Species In Fragmented Landscapes Research Articles

Effects of Population Size on Singing Behavior of a Rare Duetting Songbird

Although the genetic and ecological effects of population declines in endangered species have been well studied, little is known of the social consequences. Changes in signaling behavior may result in disrupted communication and affect both reproductive and conflict-resolution activities. The North Island Kōkako (Callaeas wilsoni) is an endangered, duetting (i.e., alternating, coordinated singing by mated pairs) songbird endemic to New Zealand temperate rain forests. Scattered populations (approximately 1500 individuals in 13 surviving and 11 translocated populations) in isolated conservation areas of different sizes have been rescued from extirpation and are currently recovering. We examined key song attributes of the Kōkako to assess whether population size or growth rate are related to song complexity, the reduction of which may compromise effective communication. We analyzed song repertoire size and phrase-type sharing (i.e., Jaccard index of similarity), vocal performance (singing rates, song switching rates, and diversity of phrase types), and song syntactical characteristics (i.e., unpredictability in sequences of phrase types) in surviving and translocated populations (populations of approximately 19-250 territorial individuals). Population size was positively correlated with a population's song repertoire, song diversity, and switching of song phrase types and negatively correlated with shared phrase types and variation in syntactical structure of songs. Population growth rate correlated positively with pair repertoire size, population repertoire size, and singing rates during song bouts. As for solo-singing species in fragmented landscapes, songs in the fragmented populations of Kōkako appear to be undergoing microevolution as occurs in island colonization events. Our results suggest that vocal changes in small populations could affect population establishment and growth, particularly in multiple-source translocations. We believe measurement of vocal behavior could be used as a supplement to periodic population censuses to allow more frequent monitoring of population size.

How complex do models need to be to predict dispersal of threatened species through matrix habitats?

Persistence of species in fragmented landscapes depends on dispersal among suitable breeding sites, and dispersal is often influenced by the "matrix" habitats that lie between breeding sites. However, measuring effects of different matrix habitats on movement and incorporating those differences into spatially explicit models to predict dispersal is costly in terms of time and financial resources. Hence a key question for conservation managers is: Do more costly, complex movement models yield more accurate dispersal predictions? We compared the abilities of a range of movement models, from simple to complex, to predict the dispersal of an endangered butterfly, the Saint Francis' satyr (Neonympha mitchellii francisci). The value of more complex models differed depending on how value was assessed. Although the most complex model, based on detailed movement behaviors, best predicted observed dispersal rates, it was only slightly better than the simplest model, which was based solely on distance between sites. Consequently, a parsimony approach using information criteria favors the simplest model we examined. However, when we applied the models to a larger landscape that included proposed habitat restoration sites, in which the composition of the matrix was different than the matrix surrounding extant breeding sites, the simplest model failed to identify a potentially important dispersal barrier, open habitat that butterflies rarely enter, which may completely isolate some of the proposed restoration sites from other breeding sites. Finally, we found that, although the gain in predicting dispersal with increasing model complexity was small, so was the increase in financial cost. Furthermore, a greater fit continued to accrue with greater financial cost, and more complex models made substantially different predictions than simple models when applied to a novel landscape in which butterflies are to be reintroduced to bolster their populations. This suggests that more complex models might be justifiable on financial grounds. Our results caution against a pure parsimony approach to deciding how complex movement models need to be to accurately predict dispersal through the matrix, especially if the models are to be applied to novel or modified landscapes.

Effects of matrix composition and configuration on forest bird movements in a fragmented Afromontane biodiversity hot spot

AbstractPersistence of forest‐dependent species in fragmented landscapes strongly relies on sufficient dispersal between patches, making it important to understand how animal movements are affected by the intervening matrix. Movements can be influenced through selection or avoidance of land cover based on their perceived suitability for foraging or providing cover. The composition and configuration of the matrix will, therefore, most likely be an important factor to consider when estimating connectivity between patches. To address this, we performed translocation experiments to understand how forest birds used different land cover types in a fine‐grained matrix of a fragmented Afromontane biodiversity hot spot (Taita Hills, Kenya). Our results revealed that use of land cover types for both the forest specialist Cabanis's greenbul Phyllastrephus cabanisi and for the forest generalist white‐starred robin Pogonocichla stellata was disproportional to their availability. However, this effect was influenced by matrix configuration; in patchy matrices, land cover selection was more pronounced compared with more uniform matrices, especially for the forest specialist. At the scale of movement steps, risk avoidance seemed to be a strong factor in the route decisions for both species. Observed steps contained on average lower proportions of open land cover and did less frequently intersect built‐up areas than expected. P. stellata did not differentiate between the alternative land cover types, whereas P. cabanisi preferred steps that contained more indigenous forest. The observed negative relationship between degree of forest dependency and matrix permeability implies that for members of the Taita bird community, which are even more dependent on intact forest habitat (i.e. the critically endangered Taita thrush Turdus helleri), current permeability of the matrix may be even lower. Matrix restoration to improve connectivity may, therefore, be a crucial instrument for the long‐term survival of forest‐dependent species in these fragmented Afromontane landscapes.

