Flexibility in the timing of post‐breeding moult in passerines in the UK

Higher temperatures resulting from climate change have led to predictions that the duration of the breeding season of many temperate bird species may be changing. However, the extent to which breeding seasons can be altered will also depend on the degree of flexibility in processes occurring at other points in the annual cycle. In particular, plasticity in the timing of post‐breeding moult (PBM) could facilitate changes in the timing of key events throughout the annual cycle, but little is known about the level of within‐ and between‐species plasticity in PBM. As part of the British Trust for Ornithology (BTO) Ringing Scheme, many ringers routinely record moult scores of flight feathers, and these can be used to provide information on the annual progression of PBM for a range of species. Here we use ringing data to investigate patterns of PBM in 15 passerines, as well as data from the BTO Nest Record Scheme to relate these differences to the timing of breeding of these species across the UK. We find considerable variation in both the mean start (19 May–29 July) and duration (66–111 days) of PBM between species, but find no evidence that species starting PBM later in the season complete it any faster. However, there is considerable within‐species variation in PBM, particularly for multi‐brooded species; PBM starts later and is completed in less time when the duration of the breeding season (difference between first and last nests) is longer. This implies that a later end to breeding can be compensated for by faster PBM, and that advances in breeding could lead to earlier and slower PBM. Our findings suggest that adaptation of PBM in response to climate‐mediated changes in the timing and duration of the breeding season is possible. However, the requirement to complete PBM prior to migration or the onset of winter might constrain the extent to which breeding seasons can lengthen, especially for later nesting species.     

Conservation insights from changing associations between habitat,territory distribution and mating system of Corn Buntings Emberiza calandra over a 20‐year population decline

Associations between habitat and animal distributions are widely used to make conservation recommendations. However, short‐term studies do not allow investigation of temporal variation in associations as habitats change or populations decline. Here we quantify changes in the habitat attributes and distribution of breeding territories in a multiple‐brooded, crop‐nesting farmland bird, the Corn Bunting Emberiza calandra, over a 20‐year period during which the study population declined by 91%. Corn Buntings were positively associated with weedy fields, overhead wires, spring cereals and, in early summer, with winter barley and forage grass. Territory associations with wires (positive) and fallow (positive in early summer, negative in late summer) were stronger in later years when the population was smaller. Trends in the proportions of males holding territories into late summer (decline), and mated polygynously or not at all (increases), suggested that habitat quality declined and became more spatially variable in later years. Field size increased and weed abundance within fields declined, reducing the availability of field‐boundary song‐posts, invertebrate‐rich foraging habitats and physical cover for nests within crops. Conservation recommendations are for weed‐rich or under‐sown spring cereals and winter barley combined with late‐cut hay and fallow, especially when offered close to song‐posts such as overhead wires. We also demonstrate the value of long‐term studies by comparing our 20‐year analysis with 3‐year periods at the start, middle and end of this period, and expose some risks of conservation recommendations derived from short studies.     

Plasticity results in delayed breeding in a long‐distant migrant seabird

A major question for conservationists and evolutionary biologists is whether natural populations can adapt to rapid environmental change through micro‐evolution or phenotypic plasticity. Making use of 17 years of data from a colony of a long‐distant migratory seabird, the common tern (Sterna hirundo), we examined phenotypic plasticity and the evolutionary potential of breeding phenology, a key reproductive trait. We found that laying date was strongly heritable (0.27 ± 0.09) and under significant fecundity selection for earlier laying. Paradoxically, and in contrast to patterns observed in most songbird populations, laying date became delayed over the study period, by about 5 days. The discrepancy between the observed changes and those predicted from selection on laying date was explained by substantial phenotypic plasticity. The plastic response in laying date did not vary significantly among individuals. Exploration of climatic factors showed individual responses to the mean sea surface temperature in Senegal in December prior to breeding: Common terns laid later following warmer winters in Senegal. For each 1°C of warming of the sea surface in Senegal, common terns delayed their laying date in northern Germany by 6.7 days. This suggests that warmer waters provide poorer wintering resources. We therefore found that substantial plastic response to wintering conditions can oppose natural selection, perhaps constraining adaptation.     

