Trichostomopsis aaronis (Lor.) Agnew & Townsend new to the U.S.S.R.

Abstract

Occurrence of Ptilidium pulcherrimum in transects and spore dispersal from a single colony have been studied in a coastal spruce forest in northern Sweden. The main substrate type was rotting wood with 75% of all occurrences. Annual spore production was 68,500 spores/m² forest, 640,000 spores/m² substrate and 44,000,000 spores/m² colony. Almost 50% of the spores were deposited within 2.5 m of the colony. Annual spore deposition between colonies was estimated to be between 24,000–39,000 and deposition on the main substrate, decaying logs, was about 340–600 spores/m² forest. P. pulcherrimum showed a clumped distribution pattern up to about a 15 m neighbourhood distance. This pattern could not be explained by a similar clumping of the substrate. Instead a limitation by distance in establishment due to a deficit of spores is assumed.     

Dispersal may limit the occurrence of specialist wood decay fungi already at small spatial scales

We used species‐specific spore traps to measure airborne dispersal of the wood decay fungus Phlebia centrifuga (spore size 6.5–9 × 2.5–3 μm) up to 1000 m distance from a point source. We fitted two simple dispersal models, an empirical power law model and a semi‐mechanistic diffusion model to the data using the Bayesian approach. The diffusion model provided a better fit than the power law model which underestimated deposition at 3–55 m and overestimated deposition at longer and shorter distances. Model fit improved by allowing overdispersion, suggesting that spores are not dispersed independently but wind can transport spores in groups inside discrete air packages up to considerable distances. Using the fitted diffusion model and available information on the establishment rates of wood‐decay fungi, we examine the distance up to which colonisation from a single fruit body is likely to occur. We conclude that the diluting effect of distance and low establishment success make the occurrence of P. centrifuga dispersal limited possibly already at the distance of tens of metres and very probably at a few hundred metres from the nearest fruit body, despite the fact that under favourable conditions a high proportion of the spores can disperse considerably further. This conclusion is likely to hold generally for those fungal species that inhabit fragmented landscapes, have specialised resource and habitat requirements, and have similar spore size and other dispersal traits as P. centrifuga.     

Abundance and viability of fungal spores along a forestry gradient – responses to habitat loss and isolation?

Regional variation in spore deposition and viability was studied for two fungi, Fomitopsis rosea (Alb. & Schwein.: Fr.) P. Karst. and Phlebia centrifuga P. Karst., both confined to old‐growth spruce forests in the boreal zone. Seven regions in Sweden were studied along a north‐south transect in which the historical impact from forestry increases and the amount old forests decreases towards the south. The two southernmost regions were located outside the distribution border of the species. Spore deposition was measured species specifically as heterokaryotisation of homokaryotic mycelia growing on wood discs. There was a significant decline in spore deposition towards the south for both species. F. rosea deposited an average amount of 111 spores m^?2 24 h^?1 in the northernmost region compared to less than 1 spore in the four southernmost regions. The corresponding values for P. centrifuga were 27 spores m^?2 24 h^?1 in the north compared to less than 2 spores in the 4 southernmost regions. No deposition was found south of the distribution borders. The viability of spores from local populations within each region was measured as germination success on nutrient media. Individual fruiting bodies from large populations in the north generally produced spores with higher germinability than fruiting bodies from geographically isolated populations in the central and southern regions. However, there was a high variation among the southern populations. Our data suggest that some populations in mid‐ and south Sweden may suffer from negative genetic effects, possibly associated with fragmentation and loss of habitat. Thus, the combination of low spore deposition and low germinability of spores may be a threat to the long‐term persistence of F. rosea and P. centrifuga in southern Sweden. Several other species may experience the same situation, especially when considering the severe decline of dead wood in Swedish forests.     

