Tuesday, September 20, 2005

Geog 316 journal - Disturbance at Steep Ravine

Jill and I spent last Friday night at the Steep Ravine cabins in Mt Tamalpais State Park. From the title you probably think this is about the mouse that ate all our hot chocolate but alas I'm going to ponder the coastal bluff scrub. So if you've been to Steep Ravine you know that the cabins are actually on an old alluvial deposit and to the north and south are steep cliffs. I noticed a lot of what I think is coastal bluff scrub (cbs) clinging to cliffsides and was wondering at what point of succession is this community.

It's apparent that there's a lot of mass wasting happening here and with that a clearing of the vegetation. So is cbs the expression of a primary successional phase? If so this is complicated by the fact that cbs is fairly limited in California - likely an endemic. So is this physical barrier of cliffside erosion contributing to the endemism of cbs? And what if the coastal erosion stopped, would cbs be succeeded by something else? Or is cbs the climax community? Overall I think the Gleason model is probably more appropriate for this community.

Just a quick note about invasive, on a fresh slide just to the north the pampas grass was doing a great job at getting established. It would easy to imagine the cbs being overtaken by this plant in the not so distant future.

Tuesday, September 13, 2005

Geog 316 journal - Coastal salt marsh gradients

When you study geography in California you inevitably come across the Sierra Nevada transect. The typical graphic will show the elevation gradient from west to east and the associated tree species often delimited by elevation. It's a great driving reference as the changes in tree types occur at a scale that may be otherwise imperceptible on foot.

So when Liam drew the example of a salinity gradient in a salt marsh I was captivated. Apparently plant communities in a salt marsh will vary depending upon how much salt is in the soil. From salty to fresh, plant communities will create a continuum of mud flat to salt marsh to sedges to cattails. I take the ferry to Larkspur whose landing is flanked on the north by some pretty good examples at Corte Madera Marsh. The great thing about a salt marsh is that the gradients happen at a smaller ecological scale and you can actually see to whole mosaic with advantage of some elevation.

I biked over and I have to say the patterns were not readily apparent. I was still in that Sierra Nevada mindset - I was thinking elevationally. The plant communities were not falling out that way though, the mosaic was more a complicated patchwork. I moved on. On my ride home I pass another little piece of salt marsh along Corte Madera creek. This one is far smaller but the gradient was immediately recognizable. The salinity barriers were being driven by the drainage network in the marsh. The meandering streams had banks of taller sedges, while the interior areas furthest from the streams (more dessication, more salt) had the salt marsh community (pickleweed and chordgrass).

I've stopped at this marsh to breathe in the relief that nature brings hundreds of times, but this time I saw it differently. Now I like it even more.

Thursday, September 08, 2005

Geog 316 journal - Environmental Gradients

So last weekend I actually stole some plants from the grocery store behind my house. I know I know but hey there plants and this a big grocery store, and besides they just left them out overnight out back....so I think they wanted people to take them. Anyway that's not the point. When I started putting these guys into the ground (basil and vinca) I couldn't help but notice the little tag that highlighted the best growing conditions. This immediately got me thinking about environmental gradients.

Apparently the basil thrived in full light conditions. And this sends me into thinking about scale and the distribution of products. The tag didn't need to say only grow these plants in temperate dry summer / wet winter climates - those climatic barriers are implicit to the sale of plants in our region. But they did say plant in full sunlight - thus taking advantage of a microclimate in your own back yard. So I planted mine in a semi sunny spot, let's see how they do at the edge of their range.