Acceleration of cyanobacterial dominance in north temperate‐subarctic lakes during the Anthropocene

Increases in atmospheric temperature and nutrients from land are thought to be promoting the expansion of harmful cyanobacteria in lakes worldwide, yet to date there has been no quantitative synthesis of long‐term trends. To test whether cyanobacteria have increased in abundance over the past ~ 200 years and evaluate the relative influence of potential causal mechanisms, we synthesised 108 highly resolved sedimentary time series and 18 decadal‐scale monitoring records from north temperate‐subarctic lakes. We demonstrate that: (1) cyanobacteria have increased significantly since c. 1800 ce , (2) they have increased disproportionately relative to other phytoplankton, and (3) cyanobacteria increased more rapidly post c. 1945 ce . Variation among lakes in the rates of increase was explained best by nutrient concentration (phosphorus and nitrogen), and temperature was of secondary importance. Although cyanobacterial biomass has declined in some managed lakes with reduced nutrient influx, the larger spatio‐temporal scale of sedimentary records show continued increases in cyanobacteria throughout the north temperate‐subarctic regions.     

Contemporary climate change in the Sonoran Desert favors cold‐adapted species

Impacts of long‐term climate shifts on the dynamics of intact communities within species ranges are not well understood. Here, we show that warming and drying of the Southwestern United States over the last 25 years has corresponded to a shift in the species composition of Sonoran Desert winter annuals, paradoxically favoring species that germinate and grow best in cold temperatures. Winter rains have been arriving later in the season, during December rather than October, leading to the unexpected result that plants are germinating under colder temperatures, shifting community composition to favor slow growing, water‐use efficient, cold‐adapted species. Our results demonstrate how detailed ecophysiological knowledge of individual species, combined with long‐term demographic data, can reveal complex and sometimes unexpected shifts in community composition in response to climate change. Further, these results highlight the potentially overwhelming impact of changes in phenology on the response of biota to a changing climate.     

Changes in satellite‐derived spring vegetation green‐up date and its linkage to climate in China from 1982 to 2010: a multimethod analysis

The change in spring phenology is recognized to exert a major influence on carbon balance dynamics in temperate ecosystems. Over the past several decades, several studies focused on shifts in spring phenology; however, large uncertainties still exist, and one understudied source could be the method implemented in retrieving satellite‐derived spring phenology. To account for this potential uncertainty, we conducted a multimethod investigation to quantify changes in vegetation green‐up date from 1982 to 2010 over temperate China, and to characterize climatic controls on spring phenology. Over temperate China, the five methods estimated that the vegetation green‐up onset date advanced, on average, at a rate of 1.3 ± 0.6 days per decade (ranging from 0.4 to 1.9 days per decade) over the last 29 years. Moreover, the sign of the trends in vegetation green‐up date derived from the five methods were broadly consistent spatially and for different vegetation types, but with large differences in the magnitude of the trend. The large intermethod variance was notably observed in arid and semiarid vegetation types. Our results also showed that change in vegetation green‐up date is more closely correlated with temperature than with precipitation. However, the temperature sensitivity of spring vegetation green‐up date became higher as precipitation increased, implying that precipitation is an important regulator of the response of vegetation spring phenology to change in temperature. This intricate linkage between spring phenology and precipitation must be taken into account in current phenological models which are mostly driven by temperature.     

Temperature‐correlated shifts in the timing of egg‐laying in House Finches Haemorhous mexicanus

Although temperature‐correlated shifts in the timing of egg‐laying have been documented in numerous bird species, the vast majority of species examined to date have been those that breed in Europe and have an animal‐based diet during breeding. However, given that the timing of breeding can be driven, either in the proximate or in the ultimate sense, by seasonal fluctuations in food availability, the relationship between temperature and laying may differ with diet. Here, we report on patterns of reproductive timing in House Finches Haemorhous mexicanus, a North American species that breeds on a primarily seed‐based diet. Analysing nest records from House Finches in California spanning more than a century, we found that egg‐laying occurred significantly earlier in warmer springs. We also found that although the timing of egg‐laying does not show long‐term changes in most of California, in the hottest region of the state (the southeast desert basin) it has advanced significantly.     

