Vegetation Conditions: Data from the Water Agreement baseline period through 2006

During summer 2006, ICWD research assistants re-inventoried vegetation in 105 parcels. Most of these parcels were monitored as part of the Technical Group’s agreement to carry out the protocol outlined in Box 1.C.1.a.ii, p. 22 of the Green Book. The re-inventory program was initiated by the Inyo/LADWP Technical Group in 1991 and has persisted every summer since that time. Some of the parcels re-inventoried in 2006 were classified as Type E (supplied with surface water by LADWP). Here, some of the data are presented to allow a view of perennial cover trends over time.

Methods

The list of parcels for re-inventory has grown and changed somewhat over time. The following guidelines have been used to assist in parcel selection: parcel contains a permanent monitoring site; actual baseline transect data exist for the parcel; parcel location allowed sampling over a wide geographic area; parcel was classified as a phreatophytic plant community, preferably in management category type B or C; parcel size is relatively small and thus more likely to contain relatively homogeneous vegetation; and parcel was free from known major confounding factors such as regular irrigation or land surface alterations. Few parcels meet all the above criteria; for example, several re-inventoried parcels containing permanent monitoring sites have no available baseline transect data, are large and heterogeneous, and were classified as management category Type A. Some parcels re-inventoried in early years of the program have been moved to a low priority because they do not meet many of the above guidelines. In 2006, a few new parcels were added to assess conditions near other monitored parcels.

Parcels are re-inventoried using the line point transect technique. Multiple transects are measured to obtain a sample of vegetation conditions within each parcel. Transect start points and compass bearings (the direction of the transect from the start point) are randomly generated in the office using computer software. In the field, researchers locate start points using GPS, then set up a temporary 50m transect using a measuring tape and portable end posts. At 50cm intervals, beginning at 50cm, researchers visually identify and record the top layer of live plant material. The number of transects per parcel varies; in 2006 it varied from 14 to 36. An original goal for determining number of transects was to reduce cover variance to manageable levels; however, it quickly became apparent that the LADWP-mapped parcels were generally very heterogeneous, at least in terms of cover. The number of transects per parcel is somewhat scaled to the size of the parcel. Ultimately, the number of transects assigned per parcel is an estimated balance between the time required to gather the data and the anticipated information gained.

In the office, total hits on plants are tallied. Transect results from the baseline period (1984-87) and all years in which parcels were re-inventoried are summarized in terms of average cover of all perennial species combined.

Results

Table 1 below, lists all parcels re-inventoried in 2006, and includes plant community designation, Water Agreement vegetation type, and an indication of whether the parcel is located in a wellfield area that was affected by groundwater pumping during the late 1980s. Plant communities are: 35400 = Rabbitbrush Scrub; 36120 = Desert Sink; 36130 = Greasewood Scrub; 36150 = Nevada Saltbush Scrub; 45310 = Alkali Meadow; 45330 = Rush/Sedge Meadow; 45340 = Rabbitbrush Meadow; and 45350 = Nevada Saltbush Meadow. Water Agreement vegetation types are A, B, C, and E. For parcels re-inventoried in 2006, 60 parcels were determined to be located in Wellfield areas according to data analysis performed several years ago, 30 were determined to be Control parcels, and no determination was made for 11 newly added parcels or the 4 Type E parcels. Control parcels are located in areas that are not affected or minimally affected by pumping, whereas wellfield parcels are affected by LADWP pumping.

Data in Table 1 show the LADWP baseline estimate of perennial cover as well as average parcel perennial cover as determined by the re-inventory random sampling.

Parcels re-inventoried in 2006 according to the Green Book methodology are accessed by selecting one of the wellfields in the map above, then click on a parcel to view it's graph.  Each graph shows the parcel's perennial cover as determined by the re-inventory random sampling (top graph); total plant cover as determined by interpretation of Landsat satellite data for the entire parcel, 1986-2005 (middle graph); and estimated average parcel depth to water table as estimated by interpolation of water levels in shallow monitoring wells.