Becky K. Kerns

Season and severity of prescribed burn in ponderosa pine forests: Implications for understory native and exotic plants

Abstract We investigated herbaceous richness and cover in relation to fire season and severity, and other variables, five growing seasons following prescribed fires. Data were collected from six stands consisting of three randomly applied treatments: no burn, spring burn, and fall burn. Fall burns had significantly more exotic/native annual/biennial (an/bi) species and greater cover of these species (6.5% exotic; 1.7% native) compared to spring and unburned areas. These patterns are likely related to indirect fire effects associated with fire severity and resource availability, rather than direct fire effects due to burn timing. CART models indicated that high native and exotic an/bi richness and cover were associated with overstory gaps and higher fire severity areas, conditions common to fall burns. Exotics may be more successful at exploiting these environments. No treatment differences were found for native perennials. Location was important for explaining native perennial patterns, but richness and cover were also positively associated with lower fire severity, greater tree cover, and coarse woody debris. Expectations for increased native perennial plant diversity and abundance following prescribed fires may not necessarily be met and exotic species spread may compromise other ecosystem attributes. Restoration in these forests presents a challenge as prescribed fires interact with present environmental conditions that are very different from historical ones.

Managing uncertainty in climate‐driven ecological models to inform adaptation to climate change

The impacts of climate change on forest ecosystems are likely to require changes in forest planning and natural resource management. Changes in tree growth, disturbance extent and intensity, and eventually species distributions are expected. In natural resource management and planning, ecosystem models are typically used to provide a “best estimate” about how forests might work in the future and thus guide decision-making. Ecosystem models can be used to develop forest management strategies that anticipate these changes, but limited experience with models and model output is a challenge for managers in thinking about how to address potential effects of climate change. What do decision makers need to know about climate models, ecological models used for impacts assessments, and the uncertainty in model projections in order to use model output in strategies for adaptation to climate change? We present approaches for understanding and reducing the uncertainty associated with modeling the effects of climate change on ecosystems, focusing on multi-model approaches to clarify the strengths and limits of projections and minimize vulnerability to undesirable consequences of climate change. Scientific uncertainties about changes in climate or projections of their impacts on resources do not present fundamental barriers to management and adaptation to climate change. Instead, many of these uncertainties can be controlled by characterizing their effects on models and future projections from those models. There is uncertainty in decision making that does not derive just from the complex interaction of climate and ecosystem models, but in how modeling is integrated with other aspects of the decision environment such as choice of objectives, monitoring, and approach to assessment. Adaptive management provides a hedge against uncertainty, such that climate and ecosystem models can inform decision making.

Modeling Tamarisk (Tamarix spp.) Habitat and Climate Change Effects in the Northwestern United States

Abstract Tamarisk species are shrubs or small trees considered by some to be among the most aggressively invasive and potentially detrimental exotic plants in the United States. Although extensively studied in the southern and interior west, northwestern (Oregon, Washington, and Idaho) distribution and habitat information for tamarisk is either limited or lacking. We obtained distribution data for the northwest, developed a habitat suitability map, and projected changes in habitat due to climate change in a smaller case study area using downscaled climate data. Results show extensive populations of tamarisk east of the Cascade Mountains. Despite the perceived novelty of tamarisk in the region, naturalized populations were present by the 1920s. Major population centers are limited to the warmest and driest environments in the central Snake River Plain, Columbia Plateau, and Northern Basin and Range. Habitat suitability model results indicate that 21% of the region supports suitable tamarisk habitat. Less than 1% of these areas are occupied by tamarisk; the remainder is highly vulnerable to invasion. Although considerable uncertainty exists regarding future climate change, we project a 2- to 10-fold increase in highly suitable tamarisk habitat by the end of the century. Our habitat suitability maps can be used in “what if” exercises as part of planning, detection, restoration, management, and eradication purposes. Nomenclature: Tamarisk, species in the genus Tamarix L., primarily Tamarix chinensis Lour. and Tamarix ramosissima Ledeb. and their hybrids.

Reintroducing fire into a ponderosa pine forest with and without cattle grazing: understory vegetation response

