Examining ground cover across an environmental gradient in a second growth forest

On January 22, 2022, I returned to the same stand of second growth CWH forest (~ 80 years old) with the intention to examine ground cover across an environmental gradient, per the requirements for this post. It was after this day I realized this is not what I want to study, but I will document my experience here, and how I came to shift my focus.

Biological attribute – ground cover (low growing vegetation)

Environmental gradient – since the forest had a creek running through it, I opted to establish a gradient based primarily on moisture, but also likely influence by soil nutrients and sunlight penetration to the ground cover. The three zones across the gradient were:

Zone 1 – flood plain (in the riparian area),

Zone 2 – the slope/bank,

Zone 3 – the terrestrial area (the forest floor).

When setting up the areas to sample, I started with the forest floor. To choose the sample point, I used a georeferenced map supplied by a representative for the landowner. The map used Lidar to determine canopy height, and this defined the second growth area, versus the adjacent areas of younger mixed forest or the newest area of regeneration forest. I focused on an area in the second growth forest that had the widest area on the map so that I could try to minimize edge effects (even though the reality is the area is too small to have a true inner forest anywhere within it) and dropped a GIS pin which I then walked to. This was my attempt to survey a random site and not be influenced by what might look more interesting. I went with the intention of doing a 1m² area but ended up with a sword fern smack in the middle and no other plants, so I expand my area to 3m²…First mistake…there are lots of plants and mosses, both alive and in varying states of decomposition (but partially standing and still identifiable) and this size area is too big and time consuming to survey if attempting to ID and count individual plants in the ground cover. I documented what I could in my notebook, took pictures of ones I could not ID more than classify to a group. Of note, the shrubs were all less than ~2m tall.

I repeated the above process in Zone 2 and then in Zone 1.

Some observations included the change in abundance across the zones for some of the plants. For example, Oregon Grape was quite abundant in Zone 3 along with moss coverage. There was also foam berry, and decomposing vanilla leaf and a fern of some sort (likely Bracken fern but could be oak fern). When looking at Zone 2 the salmon berry, sword fern, and huckleberry abundance increased and there was less Oregon Grape. Some sort of sedge also appeared in Zone 2 and there were seemed to be additional types of moss, but with less coverage. Zone 2 had the most huckleberry and salmon berry out of all three zones. Zone 1 had plants not seen in the other zones suck as elderberry, skunk cabbage, some sort of liverwort, and what may be some species of buttercup.

Based on these observations I would hypothesize that ground cover composition changes across the environmental gradient in the forest. In this case the gradient I considered is moisture, but the bank and floodplain would also have increased sunlight penetration due to decrease in canopy cover which could influence the plants. Additionally, there is likely a soil nutrient gradient as well. The creek is fish bearing and that could contribute to different nutrient levels in the flood plain versus the terrestrial forest.

Focusing on moisture only, the moisture level would decrease with Zone 1 being wettest and Zone 3 being driest. The prediction based on this hypothesis would be that the plants found in Zone 3 prefer drier soil than in Zone 2 or 1, and the plants found in Zone 1 can tolerate flood exposure and potential water immersion. The response variable is the absence/presence and abundance of each of the plants and the explanatory variable would be the moisture levels in each of the zones. The response variable is categorical, and the explanatory variable is continuous.

So back to my comment about not wanting to study this attribute. I have limited experience with plant identification. While I know some of the typical larger ones, there are others that I could not ID, even with field guides and internet searches once home. Also compounding ID challenges is the time of year, lack of flowers on some plants, and relatively new growth on others make examining key features a challenge. This was not something I expected to struggle with as much as I did and I began to consider how I could refine my study, for example to just look at shrubs. While I was in the forest, I was also observing birds in the area which I do each time I walk. I enjoy watching and taking pictures of birds and realized I should use my previous course experience from “Vertebrates of BC” for this study. Since I can ID birds both visual and through song and calls I think I will have less challenges (and frustration!).

New potential hypothesis – bird species diversity will be different in a second growth CWH forest when compared to another habitat type (e.g. a different forest age class or wetland). I may need to determine my second area before I can refine this hypothesis, but initial thoughts are that diversity will be lower in the CWH forest. My choices are the adjacent younger mixed coniferous-deciduous forest, or the riparian area. I am also considering a nearby nature reserve which consists of a small wetland and is adjacent to farmland no longer being used as such (the former UBC research farm). All the other possible study areas would be recovering from more recent disturbance than the ~80-year-old CWH forest which also leads me to think that diversity will be lower in the CWH forest. My notebook touched on the birds I saw or heard, and where I encountered them. Unfortunately, since this wasn’t the focus of my study when I started my observations, I didn’t develop many criteria to observe. I was simply noting what I saw as I took pictures out of interest.