Working paper 29: Post-wildfire restoration of structure, composition, and function in southwestern ponderosa pine and warm/dry mixed-conifer forests.

During the last several decades, uncharacteristically large wildfires have occurred at an increasing rate in the frequent-fire forests of the western United States (Westerling et al. 2006). These extensive and severely burned forests represent a serious conservation concern and restoration need. Indeed, Fule et al. (2013, p.4) remarked that "large uncharacteristic wildfires pose one of the greatest risks to ecosystem integrity in the 21st century." Such fires may be pushing forests in the western United States toward a "tipping point" that may lead to permanent changes in structure and composition, loss of carbon into the atmosphere and loss of carbon stocks (Hurteau and North 2009, North and Hurteau 2011, Hurteau et al. 2011), and changes in hydrological function (Dore et al. 2012, Adams 2013). Forests degraded by extensive high-severity fire often also exhibit accelerated soil erosion and subsequent loss of soil productivity, expansions or invasions of non-native plant populations, loss of wildlife habitat; damaged watersheds and degraded water quality to connected streams, and/or vegetation type conversions (Figure 1). Federal land management agencies have formally separated post-fire rehabilitation into short-term stabilization and long-term restoration measures. The U.S. Forest Service Burned Area Emergency Response (BAER) program includes well-researched emergency treatments "to stabilize the burned area, protect public health and safety, and reduce the risk of additional damage to valued resources, such as water supply systems, aquatic habitat and roads" (Robichaud 2009). An immediate goal of BAER is to have protection in place prior to the first damage-producing rain event following the fire. Rehabilitation activities are implemented and can be monitored for up to three years after wildfire, and include the repair of facilities and mitigation of land and resources that are unlikely to recover on their own (Robichaud 2009). Longer-term post- fire restoration efforts have generally received much less attention, although the increasing occurrence of very large wildfires has prompted more attempts to articulate and evaluate long-term strategies (Long et al. in press). As opposed to emergency rehabilitation, ecological restoration focuses on assisting the recovery of characteristic ecological structure, process, and function. This requires an understanding of natural ranges of variability for these key attributes as well as development of reference conditions to guide management activities (Egan and Howell 2001, Margolis et al. 2013). In addition, restoration activities demand long-term commitment and evaluation. However, given the altered conditions that sometimes follow high-severity fires in previously degraded forests, successful restoration to a desired state may be difficult and costly (Scheffer et al. 2001). This working paper describes the goals of post-wildfire forest restoration, identifies the unique challenges and opportunities for management of severely burned large patches, and develops principles for restoring forests that have been burned by high-severity wildfires

Estimating soil seed bank characteristics in ponderosa pine forests using vegetation and forest-floor data

Soil seed banks are important for vegetation management because they contain propagules of species that may be considered desirable or undesirable for site colonization after management and disturbance events. Knowledge of seed bank size and composition before planning management activities facilitates proactive management by providing early alerts of exotic species presence and of abilities of seed banks to promote colonization by desirable species. We developed models in ponderosa pine (Pinus ponderosa) forests in northern Arizona to estimate the size and richness of mineral soil seed banks using readily observable vegetation and fores-floor characteristics. Regression models using three or fewer predictors explained 41 to 59 percent of the variance in 0- to 2-inch (0- to 5-cm) seed densities of total and native perennial seed banks. Key predictors included aboveground plant species richness/10.8 ft2 (1 m2), litter weight and thickness, and tree canopy type (open or closed). Both total and native perennial seed banks were larger and richer in plots containing: (1) species-rich understories, (2) sparse litter, and (3) tree canopy openings. A regression tree model estimated that seed bank density of native perennials is 14-fold greater if aboveground plant richness exceeds eight species/10.8 ft2, forest-floor leaf litter is < 1 inch (2.5 cm) thick, and tree canopies are open

Canopy-tree influences along a soil parent material gradient in Pinus-ponderosa-Quercus gambelii forests, northern Arizona

