Effects of fire, ash, and litter on Tobosa production
Sharrow, Steven Harold
The effects of fire (litter removal, ash deposition, and direct heating) on soil factors (moisture, temperature, exchangeable ammonia, and nitrate) and tobosa production were studied in 1974 near Post, Texas in an effort to understand increases in tobosa yields following burning. In addition, tobosa community nitrogen levels were examined on five different ages of burns ranging from current to five years old for both convex and concave topographic sites near Colorado City, Texas in July of 1973 and 1974. Of fire's effects, only litter removal affected the soil factors measured. Plots without litter were warmer slightly drier, and had higher soil nitrate levels than plots with litter. In years of normal or above normal precipitation, the higher soil temperatures stimulate tobosa growth and soil nitrate production on plots without litter compared to the cooler plots with litter. During dry years, however, the warmer temperatures on plots without litter increased moisture stress on plants which negated the beneficial effects of warmer soil temperatures and decreased tobosa yields on burned plots. Fire consumes most of the litter and old growth originally present. Relatively large new growth yields the first two growing seasons following fire restores old growth-N to prefire levels by the end of the third growing season. Litter-N levels, however, are not restored until the end of the fifth growing season when stems produced during the first few seasons die and fall as litter. High inherent variation prevented the recognition of any meaningful trends in root or soil nitrogen levels. Concave sites tended to recover from fire more quickly than did convex sites. It appears that concave sites may be burned at five year intervals without depleting community nitrogen reserves and endangering future tobosa yields. Convex sites should not be burned more frequently than once every 7 or 8 years.