Effects of Sage-Grouse Habitat Restoration Efforts on Pollination Networks in an Arid Ecosystem

Abstract

On publicly managed lands of western North America, canopy removal is practiced as a habitat improvement for sage grouse (Centrocercus species), often with the goal of converting dominant vegetation cover from pinyon pine (Pinus edulis) and juniper (Juniperus spp.) to sagebrush (Artemisia spp.). However, it remains unclear whether habitat conversion practices impact other species of conservation concern, especially pollinators, which are sensitive to changes in vegetation cover. Here we test how bee-flower assemblages differ between pinyon-juniper and sagebrush habitats and whether removal of canopy by mastication affects bee-flower networks.

Three important findings emerged: 1) linkage density (a measure of diversity) of bee-flower interactions was 33% higher in sagebrush habitats; however, mastication treatments were associated with reduced network specialization and there was evidence of interannual variation in network indices; 2) the most-visited floral taxa in pinyon-juniper sites were woody plants (Amelanchier, Opuntia, Prunus) but, in sagebrush sites forbs (Heterotheca, Eriogonum) were more frequently visited; however, weedy taxa including Cirsium and Melilotus were highly utilized in both habitats; and 3) site physiography affected bee assemblages; incident radiation (heat load index, HLI) had larger effects than relative site position in conservation areas, with higher bee abundance and richness at cool sites with low canopy cover.

We conclude that conversion of sites from pinyon-juniper to sagebrush is not likely to negatively impact bee-flower interactions in comparison with nontreated sagebrush habitats. Several native forbs and woody species highly visited by bees can be targeted for site restoration efforts, but eradication of “weedy” taxa (Cirsium and Melilotus) may reduce habitat availability. Managers should also consider site physiography when prioritizing treatment landscapes, with an emphasis on prioritizing conservation in habitats with low HLI.