Weed invasive

Abstract

Biological invasions are increasingly attracting the attention of ecologists, so it seems that this phenomenon is relatively new. However, the beginning of the study of biological invasions is publication of the book "The Ecology of Invasions by Animals and Plants" (1958), which is classified as classic works of invasions. Research of biological invasion is focused on the study of crucial biological and ecological characteristics which enable species invasiveness, as well as the characteristics of the recipient community. Despite the intensive study of this phenomenon, there are still differing views whether only introduced alien species or even native species can be considered as invasive species. While some researchers consider that native species cannot belong to the invasive category, others thought that a species that is native, when expend to adjacent habitats, may also be considered as invasive. Understanding biological invasions as if there no difference between native and introduced allochthonous species eliminates the dilemma that arises in the case of cryptogenic species (species that cannot be clearly classified into one of these two groups), whether it is native or introduced species, the success of the spreading depends on ecological adaptations. In addition, there is also disagreement about the stages of biological invasions. One point of view is, invasion processes take place through three phases (introduction, colonization and naturalization), while to other, the introduction is an elementary requirement for invasion, colonization is an integral part of the concept of naturalization, and naturalization which is referred in to previous point of view, is the phase that corresponds to the term "invasiveness". The time and route of introduction, as well as the mode and pathways of spreading for a large number of adventitious weed species have not been precisely established. Depending on whether weed species are introduce accidentally or intentionally, they are divided into boyletophytes (intentionally introduce) and aboyletophytes (accidentally introduce), while according to period of introduction they are divided into archeophytes (introduced in the Paleozoic to Neolithic period), paleophytes (introduced during the Old and Middle Ages until the discovery of America), neophytes (introduced after the discovery of America until to World War II), and neotophytes (introduced from the World War II until nowadays). Invasive processes are very complex, and it is not easy to predict and evaluate the behavior of introduced species in a new environment. Depending on the shape, structure and size of the reproductive organs, invasive weeds can be spread in several ways: autochthonous (selfpropagating), anemohoric (spreading through the wind), hydrohorn (spreading through water), zohornous (spreading by animals) and anthroporous (spreading by human). The success of invasive processes depends on the ecological characteristics of species, environmental resources and degree of ecosystem damage into which species has reached. According to success of survival in the new environment, allochthonous species can have status of the ephemeral (species which temporarily retained in the new environment and do not form stable populations), naturalized (species that are maintained in the new habitat but do not have an expansive character) and invasive (species that are adapted to the new habitat, spreading, forming indigenous part of flora and leave fertile offspring). The ecological-genetic potential of these species is the result of genetic diversity and their capacity for ecological adaptation; mutations, recombination, hybridization and introgression are the main processes responsible for genetic diversity. In the area of introduction, allochthonous species manifest numerous negative impacts on agriculture, ecosystems, human and domestic animal health, socioeconomic relationships and can jeopardize the survival of native species. Invasions are generally classified as negative occurrences, although in some circumstances they may also have a positive effect on the environment. For example, introduction of allochthonous species can enrich biodiversity, in case when number of introduced species far exceeds the number of extinct species. Despite the great scientific and technological progress, the problem of biological invasions cannot be completely resolved, but it is possible to limit these processes and reduce their negative consequences. The European and Mediterranean Plant Protection Organization (EPPO) dedicate special attention to the risks of invasive plant species and recommends measures to prevent their introduction and spread, with special reference to organisms that cause damage in agriculture. Control of these species implies application of all available preventive and direct measures, integrated into a system of integral measures.