New Publications Online From The US Forest Service Research and Development

Going to extremes: low temperature tolerance and acclimation in temperate and boreal conifers

Strimbeck, G.R.; Schaberg, P.G. — Wed, 03 Feb 2010 14:09:17 -0500

Despite global warming, temperatures in the continental interiors of Canada and Siberia can still fall below -60°C and can remain below -40°C for weeks at a time. These extreme temperatures occur not in barren tundra regions, but taiga forests dominated by species of spruce (Picea), fir (Abies), pine (Pinus) and larch (Larix). While other plant and animal species may receive some protection from snow cover, the above-ground parts of trees, including the foliage of evergreen trees, must survive the full brunt of the winter environment.

Overview and example application of the Landscape Treatment Designer

Fri, 10 Feb 2012 12:09:55 -0500

The Landscape Treatment Designer (LTD) is a multicriteria spatial prioritization and optimization system to help design and explore landscape fuel treatment scenarios. The program fills a gap between fire model programs such as FlamMap, and planning systems such as ArcFuels, in the fuel treatment planning process. The LTD uses inputs on spatial treatment objectives, activity constraints, and treatment thresholds, and then identifies optimal fuel treatment locations with respect to the input parameters. The input data represent polygons that are attributed with information about expected fire behavior and the polygon’s overall contribution to one or more landscape management objectives. The program can be used in a number of different ways to explore treatment priority and decision rules that manifest themselves on large (1 million ha) landscapes as spatially explicit treatment strategies. This report describes the LTD program and an example application on the Ochoco National Forest. Further information including program download and a tutorial can be found at http://www.fs.fed.us/wwetac/ltd.

Tree and impervious cover change in U.S

Nowak, David J.; Greenfield, Eric J. — Thu, 09 Feb 2012 15:01:57 -0500

Paired aerial photographs were interpreted to assess recent changes in tree, impervious and other cover types in 20 U.S. cities as well as urban land within the conterminous United States. National results indicate that tree cover in urban areas of the United States is on the decline at a rate of about 7900 ha/yr or 4.0 million trees per year. Tree cover in 17 of the 20 analyzed cities had statistically significant declines in tree cover, while 16 cities had statistically significant increases in impervious cover. Only one city (Syracuse, NY) had a statistically significant increase in tree cover. City tree cover was reduced, on average, by about 0.27 percent/yr, while impervious surfaces increased at an average rate of about 0.31 percent/yr. As tree cover provides a simple means to assess the magnitude of the overall urban forest resource, monitoring of tree cover changes is important to understand how tree cover and various environmental benefits derived from the trees may be changing. Photo-interpretation of digital aerial images can provide a simple and timely means to assess urban tree cover change to help cities monitor progress in sustaining desired urban tree cover levels.

The forest-land owners of Maryland

Kingsley, Neal P.; Birch, Thomas W. — Thu, 09 Feb 2012 13:35:38 -0500

Ninety perrent of the commercial forest land in Maryland--2,280,000 acres-is in the hands of some 95,800 owners. Eighty-seven percent of these owners are individuals. The average individual owner is middle aged, well educated, relatively affluent, and from a rural or farm background. Twenty-two percent of the private owners have harvested timber from their land. These owners own 53 percent of the private woodland. Forty-seven per cent of the owners intend to harvest timber from their land at some future date . They control 69 percent of the private woodland. Most owners show little interest in forestry practices. In fact, 12 percent of the owners have received some type of forestry assistance, but a majority of the owners do not know who to contact for forestry assistance. Twenty-six percent of the owners permit the public to use their woodland for recreation.

