Aerial Seeding

Application of plant seed to burned slopes by aircraft.

Purpose: Aerial seeding, usually grasses but occasionally also legumes, is carried out to increase vegetative cover on a burn site during the first few years after a fire. It is typically done where erosion hazard is high and native plant seed bank is believed to have been destroyed or severely reduced by the fire. Seed is applied by fixed-wing aircraft or helicopter.

Relative Effectiveness: Excellent-24% Good-28% Fair-28% Poor-20% (Replies = 83). Interviewees were almost evenly divided on the effectiveness rating of aerial seeding, with a slight majority regarding it as either "good" or "fair". Respondents in Regions 1, 4, and 6 were more likely to rate seeding "excellent" or "good" than respondents in Regions 3 and 5.

Effectiveness depends on timeliness of seed application, choice of seed, pilot skill, protection from grazing, and luck in having gentle rains to stimulate seed germination before wind or heavy rains blow or wash soil and seed away. Proper timing of seed application depends on location. In some areas it is best to drop seed directly into dry ash, before any rain falls, to take advantage of the fluffy seedbed condition, while in others seed is best applied after the first snow so that it will germinate in the spring. Both conditions also reduce loss to rodents. Choice of seed determines how easily it can be applied – some grass species with long awns tend to clog in seeder buckets, and light seeds drift more than heavy ones – and how well it will grow, how long it will persist, and what impact it will have on natural regeneration. In general, legumes have not been found to be particularly effective at producing cover (there are exceptions). A skillful pilot will apply the seed evenly, rather than in strips with unseeded areas in between them, providing better ground cover once the seed germinates.

A few respondents also mentioned that straw mulch, needle cast, slope barriers such as straw wattles or contour felled logs, or ripping the soil enhanced growth of seeded grasses. Maximum cover of seeded species is not attained until summer. Many respondents reported that seeding was not particularly effective at producing protection from the first year’s storms (especially in the Southwest for fires that occur just before the monsoon season with its high intensity rains) but may provide effective cover during the second and subsequent years. Several respondents suggested that waiting to seed onto snow for spring growth would be the most effective course of action in the Southwest (Region 3), because they usually ended up having to do a second seeding anyway after the summer monsoon washed the first application away. Several respondents noted disappointing results from seeding with relatively expensive native species or Regreen (commercially available sterile wheatgrass hybrid) and would not use them again. On the other hand, cereal grains were generally reported to perform well the first growing season. Cereal grains that do not germinate in quantity the second year provide soil cover with the mulch from the dead first year growth. Both cattle and elk grazing were reported to reduce the effective cover of seeded grasses. Seeded grass cover tends to be higher on low angle slopes (less than 40 percent) than steep ones.

Implementation and Environmental Factors: Many respondents reported difficulties in contracting for seed and aircraft operators which, especially after fall fires, resulted in seed being applied too late for optimum conditions. Ground sampling, with sticky papers or by visual inspection, should be done to monitor seed application rate and evenness. Fixed wing aircraft may be less expensive per application but can be less accurate at directing seed than helicopters. The use of native seed is a major issue on many Forests. Native grass seed can be hard to acquire in large quantities or in a timely manner compared to cereal grains or pasture grasses; it is also generally more expensive. Native seed should come from a nearby source area to preserve local genetic integrity. Cereal grains will germinate and grow the second year if the ground surface is disturbed by salvage logging or grazing. Many monitoring studies have found lower cover of native plants in areas with high seeded grass cover, even where seeding increased total cover. Some-times this resulted in lower total cover after the seeded grass decreased in abundance. On the other hand, seeded grass may also inhibit growth of noxious weeds that invade sites after fire, a beneficial outcome. Rhizomatous (sod-forming) grasses make reforestation more difficult if they achieve significant cover. It is important to know the composition of prefire vegetation when proposing to seed – if the vegetation included many annuals or lots of perennial grass or sedge, there will usually be considerable cover established naturally after a fire.

Other factors: Many respondents noted that grass seeding was sometimes done primarily for "political" reasons, especially at the wildland-urban interface.

Aerial Seeding - Planning and Implementation

INTRODUCTION

Aerial seeding is often the largest cost associated with burned area emergency rehabilitation projects. The complexities involved in implementing safe and efficient aerial seeding operations demonstrate the need for a logical, planned approach for accomplishing needed work. If a project is not well-planned, opportunities exist for things to go wrong, the potential for accidents and injuries increases, and the probability of not accomplishing the work increases. In the haste of trying to get work done within short timeframes, one must ensure that critical tasks and/or responsibilities are not overlooked.

