Eliminate New Starts of Non-native, Invasive Plant Species in the Backcountry and River Corridor

Crawford, Julie

Executive Summary: Non-native invasive plant species, hereto in referred to as exotic plant species are plants that have been introduced, either accidentally or intentionally, into a region from somewhere else. They have the potential to outcompete native plants for nutrients, light, and water and can alter ecosystem processes. Exotic plants dominate disturbed lands, but many are capable of surviving and thriving in wildlands as well. Not all exotic plant species pose a threat to wildlands and not all wildlands are threatened by invasion. In wildlands such as the backcountry of Grand Canyon National Park (GRCA), it was unknown if exotic plants were a threat. Our study on Rainbow Plateau during the summer of 2003 began a quest into answering the question “do exotic plant species threaten remote areas of the Park?”. Our research consisted of the placement of 155 vegetation relevé plots on the remote Rainbow Plateau, north Rim, GRCA. This study was designed to investigate the presence and distribution of exotic plants in remote areas of the Park. We took advantage of this opportunity to expand our study to include both native and exotic plant species. In this way we can see what species are present, in what quantities, and how they are distributed across the Plateau. Rainbow Plateau was chosen as our study area because of its remote location, lack of trails or easy access, and due to its relatively natural fire regime. Our intended study site of Powell Plateau experienced a fire in June/July which hastened our decision to relocate our study to the nearby Rainbow Plateau. Results from our study revealed that this backcountry area of GRCA is indeed threatened by exotic plants. It is our goal to continue investigating other remote areas of the Park to see if this threat is consistently found. Our results revealed that in this area of frequent burn, areas of low severity fire were dominated by “weedy” native species. That is, native species with the capability to produce large quantities of easily transported seed and those that reproduce vegetatively. In areas of higher severity fire (small patches across the Plateau) there tended to be a stronger presence of exotic plant species. In all, there were 10 exotic plant species found on the Plateau with cover ranging from less than 1% to 63% in a single plot. Plant distribution was not uniform across the Plateau; the Lower section of the Plateau contained much greater quantities of both exotic and weedy native species. In addition to vegetation data, we also gathered abiotic factor data including slope; aspect; cover of ground, rock and litter; and overstory canopy cover. These data, in conjunction with anecdotal evidence of fire char height and stump / snag presence, provide a clearer picture of the reason behind the plant distribution that we encountered. The Lower section of the Plateau has more soil exposure (less litter accumulation), less overstory canopy closure, and appears to have burned hotter than any other part of the Plateau. Among the exotic plants present on Rainbow Plateau are the undesirable cheat grass (Bromus tectorum), red brome (Bromus rubens), and Kentucky bluegrass (Poa pratensis). It is a well known fact that cheat grass follows fire and, in return, fuels future fires. So it is not surprising that in areas of high severity fire cheat grass is present. What is surprising is that this and the other 9 exotic species were present in such a remote and rarely visited area of the Park. How did the plants get there? Where did the propagules come from? We can only surmise a combination of wind, animal, and human visitor/researcher dispersal initiated the infestations. With the use of proper equipment such as leather shoelaces, we may ensure that at least the human vector is lessened or eliminated.