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We analyzed national forest inventory data collected from circa 2000-2018 across 37 states in the eastern United States to better understand the influence of forest health related canopy disturbances on the regeneration and recruitment dynamics of upland oaks (Quercus). We found low levels of oak recruitment across all disturbance types examined but limited evidence of any direct effects from the type of disturbance on the population of regenerating oaks. The general lack of differences in oak regeneration response between forest health disturbances and disturbances caused by harvested or non-disturbed plots does not indicate that the effects of forest health disturbances were benign, however. Instead, low level of oak recruitment across all disturbance types highlights the pervasiveness of the trend of shifting composition in once oak-dominated forests where oak is absent or sparse in the regeneration layer. Our results show that oak recruitment was higher when oak was present as advance reproduction prior to disturbance from any cause examined. Collectively, these results lead us to conclude that the widespread inadequacy of oak advance reproduction in mature oak-dominated forests is the prevailing threat to oak forest health and sustainability. We suggest the status of advance reproduction be treated as a co-morbidity when weighing the risk and potential outcomes from other threats to upland oak forests in the eastern United States. [ABSTRACT FROM AUTHOR]

We analyzed national forest inventory data collected from circa 2000–2018 across 37 states in the eastern United States to better understand the influence of forest health related canopy disturbances on the regeneration and recruitment dynamics of upland oaks (Quercus). We found low levels of oak recruitment across all disturbance types examined but limited evidence of any direct effects from the type of disturbance on the population of regenerating oaks. The general lack of differences in oak regeneration response between forest health disturbances and disturbances caused by harvested or non-disturbed plots does not indicate that the effects of forest health disturbances were benign, however. Instead, low level of oak recruitment across all disturbance types highlights the pervasiveness of the trend of shifting composition in once oak-dominated forests where oak is absent or sparse in the regeneration layer. Our results show that oak recruitment was higher when oak was present as advance reproduction prior to disturbance from any cause examined. Collectively, these results lead us to conclude that the widespread inadequacy of oak advance reproduction in mature oak-dominated forests is the prevailing threat to oak forest health and sustainability. We suggest the status of advance reproduction be treated as a co-morbidity when weighing the risk and potential outcomes from other threats to upland oak forests in the eastern United States.

Abstract Historically, macroecology and microecology have diverged with regard to the niche concept. A better understanding of functioning ecological systems, however, depends on an integrative approach to this concept at different spatial scales. A mixed approach, merging macro‐ and microscale by validating ecological niche modeling (ENM) with the results of in situ experiments and environmental data collection was used to understand if areas identified by ENM as highly suitable for adult palms are also adequate for seedling establishment. Syagrus weddelliana's (Arecaceae) distribution range falls within the Atlantic Rain Forest, and more specifically Serra dos Órgãos region (Rio de Janeiro state), southeastern Brazil. The following steps were performed: (a) ENM to delimit the area of occurrence of S. weddelliana and locate experimental areas; (b) a seed sowing experiment in areas with presence or absence of the species in areas of high or low environmental suitability at 36 experimental stations; and (c) characterization of each microhabitat which was related back to the macroscale results of ENM. Evidence of biotic and abiotic limitations was found for S. weddelliana distribution. Areas of higher suitability had lower seed predation rates and, consequently, higher seed germination rates. On the other hand, areas with low environmental suitability at the macroscale were divided into two types: areas with microhabitat similar to that of areas with high environmental suitability that had some germination despite high predation and areas with different environmental conditions that had no germination and high predation rates. Seedlings and adults had different abiotic requirements. Microhabitat conditions were more important for the initial establishment of S. weddelliana than macroclimatic variables. This finding demonstrates that macro‐ and microecological information works in a complementary way to a better understanding of the distribution of S. weddelliana.

