Abstract
We used a Woodward Flail-Vac seed harvester to harvest slender wheatgrass (Elymus trachycaulus (Link) Gould ex Shinners [Poaceae]) from a restored grassland at Grand Teton National Park. Seed was harvested over 3 continuous d, covering an area of approximately 5.5 ha (13.6 ac). Total seed yield was 291 bulk kg (642 bulk lb) or equivalent to 53 bulk kg/ha (47 bulk lb/ac). Estimated hours of labor for 3 d of harvesting plus time processing at the Aberdeen Natural Resources Conservation Service Plant Materials Center totaled 120 h. When comparing the resources and environmental inputs required for in situ seed harvesting to the conventional native seed production, given an appropriate setting, in-field seed harvesting may offer a viable additional method to supplement the need for native seed. In addition, in situ harvesting may offer an effective, affordable, and environmentally sustainable alternative for procuring significant amounts of seed of locally adapted ecotypes for restoration plantings.
Restoration efforts following large-scale wildfires, noxious weed removal, and other disturbances create shortages in the finite amount of available native seed, particularly in the arid western US where large contiguous tracts of land require large quantities of native seed. For example, wildfires burned an average of more than 473,000 ha (1,170,000 ac) annually in the Great Basin between 2012 and 2017 (Great Basin Coordination Center 2018). Additionally, cheatgrass (Bromus tectorum L. [Poaceae]), an introduced annual grass, was found to be dominant on 10.1 million ha of public land in the Great Basin (USDI BLM 2000), with potentially 25.1 million ha at risk of invasion (as deemed by Pellant and Hall in 1994). At the same time, interest in developing and restoring habitat for native pollinators has also increased demand for native forbs in particular (Plant Conservation Alliance 2015). To address the high demand of native seed for restoration projects, the Bureau of Land Management has purchased an average of 2.0 million lb of seed annually over the past 3 y (Roller 2018) with an ever-increasing portion of the procured seed being of native species. Other land management agencies and private landowner restoration and conservation projects add to that need for seed.
Meeting seed demand, especially in years following significant wildfires, has been an ongoing challenge, often resulting in not enough native seed available for restoration. Currently, most (> 95%) of the native seed available for procurement for private and public restoration has been produced using traditional agronomic seed production techniques that include single species plant production in a row-crop setting utilizing tillage practices as well as the use of fertilizer, pesticides, and irrigation.
With increasing emphasis on local ecotype seed sources (USDI NPS 2006; USDA FS 2008; Plant Conservation Alliance 2015) and diverse seed mixes (Stachowicz 2001; Barr and others 2017), eco-regionally appropriate and site-specific native seed is in high demand for restoration and conservation plantings. Notably, natural resources conservation and land management agencies, along with private industry, are now coordinating efforts to meet these needs. Objective 1.3 of the Bureau of Land Management National Seed Strategy is to increase the supply and reliable availability of genetically appropriate seed. Action 1.3.3 of the Strategy is to identify alternative seed production methods and best management practices for in-field (in situ) seed harvesting of mixed wildland (or private) native stands as alternative future native seed sources (Plant Conservation Alliance 2015). Along with the emphasis on local ecotype seed, an increasing grasp of the importance of diversity in native seed mixes for ecological restoration is further driving demand for native species that are not readily available commercially (Jordan 1997; Stachowicz 2001; Kurtz 2013; Barr and others 2017; Judson 2017).
This demand for native eco-regionally adapted seed has resulted in the formation of various native seed networks such as the Colorado Plateau Native Plant Program, the Great Basin Native Plant Project, the Iowa Ecotype Project, the Uncompahgre Partnership, the South Texas Natives, the Southwest Seed Partnership, the Southern Rockies Seed Network, and the Willamette Valley Native Plant Materials Partnership, to name a few. The purpose of these networks is to pool resources across regions to address the native plant and seed needs, to collaborate on plant materials and seed increase technology, and coordinate eco-regional seed source and need identification to meet local restoration requirements.
