Length Of Growing Season Research Articles

Climate‐based identification of suitable cropping areas for giant reed and reed canary grass on marginal land in Central and Southern Europe under climate change

AbstractGiant reed (GR) and reed canary grass (RCG) have emerged as promising perennial industrial crops for providing sustainable bioenergy from marginal land. However, there is great uncertainty among farmers and researchers about where these crops can be grown in the future due to climate change, which complicates a timely transition to a bioeconomy. Therefore, this study quantifies marginal land and suitable cropping areas for GR and RCG in Europe, as well as their overlap. To derive these areas, the present (1991–2020) and future (2071–2100, RCP8.5) growing degree days, growing season length, annual precipitation, and aridity index were analyzed using the E‐OBS observational dataset and EURO‐CORDEX regional climate simulations. The study concludes that while marginal land will decrease by ~18%, GR and RCG will profit from the changing European climate, increasing by ~24% and ~13%, respectively. Looking at regions of overlap between marginal land and the selected crops, a decrease of ~87% and an increase of ~462% is projected for RCG and GR, respectively. This is due to marginal land shifting southward, benefitting the warm‐season grass GR, while RCG prefers cooler climates.

Trade‐offs and synergies between ecosystem productivity and stability in temperate grasslands

AbstractAimIt is crucial to monitor how the productivity of grasslands varies with its temporal stability for management of these ecosystems. However, identifying the direction of the productivity–stability relationship remains challenging because ecological stability has multiple components that can display neutral, positive or negative covariations. Furthermore, evidence suggests that the direction of the productivity–stability relationship depends on the biotic interactions and abiotic conditions that underlie ecosystem productivity and stability. We decipher the relationships between grassland productivity and two components of its stability in four habitat types with contrasting environments and flora.LocationFrance.Time period2000–2020.Major taxaGrassland plant species.MethodsWe used c. 20,000 vegetation plots spread across French permanent grasslands and remotely sensed vegetation indices to quantify grassland productivity and temporal stability. We decomposed stability into constancy (i.e., temporal invariability) and resistance (i.e., maximum deviation from average) and deciphered the direct and indirect effects of abiotic (namely growing season length and nitrogen input) and biotic (namely plant taxonomic diversity, trait diversity and community‐weighted mean traits) factors on productivity–stability relationships using structural equation models.ResultsWe found a positive relationship between productivity and constancy and a negative relationship between productivity and resistance in all habitats. Abiotic factors had stronger effects on productivity and stability compared with biotic factors. A longer growing season enhanced grassland productivity and constancy. Nitrogen input had positive and negative effects on grassland productivity and resistance, respectively. Trait values affected the constancy and resistance of grassland more than taxonomic and trait diversity, with effects varying from one habitat to another. Productivity was not related to any biotic factor.Main conclusionsOur findings reveal how vital it is to consider both the multiple components of stability and the interaction between environment and biodiversity to gain an understanding of the relationships between productivity and stability in real‐world ecosystems, which is a crucial step for sustainable grassland management.

Increased precipitation leads to earlier green-up and later senescence in Tibetan alpine grassland regardless of warming

It is debatable whether warming or increased precipitation primarily drives the changes of spring and autumn phenology in alpine grasslands at high elevations like the Tibetan Plateau. We aim to test the hypothesis that increased precipitation and soil moisture rather than warming significantly advance spring green-up dates (GUD) of dominant species in a semiarid alpine grassland, while both increases of temperature and precipitation delay their autumn senescence dates (SD). We conducted a 2-year manipulative experiment with infrared warming (ambient, +2 °C) and precipitation increase for each of rainfall events (ambient, +15 %, +30 %) during the growing season in a Tibetan alpine grassland. GUD and SD of three dominant species and the relevant soil temperature (ST) and moisture (SM) were observed. Rainy season onset as well as Pre-GUD or Pre-SD (30 days before GUD or SD) mean air-temperature (T-30d) and precipitation (P-30d) and relevant soil temperature (ST-30d) and moisture (SM-30d) were calculated for each experimental treatment. GUD dates of the three dominant species were advanced by increased precipitation rather than by warming, which showed a robust positive correlation with rainy season onset. SD dates were independently delayed by both increases of temperature and precipitation. There was no interactive effect of warming and increased precipitation on GUD and SD across species and years. In general, GUD had a significant negative correlation with Pre-GUD P-30d (SM-30d) but not with Pre-GUD T-30d (ST-30d), while SD showed a significant positive correlation with Pre-SD T-30d and P-30d or Pre-SD ST-30d and SM-30d. Our data support the hypothesis, indicating that spring and autumn phenology of monsoon-adapted alpine vegetation are more sensitive to precipitation change than to warming. The prolonged growing season length under increased temperature and precipitation is more depended on the delay of autumn senescence than the advance of spring green-up.