Historically, macroecology and microecology have diverged with regard to the niche concept. A better understanding of functioning ecological systems, however, depends on an integrative approach to this concept at different spatial scales. A mixed approach, merging macro‐ and microscale by validating ecological niche modeling (ENM) with the results of in situ experiments and environmental data collection was used to understand if areas identified by ENM as highly suitable for adult palms are also adequate for seedling establishment. Syagrus weddelliana's (Arecaceae) distribution range falls within the Atlantic Rain Forest, and more specifically Serra dos Órgãos region (Rio de Janeiro state), southeastern Brazil. The following steps were performed: (a) ENM to delimit the area of occurrence of S. weddelliana and locate experimental areas; (b) a seed sowing experiment in areas with presence or absence of the species in areas of high or low environmental suitability at 36 experimental stations; and (c) characterization of each microhabitat which was related back to the macroscale results of ENM. Evidence of biotic and abiotic limitations was found for S. weddelliana distribution. Areas of higher suitability had lower seed predation rates and, consequently, higher seed germination rates. On the other hand, areas with low environmental suitability at the macroscale were divided into two types: areas with microhabitat similar to that of areas with high environmental suitability that had some germination despite high predation and areas with different environmental conditions that had no germination and high predation rates. Seedlings and adults had different abiotic requirements. Microhabitat conditions were more important for the initial establishment of S. weddelliana than macroclimatic variables. This finding demonstrates that macro‐ and microecological information works in a complementary way to a better understanding of the distribution of S. weddelliana. [ABSTRACT FROM AUTHOR]

The regeneration ecology of many southern African threatened plant species is poorly understood. Temperature is considered the most important environmental factor governing seed germination. The germination temperature requirements of the critically endangered stem succulent, Adenium swazicum, were determined under controlled conditions, together with tetrazolium staining protocol tests to assess seed viability. The effects of soil medium, watering levels, depth of sowing and shading on germination/seedling emergence were also determined at the Lowveld National Botanical Garden (LNBG). Germination/seedling emergence was compared under nursery conditions within (Skukuza Nursery in Kruger National Park) and outside (LNBG) the natural distribution range of A. swazicum. The germination of viable seeds ranged 96.5–100% for a broad range of temperatures from 20 to 35 °C as well as for 30/20 °C (light/dark) alternating temperature. No germination was recorded at 5 °C and 10 °C, and relatively limited germination at 15 °C (42.9%) and 40 °C (15.4%). These results were modelled using a Generalized non-linear model, with a binomial error and a logit link function, best-fit models were second-order polynomials ( i.e. , quadratic). Mean Germination Time ranged from 2 to 6 days among temperature treatments. Tetrazolium together with germination results for the 20 − 35 °C temperatures showed moderate to high seed viability across populations and between years within the same population. Seedlings readily emerged irrespective of soil media (3 types) or planting depth (surface, 5 and 10 mm) but higher emergence occurred under more frequent watering. Seedlings emerged equally well under sun or shade conditions, but only subsequently survived in the shade. Despite lower temperatures recorded during October/November 2010 at LNBG (outside range: 27.2 ± 0.9 °C) compared to Skukuza (within range: 32.6 ± 0.9 °C), final germination/seedling emergence was high at both locations (LNBG: 82%; Skukuza: 94%). Together with field observations, this study shows that (a) seed germination is rapid and with high percentages after being cued by warm to hot summer temperatures, a period when rainfall is also at its highest, and (b) that seedling recruitment depends on the availability of suitably shaded microsites. This is the first study on the regeneration ecology of an Adenium sp. and will aid both in situ and ex situ conservation of A. swazicum . [ABSTRACT FROM AUTHOR]

