Whitebark Pine Seeds Research Articles

Use of Whitebark Pine (Pinus albicaulis) seeds by GPS-collared Grizzly Bears (Ursus arctos) in Banff National Park, Alberta

Seeds of Whitebark Pine (Pinus albicaulis) are a major food for Grizzly Bears (Ursus arctos) in the Yellowstone ecosystem. In Canada, Grizzly Bears are known to eat Whitebark Pine seeds, but little additional information, such as the extent of such use and habitat characteristics of feeding sites, is available. Because Grizzly Bears almost always obtain Whitebark Pine seeds by excavating cones from persistent caching sites (middens) made by Red Squirrels (Tamiasciurus hudsonicus), it is possible to infer Whitebark Pine feeding when bears are located near excavated middens in Whitebark Pine stands. During 2013–2018, I conducted a retrospective study in Banff National Park using data from 23 Grizzly Bears equipped by Parks Canada staff with global positioning system (GPS) collars. My objectives were to use GPS fixes to determine the percentage of these bears that had been located in close proximity to excavated middens containing Whitebark Pine seeds and to describe the habitat at these excavated middens. I linked 15 bears (65%) to excavated middens and, by inference, consumption of Whitebark Pine seeds. Excavated middens occurred on high-elevation (mean 2103 ± 101 [SD] m), steep (mean 26° ± 8°) slopes facing mostly (96%) north through west (0–270°). Use of Whitebark Pine seeds by at least 65% of the 23 studied Grizzly Bears suggests that conservation of Whitebark Pine in Banff National Park would concomitantly benefit the at-risk population of Grizzly Bears.

Recent findings suggest adding red fox to climate-threatened whitebark pine trophic system

Mountain ecosystems are sensitive to climate change, and climate-driven declines in primary producers can impact food webs. Whitebark pine (Pinus albicaulis Engelm.) seed, a valuable food resource for montane wildlife species, is threatened by climate change. Whitebark pine exhibit masting, and during a snowtracking study of Rocky Mountain red foxes (Vulpes vulpes macroura Baird, 1852) in the Greater Yellowstone Ecosystem that happened to coincide with masting, we unexpectedly observed red foxes consuming whitebark pine seeds from red squirrel (Tamiasciurus hudsonicus Erxleben, 1777) middens. Seed production then decreased the following year. To investigate whether whitebark pine seed availability affected winter foraging and habitat use by red foxes, we assessed interannual variance in our dietary and habitat use data. We found both seed consumption and use of habitats where seeds were available also decreased during the non-mast winter. Given the limitations of our small-scale, opportunistic analysis, we suggest whitebark pine seeds may be an important food resource for red foxes, and that their relationship warrants further research and consideration in conservation efforts for both species.

Clark’s Nutcrackers (<i>Nucifraga columbiana</i>) caching Whitebark Pine (<i>Pinus albicaulis</i>) seeds in trees

On 17 September 2017, I observed two Clark’s Nutcrackers (Nucifraga columbiana) from 8–10 m distance as they cached seeds in a stand of dead Whitebark Pines (Pinus albicaulis) at 2500 m elevation on Saint Mary Peak in the Bitterroot Mountains of Ravalli County, Montana. Over 5 minutes, the nutcrackers created 14 caches in seven different multi-trunk tree clusters in an area of about 50 m2. All caches appeared to be single Whitebark Pine seeds, positioned 2–5 m (mostly 3–4 m) above ground in dead trees. Of the 14 caches, three were placed under loose pieces of bark on a trunk (one) or large limb (two), and the remaining 11 were in encrustations of American Wolf Lichen (Letharia columbiana) growing on branches of the dead trees. Nutcrackers are known to sometimes cache seeds above ground in trees during the late summer and autumn harvest of pine seeds, but usually not to the exclusion of other microsites. The ground at the Montana site was covered by 7–9 cm of fresh snow that fell the previous day, which may have encouraged the nutcrackers to place all of their seed caches above ground in trees.