Leaf economics fundamentals explained by optimality principles.

The life span of leaves increases with their mass per unit area (LMA). It is unclear why. Here, we show that this empirical generalization (the foundation of the worldwide leaf economics spectrum) is a consequence of natural selection, maximizing average net carbon gain over the leaf life cycle. Analyzing two large leaf trait datasets, we show that evergreen and deciduous species with diverse construction costs (assumed proportional to LMA) are selected by light, temperature, and growing-season length in different, but predictable, ways. We quantitatively explain the observed divergent latitudinal trends in evergreen and deciduous LMA and show how local distributions of LMA arise by selection under different environmental conditions acting on the species pool. These results illustrate how optimality principles can underpin a new theory for plant geography and terrestrial carbon dynamics.

Optimality-based modelling of wheat sowing dates globally

CONTEXTSowing dates are currently an essential input for crop models. However, in the future, the optimal sowing time will be affected by climate changes and human adaptations to these changes. A better understanding of what determines the choice of wheat type and sowing dates is required to be able to predict future crop yields reliably. OBJECTIVEThis study was conducted to understand how climate conditions affect the choice of wheat types and sowing dates globally. METHODSWe develop a model integrating optimality concepts for simulating gross primary production (GPP) with climate constraints on wheat phenology to predict sowing dates. We assume that wheat could be sown at any time with suitable climate conditions and farmers would select a sowing date that maximises yields. The model is run starting on every possible climatically suitable day, determined by climate constraints associated with low temperature and intense precipitation. The optimal sowing date is the day which gives the highest yield in each location. We evaluate the simulated optimal sowing dates with data on observed sowing dates created by merging census-based datasets and local agronomic information, then predict their changes under future climate scenarios to gain insight into the impacts of climate change. RESULTS AND CONCLUSIONSCold-season temperatures are the major determinant of sowing dates in the extra-tropics, whereas the seasonal cycle of monsoon rainfall is important in the tropics. Our model captures the timing of reported sowing dates, with differences of less than one month over much of the world; maximum errors of up to two months occur in tropical regions with large altitudinal gradients. Discrepancies between predictions and observations are larger in tropical regions than temperate and cold regions. Slight warming is shown to promote earlier sowing in wet areas but later in dry areas; larger warming leads to delayed sowing in most regions. These predictions arise due to the interactions of several influences on yield, including the effects of warming on growing-season length, the need for sufficient moisture during key phenological stages, and the temperature threshold for vernalization of winter wheat. SIGNIFICANCEThe integration of optimality concepts for simulating GPP with climate constraints on phenology provides realistic predictions of wheat type and sowing dates. The model thus provides a basis for predicting how crop calendars might change under future climate change. It can also be used to investigate potential changes in management to mitigate the negative impacts of climate change.

