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How do weirwood trees work? The answer may lie beneath

Vermont wetland ecologist Charlie Hohn (@SlowWaterMvmt) had some intriguing thoughts about weirwood trees after reading my post about the impacts of the Wall on biodiversity (published last summer as part of a “science of Game of Thrones” blog carnival. He drafted this post in response. You can read more of his work at Slow Water Movement.

Much mystery surrounds the forests of Westeros, especially those to the north occurring in increasingly cold climates. The great trees of the northern forests must survive severe winters of uncertain length… but how?

The answer may largely lie underground. A record of excavation of a castle foundation near Winterfell reveals an intriquing surprise. An oak was removed because it laid in the path of the foundation, but when the roots were to be dug out, a massive underround structure was found deep below the tree. It was said to be roughly in the shape of an onion, but the size of several cottages. Construction was delayed for many days as the massive ‘bulb’ was excavated. The outer surface was that of hard oak wood, but the interior was wet, pulpy, and oddly sweet, and included a substance somewhat reminiscent of weirwood sap. In fact, weirwood roots were also found nearby, even though the nearest weirwood was a considerable distance away.

CS 71 1st November 2010

The strange red leaves of weirwood trees don’t appear to drop in winter like other deciduous species. Is this a clue to their ecology?

the feature thus appears to be a storage place for sugars and nutrients needed by the trees. But why weirwood sap, which is never found when oaks are cut? Why weirwood roots? This question ties into the question of why weirwoods have red leaves. It is known that some charactersitic of green leaves allows the trees to turn sunlight into food. Do weirwood trees do the same with red leaves?

The answer appears to be no. Weirwoods do not make energy from sunlight at all, as found by experiments where they were covered in darkness for years. The trees suffered no ill effect. Indeed it is unclear what purpose the leaves serve, but the trees themselves appear to function as connectors between other species. Sentinels and soldier pines, for instance, lack bulbs. But these evergreens are able to produce energy from the sun during weak winter thaws, which oaks can not. Weirwoods do not appear to be parasites. In fact, there are numerous reports of cases where forests declining and saplings failing to survive the winter after weirwoods were removed. This has been attributed to anger by the Old Gods, but in fact appears to have a more earthly cause. Weirwoods act as intermediates, perhaps as ‘tree bankers’.

Oaks store sweet sugars and ‘food’ in their bulbs. Sentinels and soldier pines can create ‘food’ when oaks can not, but not enough to survive a winter. Weirwoods link other trees together. Underground, the roots support a fungi called ‘mycorrhizae’ which can connect with other tree roots. The weirwoods can move energy between species, and even more important, can keep saplings alive over a long winter. Their blood-like sap contains a very concentrated mixture of sugar and other nutrients trees need. Thick sap is sent between pines, oaks, and other species as needed. A weirwood planted in the center of a godswood provides for health of the entire forest. Even ‘dead’ weirwoods retain a living root network underground.These roots stretch far, far beyond the canopy of the trees above.

This explains much. Why are there rarely more than one or two weirwoods in one place? They can not survive without other trees to provide the nutrients. Denser growths of weirwoods occur north of the Wall where winters are harsher, but still, other trees must be present for them to survive. Why do they sometimes grow in ring-like groves? The trees can resprout from the edges of the main root area when the central tree’s aboveground portion is killed. Even small wildflowers such as autumn coldsnaps appear to link into this great network. And the blood-bloom that often grows directly from corpses after battles? It pulls nutrients from corpses and stores them in its then engorged petals before transfering them belowground. Disturbingly, the ‘blood’ in weirwood sap sometimes bears more than mere resemblance. As fate of humans turns sour, it sweetens the life of the forest.

Followers of the Old Religion must have somehow sensed the importance of these trees to the forest ecosystem. The faces cut into some of them may even have allowed them to detect changes in the environment as the consistency and color of the sap varied slightly. Thus the trees did indeed allow one to ‘see’ the future of the forest, even though the stories of ‘greenseers’ looking through the eyes of the trees are, of course, as ficticious as the rumors of revived dragons in the east.

Categories: Guest Posts

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Jacquelyn Gill

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