U.S. DEPARTMENT OF THE INTERIORBUREAU OF LAND MANAGEMENT
|El Centro Field Office|
Imperial Sand Dunes Monitoring Studies
BLM has conducted several monitoring studies of the special status plants of the Algodones Dunes (also called the Imperial Sand Dunes), Imperial County, California, since 1998. The monitoring between 1998 and 2002 used an abundance class approach. The 1998-2000 monitoring was designed to track the following six plant species: Peirson’s milk-vetch, Algodones Dunes sunflower, sand food, Wiggins’ croton, giant Spanish needle, and Borrego milk-vetch. The 2001 and 2002 monitoring tracked only the first three species listed above. Three reports summarize the 1998-2002 monitoring, all of which are available using the links below. The 2000 report (November 2000) analyzes and interprets the 1998 data and compares those data to the data from a 1977 BLM-contracted study by the consulting firm WESTEC. The 2001 report (June 2001) compares the responses of the six plant species over all four years of measurement (1998, 1999, 2000, and the 1977 study). The 1998-2002 report (October 2004) compares the responses of Peirson’s milk-vetch, Algodones Dunes sunflower, and sand food over all six years of measurement (1998, 1999, 2000, 2001, 2002, and the 1997 study).
Because the abundance class approach used in the 1998-2002 monitoring did not result in actual estimates of density and population size, that approach was ended with the 2002 monitoring. In spring 2003 a pilot monitoring program was initiated to estimate the density and population size of Peirson’s milk-vetch, Algodones Dunes sunflower, and sand food in the Wilderness and Gecko management areas of the Algodones Dunes. The study also estimated the canopy cover of the vegetation associated with these special status plants. The 2003 report (January 5, 2004) is available through the link below.
In 2004 BLM expanded the monitoring approach tested in the 2003 pilot program to all seven management areas of the Algodones Dunes in which Peirson’s milk-vetch and Algodones Dunes sunflower occur. Twelve sampling areas were delineated within the seven management areas (some management areas had only one sampling area, some had two, and one had three). A total of 135 belt transects, ranging in length from 2.35 to 14.16 kilometers, were surveyed throughout these sampling areas. Density and population size were estimated for Peirson’s milk-vetch, Algodones Dunes sunflower, and sand food for each management area and the Dunes as a whole. In addition, estimates were made of the canopy cover of the perennial plants associated with the special status plants. The 2004 report (March 24, 2005) is available through the link below.
In 2005 BLM continued monitoring of all seven management areas of the Algodones Dunes. Based on analysis of the 2004 data, sampling was intensified in order to achieve more precise estimates of the density and population size of Peirson’s milk-vetch. Four of the 2004 sampling areas were subdivided into two sampling areas each, so that the 2005 sampling was conducted in 16 sampling areas. A total of 510 belt transects, ranging in length from 2.35 to 7.75 kilometers, were surveyed throughout these 16 sampling areas. Density and population size were estimated for Peirson’s milk-vetch and Algodones Dunes sunflower. In addition, estimates were made of the canopy cover of the perennial plants associated with the special status plants. Separate reports are provided for Peirson’s milk-vetch (Peirson’s milk-vetch 2005 report, September 8, 2005) and for Algodones Dunes sunflower and vegetation (Algodones Dunes sunflower-vegetation report, November 29, 2005), both of which are available through the links below.
Monitoring in 2006 consisted of randomly resampling some of the 25m x 25m cells that were sampled in 2005 (in 2005 plant numbers were recorded in 25m x 25m cells arrayed along 510 belt transects) in order to derive density and population estimates of Peirson’s milk-vetch for 2006. The 2006 monitoring also included the acquisition of aerial photography on Presidents’ Day weekend 2006. This aerial photography was used to determine off-highway vehicle (OHV) use patterns in Peirson’s milk-vetch habitat and to investigate whether there is a negative correlation between the level of OHV use and the number of Peirson’s milk-vetch plants.
In 2007, BLM, with technical assistance from the U.S. Fish and Wildlife Service, implemented a pilot study to determine the feasibility of sampling the seed bank of Peirson's milk-vetch. The pilot study was restricted to three of the seven management areas in which Peirson's milk-vetch occurs and to five of the 16 sampling areas that were established in 2005 to monitor above-ground plants of the species. The five sampling areas chosed for the pilot study were those with the highest numbers and densities of Peirson's milk-vetch plants in the 2005 monitoring study. A simple random sample of 25m x 25m cells was selected, stratified by management area and further stratified by areas open and closed to off-highway vehicles (OHVs). Although the study design targeted 900 cells for sampling (300 per management area), the contractors were able to sample 735 cells before the onset of hot weather, 253 cells in the Gecko Management Area, 215 cells in the Adaptive Management Area, and 267 cells in the Ogilby Management Area. Sampling in each of the cells consisted of counting seeds on the surface of the ground in a 20m x 20m area centered in each of the 25m x 25m cells. Buried seeds were sampled by means of a systematic sample of 49 soil cores within each 20m x 20m area. Separate tallies were made for seeds outside and seeds inside of pods. Counts of Peirson’s milk-vetch plants were also made in each of the 20m x 20m surveyed areas; separate tallies were made for seedling and juvenile plants and for adult plants.
No further formal monitoring of Peirson's milk-vetch took place between 2008 and 2013. During this period, the U.S. Fish and Wildlife Service designated critical habitat for the species (in 2008) and BLM was hard at work developing a new management plan, which was finalized in 2013 (Imperial Sand Dunes Record of Decision and Recreation Management Plan). This new plan prescribed monitoring for Peirson's milk-vetch; consequently, a new monitoring program was initiated in 2014 and continued in 2015. Further details of this monitoring program are provided in the pdf file below.
ZIP file of 1998 maps only:
ZIP file of all 24 maps (1.3 megabytes)
Interpreting a Study of Peirson's milk-vetch conducted by Romspert and Burk in 1978 and 1979.
In a study commissioned by BLM in 1978, Alan P. Romspert and Jack H. Burk (1979) looked at, among other things, the demography of Peirson's milk-vetch and other sensitive plants of the Algodones Dunes. Wording in their study has been interpreted by some to mean that only Peirson's milk-vetch plants older than 1 year contribute very much seed to the seedbank. John Willoughby examined the study and concluded that the "older plants" referred to by Romspert and Burk as producing significant quantities of seed were likely plants that germinated in the same growing season but that were 4 months or more old at the time Romspert and Burk began their study in June 1978. A paper detailing Willoughby's findings can be found by cllcking on the link below. Full citations to the studies referenced above are found in the Literature Cited part of the paper.
Interpretation of the observations of Romspert and Burk (1979) on the demography of Peirson's milk-vetch and reconciling them with the findings of Willoughby (2001), Phillips et al. (2001) and Phillips and Kennedy (2002). (PDF file 108 kb)