Page 274 - PC2019 Program & Proceedings

PLANT CANADA 2019

TOPIC 13: Ecology and Ecophysiology (Posters P121-P133)

P121. Short-term effects of partial and clearcuttings on woody debris and understory vegetation in
mixed-wood stands
*1
1
1
Maleki, K. ; B. Lafleur ; B.D. Harvey ; M. Mazerolle ; N. Fenton
2
3
1 University of Quebec in Abitibi-Temiscamingue; Université Laval;
2
3 Université du Québec en Abitibi-Témiscamingue (UQAT))
Ecosystem management provides a useful framework for understanding and mitigating impacts of forest
industrial activities on biodiversity and ecosystem functions. When comparing the effects of partial
cuttings on stand attributes, stand-scale silvicultural studies mostly focus on overstory attributes such as
composition, growth and survival and functions such as habitat quality and regeneration impacts, whereas
other ecosystem attributes such as deadwood and understory vegetation is often neglected. Current study
intended to determine the influence of various levels of harvesting intensities on standing and downed
dead wood, and on understory vegetation communities in northern mixed temperate forests. Twelve years
following harvesting, we compared the effects of clearcutting and partial harvesting with variable-
intensities, on the abundance of standing and downed deadwood, and on the composition of the
understory plant communities. Our results show that standing dead wood stem density and diameter
structure of the sites with moderate-intensity gap harvesting (62% basal area retention), were comparable
to unharvested control sites. Additionally, gap harvesting did not change the levels of mid- (15cm
diameter) and small-sized (<10cm diameter) downed dead wood. Moreover, the gap treatment preserved
understory communities more similar to those of unharvested control stands than those in diameter-limit
(% retention) and clearcutting treatments (% retention). These results illustrate the importance of tree
retention levels for the maintenance of dead wood and understory species associated with closed-canopy
or old-growth forests.

Kobra Maleki (kobimmm1359@gmail.com)

P122. Competition or facilitation: Examination of interactions between endangered Sida
hermaphrodita and invasive Phragmites australis
Mulholland, S. ; M. Costea; K. Stevens
*
Wilfrid Laurier University

Virginia Mallow (Sida hermaphrodita) is a perennial herb native to riparian habitats in northeastern North
America. Throughout most of its geographical distribution, however, it is considered threatened
potentially due to the loss of habitat caused by exotic European Common reed (Phragmites australis)
invasion. The biology and ecology of S. hermaphrodita are still poorly understood, and factors
contributing to the species rarity are unknown. Allelopathic and phytotoxic alterations of soil
environments have been mechanisms proposed to explain the invasion success of P. australis. Field
vegetation surveys and a greenhouse study were conducted to quantify seedling growth and arbuscular
mycorrhizal colonization of both species in soils that correspond to a gradient of vegetation ranging in
proximity to either S. hermaphrodita or P. australis to determine the potential for P. australis to
allelopathically alter soils making them inhospitable to native species. Results did not support previous
allelopathic exclusion reports since field results suggested that proximity to P. australis has no significant
effect on S. hermaphrodita seedling mortality. Additionally, greenhouse results indicated that species
performance and AM colonization may be facilitated within competitor’s soil. The soil nutrient analysis
coupled with plant performance findings, suggest that nutrient enrichment may play an important role in
P. australis invasion, and that aboveground competition for light, may be key to explaining P. australis’
success in the competition with native species like S. hermaphrodita.

Samantha Mulholland (mulh2400@mylaurier.ca)

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