# Glad we could connect at SERCAL 2025 & GRASS-Net field day! >[!abstract] Contact me **Yamina Pressler, PhD** Assistant Professor of Soil Science and Restoration Ecology Natural Resources Management and Environmental Sciences Cal Poly, San Luis Obispo [email protected] www.yaminapressler.com >[!example] Let's stay connected! > >Join **GRASS-Net email list** to get updates about our climate smart restoration toolbox: https://docs.google.com/forms/d/e/1FAIpQLSdYtx1N6q_XGUpZQC0bKVg0DeiutTQQ89-rwLz0RF6mesWW3w/viewform > >Subscribe to my **Wonder of Soil Newsletter** to learn more about soil: https://buttondown.email/wonderofsoil # Student research posters! **Click the link for a pdf of each poster** [[Giordano-Evans-SERCAL-2025.pdf|Quantifying soil organic matter distribution to inform restoration in California coastal grasslands]] *Presented by Kacie Giordano & Abby Evans at SERCAL* [[CNGA2025_Evans.pdf|Assessing Aggregate Stability Methods to Inform Grassland Restoration]] *Presented by Abby Evans at GRASS-Net Field Day* [[Weinert-SERCAL-2025.pdf|Quantifying soil aggregate stability in climate-smart agriculture practices]] *Presented by Owen Weinert at SERCAL* [[Hoang-Blemker-SERCAL-2025.pdf|Impacts of climate-smart agriculture on soil carbon dynamics in small-scale working lands in San Luis Obispo County]] *Presented by Sophia Hoang & Riley Blemker at SERCAL* [[Eckler-Pezzaglia-SERCAL-2025.pdf|Responses of soil nematode communities to compost addition in small-scale working lands in San Luis Obispo County]] *Presented by Natalie Eckler & Hana Pezzaglia at SERCAL* [[Wildman-Cameron-SERCAL-2025.pdf|Impact of Low Severity Wildfire on Soil Nematode Communities as a Proxy for Prescribed Burns]] *Presented by Nabila Wildman & Cody Cameron at SERCAL* # Notes & references from my SERCAL talk **Building a soil restoration toolbox: accessible approaches for field soil characterization** Yamina Pressler$^1$, Erika Foster$^2$, Emma McLaren$^1$, Abby Evans$^1$, Kacie Giordano$^1$, Mollie Bressler$^1$, Kylee Nielsen$^1$, Anna Buecheler$^1$, Sophia Forstmann$^3$, Cody Cameron$^1$, Nabila Wildman$^1$, Ernesto Chavez-Velasco$^4$, Tonia Brito-Bersi$^4$, Avalon Cook$^2$, Chloe Latt$^2$, Stewart Wilson$^1$, Kerry Byrne$^4$, Robert Griffin-Nolan$^5$, Justin Luong$^4$ $^1$ Cal Poly, San Luis Obispo  $^2$ Point Blue Conservation Science $^3$ Stanford University $^4$ Cal Poly, Humboldt  $^5$ California State University, Chico  >[!abstract] **Abstract** >Soils are foundational to ecological functions, long-term carbon storage, and recovery from disturbance. Restoration efforts often recognize the important role of soils in ecosystem dynamics, but most projects focus on restoring plant communities and wildlife habitat and many opportunities for greater integration of soils knowledge remains. As part of the California Grassland Research, Action, Science, and Stewardship Network (GRASS-Net), we evaluated soil properties in coastal grasslands in San Luis Obispo, Sonoma, and Humboldt counties in an effort to relate site characteristics to plant traits to inform climate-smart restoration recommendations. We compared field soil assessment techniques with in-depth laboratory measurements to evaluate the efficacy of using accessible in-situ soil measurements for making restoration decisions. Field measurements included the slake test for aggregate stability, infiltration, soil texture by feel, soil pH, electrical conductivity, pore size distribution, coarse fragments, and topographical assessment. We found general agreement between in-situ and lab-based measurements for aggregate stability across sites, but fine-scale spatial variation was more difficult to discern in the field. In this talk, we will explore a suite of accessible approaches for field soil characterization that are informative for climate-smart restoration. We will also share findings from our laboratory evaluations to characterize variability both within and across sites. Guided by these efforts, we will make recommendations for applying the field-based techniques in varying contexts to support restoration decision-making. ## Grassland soils are diverse & provide important ecological functions - Variation in climate, parent material, and topography create diverse soil types in grasslands around California - Due to deeply rooted grasses that deposit carbon into the soil via decaying roots and root exudates ("rhizodeposits"), grassland soils have the capacity to store significant amounts of organic carbon both in California and worldwide - In a variable climate, grassland soils may be better able to store carbon on the long-term compared to forest aboveground bimoass (Dass et al 2018; https://iopscience.iop.org/article/10.1088/1748-9326/aacb39/meta) ## We see opportunities for greater integration of soils knowledge into restoration - Soils are the foundation of terrestrial ecological systems, yet soils knowledge isn't always integrated into restoration projects - [Special issue on soil and restoration in 2020](https://onlinelibrary.wiley.com/toc/1526100x/2020/28/S4) highlights that the research