Forest Restoration Treatments Research Articles

Bunching as a Method to Reduce Wood Moisture through Transpirational Drying following Forest Restoration Treatments in Northern Arizona

Abstract Thinning is a necessary silvicultural activity for restoring the long-term sustainability of pine forests in much of the southwestern United States. In northern Arizona, a landscape-scale restoration effort, called the Four Forest Restoration Initiative, has been implemented to recover the long-term sustainability of 2.4 million acres on four national forests. Cost-effective and efficient thinning methods are needed due to the scale of the project to help improve habitat, conserve biodiversity, protect old growth, reduce risk of severe wildfire, and restore natural forest structure and function. Mechanical cutting using a feller-buncher is the primary method of thinning in these forests due to the extreme high number of small-diameter ponderosa pine trees. A feller-buncher places harvested trees into small piles known as “bunches.” In this review, we highlight advantages and disadvantages of bunching tree materials in restoration programs and review published studies on transpirational drying of bunches of various tree species in different forest habitats across the United States, including ponderosa pine in Arizona. Studies show that transpirational drying of trees in bunches can be an effective method to allow for wood drying, but this process can be affected by abiotic factors associated with seasonal climate and stand characteristics. Study Implications The Four Forest Restoration Initiative makes up the largest landscape-level collaborative project in the history of the USDA Forest Service with more than 2.4 million acres of forest habitat. Thinning is a necessary silvicultural activity for restoring the long-term sustainability of these forests in northern Arizona. Because of the extremely high number (i.e., average of 720 trees per acre) of small-diameter ponderosa pine (Pinus ponderosa) trees, mechanical cutting is more cost effective than individual saw cutting, which is why a feller-buncher machine is the primary thinning tool. During feller-buncher thinning, small piles of trees known as “bunches” are created. Bunching trees can allow for wood drying in the field that translates into lower operational costs because drier trees are lighter in weight, which reduces transportation costs. In northern Arizona, a 60-day time frame is allotted for transpirational drying before tree materials must be removed from the forest. However, because the drying process through bunching is affected by abiotic conditions, there may be a need to adjust this time frame to account for seasonal weather patterns. For example, during spring, when weather in northern Arizona is hot and dry, less time might be necessary for tree bunches to lose enough moisture while still rendering the thinning operation profitable and simultaneously avoiding bark beetle proliferation given that their life cycle consists of about 40 days. Furthermore, bunching studies should be developed to look at individual tree species in their respective locations and to investigate the effects of the presence, partial presence, or absence of branches and bark on trees within bunches. Studies should also be conducted to look at the effects of bunches on insect communities, particularly those that can cause extensive tree mortality.

Modelling variation in wood stiffness of Pinus ponderosa using static bending and acoustic measurements

Abstract Wood removed in Southwestern US forest restoration treatments currently has limited markets and thus low value. One important property of wood in structural products is its stiffness (measured as modulus of elasticity), which is known to vary systematically within trees. Directly measuring wood stiffness is expensive, time consuming and destructive. Therefore, we tested samples of ponderosa pine (Pinus ponderosa var. scopulorum Engelm.) from northern Arizona destructively in bending and also non-destructively using acoustic velocity (AV) methods. In total, we tested multiple pith-to-bark small clear (2.54 × 2.54 × 40.64 cm) samples from up to four heights in 103 trees. We first measured the standing-tree AV of sample trees, then the AV of small clear samples, and finally measured wood stiffness using three point static bending tests. We found that a Michaelis–Menten curve was a good fit to the radial profile of wood stiffness, with a steep increase outward from the pith that approached an asymptote. The AV of small clear samples, coupled with measured volumetric density values, approximated the static modulus of elasticity values with high accuracy (r2 = 0.86). At the stand level, a model predicting standing tree AV from tree morphology fit the data well (r2 = 0.77). Results indicate that southwestern ponderosa pine contains outerwood with relatively high stiffness that could be suitable for structural products. However, when assessed using wood stiffness, the trees take a long time to reach maturity (~50 years) and thus the corewood proportion is large. AV measurements are a good way to assess variability within and among stands and thus could be employed to segregate the resource by expected stiffness values. Segregation could help identify stands not suitable for structural uses and direct them toward more appropriate products.

Forest restoration treatments in a ponderosa pine forest enhance physiological activity and growth under climatic stress.

