Arrangement of quadrats probably is not too important provided that the placement of quadrats spans the length and width of the plot or field (Colbach et al. 2000). Some authors place quadrats over or adjacent to the point where soil cores were taken. Although logical, this may have little practical effect on the results given the extreme aggregation of many seed banks.
When to sample seed banks?
This technique (e.g. Teo-Sherrell and Mortensen, 2000) involves exhuming a soil core and replacing it with soil devoid of seeds except for those purposefully added. These studies seemingly are more natural in that the added seeds are exposed to similar microclimate, microbial, and microfaunal conditions as seed packets, but also the macrofauna that would be excluded by small-mesh nylon bags. The detraction of this method is that seeded cores must be retrieved precisely so as not to include the natural seed bank inadvertently, and then processed in a manner identical to standard soil cores for seed bank studies.
Gross, K.L. & Renner, K.A. 1989. A new method for estimating seed numbers in soil. Weed Sci. 37: 836-839.
Soil depth in the trays should be no greater than the depth from which expected species can germinate, typically less than 5 cm, with 2-3 cm best for small-seeded species. If the soil is clay-rich, it can be mixed with known volumes of clean sand or commercial potting media to improve drainage. A useful procedure to improve drainage is to line the bottom of the tray with sand, then nylon mesh, and then the soil sample. The nylon mesh allows periodic removal and stirring of the soil sample (see below) to improve germination of dormant seeds, but without unwanted contamination by the non-experimental subsoil.
A typical soil core of 5 cm diameter and 10 cm depth has a dry weight of about 200-300 g. Naturally, if labour is not in short supply, extracting seed from the entire soil core is preferred. However, a shortage of labour (or associated enthusiasm) is common in seed bank studies. Thus, some understanding of what proportion of a soil core must be examined is important. Analyses of differing amounts of well-mixed soil, in 20 g increments from typical cores indicated that, in general, 100 g was necessary for an adequate representation of the entire soil core (Forcella, 1992).
Basically, if a goal of the research is to relate seed banks to forthcoming aboveground vegetation, then seed banks should be sampled at times that follow seed shed but precede seed germination. Sampling seed banks after seedling emergence has little value, in theory or in practice. Samples need to be taken at a time that makes sense for the objectives of the study, based on the phenology of seed dispersal and germination in the habitat of interest. Thus, in temperate zones, seed banks of summer annual weeds should be sampled prior to the first springtime flush of seedling emergence. Similarly, seed banks of winter annuals should be sampled before emergence of the first seedlings in autumn. Analogous logic should be used for sampling times in semi-tropical and tropical zones with distinct wet and dry seasons. The same reasoning should apply to irrigated land regardless of season; that is, the soils should be sampled before the onset of irrigation and subsequent seed germination.
Within the Northern District of California there have been a number of designated Weed and Seed sites over the past 15 years. In the past several years there have been the following designations: Salinas, East Oakland, San Francisco and two in San Jose. West Oakland has been a graduated site for several years. Each of the sites has unique characteristics which create special challenges. At each site, the U.S. Attorney’s Office has played an important role in working with the steering committee and in bringing together the participants on both the “weeding” and “seeding” sides of the program. Most of the programs have run their individual five year program funding cycles, but continue to meet and work on Weed and Seed issues in the community.
As part of the upcoming fiscal year budget, the Weed & Seed program had ended. Funding for new Weed & Seed sites will no longer be available. However, these types of programs may still be available through the Byrne Criminal Justice Innovation Program (BCJI). This initiative was not funded in the FY 2011 final continuing resolution. However, BCJI was included in the President’s proposed FY2012 budget and is pending before Congress. For questions about this source of grant funding please consult the Weed & Seed website FAQ section.
Weed and Seed is a Department of Justice community-based program whose goal is to prevent, control and reduce violent crime, drug abuse, and gang activity in targeted high-crime neighborhoods throughout the country. Weed and Seed strategy follows a two-pronged approach: local law enforcement agencies and prosecutors cooperate in “weeding” out criminals who engage in violent crimes and drug abuse, and “seeding” brings to the area human services encompassing prevention, intervention, treatment, and neighborhood revitalization. A community-oriented policing component bridges weeding and seeding strategies: officers obtain cooperation and information from area residents while they assist residents in obtaining information about community revitalization and resources.
A variety of funding opportunities for law enforcement and other programs are listed on the Office of Justice Programs website.