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TREE-RINGS AS A HYDROMETEOROLOGICAL PROXY IN THE CARCROSS DESERT, YUKON TERRITORY, CANADA

YOUNGBLUT, DON  Carleton University.
Pisaric, Michael F.J.  Carleton University.

The sensitivity of tree growth to temperature conditions at high elevation environments from northern North America has been well documented. However, few tree-ring chronologies have been developed from this region with a response to moisture availability. In order to understand the potential consequences of environmental changes to particularly sensitive high latitude locations, it is vital to have an understanding of the variability in both temperature and precipitation patterns in these regions in the past.

The Coastal-St.Elias Mountains act as a barrier to moist maritime air creating a rainshadow effect over portions of southwestern Yukon. Annual precipitation in the Carcross area is <250mm, suggesting tree growth in this region might be limited by moisture availability. The Carcross Desert is actually a series of remnant sand dunes from when the area was covered by a large glacial lake, with the desert-like appearance maintained by strong winds blowing in from Lake Bennett and low annual precipitation levels. Reconnaissance sampling of lodgepole pine (Pinus contorta Dougl.) at this site found trees older than 350 years. The sandy and dry conditions at the site were ideal for the preservation of dead wood, with this material used to develop an annual ring-width chronology back to 1546 AD (Figure 1). Patterns of ring-width variability in the chronology differ from regional ring-width records that display cohesive patterns of variability in response to temperature conditions during the growing season.

Preliminary assessment of the climate-tree growth relationship in this chronology suggests high frequency variability in the chronology is driven by a response to moisture availability during the growing season. The strongest relationships (p<0.05) are found between annual tree growth and proximal hydrometeorological records (streamflow from Wheaton River and lake level from Bennet Lake, Figure 2). Significant, albeit weaker relationships are also found with local and gridded precipitation records using an annualisation period of pJuly-June. Cumulatively, these relationships indicate the importance of moisture availability to tree growth as water moves through the hydrological cycle (i.e., from precipitation to streamflow to lake level) during the growing season.

The ability to use paleoclimatic data can be limited by the availability and quality of the instrumental climate record. The paucity of high quality and lengthy instrumental data in the Carcross region necessitated a flexible approach in this study. When possible, the missing or low quality portions of instrumental records were estimated or verified using other records in the region. The results presented here have used the best available instrumental data and highlight the limitations of data availability for paleoclimatic research in remote areas.

Cursory analysis also indicates the presence of a ring-width signal unique to lodgepole pine in the region. These results suggest some dendroclimatic utility in exploring the response of lodgepole pine to moisture availability in this arid region of Yukon. Further sampling will target the retrieval of well-preserved snag material from this unique site.



Figure 1. Carcross standardised ring-width chronology. Vertical line denotes portion of chronology maintaining high signal strength (1683A.D.). Chronology has been rescaled to have a mean of zero.


Figure 2. Scatterplots between ring-width and Bennett Lake level (n=50) and Wheaton River streamflow (n=35). Values shown are anomalies over the common period between each record, r values significant at p<0.05.


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