Selecting the best stable isotope mixing model to estimate grizzly bear diets in the Greater Yellowstone Ecosystem.

Past research indicates that whitebark pine seeds are a critical food source for Threatened grizzly bears (Ursus arctos) in the Greater Yellowstone Ecosystem (GYE). In recent decades, whitebark pine forests have declined markedly due to pine beetle infestation, invasive blister rust, and landscape-level fires. To date, no study has reliably estimated the contribution of whitebark pine seeds to the diets of grizzlies through time. We used stable isotope ratios (expressed as δ13C, δ15N, and δ34S values) measured in grizzly bear hair and their major food sources to estimate the diets of grizzlies sampled in Cooke City Basin, Montana. We found that stable isotope mixing models that included different combinations of stable isotope values for bears and their foods generated similar proportional dietary contributions. Estimates generated by our top model suggest that whitebark pine seeds (35±10%) and other plant foods (56±10%) were more important than meat (9±8%) to grizzly bears sampled in the study area. Stable isotope values measured in bear hair collected elsewhere in the GYE and North America support our conclusions about plant-based foraging. We recommend that researchers consider model selection when estimating the diets of animals using stable isotope mixing models. We also urge researchers to use the new statistical framework described here to estimate the dietary responses of grizzlies to declines in whitebark pine seeds and other important food sources through time in the GYE (e.g., cutthroat trout), as such information could be useful in predicting how the population will adapt to future environmental change.

Whitebark Pine (<em>Pinus albicaulis</em>) seeds as food for bears (<em>Ursus</em> spp.) in Banff National Park, Alberta

The large, nutrient-rich seeds of Whitebark Pine (Pinus albicaulis Engelmann) are important food for bears (Ursus spp.) in Yellowstone National Park. In Banff National Park, studies have shown that American Black Bears (Ursus americanus) eat these seeds, but little additional information is available. We studied Whitebark Pine in Banff National Park to address this information gap. Because bears obtain Whitebark Pine seeds from Red Squirrel (Tamiasciurus hudsonicus) middens, our objective was to measure the abundance, habitat characteristics, and use by bears of middens in Whitebark Pine forests. A second objective was to determine whether Grizzly Bears (U. arctos) in Banff National Park also eat Whitebark Pine seeds. In 2011–2012, we ran 29 ha of 20–50 m wide transects at 10 sites with accessible Whitebark Pine stands and found 0–3.7 middens/ha (mean 1.23, SD 1.17, n = 10). Midden density was weakly related to total basal area of all conifers but not to basal area of Whitebark Pine. Middens were located in the upper subalpine at an average elevation of 2110 m (SD 90, n = 8) on 41–248° facing slopes with a mean steepness of 28° (SD 5, n = 8). Bears had excavated middens at all eight sites where we found middens; at the remaining two sites, middens did not occur within our transects. Overall, 24 (67%) of the 36 middens located in our transects had been dug by bears. In October 2013, we searched areas where three global positioning system (GPS)-collared Grizzly Bears had been located in late September 2013 and found five recently dug middens located less than 6 m from GPS fixes. These observations are, to our knowledge, the first conclusive evidence that grizzly Bears in Banff National Park eat Whitebark Pine seeds. Because Whitebark Pine occurs at high elevations on steep slopes where human use is low, this resource may be important in keeping bears in habitat where risk of human-caused mortality is lower. Our results may assist managers responsible for conservation of bears in Banff National Park, where both American Black Bears and Grizzly Bears are subject to high levels of human-caused mortality.

Population-Wide Failure to Breed in the Clark's Nutcracker (Nucifraga columbiana).

