Recent Pest Outbreaks and Survey Methodology Practiced in Croatian Forestry
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Forster, B.; Knizek, M.; Grodzki, W. (eds.) 1999: Methodology of Forest Insect and Disease Survey in Central Europe. Proceedings ofthe Second Workshop ofthe IUFRO WP 7.03.10, April20-23, 1999, Sion-Chateauneuf, Switzerland. Birmensdorf, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) 17-23. RECENT PEST OUTBREAKS AND SURVEY METHODOLOGY PRACTICED IN CROATIAN FORESTRY Boris Hra.Sovec Forest Protection Department Faculty of Forestry, University of Zagreb Svetosimunska 25, HR-10000 Zagreb, Croatia e-mail: boris.hrasovec@zg. tel.hr Miroslav Harapin Forestry Institute Jastrebarsko Pokomog10, HR-10000 Zagreb, Croatia INTRODUCTION Close to one half of Republic of Croatia is covered by forests and their various degradation stages (2,49 million hectares- 44% of total state area). State forests comprise 81,4% of these while only 18,6% are privately owned. Among state forests, the majority (80,1%) are managed by public enterprise "Hrvatske sume" (i.e. "Croatian Forests"), and the rest (1,3%) reside under various protection categories like national parks, natural parks, forest reserves etc. About 1 million hectares managed by state enterprise are very valuable high forests and about '14 million hectares are various continental and Mediterranean coppices. Growing stock amounts to 324 million m3, with an annual volume increment of 9,6 million m3 and annual felling of approximately 5,3 million m3. Most numerous tree species are: beech (37% by growing stock), pedunculate, sessile and other species of oak growing in lowland riparian forests and hilly belt (24%) while conifers represent only 14% by growing stock and most important one is common frr growing in mountainous natural mixed beech-fir forests. It is clear that such natural wealth, managed mainly by state company, calls for an adequate pest survey organization and related forest protection measures. This is why in 1980 the Croatian Ministry of Agriculture and Forestry established a Diagnose and Prognose Service located in Forest Research Institute Jastrebarsko. SURVEY METHODOLOGY Since ownership structure of Croatian forest land is largely dominated by state forests, ac tivity of the Diagnose and Prognose Service (DPS) is closely connected with closely related department in state enterprise "Hrvatske sume". Field data is collected by trained personnel working in 16 Regional Forestry Administrations which cover the majority of the Croatian forested land through network of 171 Forest Stations. These specialists collect data, prepare them for periodical yearly report, coordinate peld activities regarding detection, survey, evaluation and suppressive measures, should they be needed. Collected data prepared in predefined forms are sent to DPS where further analysis takes place. Here, all the regional data are summarized, biological samples are reared and tested on parasitism and health condition and finally, decisions are being made where and when to undertake suppressive measures. According to need, professionals from DPS often check the situation in the field and help regional foresters through permanent education and expertise with less often occurring pests and diseases. Various methods are applied in order to asses the population densities of most important forest pests and these being adapted to specific biological cycles and practical aspects of 17 survey techniques. Fundamental principles governing the use of certain method are as follows: it (method) should be simple enough for the field personnel to be able to conduct it, it should be accurate enough, i.e. give the satisfying density estimations and fmally, it should be finished well ahead possible damages occur so there is sufficient time left for planning the suppression measures. We can classify these survey methods in several groups. Some of the oldest ones and still very much used are those involving counting of various insect develop ment stages on sample plots or transect paths (Harapin et al. 1996). Egg masses of Lymantria dispar are counted regularly on a yearly basis and this is done both on continental (transect method) and coastal area (sample plots). Intensity of attack is ex pressed by percentage of trees with egg masses for current year and these are classified into five classes, lowest having less than 1% "attacked" trees and highest having more than 50% "attacked" trees. Regarding the qualitative analysis and determining the health state of defoli ating insects, egg masses are often checked against parasitism for the following pests: Lyman tria dispar, Euproctis chrysorrhoea, Malacosoma neustria, Thaumetopoea processionea, T. pityocampa and Neodiprion sertifer. Larvae of some insect pests are counted in some special circumstances and this applies more to forest nurseries where grubs and larvae of Scarabaeidae, Noctuidae and Elateridae are counted and if critical numbers are achieved suppressive measures have to be undertaken. On a qualitative basis, larvae are often laboratory reared and checked against parasitism or other biological agents expected to contribute the