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In degraded landscapes, recolonization by pioneer vegetation is often halted by the presence of persistent environmental stress. When natural expansion does occur, it is commonly due to the momentary alleviation of a key environmental variable previously limiting new growth. Thus, studying the circumstances in which expansion occurs can inspire new restoration techniques, wherein vegetation establishment is provoked by emulating natural events through artificial means. Using the salt‐marsh pioneer zone on tidal flats as a biogeomorphic model system, we explore how locally raised sediment bed forms, which are the result of natural (bio)geomorphic processes, enhance seedling establishment in an observational study. We then conduct a manipulative experiment designed to emulate these facilitative conditions in order to enable establishment on an uncolonized tidal flat. Here, we attempt to generate raised growth‐promoting sediment bed forms using porous artificial structures. Flume experiments demonstrate how these structures produce a sheltered hydrodynamic environment in which suspended sediment and seeds preferentially settle. The application of these structures in the field led to the formation of stable, raised sediment platforms and the spontaneous recruitment of salt‐marsh pioneers in the following growing season. These recruits were composed primarily of the annual pioneering Salicornia genus, with densities of up to 140 individuals/m2 within the structures, a 60‐fold increase over ambient densities. Lower abundances of five other perennial species were found within structures that did not appear elsewhere in the pioneer zone. Furthermore, recruits grew to be on average three times greater in mass inside of the structures than in the neighboring ambient environment. The success of this restoration design may be attributed to the combination of three factors: (1) enhanced seed retention, (2) suppressed mortality, and (3) accelerated growth rates on the elevated surfaces generated by the artificial structures. We argue that restoration approaches similar to the one shown here, wherein the conditions for natural establishment are actively mimicked to promote vegetation development, may serve as promising tools in many biogeomorphic ecosystems, ranging from coastal to arid ecosystems. [ABSTRACT FROM AUTHOR]

Plantations of Eucalyptus globulus Labill. have expanded rapidly over the last four decades across temperate parts of the globe. There has been growing concern about the potential invasiveness of this species. Portugal grows more E. globulus than any other country (by area). This study investigates poorly understood factors that may influence wilding establishment and spread from Portuguese plantations. We assessed: site-scale factors influencing the presence and abundance of E. globulus wildlings along plantation edges, as well as the size and reproductive state of these wildlings; and the dispersal distances and developmental state of wildlings away from the plantations edge. We found 1630 E. globulus wildlings in 129 survey plots (10 × 10 m) established along the edge of 67 plantations. Half of the surveyed wildlings were taller than 1.3 m. The presence and abundance of E. globulus wildlings was mainly influenced by factors such as soil cover, the age of mother-trees and their reproductive output. Around 8% of the surveyed wildlings were reproductive, including wildlings less than 1.3 m tall. The proportion of reproductive wildlings was mainly influenced by wildling size, the location relative to the plantation edge and the annual number of frost days. In 49 survey transects outside plantations we found 641 E. globulus wildlings up to a distance of 76 m. Establishment distance was associated with natural drainage lines and the dominant wind direction. We discuss the relevance of the results in terms of the potential invasiveness of E. globulus. [ABSTRACT FROM AUTHOR]

The dynamics of mixed stands are more complex and less studied than those of monospecific stands. The objective of this work was to analyze the variables involved in seedling occurrence and seedling survival in mixed stands of Pinus pinaster and P. pinea in Mediterranean areas. From 2011 to 2016, regeneration of both species was monitored at two sites located in Central Spain. We installed 72 regeneration plots where seedling dynamics were monitored. All the trees in the study areas were measured and mapped. Additionally, we took hemispherical photographs in each regeneration plot. The average density of P. pinea seedlings over the study period was almost 20 times larger than that of P. pinaster. Our results indicate that the seedlings of both species grow under moderate light conditions. In addition, we found that the occurrence of seedlings of both species was related to the structure of the stand. P. pinea seedlings grew where the density and size of P. pinaster trees were low and where P. pinea trees provided moderately sheltered conditions, whereas the number of P. pinaster seedlings was related to under intermediate densities of P. pinaster trees. Furthermore, seedling survival was positively associated with age of the seedlings and negatively with the August average maximum temperature. The temporal continuity of mixed stands of P. pinea and P. pinaster in the study area is compromised by the observed lack of regeneration of P. pinaster. [ABSTRACT FROM AUTHOR]

