Showing papers by "Marcel Rejmánek published in 2000"

Naturalization and invasion of alien plants: concepts and definitions

Abstract: . Much confusion exists in the English-language literature on plant invasions concerning the terms ‘naturalized’ and ‘invasive’ and their associated concepts. Several authors have used these terms in proposing schemes for conceptualizing the sequence of events from introduction to invasion, but often imprecisely, erroneously or in contradictory ways. This greatly complicates the formulation of robust generalizations in invasion ecology. Based on an extensive and critical survey of the literature we defined a minimum set of key terms related to a graphic scheme which conceptualizes the naturalization/invasion process. Introduction means that the plant (or its propagule) has been transported by humans across a major geographical barrier. Naturalization starts when abiotic and biotic barriers to survival are surmounted and when various barriers to regular reproduction are overcome. Invasion further requires that introduced plants produce reproductive offspring in areas distant from sites of introduction (approximate scales: > 100 m over 6 m/3 years for taxa spreading by roots, rhizomes, stolons or creeping stems). Taxa that can cope with the abiotic environment and biota in the general area may invade disturbed, seminatural communities. Invasion of successionally mature, undisturbed communities usually requires that the alien taxon overcomes a different category of barriers. We propose that the term ‘invasive’ should be used without any inference to environmental or economic impact. Terms like ‘pests’ and ‘weeds’ are suitable labels for the 50–80% of invaders that have harmful effects. About 10% of invasive plants that change the character, condition, form, or nature of ecosystems over substantial areas may be termed ‘transformers’.

Invasive plants: approaches and predictions

Abstract: Successful management of invasive weeds will require active attempts to prevent new introductions, vigilant detection of nascent populations and persistent efforts to eradicate the worst invaders. To achieve these objectives, invasion ecology offers five groups of complementary approaches. (i) Stochastic approaches allow probabilistic predictions about potential invaders based on initial population size, residence time and number of introduction attempts. (ii) Empirical taxon-specific approaches are based on previously documented invasions of particular taxa. (iii) Evaluations of the biological characters of non-invasive taxa and successful invaders give rise either to general or to habitat-specific screening procedures. (iv) Evaluation of environmental compatibility helps to predict whether a particular plant taxon can invade specific habitats. (v) Experimental approaches attempt to tease apart intrinsic and extrinsic factors underlying invasion success. An emerging theory of plant invasiveness based on biological characters has resulted in several rather robust predictions which are presented in this paper.

On the use and Misuse of Transition Matrices in Plant Population Biology

Abstract: In their recently published paper, Drayton and Primack (1999) used the transition matrix (Table 1) for the population dynamics modeling of the invasive biennial Alliaria petiolata. This matrix can be translated into the life cycle diagram (Figure 1a). If it has not been apparent from the matrix, it is now clear that the authors’ understanding of reproduction of this biennial species is somewhat confused. According to their description of theAlliaria life cycle, one plant flowering in year t produces 600 seeds in year t + 1, some of which will germinate and produce rosettes in year t + 2. However, it is well known that coming at time t + 1 (just one year later), there will be not only seeds present in the seed bank but also rosettes which did grow from seeds during the same one year time step. Therefore, by ignoring recruitment of rosettes (‘flowering-to-rosette’ transition in Table 1), Drayton and Primack’s matrix introduces an unrealistic one-year delay in the reproduction process. In other words, the matrix (Table 1) represents a strictly triennial species with seed dormancy lasting at least one year. The second important misconception is to use 600, which is the gross production of seeds, rather than the net number of surviving seeds at timet + 1. In a more realistic life cycle diagram (Figure 1b) and corresponding transition matrix (Table 2), flowering plants produce not only seeds which are in the seed