Seedling Abundance Research Articles

Complex interactions of deer herbivory, soil chemistry, and competing vegetation explain oak–hickory forest tree regeneration in central Pennsylvania, USA

The root causes of forest tree regeneration failure are difficult to resolve, although numerous studies show ungulate herbivory, soil conditions, and competition from undesirable vegetation as likely contributors. To better understand the relative importance of each issue, we conducted a 7-year manipulative experiment to assess the interactive effects of white-tailed deer ( Odocoileus virginianus) herbivory, soil acidity, and competing vegetation on tree regeneration in oak–hickory forests of central Pennsylvania, USA. Outcomes depended on initial tree seedling abundance, and all three factors had significant interactions. At low initial seedling abundance, fencing resulted in the greatest increase, but all treatments had a positive effect on seedling growth and abundance. At higher initial seedling abundance, abundance failed to recover 7 years after herbicide treatment and soil pH was an important predictor. When soil pH was >4.6 from lime application, seedling growth and abundance in unfenced controls with high initial abundance was comparable to the fenced-only treatment. Competing vegetation, assumed to be a symptom of excessive, long-term deer herbivory, does not seem to be the primary factor limiting tree regeneration in our study area. Ameliorating acid deposition warrants greater consideration as a management action because it could provide long-lasting benefits compared to short-term fence installations.

Impacts of a short-interval severe fire on forest structure and regeneration in a temperate Andean Araucaria-Nothofagus forest

BackgroundWarmer climate conditions are altering fire regimes globally, eroding the capacity of forest ecosystems to resist and recover from natural disturbances like wildfire. Severe and rapidly repeated wildfires are promoting tree regeneration failure of obligate-seeders and/or fire-sensitive species in temperate forests of the Southern Hemisphere. We collected post-fire field data to evaluate whether forest structure and tree regeneration responses varied between two Andean forest study areas dominated by the threatened Gondwanan conifer Araucaria araucana and Nothofagus species (southern beeches) — one area burned once, the other reburned after 13 years.ResultsTree mortality was high across species after a single high severity and/or repeated wildfire, although some A. araucana trees were able to survive both events. Post-fire seedling regeneration of A. araucana and Nothofagus spp. was poor in areas affected by severe wildfires, and the latter was absent from reburned plots. A key driver of this regeneration failure was increasing distance to live seed source trees, which was negatively correlated with these species’ post-fire seedling abundances. In contrast, species with the capacity to regenerate via resprouting (A. araucana, N. alpina, N. obliqua) did so after a single high severity fire; however, only a single Nothofagus species (N. alpina) resprouted abundantly after a reburn.ConclusionsOur findings suggest that high severity and short-interval fires can drastically change the structure of and limit post-fire tree regeneration in Araucaria-Nothofagus forests, promoting alternative post-fire forest ecosystem trajectories. Resprouting species of the Nothofagus genus, especially N. alpina, exhibit the greatest resilience to these emerging fire patterns. These forests are currently facing an unprecedented climatic shift toward greater fire activity, where resprouting is the favored regeneration strategy. If the occurrence of severe and short-interval fires increases in the coming decades, as predicted, we expect Araucaria-Nothofagus forests to shift toward a drier, more flammable shrubland ecosystem state.

Phylogenetic relatedness and habitat affect seedling abundance of a mid-montane humid evergreen broad-leaved forest in the Gaoligong Mountains, Southwestern China