The effects of biophysical and anthropogenic factors on the recent upper forest‐cover upward shift in the Romanian Carpathians

AbstractAimTo estimate the effects of environmental and human drivers on upper forest‐cover upward shift over the period 1945–2018.LocationRomanian Carpathians.MethodsUsing historical topographic maps and high‐resolution Sentinel‐2A satellite images, we delineated the location of the upper forest‐cover limit in 1945 and 2018 to obtain a binary raster with the “forest gains” and “no‐forest gains” for 1945–2018. The maps were overlapped over 12 independent variables to estimate how they affected the recent upper forest‐cover upward shift, and to predict its probability of expansion in the near future. To achieve this, logistic regression models were applied and then integrated into the GIS spatial analysis.ResultsForest gains of almost 35,000 ha have been detected at the upper forest limit in the study sites, leading to an average upward movement of 30 m (0.5 m per year), mainly at the altitudinal bands between 1,400 and 1,800 m a.s.l. (72%); only 9.7% of the gain was detected above the estimated potential climatic limit. The process was significantly inversely related to elevation (−17.3 ≤ β ≤ −5.7, p < 0.01), slope aspect (−1.5 ≤ β ≤ −0.4, p < 0.01), sheepfold numbers (−18.1 ≤ β ≤ −0.7, p < 0.01), and sheep (−18.3 ≤ β ≤ −0.6, p < 0.01) and cattle (−16.4 ≤ β ≤ −0.8, p < 0.01) populations. Strong direct effects were found for the slope angle (1.3 ≤ β ≤ 10.6, p < 0.01) and distance to sheepfolds (0.5 ≤ β ≤ 12.8, p < 0.01). A low contribution was indicated for the trend in mean air temperature (−1.1 ≤ β ≤ 4.3, p < 0.01), growing season length (−2.1 ≤ β ≤ 5.1, p < 0.01) and protective measures (−1.1 ≤ β ≤ 2.4, p < 0.01, for national parks; −1.8 ≤ β ≤ 1.2, p < 0.01, for natural parks).ConclusionsThe analysis demonstrated that decreased land‐use intensity and, in particular, declining traditional practices were the foremost mechanisms of the recent upper forest‐cover upward shift, whereas the effect of climate warming remains not so obvious.

Natural decadal variability of global vegetation growth in relation to major decadal climate modes

The ongoing climate change can modulate the behavior of global vegetation and influence the terrestrial biosphere carbon sink. Past observation-based studies have mainly focused on the linear trend or interannual variability of the vegetation greenness, but could not explicitly deal with the effect of natural decadal variability due to the short length of observations. Here we put the variabilities revealed by remote sensing-based global leaf area index (LAI) from 1982 to 2015 into a long-term perspective with the help of ensemble Earth system model simulations of the historical period 1850–2014, with a focus on the low-frequency variability in the global LAI during the growing season. Robust decadal variability in the observed and modelled LAI was revealed across global terrestrial ecosystems, and it became stronger toward higher latitudes, accounting for over 50% of the total variability north of 40°N. The linkage of LAI decadal variability to major natural decadal climate modes, such as the El Niño–Southern Oscillation decadal variability (ENSO-d), the Pacific decadal oscillation (PDO), and the Atlantic multidecadal oscillation (AMO), was analyzed. ENSO-d affects LAI by altering precipitation over large parts of tropical land. The PDO exerts opposite impacts on LAI in the tropics and extra-tropics due to the compensation between the effects of temperature and growing season length. The AMO effects are mainly associated with anomalous precipitation in North America and Europe but are mixed with long-term climate change impacts due to the coincident phase shift of the AMO which also induces North Atlantic basin warming. Our results suggest that the natural decadal variability of LAI can be largely explained by these decadal climate modes (on average 20% of the variance, comparable to linear changes, and over 40% in some ecosystems) which also can be potentially important in inducing the greening of the Earth of the past decades.

Carici arctisibiricae–Hylocomietea alaskani – a new class of zonal tundra vegetation

