| dc.description.abstract | This thesis synthesizes three papers on the effects of forestry practices on the growth and
fruit production of lowbush (V. angustifolium) and velvet leaf (V. myrtilloides) blueberry in i)
young jackpine, ii) boreal mixedwood and iii) lowland black spruce plantations in northwestern
Ontario. The main objectives of the three papers were to investigate: i) the impacts of forest
herbicide and alternative conifer release treatments on the growth and fruit production of
Vaccinium spp.; ii) the phenology of Vaccinium spp. in order to determine an optimal spray time
that might reduce susceptibility of blueberry to herbicide injury and iii) the morphological plasticity
of velvet leaf blueberry bushes growing in clearcut, partial cut and uncut second-growth boreal
mixedwood forests.
i) It was shown that application of Vision® herbicide significantly affects the abundance, growth
and reproductive performance of Vaccinium spp. in treated clearcuts. Compared with untreated
areas, fruit productivity of Vaccinium spp. in Vision® treated plantations was reduced by as much
as 58 % three years after disturbance. Reductions in berry production were attributed to toxic
effects of the herbicide to stems and below-ground reproductive tissue. Conversely, percent cover
and the number, dry weight and fresh weight of berries increased significantly after brushsaw
cutting.
ii) Patterns of leaf development in V. angustifolium and V. myrtilloides indicated that selective
control of competing vegetation in plantations with reduced damage to Vaccinium spp. may be possible with herbicide application before active growth of new blueberry shoots (i.e. early May)
or during leaf senescence and abscission (i.e. September to October). Foliage of blueberry turned
colour in late August with about 30 % abscission by the last week of September. With most of the
foliage lost by early autumn, application of foliar herbicides at this time may have limited effects
upon blueberry growth and fruit production, since without leaves, little herbicide can be absorbed
or translocated to below-ground vegetative organs.
iii) V. myrtilloides was able to persist in both open and closed habitats in boreal mixedwood forests
managed for commercial timber exploitation. Persistence under heavy shade conditions was
attributed to plasticity in morphological and biomass allocation. Specific leaf area, individual leaf
weight, number of berries, number of reproductive shoots and the proportion of total biomass in
stems and foliage changed along a gradient in understory light ( % PPFD) from 0 % to 67 % PPFD
in forests harvested by clearcutting and shelterwood logging. Reproductive performance of V.
myrtilloides was best under the partial shade conditions associated with shelterwood cutting.
The results of this thesis indicate that clearcut logging and silvicultural strategies of weed
suppression such as herbicide application can adversely affect both the berry production and
vegetative growth of Vaccinium spp. in northwestern Ontario. Conversely, partial cutting and
conifer release with brushsaw cutting offer a silvicultural alternative that is less destructive to
blueberry. | |
