River flow response under different silvicultural methods in Hyrcanian forests: an indicator-based statistical assessment

Abstract

Assessing the hydrological effects of different forestry management practices is important to predict future impacts and determine suitable forest management methods. This study aimed to evaluate the effects of forestry management practices on monthly river flow and hydrological indicators in Asalem forests, Gilan province. In this study, monthly river discharge data from two hydrometric stations (Kharjegil and Khalian) over a 30-year period (1986–2016) were collected, along with forest management operation data obtained from the regional forest management company; the monthly data were selected to investigate the long-term effects of forest management and reduce short-term fluctuations. Two-way ANOVA and Generalized Linear Model tests were used to evaluate the difference in monthly flow due to different forestry management practices. Additionally, One-way ANOVA for three types of forestry operations and an independent t-test for two types of forestry operations across three consecutive 10-year periods (1986–1996, 1997–2006, and 2007–2016) were used to assess significant differences in nine hydrological indicators focusing on various aspects of river flow regimes. In Kharjegil, Selective (Femel) cutting had a higher impact on monthly flow values than Shelterwood/clear cutting (p<0.05), while Near nature cutting had a more significant effect (p<0.002). No significant difference was observed between Selective cutting and Near nature cutting methods in Kharjegil and Khalian, except for the “Minimum flow index (MinF)” indicator (p<0.05) in Kharjegil. The location of the study stations may explain some differences in results. The statistical analysis suggests that Selective cutting and Near nature cutting methods have similar effects on most river flow indicators. However, in the Khalian station, Selective cutting has lower values for the “coefficient of variation (CV)” indicator compared to Near nature cutting, while Shelterwood/clear cutting has a higher impact on the MinF indicator than Selective cutting and Near nature cutting. Therefore, using Selective cutting and Near nature cutting methods instead of Shelterwood/clear cutting is recommended to minimize the impact on minimum river flow.