Day: September 4, 2011

Ness Island

WE WALK along the towpath beside the Caledonian Canal for a lunch break at the café at the Floral Hall then return to the centre of town via the footbridges to Ness Islands. I draw the standing waves at the upstream tip of the first island. It’s like sitting at the prow of a ship. Anglers stand waist deep in the river.

Giant Sequoia

At the downstream end of the second, longer island, there’s a large Wellingtonia or Giant Sequoia, Sequoiadendron giganticum, with drooping lower branches which make an effective umbrella when there’s a passing shower.

The reddish bark feels slightly spongy which must provide effective insulation from winter frosts and from the forest fires that occasionally sweep through the tree’s native habitat on the western slopes of the Sierra Nevada in California.

Each leaf scale is 2 or 3 millimetres long

Looking up into the branches (top photograph) it appears as if the tree has long slender needles like a pine or fir but if you look closely the leaves are scale-like, as seen in this photograph of a dry twig (they’re green when fresh) that I’ve taken with a low-power microscope.

The Top of the Tree


Sequoias can grow to 50 metres but how tall is this specimen?

I made a rudimentary clinometer using my hand lens (which hangs on a loop of string) as my plumb-line to establish the vertical and the long edge of my sketchbook, held to my eye, to point at the top of the tree, marking the vertical across the inside back cover of the sketchbook.

I measured the distance to the tree as 76 lengths of my hiking boots and added another four lengths to get me near the centre of the tree, which was probably an underestimate. Because the ground fell away sharply at one side I was unable to measure the girth of the trunk.

By drawing out the angle to the horizontal and the baseline distance to scale (right), I can measure the height as 96 hiking boot lengths so that’s 96 x 34 centimetres (they’re big boots, but very lightweight!); that’s 3264 cm, making the Sequoia approximately 32.64 metres tall, about 107 feet.

Errors include the gentle slope of the ground down to the river and my eye being about 1.8 metres above ground level but those two probably cancel each other out. Also from such an oblique angle I couldn’t actually see the top of the tree.

Merkinch

DESPITE THEIR NAME, I don’t often see Common Gulls in West Yorkshire, or perhaps I mistake them for Black-headed Gulls in winter plumage, so I take the opportunity to draw a birdwatcher’s field sketch when we see one on the sea wall by the old ferry ticket office at Merkinch Local Nature Reserve, where the River Ness reaches the Beauly Firth.

Helpfully a Herring Gull flies down to give us a size comparison. Looking in the book, the only character that doesn’t match is the ‘dark bill’. The Common Gull has a yellow bill in summer but by now this will be getting duller with a darker ring near the tip. I notice that, even in my quick sketch, I haven’t shown the bill to be as dark as the eye or wing bars. Seeing it against the sea might also have made it appear a little darker than it was.

Tidal Pools

Herring Gulls, Curlew, Greater-Black Backed Gull, Oystercatcher and Redshank were amongst the birds feeding, or just loafing about, by the tidal pools of the bay between the old ferry and the breakwater where the Caledoniaon Canal enters the Beauly Firth.

Channelled Wrack

There’s a band of seaweed along the lower half of the sea-wall. At the top edge of this there’s Channelled Wrack, Pelvetia canaliculata, which has swollen ends to its fronds. These are the reproductive bodies. You can see the channels that give this seaweed its name on the underside of the fronds in the lower left of my photograph.

Spiral Wrack

Growing in a band below the Channelled Wrack, Spiral Wrack or Flat Wrack, Fucus spiralis, also has swollen tips but these are usually in pairs. The fronds have a tendency to twist, hence the name and, unlike the Channelled Wrack, they have prominent midribs.

Its tough leathery fronds have no air bladders.

Knotted Wrack

Below the Spiral Wrack, at the foot of the sea-wall, Knotted Wrack, Aescophyllum nodosum, spreads out onto the beach. It is also known as Egg Wrack because of those egg-shaped air bladders.

Polysiphonia

Looking amongst the Knotted Wrack on the beach, I found this red seaweed growing attached to one of the fronds. The three wracks are Brown Algae but Polysiphonia lanosa (it doesn’t have an English name) is a Red Alga.

Edible Winkle

Lying amongst the Knotted Wrack and Polysiphonia were shells of the Edible Winkle or Edible Periwinkle, Littorina littoralis. This gill-breathing sea-snail (a mollusc that is a member of the subclass Prosobranchia) feeds on seaweed.