Sunday, July 12, 2015

What Do These Images Have in Common?

There are quite a lot of deer at the lake. So many that it wasn't hard to get a few photos while I was visiting with my family. This is the best of the bunch:

Odocoileus virginianus - white-tailed deer
Of course, when I say "deer", I mean Odocoileus virginianus, the white-tailed deer. This species is extremely abundant in many places and this excessive abundance (in response to the elimination of its natural predators, eg cougars, wolves) has had large impacts on plant populations. Odocoileus virginianus browse extensively on plant matter, especially low branches, shrubs, and herbaceous plants. Their presence seems to assist invasive species spread, by weakening native species (which they prefer to eat compared to invasives) and thus reducing their competitiveness.

People who visit at the lake will frequently ask me about this:

Shoreline of the lake
What's up with the straight, level trimmed line of the branches on the shore? A number of amusing theories have been proposed, from snow-reflection microclimates to the lake association hiring professional landscapers to trim.

But there is a connection between the deer, and this straight line.

The lake's shore primarily composed of Thuja occidentalis (northern white cedar), which is one the local Odocoileus virginianus population's primary winter food sources. In the winter the lake freezes, and the deer go out on the ice and have a chomp. So this straight line actually shows the reach limit of the deer for browsing.

In ecology terms, this is called a browse line. Overbrowsing certainly seems to be an issue at the lake; the forest understory is in many places quite bare, and there are virtually no new cedar, maple, or oaks growing in recent years because when they reach intermediate height (tall enough to poke over the snow in winter, not tall enough to exceed the reach of deer), they are browsed to death and that's that. This is a documented problem in many places which have overpopulations of Odocoileus virginianus.

It was just gorgeous at the lake last week, so I will sign off with a picture:

Island on the lake

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