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* [[Poaceae|Grasses]]: Studies in South Africa have found that grass richness reduces by more than 50% under intense bush encroachment.<ref>{{Cite journal|last=Mogashoa, R., Dlamini, P. & Gxasheka, M.|date=2020|title=Grass species richness decreases along a woody plant encroachment gradient in a semi-arid savanna grassland, South Africa.|journal=Landscape Ecol|doi=10.1007/s10980-020-01150-1}}</ref> In North America, a meta-analysis of 29 studies from 13 different grassland communities found that species richness declined by an average of 45% under bush encroachment.<ref>{{Cite journal|last=Ratajczak, Z., Nippert, J., Collins, S.|date=2012|title=Woody encroachment decreases diversity across North American grasslands and savannas.|journal=Ecology|volume=93(4)|pages=697–703|doi=10.1890/11-1199.1}}</ref> Among the severely affected flora is the [[Cypripedium candidum|small white lady's slipper]] .
* [[Poaceae|Grasses]]: Studies in South Africa have found that grass richness reduces by more than 50% under intense bush encroachment.<ref>{{Cite journal|last=Mogashoa, R., Dlamini, P. & Gxasheka, M.|date=2020|title=Grass species richness decreases along a woody plant encroachment gradient in a semi-arid savanna grassland, South Africa.|journal=Landscape Ecol|doi=10.1007/s10980-020-01150-1}}</ref> In North America, a meta-analysis of 29 studies from 13 different grassland communities found that species richness declined by an average of 45% under bush encroachment.<ref>{{Cite journal|last=Ratajczak, Z., Nippert, J., Collins, S.|date=2012|title=Woody encroachment decreases diversity across North American grasslands and savannas.|journal=Ecology|volume=93(4)|pages=697–703|doi=10.1890/11-1199.1}}</ref> Among the severely affected flora is the [[Cypripedium candidum|small white lady's slipper]] .
* [[Mammal|Mammals]]: bush encroachment can lead to the displacement of [[Herbivore|herbivores]] and other mammal types that prefer open areas. Among the species found to lose habitat in areas affected by bush encroachment are cats such as [[cheetah]] <ref>{{cite journal |last1=Nghikembua |first1=Matti T. |last2=Marker |first2=Laurie L. |last3=Brewer |first3=Bruce |last4=Mehtätalo |first4=Lauri |last5=Appiah |first5=Mark |last6=Pappinen |first6=Ari |title=Response of wildlife to bush thinning on the north central freehold farmlands of Namibia |journal=Forest Ecology and Management |date=1 October 2020 |volume=473 |pages=118330 |doi=10.1016/j.foreco.2020.118330 }}</ref> as well as antelopes such as the [[Common tsessebe]] and [[Hirola]].
* [[Mammal|Mammals]]: bush encroachment can lead to the displacement of [[Herbivore|herbivores]] and other mammal types that prefer open areas. Among the species found to lose habitat in areas affected by bush encroachment are cats such as [[cheetah]] <ref>{{cite journal |last1=Nghikembua |first1=Matti T. |last2=Marker |first2=Laurie L. |last3=Brewer |first3=Bruce |last4=Mehtätalo |first4=Lauri |last5=Appiah |first5=Mark |last6=Pappinen |first6=Ari |title=Response of wildlife to bush thinning on the north central freehold farmlands of Namibia |journal=Forest Ecology and Management |date=1 October 2020 |volume=473 |pages=118330 |doi=10.1016/j.foreco.2020.118330 }}</ref> as well as antelopes such as the [[Common tsessebe]] and [[Hirola]].