The USDA Natural Resources Conservation Service plant materials centers have developed agronomic seed production protocols for more than 400 conservation plant releases including native species (USDA NRCS 2015). These agronomic seed production methods often include intensive cultural activities such as tillage, fertilization, pesticides, and irrigation. Some native species, however, such as Leymus salinus (M.E. Jones) Á. Löve (Poaceae), Koeleria macrantha (Ledeb.) Schult. (Poaceae), Balsamorhiza sagittata (Pursh) Nutt. (Asteraceae), and Lessingia leptoclada A. Gray (Asteraceae), either do not produce enough seed to justify agricultural production and (or) are not well suited for intensive agronomic monoculture seed production methods to make seed increase profitable. In situ field harvesting for these and other species may be an additional and currently underutilized method to address the seed shortages of native species, particularly forbs, and may offer more sustainable alternative practices in native seed production methods.
In situ field harvesting has been successfully implemented during the past several decades by conservation organizations, and a few seed producers currently employ this method of native seed harvesting and production. Carl Kurtz, a native seed supplier from St Anthony, Iowa, has been in situ field harvesting in restored mixed tallgrass prairies since 1988, providing multiple species seed mixes with as many as 57 native species made up of approximately 25% native grasses and 75% native forbs (Shirley 1994). Jon Judson of Diversity Farms, another native seed supplier in Dedham, Iowa, has been harvesting mixed tall and short grass prairie seed from diverse remnant prairies and prairie reconstructions for local customers since 1997, providing upward of 40-species seed mixes comprised approximately of 10 native grass species and 30 native forb species (Judson 2017). The Nature Conservancy, the U.S. Fish and Wildlife Service, and other restoration organizations have also utilized in situ seed harvesting techniques using prairie seed harvesters to produce seed for use on public and conservation lands (Helzer 2017; Judson 2017; Oldham 2017). Some seed companies may harvest native grass seed from expired Conservation Reserve Program lands for sale to private customers, but production details and labor and equipment investment figures for in-field native seed harvesting as an additional seed source and viable alternative to agronomic seed increase methods are not readily available.
Restoration of disturbed areas, road and infrastructure improvements, and noxious weed control create a near constant native seed demand for land management agencies. Grand Teton National Park is in a unique position in which past restoration projects may provide an opportunity for within-park bulk seed harvesting with relatively low inputs. In recent years, several historic hay fields have been seeded to native seed mixes. These fields were once used as pasture or hay land by homesteaders, but they are now incrementally being restored to native vegetation with the intent of future seed harvesting to help meet the need for continuing restoration efforts. Site preparation has included multiple years of chemical treatments to reduce introduced grasses such as smooth brome (Bromus inermis Leyss. [Poaceae]) and other non-desirable species prior to seeding with a native mixture. These efforts have resulted in approximately 350 ha (875 ac) of grasslands that are relatively level and smooth with few rocks, logs, or other obstacles; low weed pressure; and young vigorous stands consisting of primarily native grasses and forbs.
SITE HISTORY
In 2016, NRCS plant materials program staff assisted the Grand Teton National Park revegetation staff in harvesting slender wheatgrass from within the Elbo West restoration field approximately 8 km (5 mi) west of Moose, Wyoming, in the Kelly Hayfield region of the park (Figure 1). The Elbo West site had been prepared by treating the existing smooth brome field with glyphosate in June and July 2010. A prescribed burn was implemented to remove thatch, and the site was then planted to a cereal rye (Secale cereale L. [Poaceae]) cover crop in September 2010. In 2011, it was treated again with glyphosate in June and later treated with aminopyralid to control emerging musk thistle (Carduus nutans L. [Asteraceae]). The site was planted to a native mix in October 2011 using a Dew Drop drill at a target rate of 305 pure live seeds (PLS)/m2 (28 PLS/ft2) (Table 1). From 2012 to 2016 the field received periodic chemical spot treatments and mechanical removal of noxious weeds.
Google Earth map of the Elbo West field and slender wheatgrass harvest site. Image source Google Earth Pro. Image date 21 Jun 2017; accessed 20 Nov 2017.
Native seed mix components for Elbo West seeding, 2011.
