Aspen Phenology Monitoring
Central Alaska Network
Alaska Botany Forum 2011
E. Fleur Nicklen
Carl Roland
Acknowledgments
Thanks to the many who have help collected this data: Robert
Liebermann, James Walton, Wendy Mahovlic, Jamie Martin,
Miranda Terwilliger, Kara Thies, Pat Sanders , Carl Stapler , Brian
Heitz, Tamas Szerenyi, Sarah Stehn, Brandon Gottung, Eric
Groth and Brian Dykstra as well and many others.
Thanks to those helping to keep the monitoring going in parks
we can’t be in at all times: Miranda Terwilliger and Pat Sanders
We thank Angie Southwould for her expert database design and
Nick Bywater for database additions that made analysis much
easier.
Phenology – the study of the timing of biological events
Conflicting incentives fundamental to plant phenology:
Maximize photosynthetic carbon gain and reproductive output
Minimize carbon and nutrient loss by frost damage
Experimental
Studies
Understand the cues that drive phenology:
Monitoring
Photoperiod
Temperature (Spring, Fall)
Thawing Degree Days
Chilling
Rainfall
Snowmelt
Soil Temp
Make good predictions about how plants will respond to changing environmental cues
Plant growth &
reproduction
Plant –animal
interactions
Factors interacting with Climate:
Carbon Exchange, Albedo,
Evapo-transpiration
Phenology Monitoring
Aspen (Populus tremuloides)
-Important component of boreal forests
-Most widely distributed tree species in North America
-Monitored in other national phenology networks
(National Phenology Network, Plantwatch)
Goal
-Detect changes in the timing of key events in the
life cycle of Aspen
-Detect potential correlations with climate data
collected from nearby locations.
CAKN Aspen phenology monitoring plots
Eagle Plot
Denali
2 Plots monitored for 6 years (2005- 2010)
Plot 1: Dry, steep, south-facing slope (560m)
Plot 2: Moist, flat, bench, mixed w/ spruce
(570m)
Fairbanks Plot
Copper Center
Denali Plots
1 Plot monitored for 3 years (2008- 2010)
Plot 1: Flat terrace mixed w/ spruce (410m)
Eagle
Gulkana
1 Plot monitored for 1 year (2008)
Plot 1: Flat, mixed w/ spruce (280m)
Copper Center Plot
Fairbanks
1 Plot monitored for 1 year (2010)
Plot 1: Gentle, south-facing slope (178m)
Anchorage
Climate Stations
All weather stations are within 25km and 100m elev of the monitoring sites
Denali: Dog Kennel weather data
Copper Center: Gulkana Airport RAWS weather station
Fairbanks: Geophysical Institute weather station
Eagle: Eagle Airport RAWS weather station
Aspen Phenology Monitoring Design
12 Trees per plot
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Observations made at 2pm
Measure Air Temp
Measure 2 Soil Temps at each tree
Spring: Mid Apr to Mid May, 3 observ./week
Flowering
No flowering
Catkins emerging
Catkins ripe
Catkins falling
Foliage
No evidence of leaf-out
Leaf buds bursting
Leaves unfurled
Leaf full-sized
Fall: Aug to Mid Sept, 3 observations/week
Foliage
Leaves green
> 25% of leaves yellow
>50% of leaves yellow
>75% of leaves yellow
100% of leaves yellow
Aspen Phenology Data Analysis
Average phenology state per plot for each observation date:
“On May 2, 2006 6/12 or 50% of the trees in the Copper Center Plot had burst buds”
Phenology Benchmark Definition
Bud Burst
Date on which 50% of trees in plot had leaf buds bursting.