* [[Bird|Birds]]: amongs the birds negatively affected by bush encroachment<ref>{{Cite journal|last=Sirami, C. and Monadjem, A.|date=2012|title=Changes in bird communities in Swaziland savannas between 1998 and 2008 owing to shrub encroachment|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1472-4642.2011.00810.x|journal=Diversity and Distributions|volume=18|pages=390-400|doi=10.1111/j.1472-4642.2011.00810.x|via=Wiley|doi-access=free}}</ref> are the [[Secretarybird]] , [[Grey go-away-bird]] , [[Marico sunbird]] , [[lesser prairie chicken]]<ref>{{Cite journal|last=Lautenbach, J. M., R. T. Plumb, S. G. Robinson, C. A. Hagen, D. A. Haukos, and J. C. Pitman|date=2017|title=Lesser Prairie-Chicken Avoidance of Trees in a Grassland Landscape|url=https://www.sciencedirect.com/science/article/pii/S1550742416300549|journal=Rangeland Ecology & Management|volume=70|pages=78-86|doi=10.1016/j.rama.2016.07.008|via=Science Direct}}</ref> and the [[Kori bustard]] .
* [[Bird|Birds]]: amongs the birds negatively affected by bush encroachment are the [[Secretarybird]]<ref>{{Cite journal|last=Hofmeyr SD, Symes CT, Underhill LG|first=|date=2014|title=Secretarybird Sagittarius serpentarius Population Trends and Ecology: Insights from South African Citizen Science Data|url=https://doi.org/10.1371/journal.pone.0096772|journal=PLoS ONE|volume=9(5) e96772|pages=|doi=10.1371/journal.pone.0096772|via=|doi-access=free}}</ref>, [[Grey go-away-bird]], [[Marico sunbird]], [[lesser prairie chicken]]<ref>{{Cite journal|last=Lautenbach, J. M., R. T. Plumb, S. G. Robinson, C. A. Hagen, D. A. Haukos, and J. C. Pitman|date=2017|title=Lesser Prairie-Chicken Avoidance of Trees in a Grassland Landscape|url=https://www.sciencedirect.com/science/article/pii/S1550742416300549|journal=Rangeland Ecology & Management|volume=70|pages=78-86|doi=10.1016/j.rama.2016.07.008|via=Science Direct}}</ref> and the [[Kori bustard]].<ref>{{Cite journal|last=Sirami, C. and Monadjem, A.|date=2012|title=Changes in bird communities in Swaziland savannas between 1998 and 2008 owing to shrub encroachment|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1472-4642.2011.00810.x|journal=Diversity and Distributions|volume=18|pages=390-400|doi=10.1111/j.1472-4642.2011.00810.x|via=Wiley|doi-access=free}}</ref>
*[[Insect|Insects]]: bush encroachment is linked to species loss of insects with preference for closed habitats, such as [[butterfly]]<ref>{{Cite journal|last=Ubach A, Páramo F, Gutiérrez C, Stefanescu C|date=2020|title=Vegetation encroachment drives changes in the composition of butterfly assemblages and species loss in Mediterranean ecosystems.|journal=Insect Conserv Divers|volume=13|pages=151-161|via=Wiley}}</ref>
*[[Insect|Insects]]: bush encroachment is linked to species loss of insects with preference for closed habitats, such as [[butterfly]]<ref>{{Cite journal|last=Ubach A, Páramo F, Gutiérrez C, Stefanescu C|date=2020|title=Vegetation encroachment drives changes in the composition of butterfly assemblages and species loss in Mediterranean ecosystems.|journal=Insect Conserv Divers|volume=13|pages=151-161|via=Wiley}}</ref>