In 2016, a section of field approximately 5.5 ha (13.6 ac) in size was flagged for harvest (Figure 2; Figure 3) based on visual estimates of high density of slender wheatgrass (50% or greater cover) and low amounts of smooth brome and musk thistle. Species also found within the harvest site included Kentucky bluegrass (Poa pratensis L. [Poaceae]), Canada bluegrass (P. compressa L.), mountain brome (Bromus marginatus Nees ex Steud.), and Idaho fescue (Festuca idahoensis Elmer [Poaceae]).
We harvested approximately 5.5 ha (13.6 ac) of the Elbo West field. Harvested area was determined based on the stand of slender wheatgrass and the reduced presence of non-native species such as smooth brome. Image source Google Earth Pro. Image date 21 Jun 2017; accessed 20 Nov 2017.
Slender wheatgrass is ready to harvest when the seed shatters easily.
We harvested seed from 15 August through 17 August 2016 using a 3.7 m (12 ft) Woodward Flail-Vac Seed Stripper (Ag-Renewal, Weatherford, Oklahoma) mounted on a John Deere 5525 Tractor (Deere and Company, Moline, Illinois). The Flail-Vac was set approximately 15 to 30 cm (6–12 in) below the base of the average seed head height at the maximum forward tilt for the most aggressive threshing of the seed heads (Figure 4). The power takeoff (PTO) was run at 2500 revolutions per min (rpm), which provided a Flail-Vac brush speed of 160 rpm. The harvested seed was loaded in a dump truck and transported back to Aberdeen Plant Materials Center for drying and processing (Figure 5; Figure 6).
We set the Flail-Vac approximately 15 to 30 cm (6–12 in) below the base of the average seed head height at the maximum forward tilt for the most aggressive threshing of the slender wheatgrass seed heads.
Loading the harvested material into a dump truck for transport from Grand Teton National Park to the Aberdeen Plant Materials Center in Idaho.
Harvested seed unloaded and dried on a clean shop floor at Aberdeen Plant Materials Center prior to cleaning.
RESULTS
During the 3-d harvest period, NPS and PMC staff ran the harvester a total of 21 h, which yielded 538 kg (1186 lb) of unprocessed materials. After processing, we obtained a total of 291 bulk kg (642 lb) of clean slender wheatgrass seed with 97% purity and 77% viability, or 74% PLS. The harvest yielded an average of 53 kg/ha (47 lb/ac). Purity analysis indicated low levels of contamination of other species. We noted 283 Bromus marginatus, 57 Festuca sp., 28 Bromus inermis, and 28 unidentified Bromus seeds per kg.
TIPS
Judge harvest timing by pinching the caryopsis of the slender wheatgrass to identify the presence of hard dough or mature seed (USDA NRCS 2006). We waited until the seed was fully mature and beginning to shatter before harvesting.
Harvest timing can be manipulated to some degree to help avoid non-desirable or non-target species.
Have 1 or 2 people walk in front of the harvester to rogue inferior or unwanted species or to clip off and remove any non-desirable seed heads.
A good starting point is to harvest contiguous areas a minimum of 0.4 ha (1 ac) or greater for in situ field harvesting.
COST BENEFITS
In our case study, in situ harvesting shows a definite cost advantage compared with standard seed production practices. Yields of agronomic production for slender wheatgrass average approximately 224 to 448 PLS kg/ha (200–400 PLS lb/ac) for dryland production and about 560 PLS kg/ha (500 PLS lb/ac) for irrigated (Smith and others 1996). Estimated labor for contract production per acre of grass seed totals approximately 230 h including planting, field cultivation, fertilization, harvesting, and processing for 2 y as harvests are not expected from the establishment year. In situ field harvesting labor at Grand Teton National Park, which included a 2-person crew for 3 d (42 labor h), plus processing time at Aberdeen Plant Materials Center (approximately 80 labor h), totals 122 labor h. (Costs for equipment and supplies such as Flail-Vac, tractors, combines, seed cleaning, fertilizer, and pesticides are not included.)
DISADVANTAGES
Harvesting with a Flail-Vac is less efficient than using a combine. We estimate the Flail-Vac removed approximately 50% of available seed. Greater yields may be possible with the use of modifications to the Flail-Vac, such as a cartridge-wafer system as demonstrated by Kees (2006) or the drag chains described by Simonson and Tilley (2016), depending on the species to be harvested.
