Abundance Of Cones Research Articles

Red foxes increase white spruce seed production at its northern range limit

The northern boreal forest treeline is usually considered to be the result of climate limiting tree reproduction. Although climate also influences the cycling of nutrients, the effects of nutrient availability on the treeline have largely been ignored. Various animal activities can alter nutrient cycling, creating microsites of highly fertile soil. Red foxes (Vulpes vulpes) act as ecosystem engineers in the nutrient-poor northern boreal woodlands by concentrating soil nutrients through their denning activities, increasing white spruce (Picea glauca) tree growth. Here, we examined how denning activity affects reproduction in white spruce by determining the number cones per tree, seeds per cone (with or without endosperm, i.e., filled or not) and their viability. Overall, seed production in the study region was low, with an average of 3.7 filled seeds and 0.73 viable seeds per cone. Denning activity affected all stages of seed production, with trees on dens producing an average of two times more cones, three times more total seeds, four times more filled seeds, and 18 times more viable seeds than trees growing away from dens. While cone counts per tree were a good predictor of filled seeds per tree, they were less reliable at predicting viable seeds per tree. Additionally, the number of cones on a tree does not predict the number of filled seeds in a cone, making it difficult for granivores like squirrels and birds to assess food availability from cone abundance. Overall, these results suggest that nutrient availability can play a crucial role in tree reproduction at the treeline and denning activities can create hotspots of seed production and seed viability, acting as a potential food source for granivores and locations for tree reproduction.

Spatial and Temporal Variation in the Antagonistic and Mutualistic Interactions among Seed Predator Arthropods, Seed-Dispersing Birds, and the Spanish Juniper.

Plants interact with both antagonistic and mutualistic animals during reproduction, with the outcomes of these interactions significantly influencing plant reproductive success, population dynamics, and the evolution of plant traits. Here, we investigated the spatial and temporal variations in the interactions between Juniperus thurifera, its seed-dispersing birds, and three specific arthropod species that attack the fleshy cones during the predispersal period. We assessed how plant traits affect levels of cone damage by arthropods and seed dispersal by birds, the occurrence of competition among arthropod species, and the impact of seed predators on the activity of frugivores. Plant traits, cone damage by arthropods, and seed dispersal by birds showed spatiotemporal variability. Fluctuation in cone abundance was the leading factor determining damage by arthropods and bird dispersal with a secondary role of cone traits. Large crops satiated predispersal seed predators, although the amount of frugivory did not increase significantly, suggesting a potential satiation of bird dispersers. Crop size and cone traits at individual trees determined preferences by seed predator species and the foraging activity of bird dispersers. Competition among arthropods increased during years of low cone production, and seed predators sometimes negatively affected bird frugivory. High supra-annual variations in cone production appear to be a key evolutionary mechanism enhancing J. thurifera reproductive success. This strategy reduces the impact of specialized seed predators during years of high seed production, despite the potential drawback of satiating seed dispersers.

Determining Photoreceptor Cell Identity: Rod Versus Cone Fate Governed by tbx2b Opposing nrl.

NRL is an influential transcription factor and central to animal modeling in ophthalmology. Disrupting NRL abrogates rod development and produces an excess of S-cones (also known as "UV cones" or "short-wavelength-sensitive1 [SWS1] cones"). Strikingly, mutations in zebrafish tbx2b produce the exact opposite phenotypes (excess rods and loss of SWS1 cones). We sought to define what genetic relationship exists, if any, between these transcription factors. We also infer whether these two phenotypes (altered rod abundance and altered SWS1 cone abundance) are independent versus inter-related. Zebrafish mutants were bred to disrupt nrl and tbx2b in concert. Rods and SWS1 cones were quantified and characterized at ultrastructural and transcriptional levels. Considering single mutant zebrafish, we confirmed previously established phenotypes and noted that the number of rods lost in nrl-/- mutants is reflected by a concomitant increase in SWS1 cone abundance. The tbx2b-/- mutants present the opposite phenotype(s) but exhibit a similar trade-off in cell abundances, with lots of rods and a concomitant decrease in SWS1 cones. Double mutant nrl-/-;tbx2b-/- zebrafish recapitulate the nrl-/- mutant phenotype(s). The tbx2b is thought to be required for producing SWS1 cones in zebrafish, but this can be over-ridden when nrl is absent. Regarding the altered cell abundances observed in either tbx2b-/- or nrl-/- mutants, the alterations in rod and SWS1 cones appear to not be two separate phenotypes but are instead a single intertwined outcome. The tbx2b and nrl are in an epistatic relationship, with nrl phenotypes dominating, implying that tbx2b is upstream of nrl in photoreceptor cell fate determination.