As the climate warms, drought will increasingly occur under elevated temperatures, placing forest ecosystems at growing risk of extensive dieback and mortality. In some cases, increases in tree density following early 20th-century fire suppression may exacerbate this risk. Treatments designed to restore historical stand structure and enhance resistance to high-severity fire might also alleviate drought stress by reducing competition, but the duration of these effects and the underlying mechanisms remain poorly understood. To elucidate these mechanisms, we evaluate tree growth, mortality, and tree-ring stable-carbon isotope responses to stand-density reduction treatments with and without prescribed fire in a ponderosa pine forest of western Montana. Moderate and heavier cutting experiments (basal area reductions of 35% and 56%, respectively) were initiated in 1992, followed by prescribed burning in a subset of the thinned units. All treatments led to a growth release that persisted to the time of resampling. The treatments had little effect on climate-growth relationships, but they markedly altered seasonal carbon isotope signals and their relationship to climate. In burned and unburned treatments, carbon isotope discrimination (Δ13 C) increased in the earlywood (EW) and decreased in the latewood (LW) relative to the control. The sensitivity of LW Δ13 C to late-summer climate also increased in all treatments, but not in the control. Such increased sensitivity indicates that the reduction in competition enabled trees to continue to fix carbon for new stem growth, even when the climate became sufficiently stressful to stop new assimilation in slower-growing trees in untreated units. These findings would have been masked had we not separated EW and LW. The importance of faster growth and enhanced carbon assimilation under late-summer climatic stress became evident in the second decade post-treatment, when mountain pine beetle activity increased locally, and tree mortality rates in the controls of both experiments increased to more than twice those in their respective treatments. These findings highlight that, when thinning is used to restore historical forest structure or increase resistance to high-severity fire, there will likely be additional benefits of enhanced growth and physiological activity under climatic stress, and the effects may persist for more than two decades.

Pyrogenic Carbon Generation From Fire and Forest Restoration Treatments

Pyrogenic carbon (PyC) is a chemically stable form of carbon (C) generated during fire events and is one of the few legacies of fire recorded in soil; however, the significance of this material as a form of C storage in forest ecosystems has received only limited scientific attention, and currently relatively little is known regarding the quantity of PyC generated during forest restoration efforts that include prescribed (Rx) fire. Quantifying the rate of PyC production during fire events is essential to estimating the potential for ecosystem C storage in forest systems where wildfire is a common natural disturbance and Rx fire is used as a fuel management practice. In this paper, we report on the average mass of PyC formation during wildfire and Rx fire events in forest ecosystems through synthesizing data across 12 published studies; and we report empirical data on the mass of PyC generated in a replicated Rx fire study in a ponderosa pine (Pinus ponderosa) forest ecosystem of the Rocky Mountain West. Our data synthesis showed that PyC (consisting of PyC from downed wood, O horizon, and mineral soil) was, on average, produced at a rate of 5.2% of biomass exposed to fire in forest ecosystems, and a single wildfire or Rx fire event generated about 2.2 Mg C ha-1 in the form of PyC. In our empirical study, we collected O horizon and surface mineral soil (0 – 10 cm) samples from the Fire and Fire Surrogates study plots in western Montana (treatments: control, thin, burn, thin&burn) that was burned in 2002 and analyzed for PyC content using a wet digestion method. The two Rx fire treatments had significantly higher PyC contents in the O horizon compared to the control. In the thin&burn treatment, PyC was formed at a rate of about 12% of total biomass consumed yielding approximately 2.24 Mg PyC C ha-1 in the O horizon. Mineral soil PyC contents were not affected by Rx fire. Wildfire and Rx fires generate a substantial amount of PyC which initially resides in the O horizon and serves as a stable form of ecosystem C.

Investigation of bed and den site selection by American black bears (Ursus americanus) in a landscape impacted by forest restoration treatments and wildfires

