Effect of buffelgrass fires on two Sonoran Desert trees: Bark and structural analyses

Abstract

The introduction of exotic buffelgrass (Pennisetum ciliare) to the Sonoran Desert has modified the structure and fuel loads of desert scrub, creating a continuous fuel bed and altering fire frequencies and intensities. The damage to native vegetation has been widely acknowledged, but the mechanisms underlying the response have been little studied. Considering bark as one of the important characteristics to protect stems from fire, this study aimed to compare bark traits of two native Sonoran desert trees (Bursera microphylla and Olneya tesota) that may promote cambium survival from fire. Physical features of trees and fuel that influence fire behavior were analyzed, and bark characteristics were examined, including anatomy and chemical composition, to determine how these properties may influence their survival to fire. Surprisingly, drought-resistant traits of Bursera microphylla, such as thicker inner bark and greater stem water reserves make this species better able to survive fires, providing up to ten times more resistance to heat inputs from buffelgrass. In contrast, Olneya tesota has a dry and narrow inner bark, a flammable outer bark, fuel material accumulation under its crown, and large branches close to the soil surface, characteristics that increase fire intensity and give less protection to stem live tissues.