Poor fen has cast of thousands

by Emily Stone
Naturalist/Educator
Cable Natural History Museum

One after another we scrambled across the fallen tree that spanned the moat. Black, bottomless water licked at our boots, and armed guards threatened nearby with needle-sharp daggers. No, we weren’t storming a castle, we were entering a poor fen.

Fens are a type of wetland with organic, peat soils composed of poorly decomposed plants. While poor fens lack nutrients and are similar to bogs, there is one main difference: fens have some water flow (either from underground springs, a flowing stream, or runoff) and that results in a neutral or basic pH. True bogs only receive water from rain, have no inflow or outflow, and are extremely acidic.

The glossy black moat we teetered across is a typical feature of these wetlands. Where runoff from the surrounding uplands contacts the bog or fen, it adds oxygen and nutrients and stimulates decomposition. Dead plants molder into slimy, insubstantial muck that gives way under floundering feet, and their leftover nutrients foster the growth of beautiful plants like water calla (related to the ornamental calla lily).

Once across the moat, we stepped gingerly onto the edge of a floating mat of vegetation and gauged its substantiality before committing full weight. Although the moss sunk and water welled around out boots, the carpet of interwoven plant remains held. One of the most fascinating things about bogs and fens is that they fill in from the top down. Shrubs and sedges anchor to the edge of an open pond and create scaffolding upon which sphagnum moss and more plants grow. In the anoxic, nutrient-poor water, the plants don’t decompose after they die. Instead, they just sink lower as new plants grow on the substrate of their bodies.

Here, near the moat, the mat of poorly decomposed vegetation was only a few feet thick and undulated like a waterbed under our weight. It grew noticeably more stable as we walked toward the center of the wetland. Sparky Stensaas, a naturalist, photographer, author, and our guide, stopped every few feet to point out patches of grass pink orchids, pitcher plants, and sundews. Sparkling dragonflies and translucent damselflies zipped through the summer heat. Jewel-like cranberries ripened in the moss. While the group paused to examine them, I got out my bog probe. This simple tool is just five, four-foot lengths of chimney sweep extension rods. They are thin but strong, and screw together securely.

The first rod was the hardest. I had to ram it forcefully into the thatch of vegetation before I felt the fibers part ways. After the second rod, resistance decreased as the rod found its way down through older and older peat. We held our breath as I screwed the fifth rod onto the set and pushed it down easily. Bottom was nowhere to be found. This told us two things. 1) Even near the edge of this fen the basin is more than twenty feet deep. 2) I need to order more extension rods.

Both amazed and disappointed, I began to extract the rods from the fen. As my hand grasped the second black wand, I gasped. It was ice cold! I know that that moss blanket on bogs and fens is an excellent insulator, and that bogs can harbor subsurface ice well into June, but on this ninety degree day the surface of the bog felt like dishwater, and the contrast in temperature was startling. That cold is one more cause of the slow decomposition here.

Without decomposition, the resources that new plants need to grow are locked up, unavailable, in the bodies of old plants. To acquire nitrogen and other nutrients, several bog and fen plants have turned to carnivory. Pitcher plants and sundews are two of the most famous carnivorous plants, and I’ve written about them before. Their brilliantly specialized leaves capture small insects, and a combination of microorganisms and digestive juices break them down.

Just beyond our probe location, near the edge of an open pool, we found great patches of small, sunny yellow flowers with a violet-like face and funny, protruding spur. These horned bladderworts don’t look dangerous, but theirs is the largest genus of carnivorous plants in the world. Under the innocentlooking flowers hide tiny traps.

Each trap is a bladder with a door that opens inward. The plant can pump water out of the bladder, flattening it and creating a vacuum inside. When a minuscule invertebrate nudges trigger hairs near the door, the flap swings inward and sucks in both water and lunch. The door snaps shut as the bladder fills. The plant sucks out the water and replaces it with digestive enzymes. Recent studies show that a vibrant microbial community in and around the traps may also play a role in attracting prey and absorbing phosphorous.

Growing up, my imagination often wandered deep inside fairytale worlds. In this fen and others like it, I’ve found that those magical places truly exist. Dragons and damsels fly above a sparkling landscape where tricky traps lie in wait to catch unsuspecting travelers. The precious gems of flowers and fruits attract treasure-seekers of all kinds. Cold danger subtends all that beauty.


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