Revision as of 05:58, 16 December 2020

bush encroachment at Waterberg Namibia
View of bush encroached land at the Waterberg Plateau Park in Otjozondjupa Region, Namibia

Bush encroachment (also shrub encroachment, woody encroachment) is a natural phenomenon characterised by the increase in density of woody plants (bushes and shrubs) at the expense of the herbaceous layer (grasses and forbs). It is often considered an ecological regime shift and a symptom of land degradation. Bush encroachment is found to have severe negative consequences on key ecosystem services, especially biodiversity, animal habitat, land productivity and groundwater recharge. Bush encroachment can refer both to the expansion of native plants as well as the invasion and spread of invasive species. The phenomenon is observed across different ecosystems and with different characteristics and intensities globally. Among the more severely affected landscapes is the Veld in Southern Africa.

Causes

The earliest published notion of bush encroachment dates back to 1954.[1] Various factors have been found to contribute to the process of bush encroachment. A distinction can be made between bush encroachment due to land intensification and bush encroachment after land abandonment.

Land intensification

In the context of land intensification, a frequently cited cause of bush encroachment is overgrazing, commonly a result of overstocking and fencing of farms, as well as the lack of animal rotation and land resting periods. A connected cause for bush encroachment is the reduction in the frequency of wildfires that would occur naturally, but are suppressed in frequency and intensity by land owners due to the associated risks. Also the reduction of browsing by herbivores, e.g. when natural habitats are transformed into agricultural land, fosters woody plant encroachment, as bushes grow undisturbed and with increasing size also become less susceptible to fire.

Land abandonment

Where land is abandoned, the rapid spread of native bush plants is often observed. This is for example the case in former forest areas in the Alps that have been converted to agricultural land and later abandoned.

Another frequently cited theory is the state-and-transition model. This model outlines how rainfall and its variability is the key driver of vegetation growth and its composition, bringing about bush encroachment under certain rainfall patterns.

Climate Change

Climate change has been found to accelerate bush encroachment. Firstly, increased atmospheric CO2 concentrations fosters the growth of woody plants. This is because woody plants with C3 photosynthetic pathway thrive under high CO2 concentrations, as opposed to grasses with C4 photosynthetic pathway.[2][3] Moreover, changes in precipitation can foster woody encroachment. Increased precipitation can foster the establishment, growth and density of woody plants. But also decreased precipitation can promote bush encroachment, as it fosters the shift from mesophytic grasses to xerophytic shrubs.[4]

Impact

Various ecosystem services are negatively impacted by bush encroachment, such as biodiversity, groundwater recharge and land productivity.

Biodiversity

Bush expands at the direct expense of other plant species, potentially reducing plant diversity and animal habitats. These effects are context specific, a meta analysis of 43 publications of the time period 1978 to 2016 found that bush encroachment has distinct negative effects on species richness and total abundance in Africa, especially on mammals and herpetofauna, but positive effects in North America.[5]

Evidence of biodiversity losses include the following:

Groundwater Recharge

Woody plant encroachment is frequently linked to reduced groundwater recharge, based on evidence that bushes consume significantly more rainwater than grasses. Concrete experience with changes in groundwater recharge is however largely based on anecdotal evidence or regionally and temporally limited research projects.While there is general consensus that bush encroachment has an ecohydrological impact, studies find that this impact on groundwater recharge differs between sandstone bedrocks and karst regions as well as between deep and shallow soils.[13]

Land Productivity

Bush encroachment directly impacts land productivity, as widely documented in the context of animal carrying capacity. In the Southern African country Namibia it is assumed that agricultural carrying capacity of rangelands has declined by two-thirds due to bush encroachment. In East Africa there is evidence that an increase of bush cover of 10 per cent reduced grazing by 7 per cent, with land becoming unusable as rangeland when the bush cover reaches 90 per cent.[14]

Also touristic pontential of land is found to decline in areas with heavy bush encroachment, with visitors shifting to less encroached areas and better visibility of wildlife.[15]

Bush Control

Prevention, rehabilitation, maintenance

The term bush control, or brush management, refers to actions that are targeted at controlling the density and composition of bushes and shrubs in a given area. Such measures either serve to reduce risks associated with bush encroachment, such as wildfires, or to rehabilitate the affacted ecosystems. Literature emphasises that a restoration of bush encraoched areas to a desired previous non-encroached state, is difficult to achieve and the recovery of key-ecosystem may be short-lived or not occur. Intervention methods and technologies must be context specific in order to achieve their intended outcome.[16]

Three different categories of measures can be distinguished:[17]

  • Responsive measures (bush thinning): the reduction of bush densities through targeted bush harvesting or other forms of removal.
  • Maintenance measures (aftercare): repeated or continuous measures of maintaining the bush density and composition that has been established through bush thinning.
  • Preventative measures (sustainable land management practices): application of proven good management practices to prevent the excessive growth of woody species, e.g. through appropriate stocking rates and rotational grazing in the case of rangeland agriculture.

