http://hdl.handle.net/10012/17547

In the Athabasca Oil Sands Region (AOSR), wetlands dominate 55 500 km2 (54%) of the landscape despite its subhumid climate and prevailing moisture deficits. The variability and complexity of the AOSR landscape has allowed for the formation and function of several wetland types (i.e. fen, bog, swamp), with treed fens being the most prevalent. Wetlands of the AOSR function as vital water and carbon storage systems as well as niche habitats for vegetation communities and wildlife. Wetlands of the AOSR are largely dominated by conifer species (Picea mariana, Larix laricina), of which are vulnerable to extreme weather and both natural and human disturbances. Thus, shifts in species development of wetland systems, due to climate warming and human disturbance, could have substantial implications for regional water and carbon storage. To define future resilience of northern wetlands to climate change and increasing ecosystem disturbance, it is critical to investigate retrospective species-specific responses to environmental conditions. To this end, we correlate long-term, intra-annual level wood anatomical parameters of 10 Picea mariana (black spruce) trees across two sites at differing elevations (320 and 740 m a.s.l.) and with varying growing season water table depths, as well as 20 trees across a treed swamp disturbed by an unpaved road. Regional daily maximum and minimum temperature and daily precipitation totals were compiled for the study period (1961-2019) for the three study sites. Ring width chronologies of all three sites indicated a potential influence of large-scale atmospheric patterns, such as the Pacific Decadal Oscillation and should be examined further. Enhanced previous summer temperature at both elevations could reduce lumen size, impede water transport to the tree apex and thus, diminish forest productivity. However, higher winter temperatures at higher altitudes and greater winter precipitation at lower altitudes could increase wood density and thus, mitigate potential for cavitation and/or tree mortality in reoccurring drought conditions. Black spruce sensitivity to drier conditions at topographic lows may limit cell lumen enlargement and hydraulic efficiency impacting stem overall water transport efficiency. The observed divergent and complex climatic responses of the study areas are likely the result of localized conditions (i.e. elevation and water table depth). Within the treed swamp study area, fugitive dust load was measured at varying distances away from the unpaved road to infer its influence on black spruce development. There was no evident shift in climatic influence on tree anatomy following road disturbance. Water table depth on opposing sides of the road showed similar temporal trends, suggesting minimal impediment of groundwater flow despite disturbance. Fugitive dust load was highest 2 m west of the road (4.01 gm-2day-1) and exhibited an exponential decline away from the road. Interestingly, cell size and cell wall thickness of the trees west of the road increased (p < 0.05) following road construction indicating a potential shift in water availability rather than fertilization via dust deposition. Nevertheless, intense human activity surrounding the treed swamp at the time of road construction prevents a definitive conclusion. These findings highlight the need for additional black spruce xylem anatomy research in disturbed wetland systems of northern landscapes.

http://hdl.handle.net/10012/17547