Dispersal of Septoria nodorum Pycnidiospores by Simulated Rain and Wind

The influence of wind on the splash dispersal of Septoria nodorum pycnidiospores was studied in a raintower/wind tunnel complex with single drops or simulated rain falling on spore suspensions or infected stubble with windspeeds of 1.5 to 4 m/sec. When single drops fell on spore suspensions (depth 0.5 mm, concentration 7.8 × 10⁵ spores/ml) most of the spore-carrying droplets collected on fixed photographic film between 0–4 m downwind (windspeed 3 m/sec) were >200 μm in diameter. However, most spores were carried in droplets with diameter > 1000 μm, 70 % of which carried more than 100 spores. When simulated rain fell on infected stubble most of the spore-carrying droplets collected beyond 1 m downwind (windspeeds 1.4 and 4 m/sec) were <200 μm in diameter and none were >600 μm; most of these droplets carried only one spore. The distribution of splash droplets (with diameter >100 μm) deposited on chromatography paper showed a maximum at 40–50 cm upwind of the target but many more droplets were deposited 20–30 cm downwind, when single drops fell on a spore suspension (concentration 1.2 × 10⁵ spores/ ml) containing fluorescein dye with a windspeed of 2 m/sec; droplets were collected up to 3 m downwind but not more than 70 cm upwind. With a windspeed of 3 m/sec, numbers of sporecarrying droplets and spores collected on film decreased with increasing distance downwind; most were collected within 2 m of the target but some were found up to 4 m. When simulated rain fell on infected stubble, increasing the windspeed from 1.5 to 4 m/sec greatly increased the number of spores deposited more than 1 m downwind. At 1.5 m/sec none were collected beyond 2 m downwind, whereas at 4 m/sec some were collected at 4 m. A few air-borne S. nodorum spores were collected by suction samplers at a height of 40 cm at distances up to 10 m downwind of a target spore suspension on which simulated rain fell.     

Dispersal of Septoria nodorum Pycnidiospores by Simulated Raindrops in Still Air

Simulated raindrops, diameter c. 3 or 4 mm, fell 13 m down a raintower onto suspensions of Septoria nodorum pycnidiospores, depth 0.5 mm, or infected straw pieces. Splash droplets were collected on pieces of fixed photographic film. It was estimated that one drop generated c. 300 spore carrying splash droplets, containing c. 6000 spores, from a concentrated spore suspension (6.5 × 10⁵ spores/ml) and c. 25 spore-carrying droplets, containing c. 30 spores, from infected straw pieces (11 × 10⁶ spores/g dry wt). When the target was a spore suspension in water without surfactant, most spore-carrying droplets were in the 200—400 μm size category and most spores were carried in droplets with diameter >1000 μm. When surfactant was added to spore suspensions, most spore-carrying droplets were in the 0–200 μm category and most spores were carried in droplets with diameter 200–400 μm and none in droplets >1000 μm. Regression analyses showed a significant (p < 0.001) relationship between square root (number of spores per droplet) and droplet diameter; the slope of the regression line was greatest when surfactant was added to the spore suspensions. The distribution of splash droplets with distance travelled from the target was better fitted by an exponential model than by power law or Gaussian models. The distributions of spore-carrying droplets and spores with distance were fitted better by an exponential model than by a power law model. Thus regressions of log, (number collected) against distance were all significant (p < 0.01); the slopes of the regression lines were steepest when surfactant was added to the spore suspension. At a distance of 10 cm from target spore suspensions most splash droplets and spore-carrying droplets were collected at height 10–20 cm, with none above 40 cm; at a distance of 20 cm there were most at heights 0–10 cm and 40–50 cm.     