Effects of Matrix Characteristics and Interpatch Distance on Functional Connectivity in Fragmented Temperate Rainforests

The connectivity of remnant patches of habitat may affect the persistence of species in fragmented landscapes. We evaluated the effects of the structural connectivity of forest patches (i.e., distance between patches) and matrix class (land-cover type) on the functional connectivity of 3 bird species (the White-crested Elaenia [Elaenia albiceps], the Green-backed Firecrown Hummingbird [Sephanoides sephaniodes], and the Austral Thrush [Turdus falklandii]). We measured functional connectivity as the rate at which each species crossed from one patch to another. We also evaluated whether greater functional connectivity translated into greater ecological connectivity (dispersal of fruit and pollen) by comparing among forest patches fruit set of a plant pollinated by hummingbirds and abundance of seedlings and adults of 2 plants with bird- and wind-dispersed seeds. Interpatch distance was strongly associated with functional connectivity, but its effect was not independent of matrix class. For one of the bird-dispersed plants, greater functional connectivity for White-crested Elaenias and Austral Thrushes (both frugivores) was associated with higher densities of this plant. The lack of a similar association for the wind-dispersed species suggests this effect is linked to the dispersal vector. The abundance of the hummingbird-pollinated species was not related to the presence of hummingbirds. Interpatch distance and matrix class affect animal movement in fragmented landscapes and may have a cascading effect on the distribution of some animal-dispersed species. On the basis of our results, we believe effort should be invested in optimizing patch configuration and modifying the matrix so as to mitigate the effects of patch isolation in fragmented landscapes.

Using binary and probabilistic habitat availability indices derived from graph theory to model bird occurrence in fragmented forests

Loss of connectivity is one of the main causes of decreases in habitat availability and, thus, in species abundance and occurrence in fragmented landscapes. It is therefore important to measure habitat connectivity for conservation purposes, but there are several difficulties in quantifying connectivity, including the need for species movement behavioral data and the existence of few consistent indices to describe such data. In the present study, we used a graph theoretical framework to measure habitat availability, and we evaluate whether this variable is adequate to explain the occurrence pattern of an Atlantic rainforest bird (Pyriglena leucoptera, Thamnophilidae). The playback technique was used to parameterize the connectivity component of habitat availability indices and to determine the presence or absence of the study species in forest patches. Patch- and landscape-level habitat availability indices were considered as explanatory variables. Two of these were landscape-level indices, which varied in terms of how inter-patch connections are defined, using either a binary or probabilistic approach. This study produced four striking results. First, even short open gaps may disrupt habitat continuity for P. leucoptera. Second, the occurrence of P. leucoptera was positively affected by habitat availability. Third, proper measures of this explanatory variable should account for the landscape context around the focal patch, emphasizing the importance of habitat connectivity. Finally, habitat availability indices should consider probabilistic and not binary inter-patch connections when intending to explain the occurrence of bird species in fragmented landscapes. We discuss some conservation implications of our results, stressing the advantages of an ecologically scaled graph theoretical framework.

