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CARING FOR THE SITE
Following installation of the native plants, continued maintenance and care for the site is often required to ensure a successful project. The amount and duration of care - mostly watering, fertilization, and insect pest control - will depend on the particular environmental conditions and location of the restoration site.
During the planning phase of the restoration project, it should be determined if it will be necessary to water the plant material for a given time period following the initial installation. The basis for this decision should include considerations of weather, site topography, plant water requirements, logistics, and cost-effectiveness. Also, in general, larger plants require more water to survive than do seeds and smaller plants. If a restoration project is conducted on a very large scale or is in a remote location, then it may not be possible, both logistically and economically, to water the site. When this is the case, one should take advantage of seasonal rainfall patterns and plant seeds and/or plants either right before or during the rainy season. Hydroseeding (or hydraulic seeding), a technique in which seed, water, and nutrients are sprayed over the ground in the form of a slurry, may also be an option on very large sites. Other options to pursue if irrigation is cost-prohibitive include site preparation to remove all competing vegetation (which brings with it other complications such as increased erosion) or mulching to conserve water.
To determine if water is needed at the restoration site, a visual inspection of the plants will usually suffice. Most plants wilt noticeably when water is limited. Leaves can become dull and fade in color, turn yellow, and, in extreme instances, die. Some species of native plants will wilt earlier than others, so these can be used as an early-warning sign of drying conditions. If water does need to be added to the site, only apply an amount equivalent to the average annual rainfall in that area. Anything above that amount would be extraneous to the needs of the native species and an unnecessary cost.
Watering needs are different in dry areas with low humidity. Container plants will usually die if natural water regimes are relied upon during the first year. Potting mixes are prone to drying out quickly in arid climates, and once artificial soil mixes are dry, they resist moistening, resulting in plant death. Plants in arid climates will require irrigation on a regular basis until established, usually until the end of the first growing season. Irrigation should be sufficient to moisten the soil below the bottom of the planting hole.
Methods for water application include basin (flood), furrow, sprinkler, and low-volume, high-frequency (e.g., drip, minisprinkler, or soaker) systems (Harris et al. 1999). The basin and furrow methods offer a low-tech solution to irrigation and can be installed during the site preparation and/or planting phases of the restoration project. With both methods, water is provided to the plants only when the basin or furrows are filled. Sprinkler systems, when properly designed and maintained, can provide uniform water distribution on both flat and hilly terrain. Sprinklers are best used early in the day, when there is little wind and foliage will be able to dry throughout the day. The drying factor is especially important for plants susceptible to water-related diseases. Drip and minisprinkler irrigation apply water slowly and in such a way that only a portion of the soil within the dripline becomes wet. Drip emitters apply water more slowly and to a smaller area than minisprinklers and are better suited to smaller, slow-growing or widely-spaced plants. They also, however, have a greater tendency to clog than do the higher-pressure minisprinklers. With any type of sprinkler or drip irrigation system, equipment breakdown may cause stress on the plants.
The benefits of vegetation in preventing erosion are well documented - their roots stabilize and anchor the soil and live plants and litter increase the absorptive capacity of the soil. However, before the newly-installed native plants become established, erosion of exposed soil could be a problem. One easy and economical way to prevent erosion during the time of plant establishment is to use weed-free mulch. This is especially true on slope plantings. Weed-free mulch protects the seeds and seedlings against rain and wind and also reduces loss of moisture during dry periods. A variety of mulch types can be used, which include hay or straw, jute netting, wood fiber or fiber netting. Other considerations regarding erosion prevention are:
- buffering or filter strips
- diverting surface water runoff away from disturbed soils
- keeping heavy equipment off exposed soil during heavy rain
- planting native grass along drainage channels to slow the rate of runoff
- planting temporary vegetation cover (e.g., annual grasses) on sites that remain exposed during the rainy season
Invasive Species Controls
Following installation of new native plants, controlling the recruitment and spread of invasive plant species is one of the most important elements to ensure the success of a restoration project. Once established, invasive species can outcompete native species, form dense stands, and eventually dominate an entire plant community. Restoration projects that involve earth-moving or alterations to hydrology are particularly vulnerable to the influx and spread of invasive species (WADOE 1993).
