The extent of plant invasions was studied in 302 nature reserves located in the Czech Republic, central Europe. Lists of vascular plant species were obtained for each reserve, alien species were divided into archaeophytes and neophytes (introduced before and after 1500, respectively). The statistical analysis using general linear models made it possible to identify the effects of particular variables. Flora representation by neophytes decreased with altitude (explained 23.8% of variance) while, with archaeophytes, the effect of altitude depended on their interaction with native species in particular vegetation types. The proportion of neophytes increased with increasing density of human population. Both the number and proportion of aliens plants significantly increased with increasing number of native species in a reserve. This relationship was affected by altitude, and after filtering out this variable, the effect remained positive for neophytes but became negative for archaeophytes in humid grasslands. The positive relationship between neophytes and native species is not a mere side effect of species-area relationship of native flora, but indicates that the two groups do not directly compete. Vegetation type alone explained 14.2 and 55.5% of variation in proportion of aliens in regions of mesophilous and mountain flora, respectively. Humid grasslands were the least invaded vegetation type. Positioning the reserve within large protected sections of landscape significantly decreases probability of it being invaded by potentially invasive alien species. Within the context of SLOSS debate, a new model -several small inside single large (SSISL) -is suggested as an appropriate solution from the viewpoint of plant invasions to nature reserves. #

Numbers of plant species were recorded in speciesrich meadows in the Bílé Karpaty Mts., SE Czech Republic, with the aim to evaluate the sampling error made by well-trained observers. Five observers recorded vascular plants in seven plots ranging from 9.8 cm 2 to 4 m 2 independently and were not time-limited. In larger plots a discrepancy of 10-20% was found between individual estimates, in smaller plots discrepancy increased to 33%, on average. The gain in observed species richness by combining records of individual observers (in comparison with the mean numbers estimated by single observers) decreased from the smallest plot (27-82% for two to five observers) to the largest one (13-25%). However, after misidentified and suspicious records were eliminated, the gain was much lower and became scale-independent; two observers added 12% species, on average, and the increase by combining species lists made by three or more observers was negligible (3% more on average). It is concluded that most discrepancies between individual observers were caused by misidentification of rare seedlings and young plants. We suggest that in species-rich meadows plants should be recorded by at least three observers together and that they should consult all problematic plant specimens together in the field, to minimize errors.

No abstract

Communities comprising alien species with different residence times are natural experiments allowing the assessment of drivers of community assembly over time. Stochastic processes (such as dispersal and fluctuating environments) should be the dominant factors structuring communities of exotic species with short residence times. In contrast, communities should become more similar, or systematically diverge, if they contain exotics with increasing resident times, due to the increasing importance of deterministic processes (such as environmental filtering). We use zeta diversity (the number of species shared by multiple assemblages) to explore the relationship between the turnover of native species and two categories of alien species with different residence times (archaeophytes [introduced between 4000 BC and 1500 AD] and neophytes [introduced after 1500 AD]) in a network of nature reserves in central Europe. By considering multiple assemblages simultaneously, zeta diversity allows us to determine the contribution of rare and widespread species to turnover. Specifically, we explore the relative effects of assembly processes representing isolation by distance, environmental filtering, and environmental stochasticity (fluctuating environments) on zeta diversity using Multi‐Site Generalized Dissimilarity Modelling (MS‐GDM). Four clusters of results emerged. First, stochastic processes for structuring plant assemblages decreased in importance with increasing residence time. Environmental stochasticity only affected species composition for neophytes, offering possibilities to predict the spread debt of recent invasions. Second, native species turnover was well explained by environmental filtering and isolation by distance, although these factors did not explain the turnover of archaeophytes and neophytes. Third, native and alien species compositions were only correlated for rare species, whereas turnover in widespread alien species was surprisingly unrelated to the composition of widespread native species. Site‐specific approaches would therefore be more appropriate for the monitoring and management of rare alien species, whereas species‐specific approaches would suit widespread species. Finally, the size difference of nature reserves influences not only native species richness, but also their richness‐independent turnover. A network of reserves must therefore be designed and managed using a variety of approaches to enhance native diversity, while controlling alien species with different residence times and degrees of commonness.

We studied the establishment and inclusion of native and alien plant species in nature reserves in the Czech Republic. Our aim was to answer the following questions: Do young and old nature reserves contain the same proportion of invasive plant species? Does the time of their introduction affect their representation in these reserves? We obtained recent lists of vascular plant species for 302 reserves established since 1838 and designated the species as native or alien. We divided the latter category into archaeophytes and neophytes, introduced before and after 1500, respectively. The increase in the number of reserves and species was evaluated by inclusion curves. For inclusion curves describing an increase in the number of reserves, the estimated time of 50% inclusion indicated when half the reserves of a particular type were established. For inclusion curves describing an increase in the number of species, the estimated time of 50% inclusion indicated when half the species of a particular category ( native species, all aliens, archaeophytes, neophytes ), reported from the country, were included in the nature reserves. The forest and dry‐grassland reserves were established earlier than those in wetlands and peat bogs, whereas humid‐grassland reserves tended to be the most recently established. Half the native species were included significantly earlier ( after 25 years ) than half of alien species ( 86 years ), and half the neophytes were included later ( 143 years ) than half the archaeophytes ( 31 years ). Early reserves harbor a significantly lower number of alien species than those established later. These reserves include a higher proportion of the Czech Republic's native species and archaeophytes than of its neophytes. There was no difference in the relative rates of inclusion of native species, archaeophytes, and neophytes. However, the fact that the same inclusion rate applies to neophytes, a group with an increasing species pool, as to archaeophytes and native species, which both have constant species pools, suggests that natural vegetation in nature reserves is an effective barrier against the establishment of alien species. On a historical time scale, the early establishment of nature reserves in a given country decreases the probability that the reserve will be invaded by alien plants.