Practices of combating bush encroachment, regardless of the exact methodology applied, are often referred to as "de-bushing". Although this term is widely used and also cited in various scientific works, it is disputed. "De-bushing" can easily be misunderstood as the practice of clearing and area of all bush plants, which is not the aim in most efforts to combat bush encroachment. The terms "bush control, "bush thinning" and "selective bush harvesting" are therefore considered more adequate terms. Efforts to counter bush encroachment fall into the scientific field of restoration ecology and are primarily guided by ecological parameters, followed by economic indicators.

Methods

Methods of bush control encompass

  • natural bush control: among others through the introduction of browsers, such as Boer goats, or controlled fires[18]
  • mechanical bush control: harvesting of bushes and shrubs with manual or mechanised equipment
  • chemical bush control: the application of herbicides, in particular arboricides

Ecosystems affected by bush encroachment

Central European Alps and Alpine Tundra

Areas that formerly were forests require continuous maintenance to avoid bush encroachment. When active land cultivation ends, fallow land is the result and gradual spread of shrubs and bushes can follow. Animal species once native to Central Europe effectively countered this natural process. These include herbivores such as European bison, auerochs (extinct), red deer and feral horse. Grassland and heath are considered to require protection due to their biodiversity as well as to preserve cultural landscapes. Bush encroachment is therefore frequently countered with selective removal of woody biomass or through the seasonal or year-round introduction of grazing animal species. such as sheep, goats, heck cattle or horses. Bush encroachment frequently occurs in the Alps, where structural change in agriculture often leads to the abandonment of land. Alnus viridis is the most widely distributed shrub species in the subalpine zone and is found to severely impair plant diversity when encroaching grassland.[19] Further, bush encroachment is common in the Alpine Tundra of Norway and Sweden[20][21]

Mediterranean Basin

The Mediterranean region is widely reported to be affected by bush encroachment. This is found to have negative effects on biodiversity and to magnify climate and related droughts. At the same time encroaching shrubs are also found to have a positive effect, reversing the desertification process.[22]

North American Grasslands

North American grasslands have been found to be affected by woody plant encroachment. In the United States, affected ecosystems include the Chihuahuan Desert, the Sonoran Desert, the Northern and Southern Rocky Mountains, the Sagebrush Steppe, as well as the Southern and Central Great Plains. Negative impacts on forage production and an interrelation with carbon sequestration are documented.[23] At the same time in the semiarid karst savanna of Texas, USA, woodly plant encroachment has been found to improve soil infiltrability and therewith groundwater recharge.[24]

Asian Temperate Savanna

Temperate savanna-like ecosystems in Northern China are found to be affected by shrub encroachment, linked to unsustainable grazing and climate change.[25]

Latin American Grasslands

Studies point at bush encroachment in several Latin American counties. This includes Nicaragua, where Vachellia pennatula is known to encroach due to land intensification as well as land abandonment.[26]

Eastern African Grasslands

Ethiopia

Grasslands in the Borana Zone in southern Ethiopia is found to be effected by bush encroachment, specifically by Senegalia mellifera, Vachellia reficiens and Vachellia oerfota.[27]

Southern African Savanna

Namibia

Causes and Extent

Various factors have been found to contribute to the process of bush encroachment. These include the reduction in the frequency of fires as well as overgrazing (e.g. caused by overstocking and fencing of farms). Another frequently cited theory is the state-and-transition model. This model outlines how rainfall and its variability is the key driver of vegetation growth and its composition. Further, climate change has been found to accelerate bush encroachment, as CO2 in the air fosters bush growth.

