Post 3 – Ongoing Observations at St. Patrick’s Island

1. Identify the organism or biological attribute that you plan to study.

The attribute that I have chosen to study is the woody plant community on St. Patrick’s Island.

1. Use your field journal to document observations of your organism or biological attribute along an environmental gradient. Choose at least three locations along the gradient and observe and record any changes in the distribution, abundance, or character of your object of study.

I chose three locations along an environmental gradient to observe the woody plant community; 

• A steep berm on the north side of a Bow River side channel, which forms the Island. At this location, the topography is the result of human alteration and construction of the berm. There is little native woody species in this location, primarily decadent Populus spp. with few understory woody species.
• Floodplain areas associated with the side channel. These areas are accessible to periodic inundation during spring high water events and have a high abundance of native woody species, living in an early successional riparian plant community. Native species include Salix spp., Cornus sericea. Naturalized species include Acer negundo.
• Island valley floor forest inbetween the side channel and the Bow River mainstem. This area is subject to inundation only during very significant flood events, due to human alteration of river flows. Woody plant communities here are dominated by old growth Populus spp. with understory communities of Betula spp., Amelanchier alnifolia, and Cornus sericea. Native woody species dominate in areas not disturbed by development (pathways, playground, benches), while non-native species dominate in historically altered streambanks, many of which are completely infested by Caragana spp., excluding almost all other plant species.

1. Think about underlying processes that may cause any patterns that you have observed. Postulate one hypothesis and make one formal prediction based on that hypothesis. Your hypothesis may include the environmental gradient; however, if you come up with a hypothesis that you want to pursue within one part of the gradient or one site, that is acceptable as well.

Some of the processes that cause the underlying patterns I have observed are:

• Disturbance regimes (both abiotic and biotic): in the river corridor ecosystem, flooding is an important disturbance regime that affects the topography of riparian habitats, as well as nutrient fluxes and the physical structure of plant communities due to scouring, burial, damage, and deposition of sediments and seeds etc. Beaver herbivory is also an important disturbance in riparian plant communites, as Beaver appear to maintain riparian forests in a highly productive early successional stage. When beaver herbivory is reduced, large longer lived species dominate and self-thin, resulting in a later successional riparian forest dominated by old Populus spp. as opposed to a young forest dominated by Cornus and Salix.
• Human alteration of floodplain structure: construction of steep berms along the side channel changed riparian plant communities and appear to result in habitats with lower native woody plant diversity and abundance, compared to the undisturbed floodplain areas where natural disturbances can still occur (flooding, herbivory).

My hypothesis is that non-native woody species have a competitive advantage in habitats not subject to flooding and/or beaver herbivory. My prediction is that physically altered habitats (steepened, flattened) which can no longer be flooded (or are flooded far less often) or which lack species on which beaver can feed, will have a higher proportion of non-native woody species than relatively undisturbed areas on St. Patrick’s Island which are regularly flooded and accessible by beaver.

1. Based on your hypothesis and prediction, list one potential response variable and one potential explanatory variable and whether they would be categorical or continuous. Use the experimental design tutorial to help you with this.

Potential response variables could be the percent cover of both non-native and native woody species (continuous), with potential predictor variables being flood return period (continuous), beaver sign evident (categorical), disturbed (categorical), and slope (continuous)