The Ephedra regional gradient experiment is up and running for round 2. In summary from our work last year, we have seven sites spanning a regional gradient of continentality, starting in Panoche Hills and ending in Tecopa/Sheephole Valley. The addition of Cuyama was great as it gave us intermediary representative that is west of the Mojave, other than Panoche Hills. At each of these sites there are 30 shrub-open pairs, totalling 420 independent plots.
At each of those plots I had a split-plot for three separate plant species (Salvia columbariae, Plantago insularis and Phacelia tanacetifolia). Each split plot was about 20 cm long and 10 cm wide. I chose these species because they represent different families and traits, but more importantly because of their regional distribution. Salvia is more eastern Mojave, Phacelia more Central valley and Plantago equally distributed. Each plot was randomized per species and 0.3 grams of each species (~30 seeds) was sowed with a light dusting of sand put on top. In total, approximately 40,000 seeds were planted.
Our experiment spans a gradient of increasing heat and decreasing precipitation. I like how it is set up because it has two sub-gradients contained within. There is the latitudinal gradient with increasing distance from ocean that generally correlates with precipitation, but also a longitudinal gradient among Tecopa, Hwy40 and Sheephole that correlates with temperature. This should be an interesting test to compare as well to see if which of the two are driving the facilitation effect as well as the overall gradient. To supplement the global datasets determining the gradient, 6 HOBO ProV2 loggers were placed at 3 shrub-open pairs at each site. These loggers will measure hourly for the entire duration of the field season to validate the gradient and compare the microclimate effects between shrub-open.
From our discussions, we are also interested in the nutrient angle. There is enough evidence now, and some great new work coming out of the Armas lab, that shrubs mechanistically alter the nutrient content within understorey canopy favouring plant growth. We are interested in seeing if along this regional gradient, nutrient content changes as well as abiotic stress amelioration. At half of the pair plots at each site I added nutrients to supplement the ground content. I predict, that the nutrient addition will have a more pronounced effect in the most extreme sites, were nutrient availability is low. We discussed conducting nutrient analysis of the soil that I believe are we still intending to do. I also put out different cellulose types (bamboo skewers and filter paper) to measure decomposition rate at these sites.
From a discussion with Ben Evans, and Mike Westphal, I think we are committing to genetically analyzing the facilitator, Ephedra californica. There has been work (Valiente-Banuet, Verdu, etc) that tests how shrubs favour genetic diversity by increasing competition between conspecifics. However, there is little work testing how the genetics of the benefactor relates to the ability to facilitate (quite a different question). Unfortunately, there is a little work on Ephedra in general and none I can find into the genome (other than a distance Old World species). I think a more simplistic genetic approach, potentially using barcoding, would be ideal. Of our seven Ephedra populations, we identify the genetic relatedness and how that effectively maps onto the facilitation effect of the shrub. I haven’t taking the samples of Ephedra yet, but it is something I will look into for my next trip to California.
This year is an El Nino year and it is expected California will get a lot of rain. Unfortunately, an El Nino year increases the probability of rain, but there are never any guarantees. This means that our extremely strong El Nino event could still result in a drought year. At the sites I went to, there was no emergence. Some area of the Mojave have seen rainfall/emergence, but I think we have successfully time our planting prior to the “big” rains. Panoche Hills the day I was leaving had a 90% probability of rain, the highest I have seen it for almost 6 months. Conclusion? If California gets its expected heavy precipitation, then our seeds should take and our phytometer in full swing. The other side to this coin is that some areas may see too much rain. For instance, hwy 58 and Death Valley had some extremely heavy rainfalls that lead to some significant damages (http://bit.ly/1Q40MHQ). It is a good thing then we have 7 sites because a dramatic rain event might erase one of them.