Philippa Kaur

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CORRESPONDENCE
13 July 2021

Italy: Forest harvesting is the opposite of green growth

Roberto Cazzolla Gatti

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Gianluca Piovesan

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Alessandro Chiarucci

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Roberto Cazzolla Gatti

Tomsk State University, Russia.

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Gianluca Piovesan

University of Tuscia, Viterbo, Italy.

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Alessandro Chiarucci

University of Bologna, Italy.

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We question plans to step up the harvesting of forest biomass, as set out in Italy’s Fourth Report on the State of Natural Capital. Rather than supporting a transition to a green economy, this could translate into more logging and perturbation of forest ecosystems.The loss of trees in Italy’s forests in recent years (go.nature.com/3yzvdp9) is only partly explained by disturbances such as Storm Vaia in 2018, and salvage logging thereafter. The dominant driver is the production of wood fuel (D. Pettenella et al. Forest@ 18, 1–4; 2021), mainly from coppice. This probably removes about 50% of estimated annual growth (see go.nature.com/3xr1mzc).The new biomass policy could threaten the functionality of forest ecosystems unless it includes measurable targets and a reliable monitoring system for tracking the impacts of removing wood. In a geographically complex country, rich in biodiversity, this could undermine progress towards the European Union’s 2030 biodiversity strategy.For Italy’s forests to contribute to the economy, provide ecosystem services, halt biodiversity loss and mitigate climate change, the country needs ecological planning, data monitoring, forest protection, restoration and rewilding.

Nature 595, 353 (2021)
doi: https://doi.org/10.1038/d41586-021-01923-x

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The authors declare no competing interests.

