Understorey Composition Research Articles

Soil nutrient availability and understorey composition beneath plantations of ecto- and arbuscular mycorrhizal Chilean native trees

Background and aimsSeveral lines of evidence indicate that arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) associations can have different effects on soil nutrient dynamics. Some lineages of ECM fungi can extract N from organic matter, with varying impacts on decomposers, soil carbon pools, mineral N availability, and plants that lack ECM. However, these effects are not always observed, and it is not clear how they are mediated by environmental factors.MethodsWe used Plant Root Simulator probes to compare soil availability of a wide range of nutrients beneath replicated 30-yr old plantations of Chilean Nothofagus (ECM) and Cupressaceae (Austrocedrus, Fitzroya: AM) on a lowland temperate site. Probes were buried for two 8-week periods in early spring and late summer. We also compared understorey composition beneath plantations, to test for evidence of different successional trajectories beneath Nothofagus and Cupressaceae.ResultsSoil organic carbon, total N and total phosphorus did not differ significantly between Nothofagus and Cupressaceae stands. Redundancy analysis revealed significant effects of both plantation type (Nothofagus vs. Cupressaceae) and season on overall mineral nutrient availability. Mineral N availability did not differ significantly between Nothofagus and Cupressaceae plots, but pH and calcium availability were significantly lower beneath Nothofagus. Manganese (Mn) was much more available beneath Nothofagus stands, which might reflect abundant Mn-peroxidase, a key enzyme involved in breakdown of lignin by ECM fungi. Understorey composition varied considerably between individual plantations, but did not differ significantly between Nothofagus and Cupressaceae plantations.ConclusionsDespite an overall effect on the stoichiometry of nutrient availability, we found little evidence of modification of the local N cycle by ECM fungi, or of divergent regeneration patterns beneath AM and ECM plantations. This might reflect the relatively N-rich character of this site, and/or mycorrhizal effects being counteracted by leaf trait differences between Chilean Cupressaceae and Nothofagus species.

Kelp forests collapse reduces understorey seaweed β-diversity.

Kelps are the primary foundation species in temperate subtidal rocky shores worldwide. However, global change is causing their decline with consequences for the organisms that rely on them. An accurate assessment of these consequences may depend on which attributes of the associated community are considered. This study shows that conventional α-diversity approaches may overlook some of these consequences compared to spatially explicit approaches such as with β-diversity. A 1-year seasonal study was conducted to compare the macroalgal understorey between healthy reefs with a Laminaria ochroleuca canopy and degraded reefs where the canopy collapsed years ago due to excessive fish herbivory. At each reef, the understorey seaweed assemblage was recorded in five replicate quadrats to estimate α-diversity (total richness, species density, Shannon index) and β-diversity (intra- and inter-reef scale). The understorey assemblage exhibited a distinct seasonal dynamic in both healthy and degraded reefs. α-Diversity attributes increased in spring and summer; turf-forming algae were particularly dominant in degraded reefs during summer. β-Diversity also showed seasonal variability, but mostly due to the changes in degraded reefs. None of the α-diversity estimates differed significantly between healthy and degraded reefs. In contrast, spatial β-diversity was significantly lower in degraded reefs. Although the loss of the kelp canopy affected the composition of the macroalgal understorey, none of the conventional indicators of α-diversity detected significant differences between healthy and degraded reefs. In contrast, small-scale spatial β-diversity decreased significantly as a result of deforestation, suggesting that the loss of kelp canopy may not significantly affect the number of species but still have an effect on their spatial arrangement. Our results suggest that small-scale β-diversity may be a good proxy for a more comprehensive assessment of the consequences of kelp forest decline.

