Written by: Kyra Mckenna, Alex Hristovski, Sabrina Luppino, and Ian Henderson
While the history of the Himalayan Balsam begins with its origins in the Western and Central Himalayan region (Chandraju, Thejovathi & Chidan, 2012) this plant was brought to our gardens into North America and Europe to make a garden more unique and interesting to the owner. Other introduced plants have naturalized and become part of the ecosystem within North America. Norway Maple, Japanese Maple, Tulips, Japanese Barberry, Russian Olive, Burning Bush, and the Himalayan Balsam are just a few. However in North America and Europe the Himalayan Balsam is an invasive species (Rusterholz, Salamon, Ruckli, & Baur, 2014). One of the earliest records of this plant being in a country different from its origin was during the seventh century in China (Rotherham, 2000). Globally, garden specimens of Impatiens glandulifera were introduced to the United Kingdom in 1839 by a surgeon in India sending samples to the Horticultural Society of London. Soon after, in 1855, it began naturalizing elsewhere in the United Kingdom. By 1898, it was considered a weed (Clements, Feenstra, Jones & Staniforth, 2007). In Ontario nurseries Himalayan Balsam can still be purchased and grown for the gardeners that wish to plant them (Hubert, 2017).
Himalayan balsam is an annual ground cover that has the ability to change a local landscape by becoming the dominant species, which reduces species richness and diversity (Hulme & Bremner, 2006). The fact that Impatiens glandulifera’s range is controlled by cool temperatures is an important ecological factor. Seeds of Impatiens glandulifera go through a stratification period in winter, before germinating in early spring. This plant requires a short, cold wet period before germinating (Skálová, Moravcová, & Pyšek, 2011). Himalayan Balsam reaches a growth height of 3 m, but more commonly reaching 2 m within a season, which makes it the tallest annual plant in the UK (Hulme & Bremner, 2006). This height results in increased shade making it difficult for other plants to grow (Ammer, Schall, Wördehoff, Lamatsch & Bachmann, 2011). Soil erosion is another issue associated with this plant as it has shallow roots. Himalayan balsam’s ability to over shade even small wooded shrubs that hold the riparian zone together has caused many issues. When they die in the fall, the shallow roots can easily be overturned causing the soil to come loose and erode (Ortin & Evans, 2013). This is a major issue for many European countries which is why they have responded to the presence of Himalayan balsam within their countries. For example, Himalayan Balsam can be found on the “…‘black list’ of harmful invasive species.”in Switzerland (Hulme & Bremner, 2006). It is listed in the UK as one of the top 20 most invasive plants, as well as having specific control measures in place in Germany (Hulme& Bremner, 2006). This is due to its high seed count of 2,500 seeds per plant which spread within 3 meters (Tanner, Jin, Shaw, Murphy, & Gange, 2014).
Table 1: Summary of the management methods that have been used for Himalayan Balsam, Impatiens glandulifera and other invasive species. (Created by Luppino, 2017; content cited in following paragraphs)
|Do Nothing||Nothing||Increased nector for pollinator species, lack of diversity of species|
|Manual Hand Pulling||$1,742.00 per 1 acre
|Somewhat effective, clears area allows for erosion|
|Chemical Control||$34.00 per 1 acre
|Somewhat effective, chemicals enter environment causing biomagnification|
|$1,942.00 per acre Expensive||Potential of another invasive species|
|Higher destruction of habitats from machine usage|
|Over-watering using slow release water systems||Not Expensive||Effective at reducing species density, large amounts of water use bad idea in drought conditions. Can cause erosion|
|Planting riparian zone trees||Most Expensive as it includes multiple plans||Long process but most likely to restore forest to natural state|
The following paragraphs further explain methods listed in Table 1.
The action of doing nothing must be considered. An important consideration to make when doing nothing is if the particular population is causing a significant issue. If the impact of the plant in the specified area is not high, leaving it may be the right thing to do. If removal occurs, the site would be a newly disturbed environment that more harmful plant species could colonize (Hulme & Bremner, 2006).
The manual hand pulling method for Himalayan Balsam is classified as effective (Beck, 2008). When manual control is done effectively it can be very successful, hand pulling of the species has to be done on a number of occasions (Beck, 2008).
Chemical control is not an effective option due to the main population living in riparian zones, chemicals can cause a large amount of damage to the water systems and within the forest biome, as many chemical compounds take years to breakdown (Carson, Darling & Darling, 2002). However using chemicals in non riparian locations is a method that is used with highly competitive invasive species (Burkhart & Nentwig, 2008). Spraying chemicals such as herbicides, spot spray and broadcast spray are examples of chemicals used with the intentions to wipe out the invasive species (Burkhart & Nentwig, 2008). Spraying chemicals on the Himalayan Balsam has been used for a removal method (Beck, 2008). This method was somewhat effective on the Himalayan Balsam population. The results show that the species often show a somewhat significant difference after being sprayed.
Biological control is an effective technique that should be considered, this can be done in a variety of ways. Using species as natural predators and reseeding native plants to an area where the manual method was performed several times are ways to implement biological control (Burkhart & Nentwig, 2008). If this is studied thoroughly, it can be successful. In one study the fungal and arthropod species utilized to target the Himalayan Balsam also affected other non-target plant species, thus making the control method undesirable (Varia, Pollard, & Carol, 2016). Only one of the species was deemed safe for release and provided some control of the Himalayan Balsam (Varia et al., 2016). The solution proposed by this study was an effective biological control agent, which was identified as the rust fungus from the Puccinia species (Varia et al., 2016).
Mechanical management is often the easiest and cheapest removal method. It can require mowing or using heavy equipment, which is not effective for the Himalayan Balsam. When Himalayan Balsam is mowed, it will cause a large amount of stress on the species and they may react by releasing large quantities of seeds.
Manipulating the environment by changing environmental conditions has been considered as a management plan. The factor that was found to have a negative influence on Impatiens glandulifera is when intensely watered three times a day, its biomass dropped without any influence of other disturbances (Cuda, Skálová, Janovsky & Pyšek, 2015). The method of over-watering could be carried out by an automatic watering system, such as Treegator, a watering bag that releases water over time (Treegator, 2017), or we could ask cottagers with the plant on their property to water it three times a day, making time and labour costs minimal.
By making the plant vulnerable in its habitat by over-watering, we can then take the next step to remove it and plant low growing, bank stabilizing trees. Staghorn sumac is an excellent stabilizer for banks and holds water (Zhanjiang, Chuangdao, Jinzheng, Huijin & Lei, 2009). Growing to a height of 6m while being native to North America, it shows invasive tendencies of quick growth and frequent reproduction (Congyan, Hongguang, Jun, Jiawei & Daolin, 2016; Farrar, 1995). Canada contains a high amount of native willows with 76 species. Willows are fast growing, easy to propagate and prefer sites with large amounts of water. The Pussy Willow is a low growing willow native to Ontario’s wetlands and riparian zones, growing to a height of 4-6 meters (Mosseler, Major & Labrecque, 2014; Farrar, 1995). By pulling the Himalayan Balsam in some of its less established areas and replacing them with young willows and sumac, this will help reestablish the natural forest and keep banks stable. However the ground cover will still have issues growing. This method is costly for manual labour, as well as time consuming and it needs to be repeated in order to ensure Impatiens glandulifera is not returning.
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