Special Issue "Role of Gap Factors in Forest Tree Regeneration and Plant Communities"

A special issue of Forests (ISSN 1999-4907). This special issue belongs to the section "Forest Ecology and Management".

Deadline for manuscript submissions: closed (15 March 2020).

Special Issue Editors

Dr. Christel Kern
Website
Guest Editor
USDA Forest Service, 5985 Highway K, Rhinelander Wisconsin, 54501-9128, USA
Interests: silviculture; forest structure and composition; ground-layer plant diversity
Dr. Jurij Diaci
Website
Guest Editor
Department of Forestry and Renewable Forest Resources, University of Ljubljana, Večna pot 83, 1000 Ljubljana, Slovenia
Interests: silviculture; forest ecology; restoration post disturbance
Dr. Jiaojun Zhu
Website
Guest Editor
Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China
Interests: forest ecology and silviculture

Special Issue Information

Dear Collegaues,

Gap-based silvicultural systems are posed as highly versatile and adaptive compared to other silvicultural systems. These systems prescribe harvest-created gaps to mimic small and partial canopy disturbances and to regenerate shade intolerant species in closed canopy forests. However, many factors complicate the outcomes of harvest gaps and their implementation to managing mixed species and multi-aged stands.
Past research has focused on gap-size relationships to tree regeneration, plant architecture, and plant community diversity. The results are varied and highlight the influence of gap characteristics, plant traits, microclimate, soil moisture, and biotic influences within gaps. More studies are needed to further refine these interactions by ecosystem and region to advance gap-based management.
Further, new studies are needed on functional relationships and belowground processes within gaps. Novel studies are needed on gaps as small-scale plantings for new ecotypes/species for anticipated climate change. Applied studies are needed to translate existing knowledge into applications, such as forest-canopy composition and heterogeneity to stand-scale prescriptions (e.g., using LiDAR). Implementation studies are needed to execute research results into operations.
Overall, with this Special Issue, the new knowledge on the context of gaps and their application will advance the knowledge and the practice of sustainable forest management.

Dr. Christel C. Kern
Dr. Jurij Diaci
Dr. Jiaojun Zhu
Guest Editors

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Keywords

  • group selection
  • openings
  • canopy structure
  • mode of regeneration
  • functional diversity
  • trophic interactions
  • competitive relationships
  • microenvironments
  • belowground processes
  • stand development

Published Papers (10 papers)