Background and Aims Models of costs and benefits of dormancy (D) predict that the evolutionarily stable strategy in long-term stable environments is for non-dormancy (ND), but this prediction remains to be tested empirically. We reviewed seed traits of species in the climatically buffered, geologically stable and nutrient-impoverished campo rupestre grasslands in Brazil to test the hypothesis that ND is favoured over D. We examined the relative importance of life-history traits and phylogeny in driving the evolution of D and assessed seed viability at the community level. Methods Germination and viability data were retrieved from 67 publications and ND/D was determined for 168 species in 25 angiosperm families. We also obtained the percentage of embryoless, viable and dormant seeds for 74 species. Frequencies of species with dormant and non-dormant seeds were compared with global databases of dormancy distribution. Key Results The majority of campo rupestre taxa (62·5 %) had non-dormant seeds, and the ND/D ratio was the highest for any vegetation type on Earth. Dormancy was unrelated to other species life-history traits, suggesting that contemporary factors are poor predictors of D. We found a significant phylogenetic structure in the dormancy categorical trait. Dormancy diversity was highly skewed towards the root of the phylogenetic tree and there was a strong phylogenetic signal in the data, suggesting a major role of phylogeny in determining the evolution of D versus ND and seed viability. Quantitative analysis of the data revealed that at least half of the seeds produced by 46 % of the surveyed populations were embryoless and/or otherwise non-viable. Conclusions Our results support the view that long-term climatic and geological stability favour ND. Seed viability data show that campo rupestre species have a markedly low investment in regeneration from seeds, highlighting the need for specific in situ and ex situ conservation strategies to avoid loss of biodiversity. [ABSTRACT FROM AUTHOR]

Despite the interest in restoring oak forests in Mexico, very little is known about their regeneration ecology. We assessed the influence of acorn burial depth on seed germination and seedling emergence for eight Mexican oak species (Q. affinis, Q. castanea, Q. coccolobifolia, Q. laeta, Q. mexicana, Q. polymorpha, Q. tinkhamii and Q. viminea). We performed a glasshouse experiment in which acorns were buried at five soil depths (0, 2, 4, 6 and 8 cm). After four months, acorn germination and seedling emergence were recorded. Buried acorns showed higher germination and seedling emergence than unburied ones, but burial depth also influenced these responses. The optimum burial depth for seedling emergence of each species was 2, 4, 6 and 8 cm depth for four species (Q. castanea, Q. mexicana, Q. tinkhamii, and Q. viminea); 2 and 4 cm for Q. laeta; as well as 2, 4 and 8 cm for Q. coccolobifolia.

Germination rate and seed mass are important factors determining the proportion of seedlings that become established in a habitat, especially where resources are limited and under adverse environmental conditions. Variation in seed attributes can determine a species' potential to adapt to new climates. This study aimed to investigate the germination behavior of Lytocaryum weddellianum along climatic gradients at two altitudes in the Serra dos Órgãos, Rio de Janeiro, Brazil. We conducted ex situ experiments on germination under two light conditions (light or dark) and three levels of water potential ( Ψ = 0, −0.4 or −0.8 MPa) over 8 months. In addition, seeds of different sizes were sown and after 6 months seedlings were divided into shoot and root components. The following growth parameters were measured: root, shoot and total biomass, leaf area, specific leaf area and leaf area ratio. Our results showed that the high- and low-altitude populations had different germination rates, seed mass, and resource allocation in seedlings. The lower altitude population, with higher temperatures and humidity, higher germination rates, produced heavier seeds, and their seedlings invested more in root and total biomass. Meanwhile, seedlings from the higher altitude site, with less available light, had a greater investment in foliar parameters. These differences in the two populations' seedling establishment strategies over an altitudinal gradient in the Serra dos Órgãos suggest that the species may have the potential to adapt to predicted climate change in this region. [ABSTRACT FROM AUTHOR]

Biofuel plants such as Jatropha curcas L. have potential to support the livelihoods of rural communities and contribute to sustainable rural development in Africa, if risks and uncertainties are minimized. Yet, recent papers have warned of the risk of biological invasions in such tropical regions as a consequence of the introduction of exotic biofuel crops. We investigated the seed dispersal risk and invasiveness potential of both J. curcas monoculture plantations and live fences into adjacent cultivated and uncultivated land use systems in Sissili province, Burkina Faso. Invasiveness potential was assessed through (i) detecting evidence of natural regeneration in perimeters around J. curcas plantations and live fences, (ii) assessing seed dispersal mechanisms, and (iii) assessing seedling establishment potential through in situ direct seed sowing. Spontaneous regeneration around the plantation perimeters of the three sites was very low. Individual seedling density around J. curcas live fences was less than 0.01 m in all sites. Seventy percent of the seedlings were found close to the live fence and most of them derived from the same year (96 %), which indicates low seed-bank longevity and seedling survival. J. curcas can be dispersed by small mammals and arthropods, particularly rodents and ants. In some sites, such as in Onliassan, high secondary seed dispersal by animals (up to 98 %) was recorded. There were highly significant differences in germination rates between seeds at the soil surface (11 %) and those buried artificially at 1-2-cm depth (64 %). In conclusion, we failed to find convincing evidence of the spreading of J. curcas or any significant impact on the surrounding environment. [ABSTRACT FROM AUTHOR]

