Summary Seed production by Picea engelmannii was monitored at 13 sites distributed across a ˜670 m elevation gradient for 40 years. Time series of annual seed output was investigated for evidence of masting behaviour and trends in seed abundance over time. We used regression models in a likelihood framework to examine climate effects on seed production for critical periods in the species' reproductive cycle. We rigorously evaluated the performance of two gridded climate data sets, PRISM and TopoWx, before using associated variables as predictors in the seed models. Seed production at these sites does not strictly conform to the classic masting concept. Seed abundance was highly variable over time and strongly synchronized among sites, but mast years could not be objectively identified due to intermediate levels of seed output. Model results indicate that climate conditions across multiple years cumulatively determine reproductive output. High seed rain is associated with elevated summer temperatures in the year that seeds are dispersed, low spring snowfall in the year preceding seed dispersal when buds are initiated, and reduced spring snowfall in a so‐called priming year two years prior to seed dispersal. Low spring precipitation putatively increases growing season length and resource accumulation in seed trees. Linear models identified significant positive trends in seed output over time. Anomalous aridity and summer warmth in the latter half of the study period were highly favourable for seed production and were associated with increases in seed abundance. Synthesis. The increases in seed output observed in this study may promote population fitness of P. engelmannii in the face of changing climate regimes and increasing frequencies of fire‐ and insect‐related tree mortality in the Rocky Mountains. Since this species lacks a persistent seed bank, re‐colonization of disturbed areas or dispersal to shifting habitats depends on adequate production of seed by surviving trees, which according to these analyses may be moderately enhanced by current climate trends. However, some evidence also indicates that increases in seed output will ultimately be constrained by threshold high temperatures in the seed maturation year.

An experimental assessment of the use of clearfell harvesting to initiate a regeneration response in commercially managed aspen forests affected by sudden aspen decline (SAD) was conducted in western Colorado in cooperation with the USDA Forest Service. Nine pure commercial quality aspen stands, with three levels of mortality attributed to SAD, were selected (three replicates per mortality level). Half of each stand was clearfelled, and half was left uncut. The aspen regeneration response was monitored for three growing seasons after harvest in the cut and uncut treatments. Cut treatments with low and moderate mortality had the best subsequent regeneration response, and those with the heaviest mortality exhibited the poorest regeneration response. Uncut treatments exhibited very little regeneration response, regardless of the initial overstory mortality level. Dead trees in the uncut overstory were projected to fall within 15 years. These results indicate that it is possible to successfully regenerate aspen forests affected by SAD, provided that treatment occurs before the majority of the aspen are dead.

Abstract: Difficulty in re-establishing native vegetation on surface mined lands in the semi-arid western U.S. prompted this study to determine the effectiveness of landscape fabric and supplemental irrigation on survival and growth of the woody perennials aspen (Populus tremuloides Michx.) and serviceberry (Amelanchier alnifolia (Nutt.) Nutt. ex M. Roem.) at a high elevation reclaimed surface coal mine site in Colorado. The study compared growth and survival of container-grown aspen and serviceberry planted with or without landscape fabric for control of competing vegetation, and with or without biweekly supplemental irrigation during the first growing season. Response after three years indicated that the landscape fabric was particularly crucial in survival and growth of aspen on sites with heavy competing vegetative cover. Serviceberry plants grew better with landscape fabric but the fabric did not increase survival. Supplemental irrigation provided only limited advantage compared to the landscape fabric. Photosynthesis and pre-dawn moisture stress measurements on the aspen indicated that they were more stressed without landscape fabric. Soil moisture was higher under the landscape fabric.

This report presents results from a research study conducted by Colorado State University under agreement with the U.S. Forest Service. This effort was an experimental assessment of using clearfell harvesting on an operational level to initiate a suckering response in forests affected by Sudden Aspen Decline (SAD). Nine aspen stands with various levels of mortality attributed to SAD were commercially harvested and aspen sucker response monitored for three subsequent growing seasons. Stands with the heaviest mortality exhibited the poorest subsequent sucker response. Stands with over half their original aspen stocking alive at the time of harvest produced levels of suckering which appear adequate for successful regeneration. Paired untreated stands exhibited very little sucker response, regardless of the initial overstory mortality level. These results indicate that management intervention can successfully regenerate aspen forests affected by SAD, provided treatment occurs before the majority of the aspen are dead.