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Research

Open AccessArticle
Regeneration Dynamics Following the Formation of Understory Gaps in a Slovakian Beech Virgin Forest
Forests 2020, 11(5), 585; https://doi.org/10.3390/f11050585 (registering DOI) - 23 May 2020
Abstract
The frequency and size of canopy gaps largely determine light transmission to lower canopy strata, controlling structuring processes in the understory. However, quantitative data from temperate virgin forests on the structure of regeneration in gaps and its dynamics over time are scarce. We [...] Read more.
The frequency and size of canopy gaps largely determine light transmission to lower canopy strata, controlling structuring processes in the understory. However, quantitative data from temperate virgin forests on the structure of regeneration in gaps and its dynamics over time are scarce. We studied the structure and height growth of tree regeneration by means of sapling density, shoot length growth and cumulative biomass in 17 understory gaps (29 to 931 m2 in size) in a Slovakian beech (Fagus sylvatica L.) virgin forest, and compared the gaps with the regeneration under closed-canopy conditions. Spatial differences in regeneration structure and growth rate within a gap and in the gap periphery were analyzed for their dependence on the relative intensities of direct and diffuse radiation (high vs. low). We tested the hypotheses that (i) the density and cumulative biomass of saplings are higher in gaps than in closed-canopy patches, (ii) the position in a gap influences the density and height growth of saplings, and (iii) height growth of saplings increases with gap size. Sapling density and biomass were significantly higher in understory gaps than under closed canopy. Density of saplings was positively affected by comparatively high direct, but low diffuse radiation, resulting in pronounced spatial differences. In contrast, sapling shoot length growth was positively affected by higher levels of diffuse radiation and also depended on sapling size, while direct radiation intensity was not influential. Conclusively, in this forest, regeneration likely becomes suppressed after a short period by lateral canopy expansion in small gaps (<100 m2), resulting in a heterogeneous understory structure. In larger gaps (≥100 m2) saplings may be capable even at low plant densities to fill the gap, often forming a cohort-like regeneration layer. Thus, gaps of different sizes imprint on the resulting canopy structure in different ways, enhancing spatial heterogeneity. Full article
(This article belongs to the Special Issue Role of Gap Factors in Forest Tree Regeneration and Plant Communities)
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Open AccessArticle
Forest Landscape Heterogeneity Increases Shrub Diversity at the Expense of Tree Seedling Diversity in Temperate Mixedwood Forests
Forests 2020, 11(2), 160; https://doi.org/10.3390/f11020160 - 31 Jan 2020
Abstract
Partial disturbances enhance spatial heterogeneity through the diversification of forest structure, which contributes to niche partitioning and consequently to species diversity. However, this heterogeneity–diversity relationship may differ between groups of species, and is potentially modified by biotic interactions at the community level. We [...] Read more.
Partial disturbances enhance spatial heterogeneity through the diversification of forest structure, which contributes to niche partitioning and consequently to species diversity. However, this heterogeneity–diversity relationship may differ between groups of species, and is potentially modified by biotic interactions at the community level. We propose that shrub diversity will be greater in heterogeneous landscapes, while tree diversity will be lower in those same landscapes, due to the biotic interactions of shrub competition. We conducted field sampling in the balsam fir/yellow birch bioclimatic domain in western Québec, a forested ecosystem disturbed by natural and anthropogenic partial disturbances. We selected 12 forested landscapes (1 km2), four in each of three classes of landscape heterogeneity (heterogeneous, moderately heterogeneous, homogenous). Shrub and tree species regeneration abundance was measured in three different size classes of canopy gaps and the forest understory. Gap proportions were assessed in each landscape using aerial LiDAR data. Tree and shrub alpha-diversity significantly responded to landscape heterogeneity, shrubs being more diverse while tree seedlings were less diverse in heterogeneous landscapes. Heterogeneous landscapes showed highest species accumulation rates for shrubs in medium-sized gaps. For tree seedlings, species accumulation rates were highest in heterogeneous landscapes in the forest understory. Our study thus supports the heterogeneity–diversity relationship with shrubs having higher alpha and beta diversity in heterogeneous landscapes whereas local-scale tree diversity was higher in homogenous landscapes. Full article
(This article belongs to the Special Issue Role of Gap Factors in Forest Tree Regeneration and Plant Communities)
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Open AccessArticle
