Shrub regrowth, antiherbivore defenses, and nutritional value following fire

Abstract

Prescribed fire is a commonly used as a follow-up procedure to mechanical top growth removal methods such as mowing and roller chopping, but the effects of fire on spinescence and tannin content of shrub sprouts produced after mechanical top growth removal are unknown. Following mowing, (1) height, spinescence, and tannin content in sprouts produced after burning; (2) nutrient and fiber contents in sprouts of the 3 study species; and (3) utilization of sprouts of each species in burned and unburned plots were determined in each of blackbrush acacia (Acacia rigidula Benth.), honey mesquite (Prosopis glandulosa Torr.), and spiny hackberry (Celtis pallida Torr.). Averaged across sampling periods, burned blackbrush acacia and honey mesquite had 54% and 94%, respectively, shorter thorns than unburned plants. Burned and unburned spiny hackberry plants had similar thorn lengths. Averaged across species, sprouts of burned plants had similar tannin levels as unburned plants 6 and 12 weeks after burning. Sprouts of burned blackbrush acacia had higher levels of tannin than sprouts of unburned plants 34 weeks after burning. Leaf material from sprouts of burned spiny hackberry plants had higher crude protein and digestible protein than leaf material from unburned plants. Blackbrush acacia sprouts in burned plots contained lower digestible dry matter and digestible energy than plants in unburned plots. Honey mesquite sprouts in burned plots contained higher digestible dry matter and digestible energy than plants in unburned plots. Burning appears to be a desirable follow-up treatment to mowing because it temporarily increases nutritional value of shrub sprouts, decreases physical defenses, and suppresses growth of shrub species that have low palatability to white-tailed deer.