The neighborhood effect has become an important framework with which to study the mechanisms that maintain the coexistence of tree species. Phylogenetic relatedness among neighboring plants directly affects species coexistence and the maintenance of tree diversity. And some studies have reported that seedling performance is negatively correlated with phylogenetic relatedness, which termed phylogenetic negative density dependence. Soil-borne fungal pathogens affected seedling performance of phylogenetically related host species, i.e., phylogenetic Janzen–Connell effect. Seedlings may be particularly vulnerable to habitat and neighbor characteristics. Although previous studies have demonstrated the influence of neighborhood effects, phylogenetic relatedness, and habitat filtering on seedling survival, growth, and mortality, the effect of variation in these factors on seedling abundance remains unclear. To address this question, we used a 4-ha (200 m × 200 m) and monitored four-year (2020–2023) seedling dataset from a mid-montane humid evergreen broad-leaved subtropical forest in the Gaoligong Mountains, Yunnan, Southwestern China, and which consisted of 916 seedlings belonging to 56 species. The results of generalized linear mixed models showed no significant effect of conspecific adult neighbors on seedling abundance at any of the intervals evaluated. In contrast, we found evidence of phylogenetic distance density dependence in the forests of the Gaoligong Mountains. Specifically, there was a significant positive effect of the relative average phylogenetic distance between heterospecific adult neighbors and focal seedlings on focal seedling abundance in 2020; however, the relative average phylogenetic distance between heterospecific seedling neighbors and focal seedlings had a significant negative effect on seedling abundance over the four-year period (2020–2023). Among the habitat factors, only light (canopy opening) had a negative effect on seedling abundance in all four years. Light resources may be a limiting factor for seedlings, and determine seedling dynamics in subtropical forests. Overall, our results demonstrated that phylogenetic density dependence and habitat filtering affected subtropical seedling abundance. Our findings provide new evidence of the impact of phylogenetic density dependence on seedling abundance in a subtropical mid-montane humid evergreen broad-leaved forest and highlight the need to incorporate the neighborhood effect, phylogenetic relatedness, and habitat factors in models assessing seedling abundance.

Light quality and spatial variability influences on seedling regeneration in Hawaiian lowland wet forests

Abstract Tropical forest understories tend to be light‐limited. The red‐to‐far‐red ratio (R:FR) is a useful and reliable index of light quality and its spatial variability can influence competition between native and non‐native seedlings. While per cent light transmittance has been quantified in some Hawaiian lowland wet forests (HLWF), no information exists on how the spatial distribution of understorey light varies in relation to species invasion, or if patterns of seedling regeneration and light are linked. We measured the R:FR of light in the understorey to assess light quality in three HLWF forest types: native‐dominated, partially invaded and Psidium cattleyanum‐ (strawberry guava) dominated to quantify light quality in the understorey (0–50 cm height). We also identified relationships between light quality and native and non‐native seedling presence, diversity and abundance. Together, these data can help to determine the restoration potential of HLWF. Linear mixed‐effect modelling showed that native‐dominated forests had significantly greater R:FR than P. cattleyanum‐dominated forests, demonstrating a transformation in the light environment with increased invasion. Heterogeneity in R:FR varied more across sites than among forest types. In both native‐dominated and partially invaded forests, there were more native seedlings in the low‐quality R:FR (0.0–0.40) category and fewer in the medium‐ (0.41–0.70), and high‐quality (≥0.71) light categories than would be expected by chance, and there were no native seedlings in the P. cattleyanum‐dominated forests. Native‐dominated forests had greater species richness and abundance of native seedlings than the partially invaded forests, likely due to propagule availability. However, the spatial clustering of seedlings, the mismatch of native seedlings in light environments less suitable, and a considerable proportion of open high‐quality microsites, highlights that conditions are not optimal for native species in HLWF in the long term. Synthesis and applications. The native‐dominated and partially invaded forests still hold conservation value, despite variation among sites. Seedling additions could be targeted to different R:FR environments and at different spatial scales, but the lack of a strong relationship between R:FR and seedling number suggests that other factors besides light quality should be considered in seedling enrichment or other management activities.

Exploration of large-scale vegetation transition in wet ecosystems: a comparison of conifer seedling abundance across burned vs. unburned forest-peatland ecotones in Western Patagonia

Altered fire regimes, combined with a warmer and drier climate, have been eroding the resilience of temperate rainforests and peatlands worldwide and leading to alternative post-fire vegetation communities. Chronic anthropogenic burning of temperate rainforests at the forest-peatland ecotone in western Patagonia appears to have shifted vegetation communities in poorly-drained sites from forests dominated by the threatened conifer, Pilgerodendron uviferum, to peat-accumulating wetlands covered by Sphagnum mosses. We collected and modeled post-reburn field data using ordinations and hierarchical Bayesian regressions to examine mechanisms through which P. uviferum forests may recover following fire or become locked into alternative development pathways by comparing biophysical factors of a reburned ecotone to those of an unburned (control) ecotone. We found that, (1) the significantly higher densities of P. uviferum trees and seedlings in the forested patches at both the reburned and control sites were associated with significantly lower seasonal water tables, lower cover of Sphagnum mosses and higher cover of other mosses (i.e., not in the Sphagnum or Dicranaloma genera); (2) despite abrupt boundaries in vegetation at both sites, successive fires homogenized the environment at the reburned site; and (3) the distinct life forms and individual species that characterized the understory plant communities across the ecotones affected seedling abundance by shaping microtopography and the substrates available for establishment. Together, our results suggest that fire can push edaphically wet P. uviferum-dominated sites towards a non-forested state by reducing the diversity of microsite structure and composition, thereby placing P. uviferum seedlings in direct competition with Sphagnum mosses and potentially limiting the availability of microsites that are protected from both seasonal inundation and seasonal drought. If wildfires continue under increasingly warmer and drier conditions, the forest-peatland ecotone of western Patagonia may be susceptible to large-scale transformation towards a non-forested state.