Patterns and drivers of early conifer regeneration following stand-replacing wildfire in Pacific Northwest (USA) temperate maritime forests

Tree regeneration is a critical mechanism of forest resilience to stand-replacing wildfire (i.e., where fire results in >90 % tree mortality), and post-fire regeneration is a concern worldwide as the climate becomes warmer. Although post-fire tree regeneration has been relatively well-studied in fire-prone forests across western North America, it is less understood in fire regimes characterized by large patches of stand-replacing fire at long intervals, such as the nominally infrequent, high-severity fire regimes of the western Cascades of Washington and northern Oregon, USA (northwestern Cascadia) where some of world’s highest-biomass forests reside. Recent wildfire activity (2015–2020) in northwestern Cascadia provides a unique opportunity to build understanding of the mechanisms underpinning forest resilience to fire, with implications for forest management and the myriad socio-ecological values associated with these landscapes. Here, we asked: how is post-fire conifer regeneration across northwestern Cascadia affected by pre-fire stand age, burn-patch size, and topo-climatic conditions? We established 39 1-ha long-term monitoring plots across four recent wildfires in northwestern Cascadia to measure post-fire conifer abundance and species composition. We used generalized linear models to test how rates of conifer regeneration (seedlings ha−1 yr−1 of all heights) and establishment (seedlings ha−1 yr−1 with heights >10 cm) respond to differences in pre-fire stand age/seral stage (young, mid-seral, late-seral), distance to the nearest live seed source, and post-fire topo-climate setting. In general, initial post-fire seedling densities suggest tree regeneration is abundant following stand-replacing fire in most areas across the region. For example, at 3–5 years post-fire, established seedlings were present in 100 % of plots, and regeneration and establishment levels exceeded state forest practices minimum density thresholds (470 seedlings ha−1) in 82.1 % and 64.1 % of plots, respectively. Post-fire conifer regeneration and tree species richness were greater when pre-fire stand age was older, and was more dominated by shade tolerant species than when pre-fire stand age was younger. Regeneration decreased with farther distances to the nearest live seed source, though seedlings were still moderately abundant at distances as far as 400 m from edges of high-severity patches. Conifer establishment was greater in areas characterized by cooler and wetter macrosite (e.g., greater post-fire precipitation) and microsite (e.g., greater bryophyte ground cover) conditions. By providing information on the drivers and conditions in which land managers can expect natural regeneration to occur or not, our findings are directly relevant to pre- and post-fire forest management objectives under future climate and increased fire activity in systems structured in part by infrequent and severe wildfires.

Fire‐regime variability and ecosystem resilience over four millennia in a Rocky Mountain subalpine watershed

