| dc.description.abstract | Fire and harvest are both major sources of disturbance in Ontario’s boreal forest.
They are largely responsible for successional patterns in forest vegetation, and influence
regimes of hydrologic change in boreal streams, owing to the relationship between
watershed and riparian disturbance and conditions in the stream. These forests and their
streams have historically developed under the influence of fire disturbance. However,
increased harvest activity and fire suppression have significantly reduced the impact of fire
within Ontario’s managed boreal forest. The degree to which harvest activity in these
regions results in similar spatial patterns of disturbance within watersheds as fire is unclear.
Accordingly, the objectives of this study were to assess if harvest disturbance resulted in a
similar extent and landscape pattern of impact as fire, both within boreal watersheds and
their riparian forests.
In the study’s first chapter fire and harvest were compared within 30 km2 (±20%
area) watersheds in the study area. Harvest was the most common of the two, impacting
~30% of the study watersheds during any given period, whereas fire disturbed ~2% of
study watersheds. Stark differences were observed between the watershed impacts of the
two types. Fire disturbed a greater median percentage of watershed land areas and resulted
in a range of impacts, including 100% disturbance. Harvest conversely resulted in lower
disturbance percentages, occupying a subset of the variability measured in fire-disturbed
watersheds, typically below 20% disturbance. Other contrasts between the types include fire
resulting in fewer and more simply shaped patches than harvest, often occurring during a
single year of a period compared with multiple years in harvested watersheds.
In the study’s second chapter fire and harvest were compared within shoreline
riparian buffers, both 30 and 90 m in width around aquatic features. Harvest was the most
common for both buffer distances impacting 20% and 25% of the 30 and 90 m buffers
respectively, compared with ~1.5% impacted by fire. Fire disturbed a greater percentage of
both buffers and resulted in a range of impacts up to 100% buffer area disturbed. Harvest
on the other hand resulted in significantly lower disturbance extents, particularly within the
30 m buffer, and only occupied a small subset of the variability resulting from fire, typically
<10% area disturbed. Other differences in impact included, more numerous, smaller, and
more intricately shaped patches spread over multiple years in harvested buffers over fire.
Differences in the watershed chapter indicate that harvest does not provide for a
similar extent and landscape pattern of disturbance and as a result, does not likely result in
similar regimes of forest succession and stream flow change as fire. In the riparian chapter it
is clear that harvest does not provide similar impacts as fire, particularly with widespread
usage of reserve forested buffers in Ontario harvest practices. Accordingly harvest is likely
not providing for similar successional patterns as fire within riparian forests, and as a result
will not provide for flow and stream temperature changes that would naturally occur. | en_US |
