The common beech is one of the most important tree species in European deciduous forests. But climate change is already affecting her, as a Europe-wide study shows. In southern Europe in particular, the growth of beeches has already decreased by up to 20 percent in the last 60 years or so. According to forecasts, this decline will intensify and spread over the coming decades: even small increases in northern Europe will then no longer compensate for the loss of beech trees in the rest of Europe. According to the research team, this could have significant consequences for the ecology and buffering function of European forests.
The common beech (Fagus sylvatica) is one of the most important forest trees in Europe. After the end of the last ice age, it spread across most of Western and Central Europe and shaped the deciduous and mixed forests in many places. In Germany, the common beech is the most common deciduous tree species and takes up a good 15 percent of the entire forest area. Old beech forests in particular are regarded as ecologically important habitats, and the hardwood of the beech is also economically valuable. Today, almost 100 beech forest areas in 18 European countries are listed as UNESCO World Heritage Sites. However, climate change and above all the increasing drought are now also increasingly affecting the actually robust beech trees, as observations in many European forests show.
Growth slowed, especially in the south
Edurne Martinez del Castillo from the University of Mainz and her colleagues have now comprehensively examined for the first time how this affects the European beech population as a whole and what consequences can be expected in the future. To do this, the international team took more than 780,000 tree ring measurements on 5,800 trees at 324 locations throughout Europe – the sample locations ranged from northern Scotland to mainland Greece. Drill cores were taken from the test trees, the annual ring pattern of which provided information about past growth. Using this data, the scientists were able to analyze to what extent certain climatic events influenced the growth rates of trees in the period from 1955 to 1985 and from 1986 to 2016. Based on this, they used climate models to create a forecast of how the beech trees could develop in the future.
The evaluations showed: In the past six decades, the growth of beech trees in Europe has slowed down significantly. “This decline in growth is widespread, there are only exceptions in locations in the northern part of Denmark, Norway and Sweden and at higher altitudes,” report Martinez del Castillo and her colleagues. While the growth rate there has even increased by ten to 20 percent, it has fallen by up to 20 percent in southern Europe. In parts of Central Europe and the German forests, too, most beech trees are now growing more slowly than they did around 60 years ago. On the other hand, the trees in the North German Plain, near the coast and in the higher elevations of the low mountain ranges and Alps fare better. Based on the climate data, the scientists attribute this development primarily to increasing warming and falling precipitation. “Our models demonstrate that the spatial differences in beech growth can be explained primarily by differences in temperature and water availability,” write Martinez del Castillo and her colleagues. These effects are most pronounced when heat and drought coincide.
Losses even with favorable climate development
What this means for the future up to the year 2090 has been examined more closely by the team for two climate scenarios. Scenario RCP2.6 assumes effective climate protection and warming of less than two degrees compared to pre-industrial values. The RCP8.5 scenario, on the other hand, describes an almost unchecked climate change with a warming of around 5.7 degrees. The result: “Even with a relatively optimistic climate development scenario, we will experience strong growth reductions of up to 30 percent in southern Europe in the period 2020 to 2050 compared to the period 1986 to 2016,” reports Martinez del Castillo. In the business-as-usual scenario, beech productivity could fall even more dramatically in large parts of Europe. In most forests in Central Europe, growth rates would fall by 20 to 30 percent. “In southern Europe, the losses could even be over 50 percent,” says the researcher. “There we have to reckon with high productivity losses due to increased drought.” Even slight increases at the northern edge of the beech distribution area could then no longer compensate for these losses.
In view of the great importance of the European beech for the forests of Europe, this would have lasting consequences. “Since the common beech is the dominant tree in large parts of European forests, this would lead to significant losses in the function of beech forests as CO2 sinks,” explains the research team. However, if the absorption of the greenhouse gas from the atmosphere and its storage in the biomass of the trees decreases, the buffering effect of the forests in the climate system also decreases. In view of these forecasts, the authors consider it urgently necessary to initiate measures to adapt forests to climate change. “The changes in growth we project for Europe in the 21st century point to serious ecological and economic consequences that must be addressed immediately,” the scientists state.
Source: Edurne Martinez del Castillo (Johannes Gutenberg University Mainz) et al., Communications Biology, doi: 10.1038/s42003-022-03107-3