Forests characterized by mixed-severity fires occupy a broad moisture gradient between lower elevation forests typified by low-severity fires and higher elevation forests in which high-severity, stand replacing fires are the norm. Mixed-severity forest types are poorly documented and little understood but likely occupy significant areas in the western United States. By definition, mixed-severity types have high beta diversity at meso-scales, encompassing patches of both high and low severity and gradients in between. Studies of mixed-severity types reveal complex landscapes in which patch sizes follow a power law distribution with many small and few large patches. Forest types characterized by mixed severity can be classified according to the modal proportion of high to low severity patches, which increases from relatively dry to relatively mesic site conditions. Mixed-severity regimes are produced by interactions between top-down forcing by climate and bottom-up shaping by topography and the flammability of vegetation, although specific effects may vary widely across the region, especially the relation between aspect and fire severity. History is important in shaping fire behavior in mixed-severity landscapes, as patterns laid down by previous fires can play a significant role in shaping future fires. Like low-severity forests in the western United States, many dry mixed-severity types experienced significant increases in stand density during the 20th century, threatening forest health and biodiversity, however not all understory development in mixed-severity forests increases the threat of severe wild fires. In general, current landscapes have been homogenized, reducing beta diversity and increasing the probability of large fires and insect outbreaks. Further loss of old, fire tolerant trees is of particular concern, but understory diversity has been reduced as well. High stand densities on relatively dry sites increase water use and therefore susceptibility to drought and insect outbreaks, exacerbating a trend of increasing regional drying. The need to restore beta diversity while protecting habitat for closed-forest specialists such as the northern spotted owl call for landscape-level approaches to ecological restoration.
Disease is often implicated as a factor in population declines of wildlife and plants. Understanding the characteristics that may predispose a species to infection by a particular pathogen can help direct conservation efforts. Recent declines in amphibian populations world-wide are a major conservation issue and may be caused in part by a fungal pathogen, Batrachochytrium dendrobatidis (Bd). We used Random Forest, a machine learning approach, to identify species-level characteristics that may be related to susceptibility to Bd. Our results suggest that body size at maturity, aspects of egg laying behavior, taxonomic order and family, and reliance on water are good predictors of documented infection for species in the continental United States. These results suggest that, whereas local-scale environmental variables are important to the spread of Bd, species-level characteristics may also influence susceptibility to Bd. The relationships identified in this study suggest future experimental tests, and may target species for conservation efforts.
We investigated the population dynamics of the keystone symbiotic N-fixing species Alnus tenuifolia (thinleaf alder) and the patterns of primary succession on the Tanana River floodplains of interior Alaska, USA. The goals of this study were to characterize (i) the variation in the population structure of thinleaf alder and its influence on ecosystem function; (ii) the role of a fungal disease outbreak in driving the population dynamics of thinleaf alder; (iii) the patterns of landscape-scale thinleaf alder recruitment; and (iv) the variation in successional pathways across the landscape. Soil N concentrations and pools increased tenfold with thinleaf alder stand age due to the accumulation of N-rich organic material. Alder stem density varied threefold among early successional stands, and was directly related to soil N. The current outbreak of a fungal disease caused widespread branch die back and mortality of alder. Young stems were disproportionately susceptible to disease-induced mortality. Overall disease incidence and mortality of young stems were positively related to alder stem density. Thinleaf alder age structures revealed that landscape-scale recruitment was pulsed over time. Multiple pathways of primary succession were found using indirect gradient analysis and associated environmental characteristics were described. The population dynamics of thinleaf alder and the inter-relationship with disease driven disturbance can strongly influence soil N accumulation and ecosystem function in primary succession on an active glacial floodplain. The temporal pattern of thinleaf alder recruitment across the landscape appears to reflect the influence of the hydrologic regime on silt bar development and alder dispersal limitation and population dynamics. Differential life history traits explain the predominant successional pathway, but an alternative successional pathway suggests this pattern can be altered by stochastic events, disturbance, environmental variation or other factors.