Bush encroachment is estimated to affect up to 45 million ha. Agricultural productivity in Namibia has declined by two thirds throughout the past decades, mainly due to the negative impact of bush encroachment. The phenomenon affects both commercial and communal farming in Namibia, mostly the central, eastern and north-eastern regions.[28]

Government response

The Government of Namibia has recognised bush encroachment as a key challenge for the national economy and food safety. In its current National Development Plan 5, it stipulates that a total of 82.200 ha of land shall be treated against bush encroachment annually, i.e. through the thinning of the bush density by means of selective bush harvesting[29] The Government of Namibia, through the Support to De-bushing Project, pursues a value addition strategy, promoting the sustainable utilisation of bush biomass, which in turn is expected to finance bush harvesting operations.

In 2019, the three Namibian farmers’ unions (NNFU, NAU/NLU, NECFU) together with the Ministry of Agriculture, Water and Forestry published a best strategy document called “Reviving Namibia’s Livestock Industry”.[30] The document states that the Namibian livestock industry is in decline due to the loss of palatable perennial grasses and the increase in bush encroachment. Namibia’s rangelands show higher levels of bare ground, lower levels of herbaceous cover, lower perennial grass cover, and higher bush densities over large areas. Bush thickening leads to direct competition for moisture with desirable forage species and detrimentally influences the health of the soil. The best practice document identifies tried and tested practices of both emerging and established farmers from communal and title deed farms. These practices include the Split Ranch Approach, several Holistic Management approaches and the Mara Fodder Bank Approach. Other best practices include bush thinning, landscape rehydration and fodder production. The unions state that there is major scope for enhancing livelihoods through the sustainable use of bush products. In addition, increased profitability and productivity of the sector will have a major impact on the 70% of the Namibian population that depends directly or indirectly on the rangeland resource for their economic well-being and food security.

Economic Activity

Increasingly, the encroaching bush is seen as a resource for a biomass industry. Economic assessments were conducted to quantify and value various key ecosystem services and land use options that are threatened by bush encroachment. The evaluation was part of the Economics of Land Degradation (ELD) Initiative,[31] a global initiative established in 2011 by the United Nations Convention to Combat Desertification, the German Federal Ministry for Economic Cooperation and Development, and the European Commission. Based on a national study, cost-benefit analysis suggests a programme of bush control to generate an estimated and aggregated potential net benefit of around N$48.0 billion (USD 3.8 billion) (2015 prices, discounted) over 25 years when compared with a scenario of no bush thinning. This implies a net benefit of around N$2 billion (USD 0.2 billion) (2015 prices, discounted) per annum in the initial round of 25 years.

The following products are currently produced from the encroacher bush biomass:[32]

Namibia has a well-established charcoal sector, which currently comprises approximately 1.200 producers, which employ a total of 8.000 workers. Most producers are farmers, who venture into charcoal production as a means to combat bush encroachment on their land. However, increasingly small enterprises also venture into charcoal making. As per national forestry regulations, charcoal can only be produced from encroaching species. In practice, it however proves difficult to ensure full compliance with these regulations, as the charcoal production is highly decentralised and the inspection capacities of the Directorate of Forestry are low. Voluntary FSC certification has sharply increased in recent years, due to respective demand in many off-take countries, such as the United Kingdom, France and Germany. Due to exclusive use of encroacher bush for charcoal production, rendering the value chain free from deforestation, Namibian charcoal has been dubbed the "greenest charcoal" in an international comparison.[33] In 2016 the Namibia Charcoal Association (NCA) emerged as a legal entity through a restructuring process of the Namibia Charcoal Producers Association, previously attached to Namibia Argicultural Union. It is a non-profit entity and the official industry representation, currently representing an estimated two-thirds of all charcoal producers in the country.

