For my field study site, I visited St. Patrick’s Island park in Calgary, AB, on September 19th, at 17:00. My field notebook entry is as follows:
Weather: Cloudy, cool, raining, 8°C.
Location: (51.048377, -114.045230)
General observations of the site:
- Leaves beginning to fall and change color, especially on Dogbane, Populus and Salix spp. Dogbane seems to be the first plant to completely go yellow in much of SW Alberta
- Water levels in the side channel of the Bow River are much lower than earlier in the season, even compared to last week
- This side channel forms the northern edge of the island. Water levels in the Bow are correspondingly low, as the side channel flows from (and back into) the Bow River
Plant communities:
- There is a large diversity of plant communities throughout the park, with noticeable differences between human altered spaces and natural areas, and between different habitats with differing disturbance regimes
- The predominant disturbance regimes on the island for plants seem to be flooding, herbivory, and trampling
- Earlier successional riparian plant communities seem to have a higher abundance and diversity in plant species
- There appear to be several species of Cottonwoods on the island, or different leaf shapes among the same species
- Several Salix species are present on the island, both native and potentially non-native cultivars (e.g. tree willows)
- In terms of woody plant species, human altered banks/terraces are dominated by non-native species, primarily Acer negundo, Caragana (multiple spp.), and Cotoneaster. (see below sketch)
- Areas dominated by late successional forests of Acer negundo, Caragana, and tree willows have little understory diversity, or no ground cover at all
- Riparian areas which are routinely flooded and are subject to ongoing herbivory by beaver appear to contain more diverse and healthier plant communities
The three questions I was pondering after spending some time observing my surroundings at the park are:
- How does the wrapping of riparian trees alter the natural successional trajectory and resulting plant community in riparian forests, due to reduction in beaver herbivory?
- How does species richness and other ecological metrics differ between human altered riparian forests and “unaltered” riparian forest areas across the island?
- What are the natural disturbance regimes at play in ecosystems where Caragana and Cotoneaster are native? And subsequently, what is different in Calgary that allows these species (especially Cotoneaster) to thrive here.