Northern Sites Research Articles

Transplanting larch trees into warmer areas increases the photosynthesis and its temperature sensitivity.

To investigate the effects of climate warming on photosynthesis, Dahurian larch (Larix gmelinii Rupr.) trees from four sites (spanning ~ 5.5° in latitude and~4 °C of warming) within the geographic range in China were transplanted into a common garden close to the warmer border in 2004. Throughout the growing season of 2018, the CO2- and temperature-response curves of the photosynthesis in the common garden and at the original sites were measured. It was discovered that warming treatment considerably increased the maximum net photosynthetic rate (Amax) by 23.4-35.3% depending on the sites, signifying that warming upregulated Amax with respect to the degree of warming. At 25 °C, warming enhanced the maximum Rubisco carboxylation rate (Vcmax), maximum electron transport rate (Jmax), and mass-based leaf nitrogen concentration (Nmass). The climate warming effect (CWE) on Amax was positively associated with the CWEs on Vcmax, Jmax and Nmass, which indicated that warming promoted Amax primarily via increasing carboxylation and photosynthetic electron transport rates and leaf nitrogen supply. The CWE in optimal photosynthetic temperature (Topt) was significant for the trees from the northern sites rather than the southern sites; however, the effect vanished for the trees transplanted to the common garden; this implied that Topt exhibited limited local thermal acclimation. Nevertheless, warming narrowed the temperature-response curve, the effect of which was positively associated with the warming magnitude. These findings implied that trees transplanted into warmer areas changed the photosynthetic optimum temperature and sensitivity. In summary, our results deepen the understanding of the underlying mechanisms of intraspecific responses of photosynthesis to temperature changes, including which of the modeling would improve the prediction of tree growth and forest carbon cycling under climate warming.

Late frost as a driver of ecotypic differentiation in sugar maple: Implications for assisted migration

Global warming advances bud break, mismatches plant phenology from the local climate, and exposes the developing leaves to higher risks of frost damage. Bud break of sugar maple [Acer saccharum (Marsh.)], a species included in recent programs of assisted migration, is sensitive to nighttime spring temperatures. This suggests a link between frost events and leaf development. In this study, we raise the hypothesis that late frost is an evolutionary driver of growth reactivation in sugar maple provenances. We investigated the ecotypic variation of bud phenology in 30 provenances planted in two common gardens within and at the northern limit of the species range, in the Province of Quebec, Canada. Eight phases of bud break were assessed twice a week during 2020 on 252 and 272 seedlings in southern and northern sites, respectively. In the southern site, bud break occurred in May, starting on average 12 days earlier and ending 3 days earlier compared to the northern site. Logistic regression was used to estimate the probability of late frost and the results showed that regions located in the north, at higher elevations, and along the northeastern coast of the native maple range showed the latest occurrences of frost events in spring. This pattern mirrored the timing of bud break. When planted in the same common garden, provenances originating from sites with later spring frosts leafed out earlier. Such differences were maintained across the eight bud phenological phases and between the two common gardens, which indicates a similar response of the provenances to changing growing conditions. To avoid frost damage to sugar maple plantations, assisted migration should account for phenotypic traits in bud phenology, ensuring that the frost regime at the origin of the provenances is compatible with that of plantations.

Exploring the role of bedrock representation on plant transpiration response during dry periods at four forested sites in Europe

