Assessing wildfire burn susceptibility to invasive plant colonization in black spruce forests of interior Alaska University of Alaska Fairbanks Katie L. Villano

ACKNOWLEDGEMENTS Committee: Christa Mulder, Teresa Hollingsworth, Matt Carlson Funding Sources: Field and Research Support: Mulder Plant Ecology Lab, Boreal Ecology Cooperative Research Unit Joint Fire Science Project, Bonanza Creek LTER, Institute of Arctic Biology Greenhouse Lowell Award

DEFINITIONS Weed- Any undesirable plant Non-native, exotic, alien, non- indigenous plant- plant whose presence in an area is due to accidental or intentional introduction by humans Invasive species- Non-native species that produces large numbers of viable offspring and have potential to establish and spread in natural areas (AKEPIC 2005) Burn age- time elapsed since burn

BACKGROUND Climatic and dispersal constraints were thought to limit invasives in AK Increased human disturbance, primarily road construction and maintenance, has facilitated invasive species spread throughout the state. So far, Alaska’s invasive plants have largely been restricted to road corridors (Shephard 2004), but natural disturbances (burned areas and river floodplains) near roads allow invasives to penetrate pristine areas (Vitousek et al. 1996, Wurtz et al. 2006). Alaska is in the unique position to prevent backcountry spread. Invasion in Alaska “The greatest remaining wilderness in North America, and perhaps the world, is northern Alaska. In Alaska alone can the emotional values of the frontier be preserved” - George Marshall, Introduction to Alaskan Wilderness

Elevated Temperatures Increased fire frequency and extent Increased Human Population Decreased fuel moisture Increased drought stress-induced litterfall Increased human disturbance Increased propogule transport Warmer winters Longer growing season exposed mineral soil, decreased competition, increased nutrient availability Increased invasive plant success

Elevated Temperatures Increased fire frequency and extent Increased Human Population Increased human disturbance Increased propogule transport Invasive plant monitoring, education and management (ACNIPM, AKEPIC ) Native vegetation re-establishes quickly (Turner et al. 2003) Increased invasive plant success

Elevated Temperatures Increased fire frequency and extent Shift in ecosystem processes and community composition ( Vitousek 1986, Mack et al. 2001, etc) Increased Human Population Increased human disturbance Increased propogule transport New successional trajectory? Change in fuel properties causes positive feedback loop (D’Antonio and Vitousek 1992, Brooks 2002 ) Increased invasive plant success

BACKGROUND As of yet, only monitoring efforts have been made to quantify invasive species in burned areas in close proximity to road corridors (ACNIPM 2006). Until summer 2006, invasive plants had only been found in burns that overlap high human use areas. Current research: Heys, Allen and Mulder (NASA-NPS-UAF)- Forecasting invasive spread onto burned lands Cortes-Burns (ANHP) burn monitoring in National Wildlife Refuges Gronquist (BLM)- Highway surveys and management adjacent to burns Lapina (ANHP)- Highway surveys adjacent to burns Seefeldt (USDA)- Spatial spread from roadside into burns AK Fire-Invasive Research

OBJECTIVE Assess characteristics that may influence black spruce burn susceptibility to colonization by invasive plant species Research Questions: Are non-native plants already established within burns or on roadsides adjacent to burns along the highway system in interior Alaska? Does burn severity and soil moisture influence the success of invasive plant establishment? Does burn age influence the success of invasive plant establishment?

STUDY SITES 2004 Burns 3 High severity/high moisture sites 3 High severity/low moisture sites 3 Low severity/high moisture sites 3 Low severity/low moisture sites Chronosequence Burns 2 sites burned in sites burned in sites burned in 1987 Unburned Control Site

METHODS Question 1: Are non-native plants already established within burns or on roadsides adjacent to burns along the highway system in interior Alaska? 1 m 100 m Roadside Surveys -Cover estimate and stem count for all invasive species in 1 x 100 m belt transects Burn Surveys - Cover estimate and stem count for all invasive species in 30 x 30 m plots - GPS point and estimated distance from road for all sightings within burn but outside of plots

METHODS Questions 2 and 3: Does burn severity/ moisture and age influence the success of invasive plant establishment? Field Work Collected intact soil cores (in 30 x 30 m plot took three cores every 5 m along three transects) Measured moss, upper (Oi/Oe) and lower (Oa/A) duff layer thicknesses