Gap Structure and Regeneration in the Mixed Old-Growth Forests of National Nature Reserve Sitno, Slovakia
Forests 2020, 11(1), 81; https://doi.org/10.3390/f11010081 - 09 Jan 2020
Abstract
Forest management mimicking natural processes represents an approach to maintain mixed, uneven-aged stands at small spatial scales. The reliance on natural processes, especially on natural regeneration leads to the use of gap-based regeneration as a fundamental silvicultural technique. As a baseline for such [...] Read more.
Forest management mimicking natural processes represents an approach to maintain mixed, uneven-aged stands at small spatial scales. The reliance on natural processes, especially on natural regeneration leads to the use of gap-based regeneration as a fundamental silvicultural technique. As a baseline for such management, we investigated mixed forest in unmanaged National Nature Reserve Sitno in the Western Carpathians, which harbours extraordinary diversity on a rather small scale. To quantify the impact of gaps on gap-filling processes and to assess the role they play in recently observed changes in tree species composition we established a large (2.5 ha) permanent research plot and surveyed the status of natural regeneration, forest structure, tree species composition, and disturbance regime. Our research highlights the long-term and contemporary difficulties in the establishment of Quercus petraea (Matt.) Liebl and Fagus sylvatica (L.). Based on the provided evidence, the native tree species diversity in one of the few preserved old-growth multi-species beech-oak forest remnants is not likely to persist, what could have many implications for future ecosystem functioning. Our results suggest that variation in gap size is an important factor contributing to composition of tree species composition of natural regeneration. The recent intermediate-scale disturbance pattern dominating the old-growth beech-oak forest is beneficial to canopy recruitment of species less shade-tolerant than Fagus sylvatica, as Acer pseudoplatanus (L.), Acer platanoides (L.), and Fraxinus excelsior (L.). We discuss possible factors behind observed shifts in tree species composition and limitations for application of gap dynamics to forest practice in managed beech-oak forest systems. Overall, results of this study may help to design silvicultural measures promoting mixed-species forests to deliver a range of desired ecosystem services. Full article
(This article belongs to the Special Issue Role of Gap Factors in Forest Tree Regeneration and Plant Communities)
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Open AccessArticle
Conversion of Pinus nigra Plantations with Natural Regeneration in the Slovenian Karst: The Importance of Intermediate, Gradually Formed Canopy Gaps
Forests 2019, 10(12), 1136; https://doi.org/10.3390/f10121136 - 12 Dec 2019
Abstract
Since the mid-19th century, Pinus nigra plantations have played a key role in the restoration of degraded European landscapes. Nowadays, these plantations are aging and prone to natural disturbances, insect infestations, and diseases. For their successful gradual conversion, knowledge of optimal gap spatiotemporal [...] Read more.
Since the mid-19th century, Pinus nigra plantations have played a key role in the restoration of degraded European landscapes. Nowadays, these plantations are aging and prone to natural disturbances, insect infestations, and diseases. For their successful gradual conversion, knowledge of optimal gap spatiotemporal dynamics is crucial. We studied herb and natural regeneration patterns along with site factors on 477 subplots within 44 plots distributed over four stand types: closed stand (14% diffuse light), open stand (21%), gap edge (23%), and gap (57%). Despite the abundant Quercus petraea, Q. cerris, and Q. pubescens mast year, no one-year seedlings were recorded, which is likely due to the summer drought. Short seedlings (h < 20 cm) of Quercus sp., Fraxinus ornus and Ostrya carpinifolia were more successful within closed stands. Short Quercus seedlings were positively associated with soil depth and negatively associated with soil nutrients, distance to seed trees, and Sesleria autumnalis coverage. Taller Quercus seedlings required more light than both of its strongest competitors and were positively related to humid soils and less rocky sites. Ungulate overbrowsing significantly impeded natural regeneration. The results indicate a satisfactory Quercus density for conversion and the importance of advanced regeneration, which should be gradually, but persistently, released by progressively widening gaps. Full article
(This article belongs to the Special Issue Role of Gap Factors in Forest Tree Regeneration and Plant Communities)
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Open AccessArticle
Do Coarser Gap Mosaics in Conifer Plantations Induce More Seed Dispersal by Birds? Temporal Changes during 12 Years after Gap Creation
Forests 2019, 10(10), 918; https://doi.org/10.3390/f10100918 - 18 Oct 2019
Abstract
The creation of canopy gaps is thought to be an efficient silvicultural operation to diversify species composition of monoculture conifer plantations; however, the shortage of regeneration materials in overclosed plantations is one of the concerns related to this operation. Seed dispersal by frugivorous [...] Read more.