practice gap in soil science and ecological restoration is still an important area to work towards closing - We have known of this challenge for a while... - [Young 2005](https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1461-0248.2005.00764.x) indicated need for greater consideration of soils in restoration - [Moorhead 2015](https://doi.org/10.3368/er.33.4.341) argues for greater integration of pedogenesis (study of soil formation) into restoration - [Callaham et al. 2008]([https://doi.org/10.1111/j.1526-100X.2008.00490.x](https://doi.org/10.1111/j.1526-100X.2008.00490.x)) and [Heneghan et al. 2008]([https://doi.org/10.1111/j.1526-100X.2008.00477.x](https://doi.org/10.1111/j.1526-100X.2008.00477.x)) called for greater integration of soil ecological knowledge into restoration practice, arguing that as systems become more complex and interconnected, the utility of soils knowledge increases ## We are studying soil properties to inform grassland restoration across coastal CA To help address the research-practice gap in soil science and ecological restoration in CA grasslands, we are developing [GRASS-Net](https://justinluong.com/menu/grassnet.html) (Grassland Restoration Action Science and Stewardship Network). 3 sites for this project: - Lacks Creek (Humboldt County) - Pepperwood Preserve (Sonoma County) - Rancho Marino (San Luis Obispo County) ## We selected coastal grasslands along a climate gradient Site selection prioritized: - ~1-2 acres within a larger natural area - > 20% native plant cover - Not previously restored - > 3 overlapping species or genera* _*Achillea millefolium_, _Sisyrinchium bellum_, and _Danthonia californica_ expected at all three sites, with many other species overlapping at 2/3 sites ## Objectives 1. Characterize coastal grassland soil properties along a climate gradient (focus of today's talk) 2. Link soil properties to plant traits 3. Build practitioner-scientist network and accessible toolbox for climate-smart restoration ## We measured soil properties in the field and lab Field measurements - Topographic assessment (slope, aspect) - Infiltration - Pore size distribution - Coarse fragments - Slake test for aggregate stability - Soil pH - Electrical conductivity (salinity) - Texture by feel Lab measurements - Bulk density - Soil organic matter (mineral-associated and particulate) C & N - Extractable nutrients - Mineralogy (Fe, Al, Si, Mn, P) - Photo-based aggregate stability - Soil pH - Electrical conductivity (salinity) - Texture by hydrometer This talk will showcase results for soil organic matter (SOM), aggregate stability, and mineralogy variability across grasslands ## We chose soil properties that are key indicators of ecological functions for climate-smart restoration **Aggregate stability** is a measure of the structural integrity of the soil - improves water infiltration and aeration - stabilizes soil and minimizes erosion - facilitates carbon storage **Soil organic matter** is a heterogeneous pool of decaying plant, animal, and microbial matter that is the basis of soil fertility and carbon storage - Soil organic matter is the basis of soil fertility and many critical ecosystem services that soils provide including water storage and habitat for soil biodiversity - Soil scientists define two pools of soil organic matter based on the dominant pathways of formation: - Particulate organic matter (POM) consists predominantly of decaying pieces of plant matter - Mineral-associated organic matter (MAOM) is predominantly microbially-processed organic molecules that interact with mineral surfaces - Cotrufo & Lavallee 2022 provide a review of SOM formation mechanisms (https://doi.org/10.1016/bs.agron.2021.11.002) ## Soil mineralogy controls soil organic matter storage Soil organic matter distribution is controlled by both formation and stabilization mechanisms - Formation is ultimately controlled by inputs from plant and animal matter both above and belowground - Stabilization (i.e. whether or not that organic matter stays in the soil for long periods of time) is based on soil properties - Mineralogy is an important property for soil organic matter stabilization - SOM can be stored on clay particles via cation sorption - SOM can be stored on amorphous oxides via anion sorption - SOM can be stored within organo-metal complexes via chelation - Mineralogy emerges from the weathering of rocks and minerals, and therefore varies between soils with different parent materials and climates - Management typically falls into the formation category by influencing plant community composition (e.g. grazing regimes, restoration plantings) or manipulating direct inputs (e.g. organic amendments such as compost) - Soil carbon has been shown to be correlated with clay % in CA rangelands by [Silver et al. 2010](https://doi.org/10.2111/REM-D-09-00106.1) - In collaboration with Dr. Stewart Wilson at Cal Poly, SLO, colleagues at Point Blue Conservation Science conducted a regional assessment of drivers of soil carbon in rangelands across Northern California and found that mineralogy (pedogenic minerals, organometal