The combined effects of long-term fire suppression, logging, and overgrazing have negatively impacted many southwestern U.S. forests, resulting in decreased habitat quality for wildlife, and more frequent and severe wildfires. In response, land management agencies are implementing large-scale forest restoration treatments, but data on how wildlife respond to restoration treatments and wildfires are often limited. We investigated bed and den site selection of American black bears (Ursus americanus) using GPS location data and a use/available study design to assess the influence of habitat characteristics, including wildfires, prescribed burns, and thinning treatments on bed and den site selection in the Jemez Mountains, New Mexico. The most supported models suggested that black bears were more likely to select bed sites with a combination of low horizontal visibility (β = −0.007, SE = 0.002; P = 0.002) and high stand basal area (β = 0.013, SE = 0.005; P = 0.004). The highest-ranking model for den site selection indicated that black bears were more likely to select den sites with low horizontal visibility (β = −0.0102, SE = 0.004; P = 0.006). Black bears used all disturbed sites to varying degrees (45% of study area), although 48% of bed sites were located in undisturbed habitat (55% of study area) while only 11% and 2% of bed sites were located in thinned and prescribed burn sites, respectively. Thirty-nine percent of bed sites were located in previous wildfire locations; however, 67% of these sites were in areas with low burn severity. Thirty-eight percent of den sites were located in previously disturbed habitat, 8 of these sites were burned by wildfires. In order to develop effective management plans for black bears, it is essential to understand responses to landscape-scale habitat disturbances due to wildfires and restoration activities, all of which are becoming more prevalent and widespread across southwestern forests. Accounting for the timing, size, and proximity of future restoration efforts would aid in mitigating potential short-term negative effects on black bears.

Climate has a larger effect than stand basal area on wood density in Pinus ponderosa var. scopulorum in the southwestern USA

Stand basal area of ponderosa pine ( Pinus ponderosa var. scopulorum Engelm.) in the US Southwest has little effect on the density of the wood produced, but climatic fluctuations have a strong effect. Wood density increases during drought, particularly if the drought occurs in late winter/early spring. Future droughts, as are predicted to increase in the US Southwest, may lead to production of smaller radial increments of higher density wood in ponderosa pine. Forest restoration treatments in the US Southwest are generating large quantities of small-diameter logs. Due to negative perceptions about ponderosa pine wood quality, this material is often seen as a “waste disposal” problem rather than a high-value resource. Our objective was to understand more about variation in southwestern US ponderosa pine wood density, an important indicator of wood quality. Specifically, we investigated the effect of stand basal area on wood density, and the effect of annual and quarterly climatic variation on wood density. We collected samples from 54 trees grown at six different basal area levels from a replicated stand density experiment. Pith-to-bark strips were used in an X-ray densitometer to obtain annual density and growth measurements from 1919 to the present. Stand density had a strong effect on growth rate, but little effect on wood density. However, climatic variation did influence wood density, which increased in drought years before quickly returning to pre-drought levels. Stand basal area is not a good indicator of wood density for foresters planning to utilize material from timber harvests in the southwestern USA. Future droughts, as are predicted to increase in the region, will likely reduce wood volume production but may increase wood density in ponderosa pine.

Forest restoration, wildfire, and habitat selection by female mule deer

Decades of fire suppression, logging, and overgrazing have led to increased densities of small diameter trees which have been associated with decreases in biodiversity, reduced habitat quality for wildlife species, degraded foraging conditions for ungulates, and more frequent and severe wildfires. In response, land managers are implementing forest restoration treatments using prescribed fire and thinning to mitigate the risk of catastrophic wildfires and improve habitat conditions for a variety of wildlife species. We monitored habitat selection by female mule deer (Odocoileus hemionus) in relation to forest restoration treatments and wildfires in northern New Mexico in 2015. Our specific objectives were to assess changes in forage abundance and determine habitat selection patterns of mule deer in relation to recent wildfires, forest restoration treatments, including duration of the post-treatment recovery, and other habitat characteristics. Herbaceous forage biomass was greater in wildfire-burned areas than in untreated areas or those treated with prescribed burns or thinning. Oak forage biomass was greater in wildfire-burned areas compared to prescribed burns, forest thinning, and untreated areas. However, thinned areas tended to have higher oak forage biomass than untreated areas. Mule deer selected for areas burned by prescribed fire and generally avoided wildfire-burned and thinned areas <5 years old. Mule deer strongly selected for thinned areas ≥5 years old. At both the landscape and home-range scale, grasslands were avoided during most seasons, pinyon-juniper woodlands were selected in winter, and oak vegetation and mixed-conifer forests were selected during summer. Our data suggests that mule deer may benefit from recent prescribed burns and older forest thinning, but the duration of post-treatment vegetation recovery influences the strength and direction of selection. Knowledge of the short- and long-term effects of restoration treatments will provide managers with the means to make more informed decisions regarding implementation of forest restoration and other vegetation treatments intended to benefit mule deer.

