SPECIES COMPOSITION OF A CACHE VALLEY, UTAH PASTURE

Transcription

1 3 October 2004 Bart Simpson Department of Forest, Range, and Wildlife Sciences Utah State University Logan, UT RH: Species Composition of Ron Ryel s Property Simpson SPECIES COMPOSITION OF A CACHE VALLEY, UTAH PASTURE BART SIMPSON, Department of Forest, Range, and Wildlife Sciences, Utah State University, Logan, UT 84322, USA Abstract: The Utah Division of Wildlife Resources is considering a piece of private property in Cache Valley for a conservation easement. In 2003, a team conducted a complete vegetation inventory of the property to determine species richness and frequency, the ratio of native to exotic species, and the presence of any rare species. We repeated this study to determine vegetation trends, and we determined the property was inappropriate for a conservation easement. We also examined the effectiveness of random sample plots for inventory purposes. JOURNAL OF WILDLIFE MANAGEMENT 00(0): Key words: Cache county, conservation easement, curly dock, Rumex crispus, Fuller s teasel, Dipsacus fullonum, indicator, inventory, random sample plots, showy milkweed, Asclepia speciosa, UDWR, Utah, vegetation trends. In 2003, private landowner Ron Ryel approached the Utah Division of Wildlife Resources (UDWR) to acquire a conservation easement for his property in Cache County, Utah. He reasoned that his property had unique vegetation and habitat value and should be protected from future development. The UDWR had a habitat specialist

2 Simpson 2 conduct an inventory of the vegetation on the property in In the fall of 2004, a second crew repeated this study. Our objectives included determining species composition by measuring species richness, species frequency, the ratio of native species to exotics, and establishing whether threatened or endangered species were present. We also estimated the density of 3 indicator species, showy milkweed (Asclepia speciosa), a native to the Intermountain west, curly dock (Rumex crispus), which indicates high nitrogen in the soil, and Fuller s teasel (Dipsacus fullonum) which is an invasive species and an indicator of disturbance. By comparing our results with the 2003 study, we established vegetation trends for the property. This study also allowed us to test the effectiveness of random plots for assessing species richness and density for future management practices. STUDY AREA The property in question was located in the city of Logan, Utah, in Cache Valley. Cache Valley ( N W) sits at an elevation of m and has a four season climate. It is about 96.6 km long and km wide. Average annual precipitation is cm. Since 1859, the valley has been the site of agriculture practices, and today the majority of the vegetation is residential or agricultural. ( About Logan ) The study site, a 90 x 50 m field, lay in a residential area. Historically, the area was part of the winter range for deer and elk from the surrounding mountains. The site was not being utilized for any purpose at the time of study, but adjacent lands included several livestock pastures and residential landscapes.

3 Simpson 3 METHODS This study was conducted 15 September Six teams worked independently on the same site and combined their findings. Using a random numbers table, we generated the coordinates of a test plot. This coordinate became the stable corner of our plot. We determined the orientation of our plot in relation to this point by using an even number to indicate left, and an odd number indicate right, and then utilizing the random numbers table again. Our established plot reached south and west from the stable corner. All the plots in the study were oriented according to this first plot. In our test plot, we counted the number of species present in a series of nested plots 0.25 m 2, 1 m 2, 4 m 2, and 16 m 2 in size. By plotting the number of species against increasing area, we created a graph of the species-area curve for the site. This curve helped us determine the appropriate plot size for sampling. (Figure 1.) A 4 m 2 plot allowed us to sample the greatest number of species with the least amount of effort. Plots larger than 4 m did not increase the number of species recorded significantly enough to justify the extra time and work involved. Each group then used the random number table to generate coordinates for five additional plots. In each plot, we counted the species present to determine species frequency and species richness. We also counted the number of showy milkweed, curly dock, and Fuller s teasel plants. The Fuller s teasel count included both the green stalks of this season s growth and the dried stalks of last year s teasels. Finally, everyone present collaborated in a full census of showy milkweed in field. Walking approximately 3 m apart in a parallel line, each individual counted the showy milkweed to their left. On the way back across, each person made a second count,

