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 moistureIncreased 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)- 2004 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 1999 2 sites burned in 1994 2 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

Family Species Common name Invasiveness Ranking

Poaceae Bromus inermis ssp. inermis smooth brome 78

Asteraceae Hieracium aurantiacum orange hawkweed 71

Fabaceae Melilotus alba white sweetclover 80

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?DC57 1994H 1994H

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.

0

5

10

15

20

25

30

35

40

45

2 year old burns 7-19 year old burns Unburned

% s

urv

ival Unreproductive

Reproductive

a

a

b

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?

B. inermis

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

Low Severity/ High Moisture

Low Severity/ Low Moisture

High Severity/High Moisture

High Severity/ Low Moisture

Burn Type

log

to

tal

bio

mas

s (g

)

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?

0

5

10

15

20

25

30

35

40

Steese Taylor Dalton

% s

urv

ival

Unreproductive

Reproductive

b

ab

a

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= 0.017 +0.023 (lower duff layer thickness) +0.269 (WHC of mineral soil)

-0.00378 (native vascular plant cover) -0.06141 (bryophyte biomass)

H. aurantiacum final biomass= 0.370 -0.020 (native vascular plant height) -0.044 (native richness)

M. alba final biomass= -0.034 +0.033 (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 10-20 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 ProgramCenter 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