Highlights: [•] We examined the crown architecture of dominant beech trees in the regeneration. [•] Crown irregularities are significantly related to light, regeneration age and density. [•] The occurrence of plagiotropic beech saplings decreases with increasing light. [•] The occurrence of forked and broom-shaped saplings increases with increasing light. [•] The number of saplings with unwanted architecture dropped dramatically over a 5-year period. [ABSTRACT FROM AUTHOR]

Abstract: Quercus rubra L. (northern red oak), a tree species having moderate shade tolerance, is failing to regenerate across its native range in North America, largely due to its inability to compete with shade-tolerant species. Throughout central Europe, where it was introduced in the 18th and 19th centuries, Q. rubra exhibits prolific regeneration even when growing with shade-tolerant trees under closed canopy conditions. A better understanding of factors that allow the proliferation of Q. rubra in its adventive range may provide insights into the conditions necessary to promote Q. rubra in North America. Our study investigated the regeneration dynamics of Q. rubra in six hardwood stands near Freiburg, Germany in relation to site conditions and the relative abundance and growth of indigenous tree species in forest understoreys. Despite high (94–98%) canopy closure at all stands, the density of Q. rubra regeneration (<2m in height) was greater than that of all other tree species combined, averaging 24stemsm−1. Density of Q. rubra seedlings reached 125stemsm−2 directly below seed trees; however, the lack of seedlings beyond 15m from a seed tree suggested limited seed dispersal. Seedlings were less abundant at relatively fertile sites with lowest densities corresponding most closely to elevated soil calcium. The abundance of Q. rubra was most highly variable in the midstorey (trees and shrubs >2.0m in height and <10cm diameter at breast height) with densities ranging from 200 to 1500stemsha−1. Periodic selective harvesting at all stands, appears to maintain a disturbed state of mid-succession that allows Q. rubra seedlings to persist and recruit into the midstorey as canopy gaps become available. Clearly, stands of this non-indigenous species are successfully regenerating and the dominance of Q. rubra appears to be sustainable. Despite its benign performance in North America, Q. rubra can be an effective competitor under suitable conditions. Our findings deemphasize the importance of canopy closure on Q. rubra regeneration and suggest that in North America, preliminary cuts performed prior to shelterwood harvests should focus on midstorey removal of competitor species especially following oak mast years. [Copyright &y& Elsevier]

Question: How does regeneration response to a host-specific, high-severity, infrequent Dendroctonus rufipennis outbreak differ from our conceptualization of high-severity, infrequent/low-severity, frequent disturbance regimes in Picea engelmannii- Abies lasiocarpa communities? Location: Southern Utah, USA. Methods: One hundred and seven plots across a high-elevation P. engelmannii forest were sampled to reconstruct pre-outbreak overstory and seedling bank densities, and calculate their associated metrics of diversity. Decade of establishment by seedling bank trees indicated 'chronic' and 'pulse' regenerators. Results: The post-outbreak overstory and seedling bank were dominated by A. lasiocarpa. Although Pinus flexilis, Pinus ponderosa, Picea pungens, and Psuedotsuga menziesii were present in the overstory, they were virtually absent in the seedling bank. Seedling bank recruitment of A. lasiocarpa and P. engelmannii has been occurring chronically for at least the last ∼205 and ∼152 years, respectively. A pulse response of seedling bank Populus tremuloides was apparent; however, results were complicated by intense ungulate browsing. Conclusions: Despite some similarities to the high-severity, infrequent/low-severity, frequent conceptualization of regeneration response to disturbance, the high-severity D. rufipennis outbreak is best described by explicitly considering host specificity and severity. Although, the outbreak simultaneously promoted both a pulse of P. tremuloides and a release of chronically regenerated A. lasiocarpa, the P. tremuloides response was generally masked by ungulate browsing, and the regeneration response came overwhelmingly from the A. lasiocarpa seedling bank. In this landscape, once dominated by P. engelmannii, the chronically regenerating seedling bank, typically thought to take advantage of canopy gaps associated with low-severity disturbances, is poised to dominate forest reorganization in response to the host-specific outbreak. [ABSTRACT FROM AUTHOR]