Implementation constraints limit benefits of restoration treatments in mixed-conifer forests

Forest restoration treatments seek to increase resilience to wildfire and a changing climate while avoiding negative impacts to the ecosystem. The extent and intensity of treatments are often constrained by operational considerations and concerns over uncertainty in the trade-offs of addressing different management goals. The recent (2012–15) extreme drought in California, USA, resulted in widespread tree mortality, particularly in the southern Sierra Nevada, and provided an opportunity to assess the effects of restoration treatments on forest resilience to drought. We assessed changes in mixed-conifer forest structure following thinning and understorey burning at the Kings River Experimental Watersheds in the southern Sierra Nevada, and how treatments, topography and forest structure related to tree mortality in the recent drought. Treatments had negligible effect on basal area, tree density and canopy cover. Following the recent drought, average basal area mortality within the watersheds ranged from 5 to 26% across riparian areas and 12 to 44% across upland areas, with a range of 0 to 95% across all plots. Tree mortality was not significantly influenced by restoration treatments or topography. Our results suggest that the constraints common to many restoration treatments may limit their ability to mitigate the impacts of severe drought.

Spotted owl foraging patterns following fuels treatments, Sierra Nevada, California

ABSTRACTWestern dry conifer forests continue to experience increased severe, stand‐replacing wildfire that is outside of historical precedent. Fuels treatments, landscape‐scale modifications of forest fuels and structure, are likely to remain a management tool to modify fire behavior and restore ecological resilience. The impacts of fuels treatments to listed species such as spotted owls (Strix occidentalis) remain uncertain and are contested because of limited available information. To evaluate spotted owl foraging habitat selection in a landscape recently modified by forest fuels‐reduction treatments, we radio‐marked and tracked 10 California spotted owls (S. o. occidentalis) for 2 years immediately following fuels treatment installation in the northern Sierra Nevada, California, USA. We categorized fuels treatments into 3 types: mechanical thin, installed within the study area as landscape‐scale fire breaks characterized by even tree spacing, open understory, and low canopy cover, or group selections; understory thin, a hand‐removal of small trees and shrubs; and understory thin followed by underburn, a controlled surface‐fuel burn that left the overstory intact. We described post‐treatment habitat using forest structural metrics derived from a Light Detection and Ranging (LiDAR) dataset that was collected 1 year after fuels treatments were completed. We collected 436 spotted owl foraging locations during 2 breeding seasons and evaluated breeding season home range size and composition using a resource selection function. We assessed possible contributors to owl foraging patterns by comparing a priori hypotheses in an information‐theoretic approach and using randomly generated points that estimated available habitat. Spotted owl breeding season home ranges contained fuels treatments in proportion to their availability on the landscape and averaged 17.1% treated area. Within the home range, owl foraging locations in the post‐treatment landscape were best predicted by lower proportions of gaps than anticipated at random, steeper slopes, and minimized distance from the owl's site center. Our results suggest that moderate to high proportions of gaps, typically a feature of forest fuels reduction and restoration treatments, may reduce the probability of spotted owl foraging. © 2018 The Wildlife Society.

Managing emerging threats to spotted owls

ABSTRACTThe 3 spotted owl (Strix occidentalis) subspecies in North America (i.e., northern spotted owl [S. o. caurina], California spotted owl [S. o. occidentalis], Mexican spotted owl [S. o. lucida]) have all experienced population declines over the past century due to habitat loss and fragmentation from logging. Now, the emerging influences of climate change, high‐severity fire, and barred owl (Strix varia) invasion also appear to be synergistically and differentially affecting population trends of each subspecies. Our objective was to review the existing literature on the spotted owl to describe historical and emerging threats and whether those threats have been adequately examined for each subspecies. Using 527 publications from a Web of Science search of the literature from 1900–2015, we statistically evaluated the emphasis placed on each subspecies regarding 4 influences: mechanical tree removal, fire, climate change, and barred owl invasion. There were 98 papers that explicitly examined the effects of ≥1 of these influences. Most of these papers were focused on the northern spotted owl, and for all 3 subspecies, most papers examined short‐term effects only. We used our results to identify significant information gaps relative to historical and emerging threats. Commercial timber harvesting remains a potential threat for all 3 spotted owl subspecies, but effects from forest thinning may be increasing because of the heightened emphasis on fuels reduction and forest restoration treatments on public lands. Owl response to mechanical tree removal, especially forest thinning, remains understudied. Climate change also may threaten all 3 subspecies. Changes in climate likely affect survival and reproduction of spotted owls and their prey, and alter habitat availability by affecting disturbance regimes and vegetation composition and succession, but little empirical information is available describing specific responses to climate change. The literature on response to high‐severity fire is sparse for some subspecies, primarily short‐term in nature, and not consistent. Barred owl invasion is a major threat to the northern spotted owl and the California spotted owl but does not currently threaten the Mexican spotted owl. Rigorous research on the response of spotted owls to all factors influencing population change, particularly for the Mexican spotted owl, is needed. The most useful information for predicting owl response to these threats stems primarily from long‐term studies of owl demography. The lack of such studies within the range of the Mexican spotted owl greatly limits our understanding of its population dynamics and our ability to predict the effects of various threats on Mexican spotted owl populations. For all 3 subspecies, we encourage long‐term studies of their responses to threats, using uniquely marked owls across large spatial extents to account for spatiotemporal variability in ecological conditions within and among subspecies. © 2018 The Wildlife Society.

