written by Grant Hamilton
Woody species utilization is an ocular method adapted from the Landscape Appearance (Key Forage Plant) Method in Utilization Studies and Residual Measurements (USDI, BLM 1996b) and Winward’s (2000) measure of woody species regeneration. It is a component of Multiple Indicator Monitoring (MIM) of riparian environments (Burton, Smith, and Cowley, 2011, pp. 34 – 39).
Woody species utilization is a short-term indicator of livestock consumption of woody plants (shrubs and trees) along streambanks. Woody plants are important to riparian environments because of their ability to reduce rates of erosion. Livestock and wildlife utilization of this resource can be quantified using this method. It is based on the amount (percentage) of the current year’s leaders on the woody species rooted within a plot 2 m wide (centered on the greenline) and the length of the sample interval. Estimates are based on a range or class of use of the available current year’s leaders on a single plant. Only shrubs with more than 50 percent of the current year’s leaders within reach of grazing animals are evaluated.
Monitoring can occur immediately before or after livestock begin grazing, to determine whether to permit grazing at a specific time, or at the end of each season. The arithmetic average of woody species use by individual plant or shrub or the weighted average for utilization all woody species at the site can be calculated.
1. Establish the Plot Size: Woody species utilization is measured within a 1 m zone extending from the greenline on each streambank. The woody species zone is divided into quadrats, the length of which is determined by the size of the study area and the needs of the researcher.
The length of the woody species use plot is the distance between quadrats. Select the first woody plant (A) within the plot and determine the utilization on that plant. This is repeated for each key woody species (B and C) within the plot. A 2-m measuring rod centered on the greenline is often used to locate plants within the plot. The monitoring frame has a 1-m-long handle, which may also be used to determine if individual woody plants are rooted within the plot.
2. Determine the Available Current Year’s Growth: Available woody species are plants having more than one-half (50 percent) of the current year’s leaders within reach of the grazing animal. When the first plant has more than 50 percent of the current year’s leaders above the reach of the grazing animal, the shrub is considered unavailable for grazing and the plant is not considered for woody species use. The following table provides accessibility by species:
|Cattle||1.5 m (5.0 ft)|
|Sheep, antelope, bighorn sheep||1.1 m (3.5 ft)|
|Horses, elk, and moose||2.1 m (7.0 ft)|
|Deer||1.4 m (4.5 ft)|
3. Evaluate the Closest Plant: evaluate the first available key woody plants rooted within the plot for grazing use (see illustration above). If the first plant of a species is not available, go to the next closest plant within the plot. Common key woody species include most species of willow, alder, birch, dogwood, cottonwood, and aspen. If no key woody plants are encountered within the plot, leave the cell in the MIM Field Data Sheet blank.
4. Determine the Woody Species Use Class: Plants are classified into a “use class” (Woody Species Use Classes and Descriptions table). These use class descriptions are the standards by which use is judged. This process is repeated for each key woody species within the plot. Review grazing class descriptions periodically while reading the plots to maintain precision and accuracy. Record by species the midpoint for the appropriate use class.
|Unavailable||Blank||Shrubs and trees that have most (over 50%) of their actively growing stems over 1.5 meters (5 feet) tall for cattle grazing. This should be adjusted for the questions needing to be answered involving other herbivores.|
|Slight (0-20%)||10%||Browse plants appear to have little or no use. Available leaders may show some use, but less than 20 percent of the current year’s leader growth has been used.|
|Light (21-40%)||30%||There is obvious evidence of use of the current year’s leader growth. The available leaders appear cropped or browsed in patches and 60–80% of the available current year’s leader growth of browse plants remains intact.|
|Moderate (41-60%)||50%||Browse plants appear rather uniformly used and 40–60% of available annual leader growth of the plants remains intact.|
|Heavy (61-80%)||70%||The use of the browse gives the general appearance of complete search. Most available leaders are used and some terminal buds remain on browse plants. Between 20 and 40% of the current year’s growth is still available.|
|Severe (81-100%)||90%||The use of the browse gives the appearance of complete search by grazing animals. Grazing use on second and third years’ leader growth. Plants show a club-like appearance indicating that most active leader growth has been removed. Only between 2 and 10% of plants remain intact.|
Woody Species Use Classes and Descriptions
- Burton, T.A., S.J. Smith, and E.R. Cowley. 2011. Riparian area management: Multiple indicator monitoring (MIM) of stream channels and streamside vegetation. Technical Reference 1737-23. BLM/OC/ST-10/003+1737+REV. U.S. Department of the Interior, Bureau of Land Management, National Operations Center, Denver, CO. www.blm.gov/nstc/library/pdf/MIM.pdf
- USDI, Bureau of Land Management. 1996. Sampling vegetation attributes. Interagency Technical Reference 1734-4. BLM/RS/ST-96/002+1730. www.blm.gov/nstc/library/pdf/samplveg.pdf
- Winward, A. H. 2000. Monitoring the vegetation resources in riparian areas. Gen. Tech. Rep. RMRSGTR-47. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. www.fs.fed.us/rm/pubs/rmrs_gtr047.pdf
Related utilization and residue measurement methods include:
- Cole Browse Method
- Extensive Browse Method
- Stubble Height
- Paired Plot Method
- Utilization – Grazed Class Method
- Herbaceous Removal-Height-Weight Method
- Herbaceous Removal-Actual Weight Method
- Herbaceous Removal-Ocular Method