The development of the forest communities in 2007 (including fauna and flora evaluated in the Part 7 – Biological Monitoring) was influenced by abiotic conditions, which can be summarized as follows:

The meteorological and hydrological conditions were atypical from several points of view. However, extreme values of one factor were often mitigated by synergic effect of the others. Formation of soil moisture storage in the winter period was limited by low precipitation amount from the beginning and low discharges during the whole period. Regarding the air temperature the winter period was very warm. Growing of vegetation started in April, which was almost without precipitation and the flow rates in the Danube fluctuated deeply below the long-term average values. Later on due to higher precipitation amount the soil moisture conditions got better, but high air temperatures unfavourably influenced the situation. The average daily air temperatures fluctuated above the long-term average values almost permanently until August. In the summer period precipitation amount varied below average again, so the decrease of soil moisture content and drying of vegetation continued more intensively. The unfavourable development was mitigated by colder August and September, which were rich in precipitation as well. In September a big flood wave occurred too, however the flooding in autumn had low importance from the vegetation point of view. In the evaluated year no artificial flooding was realized in both, left and right side inundation area. 

6.1. Slovak territory 

The forest monitoring on the Slovak side is carried out on monitoring areas in the inundation. The list of monitored sites is presented in table 6-1 and the situation is shown on Fig. 6-1. The Slovak Party in the actual year evaluated the development of basic growth parameters, weekly girth growth and the health state of trees at monitoring areas. At these stands the development of the most productive cultivated poplars are observed. The mostly spread poplar clone Pannonia gradually replaced stands of cultivated poplars I-214 and Robusta cleared in last years. The areal spreading of willow stands in the whole inundation area decreases, observation of weekly girth growth only is realized on one substitutional monitoring area at present.

The monitored forest communities mostly represent the development of the stand conditions in different parts of the inundation area after putting the Gabčíkovo hydropower structure into operation. The main aspects of the moisture development in these regions were characterized in previous Joint Annual Reports on environment monitoring (e.g. in years 2003 or 2004).

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

In spite of atypical weather conditions and unfavourable hydrological conditions several positive changes were recorded in the forest stands development on large part of the observed area. The height increase got much better on young stands, which were problematical after the reforestation. Although the height increase intensity of young stands follows the curves of lower and medium quality classes (except the monitoring area No. 2685), but no drying out of tress were registered and the trees are healthy (areas No. 2681, 2684, 2687 and 2689). The increment of the older stands after the growth culmination decreases slowly (monitoring area No. 2682). The most intense increments were registered at mid-aged forest stands in the region below the confluence of the tailrace channel and the Danube old riverbed (areas No. 3802 and 3803).

The decreasing tendency of weekly girth growth on poplar and one willow stands has changed. Trees on every observed areas reached significantly higher weekly increments than in previous years. Zero weekly girth growth values were significantly reduced as well, and they were recorded only occasionally. No evident reason of these positive changes was identified. No exact date for maximal weekly girth growth could by identified, observed trees had several smaller growing peaks.

The occurrence of illnesses and pests at the beginning of the summer was occasional, and probably due to low humidity in the summer it did not spread significantly in autumn as well. Premature yellowing and defoliation due to very warm and dry summer was registered only locally. On the other side the decreasing tendency in ground water level during this kind of weather got stronger, especially in Istragov area. The water supply of this region is not solved although it is reasoned. In other parts of inundation area the existing system of weirs have to be used more effectively for mitigation of groundwater level decrease and ensuring artificial flooding of the area.

6.2. Hungarian side 

The forest monitoring on the Hungarian side in year 2007 was carried out on monitoring areas presented in Table 6-2. All areas, except monitoring sites at Hédervár 11B and Ásványráró 45A, are situated in the inundation area (Fig. 6-1). On areas listed below the dendrometric characteristics were measured, the health state of stands were observed and on selected sites the weekly girth growth was registered. The evaluation in the actual year is only focused on long-term changes of increments in connection with changes of moisture conditions after diversion of the Danube. 

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

The standard increment of forest stands is a parameter characterizing the growth rate. By the height and width increment it reflects the wood production of forest stands in individual vegetation periods. The development of these parameters is useful to observe from the point of view of determining tree species, from among different poplar clones, the white willow and the oak are typical for the Szigetköz region.

Analysing the increment intensity of the observed tree species (sum of average values of standard wood production of stands and 95% of probability) in the period 1987-2007 it can be stated that the wood production significantly lag behind the values before diversion of the Danube. The proportion of different tree species on this difference varies, but decrease is noticeable in every tree species. It proves the general worsening of conditions for forest cultivation in Szigetköz region.

Except ecological conditions the intensity of growth increment significantly depend on the age of stands. Analysing the individual age categories it can be stated that decrease of growth increment was detected for poplar “Robusta”, poplar “Pannonia” and white willow. The decrease for pedunculate oak is not significant.

In order to determine the dependence between the growth increment and the ecological conditions an analysis of characteristic water level before and after diversion the Danube was done at Dunaremete profile during the vegetation period. It can be stated that the average water levels after the diversion fluctuate on the level of minimal values of the period before the diversion. The maximal water level values after the diversion of the Danube reach the average values of the period before the diversion. The average values and the most frequent values represent one seventh of the values before the diversion. The impact of these changes is provable. Two years after the diversion (1993-1994) wide range of increment values were recorded. During following years these values quickly decreased to one third of previous values. It seems that the river branch water supply system introduced in 1995 is not able to recover this unfavourable state to the level existing before damming the Danube.