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Friday, December 5, 2014

Living in an Annual Grassland - by Dr. Mike White, Conservation Science Director




Well here we go again, the start of another growing season in our grasslands. You see, the plants that are found in the southern San Joaquin Valley grasslands on Tejon Ranch are almost entirely “annual” species, which means they germinate from a seed in the soil, grow to maturity, reproduce (dropping their seeds for future cycles), and die all in the same year. In many parts of the country, including parts of California such as the high Sierra Nevada, vegetation goes dormant in the winter. However, in parts of California with a Mediterranean climate, fall and winter precipitation actually starts this annual growth cycle, and we see green-up of our grasslands with the onset of fall and winter rains (see the images below).

Photos of germinating annual plant species taken November 21 in the White Wolf area of Tejon Ranch. The seedlings in these two photos are primarily forb rather than grass species.

These annual plants include both grasses and the broad-leaved plants called forbs that produce our showy wildflowers. In our San Joaquin grasslands, almost all the native plants we see are forbs (although there are also nonnative forbs), while virtually all the annual grass species that occur here are not native to North America. As discussed in past blogs, in the San Joaquin grasslands on Tejon Ranch native wildflowers (forbs) like lupine, California poppy, popcorn flower, and owl’s clover are a part of the native biodiversity that we are charged with enhancing. These wildflowers are also some of the most popular resources for visitors to the Ranch.


Wildflower displays in the southern San Joaquin can carpet the hillsides. Photo courtesy of Parker Lefton.

Therefore, fall is also the time Tejon Ranch Conservancy staff start speculating on the spring wildflower bloom! We wait anxiously for news of impending El Niño events, which tend to increase the amount of rainfall in the southern part of the state. More rain means more flowers right? Well not always. A very dry year can certainly depress the wildflower bloom, but one of the interesting findings of our grassland research is that the timing and patterns of weather (rainfall and temperature) can affect the abundance of grasses vs. forbs, and thus the wildflower display that that we see in the spring. In years where weather patterns favor grasses over forbs, we may have a lot of annual plant growth but have poor wildflower displays. I’ll discuss these patterns more in a minute, but for purposes of context let’s first revisit the rainfall in the southern San Joaquin Valley since the Conservancy was established in the summer of 2008.

Rainfall totals (inches) for Bakersfield by Water Year (July 1 – June 30)
Water Year
July
Aug
Sept
Oct
Nov
Dec
Jan
Feb
Mar
April
May
June
Total
2008-2009
0
0
T
T
1.06
0.63
0.37
1.71
0.36
0.41
0.35
0.06
4.95
2009-2010
0
0
0.01
0.08
0.1
1.66
1.82
1.77
0.25
1.14
0.27
0
7.10
2010-2011
T
0
0
0.59
0.84
5.82
0.4
0.49
1.67
0.21
0.23
0.08
10.33
2011-2012
T
T
T
0.55
0.76
T
0.44
0.29
1.27
1.62
0
0
4.93
2012-2013
0.02
T
T
0.02
0.1
0.65
0.83
0.6
0.83
0.05
0.05
0
3.15
2013-2014
T
0
T
0.03
0.94
0.1
0.12
0.32
0.36
0.5
0.04
0
2.41
2014-2015
T
T
0.01
0.64
0.01







0.66














Average 1981-2010
0
0.04
0.08
0.3
0.64
1.02
1.16
1.24
1.21
0.52
0.18
0.08
6.47
T = trace amount of rain.
This table shows the monthly and annual rainfall totals for Bakersfield arranged by water year, with the long-term (29-year) averages shown at the bottom of the table. As rainfall in California occurs largely in the fall and winter, a calendar year accounting of rainfall splits our rainy season in two. A water year, running from July 1 to June 30 of the following calendar year, solves this problem and allows more biologically relevant year-to-year comparisons. If we look at the annual totals, we see that of the last six complete water years, two were above average and four were below average. As we all know, three of those drought years occurred back-to-back over the last three consecutive years, with last year being the driest in a long while. For example, over the last three years Bakersfield is 8.92” below average, or to put it another way, has a cumulative deficit of almost a year and a half worth of total rainfall! Pretty dry indeed. However, notice that timing of rainfall varies greatly from year to year. For example our driest year (last year, 2013-2014) had more rain in November than did our wettest year (2010-2011).
OK, back to our grassland research. While the results are complicated and are based on a lot of statistics that I won’t delve into (thanks to Sheri Spiegal for the analysis!), they suggest that early rain, for example during October and November, encourages annual grass growth, whereas when fall months are drier, we see more forbs.  I am simplifying things a lot but the specific weather patterns that we see each year are important determinants of what grassland plants are most abundant and therefore the extent of the wildflower display.  For example, we had good wildflower displays in the spring of 2009 and 2010, but grassy conditions in 2011.
The Old Headquarters area of Tejon Ranch on 4/1/2013.

Old HQ on 4/9/2014.



 
Old HQ on 4/9/2014. The tree in the lower-right of this bottom photo is the furthest right in the above two images.
So what will the spring bloom look like?  The safe answer is “I’m not sure.”  October was pretty wet but November was dry.  As I write this blog, we just had a nice December storm pass through that dropped a bit less than 1/2” of rain in Bakersfield.  Things are greening up quickly on the Ranch, but we are still pretty early in the water year.  However, if I was a betting man, I’d say dust off your cameras and wildflower field guides and hang on for our annual ride!