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Thomas Holst


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Mikroklima in Buchenbeständen – Teil I: Photosynthetisch aktive Strahlung


  • Helmut Mayer
  • Thomas Holst
  • Dirk Schindler

Summary, in English

Meteorological investigations were carried out in forests in the southwestern part of the Swabian Alb

(SW Germany) to analyze the influences of exposition and silvicultural treatment on the microclimate

within various stands of beech (Fagus sylvatica L.). The measurements were taken as part of an interdisciplinary

project on the effects of climate and forest management on structures and processes within

beech dominated deciduous forests. Near-surface stations for continuous recording of meteorological

variables in forests provide the basis of the investigations. Two each were installed on two opposite

slopes (NE and SW) of a narrow valley: one within a control plot (no silvicultural thinning) and one

within a silviculturally treated plot (strong shelterwood felling). Meteorological towers on each control

plot provided data for the analysis of climatic conditions above the beech stands and within their

canopies. The experimental design is well-suited for investigation of not only the influence of exposition,

but also the effects of forest management and phenophases on the microclimate within differently

handled beech stands. The plant area index PAI is used to characterize the canopy.

The present article deals with the photosynthetically active radiation PAR at the near-surface stations

and above the stands as a reference. PAR is measured horizontally. Above the stands, differences to PAR received parallel to the slopes can be estimated by use of model calculations for the incoming

solar radiation G due to the fact that PAR/G is almost constant (1.937 µmol/J) above the stands.

For PAR and the PAR-interception within the canopy in the year 2001, the following results are

discussed: mean diurnal courses in one month within the leafless period (February) and the vegetation

period (August), daily mean values over the whole year and monthly mean values. For the leafless

period the results show the influence of the exposition of both slopes on PAR at the near-surface

stations and the PAR-interception. In the vegetation period, however, the influence of the fully developed

canopy was more significant than exposition. With increasing PAI, results from regression analysis

for the entire investigation period indicate a linear decrease of PAR/G below the canopy as well as an

exponential increase of PAR-interception within the canopy and a logarithmic decrease of the PARtransmission

through the canopy. The extinction coefficient k for PAR shows a tendency towards

logarithmic decrease with increasing PAI.


  • Physical Geography


  • Fagus sylvatica L.
  • PAR
  • exposition
  • forest management
  • PAI
  • PAR/G
  • PAR-interception
  • PAR-extinction
  • PAR-transmission




  • ISSN: 0015-8003