Sugar maple and black cherry crown health and seed production in response to contrasting defoliators in northern Pennsylvania
Sugar maple, Acer saccharum Marsh. (SM) and black cherry, Prunus serotina Ehrh. (BC), are key species in the Allegheny and northern hardwood forests of Pennsylvania where seed crops have been poor and erratic for more than a decade. We monitored crown health and seed production of SM and BC since 2009 in plots established as part of other studies on the Allegheny National Forest (ANF), and, since 2008 in a long-term liming study 160 km east of the ANF on the Susquehannock State Forest (SSF), Potter County. On the ANF, 10 locations, each with 3 to 5 0.04 ha plots, were used to assess crown vigor (1: <10% dieback; 2: 10-25%; 3: 26-50%; 4: >50% dieback; 5: dead), percent defoliation (none=0, light= 1-30%, moderate=31-60%, severe >60% defoliation), and seed production (none=0, light= 1-30%, moderate=31-60%,heavy >60% of crown with seed). On the SSF, 16 0.2 ha control plots (four per site) were used to assess crown health and seed production of SM and BC on untreated control plots using similar protocols.
On the SSF, a major outbreak of forest tent caterpillar (FTC) (Malacosoma disstria Hübner) and eastern tent caterpillar (ETC) (Malacosoma americanum Fabricius), both early season defoliators, affected both SM and BC during 2010-2012. Mean SM crown vigor (n=147) was 1.4 ± 0.1 (n=147) in 2008 and deteriorated to 2.3 ± 0.1 in 2010. SM has been slow to recover and by 2014 mean vigor was 2.1 ± 0.1. Mean BC crown vigor (n=117) was not as severely affected by these defoliations remaining <2.0 through 2014. On the ANF, an outbreak of fall webworm (FWW) (Hyphantria cunea Drury), a late season defoliator, primarily affected BC from 2011-2013. Mean BC crown vigor (n=157) deteriorated slightly from 1.5 ± 0.1 in 2008 to 1.6 in 2012, the peak year of FWW infestation even though more than 70% of BC trees were infested with FWW. On the ANF, more than 80% of BC trees had light to heavy seed crops in 2010, but sparse or absent seed crops through 2014. On the SSF, BC seed crops averaged 1.8 ± 0.1 in 2012 and 1.4 ± 0.1 in 2014 with more than 70% of trees with light to heavy seed in both years. Sugar maple seed production has been poor or absent in both study areas through 2014. Inconsistent and poor seed production will have long-term consequences to forest management objectives across this region.