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MONITORING OF SMALL RODENTS IN CROATIAN STATE FORESTS FROM 2017 TO 2020 – ARE WE GETTING ANY WISER?

Monitoring of small rodents (Murinae:mice ; Arvicolinae:voles) in the state forests of Croatia has been carried out systematically for over 40 years by Croatian Forest Research Institute (CFRI) and Croatian forests, limited liability company, that is a public enterprise for forest and woodland management in the Republic of Croatia. From the beginning of the 1980s to 2016, monitoring included estimating the intensity of damage caused by rodents (%) and recording the size of forest areas (ha) with noticeable damage to seeds and saplings of economically important tree species. Since 2017, the rodent monitoring has been extended to determine the relative abundance (RA ; %) by trapping rodents, as well as to determine the share of damaged seeds and tree saplings (%). The aim of this work was to analyze the trends and results of rodent monitoring carried out from 2017 to 2020. Data was provided by CRFI (stetnici.sumins.hr) and analysed using Microsoft Excel 365. In that four year period overall damage caused by rodents in Croatian state forests were recorded on 16.506, 2 ha (avr. 4.1236, 55 ha) and rodents were treated using rodenticides (API Zinc phosphide) on 13.343, 41 ha (avr. 3.335, 85 ha). Monitoring included 11 (out of 17) (avr. 8) Forest Administrations – Subsidiaries (FAS) (Vinkovci, Zagreb, Sisak, Našice, Nova Gradiška, Osijek, Bjelovar, Požega, Koprivnica, Slatina, Karlovac), 40 (out of 169) regional forest offices (RFO) and 214 trapping locations average per year. Overall 14.263 (avr. 3.566) small rodents (mice: 11.976 ; avr. 2.994 ; voles: 2.020 ; avr. 505 ; not deremined: 267, avr. 67 ) were trapped. Average relative abundance (RA) in all FAS varied from 7, 4 % to 23% per year with maximum RA 92% that was recorded in FAS Osijek in year 2017. Average share of sedlings with damaged bark varied annualy from 0, 2 % to 9, 5 % (avr. 5, 0 % ; max. 66, 7 %) and of those with domaged root from 0, 2 % to 3, 1 % (avr. 0, 9% ; max. 23, 3 %). Damage on forest seeds varied overall from 0, 3 % to 4, 8 % (avr. 2, 6 % ; max. 36, 6 %). Eventhaugh the average annual relative abundances, nor the damage on seedlings or seeds don’t indicate rodent mass occurence at FAS level, it is important to approach and interpret rodent monitoring and provide protection measures for every regional forest office, and further more for every specific microlocation on which monitoring takes place. Can this relatively low damage on samplings be exlained by the high share of mice (> 80 %) recorded continuously during all four years? Shouldn’t we expect more severe damaged on the seeds if the species from Murinae subfamilies are so dominant over Arvicolinae? Do we need to reconsider the monitoring methodology in years to come? Continuous monitoring should provide further answers.

forest protection, monitoring, small rodents, damage, forest saplings, seeds

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