Average Annual Minimum Temperature Research Articles

Tree-ring Climatology of Larix gmelinii in Maoershan Region,Northeastern China

Through collecting the meteorological data,sampling and standardizing the data of tree rings of larch(Larix gmelinii),the climatic changes in Maoershan region were analyzed and their influences on tree ring features were studied in this paper.In the past 50 years,significant increases in temperature were found(p0.05),i.e.about 0.4℃ per decade in average annual temperature,0.3℃ per decade in average annual maximum temperature as well as 0.5℃ per decade in annual average minimum temperature were observed.However,no significant change in annual precipitation was found(p0.05).Average monthly temperature(average temperature,average maximum temperature,average minimum temperature) also showed increasing tendencies and the most significant month was in February of the winter,about 0.9-1℃ per decade.Much smaller temperature increases,ca.0.2-0.7℃ per decade was found in June to August of the summer).No significant change in monthly precipitation was found in most months(p0.05).During the coming climate warming,widths of early and whole tree rings(p0.05) might be decreased with the temperature increment in summer(June to July),while widths of early and the growth of tree rings would increase with the temperature increases in spring(May).The width of late might be increased with the temperature increases in autumn(September).These might cause the non-obvious change in ring width with annual temperature changes(p0.05).Although non-significant changes in precipitations,the significant correlations between annual precipitation and variable tree rings indices indicated the growths of early wood and whole tree rings might be positivity affected by the amount of annual precipitations.Considering the warming trend of the climate change is significant in northeast China in future but the rainfall does not.The growth of tree rings caused by spring and autumn temperatures could be offseted by too high temperatures in summer which inhibited the tree ring growth.Therefore,the influence on the radial growth of the Larix might be little.

Analysis of temporal-spatial variation characteristics of extreme air temperature in Xinjiang, China

Abstract Based on data from 1961 to 2007, this paper discusses the variation trend and the periodic temporal-spatial patterns of the extreme air temperature in Xinjiang by means of the Mann-Kendall monotonous trend test and wavelet analysis. The results are as follows: (1) In the north, south and east of Xinjiang, the annual average maximum air temperature, annual average minimum air temperature and annual minimum air temperature all rose remarkably, while the rise of the annual maximum air temperature was not significant. (2) The rising trend of the annual average maximum air temperature was stronger in the east than in the north, and it was weakest in the south. The rising trend of annual average minimum air temperature was strongest in the east, followed by the south and the north. The annual maximum air temperature rose more strongly in the south than in the north, and the rise was weakest in the east. The change in annual minimum air temperature was higher in the south than in the east and was lowest in the north. (3) The mean values of annual average maximum temperature, annual average minimum temperature, and annual minimum temperature were highest in the south, followed by the east and north. The mean value of annual maximum temperature was highest in the east, followed by the north, and it was the lowest in the south. (4) Significant periodic variations with periods of 3–11 years appeared in the extreme air temperatures. (5) Wavelet coefficients can predict well the variation trend of extreme temperature in the future based on a significant period. These results can be applied in early warning of meteorological disasters and in realizing sustainable agricultural development in the study area.

Urban and Regional Temperature Trends in Las Vegas and Southern Nevada

Urban and regional temperature trends in southern Nevada, including the rapidly growing Las Vegas metropolitan area, were analyzed over two periods, 1940–2009 and 1977–2009. The data show that minimum temperatures in Las Vegas increased by more than 4°C above the regional trend since 1940 and by approximately 3°C more than the regional average since 1977, which demonstrates that urbanization has significantly altered the nighttime climate of the city and that the changes were most pronounced in the last 30 years. In contrast, regional minimum temperature increases were not widespread and generally limited to spring and summer with a regional annual average minimum temperature increase of about 1°C since 1940 and 0.6°C since 1977. Notably, there is little evidence of winter temperature moderation throughout rural southern Nevada in either time period investigated. The analysis also suggests maximum temperature trends in Las Vegas have been moderated by urbanization, as daytime temperatures across southern Nevada increased by approximately 1°C in the last 30 years, but no increase was observed within the city suggesting that Las Vegas has developed a moderate daytime urban cool island. While no absolute change in Las Vegas dewpoint temperatures was found, a relative increase of up to 3°C was observed when the city was compared to a rural control station. The relative increase in urban dewpoint temperature is significantly correlated to the daytime urban cooling trend, minimum temperature increase, and the significant reduction in diurnal temperature range, suggesting that increased latent heat flux in Las Vegas may be a primary cause of observed urban climate changes.

