Restoration Pondering in Light of New Plant Pathogens

Collecting seed along Alameda Creek.  Photo courtesy the author.

Collecting seed along Alameda Creek.  Photo courtesy the author.

Fall 2015 Ecesis, Volume 25, Issue 3

There are particular principles involved in growing plant material for restoration projects that dictate an approach to production that is different from general horticultural production. Since the establishment of The Watershed Nursery as a restoration nursery in 2001, we have been dedicated to the principle of using site specific material not just to optimize survival due to genetic adaptation to site conditions but also to avoid dilution of adaptations of local established populations. To adhere to this principle requires planning and lead time from all entities involved in a project. Some species can be grown in several months, others take years, but for either end of the spectrum, if the timing of the project request is past fruiting time, propagation will necessarily need to be put off a year. Working with these principles along with others such as keeping abreast of hybridization issues, invasive species, pest/pathogen issues, and new restoration techniques has kept this profession an engaging endeavor and pleasant pursuit. 

Then, in 2012 the first detection was made of a new plant pathogen, Phytophthora tentaculata (USDA), in a native nursery in California and the potential for restoration nurseries to be direct vectors of pathogens to wildland sites became chillingly clear. This and subsequent Phytophthora spp. detections have raised a massive alarm for restoration nurseries and for the restoration industry overall. Our paradigm as to the “responsible” or “right way” to revegetate is being challenged. This concern has led to envisioning different approaches to revegetating a site or enhancing habitat apart from container plant material. Approaches being considered include the development of on-site nurseries, direct transplanting of vegetative material, and direct seeding. There are pros and cons and challenges to each of these approaches, but the consideration by some entities of enlisting direct seeding as a main strategy raises a few particular concerns which I’d like to highlight here.

One of the first guiding principles we adopted when starting The Watershed Nursery was the collecting protocol of the Golden Gate National Recreational Area nurseries, which focuses on limited collection of seed per plant and population, and over multiple time periods, both to increase genetic diversity and to decrease impacts on habitats which are often already experiencing compromised conditions. Employing this protocol, and our controlled nursery growing situation, we are generally collecting, at most, several grams of seed per species. Because of the higher mortality rate with direct seeding, a much greater amount of seed is required, with potentially a far greater collection impact on our existing native habitats. Entities such as the San Francisco Public Utilities Commission have already developed very detailed tracking systems for seed collection, and are diligent about limiting impact in any particular area. If direct seeding is to be developed as a larger tool in the restoration toolbox, the management, regulation, and monitoring of impacts of increased collection pressure on our local habitats must be carefully considered.

Data is emerging from current direct seeding applications as to which species can successfully establish from this approach, which raises the question as to how to manage those species which do not have successful establishment from direct seeding. Do we decrease species palette diversity? Do we container grow those species and test all material? Can we use other propagation methods on site to increase establishment? The challenge of achieving diversity goals, and timelines for achieving those goals, must be a consideration in a direct seeding approach. Answers to these questions, and the overall impact of the discovery of container material as a potential vector of pathogens on the restoration industry remain to be seen. What is clear is that this problem is going to take restoration people in all facets of the industry, from nursery growers to consultants to regulators, working together to develop approaches, expectations, and timelines which address this new risk to our restoration goals. — by Diana Benner, Principal at The Watershed Nursery