Sapling recruitment as an indicator of carbon resiliency in forests of the northern USA.

Tree regeneration shapes forest carbon dynamics by determining long-term forest composition and structure, which suggests that threats to natural regeneration may diminish the capacity of forests to replace live tree carbon transferred to the atmosphere or other pools through tree mortality. Yet, the potential implications of tree regeneration patterns for future carbon dynamics have been sparsely studied. We used forest inventory plots to investigate whether the composition of existing tree regeneration is consistent with aboveground carbon stock loss, replacement, or gain for forests across the northeastern and midwestern USA, leveraging a recently developed method to predict the likelihood of sapling recruitment from seedling abundance tallied within six seedling height classes. A comparison of carbon stock predictions from tree and seedling composition suggested that 29% of plots were poised to lose carbon based on seedling composition, 55% were poised for replacement of carbon stocks (<5 Mg ha-1 difference) and 16% were poised to gain carbon. Forests predicted to lose carbon tended to be on steeper slopes, at lower latitudes, and in rolling upland environments. Although plots predicted to gain and lose carbon had similar stand ages, carbon loss plots had greater current carbon stocks. Synthesis and applications. Our results demonstrate the utility of considering tree regeneration through the lens of carbon replacement to develop effective management strategies to secure long-term carbon storage and resilience in the context of global change. Forests poised to lose C due to climate change and other stressors could be prioritized for regeneration strategies that enhance long-term carbon resilience and stewardship.

Effects of Sheep Grazing and Nitrogen Addition on Dicotyledonous Seedling Abundance and Diversity in Alpine Meadows

Seedling is a crucial stage in the growth and development of plants, and the expansion and persistence of plant populations can be achieved through seed regeneration. Sheep grazing, fertilization, light, soil moisture, vegetation diversity and biomass, and litter all have potential impacts on species regeneration. We measured vegetation diversity, annual net primary productivity (ANPP), litter, ground photosynthetically active radiation (PAR), and soil moisture of alpine meadows under sheep grazing and nitrogen addition treatments, and studied their effects on the dicotyledonous seedling abundance and diversity using linear regression models (LMs) and structural equation models (SEMs). We found that sheep grazing reduced ANPP, increased vegetation diversity and PAR, and decreased soil moisture. Fertilization increased ANPP and litter, decreased vegetation diversity and PAR, but had no effect on soil moisture. Sheep grazing and fertilization both reduced the abundance of dicotyledonous seedlings, and simultaneously fertilization can reduce the diversity of dicotyledonous seedlings, while sheep grazing had no effect on the diversity of dicotyledonous seedlings. LMs showed that vegetation diversity, ANPP, and litter, rather than light and soil moisture, affected dicotyledonous seedling abundance and diversity. SEMs revealed that sheep grazing and fertilization indirectly influenced seedling regeneration through vegetation diversity rather than ANPP and litter. Our research will increase our understanding of the dicotyledonous plant regeneration process in alpine grasslands and facilitate the development of strategies for management and protection of alpine grassland.

