Division of Spill Prevention and Response


Tactic AM-6: Monitoring Vegetation

The health, cover, and composition of tundra vegetation are measured before and after treatment, to aid in assessing impacts and monitoring recovery of tundra affected by a spill. The effects of a spill can also be assessed by comparing vegetation in a spill area with vegetation in an area unaffected by the spill. The fastest field techniques for monitoring vegetation use visual observations of plant health, repeat photography (photo-trend plots), or the semiquantitative method of estimating plant cover in plots of a specified size (area method). The preferred method for monitoring vegetation is the point-intercept method, however, because it provides more objective data. The potential for revegetation of a site can be assessed with test plots to determine whether seeds will germinate or plants can establish and survive under certain conditions. Identification of plant species and implementing some of the monitoring techniques may require special expertise. If appropriate, consult with a plant scientist or other qualified person to develop a monitoring plan or to conduct the vegetation monitoring.

Plant Health

The health and condition of tundra plants growing on the site is evaluated qualitatively based on visual examination. Look for signs of growth, reproduction (flowers, seeds, spreading by roots) and vigor (health) using undisturbed vegetation not affected by the spill near the site as a reference. Signs of poor growing conditions, stress, or toxic effects of contaminants may include dead plants or dead leaves, discoloration such as yellow leaves, stunted plants, lack of reproduction, and slow or no growth. Remain alert to evidence of grazing by animals (e.g., torn leaves, scat, foot prints), which may have removed a significant amount of plant parts. Evaluation of the condition of plants does not require special expertise, although some training by experts in plant science may be useful to identify less obvious effects that may be important for achieving the treatment goals.

Photo-Trend Plots

Using photographs to monitor permanent plots is a popular and effective technique for monitoring the revegetation of affected tundra over successive growing seasons. This technique is most useful if the same view direction is used each time, and is dependent upon being able to relocate the plot. The corners of permanent plots can be marked with metal nails (6 to 9 inches in length) that are commonly used by surveyors, or with wooden or steel “rebar” stakes. A common method used to delineate individual plots in a photograph is to place a 1–meter-square quadrat frame made of white PVC pipe or aluminum flat-bar on the tundra (Fig. 130). A stake is then driven into the tundra soil in opposite corners to mark the location of the quadrat permanently. Prepare a map of the plot locations (Tactic AM-1) so that plots can be easily relocated over multiple years for repeat sampling. If possible, stand in the same location, and use the same camera focal length and exposure settings each time a plot is photographed. It can be very helpful to use a photo of the plot taken previously as a reference when re-taking photographs. Some photo-trend plots of experimental oil spill sites on the North Slope have been documented for over 25 years, providing valuable information about the recovery of the tundra.

Vegetation Cover

Vegetation cover is the vertical projection of vegetation from the ground as viewed from above. Vegetation cover is commonly estimated using either point or area methods (Bonham, 1989; NARSC, 1999).

• Point intercept methods are based on the number of “hits” on vegetation out of the total number of points measured; either the point “hits” a part of the plant (e.g., leaf or stem) or it does not (Fig. 131). The point is defined by shining the beam of a hand-held laser vertically down through the vegetation (i.e., PPRendicular to the ground). The plant is hit when the light beam is visible as a red dot on a plant part. A second method is based on an observer looking past cross hairs made of thin wire (similar to a gun sight); the plant is hit when it lies beneath the cross hairs. The cross hairs are mounted in a tube or frame (i.e., a point frame) (Fig. 131). The laser and sighting tube are mounted on a steel rod that is driven into the ground to provide a stable sampling point. Similarly, the stability of a point frame is maintained by driving the four legs in each corner of the frame into the tundra. Many points must be sampled in groups along a line or within a frame to provide useful information. The percent cover of live plants is calculated as the total number of hits on live plants divided by the total number of points sampled. For example, if 50 points are measured and 10 points have “hits” on plants, then the total cover of live plants would be 20%. Tundra vegetation often has multiple layers, or canopies, which can result in a plant cover >100% when using point intercept methods.

• Area methods involve placing a quadrat (a square or circle) of known area on the ground surface, and visually estimating plant cover classes (Fig. 130). Typical examples of classes are 1–5%, 6–25%, 26–50%, 51–75%, and >75%. A 20- by 50-centimeter frame is a popular quadrat size for estimating tundra vegetation cover. Usually a number of quadrats (10–30) are evaluated at a site to reduce the bias inherent in this method. If more than one person is estimating plant cover, the observers should train together and compare estimates within the same quadrats to minimize the amount of error. Although more simple to implement than the point-intercept method, the area method is greatly affected by the biases of each observer. Thus, estimates of vegetation cover using the area method are more difficult to defend as being objective and repeatable.


Figure 130. 1-m2 vegetation quadrat

Laser and point frame.jpg

Figure 131. Laser and point-frame

Vegetation Composition

Tundra vegetation communities typically include a variety of vascular plants, including sedges, grasses, forbs (broad-leaved herbs), and dwarf or prostrate shrubs, as well as nonvascular plants such as mosses, liverworts, and lichens. The number of plant species is a useful gauge of vegetation recovery at a site when compared to similar, unaffected tundra areas. Accurate identification of plants requires some training or special expertise in plant science. An on-line information source for identification of Alaskan tundra plants is available in the PLANTS DATABASE (http://www.plants.usda.gov/) maintained by the U.S Department of Agriculture. Technical publications and flower guides commonly used to identify tundra plants are provided in Table 18.

Table 18. Sources used to identify tundra plants

Vascular Plants (Sedges, Grasses, Forbs, Shrubs)

Flora of Alaska and Neighboring Territories

Hultén 1968

Willows of Interior Alaska

Collet 2004

Field Guide to Alaskan Wildflowers

Pratt 1989

Wetland Sedges of Alaska

Tande and Lipkin 2003

Flowering Plants of the High-Arctic

Threlkeld 1991

Wildflowers of the Yukon and Northwestern Canada, including adjacent Alaska

Trelawny 1983

Alaska Trees and Shrubs

Viereck and Little 2007

The Alaska Vegetation Classification System

Viereck et al. 1992

Nonvascular Plants (Mosses and Lichens)

American Arctic Lichens

Thomson 1984, 1997

Wetland Indicator Bryophytes of Interior and South Central Alaska

Seppelt et al. 2006

Mosses, Lichens and Ferns of Northwest North America

Vitt et al. 1988

Revegetation Test Plots

Before undertaking large-scale treatments such as excavation for offsite disposal (Tactic CR-13), fertilizing (Tactic TR-3 and TR-8), seeding (Tactic TR-11), or transplanting (Tactic TR-9), it may be desirable to determine if current conditions are toxic to plants. Establish plots to test seed germination or transplant survival. Seed germination and other test plots can be marked and monitored using the same methods described above.

Updated: 12/20/2010