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Harvard Forest Symposium Abstract 2012

• Title: Trees make seeds: Masting and its implications for pollinators, seed consumers, and forest carbon dynamics
• Primary Author: Joshua Rapp (Massachusetts Audubon Society)
• Additional Authors: James Crall (Harvard University); Elizabeth Crone (Tufts University)
• Abstract:

  Seed production assures the persistence of tree populations and forest cover over the long-term, and so has long interested plant demographers and foresters. Many forest tree species produce seeds at irregular intervals and synchronously across large areas, a phenomenon known as masting. In the spring 2011, a research project was initiated at the Harvard Forest on the mechanisms of mast seeding, and its impact on pollinators, seed consumers, and forest carbon dynamics. Seed production is monitored via litterfall traps and counts of seeds on trees for 20 sugar maple trees, and flower production and resource status (via sap collection) is monitored on a subset of 12 trees. Pollinator dynamics (primarily Andrenid bees) are also monitored. Expansion of the project to include red oak and a key seed consumer, the eastern chipmunk, is planned for the coming year, and acorn production was measured in one stand in the Tom Swamp tract of Harvard Forest in fall 2011.
  
  Abundant flowering and fruiting by sugar maples occurred in 2011, and initial observations have revealed intriguing patterns. Sugar maples were observed to have both male and female flowers on the same trees, with male flowers maturing first in 6 trees and female flowers maturing first in the other 6 trees. Male-first trees had a greater proportion of female flowers overall, and the proportion of female flowers was positively correlated with sap sugar concentration measured the following year. Sap sugar concentration was positively correlated with stem diameter (DBH) and with seed production. Flowering branches had fewer leaves and less twig growth than branches without flowers.
  
  This preliminary data suggest that sap sugar concentration is a faithful proxy of tree resource status and is related to seed production in sugar maples. We found corroborative evidence for this in an 11 year time series of seed production and maple syrup production from Vermont showing that syrup yield per tap was lower in the year after a mast year. Our data also suggests that a meristem limitation exists wherein buds used for flowering have a lower capacity for producing leaves, a conclusion supported by observations of reproductive and vegetative litterfall being negatively correlated across years for 5 stands dominated by sugar maple in Michigan. We will continue to monitor seed, leaf, and sap production and initiate experiments that will help to increase our understanding of how internal resource dynamics, pollination, and climate affect mast seeding, and the implications for masting on seed consumers, pollinators, and forest carbon dynamics.
  
  

• Research Category: Biodiversity Studies
  Physiological Ecology, Population Dynamics, and Species Interactions
  Regional Studies