Litter decay and the role of macroinvertebrate decomposers in limed and unlimed forests of the Adirondack Mountains

Background/Question/Methods

Acid deposition has affected biodiversity and ecosystem function in many sensitive areas, including the Adirondack Mountains (Adirondacks) of New York State.  Terrestrial application of lime can ameliorate many of the negative effects of acid deposition, but the effects of liming on forest fauna and litter decay are poorly understood.  We used a reciprocal litter-bag study at limed (crushed limestone, 10 Mg ha^-1) and unlimed plots (0.16 ha) in the Adirondacks to better understand the effect of substrate calcium content and incubation context on rate of litter decay. We also examined the role of fauna in this system by extracting litter-dwelling macroinvertebrates from litter bags and excluding macroinvertebrates from certain bags.  Two separate sets of litter bags were deployed to study litter decay and the role of fauna during years 1-2 and 5-7 following liming.

Results/Conclusions

Leaves collected from trees at limed and unlimed plots differed in %Ca, reflecting a foliar response to liming.  Rate of litter decay was slower and litter accumulation was greater in limed than unlimed plots immediately after liming.  However, during years 5-7 after liming, litter decay at limed and unlimed plots was not different.  Throughout the study there was a faster decay of litter bags containing high-calcium leaves than litter bags containing low-calcium leaves, underscoring the importance of substrate quality.  Snails increased in abundance at limed plots. Millipedes decreased immediately after liming, which may have contributed to the reduction in rate of litter decay at limed plots.  However, litter bags with fauna excluded lost mass at the same rate as litter bags with faunal access during years 5-7.  So, the importance of macroinvertebrates in litter decay may be relatively small in this system.  Mitigative liming caused positive changes (improved litter chemistry) and negative changes (macroinvertebrate loss initially) at our Adirondack sites.  Effects of liming on litter decay changed with time.  Understanding the long-term as well as immediate effects of liming is necessary to determine the advisability of lime application in regions affected by acid deposition.