vegetation

"Fire is an important tool, and it would have been used to promote the type of vegetation or landscape that was important to them."

The viscous substance is more effective than water — it hangs up on the vegetation and retains its flame-slowing properties even when it dries, he said.

Trees and bushes also have positive effects, especially when combined with grassy vegetation.

Some 1600 years after this fire surge, the ratios of types of pollen trapped in the sediment changed, too, suggesting the burning shifted the vegetation.

Schneider said the effects of water withdrawals can be seen in areas where native vegetation has dried up because groundwater levels have declined.