ABELLA, S. R. (Public Lands Institute and School of Life Sciences, University of Nevada, Las Vegas, Las Vegas, NV 89154-2040) AND J. D. SPRINGER (Ecological Restoration Institute, Northern Arizona University, Flagstaff, AZ 86011-5017). Canopy-tree influences along a soil parent material gradient in Pinus ponderosa- Quercus gambelii forests, northern Arizona. J. Torrey Bot. Soc. 135: 26–36. 2008.—The distribution of canopy trees can impose within-site patterns of soil properties and understory plant composition. At ten sites spanning a soil parent material gradient in northern Arizona Pinus ponderosa-Quercus gambelii forests, we compared soils and plant composition among five canopy types: openings, Pinus ponderosa single trees, Quercus gambelii single stems, dispersed clumps, and thickets. Soil texture on average did not differ significantly among canopy types, whereas Oi horizon thickness and weight, 0–15 cm soil loss-on-ignition, and gravimetric soil moisture differed significantly among three or more canopy types. Understory plant richness per 4 m2 ranged from five species below P. ponderosa to 12 species in openings, with richness below Q. gambelii single stems significantly greater than below Q. gambelii thickets. C4 graminoids (e.g., Aristida purpurea) inhabited openings, while C3 species like Poa fendleriana also occurred below trees. The forbs Thalictrum fendleri and Lathyrus laetivirens were strongly associated with Q. gambelii dispersed clumps and thickets. We also conducted an experimental planting with T. fendleri that was consistent with these correlational results, with outplanted T. fendleri seedling survival 2–7 times greater when planted below Q. gambelii compared to openings. Previous research and our results suggest that understory species associated with Q. gambelii canopies vary regionally, but there are consistently some associated species. Canopy types affected understory vegetation similarly across soil parent materials, not supporting a hypothesis that positive plant interactions changed along soil gradients. Our results suggest that forest management that manipulates both the density and the pattern of trees, together with the growth forms of Q. gambelii trees, can induce within-site spatial patterns of soil properties and understory species

Response of a rare endemic, Penstemon clutei, to burning and reduced belowground competition

Penstemon clutei, a rare perennial beard tongue endemic to the ponderosa pine forest of the Sunset Crater volcanic field of northern Arizona, presents an opportunity to test the hypothesis that restoration of historic ecosystem conditions may enhance the sustainability of a rare species. We tested prescribed burning and root trenching treatments as proxies for the surface fires and reduced tree densities characteristic of historic ponderosa pine ecosystems in a study area at OLeary Peak, part of the Sunset Crater volcanic field (Coconino National Forest, AZ). Prescribed burning killed many mature P. clutei plants and negatively affected density for at least 3 years post-burn. In contrast, trenching to cut root competition of overstory trees led to a 1200 percent increase in P. clutei plants. Precipitation influenced the response. Seed germination experiments showed that P. clutei does not have innate dormancy. Germination rates in the lab ranged from 5 to 70 percent under a range of environmental and fire-related conditions (i.e., cold stratification, light, exposure to ash, NH4), but these factors were not statistically significant. Tested seedling establishment rates in situ were very low (0.4(percent)). These experiments suggest that the observed P. clutei population increase following severe wildfires (1973 Burnt fire, 1996 Hochderffer fire) may have been due primarily to the removal of tree competition rather than to direct fire effects. Further experimentation is suggested to develop ecological information for thoughtful integration of ecosystem restoration with the habitat needs of rare plants

Seeding versus natural regeneration: a comparison of vegetation change following thinning and burning in ponderosa pine

The decision whether to seed with native species following restoration treatments should be based on existing vegetation, species present in or absent from the soil seed bank, past management history, microclimate conditions and soils. We installed three permanent monitoring plots in two areas (total 18.6 ha) at Mt. Trumbull, AZ. Trees were thinned and the sites burned in 1996 and 1997. A 5 ha area was seeded with native shrub, grass and forb species; the remaining 13.6 ha were unseeded. Pretreatment species richness ranged from none to five species per plot. We recorded 13 graminoid and eight shrub species in the seeded area, and four graminoid and four shrub species in the unseeded area. The greatest increase in species richness in both seeded and unseeded plots occurred approximately 1.8 years posttreatment. Perennial native species dominated plant cover by 2.8 years, although annual native forbs dominate the soil seed bank. Perennial grasses are nearly absent from the seed bank. The seeded area had the highest diversity, but it also had twice as many nonnative species (14 versus 7 in the unseeded plots). By August 1999, maximum species richness reached 51 species on the seeded plot. Of these species, 80 percent were native. Although seeding increases diversity, it may also have the long-term tradeoff of introducing new genotypes and species, both native and nonnative

