Natural Tree Regeneration Research Articles

Invasive shrub removal may be more effective at reducing granivory than coating tree seeds with capsaicin

The utility of seed addition to promote tree regeneration can be greatly limited by animals that consume seeds. Moreover, given that restoration often occurs in forests where invasive shrubs are abundant, and evidence that invasive shrubs can increase granivory, it is important to explore whether methods for reducing granivory work equally well in invaded and uninvaded habitats. We used a multi-site field experiment spanning 160 days to explore whether coating seeds of Prunus serotina with capsaicin extract leads to reduced granivory in habitats with or without invasive shrubs (Rhamnus cathartica). Capsaicin-coated seeds were removed at a similar rate to uncoated seeds, but seeds in invaded plots had a 78.8% higher rate of removal compared to plots without invasive shrubs. Our findings suggest that managers seeking to encourage regeneration of native trees using direct seeding should consider invasive shrub removal as a top priority to limit the loss of seeds once sown.

Influence of wild ungulates on the secondary succession of an Apennine silver fir forest after windthrow

Windstorms are natural factors in vegetation dynamics, but their intensity is increasing and undermines the forest resilience. Post-event interventions depend on forest types and management purposes. To promote mixed stands that are less susceptible to windthrow than monocultures, natural tree regeneration is usually recommended. However, wild ungulates attracted by the increased food supply in the new clearings can influence the secondary succession and slow down vegetation recovery. The impact of ungulate pressure on secondary successions in blowdown areas is still poorly known, especially in Mediterranean areas, which is particularly vulnerable to climate stressors. We investigated this topic using a monospecific silver fir (Abies alba) forest of artificial origin in the Apennines as a model system. The forest was left to natural succession after a severe windthrow in 2015, offering the opportunity to establish an ungulate exclosure experiment to analyse vegetation changes over six years. For the whole plant community, cover and height, α-diversity (species richness, Shannon and evenness indexes), and species composition were recorded yearly, together with tree seedling density, in open and fenced plots at increasing distances from the forest edge. Ecological and functional traits (proportion of light-demanding and forest specialists, endo-/epi-zoochorous species), and life-forms of the community samples were also analysed. Overall, we found that ungulates significantly influenced the dynamic trajectories of secondary succession. The effects on plant cover and diversity were negative and increased with distance from the forest edge. The presence of ungulates favoured generalist species and endozoochorous taxa. However, distance from the forest edge strongly reduced the latter effect. The average density of tree seedlings was overall high (ca. 10,000/ha), but it was strongly reduced by ungulates for three deciduous species and A. alba, the most browsed species. Natural recolonization after windthrow in Apennine pure silver fir stands may favour the formation of mixed, less susceptible forests, but the current ungulate pressure slows down this process, especially in the areas furthest from the forest edge.

The Influence of Logging-Related Soil Disturbance on Pioneer Tree Regeneration in Mixed Temperate Forests.

The recovery of soil properties and the proper growth of natural tree regeneration are key elements for maintaining forest productivity after selective logging operations. This study was conducted on the soil properties and natural growth of two pioneer seedling species of alder and maple which were on skid trails in the mixed beech forests of northern Iran. To examine the long-term effects, we randomly selected six skid trails, with two replicates established for each of three time periods since last use (10, 20, and 30 years ago). Random plots 4 m × 10 m in size, three plots on each skid trail and six plots on areas without soil compaction (control), were selected. Measurements included the physical and chemical properties of the soil and the growth, and the architectural and qualitative characteristics of the seedlings. The results showed that all the soil properties of the 10- and 20-year-old skid trails were significantly different from the control area (except for the soil moisture in the 20-year-old skid trail). The 30-year-old skid trail showed values of other soil properties which were not significantly different from the control area, except for the amounts of organic matter and soil nitrogen, which was less than the control. The skid trails had a negative effect on all of the growth, qualitative, and architectural indices of seedlings. The characteristics of seedlings were related to soil characteristics and had the highest correlation with the soil penetration resistance (R-value from -0.41 to -0.63 for stem growth, p < 0.05; -0.57 to -0.90 for root growth, p < 0.01; and -0.76 to -0.86 for biomass, p < 0.01). The correlation coefficient between soil penetration resistance and the Dickson quality index of alder and maple seedlings was, respectively, -0.74 and -0.72, p < 0.01. The negative effect of soil compaction on root growth (-27.69% for alder seedlings and -28.08% for maple seedlings) was greater than on stem growth (-24.11% for alder seedlings and -16.27% for maple seedlings). The amount of growth, qualitative, and architectural indices of alder seedlings were higher than that of maple seedlings. Although alder is a better choice as compared to maple seedling in the initial year, the results of our study show that it is recommended to plant both alder and maple on skid trails after logging operations.

