Soil Ecology and Restoration Group
Continued research on coastal sage scrub revegetation and restoration has provided further understanding of plant production, planting, irrigation and maintenance requirements. The more complete challenge of recreating complete coastal sage scrub ecosystems on degraded sites is still a study in progress. The low rainfall, average 10 inches, at the coast makes this a tough and demanding desert environment, benefiting only slightly from the fog and fog drip.
Shrub planting success in San Diego
The following table provides survival data for a site near USIU.
Survival after six months on a flat degraded site
|Species||Common Name||Percent Survival|
The benefits of rototilling
Although ripping and spading are preferred treatments for degraded sites even rototilling helps. At this site rototilling reduced weediness and improved survival dramatically. After six months survival overall was 80% in the tilled area and only 50% in the untilled area (the numbers were not equal in each treatment).
General guidelines for installing CSS
Site evaluation should be completed to determine the level of compaction, rate of infiltration, organic matter, salinity, pH, texture, macronutrients, micronutrients, and fungal hyphae, spores, and bacteria if possible. A site historical review should be done using historical records, old photos and aerial photos to explore past disturbance histories. A community analysis of a less disturbed reference site should be done if possible to plan planting patterns and species composition. Was it really coastal sage scrub or was it chaparral or grassland?
Seed collection should be started as soon as possible from plants on or near the site. Collect seeds from local species for several years if possible, collect from many plants as widely dispersed as possible. Clean, do germination tests, and store properly. Upgrade seed quality for container production.
Planning is critical, develop a timeline, budget, review regulations and approvals, timing, cooperators, actors etc. Plan plant production carefully. Prepare the site before planting and ensure adequate maintenance. Weed management over a couple of years can improve site conditions. Weed control may be essential on degraded sites. Irrigate and till repeatedly, solarize, use pre-emergent herbicides, burn, or fumigate to minimize weed competition.
Site preparation is typically also needed to address compaction, infiltration, and nutrient problems. This may include: ripping, spading or pitting, and should leave a rough soil surface. Add organic matter and nutrients as tests indicate. Add compost (beware weed seeds), bark, wood chips (watch seeds if landscape prunings), sawdust, or straw (esp. vertical straw bundles of native grass or rice straw). Materials with possible weed seeds should be composted thoroughly. High C:N ratio material can help tie up excess nitrogen which encourages weeds. Nitrogen input from atmospheric fallout can exceed 40 kg/ha, most from auto exhaust.
Direct seeding for shrubs rarely works well as many shrubs have long stratification requirements. Hydroseeding rarely works well in this dry environment, but a double spray with seeds in the first mix churned into the soil and then buried with a second spray with wood fiber can be much more effective than a single application. Timing is critical for hydroseeding. Ideally spraying will be done a day before gentle rains begin, or after soaking rains.
Container plants are very effective and the backbone of restoration work in CSS. Plant into prewetted, augered holes. Plants should be root dominated (young, with big roots, small tops) and planted before tops get large (standard 1 gallon pots are good with appropriate plant management but5, 10, and 15 gallon pots should generally be avoided). On large denuded, ice plant or mustard dominated sites inoculation with mycorrhizal fungi may be desirable.
A typical mix of containers might include 50% tall ones (6"x16") or gallons, 50% plant bands (2x2x14), with smaller containers only for cacti and succulents. Add a ring of large bark mulch or weed mat for each plant if possible. Flat sites may be machine-planted with a transplanter.
Plant protection is needed on most sites. Rabbits, pocket gophers, and deer may cause losses without protection. Most areas will require plant protection of treeshelters, cages or fences. Treeshtelters have proved to be very effective even with grasses. In areas with extensive pocket gopher colonies fence may have to be set into the ground to 8-12 inches.
Weed control on a continuing basis may be needed if fumigation or solarization could not be done. A large seed bank of weed seeds is almost certain to exist and weed suppression for several years may be needed. Spot weeding may be needed for the first year or two. Competition from fast growing exotic weeds may not kill native shrubs but it does reduce growth. Consider using a blanket wiper, wick, mow or graze weeds. Late spring burns will help where they can be done safely, burn before seed maturity on weeds.
Irrigation is needed in most years. Hand-water into treeshelters or install deep pipes or vertical porous hose. Spaghetti tube and even 1/2 flex tube are usually problematic as a result of animal damage by rabbits and coyotes. The Dry-water additive has not been successful in most cases. Overhead watering can encourage weeds and be detrimental to native species, but may be successful if timed to mimic natural rain events.
Coastal sage scrub can be improved and restored on almost any site if functional repairs to site hydrology and soil chemistry and structure are made. Many of the plants are vigorous and grow rapidly with water. Costs can range from $1,000 acre for a minimal job to more than $20,000 acre. Container planting with plant protection and limited supplemental irrigation is most effective. Direct seeding is limited to sites without weeds, and even there a mix of direct seeding and container plants is likely to provide faster visual and ecological recovery. Hydroseeding can work under some climatic and soil conditions, but is not recommended for general application.