The road narrowed and grew shrubby as Andrew, Maddie (a graduate student at OSU) and I pulled up, looking for a place to park. Just behind us was the rest of the team in a second vehicle—Charles, another experienced member of the crew, at the helm.
“This one is very steep,” said Andrew with a grin. “We are going to challenge some of them [crew members].”
We were at Site number 93. The area had been sampled for fire scars on the opposite side of the road already. The plan today was to focus on setting up a plot and gathering forest development data which mainly involves coring trees.
Forest development, Andrew explains, is the history of how a forest changes over time. By gathering plot data and coring trees, he hopes to understand the different development trajectories a forest might undergo in relation to its disturbance history.
Fire Record
The fire record for the site showed fires in 1759, 1836, 1844, and 1883. But you wouldn’t know it from looking at it. The trees at this site were much larger and a good deal older than the forest we had sampled earlier in the day.
The fires, Andrew predicted, must have been low severity with low tree mortality since there are so many older living trees at the site. The oldest of the trees are over 800 years old, established in 1190, possibly following a stand-replacing fire.
“Now when we core the site,” said Andrew, “It will be interesting to see if we find cohorts of hemlock and cedar related to these fires [in the 1800s] because presumably they come in because of gaps or openings.”
Plotting a Plot
After gathering all of the necessary equipment, the crew, Andrew and I headed down through a thicket of young conifers that lined the road. The slope was steep as we navigated our way over and around downed logs and branches. Eventually, we reach the ancient forest and what would be our plot center.
Andrew’s plot design follows the same format as the Forest Inventory Analysis Program of the U.S. Forest Service—with three circular plots that branch out at 120 angles from a central plot (each with a radius of 58.9 feet) and smaller subplots and microplots inside these.
Andrew staked out the center of plot one. He chose the site in hopes of capturing multiple cohorts of trees, including a large old-growth Douglas-fir that sat just downhill of the center.
While he gathered some basic plot data, he set most of his crew to work on coring trees.
Growth Rings
Gathering core samples from all the trees in the plot is both the most time-consuming and important part of the plot data Andrew’s crew collects. Each core is carefully packaged and carried back to the lab for closer analysis.
Cores can tell you a lot of things about trees. The size of the rings tells you about growing conditions, while the number of rings tells you about the age of each tree and when it was established.
Charles and some of the crew stayed nearby coring some of the smaller trees on the uphill slope. Maddy and one other crew member took a stab at the behemoth below.
Coring Efforts
I sat with Charles for a while to try and learn the secret to getting the perfect core. Charles was coring a hemlock tree—a species notorious for being rotten on the inside. The bit screeched as he rotated the handle.
“As a general rule, if a tree is leaning the pith should be away from the lean,” Charles explained. “I chose the side that is kind of oval. I want to core into the shortest side of it… to core the shortest distance.”
Charles originally studied the Classic Period in school before returning to graduate school to study forests—something he had wanted to do for years. He explained enthusiastically how the field of forest ecology has placed a greater emphasis on humans as part of the ecosystems in recent years. A change for the better. The borer clicked as he talked.
Before long, Charles reached the center and stopped coring. He rotated the handle counterclockwise, breaking the connection between the core and tree, and gently removed it on a thin metal spoon. Unfortunately, there were tiny holes in the wood indicating rot.
“I might try a few more turns,” he said.
Persistence
As Charles continued coring his hemlock, I dropped down to check out what progress was being made on the old-growth Douglas-fir at the bottom of the hill. There was likely 800 years or so of rings to get through. I couldn’t imagine the effort it would take.
The team had just extracted a couple of massive pieces of core from the tree and laid them down on a nearby log. They looked pretty good to me, but Maddy wasn’t satisfied. The core was still short of the pith.
They tried a new angle and took turns spinning the bright blue handle. Gloves were a must-have for this line of work. And work it was. Maddy and her partner would spend the remaining part of the day attempting to get a quality sample from the tree.
Old Growth
With the creaking and squeaking of borers in the background, I decided to take a little hike around the forest plot. I wanted to get a different perspective of the forest and see if I could get a view of some of the old growth treetops.
When we first arrived at the site earlier in the day, Andrew was quick to point out that despite their size, most of the trees downhill from us were not old growth. Most of the trees we were able to see from the road still had a tapered top, having not reached full height or had time to flatten out.
In fact, most of the trees were probably about 260 years old—middle-aged for a tree—establishing after the 1759 fire.
“A 500-year-old tree will be really wide at the top,” Andrew explained, “and will have wide branches…”
In short, a flat-topped tree is an old growth tree.
Balancing near a log, I took a picture of a couple gnarly looking old growth trees and their heavily branched tops.
Old Assumptions
Work continued under the tall canopy. There were a lot more trees to core and measure.
As the crew worked, Andrew told me that the data we were collecting that day might also be used to test an old assumption about old growth trees.
“One of the assumptions about old growth forest is that it has no net change in biomass,” Andrew explained. “Whatever is dying is being balanced by what is growing.”
Old growth is sometimes romanticized as a stable, unchanging system. This may be true, but as far as Andrew is concerned there is a lack of evidence to say one way or the other. Based on careful reconstructions of the history of old-forests it seems more likely that they are always changing. Sometimes change is quick, like after fires or other disturbances, and at other times slow, at an imperceptible pace for our relatively short lifetime.
“Coring all these trees, we can quantify basal area increment over time,” said Andrew. Basically, you take the width of the rings and diameter of the tree to determine the volume of wood added each year.
This sort of data could answer a myriad of questions:
Does biomass increase or decrease in these old growth stands? Or, is the answer, it depends? How quickly are the younger cohorts replacing older slower growing trees and trees that have died? Where is the stand headed in terms of what types of trees and their structure?
Only time and an increment borer will tell.
Other Measures
Of course, there is a lot more data to collect than just taking cores. For each tree in the plot, DBH (diameter at breast height), height, species, and condition are recorded. Then, there is also a host of other measurements, like slope and aspect of the plot.
As I returned from my romp through the forest, I caught Andrew taking another measurement—woody debris.
Curious, I asked what he hoped to learn from tracking the downed wood in the plot.
First, he explained that it can relate to disturbance history as you compare what is on the ground with what material is consumed.
“Different development histories produce different woody debris,” he suggested.
“Honestly,” he added, “I don’t know how it will turn out.” However, if some sort of pattern does emerge in the data, by using the same protocols as FIA, it opens up possibilities for access to an even larger data set.
Back Again Tomorrow
It was late afternoon when Andrew’s crew wrapped up for the day. They probably would have stayed out even longer if I didn’t need to get home.
On the drive back to my car we chatted about all sorts of things—family members, hiking and climbing, and of course research.
Andrew and his team are not done. They will be back tomorrow. And probably the day after.
How does a forest grow?
In a million different ways.
Ask Andrew and his crew—they have all sorts of theories to test.
Andrew Merschel is an ORISE postdoctoral fellow working with the USFS PNW Research Station and he leads the tree ring lab at Oregon State University. Andrew uses tree rings to develop a shared understanding of how different forest ecosystems function over time. He is particularly interested in how disturbances (mostly fire) and forest management have shaped and will continue to shape forest ecosystems in the Pacific Northwest. Andrew lives with his family (Vanessa, Aldo, and Sawyer) in Corvallis, Oregon and they enjoy a mixture of fishing, hiking, wildlife ecology, and chainsaw repair in their spare time.