There are a number of species found in both the uplands and wetlands of the prairie pothole region that do not belong here.  Some were brought over intentionally, while others are escapees.  These species fall into the invasive and/or non-native category.  Even though the Service has worked to control these invaders through various means, these species are very hardy, spread rapidly, and easily out-compete the more vulnerable native plant species.  Control methods include mechanical, biological, and chemical means.

Mechanical methods include mowing, clipping, hand pulling, and any other method that removes all or some of the plant. Mowing can be effective at removing plant seed heads before maturity, and forces plants to use energy resources to continue growing, instead of moving on to reproduction. If hand pulling is done at the right time, it removes the whole plant before it matures. The key to mechanical control is to get the plant before the seed matures, this way any disturbance to the seed head does not further spread the seed. 

Biological control can be anything from the use of grazing animals (grazers) to the release of insects or pathogens. Grazers act almost the same way as a mechanical treatment method by removing parts of the plant, and they also serve to trample and disturb large areas. Releasing insects or pathogens serves to weaken the plant, with hopes of decreasing the plants reproductive ability. Typically, biological control can last several to many years before results are achieved, but require less staff time each year to control. By releasing biological controls in large numbers or infestations, staff can focus on early detection and rapid response of newly established areas. For non-native insects and pathogens, research is conducted for many years before they are released into the environment to ensure that they impact only targeted plants and not natives species, or themselves become invasive.  

Chemical control is typically done with pesticides, and specifically herbicides for plants. Herbicides may be applied with hand-sprayers, backpacks, UTVs, to large tractors with spraying attachments. Spraying may be applied on a spot, directly applied to a tree stump, to sprayed or broadcast. It all depends on how the plant is dispersed and its size. Herbicides may be specific or non-specific to a plant group. Taking all these components of herbicide use into consideration, managers work to minimize the impact of herbicides to the environment and maximize their effectiveness on controlling non-native and/or invasive species.

    

 The Dust Bowl era of the 1930’s left much of the land in need of healing. When Refuges were established during this era, the main goal for managers was to enhance native wetland and upland habitats in order to speed up the process of increasing game populations. In the uplands, fruit bearing trees were planted as a source of food and cover for upland game birds. Russian olive trees were being promoted for their adaptability to semiarid and saline environments, as wind breaks in shelter belts, and as a food source for wildlife, even though it was a non-native species. At the time, not much more was known about the plant’s natural history and its ability to spread if not kept under control. Using the best available wildlife management information to them at the time, refuge staff planted olive trees on the refuge from the 1940's to the 1970's around the office and administrative area.

 

Refuge lands provided the right environmental conditions for the trees to grow and they started to spread. Left unchecked for many years the trees spread further onto refuge lands and water delivery canals. The canals were ideal for the trees to spread, as olives like the water source for growing and where the seed can be carried and spread further down the water way. Birds and other animals also ate the fruit and spread them beyond the waterways, into the uplands. Once established, a single tree can expand into a thick clump with branches covered in thorns, and eventually into a large stand of trees. 

 

With the expansion of olives over the refuge, native upland and wetland habitats became degraded. Water delivery canals were choked with trees, decreasing water delivery capabilities. Many wetlands became encircled by the trees and prairies were encroached upon, fragmenting grassland habitats throughout the refuge. Unlike the past where large expanses of native prairie and wildlife existed, the “new arrivals” brought changes to the landscapes. Changes to which the land and the native wildlife were not accustomed to. The Russian olive trees provided nesting and perching locations for a new suite of birds of prey not typical of the treeless prairie. Meso-predators such as raccoon, skunk, and fox not typically found in the open prairie, found new travel corridors created by the trees and the ability to use the trees as cover. 

The most significant effect of these invasive trees have had has been to upland nesting birds such as songbirds, waterfowl, and upland game birds. Research has proven that fragmentation of upland and wetland habitats by trees causes these bird species to abandon or avoid these areas, as the trees increase predation to nests, adults, and their young. 

Russian olive trees impeded the management and protection of the migratory bird species for which Bowdoin NWR was established. The effects of habitat loss due to fragmentation, predation, and loss to upland bird diversity and reproduction, is more significant and detrimental in the long run to migratory birds than the benefits these trees may provide to a limited group of game species and non-resident wildlife. For this reason removal of Russian olive trees is critical. Control of Russian olive trees on the refuge started in 2000, and continues today as a means to improve habitat and protect migratory birds from predation.