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Flow velocity thresholdThere were 92 Chinese sturgeon signals from 2016 to 2019, which were identified with the DIDSON dual-frequency video sonar system. The distribution map of Chinese sturgeon signals was shown in Fig. 1. The number of monitored signals in 2016 was significantly higher than in 2017–2019. The latest wild reproduction of the Chinese sturgeon occurred in 2016. Overall, most Chinese sturgeon signals were distributed within 500 m downstream from Gezhouba Dam, and there were more in the right side(facing downstream) than in the left side. The flow field of each sturgeon signal was simulated by the model, and the velocity of each signal location was obtained. According to the statistical analysis of the flow velocity values, the frequency of the sturgeon signal at different flow velocity values was shown in Fig. 2. The results show that most signals were concentrated in areas with flow velocities of 0.6–1.5 m/s, which accounted for 88.1% of the signals; areas with flow velocities below 0.6 m/s accounted for 4.3% of the signals, and areas with flow velocities above 1.5 m/s accounted for 7.6%. Therefore, 0.6–1.5 m/s was selected as the preferred flow velocity range of the Chinese sturgeon for spawning activity. This result was approximately consistent with the ranges proposed by most other researchers. The low limit of the velocity range was lower than that of other researchers. There may be two reasons for this result: the first was that the bottom velocity we analysed was lower than the surface velocity and vertical average velocity under the same conditions; the second was that our research time was after 2016, and the discharge during the spawning period was relatively low, so the velocity of the Chinese sturgeon signal was also relatively low.Figure 1Distribution map of Chinese sturgeon signals, where ○ indicates Chinese sturgeon signals monitored in 2016, ∆ indicates those in 2017, □ indicates those in 2018, and ✩ indicates those in 2019. Map generated in ArcGIS Pro (https://www.esri.com/en-us/arcgis/products/arcgis-pro/overview).Full size imageFigure 2Plots of the frequency for the different flow velocity ranges of Chinese sturgeon signals.Full size imageDifferent opening modes with identical dischargeThe discharge of 6150 m3/s on November 24, 2016, when the latest wild reproduction of Chinese sturgeon occurred, was used to study the flow velocity distribution with different opening modes. The specific opening mode cases are shown in Table 1. Case 1 was the actual situation, and the Dajiang Plant featured 7 open units: #8, #11, #13, #14, #16, #19, and #21. According to the amounts of electricity generated by Dajiang Plant and Erjiang Plant on that day, the proportion of the Dajiang River flow was 58.8%, and the average discharge of each unit was 516.6 m3/s. Case 2 and case 3 featured 7 open units with the same discharge, but in case 2, units #15–21 were continuously open on the right-side (facing downstream), and in case 3, units #8–14 were continuously open near the left side. Case 4 and case 5 were the most concentrated conditions with the discharge of 6150 m3/s because the maximum through-discharge for each unit in the Dajiang Plant is 825 m3/s19. In these cases, at least 5 units were open with an average discharge of 723 m3/s per unit. Case 4 involved continuously opening units #8–12 on the left side, and case 5 involved continuously opening units #17–21 on the right side. Case 6 involved simultaneously opening 14 units on Dajiang River, and the average discharge of each unit was 258.3 m3/s.Table 1 Calculation cases with different opening modes of units under the identical discharge.Full size tableFigure 3 shows the flow fields of the spawning ground under different opening modes with identical discharge. By comparing the areas with a velocity threshold range of 0.6–1.5 m/s in different cases, the most favourable opening mode was determined. In case 1, the velocity at the outlet of the units was higher than the 1.5 m/s velocity threshold, but the discharge of each unit was only 516.6 m3/s, so the high-velocity range was limited, and most areas were suitable. In case 2 and case 3, there was a large difference in proportions of suitable area. Because the left side was deeper than the right side, the flow velocity on the right side was higher under the same discharge, and case 3 more easily exceeded the flow threshold, which resulted in a larger unsuitable area. Case 2 was more suitable than case 1, which also demonstrated that opening the left-side units was more favourable. In case 4 and case 5, the proportions of suitable area were small. Because the units were concentrated, the discharge of each unit was too high, and the outlet velocity was more than 2 m/s, so a large area of high velocity appeared downstream of the units with backflow under the shut-down units. The proportion of suitable area in case 5 was larger than those in case 4 and case 3, which further indicates that opening the left-side units was more favourable than opening the right-side units. Case 6 was greater than that of any other case. Because the discharge of each unit was only 258.3 m3/s, the velocity of the unit outlet was less than 1.5 m/s, and almost all areas were suitable except for the small areas on both sides. The suitable-velocity area was the largest when all units of the Dajiang Plant of Gezhouba Dam were open; therefore, for a given discharge, it was best to open all units.Figure 3Flow field of the spawning ground in different opening modes with identical discharge, where the numbers at the top of each picture are the numbers of units