Growth / Yield

A map of Germany showing the average growth rates at individual Level II plots — Fig. 1: Growth rate by tree species

The growth of trees is influenced by a variety of factors. In particular, climatic and specific site conditions play a significant role, however inputs of air pollutants as well as insect and fungal infestation are also important. Level II monitoring provides extensive data for a better understanding of these relationships. For this purpose, growth parameters, such as the height and the trunk diameter, are recorded at regular intervals on the study areas. Figure 1 shows the average annual diameter growth for various tree species. On average across plots, it is around 3.1 mm for beech, 2.9 mm for pine, around 3.7 mm for oak stands and 3.6 mm for spruce. Please note that these growth rates can vary significantly based on specific site conditions.

A boxplot diagramm shows the variability in growth rate for the tree species beech, oak, spruce, and pine. Annual growth can be as low as 0.15 cm in beech and as high as 0.62 cm in oak. — Fig. 2: Variability in growth rate

Figure 2 illustrates the variability of the average annual diameter growth between different plots. This variability is influenced by several factors, including the age of the stand, stand density, soil type, precipitation, temperature, inputs of sulfur and nitrogen compounds and ozone exposure. Level II monitoring is characterized by the continuous and long-term measurement of these factors. Figures 3 to 6 show the diameter growth of individual tree species by plot. The category “low” represents the quarter of plots with the lowest diameter growth and “high” refers to the quarter of plots with the highest diameter growth. Accordingly, the “medium” category refers to the half of the plots with average diameter growth. The data presented is based on over 40,000 individual measurements from nearly 11,000 trees collected over more than 20 years, although the time span covered may vary for the individual tree species and plots. For the maps, the average annual growth of the individual trees were first calculated and then summarized as average growth per plot and tree species. These surveys are part of the International Cooperation Programme on Forests and are conducted according to its methodology. Any implausible data is filtered out according to the criteria in the ICP Forests Manual.

a map of Germany that shows the growth rate of beech at Level II sites — Fig. 3: Growth rate for beech

a map of Germany that shows the growth rate of oak at Level II sites — Fig. 4: Growth rate for oak

a map of Germany that shows the growth rate of spruce at Level II sites — Fig.5 : Growth rate for spruce

a map of Germany that shows the growth rate of pine at Level II sites — Fig.6 : Growth rate for pine

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