Whitebark Pine
Field Chronicles
Through the Years
Connie Millar
USDA Forest Service
Pacific Southwest Research Station
Albany and Lee Vining, California
Collaborators:
Bob Westfall, Matt Bokach,
Lori & Alan Flint, Deb Rogers
Whitebark Pine, Pinus albicaulis, in California
Distribution: Klamath Mtns, S Cascades, Sierra Nevada, Great Basin Mtns
2000 m – 3700 m;
Alpine & subalpine
Griffin & Critchfield,
1976
Jepson eFlora
Genetic Insights – Remember Allozymes?
PiAl in 3 watersheds of the E Sierra;
Upright trees vs. krummholz zones
Genetic differentiation
Among watersheds
Between upright & krumm zones
Among clumps within zones & sites
Fst
0.004
0.051
0.334
Rogers, Millar, Westfall 1999
Krummholz: # Genotypes/Matt: 100% > 1, range 2-14,
increasing w/ size; Relatedness among ramets: r = 0.32
 Krummholz
matts not clonal
Krummholz:
Genetic variation and # of individuals
increased downwind within
matts
Cross-watershed homogenization
Wind-pollinated,
Bird or gravity planted
Contours of genetic relationship within matt
Tree Clusters: 72% had >1 genotype/cluster; range 1-6
28% were multi-branched trees (= single genotype, up to 15 stems)
Diversity patterns among clumps similar to krumm, but relatedness
higher; r = 0.6 (= twice krumm value)
From tree-ring counts,
most clumps contained
multiple age classes
e.g., among 7 stems, 3
distinct ages
 Not all stems in a
cluster derived from
multiple-seed cache
Subsequent genetic study (unpub)
of seedling to 1.5 m tall clusters
showed pattern in # of genotypes:
Seedling clusters: 3-6
Mid-sizes:
1-3
Large-sizes:
1-12
 Initial cache less impt than
subsequent planting?
 Iterative planting by birds?
Black bears, by the way, do not depend on whitebark pine in
CA – David Graber
Pinyon nuts
provide, tho!
PiAl Responses to Climate Variability and Warming
1. No obvious attempts to recruit above treeline. Rather, adaptive
changes in crown form (flagging followed
krummholz
PDO)
flags & skirts
upright trees
Whitebark pine, a
sublimely plastic
subalpine species
Millar, Westfall, et al. 2004
2. Krummholz growth
rate doubled over
20th C, following
temperature trend
PiAl Responses to Climate Variability and Warming
3. Forest densification (Dolanc, Thorne, Safford 2012)
4. Infilling of formerly persistent snowfields
(Millar, Westfall, et al. 2004)
PiAl Responses to Climate Variability and Warming
5. Crown dieback and mortality due to lack of snow and cold
exposure. Winter 2011-2012: many evergreen shrubs and PiAl
Widespread in Sierra Nevada and
Great Basin Ranges
Also affected: Phyllodoce, Cassiope,
Arctostaphylos, Chrysolepis
affected
PiAl Responses to Climate Variability and Warming
6. Bark beetle-related mortality events
Whitebark pine (2007-2013) and Limber Pine (1988-1994) Events
Drought
Elevated Temperatures
Mountain Pine Beetle
Mistletoe Infection
Blue-Stain Fungus
+
+
+
+
=
“Global-WarmingStyle Mortality”
Event”
Millar et al. 2007; 2012
Mortality in Both Whitebark
and Limber Pine
Glass Cr/Whitewing Mtn
-N/NE slopes
-Eastward on escarpment
-Low elevation (2850-3000 m)
-Little drainage from above
-No white pine blister rust
Hilton Cr Cyn
June Mtn
PiAl Mortality Stands had High Climatic Water Deficits;
Mean for SN plots = 165; For all PiAl Mort Sites = 347
Stephenson
1990, 1998
Highest correlations of whitebark pine growth for trees that survived
and those that died was to CWD (vs temp, ppt, PDSI): r = -0.46
Mortality acted as silvical agent, Limber pine mortality
improving forest resilience
event, Sierra Nevada
Live trees remained
1988-1994
Stand mortality ~70%
Stands thinned (co-dominants
survived), less vulnerable to
beetle outbreak
Typical sparse old-growth stand
 Limber pine stands
remained healthy during
the 2007-2013 whitebark
event in the same region
Mortality acted as a geneticselection agent, improving adaptive
fitness for warming 21st C climates
Limber pine growth
Live trees remain
Millar, Westfall, et al.
2007, 2012
When variation exists for genes that affect climate fitness, including
susceptibility to bark beetles via drought vulnerability, mortality moves
the population toward genetic adaptation much more rapidly than
without mortality
directional selection
for warmer climate
S = .9
S = .1
# of gens from p0 = .01 to pt = .99
For s = .9 (mortality event), 4 gens
For s = .1 (no mort), 175 gens
Other PiAl mortality conditions for populations
of whitebark pine around eastern CA:
Similar environmental
contexts but increasing extent
of mortality northward:
S Cascades and Warner Mtns
Sierra Nevada, Burt Cyn, W Walker
Sweetwater
Mtns
By 2013 Mortality Event Had Ended
Around the Great Basin Despite
Continuing Drought
Whitebark pine,
Sierra Nevada,
E Fk Rock Cr
Whitebark pine, Pine Forest Range, NV
Whitebark pine, Drakes Pk, N Warner Mtns
Whitebark pine, E Humboldt & Ruby Ranges, NV
Possible Futures for Whitebark Pine in California
#1 Recent mortality events portend increasing
bark-beetle outbreaks at landscape scale
Catastrophic Outcome?
Why are north aspects, young, dense stands,
at lower elevations vulnerable?
Why is WPBR limited?
#2: Recent mortality event is not the
beginning of landscape-scale outbreaks,
but example of future events
Normative Disturbance?
Whitebark pine stands increase in
adaptedness to warm climates
and bark beetles?