Abstract. Forest transpiration is controlled by the atmospheric water demand, potentially constrained by soil moisture availability, and regulated by plant physiological properties. During summer periods, soil moisture availability at sites with thin soils can be limited, forcing the plants to access moisture stored in the weathered bedrock. Land surface models (LSMs) have considerably evolved in the description of the physical processes related to vegetation water use, but the effects of bedrock position and water uptake from fractured bedrock have not received much attention. In this study, the Community Land Model version 5.0 (CLM 5) is implemented at four forested sites with relatively shallow bedrock and located across an environmental gradient in Europe. Three different bedrock configurations (i.e., default, deeper, and fractured) are applied to evaluate if the omission of water uptake from weathered bedrock could explain some model deficiencies with respect to the simulation of seasonal transpiration patterns. Sap flow measurements are used to benchmark the response of these three bedrock configurations. It was found that the simulated transpiration response of the default model configuration is strongly limited by soil moisture availability at sites with extended dry seasons. Under these climate conditions, the implementation of an alternative (i.e., deeper and fractured) bedrock configuration resulted in a better agreement between modeled and measured transpiration. At the site with a continental climate, the default model configuration accurately reproduced the magnitude and temporal patterns of the measured transpiration. The implementation of the alternative bedrock configurations at this site provided more realistic water potentials in plant tissues but negatively affected the modeled transpiration during the summer period. Finally, all three bedrock configurations did not show differences in terms of water potentials, fluxes, and performances on the more northern and colder site exhibiting a transition between oceanic and continental climate. Model performances at this site are low, with a clear overestimation of transpiration compared to sap flow data. The results of this study call for increased efforts into better representing lithological controls on plant water uptake in LSMs.

Kelp Patch-Specific Characteristics Limit Detection Capability of Rapid Survey Method for Determining Canopy Biomass Using an Unmanned Aerial Vehicle

Kelp forests dominate autotrophic biomass and primary productivity of approximately 30,000 to 60,000 km of shallow temperate and Arctic rocky reef coastline globally and contribute significantly to carbon cycling in the coastal ocean. Rapid biomass turnover is driven by very high growth rates and seasonal environmental drivers. As a result, kelp biomass varies greatly with time, space, and by species. In the northeast Pacific region, bull kelp (Nereocystis leutkeana) and giant kelp (Macrocystis pyrifera) form extensive floating surface canopies with a distinct spectral signature compared to the surrounding water. Studies have shown that remote sensing is advantageous for deriving large-scale estimates of floating surface canopy biomass, which comprises more than 90% of bull and giant kelp standing stock. However, development and validation of remotely derived kelp canopy biomass is lacking because existing approaches are time intensive and costly. This study attempted to close that gap by developing a rapid survey design utilizing diver and unmanned aerial vehicle (UAV) imagery across six sites in northern and central California. Kelp sporophytes were collected and measured for morphometric characteristics and genera-specific allometry to canopy biomass. Kelp density was measured using in situ diver surveys and coupled with UAV imagery to quantify kelp canopy biomass at a range of ground sampling distances. We successfully estimated kelp canopy biomass from UAV imagery at 33% (2/6) of the survey sites, but consistently determining canopy biomass via this approach was challenged by both survey design and kelp patch-specific spatial characteristics. The morphologies of bull kelp in Monterey were significantly different than other regions measured, but further work should be conducted to fully characterize differences in canopy biomass at the regional and sub-regional scale. We use this opportunity to suggest survey design strategies that will increase the success of future methodological development of UAV biomass retrieval. We also recommend developing long-term, annual genera-specific monitoring programs across the northeast Pacific region and beyond to validate remote sensing derived biomass estimates beyond the small number of existing well-characterized sites.

Tree Maladaptation Under Mid-Latitude Early Spring Warming and Late Cold Spell: Implications for Assisted Migration.

Global warming is predicted to extend the growing season of trees and plants, and advance spring phenology. However, intensification of extreme climate events in mid-latitude forests, from weakening of the jet stream and atmospheric blockings, may expose trees to increased risk associated with more frequent late-spring frosts. Still, little is known regarding the intraspecific variation in frost tolerance and how it may be shaped by local adaptation to the climate of seed origin. As part of an assisted migration trial located in different bioclimatic zones in the province of Quebec, Canada, and following an extensive late-spring frost that occurred at the end of May 2021, we evaluated the frost damages on various white spruce (Picea glauca) seed sources tested on three sites (south, central, and north). The severity of frost damages was assessed on 5,376 trees after the cold spell and an early spring warming which advanced bud flush by approximately 10 days on average. The frost damage rate was similar among sites and seed sources and averaged 99.8%. Frost damage severity was unrelated to the latitude of seed origin but was variable among sites. The proportion of severely damaged trees was higher in the northern site, followed by central and southern sites. The proportion of severely damaged trees was linearly and inversely related to tree height before the frost event. Apical growth cancelation was not significantly different among seed sources including local ones, and averaged 74, 46, and 22%, respectively, in central, northern, and southern plantation sites. This study provides recommendations to limit the loss of plantation productivity associated with such a succession of spring climate anomalies. Implications for seed transfer models in the context of climate change and productivity of spruce plantations are discussed in the light of lack of local adaptation to such pronounced climate instability and ensuing large-scale maladaptation.

