Change Dawdles in an Ancient Forest
In a subalpine forest on Mount Elphinstone near Gibsons, British Columbia, the turnover of trees is exceptionally infrequent, putting this 1000-year-old forest at the far end of the scale for stand disturbance dynamics. For at least the last 600 hundred years, openings in the canopy have appeared one tree at a time and mostly as isolated incidents, scattered through the forest.
Some mountain hemlocks are over 1000 years old, a few yellow cedar and western hemlock top 800 years, while the oldest amabilis fir found was at 688 years.
The four conifers making up the forest canopy cope with the glacial rate of change by having an inventory of seedlings waiting in the shade, ready to take advantage of a break in the canopy overhead. The seedlings tolerate long periods of slow growth, taking over 100 years to reach a metre in height. They can also put on a spurt of growth in a dash for an opening in the canopy when the rare opportunity arises. Most overstory trees grew very slowly during their first 30 years.
Conditions favour mountain hemlock most, as it grows relatively fast and makes up 44 percent of the canopy. Amabilis fir seedlings, while most numerous, are short and stout, taking up to 169 years to grow 1.3 m tall. Due to winter snow, western hemlock only takes root on logs, which are scarce, and thus this species comprises only 5 percent of the overstory. Yellow cedar successfully establishes not from seed, but from layering, as low branches readily form roots when they reach the ground, so this conifer produces 54 percent of the saplings taller than 1.3 m.
In conjunction with this research, however, the dynamics of change for this ancient forest were abruptly altered when it was logged.
Roberta Parish and Joseph A. Antos. 2006. Slow growth, long-lived trees, and minimal disturbance characterize the dynamics of an ancient, montane forest in coastal British Columbia. Canadian Journal of Forest Research. 36(11): 2826-2838.