Specific methods for invasive species control and eradication are detailed in the "Invasive Weeds" section. It is critical and cost-effective to prevent establishment and spread of new weed invasions during and after the initial site work has been completed. Methods of doing so include the following:
- early detection and eradication of new weed invasions
- containing neighboring weed infestations
- minimizing soil disturbances
- planting native species of the local ecotype
- managing for healthy native plants
- test plots
Early detection and eradication of new weed invasions. If a new infestation is detected at an early stage and the plants are removed before seeds are produced, efforts and resources will be saved. Even if some plants are detected after seed production, but before a large population increase, less work is required than in a full-blown invasion. One method commonly used to prevent weed invasion is to regularly survey the restoration site, removing individual weed plants before they become better established and begin seed production. The weed infestation area should be identified on a map of the site, marked in the field, and continually monitored during subsequent surveys.
Containing neighboring weed infestations. Since restoration sites do not exist in a vacuum and often are situated within a larger disturbed landscape, there is a good chance that weed populations will be found in areas adjacent to or nearby the site. One approach to controlling the spread of invasives is to spray the borders of the infested area with an herbicide. Containment programs are typically designed only to limit the spread of a weed population, and thus can require a long-term commitment to herbicide application.
Minimizing soil disturbance. Most weed species have developed characteristics, such as rapid growth rates and high seed production, that enable them to move into a bare ground site quickly and aggressively. They often are able to outcompete native species in occupying disturbed soil. Because this is the case, it is important to minimize soil disturbance in a restoration project wherever possible.
Planting native species. Eliminating a weed can leave environmental resources available for the reinvasion of the same or different weed species. Revegetation with native plants can prevent reinvasion of undesirable species and can also contain the spread of remnant weed populations.
Managing for healthy native plants. In areas where native species have been planted, it is important to manage the landscape properly so that the native plants remain healthy and strong and weed encroachment is limited.
Test plots. If the project time frame allows, it may be cost effective and worthwhile to carry out recommended treatments on test plots of a smaller scale to see if desired results can be obtained. Monitoring test plots is an excellent planning tool for large-scale restoration attempts.
Following the initial planting, fertilizing native plants is only necessary in extreme cases when the condition of the soil is still in need of repair. This would be in places such as contaminated sites or abandoned mine sites where the topsoil has been completely removed or destroyed. In those instances where the soil is not yet conducive to supporting native plant populations, the revegetation aspect of the restoration plan should be postponed until soil conditions can be improved. This is described in detail in the previous section on Reduced Soil Function. Once the desired soil environment (e.g., pH, nutrient levels, diversity of microorganisms) has been created or restored, then the native plants, being adapted to those particular soil conditions, should not require additional fertilization.
Applying nutrients to a restoration site without first knowing if the soils are deficient can cause adverse effects such as salt buildup in the soil, inhibition of mycorrhizae formation, growth of invasive species, and water pollution. It has also been reported that the addition of even mild fertilizers can cause root dieback and shoot burning in many native species, particularly those that are drought tolerant. If it is decided that fertilization is an option, first take soil samples to determine what nutrients are limited. It is important to keep in mind that the pH of a soil, among many other factors, can greatly affect nutrient levels. Iron and manganese may be less available in alkaline soils, and phosphorous may be limited in acid sandy or granitic soils. Potassium levels may also be low in acid sandy soils. Always remember to keep in mind the specific needs of the native plant community being restored. These plants may be adapted to particular low nutrient conditions. In these cases adding nutrients can reduce the ability of the native species to outcompete weedy species.
It is a good idea to regularly inspect the plants at the restoration site for signs of insect pest damage. Before doing so, however, it is a good idea to find information about what pests have the greatest potential for infesting the site. Knowledge about the host plants will provide much of this information, since the large majority of pests are host-specific. Keep in mind, though, that some pests are host-specific only at certain times of the year. For example, the woolly apple aphid infests American elms in the winter and then moves to apple trees in the spring and summer; the woolly elm aphid infests serviceberries in the summer and then spends the rest of the year on elms (Harris et. al. 1999).