A matter of timing: changes in the first date of arrival and last date of departure of Australian migratory birds

Although there is substantial evidence that Northern Hemisphere species have responded to climatic change over the last few decades, there is little documented evidence that Southern Hemisphere species have responded in the same way. Here, we report that Australian migratory birds have undergone changes in the first arrival date (FAD) and last date of departure (LDD) of a similar magnitude as species from the Northern Hemisphere. We compiled data on arrival and departure of migratory birds in south‐east Australia since 1960 from the published literature, Bird Observer Reports, and personal observations from bird watchers. Data on the FAD for 24 species and the LDD for 12 species were analyzed. Sixteen species were short‐ to middle‐distance species arriving at their breeding grounds, seven were long‐distance migrants arriving at their nonbreeding grounds, and one was a middle‐distance migrant also arriving at its nonbreeding ground. For 12 species, we gathered data from more than one location, enabling us to assess the consistency of intraspecific trends at different locations. Regressions of climate variables against year show that across south‐east Australia average annual maximum and minimum temperatures have increased by 0.17°C and 0.13°C decade^?1 since 1960, respectively. Over this period there has been an average advance in arrival of 3.5 days decade^?1; 16 of the 45 time‐series (representing 12 of the 24 species studied) showed a significant trend toward earlier arrival, while only one time‐series showed a significant delay. Conversely, there has been an average delay in departure of 5.1 days decade^?1; four of the 21 departure time‐series (four species) showed a significant trend toward later departure, while one species showed a significant trend toward earlier departure. However, differences emerge between the arrival and departure of short‐ to middle‐distance species visiting south‐east Australia to breed compared with long‐distance species that spend their nonbreeding period here. On average, short‐ to middle‐distance migrants have arrived at their breeding grounds 3.1 days decade^?1 earlier and delayed departure by 8.1 days decade^?1, thus extending the time spent in their breeding grounds by ～11 days decade^?1. The average advance in arrival at the nonbreeding grounds of long‐distance migrants is 6.8 days decade^?1. These species, however, have also advanced departure by an average of 6.9 days decade^?1. Hence, the length of stay has not changed but rather, the timing of events has advanced. The patterns of change in FAD and LDD of Australian migratory birds are of a similar magnitude to changes undergone by Northern Hemisphere species, and add further evidence that the modest warming experienced over the past few decades has already had significant biological impacts on a global scale.     

Changes in first flowering dates and flowering duration of 232 plant species on the island of Guernsey

Climate change has affected plant phenology; increasing temperatures are associated with advancing first flowering dates. The impact on flowering duration, however, has rarely been studied. In this study, we analysed first flowering dates and flowering durations from a 27 year dataset of weekly flower observations on 232 plant species from the island of Guernsey in the English Channel. The aim of this study was to explore variation in trends and relationships between first flowering dates, flowering duration and temperature. We specifically looked for evidence that traits, such as life forms and phylogenetic groups, explained variation in sensitivity of first flowering and flowering duration among species. Overall trends revealed significantly earlier flowering over time, by an average of 5.2 days decade^?1 since 1985. A highly significant shortening of flowering duration was observed by an average of 10 days decade^?1. Correlations between first flowering, flowering duration and year varied between different species, traits and flowering periods. Significant differences among traits were observed for first flowering and to a lesser degree for flowering duration. Overall, in comparison to first flowering, more species had significant trends in flowering duration. Temperature relationships revealed large differences in strength and direction of response. 55% of the species revealed a significant negative relationship of first flowering dates and temperature. In contrast, only 19% of flowering durations had a significant negative temperature relationship. The advance in first flowering date together with a shortening of flowering duration suggests potentially serious impacts on pollinators, which might pose a major threat to biodiversity, agriculture and horticulture. Human health, in terms of pollen allergies, however, might benefit from a shortening of specific plant pollen seasons.     

