Journal of Applied Botany and Food Quality 85, 55 - 63 (2012) ¹Private scholars, Freudenberg, Germany ²Company for Applied Mycology and Environmental Studies, Krefeld, Germany Revitalization experiments on an old oak Alfred Becker¹, Arnold Irle¹, Jan I. Lelley² (Received July 5, 2011) Summary A common oak (Quercus robur L.) named “Bear-Oak” in South Westphalia, aged about 650, taller than 30 m and with a diameter of over 1.6 m is under preservation order. This tree was seriously ill in summer 1990. Visible causes were a lightning strike and infection with fungal saprophytes. The most obvious symptom was that rotten strong branches broke off from the crown. The original intention of the natural protection agency in charge was to exempt the tree from the preservation order and to let it “die honourably.” However, revitalization measures such as revitalization of the crown, restoration of lightning wounds, mycorrhization, and fertilization of specifi c sites were performed in September 1993 on the suggestion of the Research Institute for Mushroom Cultivation of the Rhineland Chamber of Agriculture in Krefeld. The outcome of these measures was recorded and monitored in the following years by scheduled recording of vitality parameters (extent of mycorrhization, density of foliage, periodic volume increase) to fi nd out whether the overall health of the oak had improved. Although the development of these parameters at the time of the report demonstrates variation in the productivity/vitality of the tree, it also shows that the functional capacity of the oak has recovered to a normal level. The vitalization measures can be assessed as successful, and inter- mediate to long-term survival of the tree appears to be established. Introduction The tree The old oak (Quercus robur L.) to be examined is called “Bäreneiche” by the locals (i.e. “Bear-Oak”; however, this is an individual name, and it should not be confused with the American / Canadian Oak (Quercus ilicifolia Wangenh.). It is sited in the district of Siegen- Wittgenstein close to the city of Freudenberg. It is located on a border between the villages Nieder- and Oberholzklau and grows 330 meters above sea level (Fig. 1). Fig. 1: The habit of the Bear-Oak in 2011 As an overview of the basic data at the beginning of the monitoring, the results are listed as follows: History of the tree • height: 31.0 m The exact age of the oak is not known. FRÖHLICH (1992) estimates • stem height: 12.0 m that the tree was already mentioned around 1453. Therefore, we can • circumference at breast height: 5.02 m assume that the tree already had a signifi cant and noticeable size at • diameter at breast height: 1.66 m this point of time. • timber volume: 22.6 m³ with 18.0 m³ of stem wood and 4.60 m³ of The origin of this giant tree can be estimated to be around 1350. This branches assumption fi ts relatively well to the result of an extrapolation of the • canopy projection screen: 240 m² height-to-diameter development in the last 90 years. Assuming an age between 520 and 720 years, we can roughly calculate the age to be In the list of natural monuments published by the department of around 650 to 700 years. Siegen-Wittgenstein in 1988, the Bear-Oak ranks number15 of natural monuments and is therefore protected by law. The oak holds The tree has reached such a high age for various reasons: fi rstly, it the place as one of the trees with the thickest diameter in this area. belonged to the “hohgewälde” of Keppel, i.e. an enfeoffment of the 56 A. Becker, A. Irle, J.I. Lelley Revitalization experiments on an old oak former monastery of Keppel that had tasks such as to provide the The following vitality parameters were evaluated: feudal lords, including the name-giving family Bähr (Behr) with • mycorrhiza frequency of fi ne roots and their changes from year to enough building timber in the required dimensions (HARTNACK, 1963). Secondly, the oak was already early an important boundary year • periodic volume increase (callus growth, circumference measure- mark between the villages Nieder- and Oberholzklau (BALD, 1939) and between the territories or areas of infl uence, respectively, of the ment) archdioceses Mainz and Cologne. Thirdly, being a boundary mark, The degree of foliage was documented and assessed from crown the tree was specially protected according to the forest and wood photos from the past years (Figs. 2 to 5). regulations issued by the Count Johann of Nassau in 1562. Finally, compared to average forest locations in the Siegerland, the location of the oak is exceptionally well and deeply supplied with only mode- rately acidic soil water thanks to a hollow under a slope to the West (BECKER et al., 2011). The natural monument For more than 100 years, the