Immediate damage by an earthquake to a temperate montane forest

We quantified the immediate impact of an earthquake (magnitude index M-w 6.7 in 1994) on a mountain beech (Nothofagus solandri var. cliffortioides) forest in the Southern Alps, New Zealand. Data from randomly located permanent plots (20 x 20 m) established in 1970 were used to determine the patterns and causes of damage. These plots were located 10 km southeast of the epicenter (Basin Creek, 28 plots in 920 ha) and 30 km southeast of the epicenter (Broken River, 34 plots in 2060 ha). Assessments of earthquake-induced damage in 1995 showed 24.0 +/- 5.9% tree mortality and 22.5 +/- 4.0% tree injury on Basin Creek plots tall values mean +/- 1 se), but only 0.6 +/- 0.2% tree mortality and 3.3 +/- 1.1% tree injury on Broken River plots. As a result, stem biomass declined from 149 +/- 13.8 Mg/ha in 1993 to 114 +/- 15.3 Mg/ha in 1995 on Basin Creek plots. On average, earthquake-induced landslides caused 74% of the total stem biomass mortality, and such mortality was greatest on steep slopes. Low-intensity stem biomass mortality was common in Basin Creek, with 25% of plots losing 1% to <20% of their live stern biomass. Damage intensity in that catchment depended on the scale of observation: 100% mortality occurred on 7% of the 20 x 20 m plots, 15% of the 10 x 10 m subplots, and 21% of the 5 x 5 m subplots. In contrast to previous studies, our results show that much of an earthquake's immediate impact is widespread, low-intensity damage to forests.