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 unfavourable hydrologic and climatic conditions, which can be summarized as follows:

• the flow rate regime of the Danube was atypical; Flood wave occurred in January only, which had no or only very limited effect on vegetation. Flow rates from February to mid of summer fluctuated significantly below the long-term average values. The inundation area was not flooded in the vegetation period.

• the course of groundwater level was decreasing during the year on most of monitoring areas;

• the unfavourable soil moisture conditions were slightly improved by higher precipitation amount in June and July;

• the average daily air temperatures during spring ranged above the long-term averages, but they did not reached extremely high values. The air temperatures in July decreased below the long-term daily average values, but in August and September they fluctuated above the long-term daily average values again.

6.1. Evaluation of the Slovak territory 

Monitoring sites on the Slovak side are situated in the inundation area. The list of monitored sites is presented in Table 6-1 and their position is shown on Fig. 6-1. In accordance with the intergovernmental Agreement the Slovak Party in the evaluated year observed the development of basic growth parameters, weekly girth growth and the health state of trees by terrestrial and aerial survey. After the joint, Hungarian-Slovak evaluation of aerial images in 2008 common effort was made on further improvement of the evaluation methodology, and on increasing the comparability of Slovak and Hungarian results. The Slovak Party in the evaluated year introduced further changes with the aim to improve the quality of images and their interpretation. The most significant change is the creation of a forest mask for each image. This mask differentiate categories of areas with and without forest on the pixel level, while the health characteristics are derived only from pixel classified as forest. The Hungarian Party had not taken aerial images in the evaluated year, so the evaluation was performed only on the Slovak side.

In the Slovak inundation area the development of most productive cultivated poplar stands are monitored. At present the poplar clone Pannonia had already replaced clones I-214 and Robusta, as well as the white willow stand, on all originally observed sites. On two substitutive sites the weekly girth growth of the poplar clone I-214 are temporarily observed. 

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, despite the unfavourable hydro-meteorological conditions, mostly did not go beyond the existing tendency.

The height increment quality classification of most of the observed forest stands remained unchanged or it slightly improved. Significant improvement have been registered on areas No. 2685, 2687 and 2689. Majority of stands is characterized by intensive growth increment reaching or exceeding the quality level 40 for poplar I-214. Considerably lower increment was recorded at monitoring areas No. 2681, 2683 and 2684. This is surprising since the soil moisture conditions on these areas are rather favourable.

In the young stands of Pannonia poplar the weekly girth growth measurements have been started in 2011 (monitoring areas No. 2681, 2683, 2684, 2686). The measuring equipment was removed from the substitutive monitoring sites (No. 4219, 4447, 4349 and 5504). The weekly girth growth measurements on the remaining substitutive monitoring sites No. 5573 and 4436 continues. The cumulative girth growth increment values of the young poplar stands were significantly higher in comparison with values recorded on the substitutive sites in previous year. The comparability of results, however, is very limited due to the age and different kind of poplar clones. Contrary to this, the actual values of girth growth increment recorded on the substitutive monitoring areas No. 5573 and 4436 were lower in comparison with the previous year.

The occurrence of zero weekly girth growth increments in the young poplar stands was rare, except two monitoring sites (No. 2681 and 5573), where they occurred more frequently during spring months. Since July the zero weekly girth growth increment did not occurred at all. The culmination of growth was not identified on most of observed sites. The growing period in the evaluated year was rather long, similarly to that in the previous year. The initiation of growth was registered in first two weeks of April and significant increments were still recorded at the end of September, when the measurements have ended.

The monitored cultivated poplar stands (Pannonia and Giant clones) were healthy and vital. The occurrence of diseases and pests was sporadic during the whole growing period. In comparison with the previous year retreat of fungal diseases was registered, their slight spreading was observed only during August at several monitoring sites. Also the occurrence of foliar pests in August was more frequent.

Based on results of the evaluation of aerial images it can be stated , that the portion of healthy stands in the area of interest exceeds 60 % in long-term (at present 72 % - Fig. 6-2), what proves the appropriateness and vitality of trees. Groups of damaged trees are situated in upper part of the inundation area, downstream of Dobrohošť village. The position of groundwater level in this area is unsuitable for healthy development of forest stands and for the expected wood production due to the strong drainage effect of the Danube old riverbed. Modification of regulatory structures would be required in order to ensure the increase of groundwater level. From the silviculture point of view rearrangement of tree composition, towards the hardwood lowland forest communities, would be possible in existing stands. Higher occurrence of damaged trees was registered also in between the gravel pit "B" and Bodíky village, and along the tail-race canal down to the confluence with the Danube old riverbed. In these areas, however, results partially reflect also the higher age of stands. The hypothesis of large unfavourable effect of the Gabčíkovo Hydropower structure on the health status of forest stands is not proved. In comparison with evaluation results of aerial images taken in 2008 it can be stated, that the health status of 38 % of stands have not changed, insignificant worsening of health status was registered in case of 25 %, and improving in case of 23 % of stands. Significant worsening of health status was identified at 8 % and improving at 6 % of forest stands. The health status of forest stands on the area of interest is henceforth very good and stable.

The persisting occurrence of invasive plant species of Himalayan balsam (Impatiens glandulifera) and Giant goldenrod (Solidago gigantea) in the herb layer of the observed forest stands should be emphasized. If the discharge regime in the river branch system, similar to that in the year 2011, remains unchanged further spreading of these invasive species can be expected in the inundation area. The most vulnerable part is the area with unfavourable hydrologic regime (monitoring sites No. 2681 and 2690) in the upper part of inundation. Their increasing spreading also in other parts of inundation area can be expected if decline of groundwater levels persist. In previous years (2009 and 2010), when the inundation area was repeatedly flooded, retreat or even disappearing of invasive plant species was registered. It can be supposed that also the increased discharge into the inundation area realized in years 2005-2009 contributed to stabilisation or limitation of spreading of invasive plant species.

At the end it should be pointed out that the overall tendency of groundwater levels is decreasing in last years at most of observed sites. For this reason it is necessary to emphasize the effective use of existing weirs in the river branch system for eliminating the decline of groundwater level and ensuring the annual artificial flooding of the area. Equally it is necessary to ensure the earlier increase of discharges to the river branch system, yet before the start of growing season. The results from forest monitoring have to be taken into account in proposals of hydrotechnical, silvicultural or ecological measures.

6.2.  Evaluation of the Hungarian territory 

Dendrometric characteristics and the health status of the forest stands monitored on the Hungarian side in the year 2011 were observed in the frame of the Joint monitoring on 14 monitoring plots, 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 observed (Dunasziget 16A, Lipót 4A/4, Dunasziget 22C). The aerial survey of the health state of forest on the Hungarian side was not realized in the year 2011.

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 again developed favourably.

On the monitored areas poplar stands dominate, what correspond to the present tree composition in the Szigetköz area. Cultivated poplar “Pannonia” forms the largest portion of forest stands. Their growth can be considered satisfactory at current flow rates. In the evaluated year no slowdown 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. 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 more detailed analysis would be required.