Reprinted from the JovnNAL OF FORESTRY, Vol. 60, No. 6, June 1962
Purelwsed by the lJ. S. I<'orcst Service for Official Use.
Discussion of Forest Trees Introduced into the Pacific Northwest A
c
Roy R. Sileo
.\ c'
in their native habitat.
est, detailed long-term records on Third, succesaful exotics often success of exotics are provided by are adapted to difficult site situa­ the Wind River Arboretum located tions such as poor soils, cold cli­ at 1,000-foot elevation on site III
mates, or high-water tables. In Douglas-fir land in southern Wash
such situations, the best native trees ington; Since 1912, 621 lots of
may never have succeeded in pro­ plants and seed have been_a_ guired
ducing strains as well adapted to for the arboretum and, of these,
such habitats as species from other about 429 have been tested, includ­
ing ·two or more lots of many
parts of the world.
These same factors should apply species." While tests for some
to the Pacifi Northwest, yet there species have been more adequate
have been no outstandingly success­ than for others, some attempt has .
ful introductions of trees for for­ been made to observe practically
estry purposes here, nor over most every tree in the· world that has
of North America. Unless western any promise as a commercial tim­
foresters have failed to test exotics ber species.
adequately, then a fourth, more sig- ·
For the first 16 years, both
nificant 'factor must be involved.
broad-leaved and coniferous trees
Perhaps western American trees were planted in the arboretum. Of
have inherently better growth rates. more than 200 lots of broad-leaved
This could be the fourth factor.
exotics, the best performance was
so poor . compared with conifers
Tests in the Paci11c Northwest
that in 1928 acquisition of broad­
The proper combination of intro­ leaved trees was discontinued. The
(6).
duced
tree .and suitable site seems arboretum has since been dedfcated
.
Several notable factors are usu-· not to have been found for the Pa­ exclusively to conifers.
ally associated with successful in­ cific Northwest, although many
The latest arboretum report (8)
troductions of forest tree· species exotics have · been· introduced for contains a comparison of growth
whieh complete ·records of perform­ of exotic conifers with average
(6):
First, fairly intensive· .silvieul­ ance are available.
·
! growth of natural Douglas-fir of
tur.e is always practiced in success­
Warm climate ·species such as the same age on the same site. The
ful plantings of exotics. This may Monterey cypress, Monterey pine, !\est tree in a group of 10 to 40
account in part for superior growth and even palms, ( Trackycarpus and trees of a single exotic species is
per acre, but even where the same Phoenix) have attained fair size in compared with the average Doug­
cultural practices are used- for both the mild climate of coailtal Oregon las-fir on the assumption that the
introduced and native species, as in and Washington. At the Cascade best. tree may better reflect specie
Europe, the superiority of some Head Experimental F o r est 'in capability if seed sources are care­
exotics is still evident.
coaatal Oregon, 13 subtropical and fully selected.
Second, introduced trees are temperate zone forest tree species
Of
164
introduced
conifer
often isolated from many insects were introduced nearly 30 years · species tested, only 2-Norway
and diseases that slow the growth ago. Frost has killed some of the spruce and European larch-have
rate in their original habitat. This more tender species. Animals and tI1aintained a growth rate greater
may be a major factor in growth native diseases have been important· than that of Douglas-fir for longer
differences and explain why in some factors in eliminating others (3). than 20 years. Many species start
cases introduced trees apparently But the performances and !iniits of out growing faster than Douglas­
grow at faster rates than they do introduced species are atiII not fully fir, which at Wind River requires
demonstrated in the narrow coastal 10 years to reach a height of 6
THE AUTHOR. is a reBearch foreeter, Pa­
strip where Sitka spruce and west­ feet. After 10 years, however, cific Northwest Forest and Range Expt,
Sta., Forest Service, U. B. Dept. Agrie,,
ern hemlock are the predominant Douglas-fir grows about 25 feet per Portland, Ore. He is stationed at Cor­
native forest trees.
decade. It is likely that even the
vallis in cooperation with the· School ot. Inland, in the Douglas-fir for- two fastest growing exotics at Forestry, Oregon State University.
PERFORMANCE of forest trees intro­
duced into the Pacific Northwest
has been generally disappointing
. when compared with th_e many in­
stances of success with exotics in
other parts of the world. New
evaluations of old experiments sug­
gest that this may not be acci­
dental. Success or failure with in­
troductions inay involve pattern's·of
species development that date from
the geological past.
Foresters from countries where
introduced species have been out­
standingly successful' are puzzled
about the slight use made of exotics
in the United States (1, 2; 6). This
is ,understandable in view of the
well-known success of Monterey
pine in Australia, and-the excellent
performan e of Donglas-fir, Sitka
spruce, and species of pine (lodgepole, maritime, patula, and pon­
derosa)' cypreSs, eucalyptus, ' and
acacia in various parts of the world
.
·
·
-
·
·
·
407
·