To inspect plants for pest problems, go out to the restoration site on a regular basis and systematically check plant foliage for pests and damage symptoms. A routine should be developed that is efficient for each particular restoration site. As was mentioned before, learn about the problems common to the species on the restoration site and be able to recognize signs of damage caused by pests. Also, it is important to be able to clearly distinguish the pests from beneficial organisms. The use of appropriate tools, such as a hand lens and reference materials, can aid in pest recognition.
If a pest population increases to some level that can no longer be tolerated, then it may be necessary to implement some control practices. Before spraying or introducing a predator population, it is strongly encouraged that the advice of the local extension agency be sought.
Continuous Protection of Restoration Site
Following installation of the native plants in a restoration project, it is necessary to consider what will happen to the site once the project team walks away from it. For example, if the restoration site exists in a rural area or even some urban areas, it is highly probable that there are wildlife populations nearby waiting to forage on all of the newly-installed plant material. As has been documented time and time again, grazing or browsing by domestic or wild animal populations can severely inhibit establishment of native plant populations. Other considerations for protecting the restoration site include erosion control and adapting the management plan to suit changing environmental conditions.
Protection from Grazing or Browsing
Although some matured prairie plantings benefit from occasional or light grazing (effects similar to those produced by prescribed burning), most sites should be protected from grazing or browsing. The most effective method of controlling grazing or browsing of native plant material by wildlife is to prevent access to it. For larger animals, such as deer and cows, fencing the site, plant communities or individual plants can restrict access. The fences should be tall enough to prevent deer from jumping over them and sturdy enough to withstand the weight of the animals leaning or pushing against them. Building fences of chicken wire can also prevent waterfowl grazing, but the exclosures must be small enough so that they are unable to fly in and out of them. It may also be necessary to construct a cover of fencing or other material over the site to keep out smaller birds.
Plants can also be individually protected by installing some sort of physical barrier immediately around their base. For tree seedlings, tree shelters are often used. These are tubes of translucent plastic that fit around the bottom portion of the plant. Tubes of rigid netting are also used. To protect mature trees, chicken wire or hardware cloth can be wrapped around the base of the tree. For protection from rodents which like to eat the bark at the base of young trees, aluminum foil can be wrapped around the base of each tree to a height of around 9 inches.
All protective fences and barriers should be removed later, once the plants have established.
Monitoring is the means by which it may be determined how well the native plant project meets goals and objectives. It also serves a critical function, alerting managers to possible maintenance needs to ensure continued success of the project.
Development of a monitoring program requires much planning and consideration of one's specific goals and objectives. In fact, all monitoring data should be evaluated relative to the goals and measurable criteria established at the onset of the restoration project. Take for example a goal of increasing available wildlife habitat with measurable criteria as the establishment of greater than 50 percent cover of native plant species that are providing food for wildlife. The monitoring efforts would be directed at measuring the change in percent cover over time of those native plant species known to be a food source for wildlife. The success of the restoration project would then be evaluated based on a greater-than-fifty-percent or less-than-fifty-percent-cover of native species, which would have been measured through monitoring.
Monitoring has the dubious honor of being the most forgotten or left-out element in restoration projects. Many restoration projects are resource intensive in the early stages, which makes it easy to commit all of the project budget to planning the project, purchasing the plant material, procuring equipment, site preparation, and putting the plants or seeds into the ground. All too often, not enough thought is given to what might happen to the restoration site after the plants or seeds are installed, and project failure can be the unfortunate result. Monitoring provides a long-term look at the ecological changes occurring after the initial restoration project and enables proactive management to prevent failure of the project. Some examples of factors that can interfere with the success of a restoration project include invasion of noxious weeds or invasive plants, intense browsing or grazing by wildlife, failure of introduced plantings due to drought conditions, acts of nature that severely damage restored areas, and damage resulting from human trespass.
Techniques for vegetation monitoring can include a cursory visual inspection of installed plants or a more detailed study of plant species or groups of similar plant species using randomly or systematically-placed quadrats or other sampling units. A combination of both techniques may be appropriate for most planting sites: monthly site checks to quickly ensure that plants are healthy and are not being harmed by something, and more detailed assessments once or twice a year to examine vegetation health, growth, and establishment in order to monitor project development and success.