Spatial distribution of woody plants in relation to mistletoe-infected Vachellia karroo trees in a semi-arid African savanna

By increasing resource heterogeneity, mistletoe-infected trees can restructure plant community processes and distribution patterns. No information is available on how mistletoe-infected Vachellia (Acacia) karroo trees within V. karroo dominated stands are spatially distributed, and on how they influence the spatial patterns of their surrounding conspecifics and heterospecifics. Each woody plant was stem mapped using a cartesian plane (x, y) within three 50×50 m plots located in V. karroo dominated stands in a semi-arid savanna, South West Zimbabwe. Pair correlations g(r) were used for the univariate analysis and Poisson process null models were applied to quantify and detect overall departure from randomness. For the bivariate analysis, pair correlations g12(r) under the null model of independence were used, whilst the mark correlation function (kmm(r)) was used to analyse the correlation of tree canopy area and mistletoe infection intensity. For each plot, size class distributions, based on tree height and basal stem diameter displayed negative J curves, with steep negative regression slopes across the size classes, clearly indicating a strongly recruiting population of V. karroo. The univariate patterns of all trees (infected and non-infected) were consistent with a random pattern, which is attributed to unsystematic mistletoe seed dispersal by birds. The univariate analysis of all woody plants (adults and juveniles) exhibited aggregation at small spatial scales due to the high abundance of clustered seedlings and saplings. At small spatial scales, understory woody plants (both conspecifics and non-conspecifics) were positively associated with mistletoe-infected trees due to mistletoephily which is the facilitation (or nurse protégé interactions) within the more resource-rich mistletoe-infected tree subcanopies. These results provide strong evidence suggesting that the variations in spatial pattern modification by mistletoe-infected trees could further increase spatial heterogeneity in this semi-arid savanna. As such, by increasing heterogeneity, mistletoe-infected trees can increase the resilience of semi-arid savannas in the face of perturbations and stochastic events.

Verified hypotheses on the "nurse" and "burial" effects on introduced Quercus rubra regeneration in a mesic Scots pine forest.

A previous study on the encroachment of North American northern red oak Quercus rubra L. into the mesic Scots pine forest (in central Poland) revealed high abundances of seedlings and saplings under shrubs, with lower abundances in open areas or clumps of bilberry Vaccinium myrtillus L. It was unclear whether the regeneration success of Q. rubra is enhanced by the presence of shrubs due to their "nurse effect", and how burying acorns of different sizes in soil or moss affects the survival of oak seeds and seedlings (a "burial effect"). Results of a previous observational study were verified in an experimental study: a pool of 900 large-, medium-, and small-sized acorns was sown under moss cover in open areas and within bilberry clumps and in soil under shrubs in 2018 and monitored for 3 years in natural conditions. The majority of sown acorns were lost, mainly due to acorn pilferage, lack of germination and the death of sprouting acorns. However, acorn and seedling survival depended significantly on acorn size and differed among the microsites studied. Viable seedlings were twice as likely to develop from large- and medium-sized as from small-sized acorns, and they grew mainly from acorns sown under moss cover, confirming a positive "burial effect." Seedling survival was three times higher in bilberry and open areas, than under shrubs; however, seedlings "nursed" by shrubs were less threatened by large ungulates. Only a small part of the pool of sown acorns contributes to the reproductive success of Q. rubra in the mesic Scots pine forest. Microsites characteristic to this type of forest are suitable for northern red oak regeneration; however, bilberry favors acorn survival and germination and early seedling growth, moss cover favors acorn survival and germination, while shrubs protect surviving seedlings from herbivory.

Seedling recruitment in response to stand composition, interannual climate variability, and soil disturbance in the boreal mixed woods of Canada

AbstractAimSeedling recruitment is a vital process for forest regeneration and is influenced by various factors such as stand composition, climate, and soil disturbance. We conducted a long‐term field experiment (18 years) to study the effects of these factors and their interactions on seedling recruitment.LocationOur study focused on five main species in boreal mixed woods of eastern Canada: trembling aspen (Populus tremuloides), paper birch (Betula papyrifera), white spruce (Picea glauca), balsam fir (Abies balsamea), and white cedar (Thuja occidentalis).MethodsSixteen 1‐m2 seedling monitoring subplots were set up in each of seven stands originating from different wildfires (fire years ranging from 1760 to 1944), with a soil scarification treatment applied to every other subplot. Annual new seedling counts were related to growing‐season climate (mean temperature, growing degree days and drought code), scarification, and stand effects via a Bayesian generalized linear mixed model.ResultsSoil scarification had a large positive effect on seedling recruitment for three species (aspen, birch and spruce). As expected, high mean temperatures during the seed production period (two years prior to seedling emergence) increased seedling recruitment for all species but aspen. Contrary to other studies, we did not find a positive effect of dry conditions during the seed production period. Furthermore, high values of growing degree days suppressed conifer seedling recruitment. Except for white cedar, basal area was weakly correlated with seedling abundance, suggesting a small number of reproductive individuals is sufficient to saturate seedling recruitment.ConclusionOur findings underscore the importance of considering multiple factors, such as soil disturbance, climate, and stand composition, as well as their effects on different life stages when developing effective forest management strategies to promote regeneration in boreal mixed‐wood ecosystems.