Natural regeneration in edge and interior of a forest fragment at the Catarinense Plateau

Forest fragmentation is one of the greatest challenges for forest conservation in the Catarinense Plateau region. Thus, this work aimed to evaluate the edge effect on the structure and floristics of natural tree regeneration in a fragment of Mixed Ombrophylous Forest in São José do Cerrito, Santa Catarina. The natural regeneration of the tree component in the understory was sampled in four transects placed perpendicular to the edge of the fragment. Eight plots of 20 m² were installed on the edge (contact with the surrounding matrix) and inside (100 m from the edge) of the fragment, subdivided into smaller plots according to the class of regenerants. The regenerants were identified, measured in height and classified according to their successional group, conservation status, endemism and calculated the regeneration index for each class of height and total. For statistical analysis, Non-Metric Multidimensional Scaling (NMDS) analysis was used. The results showed a significant difference between the interior and edge of the fragment, with the regenerating community on the edge being significantly more abundant and more diverse than the interior. The species with the highest rate of total regeneration towards the interior were Myrcia hatschbachii (TNR=12.1%) and Banara tomentosa (TNR=11.1%), and towards the edge it was Myrcia oblongata (TNR=15.1%). It is concluded that the edge effect appears to have been a determining factor for the alteration in the structure and floristic composition of the regenerants.

‘Mind the Gap’—reforestation needs vs. reforestation capacity in the western United States

Tree establishment following severe or stand-replacing disturbance is critical for achieving U.S. climate change mitigation goals and for maintaining the co-benefits of intact forest ecosystems. In many contexts, natural post-fire tree regeneration is sufficient to maintain forest cover and associated ecosystem services, but increasingly the pattern and scale of disturbance exceeds ecological thresholds and active reforestation may be warranted. Our capacity to plant trees, however, is not keeping pace with reforestation needs. This shortfall is uniquely apparent in the western U.S., where wildfire size and severity have increased in recent decades and long-term divestment in the reforestation supply chain has limited our ability to respond to existing needs. Here we present an analysis of key facets of both the supply and demand side of reforestation in the western U.S. and address six questions: (1) What is the current backlog of potential reforestation needs driven by high-severity wildfire?; (2) How will increasing wildfire activity through the end of the century affect potential reforestation needs?; (3) What is our capacity to meet current and future reforestation needs?; (4) How can we scale the reforestation supply chain to meet current and future demands?; (5) What approaches to reforestation can promote forest resilience to climate change and wildfire?; and (6) Where are opportunities emerging from recent policy initiatives, innovative public-private partnerships, and natural capital markets for scaling reforestation? Between 1984 and 2000, annual tree planting capacity met post-fire needs but cumulatively over the last two decades (2000 to 2021) it has fallen short of fire-driven needs by an estimated 1.5 million ha (ca. 3.8 million ac). We anticipate this gap will increase 2 to 3 fold by 2050. Scaling up reforestation efforts to close this gap will require increased investment across all facets of the reforestation supply chain, public-private partnerships, and novel approaches to reforestation that increase the resilience of western forests to drought and wildfire. We highlight emerging opportunities from recent policy initiatives and conservation finance for expanding reforestation efforts.

