Reaction to Stress

Seven weeks (09-24-17) after the Cove Fire destroyed over 30,800 acres in Modoc County CA, Leonard and I were surprised to find fireweed (Epilobium angustifolium) and spreading dogbane (Apocynum androsaemifolium) blooming amid the ashes. At three weeks post fire (08-24-17 there were a few spreading dogbane plants (see  “Resilience” on 08-28-17) reestablished at our observation site along Modoc National Forest Road 40N11, but no flowers. No fireweed plants were visible at that time. The fireweed sprouted later than the spreading dogbane.

Spreading dogbane and fireweed are both perennial plants that arise from underground rhizomes. After wildfires both species quickly regrow from rhizomes that were below the zone of heating. Under normal conditions fireweed grows to a height of 2.5 to 9 feet and blooms from July to September. Spreading dogbane stems reach lengths of 0.67 to 2.5 feet and flower during May through September.

One way plants respond to stress (cold, drought, herbicides, overgrazing and fire, for example) is to immediately flower and produce seeds. Energy is not expended on foliage or creating food reserves, rather the plant immediately attempts to insure its survival by developing and dispersing seeds.

Although fireweed and spreading dogbane normally bloom into September, the plants would be large and have extensive green foliage in addition to the flowers. Seven weeks after the Cove Fire both the  fireweed and dogbane plants had flowers. But the flowering plants were “dwarf” – many spreading dogbane plants were about 4 inches tall while the fireweed ranged from about 6 inches to a foot in height. Additionally, most of the spreading dogbane  plants lacked leaves or only had a few miniature leaves hidden amid a profusion of blossoms. The spreading dogbane consisted of little more than an inflorescence at ground level. Both species responded to fire stress by immediately producing seeds.

I expect next spring will bring a profusion of wildflowers to the Cove Fire site. In addition to seeds germinating in the spring and plants with bulbs and rhizomes sprouting, research has demonstrated that enhanced light on the forest floor after the canopy is destroyed by fire results in larger numbers of flowers blooming. Leonard and I are looking forward to an abundance of wildflowers next year.

More information about spreading dogbane and fireweed can be found in my earlier posts –  07-04-16 “Spreading Dogbane”,  08-24-11 “Fireweed” and 08-27-11 “Pollination Strategy”.

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