The physiological basis for regeneration response to variable retention harvest treatments in three pine species

Powers, Matthew D.; Pregitzer, Kurt S.; Palik, Brian J.; Webster, Christopher R. — Thu, 09 Feb 2012 11:56:04 -0500

Variable retention harvesting (VRH) is promoted for enhancing biodiversity and ecosystem processes in managed forests, but regeneration responses to the complex stand structures that result from VRH are poorly understood. We analyzed foliar stable carbon isotope ratios (δ¹³C), oxygen isotope ratios (δ¹⁸O), light-saturated photosynthetic rates A_max), stomatal conductance (g_s) and sizes of pine seedlings in Pinus resinosa stands treated with VRH systems that created different spatial patterns of overstorey retention. Pinus banksiana, P. resinosa and Pinus strobus seedlings in dispersed retention, aggregated retention between small gaps and aggregated retention between large gaps treatments had greater δ¹³C, em>A_max, g_s, diameter and height than seedlings in unharvested treatments, but seedling performance was similar among VRH treatments when averaged across stands. There were no significant differences in δ¹⁸O associated with any treatment. These results indicate seedling photosynthetic capacity, water relations and growth wereimproved by VRH, but the spatial pattern of retention had surprisingly little impact on average performance in the first 4 years after harvesting. This suggests retention treatments that produce different residual stand structures can promote similar mean rates of early seedling development when performance is averaged across all of the neighbourhood environments within each treatment.

Management impacts on forest floor and soil organic carbon in northern temperate forests of the US

Hoover, Coeli M. — Thu, 09 Feb 2012 10:30:44 -0500

The role of forests in the global carbon cycle has been the subject of a great deal of research recently, but the impact of management practices on forest soil dynamics at the stand level has received less attention. This study used six forest management experimental sites in five northern states of the US to investigate the effects of silvicultural treatments (light thinning, heavy thinning, and clearcutting) on forest floor and soil carbon pools. No overall trend was found between forest floor carbon stocks in stands subjected to partial or complete harvest treatments. A few sites had larger stocks in control plots, although estimates were often highly variable. Forest floor carbon pools did show a trend of increasing values from southern to northern sites. Surface soil (0-5 cm) organic carbon content and concentration were similar between treated and untreated plots. Overall soil carbon (0-20 cm) pool size was not significantly different from control values in sites treated with partial or complete harvests. No geographic trends were evident for any of the soil properties examined. Results indicate that it is unlikely that mineral soil carbon stocks are adversely affected by typical management practices as applied in northern hardwood forests in the US; however, the findings suggest that the forest floor carbon pool may be susceptible to loss.

Forest and grassland carbon in North America: A short course for land managers

Wed, 08 Feb 2012 10:31:18 -0500

This multimedia short-course presents a range of information on the science, management and policy of forest and grassland carbon. Forests and grasslands worldwide play a critical role in storing carbon and sequestering greenhouse gases from the atmosphere. The U.S. Forest Service, which manages 193 million acres of forests and grasslands, emphasizes the need for management to consider carbon stewardship in conjunction with other sustainable land management goals. This course aims to provide a broad background for public and private land managers who are interested in how ecosystems store and release carbon, how management can affect carbon storage and release, and how carbon can be considered in the context of other management objectives. Experts in the subject matter prepared each presentation and each talk was reviewed by a group of scientists and managers to help improve the clarity and content of the final recording. The DVD includes fifteen presentations, accompanied by references and links, and a set of quizzes on the material. Course material can also be accessed online at http://www.fs.fed.us/ccrc/carboncourse/.

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A dynamic organic soil biogeochemical model for simulating the effects of wildfire on soil environmental conditions and carbon dynamics of black spruce forests

Thu, 06 Oct 2011 13:32:47 -0400

Ecosystem models have not comprehensively considered how interactions among fire disturbance, soil environmental conditions, and biogeochemical processes affect ecosystem dynamics in boreal forest ecosystems. In this study, we implemented a dynamic organic soil structure in the Terrestrial Ecosystem Model (DOS-TEM) to investigate the effects of fire on soil temperature, moisture, and ecosystem carbon dynamics. DOS-TEM consists of environmental, ecological, disturbance effects, and dynamic organic soil modules. Changes in organic layer thickness are computed from calculated changes in carbon pools following fire and during stand succession. DOS-TEM was parameterized based on studies reported in the literature and evaluated independently at sites in interior Alaska. This evaluation reveals that (1) DOS-TEM is capable of accurately simulating the thickness and carbon content of organic soils; and (2) without the dynamic linkage between soil organic thickness and carbon content, the model overestimates soil carbon in deep mineral soil horizons of dry black spruce ecosystems of interior Alaska. Sensitivity tests were performed to investigate issues related to spatial heterogeneity of carbon dynamics including soil drainage and fire frequency. Results show that both soil drainage and fire frequency are important in the carbon dynamics simulated by DOS-TEM, and should be considered in spatial applications of the model.

