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... more common, mixed-severity fire regime is char- acterized by severities that are highly variable in space and time, creating complex patterns of tree survival and mor- tality on the landscape ( Murray and others 1998;Romme and Knight 1981;Siderius and Murray 2005) (Figure 1.15). Mixed-severity fires can occur at 60-to more than 300- year intervals and sometimes over 500 years, depending on drought cycles, fuel conditions, landscape burn his- tory, and high wind events (Arno and Hoff 1990;Morgan and others 1994b;Walsh 2005). Individual mixed-sever- ity fires can be non-lethal surface fires with differential A low-intensity, non-lethal surface fire burning in a whitebark pine forest. The species is able to survive some of these fires because of high crowns and deep roots. However, the thin bark makes it susceptible to mortality when intensities are higher. mortality, variable mortality stand-replacement fires, and, most often, fires that contain elements of both (Morgan and others 1994b). Sometimes fires burn in sparse ground fuels at low-severities, killing the smallest trees and the most fire-susceptible overstory species, often subalpine fir (Walsh 2005). Severities increase if the fire enters areas with high fuel loads or if there are high winds or drought conditions because these situations facilitate fire's entrance into tree crowns, thereby creating patches of fire-killed mortality (Lasko 1990). Burned patches are often 1 to 30 ha in size, depending on topography and fuels, and these openings provide important caching habitat for the Clark's nutcracker (Norment 1991; Tomback and others 1990) (Figure ...
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... the most common tree-level restoration activity is the protection of trees from disturbance agents, primarily fire, beetles, and rust. The best trees to protect from these agents are those that have been identified as important sources for phenotypic rust-resistant seeds ("plus" trees) (Mahalovich and Dickerson 2004). Protection of trees from damage from wildland fire (prescribed, CW, or wildfire) is difficult and costly, and yet often successful ( Keane and Parsons 2010a;Murray 2007c). Mechanical manipulation of fuel surrounding the trees by (1) raking or blowing (via leaf blower) litter and duff away from tree bases, (2) cutting competing fir and spruce, or (3) manual removal of downed woody, shrub, and herbaceous fuels has been attempted with mixed success (Keane and Parsons 2010b) (Figure 4.15). Fire crews have wrapped large whitebark pine with fire shelters to protect against fire mortality with limited success (Keane and Parsons 2010b). Modification of ignition patterns by control- ling burn severity using head fires ignited in thin strips may be the most successful way to minimize whitebark pine fire- caused mortality in prescribed burning or back-burning in ...
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... cuttings are treatments that manipulate the stand by removing trees (Figure 4.15). It is important to note that traditional silviculture has limited effectiveness in these high mountain stands because of the severity of the site, unique autecology of whitebark pine, and bird-mediated seed dispersal ( Keane and Arno 2000). Novel silvicultural strategies that are tailored to individual stands are needed to address restoration concerns in whitebark pine ( Waring and O'Hara 2005). In general, most cuttings should attempt to eliminate subalpine fir and other shade-tolerant competitors while enhancing whitebark pine. Thinnings can be used to improve the health of potential cone-producing whitebark pine, while other cuttings can be used to create fuelbeds to support prescribed burning activities. Usually, mechanical cuttings are only effective when treated stands are in close proximity to roads and are easy to work (gentle slopes, few rocks, and few wet areas, for ...
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... Because of the multiple roles that whitebark pine plays in subalpine ecosystems, it has been described as a keystone and foundation species. Over much of its range whitebark pine is declining due to a suite of stressors including a non-native, invasive pathogen (Cronartium ribicola J.C. Fisch., the causal agent of white pine blister rust), outbreaks of native pests (mountain pine beetle, Dendroctonus ponderosae Hopkins), altered fire regimes, and a rapidly changing climate (Keane et al., 2012;Schwandt et al., 2010;Tomback & Achuff, 2010). As a result, whitebark pine has been listed as an en- The Sierra Nevada of California is the southernmost range extent of whitebark pine, where it experiences warmer, drier conditions relative to other portions of its distribution (Arno & Hoff, 1989). ...