A new class, Carici arctisibiricae–Hylocomietea alaskani class nov. is described for vegetation of the tundra zone on a circumpolar scale. This higher unit in the system of Braun-Blanquet floristic (= floristic-sociological) classification unites the zonal vegetation in the intermediate habitats with respect to the substrate moisture, pH and texture, the snow cover thickness and duration, the depth of seasonal frozen ground thawing, and the growing season length on the interfluves (upland surfaces) within the tundra zone (CAVM subzones B, C, D, E = arctic, typical and southern tundra subzones in Russian zonal subdivision). Communities of the class are distributed on plains north of the tree line on two continents (Eurasia and North America), as well as on the archipelagos (Spitsbergen, Novaya Zemlya, New Siberian Islands, the Canadian Arctic Archipelago) and the large and small islands (Kolguev, Dolgy, Vaygach, Bely, Bolshoy Begichev, Ayon, Wrangel, Greenland) in the Arctic Ocean. The class comprises 3 new orders and 6 alliances. The diagnoses of higher rank units are given. Difficulties in describing and classifying zonal communities due to the specificity of their species composition and horizontal and vertical structure are discussed. The criteria distinguishing the new class from the known ones in the Europe and Asia mountains, in which zonal tundra communities are being placed until now, are presented.

Assessing Canopy Phenological Variations and Gross Primary Productivity in A Savanna Ecosystem in Yuanjiang, Yunnan Province of Southwest China

Vegetation phenology is an important indicator of environmental change and strongly connected to forest ecosystem productivity change. This study aimed to analyse the pattern of phenological variations derived from digital imagery for the interpretation of ecosystem productivity. For 2014, 2015 and 2016, the seasonal phenological development of savanna was analysed by using towerbased imagery from a digital camera. The green excess index (GEI) was the best at representing the phenological transition dates (PTDs) and useful for investigating the gross primary production (GPP) in the savanna ecosystem. There was a significant correlation between the monthly pattern of the strength of green (Sgreen), green excess index (GEI) and vegetation contrast index (VCI) and GPP throughout the year. Additionally, the annual pattern of colour indices had significant relationship (p < 0.05) with GPP but this was not seasonal. The air temperature (air T) and soil temperature (soil T) were strongly significantly correlated (p < 0.001) with the start of growing season (SGS) and caused the advance in green-up and the timing of the start of the growing season in 2014 and 2016. The short growing season length (GSL) had an impact on the productivity. The colour indices from the digital camera images not only provided the phenological pattern of a forest canopy but also revealed the forest ecosystem productivity by showing the response to environmental factors. Our results indicate that daily continuous digital camera images might be useful for ecologists to use as a tool for future prediction of the long-term phenological modelling.

Response of vegetation phenology to urbanization in urban agglomeration areas: A dynamic urban–rural gradient perspective

Being an important theme in global warming, the response of vegetation phenology to urbanization has become an increasing concern at both the local and global levels. Previous studies have focused on spatial or temporal responses across urban–rural gradients; thus, the influence of urbanization on vegetation phenology along the dynamic urbanization gradient has not been well quantified. In this study, we comprehensively analyzed the response of vegetation phenology to urbanization in the Guangdong–Hong Kong–Macao Greater Bay Area (GHM-GBA) from a dynamic urban–rural gradient perspective. The results show that the response of vegetation phenology to urbanization level has a distinct spatiotemporal difference across the urban–rural gradient. Compared to rural areas, the change rate of advancements in the start-of-season (SOS) in urban domains was 1.16 DOY/year and that of the end-of-season (EOS) was 0.63 days/year from 2001 to 2020. In the GHM-GBA region, 61.03 % of the remote sensing pixels showed an advancing trend for SOS and 55.75 % for EOS. Urbanization advanced the SOS and EOS but did not extend the growing season length, and the SOS and EOS were advanced by 7 and 6 days along the urban-to-rural gradient, respectively. For every 10 % increase in urbanization levels, the SOS and EOS advanced by 1.085 and 1.091 days across the urban–rural gradient, respectively; the spring land surface temperature (LST) advanced the SOS at a rate of 1.71 days/°C, while the autumn LST advanced the EOS at a rate of 1.88 days/°C. The phenological shift in the urban–rural gradient was more significant than that over time, which was mainly because of land surface warming under different urbanization levels. These quantitative findings are of great importance for understanding the complicated impacts of urbanization on vegetation phenology and for developing models to predict vegetation phenological changes under future urbanization.

