Effects of pocket gophers, bracken fern, and western coneflower on planted conifers in northern Idaho – an update and two more species

Abstract

Grand Fir Mosaic forests innorthern Idaho are difficult to regenerate afternatural or human-caused disturbances. Sparseconifer regeneration appears to be associated withhigh populations of northern pocket gophers (Thomomys talpoides) plus expansion by bracken fern(Pteridium aquilinum (L.) Kuhn) and invasionof western coneflower (Rudbeckia occidentalisNutt.). This report updates an earlier study(Ferguson and Adams 1994) that quantified theeffects of four treatments on survival and growth ofplanted conifers: unweeded with gophers, weeded withgophers, unweeded without gophers, and weededwithout gophers. Weeding removed only bracken fernand western coneflower. Subalpine fir (Abieslasiocarpa (Hook.) Nutt.), grand fir (Abiesgrandis (Dougl.) Lindl.), and western larch (Larix occidentalis Nutt.) had over 80% mortalityfrom pocket gophers and other causes. Lodgepolepine (Pinus contorta var. latifoliaEngelm.) had 49.2% mortality from pocket gophersand 6.8% mortality from other causes, but snowdamage is a problem for lodgepole pine. Engelmannspruce (Picea engelmannii Parry ex Engelm.)had 42.2% gopher-caused mortality and 8.4%mortality from other causes. Spruce suffered littletop damage from snowpacks and was stout enough towithstand senescing bracken fern fronds. Westernwhite pine (Pinus monticola Dougl.) had only24.1% mortality from pocket gophers after 4 years,and only 11.8% of the white pine died from causesother than gophers. Of the mortality caused bypocket gophers, 76.8% occurred the first summer andnext two winters after planting. The recommendedspecies for reforestation are Engelmann spruce andwhite pine.