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Climate-change projections suggest large changes in riverine flow regime, which will likely alter riparian communities. In northern Europe, forecasts propose lower annual spring flood peaks and higher winter flows, resulting in narrower riparian zones. To estimate the impact of climate change on habitat extent of riparian plants, we developed a framework estimating the sensitivity and exposure of individual species to streamflow change, and surveyed five reaches along the free-flowing Vindel River in northern Sweden. We modeled the hydrologic niche of riparian plant species based on the probability of occurrence along gradients of flood frequency and duration and used predicted future water-level fluctuations (based on climate models and IPCC emission scenarios) to calculate changes in flow-related habitat availability of individual species. Despite projected increases in runoff, we predict most species to decrease in riparian elevational extent by on average 12-29% until the end of the century, depending on scenario. Species growing in the upper, spring-flood-controlled part of the riparian zone will likely lose most habitat, with the largest reductions in species with narrow ranges of inundation duration tolerance (decreases of up to 54%). In contrast, the elevational extent of most amphibious species is predicted to increase, but conditions creating isoetid vegetation will become rarer or disappear: isoetid vegetation is presently found in areas where ice formed in the fall settles on the riverbank during the winter as water levels subside. Higher winter flows will make these conditions rare. We argue that our framework is useful to project the effects of hydrologic change caused by climate change as well as other stressors such as flow regulation also in other regions. With few rivers remaining unaffected by dams and other human stressors, these results call for monitoring to detect species declines. Management to alleviate species losses might include mitigatio

Question: How does germination and establishment of non-resident plant species differ among major types of wetland ecosystems in boreal forest landscapes? Location: A 250-km(2) large boreal forest landscape in northern Sweden. Methods: We performed a germination and establishment experiment to test for differences between three major wetland types: riparian zones, open wetlands and forested wetlands. These wetland types differ ecologically, hydrologically and in their distribution in the landscape. Six species of vascular plant native to the region but absent or rare in one or more of the three wetland types were sown separately in plots with two different levels of disturbance (complete vegetation removal and control) and were monitored for 3 yr. For two species, seed-sowing density was varied to test for effects of propagule pressure. Results: All six species were able to germinate and survive in all habitats and disturbance levels, suggesting that all three wetland types are invasible. There were positive correlations between germination or survival and species richness in resident vegetation for four out of six species, i.e. species-rich sites were more invasible. The germination frequency did not vary with seed-sowing density, indicating that density-dependent effects were small. All species had higher survival in their resident habitat, while the effect of disturbance was small. Conclusions: The results suggest that the low levels of plant invasion observed in boreal wetlands are better explained by low propagule pressure than high resistance to invasion. However, the habitat dependency of survival implies that population establishment is only expected in habitats to which the species are adapted. Nevertheless, levels of invasion might increase in the future, given that more species are being introduced as a result of increases in transport and trade., Originally included in thesis in manuscript form, with the title "Differences in plant invasibility among boreal wetland communities".

1. Riparian plant communities are primarily structured by the hydrological regime of the stream. Models of climate change predict increased temperatures and changed patterns of precipitation that will alter the flow of rivers and streams with consequences for riparian communities. In boreal regions of Europe, stream flows will exhibit earlier spring-flood peaks of lower magnitude, lower summer flows and higher flows in autumn and winter. We quantified the effects of predicted hydrological change on riparian plant species richness, using four different scenarios for the free-flowing Vindel River in northern Sweden. 2. We calculated the hydrological niche of vegetation belts by relating the occurrence of species and vegetation belts to data on flood duration for 10 years preceding the vegetation survey. We then used the flood duration predicted for 2071–2100 to estimate expected changes in the extent of each vegetation belt. Using species accumulation curves, we then predicted changes in plant species richness as a result of changes in extent. 3. The two most species-rich vegetation belts, riparian forest and willow shrub, were predicted to decrease most in elevational extent, up to 39 and 32%, respectively. The graminoid belt below the shrub belt will mainly shift upwards in elevation while the amphibious vegetation belt at the bottom of the riparian zone increases in size. 4. In the Vindel River, the riparian forest and willow shrub zone will lose most species, with reductions of 5–12% and 1–13% per site, respectively, depending on the scenario. The predicted loss from the entire riparian zone is lower, 1–9%, since many species occur in more than one vegetation belt. More extensive species losses are expected in the southern boreal zone for which much larger spring-flood reductions are projected. 5. With an expected reduction in area of the most species-rich belts, it becomes increasingly important to manage and protect riparian zones to alleviate other threats, thu

