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Besides habitat loss, population-biological and genetic consequences of habitat fragmentation are thought to be a major threat to species since the 1990's and thus are now in the focus of plant species conservation. Using examples, this article gives an overview on the state of the art. It aims to evaluate the relevance habitat fragmentation and the resulting small size and isolation of populations may have for Central European plant populations. Stochasticity, edge effects, pollinator limitation, genetic drift and inbreeding depression are identified as important and very widespread negative effects. Together with changed habitat quality due to eutrophication, drainage or altered land use they negatively affect the fitness of individuals and populations, resulting in an increased risk of extinction. This negative effect of small populations on the fitness of individuals is called the Allee-effect, irrespective of the underlying causes, which can only be identified by scientific experiments. Metapopulation dynamics that are supported by a habitat network may prevent a permanent extinction of plant populations and minimize the negative genetic effects of habitat fragmentation by increasing gene flow via pollen and seeds. However, existing studies from Central Europe mainly concentrated on certain plant families (Gentianaceae, Primulaceae), habitats (species- rich grasslands), insect-pollinated and outcrossing species, and species mainly relying on sexual reproduction. On the other hand, few insights exist about grasses, ruderal plants and weeds, non-indigenous, wind- and self-pollinated species, and species mainly reproducing vegetatively or via apomictic seeds. However, according to the present state of knowledge especially these plant species, and those with a high dispersal potential, have to be considered as less sensitive to habitat fragmentation. Based on these findings, habitat types are classified with regard to their sensitivity to fragmentation, and ecological characters and species traits of sensitive and less sensitive species are compared. Finally, general consequences for conservation practice are presented with regard to target species and habitats for the formation of habitat networks, minimum viable population sizes, genetic rescue of populations, and deploying plants from ex-situ conservation to natural habitats.
Die in Deutschland gegenwärtig durch Nährstoffeinträge und ausbleibenden Nährstoffentzug stark im Rückgang begriffenen Flechten-Kiefernwälder werden als Biotoptyp wie auch als Lebensraumtyp "Mitteleuropäische Flechten-Kiefernwälder" (Code 91T0) diskutiert. Die bisherige, sehr uneinheitliche Differenzierung von Flechten-Kiefernwäldern auf der Ebene von Biotoptypen wird dargestellt. Auf der Grundlage neuerer vegetationskundlicher übersichten werden Vorschläge für eine einheitliche Abgrenzung des Biotoptyps "Flechten-Kiefernwald" und des Lebensraumtyps 91T0 unterbreitet. Im niedersächsischen Naturwaldreservat "Kaarßer Sandberge" (Niedersachsen) wurde die Anwendung des Konzeptes erfolgreich erprobt. Nicht nur hier, sondern auch deutschlandweit wird der Rückgang der Erdflechten in den Kieferwäldern zugunsten von Drahtschmiele und/ oder pleurokarpen Moosen deutlich. Nach der derzeitigen Definition des Lebensraumtyps 91T0 besteht auf der Grundlage der FFH-Richtlinie nicht für alle Flechten-Kiefernwälder eine Chance der Verbesserung. Der Ausschluss von außerhalb des natürlichen Verbreitungsgebietes der Wald-Kiefer gelegenen sowie von durch Aufforstung angepflanzten Beständen bringt Probleme mit sich, die diskutiert werden. Für den Erhalt und die Wiederherstellung der größtenteils nutzungsbedingt entstandenen Flechten-Kiefernwälder sind praktikable Pflegemaßnahmen notwendig, die im Rahmen von Streunutzungsversuchen erprobt werden müssen.
Vegetation und Standort bodensaurer Buchenwälder am Arealrand : am Beispiel Mittelbrandenburgs
(2008)
Different from NW Germany, the northern part of NE Germany and the "Hohe Flaeming" region, central Brandenburg is considered as being largely devoid of natural beech forests because of its subcontinental, dry climate. In the present study the vegetation ecology of beech forests of the region is comprehensively documented for the first time, and they are compared with NW German stands in Lower Saxony. In the study area beech forests are concentrated in the Berlin-Potsdam region along the Havel river lakes which is characterised by relatively high precipitation and a specific land use history. All belong to the Luzulo-Fagetum growing on acid soils. Four subtypes are distinguished according to nutrient availability and soil moisture. The central Brandenburg Luzulo-Fagetum does not markedly deviate from other beech forests in the northern German lowlands with respect to vegetation structure and edaphic subtypes. However, numerous indicator species for humid or moist conditions are less frequent than under atlantic climate conditions in the lowlands of Lower Saxony, a pattern occurring also in other forest communities. On the other hand, nitrogen and disturbance indicators are more frequent in central Brandenburg. As expected, podzolisation of the soils and humus accumulation is lower in beech forests under subcontinental climate, but surprisingly the soils are more sandy and thus drier. However, beech forests are lacking on south-exposed slopes, and they are notably occurring in northern exposition. A combined analysis of distribution patterns and climatic data, postglacial vegetation history and forest use history, and actual rejuvenation dynamics reveals that the present-day beech forests in central Brandenburg have to be considered as near-natural relics, which are currently spreading. The range of potentially natural beech forests is larger than assumed until now, but further on it is not clearly to define.
