Tuesday, June 26, 2012

Summer Solstice Snapshot


Summer is always an interesting time to be looking at phenology and making Project BudBurst observations. There are a host of trees and wildflowers that wait for the heat of summer to become active. Some appear to be effected by local weather conditions and vary their timing according to what kind of year it has been and others are quite consistent in always flowering at the same time. Some studies have suggested that a number of tree species in the eastern US for example flower about the same time each year, especially in contrast to wildflowers that seem so sensitive to even small changes in temperature during the spring. It will be interesting to see what people find with their Project BudBurst observations for our first ever Summer Solstice Snapshot pulse this year.

The summer solstice itself is an interesting phenomenon.  While technically this means our days will get shorter from now until the winter solstice, for most people it actually means for the next several months it will get hotter and hotter.  This is because of the "lag effect" caused by the ability of the air, especially moist air to hold the heat. So even though the sun has slightly less radiation heating up the air each day, it continues to warm up because of this storage of built up heat over time.  The remarkable thing this year in Colorado is how hot it has been in the spring and early summer. We had temperatures in the 80's in March and now we have had record breaking searing heat, day after day in mid to late June.  And this is only the beginning of summer!  This heat led to wildflowers coming out an average of 3-4 weeks early, and fruits ripening at record rates. On the other hand all this heat with little rain or snow has led to huge problems for both plants and people this year.

Tales of Woe for Sweet Cherries

These patterns of heat and cold can have many effects on plants, well beyond simply leading to flowers emerging earlier.  One phenomenon which has been documented in high alpine areas of Colorado has been how warmer than normal temperatures can lead to plants becoming more susceptible to frost damage.  The idea is that if the plants are using temperature as a cue to determine when to put out new flowers, then if it is warm the flowers will emerge earlier in the spring or summer.  But if the warm temperatures are not consistent and more normal weather patterns return for a time, then this new growth and flowers could be killed by frost.

This is exactly what happened to most sweet cherries (Prunus avium) around my town. With those 80 degree temperatures in March cherries sent out leaves and flowers earlier than normal this year. Then when more normal weather returned in April  flowers were killed by frost.  This is the second year in a row of a bust in cherry production around the neighborhood.  Apparently the same thing happened in the Midwest as a friend from Michigan recently explained.  Remember those amazing warm temperatures in Chicago this spring?  Early flowers and killing frost did them in just like what happened here.  Pie cherries on the other hand normally flower a few weeks later than sweet cherries.  So there were lots of ripe pie cherries on trees around here this year. You have to be quick to pick them since the squirrels and other wildlife are quite fond of them.  My wife really wants me to plant a sweet cherry in the front yard, but I am thinking a pie cherry might be a safer bet.  This is a great example of how knowing about phenology can help explain so much of what is going on in your yard or garden!

Nearly all of our summer trees and shrubs have flowered in the past week or two, so there has been lots to contribute to the Summer Solstice Snapshot phenology campaign here.  The latest ones have been annual sunflowers, musk thistles, all three varieties of linden or basswood (American Linden, Tilia americana, Redmond Linden T. x euchlora, and small leaved  linden, T. cordata), goldenrain tree (a tree from Japan introduced by Thomas Jefferson in the early 1800's), western wheatgrass, and several other prairie grasses, as well as the weedy quack grass and smooth brome.  Just in the past few days Virginia creeper has started to flower, and there are many sunflower relatives blooming weeks or months early out in native short-grass prairies around here.

Garden Phenology
Don't forget that you can also make Project BudBurst observations with perennial garden plants too.  Herb gardens can be a great way to keep track of the progress of the season.  I will be developing descriptions of several of these species soon.  Good ones to watch are chives, common sage (Salvia officinalis), oregano, thyme, and tarragon; they generally flower in this order.  Waterwise plants such as coneflower (Echinacea spp.) black eyed susan (Rudbeckia spp.), and annual sunflowers can be good ones to watch in gardens too.

Where is the rain?
The big question here in the West is of course how this will all effect our water supplies and the already record breaking number of fires that are burning across the Rockies.  It sure would be nice if the summer monsoons were early this year!  Lately my weather station suggests that as much as a 1/4" of moisture is evaporating off my garden plants each day - sucking the moisture right out of the ground. Even with a drip irrigation system that's a lot of water.

Another phenology-weather-agriculture connection this year has been the demise of the winter wheat and pasture crops. They depend on cool temperatures and spring snow to provide early growth. Instead it has been dry as a bone, windy and dry. So now you can see lilliputian wheat fields, bronze in color, mature seedbeds, but one half or less their normal size.  A personal connection to this is now for the first time I cannot buy a bale of straw for mulching our garden. Hay and straw are premium priced this year!

Every year is different and every season is different, that's what makes doing these observations and keeping track of things so interesting. Always a lot to learn and see out there. Looking forward to seeing what you find during this interesting summer.

Paul Alaback