Leaf Unfurling
Date on which all of the trees in the plot had unfurled leaves
Complete Green-up
Date on which all trees in plot had fully expanded leaves
First Flowering
Date by which at least one tree in the plot had open catkins
Full Flowering
Date on which all of the trees in the plot had open catkins
Fruiting
Date by which ripe female catkins and empty or falling male
catkins were observed on all (flowering) trees in plot
First Yellow
Date on which at least one tree in the plot had 25% yellow
leaves
Date by which100% of the trees in the plot had 50% yellow
leaves
Date by which100% of the trees in the plot had 100%
yellow leaves
Senescence
Complete Senescence
Aspen Phenology Spring Questions
Questions:
With what climate variables are bud burst and leaf unfurling correlated?
-Spring Temperature and chilling period , fall temperatures
How do bud burst and leaf unfurling vary:
Between the two different Denali plots? -earlier in Denali Plot 1?
Between the similar Denali plot 2 and Copper Center plot?
Between years? -earlier in the warmer Plot and warmer years?
Aspen Phenology Fall Questions
Questions:
With what climate variables are first yellow and senescence correlated?
-photoperiod trigger with cold temps as accelerator (Fracheboad et al. 2009)
How do first yellow and senescence vary:
Between the two different Denali plots? –no difference?
Between the similar Denali plot 2 and Copper Center plot?
Between years? –no difference?
Aspen Phenology Flowering Questions
Very limited data!
How often does flowering occur?
Similar timing among years and plots?
Tree Gender Questions:
--Endless questions, but so little data!
How does the timing of bud burst and flowering differ
between male and female trees?
Spring Results—Climate Correlates
Correlation coefficients between selected climate variables and two
benchmarks of spring aspen phenology (n=17).
Bud Burst
Leaf Unfurling
Climate Variable
Date*
Date+
Snow-free date
0.69
0.70
Mean April Temp
-0.62
-0.60
Mean May Temp
-0.86
-0.85
Sum of Thawing DD in May
-0.84
-0.83
Sum of Thawing DD before unfurling date
-0.63
-0.80
Mean May Temp before bud burst date
-0.79
-0.56
Mean May Temp before unfurling date
-0.79
-0.64
Mean May Soil Temp (at time of sampling)
-0.12
-0.17
Mean Temp Aug 1 to growing season end
0.42
0.68
(of previous year; n =12)
*Date by which at least half of the trees in the plots had burst buds, +Date by which 100% of the trees in the plots had
unfurled leaves
Bud burst date (numerical day)
Spring Results—Climate Correlates
150
May 30
n = 17
145
140
135
130
125
May 1
120
4
6
8
10
12
Mean Daily May Temp (deg C)
14
Spring Results—Climate Correlates
4.01 ° C
0.29 ° C
Soil Temp (deg C) at time of observation
10
Denali Plot 1
8
2005
2006
2007
2008
2009
2010
6
4
Mean
Air T
At Plot
In Spring:
12.2° C
2
0
-2
-4
3
Denali Plot 2
2
10.8° C
1
0
-1
-2
-3
110
120
130
140
Numeric Day of Year
150
160
Spring Results—Comparing Denali Plots
Average aspen
growing season in
this area of Denali is
105 days, so a
variability of 17
days represents 16%
of the average
growing season
Mean Daily May Temp (deg C) Numerical Date of Bud Burst
150
DENA Plot 1
DENA Plot2
145
140
May 30
17 days
135
130
125
May 1
10
120
8
6
4
2
0
2005
2006
2007
2008
2009
2010
Spring Results—Comparing Copper Center & DENA2
Numerical Date
of Bud Burst
150
Copper Center
CC Mean
DENA Plot 2
DENA2 Mean
145
140
135
130
125
120
10
Copper Center
CC Mean
DENA Plot 2
DENA2 Mean
Mean Daily May
Temp (deg C)
8
6
4
2
0
2008
2009
2010
mean
Fall Results—Climate Correlates
Correlation coefficients between selected climate variables and two
benchmarks of fall aspen phenology (n = 17).
