Hotter? Colder? Wetter? Drier?
Elevational range shifts in response to 50 years of climatic change across western North America
Melanie Harsch, Janneke Hille Ris Lambers
Biology Department, University of Washington, Seattle, WA
INTRODUCTION
RESULTS
0
BC NR
BC SR
MT R
ID R
UT R
Number of species
138
179
177
90
146
223
44
345
% of species expanding
65.94
49.72
55.93
84.44
38.36
6.28
43.18
51.88
4.57
0.42
2.39
4.35
-3.51
-14.24
Canada BC Northern Rockies
55
NV SN
Estimated range expansion rate
Overall
-2.53
-0.04
Species expanding
10.46
10.42
10.36
5.45
5.68
2.81
8.23
7.90
Species not expanding
-6.83
-9.46
-8.32
-1.65
-9.22
-15.39
-10.71
-6.83
Canada BC Southern Rockies
2. The rate and direction of range shifts is a function of the rate of change in a) maximum
summer temperature, b) mean summer temperature, c) summer precipitation, and d) snow.
500
1000
1500
Snowfall (mm)
Preliminary data (Fig 1) suggests species are less likely
to range shift at faster declines in snow, regardless of the
amount of snow at the site.
45
Expanding
Not Expanding
WA Cascades
Expansion tended to occur at sites in which both the annual
maximum summer temperature and the annual summer
precipitation have been increasing
MT Rockies
ID Rockies
OR Cascades
If one or both climate variables were not increasing then
expansion was less likely to occur but still occurred.
40
-6 -5 -4 -3 -2 -1
Rate of change in snowfall
Additionally, winter
precipitation could
be important, as
snow insulates
plants from frost
events – thus
constraining range
0
expansions with warming.
OR C
50
However, other climatic factors may also play a role. For
example, warmer temperatures in summer coupled with
lower precipitation and earlier snowmelt could result in
greater water stress which could slow range expansions.
WA CA
Latitude
Climate warming across western North America is expected
to result in plant species distributions expanding into higher
elevations.
1. The percent of species exhibiting range expansion varied by region
UT Rockies
OBJECTIVES
1. Are mountainous regions with higher snowfall, or
less water stress more likely to exhibit expansion?
2. How do temperature and precipitation interact
to affect range expansions?
3. How does the seasonal timing and rate of
precipitation change affect range expansion?
METHODS
Percent of species exhibiting range expansion when the rates of maximum summer
temperature and summer precipitation are increasing (+) or decreasing (-).
WA CA OR CA NV SN BC NR BC SR MT R ID R UT R
Temp (-) / Prec (-)
70
40
NA
NA
NA
0
NA
NA
Temp (-) / Prec (+)
66
61
28
NA
31
4
NA
NA
Temp (+) / Prec (-)
75
71
63
NA
NA
6
37
52
Temp (+) / Prec (+)
63
NA
58
84
53
22
50
47
3. Snow and average summer temperature compensate for decreases in maximum
summer temperature and summer precipitation
-125
-120
-115
-110
Longitude
DISCUSSION
1. Location matters but …
Climatic variables that vary by geographic position (continentality index, heat
moisture indices, snowfall, rate of temperature change) did not significantly explain
variation in range expansion between regions. However, both temperature and
precipitation needed to be considered for all regions.
1. The study area was divided into regions based on topography
2. Species occurrence data were obtained from four online databases:
VegBank http://vegbank.org/vegbank/index.jsp
Forest Inventory Analysis http://apps.fs.fed.us/fiadb-downloads/datamart.html
Mountain Biodiversity Portal http://www.mountainbiodiversity.org/
British Columbia Conservation Data Centre Species Occurrences Database
http://www.env.gov.bc.ca/cdc/contribute.html
2. Temperature and precipitation change? Both matter.
Expansion is most likely to occur where both the maximum summer temperature and
summer precipitation are increasing.
3. Max or mean temperature change? Does not matter which one.
Expansion is more likely to occur where summer temperature is warming, for both
mean or maximum temperatures.
3. Analysis was limited to species within regions with at least
a) 10 occurrence observations,
b) 3 decades of occurrences
c) one occurrence record prior to 1985 and one after 1990
4.
Snowfall matters
Slower declines in snow may be able to compensate for greater potential summer
water stress due to lower summer precipitation. This was evident across both sites
with high snowfall (Rocky Mountains in Southeast British Columbia) and sites with
low snowfall (Sierra Nevadas).
4. Range expansion for the period 1970-2009 was estimated for each species in
each region as the relationship between elevation and year of each occurrence
record. Extreme range expansion rates (top and bottom 2.5%) were removed.
5. Climate data was obtained from ClimateWNA ver 4.70
(http://www.genetics.forestry.ubc.ca/cfcg/ClimateWNA/ClimateWNA.html)
6. All analyses were completed using linear mixed effects models specifying
genus as a random effect.
NV Sierra Nevadas
… range expansion is more likely if
mean summer temperature is warming
… range expansion is more likely if the rate
of change in snowfall is declining slower
Funding provided by: NSF Postdoctoral Research Fellowship in Biology DBI-1103734