Refuge Notebook 05/13/2011

community_notebook_05-13-2011

Ent Draughts and Birch Sap
by John Morton


In the Lord of the Rings, the two hobbits, Merry Brandybuck and Pippin Took, grow taller and feel their hair curling after downing a few Ent-draughts between chasing and being chased by orcs. This drink is provided by the Ents, the tree-like shepherds of their arboreal kindred.

As fictitious as this story may be, ent-draughts sound very reminiscent of birch sap. I’ve been drinking sap from the birch trees in my yard these past couple of weeks after my daughter, Charly, insisted we tap them. I’ve tapped maple trees as a boy in Wisconsin to make syrup, so this was an easy enough task. What I wasn’t excited about was the boiling down of the sap to make birch syrup. I knew that it took 100 gallons of birch sap to make 1 gallon of syrup, a ratio 2 ½ times greater than that required to make maple syrup.

So the bad news is that Charly and I burned the sap in our attempt to make syrup on the stove. I found out later that this was due to the high fructose content in birch sap (as opposed to sucrose in maple sap), which requires a lower evaporation temperature to prevent the scorched smell. Some commercial producers in Alaska use reverse osmosis to distill birch syrup rather than heat.

The good news is that we’ve discovered birch sap, a traditional health elixir that was apparently well known to native Americans, Russians, Scandinavians, Chinese, and Japanese living wherever birch grows around the globe. The fact that we’re a bit late in rediscovering this medicinal tonic and delightful drink doesn’t detract from its history of being used to treat hypertension, urinary and gastroenteric disorders, gout, arthritis and scurvey!

The sap “rises” in the spring as the birch tree prepares itself for leaf-out, typically a period from mid-April to early May on the Kenai Peninsula. It flows through the system of vascular “pipes” that we call the xylem (if you’re a biologist) or sapwood (if you’re everybody else). Not surprisingly, birch sap is mostly water and minerals carried from the roots to the embryonic leaves hiding in the buds.

More specifically, birch sap is about 98% water, 1-2% sugars (fructose, glucose and sucrose), and some maltic, citric, fumaric and succinic acids. One website I found reported that one liter of sap contains 410 mg of calcium, 350 mg of potassium, 78 mg of magnesium, 27 mg of manganese and 50 mg of phosphorus. Thiamin (vitamin B1), riboflavin (vitamin B2), vitamin C, iron and copper can also be found in the sap.

An unusual sugar found in birch sap is xylitol, used as a low-calorie sweetener in chewing gum. Xylitol actually inhibits tooth decay by suppressing Streptoccocus bacteria and so has been used in toothpastes. And xylitol is absorbed more slowly than table sugar so it has been used by diabetics because it doesn’t contribute to high blood sugar. It’s not surprising that one article I read on birch sap calls paper or white birch the “white gold of the boreal forest”.

With such rich blood coursing through the vascular system of a birch in spring, you’d think that wildlife would have figured this out as well. Perhaps because birch sap rises for such a brief period in Alaska, only three weeks in our area and as short as 10 days in the interior, wildlife don’t seem to have cued in on it.

The exception may be sapsuckers, a group of woodpeckers which includes two species in Alaska. Yellow-bellied sapsuckers have been recorded only a few times in Alaska, mostly in the interior. Red-breasted sapsuckers breed in southeast Alaska but have been found more frequently on the Kenai Peninsula in recent years. Sapsuckers drill small, square holes in rows around a tree trunk which then act as miniature wells that fill with sap. They use their long tongues with their special brush-like tips to lap up the sap, and then eat insects which are attracted to the sap.

One of the most common insects to feed on birch sap are aphids. Large infestations of these small, pear-shaped bugs can take so much sap from birch leaves that the branches may start to die back.

A very lethal insect, the bronze birch borer, can interrupt sap flow by burrowing into the inner bark of the birch, essentially girdling the tree. This beetle currently exists only in small numbers in Alaska. However, the Arctic Climate Impact Assessment forecasts that this insect may become more prevalent as temperatures warm in boreal Alaska. So even as sapsuckers extend their range northward into birch forests in response to a warming climate, so will some of the insects that may be harmful to birch.

In the meantime, I encourage you to try this spring-time treat that's healthy and free. If you’re interested in tapping birch sap and/or making birch syrup, contact the Alaska Birch Syrup Makers Association or the University of Alaska Cooperative Extension Service.

John Morton is the supervisory biologist at Kenai National Wildlife Refuge. Check us out on Facebook at http://www.facebook.com/kenainationalwildliferefuge.