Abstract Wildfires strongly influence forest ecosystem processes, including carbon and nutrient cycling, and vegetation dynamics. As fire activity increases under changing climate conditions, the ecological and biogeochemical resilience of many forest ecosystems remains unknown. To investigate the resilience of forest ecosystems to changing climate and wildfire activity over decades to millennia, we developed a 4800‐year high‐resolution lake‐sediment record from Silver Lake, Montana, USA (47.360° N, 115.566° W). Charcoal particles, pollen grains, element concentrations and stable isotopes of C and N serve as proxies of past changes in fire, vegetation and ecosystem processes such as nitrogen cycling and soil erosion, within a small subalpine forest watershed. A published lake‐level history from Silver Lake provides a local record of palaeohydrology. A trend towards increased effective moisture over the late Holocene coincided with a distinct shift in the pollen assemblage c. 1900 yr BP, resulting from increased subalpine conifer abundance. Fire activity, inferred from peaks in macroscopic charcoal, decreased significantly after 1900 yr BP, from one fire event every 126 yr (83–184 yr, 95% CI) from 4800 to 1900 yr BP, to one event every 223 yr (175–280 yr) from 1900 yr BP to present. Across the record, individual fire events were followed by two distinct decadal‐scale biogeochemical responses, reflecting differences in ecosystem impacts of fires on watershed processes. These distinct biogeochemical responses were interpreted as reflecting fire severity, highlighting (i) erosion, likely from large or high‐severity fires, and (ii) nutrient transfers and enhanced within‐lake productivity, likely from lower severity or patchier fires. Biogeochemical and vegetation proxies returned to pre‐fire values within decades regardless of the nature of fire effects. Synthesis. Palaeorecords of fire and ecosystem responses provide a novel view revealing past variability in fire effects, analogous to spatial variability in fire severity observed within contemporary wildfires. Overall, the palaeorecord highlights ecosystem resilience to fire across long‐term variability in climate and fire activity. Higher fire frequencies in past millennia relative to the 20th and 21st century suggest that northern Rocky Mountain subalpine ecosystems could remain resilient to future increases in fire activity, provided continued ecosystem recovery within decades.

Do Southeast Asia's paleo-Antarctic trees cool the planet?

Many tree genera in the Malesian uplands have Southern Hemisphere origins, often supported by austral fossil records. Weathering the vast bedrock exposures in the everwet Malesian tropics may have consumed sufficient atmospheric CO2 to contribute significantly to global cooling over the past 15 Myr. However, there has been no discussion of how the distinctive regional tree assemblages may have enhanced weathering and contributed to this process. We postulate that Gondwanan-sourced tree lineages that can dominate higher-elevation forests played an overlooked role in the Neogene CO2 drawdown that led to the Ice Ages and the current, now-precarious climate state. Moreover, several historically abundant conifers in Araucariaceae and Podocarpaceae are likely to have made an outsized contribution through soil acidification that increases weathering. If the widespread destruction of Malesian lowland forests continues to spread into the uplands, the losses will threaten unique austral plant assemblages and, if our hypothesis is correct, a carbon sequestration engine that could contribute to cooler planetary conditions far into the future. Immediate effects include the spread of heat islands, significant losses of biomass carbon and forest-dependent biodiversity, erosion of watershed values, and the destruction of tens of millions of years of evolutionary history.

Varying growth response of Central European tree species to the extraordinary drought period of 2018 – 2020

Droughts have intensified in Central Europe and will likely become a major driver of forest ecosystem change in the future. Regional studies are needed to understand drought impacts on forests and to provide guidance for adaptive management. In this study, we have investigated the effects of an extraordinary drought period in 2018 – 2020 on tree growth in the State of Bavaria (Germany). We (i) assessed overall changes in tree growth compared to pre-drought conditions, (ii) mapped the spatial configuration of drought and its impact on growth across ecoregions, (iii) quantified the standardized drought effect for the most abundant tree species, and (iv) analyzed the inter- and intraspecific variability in growth responses to drought.Covering a large environmental gradient, we compared 3,462 tree basal area growth records at 200 inventory plots with the pre-drought period of 2006 – 2017. We analyzed drought impacts on tree growth using nonparametric randomization tests and linear quantile mixed models (LQMMs).Median annual tree growth declined by 41.3% during drought. Decreases in growth were statistically significant for 13 out of 20 species. Growth reductions were most distinct in northwestern ecoregions of Bavaria. After controlling for other covariates of tree growth, the most abundant conifers, Picea abies [Karst.] and Pinus sylvestris [L.], were overall more susceptible than the common broadleaves, Fagus sylvatica [L.], Quercus robur [L.], and Quercus petraea [Matt.]. Yet, all species exhibited a high intraspecific variation in drought response.Altering tree species composition is a key strategy to adapt forest ecosystems. Our study reveals high potential to mitigate future drought impacts by admixing P. abies- and P. sylvestris-dominated forests with more drought-adapted broadleaved tree species. In addition, the high intraspecific variability in drought susceptibility indicates potential to promote provenances or individuals with low drought sensitivity to reduce the local loss of tree species.

