assessment of changes in the phosphorus status of forest ...

example the compiled data from BZE-I sites for spruce showed that 3-year old spruce
needles had 30 to 40 % lower values of P than the fully developed needles from the
current year (Fig 1). The difference between 1 st - and 3 rd year needles were
surprisingly constant across the whole range of needle P concentrations in spruce
(BMLEF 1997). In another data set shown in Table 5, foliar P levels in ten spruce
stands were measured continuously for 10 years. Three years old needles had 66 to 82
% of P present in the one year old needles. Five year old needles had further reduced
P levels (range 47% to 70%). The amount of P re-allocated from 5 year old needles to
the youngest cohort of needles equated to 30 to 50 % of the content in the current year
needles. The withdrawal was not related to any measured site property. Similar results
were also obtained for one and two years old needles of Scots pine.
Soil characteristics
In a study of 49 stands of European beech (60-or more years-old) in the Werdenfelser
Land region where the canopy conditions were monitored, Ewald (2000) analysed
foliage and soil samples from 8 sites for nutrient composition. Sites could be divided
into 2 groups. Moderate P levels were found in trees from well-developed mineral
soils, and extremely low P levels (0.6-1.0 mg/g) in immature carbonate soils where
total P levels in soils were low and Ca saturation very high. Very high N/P ratios of
30 or more were associated with low P levels. Phosphorus was a critical element in
the nutrition of beech in the calcareous Alps, which may be partly responsible for
poor vitality of this species in mixed mountain forests. Foliar P values in beech forests
on calcareous bedrocks are commonly low when compared to acid soils. As the
availability of protons is required to release P from rock minerals it is possible that
low foliar P values on calcareous bedrock may result from the high buffering of most
of the protons by carbonates which renders less protons available for silicate
weathering.
Highest values of foliar P are found in spruce and pine stands on bedrocks of basalt
type (bedrock type 8 – median value of P in the current needles of 1.5 mg P/g) and the
lowest on the calcareous type (bedrock type 1 – median values were 1.2 mg/g for
spruce and 1.3 mg/g for pine (BMELF 1997).
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