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1148RE: [beemonitoring] Seed Set, Phenology, and the Redbud Tree

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  • Cowden, Nancy
    Aug 21, 2010
      Redbud is Cercis canadensis, at least in eastern N. America; varieties/other species are found elsewhere.  In addition to possible pollinator issues, redbud does suffer from a number of fungal diseases, especially as it ages and/or is stressed.  As we put these trees under more stress (by planting them as street trees when they're actually forest understory plants as well as what we are doing to alter climate patterns), they are more susceptible to disease and death.  There is a graduate student at Clemson (Isaac Park) who is working on a phenology project using redbud as one of his subjects; I'll certainly pass the ideas along to him.
      Nancy Cowden

      From: beemonitoring@yahoogroups.com [beemonitoring@yahoogroups.com] On Behalf Of Sam Droege [sdroege@...]
      Sent: Friday, August 20, 2010 5:38 PM
      To: beemonitoring@yahoogroups.com; lebuhn@...; Jake Weltzin
      Subject: [beemonitoring] Seed Set, Phenology, and the Redbud Tree



      I was looking at some of the copious seed pods produced on Redbud Trees (Celtis americana?  ... Internet not handy) this summer in Kentucky and noticed that it was very easy to both count the number of seeds produced directly through the pod (the pods were green) and to note the number of places in the pod that should have had a seed, but, did not.  Since the Redbud is a widely occurring understory/edge tree in at least Eastern North America and widely planted as an ornamental (not sure about the West) and short in stature (making the seed pods easy to inspect) and providing abundant nectar and pollen in the spring (see email from Mark Kraemer below);  I would propose that it has the characteristics that would make it a good candidate for monitoring both phenology and to investigate patterns and changes in seed set which should be related to pollinator abundance.  That said, I am not a pollination ecologists and am thus likely am over-simplifying the situation in regards to interpretation of rates of pollination.  However, it seems likely to me that the primary factor decreasing the seed set of Redbuds (over years) would be loss of its pollinators.  

      The following characters seem to make Redbud an appealing (at least to me) candidate for looking at geographic and habitat patterns of phenology and seed set

      • It is widely planted in urban/suburban/rural human landscapes
      • It can be readily found in the wild in some parts of North America
      • The tree is easy to identify, short in stature and the pods are low hanging
      • It is easy to identify and count the seeds (and easy to photograph them)
      • The seeds hang around for a long time
      • It blooms are highly attractive to spring bees
      • It can be used to gauge spring phenology

      I would be interested in what people think might be the interpretational issues of variations (both long and short and geographic) of seed set in Redbud.  Another issue might have to do with whether there is useful information in the absolute number of possible seeds in a pod...is this fixed or, if not, what are the possible controlling variables?



      Email from Mark Kraemer
      Here are my thoughts on using Osmia as a monitor for climate change.   I’ve worked with O. lignaria in Virginia since about 2002.  
      It is likely that each geographical population of bees has adapted to local climate conditions and has its own chilling and perhaps heating degree day requirements for spring emergence.   Thus, sending cohorts from one geographical region to other regions may be a problem.  For example, if bees from a colder winter climate area are sent to a warmer one and they do not get enough chilling they will have poor emergence extended over a longer period of time, similar to fruit tree bloom when not enough chill units have been accumulated.   Nest building would be extended late into the season but have nothing to do with climate change.   If bee tubes are sent out in late winter after chilling requirements are met, you still have the problem of variable and unknown temperatures during transit.  It’s best to use local bee populations if possible.  
      I’d use eastern red bud bloom for phenological comparisons, at least in the Eastern U.S.   I found female emergence in Virginia and North Carolina closely coincides with initial bloom of Eastern redbud.  Eastern redbud provides not just pollen but nectar early in the season when few if any other trees/shrubs are flowering.   It’s a very common forest understory tree and an ornamental found throughout most of the eastern U.S.  The vast majority of pollen (>90%) that I sampled from nest cells created in the first week was redbud (4 sites), even when the trees were not nearby the shelter boxes.   Nesting was very poor and late in one site where redbuds were not found.   I would expect first nest completions to be 7-10 days after initial redbud bloom, depending on air temps.  Some of these phenology results should appear soon in Environmental Entomology.  
      I’d like to know whether our observed phenological link of female emergence with Eastern redbud bloom occurs elsewhere, and the pollen composition of the early nest cells.  If this relationship is true, and because climate has changed so radically during the past few million years, I’d speculate that the bees and trees have co-evolved a very similar mechanism for coordinating their emergence/bloom through a broad range of climate change.  
      Mark Kraemer

      Sam Droege  sdroege@...                      
      w 301-497-5840 h 301-390-7759 fax 301-497-5624
      USGS Patuxent Wildlife Research Center
      BARC-EAST, BLDG 308, RM 124 10300 Balt. Ave., Beltsville, MD  20705

      Wanting Sumptuous Heavens

      No one grumbles among the oyster clans,
      And lobsters play their bone guitars all summer.
      Only we, with our opposable thumbs, want
      Heaven to be, and God to come, again.
      There is no end to our grumbling; we want
      Comfortable earth and sumptuous Heaven.
      But the heron standing on one leg in the bog
      Drinks his dark rum all day, and is content.

            - Robert Bly

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