Stand structural effects on growth distribution and growth efficiency in Scots pine and Mediterranean pine in Spain

AbstractUnderstanding the growth efficiency of individual trees, or growth per unit of resource utilization, can inform silvicultural management strategies to maximize tree and stand growth. Stand structure—the size and spatial distributions of trees within the stand—strongly influences water, light, and nutrient availability, as well as the resource-use efficiency of each tree. Key silvicultural tools for stand management include manipulating tree density, size distribution, and arrangement by controlling natural regeneration, artificial seeding, planting seedlings, and/or subsequent thinning of established trees. We analyzed two sets of plots from even-aged stands of common coniferous species in central Spain, 106 pure Scots pine (Pinus sylvestris) and 92 pure Mediterranean pine (Pinus pinaster), to examine the dynamics of the dominance hypothesis, the relationship between stand structure and growth, and the relationship between structure and growth efficiency. Our main findings revealed a negative impact of size-class uniformity on stand growth in both Scots pine and Mediterranean pine, while the positive effect of tree size on growth efficiency was supported for Mediterranean pine stands but uncertain for Scots pine. At the operational level, our results highlight how thinning intensity is more important than the thinning method in Mediterranean pinewoods and how thinning can benefit the provision of multiple ecosystem services. We also recommend integrating dominance effects on growth into individual tree modelling.

Drivers of tree regeneration in coniferous monocultures during conversion to mixed forests in Central Europe – Implications for forest restoration management

In Central Europe, anthropogenic coniferous monocultures have been subject to conversion to more diverse mixed forests since the 1990s, however, they are still abundant across many forest landscapes. Artificial and natural tree regeneration both play a key role during conversion by determining the species composition and structure of the future forests. Many abiotic and biotic factors can potentially influence the regeneration process and its specific combinations or interactions may be different among tree species and its developmental stages. Here, we aimed to identify and quantify the effect of the most important drivers on the density of the most abundant regenerating tree species (i.e., Norway spruce and European beech), as well as on species and structural diversity of the tree regeneration. We studied tree regeneration in four former monospecific coniferous stand types (i.e., Norway spruce, Scots pine, European larch, and Douglas fir) in Southwest Germany that have been under conversion to mixed forests since the 1990s. We sampled tree regeneration in four growth height classes together with a variety of potentially influencing factors on 108 sampling plots and applied multivariate analyses. We identified light availability in the understorey, stand structural attributes, browsing pressure, and diaspore source abundance as the most important factors for the density and diversity of tree regeneration. Particularly, we revealed species-specific differences in drivers of regeneration density. While spruce profited from increasing light availability and decreasing stand basal area, beech benefited either from a minor reduction or more strikingly from an increase in overstorey density. Increasing diaspore source abundance positively and a high browsing pressure negatively affected both species equally. Our results suggest that humus and topsoil properties were modified during conversion, probably due to changes in tree species composition and silvicultural activities. The species and structural diversity of the tree regeneration benefitted from increasing light availability, decreasing stand basal area, and a low to moderate browsing pressure. We conclude that forest managers may carefully equilibrate among the regulation of overstorey cover, stand basal area, and browsing pressure to fulfil the objectives of forest conversion, i.e., establishing and safeguarding a diverse tree regeneration to promote the development of mature mixed forests in the future.

Tree regeneration and ontogenetic strategies of northern European hemiboreal forests: transitioning towards closer-to-nature forest management.

Tree ontogeny is the genetic trajectories of regenerative processes in trees, repeating in time and space, including both development and reproduction. Understanding the principles of tree ontogeny is a key priority in emulating natural ecological patterns and processes that fall within the calls for closer-to-nature forest management. By recognizing and respecting the growth and development of individual trees and forest stands, forest managers can implement strategies that align with the inherent dynamics of forest ecosystem. Therefore, this study aims to determine the ontogenetic characteristics of tree regeneration and growth in northern European hemiboreal forests. We applied a three-step process to review i) the ontogenetic characteristics of forest trees, ii) ontogenetic strategies of trees for stand-forming species, and iii) summarise the review findings of points i and ii to propose a conceptual framework for transitioning towards closer-to-nature management of hemiboreal forest trees. To achieve this, we applied the super-organism approach to forest development as a holistic progression towards the establishment of natural stand forming ecosystems. The review showed multiple aspects; first, there are unique growth and development characteristics of individual trees at the pre-generative and generative stages of ontogenesis under full and minimal light conditions. Second, there are four main modes of tree establishment, growth and development related to the light requirements of trees; they were described as ontogenetic strategies of stand-forming tree species: gap colonisers, gap successors, gap fillers and gap competitors. Third, the summary of our analysis of the ontogenetic characteristics of tree regeneration and growth in northern European hemiboreal forests shows that stand-forming species occupy multiple niche positions relative to forest dynamics modes. This study demonstrates the importance of understanding tree ontogeny under the pretext of closer-to-nature forest management, and its potential towards formulating sustainable forest management that emulates the natural dynamics of forest structure. We suggest that scientists and foresters can adapt closer-to-nature management strategies, such as assisted natural regeneration of trees, to improve the vitality of tree communities and overall forest health. The presented approach prioritizes ecological integrity and forest resilience, promoting assisted natural regeneration, and fostering adaptability and connectivity among plant populations in hemiboreal tree communities.

