California’s Alpine Zone
A Shotgun Overview
Connie Millar
USDA Forest Service
Pacific Southwest Research Station
Albany and Lee Vining, CA
and
Phil Rundel
Department of Ecology and Evolutionary Biology
University of California, Los Angeles, CA
Alpine ecosystems cover 3% of the
world’s
land area
“…the exquisite beauty of these mountain carpets
as they lie smoothly outspread in the savage
wilderness” -- John Muir 1894
What is “Alpine”? Ecosystems that lie above upper treeline
What, then, determines upper treeline?
-tree form: stems ≥ 3m tall
-continuous patches of
trees whose crowns form
at least a loose canopy
Körner 2012
Treeline: Thermally defined zone (ecotone) on the landscape
where mean growing-season temperature is ~6.4 °C
Thus, the alpine-forest ecotone is not defined by elevation,
nor by as highest limit that a tree species can grow.
E.g., Krummholz matts of whitebark pine are mostly
within the alpine zone, and can extend > 500 m above treeline
The treeline ecotone, alpine, and beyond…
Körner 2012
Minimum temperature
in growing season
enforces plant growth
limits through control
of carbon sinks not of
carbon source
Bristlecone pine
White Mtns
Foxtail pine
Southern Sierra Nevada
Minimum temperature
that permits production of
new cells and differentiation
of functional tissues
Upper limit of alpine zone
(bottom of nival zone): ≤ 3 °C
Analogy: house construction
The Plant Side of the Alpine Zone
Sierra Nevada 385 species
Mostly not alpine endemics
-48% herbaceous perennials
-24% graminoid perennials
-12% mats & cushions
-6% annuals and 6% woody
Distribution of
Alpine Ecosystems
in California
2700 – 3500 m (= treeline
across state’s latitudes)
Klamath Mtns: Trinity
Alps, Marble Mtns, Scott Mtns
S Cascades: Mt Shasta,
Mt Lassen
Sierra Nevada
Great Basin Ranges:
Warner, Sweetwater, Glass,
White-Inyo, Panamint
S California Ranges:
San Gabriel, San Jacinto,
San Bernardino
Alpine environments
develop complex
habitats
Substrates
Geomorphology and Topography
Niches
Alpine envrionments experience
complex climates
Macro-Climates: 1000 - 20 km
Global circulation, synoptic meteorology
Meso-Climates: 20 – 0.5 km
Basin to range, range to range
Topo-Climates: 0.5 km - 100 m
Solar radiation, lapse effects, N-S slopes,
frost pockets, wind-funneling
Micro-Climates: 100 m – 1 cm
Vegetation canopies, nurse rocks, talus regimes
Mediterranean Climate
of California Alpine
Ecosystems
Our Mediterranean Climate:
-- Long, warm, dry summers
-- Winters wet; Storms from Pacific
-- Summer convectional storms
S Great Basins differ w/ bimodal precip
PRISM Mean Climate Values
Alpine Regions in California
Mid-upper alpine, N aspects
1971-2000 means, 800 km grid
Extracted from PRISM website, 1/2014
A Ramble Across the Alpine Regions
of California
Klamath Mtns: Trinity Alps
Southern Cascades; Mt Shasta
Great Basin North:
Warner Mtns
N Sierra Nevada and Carson Range
Central Sierra Nevada:
W Walker Watershed
Conness and North Peak Glaciers
Mt Conness & North Pk
Mt Gibbs
Rock Glacier
Summer snowpatches in the Sierra tend
to be consistent in location among years
Snowfield sites important
in defining pocket forests,
which are increasing with
warming climates
Brawley Pks, Bodie Hills
Millar et al. 2004
S Sierra Nevada: Palisades Basin
Southern Sierra Nevada
Great Basin, South Ranges: Sweetwater Mtns
Great Basin, South Ranges : White Mtns
Snowpacks more variable in location than in Sierra Nevada
and tend to sublimate as much as melt
The few persistent
snowpatches enabled
prehistoric people to
develop alpine villages
during cool climates,
White Mtns
Alpine Ecosystem Responses to
Changing 20th-21st Century Climates
Limber pine in the White Mtns is
leapfrogging above bristlecone
pine into the alpine zone
Millar & Westfall in prep
* 300 m above current LP treeline
* Dolomitic soils only
* No live BCP
* Areas of historic BCP forest
Episodic Recruitment (What’s going on?)
Correlates with:
- Annual T min, T max
- May & June Tmin
Re-survey
2013
- Sept Precipitation
- Atlantic Multidecadal Oscillation
Pulse
~ 1970-1991
Millar et al. in prep
Whitebark pines in the alpine zone
of the Sierra Nevada are highly
plastic, and respond adaptively to
climate variability through changes
in growth & form; No
flags & skirts
advance in treeline
krummholz
Millar et al. 2004
upright trees
Region-wide growth
of flags 1945-1976;
reversed thereafter
Stem growth rates
doubled over 20th C
Forms responsive to micro-climate
as well as changing regional climate
Response to Low Snowcover in the Alpine Zone
Winter 2011 - 2012: Mortality of many evergreen
shrubs and conifer
seedlings
Widespread through
Great Basin Ranges
Pinus albicaulis, Phyllodoce breweri,
Linanthus pungens, Arctostaphylos spp.
Cold
exposure;
Lack of
snow cover
Talus-Forefield Ecosystems;
Biodiversity & Climate Refugia
Millar et al.
2008, 2010,
2012a, b,
2014, in
press
Talus landforms develop unique microclimates, decoupled
from regional climates
Cool in summer; Warm in winter
Buffered from external extremes
-Taluses maintain persistent internal ice
-Support persistent springs and wetlands
-Stable habitats resist climate warming
Talus/RG-Forefield Ecosystems
Support High and Distinct
Species Diversity
Mean # Vascular Plant Spp
Rocky Surfaces (9 ha) 22
Forefields (0.6 ha)
61
Reference (large)
51 (12)
Mean # Arthropod Morpho-Spp
Forefields (0.6 ha)
88
Reference (~1.0 ha) 29 (few)
Wetland Plants
Millar, Westfall, Evenden, Holmquist, Schmidt,
Franklin, Nachlinger, Delany, 2014
Talus-Wetand Ecosystems
- Provide potential climate refugia
under warming temps
- Enable animals that use talus and
wetlands to use a larger range
of sites than expected
Mono Basin pika distribution: 2191 – 3769 m; Span of 1578 m
White Mountains Span: 1524 m