Conflicting Perspectives on Spotted Owls, Wildfire, and Forest Restoration

Evidence of increasing fire extent and severity in the western US in recent decades has raised concern over the effects of fire on threatened species such as the spotted owl (Strix occidentalis Xantus de Vesey), which nests in forests with large trees and high canopy cover that are vulnerable to high-severity wildfire. A dichotomy of views exists on the impact of high-severity wildfire on the spotted owl. One view holds that reduction in the extent of forests with large trees and high canopy cover due to high-severity wildfire is a primary threat to spotted owls, and that fuels reduction treatments that successfully reduce the risk of high-severity wildfire can aid in sustaining desired conditions for this owl. A conflicting view maintains that high-severity wildfire was relatively common in many forest types occupied by spotted owls and does not pose an immediate threat to spotted owls, and that fuels reduction treatments are misguided because they degrade owl habitat and do not reduce the extent of high-severity fire. Based on the existing literature, we argue that considerable uncertainty remains regarding the response of spotted owls to high-severity wildfire, especially over longer time frames and across the three subspecies (California [Strix occidentalis occidentalis Xantus de Vesey], Mexican [S. o. lucida Nelson], and northern [S. o. caurina Merriam]) of spotted owls. The considerable extent of high-severity wildfire within the ranges of these subspecies over recent years, coupled with the trend toward increasing extent and severity of megafires, suggests that the cumulative effects of these fires could be significant throughout the range of this owl. Forest restoration or fuels reduction treatments may aid in reducing habitat loss, particularly when strategically located to optimize reduction of fire risk, but also may locally impact spotted owl habitat. We advocate further evaluation of both the impacts of such treatments to spotted owls and the effectiveness of such treatments in mitigating fire behavior. We also advocate wider use of managed fire to reduce risk of high-severity wildfire. Finally, given the paucity of long-term data on this topic, we recommend targeted research aimed at a decade or longer time periods after fires. These studies should include measures of demographic performance, and should be designed to elucidate differences in those metrics related to landscape pattern, forest type, and subspecies ecology. Such information would inform the debate over how to integrate the conservation of spotted owls and their habitat with fuels reduction and forest restoration objectives.

Fox squirrel response to forest restoration treatments in longleaf pine

Restoration of the longleaf pine (Pinus palustris; LLP) ecosystem and its associated fauna is a principal goal of many land-management agencies in the southeastern United States. Prescribed fire and herbicide application are 2 common methods of LLP restoration. We employed a multi-scale approach to investigate how occurrence of fox squirrels (Sciurus niger) was influenced by fire frequency and herbicide application in LLP communities of northern Florida. We sampled 9-point, 4-ha grids of camera traps with 106 grids in fire treatments, 23 herbicide treatment grids, and 27 control grids. We evaluated a priori models for occurrence of fox squirrels at point, 4-ha patch, and home-range scales, and the influence of fire and herbicides on vegetation structure. Fox squirrel occurrence was positively associated with densities of turkey oak (Quercus laevis) at the patch scale, which were significantly less abundant in herbicide-treated areas. Fox squirrel occurrence was negatively correlated with fire interval and positively correlated with oak densities at a localized point scale. Additionally, fox squirrel point occurrences declined over time since the last fire. Fire produced habitat more favorable for fox squirrels than did herbicide treatments.