More water, less light: how to improve silver fir seeding to convert Norway spruce monocultures into mixed stands in a drier region of Germany

Abstract Adaptive forest management gains importance as climate and disturbance regimes continue to change. Norway spruce monocultures are particularly vulnerable to those changes. Thus, there is a strong demand to convert pure spruce stands toward better adapted forest ecosystems. Silver fir has similar wood properties as Norway spruce, but is less vulnerable to droughts. Yet, little is known how to efficiently admix silver fir into Norway spruce monocultures. We analyzed seedling abundance in mature Norway spruce monocultures 1 year after soil scarification and silver fir seeding in a relatively dry region of southern Germany. Our objectives were to study the effect of soil scarification and seeding on regeneration density and to identify drivers of seedling abundance. We collected data on regeneration, forest structure, as well as soil and light conditions at 103 scarified and 25 untreated control plots. We used non-parametric independence tests to compare scarified and untreated plots. Subsequently, we used boosted regression trees to investigate the drivers of seedling abundance. Norway spruce strongly benefited from soil scarification (P &amp;lt; .001), with seedling numbers even exceeding those of silver fir. Both species thrived in soils with high plant available water capacity. In contrast, seedling numbers were overall negatively affected by light. Moreover, we found a higher density of silver fir regeneration at greater distance from neighboring trees and in soils devoid of carbonate. Our study indicates that water, not light, is the limiting factor for both Norway spruce and silver fir seedlings in the study region. Seeding silver fir will likely be most effective underneath an intact canopy on deep, fine-textured soils without carbonate, while maximizing the distance to Norway spruce trees. In conclusion, silver fir seeding can be optimized to become an effective adaptive measure to diversify Norway spruce monocultures, and thus to create more resistant and resilient forest ecosystems.

Arbuscular mycorrhizal and ectomycorrhizal plants together shape seedling diversity in a subtropical forest

IntroductionBurgeoning mycorrhizal research has focused on identifying the various diverse mycorrhizal strategies of forest communities. Mounting evidence suggests that mycorrhizae play important roles in regulating forest community structure and composition. However, research into the manifestation of this influence in the seedling stage is lacking, especially in small-scale plots.MethodsOur research utilized structural equation models parameterized using data from a subtropical monsoon broad-leaved evergreen forest situated in Yunnan Province, China.ResultsWe noted that seedlings included plants that utilized both arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi. More seedling plots with the relatively higher species diversity were the product of the mixed mycorrhizal strategy, meaning the coexistence of AM and EM seedlings in a small-scale plot rather than the dominance of one type of strategies. These mixed communities were primarily found on slopes and mountain ridges. The abundance of AM or EM trees indirectly affected seedling diversity by influencing the abundance of different mycorrhizal seedlings. In this case, the diversity of the mixed mycorrhizal community was also restricted by the level of leaf thickness in the community, followed by abiotic factors such as elevation, convexity, soil pH and soil available phosphorus.DiscussionThe effect of leaf thickness on mycorrhizal seedling abundance reflected the importance of water conditions in shaping seedling communities. The effect of convexity on seedling diversity also reflected the limitation of seedling communities by the distribution of humidity and heat conditions during topographic change. The results suggested that it is crucial to preserve seedling diversity via the mixed mycorrhizal strategy of communities in the subtropical forest.