Grassland plant functional groups exhibit distinct time-lags in response to historical landscape change

Recent studies have shown significant impacts of past landscapes on present distributions of species, and discussed the existence of an extinction debt. Understanding of the processes building an extinction debt is fundamentally important for explaining present and future diversity patterns of species in fragmented landscapes. Few empirical studies, however, have examined the responses of different plant functional groups (PFGs) to historical landscape changes. We aimed to reveal PFG-based differences in species’ persistence by focusing on their vegetative, reproductive, and dispersal traits. We examined whether the present distributions of PFGs of grassland species in the edges of remnant woodlands established on former semi-natural grasslands are related to the past surrounding landscapes at different time periods and spatial scales. The effects of past landscapes varied significantly among the PFGs. Richness of short, early flowering forbs and tall, late-flowering, wind-dispersed forbs showed significant positive relationships with the surrounding habitat proportions more than 50 years ago (the 1950s) and at wide spatial scales (more than 1 km2). Richness of tall, late-flowering forbs with unassisted and other types of dispersal mechanisms showed positive relationships with the surrounding habitat proportions in recent times (the 1970s) and at smaller spatial scales (0.25 km2). Our results suggested that plant growth form, flowering season and dispersal ability—with additional information on seed bank persistence—can be good indicators for identifying species’ specific sensitivity to surrounding habitat loss. Trait-based approaches can be useful for understanding present and future distributions of grassland species with different persistence strategies in human-modified landscapes.

Assessing the genetic integrity of captive and wild populations for reintroduction programs: the case of Cabot's Tragopan in China

Reintroduction of captive-bred animals into suitable habitats is an important technique for the long-term conservation and recovery of populations of endangered species in fragmented landscapes. In- breeding depression is an inherent risk when using captive populations for reintroduction programs and needs to be carefully assessed prior to reintroduction. In this study, we evaluated inbreeding levels within a captive breeding program and one remnant wild population of Cabot's Tragopan (Tragopan caboti), an endangered pheasant species endemic to China, for which reintroduction is now an essential conservation strategy for long-term population persistence. Fifteen highly polymorphic microsatellite loci were devel- oped to genotype individuals. Inbreeding coefficients ( F IS ) reveal that there is no evidence of inbreeding within the Tragopan Breeding Center of Beijing Normal University (TBCBNU) captive population and the remnant population from the Wuyi-Yandang Mountains. Diversity of origin, large founder population size and a rational breeding strategy are the most critical factors preventing inbreeding depression within the TBCBNU captive population. We suggest that the TBCBNU population is a suitable candidate stock for T. caboti reintroduction programs and that there is an urgent need to better coordinate and strengthen repro- duction management of captive T. caboti populations to sustain the long-term ex situ conservation of the species.

Landscape disturbance causes small-scale functional homogenization, but limited taxonomic homogenization, in plant communities

Summary 1. Biotic homogenization (BH), a dominant process shaping the response of natural communities to human disturbance, reflects both the expansion of exotic species at large scales and other mechanisms that often operate at smaller scales. 2. Here, we examined the relationship between BH in plant communities and spatio-temporal landscape disturbance (habitat fragmentation and surrounding habitat conversion) at a local scale (1 km²), using data from a standardized monitoring programme in France. We quantified BH using both a spatial partitioning of taxonomic diversity and the average habitat specialization of communities, which informs on functional BH. 3. We observed a positive relationship between local taxonomic diversity and landscape fragmentation or instability. This increase in local taxonomic diversity was, however, paralleled by a decrease in average community specialization in more fragmented landscapes and in more unstable landscapes around forest sites. The decrease in average community specialization suggests that landscape disturbance causes functional BH, but there was limited evidence for concurrent taxonomic BH. 4. Synthesis. Our results show that landscape disturbance is partly responsible for functional BH at small scales via the extirpation of specialist species, with possible consequences for ecosystem functioning. However, this change in community composition is not systematically associated with taxonomic BH. This has direct relevance in designing biodiversity indicators: metrics incorporating species sensitivity to disturbance (such as species specialization to habitat) appear much more reliable than taxonomic diversity for documenting the response of communities to disturbance.

Fine-scale movement decisions of tropical forest birds in a fragmented landscape

The persistence of forest-dependent species in fragmented landscapes is fundamentally linked to the movement of individuals among subpopulations. The paths taken by dispersing individuals can be considered a series of steps built from individual route choices. Despite the importance of these fine-scale movement decisions, it has proved difficult to collect such data that reveal how forest birds move in novel landscapes. We collected unprecedented route information about the movement of translocated forest birds from two species in the highly fragmented tropical dry forest of Costa Rica. In this pasture-dominated landscape, forest remains in patches or riparian corridors, with lesser amounts of living fencerows and individual trees or "stepping stones." We used step selection functions to quantify how route choice was influenced by these habitat elements. We found that the amount of risk these birds were willing to take by crossing open habitat was context dependent. The forest-specialist Barred Antshrike (Thamnophilus doliatus) exhibited stronger selection for forested routes when moving in novel landscapes distant from its territory relative to locations closer to its territory. It also selected forested routes when its step originated in forest habitat. It preferred steps ending in stepping stones when the available routes had little forest cover, but avoided them when routes had greater forest cover. The forest-generalist Rufous-naped Wren (Campylorhynchus rufinucha) preferred steps that contained more pasture, but only when starting from non-forest habitats. Our results showed that forested corridors (i.e., riparian corridors) best facilitated the movement of a sensitive forest specialist through this fragmented landscape. They also suggested that stepping stones can be important in highly fragmented forests with little remaining forest cover. We expect that naturally dispersing birds and species with greater forest dependence would exhibit even stronger selection for forested routes than did the birds in our experiments.

