| dc.description.abstract | A naturally regenerating boreal mixedwood site was remeasured 37 years after
four harvest treatments; clearcutting (CC), deferred 'softwoods only' cutting (DC),
'softwoods only' cutting (SC), and hardwoods poisoned, followed by deferred 'softwoods
only' cutting (HP). The objectives were to determine whether ; 1) harvest treatments
produced significantly different phytosociological communities: 2) harvest treatments
altered the normal trend of hardwoods dominating early succession, and allowed Picea
spp. to gain a competitive advantage; and 3) phytosociological trends and corresponding
possible environmental influences could be identified. Median polish and/or ANOVA were
used to compare; species density, dominance (basal area), frequency, cover, age, and
height for the tree stratum; species density, frequency and cover for the shrub stratum;
and species frequency and cover for the herb stratum. Median polish, species' diversity,
resemblance measures, and canonical correspondence analysis (CCA) were employed to
determine whether harvest treatments affected the overall phytosociological community.
Ratios of softwood to hardwood (S;H), spruce to fir (Spr;F), and spruce to hardwood
(Spr;H) were calculated for the tree stratum. Comparisons of pre-harvest data to
current data were made. Correspondence analysis (CA), CCA and cluster analysis were
used to search for the main phytosociological trends and to determine whether these were
related to soil moisture and depth.
Some treatment differences were evident for individual species. However,
species did not form groups that occurred exclusively or abundantly in only certain
harvest treatments. The four harvest treatments did not produce significantly different
phytosociological communities. This may be due to several factors; 1) the Initial
Floristics character of boreal forests: 2) chance factors in natural regeneration, and 3)
the confounding of treatment effects by complex environmental gradients. In terms of
improving spruce and softwood status, the results were not conclusive as to the
advantage over clearcutting of cutting only softwoods, and of poisoning hardwoods in
advance of cutting. Picea glauca (Moench) A. Voss, Populus tremuloides Michx., Populus
balsamifera L. and the Spr;H ratios, supported the expected trend of softwoods being
more prominent in HP than CC, and the reverse for hardwoods. However, Abies balsamea
(L.) Mill, Betula papyrifera Marsh., Picea mariana (Mill.) B.S.P. and the S;H ratios did
not support this trend. The Spr.F was generally higher in HP than CC. Conifers were
mostly of advance-growth origin in DC and HP, but of post-harvest origin in CC,
matching expectations that CC caused more damage to advance growth than did partial
cutting (conifer age in SC did not support this). The strongest phytosociological trend
identified was the change in canopy composition from hardwood to mixedwood to softwood
types. Understorey species distribution was related to either environmental gradients
created by canopy composition, or to some underlying gradients that determined both
canopy and understorey compositions. Soil depth and/or moisture did not appear to be
the determining factors. It is suspected that the boreal mixedwood community of the
RC17 site is best described as a continuum of species' presences and abundances,
determined by a complex set of interdependent environmental factors, which would need
to be clearly defined and accurately measured to determine conclusively whether harvest
treatments differentially affected the community. | |
