Effects on nutrient cycling of burning beech cutover land in the West Coast of the South Island of New Zealand

Effects of different intensities of logging and logging/burning on the redistribution and loss of some major nutrient elements and organic constituents were studied over a two year period (from January 1977 to' February 1979) in a beech forest located in a low terrace remnant near Reefton in the west coast of the South Island of New Zealand . Dominant tree species present before logging were silver beech (Nothofagus menziessi) and red beech (N. fusca). High intensity burns were obtained by harvesting podocarp species only. Low intensity burns were obtained by harvesting to chipwood standard (10 cm dbh). A completely randomized block design was used consisting of three replications of the following main treatments : podocarp logged (PL), podocarp logged/burned (PL/B), chipwood logged (CL) and chipwood logged/burned (CL/B ) Each main plot was 0. 08 ha . In addition, three adjacent forested sites were used for forest floor biomass determinations and N mineralization studies. Forest floor biomass, excluding logs, branches and roots greater than 2 cm in diameter, was sampled before burning, immediately after burning in the burned treatments, and two years after burning. Biomass components were sorted into leaf and branch litter, living leaves and branches, and humus. Soil samples were collected for the 0-9 and 9-60 cm depths. Chemical analysis of humus and soil samples included N, P, K, Ca, Mg, S, polypheriols, C, H₂SO₄ -soluble P, pH, CEC and exchangeable cations (Ca⁺⁺,Mg⁺⁺ ,K⁺, Na⁺). Measured forest floor biomass in the standing forest ranged from 123 to 155 t ha ⁻¹ of which 92% was contained in the humus layer. Logging caused a non-significant reduction in humus weight, ostensibly by mechanical disturbance. This was offset by a several-fold increase in litter mass and by an eventual increase in the weight of the living fraction of the forest floor. However, total forest floor mass in the standing forest was greater than that found in the logged treatments. The concentration of most nutrient elements, especially N, P and K in the different forest floor components were generally higher in all logged treatments. Two years after burning, the total forest floor content of N, P, S, Mg, Na, C and polyphenols was generally greater in the standing forest compared to the logged treatments. The content of Ca and K was greater in the logged treatments. Also in the logged treatments, higher levels of exchangeable Ca⁺⁺ and Mg⁺⁺ and H₂SO₄ - soluble P were found. Burning intensity in both burned treatments was considered light to moderate and was mainly confined to the non-humus forest floor components. Organic matter loss was approximately 16% of the measured forest floor mass. Nutrient losses in the material consumed by fire were especially high for N (66%), P (35%) and S (51%). All nutrient losses represented less than 15% of the total measured content in the forest floor biomass. Post-fire nutrient transfers in solution were monitored with non-tension lysimeters. Nutrient inputs in rainfall were also determined. Within each plot, four lysimeters were installed at each of the following depths: soil-humus interface, 9 cm and 60 cm soil depths. Water samples were analyzed for K⁺, Ca⁺⁺, Mg⁺⁺, Na⁺, total N, organic N, NH₄⁺-N, NO₃⁻-N, total P, organic P, orthophosphate P, SO₄⁻⁻ -S, pH, water-soluble polyphenols and organic C. Burning substantially increased the concentration and flux of nutrients in humus and soil leachates for two to four months after burning, due to the direct additions from the ash. The greatest effects were observed in the humus percolate and they decreased markedly with soil depth. Within the burning treatments, concentration and flux of most nutrients were affected most in the PL/B treatment. For the first year after burning, K⁺, Ca⁺⁺, Mg⁺⁺ and SO₄⁻⁻-S fluxes in the humus percolate in the burned treatments were from 1.6 to 2.5 times greater than those in the unburned treatments. Most of the increased flux was retained in the top 60 cm of soil. This amounted to between 80 to 97% of the K⁺, Ca⁺⁺, Mg⁺⁺. Greater than 80% of the Ca⁺⁺ was retained in the humus. Increased NO₃⁻-N fluxes in the burned treatments accounted for all of the increased cation fluxes in the CL/B treatment and 73% in the PL/B treatment. Burning produced no measure able effect on the concentration and flux of Na⁺ and P, although some P increases were found in the humus percolate. For the two years after burning, net leaching losses of N, P, S, Ca⁺⁺, Mg⁺⁺ and K⁺ in the 60 cm soil percolate of the CL/B treatment represented only 0.24, 0, 0.09, 0.06, 0.07 and 0.03% of the total estimated nutrient content in the site, respectively. As a percentage of the nutrient capital contained in the pre-burn forest floor biomass plus those in exchangeable form in the soil, leaching losses of K⁺, Ca⁺⁺, Mg⁺⁺ and Na⁺ were 5.7, 2.0, 4.4 and 4.7%, respectively. Ammonium N was the dominant mineral N form in the soil under the standing forest. Nitrate N was generally undetected (< 0.1 ug g⁻¹). Logging and logging/burning resulted in large increases in nitrification, with higher rates being found in the burning treatments. Seasonal patterns for NH₄⁺-N concentrations were found in the humus and soil of the standing forest. Highest concentrations occurred in the autumn (61.6 ug g⁻¹ in humus, 11.5 ug g⁻¹ in soil) and spring (46.0 ug g⁻¹ in humus, 13.6 ug g⁻¹ in soil). Lowest concentra tions occurred in winter (17.6 ug g⁻¹ in humus, 3.7 ug g⁻¹ in soil). Ammonium N levels were not monitored in the disturbed sites until eight months after logging. By that time, NH₄⁺-N levels in the humus were lower than those in the standing forest, although levels in the soil were higher. By the following spring, NH₄⁺-N levels in both the humus and soil were lower than those in the standing forest. Burning substantially increased NH₄⁺-N levels in the humus and to a lesser extent in the soil for approximately four months after burning. A maximum value of 97.5 ug g⁻¹ NH₄⁺-N was obtained in the fresh humus in the PL/B treatment. A fertilizer and herbicide trial was established to observe effects of logging intensity and logging/ burning on Pinus radiata growth. Seedling mortality was substantial in all treatments, but was especially severe in the unburned treatments where up to 70% of the trees failed to establish. Most of the mortality was attributed to excessive moisture in the humus and soil layers which caused the trees to rot. This effect was exacerbated by large accumulations of logging slash and debris in the unburned sites. Height and root collar diameter growth were greater in the burned than in the unburned treated plots. A similar effect was also observed in the chipwood logging regime compared to the podocarp logging regime. Response of trees due to weed control was observed in the first year after planting. However, there was no response due to fertilizer application.