Discuss about the weed bitou bush and the threat it poses to ecosystems along the New South Wales coast line.
According to Vranjic (2017), the Bitou bush is one of the weeds that threaten coastal dune vegetation along the New South Wales Coast Line (NSW) due to its ability to spread which impacts on the environment and ecosystem potentially. The weed has the potential to replace native flora and spreads through both distributed and undistributed areas. Furthermore, bitou bush alters the many native animals and birds that live in the New South Wales Coast Line, and it also creates the favorable environment for an infestation of other highly invasive weeds. Moreover, the reason bitou bush is the worst weed in the NSW is because it can survive in harsh conditions that often get experienced on the coastal dunes and its leaves are almost succulent and waxy. Also, the weed has an adaptation for the sandblasts experienced on the coastal dunes, and it can withstand intense temperatures in the summer (Csurhes, 2016). Another issue why bitou bush is dangerous is because it is a competitive weed which smothers native plants and invades the natural habitat and the source of food for native animals. The plants that are adversely affected are the shrubs, ferns, and herbs while the ecological communities affected are Kurnell Dune Forest and the Eastern Suburbs Banksia Scrubs (HamilitonA, 2012). This article aims at addressing these issues and how the bitou bush impacts on the ecosystem and the importance of managing the spread of this plant since it’s a hazard that is harmful to the plants, environment, and animals.
History
Bitou bush is often thought to have accidentally gotten introduced in Australia because the origin of the woody shrub is Southern Africa (Groves, 2008). Most of the spreading was through natural means either by wind, birds, and animals and was spread intentionally for dunes erosion control. According to James (2014), wherever bitous bush occurs primarily on the conserved environment, it tends to have a deleterious effect on the ecosystem affecting the heathlands, forests, and woodlands. Bitous weed was declared first a noxious weed in Shoalhaven City Council (1993), and it was later declared noxious in the remaining south coast in 1999. In NSW, noxious weeds such as bitous bush get proclaimed by the Local Control Authority which has taken the role of managing the weed problem (Thompson, 2008).
Description
The bitous bush is an evergreen shrub which is occasionally one to two meters high and its leaves are often bright green, thick and succulent while the new growing bitous bush are whitish and they get covered with fine hairs. According to Scott (2014), the noxious weed has yellow daisy flowers that have petals ranging from 11-13mm, and black fleshy fruit follows these. Each fruit has one oval with ribbed seeds that are 5-7 mm long, and the bitous bush gets peak flowering during autumn (Gross, 2017).
Habitat
Bitous bush gets adapted to humid coastal areas where they receive rainfall frequently during the summer and relatively dry during winter. Furthermore, the annual rainfall is between 1000mm to 2000 mm per annually. The weed can tolerate salt spray, water-logged soil which makes it invade the swamp edges and wetlands.
Effects on Native Plants
The bitous bush has the impact the organization of plants from the genes, species, population, and communities to the ecosystems. According to Jane (2007), bitous bush threatens the native coastal community especially in the NWS where in some areas the weed forms the virtual monoculture. The weed does not affect the physical shape of the coastline when its young but when it grows it takes over the space occupied by dunes. During this process, the bitous bush covers native vegetation which was previously there thus making the vegetation vulnerable. Therefore, the native plants are directly affected by bitous bush which may result in the loss of native plant species which is the adverse effect of bitous bush on the ecosystem (Jane, 2007)
Effects on the Ecosystem Function
It is crucial in that the biotus bush affects the functioning of the ecosystem because it causes invasion of the nutrition cycle to nitrogen that available in the soil. Furthermore, the biotus bush may alter the chemical characteristics of the ecosystem which includes soil organic chemistry. Moreover, the bitous bush affects the availability of water in the soil and to other native plants, and it also affects the availability of some inorganic compounds in the soil. Also, biotus bush may change the ecosystems’ physical properties such as the temperature, light, and humidity available in the atmosphere.
Effects on Shoot and Root Length of Native Vegetation
According to Al Harun (2016), the invasion of bitous bush in NWS has resulted in native vegetation to have difficulty in growing well-developed roots that used to go deep in the soil. It is because most of the water levels in the soil get occupied by the roots of the bitous bush resulting to nutrition competition between the native plants and the bitous bush. Thus, the native vegetation is forced to have shallow and weak roots because the competition of the resources in the soil is very high. It affects the plant in that the native plant is not as healthy as it used to be because of the bitous bush invasion.
Effects on the Soil
The leaves of the bitous bush have high alkaline content, so when the leaves fall off, they get into the soil resulting in the high chemical concentration in the soil. It affects the native vegetation in that some species of plants that do not survive in high alkaline soil content end up getting extinct from the vegetation (Dragovich, 2015). Therefore, the vegetation of the NWS will have to change because some species of native plants are no longer available due to the invasion of the bitous bush. Furthermore, the hydrophobic that bitous bush extract from its roots into the soil have an effect on L.longifolia, I. nodosa and A. megalocarpa establishment.
