Artemisia Journal

ARTEMISIA | Vol. 48 No. 1

Seed-Based Restoration

Scaling Up for the Future

Fall 2020

By Matthew Garrambone and Sunny Saroa

Ecological restoration is the process of assisting in the recovery of degraded, damaged, and destroyed ecosystems (Society for Ecological Restoration 2004).

While it can have benefits at any spatial scale, ecologists increasingly recognize the value of working at the landscape scale, at which a relatively consistent mosaic of local ecosystems or land uses repeats across a large area, such as a watershed or basin. Working at this scale can provide cumulative gains for multiple taxa by enhancing ecosystem processes as well as habitat quality and connectivity (Hobbs et al. 2014; Aavik and Helm 2018). In California and elsewhere, restoring ecosystems at the landscape scale requires adaptive, cost-effective, and spatially appropriate strategies for native plant establishment (Kildisheva et al. 2016; Pedrini et al. 2020). 

For the Irvine Ranch Conservancy (IRC), a nonprofit organization that works on behalf of Orange County Parks, the City of Irvine, the City of Newport Beach, and various other agencies to restore degraded landscapes throughout Orange County, scaling up restoration efforts has meant a wholesale adoption of seed-based restoration. This article explains the rationale behind our use of functionally diverse, locally adapted seed mixes for landscape- and sub-landscape-scale projects. It also highlights the challenges associated with acquiring sufficient seed of local provenance for restoration and the steps our organization took to address them. Lastly, it showcases efforts being made to improve access to genetically appropriate native plant materials in Southern California.

Volunteers and public participants assist in the maintenance of common goldfields (Lasthenia gracilis) at IRC’s native seed farm; Image: Courtesy of IRC.

Seed-Based Restoration

Since 2005, IRC’s restoration program has worked to restore thousands of acres of open space in Orange County that have been degraded by a history of grazing, frequent fires, and invasive species. Our projects target large patches of degraded land within a watershed or canyon, and seek to restore multiple habitat types such as coastal sage scrub, chaparral, riparian, oak woodland, and native grassland. Restoration goals and metrics for success vary across projects, but IRC’s restoration program generally aims to restore ecosystem function and enhance resilience to disturbance. To restore habitats, we use native plants of various functional groups (e.g., forbs, shrubs, and graminoids) as the building blocks. 

Due to a long history of degradation, many of the sites we aim to restore are likely seed limited, meaning the native seed bank has been partially or completely depleted. Without a functional native seed bank, these habitats are less resilient to climatic variability and natural disturbance (Poschlod et al. 2013; Ma et al. 2019). Because the seed bank is such an important component of the systems in which we work, a passive restoration approach involving weed removal without seed addition is insufficient. Instead, we work to deplete the non-native seed bank in the first phase of the project, and install native seed afterward. This approach allows us to reintroduce a diverse suite of early successional species, specifically those with adaptations such as seed dormancy. This important adaptation ensures that a fraction of the seed from each year remains dormant in soil, contributing to the development of a functional native seed bank over time (Venable and Brown 1988, Angert et al. 2009). 

Overcoming seed limitation, replenishing native soil seed banks, and reestablishing natural regeneration processes are only some of the benefits of a seed-based restoration approach. Distributing diverse seed mixes across the landscape can also help address the issue of microsite variation. Instead of placing container plants where we believe they might perform well, a widely distributed seed mix allows natural filtering processes to determine which species establish in a particular area (Grman et al. 2015; Hulvey and Aigner 2014). Distributing seed widely is fairly efficient, given that seeds are small and can be easily installed by hand or through the use of specialty equipment such as seed imprinters and drill seeders. Once in the ground, those seeds can also establish through seasonal precipitation instead of a costly irrigation system, which can provide significant cost savings over the life of a project (Brooks et al. 2019). 

Considering all of these factors, the decision to implement a seed-based restoration program was easy. The challenge, we have learned, lies in supporting that program with a consistent supply of plant material for each of the many species we want in our mixes.

To restore habitats, we use native plants of various functional groups as the building blocks. 

Plant Material Development

Establishing consistent access to native plant materials can be difficult, especially for restoration practitioners committed to local provenance, which refers to seed collected from plants growing in environmental conditions similar to those of the restoration site. When our restoration program was smaller, we could supply projects by collecting from wild populations in the vicinity of our project area, but as the program grew, so did our demand for seed. Thus, we needed a solution that would minimize the amount of seed taken from those populations while still providing adequate quantities for large-scale restoration. We also wanted to build a supply of native plant material over time in case we needed to mobilize a restoration or revegetation effort in response to an emergency such as a catastrophic fire. 

For these reasons, in 2009 we decided to implement a program focused on the development of locally sourced plant materials. Establishing our 8-acre seed amplification farm allowed us to focus our wild collection efforts on assembling small, genetically diverse, site-specific collections that could then be “bulked” into the large amounts needed to support our restoration efforts. This farmed material became the primary source of seed for our restoration and nursery production efforts, with supply matching demand in most years. These days, we maintain a rotating crop of approximately 50 native species on the seed farm that represent multiple functional groups. Investments in refrigerated seed storage have allowed us to build up a seed inventory of more than 150 species. Overall, the program has helped us maintain a consistent supply of material for our most commonly used restoration species; allowed us to integrate an ever-growing list of local species into our plant palettes; and reduced the amount of wild seed removed from the land over time, effectively lowering the impact of our restoration program on our natural populations. This model has been successful largely due to support from our landowner and agency partners, a relatively consistent stream of restoration projects, and a slow and deliberate growth strategy. However, acquiring locally sourced native plant material remains an issue for most practitioners. This problem needs to be addressed to support a growing restoration industry whose demand for locally sourced seed will only increase in time.