In highly variable environments, conditions can be so stressful in some years that entire populations forgo reproduction in favor of higher likelihood of surviving to breed in future years. In two out of five years, Clark’s nutcrackers (Nucifraga Columbiana) in the Greater Yellowstone Ecosystem exhibited population-wide failure to breed. Clark’s nutcrackers at the study site experienced substantial interannual differences in food availability and weather conditions, and the two nonbreeding years corresponded with low whitebark pine (Pinus albicaulis) cone crops the previous autumn (≤ an average of 8 ± 2 cones per tree versus ≥ an average of 20 ± 2 cones per tree during breeding years) and high snowpack in early spring (≥ 61.2 ± 5.5 cm versus ≤ 51.9 ± 4.4 cm during breeding years). The average adult body condition index during the breeding season was significantly lower in 2011 (-1.5 ± 1.1), a nonbreeding year, as compared to 2012 (6.2 ± 2.0), a breeding year. The environmental cues available to the birds prior to breeding, specifically availability of cached whitebark pine seeds, may have allowed them to predict that breeding conditions would be poor, leading to the decision to skip breeding. Alternatively, the Clark’s nutcrackers may have had such low body energy stores that they chose not to or were unable to breed. Breeding plasticity would allow Clark’s nutcrackers to exploit an unpredictable environment. However, if large-scale mortality of whitebark pines is leading to an increase in the number of nonbreeding years, there could be serious population-level and ecosystem-wide consequences.

Dietary breadth of grizzly bears in the Greater Yellowstone Ecosystem

Grizzly bears (Ursus arctos) in the Greater Yellowstone Ecosystem (GYE) are opportunistic omnivores that eat a great diversity of plant and animal species. Changes in climate may affect regional vegetation, hydrology, insects, and fire regimes, likely influencing the abundance, range, and elevational distribution of the plants and animals consumed by GYE grizzly bears. Determining the dietary breadth of grizzly bears is important to document future changes in food resources and how those changes may affect the nutritional ecology of grizzlies. However, no synthesis exists of all foods consumed by grizzly bears in the GYE. We conducted a review of available literature and compiled a list of species consumed by grizzly bears in the GYE. We documented .266 species within 200 genera from 4 kingdoms, including 175 plant, 37 invertebrate, 34 mammal, 7 fungi, 7 bird, 4 fish, 1 amphibian, and 1 algae species as well as 1 soil type consumed by grizzly bears. The average energy values of the ungulates (6.8 kcal/g), trout (Oncorhynchus spp., 6.1 kcal/g), and small mammals (4.5 kcal/g) eaten by grizzlies were higher than those of the plants (3.0 kcal/g) and invertebrates (2.7 kcal/g) they consumed. The most frequently detected diet items were graminoids, ants (Formicidae), whitebark pine seeds (Pinus albicaulis), clover (Trifolium spp.), and dandelion (Taraxacum spp.). The most consistently used foods on a temporal basis were graminoids, ants, whitebark pine seeds, clover, elk (Cervus elaphus), thistle (Cirsium spp.), and horsetail (Equisetum spp.). Historically, garbage was a significant diet item for grizzlies until refuse dumps were closed. Use of forbs increased after garbage was no longer readily available. The list of foods we compiled will help managers of grizzly bears and their habitat document future changes in grizzly bear food habits and how bears respond to changing food resources.

Use of isotopic sulfur to determine whitebark pine consumption by Yellowstone bears: A reassessment

ABSTRACTUse of naturally occurring stable isotopes to estimate assimilated diet of bears is one of the single greatest breakthroughs in nutritional ecology during the past 20 years. Previous research in the Greater Yellowstone Ecosystem (GYE), USA, established a positive relationship between the stable isotope of sulfur (δ34S) and consumption of whitebark pine (Pinus albicaulis) seeds. That work combined a limited sample of hair, blood clots, and serum. Here we use a much larger sample to reassess those findings. We contrasted δ34S values in spring hair and serum with abundance of seeds of whitebark pine in samples collected from grizzly (Ursus arctos) and American black bears (U. americanus) in the GYE during 2000–2010. Although we found a positive relationship between δ34S values in spring hair and pine seed abundance for grizzly bears, the coefficients of determination were small (R2 ≤ 0.097); we failed to find a similar relationship with black bears. Values of δ34S in spring hair were larger in black bears and δ34S values in serum of grizzly bears were lowest in September and October, a time when we expect δ34S to peak if whitebark pine seeds were the sole source of high δ34S. The relationship between δ34S in bear tissue and the consumption of whitebark pine seeds, as originally reported, may not be as clean a method as proposed. Data we present here suggest other foods have high values of δ34S, and there is spatial heterogeneity affecting the δ34S values in whitebark pine, which must be addressed. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Body and diet composition of sympatric black and grizzly bears in the Greater Yellowstone Ecosystem