Spore rain in relation to regional sources and beyond

While patterns of spore dispersal from single sources at short distances are fairly well known, information about ‘spore rain’ from numerous sources and at larger spatial scales is generally lacking. In this study, I sampled spore rain using a novel method consisting of 0.25–0.5 m² cotton cloth traps at nine sites in the boreo‐nemoral vegetation zone in eastern Sweden during two seasons, using Sphagnum spores as a model. Traps were located in various landscapes (mainland, islands). Additional trapping was done in an arctic area (Svalbard) without spore production. Spore densities were tested against distance from the nearest source and area of sources (open peatlands) within different radii around each site (5, 10, 20, 50, 100, 200, 300, 400 km). The cloth method appeared reliable when accounting for precipitation losses, retaining approximately 20–60% of the spores under the recorded amounts of precipitation. Estimated spore densities ranged from 6 million m^?2 and season within a large area source, via regional deposition of 50 000–240 000 spores m^?2, down to 1000 m^?2 at Svalbard. Spore rain for all sites was strongly related to distance from the nearest source, but when excluding samples taken within a source peatland, the amount of sources within 200 km was most important. Spores were larger at isolated island sites, indicating that a higher proportion originated from distant, humid areas. Immense amounts of Sphagnum spores are dispersed across regional distances annually in boreal areas, explaining the success of the genus to colonise nutrient poor wetlands. The detectable deposition at Svalbard indicates that about 1% of the regional spore rain has a trans‐ or intercontinental origin. The regional spore rain, originating from numerous sources in the landscape, is probably valid for most organisms with small diaspores and provides a useful insight in ecology, habitat restoration and conservation planning.     

Testing a mechanistic dispersal model against a dispersal experiment with a wind‐dispersed moss

Wind is the main dispersal agent for a wide array of species and for these species the environmental conditions under which diaspores are released can potentially modify the dispersal kernel substantially. Little is known about how bryophytes regulate spore release, but conditions affecting peristome movements and vibration of the seta may be important. We modelled airborne spore dispersal of the bryophyte species Discelium nudum (spore diameter 25 μm), in four different release scenarios, using a Lagrangian stochastic dispersion model and meteorological data. We tested the model predictions against experimental data on colonization success at five distances (5, 10, 30, 50 and 100 m) and eight directions from a translocated point source during seven two‐day periods. The model predictions were generally successful in describing the observed colonization patterns, especially beyond 10 m. In the laboratory we established spore release thresholds; horizontal wind speed sd > 0.25 m s^?1 induced the seta to vibrate and in relative humidity < 75% the peristome was open. Our dispersal model predicts that the proportion of spores dispersing beyond 100 m is almost twice as large if the spores are released under turbulent conditions than under more stable conditions. However, including release thresholds improved the fit of the model to the colonization data only minimally, with roughly the same amount of variation explained by the most constrained scenario (assuming both vibration of the seta and an open peristome) and the scenario assuming random release. Model predictions under realised experimental conditions suggest that we had a low statistical power to rank the release scenarios due to the lack of measurements of the absolute rate of spore release. Our results hint at the importance of release conditions, but also highlight the challenges in dispersal experiments intended for validating mechanistic dispersal models.     

Spore deposition of wood-decaying fungi: importance of landscape composition

The abundance of many species of wood-decaying fungi has decreased dramatically in Swedish boreal forests over the last century. Therefore, we have investigated the relationship between the spore dispersal of wood-decaying fungi and two key features of landscape composition, namely the amount and age of old forest stands at different spatial scales. Spore deposition was monitored in two regions, using sampling methods based on recording the dikaryotisation of monokaryotic mycelia on nutrient agar and wood discs. The studied species, all mainly confined to Norway spruce in the boreal forest zone, were Fomitopsis pinicola, Fomitopsis rosea , Gloeoporus taxicola , Phlebia centrifuga and Trichaptum laricinum . The study of forestry intensity showed for both regions, that the spore deposition for F. pinicola , F. rosea and G. taxicola was higher in circular plots (radius 2-km) with a high proportion of old Norway spruce forest (>80 yr) than in plots with a lower proportion of old forest. Analysis of the variation in spore deposition of F. rosea and P. centrifuga in relation to the proportion of old spruce forest within 1, 2 and 3 km of the spore sampling point showed that the proportion of old forest within a 3-km radius explained more of the variation than the proportions within 1- and 2-km radii. In addition, the proportion of forest older than 140 yr explained more of the variation than the proportion of younger forests. Thus, the results show that the spore deposition of the studied species strongly depends on the landscape composition at both regional and local scales. Further, the spore deposition at the local scale was best explained by the proportion of >140 yr old spruce forest, which exceeds the common harvest rotation period.     

