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How will climate change effect the distribution and competitive performance of Centaurea maculosa and Linaria vulgaris in south interior grasslands?
Greenall, Amber
Global warming has been underway for approximately one hundred years[2,14]. It is expected that additional warming will occur at a more rapid rate due to continuing increases in greenhouse gas concentrations in the atmosphere[6,16]. Models run through the Canadian Institute for Climate Studies at UVIC ( predict that by the year 2100 the southern interior of BC will experience an increase of as high as 7 oC, accompanied by a 25% reduction of precipitation during the summer months and a 25% increase during the winter months. During the past several decades, some terrestrial plant populations apparently extended their ranges toward the poles or to higher elevation[12]. Increased extent and abundance of shrubs in Alaskan tundra[15] may be an important example because warming in Alaska has been greater than in other parts of the continent. Phenologies of plants have also changed in some cases, with earlier-spring plant leaf expansion and flowering[12,13]. Earlier occurrence of spring biological events (and later occurrence of some autumnal events) is consistent with expected effects of warming on biological processes. While it is clear that warming has caused some changes in the seasonal timing of biological events and processes, observed increases or decreases in abundance of plant species at any particular location might be confounded by factors other than temperature change, even if the observed increase or decrease appears correlated with temperature change. Factors such as human land-use change, introduction and spread of exotic species, changes in pathogen abundance or distribution, and natural variability in the abundance and geographic distribution of plants could all be causally related to observed changes in abundance or geographic distribution of plants. It is important to be able to distinguish effects of climatic change from these other factors. A continuing FSP project proposal (Y092208: Managing the interacting effect of grazing and global climate change in BC interior rangelands) is designed to disentangle the effects of temperature, precipitation, and grazing on native grasslands, but does not investigate non-native invasive plants. In the project we propose here, we are particularly interested in understanding the dynamics of exotic plant species in BC Southern Interior rangelands. Human land management has been shown to affect the spread of non-native, invasive plants[10]. Research has been conducted on the link between species richness and invisibility[9], functional niche theory[4], and underground interactions[5]. Global climate change may further compound the spread and dominance of non-native invasives. Spotted Knapweed (Centaurea maculosa) and Yellow Toadflax (Linaria vulgaris) are two grassland invaders which are currently reducing native plant diversity and limiting forage productivity of BC?s grasslands. Although there is niche overlap between these two species, Spotted Knapweed tends to be found on dry hillsides while Yellow Toadflax more commonly occurs on moist soils that are found in draws and roadside ditches[11]. We wish to know the effect future climate change has on the potential distribution and competitive performance of these two species relative to two important forage grasses: Bluebunch Wheatgrass (Pseudoroegneria spicata) and Needle-and-Thread Grass (Hesperostipa comata). Competitive interactions between Spotted Knapweed and native grasses have been determined under current conditions and are species specific[5]. Spotted Knapweed was found to be competitively superior to Bluebunch Wheatgrass[1]; in part, because Spotted Knapweed possesses a long tap root that can access water sources unavailable to fibrous-rooted grasses. Toadflax also has a deep root system. This differentiation between rooting systems may play out in two different ways with predicted future climate: (i) native grasses may be better able to take up the limited
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Final technical report

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