The Impact of Modern Logging on Soil Disturbance, the State of Ground Cover and the Subsequent Regeneration of Trees in Boreal Forests of Russia

Abstract—The article presents materials for studying the physical properties of the upper horizons of the soil, the species diversity of the living ground cover and the natural regeneration of trees in 1–15 years old clear-cuttings. A noticeable compaction of the soil is observed in the ruts of the passage of machines, mainly in the thickness of the soil 0–10 cm, but not in the between ruts sand the cutting strips. We found that the physical properties (bulk density, total porosity and aeration porosity) of the upper soil horizons depend on the age of cutting and the study site (p 0.01). Soil compaction in the ruts decreases 9–15 years after logging to indicators in sites where the movement of machines was not carried out. The overgrowth of damaged sections in clear-cuts occurred through ruderal species and species with wide ecological amplitudes to environmental factors. This overgrowth stabilised 15 years after logging when the biodiversity level approached untouched stands. The regeneration of clear-cuts is mainly deciduous such as birch and aspen that mainly grew in the cutting strips. In the ruts and the between ruts, the amount of undergrowth is 2–7 times less than in cutting strips.

Modeling post-fire regeneration patterns under different restoration scenarios to improve forest recovery in degraded ecosystems

BackgroundChanges in disturbance regimes triggered by land use and climate change can significantly alter forest ecosystems by modifying the distribution of some species and hindering post-disturbance tree regeneration dynamics. Applied nucleation (AN) could be a valuable active restoration approach for promoting natural recovery in forest ecosystems affected by stand-replacing disturbances as it improves seed availability and microsite conditions. ObjectivesThe study aimed to investigate the potential of AN under different scenarios in a mountain forest ecosystem of the Northwestern Italian Alps dominated by Scots pine (Pinus sylvestris L.). The area was affected by a large stand-replacing fire in 2005 and post-fire salvage logging that amplified ecosystem degradation and dampened natural tree regeneration. MethodsWe assessed the main drivers guiding natural post-fire natural recovery and identified suitable sites for tree regeneration through a machine learning correlative model (Bayesian Additive Regression Tree, BART). Specifically, we used several environmental predictors (e.g., topography, wind direction, and distance from seed trees) to model the occurrence of natural tree regeneration. We predicted the probability of tree regeneration presence at landscape scale under the current situation (fire followed by salvage logging) and a set of AN scenarios characterized by an increase in nuclei density, since distance from seed trees emerged as the most important driver for natural tree regeneration. Starting from the situation 16 years after the fire, we reclassified the prediction raster into a binary map of intervention priority (priority and non-priority patches), using the probability value that maximized the model accuracy (true skill statistic; TSS) as threshold. Patches with scarce pine regeneration were considered as high intervention priority sites for AN. These predictions made it possible to assess the most efficient active management scenario in terms of promoting forest recovery. ConclusionsThe simulations showed the positive effects of AN on natural tree regeneration and the importance of site selection for plantations, proving that AN could be a promising post-fire management technique that can minimize human interventions and their associated economic and ecological costs. To our knowledge, this work is the first AN simulation in a temperate mountain ecosystem. The selection of favorable sites can be further improved by considering fine-scale characteristics through field experiments and cross-scale integration.