Inferring dispersal patterns of the generalist root fungus Armillaria mellea

Investigating the dispersal of the root-pathogenic fungus Armillaria mellea is necessary to understand its population biology. Such an investigation is complicated by both its subterranean habit and the persistence of genotypes over successive host generations. As such, host colonization by resident mycelia is thought to outcompete spore infections. We evaluated the contributions of mycelium and spores to host colonization by examining a site in which hosts pre-date A. mellea. Golden Gate Park (San Francisco, CA, USA) was established in 1872 primarily on sand dunes that supported no resident mycelia. Genotypes were identified by microsatellite markers and somatic incompatibility pairings. Spatial autocorrelation analyses of kinship coefficients were used to infer spore dispersal distance. The largest genotypes measured 322 and 343 m in length, and 61 of the 90 total genotypes were recovered from only one tree. The absence of multilocus linkage disequilibrium and the high proportion of unique genotypes suggest that spore dispersal is an important part of the ecology and establishment of A. mellea in this ornamental landscape. Spatial autocorrelations indicated a significant spatial population structure consistent with limited spore dispersal. This isolation-by-distance pattern suggests that most spores disperse over a few meters, which is consistent with recent, direct estimates based on spore trapping data.     

Long-distance spore dispersal in wood-inhabiting Basidiomycetes

Eight species of wood-inhabiting basidiomycetes ( Laurilia sulcata, Peniophora aurantiaca, Resinicium bicolor, Scytinostroma galactinum, Terana caerulea, Trichaptum abietinum, T. biforme and T. fuscoviolaceum ) were used in a spore-trapping test to evaluate their individual ability for long-distance spore dispersal. Petri dishes with single spore mycelia were used as baits. In the experiment, carried out at the Botanical Institute in Göteborg, spores from the air were regularly captured. Surprisingly, spores were captured from species whose nearest known natural occurrence was located quite far from Göteborg. The closest population of Peniophora aurantiaca is about 1000 km south of Göteborg. The results from this experiment support the hypothesis that fungal spores are widely and efficiently dispersed. Such a broad and extensive dispersal ability is of vital importance, especially for wood-inhabiting species which are highly dependent on a substrate which is onlv temporarily available.     

Dispersal potential of spores and asexual propagules in the epixylic hepatic Anastrophyllum hellerianum

Dispersal ability is of great importance for plants, which commonly occupy spatially and temporally limited substrate patches. Mixed reproductive strategies with abundant diaspore production are favoured in a heterogeneous landscape to ensure successful colonisation at different distances. In bryophytes, long-distance dispersal has been thought to take place primarily by spores, while asexual propagules are important in local dispersal and in the maintenance of colonies. In the present study, we investigated the dispersal potential of two equally sized propagules, sexually formed spores and asexually produced gemmae in the dioecious, epixylic hepatic, Anastrophyllum hellerianum, which inhabits spatially and temporally limited substrate patches. We trapped propagules at different distances (0–10 m) and directions from the source colonies in two experiments: one in a natural habitat within a forest and another involving an artificial set-up in an open habitat. Spore dispersal showed only slight distance dependence both in the open and the forest habitats, presumably as a consequence of wind affecting the dispersal pattern. Gemma dispersal was more strongly distance-dependent in the open habitat than in the forest sites. Considerably more gemmae were deposited during rainy than dry periods, possibly because of the effect of rain drops on gemma release. However, weather conditions had no effect on the dispersal patterns of spores or gemmae. In A. hellerianum, the combination of occasional spore production and practically continuous, massive gemma production facilitates dispersal both on local scale and over long distances. Unlike previously assumed, not only spores but also the asexual propagules may contribute to long-distance dispersal, thus allowing considerable gene flow at the landscape level.     