ABSTRACTThe Greater Yellowstone Ecosystem (GYE) has experienced changes in the distribution and availability of grizzly bear (Ursus arctos) food resources in recent decades. The decline of ungulates, fish, and whitebark pine seeds (Pinus albicaulis) has prompted questions regarding their ability to adapt. We examined body composition and diet of grizzly bears using bioelectrical impedance and stable isotopes to determine if 1) we can detect a change in diet quality associated with the decline in either ungulates or whitebark pine, and 2) the combined decline in ungulates, fish, and pine seeds resulted in a change in grizzly bear carrying capacity in the GYE. We contrasted body fat and mass in grizzly bears with a potential competitor, the American black bear (Ursus americanus), to address these questions. Grizzly bears assimilated more meat into their diet and were in better body condition than black bears throughout the study period, indicating the decline in ungulate resources did not affect grizzly bears more than black bears. We also found no difference in autumn fat levels in grizzly bears in years of good or poor pine seed production, and stable isotope analyses revealed this was primarily a function of switching to meat resources during poor seed‐producing years. This dietary plasticity was consistent over the course of our study. We did not detect an overall downward trend in either body mass or the fraction of meat assimilated into the diet by grizzly bears over the past decade, but we did detect a downward trend in percent body fat in adult female grizzly bears after 2006. Whether this decline is an artifact of small sample size or due to the population reaching the ecological carrying capacity of the Yellowstone ecosystem warrants further investigation. © 2013 The Wildlife Society

Symposium 9: Rocky Mountain Futures: Preserving, Utilizing, and Sustaining Rocky Mountain Ecosystems

Symposium 9: Rocky Mountain Futures: Preserving, Utilizing, and Sustaining Rocky Mountain Ecosystems

Effects of Length of Storage, and Stratification on Germination of Whitebark Pine Seeds

Abstract The effects of length of storage and stratification on germination of whitebark pine (Pinus albicaulis Engelm.) seeds were determined for 180 open-pollinated families from throughout most of the species range. Seeds came from four geographic regions and were stored from 0 to 10 years at one of four storage facilities. Seeds received a standard 1 month of warm moist treatment and 2 months of cold stratification treatment and germination regime, and germination capacity was determined for 100 viable seeds per family. A subset of families received an additional 6 months of cold stratification. Mean germination was 13.4% after 2 months of cold stratification and 76.6% after an additional 6 months of cold stratification, with a wide range among seedlots for both assessments. The length of storage did not affect germination significantly in the first test, but it was associated with a decline in the second test. Germination capacity of up to 80% was achieved with seeds that had been in storage for 10 years. High viability of stored seeds indicate that ex situ seed storage should provide a viable means of conserving genetic resources; however, we recommend that standard protocols for germination of whitebark pine seeds be modified by extending the cold stratification period.

Comparison of survey methods for monitoring Clark's Nutcrackers and predicting dispersal of whitebark pine seeds

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Variant maturity in seed structures of Pinus albicaulis (Engelm.) and Pinus sibirica (Du Tour): key to a soil seed bank, unusual among conifers?