Snow-mediated ptarmigan browsing and shrub expansion in arctic Alaska

Tape, Ken D.; Lord, Rachel; Marshall, Hans-Peter; Ruess, Roger W. — Mon, 19 Sep 2011 17:00:19 -0400

Large, late-winter ptarmigan migrations heavily impact the shoot, plant, and patch architecture of shrubs that remain above the snow surface. Ptarmigan browsing on arctic shrubs was assessed in the vicinity of Toolik Lake, on the north side of the Brooks Range in Alaska. Data were collected in early May 2007, at maximum snow depth, after the bulk of the ptarmigan migration had passed through the area. In an area of tall shrubs, half of the buds on Salix alaxensis were browsed by ptarmigan. Three percent of the buds that were buried beneath the snow were browsed, 90% of the buds that were less than 30 cm above the maximum snow level were browsed, and 45% of the buds above that height were browsed. Ptarmigan browsing was found to be a major height limiter for tall shrubs, thereby controlling shrub architecture by brooming stems at the snow surface and inducing stump shoots. These results were qualitatively extrapolated by photographing shrub morphology over a region approximately 300 km wide across a series of north-flowing arctic rivers with headwaters in the Brooks Range. Ptarmigan “hedging” of shrub patches, and shrub growth under a warmer climate, are opposing forces mediated by snow distribution.

Variation in carbohydrate source-sink relations of forest and treeline white spruce in southern, interior and northern Alaska

Mon, 19 Sep 2011 16:59:19 -0400

Two opposing hypotheses have been presented to explain reduced tree growth at the treeline, compared with growth in lower elevation or lower latitude forests: the carbon source and sink limitation hypotheses. The former states that treeline trees have an unfavorable carbon balance and cannot support growth of the magnitude observed at lower elevations or latitudes, while the latter argues that treeline trees have an adequate carbon supply, but that cold temperatures directly limit growth. In this study, we examined the relative importance of source and sink limitation in forest and treeline white spruce (Picea glauca) in three mountain ranges from southern to northern Alaska. We related seasonal changes in needle nonstructural carbohydrate (NSC) content with branch extension growth, an approach we argue is more powerful than using needle NSC concentration. Branch extension growth in the southernmost Chugach Mountains was much greater than in the White Mountains and the Brooks Range. Trees in the Chugach Mountains showed a greater seasonal decline in needle NSC content than trees in the other mountain ranges, and the seasonal change in NSC was correlated with site-level branch growth across mountain ranges. There was no evidence of a consistent difference in branch growth between the forest and treeline sites, which differ in elevation by approximately 100 m. Our results point to a continuum between source and sink limitation of growth, with high-elevation trees in northern and interior Alaska showing greater evidence of sink limitation, and those in southern Alaska showing greater potential for source limitation.

Morchella tomentosa: a unique belowground structure and a new clade of morels

Mon, 19 Sep 2011 16:56:32 -0400

Mechanisms involved in post-fire morel fructification remain unclear. A new undescribed belowground vegetative structure of Marchella tomentosa in a burned boreal forest was investigated north of Fairbanks, Alaska. The name "radiscisclerotium" is proposed to define this peculiar and elaborate belowground vegetative structure of M. tomentosa. Bayesian and maximum parsimony analyses based on ITS rRNA regions and nLSU gene strongly supported a new clade composed of M. tomentosa within the genus Morchella.