tree benefi ts from special awareness as an object of nature and natural monument protection. SCHLIECKMANN (1904), FÖRSTER (1914), JUNG (1932) as well as HOFMANN (1940) and FRÖHLICH (1992) mention the “Bear-Oak” and describe it in detail as a tree worth seeing and deserving protection. The fi les of the lower landscape authority of the district of Siegen-Wittgenstein include a lively correspondence between this authority and the long- time commissioner for natural protection and landscape conservation of the district and town of Siegen, HOFMANN, resulting in HOFMANN’S intensive and successful efforts to protect the oak. Fig. 2: Foliation of the Bear-Oak in summer 1993 First in 1937 and then again in 1938, the “Bear-Oak” was protected as a historic monument. The directive of the district law and order authorities of Arnsberg of 17 February 1988 refers to the tree as pro- tected natural monument no. 15 in the district of Siegen-Wittgenstein. The “Bear-Oak” received its recent protection status as natural monument no. 4 by the entry into force of the landscape plan of Freudenberg on 18 December 2003. Decay of the tree During an assessment of the Bear-Oak in 1989, which was im- plemented by the forest department Siegen-North, the tree showed no signs of reduced vitality, yet. In summer 1990, the oak was struck by lightning, which caused a 20 meter long and 30-60 cm wide vertical fi ssure of the bark. The bark was blasted away between the medium crown and the trunk at the bottom. However, shortly after, the tree showed a sudden loss of vitality, expressed by the breakage of a strong crown branch. Furthermore, the appearance of the root rot fungus and other parasites indicating weakness were an obvious sign of physiological stress. The lower landscape authority was notifi ed about this by the Siegen- North forestry commission offi ce. In 1991, the authority instructed a landscape architect to check state of health and stability of the oak. The consultant came to the result that the tree was seriously ill and recommended to let it die “honorably.” Finally, i.e. in 1992, the lower landscape authority announced the release of the oak from the monu- ment protection. It withdrew the decision in the same year. Material and methods In 1993, the idea emerged to recover the Bear-Oak by reconstruction treatments. The lower landscape authority agreed to the proposal of the Research Institute for Mushroom Cultivation of Krefeld and fi - nancially supported the required measures. All investigations performed since 1993 aimed at the establishment and documentation of changes in the vitality of the Bear-Oak, in- Fig. 3: Foliation of the Bear-Oak in summer 1996. The secondary crown is cluding its mycorrhiza status. clearly visible at the lower part of the tree Revitalization experiments on an old oak 57 Fig. 4: Foliation of the Bear-Oak in late summer 1997. The regeneration of Fig. 6: Location of the depot plants the primary crown has begun It was intended by this planting procedure to colonize new fi ne roots of the Bear-Oak with Paxillus involutus (Batsch) Fr. from the depot plants, because our earlier studies demonstrated intensive mycorrhization of oaks by this fungal species. Based on the paper of WÜSTENHÖFER (1989), we performed the stimulation of fi ne root formation of the Bear-Oak by selective small-site fertilization using long-term fertilizer (Osmocota Plus, Sierra) acting for approximately 12-14 months; during this period, it successively releases a mixture of nitrogen, phosphate, potassium, and magnesium. 20 g of Osmocota were transferred into every planting hole of the depot plants. We evaluated the results of the mycorrhization process fi rst in 1995. Then the evaluation was repeated for fi ve times. For this purpose we had defi ned six fi ne root sampling sites around the tree, all situated 80 to 120 cm away from the depot plants, to ensure that the fi ne roots Fig. 5: Foliation of the Bear-Oak in early summer 2011 detected in the soil samples were actually all of Bear-Oak and not of depot plant origin. We met these requirements also in fi ne root sampling in later years. 1. Remediation measures Root samples were taken with a short core sampler (25 x 6 cm). The Mycorrhization with depot plants samples containing fi ne roots were packed into plastic bags and kept In 1993, the Bear-Oak was mycorrhized with depot plants. The cool (1-3 °C) until examination. following measures were performed: The fi ne roots in the soil samples were thoroughly cleaned under • establishment of selected strongly mycorrhized young plants at the running water. Mycorhizza mostly remained undamaged. The cleaned edge of the crown canopy area of the Bear-Oak root samples were kept in a water bath until evaluation.