Benthic Organic Matter Transformation Drives pH and Carbonate Chemistry in Arctic Marine Sediments

AbstractCarbonate chemistry of the Arctic Ocean seafloor and its vulnerability to ocean acidification remains poorly explored. This limits our ability to quantify how biogeochemical processes and bottom water conditions shape sedimentary carbonate chemistry, and to predict how climate change may affect such biogeochemical processes at the Arctic Ocean seafloor. Here, we employ an integrated data‐model assessment that explicitly resolves benthic pH and carbonate chemistry along a South—North transect in the Barents Sea. We identify the main drivers of observed carbonate dynamics and estimate benthic fluxes of dissolved inorganic carbon and alkalinity to the Arctic Ocean. We explore how bottom water conditions and in‐situ organic matter degradation shape these processes and show that organic matter transformation strongly impacts pH and carbonate saturation (Ω) variations. Aerobic organic matter degradation drives a negative pH shift (pH < 7.6) in the upper 2–5 cm, producing Ω < 1. This causes shallow carbonate dissolution, buffering porewater pH to around 8.0. Organic matter degradation via metal oxide (Mn/Fe) reduction pathways further increases pH and carbonate saturation state. At the northern stations, where Ω > 5 at around 10–25 cm, model simulations result in authigenic carbonate precipitation. Furthermore, benthic fluxes of dissolved inorganic carbon (12.5–59.5 μmol cm−2 yr−1) and alkalinity (11.3–63.2 μmol cm−2 yr−1) are 2–3‐fold greater in the northern sites due to greater carbonate dissolution. Our assessment is of significant relevance to predict how changes in the Arctic Ocean may shift carbon burial and pH buffering into the next century.

Hydrothermal activity and associated subsurface processes at Niuatahi rear-arc volcano, North East Lau Basin, SW Pacific: Implications from trace elements and stable isotope systematics in vent fluids

Hydrothermal activity is abundant in the area between the North Eastern Lau Spreading Center and the Tofua intra-oceanic island arc with multiple active sites in the rear-arc at the Mata and Niuatahi volcanoes. We report geochemical data for high-temperature vent fluids sampled from within the caldera of Niuatahi volcano. Hydrothermal fluids were sampled from three vent sites: South Central, Southwestern Cone and Northern Cone located in water depths between 1607 and 1699 m. Maximum temperatures of 334 °C were measured and pH values were as low as 2.8. The vent fluids were characterized by depletions in Mg, SO4 and U as well as an enrichment of (trace) metals (e.g., Fe, Mn, K, Li) and dissolved gases (e.g., H2S, CO2, H2) relative to seawater. Water-rock ratios calculated based on concentrations (K, Li, Rb, Cs, REE) and isotope ratios (δ7Li, δ11B, 87Sr/86Sr) suggest fluid-rock interactions under rock-dominated conditions at all three vent sites.The South Central vents lie closest to the site of most recent volcanic activity in the Niuatahi caldera. Vent fluids are characterized by relatively low Cl concentrations (as low as 292 mmol/kg) that are indicative of sub-critical phase separation. These fluids also had the lowest pH values (2.8–3.1), highest H2S and lowest H2, CH4 and CO2 concentrations of the three sites. The δD and δ18O values suggest that H2O and CO2 were added in small amounts by subduction-related volcanic vapors. However, there was no evidence for magmatic SO2 input in the vent fluids at the time of sampling in 2018. Vent fluids from the Northern and Southwestern Cone sites on the caldera ring fault had a similar chemical composition, despite being situated at opposite sides of the caldera. Fluids from these sites had lower Fe/Mn ratios (<1) and H2S concentrations than those from South Central suggesting that they were affected by subsurface cooling and sulfide precipitation. This study indicates variations of the Niuatahi hydrothermal vent sites depending on the location within the caldera with variable effects of fluid-rock interaction and magmatic input on fluid compositions in agreement with previous work on fluid S isotopes and sulfides.