Effects of aspect on phenology of Larix gmelinii forest in Northeast China

The response of vegetation phenology to global climate change is one of the main forms in terrestrial ecosystem change, the study of vegetation phenology is an important complement to the understanding of how global climate change affects ecosystems in multiple dimensions. We selected the distribution area of Larix gmelinii in The Greater Khingan Mountains as a case area by eliminating the heterogeneity of vegetation types, with the support of Google Earth Engine platform, we studied the effects of different aspects and land surface temperature (LST) on remote sensing phenology (RSP) that is defined as start of growing season (SOS), end of growing season (EOS) and length of growing season (LOS) respectively in the study area through Normalized Difference Vegetation Index (NDVI) changes. The results showed that SOS advanced in different aspects during the study period, and the advance amplitude of SOS on the east and west aspect was greater than that on the south and north. Except for the east aspect, EOS showed a slight postponed, and LOS was prolonged on all aspects. The latitude difference between 51° and 53° N had no significant effect on L. gmelinii in different aspects. LST had an obviously direct effect on the RSP of L. gmelinii in different aspects, and the effect of LST on SOS and LOS was significantly greater than that on EOS. The effect of LST on SOS and LOS was significant in April and spring. The main contributor to the increase of LOS was the advance of SOS, while the postponed of EOS has a relatively small contribution to LOS. Due to the redistribution of meteorological factor by aspect, the spatial and temporal heterogeneity of RSP tends to be complex, so determining the same aspect is one of the main ways to reduce the phenological heterogeneity in the study of vegetation RSP.

Temporal dynamics in alpine snowpatch plants along a snowmelt gradient explained by functional traits and strategies.

Alpine snowpatches are characterised by persistent snow cover, short growing seasons and periglacial processes, which has resulted in highly specialised plant communities. Hence, these snowpatch communities are among the most threatened from climate change. However, temporal dynamics in snowpatch microclimate and plant composition are rarely explored, especially in the marginal alpine environments of Australia. Seven snowpatches were categorised into early, mid and late snowmelt zones based on growing season length, with soil temperatures recorded from 2003 to 2020 and plant composition surveyed in 84 1m2 quadrats in 2007, 2013 and 2020. Microclimate, species diversity, plant cover and composition, along with community-weighted trait means and plant strategies were assessed to understand snowpatch dynamics in response to climate change. We found that growing season length and temperatures have increased in late melt zones, while changes were less consistent in early and mid melt zones. There were few changes in species diversity, but increases in graminoids and declines in snowpatch specialists in mid and late melt zones. Community-weighted plant height, leaf area and leaf weight also increased, particularly in mid and late melt zones, while plant strategies shifted from compositions of ruderal-tolerant to stress-tolerant. Here, we show that snowpatch communities are rapidly changing in response to longer growing seasons and warmer temperatures, with the greatest changes occurring where snow persists the longest. The results highlight the climate-induced loss of defining biotic and abiotic characteristics of snowpatches, as temporal convergence of compositions along snowmelt gradients threatens the distinctiveness of snowpatch plant communities.

Growth of alpine grassland will start and stop earlier under climate warming

Alpine plants have evolved a tight seasonal cycle of growth and senescence to cope with a short growing season. The potential growing season length (GSL) is increasing because of climate warming, possibly prolonging plant growth above- and belowground. We tested whether growth dynamics in typical alpine grassland are altered when the natural GSL (2–3 months) is experimentally advanced and thus, prolonged by 2–4 months. Additional summer months did not extend the growing period, as canopy browning started 34–41 days after the start of the season, even when GSL was more than doubled. Less than 10% of roots were produced during the added months, suggesting that root growth was as conservative as leaf growth. Few species showed a weak second greening under prolonged GSL, but not the dominant sedge. A longer growing season under future climate may therefore not extend growth in this widespread alpine community, but will foster species that follow a less strict phenology.

