PARENT SESSION
Poster Session #19: Nutrient Cycling.
Tuesday, August 7, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Biogeochemical response of northern hardwood forests in the Catskill Mountains to several harvesting intensities.

Murdoch, Peter¹, Burns, Douglas¹, Yorks, Thad², Leopold, Donald², Raynal, Dudley², ^{1 2}

ABSTRACT- We quantified the responses of vegetation and stream water chemistry in a northern hardwood forest in southeastern New York after three intensities of timber harvesting: clearcutting, heavy timber stand improvement (TSI), light TSI (97, 29, and 10% basal area reductions, respectively), and on a reference site. After clearcutting, residual tree growth was negligible. Biomass and nutrient retention were initially dominated by growth of regenerating woody stems (up to 140 cm tall) and herbaceous vegetation, but saplings (0.1-5.0 cm DBH) became the most important contributors to biomass and nutrient accumulation within three years after harvest. Both levels of the relatively less intensive TSI harvesting resulted in a different vegetative response; trees continued to account for practically all biomass and nutrient accumulation while there was relatively little response in saplings and vegetation <140 cm tall. In addition to tree species, several early successional shrub and herbaceous species were also important in revegetation after clearcutting (e.g., Polygonum cilinode, Rubus spp., Sambucus racemosa). Clearcutting caused dramatic increases in NO₃^- and cation (e.g., inorganic monomeric Al, NH₄⁺ L^-1, Ca²⁺, Mg²⁺, and K⁺) concentrations in stream water for at least three years after harvesting. For example, NO₃^- increased from pre-harvest concentrations of 0-40 mol L^-1 to as high as 1,400 mol L^-1 and remained >200 mol L^-1 until the beginning of the second growing season after clearcutting. Neither level of TSI affected stream water chemistry.

KEY WORDS: clearcutting, nitrate, stream water chemistry, understory vegetation