to open, and the arrows indicate the direction of the water flow. Maps generated in Tecplot360 EX 2020 R1 (https://www.tecplot.com/products/tecplot-360/).Full size imageDifferent discharges under identical opening modeThe velocity distribution of the spawning field is affected by the opening mode of the units and discharge of Gezhouba Dam. To study the effect of different discharges, 14 cases were simulated, as shown in Table 2. All units of the Dajiang Plant were considered open because the proportion of suitable area was expected to be maximal under such circumstances. From 1982 to the present, the discharge during the spawning day of Chinese sturgeon under Gezhouba Dam has a wide range: the highest discharge was 27,290 m3/s in 1990, and the lowest discharge was 5590 m3/s in 2012. However, the highest design discharge of the Gezhouba Dam units is 17,930 m3/s20. Once the design discharge is exceeded, the spillway on Erjiang River discharges water, and the velocity distribution of the study area is not affected. Therefore, case 1 represents the lowest discharge of 5590 m3/s, and case 2 represents a discharge of 6000 m3/s. For each subsequent case, the discharge was increased by 1000 m3/s to case 13 with the highest flow of 17,930 m 3/s. In case 14, all units reached the design discharge, and the discharge of each unit was 825 m3/s19.Table 2 Calculation cases with the same opening mode under different discharges.Full size tableFigure 4 shows the proportion of suitable-velocity area with all units open under different discharges. According to the calculation results, the proportion of suitable area slightly fluctuated at approximately 96.2% for discharges of 5590–11,000 m3/s. Because the discharge of each unit was low, the velocity of the unit outlet was low, and most areas were within the velocity threshold. Therefore, it is advantageous to open all units when the discharge is low. After the discharge reached 12,000 m3/s, the proportion of suitable area rapidly decreased. Because the discharge of each unit was high, on the right side of Dajiang River, the velocity of the unit outlet exceeded the velocity threshold and increased with increases in discharge, and the range of effect gradually increased. In the last case, the proportion of suitable area was only 6% when the units reached the designed discharge of 825 m3/s. Because the discharge of each unit was too high, almost all areas exceeded the velocity threshold except for small areas on both sides. Therefore, at discharges below 12,000 m3/s, opening all units is favourable, and at discharge above 12,000 m3/s, a higher discharge corresponds to more unfavourable conditions.Figure 4Proportions of the suitable-velocity area with all units opened under different discharges.Full size imageOptimal scheme under high-flow conditionsHigh-flow conditions at Gezhouba Dam are considered those that exceed 12,000 m3/s because of the substantive decline in suitable habitat area at higher discharges. Because opening the units on the left side of the Dajiang Plant provides a more uniform, suitable habitat, we evaluated 20 cases with a left-side opening mode under different discharge, as shown in Table 3. Because the highest discharge of each unit in the Dajiang Plant is 825 m3/s, at least 9 units must be open when the discharge is 12,000 m3/s. Case 1 was designed to open 9 units on the left, i.e., units #13–21, and the discharge of each unit was 784 m3/s. Cases 2–5 increased by 1 unit from left to right until 13 units were opened. For discharges of 13,000 m3/s, 14,000 m3/s, 15,000 m3/s, and 16,000 m3/s, at least 10, 10, 11, and 12 units were opened. When the discharge was 17,000 m3/s and 17,930 m3/s, at least 13 units were open.Table 3 Calculation cases with different opening modes under high-flow conditions.Full size tableFigure 5 shows the proportions of suitable area for different opening modes under high-flow conditions. The calculation results show that when the discharge was 12,000 m3/s, 13,000 m3/s, and 14,000 m3/s, the proportion of suitable area showed a parabolic trend with the increase in number of units. When the discharge was 12,000 m3/s, the proportion of suitable area with 11 open units on the left was the largest, which was 8.7% larger than the value for all open units and 15% larger than the value for the lowest number of open units. When the discharge was 13,000 m3/s, 12 open units on the left had the largest proportion of suitable-flow-velocity area. When the discharge was 14,000 m3/s, the proportions of suitable area produced by opening 12 and 13 units on the left were the largest. The proportion of suitable area of the lowest number of open units was usually minimal because the discharge of each unit was too high, which resulted in a large area of high velocity that was not suitable for Chinese sturgeon to spawn. Because of the underwater topography, opening the left-side units was more favourable than opening the right-side units, so for all open units, the proportions of suitable area will be lower, and the number of units opened in the middle will be the most advantageous. For a discharge of 15,000 m3/s, with the increase in number of units, the proportion of suitable area increased, and there was no parabolic trend because the discharge of each unit exceeded 678 m3/s; thus, on the left side, there was a large area of high velocity, and the effect extended very far, which was not suitable for Chinese sturgeon.Figure 5Proportions of the suitable area for different opening modes under high-flow conditions, where 12,000–09 on the x-axis indicates that the discharge is 12,000 m3/s, and 9 units are open on the left.Full size image More

