Department of Earth and Environmental Science

Arthur H Johnson

Nutrient acquisition and cycling in old-growth forests of the Cordillera Piuchu, Chile;
Old-growth coniferous (>500 y) and evergreen broadleaf (>300 y) forests of this coastal mountain range afford an opportunity to determine how temperate forests undisturbed by logging and air pollution acquire and manage nutrients. Considerable nutrient input consequential to the forests comes via the atmosphere from distant sources.Effects of water, temperature and nutrients on the recovery of forests after severe disturbance; Any of the three preceding factors can limit the acquisition of carbon by forests. A global-scale data base of measurements made on forest chronosequences shows that forest biomass recovery rates can be reasonably well predicted given only a few stand and climate characteristics.

Effects of nitrogen availability on net primary productivity of forests at Whiteface Mt., NY; We are testing two hypotheses regarding controls on stand-level productivity: (1) that annual net primary productivity (ANPP) is N limited, and (2) that ANPP is limited by growing season temperatures. These are not mutually exclusive, as N availability is controlled, in part, by temperature.

Phosphorus biogeochemistry in the Luquillo Mts., Puerto Rico; Phosphorus is generally in short supply in tropical forests, and may be an important growth-limiting nutrient. Using recently developed chemical procedures for fractionating soil phosphorus and consensus interpretations of how available each fraction is to plants, we are exploring the dynamics of this element in the subtropical wet forest and subtropical rain forest of the Luquillo Mts. of northeast Puerto Rico. Biologically available P is in short supply. Controls on plant available P appear to be mainly biological, and P pools do not appear to be much affected by natural and human disturbances.

Biomass accumulation in Eocene forests of the Canadian High Arctic; Remarkable preservation of 45 million year-old floodplain forest ecosystems allows a reconstruction of forest composition, structure and dynamics using many of the same techniques used in modern forestry. There are >20 stacked forests preserved which grew at latitudes of about 75o N in what is judged to have been a warm temperate climate. The forests are remarkably intact, now comprised of mummified wood, cones, roots, seeds, leaves, etc. Careful excavation and longitudinal sectioning of the trunks of trees will allow interpretation of stand composition, structure, dynamics and productivity. Our initial observations suggest that these forests, dominated by Metasequoia, were dense and fast growing. Trees probably reached 40 m in height.

Manuscript- Changes in the northern hardwood forests of Vermont over three decades: Soil organic matter, productivity, sugar maple health and soil base cations..[pdf]