Изменчивость репродуктивного развития полусибов плюсовых деревьев Pinus sibirica Du Tour

Selection of Pinus sibirica Du Tour plus trees by seed productivity, breeding of half-sibs, characterized by an abundance of cones and pollen, serve as the basis for the creation of high-yielding target plantations. The aim of the research was to select families with a large percentage of early reproductive development's trees, and specimens with a lot of cones and shoots with male inflorescences. Also, to select specimens in different families of Pinus sibirica Du Tour plus trees by early reproductive development, taking into account the formation of cones and pollen. The subject of the study was the seed progeny of Pinus sibirica Du Tour trees at biological age of 31-35 years, grown on the territory of the arboretum of Reshetnev University, the site «Prodolzhenie geoshkoly» (N 55.9666666667, E 92.6166666667, 287 meters above sea level). Initially, five plus trees growing in Irkutsk (60/24) and Novosibirsk regions (98/62, 102/66, 106/70 and 110/74) for reproduction among certified plus trees by seed productivity were selected. The growing conditions and indicators of plus trees from the certificate drawn up by the commission during their certification are given. Cones from these trees were collected, then seeds were sown and planting material was grown, which was transplanted to the site of the arboretum of Reshetnev University. In 2018, 2021 and 2022, the number of cones and microstrobiles in early reproductive development semis by using binoculars was determined. The variability by early reproductive development of half-sibs in the formation of cones both between families of plus trees (7.8-25.3 psc.), and within families (60/24 – 2-22 psc.; 98/62 – 2-115 psc.; 102/66 – 4-45 psc.;106/70 – 1-54 psc.; 110/74 – 1-15 psc.) is noted. The selection of specimens by the size of the cones was not carried out. Some specimens formed both cones and pollen: 82-7, 85-10 and 87-13 in the family of the plus trees 60/24; 72-11, 79-2, 79-3, 79-4, 79-8, 80-3, 81-4, 85-22 (family 98/62); 83-1,83-6, 83-9, 84-2, 84-4, 86-9, 86-1 (family 102/66); 78-3, 78-9, 81-8, 81-9, 81-10, 85-19 (family 106/70); 79-9, 84-12, 86-5 (family 110/74). Selected specimens have a huge value and can be widely used in their vegetative reproduction and the creation of high-yielding plantations of early reproductive development.

Drivers of twoneedle pinyon (Pinus edulis) cone productivity: Implication for wildlife

Seeds of twoneedle pinyon (Pinus edulis) serve as a nutritionally dense food resource for a myriad of wildlife. Pinyons exhibit synchronist masting with high cone production occurring every 4–7 years. Per-tree cone abundance may be influenced by tree-level and site-level features. Our goal was to identify features that influence pinyon cone abundance and determine how cone production relates to habitat selection by the Oscura Mountains Colorado chipmunk (Neotamias quadrivittatus oscuraensis), an old growth pinyon-juniper specialist and seed-caching rodent. We hypothesized increased cone abundance would be exhibited by older trees and at sites with increased water availability. We hypothesized that the chipmunk would select sites exhibiting increased 8-year cone production and annual cone abundance. We used double observer abscission scar counts on five branches per tree averaged between observers to estimate tree cone abundance for the most recent eight years. We used linear modeling to determine tree- and site-level features influencing per tree cone abundance, incorporating site as a random-intercept for tree-level models. The most influential tree-level feature was diameter, with larger diameter trees having greatest cone abundance. Percent defoliation in the living tree canopy exhibited an inverse relationship with cone abundance. Water availability of a site was represented by reproductive tree density and heat load, both of which inversely influenced per-tree cone abundance. However, reproductive tree density exhibited a positive relationship with cone production across a stand. Our data did not support the prediction that the chipmunk would select sites based on mean 8-year cone production, although there was a suggestion that it preferentially used sites with higher annual cone abundance during a high mast year. Though it requires further testing, sites that produce high cone abundance might be important for maintaining chipmunk metapopulations. We encourage management of pinyon-juniper woodlands to consider drivers of pinyon cone productivity and influence of cone production on wildlife. We urge the protection of old growth stands of pinyon-juniper woodland to support wildlife, as older trees are the most influential determinant of cone abundance and concurrently provide structural complexity important for wildlife. Lastly, our study indicates thinning of pinyon-juniper woodlands as unwarranted for the goal of increasing cone production. Maximizing pinyon cone production would be best met by maintaining dense old growth stands.

