Forest mortality in high-elevation whitebark pine (Pinus albicaulis) forests of eastern California, USA; influence of environmental context, bark beetles, climatic water deficit, and warming

Whitebark pine ( Pinus albicaulis Engelm.) in subalpine zones of eastern California experienced significant mortality from 2007 to 2010. Dying stands were dense (mean basal area 47.5 m2/ha), young (mean 176 years), and even-age; mean stand mortality was 70%. Stands were at low elevations (mean 2993 m), on northerly aspects, and experienced warmer, drier climates relative to the regional species distribution. White pine blister rust was not observed; mountain pine beetle infestations were extensive. Ring widths were negatively correlated with climatic water deficit and positively correlated with water-year precipitation. Although trees that survived had greater growth during the 20th century than trees that died, in the 19th century trees that eventually died grew better than trees that survived, suggesting selection for genetic adaptation to current climates as a result of differential tree mortality. Air surveys (2006–2010) in the Sierra Nevada, Mt. Shasta, and Warner Mountains showed similar trends to the intensive studies. Observed mortality from air surveys was highest in the Warner Mountains (38%) and lowest in the Sierra Nevada (5%); northern aspects at lower elevations within each mountain region had the highest probabilities of mortality and dying stands had higher climatic water deficit. Scenarios for the future of whitebark pine in California are discussed.

Download Full-text

Cross-scale interaction of host tree size and climatic water deficit governs bark beetle-induced tree mortality

Nature Communications ◽

10.1038/s41467-020-20455-y ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Michael J. Koontz ◽

Andrew M. Latimer ◽

Leif A. Mortenson ◽

Christopher J. Fettig ◽

Malcolm P. North

Keyword(s):

Water Deficit ◽

Sierra Nevada ◽

Bark Beetle ◽

Ponderosa Pine ◽

Tree Mortality ◽

Mortality Rates ◽

Dendroctonus Brevicomis ◽

Scale Interactions ◽

Climatic Water Deficit ◽

Host Mortality

AbstractThe recent Californian hot drought (2012–2016) precipitated unprecedented ponderosa pine (Pinus ponderosa) mortality, largely attributable to the western pine beetle (Dendroctonus brevicomis; WPB). Broad-scale climate conditions can directly shape tree mortality patterns, but mortality rates respond non-linearly to climate when local-scale forest characteristics influence the behavior of tree-killing bark beetles (e.g., WPB). To test for these cross-scale interactions, we conduct aerial drone surveys at 32 sites along a gradient of climatic water deficit (CWD) spanning 350 km of latitude and 1000 m of elevation in WPB-impacted Sierra Nevada forests. We map, measure, and classify over 450,000 trees within 9 km2, validating measurements with coincident field plots. We find greater size, proportion, and density of ponderosa pine (the WPB host) increase host mortality rates, as does greater CWD. Critically, we find a CWD/host size interaction such that larger trees amplify host mortality rates in hot/dry sites. Management strategies for climate change adaptation should consider how bark beetle disturbances can depend on cross-scale interactions, which challenge our ability to predict and understand patterns of tree mortality.

Download Full-text

Response of high-elevation limber pine (Pinus flexilis) to multiyear droughts and 20th-century warming, Sierra Nevada, California, USA

Canadian Journal of Forest Research ◽

10.1139/x07-097 ◽

2007 ◽

Vol 37 (12) ◽

pp. 2508-2520 ◽

Cited By ~ 46

Author(s):

Constance I. Millar ◽

Robert D. Westfall ◽

Diane L. Delany

Keyword(s):

20Th Century ◽

Sierra Nevada ◽

Mountain Pine Beetle ◽

Tree Mortality ◽

High Elevation ◽

Dwarf Mistletoe ◽

Lower Growth ◽

Pinus Flexilis ◽

Limber Pine ◽

Temperature And Precipitation

Limber pine ( Pinus flexilis James) stands along the eastern escarpment of the Sierra Nevada, California, experienced significant mortality from 1985 to 1995 during a period of sustained low precipitation and high temperature. The stands differ from old-growth limber pine forests in being dense, young, more even-aged, and located in warmer, drier microclimates. Tree growth showed high interannual variability. Relative to live trees, dead trees over their lifetimes had higher series sensitivity, grew more variably, and had lower growth. Although droughts recurred during the 20th century, tree mortality occurred only in the late 1980s. Significant correlations and interactions of growth and mortality dates with temperature and precipitation indicate that conditions of warmth plus sustained drought increased the likelihood of mortality in the 1985–1995 interval. This resembles a global-change-type drought, where warming combined with drought was an initial stress, trees were further weakened by dwarf mistletoe ( Arceuthobium cyanocarpum (A. Nels. ex Rydb.) A. Nels.), and proximally killed by mountain pine beetle ( Dendroctonus ponderosae Hopkins). However, the thinning effect of the drought-related mortality appears to have promoted resilience and improved near-term health of these stands, which suffered no additional mortality in the subsequent 1999–2004 drought.