Evaluation of inoculum performance for enhancing gamma-linolenic acid production from Mucor rouxii

Aims: To facilitate a cost‐effective preparation of spore inoculum with good capacity for gamma‐linolenic acid (GLA) production from Mucor rouxii. Methods and Results: Sporangiospore production, mycelial growth ability and fatty acid composition of M. rouxii were determined. Compared with fungal cultivation on solid semi‐synthetic media, high spore production was achieved from M. rouxii grown on rice grains, particularly polished rice (30·7 g kg^?1 initial substrate). Variations in the fatty acid profiles were found in the spores grown on different types of solid media, whereas the spores obtained at different ages from cultivated polished rice showed a similar fatty acid profile. Using the inocula from different spore‐forming media and culture ages, and low temperature storage, not much change in the vegetative growth of submerged cultures or fatty acid composition of mycelia was observed. Conclusion: The spores generated on polished rice exhibited a high performance for GLA production. Age of spore and timing of spore storage at low temperature did not affect on fatty acid profile of the mycelial cultures. Significance and Impact of the Study: The simple, low cost method of inoculum preparation can be applied for large‐scale production of GLA‐rich oils, which reduce a time constraint and variation in fatty acid composition.     

Forest history and the development of old‐growth characteristics in fragmented boreal forests

Questions: Can small and isolated high‐conservation value forests (e.g. designated woodland key habitats) maintain old‐growth forest characteristics and functionality in fragmented landscapes? To what extent have past disturbances (natural and anthropogenic) influenced the development of old‐growth characteristics of these forests? How long does it take for selectively cut stands to attain conditions resembling old‐growth forests? Location: Southern boreal zone of central Sweden. Methods: We linked multiple lines of evidence from historical records, biological archives, and analyses of current forest structure to reconstruct the forest history of a boreal landscape, with special emphasis on six remaining core localities of high‐conservation value forest stands. Results: Our reconstructions revealed that several of these stands experienced wildfires up to the 1890s; all had been selectively harvested in the late 1800s; and all underwent substantial structural and compositional reorganization over the following 100‐150 years. This time interval was sufficient to recover considerable amounts of standing and downed dead wood (mean 60.3 m³ ha^?1), a range of tree ages and sizes (mean basal area 32.6 m² ha^?1), and dominance of shade‐tolerant spruce. It was insufficient to obtain clearly uneven tree age structures and large (>45 cm diameter) living and dead trees. Thus, these forests contain some, but not all, important compositional and structural attributes of old‐growth forests, their abundance being dependent on the timing and magnitude of past natural and anthropogenic disturbances. Our landscape‐level analysis showed marked compositional and structural differences between the historical forest landscape and the present landscape, with the latter having a greater proportion of young forests, introduction of non‐native species, and lack of large trees and dead wood. Conclusions: The remnant high‐conservation value stands were not true representatives of the pre‐industrial forests, but represent the last vestige of forests that have regenerated naturally and maintained a continuous tree cover. These traits, coupled with their capacity for old‐growth recovery, make them valuable focal areas for conservation.     

Implications of 19th century landscape patterns for the recovery of Fagus crenata forests

Questions: What is the effect of the 19th century (pre‐industrialization) landscape pattern on the recovery of climax forests in cool‐temperate mountain areas dominated by Fagus crenata (Japanese beech)? Location: Secondary forests on Mt. Daisen, western Japan. Methods: Vegetation patterns before and after industrialization were obtained from maps drawn in 1898 and 1979. Tree measurements were made in 12 plots in 1997. Correlation between current Fagus crenata dominance and forest edge in the 19th century was analysed using an S‐shaped regression curve. Fagus juvenile density was counted in the plots, and distances from each plot to the five nearest mother trees were measured to determine the dispersal kernel. Results: Secondary grassland covered a substantial area in 1898, whereas forest covered most of the area in 1997. Fagus was dominant in places in the interior forest 100 years ago, and mature Fagus trees were absent in secondary forests that had been grasslands in 1898. The expected number of juveniles decreased to one individual per 100 m² at 43.5 m from the mother tree. Conclusions: The pre‐industrialization landscape greatly affected recovery of Fagus forest. Forests found on the 1898 vegetation map might have acted as refugia for Fagus. The limited dispersal ability of Fagus suggests that it would take many generations (several hundred years) for Fagus forests to recover at the centre of what had been grasslands in the 19th century.     