Modeling the Distribution of the Dwarf Palmetto (Sabal minor; Arecaceae) in McCurtain County, Oklahoma

The dwarf palmetto, Sabal minor, reaches the northwestern limit of its geographic range in McCurtain County, Oklahoma, where it is critically imperiled. We determined that S. minor was more widespread than previously reported; 28 new localities were identified. Populations were associated positively with average annual minimum temperatures (i.e., plants were in the warmest parts of the county), negatively associated with elevation, and the species primarily occurred on silty clay soils. Although S. minor was common in a few areas near Red Slough Wildlife Management Area, it generally was uncommon and typically represented by only a few individuals. Ecological Niche Factor Analysis projected that suitable habitat was concentrated in southeastern McCurtain County, but that potentially suitable habitat was present throughout much of the county.

Analysis of rainfall and temperatures for climatic trend in Kullu valley

Kullu valley is famous for tourism and agricultural activities but recently it has assumed importance for studies on climatic variability. There is an increasing trend in minimum and maximum temperatures but no trend in annual rainfall. The slope of regression line for annual rainfall was negative at Bajaura and positive at Katrain but both were non significant. The coefficient of variation for annual rainfall (22 %) and for monsoon rainfall (33 %) was showing the consistence of annual and southwest monsoon rainfall but, a shifting of monsoon from its wettest months was observed. The rainfall was most variable during post monsoon season at Bajaura and in winter at Katrain. The decreasing rate in rainfall was higher during the recent period than the decadal period. Monthly, seasonal and annual average minimum temperature was showing decreasing trend at Bajaura and an increasing trend at Katrain, but, maximum temperature is increasing at both the stations. The minimum temperature was most variable during the winter season whereas the maximum temperature was during summer. Higher the altitude higher the variability in minimum temperature but lower the altitude higher the variability in maximum temperature. Both maximum and minimum temperatures were showing a higher rate of increasing during the recent period.

IMPACT OF GLOBAL WARMING ON THE ACCUMULATED CHILLING HOURS IN THE SOUTHERN REGION OF BRAZIL

One likely consequence of global warming, which is mainly due to the anthropogenic influence (IPCC, 2007), would be the changes in the accumulated chilling hours in temperate fruit crops. Global warming might have dramatic effects in the most warmer fruit zones, e.g., the Southern Region of Brazil. Simulations were performed to assess the effect of increasing minimum air temperature by 1°C, 3°C and 5.8°C in the chilling hours, on temperate fruit crops. Data from 81 meteorological stations of Parana (Iapar), Santa Catarina (Epagri) and Rio Grande do Sul (Fepagro) States were used to develop a model to estimate the chilling hours (Ch) as a function of the average minimum air temperature from May to September (Tmin may-sep ) and the annual average of the minimum air temperature (Tmin annual ). The generated model was used into the geographical information system (GIS) to create, through regression equations, information plans of the actual average minimum temperature (May to September) and actual annual average minimum temperatures. To the information plans generated by the equations were added the temperatures of 1°C, 3°C and 5.8°C. These data were used to generate, with GIS, maps of actual and future chilling hours. If the scenario of increasing 1°C is confirmed, it will decrease the areas with higher accumulated chilling hours (ACH) and increase the areas with lower ACH. This pattern will be more pronounced with an increase of 3°C, and culminate with an increase of 5.8°C where practically all areas with ACH would disappear, with the exception of small areas on the highest places of Rio Grande do Sul and Santa Catarina States, where the maximum ACH would be 334 hours.

