Impacts of restoration treatments on alien plant invasion in Pinus ponderosa forests, Montana, USA

Abstract

Summary 1.Invasion by alien plant species represents a challenge to land managers throughout the world as they attempt to restore frequent fire-adapted ecosystems following decades of fire exclusion. In ponderosa pine Pinus ponderosa forests of western North America, the response of alien species to restoration treatments has not been well documented, particularly for alien species capable of altering environmental conditions (transformers). Understanding alien species dynamics is critical for developing treatments that accomplish restoration goals while minimizing alien invasion. 2. We used a replicated, randomized block experiment to compare the effects of an untreated control and thin-only, burn-only and thin-burn treatments on alien and transformer understorey species at multiple spatial scales (1 m 2 , 100 m 2 and 1000 m 2 ). Data were collected pre-treatment and for multiple post-treatment years. We compared richness and cover of alien species and transformer species among treatments, and identified environmental variables correlated with transformer species cover. Indicator species analysis was used to identify transformer species associated with specific treatments. 3. Alien and transformer species richness and cover were significantly higher in the thin-burn than in all other treatments at all spatial scales. Thin-only and burn-only treatments showed greater alien and transformer species responses than the control at the larger 100-m 2 and 1000-m 2 scales. 4. Increased transformer cover was strongly correlated with increased tree crown scorch height and removal of overstorey trees. 5. The thin-burn treatment had four transformer species as indicators, the thin-only had one, while the burn-only and control had none. 6. Synthesis and applications . The results show that alien species, including transformers, respond to restoration treatments, especially the combined thin-burn treatment. Therefore monitoring for alien species invasion is an essential component of a restoration programme. Abundance of transformer species increased with increasing disturbance intensity, suggesting that less intense single-disturbance treatments (burnonly, thin-only) or incremental treatments may be preferred in some applications. Where more intense treatments are required to meet management objectives, specific strategies, such as seeding of native species, limiting grazing before and after treatment and harvesting over a protective winter snowpack, may be necessary to limit alien invasion.

The national Fire and Fire Surrogate study: effects of fuel reduction methods on forest vegetation structure and fuels

“…Alien species often respond to the severity of disturbance (Keeley et al 2003, Dodson and Fiedler 2006, Kerns et al 2006, Collins et al 2007. Because of the added activity fuels, more fuel mass was consumed by burning in this treatment than in the burning-alone treatment.…”

Fire Probability, Fuel Treatment Effectiveness and Ecological Tradeoffs in Western U.S. Public Forests

“…For instance, non-native vegetation can be influenced by high fire severity [44] and some fuel treatments [10], especially if the treatments are repeated [9].…”

“…Assessing fire occurrence and its effect on fuel treatment effectiveness also has merit because treatments can incur ecological costs, including negative impacts on aquatic systems [8], soils [7], and invasion by non-native plants [9,10]. Here, we use watershed and aquatic systems as a specific context for evaluating tradeoffs involved with treatment and non-treatment of fuels on western public lands.…”

“…Repeated treatments increase the potential for cumulative effects on aquatic ecosystems due to the persistence and additive nature of watershed impacts over time [19] and may increase the establishment of non-native plants [9]. The chronic watershed impacts from repeated treatments may be more deleterious to native fish than pulsed disturbances from wildfires [8].…”

Non-indigenous species management using a population prioritization framework

“…Permanent monitoring plots must be established to track long-term changes in the dynamics of a population (Blossey 1999;Buckley et al 2003;Jacquemyn et al 2005;Dodson and Fiedler 2006). A method of quantifying NIS population invasiveness in terms of change in density and spatial extent, using data collected annually from permanent monitoring plots has been developed by Lehnhoff et al (2006).…”