Late Pleistocene to early Holocene ENSO-related hydroclimatic changes revealed by palynological records from the coastal Xixi Basin, eastern China

We report a palaeontological record for the last 37.0 cal kyr BP in the Xixi Basin, eastern China, to better understand the correlation between hydroclimatic change and vegetation history during the late Pleistocene to early Holocene. Principal component analysis based on the 25 main palynological taxa indicated that dominant taxa fall into three groups: conifers that preferred dry conditions on the left of leading principal component (PC) 1, ferns and wetland communities associated with a humid climate responding to the positive loading of PC1, and Quercus-dominated communities principally corresponding to PC2. Based on this analysis, hydroclimatic conditions were relatively warm/dry during the latter Marine Isotope Stage (MIS) 3 with a high abundance of conifers. This was followed by a generally cold/wet MIS 2 with expansion of ferns and herbs, and a warm/dry MIS 1 with more evergreen species. The sporadic occurrence of evergreen species and drier conditions since about 19.0 cal kyr BP coincides with the beginning of the last deglaciation. An increase in sedimentary accumulation rates and changes in vegetation components at the onset of the Holocene are likely related to maximum transgression. Wet conditions coincide with several cold intervals, including Heinrich events and the Last Glacial Maximum. The overall warm/dry and cold/wet climatic patterns agree well with the palaeoclimatic records elsewhere in the middle Yangtze region, showing similar hydroclimatic forcing mechanisms related to the migration of the Meiyu Front modulated by the El Niño-Southern Oscillation (ENSO) activities. Cold/wet conditions probably correspond to enhanced ENSO and reduced insolation while warm/dry conditions correspond to dampened ENSO and increased insolation. The extremely humid conditions that occur during cold events may result from the combined effects of the Atlantic Meridional Overturning Circulation and ENSO. These results expand our understanding of the monsoonal hydroclimate in eastern China during the late Quaternary period.

Identification and Geomorphometric Characterization of Volcanic Cones in the Marius Hills, the Moon

AbstractInvestigation of the detailed geological characteristics of lunar volcanic cones can peer into their formation and emplacement processes, thus deepening our understanding of pyroclastic eruptions on the Moon. In this work, we focus on the Marius Hills region (centered at 13°N, 55°W), a volcanic plateau in south Oceanus Procellarum, which hosts the most abundant volcanic cones on the Moon, along with other volcanic features. The range of volcanic features indicates various eruption styles and complicated sequences of regional magmatic activities. Based on the SLDEM2015 topography data, with assistance from other multisource topography and image data sets, we identified 360 known and suspected volcanic cones and 22 volcanic domes in the Marius Hills. Following detailed morphological characterizations, the volcanic cones show various morphology types, including C‐shaped, elliptical‐shaped, elongated‐shaped, irregular‐shaped, and rounded‐shaped. The cones (median basal width ∼2.7 km, height ∼115 m, and volume 0.25 km3) contain summit pit craters (15%; median width ∼358 m), exhibiting smaller basal widths and summit pit crater widths compared with lunar mare domes. The mean slope (3.5°–15.6°) and rock abundance (0.3%–3.8%) of volcanic cones in Marius Hills are larger than those of the mare dome, suggesting different eruption mechanisms. Marius Hills cones also show larger basal widths and smaller height/width ratios than terrestrial volcanic cones, which are attributed to multiple factors, including subaerial environment, volatile content of the magma, eruption rate, and lava viscosity.

Satellite data reveal differential responses of Swiss forests to unprecedented 2018 drought.

