Mass Dieback of Beech (Fagus Sylvatica) in Zala County
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Lakatos & Molnár: Mass dieback of beech (Fagus sylvatica) in Zala County MASS DIEBACK OF BEECH (FAGUS SYLVATICA) IN ZALA COUNTY Lakatos Ferenc1, Molnár Miklós2 1 University of West Hungary, Institute of Forest and Wood Protection, H-9400 Sopron ([email protected]) 2 University of West Hungary, Institute of Forest and Wood Protection, H-9400 Sopron ([email protected]) Abstract The mass dieback of beech in Hungary, which started in 2003 and went on through 2004, is a typical damage-chain. The appearing symptoms are characteristic: small outflow and white spots (2-3 cm diameter) in the crown. Later branches are blackening and leaves are withering. The coming off of the bark in palm-size tiles is typical on the trunk. These symptoms are mostly eye-catching on stand margins. The decay has firstly appeared in extrazonal beech forests. The most significant reason was the dry and warm vegetation period of 2002-2004. During and after this time different pests and pathogens appeared. The root causes of the dieback were the insect species of Argilus viridis and Tophrorychus bicolor as well as the fungus species of Biscogniauxia nummularia. With the improvement of climatic aspects continuous recovery of the stands has been observed since 2005. Keywords: Fagus sylvatica, Agrilus viridis, Taphrorychus bicolor, Biscogniauxia nummularia 1 Introduction In 2003 a sort of dieback of beech that had rarely been seen before started in Hungary. Similar symptoms were only recorded once in the country in the 1880s (Piso, 1886). The detailed revelation of the reasons did not start that time. The motive of this might have been the unimportant economic role of beech or the extent of the decay, which was probably far behind some more significant problems of forest protection. Over the period of 2003-4 some countries of Europe also mentioned similar damage though (Delb, 2004). The decline, still present today, has appeared in beech forests all over the country with more or less intensity. In the western part of the country it has caused tremendous damage. In 2004 on the territory of the Zala county forestry some 80,077 m3 of beech had to be cut down from 410.8 hectares. This meant the total amount of almost half a million Euro loss for the forest company (Góber, 2005). 2 Materials and methods 2.1 The investigation area We have carried out our studies at the mostly affected west-southwest territory of the country (Zala County). We completed our field observations in the forested area of Csács at the eastern border of Zalaegerszeg, where also the first symptoms were observed. IUFRO Working Party 7.03.10 Proceedings of the Workshop 2006, Gmunden/Austria 142 Lakatos & Molnár: Mass dieback of beech (Fagus sylvatica) in Zala County The tilt of the area was typically formed from loess, which was settled on sandy and muddy alluvium. Its current terrain is changeable and its height above see level is 196-302 m. Due to the hilly-like feature shallow and deep tilts alternate with each other and with soils of medium and at some places very good fertility. In the valleys we can also find some springs and along them there are also some areas of stagnant water. Owing to the prevailing wind direction and the features of the terrain this area is characterized by mesoclimate slightly cooler and rainier than its surroundings. In accordance with this beech is flourishing on it with success; however the dominant species there is oak characteristically. 2.2 Field observation During the decline, to observe the processes we established a network of 92 study plots (area 102.6 ha). We marked five beech-trunks closest to each points, and we evaluated their health condition. We used a five degrees scale like this: 5- healthy specimen, 4- branch-ends, small branches died only, 3- one strong side-branch died, 2- several strong side-branches died, 1- died tree. The observations were done before leaf shedding, at the end of summer 2003-2006. 2.3 Xylophagous insects To define xylophagous insects we felled sample trees out of which 21, with the length of 35- 40 cm long cylinders, were put into a light eclector. We took samples from the trunk and stump as well as the crown. We collected and determined the hatched insects every week on a regular basis. 2.4 Mycological investigations From the collected trunks we put some small bark a wood samples into an incubator to take further mycological investigations. 