Climate influence on shifts in the Deep Canyon ecocline, 1977 – 2007
Anne Kelly and Michael Goulden
1
2
1 – CAL STATE LOS ANGELES, DEPT. OF BIOLOGICAL SCIENCES 2 – UC IRVINE, DEPT. OF EARTH SYSTEM SCIENCE
Climate gradients found along mountainsides provide an
opportunity to study diverse plant communities within a small
spatial extent. When the climate changes, the ecocline, or
vegetation gradient, will presumably shift to follow the plants’
ideal climate conditions (Figure 1).
This process is taking place rapidly in the Deep Canyon
Transect, a study site in the Santa Rosa Mountains in the desert
of Southern California. The climate of this area has warmed
over the past thirty years while annual rainfall variability has
increased significantly. All plant communities, from Mojave
cactus scrub to mixed conifer forest, have shifted up the
mountain concurrently. No other type of disturbance besides a
climate gradient shift could cause this synchronous move of
diverse plant communities.
Methods
Live perennial plants were surveyed along a 400 m isocontour
every 122 m in elevation, from 244 m to 2560 m in elevation.
This survey replicates the survey done in 1977 by Jan Zabriskie
(Zabriskie 1979). Climate data come from NOAA’s National
Climate Data Center (2007); the monthly data from the six
nearest weather stations, all within 75 km, were averaged.
Results
Species movement, 1977 – 2007
• Nine of the ten most widespread dominant species have
moved upwards, with an overall average of +64.7 m (Table
1).
• The change in mean elevation was independent of initial
elevation.
• The mean distribution of the ten dominant plants has shifted
asymmetrically, consistent with an upward shift (Figure 1).
Normalized top ten species coverage
Introduction
0.8
0.7
• Precipitation has increased significantly, mitigating some of
the upward pressure on plant ranges.
Conclusions
Has the vegetation moved upward?
0.6
• Nine of the ten most widespread dominant species have
shifted upwards, with a significant average shift of +64.7 m
(Table 1).
0.5
0.4
• The shape of the mean plant distribution has changed from a
symmetric distribution about the mean to a distribution
skewed upwards in elevation (Figure 2).
0.3
0.2
-366
-244
-122
0.1
Has the climate changed?
0.0
• The climate was significantly warmer in the period after the
1977 survey than before, and annual precipitation variability
doubled after 1977.
0
122
244
366
Figure 2. The Deep Canyon Transect and its location in California.
Elevation difference from central elevation (m)
Figure 1. Elevation distribution of the normalized vegetation
coverage of the top ten species in 1977 and 2007.
1977
Table 1. Mean elevation change (m) for the ten most widespread
species in the Deep Canyon Transect, 1977 - 2007.
Abies concolor
2007
2500 m
Mean elevation
(m)
1977
2007 Change (m)
Species
1
Pinus jeffreyi1
Quercus chrysolepis2
Rhus ovata3
Ceanothus greggii var. perplexans3
Quercus cornelius-mulleri3
Larrea tridentata3
Ambrosia dumosa4
Encelia farinosa4
Agave deserti5
2421.4
2517.6
96.2
2239.9
1986.6
1456.6
1601.6
1484.5
317.2
630.0
574.0
693.3
2267.4
2033.2
1517.5
1671.2
1521.5
459.0
747.8
673.6
643.0
Mean
95% CI
27.5
46.6
60.9
69.5
37.1
141.8
117.8
99.6
-50.3
64.7
33.8
1) Evergreen needleleaf tree 2) Evergreen broadleaf tree
3) Evergreen broadleaf shrub 4) Drought deciduous
shrub 5) Evergreen succulent
• Increasing climate variability, including extreme drought
events, is an expected result of greenhouse gas caused
climate warming (Trenberth et al. 2007).
• Increasing mean annual temperatures due to the urban heat
island effect were found in the nearby Coachella Valley and
San Bernardino/Riverside areas (LaDochy et al. 2007).
Has the climate warming caused the plants to move
upward?
1800 m
• Given the temperature lapse rate of –0.007 ºC m-1 and
climate warming of 0.5 C – 0.8 ºC, the temperature gradient
has shifted an equivalent of 65 m – 103 m upwards, similar
to the vegetation shift we found.
• Other causes besides climate change?


1000 m

Table 2. Change in average annual climate variables in interior
Southern California from the period 1947-1976 to 1977-2006.
Change from
1947-1976 to 1977-2006
Climate change, 1947 – 1976 & 1977 – 2006
• Precipitation variability, the snow/rain ratio, and mean
temperature have significantly changed, consistent with an
upward shift in climate contours (Table 2).
2007
1977

95% CI
Elevation
change (m)
Precipitation (cm)
7.3**
(18.2%)
3.3
-138
Precipitation cv
0.13** (27.7%)
0.06
678
Snow/rain ratio
Max. T (°C)
-0.06** (-34.7%)
327
24
0.19
(0.8%)
0.05
0.50
Min. T (°C)
0.63**
(7.6%)
0.53
83
Mean T (°C)
0.41**
(2.5%)
0.24
56
300 m
Successional changes are only an issue in the
montane chaparral, which exhibited patterns similar
to the other plant communities.
Fire regime change/forest thickening is not
occurring in Deep Canyon: no increase in A.
concolor was found.
Ozone pollution is thought to be low in the Santa
Rosa Mountains, and has not caused conifer
mortality.
Land use has changed somewhat: protection
increased to include the upper half of the Deep
Canyon Transect after 1977, yet mortality and
upslope shifts were seen at all elevations.
• The only cause of species distribution change that explains
the decrease in coverage below the mean elevation and a
simultaneous increase above the mean elevation is climate
warming and increasing precipitation variability (Figure 1,
Table 1, Table 2).
Literature cited
Acknowledgements
For further information
National Climatic Data Center (2007). Monthly Surface Data NOAA-NCDC. Retrieved July 12, 2007 from: http://cdo.ncdc.noaa.gov/CDO/cdo
LaDochy S et al. (2007). Recent California climate variability: spatial and temporal patterns in temperature trends. Climate Research 33:159-169.
Trenberth KE et al. (2007). Observations: surface and atmospheric climate change. In: Climate Change 2007 The Physical Science Basis. Fourth Assessment Report of the
Intergovernmental Panel on Climate Change. Solomon S et al., eds. Cambridge, UK: Cambridge University Press.
Zabriskie JG (1979) Plants of Deep Canyon and the Central Coachella Valley, California. Riverside, CA: Philip L. Boyd Deep Canyon Desert Research Center, University of
California, Riverside
We thank Tom Chester for botanical and surveying assistance and helpful
discussions. We also thank Ian Carbone for surveying assistance. Funding
was provided by a NSF CEA-CREST fellowship and a NASA NACP
grant.
Please contact anne.kelly@utoronto.ca. Present address: Faculty of
Forestry, University of Toronto, 33 Willcocks St, Toronto, ON M5S 3B3
Canada
More information on this and related projects can be obtained at
www.ess.uci.edu/~goulden.