Effects of beech bark disease on aboveground biomass and species composition in a mature northern hardwood forest, 1985 to 2000

We examined changes in species composition and aboveground biomass of a maturing, Adirondack northern hardwood forest over a 15-yr period in order to assess the potential effects of beech bark disease on the structure and nutrient cycling processes of the stand. Aboveground biomass of living and dead stems, and annual litter production were estimated in 1985 and 2000 within a 1.96 ha area using total stem inventories (greater than or equal to 5 cm dbb). A comparison of species composition and biomass of the forest, as well as mortality and growth rates between the two sampling years are presented. The aboveground biomass of living stems decreased from 209.8 Mg . ha(-1) in 1985 to 195.7 Mg . ha(-1) in 2000. Acer rubrum was the only species to increase in biomass. Fagus grandifolia and Acer saccharum were the most important species in 1985 and 2000, although F. grandifolia increased in importance while A. saccharum decreased in importance during this time. Large stems of F. grandifolia experienced high mortality rates, but were balanced by ingrowth of smaller stems. In 2000, 58% of F. grandifolia exhibited no to minor signs or symptoms of beech bark disease, while 28 and 13% displayed moderate and high signs of infection, respectively. Ninety-nine percent of the uninfected stems were < 15 cm dbh. Although total aboveground biomass decreased during the 15-yr period, annual litter production remained constant. Furthermore, the increase in F. grandifolia importance value did not substantially alter the lignin content of litter. We conclude that the presence of BBD is hastening the onset of uneven-aged conditions in this second-growth stand but may not lead to large changes in forest nutrient cycling processes based on the lack of change in total lignin content of the leaf litter layer. Currently it appears the canopy will continue to be dominated by shade tolerant species, although the importance of F. grandifolia and A. saccharum are changing especially with respect to the relative importance of different size classes.