Advancing forest cover development on a high-elevation Sierra Nevada mine site with nutritional amendments

Selected nutrient amendments were evaluated for their capacity to enhance growth and nutrition of established but stunted Jeffrey pine (Pinus jeffreyi Grev. & Balf.) saplings on an acidic Sierra Nevada surface mine. The amendments were applied by topdressing at three rates each and consisted of Forestcote 22-4-6 + Minors, a controlled-release formulation; Free Flow 29-3-4 and Hydro Agri 21-7-14, two conventional fertilizers, with the former featuring urea as the predominant N source, whereas that for the latter was exclusively ammoniacal and nitrate forms; and Milorganite 6-2-0 + Iron, an organic amendment based on municipal biosolids. All formulations reinvigorated sapling growth, generally more so as the amounts supplied increased, with the Free Flow and Hydro Agri amendments marginally more stimulative than Forestcote and Milorganite. Foliar analysis revealed that fertilized saplings had more N, with concentrations that generally rose with amounts supplied, and P but less Mn and Al than the control. Enhanced N nutrition in particular but also that of P probably accounted for most of the growth stimulation by the amendments, as availability of both in the soil was limiting. Of the two metallic elements, reduced Mn was likely most critical because concentrations encountered here were exceedingly elevated overall, including that in the soil, although soil Al was also high. These results suggest that a variety of nutritional amendments can be employed in forest restoration on surface mine sites and those similarly degraded, including sites for which dry climates greatly influence the selection of remedial practices.