Seedling establishment in a deciduous and an evergreen oak under simulated climate change

Climate change constitutes a major threat to global biodiversity and to the success of natural and assisted tree regeneration. Oaks are among the most emblematic tree species in the Northern Hemisphere, so it is crucial to understand the impact of changing climate on seedling recruitment and early development. In this study, we investigated the effect of air warming on the early development of one deciduous species – Quercus faginea – and one evergreen species – Quercus ilex subsp. ballota. Acorns of both species were seeded in an alluvial valley in southern Spain and subjected to an air warming treatment with Open-Top Chambers (OTC), which increased air temperature by 2 °C. We monitored seedling emergence, growth, chlorophyll concentration, and mortality in the first growing season. The simulated climate change treatment accelerated plant emergence in early spring, reduced spring shoot growth, and increased mortality from ∼ 23 % in control plots to ∼ 40 % inside OTCs. Although Q. ilex and Q. faginea are sympatric species, Q. faginea showed lower performance under simulated climate change in terms of growth. In addition, acorn fresh weight was positively related with the probability and speed of emergence (only for Q. faginea), seedling size, and relative chlorophyll content, and plants that emerged earlier had a greater likelihood of surviving. In short, larger acorns partly counter-balanced the negative impact of temperature increase on plants. This study highlights the importance of understanding plant response to climate change both to forecast potential changes in species composition and to choose adequate species and traits such as acorn size in restoration projects.

Urban forests support natural regeneration of cloud forest trees and shrubs, albeit with limited occurrence of late-successional species

In highly diverse tropical landscapes, urban and peri-urban forests can play a crucial role as reservoirs of biodiversity. However, urbanization has negatively impacted the natural and anthropogenic vegetation, including the composition, diversity, and functions of urban forests. Tree regeneration plays an essential role in the long-term functionality of forests. Few studies have investigated how natural regeneration occurs in urbanized tropical landscapes, as well as the factors that drive this process. We assessed whether natural regeneration of the tropical montane cloud forest is occurring in urban and peri-urban forests and examined the influence of environmental factors (elevation, annual precipitation, air temperature, canopy cover, and soil physicochemical characteristics) on the regeneration. We used the density and diversity of seedlings, saplings, and juveniles of trees and shrubs in 42 plots across seven urban and peri-urban sites in the Neotropical city of Xalapa, Mexico. In the natural regeneration, 42 tree and 22 shrub species were recorded. Of these species, 83% were native and 17% were non-native. There was a lower abundance of tree (34%) compared to shrub (66%) individuals. Early-successional species were more abundant (51%) than intermediate (35%) and late-successional (14%) species. The numbers of species in the seedling, sapling, and juvenile stages, and the number of early-successional species, were higher in urban than in peri-urban forests. The species richness of both native and non-native taxa was higher in urban than in peri-urban forests (95% CI). We found no significant differences in the density of the young life stages, the density of successional groups, or the density of native and non-native species, between urban and peri-urban forests, probably due to high variability across the sites. Canopy cover had a consistently positive effect on density in most groups. Forest type, soil phosphorus, and soil bulk density also explained densities, except for the late-successional species, where these factors were not statistically significant. The limited richness and density of late-successional species highlight the need to assist the regeneration of this vulnerable group. Understanding natural regeneration patterns can inform the management and restoration of urbanized areas in the distributional regions of tropical montane cloud forest, one of the most important and threatened tropical ecosystems.

An experimental approach to identify drivers of tree regeneration diversity, composition, and heterogeneity in northern hardwood forests

