last update April 9, 1998
Vegetation
Comparison of Riding and Non-Riding Areas
In the three shrub communities (mixed shrub. juniper shrub, pinyon juniper-oak
woodland) where riding and non-riding locations were explicitly compared, no
clearly defined pattern of diversity with respect to land use was found. This
was true for measurements based on both cover and density. The lack of a definitive
pattern agrees with our observations in the field that the vegetation in both
riding and non-riding areas appeared to be very similar. Plots open to riding
or adjacent to trails actually showed few signs of off trail activity. We expected
that frame sampling of native and exotic forbs and grasses would be particularly
sensitive to vegetation changes induced by OHV use. Here again the sampling
plots gave no definite pattern in the percent cover of exotics and natives with
respect to designated land use.
Comparison of Soil Ecology and Restoration Group (SERG) and Kutilek Sampling
Results
We expected that the SERG sampling method would generally show a greater
number of species
and higher diversity at any given plot than the Kutilek method as the
former is based on 200
sample points and the latter on 80 points. The more extensively one
examines an area, the more
likely one is to find additional species. Since all of the calculated
diversity indices are to a varying
degree dependent on the number of species present in a sample, diversity
indices should generally
increase with increased sampling intensity, i.e. sample size.
The instances where species numbers and diversity indices for a particular site are greater using the Kutilek method may be a result of the relatively greater spread of sampling points with respect to a patchy species distribution. The greatest distance between two sample points at a sampling location is 78 meters using the SERG method and either 70 meters or 86 meters depending on which quadrants were chosen using the Kutilek method. The nature of the Kutilek method is, however, that the sample points in each transect are on average farther apart. In a patchy vegetation, greater distance may result in detection of additional species and/or less dominance by a few species (greater species equitability). We emphasize, however, that differences between the two sampling procedures are not great and are in large part probably the result of random sampling error in a heterogeneous environment
Birds
Two of the eleven sampling sites, #72, bird concentration site, and #101, riparian woodland, demonstrated the highest number of different species observed, the highest density of birds per hectare and the largest diversity values. A common denominator that can be seen between these two sampling sites is the greater abundance of large tree species found in these areas relative to the other nine sampling plots. Both of these sites are located on large drainage systems: plot #72 along the edge of the park's southern drainage system, and plot #101 along the park's northern drainage system. The major tree species for both sites include cottonwood (Populus fremontii), willow (Salix sp.), and sycamore (Platanus racemosa). These large trees provide food, nesting and perching sites and protection from predators for a large number of birds, leading to greater species composition and high density and diversity.
Two of the sampling sites, #41, juniper shrub riding area, and #57, perennial grassland, demonstrated the lowest number of species, the lowest density of birds per hectare and low diversity values. Such low values for a perennial grassland can be expected due to the lack of shrub/tree cover and overall low plant diversity inherent in a native grassland. However, when comparing species composition, density and diversity between plot #41, juniper shrub riding area, and its non-riding control area, plot #45, there appears to be a noticeable difference. Values for all areas are lower in plot #41 than in #45. For the juniper shrub riding area, species composition is 4, density is 6 birds per hectare and the SDI value is 1.21. For the juniper shrub control area, species density is 9, density is 14 birds per hectare and the SDI value is 1.69. Such a distinction could possibly be the result of the impact of OHV activity conducted at plot #41.
A comparison between the mixed shrubland riding area, plot #18, and the mixed shrubland control area, plot #14, shows similar, though less dramatic results. Though species composition was the same at 9 different species, density (10 birds per hectare versus 19 birds per hectare) and diversity ( 1.94 versus 2.00) were lower for the mixed shrubland riding area than the mixed shrubland control area. As in the case of the juniper shrub community, this difference could also possibly be the result of OHV activity occurring on plot #18 and not on plot #14.
The last habitat comparison between riding and control areas was for the pinyon/juniper/oak woodland community. Results from this plant community were opposite of the first two comparisons. Plot #24, the pinyon/juniper/oak woodland riding area, had higher values for species composition (8 versus 6), density (17 versus 15) and diversity (1.98 versus 1.20) than plot #79, the control area. These contrary results might be the result of the different locations of the two plots. Plot #24, the riding plot, is located atop a ridge along Backbone Trail, with Freeman Canyon to the east and Hungry Valley to the west. This position allows birds to approach the site from both east and west, possibly serving as a connecting link between Freeman Canyon to the east and the main valley of the park just west of the ridge. In comparison, plot #79 is located on a steep hillside just east of Badlands Trail along the east side of Freeman Canyon. The site is extremely steep and rocky and basically situated within a dead end canyon. Access is limited and could be restricted to only those species that favor steep rocky habitats.