Despite the importance of seedling establishment in plant biology, there is no consensus on what constitutes a 'seedling'. Here we examined aspects of early plant development that could be used to mark the transition from the seedling to the post-seedling phase. Using a hypogeal species (pea, Pisum sativum) and an epigeal species (sunflower, Helianthus annuus), we investigated whether the utilization of cotyledon-stored mineral nutrients coincides with any changes in relative growth rate (RGR). We also examined how the timing of cotyledon removal at different points during early development affected subsequent growth. For both species, the timing of RGRmax, the exhaustion of cotyledon reserves, and the attainment of independence from cotyledons all roughly coincided (though exhaustion of seed reserves was not observed in the epigeal species because the cotyledons absorbed external nutrients). We conclude that because the point of attainment of RGRmax is a distinctly identifiable event, it is a more reliable marker for defining the end of the seedling stage than either the exhaustion of mineral reserves, or the cessation of dependence on cotyledon reserves. [ABSTRACT FROM AUTHOR]

Summary 1 The ability of seeds to survive desiccation is an important functional trait and is an integral part of plant regeneration ecology. Despite this, the topic has received relatively little attention from ecologists. In this study, we examine the relationships between seed desiccation tolerance and two important aspects of plant regeneration ecology: habitat and dormancy. This is done by comparative analysis of a data set of 886 tree and shrub species from 93 families. 2 The proportion of species displaying desiccation sensitive seeds declines as the habitat becomes drier, and possibly also cooler, although the latter observation requires cautious interpretation. Desiccation sensitivity is most common in moist, relatively aseasonal vegetation zones, but is infrequent in, though not absent from arid and highly seasonal habitats. 3 The highest frequency of desiccation sensitivity occurs in non-pioneer evergreen rain forest trees, although 48% of the species examined have desiccation tolerant seeds. In contrast, all pioneer taxa within the data set have drying tolerant seeds. 4 Desiccation sensitivity is more frequent in seeds that are non-dormant on shedding (c. 31%), than dormant (c. 9%). Highest frequencies of drying tolerance occur in seeds with physical or combinational dormancy, at 99% and 100%, respectively. 5 Although there is an association between non-dormancy and desiccation sensitivity in both tropical and temperate zones, the relationship does not appear to be causal. 6 Working from the hypothesis that seed desiccation sensitivity represents a derived state in extant species, we use the results to investigate and discuss possible ecological trade-offs and associated fitness advantages. These may explain the hypothesized repeated loss of this trait. The frequent association between large seed size and desiccation sensitivity is also considered. [ABSTRACT FROM AUTHOR]

