NUTRIENT CONTENT OF FOREST SHRUBS FOLLOWING BURNING

Prescribed burning under mature Larch/Douglas-fir forests produced changes in elemental uptake. Elemental analyses of individual species and existing biomass three years post-burn from hot, medium, and lightly burned sites and unburned controls showed a significant shift in species composition with burn intensity. Few species from hotly burned sites had elevated levels of ions, except phosphorus and iron, but the aboveground shrub and herb biomass did have greater total cations, percent ash, and individual cations (except Ca and Mg) on hotly burned sites. Although the hotly burned sites had the greatest total biomass, only iron, manganese, total nitrogen, sodium, and phosphorus were significantly higher (5%7 level) in biomass from hot burns compared to control biomass (g/m2 basis). Hot burns alter the soil pH to the alkaline range making some elements like iron less soluble and available. Some species growing on hotly burned sites appeared able to alter nutrient uptake making more iron, phosphorus, and other elements available for growth, even with low available levels, compared to control sites. Three-year-old western larch (Larix occidentalis Nutt.) seedlings were able to accumulate high levels of Fe, K, and P relative to controls. Marchantia polymorpha L. concentrated some ions on hotly burned soils, but it was not possible to locate this plant on unburned areas for comparison. CONTROLLED burning is a means of reducing fuel accumulations on the forest floor and is used as an effective management tool. The use of fire reduces organic matter and releases biologically essential nutrients to the soil as a natural fertilizer. When controlled burning is done with the objective of stimulating tree growth, the treatment often fails to produce a growth in trees. Many shrub species in fire-adapted forests sprout readily after fire: Vaccinium L. sp., (huckleberry), Spiraea betulifolia Pall. (spiraea) and many others have adventitious roots with latent buds which are released when the terminal bud is destroyed. The first year following a light or medium burn, these shrubs may resprout readily, producing a rapid increase in biomass. This rapid flush of growth is a logical reservoir for some of the nutrients released into the soil from burning. There is a question whether higher soil nutrient loading from hot burns of heavy fuels will result in more shrub biomass, and hence in greater total nutrient storage in the shrub compartment. This study examines that question. Athough it is most desirable to get the nutrients released from burning into the roots of trees to stimulate tree growth, the nutrients must pass into 'Received for publication 14 January 1977; revision accepted 18 July 1977. The authors are grateful to Paul Powlowski and Magdalena Catalfomo for assistance with this study. 2 The study was a cooperative effort between the McIntire-Stennis Program and the U.S. Forest Service, Northern Forest Fire Laboratory. the zone of shrub and herb roots before reaching the tree root zone. From a nutrient cycling standpoint, it is better to have the elements taken up by shrub or herb roots than to have massive nutrient losses below the tree root zone. Fire rarely kills all of the roots of shrubs, but when it does, nutrient losses from erosion and leaching can be significant (Stark, 1977). Little is known about the elemental content of vegetation following fire. The successional patterns following fire in northeastern Minnesota were studied by Ahlgren (1960) and elsewhere by Cushwa, Brender, and Cooper (1966). The influence of burning in restoring forage values has been widely studied (Grelen and Epps, 1967; Grelen and Enghardt, 1973; Pearson, Davis, and Schubert, 1972; Stark, 1973). A study in Washington by Cole, Gessel, and Dice (1967) discussed the effects of burning on Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco). An early fire study by Stark (1973) dealt with nutrient accumulations by Jeffrey pine (Pinus jeffreyi Grev. & Balf.) seedlings. The question of biomass and nutrient levels following burning remains unanswered and was the stimulus for this study (Pearson et al., 1972). The objective of the Lubrecht study2 was to examine the above and below ground effects of burning different fuel loadings under varied meteorological and fuel moisture conditions in Larch/Douglas-fir forests (Stark, 1977). This would allow the U.S. Forest Service to develop a prescription which would help the land manager