Genetic diversity and connectivity of chemosynthetic cold seep mussels from the U.S. Atlantic margin

BackgroundDeep-sea mussels in the subfamily Bathymodiolinae have unique adaptations to colonize hydrothermal-vent and cold-seep environments throughout the world ocean. These invertebrates function as important ecosystem engineers, creating heterogeneous habitat and promoting biodiversity in the deep sea. Despite their ecological significance, efforts to assess the diversity and connectivity of this group are extremely limited. Here, we present the first genomic-scale diversity assessments of the recently discovered bathymodioline cold-seep communities along the U.S. Atlantic margin, dominated by Gigantidas childressi and Bathymodiolus heckerae.ResultsA Restriction-site Associated DNA Sequencing (RADSeq) approach was used on 177 bathymodiolines to examine genetic diversity and population structure within and between seep sites. Assessments of genetic differentiation using single-nucleotide polymorphism (SNP) data revealed high gene flow among sites, with the shallower and more northern sites serving as source populations for deeper occurring G. childressi. No evidence was found for genetic diversification across depth in G. childressi, likely due to their high dispersal capabilities. Kinship analyses indicated a high degree of relatedness among individuals, and at least 10–20% of local recruits within a particular site. We also discovered candidate adaptive loci in G. childressi and B. heckerae that suggest differences in developmental processes and depth-related and metabolic adaptations to chemosynthetic environments.ConclusionsThese results highlight putative source communities for an important ecosystem engineer in the deep sea that may be considered in future conservation efforts. Our results also provide clues into species-specific adaptations that enable survival and potential speciation within chemosynthetic ecosystems.

Linkages between the temperature sensitivity of soil respiration and microbial life strategy are dependent on sampling season

The temperature sensitivity (Q10) of soil respiration (Rs) is crucial to assess the carbon (C) budget of terrestrial ecosystems under global warming. The Q10 changes along a climatic gradient as well as its seasonal dynamics remain unclear, and the underlying microbial mechanisms are not well known. Here, the seasonal Q10 of Rs at the northern, middle, and southern sites of a natural temperate mixed forest was examined. The mean annual temperature (MAT) of the sampling sites spanned from 0.5 to 4.9 °C. The Q10 pattern over the climatic zones was highly dependent on season, with Q10 increasing toward the southern region in spring and autumn, but having a similar level across the sampling sites in summer. In spring, Q10 was independent of microbial community composition and functions. Instead, spring Q10 increased with decreasing C availability from north to south, consistent with the Carbon-Quality-Temperature theory. In summer, Q10 was closely associated with the dominance of microbial r-strategy features, characterized by high copiotroph/oligotroph and labile/recalcitrant C degradation gene ratios. In autumn, however, Q10 was driven by the K-selected microbial communities, which might have been ascribed to the priming effects mediated by fresh plant litter. The seasonality of Q10 was site-dependent. The southern and middle sites had the lowest Q10 in summer, consistent with the Seasonal Plasticity Hypothesis, which predicts lower temperature sensitivity in warmer seasons. In contrast, the Q10 at the northern site remained stable during the growing season due to minor seasonal fluctuations in plant litter inputs and microbial community composition and functions. This work deepens our understanding on the complex relationships between Q10, carbon availability and microorganisms over spatial and temporal scales by translating microbial phylogenetic data into life strategies.

Improvement of soil fertility in historical ridge and furrow cultivation

AbstractRidge and furrow cultivation is the most widely used agricultural technique in medieval and postmedieval Europe, but the fertilization of soils during their use is not yet fully understood. Pedological analyses of this cultivation technique provided information, which led to the assumption that some of the investigated sites in Northern and Central Germany were manured with livestock excrements during cultivation. The objective of this study is to determine whether and how the soils have been fertilized and which materials were applied for this purpose. We investigated soils at five sites using phosphate and steroid analyses (stanols and bile acids), black carbon analyses, and a micromorphology study. The results showed that livestock waste was likely used as fertilizer at four of the five studied sites at low intensities, with pigs and herbivores being the probable sources of the excrement. But also the application of human feces to the soil might be possible at least at one site. Often used agricultural methods such as plaggen cultivation and an intentional charcoal input to enhance soil fertility could not be clearly verified for our study sites.

