On the Ecology of Mountainous Forests in a Changing Climate: A ...

80 Chapter 3
80
60
40
D (°C*d)
20
0
T m,y,l ≥ 15.5: D = -31.8 + 2.377·T m,y,l r 2 = 0.77
-20 5.5 ≤ T m,y,l ≤ 15.5: D = 187.2·10 -0.0908·T m,y,l r 2 = 0.99
T m,y,l ≤ 5.5: D = 8.52·10 0.165·T m,y,l r 2 = 0.98
-40
-10 0 10 20 30
T
m,y,l
(°C)
Fig. 3.9: Average difference (D) of estimated monthly degree-days between the more
precise estimation method by Allen (1976) and the formula used in conventional forest gap
models (Botkin et al. 1972a,b) as a function of monthly mean temperature (T m,y,l ). The data
are from the sites Bern, Bever, and Locarno.
Next, the monthly degree-day sums were recalculated taking into account the error terms
given in Fig. 3.9. A verification test for the site Bern and a validation test for the site
Basel are shown in Fig. 3.10. It can be concluded that the correction formula provides an
accurate estimate of Allen's monthly degree-day sums.
Finally, the effects of the correction formula on the annual sum of degree-days were evaluated
at all six sites (Fig. 3.11). The new formula provides estimates of the annual sum
500
2
y = 2.86 + 0.993x r = 0.996
600
2
y = - 1.45 + 0.969x r = 0.992
ForClim degree-days
400
300
200
100
500
400
300
200
100
0
0
100 200 300 400
Allen's degree-days
500
0
0
100 200 300 400 500
Allen's degree-days
600
Fig. 3.10: Performance of the empirical correction formula for estimating the monthly
sum of degree-days from monthly mean temperature. Left: Verification test for the site
Bern. Right: Validation test for the site Basel.