Climate change is expected to alter the magnitude and variation of flow in streams and rivers, hence providing new conditions for riverine communities. We evaluated plant ecological responses to climate change by transplanting turfs of riparian vegetation to new elevations in the riparian zone, thus simulating expected changes in water-level variation, and monitored the results over 6 years. Turfs moved to higher elevations decreased in biomass and increased in species richness, whereas turfs transplanted to lower elevations gained biomass but lost species. Transplanted plant communities responded slowly to the new hydrologic conditions. After 6 years, biomass of transplanted turfs was statistically indistinguishable from target level controls, but species richness and species composition of transplants were intermediate between original and target levels. By using projections of future stream flow according to IPCC climate change scenarios, we predict likely changes to riparian vegetation in boreal rivers. Climate-driven hydrologic changes are predicted to result in narrower riparian zones along the studied Vindel River in northern Sweden towards the end of the 21st century. Present riparian plant communities are projected to be replaced by terrestrial communities at high elevations as a result of lower-magnitude spring floods, and by amphibious or aquatic communities at low elevations as a result of higher autumn and winter flows. Changes to riparian vegetation may be larger in other boreal climate regions: snow melt fed spring floods are predicted to disappear in southern parts of the boreal zone, which would result in considerable loss of riparian habitat. Our study emphasizes the importance of long-term ecological field experiments given that plant communities often respond slowly and in a nonlinear fashion to external pressures.

Effects of clear-cutting on biodiversity have mainly been studied in the short-term, although knowledge of longer term effects are often more important for managers of forest biodiversity. We assessed relatively long-term effects of clear-cutting on litter dwelling land snails, a group with slow active dispersal and considered to be intolerant to microclimate changes. In a pair wise design we compared snail abundance, species density, and species composition between 13 old seminatural stream-side stands and 13 matched young stands developed 40–60 years after clear-cutting. Using a standardized semi-quantitative method, we identified all snail specimens in a 1.5 l subsample of a pooled litter sample collected from small patches within a 20 × 5 m plot in each stream-side stand. From the young stands a mean of 135 shells and 9.5 species was extracted which was significantly higher than the 58.1 shells and 6.9 species found in old forests. Only two of the 16 species encountered showed a stronger affinity to old than to young forests. In short-term studies of boreal stream-side forests land snail abundance is reduced by clear-cutting. Our results indicate that this decline is transient for most species and within a few decades replaced by an increase. We suggest that local survival in moist stream-side refugia makes the land snails able to benefit from the higher pH and more abundant non-conifer litter in young than in old boreal forests. Our results highlight the importance of longer term studies as a basis for management guidelines for biodiversity conservation.

Predictions on displacement of suitable habitats due to climate change suggest that plant species with poor colonization ability may be unable to move fast enough to match forecasted climate-induced changes in habitat distribution. However, studies on early Holocene plant migration show fast migration of many plant species that are poor colonizers today We hypothesize that warmer temperatures during the early Holocene yielded higher seed quality, contributing to explaining the fast migration. We studied how the 3 seed quality variables, seed mass, germinability, and requirements for break of seed dormancy, vary for seeds of 11 forest herb species with varying colonization capacity collected along a 1400-km latitudinal gradient. Within species, seed mass showed a positive correlation with latitude, whereas germinability was more positively correlated with temperature (growing degree hours obtained at time of seed collection). Only slow-colonizing species increased germinability with temperature, whereas only fast-colonizing species increased germinability with latitude. These interactions were only detectable when analyzing germinability of the seeds, even though this trait and seed mass were correlated. The requirement for dormancy break did not correlate with latitude or temperature. The results indicate that seed development of slow colonizers may be favoured by a warmer climate, which in turn may be important for their migration capacity.

Riparian zones are species-rich habitats also subject to wide-spread degradation and modification. The extensive habitat and biodiversity losses make conservation of riverine ecosystems a priority, especially in the few river systems that remain free-flowing. However, riparian ecosystems might also be threatened by ongoing and anticipated climate change. Models predict large changes in flow regime across the world, which is anticipated to alter riparian communities, but how is poorly known. In northern Europe, lower annual spring flood peaks and higher winter flows are expected, resulting in narrower riparian zones. To determine the impact on riparian plant species we surveyed five sites along the free-flowing Vindel River in northern Sweden. We calculated the probability of occurrence of plant species along gradients of flood frequency and duration. We then compared present and predicted future water-level fluctuations (based on climate models and IPCC emission scenarios) and thereby got an estimate of the future extent of the species based on their hydrologic requirements. The majority of the riparian species are predicted to decrease in elevational extent by on average 13−28 % until the end of the century, depending on scenario. Species growing in the upper, spring-flood controlled part of the riparian zone are predicted to decrease most, with largest reductions in species with narrow flood duration ranges (decreases of up to 54%). Many species would become less frequent than today, with stochastic extinctions expected along some reaches. Reductions may be more dramatic along rivers in the southern boreal zone where snowmelt-fed hydrographs are expected to be largely replaced by rain-fed ones. With few rivers remaining unaffected by dams and other human stressors, even moderate reductions in abundance can have grave consequences for regional conservation, calling for monitoring to detect declining species and management actions to minimize species losses. Managem