Effect of Vegetation Changes on the Fertility of a Newfoundland Forest Site

In Newfoundland many sites occupied by Picea mariana forests and Kalmia angustifolia heathland formerly supported an Abies balsamea forest. Stands of each cover type were studied to determine whether these vegetation changes affect the fertility of the sites. They were selected on the basis of similarity of soil conditions; all occurred on well—drained, sandy glaciofluvial soils and had developed after a forest fire about 65 years ago. In the Kalmia heath the raw humus horizon weighed 293 tons/ha and contained 3,070 kg N, 436 kg Ca, 118 kg P, and 99 kg K per hectare. In contrast, the raw humus of the Picea forest weighed 87 tons/ha and that of the Abies forest only 65 tons/ha; nutrient contents were proportionally lower with N showing the largest, and K the smallest, differences between cover types. The annual return of organic matter and nutrients is highest in the Abies forest and lowest in the Kalmia heath. Litter fall is the single most important source in the forests, but annual root mortality contributes most in the Kalmia heath. Additions from the moss layer amounted to about one—tenth of the annual return in the forests. The rate of organic—matter decomposition decreases from Abies to Picea to Kalmia cover type, with accumulations in the raw humus representing 14, 21, and 78 times the annual supply of the present stands, respectively. Mineralization of N and P show the same trend, but Ca and K mineralization are slower in the Kalmia heath only. A comparison of the nutrients in the Abies and Kalmia cover types showed that actual losses of K, and possibly Ca, had occurred from the Kalmia ecosystem during the 65—year period since the fire, and that the quantity of N in the Kalmia ecosystem was about double that in the Abies cover type. A net input of more than 23 kg/ha per year is required to account for this increase. No reliable comparison could be made between the Picea and Abies ecosystems, but the data available do not indicate any obvious fertility changes beyond a greater immobilization of nutrients in the raw humus of the Picea forest.