A Patch-based Survey of Ground Cover Impact on Surface Soil Properties

78% of residential land in Los Angelesis zoned for single-family housing, representing the single largest land use category. The aim of the study is to understand the effect of ground cover on soil physical, chemical and hydrological characteristics withinsingle-family residential properties, and to understand homeowners motivations behind choosing one form of ground cover over another. This is the starting point towardsdeveloping better socio-ecological approaches for improving soil development. As ground cover is often the choice of the homeowner, this is anactionable opportunity area to improve soil properties across Los Angeles County,leading to improved stormwater capture, increased resilience, reduced extreme heat, and other benefits.

A Pit-based Characterization of Urban Soil on LA Residential Properties

A complement to the patch-based approach of the Residential Landscape Diversity Study for characterizing the impact of ground cover on soil development within the first five inches, the Dynamic Urban Soil Properties Study takes on a pit-based approach to this process. The goal is to provide additional context by understanding the soil depth at which ground cover impacts “trail off” and native soil qualities “take over”. Given that soil development processes are gradual, this important knowledge allows us to interpret the impact of ground cover changes over time, which requires knowing the depth and extend of the modified zone.

This collaborative study was an opportunity for the special projects team at USDA-NRCS to improve their soil survey and particularly for the Hueneme series, more commonly found in the southern portion of Los Angeles County.

Describing the Value of Trees and other Plants on LA Residential Properties

Managed by the USDA, this environmental justice-focused study seeks to understand if trees and biodiversity are improving the well-being of residents in the Los Angeles area. The information from this research may assist partners in foregrounding equity and environmental justice when identifying, locating, and implementing future tree planting projects.

We understand trees to be an integral part of any healthy urban ecosystem, however many Angelenos view trees as a nuisance for various reasons. This study serves two main two main goals within the Climate Gardening context: To better understand the relationship that residents have with their trees, and to develop better outreach around trees.

This study investigates how soil is distributed at fine spatial scales across Los Angeles County to examine the potential to for nature-based solutions to be realized equitably. Written by Adam Berland (Ball State University), Dustin Herrmann (TreePeople), Dexter Locke (USFS), and Kirsten Schwarz (UCLA) the significant findings of this study were accepted into the Journal of Landscape & Urban Planning (vol. 260).

TreePeople environmental educators worked with Los Angeles County students to explore the role of soils, trees, and learning gardens in contributing to climate resilience in their own schoolyards. TreePeople’s education team developed an original curriculum to contextualize and engage students in the nature-based transformations on their campuses through our school greening program. Students engage in a three lesson arc, tailored to their grade level (Pre K - K, Grades 1-2, Grades 3-5, Middle School) that guides them through the process of scientific inquiry.

This SCWP-funded research study will provide field-validated design guidance for mitigating and restoring hydraulic properties of urban soil systems. Our goal is to optimize pre-disturbance ecosystem function by designing a robust and quantifiable nature-based solution strategy for building climate resilience in the Lower Los Angeles River Watershed (LLARW).

Specific objectives of this project are to:

1. Identify soil properties and model soil modifications that maximize plant-available water and minimize urban stormwater runoff;

2. Simulate the regional effects of the watershed-level mitigation strategies developed in objective 1; and

3. Develop field-validated, model-derived, feasible, and fully specified landscape designs that can be adopted into practice by emphasizing native species and supportive ecosystems that mimic and sustain pre-disturbance soil hydrologic functioning.

TreePeople, Studio MLA and Craftwater partnered with LAUSD to investigate how school campus greening can support communities with more than cooling shade. This Safe Clean Water Program Scientific Study assesses how stormwater capture and treatment infrastructure can be designed to integrate seamlessly with greener, nature-based schoolyard features to improve regional resilience to drought and increase groundwater stores. Modeling from this study suggests that stormwater infrastructure integrated across campuses in the District could potentially capture and manage almost 20 Billion gallons of stormwater and remove up to 15,000 pounds of zinc annually - enough water to support the needs of over 700,000 Angelenos every year. Untapped Potential - Leveraging Schoolyards for Stormwater Management and Climate Resilience makes the case for school districts as major contributors to stormwater targets in Los Angeles County and outlines exactly how school districts can leverage this potential through the Safe Clean Water Program while advancing the target of high performance schools.

TreePeople is working with partners at UCLA, Center for Applied Ecological Remediation, Physicians for Social Responsibility, Laboratory for Indigenous Knowledge Systems, Communities for a Better Environment, and Watts Labor Action Committee (working group collectively known as the Social Impact Collaborative) to scale and implement a set of strategies to address our co-produced soil priorities:

1. a community soil testing program and synergistic soil curriculum,

2. a novel remediation program that includes residential soil banking with co-located composting hubs, and community-engaged bioremediation on high-priority sites, and

3. policy analysis to advance urban soil systems in LA and serve as a nationwide model. The long-term goals of this work are to improve equitable access to healthy soils and services that support climate-resilient futures, co-power partners to adopt evidence-based soil strategies, and train the future generation of scientists in community-engaged co-produced science.

TreePeople is a member of the Gateway Cities Regional Climate Collaborative (GCRCC) alongside the Gateway Cities Council of Governments, the Southeast Los Angeles Collaborative, Grid Alternatives, and AltaMed. These partners have worked on multiple joint projects designed to help increase the health, wealth, and sustainability of the Southeast Los Angeles region’s individuals, families, and neighborhoods. The establishment of the GCRCC was supported through the California Strategic Growth Council’s (SGC) Regional Climate Collaboratives (RCC) Program, a capacity-building grant that enables cross-sectoral partners to deepen relationships and strengthen local coordination, leadership, knowledge, skills, and access to critical resources to drive and sustain climate action. TreePeople's role is to support the improvement of environmental health and climate resilience through nature-based solutions.

TreePeople serves as the Los Angeles Region's Community Engagement Lead Author for the 5th California Climate Assessment (5CCA). The 5CCA, which is led by the Governor's Office of Land Use and Climate Innovation (LCI), aims to compile the best available science on climate change and other informational resources at a local scale to help communities understand and develop informed responses to the impacts of climate change in their region. In addition to assembling and working closely with the Community Advisory Board, TreePeople is developing a Community Engagement Report that highlights community climate priorities in the Los Angeles Region. TreePeople presented preliminary findings on priorities alongside LCI at the Association of Environmental Professionals in April 2025.

The Next Gen Bioretention study was funded by the Safe, Clean Water program for a total award of $1.38m to assess the effectiveness of existing bioretention systems and create new design specifications for the Upper and Lower San Gabriel watersheds, and the Rio Hondo watershed. There is currently very little existing performance data for bioretention systems. We suspect that many bioretention systems have failed for a number of potential reasons. Furthermore, there is a great deal of variability within bioretention system design between County-built systems and privately-designed systems. We want to understand which ones work better, and why. Then we want to design new, customized specifications that would improve future systems design.

Objectives are to:

1. Evaluate 15 systems per watershed across 3 tiers of comprehensive testing to produce catalog of bioretention system performance in Upper and Lower San Gabriel and Rio Hondo Watershed,

2. Create site-level hydrological models that incorporate developmental ecological processes to understand system function over time. This will aid in designing new parameters for adaptive climate conditions,

3. Use findings from study to develop a design framework that outlines specification requirements for regional designs and retrofits that exceed current performance benchmarks,

4. Develop stewardship plans aimed at reducing operation and maintenance costs by better incorporating bioretention systems to be utilized as public space within communities