Diminishing Returns from Higher Density Restoration Seedings Suggest Trade‐offs in Pollinator Seed Mixes

Native forbs have become a more central component of restoration programs, especially because of their role in supporting crop pollinators. This study evaluates the success of different native forb mixes and seeding rates using shared goals of restoration practitioners and agroecologists, namely percent native species cover, floral resources, native diversity, and cost‐effectiveness. At 6 sites with hedgerows adjacent to agricultural lands in California's Central Valley, we planted 3 native forb seed mixes at 3 seeding rates and monitored germination, percent cover, and floral resources for 2 to 3 years. We also evaluated the cost of the mixes based on seeding rates and original seed prices. More than mix type, relative seeding rate strongly affected germination, cover, and floral resource success. The relative benefits of seeding with more species diminished at higher seeding rates, especially when cost was considered. Cover increased significantly over the years but diversity declined sharply after the first year. Increased cover of target species was mainly due to the effect of 1 dominant species Grindelia camporum, common gumplant. We summarize data from a similar forb restoration study showing that the species that dominated in our mix‐and‐rate experimental sites also attracted the greatest diversity and abundance of pollinators. These findings highlight trade‐offs and balance‐points within restoration and pollination services goals. We offer suggestions on how to weigh those trade‐offs, given particular priorities and how native forb plantings can support combined goals of pollination services and restoration.

[1]  S. Potts,et al.  Environmental factors driving the effectiveness of European agri-environmental measures in mitigating pollinator loss--a meta-analysis. , 2013, Ecology letters.

[2]  S. Wratten,et al.  Pollinator habitat enhancement: Benefits to other ecosystem services , 2012 .

[3]  C. Kremen,et al.  Hedgerows enhance beneficial insects on farms in California’s Central Valley , 2011 .

[4]  K. Kettenring,et al.  Lessons learned from invasive plant control experiments: a systematic review and meta‐analysis , 2011 .

[5]  W. Meek,et al.  Ecological restoration on farmland can drive beneficial functional responses in plant and invertebrate communities , 2011 .

[6]  H. Rowe.  Tricks of the Trade: Techniques and Opinions from 38 Experts in Tallgrass Prairie Restoration , 2010 .

[7]  Anne Frances,et al.  Importance of Seed and Microsite Limitation: Native Wildflower Establishment in Non‐native Pasture , 2010 .

[8]  R. Winfree.  The conservation and restoration of wild bees , 2010, Annals of the New York Academy of Sciences.

[9]  T. Sisk,et al.  Hedgerows in an agri-natural landscape: Potential habitat value for native bees , 2009 .

[10]  T. L. Dickson,et al.  Forb Species Establishment Increases with Decreased Grass Seeding Density and with Increased Forb Seeding Density in a Northeast Kansas, U.S.A., Experimental Prairie Restoration , 2009 .

[11]  K. Dixon.  Pollination and Restoration , 2009, Science.

[12]  K. Klonsky,et al.  Factors affecting adoption of hedgerows and other biodiversity-enhancing features on farms in California, USA , 2009, Agroforestry Systems.

[13]  R. Minnich.  California's Fading Wildflowers: Lost Legacy and Biological Invasions , 2008 .

[14]  James Regetz,et al.  Landscape effects on crop pollination services: are there general patterns? , 2008, Ecology letters.

[15]  D. Kleijn,et al.  At what spatial scale do high-quality habitats enhance the diversity of forbs and pollinators in intensively farmed landscapes? , 2007 .

[16]  M. Aizen,et al.  Pollination and other ecosystem services produced by mobile organisms: a conceptual framework for the effects of land-use change. , 2007, Ecology letters.

[17]  R. Sheley,et al.  Enhancing Native Forb Establishment and Persistence Using a Rich Seed Mixture , 2006 .

[18]  M. Nowakowski,et al.  Comparing the efficacy of agri‐environment schemes to enhance bumble bee abundance and diversity on arable field margins , 2006 .

[19]  N. Turner,et al.  Determining the Optimal Sowing Density for a Mixture of Native Plants Used to Revegetate Degraded Ecosystems , 2006 .

[20]  Monica L. Pokorny,et al.  Plant Functional Group Diversity as a Mechanism for Invasion Resistance , 2005 .

[21]  I. Williams,et al.  Food for insect pollinators on farmland: insect visits to flowers of annual seed mixtures , 2002, Journal of Insect Conservation.

[22]  D. Gowing,et al.  Influence of Seed Mixture and Hydrological Regime on the Establishment of a Diverse Grassland Sward at a Site with High Phosphorus Availability , 2003 .

[23]  C. Price,et al.  Managing Non‐Native Plant Populations Through Intensive Community Restoration in Cades Cove, Great Smoky Mountains National Park, U.S.A. , 2003 .

[24]  R. S. Burton,et al.  Competition, seed limitation, disturbance, and reestablishment of California native annual forbs , 2003 .

[25]  David Tilman,et al.  Plant diversity increases resistance to invasion in the absence of covarying extrinsic factors , 2000 .

[26]  J. Baudry,et al.  Hedgerows: An international perspective on their origin, function and management , 2000 .

[27]  Karen D. Holl,et al.  Paying for Restoration , 2000 .

[28]  Jonathan M. Levine,et al.  Elton revisited: a review of evidence linking diversity and invasibility , 1999 .

[29]  J. Hamilton.  Changing perceptions of pre-European grasslands in California. , 1997 .

[30]  F. Bonnieux,et al.  Valuing the Benefits of Landscape Restoration: a Case Study of the Cotentin in Lower-Normandy, France , 1997 .

[31]  J. C. Hickman,et al.  The Jepson Manual: Higher Plants of California , 1993 .