Elevation-Dependent Natural Regeneration of Abies georgei var. smithii Forest in Southeastern Tibet

The comprehensive impacts of biotic and abiotic factors on the natural regeneration of Abies georgei var. smithii (Abies) forests in Tibet are not thoroughly understood. To address this gap, our study focused on the regeneration densities of Abies seedlings, saplings, and small trees across 21 plots (each 20 m × 20 m) along an elevation gradient from 3730 m to 4330 m in the Sygera Mountains of Southeastern Tibet. We meticulously measured a suite of 11 variables that describe stand structures and ecological conditions. Through analyses using Spearman’s correlation analysis, hierarchical partitioning, and multiple linear regression, we identified key ecological drivers for successful Abies regeneration. Our results highlighted a peak in the abundance of seedlings, saplings, and small trees at an elevation of 3930 m. As the elevation rose from 3730 m to 4330 m, we observed an initial increase followed by a decrease in canopy cover (canopy), mother tree density (MotherT), 1000-seed weight (SeedW), litter thickness (LitterT), moss cover (MossC), moss thickness (MossT), soil moisture (SM), and soil bulk density, while mean annual temperature and soil depth to permafrost consistently decreased. The critical ecological drivers for Abies natural regeneration were identified as follows: MossT was pivotal for seedling density; canopy and MossC were influential for sapling density, and MotherT was the main factor affecting the density of small trees. This study suggests that a high density of mother trees and a thick and highly covered layer of moss are conducive to the natural regeneration of Abies in the Sygera Mountains. Understanding the current status of regeneration is vital for informing conservation and management strategies for Abies forests in Tibet.

Facilitation in Brazilian semiarid zone: remnant trees show a positive effect on caatinga regeneration

Arid and semiarid ecosystems display several environmental filters naturally restricting plant community composition. Such filters become more severe after some disturbance and may thus hamper the survival of young plants. The role of remnant trees in succession needs to be better understood to identify patterns and functional traits that might facilitate natural regeneration in drylands. This study evaluated the role of remnant trees in the succession process in the caatinga vegetation (Brazilian seasonally dry tropical forest), testing the effect of a typical tree, the juazeiro (Ziziphus joazeiro Mart.) in richness and abundance of seedlings in areas of abandoned pasture, in Northeastern Brazil. A perimeter was outlined around each plant (n = 20) with a diameter equivalent to each tree crown; all seedlings of woody species up to 0.5 m in height, within that perimeter, were collected and identified. Control areas with the same dimensions were delimited in adjacent locations (n = 20) without the influence of remnant trees, followed by the same data surveys. Mean species richness was of 7.8 ± 4.8 under the juazeiro canopies, compared to 2.3 ± 1.9 in the control areas. Species abundance was also greater under the presence of Z. joazeiro, with an average of 16.9 ± 4.8, against 4.1 ± 4.2 individuals in the controls. Among the abiotic factors evaluated, it is suggested that soil and air temperatures may show a greater influence on the recruitment of seedlings, benefiting natural regeneration under Z. joazeiro. Z. joazeiro ramnant trees appear to facilitate the natural regeneration of tropical drylands. We suggest considering the use of these plants as catalysts for the nucleation process in the restoration of the caatinga.

Impacts of bamboo dominance and die‐off on seedling dynamics in a tropical secondary forest (Brazil)

AbstractAulonemia aristulata is a tropical bamboo species of mixed rhizome type and monocarpic flowering that can become super‐dominant after anthropogenic disturbances in tropical forests. The synchronized reproductive events of flowering and die‐off of monocarpic bamboo systems provide a rare opportunity to evaluate the temporal effects of bamboo dominance on forest regeneration. To evaluate the effects of bamboo dominance on forest regeneration, we compared the structure (abundance, richness, composition) and dynamics (mortality, recruitment, survival and growth) of tree and shrub seedling communities from two non‐contiguous forests stands (bamboo‐dominated vs. non‐dominated sites) for 2 years, before and after a synchronized reproductive event. Bamboo dominated plots had higher abundance, floristic richness and recruitment of tree and shrub seedlings when compared with bamboo non‐dominated plots. Bamboo die‐off did not represent an opportunity to improve establishment and investment in the vertical growth (height) of seedlings in bamboo‐dominated plots. We postulate that the mode of rhizome extension seen in bamboos might be a consistent trait determining the spatial pattern of occupation and population structure and thereby playing a fundamental role in the pattern of native tree community establishment after bamboo die‐off. The formulation of a management approach is necessary in order to better understand the biological traits of bamboo species and their influence on the spatial pattern of occupation and population structure. Additionally, this influence may differently impact restoration and definition of management practices, including the need for direct intervention by manually controlling bamboo cover following die‐off to promote and maintain seedling establishment and diversity.