Namibia Biomass Industry Group is a non-profit association under Section 21 of the Companies Act (Act 28 of 2004) of Namibia, founded in 2016. It functions as the umbrella representative body of the emerging bush based biomass sector in the country with voluntary paid membership. The core objectives, as enlisted in the Articles of Association, include to develop market opportunities for biomass from harvested encroacher bush as well as to address industry bottlenecks, such as skills shortages and research and development needs. The De-bushing Advisory Service is a division of the association, mandated with the dissemination of knowledge on the topics of bush encroachment, bush control and biomass utilisation. Services are provided upon inquiry and are considered a public service and therefore not charged. According to its websites, services include technical advice on bush control and biomass utilisation, environmental advice, the strengthening of existing agricultural outreach services and linkage with service providers.[34] [35]

Environmental Regulations and Certification

Both the Forestry Act and the Environmental Act of Namibia govern bush control. Special harvesting permits as well as Environmental Clearance Certificates are applicable to all bush harvesting activities. Responsible Authority is the Ministry of Environment, Forestry and Tourism.

Effective April 2020 the Forest Stewardship Council introduced a national Namibian FSC standard (National Forest Stewardship Standard) that is closely aligned to the global FSC certification standard, but takes into consideration context specific parameters, such as bush encroachment.[36] In early 2020, the total land area certified under the FSC standard for the purpose of bush thinning and biomass processing was reported to amount to 1.6 million hectares.[37]

Botswana

Ecological surveys in Botswana have found bush encroachment affecting both communal grazing areas and private farmland, with particular prevalence in semi-arid ecosystems.[38][39] In selected areas, charcoal production has been introduced as a measure to reduce bush densities.[40][41][32] Bush encroachment in Botswana has been documented from as far back as 1971.[32]

South Africa

In South Africa bush encroachment entails the abundance of indigenous woody vegetation in grassland and savanna biomes. These biomes make up 27.9% and 32.5% of the land surface area. Research has found that about 7.3 million hectares are directly affected by bush encroachment, impacting rural communities socio-economically.[42][43]

Eswatini

Studies in the Lowveld savannas of Eswatini confirm different heavy woody plant encroachment, especially by Dichrostachys cinerea, among other factors related to grazing pressure.[44]

Other Ecosystems

Grey dunes, along the coasts of the North and Baltic Seas as well as the Atlantic, are frequently observed to suffer shrub encroachment that is largely attributed to dune stabilisation and changes in animal populations, such as a reduction of rabbits.[1]

See also

Notes

1.^ Dune shrub encroachment differes significantly from bush and shrub encroachment of grasslands. It is often intermixed with grass encroachment and both the underlying ecosystem as well as the causes differ from other contexts.

