AP Biology 8.7.D: Geological and Meteorological Change

Buffelgrass, an invasive grass species in southwestern desert ecosystems, is threatening the

saguaro cactus, a keystone species in these ecosystems. Buffelgrass is drought-tolerant and can

survive wildfires. However, the dry buffelgrass also acts as fuel for wildfires, causing the fires

to be more severe. Older saguaro cacti can survive wildfires; however, many of the young cacti

cannot.

Scientists conducted an experiment to determine whether they could control the abundance

of the buffelgrass population. The scientists identified several native grass species that, when

grown with buffelgrass, might reduce the abundance of buffelgrass. They grew buffelgrass

in the presence of several different native grass species in greenhouses, in either nondrought

(watered every 3 days) or drought (watered every 9 days) conditions. After twelve weeks, they

measured the height and dry weight of the buffelgrass in each treatment group.

Scientists have found that the population growth rates of native grasses are much slower

than the population growth rate of buffelgrass following a wildfire. The scientists claim that

wildfires will therefore increase the abundance of buffelgrass plants in the ecosystem. Based

on the information given, justify the scientists' claim.