 |
|
|
 |
|
|
|
|
|
|
|
一般影響
此物種的侵入性，部分原因是它能生產大量長壽命的種子(可能在林火之後大量發芽)，與能長出大型樹冠(遮蔽其他植物)。其枝葉可能有植物相剋性。黑荆(Acacia mearnsii)與原生植物競爭，進而取代它。它可能取代植草社群，減少土地承載能力。大量的黑荆植群會增加降雨截留和蒸發，從而導致減少徑流。黑荆下面的土壤會更快脫水。(比草下的土壤快)黑荆(Acacia mearnsii)植株也會使河岸不穩定，並降低物種多樣性物。(Adair, 2002; Sankaran, 2002; Le Maitre et al.1999; Samways et al1996)
在南非，商業種植和入侵的A .mearnsii，減少地表徑流，減少保水能力，造成估計每年280萬美元的經濟損失。根據夸祖魯-納塔爾野生生物報告(南非政府機關負責管理夸祖魯-納塔爾省保護區)，外來植物的擴張，特別是香澤蘭(Chromolaena odorata), 馬櫻丹(Lantana camara), Acacia dealbata, 與黑荆(Acacia mearnsii)，是這些區域過去與未來最嚴重的威脅(De Wit, Crookes and Van Wilgen, 2001; Goodman, 2003)。
地點特有的影響：Kolukkumalai (India) 
競爭: Acacia mearnsii invades and suppresses native vegetation. Vattavada (India)
競爭: Invades and suppresses native vegetation. Israel
降低本地生物多樣性: Acacia mearnsii has the potential to form monospecific stands, reducing biodiversity. South Africa
其他: The commercial value of Acacia mearnsii on the one hand and its invasiveness on the other, give rise to a classic conflict of interest, where the benefits accrue to a number of people (i.e. profits from timber and tannin sales for wattle growers) and while society at large bears the external costs (i.e. a loss in water supply for locals and a national decrease in biodiversity).
改變林火機制: Increases in biomass lead to increases in fuel loads (often by up to a 10 fold). Dense stands of trees prevent access needed for fire management. This leads to an increase in fire intensity and damage (Versfeld and van Wilgen 1986, van Wilgen and Richardson, 1985, de Wit, Crookes and van Wilgen, 2001).
改變水文: Commercial plantations and invasive stands of Acacia mearnsii decrease surface runoff and water ability. This is due to an increase in the height and biomass of vegetation (which increases rainfall interception and transpiration causing a reduction in stream flow).
Increases water evaporation and reduces surface stream flow. Dense infestations of black wattle occurring in the riparian zones produce high rates of evaporation. Total annual evaporation may exceed 1500mm. In comparison, annual evaporation from indigenous grasslands and fynbos shrub lands commonly varies over the range of 600 to 850mm. The removal of black wattles is predicted to increase stream flow in an area, especially in areas of high evaporative demand and with low drought stress throughout the year (Dye and Jarmain, 2004).
改變營養機制: The increases in soil nitrogen levels (caused by the nitrogen fixing bacteria that live in symbiosis with leguminous plants) can make habitats unsuitable for indigenous plants and more susceptible to invasion by other exotic species.
棲地改變: The invasion of riverbanks causes deep channelling followed by slumping during floods. In addition, increases in fire intensity results in an increase in soil water repellency and increased erosion. Causes erosion and destabilisation of stream banks.
物理干擾: Invasive plants along river banks can reduce access for anglers, canoeists, white-water rafters and swimmers.
生態系統變化: Disrupts important ecosystem processes. Acacia. mearnsii (as well as a number of other Acacia species) has become invasive in South Africa and threatens conservation areas, dune ecosystems and the potential of agricultural land (Dennill and Donnelly, 1991, Hill, Gordon and Neser, 1999).
競爭: Competition between invasive wattles and important grazing grasses reduces grass cover; this affects rural communities in grassland areas in the Eastern Cape, Mpumalanga and KwaZulu/Natal provinces. In one study 94% of households reported this as a significant factor.
經濟 /民生: Losses due to invasive wattles were estimated to amount to 577 million cubic metres of water annually in South Africa. This corresponds to an economic loss of about $1.4 billion annually (Versfeld et al., 1998, de Wit, Crookes and van Wilgen, 2001).
降低本地生物多樣性: Species richness of birds is lower in areas with Acacia mearnsii stands. Total plant cover at the ground level is lower in areas invaded by Acacia. mearnsii.
Causes a displacement of diverse indigenous plant communities by single species (monospecific) wattle stands. Almost 1900 of the 3435 plant species in the South African Red Data List are threatened at least in part by all the alien invasive plant species. Mgahinga Gorilla National Park (MGNP) (Uganda)
改變演化模式: Lejju (2004) found that the level of regeneration in the Mgahinga Gorilla National Park is influenced by the intensity of cultivation and soil nutrients. The advanced growth beneath the exotic woodlots, especially Acacia mearnsii and Eucalyptus sp. is relatively impoverished.
降低本地生物多樣性: Lejju (2004) suggests that a low level of native species biodiversity is supported by, and able to exploit, exotic tree communities (such as those created by stands of Acacia mearnsii).
|
|
|
|
 |
|
