and timber management manipulates the tree bole and 
tree canopy layers. The impact of various land-manage- 
ment activities on fish and wildlife resources can be pre- 
dicted from computer simulations that modify energy 
sources and breeding niches (rows and columns of the 
species-habitat matrix, Appendices I and II) in the 
affected strata. Computer simulations can thus display 
various management options so that development can 
occur in ways that reduce impacts on wildlife guilds. 
Systems Approach for Assessing Wildlife Habitat 
in the Decision Process 
The utility of any habitat evaluation effort is deter- 
mined by its effectiveness in the decision-making process. 
The technique described in this paper has relevance to 
land-use management decision-making because it relates 
the wildlife community to the structure of vegetative sur- 
face cover, Which can be controlled through management 
and predicted through time. This methodology deals with 
the total wildlife community and can be used to predict 
changes from established base-line conditions which deter- 
mine the wildlife guilds present at a specific point in time. 
Wildlife guilds potentially present in the future can be 
predicted by establishing species-habitat matrices for the 
seral stages of surface cover types predicted to be present 
at those future dates. A comparison of the product of area 
times guilds times years with base-line conditions repre- 
sents gains or losses associated with changes in land use 
and is essentially an assessment of potential impacts. 
A conceptual model, developed by Erickson et al. 
(1980), for assessing wildlife-land-use relationships in the 
decision-making process is reproduced in Fig. 14. Abiotic, 
biotic, and human conditions produce the existing wildlife 
habitat on a site. Areas of different cover types on a de- 
velopment site can be calculated (Table 5) and the guilds 
that occur in those cover types can be determined. The de- 
termination of guilds actually present on a site is made 
from on-site surveys which provide faunal lists for the dif- 
ferent areas of existing wildlife habitat. The species 
actually present are compared with those species forming 
the wildlife guilds to determine the guilds actually repre- 
sented on-site. 
Proposed land-use changes will impact the structure of 
vegetation so that areas of different types of vegetation 
likely to be present at different time intervals during the 
life of the proposed project can be predicted (Table 5). 
The predicted wildlife community (number of guilds) at 
any time during the project's life can be developed from 
species-habitat matrices developed for the vegetative types 
presumed present after development. 
The simple calculation of multiplying present hectares 
by present guilds and future hectares by future guilds 
(Table 5) illustrates how changes in the total wildlife com- 
munity can be predicted on the basis of the impacts of pro- 
posed land-use options on vegetative surface cover within 
a land area. These changes can be predicted for a single 
point in time or for the life of a project. 
17 
Assumption & 
Vertebrate species may be present in a habitat if suit- 
able environmental factors, including food sources and 
breeding niches, are present. The greater the number of 
suitable environmental factors present in a habitat, up to 
some point, the greater the potential species richness that 
may occur in that habitat. 
Food sources and breeding niches itemized in Appen- 
dices I and II and included in the species-habitat matrix 
(Fig. 5) are among the most important environmental fac- 
tors determining the suitability of a habitat for a species. 
The presence of food sources and breeding niches within 
guild blocks and the addition of guild blocks to habitat 
obviously affect species richness. The impact on species 
richness of modifying food sources (rows) within the 
species-habitat matrix can be simulated with the data sets 
used to develop the relationships in Figs. 9-11. For this 
illustration, the impact of moderate overgrazing is simu- 
lated by deleting rows 53-56 and 65-70 (Appendix I) from 
the computer model. This condition would be realized if 
essentially all current annual growth in the terrestrial sur- 
face strata and in the shrub strata had been removed by 
grazing. Although representatives of all the potential 
guilds remain in upland grassland, upland shrub (sage- 
brush), and upland coniferous woodland (ponderosa pine) 
habitats, following the simulation, the number of primary 
consumers in each of the three vegetative types is reduced 
(Table 6). The specialists requiring herbaceous, forb, or 
deciduous browse in the surface or shrub strata disappear 
from these three cover types when the appropriate cells 
disappear. 
Predictive associations can be developed that relate 
species richness, the total number of vertebrate species on 
an area, to the number of guild blocks and the structure of 
vegetation within the strata of different cover types. Such 
a model is described by Short (1982). 
The habitat-gradient model states that of two habitats 
with the same basic vegetative structure (and thus with the 
same number of guild blocks), the habitat with greater 
vegetative density, greater equitability of cover between 
strata, greater block size, and more persistent vegetation, 
will have more species and presumably more of the pos- 
sible guilds that can occur in the habitat type. Thus guilds 
present on an area within a particular potential vegetation 
type can be used as an assessment of habitat quality. The 
habitat-gradient model neither predicts the individual 
species likely to be present nor the actual guild structure of 
the community likely to occur on that habitat. Identifica- 
tion of individual_species occurring on a site is a product of 
animal inventory information. A comparison of animals 
found on a site with lists of species constituting potential 
guilds for that habitat type is the best way to determine 
the actual guilds occurring in an area. 
The habitat-gradient model can also be derived from in- 
terpreted aerial photography (Short 1982). An area to be 
characterized is first subjected to an on-site evaluation to 
