Monitoring whitebark pine stand health in the central Washington Cascades

Whitebark pine (Pinus albicaulis) plays a vital role in colonizing newly disturbed areas, providing shade for other tree species to germinate, and supplying food for a variety of birds and mammals, such as Clark’s Nutcrackers (Nucifraga columbiana) and grizzly bears (Ursus arctos horribilis). Decline of whitebark pine populations has been attributed to several factors, including white pine blister rust (Cronartium ribicola), mountain pine beetle (Dendroctonus ponderosae) outbreaks, and fire exclusion. In 2009, the U.S. Forest Service began to install permanent plots in whitebark pine stands in Washington and Oregon as part of a Pacific Northwest restoration strategy to track blister rust and mountain pine beetle mortality. Forest Service crews conducted surveys on these plots that included standard tree inventory measurements and assessments of blister rust, mountain pine beetle, and fire activity. During summer 2020/2021, we remeasured 12 of these plots located in 3 areas of the Okanogan–Wenatchee National Forest (Mission Ridge, Clover Springs, and Lake Ann) and 1 area within the Ahtanum State Forest (Darland Mountain). On average, 15% of trees were newly infected by blister rust, 5% of trees died from blister rust, and 12.6% died from all causes combined in the 11–12 years between surveys. Despite this, the density of live whitebark pine trees experienced a nonsignificant increase due to regeneration, while the density of whitebark pine snags increased significantly and the density of whitebark pine seedlings decreased significantly. The percentages of trees with blister rust infection, seedlings with blister rust infection, and live trees with mountain pine beetle damage were heterogeneous over space and time. Our results help quantify parameters that are central to understanding the population dynamics of whitebark pine in the Pacific Northwest and informing management decisions, but the findings should be interpreted in light of the limited sample size and spatial extent of our data. Regular monitoring of a wider array of permanent whitebark pine plots will be critical to management of this tree species

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

Food types.

<p>Percentage of known food types eaten during independent foraging events. Numbers do not add up to 100, as foods consumed during <2.5% of the events, and unknown food items are not included in the graph.</p

Clark’s Nutcracker Breeding Season Space Use and Foraging Behavior

<div><p>Considering the entire life history of a species is fundamental to developing effective conservation strategies. Decreasing populations of five-needle white pines may be leading to the decline of Clark’s nutcrackers (<i>Nucifraga columbiana</i>). These birds are important seed dispersers for at least ten conifer species in the western U.S., including whitebark pine (<i>Pinus albicaulis</i>), an obligate mutualist of Clark’s nutcrackers. For effective conservation of both Clark’s nutcrackers and whitebark pine, it is essential to ensure stability of Clark’s nutcracker populations. My objectives were to examine Clark’s nutcracker breeding season home range size, territoriality, habitat selection, and foraging behavior in the southern Greater Yellowstone Ecosystem, a region where whitebark pine is declining. I radio-tracked Clark’s nutcrackers in 2011, a population-wide nonbreeding year following a low whitebark pine cone crop, and 2012, a breeding year following a high cone crop. Results suggest Douglas-fir (<i>Pseudotsuga menziesii</i>) communities are important habitat for Clark’s nutcrackers because they selected it for home ranges. In contrast, they did not select whitebark pine habitat. However, Clark’s nutcrackers did adjust their use of whitebark pine habitat between years, suggesting that, in some springs, whitebark pine habitat may be used more than previously expected. Newly extracted Douglas-fir seeds were an important food source both years. On the other hand, cached seeds made up a relatively lower proportion of the diet in 2011, suggesting cached seeds are not a reliable spring food source. Land managers focus on restoring whitebark pine habitat with the assumption that Clark’s nutcrackers will be available to continue seed dispersal. In the Greater Yellowstone Ecosystem, Clark’s nutcracker populations may be more likely to be retained year-round when whitebark pine restoration efforts are located adjacent to Douglas-fir habitat. By extrapolation, whitebark pine restoration efforts in other regions may consider prioritizing restoration of whitebark pine stands near alternative seed sources.</p></div

Food consumed during foraging events.

<p>Food consumed during foraging events.</p

Annual indications of Clark’s nutcracker breeding.

<p>Nonbreeding years are in bold.</p><p>Annual indications of Clark’s nutcracker breeding.</p

Dying whitebark pine trees.

<p>Example of whitebark pine trees at the study site which are dying due to mountain pine beetle attacks the previous year. (Photo credit: T. D. Schaming).</p

Trapping locations, individual home ranges, and available habitat.

<p>Only trapping sites where individuals were successfully captured are shown. Specific whitebark pine categories were merged for better visualization. Burned habitat is not shown because it is not possible to see at the scale of the map.</p

Annual variation in documentation of population-wide breeding.

<p>Between years, there was variation in the dates and number of days I spent in the field, the number and dates of Clark’s nutcrackers trapped, the number radio tagged, and the number of days radio tagged birds were observed. Nonbreeding years are in bold.</p><p>Annual variation in documentation of population-wide breeding.</p

Breeding season 95% fixed kernel home range sizes for breeding and nonbreeding birds.

<p>Breeding season 95% fixed kernel home range sizes for breeding and nonbreeding birds.</p