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

Information Sources:
McAuliffe 1989;
Carlson 1991, 1992;
van Oosten 1991.
Many fungi have been
observed on balsam
poplar and black
cottonwood but only a
few␣ cause most of the
damage. Six fungi
cause␣ significant losses
in␣ cottonwood and an
approximately similar
number cause decay in
balsam poplar.
to maintain diameter growth. A target stocking of 800–900 stems per hectare is
commonly suggested with the expectation that half that many cottonwood stems will
remain at rotation age of 25 years.
The technique most commonly considered for enhancement of Populus stem
production is to introduce vigorous hybrids into intensively managed plantations. Scott
Paper Limited data from British Columbia demonstrate the height, diameter, volume,
and mean annual increment improvements possible when hybrid poplars are compared
with black cottonwood under extensive management (Figure 25).
Recent work on the coast indicated that even on the Ss – Salmonberry site series
(where the highest cottonwood indices occur — over 25 m at age 15), there is evidence
that both phosphorus and potassium are limiting to tree growth. This implies that
fertilization would increase yields even on the most productive sites. Another example
comes from the experimental irrigation with municipal wastewater at the Kalamalka
Research Station and Seed Orchard, which illustrates the potential for localized
acceleration of Populus stem biomass production. In spring 1986, 22 clones of
P.␣ trichocarpa x P. deltoides from the Washington State breeding program were planted
at 1 x 1 m spacing, using 10-week-old greenhouse container-grown rooted cuttings.
Wastewater irrigation was applied at rates that provided about 158 kg nitrogen, 60 kg
phosphorus, and 120 kg potassium per hectare over five growing seasons from 1986 to
1990. The original plantation density of 10 000 stems per hectare was reduced to about
1100 stems per hectare by the fifth growing season, at which time the best clones
averaged 11.5 cm dbh and 14 m height. That impressive growth was aided by a
wastewater irrigation rate of 30 cm in year 1 increasing to 75 cm in year 5. A density of
1100 stems per hectare is also the target density chosen by MacMillan Bloedel Ltd. for
hybrid poplar field trials on Vancouver Island and in the Powell River area, with a target
rotation of 15 years.
4.6 Management to Reduce Damaging Agents and to Maintain
Forest Health
• Although a wide range of diseases and insects affects cottonwoods and
hybrid poplars, few seriously affect thriving stands of cottonwood.
• Stem decay increases with age in black cottonwood, but occurs at a much
slower rate than for balsam poplar. In the Fort Nelson area, black
cottonwood as old as 150 years has been observed to be sound throughout
the stem.
The genetics of disease resistance among cottonwood hybrids, compared to that
among native black cottonwood, is not yet well understood. British Columbia poplar
plantation managers are already concerned about diseases that have infected large
areas of hybrid poplars in Washington and Oregon. This threat is being countered by
selection and testing of clones that appear to have greater disease resistance. In the
meantime, the best approach for the manager is to avoid establishment of large
plantations of a single clone.
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