Silver Fir Defoliation Likelihood Is Related to Negative Growth Trends and High Warming Sensitivity at Their Southernmost Distribution Limit

Table 2

Logistic regression models for declining (𝑛=28) and non-declining (𝑛=34) silver firs. The effects of growth characteristics (mean, trends, and coefficient of variation—CV) and growth sensitivity to climate (estimated as the determination coefficient between basal area increment—BAI—and annual climatic variables). The annual water budget (P-ETP) was the differences between precipitation (P) and potential evapotranspiration (ETP). The relative maximum likelihood is calculated as the percentage of maximum likelihood value obtained. Nonsignificant models are indicated by ns.

Model	Maximum likelihood	Relative maximum likelihood	P	Percent correct
				Full model	Nondeclining trees	Declining trees
1980–1999 BAI trend	12.55	1.00	<0.01	86.67	94.12	63.64
P-ETP sensitivity	18.26	0.69	<0.01	80.00	91.18	45.45
Temperature sensitivity	18.73	0.67	<0.01	73.33	88.25	27.27
1960–1999 BAI trend	21.10	0.59	0.01	73.33	91.18	18.18
SPI sensitivity	21.38	0.59	0.01	80.00	97.06	27.27
1980–1999 BAI CV	22.12	0.57	0.02	73.33	91.18	18.18
1980–1999 mean BAI	23.46	0.54	0.08	ns	ns	ns
1960–1999 BAI CV	24.38	0.51	0.25	ns	ns	ns
1960–1979 mean BAI	24.44	0.51	0.28	ns	ns	ns
1960–1979 BAI trend	24.83	0.51	0.43	ns	ns	ns
1960–1979 BAI CV	24.91	0.50	0.63	ns	ns	ns
1960–1999 mean BAI	24.97	0.50	0.74	ns	ns	ns