Download Full-text

Interaction between mountain pine beetle-caused tree mortality and fire behavior in subalpine whitebark pine forests, eastern Sierra Nevada, CA; Retrospective observations

Forest Ecology and Management ◽

10.1016/j.foreco.2019.05.052 ◽

2019 ◽

Vol 447 ◽

pp. 195-202 ◽

Cited By ~ 2

Author(s):

Constance I. Millar ◽

Diane L. Delany

Keyword(s):

Sierra Nevada ◽

Mountain Pine Beetle ◽

Tree Mortality ◽

Fire Behavior ◽

Pine Forests ◽

Whitebark Pine ◽

Mountain Pine ◽

Pine Beetle ◽

Eastern Sierra Nevada

Download Full-text

Disturbance Interactions: Mountain Pine Beetle & Blister Rust in Whitebark Pine

The UW National Parks Service Research Station Annual Reports ◽

10.13001/uwnpsrc.2006.3655 ◽

2006 ◽

Vol 30 ◽

pp. 83-84

Author(s):

Nancy Bockino ◽

Daniel Tinker

Keyword(s):

Mountain Pine Beetle ◽

Keystone Species ◽

High Elevation ◽

Snow Accumulation ◽

Pinus Albicaulis ◽

Whitebark Pine ◽

Blister Rust ◽

Disturbance Interactions ◽

Pine Beetle ◽

Greater Yellowstone

Whitebark pine (Pinus albicaulis Englem.) is a keystone species of many high elevation ecosystems in the Greater Yellowstone Ecosystem (GYE) and directly influence watershed quality by regulating snow accumulation and retention, facilitating regeneration after a disturbance, and stabilizing soil and rock on steep, harsh sites.

Download Full-text

Cross-scale interaction of host tree size and climatic water deficit governs bark beetle-induced tree mortality

10.32942/osf.io/jz964 ◽

2019 ◽

Author(s):

Michael J Koontz ◽

Andrew M. Latimer ◽

Leif A. Mortenson ◽

Christopher J. Fettig ◽

Malcolm P. North

Keyword(s):

Water Deficit ◽

Sierra Nevada ◽

Bark Beetle ◽

Ponderosa Pine ◽

Tree Mortality ◽

Mortality Rates ◽

Dendroctonus Brevicomis ◽

Scale Interactions ◽

Climatic Water Deficit ◽

Host Mortality

The recent Californian hot drought (2012-2016) precipitated unprecedented ponderosa pine (Pinus ponderosa) mortality, largely attributable to the western pine beetle (Dendroctonus brevicomis; WPB). Broad-scale climate conditions can directly shape tree mortality patterns, but mortality rates respond non-linearly to climate when local-scale forest characteristics influence the behavior of tree-killing bark beetles (e.g., WPB). To test for these cross-scale interactions, we conduct aerial drone surveys at 32 sites along a gradient of climatic water deficit (CWD) spanning 350 km of latitude and 1000 m of elevation in WPB-impacted Sierra Nevada forests. We map, measure, and classify over 450,000 trees within 9 km2, validating measurements with coincident field plots. We find greater size, proportion, and density of ponderosa pine (the WPB host) increase host mortality rates, as does greater CWD. Critically, we find a CWD/host size interaction such that larger trees amplify host mortality rates in hot/dry sites. Management strategies for climate change adaptation should consider how bark beetle disturbances can depend on cross-scale interactions, which challenge our ability to predict and understand patterns of tree mortality.

Download Full-text

Distribution of Bark Beetle Attacks After Whitebark Pine Restoration Treatments: A Case Study

Western Journal of Applied Forestry ◽

10.1093/wjaf/20.2.110 ◽

2005 ◽

Vol 20 (2) ◽

pp. 110-116 ◽

Cited By ~ 8

Author(s):

Kristen M. Waring ◽

Diana L. Six

Keyword(s):

Bark Beetle ◽

Bark Beetles ◽

Mountain Pine Beetle ◽

Prescribed Burning ◽

High Elevation ◽

Permanent Plots ◽

Whitebark Pine ◽

White Pine Blister Rust ◽

Fire Exclusion ◽

A Site

Abstract Whitebark pine (Pinus albicaulis Engelm.), an important component of high elevation ecosystems in the western United States and Canada, is declining due to fire exclusion, white pine blister rust (Cronartium ribicola J.C. Fisch.), and mountain pine beetle (Dendroctonus ponderosae Hopkins). This study was conducted to evaluate the effects of whitebark pine restoration treatments on the distribution of bark beetle attacks. At a site in Idaho, silvicultural treatments were implemented in summer 1998 and 1999, with prescribed burning implemented in Oct. 1999. Permanent plots (400m2) were established during summer 1999 within each treatment and monitored for 4 years. Within plots, tree characteristics were measured and a bark beetle survey was conducted. Bark beetle attacks remained low throughout the study; however, there was an increase in bark beetle attacks in 2000 after the prescribed burning. By years 3 and 4, there were virtually no successful attacks. Although bark beetles were not a serious concern at the site assessed in this study, our results indicate that managers should consider and monitor the bark beetle component of these ecosystems when implementing restoration treatments. If baseline bark beetle populations are high at the time of implementation, our results indicate that increases in beetle activity would be expected in some treatments, perhaps requiring mitigation. West. J. Appl. For. 20(2):110–116.

