LINK-1: Fire-plant invasions
Title: Fire as a positive feedback to plant invasion in the western U.S. and the southern hemisphere
Students: Taylor (PhD MSU)
The project is currently under design but will primarily be a Ph.D. dissertation. We will focus on two target species: Pinus contorta (lodgepole pine) in native and non-native ecosystems in the western U.S., New Zealand, Chile, and possibly Argentina, and Bromus tectorum (downy brome) a non-native invasive plant in the western U.S. WildFIRE PIRE will support the Pinus study, and a grant from Department of Energy will support ongoing study of Bromus. Data sets on P. contorta demography and expansion exist in Chile and New Zealand, and there may be the potential to develop a new data set in Argentina. Collaborators have been identified, but specific agreements are still under development. Based on draft research designs, fieldwork will be initiated in the Greater Yellowstone Ecosystem (GYE) in late May 2011. We plan to conduct foreign data collection in Year 2 and 3 (2012 and 2013).
Pines show similar invasion processes all over the world involving two main stages: (a) immigration and establishment, and (b) population growth/expansion (Richardson et al. 1994). Dispersal and establishment are widely variable among species and sites and can be promoted or discouraged by the interaction among factors. Pinus contorta invasion in South America occur in anthropogenic-created plant communities dominated by non-native forage grasses, in native shrub and grass-dominated steppe and in native forests (Langdon et al. 2010). New Zealand pine invasions have primarily occurred in antropogenic-created grasslands (Ledgard 2001) P. contorta has not been observed to invade native shrub-grass steppe or anthropogenic pastures in North America without significant disturbance including fire. The contrast between the Northern and Southern Hemisphere behavior of this species is a compelling component of the research. Fire-adapted species invading into systems that are not fire-adapted can create a novel system and possible positive feedbacks causing new successional trajectories.
Bromus tectorum is even more implicated than pines for creating positive feedback with wildfire leading to transformation of invaded communities (Knapp 1996). However, there is little empirical evidence for this hypothesis and a potential linkage with climate. The study of downy brome invasion and resulting wildfire dynamics in degraded sites has been the focus of several studies, but understanding the response to wildfires in more natural areas has not been addressed (Rew and Johnson, 2010). Existing studies on downy brome dynamics to wildfire have shown variable responses, perhaps as a result of different land-use and disturbance histories as well as climate change (Menakis et al. 2003). Increasing winter temperatures allows greater winter annual species like B. tectorum to survive increasing densities and fire fuel loads by senescing at the time of the year when lightning strikes are at a maximum. This scenario can create a positive feedback increasing B. tectorum and fire frequency (U.S. Climate Change Science Program Synthesis and Assessment Product, 2008).
Objectives: Develop a landscape invasion model for Pinus contorta in the northern GYE and one or more of the following countries: Argentina (Martín Nuñez), Chile (Anibal Pauchard) and New Zealand (Nicholas Ledgard). Compare the invasions and variables driving invasion from where the species is native (northern GYE) to where it is an invader in the Southern Hemisphere. The drivers of invasion that are of interest are: fire, climate, land use (grazing) and edaphic features.
- Develop an invasion model for Bromus tectorum in the North American sagebrush steppe that specifically determines under what conditions (climate and land use history) a positive feedback may occur between B. tectorum invasion and wildfire. Invasion models would be developed in the INL of Idaho and then tested for possible application in Argentina, Chile or New Zealand. The activities described in Syn-2 linking fire models, fuels, and climate change will be critical for this project.
Workplan: The project requires additional overseas field visits to set up. In Year 2, Maxwell and Taylor will spend 16 days in Chile with Pauchard visiting field sites and making measurements. Maxwell will also go to NZ to meet with Ledgard and colleagues at Landcare to assess their interest in collaboration.
In summers of 2012-2013, field collections will be undertaken in the GYE. We will run vegetation survey transects following methodology described by Rew et al. (2005) to identify variables driving probability of occurrence of the target species. In addition, we will use P. contorta aged tree and dead tree distributions to reconstruct the invasion and estimate colonization and extinction rates using Occupancy Modeling (MacKensie et al. 2005). The same type of sampling and analysis will be conducted for B. tectorum by repeating transects already established as part of a DOE project at INL. PIRE supports this effort by covering Taylor’s salary and hiring an undergraduate who will later become and overseas PIRE intern. Every effort will be made to recruit a student intern from one of the tribal colleges.