Landscape connectivity among coastal giant salamander (Dicamptodon tenebrosus) populations shows no association with land use, fire frequency, or river drainage but exhibits genetic signatures of potential conservation concern.

Determining the genetic consequences of both historical and contemporary events can clarify the effects of the environment on population connectivity and inform conservation decisions. Historical events (like glaciations) and contemporary factors (like logging) can disrupt gene flow between populations. This is especially true among species with specialized ecological requirements and low dispersal ability, like amphibians. We test for the genetic consequences of historical and contemporary disturbances in the coastal giant salamander (Dicamptodon tenebrosus) in the Pacific Northwest of the United States. We consider predictions based on the contemporary landscape (habitat connectivity, logging, forest fires, and topography), in addition to relatively ancient post-Pleistocene range expansion (following the last glacial retreat). To assess local versus larger-scale effects, we sampled 318 individuals across 23 sites, which were clustered in five sampling regions. Genetic variation was assessed using five microsatellite markers. We found evidence of (i) historical regional isolation, with decreased genetic diversity among more recently colonized northern sites, as well as (ii) high levels of inbreeding and loss of heterozygosity at local scales, despite relatively low overall population differentiation (FST) or strong evidence for population bottlenecks. Genetic diversity was not associated with contemporary disturbances (logging or fire), and there were no detectable effects on the genetic connectivity of populations based on intervening landscape features (habitat fragmentation and topography). However, lower genetic diversity in more northern regions indicates a lag in recovery of genetic diversity following post-Pleistocene expansion. Additionally, some populations had evidence of having undergone a recent genetic bottleneck or had high inbreeding (FIS) values. Lower genetic diversity in more northern sites means populations may be more vulnerable to future environmental changes, and managing for connectivity alone may not be sufficient given low mobility. Recent apparent reductions in some populations were not clearly linked to anthropogenic disturbances we examined. This suggests the type of disturbances this species is sensitive to may not be well understood.

Maintenance and dissemination of avian-origin influenza A virus within the northern Atlantic Flyway of North America.

Wild waterbirds, the natural reservoirs for avian influenza viruses, undergo migratory movements each year, connecting breeding and wintering grounds within broad corridors known as flyways. In a continental or global view, the study of virus movements within and across flyways is important to understanding virus diversity, evolution, and movement. From 2015 to 2017, we sampled waterfowl from breeding (Maine) and wintering (Maryland) areas within the Atlantic Flyway (AF) along the east coast of North America to investigate the spatio-temporal trends in persistence and spread of influenza A viruses (IAV). We isolated 109 IAVs from 1,821 cloacal / oropharyngeal samples targeting mallards (Anas platyrhynchos) and American black ducks (Anas rubripes), two species having ecological and conservation importance in the flyway that are also host reservoirs of IAV. Isolates with >99% nucleotide similarity at all gene segments were found between eight pairs of birds in the northern site across years, indicating some degree of stability among genome constellations and the possibility of environmental persistence. No movement of whole genome constellations were identified between the two parts of the flyway, however, virus gene flow between the northern and southern study locations was evident. Examination of banding records indicate direct migratory waterfowl movements between the two locations within an annual season, providing a mechanism for the inferred viral gene flow. Bayesian phylogenetic analyses provided evidence for virus dissemination from other North American wild birds to AF dabbling ducks (Anatinae), shorebirds (Charidriformes), and poultry (Galliformes). Evidence was found for virus dissemination from shorebirds to gulls (Laridae), and dabbling ducks to shorebirds and poultry. The findings from this study contribute to the understanding of IAV ecology in waterfowl within the AF.

