Fall color on native subalpine larches ( Larix lyallii ) at Liberty Bell Mountain , North Cascades . ( Photo courtesy Alan Majchrowicz Photography , alanmajchrowicz . com )
the intensity of fall color is heightened when preceded by sunny days and cool nights ( below 45 degrees Fahrenheit , but not freezing ), though this may not be so important for plants that turn yellow ( see below ). Frost ruptures and kills leaf cells , so it does not lead to brilliant fall color . Wind and rain storms can also cut short the fall color season ; larch needles are soft and delicate and are easily blown or knocked off once they start to turn yellow .
COLOR According to plant expert Randall Hitchin ( quoted in “ The Seattle Times ,” September 25 , 2008 ), fall color change involves “ four groups of pigments . You know about chlorophyll , the green chemical that does all the heavy lifting spring through summer . Then there are the carotenoids — carotene and a suite of related compounds — that give leaves yellow and orange coloring . Tannins produce the russets and browns . Finally , anthocyanin provides the classic autumn colors of red and purple . During the growing season , chlorophyll dominates .
It ’ s constantly being made to replace what ’ s degraded by ultraviolet light , and the leaf appears green . Depending on tree species , yellow , orange or brown pigments have been there all along , concealed by green chlorophyll . In autumn , as chlorophyll production slows and ultimately stops , the yellows , oranges or browns emerge .”
“[….] Anthocyanin is genetically controlled , so some tree species get red and some can ’ t . Unlike the carotenoids , anthocyanin isn ’ t usually present during the growing season , but is produced in leaves with fall weather conditions . In trees that can go red , the amount of it depends on environmental factors . In ideal conditions , you see vivid pinks , reds and purples — that ooh-and-ah factor . [...] The Northwest autumn is often overcast or rainy , with only minimal cooling at night ; not optimal for fall color .”
If you ’ ve seen the fall color on our native western larch ( Larix occidentalis ) and subalpine larch ( Larix lyallii ) in the Cascade Range , you ’ ll know our autumn can generate plenty of oohs and ahs . (“ Larch Madness ” becomes the focus for many fall hikers in our region .) And because carotenoids are always present in larch leaves , the yellow and gold colors remain fairly constant from year to year .
In Seattle , there are several good places to observe the larches turning golden . The wide range of species in the Washington Park Arboretum includes quite a few Larix kaempferi ( Japanese larch ) and L . laricina ( tamarack , native to Canada and the Northeast ), as well as L . decidua ( European larch ), Kurilen larch ( Larix gmelinii var . japonica ), Polish larch ( Larix decidua var . polonica ), and western larch ( L . occidentalis ). Most of these are concentrated at the south end of the Pinetum and the south end of Azalea Way .
If you want to view the golden fall foliage of larches ( in this case Larix kaempferi ) from above , Ravenna Park ’ s upper trails and the 20th Avenue N . E . bridge over the ravine are ideal . Green Lake also has a small grove of Larix kaempferi and a couple of large Larix decidua .
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