In situ harvested seed is more likely to contain non-target species than does agronomic production. A diverse harvest of native species, however, may be acceptable; or non-target species could be largely removed by additional cleaning and field roguing.
ADVANTAGES
The Elbo West field was not visually affected from the seed harvesting. Even after harvesting with the Flail-Vac, the field did not look like it had been altered. This outcome may be important to land managers wishing to preserve the aesthetic integrity of the landscape.
The less-efficient Flail-Vac may be beneficial for harvesting from natural remnant stands where the desire is not to harvest 100% of the stand.
Fields can be harvested yearly with minimal agricultural inputs, such as spot weed treatment that may be needed and ongoing.
Active restoration schedules may ensure that new potential production fields will be created in future years.
If desired, a diverse mix of native seed could be harvested.
To assess if a site is appropriate for in situ field harvesting, use the following checklist.
Site Checklist for In Situ Field Harvesting Using a Flail-Vac
✓ Is the site accessible with a tractor?
✓ Are there steep slopes, ditches, or other obstacles?
✓ Are fragile soils or ecological sites an issue?
✓ Is a continuous area of 0.4 ha (1.0 ac) or greater available for harvesting?
✓ Is the site free of noxious weeds or off-target species?
˚ If not, can the site be rogued prior to harvesting, can the timing of harvest be adjusted to avoid non-target species, and (or) can non-target species be separated during the seed cleaning process?
✓ Are facilities available to dry and process the seed?
✓ Is the seed-harvesting equipment dedicated to a particular site?
˚ If not, take care to clean equipment thoroughly to ensure that non-desirable weed seed is not brought in with the equipment.
✓ If the site is a native remnant, carefully consider the harvesting schedule and intensity, as well as how to adequately clean the harvesting equipment.
When assessing the feasibility of in situ harvesting, seed production management of the site must be included as well. Weed control and management may include chemical or mechanical spot treatments along with periodic prescribed burn implementation and possibly inter-seeding may be necessary to facilitate continued seed production. Additionally, harvest rotation schedules may be necessary to rejuvenate stands and maintain seed yield.
Take precautions to prevent the possibility of overharvesting and creating undesirable shifts in species richness, particularly on remnant native sites. Repeated annual wildland harvesting in tallgrass prairie remnants caused negative impacts on short-lived and non-clonal species stands (Meissen and others 2015; Meissen and others 2017a). Note that Meissen and others (2017b) found that populations of seed-dependent species did not decrease from triennial or low-intensity harvesting. This may be less of a concern in restored grasslands that are dominated by long-lived perennial grasses; however, adjusting the harvest schedule or intensity can help reduce the risk of negative impacts on shorter-lived species dependent on seed for recruitment (Meissen and others 2017b). The US Bureau of Land Management’s Seeds of Success program, for example, recommends harvesting no more than 20% from donor sources (USDI BLM 2015). Frequent monitoring of species richness and composition will aid land managers in developing a suitable harvesting regimen.
SUMMARY
As land management agencies have continuous demand for diverse seed of local ecotype origin, in situ field harvesting of restored or diverse native stands may provide a lower cost and more environmentally sustainable option for native seed increase. There may be opportunities within some land management agencies and private landowners with expiring Conservation Reserve Program lands for larger scale harvest of seed under certain conditions. Native stands created on previously farmed land are often flat, devoid of obstacles, and relatively weed free, allowing for the use of harvesting equipment such as a Flail-Vac or combine. Use of these tools, our case study showed, could yield relatively high quantities of seed with little cost, ultimately saving funds for additional restoration efforts. This strategy is not limited to land management agencies and restoration organizations; it could also be implemented through the emerging native seed networks as a seed source alternative on private lands to help meet seed demand, reduce environmental impacts from intensive seed production methods, and reduce restoration costs.
ACKNOWLEDGMENTS
The authors thank Kelly McCloskey, Grand Teton National Park and Jayne Jonas-Bratten, Colorado State University for review and editorial comments. Any mention of seed equipment, producers, or vendors does not constitute an endorsement.
Footnotes
This article was prepared by a U.S. government employee as part of the employee’s official duties and is in the public domain in the United States.
Photos by Derek Tilley