Successful re-establishment of aspen (Populus tremuloides Michx.) on surface-mined lands in the western United States is problematic because the species generally regenerates vegetatively by sprouting from parent roots in the soil; however, topsoil is removed in the mining process. Previous attempts to plant aspen on reclaimed mine sites have failed because transplanted root sprouts or seedlings do not have an extensive root system to access water and nutrients. This study identified factors that limit the survival and growth of aspen on reclaimed surface-mined lands by examining planted aspen saplings with supplemental irrigation and removal of competing vegetation in a fenced plot. The aspen saplings were grown on reclaimed roto-tilled, fresh-hauled soil or on dozer-cleared stored soils. Separate observations were made on survival and growth of nearby plots of natural aspen sprouts (fenced or unfenced) and on potted aspen seedlings. The best combination of conditions for aspen survival used transplanted saplings from local sources on fresh-hauled soil directly removed and placed from local aspen stands. Growth was better when competing vegetation was controlled by hand-hoeing around individual trees. The plants responded less to irrigation, but irrigation with non-saline water may enhance survival and growth in years with drought conditions. Aspen trees in an unfenced plot were heavily damaged by browsing ungulates.

The USDA Forest Service Rocky Mountain Research Station sponsored an aspen summit meeting in Salt Lake City, Utah, on December 18 and19, 2006, to discuss the rapidly increasing mortality of aspen (Populus tremuloides) throughout the western United States. Selected scientists, university faculty, and managers from Federal, State, and non-profit agencies with experience working with aspen were invited. Participants were first asked to share information on recent aspen mortality. Subject matter working groups were then asked to determine factors associated with recent aspen mortality, recommend research needs, and organize those needs into testable questions and hypotheses. This report documents their findings, and will serve as a platform for Resource Managers to address the Sudden Aspen Decline issue.

In late summer 2000 the Jasper Fire burned 34,000 ha of ponderosa pine forest in the Black Hills of South Dakota. Although regarded as a catastrophic event, the Jasper Fire left a mosaic of fire severity across the landscape, with live trees present in areas burned under low and moderate fire severity. In October 2005, we cored 96 trees from unburned, low-severity, and moderate-severity stands and assessed whether tree growth differed among fire severity classes during the 5 years postfire. We observed no differences in basal area increment (BAI) 10 years prefire among fire severities with BAI averaging 9.6 cm(2) per year. Despite severe drought conditions, BAI in moderate severity sites 2 years postfire was 58% greater than in unburned and low-severity stands. Although significant, this growth increase was short-lived. Three, 4, and 5 years postfire, no differences in growth among unburned, low-severity, and moderate-severity sites were detected, as BAI averaged 8.3, 7.5, and 7.0 cm(2), respectively. The lack of a consistent and prolonged growth response suggests that the Jasper Fire did not result in any short-term changes in growth patterns. Data extending beyond 5 years postfire are required to infer potential long-term changes in tree growth and productivity.

We examined the impacts of post-fire salvage logging on regeneration, fuel accumulation, and understorey vegetation and assessed whether the effects of salvage logging differed between stands burned under moderate and high fire severity following the 2000 Jasper Fire in the Black Hills. In unsalvaged sites, fire-related tree mortality created a large standing pool of available fuel, resulting in a rapid increase in surface fuel loads. After 5 years, fine woody debris (FWD) and coarse woody debris (CWD) increased ~1380% and 980% in unsalvaged sites, resulting in FWD and CWD loads of 13 and 25 Mg ha–1, respectively. In contrast, salvage logging limited the rate of accumulation of FWD to ~110% over the same time period and total accumulation of CWD to 16 Mg ha–1. In moderate-severity sites, regeneration was 75% lower in salvaged sites owing to low seed-tree retention, suggesting a re-evaluation of salvage guidelines during future operations in the Black Hills. The likelihood of timely regeneration in high-severity sites, regardless of salvage treatment, is low. We found no discernible effect of salvage logging on understorey development 5 years after fire. Logging caused neither a reduction in total plant cover nor an increase in the abundance of exotic species.