This problem needs to be addressed to support a growing restoration industry whose demand for locally sourced seed will only increase in time.

A Vision for the Future

The federal government’s “National Seed Strategy for Rehabilitation and Restoration 2015–2020,” developed by the Plant Conservation Alliance, a public/ private partnership chaired by the Bureau of Land Management (BLM), provides a conceptual framework for this effort. Its stated goal is to “ensure the availability of genetically appropriate seed to restore viable and productive plant communities and sustainable ecosystems” by establishing “a nationwide network of native seed collectors, a network of farmers and growers working to develop seed, a network of nurseries and seed storage facilities to supply adequate quantities of appropriate seed, and a network of restoration ecologists working on the ground” (Plant Conservation Alliance, 2015). 

While many of the elements listed above exist in California, only select ecoregions benefit from established networks working together to ensure that future resources are genetically appropriate. California’s rich diversity of plant species, large geographic area, and high degree of environmental variation at the landscape scale make establishing such networks challenging. That said, efforts to address this challenge are already underway, including projects aimed at conserving the genetic variation of our flora, establishing seed transfer zones, and developing collaborative networks. Below, we highlight just a few of the many programs and organizations working to establish the foundation upon which California’s sustainable native seed future will be built. 

A view of IRC’s Bee Flat Canyon restoration, a 64 acre landscape scale, seed-based restoration focused on restoring coastal sage scrub, chaparral, native perennial grassland, and oak woodland habitats in the Santa Ana River Watershed; Image: Courtesy of IRC.

Seed Conservation

Conserving the genetic variation of our flora is of utmost importance if we’re to be prepared for future restoration and recovery efforts, especially under the threats of climate change, catastrophic fire, and invasive species. California Plant Rescue (CaPR), a consortium of California botanic institutions, is working toward the long-term goal of securing the state’s entire flora in conservation collections such as botanic gardens and seed banks. Their work is currently focused on California’s rarest species, 75 percent of which they hope to have conserved by the end of 2020. The collaborating institutions work in partnership to monitor wild populations, make genetically diverse seed collections, and establish ex situ seed banks. The seed banks are maintained primarily as a buffer against extinction, though a portion of the materials is intended to support research, as well as future restoration and recovery programs (California Plant Rescue 2019). 

Conserving the genetic variation of our flora is of utmost importance if we’re to be prepared for future restoration and recovery efforts, especially under the threats of climate change, catastrophic fire, and invasive species.

Seed Transfer Zones

A seed transfer zone is defined as an area within which plant material can be moved from one location to another with minimal genetic risk to the population or species (Bower et al. 2014; McKay et al. 2005). Collecting from an area that is environmentally similar to where seed will be planted increases the likelihood that the material will be adapted to local conditions. It also increases the odds that the restored plant community will possess the genetic diversity necessary to successfully adapt to future conditions (Kettenring and Tarsa 2020). 

Generally, two types of seed zones exist for native plants. The first, more common type is a provisional seed zone based on climatic or other environmental factors (Bower et al. 2014). The second type is referred to as a genetic seed zone, and is based on empirical studies that characterize factors such as genetic diversity or variation (Conservation Biology Institute et al. 2020; Hufford et al. 2016). Genetic seed zones based on empirical studies are generally more accurate; however, given the significant research investment associated with delineating them, few have been established for native California species. 

One group working to address this problem is the Mojave Desert Native Plant Program (MDNPP), a BLM program in the Mojave Desert Ecoregion that has been operating since 2016. The MDNPP “coordinates seed collection, research and development of seed transfer zones, and research on restoration techniques for priority native plant species.” In collaboration with the US Geological Survey and California Botanic Garden, the program is currently using common garden studies combined with genetic studies to develop seed transfer zones for priority restoration species. In these studies, researchers collect seed of each target species, from multiple provisional seed zones across the species range within the Mojave Desert. They grow plants from each collection in a common garden and assess their performance. Then, the teams combine data from these studies with those from DNA sequencing efforts to develop empirical seed transfer zones (Simpson and Webb 2018).

Collecting from an area that is environmentally similar to where seed will be planted increases the likelihood that the material will be adapted to local conditions.

Collaborative Networks

As with all complex issues that span geographic boundaries, regional collaboration will be absolutely necessary to improve access to genetically appropriate plant materials and promote their use. One promising example of such a collaboration is the Seed LA project, a group of six nonprofit organizations in Los Angeles County working to “enhance ecosystem resilience in the greater Los Angeles region.” The group is working to develop a consistent supply of locally adapted native seed to support landscape restoration projects implemented by public and private entities, and establish public support for the use of native seed throughout the region (CNPS South Coast Chapter 2019). 

In Orange County, we need a similar collaborative if we are going to implement restoration at the scale necessary to address the current challenges facing our native habitats. While a collaborative is still in its preliminary stages, most local organizations recognize that multi-partner collaboration is critical to achieving regional conservation and restoration goals, and interest in formalizing a regional native seed network is growing. 

Improving access to genetically appropriate native plant material in support of California’s restoration industry will not be easy, but momentum is building and progress continues to be made. With this in mind, we look forward to a future where the vision described in the National Seed Strategy can be realized.

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