The Effects of Climate Change on the Ash Tree

Trees grow and flourish where local conditions suit the specific tree species’ ecology. One of the most important abiotic (non-living) factors that influences that suitability is the local climate.

Ash trees are predominantly in the genus Fraxinus; such as the white ash (Fraxinus americana) in North America, the European ash (Fraxinus excelsior) in northern Europe, the Chinese or Korean ash (Fraxinus chinensis) in northeastern Asia, and the Afghan ash (Fraxinus xanthoxyloides) in central Asia. Some species of other tree genera have been given a common name that includes “ash” in some parts of the world because of morphological characteristics that give them a similar appearance to the ash trees of the Fraxinus genus. In North America, some species of the genus Sorbus are called “Mountain ash” and some of the Zanthoxylum species are referred to as “prickly ash”, while in Australia, many of the eucalyptus species are called ash because of their similarity to some Fraxinus species in the type and quality of the timber produced.

There are approximately 50 species of trees in the Fraxinus genus that are considered to be ash trees, growing mainly in the northern temperate and subarctic regions of the globe. These ash trees are quite specialized, each having its own unique requirements. For example, the white ash, also known as the cane ash or Biltmore ash and a favored wood for baseball bats, prefers damp, elevated locations in comparison to the similar appearing green ash (Fraxinus pennsylvanica) that prefers wet floodplain forests or swampland.

Specialized species are far more susceptible to negative impacts from environmental change than more generalized species. This is even more significant to plant specialists than it is to animal specialists because the plants are rooted, they are unable to relocate to new regions that have become more favorable.

The climate change being experienced due to increasing average global temperatures is not limited to an average temperature rise in a particular geographical location. Changes induced can alter both air and water movement patterns (currents), so that some regions may experience lower rather than higher average temperatures. The rising average global temperature results in a greater amount of energy in the atmosphere and oceans, so that climate swings are more volatile (changeable) and atmospheric conditions can be more violent. “Once in a century” storms occurring every few years is an example of this. The UK’s experience of snow drifts bringing transportation to a halt in London and other unprepared localities and the long periods of high temperatures and dry weather that has allowed sociopathic arsonists to kill so many and cause such damage in Victoria, Australia in the early part of 2009 are further examples.

It is unlikely that climate change will have too severe a direct impact on established stands of mature ash trees, but if local climatic conditions vary too much from the baseline requirements of the species, it is quite possible that saplings will die off and seeds fail to germinate. Changing local climatic conditions may also favor insects and pathogens (disease causing microbes), extending their ranges and bringing them into contact with ash trees with limited defenses against them. Many of the sub-tropical species of insects are being found in temperate regions where they never previously occurred.

The ash tree species would normally adapt to global warming by moving slowly north, generation by generation. With anthropogenic causes speeding up the normal global warming pattern, they may require human assistance to do so fast enough to survive.