Potential environmental influences on variation in body size and sexual size dimorphism among Arizona populations of the western diamond-backed rattlesnake ( Crotalus atrox)

Differences in resource availability and quality along environmental gradients are important influences contributing to intraspecific variation in body size, which influences numerous life-history traits. Here, we examined variation in body size and sexual size dimorphism (SSD) in relation to temperature, seasonality, and precipitation among 10 populations located throughout Arizona of the western diamond-backed rattlesnake ( Crotalus atrox). Specifically, in our analyses we addressed the following questions: (i) Are adult males larger in cooler, wetter areas? (ii) Does female body size respond differently to environmental variation? (iii) Is seasonality a better predictor of body size variation? (iv) Is SSD positively correlated with increased resources? We demonstrate that male and female C. atrox are larger in body size in cooler (i.e., lower average annual maximum, minimum, and mean temperature) and wetter areas (i.e., higher average annual precipitation, more variable precipitation, and available surface water). Although SSD in C. atrox appeared to be more pronounced in cooler, wetter areas, this relationship did not achieve statistical significance.

Characteristics and Abrupt Change of Temperature in the Hexi corridor in recent 58 years

Based on data of the average monthly temperature,average monthly maximum and minimum temperature from 1951 to 2008 recorded by the surface weather stations in the Hexi Corridor-Dunhuang,Guazhou,Zhangye,Wuwei and Wuqiaoling,this paper analyzes trends and abrupt changes of climate in the region by means of linear fitting,moving average and Mann-Kendall.The research results show that the average annual temperature,average maximum and minimum temperature in the Hexi Corridor present increasing trends,with the temperature increment-ratio 0.19 ℃/10 a,0.14 ℃/10 a and 0.27 ℃/10 a respectively,and the increment-ratio of average annual minimum temperature is obviously greater than that of other two.Average annual temperature in 1950s' was positive anomalies,while negative anomalies in 1960-1987 and positive anomalies after 1987.The minimum of average annual temperature appeared in 1960s',and at the same time the departure from normal value is-0.3 ℃.On the other hand the positive anomaly of average annual temperature from 2001 to 2008 was 1.1 ℃,thereby the warmest time since 1958.The lowest average annual maximum temperature appeared in 1960s',while the highest appeared after 1990s'.The variation of average annual minimum-temperature slightly differed to that of average annual temperature and that of average annual maximum-temperature: the coldest time appeared in 1960s' with a positive departure from the normal value;and the warmest time appeared in 2001-2008;the average minimum-temperature of the warmest times increased of 1.7 ℃ compared with that of the coldest times.A warmly abrupt change was detected in 1997 by using Mann-Kendall method,which is 4 years later than nationwide abrupt change appeared in 1993,and 10 years later than that in north-west region.The average temperature from 1997 to 2008 was of 1.1 ℃ greater than that from 1951 to 1996.The warmly abrupt change of average annual maximum-temperature appeared in 1996,and average annual maximum-temperature from 1996 to 2008 increased of 0.9 ℃ compared with that from 1951 to 1995.The abruptly warming change of average annual minimum-temperature occurred in 1994,3 years and 2 years,respectively,earlier than that of average annual temperature and average annual maximum-temperature.The annual temperature range shown a decrease trend of 0.13 ℃/10 a,while about 0.6 ℃decreased since 2001,due to comparatively large variation in average annual minimum-temperature.The measurement revealed that annual temperature range decreased in 2002.Seasonally,average temperature increased totally,but the increasing magnitudes were different.The average winter temperature shown a steadily increase trend of 0.345 ℃/10 a,and the warming abrupt change appeared in 1986,which is earlier than other seasons.The steadily increasing ratio of average summer temperature was the smallest,and the obviously warming abrupt change was not detected.From 1951 to 2008,average maximum-temperature in winter increased of 0.27 ℃/10 a,which is the largest increasing magnitude in four seasons,and the warming abrupt change occurred in 1985.The increasing ratio of average summer temperature was 0.13 ℃/10 a-the smallest increasing magnitude in four seasons,and the warming abrupt change occurred in 2004.This illustrates that the climate warming in the Hexi Corridor starts from winter.The daily variation range of spring tended to decrease,with a ratio of 0.18 ℃/10 a from 1951-2008,when the abruptly decreasing change occurred in 1980.The daily variation range of summer and autumn decreased by a comparatively small ratio,which was 0.09 ℃/10 a and 0.05 ℃/10 a respectively,the abruptly decreasing change of summer daily variation range appeared in 2004,while that of autumn kept steady.The decreasing trend of winter daily variation range was also obvious,with a decreasing ratio of 0.13 ℃/10 a from 1951 to 2008,and abruptly decreasing change occurred in 1999.The largest increasing ratio occurred in winter and spring minimum temperature,0.42 ℃/10 a and 0.30 ℃/10 a respectively,demonstrating that the decreasing in daily variation range is due to increasing in night temperature.