The research will link with existing projects on invasive species in the northern range of Yellowstone National Park and Paradise Valley in collaboration with Dr. Lisa Rew (MSU). The location of the research will also coincide with site locations for PIRE US-3 (RM lower treeline) and possibly PIRE US-2 (RM CO/YNP). Locations for field work in South America or New Zealand will also attempt to coincide with existing and past work by Wildfire PIRE associates, including PIRE NZ-3 (Fire-beech dynamics).
Ongoing research on pine invasions in South America by Pauchard and Nuñez relate closely to the objectives, and Pauchard has agreed to collaborate on the project as it has been presented in preliminary form. The work on pines will be specific to Wildfire PIRE.
The research on B. tectorum is in association with a DOE-funded project at the Idaho National Lab (Rew and Maxwell, 2009-2011). Four undergraduate students have been hired to assist with fieldwork at the INL for the 2011 field season, with DOE funds. A large wildfire in June 2010 covering approximately half of our previously monitored plots provides an excellent opportunity to observe responses in the years following fire. Four undergraduate students have been hired to assist with fieldwork at the INL for the 2011 field season, with DOE funds.
Year 2 Update:
This project looks at the impact of non-native plant invasions on natural fire regimes, and it is an important part of the PIRE project in understanding altered fire regimes in the face of humans and climate. The study focuses on lodgepole pine (Pinus contorta) both in its natural setting and as an invasive species in New Zealand and Patagonia. It also looks at the influence of cheatgrass (Bromus tectorum) on natural fire regimes in the western U.S.
During the fall 2011, sites were selected to examine the factors driving pine invasion (or lack of invasion) into meadows in the Greater Yellowstone Ecosystem. Seedlings that were naturally invading the meadow were tagged and measured. A matching number of seedlings in the surrounding forest were randomly selected, tagged and measured, which resulted in 20-60 seedlings per site. Data on neighborhood vegetation and environmental factors around each seedling were recorded. Additionally, in each meadow 20-m-long transects were laid out beginning 10 m into the forest and continuing 10 m into the meadow. At specified points along the transect (10 m into forest, 5 m into forest, edge, 5 m into meadow and 10 m into meadow), 0.75 m x 0.75 m plots were established and 10 local lodgepole pine seeds were planted in each plot in September 2011. Each plot randomly received one of three treatments: disturbed (to mimic local animal activity), caged (to prevent seed predation) and control.
Maxwell and MSU PhD student Taylor travelled to Coyhaique, Chile in January to investigate lodgepole pine invasions with the help of Chilean collaborator Anibal Pauchard. Two sites were selected where P. contorta has been invading the vegetation surrounding P. contorta plantations for the past 15 years. At each site, transects were randomly delineated along which 10 m x 10 m plots were set up. Where possible the plots were continuous and covered the entire transect. Where lodgepole pine was very dense (50-600 trees per plot), five plots were randomly selected within every 100 m section of the transects. In each plot, the height and basal diameter of every lodgepole pine was measured and the number of cones and signs of herbivory were recorded. Off transect, trees were cored or destructively sampled (if too small to core) and the rings counted to determine age and create an age-height-diameter relationship. Pauchard will be visiting the Maxwell Lab in June to continue this research, supported by NSF EPSCoR funds.
In March, Maxwell travelled to the South Island of New Zealand and established collaborative research on lodgepole pine invasions with Drs. Duane Peltzer, Ian Dickie and Nicholas Ledgard. Three field sites were selected for Kim Taylor’s PhD research to serve as comparisons with the Montana (USA) and Chile sites. The New Zealand research will be undertaken in Year 3. In May and June 2012 Kim Taylor is making observations/measurements on her Montana field studies. In the laboratory, Taylor and Maxwell have begun work on constructing an invasion simulation model that will allow investigation of the relative importance of different factors that might be driving the rate of invasions at different sites.
Approximately two weeks were spent at the Idaho National Laboratory in July 2011 collecting data on cheatgrass and other vegetation cover in plots set up along a chronosequence of time since fire. Plots were investigated in sites that burned 1, 3, 4, 11 and 15 years ago, as well as in sites that have not burned recently.