Testing the limits of resistance: a 19‐year study of Mediterranean grassland response to grazing regimes

A synthesis of a long‐term (19 years) study assessing the effects of cattle grazing on the structure and composition of a Mediterranean grassland in north‐eastern Israel is presented, with new insights into the response of the vegetation to grazing management and rainfall. We hypothesized that the plant community studied would be resistant to high grazing intensities and rainfall variability considering the combined long history of land‐use and unpredictable climatic conditions where this community evolved. Treatments included manipulations of stocking densities (moderate, heavy, and very heavy) and of grazing regimes (continuous vs. seasonal), in a factorial design. The effect of interannual rainfall variation on the expression of grazing impacts on the plant community was minor. The main effects of grazing on relative cover of plant functional groups were related to early vs. late seasonal grazing. Species diversity and equitability were remarkably stable across all grazing treatments. A reduction in tall grass cover at higher stocking densities was correlated with increased cover of less palatable groups such as annual and perennial thistles, as well as shorter and prostrate groups such as short annual grasses. This long‐term study shows that interannual fluctuations in plant functional group composition could be partly accounted for by grazing pressure and timing, but not by the measured rainfall variables. Grazing affected the dominance of tall annual grasses. However, the persistence of tall grasses and more palatable species over time, despite large differences in grazing pressure and timing, supports the idea that Mediterranean grasslands are highly resistant to prolonged grazing. Indeed, even under the most extreme grazing conditions applied, there were no signs of deterioration or collapse of the ecosystem. This high resistance to grazing intensity and interannual fluctuation in climatic conditions should favor the persistence of the plant community under forecasted increasing unpredictability due to climate change.     

Shortened temperature‐relevant period of spring leaf‐out in temperate‐zone trees

Temperature during a particular period prior to spring leaf‐out, the temperature‐relevant period (TRP), is a strong determinant of the leaf‐out date in temperate‐zone trees. Climatic warming has substantially advanced leaf‐out dates in temperate biomes worldwide, but its effect on the beginning and length of the TRP has not yet been explored, despite its direct relevance for phenology modeling. Using 1,551 species–site combinations of long‐term (1951–2016) in situ observations on six tree species (namely, Aesculus hippocastanum, Alnus glutinosa, Betula pendula, Fagus sylvatica, Fraxinus excelsior, and Quercus robur) in central Europe, we found that the advancing leaf‐out was accompanied by a shortening of the TRP. On average across all species and sites, the length of the TRP significantly decreased by 23% (p < .05), from 60 ± 4 days during 1951–1965 to 47 ± 4 days during 2002–2016. Importantly, the average start date of the TRP did not vary significantly over the study period (March 2–5, DOY = 61–64), which could be explained by sufficient chilling over the study period in the regions considered. The advanced leaf‐out date with unchanged beginning of the TRP can be explained by the faster accumulation of the required heat due to climatic warming, which overcompensated for the retarding effect of shortening daylength on bud development. This study shows that climate warming has not yet affected the mean TRP starting date in the study region, implying that phenology modules in global land surface models might be reliable assuming a fixed TRP starting date at least for the temperate central Europe. Field warming experiments do, however, remain necessary to test to what extent the length of TRP will continue to shorten and whether the starting date will remain stable under future climate conditions.     

The importance of long‐term social‐ecological research for the future of restoration ecology

In the face of rapid environmental and cultural change, long‐term ecological research (LTER) and social‐ecological research (LTSER) are more important than ever. LTER contributes disproportionately to ecology and policy, evidenced by the greater proportion of LTER in higher impact journals and the disproportionate representation of LTER in reports informing policymaking. Historical evidence has played a significant role in restoration projects and it will continue to guide restoration into the future, but its use is often hampered by lack of information, leading to considerable uncertainties. By facilitating the storage and retrieval of historical information, LTSER will prove valuable for future restoration.     

