Changes In Soil Temperature Research Articles

Ecosystem Processes Show Uniform Sensitivity to Winter Soil Temperature Change Across a Gradient from Central to Cold Marginal Stands of a Major Temperate Forest Tree

The magnitude and frequency of soil frost events might increase in northern temperate regions in response to climate warming due to reduced insulation caused by declining snow cover. In temperate deciduous forests, increased soil frost severity can hamper tree growth and increase the mortality of fine roots, soil fauna and microorganisms, thus altering carbon and nutrient cycling. From single-site studies, however, it is unclear how the sensitivities of these responses change along continental gradients from regions with low to high snowfall. We conducted a gradient design snow cover and soil temperature manipulation experiment across a range of lowland beech forest sites to assess the site-specific sensitivity of tree growth and biogeochemical cycling to soil cooling. Even mild and inconsistent soil frost affected tree increment, germination, litter decomposition and the retention of added 15N. However, the sensitivity of response (treatment effect size per degree of warming or cooling) was not related to prevailing winter climate and snow cover conditions. Our results support that it may be valid to scale these responses to simulated winter climate change up from local studies to regional scales. This upscaling, however, needs to account for the fact that cold regions with historically high snowfall may experience increasingly harsh soil frost conditions, whereas in warmer regions with historically low snowfall, soil frost may diminish. Thus, despite the uniform biotic sensitivity of response, there may be opposing directions of winter climate change effects on temperate forests along continental temperature gradients due to different trends of winter soil temperature.

Hydrothermal Effects of Freeze-Thaw in the Taklimakan Desert

The Taklimakan Desert, also known as the “Sea of Death”, is the largest desert in China and also the world’s second largest remote desert. The road crossing the Taklimakan Desert is the longest desert road in the world and has been the center of the Silk Road since ancient times. Based on field observation data (November 2013 to May 2014) collected from the Tazhong and Xiaotang stations, we studied the interannual and diurnal variations of soil temperature, soil moisture content, and surface heat fluxes during different freezing and thawing periods. The annual and daily changes of soil temperature, soil moisture content, and surface energy fluxes at different freezing and thawing stages were analyzed. We illustrated the coupling relationship between water and heat in freezing-thawing soil in the Taklimakan Desert. We established a coupling model of soil water and heat during freezing and thawing. During the soil freezing period, the soil temperatures at different depths generally trended downward. The temperature difference between the Tazhong station and the Xiaotang station was 4~8.5 °C. The freezing time of soil at 20 cm depth occurred about 11 days after that at 10 cm depth. The effect of ambient temperature on soil temperature gradually weakened with the increase of soil depth. With the occurrence of the soil freezing process, the initial soil moisture contents at 5 cm, 10 cm, 20 cm, and 40 cm depths at the Xiaotang station were 6%, 10%, 29%, and 59%, respectively, and those at the Tazhong station were 5%, 3.6%, 4.4%, and 5.8%, respectively. As the ambient temperature decreased, the freezing front continued to move downward and the liquid soil water content at each depth decreased. The desert highway is closely related to the economic development and prosperity of southern Xinjiang. Therefore, it is important to maintain and inspect the safety and applicability of freeze-thaw zones and avoid casualties from vehicles and personnel.

Vegetation as an indicator of underground smoldering fire on coal-waste dumps

The paper presents the impact of thermal processes on the dynamics of changes in vegetation and soil properties in the area of coal-waste dumps where self-heating and self-ignition processes occur. Vegetation analysis involved the determination of species composition, life forms, and synecological affiliation. The mosaic diversity of the granulometric composition of the stored material and dynamically changing soil temperature had an impact on the character of vegetation. A specific type of flora, with various ecological requirements, was formed. Hemicryptophytes and apophytes predominated, especially in thermally active zones. The distribution of the range of vegetation due to changes in soil thermics was examined during three periods within a selected transect, in which three types of surfaces with varying soil thermics and smoldering fire directions were distinguished. Temperatures ranged from 9.9 to 139 °C at a depth of 20 cm and, simultaneously, from 3.1 to 69.0 °C on the surface. Total organic carbon content in all samples ranged from 1.7 to 7.6 and, simultaneously, from 3.1 to 4.5% in the active fire spots. The concentration of total nitrogen ranged from 0.023 to 0.29%. Soil reaction (pH) fluctuated between 5.8 and 8.0 (in H2O).The variability of the range of vegetation in time and space indicated the directions of movement of fire spots. The analysis showed that underground temperature has a significant impact on the distribution and species composition of plants growing on coal-waste dumps.

