CHEMISTRY OF RAINFALL, THROUGHFALL AND STEMFLOW IN A EUCALYPT FOREST AND A PINE PLANTATION IN SOUTH-EASTERN AUSTRALIA .3. STEMFLOW AND TOTAL INPUTS

Some factors affecting stemflow chemistry were examined. For events of similar size, the amount and frequency of antecedent rainfall were im portant for both forests. Bark type was important for the eucalypts, a s was the debarking season for the smooth-barked species. Correlations for tree basal area versus concentration were established for the pin es and three eucalypt species. On average, stemflow was responsible fo r 10% of the nutrient input for the eucalypts and 11% for the pines. F or the pines, the cation composition is dominated by Na and K. Eucalyp t stemflow is dominated by K. The relative inputs of inorganic nitroge n and the major cations are presented for the pines and four eucalypt species. There was a net uptake of NH4-N by the pines and a release of NO3-N. For the eucalypts, both were released by all species, except f or E. melliodora which absorbed NO3-N. E. rossii dominated nitrogen re lease. Apart from E. melliodora, the pH of stemflow of all eucalypt sp ecies and pines was less than that of rainfall. The pH values for E. m elliodora and rainfall were similar. The chemical concentration of ste mflow samples taken during events was greatly influenced by the intens ity and continuity of the rainfall, and different eucalypt species wer e influenced in different ways. The relative chemical inputs of rainfa ll, throughfall and stemflow of the principal cations, Ca, Mg, Na, and K, were very variable, even between events of similar total rainfall. The total cation average inputs in gha(-1) mm(-1) of rainfall were: f or the eucalypts, rainfall 10.7 (34%), throughfall 17.4(55%) and stemf low 3.4(11%); and for the pines, rainfall 10.7 (32%), throughfall 18.4 (55%) and stemflow 4.7 (14%). Thus, on average, throughfall makes the major contribution, but in individual events of similar size, rainfal l input can be anything from 25 to 78% of the total for the eucalypts and 10 to 54% for the pines. There is also a substantial variation in the cation composition of all three components. It was possible to mak e a reasonable assessment of the probable throughfall and stemflow inp uts by considering antecedent conditions, season, and certain event ch aracteristics such as the intensity and rain angle. For the eucalypt f orest, the summer debarking of the smooth-barked species affected the concentration and volume of both throughfall and stemflow. For rainfal l however, assessment of likely inputs was not possible except for som e marine-influenced easterly events.