Understory seedlings of Quercus mongolica survive by phenological escape

Understanding understory seedling regeneration mechanisms is important for the sustainable development of temperate primary forests in the context of increasingly intense climate warming events. The poor regeneration of dominant tree species, however, is one of the biggest challenges it faces at the moment. Especially, the regeneration of the shade-intolerant Quercus mongolica seedling is difficult in primary forests, which contrasts with the extreme abundance of understory seedlings in secondary forests. The mechanism behind the interesting phenomenon is still unknown. This study used in-situ monitoring and nursery-controlled experiment to investigate the survival rate, growth performance, as well as nonstructural carbohydrate (NSC) concentrations and pools of various organ tissues of seedlings for two consecutive years, further analyze the understory light availability and simulate the foliage carbon (C) gain in the secondary and primary forest. Results suggested that seedlings in the secondary forest had greater biomass allocation aboveground, height and specific leaf area (SLA) in summer, which allowed the seedling to survive longer in the canopy closure period. High light availability and positive C gain in early spring and late autumn are key factors affecting the growth and survival of understory seedlings in the secondary forest, whereas seedlings in the primary forest had annual negative carbon gain. Through the growing season, the total NSC concentrations of seedlings gradually decreased, whereas those of seedlings in the secondary forest increased significantly in autumn, and were mainly stored in roots for winter consumption and the following year's summer shade period, which was verified by the nursery-controlled experiment that simulated autumn enhanced light availability improved seedling survival rate and NSC pools. In conclusion, our results revealed the survival trade-off strategies of Quercus mongolica seedlings and highlighted the necessity of high light availability during the spring and autumn phenological periods for shade-intolerant tree seedling recruitment.

Syagrus flexuosa (Mart.) Becc. (Arecaceae) seedling recruitment at the edge and interior of Cerrado remnants.

The edge effect has impacts on seed and seedling survival due to modifications in biotic and abiotic factors. Often, large-seeded tree species lost seed vectors in the forest edge due to the rarity or absence of large frugivores at this habitat type. In this study, I compared the seedling abundance and distribution of the palm Syagrus flexuosa between edges and interiors of three large Cerrado remnants. In every remnant, the number of seedlings around parent palms in the edge was smaller than around palm individuals located in the Cerrado interior. Moreover, the distribution of seedlings around parent palms differed between edges and interiors. In the edges, most seedlings were found under parent crowns, while in the interiors, the contrary occurred. The high concentration of seedlings under parent palms suggests a decrease of seed dispersal at the edges. Because S. flexuosa is a widely distributed palm that serves as an important resource for several animals along Cerrado habitats, changes on the regeneration process of this palm due to edge effects can further impact frugivore populations. Therefore, the decline of seedling establishment along forest edges implies changes in the Cerrado regeneration dynamics, which may compromise the persistence of ecological processes and animal communities.

Географические особенности возобновления Pinus sibirica Du Tour

One of the main problems of forest ecology is to identify the patterns of the dynamics of natural populations of woody plants at the stage of their renewal, which programs the entire subsequent structure and development of plant ecosystems. The process of reforestation is determined by both the dynamics of seed production and the peculiarities of the seed distribution of forest-forming tree species. The renewal of five-needled pines of the Cembrae subsection with wingless seeds is due to their close trophic relationships with birds of the genus Nucifraga sp., which spread seeds, creating soil forage stocks. The purpose of this study is to reveal geographical features of the relationship between seed production and renewal of Siberian stone pine (Pinus sibirica Du Tour) with the intermediary participation of the thin-billed nutcracker (Nucifraga caryocatactes macrorhynchos Brehm C.L.). The research was carried out in 3 geographical regions of Pinus sibirica forests: in the forests of the Aldan Highlands in Southern Yakutia (59º40´ N., 125º24´ E.), the Northern Urals in the area of the Denezhkin Kamen mountain (60º25´ N., 59º32´ E.), and the Khamar-Daban Mountain range in the South-Eastern Baikal region (51º32´ N., 103º32´ E.). It is shown that each region of the Pinus sibirica growth differs in the dynamics of both seed production and renewal. It was found that the abundance of Pinus sibirica seedlings in the forests of the Aldan Highlands is positively associated (R2 = 0.46) with the yield of cones the previous year. The number of seedlings in the Northern Urals and Khamar-Daban is negatively related to the yield of cones of last year but is positively (R2 = 0.48–0.49) associated with the yield of cones of the year before last. We believe that seedlings in any case appear from the seeds of last year's yield. But the visible connection is due to the activity of the nutcracker. As a result of the stationary studies conducted in the Northern Urals, we identified a constant close (R2 = 0.81) positive relationship between the number of Pinus sibirica seedlings and the number of nutcrackers during the period of seed storage and dispersal in August-September of the previous year. It is assumed that the nature of the dynamics of seed production in the region affects the change in the number of nutcrackers during the seed harvesting period, which in turn determines the abundance of Pinus sibirica seedlings next year. This determines the revealed differences in the dynamics of Pinus sibirica renewal and its dependence on the yields of tree cones in the regions under consideration. For citation: Tantsyrev N.V., Sannikov S.N., Usoltsev V.А. Geographical Features of Pinus sibirica Du Tour Renewal. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 6, pp. 44–56. (In Russ.). https://doi.org/10.37482/0536-1036-2023-6-44-56

