One of the things we don’t emphasize enough at the Garden is the fact that we neighbour Pacific Spirit Regional Park. The cliffside forest to the west of the David C. Lam Asian Garden, the Garden’s entrance and our parking lot provides biodiverse frames for our views of Georgia Strait and the distant Gulf Islands. This photograph, from our parking lot, shows what can happen (oh so very rarely) when one encounters a combination of late afternoon autumn light and a retreating (or advancing) fogbank directly above where the open water meets the cliff.
Ecological processes are difficult (for me) to photograph, but I do think this image at least partially illustrates the effect of vegetation on light attentuation–where the foliage is thickest, most of the light is absorbed or reflected. Thin or no foliage, of course, permits light to pass through. Figure 1 in Schäfer, K. V.R. & Dirk, V. W. (2011) The Physical Environment Within Forests. Nature Education Knowledge 2(12):5 shows how the intensity of light reaching the forest floor and lower levels of the forest declines with canopy height in an oak forest in the summertime.
The variable amount of light reaching the forest floor in different seasons can prompt niche differentiation, defined on Wikipedia as “the process by which natural selection drives competing species into different patterns of resource use or different niches”. As an example, the floor of eastern North American hardwood forests, where one finds species such as Trillium grandiflorum flowering in the early spring, has a number of early spring-adapted plant species that complete growth and flowering before the leaves fully emerge on the canopy trees. The forest floor species that occupy the same physical space but instead grow and develop during the summer have to deal with the low intensity of light and generally drier soil conditions (but, conversely, do not have to be adapted for potential early spring conditions such as harsh frosts or snow). Occupying (potentially competing for) the same space but adapted to conditions associated with different times, spring- and summer- flowering species can be considered to niche differentiated.
Evergreen forests, like the second-growth forest of Pacific Spirit Regional Park, do not have the same springtime phenomenon. However, one can still observe the effects of light attenuation by paying close attention to the changes in species composition as one transits from the edge of the forest to the core (as one might also observe in forests bordering clearcuts, or riverbanks in the tropics). High light levels at the forest edge generally promote an elevated diversity of shrubs and herbaceous plants, whereas the forest core tends to have fewer of these types. Do note that it is not necessarily an elevated diversity of native species, as invasives tend to be better competitors in these edge sites (at least early on).
I had promised to share photograph details from time to time. This image is actually 3 photographs composited together, using a technique known as tone mapping, which “addresses the problem of strong contrast reduction from the scene radiance to the displayable range while preserving the image details and color appearance important to appreciate the original scene content”. In other words, it is a high dynamic range, or HDR, image. The three photographs were exposure bracketed, so one underexposed, one was overexposed, and one was somewhere in the middle. These were then combined in software that algorithmically composites the three into a single image, essentially drawing from the highlights of the underexposed image (so that the photo is not entirely blown out), the shadows of the overexposed image (to preserve detail in the shadows) and pulling both of these closer to the middle exposure of the photo. I’m oversimplifying, but that’s the gist of it.
HDR images have a poor reputation among many in the digital image world, with the critique that most applications of the technique exceed the boundaries of believability. If done subtly, though, the tool is useful for overcoming the limitations of a single exposure on a camera while still preserving what was seen by the photographer. I hope that today’s photograph falls into the believable group, but feel free to disagree.