Gametophyte and thallus fragments, respectively, may be an important or even the only mode of reproduction for many bryophytes and lichens species. Until now especially birds and mammals have been identifi ed as potential animal dispersal vectors of fragments. This study investigates the dispersal of bryophyte and lichen fragments by red wood ants which build large nest mounds from plant material and are abundant in European coniferous forests. We sampled nest material from 25 nest mounds in fi ve different pine and spruce forest types in Germany and found numerous fragments of 20 bryophyte and ten lichen species. As they occurred on almost all studied mounds and often in large numbers we conclude that collecting cryptogam fragments as nest material is a characteristic feature for the Formica rufa group in coniferous forests. Species number and composition of fragments on mounds coincided with the epigeic vegetation around ant nests to a large extent: Almost all collected species were present in the vegetation, and dominant fragment species occurred in large amounts in the vicinity of ant nests. Lichen fragments were larger than bryophyte fragments. Certain life forms (weft-forming bryophytes, reindeer lichens) were accumulated on mounds, while others (tall turfs, cup-type Cladonia species) were discriminated, refl ecting fragmentation features of species. Collected fragments may regenerate to mature plants if nest mounds are abandoned, and especially if they are lost during transport over several metres. We conclude that dispersal of fragments by red wood ants contributes to maintain epigeic bryophyte and lichen diversity of coniferous forests by supporting colonisation after disturbances, which occur on different spatial and temporal scales.
In northeastern German pine forests we studied re-colonization patterns of experimental gaps by four dominant bryophyte species (Dicranum scoparium, Hypnum jutlandicum, Pleurozium schreberi and Scleropodium purum) over three years. Both vegetation and litter layer were removed on 1 m(2) plots within +/- pure colonies of the experimental species, while the humus layer was left intact. All plots were vegetatively re-colonized by the species which was dominant before gap creation. Three mechanisms of re-colonization occurred and interacted: (1) advance of surrounding shoots from the edge into the gaps by clonal growth, (2) dispersal of detached single shoots as well as larger clumps of multiple shoots into the plots, resulting in new colonies by continuing growth, and (3) regeneration from a soil diaspore bank consisting of seemingly dead stem fragments in the humus layer of the gaps. Scleropodium purum, which occurs at locations with good water and nutrient supply, displayed the most rapid growth. Here, some plots were completely recovered after three years. Despite lower rates of advance from the edge, colonization of Hypnum jutlandicum was faster than and of Dicranum scoparium as fast than that of Pleurozium schreberi because of a larger diaspore bank. Thus, each bryophyte species was characterized by a different habitat occupation strategy. The different clonal colonization strategies account for the high competitive capacity and regeneration potential of the investigated bryophyte species in pine forests despite of the lack of generative reproduction. Experimental disturbance resulted in a temporary increase of bryophyte diversity, because short-lived Colonists with a low competitive capacity colonized the gaps, before they will be overgrown by the dominant Perennials
Soil seed banks near rubbing trees indicate dispersal of plant species into forests by wild boar
(2006)
Current knowledge about processes that generate long-distance dispersal of plants is still limited despite its importance for persistence of populations and colonization of new potential habitats. Today wild Large mammals are presumed to be important vectors for long-distance transport of diaspores within and between European temperate forest patches, and in particular wild boars recently came into focus. Here we use a specific habit of wild boar, i.e. wallowing in mud and subsequent rubbing against trees, to evaluate epizoochorous dispersal of vascular plant diaspores. We present soil seed bank data from 27 rubbing trees versus 27 control trees from seven forest areas in Germany. The mean number of viable seeds and the plant species number were higher in soil samples near rubbing trees compared with control trees. Ten of the 20 most frequent species were more frequent, and many species exclusively appeared in the soil samples near rubbing trees. The large number of plant species and seeds - more than 1000 per tree - in the soils near rubbing trees is difficult to explain unless the majority were dispersed by wild boar. Hooked and bristly diaspores, i.e. those adapted to epizoochory, were more frequent; however, many species with unspecialized diaspores occurred exclusively near rubbing trees. As opposed to plant species closely tied to forests species which occur both in forest and open vegetation and non-forest species were more frequent near rubbing trees compared with controls. These findings are consistent with previous studies on diaspore loads in the coats and hooves of shot wild boars. However, our method allows to identify the transport of diaspores from the open landscape into forest stands, where they might especially emerge after disturbance, and a clustered distribution of epizoochorically dispersed seeds. Moreover, accumulation of seeds of wetness indicators near rubbing trees demonstrates directed dispersal of plant species inhabiting wet places among remote wallows.