Tasmanian blue gum ( Eucalyptus globulus) has been increasingly used in forestry outside its native range, and is nowadays one of the most important pulpwood species in the world. E. globulus has great economic importance in many countries, and in Portugal it has recently become the most widespread tree species. However, there is also an increasing concern about the potential ability of eucalypts to naturally establish from seed (wildling establishment), because of negative ecological and economic impacts this could cause. The natural establishment of this fast-growing exotic species may have undesirable consequences, but little is known about its distribution, or which are the factors influencing its occurrence. In order to investigate these issues, we characterized wildling occurrence and abundance along 3111 roadside transects adjacent to eucalypt plantations distributed throughout continental Portugal. Eucalypt wildlings were found in 60 % of the sampled transects and across all natural regions, with densities ranging from 0 to 10,000 plants ha (mean = 277 plants ha). The potential influence of environmental variables on wildling establishment from plantations was assessed using boosted regression trees. The abundance of wildlings was found to be primarily affected by precipitation and distance from the sea (used as a surrogate of thermal amplitude), although topography, frost occurrence and soil type also played a significant role. Plant density peaked at around 1500 mm of annual precipitation and it decreased with both decreasing and increasing precipitation, reaching the lowest values below 800 mm and above 2400 mm. Eucalypt wildlings were also more abundant in areas with milder temperatures, namely closer to the sea (with lower thermal amplitude) and with lower number of frost days. Finally, plant density also seemed to be favoured in areas with intermediate elevation, higher slope and with certain soil types (namely Cambisols and Podzols). Knowing the regions with higher wildling density and understanding the factors influencing plant establishment may help managers to establish and prioritize eventual control plans in regions with higher probability of recruitment. [ABSTRACT FROM AUTHOR]

Abstract: Seedling emergence, survival and early growth of the Mediterranean conifer P. pinaster were studied under closed canopy and open canopy (gaps) cover conditions in a Mediterranean forest of central Spain during two consecutive years (March 2008 to January 2010). Our main objective was to understand how overstorey structure, shrubs and soil properties influence recruitment in this species. Natural emergence and seedling survival were significantly better under closed canopy cover than under open canopy during the two consecutive years of the study; survival increased as radiation decreased. Proximity to shrubs under closed canopy cover was associated with lower mortality rates as well as a positive and apparently transitive effect on early growth. Amelioration of microclimatic conditions is hypothesized as the primary facilitation agent of those observed. Younger seedlings established during the spring of 2008 experienced higher mortality rates than older seedlings established before 2008, and soil properties affected seedling survival significantly. Water stress during summer appeared to be the main cause of seedling mortality in both years. Our study suggests that seedlings of shade-intolerant species may require overstorey cover to establish successfully, and that positive plant–plant interactions in forest communities may be more important than expected in the milder conditions provided by overstorey canopy cover. [Copyright &y& Elsevier]

• The Iberian Peninsula hosts the largest occupation of Eucalyptus globulus in Europe. • One-third of surveyed roadsides had E. globulus wildlings. • The potential for recruitment is higher in areas with an Atlantic influence. • Probability of recruitment is higher in areas with high suitability for plantations. In the last century, eucalypts became one of the most popular fast-growing species in the world for production purposes. Eucalyptus globulus Labill. is currently one of the most extensively cultivated species. The Iberian Peninsula (Iberia) holds the largest concentration of E. globulus plantations, distributed mostly along the Western and Northern coasts. The naturalization of E. globulus is now a concern in many regions across the introduced range, so it is important to identify the local and regional drivers that influence the recruitment of E. globulus wildlings. Likewise, it is important to understand how this recruitment relates both with the current and the potential distribution of plantations. We analyzed wildlings count data from 4169 transects surveyed with Google Street View along roadsides adjacent to E. globulus plantations across Iberia. These data were used to calibrate a probability map of wildling recruitment, using a species distribution model developed with biomod2. The probability map was compared with both the current and the potential distributions of E. globulus. Finally, we performed a logistic regression to model the relationship between the environmental suitability for E. globulus recruitment and the suitability for plantations in Portugal and Spain. We recorded a total of 6721 wildlings in 1363 transects (33% of the total transects). Overall, wildling density was 85.3 ± 4.1 wildlings ha−1, ranging from 0 to 5882 wildlings ha−1. Regional variables had greater influence than local variables on wildling recruitment. Higher annual precipitation and lower temperature seasonality were positively related to recruitment abundance, reflecting wildling sensitivity to water deficits and extreme temperatures. At a local scale, the northern aspect and bare soil also presented a positive relationship with recruitment abundance. Recruitment potential was higher in areas with Atlantic influence along the northern and western coasts of Iberia, where plantations are already present. Nearly half of the area potentially suitable for E. globulus plantations was unfavorable for recruitment. However, we found a positive correlation between plantation suitability and recruitment suitability. This work may assist forest management by identifying zones where E. globulus recruitment is enhanced outside plantations for a better allocation of resources for monitoring and control actions. [ABSTRACT FROM AUTHOR]