Extreme events such as the summer drought of 2018 in Central Europe are projected to occur more frequently in the future and may cause major damages including increased tree mortality and negative impacts on forest ecosystem services. Here, we quantify the response of >1 million forest pixels of 10 × 10 m across Switzerland to the 2018 drought in terms of resistance, recovery, and resilience. We used the Normalized Difference Water Index (NDWI) derived from Sentinel‐2 satellite data as a proxy for canopy water content and analyzed its relative change. We calculated NDWI change between the 2017 pre‐drought and 2018 drought years (indicating resistance), 2018 and the 2019 post‐drought (indicating recovery), and between 2017–2019 (indicating resilience). Analyzing the data from this large natural experiment, we found that for 4.3% of the Swiss forest the NDWI declined between 2017 and 2018, indicating areas with low resistance of the forest canopy to drought effects. While roughly 50% of this area recovered, in 2.7% of the forested area NDWI continued to decline from 2018 to 2019, suggesting prolonged negative effects or delayed damage. We found differential forest responses to drought associated with site topographic characteristics and forest stand characteristics, and to a lesser extent with climatic conditions and interactions between these drivers. Low drought resistance and high recovery were most prominent at forest edges, but also on south‐facing slopes and lower elevations. Tree functional type was the most important driver of drought resilience, with most of the damage in stands with high conifer abundance. Our results demonstrate the suitability of satellite‐based quantification of drought‐induced forest damage at high spatial resolution across large areas. Such information is important to predict how local site characteristics may impact forest vulnerability to future extreme events and help in the search for appropriate adaptation strategies.

Facilitation differentially affects competitive responses of aspen and subalpine fir through stages of stand development

AbstractSpatial interactions between trees influence forest community succession. The objective of this study was to investigate how shifts in forest composition and proximity between tree species affect stand development over time in mixed forest systems. At six locations across the Fishlake National Forest, Utah, USA, in stands where facilitation has been documented previously, tree‐ring samples were collected from aspen and subalpine fir trees. Basal area increment was calculated to characterize the effects of the proximity of overstory trees on multidecadal growth responses of aspen and subalpine fir in aspen‐dominant and mixed aspen–conifer stands. Subalpine fir seedlings were established next to aspen (within 10 cm) when aspen was between 15 and 120 years old with a mean age of 60 years. Aspen and subalpine fir growth rates were reduced with increasing conifer abundance. Aspen trees growing next to a proximate subalpine fir tree had slower growth rates over time than aspen trees growing independently. Growth rates of subalpine fir in aspen‐dominated stands were similar when growing independently or near aspen trees. However, subalpine fir in conifer‐dominated stands maintained higher growth rates when growing next to an aspen tree than when growing independently. The data suggest that as stand competition increases with conifer abundance, the proximity of overstory trees increases competitive exclusion of aspen while having a beneficial growth effect on subalpine fir. These results underscore the importance of maintaining natural fire regimes in forest systems that keep competitive interactions in balance.

Contrasting Litter Nutrient and Metal Inputs and Soil Chemistry among Five Common Eastern North American Tree Species

Forest composition has been altered throughout Eastern North America, and changes in species dominance may alter nutrient cycling patterns, influencing nutrient availability and distribution in soils. To assess whether nutrients and metals in litterfall and soil differed among sites influenced by five common Ontario tree species (balsam fir (Abies balsamea (L.) Mill.), eastern hemlock (Tsuga canadensis (L.) Carr.), white pine (Pinus strobus L.), sugar maple (Acer saccharum Marsh.), and yellow birch (Betula alleghaniensis Britt.)), litterfall and soil chemistry were measured at a managed forest in Central Ontario, Canada. Carbon (C) and macronutrient (nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg)) inputs in litterfall varied significantly among sites, primarily due to differences in litterfall mass, which was greatest in deciduous-dominated sites, while differences in elemental concentrations played relatively minor roles. Trace metal inputs in litterfall also varied, with much higher zinc (Zn) and cadmium (Cd) in litterfall within yellow birch dominated stands. Mineral soil oxide composition was very similar among sites, suggesting that differences in soil chemistry were influenced by forest composition rather than parent material. Litter in deciduous-dominated stands had lower C/N, and soils were less acidic than conifer-dominated sites. Deciduous stands also had much shorter elemental residence times in the organic horizons, especially for base cations (Ca, Mg, K) compared with conifer-dominated sites, although total soil nutrient pools were relatively consistent among sites. A change from stands with greater conifer abundance to mixed hardwoods has likely led to more rapid cycling of elements in forests, particularly for base cations. These differences are apparent at small scales (100 m2) in mixed forests that characterize many forested regions in Eastern North America and elsewhere.

