Academic journal article The American Midland Naturalist

Effect of Nitrogen, Water and Neighbors on the Growth of Hesperis Matronalis in a Natural Community

Academic journal article The American Midland Naturalist

Effect of Nitrogen, Water and Neighbors on the Growth of Hesperis Matronalis in a Natural Community

Article excerpt

ABSTRACT.-

Disturbances may add or remove resources from communities and can facilitate the spread of some invaders. Differential successes of exotic plants to spread into different communities suggest that some habitats are more invasible than others. Hesperis matronalis (dame's rocket) is widespread across the continent and has potential to become a major problem in natural communities owing to its ability to exploit excess resources and its negative effect on native species. We grew H. matronalis seedlings in a Colorado foothill community at various levels of nitrogen and water with and without neighbors. We expected H. matronalis to maximize its growth under high resource conditions especially without neighbors because ruderal species are able to take advantage of excess resources. Our results reveal that presence or absence of neighbors was the main decisive factor for H. matronalis (aboveground biomass and relative growth rate) success, though seedlings particularly suffered under low resource conditions. Early determination of the potential invasiveness of a widespread exotic species such as H. matronalis in natural communities may promote effective management.

INTRODUCTION

Differential successes of exotic plants in spreading into various communities suggest that some habitats are more invasible than others (Lonsdsale, 1999; Stohlgren et al., 1999; Von Holle, 2005). Disturbance, resource availability, evolutionary history, propagule pressure, predation, mutualism and competition are examples of factors that may explain these differences (D'Antonio et al., 1998; Crawley et al., 1999; Kolb et al., 2002; Von Holle and Simberloff, 2005). Because these factors interact with each other and with the characteristics of individual species (Crawley et al, 1999; Richardson et al, 2000), pinpointing the causes of invasibility in individual cases is often difficult.

Disturbances are well-known catalysts of exotic species invasion, enriching or depriving disturbed communities of resources, thereby favoring the spread of some invaders (Hobbs and Huenneke, 1992; Burke and Grime, 1996). Experimental manipulations offer evidence that availability of resources can be an important determinant of invasibility by exotic plants (Lake and Leishman, 2005). Invasive exotic plant species may succeed in dominating new communities in part because they differ from native species in their resource use efficiency (Vitousek, 1990); many have the ability to respond quickly to increases in resource availability with rapid growth rates to outcompete native species (Grime, 1977; Davis, 2000). Greenhouse experiments have shown that high nutrient or water availability can increase the ability of exotic plant species to compete with native plant species (Wedin and Tilman, 1993; Claassen and Marler, 1998). Field experiments have shown interactive effects of resource availability and competition on invasibility (Burke and Grime, 1996; Thompson el al., 2001).

The relationship between species and resource availability differs among different systems, but invasion is typically higher in high resource systems (Pugnaire and Luque, 2001). Briones et al. (1998) observed that competition was absent or very low in a semiarid system when water availability was low, but the intensity of competition was positively correlated with water availability. In resource-rich systems, competition for resources such as water may increase as resources decrease. For example, decreasing soil moisture availability can enhance the competitive suppression of an invader by native perennial grasses (Nernberg and Dale, 1997).

Water and biologically available nitrogen are important limiting factors of plant productivity in Colorado Front Range canyons. Estes Park, CO (40.38° latitude, 105.51° longitude, 2365 m elevation) receives an average of 356 mm in precipitation annually, but has within the last 30 y received as much as 559 mm in a single year (WRCC, 2001). …

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