Examining USDA Forest Service recreation partnerships: institutional and relational interactions

Seekamp, Erin; Cerveny, Lee K. — Thu, 06 Oct 2011 12:28:10 -0400

Since the 1980s, the USDA Forest Service budget has experienced limited growth. Downsizing and outsourcing characterize the agency's response to constrained appropriations. The agency increasingly works with partners to meet targets that otherwise could not be achieved. Partnerships may take many structural forms (e.g., memorandums of understanding, joint venture agreements, and contracts) and have become part of the agency's organizational norms. Despite this growing emphasis on partnerships, little is known about the ways partners interact with agency personnel or the implications of partnership reliance for agency programs and services. Existing research on recreation partnerships has focused primarily on steps to build successful partnerships, while research from public administration and organizational management has focused on the determinants of partnership synergy. The majority of this research focuses on collaborative alliances that characterize process-as-outcome partnerships. To build on this knowledge base and develop a conceptual framework of recreation partnerships where products (e.g., visitor services) are the typical outcome, 21 key informant interviews were conducted with agency personnel and partners. Participants were purposively selected from multiple regions, a range of management levels, and a variety of recreation work performed. In this paper, two aspects of partnership interactions (i.e., institutional and relational interactions) are presented to specifically incorporate both institutional and actor perspectives on recreation partnerships, examine the similarities to past research on partnership success (e.g., synergy), and explore the relationship between interactions and administrative barriers. Better understanding of the institutional and relational interactions of partnerships may further the agency's capacity to provide recreation opportunities and foster stewardship. Two important risks to partnership management were identified: (a) the assumption that partners constitute a source of free labor and require minimal time or energy to administer threatens institutional capacity to manage partnerships, and (b) personnel turnover constrains maintaining partnerships and developing positive community relations, as these relationships often depend on the individual connections that are cultivated. This research helps resource managers understand partnership interactions, recognize the individual champions who invest in these relationships, and assess the institutional mechanisms that enhance management capacity.

A new time-space accounting scheme to predict stream water residence time and hydrograph source components at the watershed scale

Sayama, Takahiro; McDonnell, Jeffrey J. — Thu, 15 Sep 2011 14:11:56 -0400

Hydrograph source components and stream water residence time are fundamental behavioral descriptors of watersheds but, as yet, are poorly represented in most rainfall-runoff models. We present a new time-space accounting scheme (T-SAS) to simulate the pre-event and event water fractions, mean residence time, and spatial source of streamflow at the watershed scale. We use a physically based hydrologic model together with field data from the well-studied Maimai M8 watershed and HJ Andrews WS10 watershed to explore how catchment properties, particularly soil depth, controls the age and source of streamflow. Our model simulates unsaturated, saturated subsurface, and surface rainfall-runoff processes. We first demonstrate the ability of the model to capture hydrograph dynamics and compare the model flow component and age simulations against measured values at the two sites. We show that the T-SAS approach can capture flow and transport dynamics for the right dominant process reasons. We then conduct a series of virtual experiments by switching soil depths between the two watersheds to understand how soil depth and its distribution control water age and source. Results suggest that thicker soils increase mean residence time and damp its temporal dynamics in response to rainfall inputs. Soil depth influenced the geographic source of streamflow, whereas pre-event water sources became more concentrated to near stream zones as soil depth increased. Our T-SAS approach provides a learning tool for linking the dynamics of residence time and time-space sources of flow at the watershed scale and may be a useful framework for other distributed rainfall-runoff models.

Science exchange in an era of diminished capacity: recreation management in the U.S

Ryan, Clare M.; Cerveny, Lee K. — Tue, 20 Sep 2011 17:50:52 -0400

Promotion of effective science exchange between government scientists and managers requires thoughtful arrangement and operation of research and management functions. The U.S. Forest Service was established at the peak of the Progressive Era, when science exchange was designed to occur between researchers and resource managers who worked in distinct arms of the agency, but shared similar goals of effective forest management. In this article, the authors explore the implications of diminished agency capacity for science exchange interactions between researchers and managers in recreation management. Managers and researchers identified their current interactions, their perceptions of ideal interactions, and barriers to achieving those ideals. Reductions in agency capacity for recreation management have resulted in the erosion of interactions between managers and researchers. However, effective science exchange does occur, but requires innovative and adaptive approaches.

