Wildfire plays an important role in coastal temperate rainforests of the Pacific Northwest, but how climate, vegetation and humans contribute to fire activity on the Central Coast remains unclear. A multi-scale analysis of tree rings, fire scars and soil charcoal samples from a variety of ecosystem types were used to reconstruct the fire history of Hecate Island through the past 12,000 years. Although fire activity in the early Holocene is likely linked to climatic and vegetation changes, increased fire activity in the late Holocene is inconsistent with long-term trends of cooler and wetter conditions. My hypothesis is that cultural (Indigenous) fires played an integral role in the late-Holocene fire activity on Hecate Island, shortening the fire return interval in forested areas near formerly occupied sites. My research uses a comprehensive and interdisciplinary approach to examine ecological legacies associated with the possible use of fire as a vegetation management tool. Several fire events are recorded across the study area suggesting that cultural fires may have a broader impact on Central Coast forest dynamics than previously known.
Background: Complex interactions between climate, vegetation and human agency throughout the Holocene period make it difficult to understand how the present day landscape of the Central Coast has been affected by fire. Although it is not initially intuitive to think about fires in very wet hypermaritime forests, Holocene fire activity may have played an important role in the ecological patterns and processes visible on Hecate Island and several of the outer islands today. Although fire as a tool for vegetation management is well known in analogous and neighbouring ecosystems, this practice has not been well documented in the study area.
1. Do certain forest types, topography and/or locations have higher fire return intervals?
2. Is there a relationship between increased fire activity in the late Holocene and fires associated with areas surrounding village sites?
3. Is the ecology of Hecate Island distinct as a result of increased fire activity?
Methodologies: At each study site (1 hectare in size) I sampled up to 10 (minimum 2) of the soundest living and/or dead fire-scarred trees. Where possible, I cut cookies to pith out of the living, fire-scarred trees and cross-dated each cookie to a master fire scar chronology developed from the site. A tree ring width chronology was developed from the larger study area to confirm climate anomalies correlated to fire years (drought) and to verify any missing rings. At the center of each 1 hectare plot (n=30) I established a 400 m2 fixed-area plot, sampling the age structure, height and diameter at breast height (DBH) of all dominant and subdominant trees. Increment cores were extracted at the base of each tree to establish age structure within plots. Course woody debris was measured in each plot with 2 40 m transects. I assessed charcoal buried in the soil using Accelerated Mass Spectrometry (AMS) radiocarbon techniques to determine fire intervals throughout the Holocene period. Charcoal is a common feature in mineral and organic soils on Hecate Island and is found in situ (large chunks >5 mm), at varying depths (5 cm-130 cm) and in distinct stratigraphic units. In each fixed-area plot I completed a soil profile where soil had not been obviously disturbed by downslope movement or tip-up mounds. I collected charcoal from each layer of stratigraphy in both mineral and organic soils. Soil charcoal was selected for AMS radiocarbon dating based on depth, quality and abundance at each site.
Progress Update: I am currently analyzing my soil charcoal and fire scar data at the Paleoecology and Biogeography Lab at the University of Oregon. I am attending conferences including: the European Geophysical Union in Vienna, Austria, the NW Anthropology Conference in Eugene, Oregon and the Canadian Association of Geographers in Vancouver, B.C where I am co-organizing a special session on methods in dendrochronology.