Fern and lycopod spores rain in a cloud forest of Hidalgo,Mexico

The aim of this study was to determine the composition of the “spore rain” of ferns and lycopods in a cloud forest. We tested whether the canopy impedes spore dispersal to surrounding areas and how spore dispersal is affected by rainfall. The spores were captured with a modified Bush–Gosling trap placed at 30 cm above ground level in forested and non-forested sites from March 2009 to February 2010. We collected 2462 fern spores from 158 morphospecies of which 76 were identified to species level. Thirty-seven species were found exclusively in the spore rain, and 39 were found as sporophytes as well (local component). Mean daily spore density (spores m^?2) was calculated to find the sporulation period for each species. Twenty species showed seasonal patterns of sporulation. The highest spore density was found at the forested site (70 morphospecies and 1856 spores), of which 39 morphospecies (1482 spores) corresponded to the local vegetation. Fifty-five taxa were shared between the forested and non-forested site. In the non-forested site, 605 spores were captured belonging to 64 species. The density of spore rain between sites was significantly different. The rainfall amount was the same at both sites, with a dry period in March, April, and July 2009, and February 2010. There was a negative effect of rainfall on spore rain. The main sporulation occurred in the dry season with strong winds. Although the canopy inhibits airborne dispersal of fern spores, a small amount of spores can disperse beyond the canopy and reach surrounding areas. The rainfall might wash spores to ground and favor the colonization and the establishment of new populations.     

Impacts of Restored Patch Density and Distance from Natural Forests on Colonization Success

Abstract The reduction and fragmentation of forest habitats is expected to have profound effects on plant species diversity as a consequence of the decreased area and increased isolation of the remnant patches. To stop the ongoing process of forest fragmentation, much attention has been given recently to the restoration of forest habitat. The present study investigates restoration possibilities of recently established patches with respect to their geographical isolation. Because seed dispersal events over 100 m are considered to be of long distance, a threshold value of 100 m between recent and old woodland was chosen to define isolation. Total species richness, individual patch species richness, frequency distributions in species occurrences, and patch occupancy patterns of individual species were significantly different among isolated and nonisolated stands. In the short term no high species richness is to be expected in isolated stands. Establishing new forests adjacent to existing woodland ensures higher survival probabilities of existing populations. In the long term, however, the importance of long‐distance seed dispersal should not be underestimated because most species showed occasional long‐distance seed dispersal. A clear distinction should be made between populations colonizing adjacent patches and patches isolated from old woodland. The colonization of isolated stands may have important effects on the dynamics and diversity of forest networks, and more attention should be directed toward the genetic traits and viability of founding populations in isolated stands.     

Structure,dynamics and dendroecology of an old‐growth Fagus forest in the Apennines

