West Portal: Natural Succession at the Mount Macdonald Tunnel
A field example from David Polster | Rogers Pass, B.C.: rough-and-loose tunnel muck planted in 1989 and photographed through 2006
When CP Rail drove the Mount Macdonald Tunnel, the West Portal was left as raw, rough-and-loose tunnel muck. It was planted with trees and shrubs in 1989 and then simply photographed, year after year, from the same vantage. This is what natural succession looks like when it is given the right start: bare rock to Sitka alder to a closing conifer canopy that all but hides the portal within fifteen years.
The same view: succession at the West Portal
A matched field view shows natural succession closing bare tunnel spoil with alder and young conifers.
This pair uses the same field viewpoint from David Polster's original teaching sequence.
Notice rough and loose substrate (tunnel muck) and the general lack of a seeded cover.
Looking towards the Mount Macdonald Tunnel portal
Looking from on top of the portal. The arrow shows the planting boxes from the tree and shrub planting.
Sitka alder starting to dominate – the dense alder area corresponds to a snow slide path while the more open area will become a spruce / subalpine fir forest.
Looking towards the portal – conifers starting to poke out above the alder.
Conifers starting to dominate the canopy
Note the healthy growth rates on the confers (internode length – length between main whorls of branches). The red arrow shows the portal while the yellow arrows show the internode growth.
Portal almost obscured by tree growth
Portal obscured – tracks can barely be seen.