PS 13-175 - CANCELLED - Access to arbuscular mycorrhizal networks may modulate seedling growth and survival under different management regimes in a Northern Hardwood forest

Abstract: Over the past 400 years, forests across the eastern United States have undergone a shift from the heterogeneous oak-pine savannahs of the 1600’s to the uniform forests we see today, which are often dominated by genera such as Acer and Prunus. These changes in forest composition have parallel shifts in the symbiotic fungi associated with tree roots, in this case from ectomycorrhizal (EcM) dominated forests to arbuscular mycorrhizal (AM) dominated forests. However, environmental stressors ranging from prolonged periods of drought to invasive insects pose a threat to many AM-associating species. We sought to investigate how forest management decisions affect the survival and growth of AM-associated seedlings in order to promote forest diversity and function, and to maintain the abundance of species such as sugar maple that many Northeastern communities rely on.

Our research investigates effects of selective vs gap timber harvesting on the survival, nutrient acquisition, and mycorrhizal colonization of three prominent Northeastern deciduous trees: Sugar Maple (Acer saccharum), Black Cherry (Prunus serotina), and Black Gum (Nyssa sylvatica), all of which associate with (AM) fungi. In June 2022, we established trenching treatments in selectively harvested and quarter-acre patch-cut plots at Corinth to investigate how the exclusion of roots and AM fungal networks affect the growth and survival of A. saccharum, P. serotina, and N. sylvatica. This approach may shed light on the importance of maintaining seedling access to live adult AM-associated trees in adaptive silviculture treatments.

Data from the summer of 2022 revealed that seedlings demonstrated higher survival in the selectively harvested plots (where seedlings were closer to surrounding, mature trees) versus when they were planted in quarter-acre patch cuts. In addition, seedling growth in the selectively harvested plots was higher in seedlings with a low δ15N natural foliar abundance, a measure which may be used as a proxy for N transferred from mycorrhizae, with low δ15N values demonstrating high mycorrhizal N transfer. Soil nutrient data (nitrate to ammonium ratios), as well as root samples stained for mycorrhizal colonization measurements, are currently being processed and will be presented at the time of the conference. These data will add to our knowledge of how forest mycorrhizal networks affect seedling regeneration success under various forest management methods.