© 1994 Heron Publishing—Victoria, Canada
Crown architecture of understory and open-grown white pine (Pinus strobus L.) saplings
Barbara M. O'Connell and Matthew J. Kelty
Department of Forestry and Wildlife Management, University of Massachusetts, Amherst, MA 01003, USA / Received January 19, 1993
Summary
Crown architecture and growth allocation were studied in saplings of eastern white pine (Pinus strobus L.), a species classified as intermediate in shade tolerance. A comparison was made of 15 understory saplings and 15 open-grown
saplings that were selected to have comparable heights (mean of 211 cm, range of 180–250 cm). Mean ages of understory and
open-grown trees were 25 and 8 years, respectively. Understory trees had a lower degree of apical control, shorter crown length,
and more horizontal branch angle, resulting in a broader crown shape than that of open-grown trees. Total leaf area was greater
in open-grown saplings than in understory saplings, but the ratio of whole-crown silhouette (projected) leaf area to total
leaf area was significantly greater in understory pine (0.154) than in open-grown pine (0.128), indicating that the crown
and shoot structure of understory trees exposed a greater percentage of leaf area to direct overhead light. Current-year production
of understory white pine was significantly less than that of open-grown white pine, but a higher percentage of current-year
production was allocated to foliage in shoots of understory saplings.
These modifications in crown structure and allocation between open-grown and understory white pine saplings are similar to
those reported for more shade-tolerant fir (Abies) and spruce (Picea) species, but the modifications were generally smaller in white pine. As a result, white pine did not develop the flat-topped
“umbrella” crown structure observed in understory fir and spruce, which approaches the idealized monolayer form that maximizes
light interception. The overall change to a broader crown shape in understory white pine was qualitatively similar, but much
more limited than the changes that occurred in fir and spruce. This may prevent white pine from persisting in understory shade
as long as fir and spruce saplings.
Keywords:
apical control, crown silhouette, leaf area, overstory, productivity, shade tolerance, understory.