The seeds of Cembrae pines are dispersed by nutcrackers (Genus Nucifraga), which cache seeds in soil during autumn. The dispersal and establishment of seedlings via this mutualistic relationship is highly successful. On the other hand, irregular quality of seed crops and lack of detailed knowledge on germination process of Cembrae pine seeds hamper effective seedling production in the nursery. Therefore we studied basic structures and maturity of whitebark pine (Pinus albicaulis Engelm.) and Siberian stone pine (Pinussibirica Du Tour) seeds, as well as structural changes during a multi-step treatment of whitebark pine seeds, using field emission scanning electron microscopy, transmission electron microscopy and light microscopy. The most striking differences compared to many other conifer seeds were the solid surface structures, early structural differentiation of the embryo, clustering of the thin-walled megagametophyte cells, and great accumulation of starch in both the untreated and treated seeds. Protein bodies of the embryo were in early developmental stages, whereas in the megagametophyte their stages varied. The number, form and size of lipid bodies also varied within different parts of the seed, and lipids dissolved easily. Our results indicated that despite maturity of the seed coat and advanced differentiation of the embryo, the embryo and the megagametophyte were still immature. These morphological features and a notable proportion of storage reserves remaining in unstable form may, however, be advantageous for maintaining viability and reaching maturity within a soil seed bank. Well-controlled pre-treatment simulating natural conditions should result in improved germination.

DELAYED SEED GERMINATION IN WHITEBARK PINE AND REGENERATION PATTERNS FOLLOWING THE YELLOWSTONE FIRES

Whitebark pine (Pinus albicaulis) seeds are dispersed by Clark's Nutcracker (Nucifraga columbiana), a bird that makes caches under 2-3 cm of soil. Cached seeds may delay germination for one or more years in part because of underdeveloped embryos at the time of seed dispersal. Consequently, whitebark pine may show a soil seed bank strategy

Excavation of Red Squirrel Middens by Grizzly Bears in the Whitebark Pine Zone

Whitebark pine seeds Pinus albicaulis are an important food of grizzly Ursus arctos horribilis bears wherever whitebark pine is abundant in the contiguous United States of America; availability of seeds affects the distribution of bears, and the level of conflict between bears and humans. Almost all of the seeds consumed by bears are excavated from middens where red squirrels Tamiasciurus hudsonicus have cached whitebark pine cones. Relationships among the occupancy of middens by squirrels, the excavation of middens by bears, and site features were investigated in this study. Data were collected from radio-marked bears and from middens located from line transects on two study sites in the Yellowstone ecosystem. Densities of active middens were positively related to lodgepole pine Pinus contorta basal area and negatively related to steepness of slope. The probability that a midden was occupied by a squirrel (i.e. active) was positively related to lodgepole pine basal area in the surrounding stand, size of the midden and size of the whitebark pine cone crop, and negatively related to elevation and to bear excavation during the previous 2-12 months. The probability that a midden had been excavated by a bear during the previous 12 months was positively related to size of the midden, and to whitebark pine basal area and cone crop, and negatively related to nearness of roads and town sites. The influence of midden size on bear use was attributable to a positive relationship with the number of excavated cones. The positive association between bear excavations and whitebark pine basal area or cone crops was attributable to availability of pine seeds. Grizzly bears would benefit from the minimization of roads and other human facilities in the whitebark pine zone and from increases in the availability of whitebark pine seeds, potentially achieved by increasing the numbers of cone-producing whitebark pine trees, especially in lower elevations of the whitebark pine zone where red squirrels are more abundant.

