Biodiversity Impact Of Invasive Plants In Tropical Biodiversity Biology Essay


Tropical zone is the biodiversity hot spot (Briggs, 1996) about three-quarters of the worlds species are confined to the tropic of the world (Wilson, 1992). Though tropical forest ecosystems are more resistant to invasion by alien plants than other biome (Edward, 2009), they are exceedingly threatening by invasive species (Association for Tropical Biology and Conservation, biotropica, 2010). Invasive species are creating significant challenges to the management and conservation of the indigenous biodiversity. The distribution of invasive plant species occurred at ecosystem level, community level and at the species level (Meyer et al., 2004). At least one exotic species is present in almost all tropical areas (Usher 1991).

Invasive plants alter the local environment more favourable to them but less favourable to the native species (Hoffmann et al., 2004) and thus modified local ecosystem. Biological invasion has become a considerable economic, social, and particularly ecological problem of global impact (Cavalcante and Major, 2006). The important ecological impacts identified include reduction in native plant species richness, abundance and alternation in ecological function (Vitousek & Walker, 1989; Adair & Groves, 1998; Levine et al., 2003; Ogle, Reiners & Gerow, 2003; Vila et al., 2006; Hejda, Pysek & Jarosik, 2009 cited in Martin and Murray, 2010). Invasive plant species can covert the large area tropical vegetation to an exotic monoculture and greatly reduce the biodiversity, for example, the number of birds, mammals, tree seedlings were greatly reduced in Australia after the invasion of the area by alien plant species (Braithwaite et al. 1989) and Cogongrass (Imperata cylindrica) forms large, monotypic expanses, with Asia reporting over 35 million acres affected (Garrity et al. 1997).

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Invasive species are posing a serious threat to biodiversity (IUCN, 2000). The Millennium Ecosystem Assessment (2005) has pointed that the impacts of invasive species on the tropical ecosystems are increasing rapidly. Similarly, recognizing the increasing issue of impact of invasive species, Convention on Biological Diversity, call on contracting parties to "prevent the introduction of, control or eradicate invasive species that threaten ecosystems, habitats and species" Article 8 (h).

This systematic review attempt to summarises, appraise and communicate the results of the available studies to address the impact of invasive plants on tropical biodiversity. This protocol will provide a priori guide and allow scientific communities to comment on methodology and other relevant issues. Diverse studies are available related to impact of invasive plant species on tropical biodiversity. Some studies suggest that invasion of native vegetation by the non native plants does not always lead to decline in native biodiversity (e.g. Sax & Gaines, 2003; Sax, Kinlan & Smith, 2005). Biological invasions have been the subject of intensive ecological research during the last two decades (Fine 2001). Comprehensive studied have been done for many tropical forests e.g. the Hawaiian Islands (Fine, 2002) but some authors argues that the biological invasion research has generally ignored tropical forests ( Drake et al. 1989, Groves & Burdon 1986, Williamson 1996 cited in Fine, 2002).

In such contentious situation, it seems quite reasonable to syntheses these studies to improve the efficiency of the conservation efforts in preserving biodiversity of the tropics and develop a concrete evidence base on the impact of invasive species which will provide unbiased scientific evidence base to help decision-makers to decide and implement necessary policy intervention to stop further invasion of the tropical biodiversity and identify areas where evidence is lacking to direct research and funding on more crucial agendas.

Objective of the review

Primary question

What are the effects of invasive plants on biodiversity of the tropical zone?

Table 1: Definition of components of the primary systematic review question






in the tropical zone

Invasion by invasive plant species in tropical zone

Biodiversity in forest, savannas or grassland before the invasion or any relevant or any relevant

Any reported change in tropical biodiversity e.g.

Species richness, abundance of native plant species, tree density


3.1. Search Strategy

Relevant published and unpublished literature and data will be collated by following strategy. Due to the resource constraints only English language literatures will be taken into consideration.

3.1.1 Scope of search

I will use the following database search to retrieve the literatures and data

ISI Web of Knowledge

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Science Direct

Wiley InterScience

Cambridge Journal

Cab Direct

CSA Biological Sciences Database (CSA/CIG) 


In addition to grey literatures are searched in the website of relevant organization as listed in section 3.1.5 which helps to reveal important information about the tropical forestry and invasive species interaction. First searches are conducted on title, keyword and abstract basis and followed by full text searches. Hits are then checked for the relevance.

3.1.2 Search terms

Effective and comprehensive list of related key words as described in the table -2 will be used to retrieve the literatures from the database specified above.