A comparison of species observed at these sites appears to confirm this hypothesis. Plot #79 species included the white-throated swift (12). common raven (3) and red-tailed hawk (1); all airborne during sighting and species that normally hunt/forage in the air. The only ground species observed were one scrub jay, one Weid's crested flycatcher and one rock wren. Plot #24, on the other hand, displayed a very different species composition. With the exception of one raven and two scrub jays, both cosmopolitan species within the park, all other species were different than what was observed at plot #79. Species included the ash-throated flycatcher, Bewick's wren, canyon wren, bushtit, northern oriole and westem meadowlark: all species seen at plots located in either Freeman Canyon or the main valley. This species composition demonstrates the possible impact of the location of plot #24 between these two valleys and might explain why the pinyon/juniper/oak woodland riding area has higher species composition, density and diversity values than the control area.
Reptiles
Time Constraint Survey
The results from the mixed shrubland sites showed that the riding site had a higher diversity and density than the non-riding site. Some possible explanations for these results are the evidence of a recent fire at the non-riding site and the difference in topography between the sites. The evidence of fire at the non-riding site extended well beyond the area covered in the survey which may have had a negative effect on the abundance of the herpetofauna within this area. The differences between the species observed at the mixed shrubland sites may be attributed to the difference in topography. The riding site was primarily flat while the non-riding site was characterized by the presence of hills. Based on the differences stated above, caution should be used when comparing these sites.
No significant differences were detected between the riding and non-riding sites of the juniper shrub sites based on the summary data. One noticeable difference between the sites is the topography. The non-riding site had less open, flat terrain than the riding site.
Overall, this habitat appears to be relatively productive with respect to the other habitats sampled.
The data suggests a significant difference between the riding and non-riding sites of the pinyon/ juniper/ oak woodland habitat; however, caution should be used when interpreting this difference. According to the data the non-riding site is more productive than the riding site. Although off-road vehicle use may play a part in the absence of reptiles at the riding site, the location of the site is probably more of a contributing factor. This site is located at the top of a mountain off of Backbone Trail which has no canyons or flat terrain. Most of the reptiles at the non-riding site, which is located at the base of a mountain1 were found within small canyons.
The riparian cottonwood/ willow woodland site was the only riparian habitat sampled. This site exhibited the highest density among the sites sampled by the time constraint method. This can be attributed to the abundance of pacific tree frogs captured which may be a temporary abundance since most captures were individuals that had recently undergone metamorphosis.
Array Survey
The grassland habitats had particularly low capture rates. It is suspected that these habitats are more productive than the results suggest. It was noticed that the grasses and the soil were very dry and the presence of water was scarce. The peak activity periods for reptiles and amphibians within this habitat probably occurs earlier in the season. Based on the limited results of the grassland habitat no differences were detected between riding and non-riding sites except that different species were captured.
The bird concentration site was the most successful among the sites sampled using arrays. The presence of a permanent water source near the site may be a contributing factor because the other sites were much drier and were without a nearby water source. The results of the survey at the reptile concentration site do not appear to be representative of the herpetofauna at this site. This is supported by the results of the unofficial time constraint survey conducted at this site. One possible reason for the low number of captures at the reptile concentration site is the location of the array which was located in a narrow area of the canyon which received fewer hours of sunlight with respect to the rest of the canyon. The reptiles sighted during the unofficial time constraint survey were located in open areas of the canyon which received more hours of sunlight.
A total of sixteen species of reptiles and amphibians were observed within Hungry Valley SVRA park, however, based on range maps it is presumed that several additional species are present. Sites that were to be compared to each other based on the presence or absence of off-highway vehicle activity were selected according to the presence of similar vegetation species. Many of these sites had similar vegetation but the topography differed. Among other factors, the results suggest that topography may play an important role in the location of many species of reptiles and amphibians.
Mammals
The variety of vegetation communities found on the HVSVRA translates into a diverse mammal fauna across the Area. The patterns of diversity and abundance of small mammals observed in this study are largely a function of habitat complexity, which, in turn, is determined by plant species diversity. With respect to small mammals, lowest abundances and diversities were observed on the grassland plots, which can be characterized as being relatively homogeneous with respect to its structure; the more structurally complex shrubland and woodland habitats had higher abundances and diversities.
