Floral resources of an invasive shrub alter native bee communities at different vertical strata in forest-edge habitat

Abundant, distinct, and seasonally dynamic bee community in the canopy-aerosphere interface above a temperate forest

Our understanding of how bees (Apoidea) use temperate forests is largely limited to sampling the understory and forest floor. Studies over the last decade have demonstrated that bee communities are vertically stratified within forests, yet the ecology of bee assemblages immediately above the canopy, the canopy-aerosphere interface, remains unexplored. We sampled and compared bee communities above the canopy of a temperate forest to the understory (1 m), midstory (10 m), and canopy (20 m) on the campus of the University of Massachusetts, in Amherst, Massachusetts, United States from April to August, 2021. Overall, we found that assemblages above the canopy had more bees than in the understory, were distinct in composition from all other strata, and included the greatest proportion of unique species. Bee abundance and species richness were highest in the understory throughout the spring (April and May) and decreased as the season progressed, while bee abundance and species richness at higher strata increased into the summer months. We also found that bees with preferences to nest in moist and rotting wood were largely restricted to canopy and midstory strata. We conclude that bee assemblages occupying the space above the forest canopy are abundant and diverse, and their unique composition suggests that this canopy-aerosphere interface plays an additional role in the bee community of temperate forests. Alternatively, our findings question how forest bee communities should be defined while highlighting the need for research on fundamental processes governing species stratification in and above the canopy.

Honey-Bearing Potential of Tilia cordata Mill. Forests in the Southern Urals

This article examined the honey-bearing potential of Tilia cordata Mill. stands in the Southern Urals using forest management and taxation methods. The studies were conducted in pure and mixed even- and uneven-aged forests with T. cordata Mill. in different natural zones of the Southern Urals on the territory of the Bashkirs. These were forests of the South Ural forest-steppe region, the forest-steppe region of the European part of Russia, the area of coniferous-deciduous (mixed) forests of the European part of Russia. The research employed the method of laying temporary and permanent trial areas. T. cordata Mill. forests on the republic’s territory were divided into zones by forest districts. There is a discrepancy between the territorial localization of “nectar” (honey-bearing) linden and designated forest areas, that is, honey-bearing forest areas on the republic’s territory. It could be due to the lacking methodology for assigning linden to these categories. The increased rotation age of linden trees to 81–90 years for several decades, a ban on final cutting, reduced annual cut of soft-leaved forests by 15% enlarged the stocks of overmature forest to 48%. Depending on the age, the number of flowers on one T. cordata Mill. tree varies from 0 to 60.2 thousand pieces. The maximum amount of nectar is 69.04 kg/ha at 12-day linden flowering. The honey productivity of plants including T. cordata Mill., calculated concerning the linden age, its share in the forest composition, the average number of flowers on the tree, nectar per 1 ha of linden and the flowering period ranged from 252.8 to 662.8 kg/ha.

Decadal Patterns of Forest and Pollinator Recovery Following the Eradication of an Invasive Shrub

Invasive non-native woody shrubs pose a major threat to forested ecosystems in many parts of the world and there is an urgent need for research on the restoration and recovery of these areas. We studied patterns of tree growth and regeneration 13 years after the experimental eradication (by chainsaw or mulching machine followed by herbicide treatments) of Ligustrum sinense Lour. (Chinese privet) from riparian forests in Georgia, United States. We also followed the recovery of bee and butterfly populations using sites with no history of privet invasion as a reference. By the end of the study, the basal area of restored plots was 24% greater, on average, than still-invaded control plots. Because tree growth rates did not differ among treatments, this increase is attributable to the 60% increase in the number of regenerating native stems (dominated by Acer negundo L.) following privet removal. The benefits of privet removal on pollinators were immediate and long-lasting with the richness and abundance of bees and butterflies being consistently higher in restored plots than in control plots. The diversity, abundance, and composition of bees in restored and reference (i.e., never invaded) plots were comparable by the end of the study. This was less true for butterflies, however, possibly due to the legacy effects of privet invasion on plant communities. Our results demonstrate the long-term benefits of removing privet on forest regeneration and pollinator communities. Indeed, without such efforts, it is probable that forest cover will gradually thin and ultimately disappear from privet-invaded areas as overstory trees die without replacement.

Pollination Potential of Riparian Hardwood Forests—A Multifaceted Field-Based Assessment in the Vistula Valley, Poland

Riparian forests with oaks, ashes and elms, now highly fragmented and rare in Europe, are considered hotspots for ecosystem services. However, their capacity to provide pollination seems to be quite low, although reports from in-situ research supporting this view are scarce. Our goal was therefore to thoroughly assess their pollination potential based on multifaceted field measurements. For this, we selected six test sites with well-developed riparian hardwood forests, located in the agricultural landscape along the middle Vistula River in Poland. We used seven indicators relating to habitat suitability (nesting sites and floral resources) and pollinator abundance (bumblebees and other Apoidea) and propose a threshold value (AdjMax) based on value distribution and Hampel’s test to indicate the level of pollination potential for this type of riparian forest. The obtained AdjMax for bumblebee density was 500 ind. ha−1, for Apoidea abundance—0.42 ind. day−1, while for nectar resources—200 kg ha−1. We demonstrate that the investigated small patches of the riparian hardwood forest have a higher pollination potential than reported earlier for riparian and other broadleaved temperate forests, but the indicators were inconsistent. As forest islands in the agricultural landscape, riparian hardwood forests play an important role in maintaining the diversity and abundance of wild pollinators, especially in early spring when there is still no food base available elsewhere.