Changes In Length Of Growing Season Research Articles

Comparison of the distribution and phenology of Arctic Mountain plants between the early 20th and 21st centuries.

Arctic plants are adapted to climatic variability, but their long-term responses to warming remain unclear. Responses may occur by range shifts, phenological adjustments in growth and reproduction, or both. Here, we compare distribution and phenology of 83 arctic and boreal mountain species, sampled identically in the early 20th (1917-1919) and 21st centuries (2017-2018) from a region of northern Sweden that has warmed significantly. We test two compensatory hypotheses to high-latitude warming-upward shifts in distribution, and earlier or extended growth and reproduction. For distribution, we show dramatic upward migration by 69% of species, averaging 6.1m per decade, especially boreal woodland taxa whose upward expansion has reduced arctic montane habitat by 30%. Twenty percent of summit species showed distributional shifts but downward, especially moisture-associated snowbed flora. For phenology, we detected wide inter-annual variability in the onset of leafing and flowering in both eras. However, there was no detectable change in growing-season length, relating to two mechanisms. First, plot-level snow melt data starting in 1917 demonstrated that melt date, rather than vernal temperatures, better predicts plant emergence, with snow melt influenced by warmer years having greater snowfall-warmer springs did not always result in earlier emergence because snowbeds can persist longer. Second, the onset of reproductive senescence between eras was similar, even when plant emergence was earlier by a month, possibly due to intensified summer heat stress or hard-wired 'canalization' where senescence occurs regardless of summer temperature. Migrations in this system have possibly buffered arctic species against displacement by boreal expansion and warming, but ongoing temperature increases, woody plant invasion, and a potential lack of flexibility in timing of senescence may foreshadow challenges.

Unsynchronized Driving Mechanisms of Spring and Autumn Phenology Over Northern Hemisphere Grasslands

Global warming has impacted Northern Hemisphere (NH) grassland ecosystems to a great extent. Vegetation growing season length (GSL) has been extended by concurrent advances in spring green-up and postponements in autumn dormancy. However, the driving mechanisms of phenology are unclear as limited factors have been considered so far. Therefore, it is still elusive to what extent phenological changes shaped GSL. In this study, we used remote sensing normalized difference vegetation index (NDVI) to extract spring and autumn phenology of NH grasslands, and further explored the contribution of each phenophase to GSL through the coefficient of variation (CV) and contribution coefficient (CntC). We found that 65% of NH grasslands exhibited advanced start-of-season (SOS) and circa 58% showed delayed end-of-season (EOS) in the three decades. Changes in GSL was regulated more by EOS changes than by SOS changes, as evidenced by their respective 52 vs. 48% CntC. As for the relationship between phenology and environmental elements, the causing factor analysis revealed that climatic factors (temperature, precipitation, and their interactions) played a dominant role in SOS variations, while environmental and internal factors exerted dominant effects on EOS. Also, interactions of temperature and precipitation contributed a higher variation of SOS than either of them individually. The differentiated factors controlling the two bounding ends of the growing season suggested that it is impossible for GSL to continue to extend without limits under global warming.

Future changes in growing degree days of wheat crop in Pakistan as simulated in CORDEX South Asia experiments

Climate change has become a global phenomenon having severe ramifications on socio-economic sectors such as agriculture, water resources, environment and health. The effects of changing climate are much more prominent on developing economies as compared to the implications on well-developed industrial powers. Pakistan is one of the struggling agricultural economies confronting the issues of food insecurity as a consequence of profound climatic conditions. Notable changes in climatic factors such as temperature can have a direct effect on Growing Degree Days (GDD) and may alter the growing season length (GSL). Growing season length is an important factor in ensuring that each crop developmental stage has a sufficient period for the transition to the next developmental stage. Lengthening or shortening of GSL can have dire threats to crop development and ultimately, production. This study has been conducted to assess the changes in GSL in response to the variability in daily maximum and minimum temperatures with a base temperature of 5°C across Northern, Central and Southern Pakistan. RCP 4.5 and 8.5 have shown an increase of 2°C and 5.4°C in minimum and maximum temperatures, respectively.

A comprehensive analysis of phenological changes in forest vegetation of the Funiu Mountains, China

This paper reports the phenological response of forest vegetation to climate change (changes in temperature and precipitation) based on Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) time-series images from 2000 to 2015. The phenological parameters of forest vegetation in the Funiu Mountains during this period were determined from the temperature and precipitation data using the Savitzky–Golay filter method, dynamic threshold method, Mann-Kendall trend test, the Theil-Sen estimator, ANUSPLIN interpolation and correlation analyses. The results are summarized as follows: (1) The start of the growing season (SOS) of the forest vegetation mainly concentrated in day of year (DOY) 105–120, the end of the growing season (EOS) concentrated in DOY 285–315, and the growing season length (GSL) ranged between 165 and 195 days. There is an evident correlation between forest phenology and altitude. With increasing altitude, the SOS, EOS and GSL presented a significant delayed, advanced and shortening trend, respectively. (2) Both SOS and EOS of the forest vegetation displayed the delayed trend, the delayed pixels accounted for 76.57% and 83.81% of the total, respectively. The GSL of the forest vegetation was lengthened, and the lengthened pixels accounted for 61.21% of the total. The change in GSL was mainly caused by the decrease in spring temperature in the region. (3) The SOS of the forest vegetation was significantly partially correlated with the monthly average temperature in March, with most correlations being negative; that is, the delay in SOS was mainly attributed to the temperature decrease in March. The EOS was significantly partially correlated with precipitation in September, with most correlations being positive; that is, the EOS was clearly delayed with increasing precipitation in September. The GSL of the forest vegetation was influenced by both temperature and precipitation throughout the growing season. For most regions, GSL was most closely related to the monthly average temperature and precipitation in August.

