(Figure 19

(Figure 19.15) Researchers in Glacier Bay, Alaska, planted Sitka spruce seeds (Picea sitchensis) in four seral stages recovering from deglaciation: pioneer stage (dominated by lichens, mosses, and herbs), low-shrub stage (dominated by Dryas drummondii), alder stage (dominated by Alnus sinuate shrubs), and spruce stage (dominated by P. sitchensis). The researchers originally hypothesized that each seral state facilitates species in the subsequent stage. Do the data shown in the figure support their hypothesis? If so, explain. If not, what would explain the results? What type of successions is this area undergoing?