Natural regeneration in tropical forests along a disturbance gradient in South-East Cameroon

The dynamics of tropical forests are highly dependent on the forest understorey. Understanding its diversity and composition is essential to ensure sustainable management of forest ecosystems. In this study, following a gradient of human disturbance, we analysed the density, diversity and floristic composition of the forest understorey in three land use types of south-eastern Cameroon: a protected area, a selective logging concession and community forests. Vegetation was inventoried in thirty-three permanent one-hectare plots. Woody individuals (tree, shrub, liana) were classified in four strata depending on their diameter: seedling (dbh < 1 cm), sapling (1–9.9 cm), small trees (10–29.9 cm), large tree (≥30 cm). A total of 4,159 individuals (dbh < 10 cm) belonging to 418 species and 232 genera were recorded. They mainly represent tree species (65%) and shade tolerant plants (77%), with diaspores disseminated by animals (74%). Life forms and modes of dissemination were significantly different between land use types. Abundance, species richness and diversity of juveniles varied significantly between strata and land use types: they were globally the highest in plots that have been logged less than five years before inventory. In terms of species composition, the different land use types were not clearly separated, indicating some resilience to disturbance. A low similarity between strata was observed. In all types, most canopy species are light demanding and cannot regenerate in the understorey. This indicates a natural evolution of the forest stands in the absence of silviculture. The presence of species that currently dominate the canopy of these forests will be gradually reduced without human intervention.

Canopy Composition and Spatial Configuration Influences Beta Diversity in Temperate Regrowth Forests of Southeastern Australia

Structural features of the overstorey in managed and unmanaged forests can significantly influence plant community composition. Native Acacia species are common in temperate eucalypt forests in southeastern Australia. In these forests, intense disturbances, such as logging and wildfire, lead to high densities of regenerating trees, shrubs, and herbs. The tree layer is dominated by Acacia and Eucalyptus, that compete intensely for resources in the first decades after stand establishment. The relative abundance and size of Acacia and Eucalyptus varies widely due to stochastic factors such as dispersal, microsite variability, and weather and climatic conditions. This variability may influence the structure and composition of the herbaceous and shrub species. In the temperate forests of southeastern Australia, understorey plant diversity is assumed to be influenced by Acacia species density, rather than Eucalyptus density. To quantify the influence of Acacia and Eucalyptus density on plant community composition, we used remote sensing and machine learning methods to map canopy composition and then compare it to understorey composition. We combined unoccupied aerial vehicle (UAV or drone) imagery, supervised image classifications, and ground survey data of plant composition from post-logging regrowth forests in the Central Highlands of southeastern Australia. We found that aggregation and patch metrics of Eucalyptus and Acacia were strongly associated with understorey plant beta diversity. Increasing aggregation of Acacia and the number of Acacia patches had a significant negative effect on plant beta diversity, while the number of Eucalyptus patches had a positive influence. Our research demonstrates how accessible UAV remote sensing can be used to quantify variability in plant biodiversity in regrowth forests. This can help forest managers map patterns of plant diversity at the stand-scale and beyond to guide management activities across forested landscapes.

