Simulation of the impact of pest outbreak and forest harvesting on stand mixture in the Hhyrcanian forest (Case study: Lireh Sar forests, Tonekabon)

Species composition are affected by disease outbreaks, pest outbreaks, and harvesting. In the Hyrcanian forests, alder brown leaf beetle is among the most common biological disturbances, which along with timber harvesting can alter its species composition. The present study aimed to simulate the species composition of the Hyrcanian forest at stand level under the mentioned natural and anthropogenic disturbances.

Using random-systematic sampling with a circular plot within a 200*200 grid, 667 plots (1000 m2) were sampled for evaluating the current state. A LANDIS-II landscape change model was used to simulate the study area under different scenarios for 5-years’ time periods over 100 years.

By accelerating the removal of pure hornbeam stands from the landscape, biological disturbance is likely to increase the mixture of tree composition by allowing Carpinus-Diospyros and Carpinus-Parrotia to replace them. Similarly, tree harvesting will also create the same situation by establishing mixed broadleaf and Alnus-Carpinus forest types. In the presence of biological disturbance and tree harvesting, diversity peaked so that the highest mixture stands were produced by scenario of alder brown leaf beetle in the presence of tree harvesting.

When biological disturbance occur, Caucasian alder species that host this pest can be preserved by implementing appropriate harvest management techniques and creating a more mixed forest ecosystem.