Are Dead Riparian Buffers Effective at Reducing Nutrients Generated by Harvesting in Forests Killed by Mountain Pine Beetle?.

Bark beetles currently threaten 10s of millions of hectares of pine forest in the United States.  In Colorado, where mountain pine beetle outbreaks are forecast to kill most of the State’s mature lodgepole pine forests, there is an immediate need to assess how well riparian forests consisting of beetle-killed trees protect watershed resources in areas affected by insect outbreak and subsequent salvage logging.  In this study we evaluate riparian zone filtering by comparing soil nutrient pools and nutrient leaching across upland to riparian gradients for 1) unharvested beetle-killed hillslopes, 2) harvested hillslopes with 30 m wide riparian buffers and 3) harvested hillslopes with harvested riparian forests.  Harvesting increased resin nitrate almost 7-fold and nearly doubled resin ammonium compared to uncut beetle-killed forests.  Removal of the riparian overstory increased resin nitrate and ammonium by 62 and 30% compared to harvested areas with intact beetle-killed riparian forest.  Nitrate concentrations in soil leachate were 2.5-fold higher in harvested compared to unharvested hillslopes and removal of forest buffers doubled leachate nitrate compared to areas with uncut riparian buffers.  Current riparian buffers appear to be effective for attenuating nitrate generated by forest harvesting in areas affected by severe pine beetle outbreak.