Climate Variable
First Yellow*
Senescence+
Total precipitation May – Aug
-0.14
-0.64
Mean Temp Aug 1 to growing season end
0.52
0.03
Mean Min Temp Aug 1 to growing season end
0.61
0.08
Mean Temp Aug 15 to Sept 15
0.48
0.32
Mean Min Temp Aug 15 to Sept 15
0.48
0.39
First date of minimum Temp below 2°C++
0.64
-0.1
Mean Temp 14 days before growing season end
0.33
0.14
Mean Min Temp 14 days before growing season end
0.48
0.12
Mean Soil Temp at time of observations (aug-sept)
0.15
-0.33
*Date of first tree in plot with at least 25% yellow leaves. + Date 100% of trees in plot with at least 50% yellow leaves.
++Excluding the early freeze in 2009 that occurred on Aug 2.
Fall Results—Comparing Denali Plots
250
Sept 6
Numerical Date
of First Yellow
245
240
235
230
225
Aug 8
220
265
DENA Plot 1
DENA 1 Mean
260
Numerical Date
of Senesence
Sept 22
DENA Plot 2
DENA 2 Mean
255
250
245
240
Aug 23
235
20
05 006 007 008 009 010 Avg
2
2
2
2
2
Fall Results—Comparing Copper Center and DENA 2
240
Aug 27
Numeric Date
of First Yellow
238
236
234
232
230
Copper Center
DENA Plot 2
228
Aug 14
Numeric Date
of Senescence
226
258
Sept 15
256
254
252
250
Sept 4
248
2008
2009
2010
Flowering Results
140
135
DENA 1 (2005-2010)
DENA 2 (2005-2010)
Copper C (2008-2010)
Fairbanks (2010)
Eagle (2008)
125
120
no flowering
130
no flowering
Numerical Date of
Full Flowering
May 24 145
April 25 115
2004 2005 2006 2007 2008 2009 2010 2011
Flowering Results—Comparing Genders
140
Numerical Date
138
136
Full Flowering
Bud Burst
134
132
130
128
126
124
122
Female
Male
n = 26
n = 38
Conclusions
-Spring Time temperature is highly correlated with the timing of
bud burst and leaf unfurling—implications for growing season
-First yellow and senescence varied across sites and years,
suggesting controlling factors in addition to photoperiod
-The onset and progression of senescence were correlated with
different climate variables, suggesting that these are separate
processes with different controlling factors—min T and precip
-Mass flowering occurs every 5 years or so?
-Earlier flowering in the warmer year and areas
-Female and male trees differ in their timing of bud burst, but
not flowering
References
Chuine, I. and P. Cour. 1999. Climatic determinants of budburst seasonality in four temperate-zone tree species. New
Phytol 143: 339-349
Fracheboud, Y., V. Luquez, L. Bjorken, A. Sjodin, H. Tuominen and S. Jansson. 2009. The Control of Autumn
Senescence in European Aspen. Plant Physiology 149: 1982-1991
Heide, O.M. 2003. High Autumn temperature delay spring bud burst in boreal trees, counterbalancing the effect of
climatic warming. Tree Physiology 23: 931-936
Hunter, F.H and M.J. Lechowicz. 1992. Predicting the timing of budburst in temperate trees. Journal of Applied
Ecology 29: 597-604
Grant, M.C. and J.B. Mitton. 1979. Elevation gradients in adult sex ratios and sexual differentiation in vegetative
growth rates of Populus tremuloides michx. Evolution 33(3): 914-918
Pop. E.W., S.F. Oberbauer, and G. Starr. 2000. Predicting vegetative bud break in two arctic deciduous shrub species,
Salix pulchra and Betula nana
Samish, R.M. 1954. Dormancy in woody plants. Annual Review of Plant Physiology 5: 183-204
Wyckoff, G.W. and J.C. Zasada. 2008. Woody Plant Seed Manual: Populus L. USDA FS Agricultural Handbook 727 –
The Woody Plant Seed Manual. http://www.nsl.fs.fed.us/nsl_wpsm.html Accessed Dec 31 2010