Long‐term amelioration of acidity accelerates decomposition in headwater streams

The secondary production of culturally acidified streams is low, with a few species of generalist detritivores dominating invertebrate assemblages, while decomposition processes are impaired. In a series of lowland headwater streams in southern England, we measured the rate of cellulolytic decomposition and compared it with values measured three decades ago, when anthropogenic acidification was at its peak. We hypothesized that, if acidity has indeed ameliorated, the rate of decomposition will have accelerated, thus potentially supporting greater secondary production and the longer food chains that have been observed in some well‐studied recovering freshwater systems. We used cellulose Shirley test cloth as a standardized bioassay to measure the rate of cellulolytic decomposition, via loss in tensile strength, for 31 streams in the Ashdown Forest over 7 days in summer 2011 and 49 days in winter 2012. We compared this with data from an otherwise identical study conducted in 1978 and 1979. In a secondary study, we determined whether decomposition followed a linear or logarithmic decay and, as Shirley cloth is no longer available, we tested an alternative in the form of readily available calico. Overall mean pH had increased markedly over the 32 years between the studies (from 6.0 to 6.7). In both the previous and contemporary studies, the relationship between decomposition and pH was strongest in winter, when pH reaches a seasonal minimum. As in the late 1970s, there was no relationship in 2011/2012 between pH and decay rate in summer. As postulated, decomposition in winter was significantly faster in 2011/2012 than in 1978/1979, with an average increase in decay rate of 18.1%. Recovery from acidification, due to decreased acidifying emissions and deposition, has led to an increase in the rate of cellulolytic decomposition. This response in a critical ecosystem process offers a potential explanation of one aspect of the limited biological recovery that has been observed so far, an increase in larger bodied predators including fish, which in turn leads to an increase in the length of food chains.     

Identifying drivers of species compositional change in a semi‐natural upland grassland over a 40‐year period

Question: Few long‐term studies exist with integrated vegetation and soil composition data, coupled with detailed environmental driver records. Can changes in community composition in an upland grassland be identified by revisitation after a 40‐year period and allow the main environmental drivers of change to be identified? Location: Snowdon, Wales, UK. Methods: Changes in plant community and soil composition were assessed by resurveying an upland Agrostis–Festuca grassland in 2008, 40 years after the original survey. PCA and ecological indicators were used to determine changes in plant community composition. Redundancy analysis (RDA) allowed the impact of soil chemical composition on the vegetation community to be assessed. Results: A significant shift in community composition was found between years. A 35% reduction in species richness and an increase in the grass:forb ratio, suggest significant ecosystem degradation. Indicator values suggest acidification of the community with an increased acidity preference of species recorded in 2008. However, soil pH measurements showed that soil pH had increased. RDA suggested that the main shifts in species composition were correlated with an increase in pH and a reduction in soil exchangeable base cation concentration. Clear ecosystem responses to climate, land‐use change or nitrogen enrichment were not observed. Conclusions: Shifts in vegetation and soil composition are clearly identifiable after 40 years. The shifts in community composition are consistent with ecosystem degradation due to acidification during the period between surveys. Ecological indicator values and soil chemical composition displayed differing degrees of change. Whilst soils appear to be recovering from historic effects of sulphur deposition, vegetation community composition changes appear to lag behind those in soil chemistry.     