Growing season extension and its impact on terrestrial carbon cycle in the Northern Hemisphere over the past 2 decades

A number of studies have suggested that the growing season duration has significantly lengthened during the past decades, but the connections between phenology variability and the terrestrial carbon (C) cycle are far from clear. In this study, we used the “ORganizing Carbon and Hydrology In Dynamic Ecosystems” (ORCHIDEE) process based ecosystem model together with observed climate data to investigate spatiotemporal changes in phenology and their impacts on carbon fluxes in the Northern Hemisphere (>25°N) during 1980–2002. We found that the growing season length (GSL) has increased by 0.30 days yr−1 (R2 = 0.27, P = 0.010), owing to the combination of an earlier onset in spring (0.16 days yr−1) and a later termination in autumn (0.14 days yr−1). Trends in the GSL are however highly variable across the regions. In Eurasia, there is a significant trend toward earlier vegetation green‐up with an overall advancement rate of 0.28 days yr−1 (R2 = 0.32, P = 0.005), while in North America there is a significantly delayed vegetation senescence by 0.28 days yr−1 (R2 = 0.26, P = 0.013) during the study period. Our results also suggested that the GSL strongly correlates with annual gross primary productivity (GPP) and net primary productivity (NPP), indicating that longer growing seasons may eventually enhance vegetation growth. A 1‐day extension in GSL leads to an increase in annual GPP of 5.8 gC m−2 yr−1 (or 0.6% per day), and an increase in NPP of 2.8 gC m−2 yr−1 per day. However, owing to enhanced soil carbon decomposition accompanying the GPP increase, a change in GSL correlates only poorly with a change in annual net ecosystem productivity (NEP).

The impact of growing-season length variability on carbon assimilation and evapotranspiration over 88 years in the eastern US deciduous forest

Recent research suggests that increases in growing-season length (GSL) in mid-northern latitudes may be partially responsible for increased forest growth and carbon sequestration. We used the BIOME-BGC ecosystem model to investigate the impacts of including a dynamically regulated GSL on simulated carbon and water balance over a historical 88-year record (1900-1987) for 12 sites in the eastern USA deciduous broadleaf forest. For individual sites, the predicted GSL regularly varied by more than 15 days. When grouped into three climatic zones, GSL variability was still large and rapid. There is a recent trend in colder, northern sites toward a longer GSL, but not in moderate and warm climates. The results show that, for all sites, prediction of a long GSL versus using the mean GSL increased net ecosystem production (NEP), gross primary production (GPP), and evapotranspiration (ET); conversely a short GSL is predicted to decrease these parameters. On an absolute basis, differences in GPP between the dynamic and mean GSL simulations were larger than the differences in NEP. As a percentage difference, though, NEP was much more sensitive to changes in GSL than were either GPP or ET. On average, a 1-day change in GSL changed NEP by 1.6%, GPP by 0.5%, and ET by 0.2%. Predictions of NEP and GPP in cold climates were more sensitive to changes in GSL than were predictions in warm climates. ET was not similarly sensitive. First, our results strongly agree with field measurements showing a high correlation between NEP and dates of spring growth, and second they suggest that persistent increases in GSL may lead to long-term increases in carbon storage.

Responses of Snowbed Plant Species to Changes in Growing‐Season Length

We assessed the role of growing—season length in regulating absolute and relative cover of six coexisting dominant plant species in an alpine snowbed habitat. To help explain disparity in species—specific responses to growing—season length, we examined the developmental phenology and distribution of each species in relation to natural snow depth variation. Season length varies from °50 d on early—melting edges of the snowbed to 35 d in the late—melting center, 100 m away. By experimentally altering snowpack, we uncoupled the relationship between spatial location and snowmelt schedule in three consecutive years, imposing the same early dates of snow release in a "long growing—season" treatment and the same late dates of snow release in a "short growing—season" treatment near the edge and center of the snowbed. Over the course of the experiment, growing—season length had significant effects on absolute and relative cover of the species studied (P < 0.025 and P < 0.005, respectively), and these effects were similar near both the edge and center of the snowbed. Yet, only for the snowbed specialist, Sibbaldia procumbens, were changes in absolute and relative cover under early and late snowmelt schedules predictable from the species' distribution along the historical snow depth gradient. S. procumbens increased in cover under a long growing—season and was more common in historically early—melting portions of the snowbed. Other species (e.g., Ranunculus adoneus, Artemisia scopulorum) were equally common in historically early— and late—melting locations within the snowbed, but showed discordant responses to experimentally imposed changes in snowmelt schedule. That the cover of many species under long—vs. short growing seasons was not predictable from their current distributional affinities in relation to snowmelt pattern likely reflects the disparity between the rates of processes exerting long—term control on species' abundances (colonization, soil development) and more immediate effects of growing—season length on plant growth. Consistent with this view, differences in developmental phenology better predicted species—specific responses to snowmelt schedule than distributional affinities. Species having leaf expansion schedules that are poorly synchronized with snowmelt typically had similar cover under early vs. late schedules of snow release (Geum rossii, Trifolium parryi, and Poa alpina). In contrast, species in which leaf expansion schedules are synchronized with snowmelt responded positively to early snow release (Ranunculus adoneus and Sibbaldia procumbens). We hypothesize that maintaining metabolic "readiness" under snowcover provides a mechanism for monopolizing nutrient flushes and competitor free intervals at snowmelt, and exploiting occasional long intervals for growth in years of little snow accumulation, but incurs a respiratory cost that is manifest as reduced growth and vegetative cover when snowmelt is delayed. Our results suggest that interspecific differences in growth phenology of coexisting species will promote shifts in snowbed plant communities with climate change within generations.