Abstract Detail

Ecology

Antos, Joseph [1], McPherson, Audrey [2], Guest, Heidi [3].

Very slow growth and flattened crowns typify Abies amabilis in the seedling bank of an ancient coniferous forest.

The dynamics of natural forests is contingent on the regeneration characteristics of the constituent tree species. Shade-tolerant tree species often form a seedling bank – small trees persisting in the understory until canopy openings allow increased height growth. Seedling bank trees are abundant in some old-growth forests, and appear to be critical to the population dynamics of many shade-tolerant tree species. We studied the growth and morphology of Abies amabilis 0.1-1.3 m tall in the seedling bank of an ancient (>1300 years old) subalpine conifer forest on Vancouver Island, western Canada. We collected all individuals <1.3 m tall from eight 5 x 5 m plots, and measured their growth rates and crown morphology. For the 70 individuals >0.2 m tall we sectioned the main stem at 10 cm intervals and counted growth rings at each interval to determine patterns of height growth. For all 94 A. amabilis 0.1-1.3 m tall we measured the length and location along the main stem of each branch to assess crown morphology. These small trees were very old (mean, 112 years; range 54-205 years), and had grown very slowly in height, averaging 0.79 cm per year. Regressions indicated that individuals 1 m tall would average about 170 years old. This ability to persist for long periods in the understory is related to alterations in crown morphology. Instead of the typical “Christmas tree” conical form of open-growth Abies, these seedling bank individuals had flat umbrella-shaped crowns. The mean branch position was >90% of the distance along the main stem; no trees had branches on the lower half of the stem. The proportion of the main stem with branches was unrelated to tree age, indicating a consistent crown architecture. The stem base to tip-of-longest-branch distance was significantly longer (ca. 1.6 times) than the length of the main stem. This strong relationship (r² = 0.915) indicates that long branches occurred near the top of trees of all sizes. Thus more resources are allocated to lateral versus vertical growth, which is consistent with maximizing light interception in the forest understory. The ability to grow slowly and adjust crown morphology allows these seedling bank trees to persist for decades to centuries, and to retain the possibility of increasing in growth and ultimately forming canopy trees following disturbance.

1 - Department Of Biology, Po Box 3020 Stn Csc, Victoria, BC, V8W 3N5, Canada
2 - University of Victoria, Department of Biology, PO Box 3020 STN CSC, Victoria, BC, V8W 3N5, Canada
3 - Royal British Columbia Museum, Herbarium, 675 Belleville Street, Victoria, BC, V8W 9W2, Canada

Keywords:
seedling bank
Abies amabilis
old-growth forest
tree regeneration
tree growth
shade-tolerant trees
coniferous forests.

Presentation Type: Oral Paper
Session: ECO4, Ecology 4: Plant, Population, Community and Ecosystem Response to Environmental Stressors and Change PLUS Plant Biology (Aeroallergens and Phytochemical Differences)
Location: San Luis 1/Starr Pass
Date: Wednesday, July 31st, 2019
Time: 11:15 AM
Number: ECO4013
Abstract ID:545
Candidate for Awards:None