Bitou Bush Affects Fauna
In spite of the less presence of litter in habitats that have been invaded by the bitou bush, there is richness and abudance in litter invertebrates which are not adversely affected by invasion of the bitou bush. Though, there is composition change in the assemblage of the invertebrates due to cooler and moisture environment of the sites that have gotten invaded. Therefore, there is the presence of some invertebrate groups which are more abundant especially species that thrive due to the moisture such as the millipedes, amphipods, earthworms, and springtails. Moreover, some of the invertebrates are less abundant which include centipedes, spiders, native cockroaches and ants (TAP, 2006). These changes to ecosystem imply that it results in the shift in food webs although there is an increase in species that mostly thrive on decomposition. These decomposition species may be the cause of the observed decomposition increase rate. Also, there were observations that the Heteroptera did respond to the mesic conditions present in the invaded areas by bitou bush as compared to the arboreal invertebrates. According to French (2008), the invasion of the bitou bush has the variable effect on the bird assemblage thus affecting birds that depend on plant resources for food. Such birds that have been changed due to the bitou bush invasion are frugivores and nectrarivores which have decreased in the invaded regions. Thus, the NWS regions invaded by the bitou bush provide inadequate food resources for the frugivores and nectrarivores. However, there was little impact on the foraging canopy species and few changes on some insectivores habitats. Furthermore, there were few changes in the behavior of the silvereyes, Holland honeyeaters, little wattlebirds, and superb fairywrens. These species spent less time undertaking behaviors differently in NWS regions that were affected by the bitou bush and NWS regions that were not affected. However, there were observations that bitou bush changed NWS regions has three of these bird species depending on the native plants for food resources. Therefore, the reduction in native plants abundance in NWS invaded habitats gives a good reason why some of the bird species were no longer present in these bitou bush invaded habitats. Moreover, nectarivores reliance on the native plants in NWS regions has decreased because there is less abundance of food resources in NWS invaded habitats.
Bitou bush Seedlings Germinate Rapidly and the Growth Rate in High
According to French (2008), the bitou bush is a very hazardous weed because it thrives to displace the native species in their early life when growing as compared to native adult plants. Observations made indicate that growth rate, flower production and photosynthetic stress indices on adult native plant species (Monotoca elliptica. Lomandra longifolia and Correa alba) were not affected by the invasion of the bitou bush habitat in NWS. Hence, it is evident that the bitou bush does not change native adult plants in the NWS habitat thus having less impact on the adult plant vegetation. However, observations made show that the bitou bush seedlings grew rapidly than the NWS coastal wattle seedlings which were a clear indication that the bitou bush focused on displacing the native seedlings. For instance, the bitou bush seedlings increased in biomass a bit faster and decreased the biomass of Ficinia nodosa and the Banksia intergrifolia. Furthermore, habitats in the NWS that did not get cleared due to bitou bush invasion had germination of more bitou bush seeds, and they grew more rapidly as compared to the native seeds. Hence, the growth rate of the bitou bush had an adverse effect on the native seedlings which made the invasion of the bitou bush on the habitat more effective.
Bitou bush Emit Chemicals in Soil Processes Which Influence Growth of Seedlings
The bitou bush tends to influence the growth of dominant shrub such as the Acacia sophorae which has chemical interference within the soil layers thus facilitating the bitou bush invasion in NWS habitat. Recent research shows that the bitou bush invades the seedling growth rate of various species through toxic emissions from its roots into the soil which affects the native seedlings (Lindsay, 2005). Thus the coastal wattle seedlings in the NWS were affected by the emissions made by the bitou bush into the soil which effectively facilitated the impact that the bitou bush has on the NWS native plants.
Management Regimes Impact Differently on the Bitou bush
The management regimes that are put in place to deal effectively with the invasion of the bitou bush may also have an impact on the native plant species. For instance, the use of bush regenerators improved the recovery of the native plant species compared to the use of non-targeted aerial spraying. The two techniques used are meant to reduce and manage bitou bush invasion though more weed species were observed to thrive in areas were weed control activities did not get implemented. It got caused by the increase in the soil disturbance and the weed propagules that got imported on workers’ clothing and tools. Moreover, a native species tended to establish after spray-burn treatments which also increased the invasion of bitou bush and other weeds. Also, the use of herbicides sprays using metsulfuron methyl and glyphosate are effective bitou bush control methods through the herbicides reduced the abundance of some native plant species (Turner, 2013). For instance, the glyphosate has an impact that has endangered the Pimelea spicata plant species which has had the adverse effect on the native vegetation in the NWS habitat. Furthermore, the herbicides have affected non-targeted organisms such as the invertebrates since some of the invertebrates consume dead decomposing native plants. Also, the frugivorous birds decreased their abundance in NWS habitats that were herbicide treated when trying to manage the bitou bush invasion. Moreover, the use of the biocontrol agents may affect the ecosystem by having an impact on the herbivore-plant interactions. For instance, the tephritid fly was biocontrol agent that was released to manage the bitou bush invasion though it also influenced the native food webs. The tephritid fly reduces the number of species that enhanced interactions among plants such as the parasitoids in spring which increased the native parasitoids abundance.
