Heatwaves and trees


Recently, several homeowners in Hopkins County have called the Hopkins County Extension Office commenting their concerns related to their trees. Trees have an interesting effect in people: for some, trees are a top priority for their landscape, while for others, they are not that significant.

While an important asset to our landscape, trees have an important requirement difficult to substitute: it takes time to grow a tree and because of that, trees command an important economic decision to make. As I did some research in the subject, I found a small amount of published data related to the impact of heatwaves on trees. Because we are going through a series of heatwaves typical of the summer season, heat impact is one of those causes of stress during this time of the year.

According to Teskey et. Al. 2014, “The number and intensity of heat waves has increased, and this trend is likely to continue throughout the 21st century. Often, heat waves are accompanied by drought conditions. It is projected that the global land area experiencing heat waves will double by 2020 and quadruple by 2040.

“Extreme heat events can impact a wide variety of tree functions. At the leaf level, photosynthesis is reduced, photooxidative stress increases, leaves abscise and the growth rate of remaining leaves decreases. In some species, stomatal conductance increases at high temperatures, which may be a mechanism for leaf cooling. At the whole plant level, heat stress can decrease growth and shift biomass allocation.

“When drought stress accompanies heat waves, the negative effects of heat stress are exacerbated and can lead to tree mortality. However, some species exhibit remarkable tolerance to thermal stress. Responses include changes that minimize stress on photosynthesis and reductions in dark respiration. Although there have been few studies to date, there is evidence of within-species genetic variation in thermal tolerance, which could be important to exploit in production forestry systems.

“Understanding the mechanisms of differing tree responses to extreme temperature events may be critically important for understanding how tree species will be affected by climate change.”

For the homeowner, the effect of heatwaves might impact the tree population in different ways if the trees have a different genetic background (unrelated) since their capacity to cope with heat might be different. If those trees are related (as often happens with wild-type trees), the heatwaves effect might cause similar damage to the trees.

Homeowners should expect change in color (photosynthesis impact), loosing of limbs and leaves (biomass shifting) and potentially death due to heatwaves. Because of the genetic difference of the trees (or lack of) the heatwave impact might be similar to some trees (those closely related) or very different in unrelated trees.

It is important for homeowners to evaluate the potential consequences of the effect of loosing a tree in the landscape: the biomass of a dead tree is very significant, and the impact in existing structures and people or animals living in the location must be considered when big trees fall down because of the potential damage that this can cause. It is always recommended to be extremely cautious when making the decision to take down a tree and err on the safety side if needed.