Resilience of a tropical montane pine forest to fire and severe droughts

Abstract Higher temperatures, declining precipitation, changing cloud cover and increased wildfires threaten tropical montane pine forests by overriding the environmental heterogeneity that typically buffers these systems from catastrophic fires. Severe fires threaten to overwhelm forest resilience and tip this biome into alternate vegetation states. This study focused on long‐term dynamics of montane Pinus occidentalis forests in the Cordillera Central, Dominican Republic after a ~1000 km2 fire in 2005, the largest since 1965. We used long‐term records to investigate climate before and after the fire, and 19‐year dataset of pre‐ and post‐fire vegetation change from a network of 55 permanent plots (20 small 0.05 ha plots and 35 large 0.1 ha plots) established in 1999 to model overstorey and understorey vegetation dynamics. The 2005 fire was synchronized with the most extreme drought in the region in over 60 years. The fire burned from &lt;1600 to &gt;3000 m a.s.l. in elevation across windward and leeward slopes, creating a mosaic of low‐, moderate‐ and high‐severity patches. Lower elevations, leeward slopes and stands with a higher proportion of smaller pine trees all burned at higher severities. Growth rates of trees that survived the fire remained lower than pre‐fire rates 13 years after the fire. The highest post‐fire mortality rates were soon after the fire and in the census immediately following subsequent post‐fire droughts. Post‐fire pine seedling abundance was significantly greater in stands with higher basal area of live canopy trees and significantly reduced by increased shrub abundance in the understorey. Understorey composition recovered rapidly to pre‐fire states in sites affected by low‐ and moderate‐severity fires, but sites affected by high‐severity fires remained dissimilar to pre‐fire composition 13 years after the fire. Even though high‐severity patches had persistently low pine regeneration, 100% of small plots and 96% of large plots had at least one pine sapling or canopy tree recruit by 2018. Shrub taxa survived the fire in higher numbers and recovered to pre‐fire densities much faster than the pine, especially in high‐severity burns. Synthesis. Climate change has increased the likelihood of wildfires in tropical montane pine forests, with long‐lasting effects on vegetation dynamics. However, this biome may prove resilient to increasingly severe fires in the near future, given the ongoing recovery of Pinus occidentalis forests in Hispaniola despite repeated severe droughts. Nevertheless, highly drought‐ and fire‐resistant taxa (e.g. shrubs) may form alternate stable states in drier portions of tropical montane landscapes in the future as droughts and high‐severity fires become more common.

Silvicultural management and altitude prevail on soil properties and fungal community in shaping understorey plant communities in a Mediterranean pine forest

Understorey vegetation plays a key role in Mediterranean forest ecosystem functioning. However, we still lack a thorough understanding of the patterns and drivers of understorey composition and diversity. As a result, understoreys are often ignored during assessments of forest functioning under climate change. Here we studied the effect of silvicultural management, topography, soil fungal community composition and soil physical and chemical properties on understorey community composition and diversity. The plant cover and number of individuals of understorey perennial plants, shrubs and non-dominant trees was recorded on 24 plots (paired: control-thinned) in a Mediterranean pine-dominated mountainous area in Northeast Spain. The study area represented a broad thinning intensity gradient (from 0 to 70 % in removed stand basal area) along a 400-m altitudinal range (from 609 m to 1013 m). Our results showed that thinning intensity and topography explained the greatest proportion of the total variance in the understorey species composition, i.e., 18 % and 16 %, respectively. Interestingly, the effects of the silvicultural treatments were significant only when considering the altitudinal effect, so that, the main impacts of thinning on the understorey community composition occurred at low altitudes (between 609 m and 870 m). Moreover, we found a significant decrease in both richness and abundance of understorey species in both the control and thinned plots with increasing altitude, with thinned plots being significantly richer in species compared to the control plots. The difference in the understorey community sensitivity to forest thinning along the altitudinal gradient suggests changes in factors that limit plant growth. Low elevation plots were restrained by light availability while high altitudes plots limited by winter freezing temperature.

Factors explaining the composition and diversity of vascular plant understories along a transcontinental gradient in the Canadian boreal forest

AbstractAimImpacts of longitudinal gradients on species distributions have received less attention than latitudinal gradients. In Canada, precipitation varies longitudinally, with direct effects on plant growth and fire regimes. Despite the geographical extent of Canadian boreal forests, vascular plant diversity is relatively limited, with just under 300 species. Understorey communities comprise most of this diversity and play key roles in forests, affecting succession, nutrient cycling and wildlife habitat. Our objective was to evaluate the relative impacts of local and regional environmental conditions on vascular plant community composition and diversity in the boreal forest.LocationSampling took place in 33 trembling aspen (Populus tremuloides) stands along a transcontinental gradient in precipitation and fire regimes in boreal Canada.MethodsWe measured community composition and vegetation diversity indices of the vascular understorey in 400‐m2 plots and measured environmental variables at the local (drainage, nutrient and light availability, site heterogeneity) and regional (annual temperature and precipitation, fire weather index, landscape heterogeneity) scales. Multivariate analyses and hierarchical model selection were used to analyze patterns.ResultsSpecies composition varied longitudinally, with western and eastern species pools. Western indicator species tended to be fire‐adapted pioneer species, while indicator species at eastern sites were fire avoiders and late‐successional species. Species richness and intra‐site beta diversity seemed primarily driven by local variables and did not vary across the country. Species evenness, however, was slightly higher in the western region and decreased under higher precipitation, colder temperatures, and higher landscape‐level heterogeneity.ConclusionOur results suggested that even for similar canopy composition environmental variables play a key role in the establishment of plant communities and structure local plant assemblages by selecting or eliminating species from the regional pool, which was also controlled by fire regimes.