complexes and extractable cations) explained up to 90% of variability in a random forest model. This suggests strong relationships between soil organic matter and mineralogy that we are continuing to explore in subsequent studies in coastal CA grasslands. (Wilson et al., in revision) - In another study from our group of San Luis Obispo Ranches, we also found that mineralogy explained significant variation in SOM distribution across ranches with different grazing regimes. Learn more here: [[Understanding plant-soil linkages to restore California rangelands]] ## Aggregate stability lab method captures more variability within a site - We measured aggregate stability using two different methods - Field-based slake test - Lab-based photo method - While both methods were able to differentiate the three sites, only the lab-based method captured variation within a site - For practitioners who want to either monitor aggregate stability over time use aggregate stability to inform site selection, a photo-based method with replication may be better suited - The Soil Health Institute has developed the [Slakes App](https://soilhealthinstitute.org/our-work/initiatives/slakes/) to help facilitate this - For a quicker estimate of aggregate stability between sites, the field-based method may be a good choice >[!info] Check out Abby Evan's poster for more here: [[CNGA2025_Evans.pdf]] ## Soil organic matter varies with depth and site - Soil organic matter varied predictably by depth at the two southern sites (Rancho Marino in SLO County, Pepperwood Preserve in Sonoma County) - Highest concentration of soil carbon at surface, near plant inputs, decreasing with depth - However, particulate organic matter (fragmented plant litter) decreased more dramatically with depth, whereas mineral-associated organic matter had a more consistent decrease. - The two sites also differed in the amount of carbon stored, with higher concentrations at Rancho Marino overall >[!info] Check out Kacie Giordano & Abby Evan's poster for more: [[Giordano-Evans-SERCAL-2025.pdf]] ## Soil mineralogy varies between sites based on weathering intensity - We expected the differences in soil organic matter to align with variation in mineralogy between the sites - Early results indicate that the mineral components differed greatly between the sites and may explain cross-site differences in other soil properties - Poorly crystalline iron (amorphous iron) and organo-mineral iron were both much higher at wettest site (Lack's Creek in Humboldt County) - These soils are more highly weathered due to the climate ## Next, we will link plant traits to soil properties to inform restoration toolbox - As part of [GRASS-Net](https://justinluong.com/menu/grassnet.html), we are working on linking variation in aggregate stability, soil organic matter, and mineralogy with key plant traits relevant for climate-smart restoration in coastal CA grasslands - Aboveground traits include plant height, specific leaf area, leaf dry matter content, leaf nitrogen content, leaf C:N ratio, maximum photosynthetic rate, leaf osmotic potential at full turgor pressure, lethal drought index (LD50), leaf senescence at LD 50, leaf water content at LD50, stomatal closure - Belowground traits include specific root length, root:shoot ratio, root diameter, root dry matter content >[!tip] Toolbox coming soon! >We are working on developing accessible protocols for practitioners looking to integrate soils knowledge into grassland restoration in CA. > >Join **GRASS-Net email list** to get updates about our climate-smart restoration toolbox: [https://docs.google.com/forms/d/e/1FAIpQLSdYtx1N6q_XGUpZQC0bKVg0DeiutTQQ89-rwLz0RF6mesWW3w/viewform](https://docs.google.com/forms/d/e/1FAIpQLSdYtx1N6q_XGUpZQC0bKVg0DeiutTQQ89-rwLz0RF6mesWW3w/viewform) # Thank you to our funders and partners! Project partners: - Point Blue Conservation Science - Rancho Marino Reserve - Pepperwood Funding provided by: - University of California Office of the President Climate Action Grant - California State University Agricultural Research Institute >[!abstract] Learn more about GRASS-Net > >GRASS-Net envisions successful grassland restoration projects that take best practices into consideration, that are cost effective, prepared for the erratic drought regimes of the climate crisis, and promote regionally diverse and culturally significant species. We aim to bring together restoration practitioners across the state to share knowledge and minimize biotic homogenization in restored areas. Biologically diverse California (CA) range and grasslands are an increasingly crucial solution to carbon capture and climate change mitigation opportunities. California’s grasslands are biodiversity hotspots and globally unique, but climate change will make it unsuitable for endemic species; so innovative restoration must focus on climate resilience for a diverse suite of species. > >**If you would like to receive updates from GRASS-Net, please sign up for our email list here:** https://docs.google.com/forms/d/e/1FAIpQLSdYtx1N6q_XGUpZQC0bKVg0DeiutTQQ89-rwLz0RF6mesWW3w/viewform