Long-term effects of prescribed fire on ashe juniper communities



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Texas Tech University


This study evaluates the long term impact of prescribed fire on ashe juniper communities. Soil pits were dug to determine soil series and their chemical characteristics where ashe juniper communities occur on Spring Mesa. Eight soil groups were found on the area, all of limestone origin. The major differences in the soils formed on Spring Mesa was their water holding capacity. The soils formed on the toeslopes had the greatest water holding capacity followed by those on the benches, footslopes and backslopes. The Speck soil series formed on both plateaus though the Speck soils on the upper plateau had higher salinity levels. Brush succession measured by line and belt transects following dozing and dozing plus prescribed burning depended on soil series. Only toeslope soils maintained low woody cover (17%) 13 to 16 years following dozing. Other soils had reached untreated levels (60%). Prescribed fire effectively reduced ashe juniper on all soils for at least 14 years. Ashe juniper was replaced by white shin oak (Quercus mohoriana) on Speck soils formed on the upper plateaus. Brush cover was reduced and species composition altered on other soil series by prescribed fire. Flameleaf sumac (Rhus lanceolata) was the dominant species found on the lower plateau, backslopes, and footslopes. Toeslopes maintained low total woody cover (<7%) with live oak (Quercus virginiana), netleaf hackberry (Celtis reticulata), and flameleaf sumac dominating. Impact of the dominant brush species (ashe juniper and flameleaf sumac) on herbaceous vegetation was assessed using grazing exclosures placed on lines with various canopy covers for each species. Influence of ashe juniper and flameleaf sumac on herbaceous yield and species composition depended on precipitation and soil depth. On shallow soils ashe juniper reduced forage yields regardless of precipitation, whereas on deeper soils forage yields increased when canopy cover of ashe juniper was less than 15%. Flameleaf sumac enhanced forage yields until they reached 35% during a dry growing season. No relationship was found between flameleaf sumac and forage yield during an average precipitation growing season. Species composition of the herbaceous foliar cover was altered by the canopy cover of both brush species. As canopy cover increased cool season grasses increased and annual forbs decreased. Germination characteristics of flameleaf sumac seeds were determined in a controlled environmental growth chamber. Seeds must be scarified before germination can occur. Heat treatments can scarify flameleaf sumac seeds if temperatures reach 76 C in wet environments or 82 C in dry environments. Once scarified optimum germination occurred when seeds were subjected to alternating temperatures of 10/20 C with light. Surrounding medium must have a low osmotic potential (-0.1 MPA) and a pH of 10. No differences in emergence occurred when seeds were placed 0 to 6 cm in the soil profile. Prescribed fire enhances these conditions thus aiding the establishment of flameleaf sumac following burning.



Prescribed burning -- Texas -- Callahan County, Brush -- Control -- Texas -- Callahan County, Ashe juniper, Rhus lanceolata