Artemisia sieberishrubs have contrasting specific effects on understory species in Iranian steppes

AbstractQuestions(a) Are there contrasting short‐ and long‐term effects of shrubs on understorey species that may balance at the community level? (b) Are these effects due to the responses of different understorey species groups? (c) Are these effects contributing to community composition?LocationAnArtemisiasteppe community in Golestan National Park (North‐East Iran).MethodsWe used both the removal and observational methods to separate short‐ from long‐term effects ofArtemisia sieberiBesser on the cover of 18 subordinate species and the relative interaction index (RII) to calculate species’ responses. We conducted a principal components analysis (PCA) on species RII and grouped species with a cluster analysis depending on their responses to the shrubs. Another PCA on understorey composition plots was conducted to assess the consequences of shrub effects for community composition.ResultsArtemisiahad negative short‐term and positive long‐term community‐level effects that balanced each other to produce neutral net effects. Short‐ and long‐term effects were due to the responses of different species groups, dominantly annuals and perennial grasses, respectively. Although balancing at the community level, the different shrub effects significantly contributed to explain community composition.ConclusionsOur study highlights that a dominant foundation shrub may have contrasting short‐ and long‐term effects on different groups of understorey species that contribute to explain community composition, although balancing at the community level.

Tree recruitment in a drought- and herbivory-stressed oak-beech forest: Implications for future species coexistence

Mixed oak-beech forests are particularly valuable from an ecological and socioeconomic perspective but are increasingly exposed to anthropogenic impacts. We wonder whether anthropogenic change drivers, such as increased drought and ungulate populations affect optimal regeneration niches, species coexistence, and mixed-species forest dynamics. We compared understorey composition, structure and distribution with the overstorey counterpart in an oak-beech forest located at its southernmost European distribution (Central Spain) with increasing drought and ungulate herbivory for the last decades.Results showed that Ilex aquifolium and Prunus avium had greater representation in the recruitment layer as compared to the understorey layer whereas, for the dominant Quercus spp. and Fagus sylvatica, there was a tendency suggesting an expansion of Fagus at the expense of Quercus. Density of tree recruits showed strong differences across microsites. The greatest density was found under tree and under shrub cover whereas the lowest was found under woody debris. By species, Quercus regenerated better in open and shrub microsites whereas Fagus and Ilex regeneration was higher under tree cover. Large patches of shrub cover favoured Prunus avium recruitment, particularly against ungulate herbivory as it was the most heavily browsed species, followed by Quercus, Ilex and Fagus in a descending order. Herbivory occurrence and intensity on tree recruits strongly varied with the microsite, with greater herbivory levels in open microsites. Woody debris on the ground only protected tree recruits from browsing when they were located under tree cover.Overall, fenced areas with no ungulates showed greater tree species coexistence (28% increase in species richness) and recruitment abundance (81% increase) after 7 years of exclusion. We also found a large increase in tree recruit growth and height:diameter ratio (h:d) for all studied species when fenced. Fagus and Prunus avium showed the greatest growth and h:d increase, much greater than those of Quercus and Ilex. The h:d was identified as a reliable indicator of ungulate herbivory and reference values (under null levels of ungulate herbivory) were provided for each species.We conclude that there is an imperative need for adaptive management strategies that address the joint effects of climate change (e.g. increased drought) and ungulate herbivory in mixed oak-beech forests. The provision of different microsites, including patches of shrub cover in open microsites and woody debris under dense tree cover, will facilitate the availability of suitable regeneration niches for most species and will therefore promote future species coexistence.

