Lisa DeSandoli
Contact Information:

Thesis summary

Fire, natural or anthropogenic, is a common occurrence in the open forests and grasslands of Western North America. The effects of burning on soil and vegetation depend largely on the soil temperatures and the duration or residence time of the burn. These effects range from minor transient changes to soil and vegetation properties, to major changes that can render communities inhospitable to native biota indefinitely. Generally, the more severe the fire, the more significant the changes are to soil and vegetation. While low to moderate severity fires generally promote the establishment and spread of invasive species, the relationship between the most severe fires, or where the soil has been oxidized to a red colour, and invasive species is unknown. Resource availability may increase on these soils, leading to favourable conditions for invasive species. However, the disturbance to soils may also be so severe that nothing is able to grow for an indefinite period of time. I executed two studies to investigate the relationship between invasive species and red-burned soil, and to examine restoration techniques if invasive species are problematic. The first study occurred in the ponderosa pine forests surrounding Kamloops, British Columbia. To reduce the threat of interface fires, excess timber was harvested, piled and burned on site (pile burning), created multiple burn scars that were denuded of vegetation and with disturbed soil which contained large areas of red soil. I selected multiple burn scars across three sites for study. I investigated soil nutrient flux differences between red-burned and unburned soil using ion-exchange resin technology. I also investigated three restoration methods to control invasive species: the addition of agronomic or native seed, the addition of arbuscular mycorrhizal fungi (AMF) inoculum, and the addition of soil cover. The treatments were crossed for a fully factorial experiment, executed on 1 m2 plots consisting of primarily red soils. Non-native species cover was generally high on red soil 2 years after burning, which may be linked to the higher plant-available nutrients I measured on these soils. Only the addition of agronomic seed was successful at suppressing non-native species cover, with the other treatments having no effect on non-native species cover. The second study compared the growth responses of native, agronomic and invasive species on unburned and red-burned soil. This study took place in a greenhouse at Thompson Rivers University in Kamloops, BC. Both red-soil and unburned soil were collected from a site which was subject to the identical treatment as previously described, and transferred to 10 cm2 pots. Treatments were soil burning, AMF addition, and watering. The experiment was fully factorial, with AMF addition and water level nested within soil burning. One species was chosen as a representative from each group: the native species Festuca campestris, the agronomic species Lolium multiflorum, and the invasive species Bromus tectorum. Only the native species was affected by burning, with aboveground biomass increasing on red-burned soil. AMF addition increased invasive species aboveground biomass, but decreased agronomic and native species aboveground biomass. Watering increased aboveground biomass only for the agronomic and invasive species. The findings here, when compared to similar studies of restoration of burn scars would suggest that pile burning creates areas that are susceptible to colonization of non-native species. Restoration efforts should be directed at these sites as soon as possible after burning to ameliorate the effects of invasive species colonization. I am co-supervised by Lauchlan Fraser at Thompson Rivers University in Kamploops BC.


The effects of fertilization and herbivory on the phenology of the understory vegetation of the boreal forest in north-western Canada. (Arctic, Antarctic, and Alpine Research – accepted 28 July 2010)