The creation of canopy gaps is thought to be an efficient silvicultural operation to diversify species composition of monoculture conifer plantations; however, the shortage of regeneration materials in overclosed plantations is one of the concerns related to this operation. Seed dispersal by frugivorous birds may play an important role in inducing the spread of native broad-leaved trees in canopy gaps in plantations in the warm temperate zone of central Japan because bird-dispersed woody species are abundant in this area. We monitored the dynamics of the abundance and species composition of bird-dispersed seeds over 12 years after gap creation in the canopy of a Japanese cypress (Chamaecyparis obtusa (Siebold et Zucc.) Endl.) plantation. We also studied the effects of gap-mosaic patterns (from many small gaps to fewer large gaps) on dispersal. We used a hierarchical Bayesian zero-inflated Poisson model to analyze the factors affecting seed dispersal by frugivorous birds. Seed dispersal by birds increased with gap age except for just after gap creation. Dispersal in coarser gap mosaics was more abundant than that in finer gap mosaics. The species diversity of dispersed seeds in each seed trap (α-diversity) and plot (γ-diversity) showed similar trends in terms of temporal changes and differences between plots related to seed dispersal abundance; β-diversity did not. These trends might have been caused by shrub-vegetation development after gap creation. The effects of shrub vegetation were classified into the attraction by fruits borne within the vegetation, as well as other effects related to vegetation, such as functions of perch availability and insect presence as a food source. The presence of bird-dispersed seeds was strongly promoted by vegetation in all seasons, but only marginally by the presence of fruit-bearing vegetation. However, fruits attracted seed dispersal by frugivorous birds in the winter season. Our results suggest that both vegetation development and fruiting are important for promoting seed dispersal by frugivorous birds, and those effects are different in different seasons according to vegetation conditions and shifting food resources. Full article
(This article belongs to the Special Issue Role of Gap Factors in Forest Tree Regeneration and Plant Communities)
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Open AccessArticle
Evaluating Short-Term Impacts of Forest Management and Microsite Conditions on Understory Vegetation in Temperate Fir-Beech Forests: Floristic, Ecological, and Trait-Based Perspective
Forests 2019, 10(10), 909; https://doi.org/10.3390/f10100909 - 16 Oct 2019
Abstract
Forest understory vegetation is largely influenced by disturbances and given local abiotic conditions. Our research focuses on the early response of understory vegetation to various forest management intensities in Dinaric fir-beech forests in Slovenia: (i) control, (ii) 50% cut of stand growing stock, [...] Read more.
Forest understory vegetation is largely influenced by disturbances and given local abiotic conditions. Our research focuses on the early response of understory vegetation to various forest management intensities in Dinaric fir-beech forests in Slovenia: (i) control, (ii) 50% cut of stand growing stock, and (iii) 100% cut of stand growing stock. Apart from identifying overstory removal effects, we were interested in fine-scale variation of understory vegetation and environmental determinants of its species composition. Vegetation was sampled within 27 karst sinkholes, which represent a dominant landform in studied forests. Within each sinkhole, five sampling plots, varying in slope aspect (centre, north, east, south, west), were established (135 in total), where pre-treatment (in 2012) and post-treatment (in 2014) floristic surveys were conducted. The sampled understory species were characterized in terms of Ellenberg’s indicator values (EIVs) and plant functional traits (plant height, seed mass, specific leaf area, leaf dry matter content). Diversity metrics (species richness, total cover, Shannon index) increased in plots where the silvicultural measures were applied. Tree species richness also increased in 100% cutting. A redundancy analysis revealed that species composition was related to environmental variables, which are directly influenced by management interventions (overstory canopy cover, microclimate—maximum daily temperature, soil properties—thickness of organic soil layer) as well as by topographic factors (slope inclination and surface rockiness). EIVs for light were significantly affected by treatment intensity, whereas soil-related EIVs (moisture, reaction, nutrients) depended more on the within-sinkhole position. Canopy gaps, compared with uncut control plots, hosted a higher number of colonizing species with a higher plant height and smaller seeds, while leaf traits did not show a clear response. We found a negative correlation between pre-treatment species (functional) richness and post-treatment shifts in floristic (functional) composition. Plots with higher richness exhibited smaller changes compared with species-poor communities. Incorporating different perspectives, the results of this study offer valuable insights into patterns of understory vegetation response to forest management in fir-beech forests. Full article