crack-down of heavy infestation period. Besides formerly mentioned defoliators larvae of Tortrix viridana, Apethymus abdominalis, various Geometridae and some more important Scolytidae are also being laboratory checked. In the continental region caterpillar nests of overwintering E. chrysorrhoea are counted on a transects in lowland riparian forests. The same is done throughout coastal and island pine forests with T. pityocampa. Pupae or cocoons are sometimes being counted and used for assessment of population buildup for several pests among which more often T. pityocampa, N sertifer, Stereonychus fraxini and Dendrolimus pini. Laboratory analysis of qualitative population elements is periodically carried out on pupae of the above mentioned pests. Adults are also targeted for population density assessment and this is done in several ways. Most often, adults are collected by some means of trapping technique. Well established method for assessment of population densities and critical population levels is used for two of the most important loopers: Erannis defoliaria and Operophthera brumata. Their wingless females are caught and counted on sticky trap-belts during the emergence period October January. Another method for trapping the soil emerging pests is by using the wire-mesh covered cages (some Geometridae, A. abdominalis and acorn pests such as Curculio spp. and Cydia spp. ). Modem methods for adult trapping in monitoring purposes involving sexual pheromones are used only fragmentary and more as an experimental addition to permanent evolvement of survey techniques (Paranthrene tabaniformis, Gypsonoma aceriana, Ostrinia nubilalis, Zeu zera pyrina). Aggregation pheromones of lps typographus, Pityogenes chalcographus and Trypodendron lineatum are being consistently used as a monitoring tool in continental region. Though spruce forest in Croatia are not nearly endangered as those in Central Europe, this method has caught foothold especially in those limited areas where spruce has been introdu ced during mid century and where it grows out of its natural habitat. There is however one special method of branch sampling developed for specific needs of population density and defoliation risk assessment in our broadlived oak forests. Its originator, Dr. Miroslav Harapin introduced it by the late eighties with intention to better 18 assess unclear situation regarding flowering and acorn production and causes for early crop loss (Harapin 1993). Another important issue were problems with population density assessment of some early defoliators which overwinter on oak twigs in egg stage. Today, this has become a widely accepted method providing fairly accurate predictions of what is going to happen in sampled forests in the following spring. Table 1. Sample results of a four-year branch analysis regarding flowering capacity, defoliation prediction and insect pests involved (regional forestry administration samples given in the table represent larger part of Quercus robur forests in Croatia, "?" symbol means no data available) Number Flowers Defolia- Number Dead Year of tion of twigs Sprouted shoot tips Pest samples Male Female (%) BJELOVAR REGIONAL FORESTRY ADMINISTRATION 1989/90 12 88 57 30 15 8 25 leafroll., loopers, casebearer, sawfly 1990/91 36 252 130 74 585 119 35 leafroll., loopers, casebearer, sawfly 1991192 62 400 233 166 1810 425 20 leafroll., loopers, casebearer, sawfly 1992/93 53 283 228 168 732 239 75 leafroll., loopers, casebearer, sawfly :E(%) 163 1023 648 (63) 438 (42) 3142 791 (20) 39 KARLOVAC REGIONAL FORESTRY ADMINISTRATION 1989/90 2 68 63 - 628 7 15 leafrollers, loopers 1990/91 11 88 56 41 1217 132 60 oak sawfly 1991192 3 17 6 16 67 47 -- 1992/93 17 73 55 67 295 198 30 leafrollers, loopers L (0/o) 33 246 180 (73) 124 (50) 2207 384 (15) 35 ZAGREB REGIONAL FORESTRY ADMINISTRATION 1989/90 10 67 36 - 471 8 30 leafrollers, loopers, casebearer 1990/91 27 187 125 32 633 209 45 oak sawfly, loopers 1991192 12 88 35 47 164 8 15 oak sawtly, loopers 1992/93 65 367 256 157 936 274 65 oak sawfly, loopers, casebearer :E(%) 114 709 452 (64) 236 (33) 2204 499 (18) 36 VINKOVCI REGIONAL FORESTRY ADMINISTRATION 1989/90 40 219 170 29 1357 95 50 leafroll., loopers, casebearer, sawfly 1990/91 41 229 210 41 868 170 20 oak sawtly, 1oopers, casebearer 1991192 ? ? ? ? ? ? ? ? 1992/93 25 164 86 73 104 42 25 leafroll., loopers, casebearer, sawfly :E(%) 106 612 466 (76) 143 (23) 2329 307 (12) 32 :E<%>1 422 2590 1746 (67) 941 (36) 9882 1981 (17) 36 During late fall and winter, samples are taken from randomly chosen oak trees from upper strata. Usually, trees are felled down (which is mainly during the normal felling period in these forests), then 4-7 branches, 7(}-80 ems in length, are taken from upper parts of crown, preferably from all four aspects. Branches are transported to a centralized laboratory managed by DPS service where they are given water supply, room temperature and daily supply of sunlight. Underneath, white sheets of paper are secured on which early signs of defoliation can be recorded (excrements). Also, the defoliating fauna, their composition and densities can be easily assessed and related to available food supply, i.e.