The use of foliar chemistry to indicate vitality in Swedish
beech (Fagus sylvatica L.) and oak (Quercus robur L.)
I. Stjernquist1 and K. Sonesson2
1
2
Department of Ecology, Lund University, SE-223 62 Lund, Sweden
Southern Swedish Forest Research Centre, P.O. Box 49, SE-230 53 Alnarp, Sweden
Foliar chemistry of beech and oak in Sweden
Foliar chemistry has been identified as a useful tool for monitoring forest vitality and longterm environmental change in scientific studies, as well as in the European Forest Monitoring
programmes. In Sweden, foliar chemistry of conifers is measured, on a national scale, by the
National Forest Inventory. Beech and oak, which both have their northern limit through
central Sweden, are of economic interest only in the southern part of the country.
Consequently vitality monitoring of these is concentrated to the five southernmost counties
(Sonesson & Anderson, 2001). A number of Swedish studies from the last decade indicates
low levels of foliar nutrients in beech and oak as compared to the ranges suggested for
Europe by ICP-forests (Balsberg-Påhlsson, 1992; Schlyter et al., 2002; Sonesson, 2000;
Stefan et al., 1997). The differences may be interpreted as nutrient deficiency, alternatively,
as an imbalance due to environmental factors – in particular as beech and oak have shown a
significant decline in vitality during the last two decades owing to anthropogenic stress
factors.
The present study will analyse if the foliar nutrient concentrations, and nutrient ratios to N, in
Swedish beech and oak are systematically lower than in Europe, and further, if observed
levels allow sustainable growth in southern Sweden. We will also discuss if European
nutrient standards are relevant vitality thresholds for Scandinavian monitoring?
Method and data bases
The Swedish foliar nutrient chemistry database covers all available measurements of mature
beech and oak during the last two decades, i.e. forest inventories and scientific
measurements, published as well as from ongoing projects (e.g. Balsberg-Påhlsson, 1992,
Hagen-Thorn, 2003; Nihlgård et al., 2000, Schlyter et al., 2000; Sonesson, 200X; Stjernquist,
200X). The samples have been collected in August in accordance with the ICP Forests
guidelines (Manual part IV) for sampling and analysis. The European database is compiled
from scientific studies in 12 countries (not incl. Sweden) during the same period and follow
the above European monitoring standards. The Swedish and continental European nutrient
variation of foliar concentration and foliar nutrient ratios to N were calculated from the data
bases and are given as frequency spans. The variation in the European data-set was tested
with or without Level I values included. The results are compared with the vitality
classification adopted by the participants of the 3rd Expert Panel meeting in Vienna 1995
(Stefan et al., 1997).
Results and discussion
Beech and oak in Sweden have lower foliar nutrient concentrations as compared to
European stands. This is true both for macro and micro nutrients. In the European data there
appears to be no significant difference in the spans with, or without, the Level I data. The
results show that:
• The Swedish nutrient spans of N, P, K, Mg, Cu and Zn are more narrow than the
European. There are, however, no differences at the lower end of the frequency graph. It
is noteworthy that higher foliar concentrations are persistently not represented in the
Swedish beech and oak stand data.
• Nearly half of the continental European beech sites have foliar values of N, Mg and Ca in
the highest class of the ICP Forest European classification system. The corresponding
figure for Sweden is 5-10%. Among the Swedish beech sites, 40% have very low K
concentrations.
• The Swedish oak sites have a low foliar N concentration compared to continental Europe;
20% of the Swedish stands and 75% of the European have foliar values above 25 mg/g.
The same tendency but with a smaller difference between Sweden and continental
Europe is also present for P and K.
The major part of the foliar samples collected in the Swedish beech and oak investigations
represent local provenances growing on podzols and dystric cambisols. These soils have
low pH and a low base saturation, only 24% of the stands have a base saturation in the 2030 cm above 20% (Sonesson & Anderson, 2001). This conditions is due to the fact that most
Swedish forests are located on poor till soils and many, further more, affected by leaching of
base cations from the root zone owing to soil acidification (Stjernquist et al., 2002).
Deficiency levels and target values for sustainable forestry, defined as nutrient ratios to N,
may, therefore, be lower than the main European thresholds.
The Swedish nutrient ratios to N reflect low but in general balanced nutrient conditions. The
only exceptions being Ca/N and Mg/N which show a more narrow span, and lower ratios,
than that present in the continental European data. In spite of the nitrogen accumulation in
the soil, and soil acidification due to deposition of air pollutants, the growth of beech and oak
is sustainable under the current forest management conditions.
Conclusions
European nutrient standards for monitoring sustainable forestry should not be uncritically
applied for Sweden. For operative use for monitoring beech and oak vitality in Sweden there
is, depending on element, a need for regional adjustments of the nutrient concentrations and
ratios.
Acknowledgment
We thank the Swedish National Board of Forestry and the Regional Board of Forestry, Södra
Götaland for survey data of beech and oak.
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