(This article belongs to the Special Issue Role of Gap Factors in Forest Tree Regeneration and Plant Communities)
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Open AccessArticle
The Composition and Height of Saplings Capturing Silvicultural Gaps at Two Long-Term Experiments in Managed Northern Hardwood Forests
Forests 2019, 10(10), 855; https://doi.org/10.3390/f10100855 - 01 Oct 2019
Cited by 1
Abstract
Managing forests for mixtures of canopy species promotes future resilience and mitigates risks of catastrophic resource loss. This study describes the compositions, heights, and locations within openings of gap-capturing saplings in two long-term group-selection experiments in managed northern hardwoods. We expected opening size [...] Read more.
Managing forests for mixtures of canopy species promotes future resilience and mitigates risks of catastrophic resource loss. This study describes the compositions, heights, and locations within openings of gap-capturing saplings in two long-term group-selection experiments in managed northern hardwoods. We expected opening size to affect the composition of gap-capturing saplings and that composition would match advance regeneration where relatively large stems remained following harvest. We also expected sapling height to respond positively to opening size, but plateau in gap areas above 200 m2, and legacy-tree retention to negatively affect sapling height. In two group-selection experiments, we found that the composition of gap-capturing saplings was not affected by opening size at 15 and 23 years post-harvest, respectively, and that composition matched advance regeneration only when larger stems (>2.5 cm breast height, dbh) were removed during harvest. Gap-capturing sapling composition did not match the surrounding canopy in either study site. Sapling height was positively correlated with gap area, but, as we expected, plateaued in larger openings. In openings without legacy-retention, gap area did not significantly predict sapling height in openings larger than 100–200 m2, whereas this threshold was between 300–400 m2 in openings with single legacy-tree retention. Sapling height was negatively associated with distance into openings when legacy-trees were present. Group selection appears to recruit modestly higher proportions of shade-midtolerant and intolerant species to the canopy compared to adjacent unmanaged second-growth or managed, uneven-aged northern hardwoods. Full article
(This article belongs to the Special Issue Role of Gap Factors in Forest Tree Regeneration and Plant Communities)
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Open AccessArticle
Forest Gap Size Alters the Functional Diversity of Soil Nematode Communities in Alpine Forest Ecosystems
Forests 2019, 10(9), 806; https://doi.org/10.3390/f10090806 - 16 Sep 2019
Abstract
Changes in the microenvironment driven by forest gaps have profound effects on soil nutrient cycling and litter decomposition processes in alpine forest ecosystems. However, it is unclear whether a similar forest gap effect occurs in the soil decomposer community. A field experiment was [...] Read more.
Changes in the microenvironment driven by forest gaps have profound effects on soil nutrient cycling and litter decomposition processes in alpine forest ecosystems. However, it is unclear whether a similar forest gap effect occurs in the soil decomposer community. A field experiment was conducted in an alpine forest to investigate the composition and structure of the soil nematode community among four treatments, including under a closed canopy and in small (<10 m in diameter), medium (10–15 m in diameter), and large (15–20 m in diameter) gaps. A total of 92,787 individuals and 27 species (genera level) of soil nematode were extracted by elutriation and sugar centrifugation, respectively. Filenchus was the most abundant dominant taxa and represented 24.27–37.51% of the soil nematodes in the four treatments. Compared to the closed canopy, the forest gaps did not affect the composition, abundance, or species diversity of the soil nematode community but significantly affected the functional diversity of the soil nematode community. The maturity indices (MI, ∑MI, and MI2‒5) of the soil nematode community in the closed canopy were significantly lower than those in the forest gaps. Moreover, the proportion of plant parasitic index and maturity index (PPI/MI) values of the closed canopy and small gaps were significantly higher than those of the medium and large gaps. Our results suggest that the forest gap size substantially alters the functional diversity of soil nematodes in the debris food web, and changes in soil nematode community structure due to gap formation may have profound effects on soil biogeochemical processes in alpine forests. Full article
(This article belongs to the Special Issue Role of Gap Factors in Forest Tree Regeneration and Plant Communities)
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Open AccessArticle
Analyzing Spatial Distribution Patterns of European Beech (Fagus sylvatica L.) Regeneration in Dependence of Canopy Openings