Reduction of crown fire hazard in Pinus ponderosa forests in the Black Hills, SD, often focuses on the removal of overstorey trees to reduce crown bulk density. Dense ponderosa pine regeneration establishes several years after treatment and eventually increases crown fire risk if allowed to grow. Using prescribed fire to control this regeneration is hampered by the limited knowledge of fire-related mortality threshold values for seedlings (<1.4 m tall) and saplings (0.25 to 10 cm diameter at breast height). The present study was initiated to assess fire-related mortality of ponderosa pine seedlings and saplings on prescribed burns across the Black Hills. We established plots in several burn units after the first post-fire growing season to measure crown volume scorch, crown volume consumption, basal scorch, and ground char for ponderosa pine seedlings and saplings. Logistic regression was used to model the probability of mortality based on tree size, flame length, and direct fire effects. Tree size, flame length, crown damage, ground char, and basal char severity were all important factors in the prediction of mortality. Observed mortality was >70% for seedlings but was only 18 to 46% for sapling-sized trees. The differences in mortality thresholds for ponderosa pine seedlings and saplings highlight their susceptibility to different damage pathways and give managers several options when designing burn prescriptions.

We evaluate whether current procedures used in fire behavior prediction models such as FVS-FFE provide predictions of CBD and CBH suitable for evaluating fire behavior in response to fuel treatments. Currently, FFE-FVS uses a geographic non-specific set of tree allometries and assumes a uniform distribution of crown mass when estimating CBH and CBD. We develop allometric equations to predict crown mass specific to ponderosa pine in the Black Hills (Pinus ponderosa Dougl. ex Laws.) from a sample of 80 felled trees in 16 forest stands spanning a wide range in tree size and stand. We develop a non-uniform description of vertical crown mass within individual trees using the Weibul distribution. We relate the parameters of the distribution to stand structure, so that a vertical canopy biomass profile can be estimated for any stand from standard inventory information. We modify the existing FVS-FFE program to include our results. Estimates of CBD increased by an average of 78% when using our local biomass and non-uniform vertical distribution models compared to current procedures in FVS-FFE. On average, 47% of the underprediction of the current procedure compared to our new models resulted from site specific allometries and additional 31% of the under prediction resulted from a non-uniform distribution of crown mass. Our results suggest locally-derived crown mass equations in addition to non-uniform estimates of crown mass distribution should be used to calculate CBH and CBD as used in fire prediction models. Current management efforts to create stand structures more resistant to the initiation and spread of crown fire include increasing CBH and reducing CBD below the threshold where crown fire can be initiated and carried through the tree canopy. Of the 16 stands sampled in this study, only two had CBD estimates >0.100 kg m (i.e. the CBD where active crown fire would be expected) as currently implemented in FFE-FVS. When local crown mass equations and distribution models were applied to the data, 12 out of the 16 stands had CBD estimates >0.100 kg m threshold. Consequently, FFE-FVS, as presently formulated, would misdiagnose fire hazard in a substantial number of Black Hills ponderosa pine stands. Further, where FFE-FVS is used to design and evaluate fuels treatments, it is probable that either the amount of density reduction necessary to achieve a desired effect will be underestimated, or the longevity of effectiveness of a given treatment will be overestimated. BACKGROUND AND PURPOSE Long-term maintenance of fuels reduction treatments is a primary goal for forest management in the ponderosa pine (Pinus ponderosa Laws.) forests of the Black Hills, South Dakota. The Black Hills are dominated by young, dense, even-aged ponderosa pine stands and the prevalence of these stands can result in large, catastrophic wildfires, such as the 34,000 ha Jasper fire of 2000. Many of these stands are in the wildland – urban interface, where reducing the likelihood of crown fire behavior in the event of a wildfire is extremely important. Annually, ~2,300 ha are being treated to reduce the potential for crown fire, primarily by thinning to reduce canopy density. Fire resistant structures created by stand level fuels treatments are not static: canopy density increases with time as trees grow and regeneration is recruited into the overstory canopy. With this increased canopy density, active crown fire behavior again becomes likely. Accurate projections of how canopy density changes with initial treatment and how canopy density increases with time are crucial in determining how, when, and how often fuels treatments are preformed. We propose to develop improved methods for estimating the amount and vertical distribution of canopy fuels from forest inventory data and to integrate these estimators of canopy fuels with models of forest growth and fire behavior (i.e. the Forest Vegetation Simulator (FVS) and the Fire and Fuels Extension (FFE). Fuels treatments to reduce crown fire behavior in Black Hills ponderosa pine forests are most commonly commercial or precommercial thinning to reduce stand