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The gobi region ecosystem has low stability because of its single species composition and simple structure (Fig. 8a). Large-scale shrub planting destroyed the original stable state (Fig. 8b) and resulted in another stable state via self-adjustment. In this process, the planted shrubs deteriorated the original ecosystem by competing for water and a chain reaction may ensue, leading to greater ecological problems. The original intention of the large-scale planting of shrubs was to maintain regional ecological balance, protect biodiversity, and fix sand, thus improving the environment (Fig. 8c). However, given the poor choice of the planting location, the expected results were not achieved. In fact, the opposite results of the original good intentions were achieved (Fig. 8d).Figure 8Diagram of different development stages of large-scale afforestation in the gobi region (a: original ground surface; b: holes dug for afforestation; c the living trees planted; d: ground surface when the trees are dead).Full size imageChina has a large expanse of arid areas, and has suffered from droughts for a long time. Land afforestation has been at the forefront of China’s policy principles, and there are government departments specializing in this field. In recent years, the Chinese Government has recommended a series of major strategies, for example, the “construction of ecological civilization” and “lucid waters and lush mountains are invaluable assets”, and also promoted greening projects, including “Three North Shelterbelt Project”, “Beijing-Tianjin Sandstorm Source Control Project”, and the “Natural Forest Protection Project”. More recently, desert greening has been conducted by people and enterprises, for example, the Ant Forest and Society of Entrepreneurs & Ecology (SEE). As a result of these projects and initiatives, China’s greening has contributed to global greening totals15,16. For afforestation, China’s policy departments have recommended the principles of “sticking to local conditions, suitable land for green, suitable trees for trees, suitable shrub for shrub, suitable grass for grass” and promoting the overall protection of “Mountain-River-Forest-Farmland-Lake-Grass-Desert system”, with particular references to desert. Their goal is to scientifically promote afforestation of the land and to clarify “where to afforest, what to afforest, how to afforest, how to manage”. However, problems arise very easily when grassroots executors are involved.The total area of the gobi region in China is approximately 56.95 × 104 km2, accounting for 13.36% of the national area, and is primarily distributed in the northwest extreme arid regions17. As mentioned above, gobi refers to a special arid landform that has a notably low water supply and is unsuitable for growing trees and shrubs. As an important natural landform, the gobi plays a key role in ecological protection; hence, its reference as “black vegetation”. However, there is a lack of understanding of the gobi, and it is often regarded as an area that needs to be greened or reformed. However, gobi, as an extremely arid region, is a fragile ecosystem. Once the gravel on the gobi surface is destroyed, it could lead to a series of ecological and environmental problems. Therefore, afforestation in arid areas is both a scientific and technical issue which must be conducted according to different regional characteristics, rather than by blindly planting trees in unsuitable areas. This study aims to attract more attention from the government forestry department and implementation personnel involved in afforestation activities so as to revise relevant policies. In response to the findings of this study, we have several recommendations: (1) it is necessary to popularize the understanding of scientific greening within the general public; (2) scientific understanding of the gobi needs to be increased, and awareness must be raised to promote its protection; (3) afforestation projects and management must be scientifically and systematically improved to ensure long-term effectiveness, and; (4) restoration and protection measures should be taken immediately in the gobi regions that have been afforested or destroyed.One of the most important causes of all these problems is the implementation of national policies on subsidies for greening and planting trees in desert areas. According to our survey, personnel who specifically plant trees and engage in afforestation are businessmen, farmers, or others, with most of them being businessmen from abroad, and only a few being local people. All the personnel are more concerned about the subsidies than greening and planting trees itself. According to the policy, they will receive majority of the subsidy if the planted trees live for three years, irrespective of whether the trees survive after that. Therefore, to guarantee the survival of the planted trees for three years, they even use water tankers to carry water to the trees from a great distance. However, after three years, the people stop watering the trees planted in the Gobi region, thereby leading to the death of trees after a few years as they cannot survive only on natural precipitation and groundwater. In pursuit of maximum profits, these businessmen will pursue larger areas for planting trees, which will cause further damage to the ecological environment in the Gobi region. Based on the current situation, we propose the following suggestions: (1) Trees that are planted must be monitored over a long time period, which will greatly reduce the short-term profit motive of the people engaged in planting trees. (2) We must plan greening and planting trees according to local conditions, respecting the laws of nature. Not all areas should be greened; moreover, we should not plant trees, especially in the gobi region, where planting trees can possibly destroy the gobi ecological environment, which is a very fragile desert ecosystem. (4) Personnel responsible for the destruction of the gobi ecological environment by unscientific greening and planting of trees must be obligated to restore the surface conditions of the gobi to prevent the aggravation of wind erosion and desertification, which will increase their awareness of environmental protection and receive punishment for environmental damage. More