Habitat Loss, the Dynamics of Biodiversity, and a Perspective on Conservation

Habitat Loss, the Dynamics of Biodiversity, and a Perspective on Conservation

Can seed dispersal by human activity play a useful role for the conservation of European grasslands?

Objective: To review the recent research into human-mediated dispersal (HMD) in the European rural landscape, and explore the potential positive aspect of HMD for grassland conservation, in contrast to it's common association with the spread of invasive species. Methods: A literature search was undertaken to identify HMD vectors in the rural landscape for discussion regarding dispersal potential past and present, implications for management, and the identification of future research needs. Results: Grazing animals are important propagule dispersers, but the reduced movement of livestock through the landscape has also meant a reduction in seeds dispersed in this way. Other, non-standard human-mediated dispersal vectors such as clothing and motor vehicles can also transport seeds of many species, and HMD vectors often transport seeds with a variety of dispersal specialisations. Recommendations: There should be a greater movement of grazing animals throughout the landscape, either within larger grazing areas or between existing grasslands. Where this is not possible, other, more directed dispersal of propagules from species-rich communities to target sites should be considered. The potential of non-standard HMD vectors to make a positive contribution to biodiversity should be considered, but more research into all types of HMD vectors is important if we are to fully understand their role in the dispersal of plant species in fragmented landscapes.

Dispersal behaviour of Brown Treecreepers predicts functional connectivity for several other woodland birds

The persistence of native species in fragmented landscapes is dependent on dispersal or foraging movements between habitat patches, which may be limited. Although corridors have been heralded as solutions, their effectiveness depends on species’ movement behaviour, which has rarely been studied. We previously analysed dispersal movements of Brown Treecreepers (Climacteris picumnus), concluding that scattered trees may provide greater connectivity than corridors, and the length of corridors and size of any gaps within may be more important than corridor width. However, conclusions from a single species may not be representative. Here, we analyse dispersal movements of two sedentary birds—Eastern Yellow Robins (Eopsaltria australis) and White-throated Treecreepers (Cormobates leucophaeus)—and foraging movements of two semi-nomadic birds—Fuscous Honeyeaters (Lichenostomus fuscus) and White-plumed Honeyeaters (L. penicillatus). Despite differences in their ecologies and purpose of movements, we found the movement strategies of these species at the local landscape scale were similar. The types of connectivity used and gap distances crossed were similar to those for Brown Treecreepers, strengthening our understanding of how to provide connectivity. We suggest that decision rules for movement have been shaped over evolutionary time by variability in the landscape, so movement behaviour may be less species-specific than previously assumed.

Between-Patch Bird Movements within a High-Andean Polylepis Woodland/Matrix Landscape: Implications for Habitat Restoration

The movement ability of species in fragmented landscapes must be considered if habitat restoration strategies are to allow maximum benefit in terms of increased or healthier wildlife populations. We studied movements of a range of bird species between woodland patches within a high-altitude Polylepis/matrix landscape in the Cordillera Vilcanota, Peru. Movement rates between Polylepis patches differed across guilds, with arboreal omnivores, arboreal sally-strikers and nectarivores displaying the highest movement rates, and understorey guilds and arboreal sally-gleaners the lowest movement rates. Birds tend to avoid flights to more distant neighboring patches, especially when moving from patches which were themselves isolated. The decline in bird flight frequencies with increasing patch isolation followed broken-stick models most closely, and while we suggest that there is evidence for a decline in between-patch movements over distances of 30–210 m, there was great variability in movement rates across individual patches. This variability is presumably a result of complex interactions between patch size, quality and configuration, and flight movement patterns of individual bird species. Our study does, however, highlight the contribution small woodland patches make toward fragmented Polylepis ecosystem functioning, and we suggest that, where financial resources permit, small patch restoration would be an important compliment to the restoration of larger woodland patches. Most important is that replanting takes place within 200 m or so of existing larger patches. This will be especially beneficial in allowing more frequent use of woodland elements within the landscape and in improving the total area of woodland patches that are functionally connected.

