Climate change is expected to cause increased temperatures in Southeastern Alaska while potentially changing precipitation patterns, as was seen with the extreme warmth and drought during the summer of 2019. These factors can affect the growth of the major tree species in the area and are recorded in tree cores. We collected tree cores from Sitka Spruce (Picea sitchensis), Western Hemlock (Tsuga heterophylla), and Shore Pine (Pinus contorta) in three locations in southeastern Alaska: Gustavus, Juneau, and Sitka, during 2019. Tree cores were examined under a dissecting microscope and the growth rings were measured and compared to yearly weather data from the Juneau Airport. We looked at the average temperature and precipitation that was recorded both annually and during the growing season (May-September) for the past 70 years (1949-2019). Regression was used to determine any changes in weather parameters or growth rates through time, and ANOVA was used to compare differences among species and locations.
Results/Conclusions
We found that both temperature (annual: F= 38.57, P<0.0001; growing season: F=28.23, P<0.0001) and precipitation (annual: F=24.38, P<0.0001; growing season: F=15.11, P=0.0002) have significantly increased over the past 70 years in Juneau. Annual temperature is increasing by 0.03oC per year and precipitation has increased 0.69 cm per year. These increases have increased growth in Spruce (SS - F= 3.76, P=0.05) and Hemlock (WH - F=30.14, P<0.0001) in Gustavus, but decreased growth in Shore Pine (SP - F= 353.35, P<0.0001) and Hemlock (F=9,16, P=0.003) in Juneau and Shore Pine (F=36.01, P<0.0001) and Spruce (F=27.17, P<0.0001) in Sitka. These species (F=12.75, P<0.0001) and location (SS: F= 185.75, P<0.0001; SP: F= 104.63, P<0.0001; WH: NS) differences lead to difficulty in making a conclusion about the effect of climate change on Southeastern Alaska trees: in some locations the trees are responding by increasing their growth rates, but in others they are slowing their growth. This is especially concerning in the shore pines, which serve as a keystone species in the muskeg ecosystems in this region. Already the shore pines in Gustavus have been decreasing due to Dothistroma Needle Blight, decreased growth due to climate change throughout the region may exacerbate this decline.