density below 12 m/ha (50 ft/acre) of basal area. These densities are thought to reduce the amount of canopy fuels below the level that will support crown fire. Stands thinned to these densities will have high basal area growth rates, with rapid development of canopy density. Also, ponderosa pine regeneration will be prolific at these stand densities, and will create ladder fuels and increased canopy density as regeneration grows in height and crown size. Initial treatment effectiveness and longevity of treatment effects are evaluated using estimates of surface fuels and canopy structure in surface and canopy fire behavior models. Two types of crown fire behavior are predicted based on stand structure and weather conditions – passive or active crown fire. Passive crown fire occurs when there is a sufficient density of canopy fuels to spread surface fire vertically from lower to upper canopy reaches at a given wind speed. The height in a canopy where there are sufficient fuels to spread flames vertically is called the canopy base height (CBH). Active crown fire occurs when there is sufficient density of fine fuels (e.g. foliage and small branches) at any height in the canopy to indicate sufficient continuity of canopy fuel to carry fire from tree to tree at a given wind speed. The density (kg/m) of needles and small branches used to determine continuity of canopy fuels is called canopy bulk density (CBD). Estimates of the amount and vertical distribution of canopy fuels are critical to accurate estimates of the threshold wind speed where passive or active crown fire will occur. The primary method by which federal land managers predict CBD is through the use of the growth and yield model, the Fire and Fuels Extension to the Forest Vegetation Simulator (FVS-FFE). While FVS-FFE provides a working prediction of CBD through time, the underlying assumptions and equations used to calculate and predict CBD may not accurately represent CBD or CBH. The equations used by FVS-FFE to predict crown mass for ponderosa pine created by Brown (1978) are based on trees from northern Montana and Idaho. These equations, therefore, may not capture variability in crown mass due to geographic, site, or stand variability. Currently, when calculating CBD, FVS-FFE uses a uniform distribution of foliage and branchwood within individual crowns (eg. crown mass divided by crown length). But, crown mass is not evenly distributed within individual tree crowns – crown mass is distributed as a skewed normal distribution, with less mass at the top and bottom a tree crown and most of the mass concentrated near the center of the crown . We hypothesize that both of these problems may result in the underestimation of CBH and CBD in FVS-FFE and therefore provide inaccurate estimates of potential fire behavior. There are many potential benefits from this proposed research. First, accurately predicting crown mass is the foremost important step in calculating CBD. If current crown mass equations for ponderosa pine do not adequately describe crown mass in different geographic regions, current predictions of CBD may be inaccurate. By comparing crown mass equations for ponderosa pine in the Black Hills to those calculated by Brown (1978) and used in FVS-FFE, this research will help determine if there is a need for region specific crown mass equations for individual species. Second, by incorporating a correction factor for foliage distribution into CBD calculations, effects of density and canopy position on canopy fuel distribution will be taken into consideration vastly improving the accuracy of CBD predictions. We suggest that the proposed modifications to the current methodology for predicting CBD will greatly improve land managers ability to evaluate initial treatment effectiveness and to plan for maintenance of fuels treatment projects. 1. We develop equations to predict the amount of forest canopy fuels for Black Hills ponderosa pine to be used with standard forest inventory data and that are compatible with fire behavior models such as FVS-FFE. Equations currently used to estimate canopy fuels are based on a small sample size from a specific and limited geographic range. Our results identify whether current techniques produce sufficiently accurate estimates of canopy fuels to provide a realistic analysis of changed fire behavior from fuel treatments. 2. We develop a technique to accurately predict the vertical distribution of fuels within treated canopies and untreated canopies of Black Hills ponderosa pine. The current approach to estimate CBD from tree inventories assumes a uniform distribution of crown mass. This approach may cause an underestimate of canopy bulk density and an inaccurate estimate of canopy base height. Our results identify whether a more accurate technique for vertical distribution of fuels within tree crowns will improve estimates of canopy bulk density. 3. We test the effect of our estimators of canopy fuel and canopy fuel distribution on the determination of canopy bulk density, canopy base height, and potential crown fire behavior in stands treated for fuels reduction in Black Hills ponderosa pine as compared to the current methods of prediction in FVS-FFE. We will provide our results to the Forest Management Service Center as a set of equations and documentation intended for incorporation into the FVS-FFE model. STUDY DESCRIPTION AND LOCATION

We evaluated changes in forest structure related to fire severity after a wildfire in ponderosa pine forests of the Black Hills, South Dakota, where 25

