PARENT SESSION
Oral Session 5: Disturbance Ecology I: Scaling, Wind, and Ice.
Presiding: D McKenzie
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room B 113.
Is freezing injury a contributor to yellow-cedar decline?
Schaberg, Paul*,1, Hennon, Paul2, D'Amore, David2, Hawley, Gary 3, Borer, Catherine 3, 1 USDA Forest Service, Burlington, VT, USA2 USDA Forest Service, Juneau, AK, USA3 The University of Vermont, Burlington, VT, USA
ABSTRACT- Yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach) is an ecomically important species that has experienced a dramatic decline in southeastern Alaska during the past 100 years. Extensive research has indicated that this decline has no likely biotic cause, but suggests that one or more abiotic factors may have instigated decline. To evaluate the possibility that inadequate cold hardiness is a contributor to this decline, we measured the foliar freezing tolerance of yellow-cedar trees in declining and non-declining stands in southeastern Alaska. Because yellow-cedar mortality is concentrated in open canopy stands below 130 m, differences in stand canopy closure and elevation were used as factors directing study design and sample plot selection. Foliar freezing tolerance of western hemlock (Tsuga heterophylla (Raf.) Sarg.), a sympatric species not experiencing unusual mortality, was measured for comparison. Freezing tolerance was assessed in the fall, winter and spring to determine if seasonal differences in hardiness help explain species-specific injury. Significant differences in freezing tolerance associated with elevation, canopy closure, species, and the interaction of canopy closure and species were detected for one or more seasons. However, only two results consistent with field reports of yellow-cedar decline were found: 1) because yellow-cedar trees dehardened about 13° C more than western hemlock trees between winter and spring, yellow-cedar trees were uniquely vulnerable to vernal freezing injury, and 2) stands below 130 m appeared more vulnerable to freezing injury than stands above 130 m. Although these results support the possibility that limited foliar cold hardiness during spring contributes to the decline of yellow-cedar trees at low elevations, we are now evaluating whether root freezing tolerance, which seasonally parallels foliar freezing tolerance, may be more directly pertinent to decline in the field.
Key words: freezing tolerance, foliage, Chamaecyparis nootkatensis, spring dehardening