Abstract. Question: Which are the structural attributes and the history of old‐growth Fagus forest in Mediterranean montane environments? What are the processes underlying their structural organization? Are these forests stable in time and how does spatial scale affect our assessment of stability? How do these forests compare to other temperate deciduous old‐growth forests? Location: 1600–1850 m a.s.l., Fagus forest near the tree line, central Apennines, Italy. Methods: An old‐growth Fagus forest was studied following historical, structural and dendroecological approaches. History of forest cover changes was analysed using aerial photographs taken in 1945, 1954, 1985 and 1994. The structural analysis was carried out in the primary old‐growth portion of the forest using 18 circular and two rectangular plots. Dendroecological analyses were conducted on 32 dominant or co‐dominant trees. Results: These primary old‐growth Fagus remnants consist of four patches that escaped logging after World War II. Both living and dead tree components are within the range of structural attributes recognized for old‐growth in temperate biomes. Dendroecological analyses revealed the roles of disturbance, competition and climate in structuring the forest. We also identified a persistent Fagus community in which gap‐phase regeneration has led to a mono‐specific multi‐aged stand at spatial scales of a few hectares, characterized by a rotated‐sigmoid diameter distribution. Conclusion: Even at the relatively small spatial scale of this study, high‐elevation Apennine Fagus forests can maintain structural characteristics consistent with those of old‐growth temperate forests. These results are important for managing old‐growth forests in the Mediterranean montane biome.     

Expanding forests and changing growth forms of Siberian larch at the Polar Urals treeline during the 20th century

The ongoing climatic changes potentially affect plant growth and the functioning of temperature‐limited high‐altitude and high‐latitude ecosystems; the rate and magnitude of these biotic changes are, however, uncertain. The aim of this study was to reconstruct stand structure and growth forms of Larix sibirica (Ledeb.) in undisturbed forest–tundra ecotones of the remote Polar Urals on a centennial time scale. Comparisons of the current ecotone with historic photographs from the 1960s clearly document that forests have significantly expanded since then. Similarly, the analysis of forest age structure based on more than 300 trees sampled along three altitudinal gradients reaching from forests in the valleys to the tundra indicate that more than 70% of the currently upright‐growing trees are <80 years old. Because thousands of more than 500‐year‐old subfossil trees occur in the same area but tree remnants of the 15–19th century are lacking almost entirely, we conclude that the forest has been expanding upwards into the formerly tree‐free tundra during the last century by about 20–60 m in altitude. This upward shift of forests was accompanied by significant changes in tree growth forms: while 36% of the few trees that are more than 100 years old were multi‐stem tree clusters, 90% of the trees emerging after 1950 were single‐stemmed. Tree‐ring analysis of horizontal and vertical stems of multi‐stemmed larch trees showed that these trees had been growing in a creeping form since the 15th century. In the early 20th century, they started to grow upright with 5–20 stems per tree individual. The incipient vertical growth led to an abrupt tripling in radial growth and thus, in biomass production. Based on above‐ and belowground biomass measurements of 33 trees that were dug out and the mapping of tree height and diameter, we estimated that forest expansion led to a biomass increase by 40–75 t ha^?1 and a carbon accumulation of approximately 20–40 g C m^?2 yr^?1 during the last century. The forest expansion and change in growth forms coincided with significant summer warming by 0.9 °C and a doubling of winter precipitation during the 20th century. In summary, our results indicate that the ongoing climatic changes are already leaving a fingerprint on the appearance, structure, and productivity of the treeline ecotone in the Polar Urals.     

Does proximity to a mature forest contribute to the seed rain and recovery of an abandoned agriculture area in a semiarid climate?

Proximity to forests contributes to the recolonisation of anthropogenic‐disturbed areas through seed input. We evaluated the role of proximity to a mature forest in the recolonisation of an agricultural area that has been abandoned for 18 years and is currently a young forest. Seed rain was monitored at fixed distances from the mature forest. The type of surface recolonisation (germination versus resprouting) and the reproductive season were measured in both forests. The majority of plants recolonising the young forest originated from seed germination. Proximity to the mature forest contributed to the seed rain in the young forest; however, 18 years has not provided sufficient time for the recolonisation of 80 species present in the mature forest. Some species shared between forests differed in their fruiting season and seed dispersal. The seed rain had a total species richness of 56, a total density of 2270 seeds·m^?2·year^?1 and predominance of self‐ and wind dispersal. A significant reduction in seed rain with increasing distance from the mature forest was observed. The young forest contained 35 species not observed in the mature forest, and the floristic similarity between the two forests was 0.5, indicating that the two forests are floristically distinct.     

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.