We are McGill university undergrad students studying environmental biology. In the course St. Lawrence Ecosystem (ENVB 222), we will be conducting a research project geared at evaluating earthworm abundance in the Morgan Arboretum. To expand on the data collected by researchers in last year’s class, we chose to further study earthworms, but in relation to their distribution with compaction. This specific aspect was chosen because the Morgan Arboretum has distinct paths and trails used for both recreation and research. We were interested in viewing the impact of human interactions with the earthworm habitat. This lead to the formation of our research question:
How does earthworm abundance in the Morgan Arboretum change in relation to soil compaction taking into consideration the acidity and temperature of the soil, in two different soil series?
What is an earthworm?
Earthworms are hermaphroditic annelids that are composed of repeating segments called metameres, each of which contains the same internal structures. Externally, earthworms are covered in hair-like structures called setae, which attach to the surface they are digging in and aid in locomotion. These invertebrates feed on dead and decaying plant matter and excrete humus, which is the organic component of soil (Edwards C.A.).
When broken down, the present nutrients become more readily available for plants. In addition, earthworms aerate the soil by their burrowing actions, allowing for more air and water infiltration. These actions can be very advantageous for gardens and other small
and controlled environments, but there is a growing concern about how earthworms (especially the invasive species from Europe) are influencing our North American forest ecosystems.
Why are earthworms considered invasive species?
An invasive species is a plant or animal that is not native to a specific location that has a tendency to outcompete a native species and be detrimental to the environment. There are 180 species of earthworms in North America, 60 of which are invasive (Wikipedia). Our research will be conducted in the Morgan Arboretum, which is a 245 hector forested reserve located on McGill university’s MacDonald campus. Like many-forested regions in North America, the Morgan Arboretum has adapted to having a large amount of leaf-litter on the forest floor, which has influenced production by protecting seedlings and insulating the earth and organisms lying underneath. With the addition of invasive earthworms to North American soils, the composition of the earth is threatened.
One worry is that this will increase soil erosion, as there is less to inhibit the flow of water, which would cause more topsoil to be removed, as well as leach away the vital minerals and chemicals required by the local vegetation (Bohlen, P.J.).
Where do you study earthworms?
Our research project took place over three weeks, where we had three laboratories of four hours to collect our data. Based on last year’s researchers, we chose St. Bernard soil series as our primary area of study as it exhibits desirable living conditions for earthworms. We randomly chose another soil series (St-Amable) in order to compare the results. St. Amable is characterized by sandy conditions, so we expected to find fewer earthworms in this soil.
Methods of study
It was important to ensure that our dig sites were representative of the area, so we chose to use random sampling. During the first two laboratories, our research question was misleading so we hadn’t yet developed a regular method of data collection, so we hadn’t yet determined a proper way to measure compaction. Non-the less, we started by using a measuring tape to dig holes 25cm in diameter and 15cm depth. We used a generic garden shovel to dig these holes. We dug holes near the path at first, then at further distances perpendicular from the path. At this point we had not developed a standardized method of sampling so our intervals varied randomly. As our research question became clearer, we refined our methods and dug holes at 0, 1, 3, 5 and 15 meters away from the path. If there were trees or large rocks in our way we would take three steps to the right (parallel to the path) and continue digging. This ensured that the distance from the path had not been changed. We repeated these steps twice in the two different soil series. Our refined methods allowed us to more accurately determine if earthworm abundance changed with soil compaction at the path.
After digging the hole, we would sift through the earth in search of earthworms. It should be noted that for this research, due to time constraints, it was not feasible to identify specific earthworm species and therefore all earthworms were considered.
A penetrometer was used to measure soil compaction. It was important to measure soil compaction before disrupting the area, to ensure that the soil had not yet been altered by our presence. At each dig site, we took 5 readings from the penetrometer to obtain a representative average. If the soils were too wet, the penetrometer would slip into the ground without producing a reading. In such cases, several steps were taken in each direction of the dig site in order to obtain proper compaction readings.
Temperature and acidity readings were also collected for each hole. Knowing that “[earthworm] density, diversity, and survival are typically low in acidic soils” (Moore, J.-D.), we were expecting less worms in lower pH. Our readings were taken halfway down the hole in order to account for discrepancies in temperate and acidity from the soil surface to the base of the hole. Temperature was an important variable to measure because as we continued our research throughout the months of October and November, the ground temperature continued to decrease and it is a fact that low temperatures limit earthworm distribution (Greiner, H. G.).
Clive A. Edwards and P.J. Bohlen (1996) Biology and Ecology of Earthworms, Volume 3.Champlain & Hall, London, 433 pages.
Great Lakes Worm Watch. (n.d.). Retrieved November 7, 2014, from http://www.nrri.umn.edu/worms/default.htm
Holly G. Greiner, Andrew M. T. Stonehouse, and Scott D. Tiegs (2011) Cold Tolerance among Composting Earthworm Species to Evaluate Invasion Potential. The America Midland Naturalist 166 (2) : 349-357.
Invasive earthworms of North America. (n.d.). Retrieved November 7, 2014, from http://en.wikipedia.org/wiki/Invasive_earthworms_of_North_America
Jean-David Moore, Rock Ouimeta and Patrick J. Bohlenb (2013) Effects of liming on survival and reproduction of two potentially invasive earthworm species in a northern forest Podzol. Soil Biology and Biochemistry 64 : 174-180.
Patrick J Bohlen et al. (2004) Non-native invasive earthworms as agents of change in northern temperate forests. Frontiers in the Ecology and the Environment 2 (8): 427-435.
Salamanders: Their natural history and our research. (2013, November 11). Retrieved November 7, 2014, from https://stlawrencelowlands.wordpress.com/2013/11/25/salamanders-their-natural-history-and-our-research/