Температурний режим грунтових масивів Як геологічний вплив на основи будівель

Проаналізовані результати спостережень за температурою ґрунту на 11 метеостанціях України. Розроблена методика визначення мінімальних та максимальних розрахункових значень температури ґрунту. Визначені розрахункові значення температури ґрунту для глибин до 3,2 м, проаналізовані та описані їх залежності від глибини й періоду повторюваності. Результати дослідження можуть бути використані в теплотехнічних розрахунках підземних частин будівельних об’єктів.

РЕЗУЛЬТАТЫ ЭКСПЕРИМЕНТАЛЬНЫХ ИССЛЕДОВАНИЙ ВЛИЯНИЯ ТЕМПЕРАТУРЫ ПОЧВОГРУНТОВ КРИОЛИТОЗОНЫ НА ИХ ФИЗИКО-МЕХАНИЧЕСКИХ СВОЙСТВА

Establishing the regularities of the temperature influence of frozen soils on their physical and mechanical properties makes it possible to make more accurate estimates of the parameters of the interaction process of forest machines and skidding systems with the soil mass when performing logging operations with predetermined static loads. An adequate assessment of the state of the edge part of frozen soil mass is the basis for the formation of initial conditions when calculating the parameters of the destruction of the stress-deformed frozen soil layer, the processes of its compaction and deformation under the influence of static loads arising from the operation of various forest machines and skidding systems. The article presents methodology, hardware and the results of data processing obtained in field experimental studies to determine the effect of frozen soil temperature on its strength and deformation properties. To reveal the regularities of the change in soil temperature in depth, as well as in order to take soil samples for testing the mechanical properties in depth, soil benches with an area of 1×1 m and a depth of up to 1.0 m were opened. Sections were investigated in three areas with a predominance of: permafrost pale brown soils with sandy loam soil base; humus-carbonate soils with a loamy base; cryozem gley soils with a clay base. Soil temperature was measured near the ledge surface with a HI 98501 Hanna soil electronic thermometer (Germany) with a resolution of 0.1°C and an error of ± 0.3°C. The temperature value was measured as the depth increased with the help of a penetrating thermometer probe in the control holes along the depth of the ledge with a step of 0.1 m

Long‐term changes in layered soil temperature based on ground measurements in Jiangsu Province, China

AbstractWhile air temperature has been widely investigated to better understand the recent climate changes, the importance of soil temperature has been underestimated and rarely studied. Here, the long‐term soil temperature changes and the occurrence of extreme heats have been studied based on daily measurements in Jiangsu Province for 1970–2017. A general warming trend in soil temperature is observed at most stations, and these trends are more pronounced in the cold seasons than the warm seasons. Due to the asymmetric warming of maximum and minimum soil temperatures over the past 48 years, the diurnal range shows a long‐term decreasing trend with a rate of −0.34°C/10a. The occurrences of extreme soil temperatures have been analysed based on the probability density functions. It is found that the hot soil days have increased and cold soil days have decreased significantly, and these changes are particularly significant in the most recent decades.

Changes in soil temperature and water content under mobile soil steam disinfection

The soil steam injection method is one of the most effective disinfection methods, and the determination of the steam pipe structure parameters is very important. The steam capillary diameter (SCD) affects the steam flow field in each pipe, which in turn affects the steam changes in the soil flow range and soil temperature (ST). Larger SCD would make lower ST in clay loam, silt loam, and sandy clay loam. The effectiveness of an SCD of 10 mm was verified by a mobile disinfection test at walking speeds of 10 cm/min and 30 cm/min under soil water content (SWC) of 15% and 35%, respectively. The results showed that when the walking speed was 10 cm/min, the initial SWC was proportional to the ST. However, when the walking speed was 30 cm/min, the law was exactly the opposite; that is, the initial water content is inversely proportional to the ST. The research can provide a theoretical research foundation for increasing soil temperature for efficient soil steam disinfection. Keywords: soil steam disinfection, steam capillary diameter, steam capillary vent, soil temperature, soil water content DOI: 10.25165/j.ijabe.20211403.5026 Citation: Yang Z J, Wang X C, Ameen M. Changes in soil temperature and water content under mobile soil steam disinfection. Int J Agric & Biol Eng, 2021; 14(3): 140–147.