METHODS Questions 2 and 3: Does burn severity/ moisture and age influence the success of invasive plant establishment? Greenhouse Work Sowed seeds of three species on core tops Two watering treatments (for low and high moisture site types) Harvested weeds at 1 month, 3 months, 5 months Estimated % cover of surface types and native vegetation on core top Determined water holding capacity and bulk density of each soil horizon

METHODS Invasive Non-Native Species FamilySpeciesCommon nameInvasiveness Ranking PoaceaeBromus inermis ssp. inermissmooth brome78 AsteraceaeHieracium aurantiacumorange hawkweed71 FabaceaeMelilotus albawhite sweetclover80 Table 1. Species invasiveness ranking according to the Alaska Natural Heritage Program’s Weed Ranking project based out of the University of Alaska Anchorage. A rank of 0 indicates no threat of rapid invasion of interior boreal forests, while a rank of 100 indicates extremely high threat of successful colonization. Bromus inermis ssp. inermisHieracium aurantiacumMelilotus alba

RESULTS Question 1: Are non-native plants already established within burns or on roadsides adjacent to burns along the highway system in interior Alaska? DC571994H DC56

Figure 1. Total number of sites along the Steese Hwy, Taylor Hwy, Dalton Hwy, and Delta Chronosequence where exotic plants were present on roadsides and within burns. Exotic plants were found in burns on the Dalton Highway and in the Delta Chronosequence older burns.

Overarching Question: Are black spruce forests more susceptible to invasion after fire? Figure 2. Percent invasive plant survival and proportion of plants reaching reproductive maturity. Data represents all species after 150 days growing in cores taken from burn sites of different age classes. Letters above bars indicate significant differences between treatments. In the greenhouse, invasive plants in burned soil cores showed higher survival than in unburned cores.

Question 2: Does burn severity and soil moisture influence the success of invasive plant establishment? Figure 3. Survivorship curves for three invasive plant species sown in soils taken from burns of different severities and moistures. No significant differences between invasive survival (or biomass) in different burn site types at any point in the experiment. Germination appears to be limiting stage in H. aurantiacum and B. inermis survival.

Question 2: Does burn severity and soil moisture influence the success of invasive plant establishment? Significant ANOVA model terms for final biomass: M. alba- none H. aurantiacum- highway B. inermis- highway moisture

Question 2: Does burn severity and soil moisture influence the success of invasive plant establishment? Figure 2. Percent invasive plant survival and proportion of plants reaching reproductive maturity. Data represents all species after 150 days growing in cores taken from burn sites on the Steese, Taylor and Dalton Highways. Letters above bars indicate significant differences between treatments. Overall invasive survival did not differ between highways. Final biomass and proportion of reproductive survivors significantly differ between highways.

Question 2: Does burn severity and soil moisture influence the success of invasive plant establishment? Stepwise model selection reveals potential mechanisms explaining variability at a finer scale B. inermis final biomass= (lower duff layer thickness) (WHC of mineral soil) (native vascular plant cover) (bryophyte biomass) H. aurantiacum final biomass= (native vascular plant height) (native richness) M. alba final biomass= (lower duff layer thickness)

Question 3: Does burn age influence the success of invasive plant establishment? In the field: 50% of older sites had invasives within the burn, while only 17% of 2004 burn sites had invasives within burn. Established populations and developed invasive seed bank in 1994 burn.

Both burn age and severity influence invasive plant establishment for all species in older burns. All invasive species do better in low severity cores. These data suggest increasing invasive establishment success through time. Question 3: Does burn age influence the success of invasive plant establishment? Back in the greenhouse:

SUMMARY Invaders are here. Invaders like burns. (particularly on the Dalton Highway, and in low severity older burns) Pre-fire soil conditions appear to be important factors in site invasibility after fire. Initial burn severity is likely to become increasingly important to invasive plant establishment and growth over time.

MANAGEMENT IMPLICATIONS Burned areas with both high propogule pressure and most suitable soils should take highest management priority (i.e. Dalton Highway). Invasive plant monitoring should not be restricted to recent burns. Black spruce burns yrs old are likely to be the most vulnerable to invasion.

COMMUNITY OUTREACH Collaborators- Chris Villano and Deana Martin-Muth, Denali Elementary Funding Partners- BECRU-Joint Fire Science Program Center for Global Change and Arctic System Research Schoolyard LTER (BNZ) Salcha-Delta Soil and Water Conservation District Invasive Plants of Alaska K-6 Curriculum Development Project