Inclusion of Native and Alien Species in Temperate Nature Reserves: an Historical Study from Central Europe

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. Resumen: Estudiamos el establecimiento e inclusion de especies de plantas nativas y exoticas en reservas naturales en la Republica Checa. Nuestra meta era contestar las siguientes preguntas: ?Contienen la misma proporcion de especies de plantas invasoras las reservas recientes y antiguas? ?El tiempo que llevan introducidas afecta su representacion en estas reservas? Obtuvimos listas recientes de las especies de plantas vasculares para 302 reservas establecidas desde 1838 y designamos a las especies como nativas o introducidas. Dividimos a esta ultima categoria en arquefitas y neofitas (introducidas antes y despues de 1500, respectivamente). Se evaluo el incremento en el numero de reservas y especies mediante curvas de inclusion. Para curvas de inclusion que describian un incremento en el numero de especies, el tiempo estimado de 50% de inclusion indicaba cuando se incluyeron la mitad de las especies registradas para el pais, de una categoria particular ( especies nativas, todas las exoticas, arquefitas y neofitas ) en reservas naturales. Las reservas forestales y de pastizales secos se establecieron antes de que se establecieran las de humedales y turberas, mientras que las reservas de pastizales humedos tendieron a ser las establecidas mas recientemente. La mitad de las especies nativas se incluyeron significativamente antes ( despues de 25 anos ) que la mitad de las especies exoticas ( 86 anos ), y la mitad de las neofitas fueron incluidas despues ( 143 anos ) que los arquetipos ( 31 anos ). Las reservas mas antiguas contienen un numero significativamente menor de especies exoticas que las establecidas mas recientemente. Estas reservas incluyen una mayor proporcion de especies nativas y de arquetipos que de neofitas de la Republica Checa. No hubo diferencia en las tasas relativas de inclusion de especies nativas, arquefitas y neofitas. Sin embargo, el hecho de que la misma tasa de inclusion vale tanto para neofitas, un grupo cuyo numero de especies aumenta, como para arquefitas y especies nativas, con numeros de especies constantes, sugiere que la vegetacion natural en las reservas constituye una barrera efectiva contra el establecimiento de especies exoticas. En una escala de tiempo historico, el establecimiento temprano de reservas naturales en un pais determinado disminuye la probabilidad de que la reserva sea invadida por especies exoticas.