Effect of Different Irrigation Patterns and Covering Methods on Soil Temperature of Onions Under Membrane Drip Irrigation

In order to investigate the influence of the soil temperature of onions in the West Hebei Oasis, this paper tested the soil temperature of onions in the Oasis by using the early golden dragon onion as a test material and randomly grouped it into different irrigation modes and cover methods. There were five treatments in the experiment, and the soil temperature of onion was measured in each reproductive period, and the results showed that: The most significant changes in soil temperature were found in the 5 cm soil layer, where the soil temperature was more affected by external influences, and in the 10 and 20 cm soil layers, where the soil temperature was less affected by external influences. The difference in soil temperature was not significant between full irrigation and regulated deficit irrigation. The soil temperature in the black mulch layer was higher than that in the transparent mulch layer and fine sand mulch layer at the seedling and leaf development stages, while the soil temperature in the black mulch layer was higher than that in the transparent mulch layer and fine sand layer at the bulb expansion and maturity stages.The soil temperature of the onion can be best controlled by irrigation while covering the onion with black mulch throughout the growing season, which is of great significance for onion cultivation in the Hexi Irrigation Zone.

Analysis of ground thermal potential reduction and thermal interaction between boreholes during operation of ground source heat pump in Moscow city environments

Geothermal energy is a renewable energy resource. Nowadays it can be considered as a promising alternative to various fossil fuels. Ground source heat pumps are efficient installations enabling the intensive use of underground energy for heating and cooling of modern residential and commercial buildings. However, climatic conditions often limit the use of this type of installation to a certain extent. This paper presents a description of an existing system comprising a liquid-toliquid heat pump and a geothermal field consisting of 4 boreholes. The system is used to investigate the intensity of ground temperature potential decrease in winter and its recovery in summer in the Moscow city environment with a detailed study of the properties of individual soil layers, as well as to study the mutual influence of boreholes on each other, represented by the conditional radius of thermal influence of individual boreholes. Graphs of soil temperature changes at different depths are presented.

Delayed Sowing Dates Affected Alfalfa Overwintering Survival Rates by Reducing Soil Temperature Stress

This study explored the effect of sowing time on alfalfa overwintering and its mechanisms. Gongnong No. 1 alfalfa was sown on July 1, July 16, August 1 and August 15, 2017, and was not cut at the end of autumn. The soil temperature changes in the 10 and 20 cm soil layers were monitored during the overwintering period, and bare land was monitored as a control. The growth characteristics of alfalfa were observed at the end of autumn, and the overwintering survival rate was measured at the end of April 2018. Research shows that as the sowing delay increased, the alfalfa hay yield, plant height, root collar diameter and overwintering survival rate decreased gradually. The minimum temperature of the 10 and 20 cm soil layers decreased as the sowing delay increased, and the diurnal temperature difference increased. Compared with that of alfalfa sown on August 15, the aboveground biomass of alfalfa sown on July 1 increased the average minimum temperature difference in the 10 and 20 cm soil layers by 3.12°C and 2.99°C, respectively, and reduce the average diurnal temperature difference by 3.33°C and 2.15°C. These results indicated that delaying alfalfa sowing reduces the cover on the field, which results in substantial differences in the minimum temperature and the diurnal temperature difference between the 10 and 20 cm soil layers. Our research has suggested that the minimum temperatures of the 10 and 20 cm soil layers and the increase in the diurnal temperature difference are important reasons for low overwintering survival rates in alfalfa. Therefore, sowing should occur in early July, and mowing should not be performed at the end of autumn in northern China.

Effects of slope aspect on altitudinal pattern of soil C:N:P stoichiometry in alpine forest of Tibet

