The role of environmental gradients in non‐native plant invasion into burnt areas of Yosemite National Park, California

Abstract

Fire is known to facilitate the invasion of many non‐native plant species, but how invasion into burnt areas varies along environmental gradients is not well‐understood. We used two pre‐existing data sets to analyse patterns of invasion by non‐native plant species into burnt areas along gradients of topography, soil and vegetation structure in Yosemite National Park, California, USA. A total of 46 non‐native species (all herbaceous) were recorded in the two data sets. They occurred in all seven of the major plant formations in the park, but were least common in subalpine and upper montane conifer forests. There was no significant difference in species richness or cover of non‐natives between burnt and unburnt areas for either data set, and environmental gradients had a stronger effect on patterns of non‐native species distribution, abundance and species composition than burning. Cover and species richness of non‐natives had significant positive correlations with slope (steepness) and herbaceous cover, while species richness had significant negative correlations with elevation, the number of years post‐burn, and cover of woody vegetation. Non‐native species comprised a relatively minor component of the vegetation in both burnt and unburnt areas in Yosemite (percentage species = 4%, mean cover < 6.0%), and those species that did occur in burnt areas tended not to persist over time. The results indicate that in many western montane ecosystems, fire alone will not necessarily result in increased rates of invasion into burnt areas. However, it would be premature to conclude that non‐native species could not affect post‐fire succession patterns in these systems. Short fire‐return intervals and high fire severity coupled with increased propagule pressure from areas used heavily by humans could still lead to high rates of invasion, establishment and spread even in highly protected areas such as Yosemite.

Impacts of mixed severity wildfire on exotic plants in a Colorado ponderosa pine–Douglas-fir forest

“…Exotics repeatedly have been found to be least stimulated in lightly burned forests where overstory tree mortality and forest floor consumption are minimal, and most stimulated in severely burned forests where tree crowns and forest floor are largely consumed (Crawford et al 2001;Freeman et al 2007;Hunter et al 2006). The response of exotic plants after fire also often varies with time since fire (Klinger et al 2006;Koniak 1985;Nelson et al 2008). Additionally, there can be a significant interaction between fire severity and time since fire, as found by Keeley et al (2003).…”

Do Wildfires Promote Woody Species Invasion in a Fire-Adapted Ecosystem? Post-fire Resprouting of Native and Non-native Woody Plants in Central Argentina

“…To reduce reinvasion these strategies must be accompanied with education programs for promoting the use of native plants in urbanizations, roadsides and other human modified sites (Brooks 2008;Stone 2009). Finally, the prevention of invasion is always the best strategy, since control and eradication are costly and may never be complete (Klinger et al 2000).…”

Natural and cultural history of beargrass (<em>Xerophyllum tenax</em>)

“…High-elevation sites are relatively protected from invasive species owing to (1) minimal human activity and limited potential for propagule spread by humans, and (2) harsh climates and environmental conditions correlated with elevation, such as reduced moisture, low temperatures, and short growing seasons (Klinger et al 2006(Klinger et al , 2008Randall et al 1998). According to a recent evaluation by Anzinger and Radosevich (2008) …”