Forest floor carbon and nitrogen losses due to prescription fire

Fire is the dominant factor affecting C and N losses from the semiarid forests of the eastern Sierra Nevada. As prescription fire becomes a best management practice, it is critical to develop an estimate of these fluxes. The objectives of this study were (i) to test and refine methods to estimate the volatilized C and N losses from the forest floor following fire, (ii) to investigate the interactions between O-horizon temperature and nutrient loss, and (iii) to assess measured N losses in the context of atmospheric N deposition, leaching, and N fixation. The quantities of C and N volatilized from the forest floor by prescription fire in the Sierra Nevada were measured using two different field-based methods: weight loss estimation and Ca/element ratio determination. Three sites were included in the study: Marlene, Sawtooth and Spooner. The weight method indicated C losses of 6.12, 7.39, and 17.8 Mg C ha(-1) at the Sawtooth, Marlene, and Spooner sites, respectively. The ratio method indicated comparable C losses from the Sawtooth (6 Mg C ha(-1)) site, but greater losses at Marlene (16 Mg C ha-1) and Spooner (24 Mg C ha(-1)) sites. The weight method indicated N losses of 56.2, 60.8, and 362 kg N ha(-1), at the Sawtooth, Marlene, and Spooner sites, respectively. The ratio method indicated comparable N losses of 59.9 kg N ha(-1) at the Sawtooth site, but considerably greater losses at Marlene (243 kg N ha(-1)) and Spooner (524 kg N ha(-1)) sites. The Ca-element method was preferred because of minimal needs for preburn sampling. Regardless of method, the estimated losses were significant, particularly for N, compared with deposition and leaching rates. Volatilization will represent the major mechanism for N loss from forest ecosystems of this region subjected to prescribed fire.