Figure 19.13 Testing the mechanism of spruce succession. Across four successional seral stages in Glacier Bay, Alaska, researchers examined (a) germination success of planted spruce seeds and (b) biomass of 2-year-old spruce seedlings. They also measured (c) the number of spruce seeds arriving naturally at each seral stage. These data demonstrate that while spruce trees can germinate and grow well in earlier seral stages, they are absent from the early seral stages because very few seeds get dispersed to these sites. Error bars are standard errors.

Data from F. S. Chapin III et al., Mechanisms of primary succession following deglaciation at Glacier Bay, Alaska, Ecological Monographs 64 (1994): 149–175.