Population Structure of an African Cycad: Fire May Stimulate the Coning Phenology of Encephalartos lanatus (Zamiaceae) and Also Predispose Its Cones to Damage

Cycads are the most threatened group in the plant kingdom. Fire is identified as one of the major factors heightening cycad extinction risk. However, compared to South American cycads, we know little about how fire negatively affects the demography of African cycads. Here, we collected a snapshot of demographic data on the largest known population of South Africa’s cycad species, Encephalartos lanatus, in unburnt and regularly burnt habitats. We fitted several statistical models to investigate the effects of fire on the population structure of E. lanatus. First, we found that the population follows a ‘J’ structure with more adults than any other life stage. Contrary to popular belief, this ‘J’ structure may not necessarily imply the future of the population is at risk, given that E. lanatus is a long-lived species. Second, we found that the abundance of adults explains 25% of the abundance of seedlings but does not predict the abundance of suckers, perhaps suggesting the adults ensure preferential seedling rather than clonal recruitment. Third, irrespective of life stages, the subpopulation in fire-prone habitats is, in term of size, proportionately lower than the subpopulation in unburnt areas, suggesting that fire may negatively affect the dynamic of the population. However, fire is not linked to differences in sex ratio across the population; not only do fire-prone subpopulations have more cones, but they also tend to have more damaged cones than unburnt populations. Overall, although we raised some limitations of the present study, we also inferred that fire may shape the observed ‘J’ structure of the population of E. lanatus, but, contrary to traditional belief, the ‘J’ structure is not enough to raise concern about the future of the population. A population dynamics study is required to determine if the future of the population is at risk.

Spatially explicit models of seed availability improve predictions of conifer regeneration following the 2018 Carr Fire in northern California

For many conifer species in dry conifer forests of North America, seeds must be present for postfire regeneration to occur, suggesting that seed dispersal from surviving trees plays a critical role in postfire forest recovery. However, the application of tree fecundity and spatial arrangement to postfire conifer recovery predictions have only recently become more common, and is often included at relatively coarse scales (i.e., 30 meters). In this study, we mapped surviving trees using lidar and created a spatially explicit estimate of seed density (seed shadows) with 10 m, 50 m, and 100 m median dispersal distances. We estimated the number of seeds produced by each tree using allometric relationships between tree size and fecundity. Along with the seed shadows, we used a suite of topographic variables as inputs to negative binomial hurdle models to predict conifer seedling abundance in 131 plots following the 2018 Carr Fire in northern California, USA. We compared models using each of the seed shadows to each other as well as to a model using the distance to the nearest surviving tree, which served as a baseline. All model formulations indicated that estimated seed availability was positively associated with conifer regeneration. Despite the importance of seed availability plays in regeneration and the substantial differences in seed availability represented by the different seed shadows in our analysis, we found surprisingly little difference in model performance regardless of which seed shadow was used. However, the models employing seed shadows outperformed the models with distance to the nearest live tree. Although we have demonstrated a modest improvement in predicting postfire conifer regeneration, the uncertainty in our results highlights the importance of tree detection and classification in future studies of this kind. Future studies may find it useful to consider other factors such as predation, site suitability, and seed mortality as potential drivers of discrepancies between total and realized dispersal kernels.