Modelling stand dynamics in whitebark pine ( Pinus albicaulis) forests

The ecological process model firesum (a fire succession model) has been adapted to whitebark pine ( Pinus albicaulis) forests of the inland Northwest and Rocky Mountains, U.S.A. firesum simulates tree establishment, growth, and mortality on a 400-m 2 plot. Also modelled are live and dead fuel accumulations, fire behavior, fuel reduction, and insect and disease mortality. The following influences on tree establishment and growth are simulated in the model: temperature, water stress, site quality, and light conditions. An additional submodel in firesum simulates the mutualistic relationship between the Clark's nutcracker ( Nucifraga columbiana) and the whitebark pine. Seed caches made by the Clark's nutcracker are evidently responsible for most whitebark pine regeneration. Whitebark pine seeds are also an important food for red squirrels ( Tamiasciurus hudsonicus), black bear ( Ursus americana), and especially grizzly bears ( Ursus arctos horribilis). Infestations of white pine blister rust ( Cronartium ribicola) and mountain pine beetle ( Dendroctonus ponderosae), and successional replacement by shade-tolerant conifers can reduce whitebark pine populations, which can adversely impact dependent wildlife species. The model firesum was used to investigate the effects of fire, insects, and disease on whitebark pine regeneration and growth. Model predictions of basal area by tree species are presented for contrasting disturbance scenarios. Simulation predictions indicate severe reduction in some whitebark pine populations if current trends are not altered. Model predictions from a test were compared with inventory data from actual postfire stands.

Food habits of Yellowstone grizzly bears, 1977–1987

Food habits of grizzly bears were studied for 11 years in the Yellowstone area of Wyoming, Montana, and Idaho by analyzing scats. Ungulate remains constituted a major portion of early-season scats, graminoids of May and June scats, and whitebark pine seeds of late-season scats. Berries composed a minor portion of scats during all months. The diet varied most among years during May, September, and October, and was most diverse during August. Defecation rates peaked in July and were low in April through June. Among-years differences in scat content were substantial; estimates of average scat composition took 4–6 years to stabilize. Major trends in diet were evident and reflected long-term variation. We suggest that long-term studies are necessary to adequately document bears' food habits in variable environments; the Yellowstone grizzly bears' diet varied with seasonal and yearly availability of high-quality foods, lack of berries and large fluctuations in the size of pine seed crops were major factors limiting bear density in the Yellowstone area, and the availability of edible human refuse buffered the limitations imposed by inadequate berry and pine seed crops prior to the 1970s.

EFFECTS OF AVIAN SEED DISPERSAL ON THE GENETIC STRUCTURE OF WHITEBARK PINE POPULATIONS.

We used allozyme analysis to examine family structure, the spatial patterning of related individuals, in two populations of whitebark pine (Pinus albicaulis), a subalpine conifer that commonly displays a multistem form. The individual stems within clumps are genetically distinct individuals, having arisen from separate seeds. Individuals within a clump are genetically more similar than individuals in different clumps, but individuals in neighboring clumps do not appear to be more similar than individuals in distant clumps. This family structure appears to be a direct result of the seed-caching behavior of Clark's nutcrackers (Nucifraga columbiana), the primary dispersal agent for whitebark pine seeds.

Dispersal of Whitebark Pine Seeds by Clark's Nutcracker: A Mutualism Hypothesis

(1) Clark's nutcrackers (Nucifraga columbiana) store a mean of only 3.7 whitebark pine (Pinus albicaulis) seeds per cache, which reduces competition for moisture and space. The mean depth at which seeds are stored, 2.0 cm, is compatible with germination requirements, and many sites selected appear suitable for seed germination. (2) One nutcracker stores about 32 000 whitebark pine seeds at subalpine elevations each year, which represent 3-5 times its energetic requirements. Although parent nutcrackers feed stored seeds to juveniles, in some years there is probably an excess of seeds stored by the population as a whole. (3) Experimental results suggest that seeds retrieved from nutcracker caches are as viable as seeds extracted by hand from cones and that seedlings originating in nutcracker caches have a good survival rate: 56% over the first year and 25% by the fourth year. (4) In comparison with Clark's nutcracker, alternative disperal agents, i.e. rodents and cone disintegration, disperse fewer seeds, disperse seeds shorter distances from parent trees, place seeds in sites less suitable for germination, and/or make large seed caches which lower reproductive potential. Nutcrackers disseminate seeds throughout the subalpine habitat and are, in part, responsible for the 'pioneering' status of whitebark pine. (5) The evolution of wingless seeds and indehiscent cones in the Cembra pine group was probably a consequence of seed dispersal by an ancestral nutcracker form. It appears that the Clark's nutcracker-whitebark pine interaction is both coevolved and mutualistic.