast, studies that describe increased herbivory due to heterospecific neigh- bors (associational susceptibility) are relatively rare. In this study we document associational susceptibility among hosts of the fall cankerworm (Alsophila pometaria). Cottonwoods (Populus angustifolia X P. fremontii) located under box elder (Acer negundo) were col- onized by two to three times more cankerworms, and suffered two to three times greater defoliation than Cottonwoods growing under mature Cottonwoods, or Cottonwoods growing in the open. This associational pattern reflects fall cankerworm's strong preference for box elder over Cottonwood: egg densities were 26 times greater on box elder than Cottonwood, first instar larvae consumed 75 times more box elder than Cottonwood in larval palatability trials, and fourth instar larvae consumed three times more box elder than Cottonwood. In terms of larval performance, first instar larvae exhibited approximately six times greater mortality and 40% slower development time on Cottonwood relative to box elder, whereas fourth instar larval performance did not differ between the hosts. Based on these and other findings, we predict that, when generalist herbivores reach outbreak proportions and con- sume their preferred hosts, they will then move to nearby less-preferred hosts to complete their life cycle. This "spillover" effect will result in associational susceptibility for less- preferred hosts and is likely common in forest outbreak situations where herbivore densities are high. With increased emphasis on diversified plantings in agriculture and forestry, it is important to understand potential drawbacks such as associational susceptibility.
James R Ehleringer - One of the best experts on this subject based on the ideXlab platform.
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ecophysiology of riparian Cottonwood and willow before during and after two years of soil water removal
Ecological Applications, 2010Co-Authors: Kevin R Hultine, S E Bush, James R EhleringerAbstract:Riparian Cottonwood/willow forest assemblages are highly valued in the southwestern United States for their wildlife habitat, biodiversity, and watershed protection. Yet these forests are under considerable threat from climate change impacts on water resources and land-use activities to support human enterprise. Stream diversions, groundwater pumping, and extended drought have resulted in the decline of Cottonwood/willow forests along many riparian corridors in the Southwest and, in many cases, the replacement of these forests with less desirable invasive shrubs and trees. Nevertheless, ecophysiological responses of Cottonwood and willow, along with associated ecohydrological feedbacks of soil water depletion, are not well understood. Ecophysiological processes of mature Fremont Cottonwood and coyote willow stands were examined over four consecutive growing seasons (2004-2007) near Salt Lake City, Utah, USA. The tree stands occurred near the inlet of a reservoir that was drained in the spring of 2005 and remained empty until mid-summer of 2006, effectively removing the primary water source for most of two growing seasons. Stem sap flux density (Js) in Cottonwood was highly correlated with volumetric soil moisture (h )i n the upper 60 cm and decreased sevenfold as soil moisture dropped from 12% to 7% after the reservoir was drained. Conversely, Js in willow was marginally correlated with h and decreased by only 25% during the same period. Opposite patterns emerged during the following growing season: willow had a lower whole-plant conductance (kt) in June and higher leaf carbon isotope ratios (d 13 C) than Cottonwood in August, whereas kt and d 13 C were otherwise similar between species. Water relations in both species recovered quickly from soil water depletion, with the exception that sapwood area to stem area (As:Ast) was significantly lower in both species after the 2007 growing season compared to 2004. Results suggest that Cottonwood has a greater sensitivity to interannual reductions in water availability, while willow is more sensitive to longer periods of soil water depletion. These data shed light on the linkage between soil water deficits and ecophysiological processes of threatened riparian forests given potential land-use and long-term drought impacts on freshwater resources.