Population trends of breeding birds in British woodlands over a 32-year period: relationships with food, habitat use and migratory behaviour

This paper outlines population trends (with confidence intervals) for 49 species in woodland habitats in Britain as monitored by the British Trust for Ornithology's (BTO) Common Bird Census (CBC) between 1967 and 1999. Additionally, the possible causes of these population trends are investigated by relating the ecological characteristics of species to the degree of population change they have undergone over different time periods. Over the whole period, 17 species showed significant decreases in abundance and 12 species showed significant increases. Whilst population trajectories were diverse, long-distance migrants showed more negative trends than other species and the timing of the changes in their populations was related to their wintering latitude, suggesting that these species may be suffering from environmental changes in the non-breeding season. There was also support for habitat specializations being related to population changes, with species classified as scrub and understorey specialists declining on average, but this was only evident across the entire study period. Additionally, species eating seeds in summer declined and those eating vegetation and making use of the agricultural landscape matrix increased. Therefore wide-scale factors such as landscape-scale processes or processes operating outside of Britain appear to be important in addition to local habitat change, especially for long-distance migrants.     

Increased lifetime reproductive success of first‐hatched siblings in Common Kestrels Falco tinnunculus

Order of birth has profound consequences on offspring across taxa during development and can have effects on individuals later in life. In birds, differential maternal allocation and investment in their progeny lead to variance in the environmental conditions that offspring experience during growth within the brood. In particular, laying and hatching order have been proposed to influence individual quality during the growing period, but little is known about the fitness consequences that these two factors have for offspring from a lifetime perspective. We explored the effect of laying and hatching order on post‐fledgling survival (measured as recruitment probability) and lifetime reproductive success (LRS) in Common Kestrels Falco tinnunculus, using a long‐term and individual‐based dataset. First‐hatched chicks showed higher survival probability and LRS than their siblings. This effect was not due to body condition of the individuals at adulthood, the quality of their mates or the reproductive outcome compared with later‐hatched individuals. Instead, first‐hatched chicks had a higher recruitment probability. This could be explained by the higher body condition attained by first‐hatched chicks at the end of the nesting period, perhaps due to an enhanced competitive advantage for food over their siblings at the time of hatching. Laying order, in contrast to hatching order, appeared to have little or no effect on LRS. Our results suggest that hatching order within siblings predicts fitness, and that better early‐life conditions during growth experienced by first‐hatched chicks improve first survival and then recruitment, resulting in an enhanced LRS.     

Testing for changes in biomass dynamics in large‐scale forest datasets

Tropical forest responses to climate and atmospheric change are critical to the future of the global carbon budget. Recent studies have reported increases in estimated above‐ground biomass (EAGB) stocks, productivity, and mortality in old‐growth tropical forests. These increases could reflect a shift in forest functioning due to global change and/or long‐lasting recovery from past disturbance. We introduce a novel approach to disentangle the relative contributions of these mechanisms by decomposing changes in whole‐plot biomass fluxes into contributions from changes in the distribution of gap‐successional stages and changes in fluxes for a given stage. Using 30 years of forest dynamic data at Barro Colorado Island, Panama, we investigated temporal variation in EAGB fluxes as a function of initial EAGB (EAGB_i) in 10 × 10 m quadrats. Productivity and mortality fluxes both increased strongly with initial quadrat EAGB. The distribution of EAGB (and thus EAGB_i) across quadrats hardly varied over 30 years (and seven censuses). EAGB fluxes as a function of EAGB_i varied largely and significantly among census intervals, with notably higher productivity in 1985–1990 associated with recovery from the 1982–1983 El Niño event. Variation in whole‐plot fluxes among census intervals was explained overwhelmingly by variation in fluxes as a function of EAGB_i, with essentially no contribution from changes in EAGB_i distributions. The high observed temporal variation in productivity and mortality suggests that this forest is very sensitive to climate variability. There was no consistent long‐term trend in productivity, mortality, or biomass in this forest over 30 years, although the temporal variability in productivity and mortality was so strong that it could well mask a substantial trend. Accurate prediction of future tropical forest carbon budgets will require accounting for disturbance‐recovery dynamics and understanding temporal variability in productivity and mortality.     