Airflow and teleconnection patterns driving the spatial and temporal variability of high 7Be air concentrations in Europe

The long-term monitoring of the cosmogenic 7Be activity concentrations has been used to better understand the influence of large-scale atmospheric circulation dynamics in the troposphere. With an aim, this study analyzes weekly 7Be data from 15 sampling stations in Europe over 2005–2014. We first define peak (or extremely high) events in each station as those activity concentrations above the 90th percentile, and then investigate their temporal and spatial variability. These events are most frequent in the spring and summer seasons, with a notable latitudinal variability in their number. Next, we use back-trajectory cluster analysis to identify the main advection pathways associated with these high concentrations. To achieve this, persistent periods, i.e., sampling periods over which at least 60% of the calculated backward trajectories arriving at a given site correspond to the same airflow pattern, are taken as reference. This method reveals large differences in the association between the airflow patterns observed at different stations in connection with the 7Be peaks. A comparison between stations shows no clear spatial pattern, which suggests a further influence of mesoscale/local physical processes on the surface 7Be activity concentrations. Finally, the main airflow pattern at each sampling site and the associated 7Be peaks, are related to the main teleconnection patterns of large scale and regional climate variability in Europe: North Atlantic Oscillation, Arctic Oscillation, East Atlantic, East Atlantic/Western Russia, Scandinavian pattern and Western Mediterranean Oscillation. The results point out the connection between the negative phases of NAO and We-MO, and the positive phase of EA with the spatial and temporal variability and occurrence of the 7Be peak activity concentrations. These results show a latitudinal division between northern and southern sites, with similar influence of teleconnection patterns, while those located in the central part of Europe present larger variability in the impact of teleconnection patterns.

Assessment of the acidification risk of the acid sulfate soil materials in a tropical coastal peat bog:Muthurajawela Marsh, Sri Lanka

Coastal regions in tropical countries encompass a diverse set of highly productive ecosystems with underlying acid sulfate (AS) soil materials. Muthurajawela Marsh is a tropical, saline, peat bog on the western coast of Sri Lanka and is known to contain AS soil materials. It is a critically important coastal wetland ecosystem and provides a multitude of benefits and services to the surrounding environment and the people in the area. At present, the AS soil materials in the marsh are at risk of exposure due to development activities in the surrounding areas. In this study, net acidity (NA) was quantified using an acid base accounting approach which includes retained acidity (RA) in addition to actual and potential sulfidic acidity (AA and PSA). The NA and the other soil characteristics were investigated in three soil profiles down to 1.5 m, along a north–south transect. All sites contained hypersulfidic soil materials as confirmed by field pH (pHF) > 4, field oxidation pH (pHFOX) < 4 and sulfide content > 0.01%. Net acidity values ranged from 23 to 4000 mol H+ t-1which was above the recommended management requirement value for peat and medium clay soils (i.e. 18 and 36 mol H+ t−1). At the northern site (S1), PSA was the main contributor to the NA, indicating future risk if the site were to become exposed to air. Both AA and RA were major contributing fractions at the middle (S2) and southern (S3) sites, with a possible imminent acidity discharge. All sites lack inherent buffering capacity, consequently, acidity can be released from the oxidation of the AS soil materials leading to the potential impact on the marsh ecosystem. The findings of this study indicate that human activities should be carefully managed to minimize the hazards that can occur due to exposing AS soils in the marsh.

Residency, movement patterns, behavior and demographics of reef manta rays in Komodo National Park.

