PART 6

Forest Monitoring

Both countries examine the growth and the health state of trees on forest stands in similar way. Monitoring sites on the Slovak and Hungarian territories, included in the joint monitoring are shown on Fig. 6-1 . Both, the Slovak and Hungarian Parties in the present report evaluate the weekly girth growth as well as the health state of trees on forest stands for the year 2000. In evaluation of the yearly wood yield data the Hungarian Party use only the data for year 1999. In 1999 an aerial survey of the forest health state in the inundation area was performed. The evaluation of the aerial photographs from the Slovak side was finished in 1999 and presented in the previous Joint Report. Evaluation of the aerial photographs from the Hungarian side was still not completed in 2000.

6.1. The Slovak territory

 The forest monitoring on the Slovak side is carried out on twelve forest monitoring areas (Tab. 6-1). All of them are situated in the inundation area (Fig. 6-1), where the most productive, rapidly growing wetland forest communities occur. These communities have high demand on water and have relatively high resistance to biotic harm. These forest stands were considered as the most endangered after construction the Gabčíkovo hydropower structure, but the assumptions were not confirmed.

Table 6-1: List of the forest monitoring areas on the Slovak side

 Favourable situation, from the ground water level point of view, exists on monitoring sites No. 2683-2690 due to the intake object in Dobrohošť a system of small regulation weir throughout the inundation area. Raising the water level in the Danube by appropriate underwater weirs could influence negative effects of the Danube drainage on the monitoring areas lying close to the riverbed (e.g. area No. 3800). Positive influences of this kind of measures would be probably observed on the whole inundation area.

Some characteristics in development of plants in E1 coverage indicate the needs to preserve the flooding regime in the whole influenced area.

The year 2000 from the point of view of climatic characteristics and the Danube discharge regime in the first half of the vegetation period was suitable for objective evaluation of the forest stands in the influenced area.

The yearly increments in the year 2000 of the white willow stand on monitoring area No. 2681 remained on the stabile level and the values are despite of the age rather high. The health state of the willow stand in the evaluated year remained good.

The cultivated poplar stands (Populus x euroamericana var. “Robusta” and var. “Italica” – I-214) are widely spread in the inundation area. Most of the monitoring area reached the age of cutting, but the increment values decreasing only slowly and the growing is satisfactory. Height increments on most of them still meet the curves for the I. growth class. The values of weekly girth growth measures prove the positive influence of the artificial floods on some of the monitored areas, as well as the significant influence of precipitation at the beginning of the vegetation period. Raising the water level in the Danube old riverbed could mitigate the negative influence of insufficient precipitation, especially at the beginning of the vegetation period.

In the year 2000 a higher sensibility on biotic factors was observed at the “Robusta” species. But similar phenomenon occurred in other areas as well. The health state of the observed stands in general was satisfactory.

On monitoring sites No. 2681 and 2682 there was a slight decrease of ground water level observed after putting the Gabčíkovo power plant into operation, but thanks to the backwater effect no significant change of natural conditions occurred. Since 1999 two new monitoring areas had been included into the joint monitoring – area No. 3802 planted with Populus x euroamericana Pannonia and area No. 3803 planted with Populus x euroamericana Giant. Areas No. 3802 and 3803 are situated downstream the confluence of the tailrace canal and the Danube. Intensive growth of young trees proves very favourable moisture conditions on these stands. Direct influence of the waterworks structures is not observed.

In case of continuous low water level in the Danube the forest stand on area No. 3800 could be considered as endangered due to the strong drainage effect of the Danube. The low ground water level combined with unfavourable climatic conditions creates unfavourable moisture conditions and increments of the young trees are lower than increments on the comparable area No. 3802.

6.2. The Hungarian side

 The forest monitoring on the Hungarian side in the year 2000 was carried out on eight monitoring areas (Tab. 6-2), which, except one, are situated in the inundation area - Fig. 6-1. The moisture conditions in the year 2000 can be marked as moderate, because of irregular precipitation distribution, when most of them were concentrated at the beginning of the vegetation period.

Table 6-2: List of the forest monitoring areas on the Hungarian side

When analysing the yearly growth increments, belonging to the year 1999, it can be stated that the tendencies had stabilised. After introducing the water supply in 1995 during the last years the decrease of increments stopped, however on certain areas the values still lag behind the expected increment values. The growing period in the year 2000 was little bit longer and lasted 24 weeks.

The girth growth data still lag behind the expected values and does not reach the level recorded in the period before damming the Danube. On the other side the positive influence of the improved hydrologic conditions after introducing the water supply is evident.

The comparison of eight poplar stands on experiment area at Lipót 4A shows that at the present conditions the growth of “Agathe F” and “H-528” clones are better. The growth of “Kopeczky” ad “Pannonia” clones is less favourable.

Poplars were found to be in a better health conditions comparing to the previous year, although the challus infection was common. During the spring crown-damage survey only a small insect damage was observed. Generally it can be said that the poplar clone “I-214” developed thinner crowns, and the leaves were often considerably smaller. The general health condition of willows was moderate in the first half of the year, but as a consequence of missing floods the areas covered by willow became not suitable for them.

Because of very dry summer period the size and density of the herb-layer was slightly lower from what has been experienced in the previous year.

		Fig. 6-1 Monitoring network of observation objects agreed in the frame of the Joint monitoring