Patch dynamics of a native grass in relation to the spread of invasive smooth brome (Bromus inermis)

Abstract

The effects of invasive species on the patch dynamics (establishment, growth, and local extinction) of native species are not well studied, owing to the need for relatively fine-scale data on the distribution of species. Within the prairie pothole region of the United States and Canada, the grass, Bromus inermis (smooth brome) has become established by invading disturbed prairies, and through repeated introductions for soil retention and animal graze. In this study, the impact of smooth brome on the patch dynamics of a dominant native grass species, Spartina pectinata (prairie cordgrass), was assessed using fine-scale (sub-meter) mapping of the distribution of cordgrass and brome in three prairie fragments from 2000 to 2006. Using GIS spatial analyses, we determined that cordgrass patch growth was two times greater in areas not invaded by smooth brome versus areas that were heavily infested with smooth brome. Among sites and time periods, there was a consistent significant negative relationship between the amount of smooth brome surrounding a patch of cordgrass and the growth of that cordgrass patch. The probability of establishment of a new patch of cordgrass averaged 1.3 times higher in areas of low brome coverage (\25%) than areas of high brome coverage ([75%).Conversely, existing cordgrass patches were 7.8 times more likely to go extinct in areas of high than low brome coverage. This is one of only a few field studies to provide evidence of the negative impact of smooth brome on native flora and hopefully will serve as justification for the development of a formal management plan to limit the distribution of this species in tallgrass prairie ecosystems.

Effects of exotic grass invasion on spatial heterogeneity in the ground-layer of grassy woodlands

“…This was because the exotic forbs were arranged in a similar way to the exotic grasses, generally being smaller and closer together, and with less variation than the native forbs. These kinds of changes in structural heterogeneity in the presence of invasive grass species have rarely been quantified (Dillemuth et al 2009), particularly with regards to the magnitude or scale of the change. Fig.…”

“…EAGs are more likely to outcompete the native grasses when soil nutrients are elevated (Groves et al 2003), which is often the case for woodlands which have been grazed by livestock in the past (Lindsay et al 2010). Just as the invasive Bromus inermis (smooth brome) is detrimental to the patch dynamics of Spartina pectinata (prairie cordgrass) grasslands in North Dakota (Dillemuth et al 2009), it is likely this assemblage of EAGs are detrimental for the recruitment, survival, growth of native plant species. The uninvaded woodlands contained a range of gap sizes, and as is typical, grasses only occupied 30-50% of the ground cover (Lunt et al 1998).…”

“…Chrysanthemoides monilifera (French et al 2008)) on the local vegetation might be more visually obvious than if the invader is a annual grass or forb. Grassy ecosystems can have great spatial and temporal heterogeneity at a fine scale (sub-meter), and so the interaction between exotic and native plants may occur at a similarly fine spatial scale (Dillemuth et al 2009;Theoharides and Dukes 2007). Exotic plant invasions which alter the ground layer vegetation structure and lead to loss of heterogeneity could have impacts on many aspects of grassy ecosystems, and this is the focus of this study.…”

“…Exotic plant invasions may make the vegetation structure more homogeneous (Gentle and Duggin 1997;Gordon 1998;Parker 2000), but this is rarely quantified, especially for grass dominated systems (Dillemuth et al 2009). In this paper we examine the effects of exotic annual plant invasion on the woodland ground-layer.…”

Influence of Richness and Seeding Density on Invasion Resistance in Experimental Tallgrass Prairie Restorations

“…These species were selected because they are aggressive and commonly encountered in Nebraska grassland restorations. All are undesirable in natural areas because they can become widespread and reduce the cover and growth of native plant species (Forcella and Randall 1994, Wolf et al 2003, Vinton and Goergen 2006, Otfinowski et al 2009, Dillemuth et al 2009, Van Riper and Larson 2009. In addition, the sharp spines of bull thistle can interfere with livestock grazing (Forcella and Wood 1986) and sweet clover may facilitate the growth of other invasive plant species (Wolf et al 2003, Van Riper andLarson 2009).…”