Answers to Figure Legend Questions

FIGURE 25.3 Deforestation would immediately lower the flux of carbon from the atmosphere to the land surface due to photosynthesis, but would increase the flux from the land surface to the atmosphere due to respiration.

FIGURE 25.7 Reactive N is chemically and biologically active, as the name implies. As a result, the pool of reactive N is a potential source of nutrients for organisms. In addition, it can influence soil chemistry and the health of organisms, as we will see later in the chapter. N₂, on the other hand, is chemically inert and must be converted to other chemical forms by nitrogen fixation to be used by organisms.

FIGURE 25.16 In Chapters 3, 16, and 17 we discussed several factors that determine the makeup of vegetation assemblages. These factors include physiological tolerances, biotic interactions such as competition and herbivory, and dispersal ability. Following deglaciation, combinations of temperature and precipitation different from any found today occurred in parts of North America, which resulted in unique combinations of plants relative to those that occur today. In addition, by differentially consuming specific plant species, particular species of herbivores can have an effect on vegetation types. As noted in the Case Study in Chapter 3, the animals that occurred at this time were quite different from those found today, including sloths, mastodons, and camels. Finally, the rates at which different species dispersed into the newly exposed substrate would have influenced the composition of the vegetation.