Lab Report-Growth suppression of native grass species Pseudoroegneria spicata

Title and Lab Theme

Growth suppression of native grass species Pseudoroegneria spicata (Bluebunch wheatgrass) in response to changing distance between this native grass species and space invading species – Centaurea maculosa (Spotted Knapweed), Space invaders

Question Statement

If, and how competition between invading species and native plant species is affected by the distance between the two species?

Why is it important?

Fierce competition from invading plant species can lead to declines in abundances, and in many cases, cause localized extinctions of native plant species in a region. However, some native plant species may co-exist with invasive plant species. The growth of these native plant species adapting to the invading species may be affected by the distance from invasive species. Since invasive species may pose threat to environmental biodiversity and affect native plant growth, the understanding of factors that affect competition between the two is crucial.

Experimental Systems

Centaurea maculosa Lam will be used as the model space invasive plant species. It is listed as a noxious weed, posing a serious threat to western rangelands in the US. It is a short-lived herbaceous plant, hence making it a practical model. All conditions i.e. temperature, carbon dioxide concentration, water, etc., all will remain constant throughout the experiment.

Independent Variables

Independent variables will be the distance or space between the two species, and the ratio of plants i.e. number of each type of plant in each pot. The distance between the species will be varied by planting the species at varying distances. The second independent variable is the number of each plant type in a pot. Both the variables are simple to acquire.

Levels of Each Factor

The space between the two species will be varied by using different sized pots i.e. small, medium, and large. Same sized plots will be planted with different ratios of the two plant species (native and invader) i.e. in the case of small pots (total four small pots); one pot will be planted with one native and one invading species seed, one pot will be planted with one space invader and four native species, one pot will be planted with one native plant species and four invading plant species, one pot will be planted with all space invading plants, while the fourth spot will be planted with all native species. The same will be done for medium and large-sized pots.

Dependent Variables

The dependent variables we’ll be measuring are stem height and biomass. These variables will measure the general growth of the two species.


If competition between the native and invading species is affected by space between the two species and the ratio of the two species, a better understanding of how invading species affect the native plant species will be obtained and can further help us in understanding if native plant species can adapt themselves, and compete with invading species.


Field Identification Guide to Invasive Plants in Michigan’s Natural Communities. Michigan Department of Natural Resources, 2009.

Davis, Edward Stuart. “Spotted knapweed (Centaurea maculosa L.) seed longevity, chemical control, and seed morphology.” Ph.D. diss., Montana State University-Bozeman, College of Agriculture, 1990.

Oduor, Ayub MO. “Evolutionary responses of native plant species to invasive plants: a review.” New Phytologist 200, no. 4 (2013): 986-992.

Lindquist, John L., Bruce D. Maxwell, and T. Weaver. “Potential for controlling the spread of Centaurea maculosa with grass competition.” The Great Basin Naturalist (1996): 267-271.

Leave a Reply