What A Decade Of Counting Seeds Tells Us About Future West Coast Forests

Apr 1, 2021

Not far from the UC Santa Cruz campus is a 40 acre forest plot. Students have been counting seeds and measuring trees on this plot for more than a decade. That data has been used in a new study that aims to understand what our forests will look like in generations to come. And the findings suggest that change is on the horizon.

A short walk away from the roadway and into the UCSC Campus Natural Reserve; along a slim and recently rain soaked dirt path; passing Redwoods, Douglas Firs and Pacific Madrones; Gregory Gilbert finds what he’s been looking for… a seed trap.

“So there's actually some really cool fruits in here,” said Gilbert. 

The trap looks like an elevated netted basket that’s been collecting a whole lot of debris that’s fallen from the trees above. 

The UCSC environmental studies professor ramages through what’s in the trap. He’s excited by what’s been collected. 

“There's probably several dozen redwood seeds in here and there's one cone of a Douglas fir that fell. And so it's got a bunch of seeds inside it. And there's one fruit, one seed of a hazelnut of a California hazelnut. And it's great to actually find this. I hardly ever get to see them because the squirrels all come and eat them before I ever find them.” said Gilbert.

UCSC Environmental Studies Professor Gregory Gilbert displays some of the seeds that have landed in one of the Forest Ecology Research Plot's (FERP) seed traps. On the left is the seed of a California hazel and on the right is a cone of a Douglas fir which has many seeds inside.
Credit Michelle Loxton.

 

These traps are scattered throughout a 40 acre plot called the FERP, or Forest Ecology Research Plot. The FERP is part of the larger reserve. And every two weeks since 2008 students have recorded every seed, leaf and fruit that has landed in the traps. 

Students like Ishana Shukla who’s studying ecology and evolutionary biology. 

“I have been out here, I think, more times than I can count. The FERP kind of feels like a second home to me,” said Shukla. “It’s very, very detailed work so you have to make sure you're being precise when you're counting seeds or if you're measuring a tree, you have to make sure you're getting the millimeters extremely correct.”

And it's thanks to long-term data collection like this, in monitoring sites across North America, that scientists have been able to determine that climate change is causing declines in seed production for older and larger trees in western forests.

“The amount of seeds that our trees are producing are sort of hitting a kind of plateau, right here. So for right now, it's fine. But as trees eventually die through diseases, through pests, through fires, through lightning strikes, the species that are going to replace that are going to depend on what seeds are available,” said Gregory Gilbert. 

Meaning over long periods of time, we’re talking generations, west coast forests could look different. These changes could mean the loss of regional flora and diversity in our forests. 

Gilbert is a co-author of this new study along with UCSC Assistant Professor of Environmental Studies Kai Zhu.

 

“Over generations, this will not happen immediately, but over generations we are likely to see few smaller individuals that are replacing large individuals,” Zhu said.  

He says a study like this is so important because it addresses what he feels has been missing from the study of how climate change is affecting trees -- the beginning of a tree’s life.

“So without the reproduction piece, our understanding will be incomplete and that will sort of decrease our ability to anticipate the change in the future,” said Zhu.

And that’s where forest management comes in. If foresters can predict what future forests may look like, they have the option to adapt. 

Kai Zhu (left), Gregory Gilbert (center) and Ishana Shukla stand by a moss-covered Pacific Madrone that has died. Gilbert says Pacific Madrones and Tan Oaks have been declining quickly over the last few years.
Credit Michelle Loxton

As we prepared to leave the forest, Gregory Gilbert reflects on the changes that are already very much apparent. 

“If we look around, you can see I can count one, two, three, four, five, six, seven, eight, nine, 10, 11, at least 11 Madrones that I can see here that have all died in the last five years,” said Gilbert.

He calls these trees awesome, with their peeling bark and red coloring, growing at strange angles. 

“Who's going to replace it? Is it going to be other Madrones and other Tan Oaks or is it going to be completely taken over by Douglas Fir or some other species that comes in?,” said Gilbert.  

What is likely is that the forests of the future will look different from the forests of today. 

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