References

  1. ^ Walter, H. (1954). "Die Verbuschung, eine Erscheinung der subtropischen Savannengebiete, und ihre ökologischen Ursachen". Vegetatio Acta Geobot (in German). 5: 6–10. doi:10.1007/BF00299544 – via Springer.
  2. ^ Tabares, Ximena; Zimmermann, Heike; Dietze, Elisabeth; Ratzmann, Gregor; Belz, Lukas; Vieth‐Hillebrand, Andrea; Dupont, Lydie; Wilkes, Heinz; Mapani, Benjamin; Herzschuh, Ulrike (January 2020). "Vegetation state changes in the course of shrub encroachment in an African savanna since about 1850 CE and their potential drivers". Ecology and Evolution. 10 (2): 962–979. doi:10.1002/ece3.5955. PMC 6988543. PMID 32015858.
  3. ^ Luvuno, Linda; Biggs, Reinette; Stevens, Nicola; Esler, Karen (2018). "Woody Encroachment as a Social-Ecological Regime Shift". Sustainability. 10 (7): 2221. doi:10.3390/su10072221.
  4. ^ Archer SR, Davies K.W, Fulbright T.E, McDaniel K.C, Wilcox B.P., Predick K.I (2011). "Brush management as a rangeland conservation strategy: a critical evaluation.". Conservation benefits of rangeland practices: assessment, recommendations, and knowledge gaps. Allen Press. ISBN 0984949909.{{cite book}}: CS1 maint: multiple names: authors list (link)
  5. ^ Stanton RA Jr, Boone Iv WW, Soto-Shoender J, Fletcher Jr RJ, Blaum N, McCleery RA (2018). "Shrub encroachment and vertebrate diversity: a global meta-analysis". Glob. Ecol. Biogeogr. 27: 368–379. doi:10.1111/geb.12675 – via Wiley.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. ^ Mogashoa, R., Dlamini, P. & Gxasheka, M. (2020). "Grass species richness decreases along a woody plant encroachment gradient in a semi-arid savanna grassland, South Africa". Landscape Ecol. doi:10.1007/s10980-020-01150-1.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ Ratajczak, Z., Nippert, J., Collins, S. (2012). "Woody encroachment decreases diversity across North American grasslands and savannas". Ecology. 93(4): 697–703. doi:10.1890/11-1199.1.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. ^ Nghikembua, Matti T.; Marker, Laurie L.; Brewer, Bruce; Mehtätalo, Lauri; Appiah, Mark; Pappinen, Ari (1 October 2020). "Response of wildlife to bush thinning on the north central freehold farmlands of Namibia". Forest Ecology and Management. 473: 118330. doi:10.1016/j.foreco.2020.118330.
  9. ^ Hofmeyr SD, Symes CT, Underhill LG (2014). "Secretarybird Sagittarius serpentarius Population Trends and Ecology: Insights from South African Citizen Science Data". PLoS ONE. 9(5) e96772. doi:10.1371/journal.pone.0096772.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ^ Lautenbach, J. M., R. T. Plumb, S. G. Robinson, C. A. Hagen, D. A. Haukos, and J. C. Pitman (2017). "Lesser Prairie-Chicken Avoidance of Trees in a Grassland Landscape". Rangeland Ecology & Management. 70: 78–86. doi:10.1016/j.rama.2016.07.008 – via Science Direct.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  11. ^ Sirami, C. and Monadjem, A. (2012). "Changes in bird communities in Swaziland savannas between 1998 and 2008 owing to shrub encroachment". Diversity and Distributions. 18: 390–400. doi:10.1111/j.1472-4642.2011.00810.x – via Wiley.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  12. ^ Ubach A, Páramo F, Gutiérrez C, Stefanescu C (2020). "Vegetation encroachment drives changes in the composition of butterfly assemblages and species loss in Mediterranean ecosystems". Insect Conserv Divers. 13: 151–161 – via Wiley.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  13. ^ Acharya, B.S.; Kharel, G.; Zou, C.B.; Wilcox, B.P.; Halihan, T. (2018). "Woody Plant Encroachment Impacts on Groundwater Recharge: A Review". Water. 10: 1466. doi:10.3390/w10101466 – via MDPI.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  14. ^ Oba G, Post E, Syvertsen PO, Stenseth NC (2000). "Bush cover and range condition assessments in relation to landscape and grazing in southern Ethiopia". Landscape Ecology. 15: 535–546. doi:10.1023/A:1008106625096 – via Springer.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  15. ^ Gray, E.F. & Bond, W.J. (2013). "Will woody plant encroachment impact the visitor experience and economy of conservation areas?". Koedoe. 55(1): Art. #1106, 9 pages. doi:10.4102/koedoe.v55i1.1106.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  16. ^ Archer, S., Predick, K. (2014). "An ecosystem services perspective on brush management: research priorities for competing land-use objectives". Journal of Ecology. 102: 1394–1407. doi:10.1111/1365-2745.12314 – via WILEY.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  17. ^ http://www.dasnamibia.org/wp-content/uploads/2016/07/De-Klerk-Bush-Encoachment-in-Namibia-2004.pdf
  18. ^ I. P. J. Smit, G. P. Asner, N. Govender, N. R. Vaughn, B. W. van Wilgen, J. (2016). "An examination of the potential efficacy of high-intensity fires for reversing woody encroachment in savannas". Appl. Ecol. 53: 1623–1633. doi:10.1111/1365-2664.12738.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  19. ^ Zehnder, T., Lüscher, A., Ritzmann, C. (2020). "Dominant shrub species are a strong predictor of plant species diversity along subalpine pasture-shrub transects". Alp Botany. doi:10.1007/s00035-020-00241-8 – via Springer.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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Sources

External links


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