Current issue: 54(2)
A range of different indices are available for assessing the health of trees in forests. An even larger range can be used for the assessment of the health of forest ecosystems. Most studies made in connection with ”forest decline” and the impact of air pollution and other environmental stresses on forests have concentrated on the assessment of crown transparency and crown discoloration in individual trees. These are non-specific indicators which are now known to be sometimes of relatively little value when determining the health of a forest ecosystem. Numerous problems exist with both, and the standardisation of assessments between and even within countries has not been achieved. Consequently, studies claiming to compare ”defoliation” between different countries cannot be substantiated. The emphasis on crown transparency and crown discoloration has resulted in the neglect of a number of other indices that could be of considerable value. These include a variety of visual measures of crown condition and also several non-visual bioindicators. Some of these techniques are objective, reducing the present reliance on observed standardization. A large number of potential techniques are currently at the research stage and have yet to be adequately tested in field trials. This represent an area where a substantial amount of further research is required.
The woodland mosses Pleurozia shcreberi (Willd. ex Brid.) Mitt. and Hylocomnium splendens (Hedw.) Schimp. were used in air pollution monitoring. During late summer and autumn 1977, 44 samples of Pleurozia shcreberi were collected in semi-open coniferous forests from Southern Finland (60°N) to Northern Finland and Northern Norway (70°N). Additional 26 samples of Hylocomnium splendens were collected in similar places south of 61°30’N. Analysis of both moss species revealed decreasing concentration gradients from south to north for Cu, Fe, Pb and Zn. Conversely, Mn and Mg levels increased with latitude, while Ca did not change significantly. Some decreasing west to east concentration gradients for Cu, Zn and Pb were measured in P. schreberi and in H. splendends collected from Southern Finland.
A comparison between these two mosses showed significant differences in Cu content (ave. 22% higher in H. splendends) and Zn content (ave. 8% higher in P. schreberi). However, the differences were considered minor in relation to regional differences in Finland.
In local study of emissions from the Koverhar steel works in Southern Finland, Fe and Zn concentrations in P. schreberi and H. splendens were found to decrease significantly with increasing distance up to 6 kilometres north and south of the source.
The PDF includes a summary in Finnish.
The use of forest mosses as bioindicators was tested with transplanted experiments. One transplantation experiment was made to study effects of air pollutants on two forest moss species, Hylocomnium splendens (Hedw.) Schimp. and Pleurozium schreberi (Willd. ex Brid.) Mitt. Another transplantation was used to study the nitrogen fixation capacity of blue-green algae in the Hylocomnium and Pleurozium moss layers. The surface structure of the moss species was studied by scanning electron microscopy. The air pollution induced changes in the surface structure of moss cells were observable soon after the transplantation. In polluted industrial areas the fertilizing effect of air-borne nitrogen compounds increased the photosynthetic activity of mosses before their destruction. Stress respiration was also observable in polluted areas. The nitrogen fixing capacity decreased or was almost inhibited in all the air-polluted environments.
Several studies of air polluted forest environments have shown that dwarf shrubs suffer from air pollution. In many cases the disturbances have been attributed to the susceptibility of the dwarf shrubs, while in some cases the vegetational competition factor has been discussed. The growth pattern of dwarf shrubs is very complicated and a single individual can cover large areas due to vegetative reproduction. Since dwarf shrub individuals cannot be transplanted for the purpose of laboratory or field tests, the only possibility is to use small cuttings for the bioindication studies. Some preliminary results are discussed.
The ultrastructure of Hypogymnia physodes (L.) Nyl. and Alectoria capillaris (Bryoria capillaris (Ach.) Brodo & D. Hawksw.) grown or transplanted near a fertilizer plant and a pulp mill was compared to normal ultrastructure of these lichen species. The ultrastructural changes observed were highly similar in the symbionts of both species and near both the factories although the emissions are different. In the lichens grown near the factories the number of algae had clearly increased. The appearance of the chloroplasts was roundish compared to controls. The pyrenoglobuli and cytoplasmic storage bodies were smaller than normally and the number of polyphosphate bodies had increased. Also, in mycobionts storage droplets were very small or absent and many vacuoles and dark inclusions appeared to hyphae in contrast to controls. In transplanted lichen there existed mainly the same ultrastructural changes as in the lichen grown near factories. Near the fertilizer plant the damage was, however, more severe because all the lichens died during 6–7 months after transplantation. Near the pulp mill part of the lichens survived and seemed to adapt to air pollution.
A semi-statistical model is suggested for monitoring injuries of plants for long-time field exposures (months). The model is based on the following assumptions:
1. The concentrations of air pollutants in the atmosphere follow the Johnson SB distribution.
2. The degree of plant injury is proportional to the logarithm of air pollutant dose.
3. No injuries occur below a certain dose level.
4. A dose is defined as the air pollutant concentration multiplied by the duration of exposure raised to an exponent.
Based on the air pollutant frequency distribution a total dose for the exposure period is calculated by integration, and the total dose is related to the observed plant injury by non-linear regression. The model is tested for long-time exposures of sulphur dioxide to transplant lichen in natural environment.
A technique for instrumental scoring of damaged leaves on tobacco (Nicotiana tabacum) indicator plants caused by ozone in the lower atmosphere is being developed. The leaves are photographed in situ with an integrated unit, which illuminates the leaf from behind and keeps the camera in a well-defined position. By using microfilm and a minus green filter, it is possible to obtain negatives where the necrotic flecks appear as dark spots on a white leaf. The negatives are scanned in a TV-system and the size of the damaged fraction of the leaf is calculated by a microprosessor and is shown as a percentage of the leaf.
A monitoring program is planned for the terrestrial environment around industries in Sweden, which emit acid compounds and heavy metals. Directions for the County Government Boards are being prepared. The paper deals with the present pollution situation in Sweden, based on recent scientific results, the justifications for local monitoring, and the organizing of the monitoring including the parameters suggested.
Four examples from a case study at an oil power station illustrate reporting of the data and the difficulties in interpreting the results. The examples are the distribution of a lichen indicator, heavy metal content and phosphatase activity in the moor layer, soil respiration and tree growth.