Shrubs, grasses, sedges, and forbs form a vital part of ponderosa pine forest ecosystems (Springer and Egan 2007). Many ponderosa pine forests have only one or a few tree species but support dozens of species in the forest floor understory. Restoration treatments often focus mainly on the trees, but it is as important to restore the natural diversity and productivity of the understory plant community.

A healthy understory provides wildlife habitat, provides fuel for low-intensity fires that maintain forest structure, and has great aesthetic benefits. Restoring understory plants often requires controlling invasive species.

Understory plant restoration can also be aided by seeding, which is described on this page. Restoring a healthy understory may require little work or a great deal, depending upon site conditions. Some forest restoration sites may still support many native species before treatment, in which case thinning of overstory trees and conducting some prescribed fires may be enough to promote the growth of understory species. Other sites may lack native species and their seeds, in which case it may be necessary to reintroduce native plants either as seedlings or seeds.

Site Assessment

The first step in restoring understory plants consists of learning what does or could grow in the area. If you have a great many resources to devote to this, see the full assessment list in Korb and Springer (2003). Forest managers lacking time and money should still focus on several critical factors, specifically:

• Surveys of the restoration site and of the surrounding plant community are essential in formulating a species list that describes what grows in the area.
• Soil and precipitation characteristics should be considered when determining desired species for planting.

Seed Collection and Seeding

With adequate planning and basic knowledge of life cycles, it is possible to collect seeds from species present in the study area; to learn more about this, see Busco and Maschinski (1999) or Knapp and Rice (1994). Collecting seeds requires appropriate permits from land management agencies. To decrease the risk of negatively impacting local genetic adaptations of species in the treatment area, seed should be collected on, or within a few miles of, the area undergoing restoration.

Seed collection is time-consuming and requires knowledge of each species’ phenology (timing of life cycles). For optimal results, plants must be monitored so that seed is collected at the appropriate time to obtain maximum germination potential. Seed can also be collected onsite in limited quantities and then planted in a production garden at or near the restoration site, where it can be closely monitored and harvested at the appropriate time in larger quantities. This approach is challenging in the arid climate of the Southwest. A similar method is to “farm out” seed by shipping it to farms or ranches where it can be irrigated, harvested, and shipped back to the restoration site for planting.

Seed Collecting Tips

For best results in collecting seeds, it is important to consider the following:

• Annual seed production can be highly dependent on weather conditions. It is not unusual to find successful reproduction in a nearby area or similar habitat if plants have failed to set seed at one location.
• Seed should be collected in areas free of invasive, nonnative species. If this is not possible, less mechanized, more labor-intensive means of seed collection should be employed.
• Native perennial grasses are important understory plants that help carry low-intensity fire; their growth should be promoted.
• Including native forbs that colonize quickly can help prevent the spread of nonnative, invasive species.
• Knowledge of weather patterns and animal movements can aid in collecting seed before it is damaged by frost, hail, grazing, wind, or other environmental factors.
• To maintain genetic integrity and environmental adaptations, collect seed from many plants; several hundred to a few thousand may be necessary for some genotypes. Local populations, though, can be harmed by overcollecting.
• Because neighboring plants may be related, collect seed from widely separated plants. Using a transect, or collecting perpendicular to prevailing winds, may reduce risks of collecting seed from related plants.
• Seed should be collected from plants in microclimates similar to those of the restoration site, and from plants of varied appearance, including both robust and less vigorous plants. Plants growing in poor environments may have adaptations to those conditions.
• Seed should be handled carefully, kept from excessive heat, cold, and moisture, and be stored in a cool, dry place free of insects and rodents. Pre-storage treatment (e.g. freezing, or insecticide or desiccant use) can help prevent losses to insects and rodents.

Seed Collecting Pitfalls

The main pitfalls to collecting native species are these:

• some native species have seed production that is cyclical or tied to varying weather patterns, thereby hampering collection;
• few large, accessible areas with native seeds lack exotic weeds;
• environmental factors such as frost, hail, grazing, and wind, and physiological characteristics such as seed shatter, impede collection;
• improper collection, storage, and cleaning practices can cause seed mortality.

Using Commercial Seeds

If seed must be obtained commercially, it should stem from approximately a 100-mile (160-kilometer) radius of the restoration site, and from a similar habitat. Commercial seed mixes can introduce invasive species. The extra expense of certified weed-free seed is often justified when weed-control costs are considered. Seed should be inspected visually before planting, and rejected if it is of the wrong species or if a high proportion of undesirable species is detected. After germination, revegetated areas should be selectively weeded if invasive species are present. Prevention before infestation pays off in the long run.

Planting

The best time to seed varies by species, but if seeding must be accomplished at one time, it should be done prior to the summer monsoon (typically mid-June to early July). Seeds often fail to germinate, or seedlings often die, if monsoonal rains are insufficient. In areas of dependably heavy snowfall, seed may also be planted after September 15.

Seedbed preparation is critical. Roughening up the soil to provide wind barriers and tiny water catchments can help seedling survival, as can moisture-holding mulch. One abundant mulching material is pine needles; a light application a few centimeters thick will help conserve moisture. In the Mt. Trumbull area in northern Arizona the rate of seed germination was doubled by dragging a weighted bar over the seeded ground behind an all-terrain vehicle or Bobcat in order to cover the seeds. Fertilization after seeding is generally not required.

To learn more about the seeding requirements of species found in southwestern ponderosa pine forests, see Young and Young (1986) and Baskin and Baskin (1998), contact the nearest USDA Natural Resources Conservation Service Plant Materials Center, or see resources provided by the Native Plants Network. At some sites transplanting of seedlings has also been attempted; to learn more about this, see Korb and Springer (2003).

Monitoring and Maintenance

Monitoring and documentation of methods, precipitation, and timing of planting are essential in determining restoration success and planning future modifications. Restored areas should be protected from grazing and recreational impacts for at least two to five years to prevent soil compaction and allow understory plants to become established. Areas severely impacted by past management practices, recent drought, or other factors that have slowed plant community recovery may require deferrals of grazing or recreation much longer.

References

• Baskin, C.C., and J.M. Baskin. 1998. Seeds: Ecology, biogeography, and evolution of dormancy and germination. San Diego: Academic Press.
• Busco, J.K., and J. Maschinski. 1999. Propagation of promising high-elevation species native to the Colorado Plateau. International Plant Propagators' Society Combined Proceedings 49:576-580.
• Knapp, E.E., and K.J. Rice. 1994. Starting from seed: Genetic issues in using native grasses for restoration. Restoration & Management Notes 12:1(40-45).
• Korb, J.E., and J.D. Springer. 2003. Understory vegetation. Pp. 233-250 in Ecological restoration of southwestern ponderosa pine forests, ed. P. Friederici. Washington, D.C.: Island Press.
• Springer, J.D., and D. Egan. 2007. Working Paper 19: Understory Seeding in Southwestern Forests Following Wildfire and Ecological Restoration Treatments. NAU Ecological Restoration Institute.
• Young, J.A., and C.G. Young. 1986. Collecting, processing, and germinating seeds of wildland plants. Portland, Oregon: Timber Press.