Richard Cobb

Primary Interests:

Ecosystem ecology with an emphasis on the response of functional ecosystem processes to natural and anthropogenic disturbances.

HWA Objectives:

I am collaborating with the HWA ecosystem group to document changes in litter decomposition that occur as hemlock forests decline. Harvard Forest and other researchers have found increased rates of N cycling in HWA infested forests and increased rates of decomposition have been suggested as a mechanism driving these changes.

We quantified the effects of HWA herbivory and altered microclimate on green litter decomposition by incubating HWA infested and uninfested foliage within the long-term ecosystem study sites (see Orwig et al). Changes in microclimate altered the physical breakdown of foliage; dry conditions at the soil surface retarded rates of mass loss. HWA herbivory had no effect on physical breakdown but significantly increased rates of N immoblization in decomposing foliage. This study is currently in review and the data are available to interested researchers.

We are pursuing an on-going study with the objective of quantifying long-term changes in litter decomposition that accompany altered litter inputs in HWA infested stands (Orwig and Foster 1998). We have incubated senescent hemlock, black birch, and mixed litter bags across a chronosequence of HWA caused hemlock stand decline. Preliminary data show significantly higher rates of litter mass loss in black birch litterbags and overall higher rates of litter mass loss in stands where black birch is well established.

Publications:

Cobb, R.C., and Orwig, D.A. 2002. Impacts of hemlock woolly adelgid infestation on decomposition: An overview. In: Symposium on the hemlock woolly adelgid in eastern north America. Reardon, R.C., Onken, B.P., and Lashomb, L. (eds). New Jersey Agricultural Experiment Station, New Brunswick, NJ. pp 317-323.