Fig 1.
Locations of sampling regions, Denali and Koyukuk, in Alaska, USA.
Fig 2.
(a) Most spruce were 10–20 years of age when browsed at both Denali and Koyukuk. (b) Browsing history (no browsing (NB), moderate browse (MB), severe browse (SB)) alters the relationship between spruce height (cm) and age (years). Stippled gray lines indicate age difference of escaping herbivory (height = 200 cm) for browsed or not browsed spruce. Letters denote significant differences among browse categories. Shaded regions reflect the 95% confidence interval around each regression line.
Table 1.
Six models were hypothesized to explain variation in spruce height at treeline (log-transformed).
Final model selection was determined by calculating the Bayesian Information Criterion (BIC) for each model. Fixed effects included were spruce age (Age), browsing history (Browse), the proportion of associated deciduous woody vegetation browsed (pDeciduous), and habitat type (Habitat, upland or floodplain). Final model is indicated in bold.
Table 2.
Results of linear mixed effects model for white spruce seedling height at treeline in Alaska.
The response variable, spruce height, was log-transformed.
Fig 3.
An unknown is the missing record of spruce that die because of hare browsing, as exemplified in the photograph of individuals likely to soon die by browsing hares at Koyukuk.
Table 3.
The density of woody vegetation near treeline.