Convergent ecosystem responses to 23‐year ambient and manipulated warming link advancing snowmelt and shrub encroachment to transient and long‐term climate–soil carbon feedback

Ecosystem responses to climate change can exert positive or negative feedbacks on climate, mediated in part by slow‐moving factors such as shifts in vegetation community composition. Long‐term experimental manipulations can be used to examine such ecosystem responses, but they also present another opportunity: inferring the extent to which contemporary climate change is responsible for slow changes in ecosystems under ambient conditions. Here, using 23 years of data, we document a shift from nonwoody to woody vegetation and a loss of soil carbon in ambient plots and show that these changes track previously shown similar but faster changes under experimental warming. This allows us to infer that climate change is the cause of the observed shifts in ambient vegetation and soil carbon and that the vegetation responses mediate the observed changes in soil carbon. Our findings demonstrate the realism of an experimental manipulation, allow attribution of a climate cause to observed ambient ecosystem changes, and demonstrate how a combination of long‐term study of ambient and experimental responses to warming can identify mechanistic drivers needed for realistic predictions of the conditions under which ecosystems are likely to become carbon sources or sinks over varying timescales.     

Long‐term antagonistic effect of increased precipitation and nitrogen addition on soil respiration in a semiarid steppe

Changes in water and nitrogen (N) availability due to climate change and atmospheric N deposition could have significant effects on soil respiration, a major pathway of carbon (C) loss from terrestrial ecosystems. A manipulative experiment simulating increased precipitation and atmospheric N deposition has been conducted for 9 years (2005–2013) in a semiarid grassland in Mongolian Plateau, China. Increased precipitation and N addition interactively affect soil respiration through the 9 years. The interactions demonstrated that N addition weakened the precipitation‐induced stimulation of soil respiration, whereas increased precipitation exacerbated the negative impacts of N addition. The main effects of increased precipitation and N addition treatment on soil respiration were 15.8% stimulated and 14.2% suppressed, respectively. Moreover, a declining pattern and 2‐year oscillation were observed for soil respiration response to N addition under increased precipitation. The dependence of soil respiration upon gross primary productivity and soil moisture, but not soil temperature, suggests that resources C substrate supply and water availability are more important than temperature in regulating interannual variations of soil C release in semiarid grassland ecosystems. The findings indicate that atmospheric N deposition may have the potential to mitigate soil C loss induced by increased precipitation, and highlight that long‐term and multi‐factor global change studies are critical for predicting the general patterns of terrestrial C cycling in response to global change in the future.     

Modeling and empirical validation of long‐term carbon sequestration in forests (France, 1850–2015)

The development of appropriate tools to quantify long‐term carbon (C) budgets following forest transitions, that is, shifts from deforestation to afforestation, and to identify their drivers are key issues for forging sustainable land‐based climate‐change mitigation strategies. Here, we develop a new modeling approach, CRAFT (CaRbon Accumulation in ForesTs) based on widely available input data to study the C dynamics in French forests at the regional scale from 1850 to 2015. The model is composed of two interconnected modules which integrate biomass stocks and flows (Module 1) with litter and soil organic C (Module 2) and build upon previously established coupled climate‐vegetation models. Our model allows to develop a comprehensive understanding of forest C dynamics by systematically depicting the integrated impact of environmental changes and land use. Model outputs were compared to empirical data of C stocks in forest biomass and soils, available for recent decades from inventories, and to a long‐term simulation using a bookkeeping model. The CRAFT model reliably simulates the C dynamics during France's forest transition and reproduces C‐fluxes and stocks reported in the forest and soil inventories, in contrast to a widely used bookkeeping model which strictly only depicts C‐fluxes due to wood extraction. Model results show that like in several other industrialized countries, a sharp increase in forest biomass and SOC stocks resulted from forest area expansion and, especially after 1960, from tree growth resulting in vegetation thickening (on average 7.8 Mt C/year over the whole period). The difference between the bookkeeping model, 0.3 Mt C/year in 1850 and 21 Mt C/year in 2015, can be attributed to environmental and land management changes. The CRAFT model opens new grounds for better quantifying long‐term forest C dynamics and investigating the relative effects of land use, land management, and environmental change.