Sunday, May 4, 2008

A Tale of Two Trees

The two trees that were planted on my street in March leafed out over the last three weeks, and emerged as beautiful young Zelkova trees, most likely Japanese Zelkova, (Zelkova serrata) as these are a species listed on the NYC Department of Parks and Recreation list of approved trees for street tree planting. The majority of the existing trees on the block are Callery Pear (Pyrus calleryana), but there already is a mixture of a few other species that the two new Zelkovas are joining, including Ginko, European Hornbeam, Green Ash, and a few older Zelkovas.

Although they were planted on the same street, on the same day, these two trees have had very different experiences. The tree on the southern side of the street has had a much rougher go of it. A branch was torn off of the south side tree in early April, leaving a jagged wound. Coming home from work one day, I saw the damage done, and was afraid that this wound would provide an entry for insects and fungus to attack my new neighbor, stunt its growth, and possibly kill it. Luckily, another neighbor also realized the danger to the young tree, as the torn branch was pruned within a week.

To add insult to injury, the tree on the south side of the street remains shaded by neighboring buildings much more of the day than the tree on the north side of the street. This may not seem like such a big deal to us who can walk to the grocery store to get our food, but the Zelkova is stuck waiting for the sun to bring food to it, so building shadows can really get in the way of a good meal. In fact, the south side tree leafed out a few weeks later and continues to lag behind the north side tree in foliage growth. There undoubtedly were other factors effecting the slower growth rate of the south side tree (the wound, perhaps differential treatment at the nursery or during planting), but the southern exposure that the north side tree experienced certainly gave it a leaf up. Further down the street, the Callery Pear trees on the south side and at the corners (where they were able to get more sunlight) also flowered sooner and more this spring. Most people do not realize just how much of an impact building shadows have not only on what can or cannot grow, but also on the size, shape, and speed of growth of whatever is planted there.

North Side Zelkova

South Side Zelkova


Anonymous said...

Very interesting post Katydid.

Your observation underscore the importance of matching tree growth requirements to planting site characteristics. The tree planter might have considered access to sunlight in choosing a species for the southern side of your street.

I am still amazed to see urban design plans with both sides of a street planted with the same species. I recognize the particular aesthetic gained from uniformity but plant health should be an equal if not greater factor in species selection and streetscape design.

In terms of shade, unfortunately, there are few "desirable" species that are shade tolerant. (Ashes are shade tolerant but they are susceptible to disease and structural problems.) And of the ones that are tolerant, other site characteristics must be accounted for like the size of the planting area. Little leaf linden, red oak, and sycamore are shade tolerant but require a lot of root and overhead space.

Finally, if the southern side of the street is shady, a "shade tree" - an alternative name for a "street trees" - might not be necessary. Of course, city trees provide more than shade.

I look forward to your next post.

Anonymous said...

Any new posts in the pipeline?