Forests 2019, 10(8), 637; https://doi.org/10.3390/f10080637 - 28 Jul 2019
Abstract
The use of natural regeneration techniques is one of the key elements of modern (close-to-nature) forestry. In natural forests, changes in canopy cover, such as the emergence and successive re-closure of canopy gaps are particularly important, as they influence the light availability on [...] Read more.
The use of natural regeneration techniques is one of the key elements of modern (close-to-nature) forestry. In natural forests, changes in canopy cover, such as the emergence and successive re-closure of canopy gaps are particularly important, as they influence the light availability on the forest floor. Creating canopy gaps of different size is a promising silvicultural tool allowing the regulation of the light availability in managed forests in order to control regeneration composition and development. In this study, we used terrestrial laser scanning data to investigate the relationship between canopy-gap dimensions and emerging natural regeneration along a gradient of management in forests dominated by European beech (Fagus sylvatica L.). We analyzed the spatial distribution and height of regeneration patches in dependence of gap characteristics. Mean regeneration height decreases progressively from the gap polygon over a transition zone towards the area under the canopy, while the tallest regeneration plants were placed in positions midway between center and gap edge, and not directly in the gap center as we initially assumed. The centers of regeneration patches were not displaced when compared to the associated canopy gap centers, as has been reported in other studies conducted on the northern hemisphere for various tree species. The observed patterns did not depend on management strategies, indicating that regeneration responded equally to naturally created gaps and gaps that were caused by logging. We conclude that establishment and development of shade-tolerant European beech regeneration in forest stands is driven by gap openings, but not necessarily direct radiation. If at all, pronounced direct radiation mainly occurs at the northern edge of large gaps. Neither regeneration patch center, nor regeneration tree height pointed in that direction. Our study suggests that in the investigated beech-dominated forests the effect of increased light availability at the northern edge of a gap is overruled by other factors increasing towards the gap edge, such as increased belowground competition of the overstory trees. Full article
(This article belongs to the Special Issue Role of Gap Factors in Forest Tree Regeneration and Plant Communities)
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Open AccessArticle
Size-Dependent Patterns of Seed Rain in Gaps in Temperate Secondary Forests, Northeast China
Forests 2019, 10(2), 123; https://doi.org/10.3390/f10020123 - 04 Feb 2019
Cited by 1
Abstract
Secondary forests have become the major forest type worldwide, and are experiencing various disturbances and exhibiting obvious vegetation degradation (e.g., reduced biodiversity and decreased productivity) compared with primary forests. Forest gap is a common small-scale disturbance in secondary forests. Promoting natural regeneration under [...] Read more.
Secondary forests have become the major forest type worldwide, and are experiencing various disturbances and exhibiting obvious vegetation degradation (e.g., reduced biodiversity and decreased productivity) compared with primary forests. Forest gap is a common small-scale disturbance in secondary forests. Promoting natural regeneration under gap disturbance is an important approach to recover biodiversity and ecosystem services for temperate secondary forests. The gap size is the crucial characteristic controlling natural regeneration of many tree species. However, little is known about the spatiotemporal pattern of seed rain for gravity-dispersed and wind-dispersed tree species in gaps of varying sizes. The objectives of this study were to determine how seed rain of dominant tree species depend on gap size, and consequently, to explore some gap-based silviculture solutions for restoring secondary forests from the view of seed dispersal. The spatial distribution of seed rain in gaps with three sizes (large gaps of 250–350 m2, medium gaps of 150–250 m2, and small gaps of <150 m2), the temporal dynamics of seed rain over three years, and the relationship between seed rain and soil seed banks were explored in temperate secondary forests. The results showed that more than 90% of the seeds in seed rain were wind-dispersed, and their seed rain density and the contribution of seed rain to soil seed bank in medium gaps reached the highest (p = 0.03). The results suggest that establishing medium-sized gaps (i.e., gap size with 150–250 m2) in the secondary forests is more favorable for improving the natural regeneration potential (arrival of seeds and forming soil seed bank) of gap-dependent and wind-dispersed species (e.g., Acer mono) in gaps. Full article
(This article belongs to the Special Issue Role of Gap Factors in Forest Tree Regeneration and Plant Communities)
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