Tamarisk Excavation: A Bandage not a Cure

Heather Bowen

The Green River is one of several ecosystems suffering from the invasion of Tamarix spp. How it arrived is of some debate, but for most it does not matter. Tamarisk was introduced to the Green River sometime in the 1930’s (Cooper et al. 2003) and has done overwhelmingly good for itself since the construction of Flaming Gorge Dam. Tamarisk alone has been named the culprit behind reported changes in channel morphology including terrace formation and channel narrowing. Tamarisk is a shrub-like tree with deep, expansive roots which are capable of extracting water from unsaturated soils. In drought like conditions tamarisk can exert stomatal control of water loss. They tolerate prolonged inundation and are capable of establishing on a variety of sediment grain sizes. Tamarisk also produces exorbitant amounts of seeds that will often rain for a greater amount of time than its native counterparts. All of these morphological characteristics of tamarisk increase their rate of survival, and native species don’t even come close to matching them. Coyote willows and cottonwoods are facing Olympic competitions they have not yet trained for.

Tamarisk is not perfect however. It may be susceptible to herbivory by beaver and beetles, and is still unable to adequately defend itself from saw, shovel and chemical. The later approach tends to exert a more timely and rewarding impact on tamarisk populations, rather than waiting for beetle and beaver populations to take a turn for the better. As evident by the giant pits (Figure 1) present in the active and intermediate floodplains of Winnie’s bar, the laborious task of Tamarisk digging and cutting was successfully accomplished only a few years ago (Jack Schmidt Comm.). Yet, this large expansion bar downstream of the debris-fan where we observed these pits is completely covered with new tamarisk recruits that apparently survived this year’s peak flooding events. Farther downstream at river mile 233, several stumps remain hazardously protruding from the arid ground as several live tamarisks of various ages move in around them (Figure 2). These short-term results leave us contemplating what can be done to eradicate such obnoxious plants.

Figure 1. (below) Pit remaining several years after complete tamarisk exaction attempt at Winnie’s bar.
Figure 2. (right) Young tamarisk growing near remnant stumps of previous eradication attempt at River Mile 233.