The status of freshwater fishes continues to decline despite substantial conservation efforts to reverse this trend and recover threatened and endangered aquatic species. Lack of success is partially due to working at smaller spatial scales and focusing on habitats and species that are already degraded. Protecting entire watersheds and aquatic communities, which we term "native fish conservation areas" (NFCAs), would complement existing conservation efforts by protecting intact aquatic communities while allowing compatible uses. Four critical elements need to be met within a NFCA: (1) maintain processes that create habitat complexity, diversity, and connectivity; (2) nurture all of the life history stages of the fishes being protected; (3) include a large enough watershed to provide long-term persistence of native fish populations; and (4) provide management that is sustainable over time. We describe how a network of protected watersheds could be created that would anchor aquatic conservation needs in river basins across the country.
It is suggested that diversity destabilizes individual populations within communities; however, generalizations are problematic because effects of diversity can be confounded by variation attributable to community type, life history or successional stage. We examined these complexities using a 40-year record of reassembly in forest herb communities in two clearcut watersheds in the Andrews Long-term Ecological Research Site (Oregon, USA). Population stability was higher among forest than colonizing species and increased with successional stage. Thus, life history and successional stage may explain some of the variability in diversity-stability relationships found previously. However, population stability was positively related to diversity and this relationship held for different forest communities, for species with contrasting life histories, and for different successional stages. Positive relationships between diversity and population stability can arise if diversity has facilitative effects, or if stability is a precursor, rather than a response, to diversity.
Alterations to natural herbivore and disturbance regimes often allow a select suite of forest understory plant species to dramatically spread and form persistent, mono-dominant thickets. Following their expansion, this newly established understory canopy can alter tree seedling recruitment rates and exert considerable control over the rate and direction of secondary forest succession. No matter where these native plant invasions occur, they are characterized by one or more of the following: (1) the understory layer typically has greater vegetation cover and lower diversity than was common in forest understories in the past; (2) this layer can delay stand renewal and alter species composition by inhibiting tree regeneration; and (3) once this layer is formed, it can resist displacement by other species and remain intact for decades. In this paper, we evaluate the processes that trigger the expansion of several plant species native to forests and review their ecological characteristics to provide general guidelines in assessing native invasion risk in forest stands. We argue that major anthropogenic changes to disturbance and browsing regimes bring about the monopolization of the forest understory by native plants. In all cases reviewed, aggressive understory plant expansion followed alterations in overstory disturbance regimes. Although these disruptions included predictable and manageable impacts such as tree harvesting, other less predictable overstory disturbance agents including catastrophic fires, insect outbreaks, and pathogens were involved. Assessing and managing risk from these alternative threats is challenging as their occurrence is often erratic, hard to control, and not limited by land ownership and administrative boundaries. In many cases, the risk to forest understories was particularly acute if the effects of multiple stressors occurred in a stand, either in tandem or within a short period of time. Specifically, the synergy between overstory disturbance and uncharacteristic fire regimes or increased herbivore strongly controls species richness and leads to depauperate understories dominated by one or a few species. We suggest that aggressive expansion by native understory plant species can be explained by considering their ecological requirements in addition to their environmental context. Some plant species are particularly invasive by virtue of having life-history attributes that match one or more of the opportunities afforded by multiple disturbances. Increased overstory disturbance selects for shade-intolerant species with rapid rates of vegetative spread over slower growing, shade-tolerant herbs and shrubs. Altered fire regimes select for only those species that can survive the fire or resprout thereafter. Finally, overbrowsing selects for only those species that are well defended or tolerant to browsing. Ultimately, these processes create novel conditions that favor only a small subset of species that possess some combination of the following life-history characteristics: rapid vegetative growth, relatively shade intolerant, fire tolerant, and herbivore tolerant. The result is a low diversitybut dense understory that can persist for long periods of time even if the canopy closes. The framework advanced by this review could aid land managers in implementing informed management policies and practices that both limit the spread of these plants and target control and remediation treatments directed at the precise mechanism of interference. We suggest vigilant monitoring of stand conditions to ensure that alterations to the overstory and understory disturbance regimes do not operate concurrently, particularly when control over these factors falls under the purview of different management agencies (e.g., wild game vs. forestry management agencies).
The red fox is one of the most widespread and adaptable mammals on Earth. In the American West, however, there are populations of native red foxes that occur only in alpine and subalpine habitats, which may be at risk from human-caused and natural pressures. One potential threat is global climate change, which is likely to reduce both the amount and connectivity of suitable habitat for these unique red foxes. Until recently, the evolutionary history of native North American red foxes, which also occur in the boreal forests of Canada and Alaska, was largely speculative.