A Psammodromus algirus lizard in Spain, where wildfires can confer long-lasting relief from parasites. Credit: Philippe Clement/Nature Picture Library

Ecology
13 July 2021
Destructive fires serve as pest control for lizards

Mediterranean lizards in burnt areas are less likely to be afflicted by mites than their neighbours in unburnt woodlands.

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Occasional wildfires can help lizards to keep a clean house: the blazes cleanse natural areas of mites that can infest the reptiles’ skin.High-intensity fires in Mediterranean shrublands and woodlands renew vegetation, shoo away seed eaters and keep tree diseases in check. Lola Álvarez-Ruiz at the Desertification Research Centre in Valencia, Spain, and her colleagues were curious to know whether the flames could also be beneficial to animals.Between 2016 and 2018, the researchers sampled Psammodromus algirus, a species of ground-dwelling lizard, in eight burnt and adjacent unburnt areas in Spain. They then counted either how many mites were attached to the creatures’ skin or how many raised scales the lizards had — an indication of previous infection with the parasite.Lizards that lived in unburnt areas were four times more likely to carry mites than were those in recently scorched environments, and were also more likely to have raised scales. The results suggest that there was a lower incidence of parasitism even several years after a fire had occurred.

Proc. R. Soc. B (2021)

Ecology More

Oceanographic context of the sampling locationAll Trichodesmium colonies used in this study were collected from the same phytoplankton net which sampled a surface-ocean Southern Caribbean Sea community (Fig. 1a). At the sampling station the phosphate concentration was low (0.13 μM at 100 m) as is typical in an oligotrophic environment, while the surface dissolved iron concentration was relatively high (2.02 nM at 100 m), consistent with coastal or atmospheric inputs being mobilized in this region (Fig. 1a). By far the most abundant Trichodesmium species at this location was an uncharacterized Trichodesmium thiebautii species, as determined by Trichodesmium-specific metagenome-assembled-genome recruiting (see Table S1).Thirty individual colonies of mixed morphology were separated by hand-picking, immediately examined, and photographed by fluorescent microscopy (385 excitation, >420 nm emission), then frozen individually for particle characterization and metaproteomic analysis (Fig. S1). All colonies used in this study presented as healthy with reddish-orange pigmentation and well-defined shape. When the particles were present they auto-fluoresced in the visual light range, appearing as yellow, red, or blue dots. In general, the particles were concentrated in the center of puff-type colonies, though they were also present in tufts but in smaller numbers. Strikingly, colonies either had many such particles or none at all. Based on prior experimental evidence demonstrating that Trichodesmium colonies can capture mineral particles and access iron from them [14,15,16, 21], we hypothesized that these particles were terrestrially derived minerals (Fig. 1c–h). Therefore, we embarked to understand the morphological heterogeneity by characterizing the particles and the colony’s molecular response to them.Mineralogical characterization of the colony-associated particlesTo find out whether these natural colonies of Trichodesmium had captured iron-rich mineral particles, we performed synchrotron-based micro-X-ray fluorescence (μ-XRF) element mapping of representative colonies with the observed particle associations. Prior evidence of Trichodesmium–particle associations has been based mainly on experimental “feeding” of dust to cultured or captured colonies [15, 16, 20, 22,23,24,25], and it was therefore important to establish these specific Trichodesmium–particle relationships, which developed in nature. We examined one tuft- and two puff-type colonies, all of which had particles associated with them. The element maps were consistent with the hypothesis that there were mineral particles enriched in iron (Fe), copper (Cu), zinc (Zn), titanium/barium (Ti/Ba, which cannot be distinguished by this method), manganese (Mn) and cobalt (Co), though the concentrations approached the limit of detection for the latter two elements (Fig. 2, Figs. S2 and S3). Iron concentrations were particularly high in the particles. Micro-X-ray absorption near-edge structure (μ-XANES) spectra for iron were collected on six particles—three each from the two puffs (Fig. 2 and Fig. S4). The particles contained mineral-bound iron with average oxidation states of 2.6, 2.7, two of oxidation state 2.9, and two of oxidation state 3.0 (Table S2, Fig. S5). While the mineralogy of these particles could not be definitively resolved using μ-XANES, the structure of the absorption edge and post-edge region provided insight into broad mineral groups. Both Fe(III) (oxy/hydro)oxides and mixed-valence iron-bearing minerals consistent with iron silicates were present, suggesting heterogeneous mineral character. While