Twelve-year dynamics of alien and native understorey plants following variable retention harvesting in Nothofagus pumilio forests in Southern Patagonia

Disturbances have frequently been shown to increase the invasibility of plant communities. Harvesting, the most common and severe type of anthropogenic disturbance in forests, creates pulses of enhanced resource availability for alien plants and for native colonizers. However, it is unclear for how long initial changes in species composition of the understorey persist after harvesting. Using annually surveyed permanent plots (n = 72 plots across six stands), we analysed temporal changes of plant understorey composition of Patagonian Nothofagus pumilio forests during 12 years under three different conditions created by variable retention harvesting: retained forest patches (aggregates) of 30 m radius in a density of one patch ha−1 (AR), dispersed retention within the influence of the aggregate (DRI), retained dispersed single trees (DR); and primary unharvested forests as control (PF). Our results show that: (i) cover of native forest species in the understorey declined only very slowly in AR, but alien species cover increased strongly and became dominant nine years after harvesting (YAH); (ii) DR and DRI supported higher cover of alien species in the understorey than AR and PF, and alien species became dominant two to three YAH. Yet, they started to decline following a peak at eight YAH; (iii the cover of native forest species in the understorey was high in the beginning but alien species became dominant in DR and DRI after four and seven YAH, respectively. Tree regeneration significantly influenced understorey dynamics, i.e. (iv) in DR, a negative relationship with alien species cover, and a positive relationship with native colonizers from other habitats; (v) in DR and in DRI, this relationship was negative with alien species richness; (vi) in DRI, it was positive with native colonizers from associated environments (cover and richness). We conclude that alien plants invade Patagonian forests after harvesting, but decline with time when tree regeneration is established. Our results highlight the role of harvesting in facilitating plant invasions in forests, and how the spatio-temporal trajectories of such invasions are influenced by different levels of disturbance created by harvesting according to the position within the resultant matrix.

Interactive effects of past land use and recent forest management on the understorey community in temperate oak forests in South Sweden

AbstractQuestionsPast agricultural land use and forest management have shaped and influenced the understorey composition in European forests for centuries. We investigated whether understorey vegetation assemblages are affected by (a) legacies from a historical infield/outland agricultural system (i.e., a system with nutrient‐enriched vs nutrient‐depleted areas), (b) recent management intensity (i.e., thinning/felling activities), and (c) the interaction of recent management and potential legacies.LocationOak forests in Skåne, south Sweden.MethodsWe use three vegetation surveys (1983, 1993/94 and 2014) and notes on management and land‐use history, available for 62 permanent 500 m² plots. We conducted linear mixed effect modelling to detect both main and interactive effects of past land use and recent management on understorey diversity measures and vegetation indicator values for light and fertility. We combined nonmetric multidimensional scaling with permutational multivariate analysis of variance and indicator species analysis to detect compositional differences caused by past land use and/or recent management.ResultsUnderstorey diversity was mainly affected by management activities, but the former infield/outland agricultural system was an important determinant of understorey composition. Understorey composition of former infields reflected higher nutrient availability and lower light availability compared to former outland. Past land use and recent management had interactive effects on light‐related understorey variables: for the less intensively managed plots, the outland plots contained more light‐demanding species than the infield plots, while for the more intensively managed plots, the light‐demanding signature of the understorey was similar for infield and outland plots.ConclusionsDifferent intensities of past land use as well as recent forest management influenced the composition of the forest understorey, and interactions were present. Therefore, careful consideration of both the long‐term land‐use history and the more recent disturbances due to forest management are necessary when making future predictions of understorey composition and diversity.

A general framework for quantifying the effects of land-use history on ecosystem dynamics

Abstract Land-use legacies are important for explaining present-day ecological patterns and processes. However, an overarching approach to quantify land-use history effects on ecosystem properties is lacking, mainly due to the scarcity of high-quality, complete and detailed data on past land use. We propose a general framework for quantifying the effects of land-use history on ecosystem properties, which is applicable (i) to different ecological processes in various ecosystem types and across trophic levels; and (ii) when historical data are incomplete or of variable quality. The conceptual foundation of our framework is that past land use affects current (and future) ecosystem properties through altering the past values of resources and conditions that are the driving variables of ecosystem responses. We describe and illustrate how Markov chains can be applied to derive past time series of driving variables, and how these time series can be used to improve our understanding of present-day ecosystem properties. We present our framework in a stepwise manner, elucidating its general nature. We illustrate its application through a case study on the importance of past light levels for the contemporary understorey composition of temperate deciduous forest. We found that the understorey shows legacies of past forest management: high past light availability lead to a low proportion of typical forest species in the understorey. Our framework can be a useful tool for quantifying the effect of past land use on ecological patterns and processes and enhancing our understanding of ecosystem dynamics by including legacy effects which have often been ignored.

Tree species identity outweighs the effects of tree species diversity and forest fragmentation on understorey diversity and composition

Background & aim : In general, biodiversity has positive effects on ecosystem functioning. In forests, understorey vegetation is influenced by both the composition and species richness of the overstorey through species-specific effects on environmental conditions at the forest floor. Forest fragmentation is also known to influence understorey vegetation composition and richness. However, the combined effects of tree species diversity and forest fragmentation have not been studied yet. With the TREEWEB research platform, consisting of 53 forest plots along a tree species diversity and forest fragmentation gradient, we aim to unravel the combined effects of tree species diversity, tree species identity and forest fragmentation on the understorey composition and diversity. Methods : The TREEWEB platform includes forest plots of three tree species richness levels, containing all possible species combinations of Quercus robur, Quercus rubra and Fagus sylvatica. Complete dilution is avoided in the design, allowing separation between tree species identity and diversity effects. Vegetation surveys were conducted in all plots to investigate the species richness, species diversity, compositional turnover and cover of the herb layer as well as the shrub layer cover. Key results : Within the TREEWEB platform, overstorey-understorey diversity relationships were mainly characterised by tree species identity effects. No clear effects of tree species diversity and forest fragmentation on understorey composition and diversity were found. Conclusion : Tree species identity effects were most important in explaining the observed patterns in the understorey vegetation. Further in-depth research will allow us to disentangle which mechanisms underlie these patterns and whether effects of fragmentation are more pronounced at higher trophic levels.

Frequent wildfires erode tree persistence and alter stand structure and initial composition of a fire‐tolerant sub‐alpine forest

AbstractQuestionFrequent severe wildfires have the potential to alter the structure and composition of forests in temperate biomes. While temperate forests dominated by resprouting trees are thought to be largely invulnerable to more frequent wildfires, empirical data to support this assumption are lacking. Does frequent fire erode tree persistence by increasing mortality and reducing regeneration, and what are the broader impacts on forest structure and understorey composition?LocationSub‐alpine open Eucalyptus pauciflora forests, Australian Alps, Victoria, Australia.MethodsWe examined tree persistence and understorey composition of E. pauciflora open forests that were unburned, burned once, twice or three times by high‐severity wildfires between 2003 and 2013. At each of 20 sites (five per fire frequency class) we assessed extent of top‐kill and mortality of eucalypt clumps, spatial configuration of surviving and dead clumps, densities of new and lignotuberous eucalypt seedlings, and shrub and grass cover.ResultsAt least 2 yr after the last wildfire, proportions of top‐killed E. pauciflora stems were significantly higher, and densities of live basal resprouts significantly lower, at sites burned two or three times compared to once burned or unburned sites. Clump death increased to 50% of individuals at sites burned by three short‐interval wildfires, which led to changes in live tree patchiness, as indicated by nearest‐neighbour indices. Increased tree mortality was not offset by seedling recruitment, which was significantly lower at the twice‐ and thrice‐burned sites relative to single‐burn sites – although seedling recruitment was also influenced by topography and coarse woody debris. In addition to changes in the tree layer, the prominence of understorey shrubs was substantially reduced, and the frequency of grasses markedly increased, after two, and particularly three wildfires.ConclusionsOur study provides strong empirical evidence of ecologically significant change in E. pauciflora forests after short‐interval severe wildfires, namely, erosion of the persistence niche of resprouting trees, and a shift in understorey dominance from shrubs to grasses. Our findings highlight the need to consider the impacts of compounded perturbation on forests under changing climates, including testing assumptions of long‐term persistence of resprouter‐dominated communities.

Landscape-scale effects of geomorphological heterogeneity on variability of oak forest structure and composition in a monogenetic volcanic field

Background: Eruptive events in monogenetic volcanic fields create mosaics of lava fields that result in different successional times and stages, and environmental conditions. Such geomorphological heterogeneity may be related to patterns of vegetation structure, diversity, and composition across a landscape.Aims: To examine landscape-scale effects of geomorphological heterogeneity on the spatial variability of oak forest structure and composition in a monogenetic volcanic field.Methods: We sampled oak forests in six geomorphological units within a monogenetic volcanic field in El Tepozteco National Park and carried out redundancy analyses to relate environmental variables to forest composition and structure.Results: Geomorphological heterogeneity explained 28.8 and 25.7% of the variation in canopy structure and composition, respectively, and 21.6% of the variation in understorey composition. Exposed rock was the most important predictor of understorey composition and canopy structure, while elevation was a better predictor of canopy composition. The role of chronic human disturbance as a driver of forest composition and structure was minor compared to that of geomorphological heterogeneity.Conclusions: The geomorphological heterogeneity created by volcanic activity in this landscape drives oak forest variability; however, considerable unexplained variation in vegetation traits remains, which could be associated with unmeasured dimensions of environmental heterogeneity, neutral processes, and the effects of long-term human activity in the area.

Effects of alternative establishment systems on resource availability, understorey composition and tree performance in juvenile hybrid poplar plantations

Effects of alternative establishment systems on resource availability, understorey composition and tree performance in juvenile hybrid poplar plantations

European Impacts on Coastal Eastern Tasmania: Insight from a High-Resolution Palynological Analysis of a Salt-Marsh Core

A high-resolution pollen and micro-charcoal (>5 μm) record has been produced from a short sediment (50 cm) core recovered from a salt marsh in the Little Swanport Estuary, eastern Tasmania. This record suggests that there are four phases associated with the European settlement of the region. An initial phase from around 1830 to 1858 AD, which is similar to the previous Aboriginal period; a relatively low impact transitional phase from 1859 to 1898 AD; a rapid and marked deforestation period from 1899 to 1932 AD; and establishment of the contemporary landscape, with reforestation occurring, but with marked differences in species composition (i.e. greater representation of exotic taxa and altered understorey composition) from 1933 to 2006 AD. Key similarities are seen across Australia with the European settlement phase (i.e. addition of exotic taxa, deforestation and/or changes in vegetation composition, alterations in fire regimes and increased sedimentation rates), but high-resolution analysis suggests that these impacts may manifest in different ways depending on the local environmental setting and/or historical context of the settlement location. Furthermore, Amaranthaceae pollen representation appears to be impacted by changes in sea level. However, other factors such as human modifications, particularly grazing, and climate variability may play additional roles and further research is required to disentangle the relative effects of these factors.

Negligible structural development and edge influence on the understorey at 16–17‐yr‐old clear‐cut edges in black spruce forest