Effects of Shifting Spring Phenology on Growing Season Carbon Uptake in High Latitudes

AbstractPhenological shifts not only alter the growing season length, but also modify land‐atmosphere exchanges of water and energy, which in turn affects ecosystem carbon uptake. However, how changes in the start of the growing season (SOS) affect carbon uptake throughout growing season has not been fully explored for high‐latitude ecosystems. Here, we investigated the impacts of SOS shifts on carbon uptake and the mechanisms over 2000–2020 in the northern high latitudes (>50°N) using multiple satellite and climate data sets. We found a contrasting response of gross primary productivity (GPP) in the early (April–June) and late (July–September) growing season to SOS shifts. Advanced SOS resulted in increased early‐season GPP, whereas slightly decreased late‐season GPP. The earlier SOS resulted from a warmer early season, which induced a decline of snow to precipitation ratio, therefore drier soil and atmosphere. In the early season, when water requirement of vegetation was low, the warm and dry conditions ensured favorable solar radiation and improved vegetation water use efficiency (WUE), thus enhancing photosynthesis. The dry soil and atmosphere conditions extended to the late season due to less snow and excessive water utilization by vegetation in the early season, which therefore slightly suppressed photosynthesis by weakening WUE. Conversely, the delayed SOS resulted in reduced early‐season GPP and slightly enhanced late‐season GPP due to the opposite thermal and moisture conditions to that of advanced SOS. The SOS is likely to be further advanced as warming continues in the high latitudes, intensifying seasonal contrasts in vegetation photosynthesis capacity.

Three decades of environmental change studies at alpine Finse, Norway: climate trends and responses across ecological scales

The International Tundra Experiment (ITEX) was established to understand how environmental change impacts Arctic and alpine ecosystems. The success of the ITEX network has allowed for several important across-site syntheses, and for some ITEX sites enough data have now been collected to perform within-site syntheses on the effects of environmental change across ecological scales. In this study, we analyze climate data and synthesize three decades of research on the ecological effects of environmental change at the ITEX site at Finse, southern Norway. We found a modest warming rate of +0.36 °C per decade and minor effects on growing season length. Maximum winter snow depth was highest in winters with a positive North Atlantic Oscillation. Our synthesis included 80 ecological studies from Finse, biased towards primary producers with few studies on ecological processes. Species distributions depended on microtopography and microclimate. Experimental warming had contrasting effects on abundance and traits of individual species and only modest effects at the community level above and below ground. In contrast, nutrient addition experiments caused strong responses in primary producer and arthropod communities. This within-site synthesis enabled us to conclude how different environmental changes (experimental and ambient warming, nutrient addition, and environmental gradients) impact across ecological scales, which is challenging to achieve with across-site approaches.

Turning points in the impact of earlier green-up on evapotranspiration and gross primary productivity in a semi-arid grassland watershed

Warming-induced shifts in vegetation phenology affect ecosystem functions and the hydrological cycle. Research has so far focused on phenological trends, drivers and feedback across temperate and tropical forests, while their impacts on carbon assimilation and hydrological processes in temperate semi-arid grasslands remain poorly understood. Based on remote-sensing datasets from the Moderate Resolution Image Spectroradiometer (MODIS), we examined the trends in vegetation phenology, gross primary productivity (GPP) and evapotranspiration (ET) in the Chabagou watershed of the Loess Plateau, China, for 2001–2020. The results revealed that the start of the growing season (SOS) had advanced significantly between 2001 and 2020, at an average rate of –1.47 days yr−1 (p < 0.05), while the end of the growing season (EOS) had delayed non-significantly by about 0.04 days yr−1. SOS robustly regulated growing season length (GSL), which was extended by an average rate of 1.60 days yr−1. Regression analysis between phenology and two main climatic factors (temperature and precipitation) reveals that precipitation is the main climatic factor affecting SOS, while temperature plays a relatively important role in EOS delay in the study area. Consistent with the phenological trend, annual ET and GPP increased steadily from 2001 to 2020. Based on the Regional Hydro-Ecological Simulation System (RHESSys), we further investigated the net effects of phenological change on carbon and water fluxes. The simulation results indicated that, for our study site, the correlation between SOS and summer ET would transform from positive to negative once SOS had advanced to around 129 days of the year (DOY) (and 125 DOY for summer GPP). Summer ET and GPP increased as SOS advanced (and GSL extended) until the SOS reached the turning points, and decreased if the SOS (and GSL) advanced beyond the turning points. The mechanism of variations in water and carbon fluxes responding to phenology dynamics could be more complex than we acknowledged to date because the climate is now approaching turning points. We, therefore, suggest improving the dynamic phenologic models for better predicting trends of ecosystem carbon gain and water loss with ongoing climate change.