One purpose of this study was to compare mammal communities between similar habitat types in riding and non-riding ("control") areas to determine differences in the communities which might be attributed to vehicular activity. While the design of the study does not allow rigorous statistical testing, the observed patterns are suggestive. Generally, there appears to be no consistent pattern suggesting adverse effects of vehicles on the small mammal communities. In the comparison of grasslands, the perennial grassland plot (Plot #7) was in a riding area, but it had a diversity estimate (H' = 1.225) over twice that of the annual grassland, which was not in a riding area (H' = 0.562); a similar pattern was seen when these plots are compared with respect to the number of individuals captured. Both diversities and abundances on riding and non-riding plots in mixed shrubland (Plots #18 and #14) are similar, while those for riding and non-riding plots in pinyon/juniper/oak woodland (Plots #24 and #79) are virtually identical. Only when the juniper shrub plots were compared was diversity and abundance noticeably greater on the control plot (Plot #45; H' = 1.990. N = 24) than on riding plot (H' = 1.306, N = 13).
It is difficult to assess the impact of vehicular activity on the large mammals found at HVSVRA because these larger, more vagile species undoubtedly perceive the environment as "coarse- grained". That is, these species have large home ranges and move over large areas, which renders the "riding area-control area" design used in this study inappropriate. For example, it is unlikely that coyotes, with their large home ranges, are restricted to only riding or non-riding areas. However, ungulates and carnivores are dependent upon plants and small mammals, respectively, for food and adverse impacts on those species can be expected to impact on their predators.
Vegetation
It is recommended that the park establish an on site voucher system, particularly for annual species. This would provide the basis for maintaining a complete listing of plant species found within the park's boundaries with annotations pertaining to specific species as they exist in the park and not in a generalized field guide or text. Specimens should be kept in a pest proof herbarium case, located on the park grounds, and maintained and used by the park's resource ecologists. This would entail some training in the proper management of herbarium specimens which could be obtained from one of the local universities such as the University of California at Riverside or San Diego State University.
The accuracy of future surveys by park personnel will be based on their knowledge of the plant species to be found within the park. Having specimens to view before, during and after such surveys are conducted will greatly benefit those individuals involved and allow for a more accurate identification program for the future. Due to the variable climatic influences on the Hungry Valley area, many annual species many appear on only rare occasions and are not easily identified unless a voucher specimen is available for comparison. Personnel turnover, a normal occurrence for state parks, can also lead to new individuals being responsible for conducting future surveys who are unfamiliar with the local flora. Thus, a voucher program would be of ever increasing value as an accurate way of ensuring the park maintains its vegetation monitoring program and in assuring scientific verification of the plant species present in the HVSVRA.
Changes in perennial vegetation, particularly shrubs that are in semi-arid environments, are of an order such that we believe that annual surveys of perennial species are not necessary. We recommend a two a year sampling interval for shrublands. This would benefit those plots located on steep slopes and subject to considerable disturbance during sampling. Plots may be broken into two groups sampled every other year in order to reduce the yearly sampling effort. However, riding and non-riding plots in the same vegetation type should be sampled during the same season. All sites should be visually monitored on a regular basis and we recommend that frame sampling be conducted at least once yearly. The growth of annuals should be monitored so that sampling can be conducted at peak biomass.
Results of the SERG and Kutilek sampling methods suggest that a d~tailed releve should be performed at each one hectare sampling site on a yearly basis. As for the frame sampling procedure, the releve should be conducted at the time of peak annual biomass. Photographic records in the form of a panoramic view from the plots' carsonite markers could prove to be of great value. An appropriate lens could do such a panorama in the four cardinal directions.
Further modifications to the CNPS field forms based on the experience gained from this first monitoring event would be helpful to those performing future surveys. Such changes, though slight, could help reduce any possible confusion and ambiguity in the collection of data by future different personnel.
Birds
The two sites displaying the greatest number of species and the highest density and diversity of birds were areas dominated by dense vegetation and large tree species situated along the two main drainage systems of the park. The protection and food supply provided by these areas, and, most importantly, the nesting sites made available for a large variety of bird species, lead these two areas, represented by plots #72 and #101, to be invaluable habitats for both resident and migrating birds. Plot #101, located on the northern drainage system near Interstate 5, has not been impacted by OHV activity and, due to its location and physical structure, will probably remain so. However, plot #72 does show signs of OHV impact with a fairly large trail running the length of the canada. An unofficial walk through the canada, not part of the survey, resulted in a large number of additional species of birds not observed during the survey of plot #72. Based on the data gathered during this survey, it is recommended that the Canada, represented by plot #72, be classified as a non-riding area to ensure the protection of one of the park's most valuable bird habitats.