... The combination of population stability in some long-term monitoring locations (Nesmith et al., 2019), neutral to positive growth trends in most sampling sites, and high genetic connectivity may be signs that whitebark pine was relatively healthy in specific regions of the Sierra Nevada. This contrasts with other parts of the species' range, where whitebark pine is in rapid decline (Goeking & Izlar, 2018;Keane et al., 2012). Increasing temperatures may be related to faster growth for Sierran whitebark pine, although future changes to growing conditions or more extreme drought may eventually reduce growth (Ullrich et al., 2018). ...
Whitebark pine (Pinus albicaulis Engelm.) has experienced rapid population declines and is listed as threatened under the Endangered Species Act in the United States. Whitebark pine in the Sierra Nevada of California represents the southernmost end of the species' distribution and, like other portions of its range, faces threats from an introduced pathogen, native bark beetles, and a rapidly warming climate. Beyond these chronic stressors, there is also concern about how this species will respond to acute stressors, such as drought. We present patterns of stem growth from 766 large (average diameter at breast height >25 cm), disease-free whitebark pine across the Sierra Nevada before and during a recent period of drought. We contextualize growth patterns using population genomic diversity and structure from a subset of 327 trees. Sampled whitebark pine generally had positive to neutral stem growth trends from 1970 to 2011, which was positively correlated with minimum temperature and precipitation. Indices of stem growth during drought years (2012 to 2015) relative to a predrought interval were mostly positive to neutral at our sampled sites. Individual tree growth response phenotypes appeared to be linked to genotypic variation in climate-associated loci, suggesting that some genotypes can take better advantage of local climatic conditions than others. We speculate that reduced snowpack during the 2012 to 2015 drought years may have lengthened the growing season while retaining sufficient moisture to maintain growth at most study sites. Growth responses may differ under future warming, however, particularly if drought severity increases and modifies interactions with pests and pathogens.
... Population models suggest beetle outbreaks may become increasingly frequent at higher elevations and latitudes as the climate continues to warm (Bentz et al., 2010), though the shrub-like mats that WBP tends to form on high-elevation exposed ridgetops (the "krummholz" growth form) lack the large boles that mountain pine beetles preferentially attack (Perkins & Roberts, 2003;Shanahan et al., 2016) and may serve as refugia from beetles (Maher et al., 2021). Extreme cold snaps and lack of host trees are identified as primary factors in stopping mountain pine beetle outbreaks in the US northern Rocky Mountains (Keane et al., 2012), where warmer winters, in particular, have been suggested to promote mountain pine beetle persistence (Logan & Powell, 2001). Using hand-sketched aerial surveys, Millar et al. (2012) found that WPB mortality in California was positively associated with higher temperatures, less precipitation, and greater climatic water deficit, suggesting detrimental biophysical effects of these factors that may directly kill trees and/or predispose them to pest attacks. ...
Whitebark pine (Pinus albicaulis Engelm.) is a keystone high‐elevation tree species occurring across much of western North America, yet it has been listed as threatened under the US Endangered Species Act due to rapid population declines and extensive ongoing pressures from white pine blister rust (Cronartium ribicola), mountain pine beetle (Dendroctonus ponderosae), and increasing temperature and aridity associated with climate change. Past research has shown that whitebark pine mortality is more likely in hotter and drier sites, but no broad‐extent analyses spanning multiple ecoregions have directly quantified the relationship between mortality probability and its environmental drivers at a fine spatial scale. To address this gap, we used spatially continuous high‐resolution (30 m) maps of mortality in California produced by a remote sensing‐based change detection algorithm, and we developed generalized additive models to explain this mortality variability using relevant biophysical variables. We found that maximum daily temperature was strongly positively associated with mortality intensity and that mortality was also generally more intense in sites with greater solar exposure (e.g., south‐facing slopes). Our results support the interpretation that as climate warms and aridity increases, populations in “trailing edge” (i.e., hot, dry) sites are most vulnerable. The environmental relationships we quantify will aid in identifying the locations and environments with the greatest risk of future mortality as well as those likely to serve as refugia.