Arctic landscapes in transition: responses to thawing permafrost

Mon, 19 Sep 2011 16:53:14 -0400

Observations indicate that over the past several decades, geomorphic processes in the Arctic have been changing or intensifying. Coastal erosion, which currently supplies most of the sediment and carbon to the Arctic Ocean, may have doubled since 1955. Further inland, expansion of channel networks and increased river bank erosion has been attributed to warming. Lakes, ponds, and wetlands appear to be more dynamic, growing in some areas, shrinking in others, and changing distribution across lowland regions. On the Arctic coastal plain, recent degradation of frozen ground previously stable for thousands of years suggests 10-30% of lowland and tundra landscapes may be affected by even modest warming. In headwater regions, hillslope soil erosion and landslides are increasing. Although some level of landscape change is expected in response to natural climate variability, the scale and rapidity of recently observed changes suggest that Arctic landscapes may be particularly sensitive to climate change and capable of rapid geomorphic responses to perturbations. Scientists require improved understanding of mechanisms and feedbacks driving landscape processes to better predict geomorphic responses to climate change.

Constructing a community-level amenity index

Paulson Ganning, Joanna; Flint, Courtney G. — Wed, 21 Sep 2011 12:55:23 -0400

The study of amenity-driven regional change has proliferated in recent years, especially in the American West. While methods of quantifying amenity levels have progressed, they usually rely on traditional and inflexible methods of creating indices. This research note describes a method of manual indexing that allows a flexible and replicable way of assessing amenity levels for various geographic scales and research contexts. We apply this method to nine amenity-based communities in Colorado and direct researchers to resources for exploring alterations for other applications. Results show that the method permits ranking and grouping communities according to relative amenity levels.

Capturing community context of human response to forest disturbance by insects: a multi-method assessment

Qin, Hua; Flint, Courtney G. — Fri, 27 Jan 2012 17:30:33 -0500

The socioeconomic and environmental features of local places (community context) influence the relationship between humans and their physical environment. In times of environmental disturbance, this community context is expected to influence human perceptual and behavioral responses. Residents from nine Colorado communities experiencing a large outbreak of mountain pine beetles (Dendroctonus ponderosae) were surveyed in 2007. Multiple analytic methods including ordinary least squares regression and multilevel modeling techniques were used to evaluate a community-context conceptual model of factors influencing individual actions in response to forest disturbance by beetles. Results indicated that community biophysical and socioeconomic characteristics had important impacts on participation in beetle-related actions and influenced the relationships of individual-level variables in the conceptual model with beetle-related activities. Our findings have implications for natural resource management and policy related to forest disturbances, and for developing a methodology appropriate to measure the general community context of human-environment interactions.

The browning of Alaska's boreal forest

Parent, Mary Beth; Verbyla, David. — Mon, 19 Sep 2011 16:46:27 -0400

We used twelve Landsat scenes from the 1980s-2009 and regional 2000-2009 MODIS data to examine the long-term trend in the normalized difference vegetation index (NDVI) within unburned areas of the Alaskan boreal forest. Our analysis shows that there has been a declining trend in NDVI in this region, with the strongest "browning trend" occurring in eastern Alaska where the climate during the growing season is relatively dry and warm. Possible reasons for the "browning trend" are decreased vegetation due to temperature-induced drought stress and increased infestations of insect pests.

Validation of the ICEsat vegetation product using crown-area-weighted mean height derived using crown delineation with discrete return lidar data

