PMV Update: The Dry Winter Takes Its Toll
Dr. Art Phillips, ASA Botanist
ASA-sponsored Peirson's Milkvetch (PMV) studies for the 2006-07 season continued in early March with a study trip to the dunes March 4th through 6th when Deb Kennedy, Daniela Roth, and I visited our 25 study sites to examine the effects of the dry winter on the plant. Our December survey had shown that a late-October storm dropped enough rain to cause germination of over 10,000 PMV seedlings. Most of these were in the Gordon's Well area. One site at Glamis had about 2,000, and there were none at Buttercup. In December they were already looking stressed after two months of dry weather, so we were not too optimistic about their well-being in March after the drought continued through the winter.

Our expectations were confirmed. The March survey showed that only 23% of the seedlings counted in December had survived the winter. Many of these appeared severely stressed. Only 50 of the October 2006 seedlings were flowering in March 2007. This was in contrast to the 2004-05 season when over 60% of the plants that germinated in October were flowering in March. Well-timed rainfall is essential for germination, survival, flowering, and ultimately seed production.

Although we had scheduled additional seed bank studies in March, we rethought that plan when we realized that the dry winter with minimal germination would have little effect on the numbers of dormant seeds we documented a year ago. Our seed bank studies in 2002 and 2006 showed that millions of dormant seeds wait in the sand for the next good rainfall season, whenever that may be.

We'll return for a quick trip in mid-April to get a final count of how many of the October 2006 seedlings have survived to flower. This will also provide a baseline number of plants for survival counts in December 2007.

Only 19 of the 30 surviving perennials we found at our sites in December were still alive in March.

These are the last survivors from the hundreds of thousands that dotted the dunes two years ago. By next fall it is likely that PMV's of any age will be scarce.

I thank the duning community for stepping up to help when needed, allowing us to continue learning about the life history of this fascinating dune dweller. These studies would not have been possible without the generous help of dunes enthusiasts