Response of soil microbial community composition and function to a bottomland forest restoration intensity gradient

Terrestrial ecosystems are globally under threat of loss or degradation. To compensate for the impacts incurred by loss and/or degradation, efforts to restore ecosystems are being undertaken. These efforts often focus on restoring the aboveground plant community with the expectation that the belowground microbial community will follow suit. This ‘Field of Dreams’ expectation – if you build it, they will come – makes untested assumptions about how microbial communities and their functions will respond to aboveground-focused restoration. To determine if restoration of aboveground plant communities equates to restoration of belowground microbial communities, we assessed the effects of four forest restoration treatments – varying in intensity from unmanaged to interplanting tree species – on microbial (i.e. prokaryotic and fungal) community composition and function (i.e. catabolic profiles and extracellular enzyme activities). Additionally, effects of the restoration treatments were compared to both degraded (i.e. active arable cultivation) and target endpoint communities (i.e. remnant bottomland forest) to determine the trajectory of intensifying aboveground restoration efforts on microbial communities. Approximately 16 years after the initiation of the restoration treatments, prokaryotic and fungal community composition, and microbial function in the four restoration treatments were intermediate to the endpoint communities. Surprisingly, intensification of aboveground restoration efforts led to few differences among the four restoration treatments and increasing intensification did not consistently lead to microbial communities with greater similarity in composition and function to the target remnant forest communities. Together these results suggest that belowground microbial community composition and function will respond little to, or will lag markedly behind, intensifying aboveground restoration efforts. Reliance on a ‘Field of Dreams’ approach, even if you build it better, may still lead to belowground microbial communities that remain uncoupled from aboveground communities. Importantly, our findings suggest that restoring aboveground vegetation may not lead to the intended restoration of belowground microbial communities and the ecosystem processes they mediate.

Forest restoration treatments have subtle long‐term effects on soil C and N cycling in mixed conifer forests

Decades of fire suppression following extensive timber harvesting have left much of the forest in the intermountain western United States exceedingly dense, and forest restoration techniques (i.e., thinning and prescribed fire) are increasingly being used in an attempt to mitigate the effects of severe wildfire, to enhance tree growth and regeneration, and to stimulate soil nutrient cycling. While many of the short-term effects of forest restoration have been established, the long-term effects on soil biogeochemical and ecosystem processes are largely unknown. We assessed the effects of commonly used forest restoration treatments (thinning, burning, and thinning+burning) on nutrient cycling and other ecosystem processes 11yr after restoration treatments were implemented in a ponderosa pine (Pinus ponderosa var. scopulorum)/Douglas fir (Pseudotsuga menziesii var. glauca) forest at the Lubrecht Fire and Fire Surrogates Study (FFS) site in western Montana, USA. Despite short-term (<3yr) increases in soil inorganic nitrogen (N) pools and N cycling rates following prescribed fire, long-term soil N pools and N mineralization rates showed only subtle differences from untreated control plots. Similarly, despite a persistent positive correlation between fuels consumed in prescribed burns and several metrics of N cycling, variability in inorganic N pools decreased significantly since treatments were implemented, indicating a decline in N spatial heterogeneity through time. However, rates of net nitrification remain significantly higher in a thin + burn treatment relative to other treatments. Short-term declines in forest floor carbon (C) pools have persisted in the thin+burn treatment, but there were no significant long-term differences among treatments in extractable soil phosphorus (P). Finally, despite some short-term differences, long-term foliar nutrient concentrations, litter decomposition rates, and rates of free-living N fixation in the experimental plots were not different from control plots, suggesting nutrient cycles and ecosystem processes in temperate coniferous forests are resilient to disturbance following long periods of fire suppression. Overall, this study provides forest managers and policymakers valuable information showing that the effects of these commonly used restoration prescriptions on soil nutrient cycling are ephemeral and that use of repeated treatments (i.e., frequent fire) will be necessary to ensure continued restoration success.