Knowledge of altitudinal patterns in soil C, N and P distribution is important for understanding biogeochemical processes in mountainous forests, yet the influence of slope aspects on soil stoichiometry has been largely neglected in previous studies. In this paper, a total number of 150 topsoil samples at four altitudes (3700, 3900, 4100, 4380 m a.s.l.) on sunny and shady slopes of Sygera mountains in the Southeastern Tibet were collected. Soil C, N and P contents, and pH, were measured. Soil temperature, moisture and richness of plant species were investigated at each sampling site. The results showed that: 1) in sunny slope, soil C, N and P concentrations increased with the increase in altitude, whereas soil C:N, C:P, and N:P decreased along the altitudinal gradient on s. Soil moisture was the main regulator of soil nutrition and stoichiometric ratios. 2) In shady slope, soil C and N contents had no significant difference along the altitudinal gradient except the higher values at low altitude, whereas soil P increased first and then decreased. Soil C:N increased with the increase in altitude, whereas C:P and N:P decreased first and then increased. Soil temperature and species richness were the main factors influencing soil nutrition and stoichiometric ratios. 3) Decoupling of soil C:N:P stoichiometry was observed in shady slope owing to changes in soil pH and temperature. 4) The rich contents of soil C and P were observed at two slopes along the altitudinal gradient, and high capacity of N supply existed at the topsoil in shady slope. These results suggested that slope aspect plays an important role in shaping the altitudinal pattern of soil C:N:P stoichiometry in mountainous forests.

Study on the Hydro‐Thermal‐Mechanical Characteristics of the Lime‐Soil Compaction Pile in the Forming Process

To study the effect of the lime‐soil compaction pile on the collapsible loess foundation and the influence of water‐heat‐force characteristics on the soil during compaction, the field test of lime‐soil compaction pile treatment of collapsible loess foundation is carried out. This paper monitors the process of soil temperature, water, and soil pressure change in the process of pile forming. According to the macroprocess and micromechanism of lime‐soil compaction pile treatment of collapsible loess foundation, the qualitative law of water‐heat‐force change in the process of pile forming is obtained. Meanwhile, the influence of soil damage is introduced in the process of compaction expansion. The model of pore expansion under linear damage conditions in the plastic zone is established. The formula of radial stress distribution under damage conditions is given. The influence of different damage factors on the expansion process is analyzed.

Comparison of Soil Moisture, Soil Temperature, and Micro-Gradient Change Influence on CO2 Efflux in Three Land Types within the Blackwater Conservation Area

Comparison of Soil Moisture, Soil Temperature, and Micro-Gradient Change Influence on CO2 Efflux in Three Land Types within the Blackwater Conservation Area

Effects of warming and clipping on CH4 and N2O fluxes in an alpine meadow

Methane (CH4) and nitrous oxide (N2O) are two greenhouse gases with much more warming potential than carbon dioxide (CO2). However, there have been less studies on their responses to climate warming and land use practices, such as hay harvest in grasslands. Especially, their fluxes are not well estimated during the nongrowing season. In this study, we investigated year-round (August 2015–August 2016) continuous measurements of CH4 and N2O fluxes in response to simulated warming, clipping (as a mimic of hay harvest), and their interaction in an alpine meadow on the Qinghai-Tibetan Plateau. Compared to the control, warming alone and in combination with clipping significantly increased CH4 uptake by 42% and 51%, respectively, on the annual basis. Warming alone also significantly decreased year-round N2O emission by 57% relative to that under control. However, clipping alone did not affect CH4 and N2O fluxes during the study period, and no significant interactive effect of clipping and warming was detected. Furthermore, warming had larger effects on CH4 uptake but smaller effects on N2O emission in the growing than nongrowing season. We also found that the responses in CH4 and N2O fluxes to different treatments were regulated by changes in soil temperature and moisture. Based on sustained global warming potential approach and expressed as CO2-equvalents, the ecosystem switched from a net source of these two gases in the control (1.2 g CO2-eq m-2) to a net sink in warming (-11.3 g CO2-eq m-2) and its combination with clipping (-9.9 g CO2-eq m-2). The findings highlight the importance of understanding greenhouse gas fluxes in the nongrowing season and suggest the increase of CH4 uptake and reduction in N2O emission under climate warming will benefit ecosystem feedback and help mitigate climate change.

Evaluation and Analysis of Soil Temperature Data over Poyang Lake Basin, China

Soil temperature reflects the impact of local factors, such as the vegetation, soil, and atmosphere of a region. Therefore, it is important to understand the regional variation of soil temperature. However, given the lack of observations with adequate spatial and/or temporal coverage, it is often difficult to use observational data to study the regional variation. Based on the observational data from Nanchang and Ganzhou stations and ERA-Interim/Land reanalysis data, this study analyzed the spatiotemporal distribution characteristics of soil temperature over Poyang Lake Basin. Four soil depths were examined, 0–7, 7–28, 28–100, and 100–289 cm, recorded as ST1, ST2, ST3, and ST4, respectively. The results showed close correlations between observation data and reanalysis data at different depths. Reanalysis data could reproduce the main spatiotemporal distributions of soil temperature over the Poyang Lake Basin but generally underestimated their magnitudes. Temporally, there was a clear warming trend in the basin. Seasonally, the temperature increase was the most rapid in spring and the slowest in summer, except for ST4, which increased the fastest in spring and the slowest in winter. The temperature increase was faster for ST1 than the other depths. The warming trend was almost the same for ST2, ST3, and ST4. An abrupt change of annual soil temperature at all depths occurred in 1997, and annual soil temperatures at all depths were abnormally low in 1984. Spatially, annual soil temperature decreased with latitude, except for the summer ST1. Because of the high temperature and precipitation in summer, the ST1 values were higher around the lake and the river. The climatic trend of soil temperature generally increased from south to north, which was opposite to the distribution of soil temperature. These findings provide a basis for understanding and assessing the variation of soil temperature in the Poyang Lake Basin.

EFFECTS OF HURRICANE-DRIVEN DEFORESTATION AND REFORESTATION ON DIURNAL SOIL TEMPERATURE CHANGES IN THE TATRA MOUNTAINS IN SOUTHERN POLAND

Aim of the study: The aim of the study was to investigate the effect of hurricane-driven deforestation and reforestation on diurnal changes in soil temperatures in the Tatra Mountains (Poland). Material and methods: Soil temperature was measured at 0.20 m of depth in the mineral soil horizons on both north-facing and south-facing slopes in the deforested subcatchment and in the control woodland subcatchment. Soil temperature measurements were collected every 10 minutes in 2015–2020. The cross-correlation analysis was applied in order to determine the magnitude of the delay of soil temperature to air temperature changes at four studied sites during a day. Results and conclusions: The effect of deforestation on diurnal changes in soil temperature manifested itself mainly via a larger range of diurnal soil temperatures during warmer part of the year. In the summer months the diurnal soil temperature range for deforested slopes was 1 to 3℃ higher than that for wooded slopes. Diurnal soil temperature ranges were found to strongly decline with reforestation. Deforested slopes were characterized by a more rapid soil temperature reaction to changes in air temperature over the course of the day. Cross-correlation revealed that soil temperature changes on a deforested, south-facing slope occurred 4 to 5 hours later relative to changes in air temperature, while the delay for a wooded slope facing the same direction was usually 7 to 8 hours. Soil temperatures in the summer, both during the day and at nighttime, were higher on deforested slopes than wooded slopes. This indicates that deforestation may significantly intensify soil warming caused by global climate warming.

Shoot removal interacts with soil temperature to affect survival, growth and physiology of young ramets of a bamboo

Global climate change has great effects on ecosystems via changes in air and soil temperature. While the effects of temperature have been extensively studied, relatively few studies have truly separated the impact of soil temperature from that of air temperature. Furthermore, little is known about how removal of older ramets may affect the performance of their interconnected younger ramets of bamboos. By maintaining air temperature constantly (at 17 °C) in growth chambers and manipulating soil temperature (2, 7, 12, 17 and 22 °C) using thermostatic water bath systems, we tested the effects of soil temperature and removal of the older ramets on survival, growth and physiology of its interconnected young ramet of a bamboo Indocalamus decorus. Soil temperature significantly affected the survival of the young ramet of I. decorus and also the growth and photosynthetic rate of the surviving young ramet when the shoots of its connected older ramets were not removed. Removing shoots of the older ramets greatly enhanced the survival of the young ramet at the two highest soil temperatures (17 and 22 °C) and the growth of the surviving ramet at 7 and 12 °C. We conclude that shoot removal of older ramets can interact with soil temperature to affect survival and growth of young ramets of the bamboo, and that resource sharing (translocation of photosynthates) from older ramets to young ramets of the bamboo is rather limited. Instead, newly emerged, interconnected ramets of bamboos may compete fiercely for resources stored in rhizomes. These results suggest that bamboo forest management should consider the balance between resource sharing and competition for resources stored in rhizomes under ongoing global climate change.

