Lichen-substrate dynamics: influence of lichens on nutrient cycling and biological communities

Background/Question/Methods

In arctic regions, lichens are recognized as important components of the food web and biogeochemical cycles, but the lichen role in temperate areas lichen has been overlooked.   In the Pinelands of NJ, lichens constitute an important component of the forest; many trees have >60% lichen cover and in some places the biomass of lichens on the forest floor (1.02 tons/acre) represents slightly more carbon than the biomass of leaf litter. My research asks: how do lichens influence the landscape they grow in? My studies address lichens living both on trees and on the soil.  To investigate how epiphytic lichens influence stemflow chemistry (in particular whether lichens intercept aqueous N deposition) I compared the chemistry of stemflow from lichen-covered vs. non-lichen covered bark of chestnut oak (Quercus prinus L., the tree that harbors the most lichens in pine-oak forests of the area). To investigate lichen influence on soil processes, I conducted a transplant study with randomized block design and measured the differences in soil moisture, arthropod communities, nutrients, and enzyme activity beneath plots covered in lichens (Cladonia sp.), as compared with bare plots and plots covered with other leaf litter types.

Results/Conclusions

I expected to find N uptake by lichens, but this was not evident in my results on either trees or soils.  In the epiphyte study, I found no significant difference in N retention between lichen covered and lichen-free trees (which I attribute to the lower lichen biomass here than in other studies). However the presence of epiphytic lichens did produce a statistically significant difference in carbon and water retention on the trees (21% increase in water retention w/ lichens, and 43% increase in C retention in the growing season).  In the transplant study, soils beneath lichens did not have significantly different levels of available N compared with soils under other covers, but 6 months after transplantation, they did have significantly less available P (avg. 2.3ug PO₄-P/g soil under lichens vs. avg. 3.3ug PO₄-P/g soil under other ground covers), which represents a particularly important trend in this nutrient-limited system.  Soil moisture and arthropod community composition under lichen litter did not show significant differences compared with other plots until almost a year after the transplant/disturbance.  When assessing the influence of slow growing organisms like lichens, it is valuable to consider that their effects may build over time.