Response in Abert's Squirrel Abundance to Forest Treatments on Camp Navajo, Arizona

Abert's squirrels (Sciurus aberti) are dependent upon ponderosa pine (Pinus ponderosa) forests in northern Arizona. Abert's squirrels feed primarily on the inner bark of ponderosa pine branches, as well as the tree's seeds and the hypogenous fungi associated with ponderosa pines. Abert's squirrels require interlocking tree canopies for escape cover and for feeding, particularly in winter months when snow impedes ground travel and the ability of Abert's squirrels to access fungi and hoarded food. In the Southwest, land managers in the ponderosa pine belt are implementing large-scale forest restoration treatments to reduce fire risk and return forest structure to pre-European settlement conditions. Restoration may decrease intrastand structural diversity and interstand heterogeneity for several decades, reducing the amount of habitat available to Abert's squirrels and reducing overall abundance. We estimated Abert's squirrel densities by enumerating squirrel feeding sign (branch clippings, clipped cones, truffle digging) over 9 years on 15 sites on Camp Navajo, an Arizona Army National Guard base in northern Arizona. Sites were treated at different times throughout the duration of the study. We evaluated the effects of forest restoration treatments on Abert's squirrel densities. We found no difference in Abert's squirrel densities on sites experiencing different treatment types. However, we did find a difference in Abert's squirrel densities between years.

Landscape Biology of Western White Pine: Implications for Conservation of a Widely-Distributed Five-Needle Pine at Its Southern Range Limit

Throughout much of the range of western white pine, Pinus monticola Dougl., timber harvesting, fire exclusion and the presence of Cronartium ribicola J. C. Fisch., the white pine blister rust (WPBR) pathogen, have led to negative population and genetic consequences. To address these interactions, we examined population dynamics and genetic diversity in 10 populations of western white pine in upper montane forests of the Lake Tahoe Basin. We documented negative population trends for three of the 10 populations. These populations exhibited low estimated growth rates (λ), moderate to high incidences of WPBR and mountain pine beetle (MPB), and high levels of mortality. In contrast, seven populations appear to be stable (λ ≥ 1.0), with low to moderate disease and insect incidence, and evidence for genetic resistance to WPBR. Genetic diversity (HE) for a set of 160 single nucleotide polymorphisms was in the range of 0.245–0.272 across populations, and population-specific estimates of FST ranged from 0.0062 to 0.0244. Allele frequency of the Cr2 gene, which confers complete resistance to C. ribicola in western white pine, was low, averaging 0.009 for all populations sampled. However, a low frequency of pollen receptors (i.e., susceptible maternal parents pollinated by a local resistant parent) was found in nine of 10 populations. A moderate and negative relationship was found between the frequency of pollen receptors in a population and the incidence of WPBR (r2 = 0.32). In the context of an introduced pathogen, climate driven outbreaks of MPB, fire exclusion, and prolonged drought, conservation and management strategies are warranted for this species in the Lake Tahoe Basin and likely other locations in California. These strategies include gene conservation of western white pine, WPBR resistance screening, and forest restoration treatments.

Restoration treatments in urban park forests drive long-term changes in vegetation trajectories.

Municipalities are turning to ecological restoration of urban forests as a measure to improve air quality, ameliorate urban heat island effects, improve storm water infiltration, and provide other social and ecological benefits. However, community dynamics following urban forest restoration treatments are poorly documented. This study examines the long-term effects of ecological restoration undertaken in New York City, New York, USA, to restore native forest in urban park natural areas invaded by woody non-native plants that are regional problems. In 2009 and 2010, we sampled vegetation in 30 invaded sites in three large public parks that were restored 1988-1993, and 30 sites in three large parks that were similarly invaded but had not been restored. Data from these matched plots reveal that the restoration treatment achieved its central goals. After 15-20 years, invasive species removal followed by native tree planting resulted in persistent structural and compositional shifts, significantly lower invasive species abundance, a more complex forest structure, and greater native tree recruitment. Together, these findings indicate that successional trajectories of vegetation dynamics have diverged between restored forests and invaded forests that were not restored. In addition, the data suggest that future composition of these urban forest patches will be novel assemblages. Restored and untreated sites shared a suite of shade-intolerant, quickly-growing tree species that colonize disturbed sites, indicating that restoration treatments created sites hospitable for germination and growth of species adapted to high light conditions and disturbed soils. These findings yield an urban perspective on the use of succession theory in ecological restoration. Models of ecological restoration developed in more pristine environments must be modified for use in cities. By anticipating both urban disturbances and ecological succession, management of urban forest patches can be adjusted to better predict and direct long-term outcomes. An urban approach to ecological restoration must use realistic, flexible targets to preserve and enhance urban biodiversity for both short-term benefits and long-term sustainability.

