Inhibition of woody colonization on a reclaimed anthracite mine: Seed rain and seed bank dynamics

Background/Question/Methods

Federal law established in 1977 mandates that sites impacted by mining be reclaimed using approaches to reestablish original surface contours and establish vegetative cover.  Since that time, reclamation specialists have reclaimed minelands using mixtures of non-native grass/ legume seed mixtures.  Studies conducted on reclaimed mines in the eastern United States have shown such reclaimed mines resist tree invasion, thereby creating states of arrested succession.  Poor tree colonization can result from lack of seed rain, low rates of seed germination, or poor seedling survival. We investigated whether the lack of native tree colonization on a reclaimed anthracite mine site near Wilkes-Barre PA is due to insufficient seed rain.  The site consists of a 400m long slope, at the top of which was a remnant hardwood forest that has the potential to act as a seed source.   We deployed 21 seed traps along five parallel transects each extending up the slope within the reclaimed mine in fall 2010.  Seed banks were concurrently assessed by obtaining thirty 10” x 8” x 1” deep soil samples from the reclaimed mine.  Samples were placed in aluminum pans in a greenhouse, and watered periodically.  Seedling emergence within the pans was subsequently monitored. 

Results/Conclusions

Examination of the seed traps in December revealed no native tree seeds, regardless of distance from the forest.  Flushes of seedlings were observed in each pan.  However, all were of herbaceous weedy species such as Daucus carota, Erigeron sp., and Solidago sp.  No tree seedlings were noted. The data collected to date suggest that poor tree colonization results from lack of seed rain, though further yearlong investigation is warranted.  Lack of natural tree colonization lends further support to the Forest Reclamation Approach (FRA) to land reclamation in which seedlings of native trees are directly planted on mined sites.  While more expensive and labor intensive than conventional reclamation approaches, FRA has been shown elsewhere to promote succession to native forest, and is especially needed where development of economically valuable trees is desired.