The choice of specific monitoring methods for the more detailed assessment will depend on the type and density of vegetation that is being restored. If the planting involved mainly woody vegetation where it is easy to relocate individual plants, assessments may involve counting numbers of surviving versus dead individuals and measurements of growth such as height, stem width, and numbers of new branches. If the project involved planting of herbaceous plants or mainly seeding, it may be better to establish monitoring plots throughout the site. Ideally all the monitoring plots combined should cover at least five percent of the total project area. They should be placed so that they can provide a fairly accurate picture of the success of the overall site. This may mean stratifying the site (dividing it up into different sections based on site differences) and then randomly placing a proportional number of sampling plots within each section. Within the plots some of the measures of vegetation that could be used include diversity, density, percent cover, frequency, and biomass. Each of these is explained briefly below. They should be evaluated in comparison with reference areas and take into consideration the natural dynamics of an ecosystem over time.
If time and funding prevent intensive monitoring of a restoration site, at least take photographs of before and after restoration at the same spot. These photos can also be retaken in future years to help chart the progress of a site.
Diversity measures both the absolute number of species in an assemblage, community or sample, as well as their relative abundance. Low diversity refers to few species and/or unequal abundances, while a measure of high diversity corresponds to many species with equal abundances.
Density is the number of individuals in a given unit of area. While density is a commonly-used metric due to its being easily obtained and understood, it does have some limitations. The major limitation is that the critical unit of measurement is the individual plant, which may be difficult to identify in some instances. For example, rhizomatous perennials grow by vegetative spread, making it difficult to determine whether one or several stems belong to a single individual. Therefore, it is important to first determine the individual unit of interest, making sure it is a unit easily identifiable in the field.
Percent cover typically refers to the vertical projection of vegetation or litter onto the ground surface when viewed from above. This measure is considered as an approximation of the area over which a plant exerts its influence on other parts of the ecosystem, or its dominance relative to other plants or species. Variations of this concept include vegetation cover, the total cover of vegetation on an area; crown cover, the spatial extent of tree or shrub canopies; ground cover, the cover of plants such as shrubs, grasses, and herbs as well as cover of litter, bare ground, and rock; and basal cover, the cover of the basal portion of plants. Percent cover is one of the most commonly measured vegetation attributes and provides a quantitative measure for species that can not be easily or accurately measured by density or biomass. When the cover of individual species or species guilds are measured separately, the total cover within a sample may exceed 100 percent due to overlap of the plant crowns or foliage.
Frequency is the proportion of time a species or guild occurs within a given number of samples. It is a useful means of detecting differences in vegetation structure between two or more plant communities and is sensitive to change over time (The Nature Conservancy 1997). If a species has a frequency of 20 percent, then it should occur once in every 20 quadrats examined. The measure is obtained simply by recording whether a species is present in a series of quadrats. A major benefit to collecting frequency data is the ability to collect a lot of data within a relatively short time period. However, the information gathered from this method is limited such that it does not provide an idea about the relative dominance and abundance of a species in the community.
Measuring biomass in vegetation monitoring is used infrequently mostly since it involves some degree of destructive sampling. It can, however, provide a good measure of seasonal and annual changes in growth.
Maintenance Using Prescribed Burning
Future management of restored prairie and other fire-dependent plant communities can utilize prescribed burning as a tool. Planning ahead for using fire requires a firebreak. Many times this can be done by planting a green break, or short cool-season grasses around the perimeter of the project site. Green breaks have proven to be valuable in reducing the time and expense of maintaining these sites.
Adaptive management is a systematic approach for improving management by learning from past mistakes. Management objectives and actions are continuously adjusted as new information is gathered through monitoring and more is known about which management techniques work and which do not. This approach to management is especially applicable in a restoration context, where environmental conditions are changing rapidly and there still is much uncertainty about how to design and implement a successful project. For example, a restoration site existing in a highly urbanized area was planted with native species, and, due to the absence of wildlife in the area, no plans for protection of the plant material from wildlife were made. Then in the second year of the project, some deer moved onto the site and proceeded to graze on the tender shoots that had been planted the year before. If the original project management plan was not modified to install fencing or some other physical barrier around the site, then chances are good that the deer would cause considerable damage to the new plant material. Adaptive management of a restoration site can lead to more effective decision making and increase the likelihood of project success.
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