2.5 Environmental factors We also examined the environmental impacts and within these analysed the formation of climate in detail. To introduce the climate we utilized, with a retroactive effect of the past 45 years, the temperature and precipitation data of a meteorological station closest to the examined area (Zalaegerszeg-Andráshida) (samples in Table 1.). For the investigation we used the longest data-set so as to receive the most complete picture about the climate changes during the life of the forest. We evaluated the formation of the climate characteristics with different models, e.g. Pálfai-type drought index: H ave PAI 0 = ⋅100 0,1⋅Csoct + 0,4⋅Csnov + 0,5⋅()Csdec + Cs jan + Cs feb + Csmar + Csapr + 0,8⋅Csmay +1,2⋅Cs jun +1,6⋅Cs jul + 0,8⋅Csaug • PAI0: Pálfai-type drought index [%] • Have: Average temperature during the vegetation period [C°] • Csi: Precipitation in the „i” month [mm]) IUFRO Working Party 7.03.10 Proceedings of the Workshop 2006, Gmunden/Austria 143 Lakatos & Molnár: Mass dieback of beech (Fagus sylvatica) in Zala County Table 1. Average precipitation and temperature Total precipitation (mm) Average temperature (C°) April - October - April - October - Year Year September March September March 1961- 683 426 257 9,8 16,2 3,4 2005 2000 445 271 174 12,1 18,3 6,1 2001 459 327 132 11,1 17,1 5,0 2002 504 336 168 11,7 17,7 5,8 2003 436 270 166 11,1 18,8 3,4 2004 588 329 259 10,5 16,7 4,4 3 Results 3.1 Field observations The age of the examined stands was between 60-122 years. The symptoms in each forest part appeared in the same way. We did not find correlations among the social situation of the specimens, the exposition of the stand, the site and the health conditions. Our experience shows that the intensity of damage is up to the quantity of the sunlight reaching the trunks. In divided stands, on the open edges and on tall specimens, a lot more symptoms were to be seen than on trunks in closed stands. In the course of the certain returns we were able to investigate less and less trunks. Logging operations aiming at the control and elimination of the damage also touched the examined trunks and some diseased trees fell, too (Figure 1.). 500 450 400 350 300 250 200 150 100 50 0 2003 2004 2005 2006 5 4 3 2 1 died/cutted Figure 1. Health conditions of the investigated trees IUFRO Working Party 7.03.10 Proceedings of the Workshop 2006, Gmunden/Austria 144 Lakatos & Molnár: Mass dieback of beech (Fagus sylvatica) in Zala County 3.2 Xylophagous insects From almost every collected sample trunk we were able to rear the specimens of Agrilus viridis and Taphrorychus bicolor. It is intriguing that the generally two-hole pupation chambers of Agrilus viridis showed up with single holes in most cases. It is important to mention that for Agrilus viridis the totally dried xylem is not a suitable living space anymore. Lumps were mostly characteristic on healthy bark-parts. We encountered extensive galleries and exit holes, for the most part, above the level damaged by fungal infection. Above the totally dry wood level we found a number of imagines that had died before or at the time of the emergence. 3.3 Mycological investigations After the incubation we experienced some blackish discolouration the causers of which were different conidial and ascomicetic fungi. We encountered on the bark surface hyphas, mycelias and rhysomorphas of basidiomycetic fungi too. The most common we can find was Biscogniauxia nummularia and Nectria coccinea primarily on the sides damaged by insects. 3.4 Climate analysis Characteristic of the area is the annual precipitation of 680 mm, more than 60% of which falls during the vegetation period. The average annual temperature is 9.8 °C. The hottest month is July (average temperature 9.8 °C), and the coldest one is January (average temperature – 1.1 °C). This means that from the point of view of climate the site cannot be regarded as favourable for beech (Figure 2.). During the evaluation of the data-set we stated that until 2000 the temperature, with a small extent, was continuously increasing (Figure 3.) and in parallel with this the quantity of precipitation was continuously decreasing (Figure 4.). Besides the decrease in precipitation there was some change in the dispersion of it, too. The quantity of spring and summer rainfall, significant for vegetation, was reduced and the precipitation due at the end of the summer was postponed for the autumn season (Figure 5.). Observing the data after the millennium we can see that 35 % of the precipitation of the vegetation period was left out, and the year of 2004 was drier than the average. In parallel with this the average temperature was higher than that of many years. From the data of the Pálfai-type drought index, suitable for getting measures of the average of precipitation and temperature, we can obviously declare that the drought following the millennium was very similar to the drought of the years 1992-93 (Figure 6.).