Mon, 19 Sep 2011 16:45:48 -0400

The Geoscience Laser Altimeter System (GLAS), a spaceborne light detection and ranging (lidar) sensor, has acquired over 250 million lidar observations over forests globally, an unprecedented dataset of vegetation height information. To be useful, GLAS must be calibrated to measurements of height used in forestry inventory and ecology. Airborne discrete return lidar (DRL) can characterize vegetation and terrain surfaces in detail, but its utility as calibration data for GLAS is limited by the lack of a direct relationship between the canopy height measurements collected by airborne and spaceborne lidar systems and coincident field data. We demonstrate that it is possible to use DRL to directly estimate the crown-area-weighted mean height (Hcw), which is conceptually and quantitatively similar to the Lorey's height, which is calculated from forest inventory data, and can be used to calibrate GLAS without the use of field data. For a dataset from five sites in western North America, the two indices of height (Hcw from DRL and Lorey's from forest inventory) are directly related (r² = 0.76; RMSE of 3.8 m; intercept and slope of 0.8 m and 0.98, respectively). We derived a relationship between the DRL-derived Hcw and height information from coincident GLAS waveforms; the resulting equation explained 69% of variance, with an RMSE of 6.2 m.

Present-day and future contributions of glacier runoff to summertime flows in a Pacific Northwest watershed: implications for water resources

Nolin, Anne W.; Phillippe, Jeff; Jefferson, Anne; Lewis, Sarah L. — Fri, 27 Jan 2012 16:32:47 -0500

While the impacts of long-term climate change trends on glacier hydrology have received much attention, little has been done to quantify direct glacier runoff contributions to streamflow. This paper presents an approach for determining glacier runoff contributions to streamflow and estimating the effects of increased temperature and decreased glacier area on future runoff. We focus on late summer streamflow (when flow is lowest and nonglacier contributions to flow are minimal) of a small glacierized watershed on the flanks of Mount Hood, Oregon, United States. Field and lab measurements and satellite imagery were used in conjunction with a temperature-index model of glacier runoff to simulate potential effects of increased temperature and reduction in glacier area on late summer runoff in the watershed. Discharge and stable isotope data show that 41-73% of late summer streamflow is presently derived directly from glacier melt. Model simulations indicate that while increased temperature leads to rapid glacier melt and therefore increased streamflow, the consequences of glacier recession overcomes this effect, ultimately leading to substantial declines in streamflow. Model sensitivity analyses show that simulation results are most sensitive to degree day factor and less sensitive to uncertainties in debris-covered area and accumulation area ratio. This case study demonstrates that the effects of glacier recession on streamflow are a concern for water resource management at the local scale. This approach could also be extended to larger scales such as the upper Columbia River basin where glacier contributions to late summer flows are also thought to be substantial.

The carbon budget of the northern cryosphere region

Mon, 19 Sep 2011 16:39:19 -0400

The northem cryosphere is undergoing substantial warming of permafrost and loss of sea ice. Release of stored carbon to the atmosphere in response to this change has the potential to affect the global climate system. Studies indicate that the northern cryosphere has been not only a substantial sink for atmospheric CO₂ in recent decades, but also an important source of CH₄ because of emissions from wetlands and lakes. Analyses suggest that the sensitivity of the carbon cycle of the region over the 21st Century is potentially large, but highly uncertain because numerous pathways of response will be affected by warming. Further research should focus on sensitive elements of the carbon cycle such as the consequences of increased fire disturbance, permafrost degradation, and sea ice loss in the northern cryosphere region.

An analysis of the carbon balance of the Arctic Basin from 1997 to 2006

Thu, 15 Sep 2011 14:00:26 -0400

This study used several model-based tools to analyze the dynamics of the Arctic Basin between 1997 and 2006 as a linked system of land-ocean-atmosphere C exchange. The analysis estimates that terrestrial areas of the Arctic Basin lost 62.9 Tg C yr^-1 and that the Arctic Ocean gained 94.1 Tg C yr^-1. Arctic lands and oceans were a net C0₂ sink of 108.9 Tg C yr^-1, which is within the range of uncertainty in estimates from atmospheric inversions. Although both lands and oceans of the Arctic were estimated to be C0₂ sinks, the land sink diminished in strength because of increased fire disturbance compared to previous decades, while the ocean sink increased in strength because of increased biological pump activity associated with reduced sea ice cover. Terrestrial areas of the Arctic were a net source of 41.5 Tg CH_/4/yr^-1 that increased by 0.6 Tg CH₄/yr^-1 during the decade of analysis, a magnitude that is comparable with an atmospheric inversion of CH₄. Because the radiative forcing of the estimated CH₄ emissions is much greater than the C0₂ sink, the analysis suggests that the Arctic Basin is a substantial net source of green house gas forcing to the climate system.

