Research 

My PhD work is focused on trees common in Swiss forests (Abies alba, Acer pseudoplatanus, Fagus sylvatica, and Picea abies) and how differences in heat and drought tolerance between juveniles and adult trees might influence the regeneration of forests as climate change progresses. By better understanding the regeneration niche of species, we may be able to better predict their responses to climate change. 

My dissertation work consists of three parts: the first explores whether there are differences in the number of xylem emboli triggered by a freeze-thaw event for juvenile and adult stems and what anatomical traits might be linked to freeze-thaw embolism vulnerability. The second component contrasts juvenile and adult trees sampled from four sites in Switzerland, comparing them by age class, species, and site in terms of several anatomical and physiological traits related to climate tolerance. These traits include conduit diameter, leaf thickness, vein density, stomatal density, leaf cooling capacity, leaf economic spectrum traits, and the ratio of petiole xylem to leaf area as a measure of hydraulic capacity. The last component is a greenhouse study in which I plan to track changes in the same traits for the same species over the first two years of growth to track when shifts in climatic vulnerability occur, and hopefully find developmental milestones they may be linked to.

Plant species with affinity for harsh substrates often have well-defined edaphic (soil) niches and species that occur on heterogeneous landscapes present an ideal system for exploring questions of niche and community assembly. Vertic clay soils are both chemically and physically challenging to plant establishment and productivity, and annual plant communities associated with these soils of the San Joaquin Desert form a distinctive mosaic pattern of species distribution that reflect differences in soil properties across the landscape. For my Master's thesis work, I conducted fieldwork and a pot study with 12 native annual forb species with an affinity for vertic clay soils to determine whether soils at two sites in the San Joaquin Desert were heterogeneous, whether species differed in their realized and fundamental soil niche, and to examine the competition effects of an invasive annual grass (Bromus rubens) on these species’ edaphic niches. From the field study, I found that the vertic clay soils at both sites are internally heterogeneous and that my study species have different realized edaphic niches. From my pot study, I found that competition from B. rubens reduced biomass for all species, and that the effect of competition differed between soil types. I found that species’ edaphic niche optima shifted when competition is present, and that competitive ability differed across the gradient of edaphic stress in our treatment soils; the combination of competitive pressure and abiotic stress drove differences between the realized niche and fundamental niche for these species. 

Watch my thesis defense here!

Soils high in clay can be an extremely stressful substrate for plant life. Clay soils have a much higher surface-area-to-volume ratio than coarser soils, which can ultimately cause clay soils to "hold" water so tightly than plant roots may be unable to take up water from the soil matrix. Percolation in soil is typically reduced as well, therefore clay soils may become waterlogged as water pools at the surface, creating an alternative form of hydrologic stress. Clay is transported readily in water, and so clay soils are common in basins where they are also often sodic or saline, and will therefore also tend to be more common in arid regions, compounding water stress and introducing chemical stress. Some clay soils high in 2:1 clays like smectite will swell substantially on wetting, and shrink upon drying in a manner that causes cracking and "pedoturbation" over cycles of wetting and drying, thereby causing physical stress that can tear plant roots. We know from other challenging substrates like serpentine that adaptation to such stressors can lead to specialization and if that specialization reduces fitness on lower-stress substrates, species may become endemic to the higher-stress substrate. Given the stressors present in clay soil, and based on our own observations in the field, we were interested in seeing whether clay endemism might also exist. 

We compiled an initial list of vascular plant species with potential association, affinity, or endemism to clay soils based on ecology notes in the Jepson eFlora and the California Rare Plant Inventory, personal field observations, and a comprehensive search of the Consortium of California Herbaria's online database (CCH2) for species with a substantial number of records containing terms indicating clay soils.  We analyzed over 53,000 individual herbarium records for evidence of clay affinity in collectors' voucher notes, and determined what proportion of records with notes indicating soil texture were on clay soils. Following a framework modified from the serpentine affinity rankings of Safford et al., we binned species into categories: clay tolerant, weak affinity, moderate affinity, high affinity, endemic, or strict endemic. 

We found over 40 strict clay endemic species, and many more with substantial affinity to clay soils; A species list with affinity rankings and additional information of ecology, rarity, and special status may be viewed here. 

If you have suggestions for species to add to this list, please do so here!