Testing Ecological Resilience Theory in Pine-lichen Ecosystems of West Central British Columbia
Project Reference Number: 2009-06
Project Status: Complete
Led by: Sybille Haeussler, PhD, UNBC, Smithers
Alana Clason, NSERC Industrial Scholarship; Beth Henderson, Bulkley Valley Research CentreFunder: NSERC; University of Alberta; Private Donation; Ministry of Forests (In-Kind Support)
The response of ecosystems to changes in environmental conditions is typically non-linear (Scheffer et al. 2001; Schneider 2004). Instead of shifting incrementally, ecosystems often display threshold-type behaviour whereby significant events serve as tipping points, precipitating a sudden switch from one state to another. A massive event such as the mountain pine beetle (MPB) outbreak that recently spread through BC provides an unparalleled opportunity to investigate such tipping point behaviour in forest ecosystems.
In 2007, scientists from the Bulkley Valley Research Centre, UBC Forest Sciences Dept & MoFR undertook a 1 yr study (BC Forest Science Program Project M08-1568) to demonstrate tipping point behaviour in whitebark pine-lichen ecosystems south of Smithers. We hypothesized that cumulative effects of MPB, white pine blister rust, fire exclusion & climate change would cause Pine-Lichen ecosystems to shift towards mesic Subalpine Fir-Hemlock-Moss ecosystems with a net loss of ecosystem diversity (homogenization) across the subalpine landscape. Our study was prompted by Bulkley Valley Research Centre project 2007-22 which showed short-term increases in Ericaceous shrubs or mosses & declines in lichen abundance after MPB.
The results were decidedly equivocal: 3 study sites showed evidence of a shift towards mesophytic vegetation over 25-30 yr, whereas 2 sites had increases in lichens & associated oligotrophic species. The net result was no significant change in ecosystem condition across 5 study sites & no statistically significant evidence of lower ecosystem diversity.
We now believe that a threshold exists whereby Pine-Lichen ecosystems below the threshold shift into the mesic Fir-Hemlock-Moss stability domain, whereas ecosystems above the threshold retain (even amplify) their distinct soil & vegetation features after MPB outbreaks through positive plant-soil feedback processes. Rather than becoming homogeneous, the ESSF landscape should thus retain nodes of highly resilient Pine-Lichen woodlands within a matrix of Fir-Hemlock-Moss forest. We refer to our revised hypothesis as the ‘Wal-Mart’ hypothesis because an analogous situation arises when highly competitive chain stores move into a retail landscape: local businesses that are not sufficiently distinctive go under, whereas specialty stores often demonstrate high resilience & enhanced competitiveness by increasing their distinctiveness from the superstore.
Graduate Student Alana Clason who holds an NSERC Industrial Scholarship jointly at the Bulkley Valley Research Centre and the University of Alberta is testing the Wal-Mart hypothesis by remeasuring vegetation and soils at existing 25-30 yr old ESSFmc/02-03, & ESSFmk/02-03 Biogeclimatic Ecosystem Classification plots within the study area. The increased sample size should confirm whether or not there has been a net homogenization & identify threshold conditions (soil, landform, past disturbance, stand structure) that create resilient Pine-Lichen ecosystems. Her results will guide forest management activities seeking to enhance the ecological resilience of the future forest.
REFERENCES:
Scheffer et al. 2001. Nature 413:591-596
Schneider, S.H. 2004. Global Env. Chg. 14:245-258
To see all the work that the Bulkley Valley Research Centre has undertaken with respect to whitebark pine, please view our Whitebark Pine website at http://bvcentre.ca/whitebark.
