The more we know about aspen in California, the better we can restore degraded or lost aspen stands. The restoration of aspen stands has a cascade effect benefiting species such as birds through an increase in their habitat, and beavers as a food source. To this end, this spring SYRCL staff worked with UC Berkeley and the Institute of Bird Populations on a novel research project: Aspen Seed Collection in California. The objective of this research project was to:  

• identify and monitor flowering aspen trees for seed development 
• collect seeds for germination and nursery-rearing 
• conduct genetic analyses using leaf tissue samples.  

This project had many volunteer community scientists, known as Aspen Ambassadors. The Aspen Ambassadors submitted observations on the phenology (the biological life cycles) of the aspen and collected seeds. The research lab at UC Berkeley then germinated those seeds and are now growing them in their nursery.  

Success in finding flowering aspen during this project was much higher than expected. After the incredibly successful seed collection, we are now looking forward to results from genetic analysis of the seedling rearing in the UC Berkeley nursery. 

Scouting for Aspen  

In December 2025 and January 2026, the project team started at step 1: find the aspen and determine which trees were flowering. As highways and back roads opened and snow retreated, we searched for aspen flower buds, mapping them for future visits when seeds could be collected.  

Aspen Flowers 

Aspen flowers are catkins, elongated tassels with small simple flowers attached. Since aspen are separated sexed (meaning there are male, female, and the rare intersex), the team first identified the males and the females. Once identified, we monitored females carefully as seeds were fertilized and matured. As the seeds developed, the green catkins became harder to spot in the trees as the verdant foliage emerged and camouflaged the catkins.  

In a short window of time, the catkins began to release small, bright, and fluffy seeds. The research team rushed to collect the catkins before they fell to the ground. Once gathered, the seed samples were shipped to the lab at Berkeley for germination in their nursery.  

Aspen Seedlings and the Potential for Restoration  

As the aspen seeds germinate and grow, we can reflect on what has been achieved already. The collection of genetic stock from aspen specific to California is a huge step for aspen restoration. Aspen saplings available to purchase from high-elevation nurseries often come from the Intermountain West and are not necessarily genetically similar to the aspen in California. When planting any native plant in a restoration project, a key focus is locally adapted seed sources.  

Through the collection of seeds from across California, this project can provide a framework for how to replant aspen, as we can better understand how related aspen are across the state and use that knowledge to plant trees that are adapted to the site. California seedling stock allows local restoration projects to utilize trees that have the genetic tools to survive and thrive.  

As we investigate more about aspen and their restoration potential, we have identified gaps in aspen restoration and regeneration. Stands, which may have once been continuous from meadows with fingers running up creeks to the next meadow, are now broken into pieces, separated from their clones and isolated, quickly becoming hidden by encroaching conifers. By using aspen seedlings in our projects, we can connect these networks and rapidly accelerate aspen restoration, increasing the pace and scale of the work.  

Volunteers help with this project 

This project would not have been possible without the countless hours of dedicated community scientists. They allowed us to have thousands of eyes on aspen throughout the state by downloading the Survey123 app and submitting a form and a photo. These observations were incredibly important as they tracked the stages of flowering aspen, allowing the research team to know what stage the aspen flowers were at. Some volunteers even collected aspen seeds and mailed them to UC Berkeley following their protocol!  

What’s next?  

More research! While genetic stock was collected and seeds are in the process of germination, a single snapshot of one year is not enough. The research team and partners are applying for more funding. If received, we will be asking for volunteers to help with observations and collections again!  

Check out the UC Berkeley Macrosystems Ecology Laboratory page to learn more about the project!  

Collaborators:  

Funded by the BLM: