Early Successional Species Research Articles

Dendroclimatology of sugar maple (Acer saccharum): Climate-growth response in a late-successional species

Sugar maple (Acer saccharum) is a shade-tolerant, late successional dominant species in the North American eastern deciduous forest. The objective of this study was to quantify the relationship between climate and radial growth in sugar maple and to identify spatial and temporal patterns in dendroclimatic response. We used a combination of archived sugar maple tree-ring chronologies and newly sampled sites to calculate dendroclimatic response of sugar maple at 13 sites in the United States and Canada. At all sites, sugar maple growth was significantly correlated to monthly temperature, precipitation, or Palmer Drought Severity Index. However, there were no generalizable patterns in sugar maple’s growth response to climate. Individual sites had unique dendroclimatic responses with respect to: a) which climatic variables were correlated to radial growth; b) what months had significant correlations between climate and radial growth; and c) what years had significant correlations between climate and radial growth. The individualistic dendroclimatic response of sugar maple appears to reflect a plastic response of the species to changes in climate perhaps related to its status as a strong competitor in late-successional forests. This ability to survive a wide range of environmental conditions may bode well for the species persistence under variable future climatic conditions. It also points to the need for more research on late-successional species in examining forest response to potential climate change scenarios because these species may be more resilient than early-successional species.

Stimulation of isoprene emissions and electron transport rates as key mechanisms of thermal tolerance in the tropical species Vismia guianensis.

Tropical forests absorb large amounts of atmospheric CO2 through photosynthesis, but high surface temperatures suppress this absorption while promoting isoprene emissions. While mechanistic isoprene emission models predict a tight coupling to photosynthetic electron transport (ETR) as a function of temperature, direct field observations of this phenomenon are lacking in the tropics and are necessary to assess the impact of a warming climate on global isoprene emissions. Here we demonstrate that in the early successional species Vismia guianensis in the central Amazon, ETR rates increased with temperature in concert with isoprene emissions, even as stomatal conductance (gs ) and net photosynthetic carbon fixation (Pn ) declined. We observed the highest temperatures of continually increasing isoprene emissions yet reported (50°C). While Pn showed an optimum value of 32.6±0.4°C, isoprene emissions, ETR, and the oxidation state of PSII reaction centers (qL ) increased with leaf temperature with strong linear correlations for ETR (ƿ=0.98) and qL (ƿ=0.99) with leaf isoprene emissions. In contrast, other photoprotective mechanisms, such as non-photochemical quenching, were not activated at elevated temperatures. Inhibition of isoprenoid biosynthesis repressed Pn at high temperatures through a mechanism that was independent of stomatal closure. While extreme warming will decrease gs and Pn in tropical species, our observations support a thermal tolerance mechanism where the maintenance of high photosynthetic capacity under extreme warming is assisted by the simultaneous stimulation of ETR and metabolic pathways that consume the direct products of ETR including photorespiration and the biosynthesis of thermoprotective isoprenoids. Our results confirm that models which link isoprene emissions to the rate of ETR hold true in tropical species and provide necessary "ground-truthing" for simulations of the large predicted increases in tropical isoprene emissions with climate warming.

Boreal tree regeneration after fire and fuelwood harvesting in coastal Nunatsiavut

Consecutive landscape-scale disturbances are known to influence boreal forest regeneration, yet few published data exist on the compounding effects of natural and anthropogenic disturbance on regeneration in subarctic forests. We conducted a dendroecological study of eastern coastal boreal forest regeneration two decades after fire at three subarctic forest stands that are important sources of fuelwood for the people of Nunatsiavut (Labrador, Canada). We quantified spruce (Picea spp.) and balsam fir (Abies balsamea (L.) Mill.) seedling regeneration, standing dead tree density, trees harvested within burned forests, and aged proximal unburned stands. Age of unburned forest varied with site; however, each exhibited continuous regeneration over several decades. Despite low seedling regeneration at each site (stems·m−2; less than 35% of pre-fire stem density), model results indicated harvesting post-fire did not impact seedling regeneration. Findings suggest a negative pressure on seedling abundance from increased presence of tall multi-stemmed shrubs, yet we argue that because stands exhibit a range in tree age, shrubs may be a set of early successional species rather than indicating a change in successional trajectory. Examination of a larger chronosequence within coastal forest stands of Nunatsiavut is warranted to further understand forest regeneration in the eastern subarctic under changing disturbance regimes.

Artemisia halodendron Litters Have Strong Negative Allelopathic Effects on Earlier Successional Plants in a Semi-Arid Sandy Dune Region in China.

Artemisia halodendron Turcz. ex Besser occurs following the appearance of a pioneer species, Agriophyllum squarrosum (L.) Moq., with the former replacing the latter during the naturally vegetation succession in sandy dune regions in China. A previous study revealed that the foliage litter of A. halodendron had strong negative allelopathic effects on germination of the soil seed bank and on the seedling growth. However, whether this allelopathic effect varies with litter types and with the identity of plant species has not yet been studied. We, therefore, carried out a seed germination experiment to determine the allelopathic effects of three ltter types of A. halodendron (roots, foliage, and stems) on seed germination of six plant species that progressively occur along a successional gradient in the semi-arid grasslands in the Horqin Sandy Land of northeastern China. In line with our expectation, we found that the early-successional species rather than the late-successional species were negatively affected by A. halodendron and that the allelopathic effects on seed germination increase with increasing concentration of litter extracts, irrespective of litter types. Our study evidenced the negative allelopathic effects of A. halodendron on the species replacement and on the community composition during dune stabilization in the Horqin Sandy Land. Further studies are needed to better understand the successional process and thus to promote the vegetation restoration in that sandy dune region as A. halodendron itself disappeared also during the process.

Functional trait representation differs between restoration plantings and mature tropical rainforest

The planting and attempted restoration of tropical forest landscapes is increasing rapidly across the globe. Two limiting aspects of large-scale forest restoration are the demand for appropriate quantities of seeds and seedlings of native species, and the ability to facilitate succession in planted sites. Species functional traits such as seed type, tree size, germination time, and wood density may influence the quantity of seedlings that can be produced for restoration, and the potential of these seedlings to persist and facilitate site succession. Therefore, it is important to understand the species composition and functional trait representation of restoration plantings. We explored the species composition and functional trait representation of 846 restoration plantings in the Australian Wet Tropics containing > 465,000 seedlings from 599 species, using seedling supply records from six nurseries over a six year period (2012–2017). Despite restoration plantings in the Australian Wet Tropics containing an impressive number of species, just 52 species contributed over half of all individual seedlings. We found that species with small animal-dispersed seeds and low wood density were more abundant, on average, and had greater representation in restoration plantings than in mature rainforest. Despite this, we did not find evidence that restoration plantings had a diminished capacity to grow tall or sequester carbon as there was no significant difference in the relative abundance of tall tree species or species with high wood density. Small seeded and fast growing species may be cheaper to produce in nurseries and may accelerate site succession as these characteristics are associated with pioneer and early successional species, however these traits are also associated with higher mortality rates. Understanding how functional trait representation influences the success of restoration plantings will require further insight into temporal aspects of site succession.

Early-successional saproxylic beetles inhabiting a common host-tree type can be sensitive to the spatiotemporal continuity of their substrate

Intensive forest management has drastically reduced the amount and diversity of dead wood resulting in population decline of saproxylic species. Forestry practices can also disrupt spatiotemporal continuity of dead wood habitats. We studied the effects of stand- and landscape-level densities of host trees on the incidence (proportion of occupied trees) of saproxylic beetles inhabiting recently dead standing Scots pines, a common host-tree type both in natural and managed boreal forests. We compared the occurrence patterns of eight rare specialist and eight common generalist species. Saproxylic beetles were collected from a total of 315 trees in 67 forest stands, including both managed and natural forests, located in three regions which form a gradient in forest-use intensity. Species richness of the entire community at tree and stand level did not respond to the stand- and landscape-level host-tree density. The incidence of six common generalist species did not depend on the stand-level host-tree density, whereas the incidences of four rare specialist species increased with increasing host-tree density. Five out of eight rare specialist species were either significantly less common or absent from the region with the lowest landscape-level density of host trees. We conclude that rare specialist species living in recently dead pines are susceptible to changes in spatiotemporal dynamics of their host trees. To conserve rare early-successional species, it is necessary to ensure continuous input of dying trees by prolonging rotation times in mature forests, regenerating stands using seed-tree cutting and leaving as many permanent retention trees as possible.

Assessing the Influence of Physical Factors and Human-Related Disturbances on Forested Wetland Communities in Georgia

Forested wetlands act as buffers between human civilization and aquatic ecosystems, providing numerous services. Due to widespread human influence, most existing forested wetlands are secondary forests. This study investigated 3 forested wetlands in the Oconee basin in middle Georgia to assess the influence of physical factors and anthropogenic disturbances on the tree composition. Our analyses revealed that the northernmost wetland had experienced the most recent major anthropogenic disturbance based on the dominance of an early successional species. The southernmost site, a floodplain forest, was the most diverse due to the short flooding durations that support a larger suite of species. The middle site was the least diverse but had the largest trees and total basal area.

Simulated Increases in Fire Activity Reinforce Shrub Conversion in a Southwestern US Forest

Fire exclusion in historically frequent-fire forests of the southwestern United States has altered forest structure and increased the probability of high-severity fire. Warmer and drier conditions, coupled with dispersal distance limitations, are impeding tree seedling establishment and survival following high-severity fire. High-severity patches are commonly dominated by non-forest vegetation, a state that can be reinforced by subsequent fire events. We sought to determine the influence of fire probability on post-fire vegetation development in a severely burned landscape in New Mexico, USA. We used LANDIS-II to simulate three fire probability scenarios—historical fire probability, contemporary fire probability, and the mean of the two—with contemporary climate. As fire probability increased, the mean size of the largest fires and the mean landscape fire severity increased. These changes in fire characteristics resulted in decreased total aboveground biomass and photosynthetic capacity on the landscape after 50 years. Additionally, the distribution of individual species biomass shifted, with early successional species, especially those that resprout after fire, increasing as a fraction of total biomass with increasing fire occurrence. Counter to empirical data, our simulations did not show a conifer establishment limitation, suggesting a source of uncertainty that will need to be addressed to improve projections of forest dynamics under future climate. Even without limited conifer regeneration, continued increases in fire frequency are likely to favor resprouting species and result in a loss of forest biomass and ecosystem productivity in this southwestern forest landscape.

Leaf isoprene and monoterpene emission distribution across hyperdominant tree genera in the Amazon basin

Tropical forests are acknowledged to be the largest global source of isoprene (C5H8) and monoterpenes (C10H16) emissions, with current synthesis studies suggesting few tropical species emit isoprenoids (20–38%) and do so with highly variable emission capacities, including within the same genera. This apparent lack of a clear phylogenetic thread has created difficulties both in linking isoprenoid function with evolution and for the development of accurate biosphere-atmosphere models. Here, we present a systematic emission study of “hyperdominant” tree species in the Amazon Basin. Across 162 individuals, distributed among 25 botanical families and 113 species, isoprenoid emissions were widespread among both early and late successional species (isoprene: 61.9% of the species; monoterpenes: 15.0%; both isoprene and monoterpenes: 9.7%). The hyperdominant species (69) across the top five most abundant genera, which make up about 50% of all individuals in the Basin, had a similar abundance of isoprenoid emitters (isoprene: 63.8%; monoterpenes: 17.4%; both 11.6%). Among the abundant genera, only Pouteria had a low frequency of isoprene emitting species (15.8% of 19 species). In contrast, Protium, Licania, Inga, and Eschweilera were rich in isoprene emitting species (83.3% of 12 species, 61.1% of 18 species, 100% of 8 species, and 100% of 12 species, respectively). Light response curves of individuals in each of the five genera showed light-dependent, photosynthesis-linked emission rates of isoprene and monoterpenes. Importantly, in every genus, we observed species with light-dependent isoprene emissions together with monoterpenes including β-ocimene. These observations support the emerging view of the evolution of isoprene synthases from β-ocimene synthases. Our results have important implications for understanding isoprenoid function-evolution relationships and the development of more accurate Earth System Models.

Effects of tree retention and woody biomass removal on bird and small mammal communities

Contemporary forest management is increasingly focused on maintaining ecosystem function and services including biodiversity conservation. As a result, harvest guidelines related to retention of live trees and woody biomass (fine and coarse residue arising from harvesting) have been developed to provide benefits for wildlife, but there is much uncertainty on the effectiveness of these guidelines depending on stage of succession, retention levels, and focal taxa. We used an operational-scale, fully replicated factorial experiment to determine the effects of both tree retention (none, dispersed, aggregated) and woody residue harvesting (no removal, 20% retention, all removed) on breeding bird and small mammal communities in aspen forests 7–8 years after harvest. Bird community metric responses showed a clear and consistent positive response to tree retention; both tree retention configurations resulted in higher total abundance, increased diversity, and higher species richness compared to stands with no tree retention. There was no difference in community metrics between the retention configurations and no evidence that early successional species were negatively affected by tree retention. Total abundance of small mammals was lower in clear-cuts compared to tree retention treatments; moreover, clear-cut stands had lower species diversity compared to stands with the aggregated tree retention. There were limited effects of biomass harvest treatments on small mammal communities, likely because actual biomass removal was much lower than experimental targets. Overall, our results provide conclusive evidence on the continued benefits of tree retention on wildlife communities se0ven and eight years post-harvest in regenerating aspen forests.

Doubling of biomass production in European boreal forest trees by a four-year suppression of background insect herbivory

Background insect herbivory, i.e. the minor but chronic plant damage caused by insects, is usually considered ‘negligible’ for plants when compared with the severe defoliation associated with forest pest outbreaks. We experimentally tested the hypothesis that the impacts of background herbivory on tree growth and mortality accumulate over years, resulting in much larger effects than usually assumed. In boreal taiga forests near Arkhangelsk (Northern Russia), application of insecticide at 10-day intervals for four growth seasons (June–September of 2014–2017) decreased foliage losses to insects in our study species (early successional deciduous Betula pubescens and Populus tremula; late successional coniferous Picea abies and Pinus sylvestris) from 2.04–6.35% to 0.72–1.18%. The magnitude of the insecticide treatment effect on plant losses to defoliating insects varied considerably among the study species, with the highest effect observed in white birch and the lowest effects in the two late successional species. Across all tree species, insecticide treatment nearly doubled the increase in tree biomass relative to control plots, demonstrating that background insect herbivory has major negative impacts on tree growth and productivity. The insecticide-treated plots showed the largest increase in biomass in Norway spruce and the smallest increase in European aspen when compared to the control plots. The changes in birch growth following the release from insect herbivory were three times greater than the effects of the same level of simulated herbivory in an earlier experiment, thereby hinting at the importance of herbivore-specific elicitors in the growth suppression of trees damaged by insects. The mortality of late successional species in the treatment plots increased nearly three-fold, whereas the mortality of early successional species did not change relative to controls, suggesting an increase in competitiveness of the early successional trees released from herbivory. Thus, in agreement with an earlier modelling study, we conclude that minor herbivore damage, over the long term, substantially reduces biomass production in North European forest trees. Due to differential effects on coexisting tree species, this damage has a pronounced impact on plant competitiveness and affects both the productivity and the structure of boreal forests.

Synchronous and asynchronous root and shoot phenology in temperate woody seedlings

Understanding variation in root and shoot growth phenology among species is crucial to understanding underlying mechanisms of temporal niche differentiation. However, little is known about the relationship between root and shoot phenology, or how this relationship varies among functional traits. We examined fine root and shoot phenology of 42 seedlings representing a variety of woody species that inhabit the cool temperate forests of northern Japan. Some aspects of phenology were common to the pool of species examined: we found positive relationships between root and shoot phenology for the end of growth, and for the duration of growth, but not for the start of growth. Further, seedlings that started root growth relatively early also ended root growth relatively late. Other aspects of phenology varied predictably with functional traits, i.e. leaf habit and successional status: first, root growth in evergreen species started significantly earlier and ended later than in deciduous species; second, early successional species had the longest duration of shoot growth among all successional types. Our results suggest that niche differentiation may be promoted by differences in phenology between root and shoots, likely contributing to the co‐existence of woody seedlings in temperate forests.

Spontaneous development of early successional vegetation improves Norway spruce forest soil after clear-cutting and renewal failure: a case study at a sandy-soil site

Clear-cutting is the most common silvicultural system. Sometimes, if the new crop is not established successfully, clearcut is left unreforested. This study focused on a site where early successional species such as silver birch (Bi) and rowan (Ro) were accompanied with Norway spruce (Sp) in 13-year-old stand from natural regeneration at 550 m of altitude at an acidic site with eastern aspect and 25% slope. We found five types of stand composition: treeless gaps, Ro-Bi, Ro-Bi-Sp, Bi-Sp and monospecific Sp. Besides these juvenile ones, adjacent 100-year-old spruce (Sp old) stand representing pre-harvesting conditions was studied. In addition to the performance of trees, organic layer (Hum), topsoil (Ah) and upper subsoil (B) horizons were sampled to study an expected shift of chemical properties after clear-cutting and secondary succession at the site of interest. Birch dominated the natural regeneration; rowan and spruce were present mostly in understorey. Old spruce was more acidic and nutrient-poorer compared to the juvenile treatments. The treeless treatment showed also slightly higher pH and comparable nutrients compared to the young mixtures. Young spruce was higher in nitrogen compared to Ro-Bi-Sp mixture.

Shade avoidance and reproductive strategies of an early successional species Penthorum chinense in relation to shade treatments.

Shade avoidance is expected to be favoured under moderate light. However, in previous studies, shade avoidance was highest in the deepest shade, despite the fact that the plants incur the costs of shade avoidance without the benefits of being exposed to increased light. We performed shading experiments under different light intensities to understand: (i) how shade avoidance traits of Penthorum chinense could peak in moderate light, and (ii) if there was a trade-off between plant height and allocation of seeds along the light gradients. Penthorum chinense increased shade avoidance traits such as height per total dry mass as the amount of light decreased. Side stem number per total dry mass of P. chinense decreased as shade became deeper, from full light to low light. Regressions on seed mass fraction and height were significant with a linear model (y=-0.0006x+0.1338). There were more resources allocated to seeds under low light than under moderate light. Penthorum chinense increased shade avoidance traits with the decrease in light amount, as found in previously studied species. There was a trade-off between height and production of more seeds. The reproductive strategy of P. chinense was to increase seed mass fraction under low light more than under moderate light. This species might be able to expand established populations by both rhizomes and seeds under low light environments.

Is the soil seed bank a reliable source for passive restoration of bush-cleared semi-arid rangelands of South Africa?

BackgroundBush clearing of encroached rangelands is crucial for restoration of herbaceous cover and diversity. Regeneration after bush clearing depends largely on the soil seed bank (SSB) size and composition. To assess the potential of the SSB to facilitate post-clearing herbaceous restoration, we examined the SSB density, composition and diversity and similarity between SSB and aboveground vegetation (AGV).MethodsThe study was conducted in semi-arid rangelands of Maseding and Kgomokgomo in North-West Province of South Africa. In each rangeland, all woody plants in three 1250 m2 plots were cut using saws and loppers, with the stumps treated with picloram. Paired observations were conducted in cleared and uncleared microsites. Soil samples were collected at three depths (0–10, 10–20 and 20–30 cm) in each microsite in April (pre-treatment), August, October and December 2016 and in April and August 2017. SSB was assessed using seedling emergence method, whereas pre- and post-clearing surveys of AGV were conducted in February 2016 and 2017, respectively.ResultsCleared microsites had significantly (p < 0.01) higher seed bank densities (1872 and 693 seeds m-2 at Maseding and Kgomokgomo, respectively) relative to uncleared microsites in August 2017, with grasses accounting for higher densities than other plant functional groups in the upper 0–10 cm. Pioneer grasses (Aristida congesta subsp. barbicollis, Brachiaria eruciformis and Tragus berteronianus) and invasive forbs (Bidens pilosa and Schkuhria pinnata) dominated the SSB in cleared microsites at Maseding, whereas succulents (Portulaca spp.) and pioneer grasses (T. berteronianus and Urochloa mosambicensis) were abundant at Kgomokgomo in August 2017. SSB and AGV were dissimilar until December 2016; thereafter, similarity increased significantly (p < 0.05) in cleared microsites (Sørensen’s coefficient = 0.60 to 0.66 at Maseding and 0.43 to 0.52 at Kgomokgomo) compared to uncleared microsites. Species diversity was highest in August 2016 and April 2017 at Maseding, but it did not differ between two microsites (p > 0.05). At Kgomokgomo, SSB was more diverse in cleared than uncleared microsites in April and August 2017.ConclusionHigh seed bank densities in the upper soil layer in cleared microsites would promote passive restoration, but regeneration is likely to be initiated by early successional species. However, close monitoring and eradication of invasive forbs and succulents is necessary following bush clearing. The tendency of SSB resembling AGV over time in cleared microsites signifies that seed production from AGV is important for passive restoration following bush clearing.

Species traits, patch turnover and successional dynamics: when does intermediate disturbance favour metapopulation occupancy?

BackgroundIn fragmented landscapes, natural and anthropogenic disturbances coupled with successional processes result in the destruction and creation of habitat patches. Disturbances are expected to reduce metapopulation occupancy for species associated with stable habitats, but they may benefit species adapted to transitory habitats by maintaining a dynamic mosaic of successional stages. However, while early-successional species may be favoured by very frequent disturbances resetting successional dynamics, metapopulation occupancy may be highest at intermediate disturbance levels for species with mid-successional habitat preferences, though this may be conditional on species traits and patch network characteristics. Here we test this ‘intermediate disturbance hypothesis’ applied to metapopulations (MIDH), using stochastic patch occupancy simulation modelling to assess when does intermediate disturbance favour metapopulation occupancy. We focused on 54 virtual species varying in their habitat preferences, dispersal abilities and local extinction and colonization rates. Long-term metapopulation dynamics was estimated in landscapes with different habitat amounts and patch turnover rates (i.e. disturbance frequency).ResultsEquilibrium metapopulation occupancy by late-successional species strongly declined with increasing disturbance frequency, while occupancy by early-successional species increased with disturbance frequency at low disturbance levels and tended to level-off thereafter. Occupancy by mid-successional species tended to increase along with disturbance frequency at low disturbance levels and declining thereafter. Irrespective of habitat preferences, occupancy increased with the amount of habitat, and with species dispersal ability and colonisation efficiency.ConclusionsOur study suggests that MIDH is verified only for species associated with mid-successional habitats. These species may be particularly sensitive to land use changes causing either increases or decreases in disturbance frequency. This may be the case, for instance, of species associated with traditional agricultural and pastoral mosaic landscapes, where many species disappear either through intensification or abandonment processes that change disturbance frequency.

Macroalgal vegetation on a north European artificial reef (Loch Linnhe, Scotland): biodiversity, community types and role of abiotic factors

Very little is known about the marine macroalgae of artificial reefs—especially in the North Atlantic—despite the growing number and extent of man-made structures in the sea, and even though seaweed communities have paramount importance as primary producers, but also as feeding, reproductive and nursery grounds in coastal ecosystems. This paper explores the macroalgal diversity of a large system of artificial reefs in Loch Linnhe, on the west coast of Scotland, in a quantitative and qualitative study based on diving surveys and correlates the observations with the prevalent abiotic factors. The study was conducted in order to test the hypothesis that artificial reefs can enhance seaweed habitats—in particular, for kelps—and that there is a clear correlation with substrate type. While the reef is home to a large range of biota and abundance of early-successional species of turf and bushy macroalgae, totalling 56 taxa and with Delesseria sanguinea as the dominant species, canopy-forming perennial kelp species are conspicuously relatively rare. Macroalgal vegetation is explored in correlation with reef geometry/geography and depth. Statistical analysis shows benthic communities were strongly affected by substrate type, with turf algae and invertebrates dominating the artificial reefs, while bushy algae dominate the natural ones. Common macroinvertebrates associated with the phytobenthic communities are assessed qualitatively.

Early succession on slag compared to urban soil: A slower recovery.

Slag, waste from the steel-making process, contains large amounts of calcium, magnesium, iron and other heavy metals. Because of its composition, high pH and low water retention ability, slag is considered inhospitable to plants. Nevertheless, the spontaneously generated plant communities on slag are surprisingly diverse, but the assembly and structure of such communities are poorly studied. Previous studies suggest reduced rates of succession due to low growth rate and slow accumulation of topsoil. To investigate whether slag communities display similar patterns, we used two former industrial sites on the South Side of Chicago, IL, both with high pH (8-9.2) sand content (80%) and calcium concentration (> 9000 ppm). We removed all vegetation from both slag and non-slag plots to test whether recovery differed over one growing season (4 months). To directly assess plant growth, selected focal species were planted on both sites and harvested. We show that recovery from removal differed at slag and non-slag sites: the recruitment process on slag, measured by percent vegetative cover and number of species in plots, was significantly slower at 6-8 weeks of the manipulation and beyond, suggesting a potential stage-dependent effect of slag on plant growth. Certain slag plots recorded less cover than non-slag plots by >30% at maximum difference. Functional trait analysis found that graminoid and early successional species preferentially colonized slag. Overall, slag plots recovered more slowly from disturbance, suggesting a slow succession process that would hinder natural recovery. However, slag also has the potential to serve as plant refugia, hosting flora of analogous habitats native to the area: one of our industrial sites hosts nearly 80% native species with two species of highest Floristic Quality Index (10). Restoration efforts should be informed by the slow process of natural recovery, while post-industrial sites in urban areas serve as potential native plant refugia.

The Demography of Gentiana autumnalis in Populations Under Varying Management Regimes in New Jersey

Gentiana autumnalis (pine barren gentian) is a rare, fall-flowering perennial that is endemic to pine barren habitat from New Jersey to South Carolina. This disturbance-adapted, early successional species is at risk in New Jersey as a result of human interactions, namely growing season mowing and fire suppression. We used a repeated measures design to compare the differences between managed (mowing and prescribed fire) and unmanaged G. autumnalis populations for density, life stage, mortality, and fecundity. Managed populations had a greater gentian density, proportion of reproductive individuals, and seedlings compared to unmanaged populations. Implementing prescribed burns and mowing at previously unmanaged sites prior to spring growth increased gentian density, flowering, and seed set the same year. Our data support that prescribed burning and mowing can be beneficial management tools for the conservation of G. autumnalis and other disturbance-adapted species that require open early-successional habitat. However, their implementation can have negative consequences if conducted during the growing season, especially for roadside populations that are periodically mowed. Declining rare plant populations have the potential to benefit from management practices that facilitate ideal growing conditions and influence life stage transitions that will best improve population growth rate over time.

Silvicultural treatment effects on commercial timber volume and functional composition of a selectively logged Australian tropical forest over 48 years

Post-logging silvicultural treatments involving thinning are commonly recommended to increase the commercial timber production under polycyclic harvesting regimes in tropical forests. However, thinning practices intentionally designed to improve commercial timber production may alter species composition and functional composition. Low, medium, and high intensity thinning following logging plus a logged only control was applied in an Australian tropical forest in 1969 to assess the long-term liberation thinning impacts on the commercial timber volume and the functional composition of the regenerating forest. Over 46 years following thinning, only medium- and high-intensity thinning promoted recruitment of commercial trees into the >10 cm diameter class. All three thinning treatments enhanced the standing volume of most desirable commercial species, mainly driven by the growth of remaining non-harvested trees in the 10–20 cm diameter class. The merchantable timber volume of other less desirable species was also promoted in the four treatments. Over the first 28 years after treatment (1969–1997), the average annual timber volume accumulation rate was highest in the medium-intensity thinning (1.97 m3 ha−1 year−1). The positive impacts of medium- and high-intensity thinning on commercial timber volume growth lasted longer than the low-intensity thinning. From 1997 to 2015, average annual volume increments increased in the medium- and high-intensity thinning, changed little in the low-intensity thinning, and decreased in the untreated control. Moreover, the medium- and high-intensity thinning led the community functional composition to shift towards early-successional species, which reduced community-weighted mean wood densities. The changes induced by intensive thinning treatments may affect the recovery of forest biomass and biodiversity. Hence, the trade-off between enhancing timber stocks and maintaining functional composition should be considered during planning and implementation of tropical forest management.