Aerial seeding requires contracting assistance. It requires the purchase of often large amounts of seed and the use of specialized equipment to implement emergency prescriptions to stabilize watersheds. We must be able to secure these goods and services on short notice; and we must be able to organize to effectively and safely implement these kinds of projects.

Regardless of size, aerial seeding projects can range from simple to very complex. Each can (and will present its own set of challenges. We must be able to assess and respond to these situations.

Factors to consider when prescribing seed include:

PREPARING FOR AERIAL SEEDING PROJECTS (PRE-INCIDENT)

Burned Area Emergency Stabilization and Rehabilitation (ESR) projects are EMERGENCY situations. Anything that can be done to facilitate the process prior to the need arising will most certainly be helpful. Because of the many complexities involved in implementing aerial seeding prescriptions, a project manager should not go into an incident cold. He or she will be much better off some preplanning has been done.

There are many tasks that can be completed ahead of an incident that will facilitate efficient implementation of aerial seeding prescriptions. These include but are not limited to the following:

PREPARING FOR AERIAL SEEDING PROJECTS (ON-INCIDENT)

Once assigned the responsibility of implementing an aerial seeding project, a number of factors must be considered when planning and organizing the operation, and in developing contracts. An excellent means of getting an early start is to get involved with the ESR survey team. This will provide you with an understanding of the prescriptions being considered and important characteristics of the land area to be treated.  Some of the most important items that need to be considered include the following:

Calculating Seed Rates Based on Pure Live Seed per Square Foot

Seeding rates for grasses are generally expressed in pounds per acres. However, if a seeding prescription is based on pounds per acre instead of Pure Live Seed (PLS) per square foot, excess costs can be experienced. Generally, to achieve efficient erosion control, seeding rates should be in the range of 30 to 60 PLS per square foot.

Seeding rates can be calculated if you know the following:

Example:

Seed one acre with Standard Crested wheatgrass which has 175,000 seeds per pound and is 76% PLS to get a result of 40 PLS per square foot.

(1 acre)*(43,560 ft²/acre)*(40)=1.742,000 PLS
(175,000)*(0.76)=133,000 PLS/lb
(1,742,400)/(133,000)=13.1 lb

Example:

Seed one acre with three species at different rates to obtain a coverage of 30 PLS/ft²

Species 1 = 175,000 seeds/lb; 76% PLS; 30% of mix
Species 2 = 645,000 seeds/lb; 71% PLS; 40% of mix
Species 3 = 227,000 seeds/lb; 87% PLS; 30% of mix

(1 acre)*(43,560 ft²/acre)*(30)=1,306,800 PLS

Species 1: (1,306,800)*(0.30)=392,040 PLS
                    (175,000)*(0.76)=1333,000 PLS/lb
                    (392,040)/(133,000) = 2.95 lb

Species 2: (1,306,800)*(0.40)=522,720 PLS
                    (645,000)*(0.71)=457,950 PLS/lb
                    (522,720)/;(457,950) = 1.14 lb

Species 3: (1,306,800)*(0.30)=392,040 PLS
                    (227,000)*(0.87)=197,490 PLS/lb
                    (392,040)/(197,490) = 1.99 lb

 SEED PROCUREMENT

In order to purchase seed, we need to establish and state what is minimally acceptable to the government. Although the need for seed may be great, it is important to provide all necessary information for seed procurement to prevent problems which may occur later. The following are items which should be addressed in the solicitation:

AERIAL APPLICATION OF SEED

Aerial application of seed may be accomplished by using either of two basic types of contracts:  Full Service or Call When Needed (CWN) or Job Contract.

Even though a job contract may be used on an aerial seeding project, an approved aviation safety plan must be in place before the contract can be awarded. The contractor must comply with all Office of Safety and Health Administration (OSHA) safety regulations.

OPERATIONS PLAN

A detailed operations plan is a necessity for all aerial seeding projects. On such projects, a large amount of work needs to be accomplished in short time periods people are working in situations that may be considered dangerous, and people are asked to perform tasks that may be unfamiliar to them. Some people assigned to the incident may be from other administrative units and may not be familiar with the local geographic area or local administrative procedures.

Some of the topics that should be covered in an incident procedures plan include the following:

AIRCRAFT CONSIDERATIONS

Helicopters versus Fixed Wing.