we could not positively identify the silicate mineral phases based on XANES, the spectroscopic similarity of some samples to iron-smectite and the geologic context suggest iron-bearing clays were present (Fig. S5). In this geographic region, iron oxides and clays could be sourced from atmospheric dust deposition, which is common in this region [27, 28] and/or from riverine sources such as the Orinoco and/or Amazon rivers [29, 30].Fig. 2: μ-XRF-based element maps of a Trichodesmium tuft (left) and puff (right) colony (beamsize 3 ×3 μm).White/gray contours, based on the sulfur panel, which is indicative of biomass, have been provided (white = high [S] threshold, gray = lower [S] threshold). The color scale is the same for each image, with the maximum concentration for each element indicated in parentheses; iron is displayed using two scales. Iron oxidation states were determined via μ XANES for three particles in the puff colony, and these are annotated in yellow. The corresponding XANES spectra are shown in Fig. S4 and tabulated data in Table S2.Full size imageThese colony-associated mineral particles likely serve as a simultaneous source of nutritional (Fe, Ni, Co, Mn) and toxic (Cu) metals to the colonies. The elemental composition of the particles is similar to a recent characterization of Trichodesmium-particle associations in the South Atlantic [30]. Release of metals from the particles likely vary over time, with copper, nickel, zinc, and cobalt continually leaching and iron leaching initially, then re-adsorbing back onto particles unless organic chelates assist in solubilization [31].Proteome composition is altered by particle presenceTo understand the impact of the particles on colony diversity and function, we performed comparative metaproteomic analysis of the individual Trichodesmium colonies and their microbiota. Seven puffs without particles, 14 puffs with particles, and 4 tufts with particles were analyzed by a new single-colony metaproteomic method. This approach allowed for the first time the molecular profiles of heterogeneous Trichodesmium colonies to be examined individually. Compared to bulk population-level metaproteomes from this location, which achieved deeper resolution of low-abundance proteins by integrating biomass from 50 to 100 colonies (4478 proteins identified) [32], proteome coverage for the low-biomass single colonies was lower yet sufficient for characterizing colony function (2078 proteins identified, Fig. S6) [32]. In total, 1591 Trichodesmium and 487 epibiont proteins were identified across the 25 single-colony metaproteomes versus 2944 Trichodesmium and 1534 epibiont proteins across triplicate population-level metaproteomes (Tables S3 and S4). Phylogenetic exclusivity was checked such that peptides used to identify epibiont proteins were not present in the Trichodesmium genome (Table S5 and Fig. S7) [33, 34].Trichodesmium’s epibiont community plays crucial roles in colony health and physiology, and together the single-colony proteomes demonstrated a diverse and functionally active microbiome associated with the colonies (Fig. 1b and Fig. S8). The proteomic analysis generally reflected the more abundant, “core” members of the epibiont community as was expected given their low-biomass proportion relative to Trichodesmium cells. Many commonly identified epibiont groups were present including Alphaproteobacteria, Microscilla, and non-Trichodesmium cyanobacteria [12, 35, 36]. In general, epibiont abundance was unaffected by particle presence, with one exception: Firmicute proteins were more abundant in tufts and puffs with particles, suggesting enhanced, possibly anaerobic, metabolism. Greater differences were identified between the puff and tuft morphologies, independent of particle presence and consistent with prior characterizations finding that puffs and tufts harbor distinct epibiont communities [12]. Specifically, eukaryotic proteins were more abundant in puffs compared to tufts. These proteins likely represent copepods due to sequence similarity to the model organism Calanus finmarchicus, and this result is consistent with observed associations between copepods and puffs at this location (Fig. S8B). Notably, proteins from the PVC superphylum, particularly an uncharacterized eukaryote pathogen species related to Chlamydia, were also more abundant in puffs. Eukaryotes are often observed in association with Trichodesmium colonies, but are not always identified due to differences in sampling protocols that could wash them away [12], as well as due to biases in analytical methods, for instance in studies with a focus on bacterial 16S or metagenomic analyses. Overall, the differences in the epibiont community were small, suggesting that these do not explain the observed morphological heterogeneity. We therefore turn our attention to describing how the particles impacted the proteome of Trichodesmium specifically.Mineral presence was associated with significant differences in the Trichodesmium proteome. In total, 131 proteins were differently abundant in puffs with particles versus without particles (p  More