Long-Term Forest Floor Fuels Accumulations in Sierran Mixed Conifer Subjected to Forest Restoration Treatments

Long-term influences of mechanized thinning using a cut-to-length approach combined with on-site slash mastication along with those of prescription under burning on downed and dead fuel accumulations were evaluated in an uneven-aged eastern Sierra Nevada mixed conifer stand. Based on an initial inventory conducted soon after treatment implementation, accumulations in an unburned portion of the stand subunit subjected to thinning were elevated with respect to both 1+10 hr time lag and total fuel loads. In contrast, the near immediate effect of the under burn on these fuels was marked diminishment in their abundance. Nearly a decade later, however, effects of the mechanized and fire treatments had largely dissipated. In the interim between inventories, the thinned but unburned treatment combination exhibited the greatest reduction in 1+10 hr and total fuels while the unthinned and unburned combination also exhibited a large reduction in the former. Furthermore, diminished reductions in 1+10 hr fuels were apparent within the burned portions of the thinned and unthinned stand subunits, and the unthinned but burned combination was the only one to incur an increase in total fuels. These findings offer land managers insight regarding the persistence of fuel bed alterations induced by these increasingly common management practices in Sierran mixed conifer and similar forest cover types.

Long-term Herbivore Exclusion for Recovery of Buckbrush (Ceanothus fendleri ) Populations During Restoration of Ponderosa Pine Forests in Northern Arizona

Open conditions created by restoration activities in ponderosa pine ( Pinus ponderosa ) forests of the American Southwest can lead to increases in understory plant productivity but also attract large ungulate herbivores. In this study, we remeasured buckbrush ( Ceanothus fendleri ) plants on permanent plots to determine effects of long-term herbivore exclusion on population abundance and potential reproduction. Results showed that survival of buckbrush was significantly lower on unprotected plots compared with plants given long-term herbivore protection. A greater proportion of the highest stem density class ( 50 stems m−2 ) was found on long-term protection plots compared with short-term protection or unprotected groups. The unprotected group was overwhelmingly (90%) made up of plots with less than 10 aerial stems m−2 . Plots with long-term protection had a significantly greater proportion of plots in the highest flowering class ( 50% of aerial stems flowering) than unprotected plots. Logistic regression showed a strong, positive relationship ( p = 0.61) between the probability of flowering and plant height. Results indicated that short-term protection following forest restoration treatments marginally improves survival of buckbrush in these ecosystems. However, herbivory pressure remained high over the 12-year study period and detrimentally affected potential reproduction of plants exposed to large herbivores. These findings generally suggest that short-term protection may not be sufficient to conserve buckbrush populations over time and high herbivory pressure may be constraining understory responses and slowing restoration success.

Macro-particle charcoal C content following prescribed burning in a mixed-conifer forest, Sierra Nevada, California.

Fire suppression and changing climate have resulted in increased large wildfire frequency and severity in the western United States, causing carbon cycle impacts. Forest thinning and prescribed burning reduce high-severity fire risk, but require removal of biomass and emissions of carbon from burning. During each fire a fraction of the burning vegetation and soil organic matter is converted into charcoal, a relatively stable carbon form. We sought to quantify the effects of pre-fire fuel load and type on charcoal carbon produced by biomass combusted in a prescribed burn under different thinning treatments and to identify more easily measured predictors of charcoal carbon mass in a historically frequent-fire mixed-conifer forest. We hypothesized that charcoal carbon produced from coarse woody debris (CWD) during prescribed burning would be greater than that produced from fine woody debris (FWD). We visually quantified post-treatment charcoal carbon content in the O-horizon and the A-horizon beneath CWD (> 30 cm diameter) and up to 60 cm from CWD that was present prior to treatment. We found no difference in the size of charcoal carbon pools from CWD (treatment means ranged from 0.3–2.0 g m-2 of A-horizon and 0.0–1.7 g m-2 of O-horizon charcoal) and FWD (treatment means ranged from 0.2–1.7 g m-2 of A-horizon and 0.0–1.5 g m-2 of O-horizon charcoal). We also compared treatments and found that the burn-only, understory-thin and burn, and overstory-thin and burn treatments had significantly more charcoal carbon than the control. Charcoal carbon represented 0.29% of total ecosystem carbon. We found that char mass on CWD was an important predictor of charcoal carbon mass, but only explained 18–35% of the variation. Our results help improve our understanding of the effects forest restoration treatments have on ecosystem carbon by providing additional information about charcoal carbon content.