Download Climate Change and Invasive Plants in Alaska

Climate Change and Invasive Plants (in Alaska)
Or: Do We Know Anything At All?
Christa Mulder
Institute of Arctic Biology and
Department of Biology and Wildlife
University of Alaska Fairbanks
Most introduced species don’t
become invasive!
• Examples:
– Australia: only 12% (in undisturbed habitats) to 25%
(in heavily disturbed habitats) of introduced species
became dominant
– Canadian forest communities: no exotics have
become dominant
• Why not?
Climate
change
effects
are likely to
be indirect
–
–
–
–
At limit of their physical tolerance
Insufficient resources (nutrients, water, light)
Competition with native plants
Lack of mutualists (pollinators, mycorrhizal partners,
seed dispersers)
– Impacts of herbivores and pathogens
1
Global change variables that may
affect invasive plants
1. ÃTemperature (minimum, maximum, mean)
2.
CO2 concentrations
3. » Precipitation (quantity and timing)
4.
5.
6.
7 Snow (quality, quantity, and timing)
Frequency and intensity of extreme events (e.g. hurricanes,
fires, ENSO)
UV-B radiation
Other anthropogenic effects:
1.
2.
3.
Ã
Atmospheric wet and dry nitrogen deposition
Acid rain
Increase in ozone (O3)
Temperature: global patterns
Ã
http://www.epa.gov/climatechange/science/recenttc.html
• Globally, surface temperatures have been increasing by
0.22°F (0.11°C) per decade between 1958 and 2006
• Minimum temperatures are rising faster than maximum
• Winter temperatures are rising faster than summer
• # days below freezing has greatly decreases
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Ã
Climate Change in Interior Alaska
Ã
Since 1960’s
3˚C increase in annual temperature
4.5˚C in winter (AK Regional Assessment Group)
Growing season: +2.6 days / decade
Leaf onset: -1.1 day/ decade (Keyser et al. 2002
Predicted by 2075
+0.75 to 2.5˚C in summer
+1.0 to 6.0˚C in winter
Ã
Ã
Example 2: Expansion of introduced species
in NW Europe
• Looked at Fallopia japonica
(Japanese knotwood, a perennial)
and Impatiens glandulifera
(Himalayan balsam, an annual)
• Tested whether temperature or
length of growing season mattered
for survival, growth, and
reproduction
• For F. japonica both minimum
temp and length of growing
season mattered (expansion from
63 ºN to 68 ºN under an increase
of 1.5 º C)
• For I. glandulifera only length of
growth season mattered
(expansion from 64 ºN to 69 ºN).
http://www.knottybits.com/isw/GiantKnotweedSeattle.jpg
http://f-lohmueller.de/botanic/Balsaminaceae/Impatiens/imgf04051.jpg
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Ã
Example 1: Range expansion of native species
into adjacent habitat types
Ã
Shrub expansion into tundra in Alaska (photo from Tape et al. 2006) and the Yukon (photo from http://www.ualberta.ca/~myerssmi/home_files/Research_files/image002.jpg)
• Shrub expansion is currently occurring in Alaska
and Yukon tundra
• Presence of shrubs results in a positive feedback loop through changes in albedo and snow
depth
Ã
Effects of temperature on
herbivores
Ã
• For insects, temperature
is probably more
important than other
aspects of climate
change
• Effects can be direct (e.g.
overwintering survival,
growth rate in summer) or
indirect (e.g. change in
host plant chemistry,
synchrony in phenology
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Impacts on herbivores: range
extension and phenology
• Overwintering survival is likely
to increase with temperature
• Growth in summer is likely to
increase (but so is drought
stress)
• Generally, insects ranges are
expected to expand northward
(in the N hemisphere)
• Studies in Norway and
Greenland have shown
increases in number of host
species due to changes in
phenology
http://www.mais-web.org/eco-mais/looking_for_insects_under_log.jpg
Photo: B. Roy
What does this mean for Alaska?
Aphids on fireweed
(Epilobium angustifolium)
• More herbivores may
hit native plants
harder than
introduced plants
because introduced
species are more
likely to have coexisted with these (or
similar) herbivores
elsewhere
Caterpillar damage on cranberry
(Vaccinium vitis-idaea)
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Outbreak species and disturbance:
spruce bark beetle on the Kenai
• Outbreaks of insects
on dominant tree
species cause a
major disturbance
• High light levels,
higher nutrient levels
etc. usually benefit
“weeds”, often
introduced species
Carbon dioxide (CO2)
CO2 concentrations have
increased globally:
• Pre-industrial CO2:
approx 270 ppm
• Rapid increases since
industrialization
• Currently approx. 380
ppm
• Expected to continue
increasing
http://environment.newscientist.com/data/images/ns/cms/dn11638/dn11638-2_640.jpg
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CO2 example 1: Centaurea solstitialis (yellow
starthistle) in Californian serpentine grassland
• Mediterranean, deep-rooted
annual that flowers after most
native species
• Lower transpiration rates under
higher [CO2] results in higher
late-season water
• Higher net mineralization
under leads to greater N
availability
• In greenhouse experiments,
yellow starthistle benefits from
greater CO2
• (Additional factor: increased N
deposition)
http://commons.wikimedia.org/wiki/Image:Yellow_star_thistle.jpg
http://www.elkhornsloughctp.org/uploads/1114451899VulpiaMicrostachysCoyoteRid.jpg
Ex. 2: Acacia nilotica (prickly
acacia) in Australia
• Highly invasive woody
legume
• Changes ecosystems by
adding N
• Increased [CO2] is likely
to lead to greater water
use efficiency (WUE)
• Bioclimatic models
suggest even a small
increase in WUE could
allow it to invade drier
habitats than it currently
can.
