Hay-scented fern (Dennstaedtia punctilobula) is an invasive, rhizomatous, perennial fern native to North America (Hippensteel and Bowersox, 1995). This species grows in many different conditions and spreads itself by dispersing its spores with the help of wind. This perennial fern is about 1-3’ tall, with deciduous leaves that are erect to ascending. It is of yellowish green color, with 10-20 pairs of sub-leaflets that become slender towards the tip (de la Cretaz and Kelty, 1999; Lyon and Sharpe, 1996; Sharpe and Halovsky, 2007).
Studies have shown that in Pennsylvania, the effects of hay-scented ferns on local species seedlings has been observed, having notable effects on seedlings of the northern red oak (Quercus rubra) (Lyon and Sharpe, 1996). Seedlings had a decrease in height, foliar, stem and root biomass in presence of the invasive fern. Black cherries have also faced a decline in their seedling establishment (Horsley, 1993). The main factor causing decline in seedling establishment was the reduced light intake of the black cherry and red oak due to the overwhelming hay-scented fern canopy located above them. The presence of the ferns didn’t have any effect on other factors such as water availability, phosphorus levels, ammonium concentration in the soil and soil nitrogen availability (Horsley, 1993). Although the presence of ferns reduced the number of ectomycorrhizal infections in oak trees (Lyon and Sharpe, 1996), this particularity was not observed on black cherries (Horsley, 1993).
The Morgan Arboretum has various types of reconstituted forests where fern growth has been observed alongside many species of trees, including sugar maples (Acer saccharum). This particular tree can be found in a pure sugar maple plantation, as well as in the maple-ash tree mixed forest and the overall mixed forests (Administrator, 2011). As hay-scented fern spreads across North America, it is evident that it could easily implant itself in Quebec forests such as the Morgan Arboretum and have a negative effect on sugar maple trees reproduction and seedling growth. This is of great interest to us since the sugar maple is one of the most important Canadian tree. It is the main source of sap for maple syrup and is a desirable wood with a lot of commercial value (Sharpe and Halovsky, 2007). With this in mind, the following research question was proposed;
Does the presence of the hay scented fern in the Morgan Arboretum decrease reestablishment and growth of sugar maple tree seedlings?
For our experiment, we took samples from three different forest types. The forest types selected were the sugar maple forest, the sugar and ash forest and lastly the sugar maple, hickory, ash, oak and red maple forest.
In each of the forest types, 4 random samples were taken each consisting of a circular plot with a radius of 6m. The center of the plot was determined and the limits were marked with flags in order to indicate what is in or out of the plot. The random samples were chosen by drawing a grid over each forest type on the Morgan Arboretum Discovery Map. Each grid was numbered from 1-20 and four numbers were chosen from random (pull out of a hat). The grid number that corresponds to the randomly chosen numbers was to be our sample areas for that forest type. This procedure was repeated for each of the three different forest types and the project was conducted over a period of 3 weeks.
Once each circular plot was set up we observed the abundance of hay-scented ferns as well as the amount of mature, juvenile and saplings of the sugar maple trees. To differentiate between adult and juvenile, using a diameter tape, we measured the diameter at breast height (1.3m off the ground) and decided that anything 2cm or under would be considered a juvenile. Saplings were determined as being a max height of 60cm, and at a breast height of 50cm having a diameter of 0.5cm or lower.
Attached is a video explaining our design.
Results and Observations:
So far, our findings have shown that areas with a high abundance of hay-scented ferns, have saplings and juvenile sugar maple trees. This was true for all forest types. In the sugar maple forest, there were less ferns except for one outlier plot that had drastically more than any other. In the sugar maple forest plots, there were consistently more sapling sugar maples than the other forest types, except for the plot with a large number of ferns. The other two forests were extremely variable from plot to plot. In the ash and sugar maple forests, the number saplings and juvenile sugar maples stayed fairly consistent despite varying numbers of hay-scented ferns. In the mixed forest, the one plot that had less ferns than the rest had significantly saplings and juvenile sugar maples than the rest. Overall, where there was a higher abundance of the hay-scented fern there was a lower abundance saplings and juvenile maple trees. Some of the challenges we faced was when entering the forest, we had trouble finding exactly where the random samples were in relation to the ones we noted on the discovery map. Furthermore, as the weeks progressed much more leaf litter had accumulated, covering most of the forest floors, so we had to make sure to moves the pile of leaves in order to find and count all the sprouting sugar maples.
Figures 4 & 5. Classmates setting up the circular sample plot, where flags are put at a 6m radius from the center. High abundance of fern was seen in this Sugar Maple, Ash, Oak and Hickory forest.
Administrator. (2011) Tree Collections. Morgan Arboretum-Arboretum Morgan. http://www.morganarboretum.org/arboretum/the-tree-collections.html.
De la Cretaz, A. L. & Kelty, M. J. (1999) Establishment and Control of Hay-scented Fern: a Native Invasive Species. Biological Invasions, 1, 223-236. https://doi.org/10.1023/A:1010098316832
Hippensteel, T. E. & Bowersox, T. W. (1995) Effects of Hay-scented Fern Density and Light on White Ash Seedling Growth. Proceedings. 10th Central Hardwood Forest Conference, 256-270.
Horsely, S. B. (1977) Allelopathic Inhibition of Black Cherry. II. Inhibition by woodland grass, ferns, and club moss. Canadian Journal for Forest Research, 7, 515-519. https://doi.org/10.1007/BF02211693
Lyon, J. & Sharpe, W. E. (1996) Hay-scented fern (Dennstaedtia punctilobula (Michx.) Moore) interference with growth of northern red oak (Quercus rubra L.) seedlings. Tree Physiology, 16, 923-932. doi: 10.2307/1934157
Sharpe, W. E. & Halosky, J. E. (2004) Hay-scented Fern(Dennstaedtia punctilobula) and Sugar Maple(Acer saccharum) Seedling Occurrence With Varying Soil Acidity in Pennsylvania. Proceedings. 14th Central Hardwood Forest Conference, 265-270.