Bee diversity decreases rapidly with time since harvest in intensively managed conifer forests.

Despite widespread concerns about the anthropogenic drivers of global pollinator declines, little information is available about the impacts of land management practices on wild bees outside of agricultural systems, including in forests managed intensively for wood production. We assessed changes in wild bee communities with time since harvest in 60 intensively managed Douglas-fir (Pseudotsuga menziesii) stands across a gradient in stand ages spanning a typical harvest rotation. We measured bee abundance, species richness, and alpha and beta diversity, as well as habitat characteristics (i.e., floral resources, nesting substrates, understory vegetation, and early seral forest in the surrounding landscape) during the spring and summer of 2018 and 2019. We found that bee abundance and species richness declined rapidly with stand age, decreasing by 61% and 48%, respectively, for every 5 years since timber harvest. Asymptotic estimates of Shannon and Simpson diversity were highest in stands 6-10 years post-harvest and lowest after the forest canopy had closed, ~11 years post-harvest. Bee communities in older stands were nested subsets of bee communities found in younger stands, indicating that changes were due to species loss rather than turnover as the stands aged. Bee abundance-but not species richness-was positively associated with floral resource density, and neither metric was associated with floral richness. The amount of early seral forest in the surrounding landscape seemed to enhance bee species richness in older, closed-canopy stands, but otherwise had little effect. Changes in the relative abundance of bee species did not relate to bee functional characteristics such as sociality, diet breadth, or nesting substrate. Our study demonstrates that Douglas-fir plantations develop diverse communities of wild bees shortly after harvest, but those communities erode rapidly over time as forest canopies close. Therefore, stand-scale management activities that prolong the precanopy closure period and enhance floral resources during the initial stage of stand regeneration will provide the greatest opportunity to enhance bee diversity in landscapes dominated by intensively managed conifer forests.

Partial shading by solar panels delays bloom, increases floral abundance during the late-season for pollinators in a dryland, agrivoltaic ecosystem.

Habitat for pollinators is declining worldwide, threatening the health of both wild and agricultural ecosystems. Photovoltaic solar energy installation is booming, frequently near agricultural lands, where the land underneath ground-mounted photovoltaic panels is traditionally unused. Some solar developers and agriculturalists in the United States are filling the solar understory with habitat for pollinating insects in efforts to maximize land-use efficiency in agricultural lands. However, the impact of the solar panel canopy on the understory pollinator-plant community is unknown. Here we investigated the effects of solar arrays on plant composition, bloom timing and foraging behavior of pollinators from June to September (after peak bloom) in full shade plots and partial shade plots under solar panels as well as in full sun plots (controls) outside of the solar panels. We found that floral abundance increased and bloom timing was delayed in the partial shade plots, which has the potential to benefit late-season foragers in water-limited ecosystems. Pollinator abundance, diversity, and richness were similar in full sun and partial shade plots, both greater than in full shade. Pollinator-flower visitation rates did not differ among treatments at this scale. This demonstrates that pollinators will use habitat under solar arrays, despite variations in community structure across shade gradients. We anticipate that these findings will inform local farmers and solar developers who manage solar understories, as well as agriculture and pollinator health advocates as they seek land for pollinator habitat restoration in target areas.

Headwater riparian forest-floor invertebrate communities associated with alternative forest management practices.

Headwater streams and their riparian zones are a common, yet poorly understood, component of Pacific Northwest, USA, landscapes. We describe the ecological importance of headwater stream riparian zones as habitat for forest-floor invertebrate communities and assess how alternative management strategies for riparian zones may impact these communities. We compared community composition of forest-floor invertebrates at increasing distances along trans-riparian (stream edge to upslope) transects in mature forests, clearcuts, and riparian buffers of approximately 30-m width with upslope clearcuts. Invertebrates were collected using pitfall traps in five replicate blocks of three treatments each in the Willamette National Forest, Oregon, USA. We measured microclimate and microhabitat variables at pitfall locations. Despite strong elevation and block effects on community composition, community analyses revealed a distinct "riparian" invertebrate community within 1 m of the stream edge in mature forest treatments, which was strongly related to cool, humid microclimate conditions. Invertebrate community composition in buffer treatments was far more similar to that of mature forests than to clearcuts; a pattern mirrored by microclimate. These results suggest that, within our study sites, forest-floor invertebrate distributions are strongly associated with microclimate and that riparian buffers of approximately 30-m width do provide habitat for many riparian and forest species. Riparian reserves may serve as effective forest refugia and/or dispersal corridors for invertebrates and other taxa, and their incorporation into watershed management plans likely will contribute to meeting persistence and connectivity objectives.

Niche specialization and species diversity along a California transect.

The structure of the food-web at the flower-herbivore interface was examined along a transect of fourteen communities across central California. All results are commensurate with the hypothesis that in most environments there is selective pressure towards specialization. However, it is only in the most predictable or stable environments that the resultant diminishment of behavioral and genetic flexibility is in a sense "permitted" by subsequent natural selection. In the most extreme environments, behavioral specialization may be a necessary prerequiste permitting briefly thriving ephemeral populations which must recolonize frequently. The data results indicate: 1) Total species number increases with stability and predictability of the climate; 2) As the climate ameliorates, niche-specialization is a progressively more successful strategy; 3) The percentage of niche-specialized species of both plants and flower-feeding herbivores increases in the most severe environments at the expense of the more moderately specialized species; 4) Energetic flow chart redundancy increases in extreme environments; 5) Especially important to an understanding of pollination interactions is the fact that similar physiognomic communities at very different altitudes are in all cases much more similar than different community types within a research site.

Niche specialization and species diversity along a California transect.

The structure of the food-web at the flower-herbivore interface was examined along a transect of fourteen communities across central California. All results are commensurate with the hypothesis that in most environments there is selective pressure towards specialization. However, it is only in the most predictable or stable environments that the resultant diminishment of behavioral and genetic flexibility is in a sense "permitted" by subsequent natural selection. In the most extreme environments, behavioral specialization may be a necessary prerequiste permitting briefly thriving ephemeral populations which must recolonize frequently. The data results indicate: 1) Total species number increases with stability and predictability of the climate; 2) As the climate ameliorates, niche-specialization is a progressively more successful strategy; 3) The percentage of niche-specialized species of both plants and flower-feeding herbivores increases in the most severe environments at the expense of the more moderately specialized species; 4) Energetic flow chart redundancy increases in extreme environments; 5) Especially important to an understanding of pollination interactions is the fact that similar physiognomic communities at very different altitudes are in all cases much more similar than different community types within a research site.