Climate Change Effects upon Pasture in the Alps: The Case of Valtellina Valley, Italy

In this study, we assessed the potential effects of climate change upon the productivity of mountain pastures in the Valtellina valley of Italy. Two species, Trisetum flavescens and Nardus stricta, among the most abundant in Italian pastures, were chosen for the simulation of low- and high-altitude pastures, respectively. We introduced some agroclimatic indices, related to growing season parameters, climate, and water availability, to evaluate the impacts of climate change upon pasture production. First, the dynamic of the pasture species was evaluated for the present period using the climate-driven, hydrologically based model Poli-Hydro, nesting the Poli-Pasture module simulating plants growth. Poli-Pasture was validated against yield data, at province scale, and at local scale. Then, agroclimatic indices were calculated. Subsequently, IPCC scenarios of the Fifth and Sixth Assessment Reports (AR5 and AR6) were used to project species production and agroclimatic indices until the end of the 21st century. In response to increased temperature under all scenarios, a large potential for an increased growing season length and species yield overall (between +30% and +180% for AR5 at 2100) was found. Potential for decreased yield (until −31% for AR5) is seen below 1100 m asl in response to heat stress; however, it is compensated by a large increase higher up (between +50% and +140% for AR5 above 2000 m asl). Larger evapotranspiration is foreseen and larger water demand expected. However, specific (for hectares of pasture) water use would decrease visibly, and no significant water limitations would be seen. Results provide preliminary evidence of potential livestock, and thereby economic development in the valley at higher altitudes than now.

Decoupled leaf-wood phenology in two pine species from contrasting climates: Longer growing seasons do not mean more radial growth

Climate warming is expected to lengthen the growing season of tree species and enhance radial growth rates. Alternatively, a longer growing season could not lead to improved radial growth if wood production depends more on growth rate than on growing season length. We test these ideas by comparing leaf phenology data and the estimated start and end dates of wood formation predicted by the VS-Lite growth model. We analyzed long-term series of leaf unfolding and fall dates and reconstructed radial growth of two pine species under contrasting climatic conditions: Scots pine (Pinus sylvestris) in a Russian boreal site and Aleppo pine (Pinus halepensis) in a Spanish Mediterranean site. On average, leaf onset occurred in days 99 and 163 in P. halepensis and P. sylvestris, respectively, about 40 days earlier than the estimated start date of wood formation. The onset of leaf unfolding advanced 2.1 days per decade in P. sylvestris in response to warmer May temperatures. Radial growth was enhanced by warm-wet spring-summer conditions in P. sylvestris and by wet soil conditions from prior winter up to current summer in P. halepensis. In this species the growing season length and the radial growth rate were not coupled because the growing season length shortened during cool-wet periods whereas growth rates increased. In P. sylvestris leaf onset was delayed during years with low growth rates suggesting a potential coupling between warmer spring conditions, earlier leaf onset and enhanced growth whenever soil water content is high enough. Overall, we show that longer growing seasons do not necessarily imply higher radial growth rates.

Wetland phosphorus dynamics and phosphorus removal potential.