... How are core areas to be identified? In consultation with the U.S. Fish and Wildlife Service, we integrated the principles of their Species Keane et al. (2012;, this issue) for basic principles and climate change mitigation. WPBR = white pine blister rust. ...
Whitebark pine (Pinus albicaulis Engelm.), a high-elevation five-needle white pine (Genus Pinus, Subgenus Strobus), inhabits the higher mountains of western U.S. and Canada, across about 32.6 million ha (about 80.6 million acres), with 70% of its range in the U.S. Whitebark pine, recognized as a keystone and foundation species, is declining nearly range-wide from the introduced pathogen Cronartium ribicola J.C. Fisch., mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreaks, and altered fire regimes driven by climate warming. It is categorized as endangered by the International Union for Conservation of Nature, endangered in Canada under the Species at Risk Act, and proposed for listing in the U.S. as threatened under the Endangered Species Act. At risk from the same threats are other high elevation, five-needle white pines, including limber pine (P. flexilis James), southwestern white pine (P. strobiformis Engelm.), foxtail pine (P. balfouriana Balf.), Rocky Mountain bristlecone pine (P. aristata Engelm.), and Great Basin bristlecone pine (P. longaeva D.K. Bailey). Several challenges to devising a restoration plan for whitebark pine include a large range across multiple federal and tribal jurisdictions, limited funding and field personnel to implement restoration, and restrictions on whitebark pine restoration in Wilderness Areas. Here, we describe the development of the National Whitebark Pine Restoration Plan (NWPRP), a conservation strategy for restoring whitebark pine across its U.S. range and across multiple jurisdictions. The plan, conceived by the Whitebark Pine Ecosystem Foundation (WPEF) and American Forests (AF) in consultation with the U.S. Forest Service, is the product of a collaborative interagency partnership with the U.S. Forest Service, National Park Service, Bureau of Land Management, and tribal governments. The NWPRP is a geographic restoration plan based on priority or “core areas” nominated by land management agencies and tribal governments and includes process and criteria for prioritizing these areas, proposed restoration treatments and conservation actions, estimated costs for these management applications, and a monitoring and adaptive management plan for each type of treatment or management action. AF and the WPEF in collaboration with partners are developing a multi-pronged funding strategy for the NWPRP that includes federal and corporate funding opportunities but also national and global opportunities related to climate and biodiversity goals. The steps in assembling and funding the NWPRP can be used as a blueprint for constructing restoration plans for the other high elevation five-needle white pines, which experience many of the same restoration challenges as whitebark pine.
... Within conifers, seed size tends to be larger for species with animaldispersed seeds compared to those with seeds dispersed primarily by wind (Leslie et al. 2017), but animal dispersed species may be able to more easily colonize large, high severity patches in post-fire landscapes. In the case of Pinus albicaulis, animal dispersal of seeds into post-fire landscapes may be key to its ability to persist under historical fire regimes (Keane et al. 2012). ...
Ecosystems are dynamic systems with complex responses to environmental variation. In response to pervasive stressors of changing climate and disturbance regimes, many ecosystems are realigning rapidly across spatial scales, in many cases moving outside of their observed historical range of variation into alternative ecological states. In some cases, these new states are transitory and represent successional stages that may ultimately revert to the pre-disturbance condition; in other cases, alternative states are persistent and potentially self-reinforcing, especially under conditions of altered climate, disturbance regimes, and influences of non-native species. These reorganized states may appear novel, but reorganization is a characteristic ecosystem response to environmental variation that has been expressed and documented throughout the paleoecological record. Resilience, the ability of an ecosystem to recover or adapt following disturbance, is an emergent property that results from the expression of multiple mechanisms operating across levels of organism, population, and community. We outline a unifying framework of ecological resilience based on ecological mechanisms that lead to outcomes of persistence, recovery, and reorganization. Persistence is the ability of individuals to tolerate exposure to environmental stress, disturbance, or competitive interactions. As a direct expression of life history evolution and adaptation to environmental variation and stress, persistence is manifested most directly in survivorship and continued growth and reproduction of established individuals. When persistence has been overcome (e.g., following mortality from stress, disturbance, or both), populations must recover by reproduction. Recovery requires the establishment of new individuals from seed or other propagules following dispersal from the parent plant. When recovery fails to re-establish the pre-disturbance community, the ecosystem will assemble into a new state. Reorganization occurs along a gradient of magnitude, from changes in the relative dominance of species present in a community, to individual species replacements within an essentially intact community, to complete species turnover and shift to dominance by plants of different functional types, e.g. transition from forest to shrub or grass dominance. When this latter outcome is persistent and involves reinforcing mechanisms, the resulting state represents a vegetation type conversion (VTC), which in this framework represents an end member of reorganization processes. We explore reorganization in greater detail as this phase is increasingly observed but the least understood of the resilience responses. This resilience framework provides a direct and actionable basis for ecosystem management in a rapidly changing world, by targeting specific components of ecological response and managing for sustainable change.
