Ephedra regional gradient
My biggest project examines positive interactions along a regional gradient of continentality. The immediate question though is what is continentality? What abiotic and biotic variables change along this gradient in addition to plant-plant interactions. When we initially constructed this gradient the two main considerations were aridity and cold stress. For plants in the Deserts of California these are two very important considerations. After two years of conducting this experiment, I had very different climate profiles during the seasons. The most striking was the differences in my plant phytometers between the two seasons. In 2015-2016 growing season, the majority of my plants were present in the San Joaquin Desert. This desert is generally colder and wetter than the more continental Mojave Desert to the east. However, in the 2016-2017 the San Joaquin Desert sites had few plants of my chosen phytometer relative to the abundant Mojave Desert sites. All my plants were present at all my sites at some point, suggesting that this gradient shifts with inter-annual variability. Let’s take a look at what some of that looks like:
San Joaquin Desert year
The 2015-2016 shown in black had similar temperatures on average relative to the 2016-2017 growing season (in grey). The precipitation patterns though were different between years. These sites form a parabola with distances from the ocean. Sites closest to the ocean and most inland have the highest precipitation, while sites in the middle are the least. Overall the 2016-2017 season saw significantly more rainfall. Sites in the 2015-2016 season were extremely arid. For instance, Barstow and my site along Hwy40 saw as little as 30 mm of rainfall. The low abundance of my phytometer in the Mojave sites for that season is therefore likely because of low rainfall amounts. However, the San Joaquin sites has similar rainfall between years so then why so few plants in the 2016-2017. I believe this has to do with the cold stress factor:
Precipitation in mm (black) and temperature in C° (red) during the 2015-2016 growing season for the San Joaquin desert (top) and Mojave Desert (bottom).
Precipitation in mm (black) and temperature in C° (red) during the 2016-2017 growing season for the San Joaquin desert (top) and Mojave Desert (bottom).
Mojave Desert year
Both of these seasons had similar precipitation and temperature patterns. The patterns were also similar between the two deserts, but the noticeable difference that I believe contributed to low plant abundance in the San Joaquin in 2016-2017 is temperature. The year before had warmer temperatures from January onward, which is a key period for plant development. In January 2017 following the majority of rainfall there was a long freeze period of approximately 5 days, followed by another cold period with freezing temperatures end of February. This pattern was much warmer in 2016 and is why I believe cold stress negatively affected plants in San Joaquin Desert for 2017. On the other hand, the Mojave saw significantly ore precipitation and cooler temperatures that all contributed to greater plant abundance.
Slicing through this climate data was interesting and challenging because of all the different ways to summarize variables. Using season means collapses a significant amount of the information and can make conclusions more difficult to derive. I am primed and excited now to dig into the plant responses!
The growing season of 2015-2016 has come and gone with disappointing results from the supposed El Niño year. The 2016-2017 season is approaching and a few had feared that it would just continue the current pattern of drought. I was especially fearful having battling drought four years in a row in my study of plant interactions. It would be nice to have a chance with at least “average” precipitation amounts. Half way through the rain season and this year looks promising. Areas of California have been seeing some pretty significant precipitation including some potential floods. While this is great news in terms of drought relief for coastal cities and the Sierra Nevada snow pack, I wonder what the consequences will be for the deserts? In particular, the Mojave always seems to be in the unluckiest of rain shadows, missing most of the precipitation that the rest of the state experiences. I took a snap shot of the rainfall and average temperatures since seeding at the end of October. Here are the results:
The right combination of rain, temperature, and timing are absolutely crucial in desert ecosystems in regards to how the plant composition will respond. In an older paper by Beatley (1974) is a description of how these three variables determine plant composition. From this and my own experience, the absolute minimum rain to see any annual vegetation on the ground is 2.5 cm. However, these plants usually die within a month if there is no subsequent rain. I have seen this occur in multiple years where Halloween rain is not followed by any other precipitation until mid-January. The result? Many dead plants, and a new representation for plant communities. The Mojave has seen enough rain to begin germination and this rain has all occurred within the last 3 weeks. This, plus continued cold temperatures, should encourage the persistence of annuals for at least another month. If at least one other major rain storm passes through in that time I would expect to see these plants make it to flowering. On the more westerly side of the state, my sites have been seeing fairly consistent rain. This is great news for my Panoche Hills site that likely has passed its precipitation threshold that guarantees emerged plants to flowering.
Fingers crossed as always!
Several weeks ago I completed my first progress report for my MSc program. This involved a giving a short presentation (slides above) followed by a question/discussion period. My thesis focuses on pollination facilitation – non-competitive pollinator sharing between plant species that improves the reproductive success of at least one of the participants. I will be investigating these interactions in the Mojave Desert, a biodiversity hotspot supporting 659 species of bees and 1680 annual plants.
Why spatial? The study of ecology is normally separated into hierarchies, however, we know that these different levels are integrated and interact despite studying them in isolation. All interactions take place in space, and so explicitly including spatial dimensions to a study can be a way of connecting these levels, leading to a deeper understanding of the observed interactions.