Table 2: Search terms for review

Subject term

Intervention term

combine with OR


combine with OR

Tropic* biodiversity

Species richness

Invas* plant

non native plant

exotic plant

alien plant

introduced plant

Search term combinations

Table: 3 Search term combinations and no of hits

Key word 1

Key word 2

Total hits

(Topic search)

Refined hits in

Web of science

Tropic* biodiversity


Invas* plant


Tropic* biodiversity


Non native plant


Tropic* biodiversity


exotic plant


Tropic* biodiversity


alien plant


Tropic* biodiversity


non-indigenous plant


Tropic* Species richness


Invas* plant


Tropic* Species richness


Non native plant


Tropic* Species richness


exotic plant


Tropic* Species richness


alien plant


Tropic* Species richness


non-indigenous plant


tropical biodiversity


(exotic plant) OR (invasive plant) OR(non native plant) OR (non indigenous plant)



No of hits and the retrieval of relevant literature varies between the data base searches, in the above table hits obtained by web of science is mentioned as an example. The same search tem combination give quite different hit in another database search, for example, for the first search term [tropic*biodiversity AND invas*plant] Cab direct retrieved 56 articles.

In addition to the web of science the search databases mentioned in section 3.1.1 have been used in the preparation of this protocol and will also be used in final systematic review.

3.1.3 Specialist web sources will be conducted

3.1.4. Internet Search

The internet will be searched using the search engines. The first

70 hits for each search will be recorded and examined for relevance.

3.1.5 Specialist agencies and organization data search

At global level:

Food and Agriculture Organization of the United Nations (FAO)

IUCN/Invasive species specials group

CABI- invasive species compendium

Convention on biological diversity (CBD)

International Weed Science Society (IWSS)

UNEP-World Conservation Monitoring Centre (WCMC)

Global Invasive Species Information Network (GISIN)

Global Invasive Species Programme (GISP)

In addition to this regional level agencies and organization in tropical countries will also consulted.


Association of Southeast Asian Nations , Regional Centre for Biodiversity Conservation (ARCBC)

Invasive Alien Flora of India

Weed Science Society of Japan

Weed Science Society of China

Asia-Pacific Forest Invasive Species Network (APFISN

Asia-Pacific Forest Invasive Species Network (APFISN)


Invasive Species Council

South America:

Inter-American Biodiversity Information Network - IABN Invasive Information Network

3.2. Study Inclusion criteria

The relevant studies (articles, literatures, book sections) to be included in meta-analysis will be based in hierarchical judgment by first scanning the article titles followed by key words, abstracts and full text. The relevancy is determined by criteria as described below. If the data presented in the studies are not clear and needed to take more detailed description original authors and their respective organization will be contracted. Kappa analysis will be carried out for repeatability. Disputes between two reviewers will be solved by third independent reviewer.

Geographical location:

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Study area of the relevant studies should be within the tropics (23.438°S to 137 23.438°N).

3.2.1. Relevant subjects:

Any studies related to biodiversity changes in the tropical zone because of invasive plant species.

3.2.2. Types of intervention:

Invasion of the tropical zone (forest land, agriculture land, grass land or savannas) by invasive plant species

3.2.3. Types of comparators:

Any relevant studies and studies comparing the biodiversity of the tropical zone assessing before and after the effect of invasive plant species

3.2.4. Types of outcomes:

Any study which shows biodiversity change (indicators like relative species richness or abundance)

3.2.5. Types of studies:

Any study which describes qualitatively or quantitatively the effect of invasive plant species in the biodiversity (species richness, abundance) in forest land, grassland. Range land, agriculture land, savannas. Those studies which present comparison of before and after the invasion or the comparison of the proportion of exotic species to native species will be included. Studies can be articles in peer reviewed journals, book chapters or grey literatures

3.3. Potential effect modifier and reasons for heterogeneity

Different edaphic, biotic, topographic and climatic condition which governs the vegetation type of the tropics such as soil quality, altitude, aspects, forest types and intensity of human disturbances which may respond to plant invasions in different ways affect the study outcomes. Furthermore, the biological characteristics of the invasive species also affect the study.

3.4. Study quality assessment

The searched articles, grey literatures and documents will be assesses according to the previously designed study inclusion criteria. These are then checked independently for validity, reliability and applicability. A Quality assessment checklist is developed as shown below with the consultation of the review team and will be amended after stakeholders' feedbacks. Internal and external validity will be checked using a set of criteria.

Table 4: Quality assessment checklist for checking validity, reliability and applicability





Target population and intervention defined


Sample representative


Experimental design/randomization


Base line information


Valid data collection


Description of confounding factors


Applicability of the research


Any biases

Source: Adapted from class notes, 2010 and literature review

3.5. Data extraction strategy

Qualitative and quantities information will be extracted from the studies included for the review. Information on invasive species, their effects on tropical biodiversity (species richness, abundance and competition) will be extracted in to a specially designed extraction form as shown in annex-1. Where data are available, data will be extracted as before and after data and other data will be extracted as appropriate.

3.6. Data synthesis and presentation

Data synthesis method will be determined by the availability of the data and data type. The studies will be grouped according to the type of information available e.g. review article, original research. If sufficient quantitative information is available meta-analysis will be conducted to know the significance of the effect of invasive plant species to the tropical biodiversity. If in sufficient quantitative information is available qualitative analysis of evidence will be undertaken.