... Furthermore, the exclusion of wildland fire in these ecosystems over the last 100 years through fire suppression has resulted in greater surface and canopy fuel loadings and successional replacement of some HEFNPs with more shade tolerant conifers (Keane, 2001). Climate change, however, has the potential to exacerbate WPBR and MPB outbreaks, increase wildfires above historical levels, and reduce suitable HEFNP habitat (Koteen, 1999;Kendall and Keane, 2001b;Keane et al., 2012;Smith-McKenna et al., 2014;Dudney et al., 2020). Forests of the other HEFNPsfoxtail pine (P. ...
... Now, frequent and intense wildfires, fostered by climate change-mediated drought and suppression-era fuel buildups, occur on many high elevation landscapes and kill HEFNPs that are potentially resistant to both MPB and WPBR (Loehman et al., 2011;Keane et al., 2017b;Shepherd et al., 2018). Few healthy cone-bearing trees remain in stands decimated by MPB and/or WPBR, especially in the US northern Rocky Mountains (Keane et al., 2012). In hard-hit stands, seeds from the relatively few surviving HEFNP trees may be quickly harvested before seed ripening by pine squirrels (Tamiasciurus spp.) or Clark's nutcrackers (Nucifraga columbiana), the bird species that is the major seed disperser for several HEFNP species (e.g., (Tomback, 1998;McKinney and Tomback, 2007). ...
... These interacting factors create a possible extirpation pathway for keystone HEFNP forests in many parts of their ranges. Therefore, proactive restoration measures are critically needed to ensure the HEFNP species remain on high elevation North American landscapes (Schwandt, 2006;Schoettle and Sniezko, 2007;Keane et al., 2012). ...
Many ecologically important high elevation five-needle white pine (HEFNP) forests that historically dominated upper subalpine landscapes of western North America are now being impacted by mountain pine beetle (Dendroctonus spp.) outbreaks, the exotic disease white pine blister rust (Cronartium ribicola), and altered fire regimes. And more recently, predicted changes in climate may reduce HEFNP habitat and exacerbate adverse impacts of fire, beetles and rust. Management intervention using specially designed tactics implemented at multiple scales (range-wide, landscape, stand, and tree levels) are needed to conserve these keystone tree species. A goal of this intervention is to promote self-sustaining HEFNP ecosystems that have both resilience to disturbances and genetic resistance to white pine blister rust in the face of climate change. Many tools and methods are available for land managers, and in this paper, we summarize possible multi-scaled actions that might be taken as steps toward restoration of these valuable HEFNP forests. Long-term programs, such as inventory, mapping, planning, seed collection, seedling production, education, and research provide the materials for effective restoration at finer scales. Stand- and landscape-level passive and active treatments, such as silvicultural cuttings and prescribed fires in both healthy and declining forests, are described in detail and grouped by objectives, methods, and tactics. And last, there are critical pro-active tree-level actions of planting and protection that may be used alone or together to enhance success of other restoration actions. Administrative, policy, legislative, and societal barriers to implementation of an effective restoration effort are also discussed.
... COSEWIC (2010) estimated the range at about 34 million ha, with ~ 15 million ha in the U.S. (44%) and ~ 19 million in Canada (66%). Keane et al. (2012) estimated the U.S. distribution at ~ 5.8 million ha based on a combination of geospatial information and modeling, and Goeking and Izlar (2018) estimated 4.1 million ha based on U.S. Forest Service, Forest Inventory and Analysis (FIA) data. ...