Bitou bush invasion Lowers Abundance of Many Native Plant Species
Though the NSW legislation indicates that bitous bush threatens only 46 species the truth is that the threat is more significant than the species listed. Surveys along the NSW coastline suggest that many plant species are at risk due to the widespread bitou bush invasion. For instance, the Spinifex sericeus, Carpobrotus glaucescens and the Acacia longifolia have a decreased abundance in the areas that have been invaded by the bitous bush along the NSW coastline.
Bitou bush Changes the Ecosystem processes and Properties
The invasion by the bitou bush has resulted in the change in the characteristics of the NWS coastal ecosystems. Generally, in Australia, the bitous bush affected habitats are cooler, darker and have more moisture than habitats that did not get invaded by the bitous bush. Furthermore, bitou bush decomposes a bit faster compared to the native species which has reduced the leaf litter layer. Also, this has resulted in the decrease in leaves biomass falling in the invaded NWS habitats. Hence, the nutrients released into the soil get absorbed quickly into the invaded habitats which results in only a few nutrients getting stored in the litter layer. Moreover, habitats along the NWS coastline that have been invaded by the bitous bush have a different pattern of fleshy fruit production. It got observed that areas in the ecosystem that were not invaded by the bitous bush produced large quantities of fruits while the native fruits of the invaded habitats were scarce and less. Also, about 18 bird species depend on the bitou bush fruits for food resources which increases the possibility of seed dispersal which may increase the invasion of the bitous bush.
Control and Management Implication of the Bitou bush
Preventing the Spread of Bitou bush
It got observed that the bitou bush seedlings have the adverse effect on the native seedlings compared to the native adult plant hence effective control can get achieved better if it gets implemented during the early stages of the bitous bush seedlings. It can get done by changing the space occupation probabilities during the early stages of the bitous bush seedlings. There were little bitou bush seeds in the soil of native areas adjacent to NWS habitat that were affected by the bitous bush. It meant that seed dispersal is rare thus controlling the spread of bitous bush at the early stages could be useful. Furthermore, the dispersal pattern used by the frugivores suggests that dispersal that is localized can be supplemented by long-distance dispersal which will cause distant bitou bush patches forming on the NWS coastal line (Broese, 2002). Hence, since the establishment and growth of bitous bush seedlings are rapid compared to the native seedling establishment at the NWS coastline, any bitous bush seedling that germinates have a high chance of forming a new bitous bush patch. Moreover, removing the weed seedlings will help in prevent accumulation of soil-based allelopathic chemicals thus allowing the establishment of native species after the biotus bush has gotten controlled along the NWS coastline (Gallagher, 2014).
Weed Removal Activities
According to Lindenmayer (2015), the use of aerial spraying and intensive hand pulling of the weeds has not proven to be effectively regeneration on the bitous bush though the use of burning of sites invaded by the bitous bush has shown to be effective. It is because burning these sites support the regeneration of the native vegetation along the NWS coastline. Furthermore, burning enhances germination of the soil seed bank and also it enables seedling of the native species to increase. Thus, burning helps in restoration of vegetation to its previous state before the invasion of bitous bush took effect. However, burning is not suitably effective unless there is the use of additional management actions that will ensure that the native species get reestablished on the NWS coastline. For instance, spray-burn spray treatment is more effective than just spraying; therefore, the second spraying treatment should get replaced by hand pulling (Lindenmayer, 2015). It is because repeat spraying may reverse many benefits that got contributed by burning. Most of the native species especially seedlings are often susceptible to glyphosate because about seven species of native seedlings are affected by spraying. It is also important that after bitou bush control by burning there be resources that will help in managing the competitive bitou bush seedlings. Moreover, the loss of native plant species and reduction in the native seedbanks to assist in the regeneration along the NWS coastline may pose difficulty in the restoration of the invaded habitat to its previous healthy state.
Community Groups and Bitou bush Control
There are community groups in the NWS coastal line that are not undertaking the severe steps in ensuring that bitou bush management has gotten implemented effectively. Therefore, it is crucial that the community is educated about the significance of bitou bush management because it poses a threat to the ecosystem in the coastal NWS habitat. According to Council (2012), this will help in public awareness about the importance of controlling this noxious weed because there would be volunteers who would be will to participate in the management of this weed.
Conclusion
It is evident that bitou bush is one of the noxious weeds that is affecting the ecosystem at the NWS coastline and there is urgent need to manage it. Furthermore, the weed has numerous effects on the native vegetation in that it affects the root and shoot length of the native plants. Moreover, bitous bush seedlings have an adverse impact on the growth of the native seedlings because they grow rapidly thus the noxious weed depends on displaced as its effective way of impacting on the native vegetation. Also, the article details the implications that bitou bush has on the ecosystem which affects the food resources of the frugivores, and this has affected the bird population in the NWS. It is there vital that the bitou bush gets managed and controlled to ensure the restoration of the native vegetation along the NWS coastal line.
References
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