Mast Year Seed Collection

This September was incredibly busy with seed collection because 2024 proved to be a mast year for sugar pines and most conifers in the Tahoe region. This is significant because reforestation starts with collecting seed.

A “mast year” is when an entire population of a certain tree or shrub produces a large amount of fruit, seeds, or nuts, which are collectively referred to as mast. (The term "mast" comes from the Old English word mæst, which refers to the nuts of forest trees that accumulate on the ground.)

Mast years occur at irregular intervals every few years – and the timing is different for different species. Sugar pines, which take two years to produce fully mature cones, may mast every 2-7 years.

The exact reasons why trees mast are still a mystery to scientists, but factors that may play a key role include temperature, rainfall, and predation. In the Sierra Nevada, water is the most limiting factor for most plants and trees. To produce a healthy cone crop, trees need the right combination of moisture and temperature in the spring. The big snow year of 2022-3 along with last year’s wet summer may be the main reason behind many species experiencing a mast year in 2024.

While no one can really say why this year was a mast year, we didn’t have time to scratch our heads about it. We had to hustle to collect as much seed as possible because the early cold snap in August seemed to trigger sugar pine cones to open (or “flare”) earlier than we’ve ever seen before. Sugar pine cones look like long, sticky, green torpedoes towards the end of summer. Inside the green cones is the ripening seed.

Mid-September is usually when the Sugar Pine Foundation climbs known Major Gene Resistant (MGR) trees that can survive white pine blister rust and collects the cones while still green yet full of ripe seed. We must get the green cones before they flare and drop their seed. This year, we had a very short window in the first week of September to collect the bumper crop of seed.

It is very important to collect seed during mast years because, quite simply, it delivers the most “bang for the buck.” When the trees are full of cones, it takes much less effort to collect a lot more seed in one given climb.

Mast years offer a great opportunity to store a lot of seed for future restoration needs. There is a general shortage of seed for wildfire restoration and planting needs in California, but mast years like this one can help re-stock seed banks since seed can keep for decades in cold storage.

We took advantage of this mast year by collecting seed from many species. We will use the seed for reforestation in the Caldor Fire and other fires, such as the recent Davis Fire on Mount Rose.

This year, we harvested:
55,000 sugar pine seeds
40,000 western white pine seeds
30,000 incense cedar seeds
20,030 mountain hemlock seeds
6,000 Jeffrey pine seeds

We already had 30,000 Jeffrey pine seeds in storage, which is why we didn’t harvest more of this species.

We harvest most of our seed by climbing into the very tops of trees laden with cones. The climber clips or shakes the cones off of the branches and a ground crew collects the fallen cones full of seed in burlap sacks. We then take the cones to the Placerville Nursery for seed extraction. The first step of this process is to dry the cones on racks. Next, the cones are shaken in a machine to get the seeds out. Another machine is used to clean the seed.

Most of the seed we collect gets stored in the freezer, but we send some of it to nurseries to be grown into seedlings for our restoration plantings.

The first step in growing seedlings is to stratify the seed – which involves imitating fall, winter and spring by soaking the seed and keeping it refrigerated for three months – so that the seeds will sprout, or germinate when it's planted in Styro plug planters.

We get the seedlings back from the nursery once they are a year old for our restoration plantings in fire scars and other areas in need of rehabilitation around Lake Tahoe.