Laser-Induced Fluorescence—A Method To Detect the Vitality of Scots Pines

Abstract

Fluorescence measurements were carried out with the ground-based DLidaR-2 of the German Aerospace Center (DLR) in October 1994 on pine trees ( Pinus sylvestris L.) located in two differently polluted areas of eastern Germany. The DLidaR-2 instrument is a far-field fluorescence lidar exciting the leaves with a doubled or tripled air-cooled Nd:YAG laser. The lidar is configured as a coaxial system with variable beam divergence in front of the receiving telescope. The detection unit is set up with several channels equipped with sensitive photomultiplier and interference and blocking filters for spectral separation. At two test sites (Neuglobsow, Rösa) as part of the SANA project, five areas including three groups with five pine trees were selected for the fluorescence lidar measurements. At each area twigs in the upper crown of the 15 selected trees were cut. The young needles (first needle age class) were prepared for pigment analysis (chlorophyll a and b), nutrition element analysis (e.g., Mg, K) and for the determination of biochemical parameters (e.g., reduced glutathione—GSH; glutathione reductase—GLR; superoxide dismutase—SOD, and soluble protein—PROT). Additional tip necroses were estimated for both needle age classes. The results show that the current year’s needles from the polluted site (Rösa) contain more SO 4–S and antioxidants than those from the reference area (Neuglobsow). For both test sites a correlation between the detoxification enzyme SOD and the chlorophyll fluorescence ratio ( F685/ F730) is observed r=0.82 as well as for chlorophyll a and b concentration and the chlorophyll fluorescence ratio r=0.82 . The blue-green fluorescence ratio ( F440/ F520) is also correlated with damage symptoms as, for example, the needle damage index r=0.83 , which is derived from visual inspection of the needles. Taking into account that the fluorescence lidar measurements present an average over different twigs and needles of different age, it can be summarized that lidar measurements from the ground can yield useful information about the vitality state of the trees. Therefore, a differentiation between stressed and nonstressed trees is obvious.