Dynamics of bark-beetle infestation spreading in a natural maple-spruce forest in the Zadna Polana reserve | Dynamika šírenia sa chrobačiarov napadnutých lykožrútmi v prírodnej javorovej smrečine v NPR Zadná Poľana

We have attempted to analyse the dynamics of spreading bark-beetle infested spruces in a forest stand based on data on a number of new infested trees attacked by the spruce bark beetle (Ips typographus) within the permanent monitoring plot situated in a maple-spruce (Acereto-Piceetum) natural forest in the Zadna Polana reserve (central Slovakia) in 1995-2005. Based on a simple nonlinear dynamic model, we have analysed behaviour of the model system in time based on system state trajectories in a phase space using principles of the chaos theory. System trajectories in the phase space showed that spreading of infested spruces within the plot is chaotic with a tendency of cyclic fluctuations that are not regular, but they are liable to chaotic oscillations with averagely a 3(-4) years long period of cycles and with a mean increase of 13-14 infested spruces/ha/year. During a low number of infested spruces within a forest stand (about under 8/ha) the system behaviour is chaotic because there are up to 5 scenarios of further spreading of infested spruces in a forest stand with a non-zero probability of realisation. Thus, possibilities to predict trajectories of further system development are highly reduced. During a higher number of infested spruces (over 8/ha roughly) the system will go through cyclic fluctuations with chaotic oscillations. In fact, different system states could occur during sufficiently long time period without a possibility of a exact prediction. Because there is some immigration potential as well as instability of a model system, we could expect that early removing of infested spruces from a forest stand would only halve the total number of infested spruces during the next 10 years compared with a case without sanitation felling. So, the effect of sanitation felling is not significant in this case and this intervention into the model system does not play an important role in further spreading of infested spruces.