Understory Vegetation 

 Inventory: 



An Efficient Procedure 



Renee O'Brien 

 Dwane D. Van Hooser 



INTRODUCTION 



To meet the requirements for national assessments 

 mandated by the Forest and Rangeland Renewable 

 Resources Planning Act of 1974 and other legislation, 

 the USDA Forest Service's Forest Survey has expanded 

 traditionally timber-oriented inventories to include data 

 on understory vegetation. Such information, in combina- 

 tion with overstory data, provides a structural picture of 

 the plant community that can be used in many 

 disciplines with broad application for wildlife habitat and 

 forage evaluation, grazing use potential, and estimation 

 of land productivity in terms of biomass. 



Several schemes for sampling understory vegetation 

 provide useful information (Cost 1979; Pearson and 

 Sternitzke 1974; USDA Forest Service 1980, 1981a, 

 1982a). Each has been developed in relation to the 

 vegetational characteristics peculiar to a general 

 geographic location, attendant wildlife species, land use 

 patterns, and according to the needs and demands of 

 data users. To be suitable for use by Forest Survey, a 

 procedure should: 



1. Be adaptable to an extensive, sample-based 

 inventory. 



2. Be easily integrated into the existing physical pro- 

 cedures and time frame of Forest Survey. 



3. Consist of objective observations that personnel 

 with limited taxonomic skills can perform. 



4. Be applicable throughout the field season (April 

 through October). 



5. Cause no disturbance to vegetation on permanent 

 plots. 



The procedure presented here was developed for use in 

 the Rocky Mountains (fig. 1) by Forest Survey at the In- 

 termountain Forest and Range Experiment Station. It is 

 an adaptation of several established methods. 



Forest Survey conducts an extensive inventory that 

 provides data for RPA assessments, national level deci- 

 sionmaking, and State level analysis of the resource 

 situation. The extensive nature of the inventory lends 

 itself to a brief and simple estimate of the character- 

 istics of the vegetation. In the Intermountain area, 

 a list of major species of a site and an estimate of 

 composition and vertical diversity provides the basic 

 structural picture needed for general biomass, wildlife 

 habitat, and range interpretations. 



PROCEDURE 



The Understory Vegetation Inventory Procedure was 

 used in the 1981 inventory of State and private lands in 

 Idaho, in 1982 in a similar inventory of Colorado, and in 

 1983 in the South Dakota and Wyoming inventories. 

 The procedure proved efficient and satisfactory in pro- 

 viding some basic information about the plant communi- 

 ty at each field location sampled by Forest Survey 

 crews. Such information is sufficient for most general 

 understory vegetation interpretations. 



Made up of two parts, the Understory Vegetation In- 

 ventory uses a 1/20-acre circular plot surrounding each 

 of the five cluster sample points used for the timber in- 

 ventory. A more complete explanation of this procedure 

 can be found in the Forest Survey field manuals (USDA 

 Forest Service 1981b, 1982b, 1983a, b). 



Part I provides individual species information. For 

 each of the four plant groups— trees, shrubs, forbs, and 

 graminoids— up to four species occurring with a crown 

 canopy cover of at least 5 percent are recorded. Crown 

 canopy cover is the area of ground surface covered by 

 the canopy of a plant. Canopy coverage for each species 

 recorded is visually estimated and assigned one of the 

 following coverage classes (Daubenmire 1959): 



Crown 



Percent 



canopy 



crown 



cover 



canopy 



class codes 



coverage 



1 



5 



2 



6- 25 



3 



26- 50 



4 



51- 75 



5 



76- 95 



6 



96-100 



Rarely do more than four species occur for any one plant 

 group with 5 percent crown canopy cover or greater. The 

 5 percent canopy cover stipulation reduces the number 

 of plant species requiring identification by field crews. A 

 crown canopy cover class is assigned each species 

 recorded. Part I provides an indication of the major 

 species composition and horizontal diversity of a plot. 



1 



