A struggling maple tucked away in the pavement of Crown Point’s massive Barton Centre retains few leaves. It’s barren branches stick out like accusatory fingers, “why has no one cared for me?” It is not alone. Apart from the hardy honeylocust, many of its parking lot comrades are defoliated or dead. They are isolated from the protection of other trees, and exposed to high levels of road salt, car traffic, heat and wind. Often when a new development is completed, contractors are required to care for the site’s trees for a certain period of time. We have our doubts that, by this point, the Centre’s 200+ trees are not being regularly loved. But perhaps trees are more resilient than we think?
One way in which trees are able to survive in unfavourable conditions is to regulate their leaf temperature. An interesting National Geographic article explains how tree leaves can keep the same temperature, from tundra to tropics (link below).
The article features a study of 39 species of trees on the North American continent by researchers at the University of Pennsylvania. These coniferous and deciduous species came from the chilly North all the way to the warm South. The study looked at the ratio of two different oxygen forms in tree rings since the specific ratio is linked to ambient temperature and humidity. Using this air temperature and humidity, they worked out the average leaf temperature of all 39 species to be around 21.4 degrees Celsius.
The researchers believe that 21 degrees is ideal for photosynthesis, and that the trees aim to have their leaf temperature fluctuating about that point. So how do the leaves roughly maintain this temperature despite varying climates? They heat up in cool weather and cool down in hot weather by manipulating the processes of evaporation and light detection. In the heat, tree leaves bend downwards to avoid light, release water for the cooling effect as it evaporates, and reflect light with little hairs. In the cold, leaves are bunched together to reduce the rate of individual heat loss from each leaf.
Although many Barton Centre trees are not happy in their environment, they may try employing some of the techniques above to survive. We’re cheering them on!