Silviculture methods such as clearcutting, shelterwood seed cutting, and selection system are used to manipulate the canopy and regenerate new cohorts in hardwood stands. Additionally, site preparation can be utilized to alter seedbed conditions with the aim to promote changes in species composition. However, limited seed availability and increased ungulate browsing may limit successful natural regeneration in some areas. Our objective was to investigate the influence of regeneration method, site preparation, deer exclusion, and direct seeding on the regeneration of a managed northern hardwood forest. Utilizing a randomized split-plot design with three splitting levels, we examined the effects of four different regeneration methods, two site preparation treatments, seed limitation and deer browsing on composition, compositional heterogeneity, and richness of regenerating tree species. We observed significant differences in the resulting species composition related to the regeneration and site preparation methods. Shelterwood seed cutting implemented with 60% and 30% residual canopy cover, along with scarification, increased species richness and species compositional heterogeneity. However, the combination of deer exclusion and direct seeding resulted in the highest species richness across all treatment combinations. Deer exclusion alone did not enhance richness or compositional heterogeneity, highlighting the impeding effect of limited seed availability. We found that direct seeding successfully altered species composition and increased species richness. Our results suggest that while the regeneration and site preparation methods can benefit natural tree regeneration, approaches that also address both seed limitations and deer browsing will be necessary to increase the tree species diversity in some cases.

More than trees: Stand management can be used to improve ecosystem diversity, structure and functioning 20 years after forest restoration in drylands

In Mediterranean drylands, extensive areas have been restored by reforestation over the past decades to improve diversity, soil fertility, and tree natural regeneration, contributing to halting desertification and land degradation. However, evaluating reforestation success usually relies on tree survival, while holistic and long-term evaluations of reforestation success based on ecosystem diversity, structure and functioning are scarce. In this work, we provide the first assessment that combines the evaluation of planted trees and indicators of ecosystem diversity, structure, and functioning in established reforestations with three native Mediterranean species along a climatic gradient. We sampled 43 20-year-old stands with umbrella pine, holm oak and cork oak in Portugal, and tested the effects of tree species composition, stand management (i.e., differences in tree density and shrub cover), and edaphoclimatic conditions, on the size of planted trees, species diversity, structural complexity and indicators of ecosystem functioning related to productivity, soil nutrients and tree natural regeneration.Our results show that, after 20 years of reforestation, stand management was an essential driver of plant diversity and ecosystem functioning. Higher tree density, particularly of oaks, and higher shrub cover improved plant diversity, ecosystem productivity, and oak regeneration. The latter was also improved by structural complexity. Tree composition effects highlighted the importance of pine management to avoid competition. Since we evaluated these reforestations along a climatic gradient, we also conclude that climate influenced pine and holm oak size, ecosystem productivity, and soil C/N. Our research, by being based on assessing the long-term reforestation success in a more holistic way, highlighted the importance of stand management for improving ecosystem diversity and functioning in these restored systems. Practices such as increasing tree density up to ~800 trees/ha and allowing a shrub cover of ca. 30 %, may improve the ecological condition of future and currently reforested areas across the Mediterranean region.

Post-storm management determines early tree species composition and browsing intensity in regenerating beech forest

Natural disturbances such as fire, insect pests, and windstorms are affecting forests with increasing intensity. Fallen and damaged trees are commonly removed by salvage logging, which can affect tree regeneration and browsing pressure. Yet, the interaction of logging intensity and browsing and their cumulative effects on natural tree regeneration remain poorly understood. We applied three treatments of differing logging intensity to temperate beech (Fagus sylvatica) forest affected by windstorm, using adjacent undamaged forest as reference. We monitored tree regeneration for the first four years following disturbance, and browsing on experimentally planted one-year-old Quercus robur saplings for one year on a total of 20 plots. Natural tree regeneration was present on all plots, regardless of treatment. Species richness and cover of natural regeneration did not differ between disturbance treatments, tree species composition shifted towards early successional species with increasing management intensity, i.e., decreasing amount of deadwood remaining on-site. Community composition of regenerating trees on plots with intensive logging was significantly dissimilar to undamaged forest. Browsing intensity by roe deer decreased with decreasing logging intensity. Browsing by voles and mice showed the opposite effect direction. We show that salvage logging intensity influences species composition of natural regeneration, and that dead wood retention modulates browsing. Salvage logging of moderate intensity promotes the regeneration of early- and late-successional tree species similarly, thereby reducing the need for afforestation.

