Tree Advancement Patterns

TREELINE ADVANCE PATTERNS OF ALASKAN WHITE SPRUCETREELINE ADVANCE PATTERNS OF ALASKAN WHITE SPRUCE
Keena Auld, Kenneth Chadwell, Turner Glasgow, David Cairns, and Keith Gaddis
Texas A&M University Department of Geography, College Station, Texas
Is P. glauca treeline advancing?
Question
Hypothesis
1. If treeline is advancing, trees
establishment date will decrease (become
more recent) as elevation increases
2. If treeline advance is not occurring, then
there will be no relationship between
elevation and tree establishment date
Methods
Lab Methods
In the fall of 2015, we
measured the
establishment date of
each tree by counting
the tree rings on
extracted tree cores.
Abstract
Many recent studies have indicated altitudinal
treeline advance throughout the world due to global
climatic changes. These advances have major
implications for the assembly and survival of
species throughout the world that may become
marginalized as their habitat is destroyed by this
advance. Given this fact, we set out to examine
treeline advance patterns in the dominant North
American treeline forming species, white spruce
(Picea glauca) throughout south-central Alaska.
We examined Dendrochronological data rom 17
sites and have found a variable arrangement of
treeline pattern across the study area with some
sites showing a clear pattern of advance and others
maintaining stabile over the recent past.
Background
Treeline is an ecotone
where the forest biome
transitions to a tundra at
the highest elevation point
where trees can grow
Changes in climate have a
direct link the global treeline
position. Long winters limit
establishment of seeds and
permafrost prevents deep roots
from penetrating the soil. As
global climates have warmed,
forest biomes have began to
encroach on that of the tundra
leading to treeline advance.
Study System
White spruce (Picea glauca) is
native to the boreal forest of
North America. It has
evergreen needles
accompanied by narrow,
oblong cones. The species
disperses through seeds or
layering (where lower branches
take root to form new trunks
that later separate from the
maternal tree forming a clone).
The area used in this study was south-
central Alaska. The climate of region is
subarctic with temperatures averaging -12
to 18 ˚C throughout the year. Climatic data
has indicated a warming trend in this area.
This region is heavily forested, with high
mountainous terrain.
Results Conclusion
Treelines are advancing
• 5/17 show definite treeline advance
• 3-6 sites show younger trees at treeline
• Recent advance over a short spatial scale
Topography determines advance
• The correlation between tree age and
distance from treeline was explained by
the slope at the sample site.
• Low sloped sites have greater treeline
advance rates.
Acknowledgements
Future Work
How does climate influence advance?
• We will determine if contemporary climate
to influence advance rates.
• We will use climate modelling to identify if
areas with greatest climatic change have
experienced greater advance.
• We will analyze additional topographic
variables (slope, aspect, curvature)
How do dispersal and reproduction
affect influence treeline advance?
• We will relate this work to our existing
analysis of dispersal and reproductive
pattern using genetics.
Treeline Advance
Infilling
No Pattern
We would like to thank Rachel Clausing, Zac
Harlow, and Michelle Lee for tireless field collection.
Clint Magill provided guidance and laboratory
resources to conduct genetic work. Parveen Chhetri
assisted in lab work and analysis.
1840
1860
1880
1900
1920
1940
1960
1980
2000
2020
0 100 200 300 400 500 600
EstablishmentYear
Distance From Treeline (m)
Site 16 P-value > 0.05
1900
1920
1940
1960
1980
2000
2020
2040
0 100 200 300 400 500 600
EstablishmentYear
1750
1800
1850
1900
1950
2000
2050
0 100 200 300 400 500 600
EstablishmentYear
1900
1920
1940
1960
1980
2000
2020
2040
0 100 200 300 400 500 600
EstablishmentYear
1750
1800
1850
1900
1950
2000
2050
0 100 200 300 400 500 600
EstablishmentYear
1750
1800
1850
1900
1950
2000
2050
0 100 200 300 400 500 600
EstablishmentYear
Site 33 Adjusted R-squred: 0.08
P-value < 0.05
1450
1550
1650
1750
1850
1950
2050
0 100 200 300 400 500 600
EstablishmentYear
1860
1880
1900
1920
1940
1960
1980
2000
2020
2040
0 100 200 300 400 500 600
EstablishmentYear
P-value < 0.001
1650
1700
1750
1800
1850
1900
1950
2000
2050
0 100 200 300 400 500 600
EstablishmentYear
P-value < 0.05
1850
1900
1950
2000
2050
0 100 200 300 400 500 600
EStablishmentYear
1850
1900
1950
2000
2050
0 100 200 300 400 500 600
EstablishmentYear
1650
1700
1750
1800
1850
1900
1950
2000
2050
0 100 200 300 400 500 600
EstablishmentYear
1900
1920
1940
1960
1980
2000
2020
2040
0 100 200 300 400 500 600
EstablishmentYear
P-value < 0.001
1800
1850
1900
1950
2000
2050
0 100 200 300 400 500 600
EstablishmnetYear
P-value < 0.001
1860
1880
1900
1920
1940
1960
1980
2000
2020
2040
0 100 200 300 400 500 600
EstablishmentYear
1800
1850
1900
1950
2000
2050
0 100 200 300 400 500 600
EstablishmentYear
P-value < 0.001
1650
1700
1750
1800
1850
1900
1950
2000
2050
0 100 200 300 400 500 600
EstablishmentYear
Field Methods
In the summer of 2015,
we sampled cores from
trees spaced on 500 m
transects parallel and
perpendicular to
treeline. Five trees were
sampled every 50 m.
We collected a total of
1,870 white spruce tree
cores across 17 sites.
Analysis
We used linear regression to
examine the age of trees
relative to the distance from
treeline. An additional analysis
examining topographic effects
was conducted using logistic
regression
y = 0.0569ln(x) + 0.0805
R² = 0.3586
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
CorrelationCoefficient(r)
Slope of Sample Site
Does topography influence treeline advance ?
We conducted a
preliminary analysis
to examine
topographic effects
(slope at each
sample site) on
treeline advance,
using a logistic
regression.

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