4 Simpson 4 this time to their right, to ensure no plants were missed. We used Excel for all data analysis. RESULTS Out of 21 species originally documented on the property, 16 were observed in this study. Species richness declined 11% between 2003 and Species frequency also fell; 75% of the native species and 59% of the introduced species we observed decreased in frequency. Trends for individual species are presented in Table 1. Our estimates of showy milkweed, curly dock, and Fuller s teasels in our sample plots yielded mean population estimates of 30.41, , and respectively, and confidence intervals of ± 59.59, ± , and ± Our actual census revealed 6 showy milkweed and 70 curly dock plants present in the field. DISCUSSION During this study we tested the effectiveness of random sample plots in determining species richness and density. We succeeded in establishing an efficient plot size; we were able to detect 16 of 21 known species with minimal effort. However, the confidence intervals for our population estimates of curly dock and showy milkweed include 0, meaning we ve included the possibility that these species don t exist at all when we know in fact they do. Our confidence interval for Fuller s teasels did not include 0, but many of our sample plots recorded 0 teasels. Obviously, random sample plots are less effective at detecting rare or patchy species. Without a second survey method like transect lines or a complete census, these species may be missed all together. Future vegetation surveys should take into consideration the distribution pattern and

5 Simpson 5 likely frequencies of species in a study site before relying entirely on information from random sample plots. MANAGEMENT IMPLICATIONS As a habitat specialist, I would not recommend this site for a conservation easement. Of the 21 species originally listed on property, 81% are introduced species. During this study, introduced species showed up in the highest frequencies. This indicates the site has been disturbed in the past, probably multiple times considering the history of the area. Several of the introduced species, such as goat s rue (Galega officinalis) and Canada thistle (Cirsium arvense) are increasing in frequency. Without intervention, I would expect species richness to continue declining as the more competitive invasives dominate the field. There is also a high risk of reestablishment by invasives following any treatment because of adjacent pastures and fields containing large populations of these plant species. The property is only 0.5 ha in size which limits its value as wildlife habitat or as a reserve for unique plant species, especially considering the high potential for development surrounding the site. However, no threatened or endangered plant species were observed in either inventory. Considering the high frequency of invasive species, the declining species richness, the lack of any unique species, and the size and location of the property, there is little reason for the UDWR to create a conservation easement.

6 Simpson 6 LITERATURE CITED About Logan Utah. Logan Library Cache Valley Almanac. Sept Online. Retrieval 4 Oct

7 Simpson 7 Species-Area Curve Species richness Sample plot area (square meters) Figure 1. Species-area relationship of vegetation at Ron Ryel s pasture, Logan

8 Simpson 8 Table 1. Vegetation inventory, species frequency, and individual species trends of Ryel s pasture, Logan Frequency Common Name Scientific Name Nativity a Trend b Fuller's teasel Dipsacus fullonum I Common mallow Malva neglecta I Prickly lettuce Lactuca serriola I Common bindweed Convolvulus arvensis I Goat's rue Galega officinalis I Curly dock Rumex crispus I Canadian thistle Cirsium arvense I Bull thistle Cirsium vulgare I Showy milkweed Asclepias speciosa N Common burdock Arctium minus I Wild mustard Brassica kaber I Common dandelion Taraxacum officinale I Yellow salsify Tragopogon dubius I Kentucky bluegrass Poa pratensis N Smooth brome Bromus inermis I Orchardgrass Dactylis glomerata I Meadow foxtail Alopecurus pratensis I Western wheatgrass Pascopyrum smithii N Slender wheatgrass Elymus trachycaulus N Quackgrass Elytrigia repens I Johnsongrass Sorghum halepense I a. I = introduced, N = native b. + = increasing frequency, - = decreasing frequency