It can be a little intimidating to stand in front of your committee and tell them your ideas, but they are there to support you. I received some great feedback which I am using retool my experimental design in preparation of the upcoming field season. Advice: Be careful about your clipart choices! I used a picture of queen honeybee (they don’t pollinate!!) in an interaction diagram explaining pollination facilitation. This isn’t as bad as the infamous biology textbook “Bees of the World” showing a pollinating fly on the cover, but it was noticed right away.
ESA 101 at Fort Lauderdale is coming up! I will be presenting on recent findings from an experiment we conducted over two years. I am extremely excited for both the presentation and the results! Here is the slide deck, statistical analyses and program outline.
The stress gradient hypothesis original purposed the frequency of plant interactions along countervailing gradients of abiotic stress and consumer pressure. However, research to date has studied these two stressors in isolation rather than together, thereby potentially neglecting the interaction of these factors on plant composition. In the arid central valley of California, we artificially manipulated a soil moisture gradient and erected animal exclosures to examine the interactions between dominant shrubs and the subordinate annual community. We conducted this experiment in an extreme drought year (2014) and a year of above-average rainfall (2016).
Shrubs positive affected the abundance and biomass of the annual community at all levels of soil moisture and consumer pressure. In the drought year, shrub facilitation and water addition produced similar positive effect sizes on plant communities; however, the shrub facilitation effect was significantly greater in watered plots. During the year with higher rainfall, there was no observed water or exclosure effect, but shrubs still significantly increased biomass of the subordinate plants. Shrubs and positive interactions maintain productivity of annual plant communities at environmental extremes despite reductions in droughts stress or consumer pressure and these positive effects are even more pronounced with water addition. The relationship between consumer pressure and abiotic stress on plant interactions is non-linear particularly since shrubs can facilitate understorey plants through a series of different mechanisms.
As the plant field season comes to a close, the lizard field season kicks off. Here are some picture highlights.
Phacelia tanacetifolia glistening in the sun at Carrizo plain – cred to ARL
Eschscholzia californica in Cuyama Valley
Rocking my favourite phytometer species: Salvia columbariae
The hemi-parasitic Castilleja exserta, surrounded by Lasthenia
An excellent post from near (and at one) of the sites within the San Joaquin Desert gradient that Alex and others study was written by the director of the Tejon Ranch. The Cuyama Valley where I have been leading some field research on the capacity for foundation plant species to buffer global change is about in the middle of the extended gradient we work on from Panoche Hills Ecological Reserve to the Mojave.
The phenology was incredibly variable from site to site within the Cuyama Valley. We did not pick up an elevation or aspect signal to explain the variation from emergent and established plants to individuals nearing senescence. Apparently, prolonged drought and very sporadic rains even for desert ecosystems have introduced considerable micro-environmental variation.
Whilst in other spots, within just a few miles, same species, similar micro-environmental strata, we had these glorious showings!
Over at Carrizo National Monument, there were similar sets of patterns from full flower to early senescence.
Hitting the field again tomorrow. Likely at least two weeks early from ‘regular’ desert seasons. A bit of rain and high temperatures has apparently lead to massive ‘all-chips-in’ for the native annuals that have been holding on for 5+ years of drought.
The very likely consequence is a mismatch with the pollinators within the region that are NOT up and busy yet.
Leap year indeed.
Photos by Brent Johnson on Feb 27th, 2016.
Super excited. Watch out small desert creatures, you are on candid camera(s).
In this study we surveyed 3 deserts along the extension of the Atacama Desert: Atiquipa (15.7 S), Romeral (29.5 S) and Fray Jorge (30.5 S) over 3 years. Within each desert we sampled 5 sites, each separated at lest 2 km from each other. This allowed us to sample extensively the effects of dominant plants (shrubs) on plant communities within these deserts.
Results, as can be seen in the figures above, indicate that at extreme aridity conditions such as in Romeral and especially Fray Jorge (the most arid sites), dominant plants have a negative effect on both richness and abundance of arid plant communities. Surprisingly at Atiquipa, the strongest positive effects occurred during the driest year of the 3 years surveyed.
Its 2016 whoa!
I enjoyed a solid break at the end of December but am looking forward to getting back into the grind. There are some crucial things I would like to tackle before my progress reports:
- RDM paper – I have finalized the statistics and need to get back to the writing. I am reading the literature to get a better idea on how to properly structure an animal distributions paper. Something I’m not accustom to.
- Field work – Gradient – I’m very excited for this experiment. It is been raining in California so am hoping for some heavy germination. The rain patterns have somewhat followed my gradient pattern as well with my more coastal sites seeing higher precipitation. About time the rain came
- Field work – Exclosures – I am reconducting my exclosure experiment and building 60 new plots. Recreating the experiment I did two years ago in the worse drought, now in heavy rains will be the perfect contrast. It shall be interesting to see which way the trends flip
- Other stuff? – There is a lot but two primary ones I need to get done is finalize the Ecography paper before the due date and come up with a workflow for the facilitation ecologists who want to write a synthesis paper.
Overall, please with the way my winter is shaping up. Cali is a lot colder than it has been in the past, but lots of rain makes for a happy ecologist! I am also going to try to shoot a video short during my time in the field. Stay tuned for all the gory details!