A second recommendation concerns the continuance of bird surveys on a regular basis. This survey provided a one time picture of bird species composition, density and diversity within the boundaries of Hungry Valley State Vehicle Recreation Area during late spring. To gain a more complete picture of the avian fauna of the park, not only should this type of survey be conducted on a regular basis, but needs to occur, at a minimum, twice a year, once in the spring and once in the fall. By conducting biannual surveys at these times, data will be collected during the high use periods of spring and fall migrations when migrating birds will be transiting through the park. Hungry Valley not only provides valuable habitat for local resident birds, but food and protection for those many migrating species that use the western flyway each year. Only through the conduct of regularly scheduled biannual surveys will a complete and thorough data base be gathered and thus be available for future land management decisions.
Reptiles and Amphibians
If one of the goals of this monitoring program is to determine the effects of OHV activity on reptile and amphibian populations, then it is advantageous to use a mark and recapture method. This involves the capture, mark and release, and subsequent recapture or resighting of a specimen. By using this method, one can estimate a population size, demographic parameters (survival rates), space use patterns (home range size and utilization), and individual growth rates.
Based on range maps, it is probable that more reptile and amphibian species exist within the borders of the park than were observed during this study. Range maps indicate that the western spadefoot toad (Spea hammondii), a California protected amphibian may occur within Hungry Valley SVRA. In addition, the following threatened and endangered amphibians and reptiles may occur in the park: the Tehachapi slender salamander (Batrachoseps stebbinsi), the blunt-nosed leopard lizard (Gambelia silus), and the southern rubber boa (Charina bottae). Additional sampling should be conducted in order to determine if these species occur within the borders of the park. While conducting surveys, data should be recorded that provides useful information in determining the population size of the coast horned lizard found within the park (i.e. mark and recapture data). The specimens of the long-nosed leopard lizard that were captured exhibited characteristics similar to those found in hybrid specimens as described by Montanucci, since only two individuals were observed, further investigation is needed to determine if the hybrid zone has migrated within the boundaries of Hungry Valley SVRA.
To obtain a complete description of the diversity and density of the herpetofauna at Hungry Valley SVRA, surveys should be conducted under favorable conditions. It is recommended that time constraint searches are conducted at least once in the late spring and early summer (May through July). Along with time constraint surveys, arrays can be an effective method of sampling, this method is especially useful in areas where dense brush and topography make time constraint surveys difficult. The grassland habitat is a good example of an area in which the observation of specimens is difficult. When using the array method, it is suggested that sampling is performed year-round with the pit-fall traps open for 10 days and at 30 day intervals between the sample periods. If time and personnel are limiting factors, sampling should begin in early spring and continue through the end of summer (March through August). The traps should be open for 10 days with a 10 day interval between each sample period.
As stated earlier, topographical differences made it difficult to compare the similarities and differences in herpetofauna between the riding and non-riding sites. Due to the topographical differences between the pinyon/ juniper/ oak woodland sites, it is recommended that a new riding site should be selected. In addition, the reptile concentration site should be relocated to a location in the canyon which is approximately 50 - 75 meters south of the original location. This would place the array in a location where most of the reptiles were observed during the unofficial time constraint survey.
Mammals
Several recommendations concerning future monitoring and management can be made based on the results of this survey. First, long-term monitoring of the mammal communities on the HVSVRA can be important for assessing temporal trends in species diversity and density and, in turn, for making management decisions. Temporal changes in mammal communities may be due to inter- year variation in physical and/or biotic factors, impacts of OHV activity or some combination of factors, and the monitoring of suitable control plots is very important for identifying factors impacting on mammal communities. It is recommended that monitoring of small mammals on both control and riding plots continue on at least an annual basis. Semi-annual sampling (e.g. spring and fall) of plots would provide a seasonal perspective that would be desirable.
Second, it would be desirable to extend the live-trapping periods beyond 3 days in order to ensure that all small mammal species present on the plots are captured. On several of the study plots, new species were being captured on the third night of trapping.
Third, a voucher collection of specimens representing captured species of small mammals should be initiated. Experts in the field of mammalian systematics should be periodically consulted to determine the presence of species which might be expected to occur at HVSVRA, but that were not documented in this survey (e.g. Hermann's kangaroo rat, Dipodomys heerrnanni; the white-eared pocket mouse, Perognathus alticola).
Fourth, it is recommended that spotlight surveying be conducted to complement tracking stations. This additional survey technique may be useful in documenting the presence of species present at HVSVRA but which may not be detected by tracking stations.
Fifth, efforts should be made to protect the riparian woodland habitat (Plot #101) from degradation or disturbance to the extent that it is possible to do so. This habitat is unique in that it had high species diversity and the greatest number of captures of any of the plots surveyed. In addition, it was the only plot where the California vole (Microtus californicus) was captured during the survey.