AbstractQuestionsWhat is the distance of edge influence on the structure and understorey composition at 16–17‐yr‐old cut edges in black spruce boreal forest? How do these edges compare with more recent 2–5‐yr‐old cut edges in the same region?LocationNorthwestern Quebec, Canada.MethodsForest structure and understorey composition were sampled along transects perpendicular to ten 16–17‐yr‐old clear‐cut edges, and compared to published results from 2–5‐yr‐old cut edges. We used randomization tests to assess the magnitude and distance of edge influence, and to compare edge influence between different edge ages.ResultsBlack spruce forest next to the 16–17‐yr‐old cut edges was structurally and compositionally very similar to interior forest, with little edge influence from harvesting beyond 5 m into the forest. Edge influence on the understorey was weak (low magnitude) and not very extensive (short distance) at these edges, with no significant edge influence on the abundance of individual species. Logs peaked in abundance on the forest side of the edge, with values higher than in either adjacent ecosystem.ConclusionsOverall, 16–17‐yr‐old cut edges in black spruce forest showed little evidence of further structural change compared to the 2–5‐yr‐old cut edges. Structural development of these edges as well as regeneration of the disturbed areas also resulted in reduced edge influence on the understorey. Instead, clear‐cut edges in black spruce forest may experience more forest influence on the regenerating disturbed area.

Driving mechanisms of overstorey–understorey diversity relationships in European forests

Forest ecosystem multifunctionality and the provision of ecosystem services benefit from high biodiversity, including from the understorey. Hence, it is crucial to get insight into the mechanisms that influence the composition and diversity in this forest layer. Understorey species have specific environmental requirements which are influenced by the overstorey in a species-specific way. Mixing tree species may create a heterogeneous pattern of environmental conditions similar to the component species’ monocultures, or induce new environmental conditions. We quantified overstorey–understorey taxonomic and functional diversity relationships at different spatial scales in an innovative large-scaled European diversity-oriented research platform that allows the separation of tree species identity and diversity effects. We considered our results in relation to the divergent patterns expected, depending on whether environmental heterogeneity or novel environment creation is the mechanism driving overstorey–understorey diversity relationships.We examined the understorey in mature forests in six European regions. Per region, three to five tree species were selected and 28–43 plots of 30m×30m were established (209 in total), covering a tree species richness gradient from monocultures to three- to five-species mixed plots. Within each plot, we performed vegetation surveys in three vegetation quadrats. We examined the understorey compositional variation among and within regions and the influence of overstorey taxonomic and functional diversity on understorey diversity at different spatial scales.The understorey composition showed clear interregional differences. We found lower compositional differentiation among quadrats with a higher tree species richness level (Finland, Germany and Italy). These quadrats share more tree species and probably have more similar environmental conditions. Neither overstorey taxonomic nor functional diversity affected the stand-level understorey species richness. At the forest-level, adding two-species mixtures to component monocultures clearly increased the understorey species richness, while adding mixtures with a higher tree species richness level to component monocultures had a negligible or negative impact.Overstorey–understorey diversity relationships depend on the spatial scale. At the stand-level, our results lacked support for the environmental heterogeneity hypothesis and revealed the possibility of novel environment creation in tree-by-tree mixed stands. At the forest-level, favouring the mixture of two-species mixed stands and their component monoculture stands offers the best prospects for a higher understorey species richness.

Wild boar rooting intensity determines shifts in understorey composition and functional traits

In recent decades, the European populations of wild boar have grown substantially, as has the impact of this species, owing above all to its rooting activity. Our aim was to investigate the relationships between vascular plant understorey and wild boar rooting intensity. The questions we addressed are: does rooting intensity influence understorey species composition and diversity? Which functional traits are associated with different levels of rooting? We performed a comparative analysis of plant communities in areas with contrasting levels of rooting intensity within a Mediterranean deciduous lowland forest in central Italy. Besides comparing species composition and diversity, we tested the association between species traits and rooting levels through fourth-corner analysis. We found that contrasting levels of rooting were associated to different understorey species composition and evenness, while we observed no significant difference in species richness. In contrast with our expectations, sites with lower rooting returned i) lower evenness values and ii) a higher proportion of species characterized by traits related to resistance or response to herbivory, i.e., spinescence, clonality, endozoochory, underground storage organs, and low height values. Our findings suggest that current vegetation patterns partly depend on the legacy effect of past rooting disturbance, since the areas currently subjected to low rooting intensity were likely to be intensely rooted in the past. These areas may have developed a marked dominance of clonal thorny species that, in turn, inhibited further feeding activities by wild boar.