Forest Investment Account (FIA) - Forest Science Program
FIA Project Y091081

    How will climate change effect the distribution and competitive performance of Centaurea maculosa and Linaria vulgaris in south interior grasslands?
Project lead: Fraser, Lauchlan (Thompson Rivers University)
Contributing Authors: Greenall, Amber; Fraser, Lauchlan H.
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
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 summer precipitation by having their roots close to the surface; and, (ii) if the invasives are able to continually access a lower groundwater source they will have a competitive advantage over the fibrous-rooted native grasses. It is unclear how global climate change will influence timing and displacement of soil moisture and groundwater, but water limitation would appear to be a critical factor affecting future plant species distribution and abundance in BC grasslands. Therefore, we need to know how plant species will respond to different soil moisture levels. If Spotted Knapweed or Yellow Toadflax become increasingly aggressive, management can be advised to increase control measures.

The presence of these invasive species can alter the site level structure, diversity and habitat value of grassland ecosystems. Diverse grassland structure is replaced with monoculture stands and valuable habitat and food resources are lost. Knowing the response of invasive plants to future climate change scenarios will enable a better understanding of their potential change in range and distribution and their relative interaction with native grasses.

We propose to investigate the response of two invasive species (Spotted Knapweed and Yellow Toadflax) and two forage grasses (Bluebunch Wheatgrass and Needle and Thread Grass) to climate manipulations and competition across a soil moisture gradient. We will study plants’ growth and reproduction responses to soil moisture and competition in the field and in matching greenhouse experiments. Responses to soil moisture and competition in the field will be linked to individual plant traits in the greenhouse. This information will allow rangeland managers to predict the potential spread of Spotted Knapweed and Yellow Toadflax under future climate conditions.

We can therefore test the following hypotheses:
1) Spotted Knapweed is the best competitor under dry soil conditions. We predict that Spotted Knapweed will outperform native grasses and Yellow Toadflax under very dry soil conditions.
2) Yellow Toadflax is the best competitor under moist soil conditions. We predict that Yellow Toadflax will outperform native grasses and Spotted Knapweed under moist soil conditions.
3) The natural distribution and abundance of Spotted Knapweed and Yellow Toadflax will reflect soil moisture and soil nutrient levels in the field. Resent reports have shown that nitrogen may not be the only limiting nutrient in grasslands[7,8], and that competition for phosphorous might be increasingly important[3].

This proposal requests funds to expand an existing multiyear research project by Thompson Rivers University, and supported by FSP, to produce both empirical and practical results. The effects of climate change on competitive interactions of invasive plants will help us refine predictions regarding the future composition of grassland communities. The inclusion of invasive species will allow land managers to make informed decisions about resource allocations. The results will also contribute to the growing body of literature on Spotted Knapweed and the limited body of literature on Yellow Toadflax. Characteristics of the little studied IDF grasslands of the Cariboo will be quantified.

1. Blicker et al 2002 Plant and Soil 247:261-269.
2. Brohan et al 2006 J Geophysical Res 111:D12106.
3. Callaway & Aschehoug 2000 Science 290:521-523.
4. Dukes 2001 Oecologia 126:536-568.
5. Emery & Gross 2006 Oikos 115:549-558.
6. Greene et al 2006 J Climate 19:4326-43
7. Herron et al 2001 Rest. Ecol. 9:326-331.
8. LeJeune & Seastedt 2001 Cons. Biol. 15: 1568-1574.
9. Levine & D’Antonio 1999 Oikos 87:15-26.
10. Myers & Bazely 2003 Cambridge U Press.
11. Parish et al 1996 BC MoF and Lone Pine Pub.
12. Parmesan & Yohe 2003 Nature 421:37-42.
13. Root et al 2003 Nature 421:57-60.
14. Smith & Reynolds 2005 J. Climate 18:2021-36.
15. Tape et al 2006 Global Change Biol 12:686-702.
16. Tebaldi et al 2005 J Climate 18:1524-40.


Final technical report (0.1Mb)
Presentation (5.5Mb)

To view PDF documents you need Adobe Acrobat Reader, available free from the Adobe Web Site.

Updated August 16, 2010 

Search for other  FIA reports or other Ministry of Forests and Range publications.

Please direct questions or comments regarding publications to