Effects of Sitka spruce masting on phenology and demography of siskins Spinus spinus

Masting behaviour of Sitka spruce Picea sitchensis may influence Eurasian siskin Spinus spinus breeding ecology as breeding siskins specialize on spruce seeds. We caught siskins and other small passerines over 16 years using mist nets adjacent to large plantations of mature Sitka spruce. We sexed, aged, measured and weighed the birds and collected feather samples from fledglings to measure nitrogen and carbon stable isotope ratios. Siskins departed in late summer, and returned, and bred earlier in years of higher cone abundance. Nitrogen and carbon isotopes indicated that siskins fed their chicks on Sitka spruce seeds in most years, and more so in years of high cone production. More siskins were caught following heavy rainfall, when the cones had closed, encouraging the birds to seek alternative food sources. Fledglings were not heavier or larger in years with higher cone crops but were more numerous. However, the age ratio of siskins caught the following year was unaffected by cone crop. Given their reliance on Sitka spruce seeds, climate change may have a major impact on siskin numbers by altering the availability of Sitka spruce seeds, either through changes in masting patterns or cone opening, or due to climate-related changes in forestry practices. Siskins represent a valuable study system to conservation ecology, where a native species is ecologically reliant on introduced taxa.

Seafood Salad: A diverse latest Cretaceous flora from eastern Montana

The Cretaceous-Paleogene boundary (KPB) marks a mass extinction resulting in global biotic turnover. Exposures of the Hell Creek Formation in northeastern Montana contain some of the most well-studied vertebrate localities recording this mass extinction; however, very little is known of the floral record in this area. As part of an effort to reconstruct floral changes across the KPB in northeastern Montana, this study presents a taxonomically diverse flora from the Seafood Salad locality, located ~65 m below the KPB in the Hell Creek Formation, Garfield County, Montana. Leaves, stems, and reproductive structures (e.g., cones and seeds) are preserved as compression and impression fossils in massive, bedded siltstones and very fine sandstones. Seafood Salad is significant in that it represents a “pre-disaster” community approximately 1.3 m.y. before the Cretaceous-Paleogene mass extinction. We interpret the plants in these deposits as reflecting a local riparian community. The vegetation was taxonomically diverse and dominated by angiosperm trees; it also included abundant conifer specimens of a few taxa and relatively few ginkgoes and ferns. We describe 34 morphotypes and propose taxonomic affinities to modern groups and to fossil taxa from contemporaneous-age deposits in Montana and North Dakota. The Seafood Salad flora shares several taxa with other Late Cretaceous floras of the Western Interior, but substantial differences in taxonomic composition and relative abundances among these assemblages indicate that regional plant communities in the latest Cretaceous were spatially heterogeneous, rapidly changing, or both.

Climate and size of previous cone crops contribute to large-scale synchronous cone production in balsam fir

Mast year occurrence in trees is often synchronized across large regions. In this study, we used dendrochronological methods based on cone scar characteristics on tree branches in order to reconstruct male and female cone production in balsam fir (Abies balsamea (L.) Mill.) during the period 1988–2018. Results indicate that mast years generally occur every second year and can be synchronized across distances >1000 km. The main predictors of current-year cone abundance were cone abundance during the two previous years, which can be considered a proxy for resource availability for cone bud development during the current year, together with relatively warm temperature during cone bud development. Presence of aborted male cones was positively correlated with the occurrence of relatively cold episodes during cone bud development. This finding suggests that the influence of weather on cone crop abundance is at least partly mediated by growth cessation in the developing cone buds. We also suggest that a change in weather patterns before and after the 2005–2010 period is responsible for a switch in mast years from even to uneven calendar years around that time.

Drought-Induced Xylem Embolism Limits the Recovery of Leaf Gas Exchange in Scots Pine.