BackgroundThe reef manta ray (Mobula alfredi) is a globally threatened species and an iconic tourist attraction for visitors to Indonesia’s Komodo National Park (NP). In 2013, manta ray fishing was banned in Komodo NP and its surroundings, preceding the nationwide manta ray protection in 2014. Over a decade ago, a previous acoustic telemetry study demonstrated that reef manta rays had high fidelity to sites within the park, while more recent photo-identification data indicated that some individuals move up to 450 km elsewhere. Characterization of manta ray demographics, behavior, and a focused assessment on site use of popular tourism locations within the park is vital to assist the Komodo NP Management Authority formulate appropriate manta ray conservation and management policies.MethodsThis study uses a long-term library (MantaMatcher.org) of photo-identification data collected by researchers and citizen scientists to investigate manta ray demographics and habitat use within the park at four sites frequented by tour operators: Cauldron, Karang Makassar, Mawan, and Manta Alley. Residency and movements of manta rays were investigated with maximum likelihood analyses and Markov movement models.ResultsA total of 1,085 individual manta rays were identified from photographs dating from 2013 to 2018. In general, individual manta rays displayed a higher affinity to specific sites than others. The highest re-sighting probabilities came from the remote southern site, Manta Alley. Karang Makassar and Mawan are only ~5 km apart; however, manta rays displayed distinct site affinities. Exchange of individuals between Manta Alley and the two central sites (~35.5 km apart) occurred, particularly seasonally. More manta rays were recorded traveling from the south to the central area than vice versa. Female manta rays were more mobile than males. Similar demographic groups used Karang Makassar, Mawan, and Manta Alley for foraging, cleaning, cruising, or courtship activities. Conversely, a higher proportion of immature manta rays used the northern site, Cauldron, where foraging was commonly observed. Fishing gear-related injuries were noted on 56 individuals (~5%), and predatory injuries were present on 32 individuals (~3%). Tourism within the park increased from 2014 to 2017, with 34% more dive boats per survey at Karang Makassar and Mawan.DiscussionThe Komodo NP contains several distinct critical habitats for manta rays that encompass all demographics and accommodate seasonal manta ray movements. While the present study has not examined population trends, it does provide foundational data for such work. Continued research into manta ray abundance, long-range movements, and identifying and protecting other critical aggregation areas within the region is integral to securing the species’ recovery. We provide management recommendations to limit undue pressure on manta rays and their critical habitats from tourism.

Food Sources for Benthic Grazers in Trophic Networks of Macrophyte Habitats in a Transitional Baltic Ecosystem

In this study, we provide insights into that characteristics of two sites representing different conditions of productivity and salinity impact on trophic network structures of macrophyte habitats and diet of benthic grazers at the active vegetation period in the Curonian Lagoon (southeastern Baltic Sea). Regarding the epiphytic growth, macrophytes were more overgrown in the relatively less productive (northern) site with a muddy bottom and more frequent marine water inflow than in the (southern) site with higher productivity and freshwater sandy habitat. Stable isotope analysis revealed that organisms’ samples from the northern site were more enriched with the heavier carbon isotopes, but depleted in the heavier nitrogen isotopes than those from the southern site. Gastropods and amphipods mainly consumed sedimentary organic matter in the southern site, while they grazed epiphytes together with sedimentary organic matter in the northern site. Although to a low extent, gastropods consumed more charophytes than pondweeds in the southern site. This study contributes to a better understanding of the functioning and structure of lagoonal systems, highlighting the importance, often overlooked, of the benthic compartment, which, however, may have a relevant influence on the productivity of the whole system.

Forest Fire History in Amazonia Inferred From Intensive Soil Charcoal Sampling and Radiocarbon Dating

Fire has a historical role in tropical forests related to past climate and ancient land use spanning the Holocene; however, it is unclear from charcoal records how fire varied at different spatiotemporal scales and what sampling strategies are required to determine fire history and their effects. We evaluated fire variation in structurally intact, terra-firme Amazon forests, by intensive soil charcoal sampling from three replicate soil pits in sites in Guyana and northern and southern Peru. We used radiocarbon (14C) measurement to assess (1) locally, how the timing of fires represented in our sample varied across the surface of forest plots and with soil depth, (2) basin-wide, how the age of fires varies across climate and environmental gradients, and (3) how many samples are appropriate when applying the 14C approach to assess the date of last fire. Considering all 14C dates (n = 33), the most recent fires occurred at a similar time at each of the three sites (median ages: 728–851 cal years BP), indicating that in terms of fire disturbance at least, these forests could be considered old-growth. The number of unique fire events ranged from 1 to 4 per pit and from 4 to 6 per site. Based upon our sampling strategy, the N-Peru site—with the highest annual precipitation—had the most fire events. Median fire return intervals varied from 455 to 2,950 cal years BP among sites. Based on available dates, at least three samples (1 from the top of each of 3 pits) are required for the sampling to have a reasonable likelihood of capturing the most recent fire for forests with no history of a recent fire. The maximum fire return interval for two sites was shorter than the time since the last fire, suggesting that over the past ∼800 years these forests have undergone a longer fire-free period than the past 2,000–3,500 years. Our analysis from terra-firme forest soils helps to improve understanding of changes in fire regime, information necessary to evaluate post-fire legacies on modern vegetation and soil and to calibrate models to predict forest response to fire under climate change.

