Have Changing Forest Conditions Contributed to Native Pollinator Decline
Forest Service researchers selected five stands in each of seven forest types including: cleared forest, dense young pines, thinned young pines, mature open pine with extensive shrub andsapling cover, mature open pine with extensive grass andherbaceous plant cover and little shrub cover, mature upland hardwood forest, and mature riparian hardwood forest. They sampled bees for one year and measured overstory tree density, understory herbaceous plant and shrub diversity and cover, light penetration, and leaf area index. Bee abundance and species richness were highest in cleared pine forest and in mature pine stands with a grass and herbaceous plant understory. Bee species richness was lowest in dense young pine stands. Likewise, open bottomland hardwood forest, cleared forest and open pine forests with a grass understory had the highest asymptotic species richness estimates. Leaf area index and basal area were negatively correlated with both bee species richness and bee abundance while canopy openness and plant richness were positively correlated with both, although weakly so with plant richness. Two conservation goals of the early 20th Century, extensive reforestation and reduced wildfire through fire exclusion, may have contributed to declining pollinator abundance over time as forests became denser and shrub covered. These research results combined with many others suggest that thinning forests combined with shrub control can provide good bee habitat; it is compatible with habitat restoration and management for the red-cockaded woodpecker Picoides borealis; and, the resulting forests will be healthier and less susceptible to old (southern pine beetle) and new (European woodwasp) threats.
Forest Service Partners