Simulating direct and indirect effects of climatic changes on rare perennial plant species in fragmented landscapes

Question: How does climate change influence plant species population dynamics, their time to extinction, and proportion of occupied habitats in a fragmented landscape? Location: Germany and Central European lowland. Methods: We apply a mechanistic general simulation model to test the response of plant functional types to direct and indirect effects of climate change. Three functional types were chosen to represent a set of well-studied perennial plant species: Juncus atratus, Gentiana pneumonanthe and Primula veris. We link local population dynamics within a heterogeneous, fragmented landscape context. “Species spheres”, i.e. multi-dimensional parameter ranges rather than single parameter realizations, based on field and literature data served as proxy for life stage transition parameters. Four climatic scenarios summarizing different cumulative weather effects on demographic rates and different local disturbance frequencies were run. The model predicts “time to extinction” (TE) and “proportion of occupied habitat” (POH) as regional indicators for species extinction risk. Results: TE decreased for all species when weather conditions worsened, and even more so when the frequency of local destructive events additionally increased. However, management towards fewer disturbance events could buffer the negative effect of climate to some extent. The magnitude of these responses varied with species type. POH declined with an increase in bad weather as well as with increasing disturbance frequency. The better the climatic conditions, the less severe were disturbances on population performance. Conclusions: The “species spheres” proved to be a valuable approach for predictive trends. As climate change usually also implies destructive events such as land-use change, flooding or fire, our model on local and regional extinction risks can support conservation issues and management actions.

Modelling functional landscape connectivity from genetic population structure: a new spatially explicit approach

Functional connectivity between spatially disjoint habitat patches is a key factor for the persistence of species in fragmented landscapes. Modelling landscape connectivity to identify potential dispersal corridors requires information about those landscape features affecting dispersal. Here we present a new approach using spatial and genetic data of a highly fragmented population of capercaillie (Tetrao urogallus) in the Black Forest, Germany, to investigate effects of landscape structure on gene flow and to parameterize a spatially explicit corridor model for conservation purposes. Mantel tests and multiple regressions on distance matrices were employed to detect and quantify the effect of different landscape features on relatedness among individuals, while controlling for the effect of geographic distance. We extrapolated the results to an area-wide landscape permeability map and developed a new corridor model that incorporates stochasticity in simulating animal movement. The model was evaluated using both a partition of the data previously set apart and independent observation data of dispersing birds. Most land cover variables (such as coniferous forest, forest edges, agricultural land, roads, settlements) and one topographic variable (topographic exposure) were significantly correlated with gene flow. Although inter-individual relatedness inherently varies greatly and the variance explained by geographic distance and landscape structure was low, the permeability map and the corridor model significantly explained relatedness in the validation data and the spatial distribution of dispersing birds. Thus, landscape structure measurably affected within-population gene flow in the study area. By converting these effects into spatially explicit information our model enables localizing priority areas for the preservation or restoration of metapopulation connectivity.

Habitat use and dispersal characteristic by Stethophyma grossum: the role of habitat isolation and stable habitat conditions towards low dispersal

Species in a highly fragmented environment, such as the intensively used agricultural landscapes of Europe, are expected to be in danger of extinction. We hypothesize according to Kisdi’s theory (Am Nat 159:579–596, 2002) that species in fragmented landscapes with isolated habitats in general tend to possess low dispersal. In order to verify this hypothesis we studied the movement patterns of Stethophyma grossum, a hygrophilous species of wetlands, by mark–release–recapture techniques in a landscape with scattered suitable habitats over 3 years. The study focused on the major population in this landscape (site #1) as dispersal behaviour was assumed to be greatest. Actually, marked individuals of S. grossum were never found in any further suitable habitats in close vicinity to site #1. Despite that the peatland meadow of study site #1 was all over covered with homogenous vegetation only 6% (1.8 ha) of the whole area (30 ha) were occupied by S. grossum. The mean recapture rate over 3 years amounted to 39% with no significant differences between males and females. Both covered little distances within their mean range size of 1.8 ha; the median distances were 36.91 m for males and 26.65 m for females. We confirm the hypothesis that sub-populations of species in longstanding naturally isolated habitats, which habitat conditions have been stable; evolved low dispersal with little movements which are routine movements to find mating partners or food.

