Improving Native Seeding Strategies

Improving Native Seeding Strategies

November 1, 2013

Dan Mummey discusses strategies used this fall and spring to stagger species arrangement in time and space to create more diverse communities.

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High seeding rates may fill niche space and combat weeds (Sheley et al., 2008; Carter and Blair 2012), but competition between seedlings increases with increased seed number. Some species will win, and other species- often subdominant forbs and small grasses- will lose when seedling competition is high (Dickson and Busby, 2008). This early competition results in a spatially homogeneous, low diversity plant community (Carter and Blair 2012). Here we discuss strategies we will use this fall and spring to stagger species arrangement in time and space to create more diverse communities. We seek to create a patchwork of spatially aggregated species and plant communities that take up niche space and use resources more efficiently than standard drill-seeding practices.

Rapid establishment of a competitive native community improves invasive species control. We will try staggering seeding times for different species to increase diversity by altering competitive relationships. Established plants are more difficult to displace than seedlings. Sowing weak competitors before aggressive species can facilitate coexistence by giving weak competitors time to establish (Young et al., 2001; James et al., 2012). Spatial aggregation of seeds may present a way to reproduce natural plant co-occurrence patterns. Interactions such as facilitation and competition that display spatial heterogeneity on multiple scales maintain species diversity. Modeling studies and empirical work suggest that spatially aggregating seeds will facilitate weak competitors and increase diversity by giving weak competitors establishment priority (Potthoff et al., 2006; Turnbull et al., 2007; Wassmuth et al., 2009; Porensky et al., 2012; Houseman, 2013).

Strategy #1 - Imprinters on alternate rows will facilitate broadcast seeding. - We will seed each field twice, once in the fall and once in the spring. - Large grasses will compose the first drill mix. - Species that require cold stratification will compose the first broadcast mix. - Small grasses and forbs will compose the second drill mix. - Grasses and forbs the do not require cold stratification will compose the second broadcast mix.

Strategy #2 - Paired broadcast imprinters and drilled rows will alter the spatial scale of species interactions compared with Strategy #1. - Increased patch size will decrease heterospecific competition over larger areas.

The proposed seeding strategies will increase the range of interactions between sown species compared with standard seed drilling practices. Seed density will vary at small scales within each row. Each seeded species will experience different amounts of competition or facilitation from other seeded species over multiple spatial scales. Niche space will be increased even for subordinate species. Spaces between seeded rows provide niches for weeds to establish and compete with natives (Bakker et al., 2003; Yurkomis et al., 2010). This strategy decreases unseeded areas between rows that could host weedy species. There are advantages and disadvantages to both fall and spring seeding. Seedling establishment and survival hinges on unpredictable climate conditions. Dormant seeding in the fall allows plants to take advantage of early season conditions favorable for seedling growth, but not for seeding. Seeds experience natural cold stratification when sown in the fall.

Evaluation- Do restorations mimic functional trait spatial stratification of natural communities? Spatial analyses will be used to evaluate differences in spatial community assemblage over time. Vegetation survey crews will place permanent markers on blocks of rows within each treatment and treatment area. We will compare taxa diversity, richness, small-scale co-occurrence, spatial patterns between treatments, and plant functional trait indexes. Species co-occurrences will be evaluated in 6 inch cells positioned down each row. Species co-occurrences that, after correction for species abundances, occur less often than expected by random chance will indicate competition. Cooccurrences that occur more often than expected by chance alone suggest facilitation. Neutral co-occurrences suggest that species occupy a different temporal or spatial niche space. Most information about plant community structure is derived from analysis of adult plant communities. The proposed analyses will provide information about how restoration species interact at all growth stages and develop into adult communities.

References

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