German and Romanian researchers have been studying the microclimate of beech and oak forests and have found that beech forests provide better protection against global warming. Forests dominated by beech have a significantly wetter and cooler climate inside the forest.
Measurements of air temperature and relative humidity between beech forests and thermophilic oak forests show the following:
- The shade layer in oak forests is up to 3°C warmer in beech forests.
- Relative humidity is on average 4% lower in the shaded layer of oak forests than in beech forests.
This is due to the characteristic development in beech of several layers of foliage and a higher total surface area of foliage compared with other temperate zone hardwoods.
Beech is currently suffering from drought in many parts of Europe. As a result, its southern range is shrinking and it is migrating to northern, high-altitude sites. Such a change in vegetation not only alters the structure of the forest and the species composition, but also fundamentally changes the climate within the forest, moving from a cool, damp environment to a hotter, more arid one.
Temperate oak forests in Europe often form mixed forests with other broadleaved trees such as hornbeam, lime and ash, which can form multi-layered crowns with relatively high leaf area indices and low canopy cover. However, when oaks are dominant, solar radiation penetrates the canopy more easily because the lower crown of the tree in this species is very poorly developed.
These findings support the need to practise species mixing, vertical layering of vegetation strata and to limit large-scale interventions that have a significant impact on the forest environment, even in the short term.