Tuesday, April 19, 2011

Philadelphia in the Spring

Philadelphia is famous for its historical public squares, which this week are filled with vibrant colors of spring. Here is Rittenhouse Square with saucer magnolias and crabapples in bloom.

I had the great pleasure of traveling to Philadelphia last week, during which there were nice sunny days and lots of new flowers and leaves coming out on trees and shrubs and even wildflowers. Compared to Colorado Philadelphia is a week or two ahead in its phenology. You can see this by looking at common ornamental plants like white flowered crabapples, cherries and saucer magnolias (Magnolia soulangiana) which are common in both places. In the city there were many spring colors, in more wild areas with native plants spring was a bit more subtle. While I was there black cherry (Prunus serotina) came into flower next to the house I was staying in, going from one flower on one branch the first day, then about 5 branches with flowers the next day, or the first flower stage (4/15) then all the way to the full flower stage (more than half the branches with flowers) by the time I was leaving on 4/17).

Normally when you travel the occasional observer protocol could be used to record budburst observations since it is hard to know if you are really seeing the first day that a given plant put out leaves or new flowers. But if you have a chance to observe the same plants even for a few days during a rapidly changing time of the year like Philadelphia and many other places last week you can actually make some good regular budburst observations as well.

I also had the opportunity to visit some places outside the city to see how it compared with what was happening in the city. Normally you would expect the first flowers to occur in the city because of the "urban heat island" effect, where concrete tends to capture heat more quickly than soil so it is a little warmer and plants should become active sooner. For example black cherry was just starting to flower in the city but was still in the bud stage in the country.

I also had a chance to see budburst in action with many elementary school classes coming to the John Heinz Wildlife Refuge on Friday, working on pollinator gardens and other projects which will include making budburst observations on the plants that are developing there. Wildlife refuges can make for great places to make budburst observations since they have a wide range of natural habitats and are often easy to access, and may even include nature centers where you can get more information on local plant species. The most obvious wildflower in bloom on Friday was the marsh marigold (see above).

Another highlight was being able to see the oldest and one of the most unique botanical gardens in the country. This is the garden of John Bartram, who was a naturalist and botanist that helped establish botany and other sciences in the US and whose writings in the late 1700's inspired Henry David Thoreau and many other naturalists and scientists then and today. These places can be great places to make budburst observations since you can then compare dates of flowering with historical records, in this case over 200 years ago!

Coming back to Colorado on Monday I saw several changes since I left, again showing how now is the time to be watching your plants for budburst - they may change every day! Sweet cherries (Prunus avium) are now in bloom, the first japanese crabapples are in bloom, and several more cottonwoods came into bloom while I was gone. Eastern redbud has just come into bloom as well.

Earth day is coming up this week, it should be a great time to make budburst observations and introduce new people to our program. And it should be a great excuse to enjoy more of this lovely if not ever changing spring weather and enjoy learning some new flowers.

A beautiful forest in Bartram's gardens, with some trees planted as much as 200 years ago. Here you can see redbuds (Cercis canadensis) and sweet cherries (Prunus avium) coming into bloom.

Paul Alaback

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