Climate change increases the occurrence of prolonged drought periods with large implications for forest functioning. Scots pine (Pinus sylvestris) is one of the most abundant conifers worldwide, and evidence is rising that its resilience to severe drought is limited. However, we know little about its ability to recover from drought-induced embolism. To analyze postdrought hydraulic recovery, we investigated stress and recovery dynamics of leaf gas exchange, nonstructural carbohydrates, and hydraulic properties in 2.5-year-old Scots pine seedlings. We quantified the degree of xylem embolism by combining in vivo x-ray microtomography with intrusive techniques including measurements of hydraulic conductivity and dye staining during drought progression and short-term (2 d) and long-term (4 weeks) recovery. Seedlings were grown under controlled conditions, and irrigation was withheld until stomata closed and xylem water potential declined to -3.2 MPa on average, causing a 46% loss of stem hydraulic conductivity. Following drought release, we found a gradual recovery of leaf gas exchange to 50% to 60% of control values. This partial recovery indicates hydraulic limitations due to drought-induced damage. Whereas xylem water potential recovered close to control values within 2 d, both x-ray microtomography and intrusive measurements revealed no recovery of stem hydraulic conductivity. Moreover, we did not find indications for nonstructural carbohydrate reserves limiting hydraulic recovery. Our findings demonstrate that Scots pine is able to survive severe drought and to partially recover, although we assume that xylem development during the next growing season might compensate for some of the hydraulic impairment. Such drought-induced legacy effects are important when considering vegetation responses to extreme events.

Reproductive maturity and cone abundance vary with tree size and stand basal area for two widely distributed conifers

AbstractUnderstanding potential limitations to tree regeneration is essential as rates of tree mortality increase in response to direct (extreme drought) and indirect (bark beetle outbreaks, wildfire) effects of a warming climate. Seed availability is increasingly recognized as an important limitation for tree regeneration. High variability in seed cone production is a trait common among many northern temperate conifers, but few studies examine the determinants of individual tree cone production and how they vary with stand structure. In subalpine forests in the southern Rocky Mountains, USA, we monitored >1600 Picea engelmannii (Engelmann spruce) and Abies lasiocarpa (subalpine fir) trees for cone presence (an indicator of reproductive maturity) and a subset of those trees for cone abundance (an indicator of seed production) from 2016 to 2018. We constructed mixed models to test how individual tree cone presence and cone abundance were affected by tree size and age as well as forest attributes at the neighborhood‐ and stand‐scales. The probability of cone presence and cone abundance increased with tree size and age for A. lasiocarpa and P. engelmannii. The youngest ages of trees with cones present were more than 100 yr later for individuals in high basal area (BA) stands (>65 m2/ha) relative to low BA stands (<25 m2/ha). P. engelmannii produced many more cones than A. lasiocarpa at similar sizes, especially in young, low BA stands. Our findings reveal how differences in tree sizes and stand structures typically associated with time since last disturbance can affect seed production patterns for decades to well over a century. The consistent regional pattern of earlier and more abundant postfire establishment of P. engelmannnii vs. the delayed postfire establishment by A. lasiocarpa may be partially explained by species’ differences in cone abundance by stand structure. The increasing loss of large, dominant cone‐producing trees will significantly reduce seed production to support future tree regeneration and maintain forest cover. However, seed availability and resilience following disturbances may be less limiting than expected for species like P. engelmannii that have the capacity to produce more cones in open‐canopy forests, such as recently disturbed areas.

Amber- and plant-bearing deposits from the Cenomanian of Neau (Mayenne, France)

A new Cenomanian amber- and plant-bearing deposit has been discovered at Neau, in the Mayenne department (France). The Cenomanian fossiliferous lignites are located in karst filling in a substratum of Cambrian limestones. The amber corresponds mainly to tiny millimetric grains, devoid of arthropod inclusions, but rich in microorganisms, especially the sheated bacteriaLeptotrichites resinatus, and containing pollen grains (Classopollis) and wood fibers (Araucariacae or Cheirolepidiaceae). The lignites provide abundant conifer and ginkgoale cuticle fragments (Frenelopsis,Eretmophyllum) and a lot of palynomorphs (e.g. Gleicheniidites senonicus,Cyathidites,Deltoidospora,AppendicisporitesandCicatricosisporites). The chemical signature of the amber suggests it was produced by conifers of the extinct family Cheirolepidiaceae. According to the palynological assemblage, the age of the lignites is upper lower Cenomanian or lower mid Cenomanian. The deposit environment corresponded to the upstream portion of a mangrove or the most inner part of a lagoon.