FRDA Report: Black Cottonwood and Balsam Poplar Managers ...

Information Sources:
Hiratsuka and Loman
1984; Hiratsuka 1987;
Ives and Wong 1988;
Ostry et al. 1989; DeBell
1990; Zasada and Phipps
1990; Wang and van der
Kamp 1992; Wood 1992;
P. McAuliffe, pers.
comm., Dec. 1993;
Callan and Ring 1994;
Armstrong and Ives
1995; Callan 1995;
Canadian Forest Service
1995; Hiratsuka et al.
1995; B. Callan, pers.
comm., Nov. 1995; L.
Humble, pers. comm.,
Feb. 1996; Callan
(In␣ press).
In addition to Venturia and Septoria leaf blights, hybrid poplar plantations in British
Columbia have also been host to Taphrina populina, Taphrina populi-salicis, Linospora
tetraspora, and Marssonina spp. In general, the hybrid poplars used in plantations to
date in British Columbia have been resistant to endemic strains of rust. However,
Melampsora medusae f. sp. deltoidae is a potential threat to hybrid Populus trichocarpa
x P. deltoides in the Fraser valley and on Vancouver Island. This is leading to replacement
of susceptible hybrid clones with more resistant clones of Populus trichocarpa x
P.␣ maximowiczii.
Field trials involving five cottonwood clones from the Fraser valley and nine clones
from southern interior locations in British Columbia, all of which had been inoculated
with the native cottonwood-conifer rust Melampsora occidentalis, revealed that tolerance
to this rust varies significantly between clones. Severe infections resulted in substantial
mortality in the following winter and reduced initial stem volume growth in the following
growing season. Reduction in dry weight resulting from this rust infection is much
greater for roots than for stems. For plantation planning, a manager can use the
concepts␣ of resistance, tolerance, and disease hazard to predict early yield of plantation
cottonwood and to select the most appropriate clones for different disease
hazard␣ conditions.
External indicators of decay in balsam poplar are mainly rotten knots and large
scars. As in aspen, there is no clear distinction made in the literature between incipient
and advanced decay or between stain and incipient decay. In balsam poplar, decay
patterns are more influenced by clone origin and less by site or age. Mapping of decayfree
clones based on individual examination has been suggested as part of a genetic
improvement program.
The most common insects observed on cottonwood, balsam poplar, or hybrid
poplars are listed in Table 16. None of these insects currently causes economically
important damage to Populus, but defoliators such as tent caterpillars or the fall
webworm can cause very noticeable defoliation. There are no data to indicate differences
in insect susceptibility between black cottonwood and balsam poplar. Also, there is
insufficient experience to know whether plantations of hybrid poplars may eventually
experience insect attacks different from those in natural cottonwood or balsam poplar
stands. A reasonable approach for a forest manager would be to assume that any of
black cottonwood, balsam poplar, or hybrid poplars could be equally susceptible to
damage by any of the insects now known to be present on this group of Populus species.
Several animal pests can damage both cottonwood and hybrid poplar plantations.
Voles gnaw the bark and can girdle a stem, especially in plantations with grass
surrounding the stems. The damage they cause can occur both under and above snow.
Voles create the largest potential impediment to plantation establishment for native
cottonwoods and hybrid poplars. Beavers can also cause damage and can harvest small
patches of plantation trees. Black-tailed deer are considered a minor problem for browse
damage; Roosevelt elk can cause severe damage in plantations.
Mechanical damage to alluvial cottonwood stands occurs from wind and ice storms,
a frequent problem in coastal valleys. Mechanical damage to stems of young whips can
occur in young plantations from wind abrasion of the bark above the snow line. Older
stands often have signs of frost cracks and top damage followed by resprouting. Stems
can also show deformed shape. Broken tops and branches become entry courts for
decay fungi and accelerate the onset of heart and butt rots in cottonwood. Balsam
poplar suffers many similar types of mechanical damage from frost and erosion. As
well, river channel changes are capable of destroying significant areas of balsam
poplar␣ stands.
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