Download Full-text

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

The Canadian Field-Naturalist ◽

10.22621/cfn.v135i1.2165 ◽

2021 ◽

Vol 135 (1) ◽

pp. 61-67

Author(s):

David Hamer

Keyword(s):

National Park ◽

Ursus Arctos ◽

High Elevation ◽

Habitat Characteristics ◽

Grizzly Bears ◽

Pinus Albicaulis ◽

Whitebark Pine ◽

Gps Collars ◽

Additional Information ◽

Banff National Park

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.

Download Full-text

Implementation constraints limit benefits of restoration treatments in mixed-conifer forests

International Journal of Wildland Fire ◽

10.1071/wf18141 ◽

2019 ◽

Vol 28 (7) ◽

pp. 495 ◽

Cited By ~ 6

Author(s):

Jamie M. Lydersen ◽

Brandon M. Collins ◽

Carolyn T. Hunsaker

Keyword(s):

Sierra Nevada ◽

Forest Structure ◽

Forest Restoration ◽

Tree Mortality ◽

Canopy Cover ◽

Basal Area ◽

Severe Drought ◽

Conifer Forest ◽

Mixed Conifer ◽

Trade Offs

Forest restoration treatments seek to increase resilience to wildfire and a changing climate while avoiding negative impacts to the ecosystem. The extent and intensity of treatments are often constrained by operational considerations and concerns over uncertainty in the trade-offs of addressing different management goals. The recent (2012–15) extreme drought in California, USA, resulted in widespread tree mortality, particularly in the southern Sierra Nevada, and provided an opportunity to assess the effects of restoration treatments on forest resilience to drought. We assessed changes in mixed-conifer forest structure following thinning and understorey burning at the Kings River Experimental Watersheds in the southern Sierra Nevada, and how treatments, topography and forest structure related to tree mortality in the recent drought. Treatments had negligible effect on basal area, tree density and canopy cover. Following the recent drought, average basal area mortality within the watersheds ranged from 5 to 26% across riparian areas and 12 to 44% across upland areas, with a range of 0 to 95% across all plots. Tree mortality was not significantly influenced by restoration treatments or topography. Our results suggest that the constraints common to many restoration treatments may limit their ability to mitigate the impacts of severe drought.

Download Full-text

Understanding and Defining Mortality in Western Conifer Forests

Western Journal of Applied Forestry ◽

10.1093/wjaf/22.2.105 ◽

2007 ◽

Vol 22 (2) ◽

pp. 105-115 ◽

Cited By ~ 11

Author(s):

Gregory M. Filip ◽

Craig L. Schmitt ◽

Donald W. Scott ◽

Stephen A. Fitzgerald

Keyword(s):

Bark Beetles ◽

Tree Mortality ◽

Water Movement ◽

High Elevation ◽

Regression Equations ◽

Conifer Forests ◽

Dead Tree ◽

Related Factors ◽

Tree Survival ◽

Considerable Controversy

Abstract Tree mortality in western conifer forests is a complex process involving several related factors. Conifer mortality tends to be more common in high-elevation forests where stress from weather, insects, and disease result in higher rates of mortality and in the drier interior forests where mortality from fire, insects, and disease are common. Immediate mortality from fire damage may be obvious, but currently there is considerable controversy about labeling fire-injured green trees as dead that have a high probability of experiencing delayed mortality. Trees die when carbohydrates used in respiration exceed those produced in photosynthesis or water movement is impaired, the tree desiccates, and photosynthesis ceases. Immediate or delayed tree mortality may be directly due to biotic or abiotic causes and may be affected by previous damage, current condition (vigor), and attack by secondary agents such as bark beetles. A particular pathogen or insect usually attacks, damages, or kills only one portion of a tree. Trees that are damaged or attacked by pests and expected to have a dead or nonfunctional root system or a nonfunctional stem within 5 years may be considered either dead or death is imminent. Numerous studies have produced logistic regression equations or other statistical models to help determine probability of tree survival. We define and propose that a “dead tree” designation is justified for most species when at least three of the four quadrants from around the base of the root collar has cambium, inner bark, or phloem that are discolored and dead. For large ponderosa pines, a dead tree has all four quadrants with dead cambium.

Download Full-text