Long-term effects of repeated N fertilization and straw application in a jack pine forest .2. Changes in the ericaceous ground vegetation

The cover of the ericaceous shrub Kalmia angustifolia L. in a jack pine (Pinus banksiana Lamb.) forest was reduced after repeated fertilization with N or N-P-K, or a single application of straw. Kalmia reductions were greatest in plots that received the highest total N loading (1344 kg N . ha(-1)), but were also apparent in plots that received 672 kg N . ha(-1). The reductions could not be attributed to shading, since tree volume response was small in the plots that received the highest N loading. There was an overall reduction in the amount of ground vegetation in the fertilized plots, so the decline could not be attributed to increased competition from invading species. There was a general negative relationship between the abundance of Kalmia and N availability in the forest floor, in fertilized and straw-amended plots. The reductions in Kalmia cover were still apparent 14 years after the last fertilization and 24 years after the straw application, as was higher N availability. Treatments such as repeated N fertilization or organic amendments that increase N availability in the forest floor may be an option for control of Kalmia in conifer plantations.