Reestablishing historical fire regimes is a high priority for North American coniferous forests, particularly ponderosa pine (Pinus ponderosa) ecosystems. These forests are also used extensively for cattle (Bos spp.) grazing. Prescribed fires are being applied on or planned for millions of hectares of these forests to reduce fuel loads, alter forest structure, and maintain and enhance the productivity of native plant communities. However, cattle grazing is ubiquitous in ponderosa pine forests and the consequences of post-fire cattle grazing on plant communities are not well understood. We evaluated cattle grazing effects (grazing, no grazing) on upland bunchgrass and Carex geyeri dominated ponderosa pine plant communities over five growing seasons after prescribed fires (spring reburn, fall reburn, no burn). Vegetation was measured prior to a 5-year interval reburn and the subsequent exclusion of cattle, and in the second and fifth growing seasons thereafter. We found no interactions between reburning and grazing for the understory response variables. For all reburn treatments, including unburned areas, five growing seasons of cattle grazing exclusion significantly increased: (1) total vegetative cover, (2) native perennial forb cover, (3) grass stature, (4) grass flowering stem density, and (5) the cover of some shrub species and functional groups. Grazing exclusion did not strongly affect plant compositional patterns, although differences were detected. Compared to unburned areas, neither spring nor fall reburning increased perennial native species cover or richness, and reburning reduced sedge cover. Fall reburning increased cover of native colonizers, and exotic species cover and richness (largely Bromus tectorum and Cirsium vulgare), although overall exotic cover remains low (<1%). We document several potentially chronic impacts of cattle grazing in both burned and unburned areas, and show that the understory release from a long history of cattle grazing caused a greater degree of change than the initial reintroduction of fire. If a goal of ecological restoration in these forests is increased cover of native perennial plants, and the potential for increased native perennial grass reproduction, then cattle grazing exclusion, or a change in cattle management, could provide critically important options in restoration plans.

Huckleberry Abundance, Stand Conditions, and Use in Western Oregon: Evaluating the Role of Forest Management

Huckleberries are major components of the understory vegetation in coniferous Pacific Northwest forests of the United States. Vaccinium species also have a long history of human use. However, little research has been done to ascertain how they respond to common forest management practices. We used data obtained from old-growth, young thinned, and young unthinned Douglas-fir stands in western Oregon to evaluate how forest management could potentially influence species abundance and product supply. Our analysis focused on three species: Vaccinium ovatum, V. parvifolium,and V. membranaceum. Results were variable, but indicate that overstory stand conditions and forest management can affect huckleberry species abundance. However, to assess fully the effects of forest management on these species, studies specifically designed to target areas where people harvest these products are needed. Measuring relevant product attributes such as commercial productivity is also critical.

Disturbance Regimes and Stressors

The effects of climate change on insect outbreaks, wildfire, invasive species, and pathogens in forest ecosystems will greatly exceed the effects of warmer temperature on gradual changes in forest processes. Increased frequency and extent of these disturbances will lead to rapid changes in vegetation age and structure, plant species composition, productivity, carbon storage, and water yield. Insect outbreaks are the most pervasive forest disturbance in the United States, and rapid spread of bark beetles in the western United States has been attributed to a recent increase in temperature. Wildfire area burned has increased in recent decades, although frequency and severity have not changed, and is expected to greatly increase by 2050 (at least twice as much area burned annually in the West). More frequent occurrence of fire and insects will create landscapes in which regeneration of vegetation will occur in a warmer environment, possibly with new species assemblages, younger age classes, and altered forest structure. Increased fire and insects may in turn cause more erosion and landslides. Invasive plant species are already a component of all forest ecosystems, and a warmer climate will likely facilitate the spread of current and new invasives, particularly annuals that compete effectively in an environment with higher temperature and frequent disturbance. The interaction of multiple disturbances and stressors, or stress complexes, has the potential to alter the structure and function of forest ecosystems, especially when considered in the context of human land-use change. Occurring across large landscapes over time, these stress complexes will have mostly negative effects on ecosystem services, requiring costly responses to mitigate them and active management of forest ecosystems to enhance resilience.

Compatible Management of Understory Forest Resources and Timber

Many native mosses, lichens, ferns, herbs, shrubs, and fungi are harvested by humans from the understories of Pacific Northwest forests. These understory products are used personally and commercially for decorative, culinary, medicinal, cultural and educational purposes. Understory species harvested for any of these purposes are typically and awkwardly referred to as nontimber or special forest products (Vance et al. 2001, IFCAE 2002, Table 1). Hereafter, we refer to these species simply as understory forest resources and understory products. These species have important ecological roles in forest communities. They contribute to biological diversity and long-term ecosystem productivity (Alaback and Herman 1988, Halpern and Spies 1995), underpin mammalian and avian abundance (Morrison 1982, Carey 1995, Carey and Johnson 1995) and are important aesthetic components of forests.

Inter-comparison of multiple statistically downscaled climate datasets for the Pacific Northwest, USA

Statistically downscaled climate data have been widely used to explore possible impacts of climate change in various fields of study. Although many studies have focused on characterizing differences in the downscaling methods, few studies have evaluated actual downscaled datasets being distributed publicly. Spatially focusing on the Pacific Northwest, we compare five statistically downscaled climate datasets distributed publicly in the US: ClimateNA, NASA NEX-DCP30, MACAv2-METDATA, MACAv2-LIVNEH and WorldClim. We compare the downscaled projections of climate change, and the associated observational data used as training data for downscaling. We map and quantify the variability among the datasets and characterize the spatio-temporal patterns of agreement and disagreement among the datasets. Pair-wise comparisons of datasets identify the coast and high-elevation areas as areas of disagreement for temperature. For precipitation, high-elevation areas, rainshadows and the dry, eastern portion of the study area have high dissimilarity among the datasets. By spatially aggregating the variability measures into watersheds, we develop guidance for selecting datasets within the Pacific Northwest climate change impact studies.