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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. à Atmospheric wet and dry nitrogen deposition Acid rain Increase in ozone (O3) Temperature: global patterns à 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 2 à Climate Change in Interior Alaska à 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 à à 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 3 à Example 1: Range expansion of native species into adjacent habitat types à 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 à Effects of temperature on herbivores à • 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 4 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) 5 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 6 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 7 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 8 » » 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 9 » » 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 7 7 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. 10 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 11 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. 12