Bioremediation of polycyclic aromatic hydrocarbons contaminated soil under the superimposed electric field condition

An innovative superimposed electric field (SEF) was designed with the aim to achieve uniform removal of polycyclic aromatic hydrocarbons (PAHs) in soil. Also the influence of SEF on the bioremediation efficiency of PAHs was investigated in compared with the common electric field (CEF). Five experiments were conducted in this study, namely EK-CEF (applied CEF), EKB-CEF (CEF enhanced bioremediation), EK-SEF (applied SEF), EKB-SEF (SEF enhanced bioremediation), and Bio (bioremediation). The results indicated that electric field with periodically reversed polarity could effectively prevent the occurrence of large changes in soil pH, temperature, and electric current. The electric field intensity of SEF was concentrated in the range of 0.5–1.5 V/cm, and the difference between the maximum and minimum PAHs removal percentage in EK-SEF was just 5.4%, in comparison to 14.8% in EK-CEF. The bioremediation promoting effect did not show significant difference between SEF and CEF. Compared to Bio, the removal percentages of the 5-ring and 6-ring PAHs attributed to the degrading bacteria were much higher in EKB-SEF and EKB-CEF. Moreover, the microbial number increased with the distance away from electrodes, and the microbial community changed correspondingly. All these would be resulted in differences removal efficiencies among different PAHs components. Despite its intrinsic advantages, the influence of SEF on soil physicochemical and biological properties needs further study.

Effects of planned grazing and burning to restore tallgrass species in old-field sites under drought conditions in Texas Blackland Prairie

We examined if reintroduction of grazing with or without burning would enhance succession towards native prairie vegetation on previously over-seeded old-field tallgrass prairie subjected to mowing or burning. We hypothesized that returning grazing and fire to these seeded and old-field sites would change establishment and competitive relationships among plant species to benefit fire-tolerant prairie species. Grazing and burning had neutral effects on native prairie species on the previously seeded and unseeded sites over a study period that experienced 70 % of normal precipitation. Herbaceous group categories included old-field grasses, seeded tallgrasses, other grasses (< 2%), seeded perennial forbs, other perennial forbs, and annual forbs. Seeded species comprised about 70 % of the community on seeded plots and 10 % on unseeded plots for the eight years of this study. Seeded-ungrazed tallgrass biomass increased 19 % and on seeded-unburned sites biomass increased 11 %. Tallgrass biomass of unseeded-grazed burned treatment remained at about 4% throughout the study, but with no grazing or no burning biomass, doubled. Changes in biomass associated with treatments led to changes in soil temperatures near the soil surface in summer months. Community dissimilarity was most affected by seeding followed by year, grazing, and burning (P’s = 0.001). Collectively, seeded or unseeded, grazed, or ungrazed site soil temperatures averaged 4.8 °C higher than tree-shaded sites in afternoons of hotter months. Soil temperature differences were inversely proportional to successful site restoration. During afternoons of hotter months, soil temperatures of seeded sites were 1.1 °C lower than unseeded sites, while grazed sites were 2.0 °C greater than ungrazed sites, and burned sites were 1.6 °C higher the year of the burn than unburned sites (P’s < 0.05). While grazing and burning had neutral effects on previously seeded and unseeded prairie sites, seeding accounted for about 70 % of the community on seeded plots and 10 % on unseeded plots.

Strong stabilizing selection on timing of germination in a Mediterranean population of Arabidopsis thaliana.

PremiseTiming of germination can strongly influence plant fitness by affecting seedling survival and by having cascading effects on later life‐history traits. In seasonal environments, the period favorable for seedling establishment and growth is limited, and timing of germination is likely to be under stabilizing selection because of conflicting selection through survival and fecundity. Moreover, optimal germination time may vary among genotypes because of inherent differences in later life‐history traits.MethodsTo examine how germination time affects survival, fecundity, and the relative fitness of two genotypes differing in time to first flower, we conducted a field experiment in an Italian population of the winter annual Arabidopsis thaliana, in which seedling establishment occurs mainly in November. We transplanted seedlings of the local genotype and of a Swedish genotype monthly from August to December and monitored survival and fecundity.ResultsOnly seedlings transplanted in November and December survived until reproduction, and fitness of the November cohort was 35 times higher than that of the December cohort, indicating strong stabilizing selection on timing of germination. There was no evidence of conflicting selection: seedling survival, adult survival, and fecundity were all highest in the November cohort. Moreover, the relative fitness of the two genotypes did not differ significantly between cohorts.ConclusionsThe very narrow window of opportunity for seedling establishment was related to rapid seasonal changes in soil moisture and temperature, suggesting that rate of seasonal change is an important aspect to consider for understanding spatiotemporal variation in selection on phenological traits.