Carbon and Water Cycling in Two Rubber Plantations and a Natural Forest in Mainland Southeast Asia

AbstractRubber plantations have rapidly replaced natural forests (NFs) in Mainland Southeast Asia, yet the relevant impacts on the terrestrial carbon cycle remain uncertain especially with an increase in drought frequency. Our study compared eddy‐covariance measurements of carbon and water fluxes from two rubber monoculture plantations (at a northern marginal site and a southern traditional plantation site) with a second‐growth NF between 2015 and 2018, and their responses to a prolonged drought during 2015/2016. The NF had higher light use efficiency, water use efficiency and gross primary productivity (GPP, 2.94 ± 0.41 kg C m−2 yr−1) than the northern rubber (NR) monoculture (2.45 ± 0.17 kg C m−2 yr−1), while lower ecosystem carbon use efficiency (eCUE) caused a lower net ecosystem productivity (NEP, 0.75 ± 0.25 kg C m−2 yr−1) compared to the plantation (1.19 ± 0.22 kg C m−2 yr−1). Drought decreased the NF eCUE by 23% with significant carbon uptake restrictions across multiple seasons, while the rubber GPP reduction was only substantial in the warm‐dry season with an overall 17% decline in eCUE. The NR site's GPP was mainly controlled by soil water content throughout the year. Higher light availability offset the negative effect of drier conditions on the rubber GPP, resulting in larger carbon uptake compared to the southern plantation (GPP, 2.12 ± 0.12 kg C m−2 yr−1; NEP, 1.07 ± 0.14 kg C m−2 yr−1). In contrast, the NF GPP was mainly restricted by vapor pressure deficit, especially during the drought.

A temperature‐driven model of phenological mismatch provides insights into the potential impacts of climate change on consumer–resource interactions

Anthropogenic climate change increasingly affects species phenology. Because trophic interactions often occur at specific phenological stages, changes in one species' phenology may affect others through phenological mismatch. When a consumer and a resource both exhibit a seasonal resting period, the synchrony of the end of their respective resting periods is fundamental for the persistence of their interaction. Since the consumer and its resource may react differently to changes in temperature regime, the synchrony between them could be altered. We investigate potential effects of climate change on species' synchrony. We propose a general model that determines the duration of the resting period according to temperature, and its effects on the mismatch between phenological stages of two interacting species. We illustrate our approach using the spruce budworm–balsam fir system in eastern Canada. We find that an increase in temperature advances the end of the resting period. However, the effects of a warm or cold spell during the resting period strongly vary according to the timing and the duration of the spell. Depending on how a consumer and its resource react to the same temperature shift, the mismatch between them may increase or decrease. The spruce budworm–balsam fir model predicts that an increase in temperature may increase the mismatch between the insect and the tree in southern sites, but may increase the synchrony in northern sites. This modelling approach is of prime importance to investigate potential effects of climate change on consumer–resource systems.

Disturbance: a double‐edged sword for restoration in a changing climate

Ecological restoration often relies on disturbance as a tool for establishing target plant communities, but disturbance can be a double‐edged sword, at times initiating invasion and unintended outcomes. Here we test how fire disturbance, designed to enhance restoration seeding success, combines with climate and initial vegetation conditions to shift perennial versus annual grass dominance and overall community diversity in Pacific Northwest grasslands. We seeded both native and introduced perennial grasses and native forbs in paired, replicated burned‐unburned plots in three sites along a latitudinal climate gradient from southern Oregon to central‐western Washington. Past restoration and climate manipulations at each site had increased the variation of starting conditions between plots. Burning promoted the expansion of extant forbs and perennial grasses across all sites. Burning also enhanced the seeding success of native perennial grass and native forbs at the northern and central site, and the success of introduced perennial grasses across all three sites. Annual grass dominance was driven more by latitude than burning, with annuals maintaining their dominance in the south and perennials in the north. At the same time, unrestored grasslands surrounding all sites remained dominated by perennial grasses, suggesting that initial plot clearing may have allowed for annual grass invasion in the southern site. When paired with disturbance, further warming may increase the risk of annual grass dominance, a potentially persistent state.