UBC Theses and Dissertations
Vascular plant response to slashburning and clearcutting in central British Columbia : a 20 year study of plant functional type resilience Chandler, Julia Rae
How resilience is understood and measured has become increasingly challenging for ecologists, particularly as terrestrial ecosystems are undergoing radical change as climate changes. This body of work proposes a specific approach to studying resilience and applied it to Interior Cedar-Hemlock (ICH), Sub-Boreal Spruce (SBS) and Engelmann Spruce-Subalpine Fir (ESSF) forests extending across central British Columbia, Canada. Repeated measurements (% cover and height) of vascular plants were collected between 1981 and 2008 (1, 2, 3, 5, 10 and 20 years after clearcutting and slashburning) in permanent research installations. Individual species sensitive to the forestry treatment (recorded exclusively pre-burn) included Rhododendron albiflorum, Menziesia ferruginea and Prosartes hookeri in the ICH; Rubus pedatus in the SBS; and Orthilia secunda, Listera cordata and Moneses uniflora in the ESSF. Post-burn shifts in species dominance consisted of substantial loss of Abies lasiocarpa, Oplopanax horridus and Listera cordata, and increases in Alnus spp., Salix spp., Epilobium spp. and Calamagrostis spp., indicating possible transition from conifer forest to mixed forest or open meadow ecosystems at several study sites. To overcome the difficulty of evaluating ecosystem resilience from measurements of 183 individual species recorded in experimental plots, I created plant functional types (PFTs) based on 15 common plant traits. PFTs were determined by grouping together plants that behave in similar ways or produce similar outcomes despite having different physical characteristics or evolutionary paths. PFT models of abundance and richness along gradients of soil nitrogen and fire severity over time indicated linear and non-linear response trends, and lasting and temporary effects. Structural equation modeling (SEM) was used to measure the relative importance of factors driving the responses observed. The SEM indicated that mean annual precipitation (MAP) negatively influenced fire severity; mean annual temperature (MAT) positively influenced fire severity and soil nutrients; and MAP and MAT directly and/or indirectly influenced most PFTs. My research suggests that clearcutting and slashburning do not alone alter the diversity or function of mesic ESSF, SBS and ICH forests; however, past and future anthropogenic disturbances combined with non-historical climate and interrelated edaphic factors may place long-term stability of these ecosystems at risk.
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Attribution-NonCommercial-NoDerivs 2.5 Canada