The development of forest communities, as well as plant and animal communities evaluated in Part 7 – Biological Monitoring, was on both sides of the Danube, Slovak and Hungarian, influenced by abiotic conditions, which can be summarized as follows:

• the flow rate regime of the Danube was typical;

• influenced by highly above average precipitation in the Austrian and German Danube catchment area in late May a big flood wave occurred at the beginning of June 2010, which flooded a substantial part of the inundation area. After the flood there more discharge waves occurred in July, August and at the beginning of September.

• the tendency in groundwater levels had been slightly increasing at most areas;

• the average daily air temperatures since the end of June till mid of July ranged far above the long-term averages, but the vegetation was not affected because of the high precipitation amounts.

6.1. Evaluation of the 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 on monitoring areas in the actual year evaluated the development of basic growth parameters, weekly girth growth and the health state of trees by terrestrial survey. In the Slovak inundation area the development of the most productive cultivated poplars is observed. The poplar clone Pannonia had already replaced the clones I-214 and Robusta on all originally observed sites. In stands of these two clones, as well as in a stand of white willow only the weekly girth growth are temporarily observed in substitutive sites.

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

* - on substitutive areas marked by letters “a” or “b” temporary measurement of weekly girth growth is carried out only

The development of forest stands in the evaluated year mostly did not go beyond the existing tendency.

The growth characteristics in young or middle-aged forest stands are basically stable. The best height increment according to results of quality classification show stands exceeding the age of 10 years and approaching the culmination age (areas No. 2685, 3802, 3803). Stands with the “Pannonia” poplar clones in the age 5-10 years are characterised by stable growth increment at moderate level (areas No. 2686, 2687 and 2689), or at lower level (areas No. 2681 and 2684). The growth increment of young stands that are below the age of 5 years (areas No. 2682 and 2683) is relatively slow in first years of monitoring, even though that significant improvement was recorded in the evaluated year on the area No. 2682.

From the invasive plant species point of view (Impatiens glandulifera, Solidago gigantea), to which greater attention is paid in last years, it can be stated, that several flooding in last two years led to their decline or even extinction on several areas. Their spreading occurred only on the area No. 2689, which is significantly affected by the drainage effect of the Danube. It is surprising that the long-term flooding on the area No. 3803 eliminated the population of Impatiens glandulifera, while the abundance of Solidago gigantea has increased.

Based on weekly girth growth increments (according to data from substitutive areas No. 4219, 4447, 4349, 5504, 5573 and 4436) significant improving of width increments of poplar and white willow stands was registered in the whole area in years 2007 and 2008. In the year 2009 the tendency of improving did not continued, but increments mostly remained at similar level. In those years the occurrence of zero weekly increments was sporadic. In the year 2010 a significant decrease of width increment intensity was recorded in all evaluated areas, and the zero weekly increment occurred several times. Unusual is their occurrence at the turn of June and July, since the moisture conditions in this and in the previous period were favourable. Neither the unambiguous reason of the intensive increment of trees in the previous three years, nor its actual decrease was identified. The length of growing period in the evaluated year was comparable to that in the previous year.

The monitored cultivated poplar stands are healthy, the trees and also seedlings were vital. Due to high relative humidity after frequent rainfall slight increase of fungal diseases on almost all areas was registered in early summer, but in spite of this their spreading was sporadic. Further spreading of fungal diseases in the coming months was not registered. The occurrence of foliar pests in the observed stands was only sporadic during the whole growing period.

Although the hydro-meteorological conditions of recent years have been quite favourable in terms of moisture requirements of the observed floodplain forests, it is necessary to take into account the effective use of existing weirs in the river branch system for eliminating the decline of groundwater level and ensuring artificial flooding in case of absence of natural floods. Equally it is necessary to ensure the earlier beginning of filling the river branch system, yet before the start of growing season. In region of Istragov, without manageable groundwater level, it is necessary to resolve the recharge of the river branch system by water. The impact of riverbed erosion downstream of the confluence of the Danube old riverbed and the tailrace canal has to be monitored.

6.2.  Evaluation of the Hungarian territory

In the year 2010 the dendrometric characteristics and the health status of stands were observed in the frame of forest monitoring on the Hungarian side on 14 monitoring areas, which are situated in the inundation area (Fig. 6-1) and listed in Table 6-2. In addition the Table 6-2 lists areas, where the weekly girth growth increments are monitored (Dunasziget 16A, Lipót 4A/4, Dunasziget 22C).

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

Based on the detailed analysis of actual growth characteristics of forest stands it can be stated that no change have been registered in the existing growth tendency. The growth of trees in the evaluated year developed favourably.

On the monitored areas poplar stands dominate, what correspond to the actual tree composition in the Szigetköz area. Cultivated poplar “Pannonia” forms the largest portion of forest stands. Their growth is considered satisfactory at current flow rate. No slowdown in the evaluated year was recorded even in case of slow-growing native species.

The weekly girth growth increments were low in all four observed stands, despite of high precipitation amounts, which is in harmony with results on the Slovak side. In case of poplar stand on the area Lipót 4A this could be explained by high age of trees, but in case of other areas any unambiguous reason can not be determined. Detection of possible causes would require a detailed analysis.