Using redbuds as model systems in phenology studies sounds like a good idea but there are two things that trouble me.
1) What is the genetic difference between wild and cultivated trees? How are redbuds propagated for the horticultural trade? Are they grown from seed or via some mode of vegetative propagation? Are we dealing with some sort of genetic bottleneck that will canalize the performance of the cultivars vs. the wild, self-planted trees? You have to be careful of this, for example, when dealing with color changes in tree leaves in the autumn. If you buy a tree or bush for Fall color it's best to select it for purchase in the fall when you can see the color change in the leaves. What you see is what you get. Growing it in a "nicer site" doesn't mean better color. There's a whole range of liquidambers, for example. In some, the leaves always turn vivd red orange. In others the change is incomplete and the leaf is green, yellow and red in a series of blotches.
2) Yes, you do have those nice flat pods to check out seed set but the question is are you certain that a bump in the pod represents a fertilized developing seed? Each pistil will contain a certain number of ovules but. in some plants, those ovules continue to develop a bit as the ovary enlarges. It doesn't matter whether they've been fertilized or not. Someone needs to do a little research on when you can approach a pod, count the number of bumps and be relatively assured you are counting the number of fertilized seeds.
On Sat, Aug 21, 2010 at 1:33 PM, Cowden, Nancy <Cowden@...>
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.
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
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?
- 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
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.
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