http://www.worldwidewattle.com/images/nilotica.jpg
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Ex. 3: Increased [CO2] can affect
plant defenses against herbivores
In two species of birch (in
North America and
Finland), herbivory by
hares or rabbits
decreased under higher
[CO2]
In general, plants that
defend themselves using
carbon-rich compounds
(e.g. phenolics) may
benefit from increase CO2
http://www.dgsgardening.btinternet.co.uk/rabbit1.jpg
http://forest.mtu.edu/kidscorner/ecosystems/images/birchtrail.jpg
http://www.marietta.edu/~biol/biomes/images/
taiga/snowshoe_hare_1298.jpg
http://www.bbc.co.uk/cumbria/content/images/2007/03/12/silver_birch_353x470.jpg
What does this mean for Alaska?
We don’t really know, because no one has
studied it, but..
• In habitats where water is limiting, it could
give an edge to faster-growing introduced
species
• Whether indirect impacts via changes in
host chemistry are positive or negative
may depend on both the invasive plants
and the native competitors
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»
»
Precipitation in Alaska
• Much more difficult to predict:
– Overall, precipitation in Alaska increased by
30% between 1968 and 1990
– Models differ in their predictions into the
future and include both decreases (in early
summer) and increases (all summer or in late
summer)
– For plants, the combination of temperature
and precipitation determines water availability
»
»
Precipitation
• Lots of studies have shown the
impact of precipitation on
invasive plants
• Examples:
– June precipitation and growth
in Alliaria petiolata (mustard
garlic)
– Pennisetum setaceum
(fountaingrass) is much more
invasive in Hawai’i than in
Arizona and Southern
California, likely due to
precipitation
– In China, expansion of
Eupatorium adenophorum
(Crofton weed) can be
explained by precipitation in
the coldest quarter
http://www.uaf.edu/ces/cnipm/images/Allaria_petiolata.jpg . Photo John Meade
http://hbs.bishopmuseum.org/good-bad/fountaingrass.jpg
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»
»
Shifts in precipitation events
• Dispersal of Mimulus guttatus
(monkey flower) in Northern
Europe: increased by shortterm high-flow events (flood
pulses)
• Increased growth and
reproduction of Phragmites
australis in coastal brackish
saltmarshes of New England in
high-precipitation El Nino
years.
• Phenology of plants may be
affected by precipitation: early
flowering in Lythrum salicaria
L. in Ontario in years with
ENSO events (warm spring but
low precipitation)
http://upload.wikimedia.org/wikipedia/commons/thumb/8/8c
/Mimulus_guttatus_flower_2003-03-13.jpg. Photo by Curtis Clark
http://www.botgard.ucla.edu/html/botanytextbooks/worldvegetation/marinewetlands/images/marinewetlands/saltmarsh/Phragmites3.jpg
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Snow depth and snow melt
• Greater snow depth should lead to greater
insulation (warmer soils)
– Potentially advantageous to invasives
• Early snow melt may lead to more freethaw events at a time when plants are
vulnerable (flower buds already produced)
– Effects on invasives???
• Overall effect on plants is likely to be
highly species dependent.
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7
7
Snow depth and invasives
Experimental research
on snow depth and
invasives:
NON-EXISTANT???
http://instaar.colorado.edu/tundracam/img_gallery3/snow_fence_in_action.jpg
Extreme Events
• Extreme events of many
kinds are predicted to
increase with climate
change
• This includes more
frequent or larger
hurricanes, floods, fires,
droughts, ENSO
• These represent
disturbances, from which
invasives usually benefit
• Ex: high-flow events and
Mimulus guttatus
http://coastal.er.usgs.gov/hurricanes/rita/images/hurricane-ritaLG.jpg
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Extreme events and feedback loops via invasives:
Example 2: fire
• In habitats in which
invasives are MORE
flammable than the
natives, there may be a
POSITIVE feedback loop
• In habitats in which
invasives are LESS
flammable than the
natives, there may be a
NEGATIVE feedback
loop
+
invasives
+
+
invasives
http://www.savanna.org.au/all/images/Woody-weed-fire.gif
Conclusions
1)
We lack information on most impacts of climate change in Alaska
to make decent predictions! Specifically we could use information
on:
•
•
Impacts of CO2 concentrations
Impacts of snow depth and timing of snow melt
2) What information we do have suggests climate change will generally
benefit invasives and increase their rate of spread
–
–
–
Increased temperatures: impacts on plants and herbivores
Impacts of insect outbreak events on the plant community
Disturbance due to extreme events
3) We really need to know more about the biotic factors that affect
invasives, particularly those that prevent them from becoming
dominant.
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