October 3, 2007

Tree Walk Wednesday: The liquid amber of sweetgums

The colour made me stop. I made a u-turn with my bicycle so I could photograph a row of Liquidambar styraciflua, or sweetgums (below). The red leaves were like liquid amber against the drab backdrop of the North Berkeley BART station and parking lot.



The genus designation, Liquidambar, refers to the resin (or sap, or balsam) from the tree which resembles a liquid form of amber. The resin is also sweet, hence the popular name, sweetgum. According to the author of The Urban Tree Book, the "yellowish gum" produced by the tree is used to prepare syrups and ointments for "skin irritations and wounds." Plotnick also observes that with "plenty of sun, moisture, and ample root space" sweetgum saplings can grow between 12 and 30 feet in six years. These conditions, with the exception of sun, are generally associated with street tree planting areas, but Plotnick also notes that well-established sweetgums can tolerate "most soils, poor drainage, and the usual urban stresses and deprivations."

It is important to water young trees - about 10 gallons per diameter inch per week - for the first two years of establishment (varies with species and setting). For more information about watering, read Canopy's young tree watering fact sheet or City of Boston tree watering tips. In addition to its tolerance of urban environments, the sweetgum's leaf and fruit are other notable features of the species. The leaf is star-shaped and reminds me of a starfish. The spiny fruit contains seed capsules of 1-2 seeds per capsule. According to the Lady Bird Johnson Wildflower Center website, the fruit and its seeds attract both fruit birds and mammals, but the USDA Plants website notes that the sweetgum has moderate food value for small mammals, minor food value for water birds, and low food value for terrestrial birds, based on Martin et al.'s American wildlife and plants: A guide to wildlife food habits. This bears further investigation.



In the meantime, let's celebrate the breakdown of chlorophyll and the revelation of anthocyanins which make sweetgums so spectacular in this season.

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