1. Light availability was not the only limiting factor to seeding recruitment under R. maximum. Although, light availability ( total and sunfleck frequency) was an important associate with seedling inhibition.

2. Allelopathy is not likely the cause for inhibition of seed germination, seedling survival or seedling growth.

3. Some soil resources (water and nutrients) were reduced under a thicket of R. maximum compared to forest without a thicket of R. maximum.

4. Mycorrhizal diversity was similar in forest with or without a thicket of R. maximum based on sporocarp occurrence.

5. Mycorrhizal abundance was reduced on seedling or Hemlock and red Oak under a thicket of R. maximum compared with forest without a thicket of R. maximum.

Those previous studies were limited because the experiments were restricted to sites that had either high density of R. maximum or no R. maximum. In the current research program we are using a more experimental approach and we are including Kalmia latifolia thickets. The current study is based on four general activities:

1)      In three different forest locations we have randomly established 60 2X2m plots.  All resources (nutrient, water, light) are carefully quantified.  In addition, the shrub and tree vegetation in wide rings around each plot has been measured.  Each plot is split, and seedlings of two species were planted in each split.  In one split the seedling root systems were sterile, and in the other split the seedlings were inoculated with a generalist mycobiont (Scleroderma).  All seedlings are carefully monitored for health all year.  Twice during the first year we have randomly harvested one seedling of each species from each split for  careful growth, allocation, nutrition, and mycorrhizal analysis.

2)     In the second experiment we established 10 sets of four 2X2m plots. Two of each set are in a thicket of R maximum and two are in neighboring forest without R. maximum.  In one plot (in R. maximum thicket) the shrubs have been tied out of the way to increase light availability without disturbing below-ground processes.  A frame of neutral density shade has been added above one of the plots in forest without R. maximum. Each plot was split and planted with seedlings as done for experiment one.  By comparing seedling responses in this blocked design with ANOVA we will be able to determine the relative significance of light intensity and mycorrhizal colonization rate to the inhibition of canopy tree seedlings.

3)      Associated with this study is a careful examination of the pre-germination filters to seedling occurrence.  We have established 10 pairs of seed traps in two different forest locations.  Each pair of traps has one under a shrub thicket and the other in nearby forest without the thicket.  We have detailed the tree and shrub vegetation around each trap, and we are collecting seed rain from all traps for three years.  We have also evaluated the seed bank around each trap on three separate occasions.  Finally we survey the extant seedlings around each trap.  In this way we will evaluate the seed rain, seed survival in the soil, and seedling establishment success in forest with and without the shrub species.  We will also test the toxicity of leaf litter, humus, and organic matter around each trap with test species and native species.

4)      We are examining the carbon gain potential of  a stratified random selection of seedlings in experiment one and two.  Light response curves, A/Ci curves, and sunfleck responses are being collected.  These data, along with geometric data will be used with a modified Y-PLANT model to analyze carbon gain properties of seedlings in the presence of varying density of shrub cover.

SUMMARY

The culmination of all these studies will be a descriptive model of the influences of shrub density on seedling performance and the mechanisms causing that influence. The experiment is scheduled to be concluded in September of 2004.