Tree regeneration potential in urban spruce-dominated forests is shaped by management history

With projected climate change, urban spruce-dominated forests are facing increasing risks of forest damages, encouraging management for mixed stand structures. In the major cities of southern Finland, forests are preferentially maintained continuously covered, and tree regeneration is mostly reliant on naturally emerging sapling stock. To understand the role of forest management in shaping natural tree regeneration in urban forests, we studied the occurrence and abundance of tree saplings in spruce-dominated tree stands on a management continuum ranging from partially logged to undisturbed near-natural stands. Study sites (N = 74) were located in three urban centers in southern Finland: Tampere, Lahti and Helsinki region. We analyzed the data by comparing tree regeneration potential between management classes reflecting the timing and intensity of past logging, and by relating the occurrence of saplings with current structures of the living tree stand.Compared to undisturbed stands, partially logged sites had increased regeneration of broad-leaved trees and repressed regeneration of spruce, while the most abundant sapling tree species across all management classes was rowan. We conclude that partial logging can be a successful way of directing tree regeneration towards lower dominance of spruce. However, when the canopy is only partially opened, created gaps may end up being filled primarily by rowans that are comparatively shade-tolerant. Because the ingrowth of rowan and many other broad-leaved tree species is strongly restricted by dense populations of large browsing animals in non-urban areas, urban forests may develop stand structures and tree species composition that are otherwise rare in the Fennoscandian boreal forests.

Early natural tree regeneration after wildfire in a Central European Scots pine forest: Forest management, fire severity and distance matters

In the last years, several wildfires destroyed large areas in Central European forest stands and the risk for fires is predicted to increase in the future. However, little is known about post-fire succession including the effect of forest management for this region. We studied recolonization patterns of natural regeneration of the pioneer tree species Betula pendula Roth (silver birch), Pinus sylvestris L. (Scots pine), Populus tremula L. (European aspen) and Salix caprea L. (goat willow) on 200 plots in a large, 334 ha burned pine forest stand two years after a severe wildfire. Natural regeneration in general was high, reaching higher densities than artificial regeneration on most plots. The influence of fire severity, post-fire forest management (complete and partial salvage logging and soil disturbance like skidder traffic, ploughing and raking) and distance to the next potential seed source on the number of tree regeneration was tested with multiple linear regression. High fire severities decreased abundance of pine, aspen and willow. The regeneration of all four investigated tree species was influenced by forest management. High birch regeneration was predicted for completely salvage logged plots in combination with skidder traffic or early ploughing and plots without any forest management. Pine regeneration was predicted to be highest on completely salvage logged and sites without any salvage logging. Forest management which includes partial salvage logging showed mostly lower predicted regeneration of birch, pine and aspen as probably an effect of timing. Willow regeneration was promoted by forest management which includes late ploughing. Regeneration of birch and pine decreased with increasing distance to the next potential seed tree, while aspen and willow sapling densities were not affected by distance due to their excellent dispersal by wind. For birch and especially pine, close seed trees are crucial for sufficient natural regeneration. Recolonization of burned areas is a highly dynamic process dependent on several factors. However, natural regeneration provides a fast, cost-effective way of reforestation which can be facilitated by suitable silvicultural treatments. We recommend to keep survived trees as green islands on site to provide close seed sources. To avoid seedling disturbance, forest management activities should be complied according to life cycles of naturally established tree seedlings. We also suggest using the benefits of deciduous pioneer trees in forestry in order to establish more diverse, less fire-prone forests after wildfires in the long term.

Restoring mixed forests through conversion of Norway spruce stands: effects of fencing and mechanical site preparation on performance of planted beech and natural tree regeneration