Wetlands are typically defined as inundated areas with hydric soils forming a transitional zone between terrestrial and aquatic systems. Wetlands have numerous ecosystem benefits, one of which is the potential to mitigate or reverse eutrophication of surface water bodies. The physical, chemical, and biological processes governing phosphorus cycling in wetlands are nuanced and complex; understanding these has direct relevance to the restoration of wetlands, particularly for projects aimed at improving water quality in adjacent water bodies. This literature review summarizes these processes and provides recommendations relevant to restoration of permanent and semipermanent flow-through wetlands, such as those in the Upper Klamath Basin of Oregon. It also reviews several wetland restoration studies assessing phosphorus removal. In summary, appropriately designed and managed wetlands can remove 25% to 44% of inflowing total phosphorus. Deposition of particulate matter, adsorption, uptake by biomass, and peat accretion are the primary phosphorus sequestration mechanisms in wetlands, depending on site-specific conditions (e.g., growing season length, vegetation communities, and soil type). In areas with relatively short growing seasons and where wintertime loads are targeted for treatment, as in the Upper Klamath Basin, deposition of particulate matter will be the primary mechanism for phosphorus sequestration in wetlands given that two of the three remaining processes occur during the growing season. Recommendations to maximize phosphorus sequestration in wetlands include the following: designing wetlands for hydraulic residence time of several days to weeks, managing wetlands for rapid establishment of wetland vegetation with limited decomposition potential (e.g., tule [hardstem bulrush] to facilitate peat accretion), and flooding during periods with low water temperatures and initially isolating restored wetlands from adjacent water bodies (both to minimize diffusive flux of phosphorus from wetland sediment to the water column). Relevant to the Upper Klamath Basin, there is also justification to prioritize areas with relatively high particulate phosphorus load given the potential limited capacity for phosphorus treatment associated with other sequestration mechanisms. Finally, a combination of mitigation and restoration strategies is necessary to achieve water quality objectives, meaning that wetland restoration alone may not be sufficient. Monitoring is advised to facilitate application of adaptive management principles. PRACTITIONER POINTS: Appropriately designed and managed wetlands can remove 25% to 44% of inflowing total phosphorus. Deposition of particulate matter, adsorption, uptake by biomass, and peat accretion are the primary phosphorus sequestration mechanisms in wetlands, depending on site-specific conditions (e.g., growing season length, vegetation communities, and soil type). Recommendations to maximize phosphorus sequestration in wetlands include designing wetlands for hydraulic residence time of several days to weeks; managing wetlands for rapid establishment of wetland vegetation with limited decomposition potential (e.g., tule [hardstem bulrush], to facilitate peat accretion); and flooding during periods with low water temperatures and initially isolating restored wetlands from adjacent water bodies (both to minimize diffusive flux of phosphorus from wetland sediment to the water column). A combination of mitigation and restoration strategies are necessary to achieve water quality objectives, meaning that wetland restoration alone may not be sufficient. Monitoring is advised to facilitate application of adaptive management principles.

Possible negative effects of earlier thaw onset and longer thaw duration on vegetation greenness over the Tibetan Plateau

The Tibetan Plateau (TP), also known as the world's Third Pole, is underlain by frozen ground and is highly sensitive to climate change. However, it remains unclear how the variations in soil freeze-thaw could affect vegetation dynamics across the TP. In this study, we adopted the latest datasets for vegetation, climate and soil freeze-thaw in the past two decades to explore the possible impacts of changes in soil freeze-thaw on vegetation greenness and phenology on the TP. According to the satellite-based observations, the TP showed an overall greening trend during 2001-2020, and the growing season length increased significantly at a rate of 3.6 days/10a, mainly contributed by the advances of the start of the growing season (2.7 days/10a). Based on ridge regression and partial correlation analysis, air temperature and precipitation were found to be the major dominant factors of vegetation dynamics on the TP, and precipitation played a dominant role in the relatively warm-dry southwestern TP where vegetation browning and spring phenology delays were observed. In the relatively cold regions, earlier soil thaw onset generally facilitated spring phenology, and longer soil thaw duration tended to increase the growing season soil moisture content, which could in turn enhance vegetation greenness. In the relatively warm regions, however, earlier thaw onset and longer thaw duration could possibly exacerbate the growing season water stress and limit vegetation growth. The negative impacts were more evident in the regions with unstable and completely degraded permafrost according to the results in the source region of Yellow and Yangtze rivers. Our findings highlight the spatially varying role of soil freeze-thaw changes in vegetation dynamics, which have important implications for the carbon budget of the TP in a warming future climate as frozen ground continues to degrade.