Concentrated patches of recent trembling aspen (Populus tremuloides) mortality covered 515,091 ha of Colorado forests in 2006. Mortality has progressed rapidly. Area affected increased 58% between 2005 and 2006 on the Mancos-Dolores Ranger District, San Juan National Forest, where it equaled nearly 10% of the aspen cover type. In four stands that were measured twice, incidence of mortality increased from 7-9% in 2002/2003 to 31-60% in 2006. Mortality generally decreased with increasing elevation over the primary elevation range of aspen and occurred on less steep slopes than healthy aspen. Slope-weighted mean aspects of aspen cover type were northern at low elevations and generally southern at high elevations. Relative frequency of mortality was generally highest on southern to western aspects. In 31 stands measured in detail, mortality ranged from 0 to 100% (mean 32%) and was negatively correlated with stand density (P = 0.033). Size of trees affected was strongly correlated with amount of current mortality (P < 0.001), and current mortality was skewed toward larger diameter classes. Density of regeneration was in a low range typical of undisturbed stands and did not increase with overstory mortality.Agents that typically kill mature trees in aspen stands were unimportant in this mortality. Instead, a group of interchangeable, usually secondary agents was most commonly associated with mortality, including Cytospora canker (usually caused by Valsa sordida), aspen bark beetles (Trypophloeus populi and Procryphalus mucronatus), poplar borer (Saperda calcarata), and bronze poplar borer (Agrilus liragus). The rapidity of mortality, mortality agents involved, and probably other causal factors distinguish this phenomenon from the long-term loss of aspen cover usually attributed to successional processes operating in an altered disturbance regime (and often exacerbated by ungulate browsing). Our data are consistent with a hypothesis that (a) predisposing factors include stand maturation, low density, southern aspects and low elevations; (b) a major inciting factor was the recent, acute drought accompanied by high temperatures, and; (c) contributing factors and proximate agents of mortality are the common biotic agents observed. On sites with poor regeneration and weak root systems, clones may die, resulting in the long-term loss of aspen forest cover. Published by Elsevier B.V.

Ceratonia siliqua L. - carob, St. John's bread, or locust - is a small to medium-sized broadleaf, evergreen tree that may grow to 20 m in height under ideal climatic conditions (Catarino 1993) but usually reaches heights of 8 to 15 m (Goor and Barney 1968). Carob is thought to be a tropical plant that has adapted well to Mediterranean climates by utilizing its deep rooting habit and xerophilous leaves to avoid water stress (Catarino 1993). The deep taproot's penetration into moist regions of the soil profile effectively lengthens the active growth period for carob leaves during the Mediterranean dry season (Rhizopoulou and Davies 1991).

Saltcedar (Tamarix chinensis (Lour.)) and smallflower tamarisk (T. parviflora DC.) hybridize in the Southwest (Baum 1967; Horton and Campbell 1974) and are deciduous, pentamerous tamarisks that are both commonly referred to as saltcedar. Saltcedar is a native of Eurasia that has naturalized in the southwestern United States within the last century. It was introduced into the eastern United States in the 1820s (Horton 1964) and was once widely cultivated as an ornamental, chiefly because of its showy flowers and fine, graceful foliage.

Nutrient availability is an important constraint on sustainable forest productivity, and it is crucial to understand the long-term effects of management practices, including soil scarification, on soil microbial communities because they store and cycle nutrients. In addition, because forests are subject to wildfires, it would be useful to understand potential interactive effects of wildfire and management practice on forest soil ecosystems. We studied the individual and combined effects of soil scarification and a subsequent wildfire on microbial community structure of a ponderosa pine (Pinus ponderosa C. Lawson) forest soil in the central Rocky Mountains. Experimental plots were scarified by rototilling in 1981, and in 2002, some of the plots were burned during a mixed-severity wildfire. In 2005, mineral soil samples (0-10-cm depth) were collected and assayed for soil chemical properties, fungal and bacterial biomass, C mineralization potential, and microbial community fatty acid composition. Compared with undisturbed soil, soil from scarified-only plots was relatively high in pH, low in total C and organic matter (OM) concentrations, low in fungal and bacterial biomass, and enriched with Gram-positive biomarkers. Regardless of scarification treatment, soil from burned plots was relatively high in pH and extractable P, low in fungal but not bacterial biomass, and enriched with Gram-negative bacterial biomarkers. Compared with scarified-only plots, scarified-plus-burned plots had greater soil C and OM concentrations. Carbon mineralization rates were not different among the plot soils. While scarification is a positive practice for aiding seedling establishment, we found long-term effects on soil C reserves and microbial communities.