Bird movement in a fragmented Atlantic Forest landscape

Isolation is purported to increase the loss of species in fragmented landscapes due to poor bird dispersal ability. I followed the movements of 1282 banded birds of 92 species of passerines between 1995 and 2000 in forest fragments in southeastern Brazil. Twenty-five (48%) out of 52 forest-dependent species were able to use or disperse across open areas of at least 150 m of grasslands. Birds dispersed up to 2000 m between banding sites in different forest fragments separated by as much as 650 m of grasslands. These results did not support the widespread assumption that forest birds have low dispersal ability.

Open areas in a landscape enhance pollen-mediated gene flow of a tree species: evidence from northern Switzerland

Habitat fragmentation often has negative consequences for genetic diversity, and thereby for the viability of populations. However, these negative consequences might be counteracted by gene flow as the latter provides functional connectivity between apparently isolated habitat fragments. Gene flow is itself influenced by landscape structure and composition, and it is therefore important to understand the relationship between gene flow and landscape structure and composition. We used linear LAD regression models to investigate the relationship between contemporary gene flow by pollen in the rare, insect-pollinated forest tree Sorbus domestica and several landscape features. None of the landscape components—which included closed forest, deep valleys, open land and settlements—proved to be an impermeable barrier to gene flow by pollen. We found evidence that settlements, large open areas, and a pronounced topography increased long-distance gene flow in the landscape as compared to a random model including all possible gene flow trajectories. These results are encouraging from a conservation view, as gene flow in species pollinated by generalist insects seems to provide functional connectivity and may help to maintain genetic diversity in rare plant species in fragmented landscapes.

Isolation and characterization of seventeen polymorphic microsatellite markers in the cleptoparasitic cuckoo wasp Hedychrum nobile (Hymenoptera: Chrysididae)

We report the isolation and characterization of seventeen microsatellites from the haplo-diploid cleptoparasitic cuckoo wasp Hedychrum nobile (Hymenoptera: Chrysididae). The microsatellite markers were studied in 14 diploid females and 29 haploid males of the wasp collected in Rhineland Palatinate, Germany. All markers are polymorphic, with 3–25 alleles per locus. The observed frequency of null alleles was 0.00–0.03, and no significant difference was found between the observed and the expected heterozygosity. At least three pairs of markers are in linkage disequilibrium. We tested the markers in Hedychrum chalybaeum, Hedychrum gerstaeckeri, Hedychrum niemelai, and Hedychrum rutilans and amplified 11, 6, 13, and 5 of them in the respective species. The reported markers will help to understand the dispersal abilities and genetic isolation of Hedychrum nobile and congeneric species in fragmented landscapes where the wasps’ hosts occur in isolated populations.

Travelling to a former sea floor: colonization of forests by understorey plant species on land recently reclaimed from the sea

Questions: What are important forest characteristics determining colonization of forest patches by forest understorey species? Location: Planted forests on land recently reclaimed from the sea, the Netherlands. Methods: We related the distribution of forest specialist species in the understorey of 55 forests in Dutch IJsselmeer polders to the following forest characteristics: age, area, connectivity, distance to mainland (as a proxy for distance to seed source) and path density. We used species of the Fraxino-Ulmetum association for the Netherlands as reference for species that could potentially occur in the study area. Results: Area and age of the surveyed forests explained a large part of the variation in overall species composition and species number of forest plant species. The importance of connectivity and distance to the mainland of forest habitats became apparent only at a more detailed level of dispersal groups and individual species. The importance of forest parameters differed between dispersal groups and also between individual species. After 60 years, 75% of the potential pool of wind-dispersed species has reached the polders, whereas this was only 50% for species lacking specific adaptations to long-distance dispersal. However, the average percentage of successful colonizing species present per forest was substantially lower, ranging from 15 to 37%. Conclusions: The data strongly suggest that the colonization process in polder forests is still in its initial phase, during which easily dispersed species dominate the vegetation. Colonization success of common species that lack adaptations to long-distance dispersal is affected by spatial configuration of the forests, and most rare species that could potentially occur in these forests are still absent. Implications for conservation of rare species in fragmented landscapes are discussed.