As a doctoral student in the early 1980s, Keith Aubry, now a research wildlife biologist with the Pacific Northwest Research Station, conducted an intensive study of North American red foxes, especially the montane populations. Based on fossil, archeological, historical, and ecological evidence, he hypothesized that, contrary to prevailing theory, native red foxes arose from two distinct lineages that had been isolated from each other during the last glaciation. Using modern molecular genetics, a team of researchers led by Aubry has confirmed his hypothesis and revealed important new details about the evolutionary history of North American red foxes. Their analyses provide the foundation for revealing the red fox's genealogy at finer levels, and aid conservation efforts by making it possible to distinguish native from non-native populations and identify those that may be threatened.
"What are truffles"," opens with a dramatic painting of lightning, tree roots, mycorrhizae and truffles to introduce truffles in history, including ancient speculations (myths) about their origin. A new one to me is that they come from the testicles of Adonis, buried and multiplied by The Furies. Indeed, one Spanish term for a truffle is "turma de tierra," literally a testicle of the earth (we'll return to "turma" later). The relationship of hypogeous to epigeous fungi is briefly noted.
Building probabilistic risk models for highly random forest disturbances like wildfire and forest insect outbreaks is a challenging. Modeling the interactions among natural disturbances is even more difficult. In the case of wildfire and forest insects, we looked at the probability of a large fire given an insect outbreak and also the incidence of insect outbreaks following wildfire. We developed and used a probabilistic model framework for estimating (1) the probability that a wildfire, at a given location and time, reaches a given size class under the conditions at the site—including history of insect outbreaks; and (2) the probability of an insect infestation at a given location and year under the conditions at the site—including history of fire occurrence and size. The study used historical data (1980 through 2004) on fire occurrence and forest insect outbreaks collected in Oregon and Washington. Spatial data on insect activity was obtained from aerial sketch maps created by the Forest Service Forest Health Protection program. Federal wildfire data obtained from the Desert Research Institute included information on the date, location, and size of the fire. Average monthly temperature and Palmer Drought Severity Indices were obtained from the National Climatic Data Center’s climate division data set Web page. The methods employed provide an objective tool for modeling complex hybrid processes and estimating associated probability maps.
In this study, microhabitat structures in Douglas-fir (Pseudotsuga menziesii) forests were defined and their frequency and abundance in natural stands and stands of varying active management histories and stand ages was compared. Indicator microhabitat structures for natural forests were determined and the relationship of the abundance of microhabitat structures with tree diameter of Douglas-fir trees was analyzed. Most of the investigated microhabitats are indeed indicators of natural mature and natural old-growth stands, e.g., broken tree top, bayonet top, crack or scar, bark loss, hollow chamber, stem cavity with decay, bark pocket with and without decay, bark bowl, burl, heavy resinosis, and bark burst. In Douglas-fir trees, resin drops and heavy resinosis were the dominant microhabitats in trees with >20.0-40.0 cm diameter at breast height (dbh), whereas bark structures such as bowls in the bark, bark pockets, and bark pockets with decay were the most abundant microhabitats in Douglas-fir trees >80.0 cm. Both management history (including no treatment in natural stands) and stand age determined the abundance of microhabitats and microhabitat composition of stands in our study. The observed microhabitat variability was highest in stands that had not been harvested or otherwise treated silviculturally in many years (low treatment history) and the natural stands and lowest in the recently managed stands. Recently managed stands had, on average, 115 microhabitats/ha, stands with a low treatment history had 520 microhabitats/ha, and natural mature and natural old-growth stands had 745 microhabitats/ha.
Active management for microhabitats in silviculturally-treated stands is important if the aim is to create structural complexity for a variety of organisms and ecosystem functions in even-aged Douglas-fir stands. Although the management of microhabitats with respect to biodiversity and economic objectives often seem to be in conflict, we suggest silvicultural measures to reduce the current homogenization of forest stands with relatively minor losses of wood production especially if the reduced timber output is compared with the expected long-term social, economic, and ecological benefits. It may, however, take many decades to obtain stands that approximate the criteria for old-growth according to the interim minimum standards for old-growth Douglas-fir forests in their native western Washington and Oregon.