How old is streamwater? Open questions in catchment transit time conceptualization, modeling and analysis

Thu, 15 Sep 2011 13:57:57 -0400

The time water spends travelling subsurface through a catchment to the stream network (i.e. the catchment water transit time) fundamentally describes the storage, flow pathway heterogeneity and sources of water in a catchment. The distribution of transit times reflects how catchments retain and release water and solutes that in turn set biogeochemical conditions and affect contamination release or persistence. Thus, quantifying the transit time distribution provides an important constraint on biogeochemical processes and catchment sensitivity to anthropogenic inputs, contamination and land-use change. Although the assumptions and limitations of past and present transit time modelling approaches have been recently reviewed (McGuire and McDonnell, 2006), there remain many fundamental research challenges for understanding how transit time can be used to quantify catchment flow processes and aid in the development and testing of rainfall-runoff models. In this Commentary study, we summarize what we think are the open research questions in transit time research. These thoughts come from a 3-day workshop in January 2009 at the International Atomic Energy Agency in Vienna. We attempt to lay out a roadmap for this work for the hydrological community over the next 10 years. We do this by first defining what we mean (qualitatively and quantitatively) by transit time and then organize our vision around needs in transit time theory, needs in field studies of transit time and needs in rainfall-runoff modelling. Our goal in presenting this material is to encourage widespread use of transit time information in process studies to provide new insights to catchment function and to inform the structural development and testing of hydrologic models.

Defensive effects of extrafloral nectaries in quaking aspen differ with scale

Mortensen, Brent; Wagner, Diane; Doak, Patricia. — Thu, 15 Sep 2011 14:02:35 -0400

The effects of plant defenses on herbivory can differ among spatial scales. This may be particularly common with indirect defenses, such as extrafloral nectarines (EFNs), that attract predatory arthropods and are dependent on predator distribution, abundance, and behavior. We tested the defensive effects of EFNs in quaking aspen (Populus tremuloides Michx.) against damage by a specialist herbivore, the aspen leaf miner (Phyllocnistis populiella Cham.), at the scale of individual leaves and entire ramets (i.e., stems). Experiments excluding crawling arthropods revealed that the effects of aspen EFNs differed at the leaf and ramet scales. Crawling predators caused similar reductions in the percent leaf area mined on individual leaves with and without EFNs. However, the extent to which crawling predators increased leaf miner mortality and, consequently, reduced mining damage increased with EFN expression at the ramet scale. Thus, aspen EFNs provided a diffuse defense, reducing damage to leaves across a ramet regardless of leaf-scale EFN expression. We detected lower leaf miner damage and survival unassociated with crawling predators on EFN-bearing leaves, suggesting that direct defenses (e.g., chemical defenses) were stronger on leaves with than without EFNs. Greater direct defenses on EFN-bearing leaves may reduce the probability of losing these leaves and thus weakening ramet-scale EFN defense. Aspen growth was not related to EFN expression or the presence of crawling predators over the course of a single season. Different effects of aspen EFNs at the leaf and ramet scales suggest that future studies may benefit from examining indirect defenses simultaneously at multiple scales.

Elucidating the nutritional dynamics of fungi using stable isotopes

Mayor, Jordan R.; Schuur, Edward A.G.; Henkel, Terry W. — Mon, 19 Sep 2011 16:35:17 -0400

Mycorrhizal and saprotrophic (SAP) fungi are essential to terrestrial element cycling due to their uptake of mineral nutrients and decomposition of detritus. Linking these ecological roles to specific fungi is necessary to improve our understanding of global nutrient cycling, fungal ecophysiology, and forest ecology. Using discriminant analyses of nitrogen and carbon isotope values from 813 fungi across 23 sites, we verified collector-based categorizations as either ectomycorrhizal (ECM) or SAP in > 91% of the fungi, and provided probabilistic assignments for an additional 27 fungi of unknown ecological role.