... Another landmark publication was a special issue of Forest Pathology edited by Shaw and Geils (2010); the papers in this journal issue outlined the major threats to five-needle white pines represented by WPBR and detailed the components of a continent-wide pathosystem. This publication was followed by Keane et al. (2012), which synthesized and described rangewide conservation and restoration approaches for whitebark pine at individual tree to landscape scales. ...
... Basic management approaches for whitebark pine were previously summarized by Keane et al. (2012Keane et al. ( , 2021, which presented a workflow sequence to guide the selection of whitebark pine communities and stands for restoration and the appropriate conservation approaches. The four restoration principles emphasized in Keane et al. (2012) were (1) conserve genetic diversity, (2) promote rust resistance, (3) protect seed sources, and (4) employ restoration treatments. ...
Whitebark pine (Pinus albicaulis Engelm.) is an ecologically important subalpine and treeline forest tree of the western U.S. and Canada. It is categorized as endangered by the IUCN and by Canada under the Species at Risk Act and was recently proposed for listing in the U.S. as threatened under the Endangered Species Act. Whitebark pine populations are declining nearly rangewide primarily from the spread and intensification of Cronartium ribicola J.C. Fisch., the exotic, invasive pathogen that causes white pine blister rust (WPBR); recent, large-scale outbreaks of mountain pine beetles (MPB) (Dendroctonus ponderosae Hopkins); altered fire regimes; and, multiple impacts from climate change. For more than two decades, researchers and managers within the U.S. Forest Service and Canadian forestry agencies have been developing restoration and conservation tools and techniques to help mitigate these threats. Four conservation and restoration principles for whitebark pine were previously emphasized: (1) conserve genetic diversity, (2) promote WPBR resistance, (3) protect seed sources, and (4) deploy restoration treatments, while mitigating for climate change. These principles are served by ten additional management or conservation actions that form the basis of a restoration and adaptive management plan but apply primarily to regions with moderate to high levels of WPBR and MPB outbreaks. Where the pathogen and MPB are absent or present at low levels, managers can implement proactive management to build resilience to prevent the future loss of ecological function. Here, we review the key management actions currently used for whitebark pine conservation and restoration in the U.S. and Canada, which include gene conservation, increasing natural genetic resistance to C. ribicola, cone collections, growing and planting seedlings or directly sowing seeds, protecting seed sources, prescribed fire and silvicultural thinning to reduce competition in late seral communities, proactive intervention, stand health surveys and monitoring, and monitoring the impacts of restoration for adaptive management. This review is the outcome of an experts’ workshop held in association with the development of the National Whitebark Pine Restoration Plan (NWPRP), a collaborative U.S. multi-agency and tribal effort initiated in 2017 in consultation with the U.S. Forest Service and facilitated by the non-profit organizations, the Whitebark Pine Ecosystem Foundation and American Forests.
... The projections also predict that viable conditions for whitebark pine no longer occur will in the PFR in the next 50 years (Warwell et al. 2006). Climate projections do not predict the persistence of whitebark pine in many areas; however, restoration and protection efforts show some promise (Keane and Parsons 2010;Keane et al. 2012Keane et al. , 2017. Genetic diversity, ecosystem resilience, limitations of species distribution models to capture nuanced processes, and existence of current and historic whitebark pine communities over a large elevational range provide evidence that whitebark pine may be able to persist in many places where extirpation is predicted by climatic models alone (Keane et al. 2017). ...