Using a Diverse Seed Mix to Establish Native Plants on a Sonoran Desert Burn

Revegetating burned areas is a formidable challenge facing resource managers in southwestern United States arid lands. Natural revegetation of desert burns by native species may be slow, or dominated by exotic annual grasses that perpetuate a frequent-fire regime. Resource managers may have several reasons for actively revegetating burns with native species, such as for providing competition with exotic species, minimizing soil erosion and dust pollution, and improving aesthetics. The use of native species in revegetation has been limited by a lack of available seed and by findings that native desert species are difficult to establish (e.g., Bainbridge and Virginia 1990, Banjerjee et al. 2006). Seeding may be one of only a few feasible options for reintroducing propagules to large desert burns covering thousands of hectares. Our objective was to assess the outcome of a 28-species (all native) operational seeding project for revegetating a 2005 burn in the Arizona Upland Subdivision of the Sonoran Desert

Changes in ponderosa pine forests of the Mt. Trumbull Wilderness

Ponderosa pine forests in the Mt. Trumbull Wilderness on the Arizona Strip have become dense with young trees and highly susceptible to catastrophic wildfire due to exclusion of the natural frequent-fire regime. As part of a broader regional ecological restoration study, the Mt. Trumbull Wilderness was sampled for fire scarred trees, vegetation, and fuels in 1997 and 1999. Reconstructed fire histories show that fires recurred about every 4.4 years prior to settlement, with larger fires burning every 9.5 years. Frequent fires ceased after 1863 in the Mt. Trumbull Wilderness, coincident with the time of Euro-American settlement around 1870, beginning a fire-free period that has lasted up to the present except for a few small fires and a larger 1989 wildfire. Current forests are dense, averaging approximately 1,200 trees/ha, and dominated by small trees. Throughout the wilderness, tree canopy cover averages over 65(percent) and tree basal area is high, 35- 36 m2/ha. Understory plant cover is about 20(percent) and understory species diversity averages 11.4 species/sample plot. Living and dead fuels, including plants, woody debris, and the forest floor, will easily support high-intensity wildfires. In contrast, the presettlement forest was relatively open, with tree density of approximately 62 trees/ha and basal area averaging 8.9 m2/ha, dominated by large ponderosa pine trees. In ecological terms, prospects are good for restoring the Mt. Trumbull Wilderness to emulate the ecological structure and fire disturbance regime of the presettlement reference condition. The current forest condition is perhaps least affected by recent degradation of any site in the Uinkaret Mountains. However, ecological information is only one component contributing to the debate over appropriate management values and practices in wilderness areas on public lands

Soil Seed banks in a Mature Coniferous Forest Landscape: Dominance of Native Perennials and Low Spatial Variability

AbstractSoil seed banks are important to vegetation recruitment, ecosystem functioning and land management. We evaluated composition of 0–5 cm soil seed banks and relationships of seed banks with forest community types (ranging from low-elevation pinyon–juniper to high-elevation bristlecone pine), vegetation cover and environmental variables within a 40,000-ha relatively undisturbed coniferous forest landscape in Nevada, USA. We collected samples from 36 sites and used the emergence method to assay seed banks. Seed density averaged 479 seeds m− 2across sites and a total of 39 taxa were detected. Most (79%) of these taxa were perennials and 35 of 39 (90%) were native. Moreover, 62% of seed-bank taxa were in the vegetation of mature forests, an uncommon finding in studies of forest soil seed banks. Seed-bank density, species richness and composition did not display strong relationships with forest community types, vegetation cover or environmental variables. Weak relationships likely arose from the relatively uniform seed-bank density among sites, where 50% of sites had seed densities in the range of 106–282 m− 2. Results suggest that while seed banks on this landscape are not large, they provide recruitment potential for some native perennial species of mature, relatively undisturbed communities.</jats:p