A special meeting of the Board of Selectmen on Wednesday will include a 7:30 p.m. discussion with NStar officials regarding the utility company’s tree-removal and vegetation-management program around electric transmission lines running through town. Company officials have pledged to negotiate mitigation measures with individual property owners in the Oak Hill and Meadow View Road neighborhood following the completion of the tree-removal program and to protect wellheads, safeguard against erosion, and use approved herbicides next year.