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Unlocking the mysterious tamarack

October 10, 2014
By SHAUN KITTLE - Outdoors Writer (skittle@adirondackdailyenterprise.com) , Lake Placid News

PAUL SMITHS - October is an ideal time to plod through a wetland.

While most of the Adirondacks' showiest leaves have already drifted to the forest floor, decorating it with striking variations of reds, browns and yellows, the fiery gold of the tamarack is just starting to peak.

The spindly, medium-sized tree is fairly common in wetlands throughout the Park, but it isn't entirely understood. The biggest mystery surrounding it occurs annually - it's the only deciduous needle-bearing tree in the Adirondacks, meaning it sheds its needles every fall, just like maples, ashes and birches lose their leaves.

Article Photos

Plant physiologist and Paul Smith’s College professor Celia Evans, left, and students Rob Desotle and Chloe Mattilio unpack equipment and prepare to collect data on the growing conditions for tamaracks in the Heron Marsh at the Paul Smith’s VIC.
News photo — Shaun Kittle

Celia Evans, a plant physiologist and professor at Paul Smith's College, said no one knows why that happens, so she's enlisted Paul Smith's students Rob Desotle and Chloe Mattilio to help her figure it out. The students are part of the National Science Foundation's Scholarships in Science, Technology, Engineering and Mathematics program, which provides funds so students can do graduate-level science research while in undergraduate school.

"You're a professional as a student," Desotle said. "We're doing what professionals do in the field, and that's a great, unique opportunity."

Evans knows that understanding tamaracks means getting up close and personal to them, so in September the researchers began by setting up data collection plots at the VIC's Heron Marsh.

Before sliding into a pair of rubber boots, though, it's important to first consider what happens when other deciduous trees lose their foliage. Evans explained that scientists don't understand everything about what triggers the autumnal color show, but they have figured out which chemicals are responsible for the display.

Summertime greens are produced by a pigment called chlorophyll, which converts sunlight to chemical energy. Trees typically begin producing less chlorophyll sometime around mid August. As the pigment becomes less abundant, colors from the auxiliary pigments begin to show.

Yellows come from a pigment group called carotenoids, which are always present in the leaves. Reds are produced by a diverse and common group of pigments called anthocyanins, which are also responsible for the blue in blueberries.

"Reds are produced in the fall in response to the weather," Evans said. "The thing that makes the reds pop is sunny days where there's a lot sun and cool nights. Whatever is left of the chlorophyll is producing a lot of sugar. It's kind of the same conditions we get maple syrup from in the spring."

That's about as far as scientists have gotten, though.

"Nobody knows the whole story," Evans said. "There's probably something about soil moisture, not being too wet or too dry, because when we get really dry soil I think that tends to accelerate the turning and the going to brown. If we keep that moderate level of moisture and sunshine, I think we get better colors."

Nobody knows the whole story about why the auxiliary pigments are produced, either. Evans said one hypothesis states that the ever-present carotenoids work to channel excess solar radiation away from the leaves, essentially preventing them from getting a sun burn.

"Sometimes the sun is so bright that the chlorophyll can't absorb all of the light that's hitting the leaf," Evans said. "They're made up of cells, and you've got ultraviolet radiation. A lot of these wavelengths can be damaging. The energy that can't get funneled into that practical and very efficient process of making sugar by chlorophyll molecules, some of those other pigments absorb some of that and re-release it as heat so it doesn't damage the leaf."

Similarly, the fall production of the red-inducing anthocyanins might be a way to protect leaves.

The needles on a tamarack are noticeably softer, or more leaf-like, than other needle bearers, especially compared to those of the prickly spruces. The prevention of desiccation and water loss are the two main reasons scientists think trees lose their leaves, so it's possible tamaracks are attempting to protect their needles from harsh winter conditions by simply getting rid of them.

The problem is, tamaracks prefer nutrient-deficient environments. And so the conundrum begins.

"They have to re-uptake all of those nutrients and basically make a whole new leaf," Evans said. "It's a huge amount of energy, and a lot of nutrients. Why would something that's a conifer have this deciduous feature when it's living in what's very often the most stressful environments around?"

It's the kind of question that keeps plant physiologists up at night and inspires them to take to a marsh to find answers.

Standing on a soft carpet of sphagnum moss, Evans, Desotle and Mattilio unpack instruments that measure things like the oxygen content in water, the amount of solar radiation permeating the canopy, pH levels and water depth and temperature.

They start at the first plot in a transect that begins in a thick forest and extends into the neighboring Heron Marsh.

The forest is a quiet, moss-cloaked place dominated by black spruce. Spruces don't mind close quarters and their long, straight trunks support a high evergreen canopy that only allows occasional beams of sunlight to poke through. Tamaracks are almost non existent here.

The students explain that the forest borders the marsh, which is prime tamarack territory, so it's an important ecosystem to include in the data collection.

Moving into the marsh, Desotle stops at each plot and plunges one end of a piezometer into a hole containing a half-meter length of PVC pipe.

Every plot containing tamaracks has a pipe placed near the base of one of those trees, which is called the plot's focal tree. The piezometer measures some of the in-ground growing conditions - water oxygenation, temperature and acidity - which will become part of a gradient that will help the scientists understand which of those conditions tamaracks prefer.

While Desotle records the readings, Mattilio collects a few bundles of needles from the focal tree.

"I'm just trying to get as much time in the field as I can to learn different techniques," Mattilio said, dropping the bundles into a paper bag. "I almost feel like, the more I study, the more questions I have. I think that's how it's supposed to work, so that's a good sign."

The needles from each tree will be taken back to the lab, where they will be dried and crushed so their nitrogen content can be measured. Evans said all trees reabsorb some nutrients from their foliage, but studies have shown that tamaracks absorb an exorbitant amount.

The researchers will continue the weekly data collections for the next month or so. It's all part of studying how conditions change with the seasons and how tamaracks respond to those changes.

After the last tamarack needle hits the sphagnum and the snow begins to fly, Evans, Desotle and Mattilio will take to the lab to see what the data reveals. But first, there is an ethical discussion looming on the horizon. Two key data points, the age and incremental growth rate of each focal tree, are unattainable unless they decide to cut those tamaracks down to gain access to their rings.

"There aren't tamaracks in every plot," Evans said. "Of 21 plots along one transect, only 13 have the tree. None of us wants to cut down a tree, so we have to decide whether the sacrifice is worth the information or not."

The big picture for the research, Evans said, is also to get a handle on how climate change could affect wetlands, and how the species living there, like tamaracks, respond to those changes.

"With climate change, changes in precipitation, potentially, and the drying out of wetlands, which is something that has been predicted in places, we might see that some key species like spruce and tamarack are going to do better with the drying of the bog," Evans said. "That's one way this research could be applied, besides the fact that tamaracks are this unique, magical tree that's just really cool."

 
 

 

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