Forest Residue Management Impact on Rodent (Rodentia: Murinae, Arvicolinae) Damage in Pedunculate Oak (Quercus robur L.) Forests in Croatia

Small rodents (Rodentia, subfam. Murinae: real mice, Arvicoline voles) greatly affect natural regeneration, stability and dynamics of forest communities worldwide. Every 3–4 years rodent damage in Croatian state forests is the most severe in forest regeneration stands, especially in pedunculate oak (Quercus robur L.) and narrow-leaved ash (Fraxinus angustifolia Vahl.) forests, where rodents can seriously impede natural regeneration by damaging seeds, stems and roots of saplings. These negative interactions are an even bigger challenge nowdays as pedunculate oak and narrow-leaved ash have become more vunerable in the last decades and are known as the most sensitive species of lowland forests in Croatia due to microclimatic and macroclimatic changes and the unfavourable interaction of a whole series of anthropogenic, abiotic and biotic factors. In the last 40 years, in Croatian state forests, rodent management consisted of monitoring and mainly rodenticide use. Trying to implement IPM (Integrated Pest Management) postulates into practice over the years, different prevention methods against small rodents were tested, but not many came to use. The aim of this research was to look into different logging residue management approaches and their effect on the rodent damage in two pedunculate oak forest regeneration stands in central Posavina in Croatia. Rodent damage on stem and root of tree saplings was recorded by visual inspection on three plots (5x5 m) with scattered logging residue, and one plot (5x5 m) with no residue at one micro-depression site (95 m a.s.l.), and on one micro-elevation (99 m a.s.l.) site. Plots with scattered logging residue represented a type of forest residue management in which logging debris (branches) is cut to smaller lengths and distributed evenly at the forest regeneration stand. Plot with no logging debris represented a residue management method in which wood mass is completely removed from the regeneration stand after felling. We counted, determined and inspected tree saplings found at chosen plots for rodent damage (on stem and roots) and also determined the average weight and moisture content of logging residue (branches around 5–7 cm in diameter) found at the site. In spring 2017, 3380 tree saplings (2978; 81% pedunculate oak, 7; 0.2% narrow-leaved ash and 395; 11.7% other deciduous species) were inspected for rodent damage. At micro-depression site, on a plot with no logging residue, only 13.4% of the saplings were damaged, while the average share of damaged saplings on three plots with scattered residue was more than six times higher; 87.8%. The average mass of the logging residue weighed at site with scattered residue was 10.14 kg kg/m2 and moisture content was 19.2%. At micro-elevation site, 25.4% of the saplings were damaged on a plot with no logging residue, while the average share of damaged saplings on three plots with scattered residue was two times higher; 51.4%. The average mass of the logging residue weighed at SRP 1–3 was 5.1 kg/m2. We also determined moderately strong positive correlation (R=0.69133) between the mass of logging residue and rodent damage and strong negative correlation (R=–0.89598) between wood moisture content of the logging residue and rodent damage. In years ahead, with unpredictable climate effects and potentially very variable small rodent dynamics, removing the logging residue after the felling could represent a residue management that contributes to a more effective and ecologically based rodent management. It could also become a usable preventive method within IPM and help prevent sever rodent damage, even during the outbreaks in pedunculate oak regeneration stands.