Leaves

Over two weeks ago I was looking out my office window pondering problems for projects in a rather diverse community.  By race and ethnicity, Fitchburg is the most diverse municipality in Dane County.  It is also the most diverse from a land use perspective, going from rural to high density areas.  It is the only city in Wisconsin to have exclusive agricultural zoning, and the only community in Wisconsin to adopt the transect based SmartCode zoning, which is a form-based neo-traditional zoning code.  The landscape I viewed out my north office window is also diverse.  I see standard  suburban development with the resultant expanse of asphalt; I see prairie; and I see the dome of the state capitol building almost directly north.  I see the University of Wisconsin campus, and on dark days, if the Camp Randall score board is on, I can see that too.  What struck me was not the urban use or the prairie landscape, but the landscape of shade trees in the islands of the Community Center parking lot as I view north.  A few weeks ago, of the five honey locust trees, one was still all green, two were well changed in color to a legal-pad yellow, one was beyond the yellow to a golden rust color losing its leaves, and one was just starting to turn.  A few weeks later the legal-pad yellow colored trees were the golden-rust, the golden rust has lost all its leaves, and the even the one starting to turn yellow, is now the golden rust.  The tree that was all green leavea a few weeks ago is now yellow and its leaf loss is now in progress, while as of October 17, the others are pretty well leaf-less.  

Community Center north parking lot.  Oct. 11, 2016
More than a week after my first observation of the locust trees
(Taken on one  of the few days of sun this fall)

Living organisms all have some differences.  Given this I would expect differences among the honey locust trees, but the differences in leaf cycle of the trees is all the more striking considering their similarities.  The trees share a very similar macro and micro-climate, soil conditions, and other climatic factors.  They are all within 130’ of one another.   They all were purchased at the same time, from the same nursery, transported to the site the same way, at purchase all near the same size, all are the same variety and all were planted on the same day 28 years ago.  Changes have occurred over the last 28 years.  City Hall has been constructed to the west of the Community Center, although tree root zones were little affected by construction.  Curb and gutter was installed around the parking lot islands about 12 years ago, and about four years ago an addition to this parking lot side of  the Community Center was constructed.  The trees span over a month  in their leaf cycle, from when I first noticed the striking differences three weeks ago. 

Front yard locust tree (Autumn Purple Ash behind)
notice most all leaves are off.

Leaf cycle is said to be related to a number of factors, but the one major factor to lead to the changing color of leaves is said to be the change in day light.  From the summer solstice the days get shorter and shorter and about the third week of September we have the autumnal equinox which provides the same amount of day light as does the spring equinox in March.  Given this supposed major factor, the difference in leaf cycle seems rather remarkable.  I have noticed the difference among locust trees at my house.  However, they were planted in different years, and of varied size at time of planting.  Their microclimates are rather different, as one is near the street and drive, and two are in the backyard.  Of the two in the back yard one is in more shade than the other.  The tree by the street changes first and as of the week of October 10 has lost almost all its leaves.  The more shaded of the two in the backyard is now losing its legal-pad yellow leaves, and the other is still very much green, and receiving its tinge of yellow color. 

Locust trees in backyard. one to left, partially obscured is yellow and loosing leaves,
one in center is mainly green

The one difference of my unscientific experiment of locust trees at the Fitchburg Community Center is that the one that turned late has a bio-infiltration facility next to it.  During its construction four years ago this facility would have disturbed some of the tree’s root zone.  Does the extra water in a rain garden that does not work well (water stays in for weeks so it is almost a pond that a bio-filtration facility) affect its change of color?  Or perhaps in combination of the water it is added nutrients that can enter its root zone from the trapped storm water?  In addition to recharge of storm water, another purpose of bio-infiltration facility is to trap nutrients in the soil structure and avoid their transfer to surface waters.  I made an inquiry to the city’s urban forester, and she commented that it the change of color is most related to shortening days and was surprised at the significant difference.  The problem is,  I just noticed the difference this year, and do not recall if the difference was present before the building addition and rain garden were built.

Looking up at tree in backyard that was well turned, with non-turned locust to the right.

The power of observation would have served me better if I had recalled having noticed differences among the trees in this one parking lot during a prior year.  (Even the forester, whose job it is to look and observe trees, had not noticed the differences.) Maybe there were no significant differences, and that is why it did not register.  We observe much, but not all resonates in our mind.  Memory can be selective, but observation can also be powerful, and if we take sometime to think of what we see we may see the beauty and diversity of nature at play.