The montane sky islands of the Great Basin are characterized by unique, isolated habitats and communities that likely are vulnerable to extirpation with environmental change. A subspecies of yellow pine chipmunk, the Humboldt yellow pine chipmunk (Tamias amoenus celeris), is associated with the whitebark and limber pine forests of the Pine Forest Range (PFR) in Nevada. We sampled T. amoenus and least chipmunks (T. minimus) from the isolated PFR and compared genetic diversity between these populations and more “mainland” populations, including other subspecies of chipmunks. Given the high frequency of hybridization in Tamias, we tested for hybridization between T. amoenus and T. minimus in the PFR. We examined phylogenetic relationships, population divergence and diversity, and screened populations for a common pathogen, Borrelia hermsii, to gain insight into population health. We found T. amoenus of the PFR are closely related to T. amoenus in the Warner Mountains and Sierra Nevada, but maintain substantively lower genetic variation. Microsatellite analyses show PFR T. amoenus are highly genetically differentiated from other populations. In contrast, PFR T. minimus had higher genetic diversity that was comparable to the other T. minimus population we sampled. Pathogen screening revealed that T. amoenus carried higher pathogen loads than T. minimus in the PFR, although the prevalence of infection was similar to other Tamias populations. Our assessment of habitat associations suggests that the Humboldt yellow pine chipmunk almost entirely is restricted to the conifer systems of the PFR, while least chipmunks are prevalent in the other forests. Our work highlights the need for continued conservation and research efforts to identify how response to environmental change can be facilitated in isolated species and habitats.
... In response to major declines in several white pine species, various national and regional efforts are underway to help conserve and restore these species. Restoration efforts are guided by several key strategies, including protecting and maintaining genetic diversity, documenting current conditions and trends, protecting known rust-resistant seed sources, and using forest management practices to improve forest health (Millar et al. 2007, Schoettle and Sniezko 2007, Keane et al. 2012. Multiple restoration tools include the following: ...
Invasive pathogens and bark beetles have caused precipitous declines of various tree species around the globe. Here, we characterized long-term patterns of mountain pine beetle (Dendroctonus pon-derosae; MPB) attacks and white pine blister rust, an infectious tree disease caused by the pathogen, Cronar-tium ribicola. We focused on four dominant white pine host species in Sequoia and Kings Canyon National Parks (SEKI), including sugar pine (Pinus lambertiana), western white pine (P. monticola), whitebark pine (P. albicaulis), and foxtail pine (P. balfouriana). Between 2013 and 2017, we resurveyed 152 long-term monitoring plots that were first surveyed and established between 1995 and 1999. Overall extent (plots with at least one infected tree) of white pine blister rust (blister rust) increased from 20% to 33%. However, the infection rate across all species decreased from 5.3% to 4.2%. Blister rust dynamics varied greatly by species, as infection rate decreased from 19.1% to 6.4% in sugar pine, but increased in western white pine from 3.0% to 8.7%. For the first time, blister rust was recorded in whitebark pine, but not foxtail pine plots. MPB attacks were highest in sugar pines and decreased in the higher elevation white pine species, whitebark and foxtail pine. Both blister rust and MPB were important factors associated with elevated mortality in sugar pines. We did not, however, find a relationship between previous fires and blister rust occurrence. In addition, multiple mortality agents, including blister rust, fire, and MPB, contributed to major declines in sugar pine and western white pine; recruitment rates were much lower than mortality rates for both species. Our results highlighted that sugar pine has been declining much faster in SEKI than previously documented. If blister rust and MPB trends persist, western white pine may follow similar patterns of decline in the future. Given current spread patterns, blister rust will likely continue to increase in higher elevations, threatening subalpine white pines in the southern Sierra Nevada. More frequent long-term monitoring efforts could inform ongoing restoration and policy focused on threats to these highly valuable and diverse white pines.
... Further, whitebark pine populations in the GYE and elsewhere are faced with disturbance factors in addition to changing fire regimes: the exotic fungal pathogen Cronartium ribicola J.C. Fisher, which causes the often fatal disease white pine blister rust (WPBR), large-scale outbreaks of mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins), and previous fire exclusion practices leading to successional replacement (Arno and Hoff 1989, Arno 2001, Tomback et al. 2001a. Management strategies for whitebark pine populations to prevent and reverse its decline (e.g., Keane et al. 2012) have been developed using a variety of approaches including matrix projection and forest process models, which have considered the demographic influences of WPBR (e.g., Ettl andCottone 2004, Field et al. 2012), MBP (Jules et al. 2016), and climate change (e.g., Ireland et al. 2018). Although some have considered the effects of climate change, few have explicitly considered the effect of altered fire frequency or size on whitebark pine persistence (e.g., Keane et al. 2017). ...