The shortage of forest products and unsustainability of current land use practices experienced by many hillside farmers in the Caribbean is associated with increasing rates of conversion and degradation of remaining natural forests. This pressure could be alleviated by the establishment of trees in community/farm forests or more integrated agroforestry systems. Indigenous tree species are largely untried for these applications and represent an underexploited resource that may offer a good combination of tolerance of local environmental conditions, together with potential to restore degraded environments. These needs were addressed in the Blue Mountains of Jamaica in a study that combined: eliciting local people’s knowledge about the utility of tree species for a wide range of products and services, assessment of the ecological characteristics of the tree species, and testing the establishment and growth of selected species over three and a half years in on-farm environments.Detailed interviews were conducted with 16 male and 11 female local respondents. Together they reported on the uses of 80 taxa of trees and shrubs, 43 of them indigenous (each respondent naming, on average, 19 taxa). All but one of the trees already present on farmland were exotic, but the majority of respondents were interested in planting more trees. The overall local valuations of each of the species were calculated for 10 uses. Timber and fruit were the highest rated individual uses but, for planting, multipurpose tree species were valued most highly. The respondents were familiar with most, but not all, of the indigenous species that have been recognised as having high commercial timber value.Farm environments on the southern slopes of the Blue Mountains are subject to significant drought as well as frequent disturbance from fire. Fifty-eight tree species indigenous to the montane forests were assessed for their potential suitability for growing in this environment by two indices of their distribution and three of their ecology. Their potential for timber production was also assessed in terms of their maximum size and wood density. Twenty-four of these species (together with one other indigenous timber species and the most highly valued exotic multipurpose tree species) were selected for a species elimination trial with a blocked structure replicated in two sites. After 42 months the species were strongly differentiated in terms of their rates of survival (from 0 to 48%), diameter growth (from 1.7 to 5.1 cm increment over the 42 months for the montane forest species), height growth (84–258 cm increment) and crown and stem form. Performance of most species in the trial could be explained post hoc by selective reference to their distribution and ecological traits in the natural montane forests. However, none of the traits taken alone provided accurate predictions of species’ performance in the trial. The best prediction was provided by a classification of species’ regeneration type with pioneer species tending to do better and shade-tolerant species worse, however there were many exceptions. No relationship was found between species’ performance in the trial and their altitudinal range, abundance in southern slope forest, in secondary forests or on landslides, or their growth rate or maximum stem density in mature forest stands.From the combination of local valuation and trial performance 10 species are recommended for more detailed testing. Of the undomesticated indigenous species, Juniperus lucayana and Clethra occidentalis are particularly recommended, and it is suggested that Turpinia occidentalis, Cinnamomum montanum, Viburnum alpinum, Dendropanax arboreus, Podocarpus urbanii and Prunus occidentalis also be considered because of their good combination of establishment and utility. In addition, from the analysis of ecological characteristics a further 19 species (11 already known to be valued for their utility) are recommended for an additional trial. [Copyright &y& Elsevier]

The non-native invasive plant Chromolaena odorata (Asteraceae) was studied at 6 sites, with a chronosequence of ages from <1 to ≥15 years, at St Lucia, South Africa. C. odorata density, biomass, seed production and soil seed banks were quantified in three microsites: sun, semi-shade and shade. C. odorata density decreased with invasion age, apparently as a self-thinning process. Biomass per unit area and seed production/plant increased over the first 10 years, but declined greatly at ≥15 years. C. odorata plants grew larger and had much greater seed production in the sun relative to semi-shade, with small plants producing few if any seeds in the shade. Seed production in the sun varied from 2000 (<1-year old site) to 260 000 (10 year) seeds m−2 annum−1. About 20–46% of seeds produced were germinable and showed the same trend with age of invasion, but was particularly low after ≥15 years. Assessment of soil seed banks immediately prior to seed production (seed ≥10 months old), indicates that about 5–10% of seeds in the sun and 11–22% in the shade were still germinable, resulting in germinable seed densities of 12–385 and 158–511 m−2, respectively (excluding the ≥15-year old site). A greenhouse trial showed that burial of seeds, relative to those at the surface, and provision of less water, significantly improved seed persistence in the soil, while light intensity had no effect. Control of C. odorata is difficult due to rapid attainment of reproductive maturity, large production of wind-dispersed seeds and a short-term persistent seed bank. An integrated control strategy either excluding fire (coastal forest sites) or using fire prior to seed release in July/August to kill plants and soil-stored seeds immediately prior to seed production, together with biological, chemical and/or physical control, should be explored. [ABSTRACT FROM AUTHOR]