Conversion of Norway spruce (Picea abies) plantations to more diverse and resilient forest types is an important task for European forest managers in the face of climate change and increased focus on ecosystem services beyond timber production. However, there is a lack of knowledge on how to cost-effectively restore such forests. This study reports the influence of vicinity (distance) of forest type (mixed or spruce), fencing and mechanical site preparation (MSP) on the early performance of planted beech (Fagus sylvatica) seedlings and natural regeneration of other tree species following clear-cuts of Norway spruce in southern Sweden. After 6 years, we found clear effects of fencing and MSP, but not of vicinity of forest type. Fencing had a positive effect on height growth of Scots pine (Pinus sylvestris) but not on height of planted beech and naturally regenerated birch (Betula pendula, B. pubescens). There was a positive effect of MSP on survival and height growth of planted beech, and on the amount of natural regeneration of Scots pine. We conclude that establishment of beech forest is greatly accelerated by active regeneration approaches such as planting. In addition, the combination of planting beech, natural regeneration of other species, fencing and MSP is effective to promote the transition to mixed and diverse stands with both broadleaves and conifers. Fencing represented the highest cost among the treatments, and its cost-effectiveness depends on the local ungulate browsing pressure. In our study, fencing was critical to protect natural regeneration of Scots pine from browsing. Finally, natural regeneration of birch was abundant in our study and relatively unaffected by fencing and MSP treatments. With time, pre-commercial thinning of the naturally regenerated birch will be needed to maintain a diverse mixture of tree species.

Effects of best land management practices on the structure, composition and diversity of woody vegetation in agroforestry parklands: case of Dan Saga and Tabofatt villages in Niger republic

The large-scale use of best land management practices has been instrumental in the accession of recent regreening in certain Sahelian areas. This study therefore aimed at highlighting the effect of the wide use of these practices on the structural and ecological parameters of the woody flora in agroforestry parklands. To this end, an inventory of ligneous vegetation was carried out on radial transects in an East–West and North–South direction in the villages clusters of Dan Saga and Tabofatt in Niger Republic. A variance comparison test was applied on the values from plots with practice compare to those from plots without practice (controls). In Dan Saga site, the results obtained show the significant effect of the practice of assisted natural tree regeneration on the density of trees (97 against 58 plants/ha for the control plots), on the basal area (3.04 against 1.98 m2/ha for the control plots), on regeneration (61.96% against 40.91% for the controls) and on floristic diversity (2.93 against 2.41 bits for the control plots) with a clear dominance of Combretaceae. On the other hand, this effect is relatively less significant in the case of Tabofatt site’s where the practice of planting trees coupled with water and runoff collection structures induced positive effect particularly on the basal area (2.29 against 1.90 m2/ha for plots controls), on the structure of the vegetation stood by the abundance of plants with average diameter (class from 5 to 10 cm) as well as the species diversity (2.54 against 2.18 bits for the controls) with a dominance of species of the Mimosaceae family. These results can be used as decision support tools to guide actions to scale up regreening in the Sahelian context.

Establishment and Natural Regeneration of Native Trees in Agroforestry Systems in the Paraguayan Atlantic Forest

The establishment of planted trees and the natural regeneration of trees in agroecosystems is challenging. This study evaluated the establishment and natural regeneration of the following six native tree species in two agricultural systems in the Atlantic Forest in Paraguay: Cedrela fissilis Vell., Cordia trichotoma (Vell) Arráb. ex Steud., Handroanthus albus (Cham.) Mattos, Handroanthus impetiginosus (Mart. ex DC.) Mattos, Peltophorum dubium (Sprengel) Taubert, and Cordia americana (L.) Gottschling and J.S.Mill. At the study site in Caaguazú, 18 plots of 100 m2 each were established in 2 agronomic systems (conventional or agroecological) featuring 3 plantation types (pathsides, agricultural field edges, and islets). Trees were planted at this site in spring 2010 at a density of 1800 individuals ha−1, and the site was monitored for six years. At the study site in Itapúa, 30 plots of 50 m2 each were established in three agronomic systems (conventional, traditional, or agroecological). Trees were planted at this site in spring 2012 at a density of 1600 individuals ha−1, and the site was monitored for four years. Survival and relative growth rates of the planted species and natural regeneration were analyzed using generalized linear mixed models that considered species, agronomic system, and plantation type as fixed factors, and time and plot as random factors. At both sites, survival varied among species. Here, C. fissilis showed lower survival and C. trichotoma higher growth than the other species. Naturally regenerated species were C. trichotoma, H. albus, and P. dubium. The agronomic system and species affected growth and natural regeneration at both locations. Plantation type affected survival and growth in Caaguazú only. We conclude that species contributes more than agronomic system or plantation type to determining the survival, relative growth rate, and natural regeneration in agroforestry systems in the Paraguayan Atlantic Forest.