Climate change is transforming forest structure and function by altering the timing, frequency, intensity, and spatial extent of episodic disturbances. Wildland fire regimes in western U.S. coniferous forests are now characterized by longer fire seasons and greater frequency, with further changes expected. Identifying the impacts of altered fire regimes on forest resources may enable land managers to plan miti-gation strategies or prepare for novel or altered communities. We created a stochastic, density-dependent, matrix projection model for a whitebark pine (Pinus albicaulis) metapopulation to estimate the impacts of increasing fire frequency on metapopulation persistence. Whitebark pine is a widely distributed foundation species of management concern found in upper subalpine and tree line forests of the Northern Rocky Mountains. We parameterized the model using empirically based demographic data from the Greater Yel-lowstone Ecosystem (GYE) and validated the model by comparing observed whitebark pine densities to those projected by the model when parameterized with historical demographic rates and fire frequencies. We reparameterized the model with current demographic rates including mortality from insect outbreaks and exotic disease. We compared odds of functional extirpation among six scenarios comprising three altered fire frequencies (fires suppressed, historical fire return interval of 268 yr, and decreasing fire return intervals from current to 97 yr) and two seed dispersal probabilities. Historical parameterization with high dispersal probability projected median whitebark pine densities (40.95 trees/ha, first and third quartiles: 21.89, 67.25), which were similar to empirically estimated densities (40.62 trees/ha, first and third quartiles: 12.04, 114.15). Odds of functional extirpation with increasing fire frequency were 8.26 and 139.91 times higher than historical fire frequency and fire suppression, respectively. In decreasing fire return interval scenarios, odds of functional extirpation were 1.76 times higher in low than high dispersal probability scenarios. These findings suggest that fire suppression may be required to maintain whitebark pine metapop-ulations in the GYE and that maintaining stand networks connected by high rates of seed dispersal could increase metapopulation resiliency.
... Among the various groups of pathogens that infect plants, fungal pathogens are regarded as the most important in terms of potential impacts (Van Alfen 2001). Notable examples of invasive fungal pathogens include Ophiostoma ulmi, the cause of Dutch Elm disease, which is responsible for the mortality of millions of trees in North America and Europe (Strobel and Lanier 1981); Phytophthora cinnamomi, a soil-borne pathogen which has caused extensive dieback of woodlands (especially of Proteaceae species such as Banksia) in Western Australia as well as impacts to other vegetation communities (Burgess et al. 2009); and Cronartium ribicola or white pine blister rust, whose host Pinus albicaulis has been declared endangered in Canada as a result of the pathogen's severe impacts (Government of Canada 2012; Keane et al. 2012). ...
In 2010, the invasive pathogen Austropuccinia psidii was detected in Australia, posing a threat to vegetation communities containing susceptible Myrtaceae species. A large-scale field experiment tested the direct and indirect effects resulting from the infection of two highly susceptible rainforest species, Rhodamnia rubescens and Rhodomyrtus psidioides. Community-level impacts were assessed at three sites per study species in New South Wales, Australia. For R. rubescens, 20 plots containing an adult tree each were established per site. Each plot was designated one of four treatments: fungicide spray of the understorey only, canopy only, both or none (control). For R. psidioides, 10 plots containing only seedlings were established per site, with each plot designated to one of two treatments: fungicide spray or no spray (control). Richness and abundance of co-occurring understorey species were assessed every 4 months for a 24-month period, and changes in canopy transparency were assessed for R. rubescens. The R. rubescens control canopy plots were found to have greater canopy transparency (direct effect) which caused a reduction in the understorey richness and total abundance (indirect effects). For treated canopy plots, richness was similar but total abundance increased in fungicide treated understorey plots, suggesting a direct effect of the pathogen on understorey species. Understorey plots treated with fungicide had significantly greater abundance of R. rubescens and R. psidioides seedlings compared to control plots. This study shows that in a short time period, infection by an invasive fungal pathogen has resulted in changes in species richness and abundance in Australian rainforest communities.
