Tuesday, November 22, 2011

Grazing Through Climate Change

Tarplant in 2007
Today's article in the Santa Cruz Sentinel, Coastal panel staff back Arana Gulch plan, includes the following from the California Coastal Commission (CCC) Staff Report for the upcoming hearing on the Arana Gulch Master Plan:

"The report notes that tarplants in the former dairy site have dropped from 100,000 in the 1980s to 32 this year. The report cites the end of grazing, invasive species and "unmanaged public access" that led to unauthorized trails."



Tarplant numbers were not studied in the 1980s during grazing on Arana Gulch, therefore we have no baseline on which to compare current trends. A contributing factor that has not been studied is change in the timing and amount of precipitation in the area.

Tarplant in 2011
We have just come out of a multi-year drought and we are observing a significant change in precipitation patterns, for example, earlier rains in the fall/early winter season, and extended rains into late spring and early summer, in addition to increased precipitation in our normal winter rainy season. Tarplant numbers at the airport and Tarplant Hill in Watsonville, and in Twin Lakes State Park, have fluctuated in parallel with those of Arana Gulch, yet the other sites have not had large scale grazing that ended in 1989, coincident with declines in tarplant numbers. This would argue that some factor other than cessation of grazing is responsible for the decline in tarplant numbers at all of these sites.

It is more likely that the decline has as much to do with natural local climate variation as with changes in herbivory with the removal of dairy cattle from Arana Gulch.

The recent increase in tarplant individuals suggests that changes in precipitation patterns is a possible contributing factor to tarplant success or decline and would therefore influence the success of the City's plans for industrial scale grazing on Arana Gulch..