If an endpoint of continued circulation (endemicity rather than eradication) seems likely, this still leaves us with questions about the range of outbreak sizes, their intensity and seasonality. Surprisingly, some basic epidemiological parameters for predicting these dynamical features are still uncertain. For example, R0, the reproductive number, which captures the infectiousness of the pathogen, is typically measured from the growth of the epidemic and is harder to estimate once non-pharmaceutical interventions (NPIs) are in place. Similarly, changes to R0 for evolved SARS- CoV-2 variants are difficult to ascertain given simultaneous changes to behaviour and interventions. It is not yet clear whether there is an evolutionary limit to strain infectiousness. To date, structural changes to the SARS-CoV-2 spike furin cleavage site7 as well as enhanced binding of the receptor binding domain to the human ACE2 receptor8 have been associated with enhanced transmissibility in variant strains, but in the longer term, transmission increases may saturate and viral evolution may modulate other aspects of disease transmission including host susceptibility. Nevertheless, any present or future changes to R0 will affect long-term epidemic dynamics, including the intensity of outbreaks and the age-structure of infections.The transmission of many respiratory pathogens varies seasonally, driven either by climatic factors or seasonal changes in behaviour such as schooling. The role of climate in driving transmission of SARS-CoV-2 is currently unclear: high susceptibility during the early pandemic likely limited any climate effect9, and statistical analyses of the climate-SARS-CoV-2 link have been confounded by trends in the data and regional differences in reporting and control measures. This has not been helped by the relatively short case time series (that is, just over a year’s worth of data) compared to typical climate–disease studies that look for climate links over many seasons. An alternative line of evidence comes from the four endemic coronaviruses, which exhibit seasonal wintertime outbreaks. It is possible that SARS-CoV-2 will follow suit. Disentangling the climate drivers of SARS-CoV-2 will become easier over time as both longer time series are available, and susceptibility declines9.A further question is the extent to which SARS-CoV-2 endemic dynamics will be affected by interactions with other circulating pathogens, including the endemic coronaviruses. Both modelling and laboratory work implies a degree of cross-immunity between coronaviruses10,11,12. The NPIs put in place to limit the spread of SARS-CoV-2 have also limited the circulation of many other pathogens, such that infection interactions have not been observed in current case trajectories13. However, as NPIs are relaxed, signatures of cross-species interactions will likely become increasingly visible.Beyond cross-immunity with other pathogens, the longitudinal trajectory of immunity, as depicted in Fig. 1, will play a crucial role in determining SARS-CoV-2 endemic dynamics14. For immunizing infections, susceptibility is driven by birth rates, and infections may be concentrated in younger age groups. For infections with waning immunity or antigenic evolution, susceptibility is driven by the rate at which immunity wanes or the rate the pathogen evolves as well as characteristics of secondary infections. The disease dynamics of pathogens with high rates of antigenic evolution are particularly hard to predict: evolved strains may have variable transmission rates and manifest variable immune responses. An analogy can be made with influenza, where the size and intensity of the seasonal influenza peak is typically very difficult to forecast15.The future course of SARS-CoV-2 remains uncertain. The next few months to a year represents a critical time where we will begin to develop an understanding of key parameters, such as the strength and duration of vaccinal and natural immunity, the seasonality of transmission and the possible interaction of SARS-CoV-2 with other circulating pathogens. In combination, these parameters will allow improved prediction of both long-term SARS-CoV-2 epidemic dynamics, as well as the likelihood of elimination and eradication. An area of particular focus will be the rate of antigenic evolution and the extent to which vaccines remain protective against evolved strains. In all scenarios, rapid and equitable distribution of vaccines presents the greatest hope for minimizing future severe outbreaks. More