Cold Hardiness of Weigela (Weigela florida Bunge) Cultivars

Abstract Factual information regarding the low-temperature tolerances of weigela (Weigela florida Bunge) cultivars is essential for identifying cultivars to grow and sell in northern regions of the country [USDA Hardiness Zone 4a;−32 to−34C (−25 to−30F) average annual minimum temperature]. In this study, laboratory freezing tests and a replicated field trial were utilized to compare the relative stem hardiness of 11 recent weigela introductions with that of four standard cultivars representing a known range of hardiness. Freezing tests were conducted monthly from October 2005 to April 2006 on containerized plants over-wintered in a minimally-heated greenhouse under a non-lethal temperature regime conducive to cold acclimation. The cultivars differed substantially in both timing and rates of cold acclimation and de-acclimation in the fall and spring, respectively, as well as maximum midwinter hardiness levels. All of the cultivars, including the cold-hardy standards ‘Minuet’ and ‘Java Red’, were relatively slow to acclimate in early October, but subsequent acclimation rates among cultivars ranged from 0.3 to 0.7C (0.6 to 1.25F) per day between mid-October and mid-November. Maximum midwinter hardiness levels of the new cultivars were within the range defined by the most and least cold tolerant standard cultivars (‘Java Red’ and ‘Variegata’, respectively). With the exception of ‘Java Red’, all cultivars had de-acclimated substantially by March 16, but actual hardiness levels among the new cultivars on this date differed by as much as 10C (18F). Overall, ‘Pink Poppet’, ‘Dark Horse’ and ‘Ruby Queen’ were the hardiest of the new cultivars evaluated with a maximum midwinter hardiness level of−35C (−31F). ‘Alexandra’, ‘Evita’, and ‘Sunny Princess’ exhibited hardiness comparable to that of the moderately hardy standard ‘Red Prince’ and would likely experience moderate to severe injury during colder winters in Zone 4a. ‘Brigela’, ‘Carnaval’, ‘Elvera’, ‘Goldrush’ and ‘Rubidor’ appear to be unsuitable for use in Zone 4a due to late acclimation, insufficient midwinter hardiness, early de-acclimation or a combination of these characteristics. Results of limited testing conducted in 2007–2008 indicate ‘Verweig’, a more recent introduction, is sufficiently cold tolerant for Zone 4a.

Global plant hardiness zones for phytosanitary risk analysis

Plant hardiness zones are widely used for selection of perennial plants and for phytosanitary risk analysis. The most widely used definition of plant hardiness zones (United States Department of Agriculture National Arboretum) is based on average annual extreme minimum temperature. There is a need for a global plant hardiness map to standardize the comparison of zones for phytosanitary risk analysis. Two data sets were used to create global hardiness zones: i) Climate Research Unit (CRU) 1973-2002 monthly data set; and ii) the Daily Global Historical Climatology Network (GHCN). The CRU monthly data set was downscaled to five-minute resolution and a cubic spline was used to convert the monthly values into daily values. The GHCN data were subjected to a number of quality control measures prior to analysis. Least squares regression relationships were developed using GHCN and derived lowest average daily minimum temperature data and average annual extreme minimum temperatures. Error estimate statistics were calculated from the numerical difference between the estimated value for the grid and the station. The mean absolute error for annual extreme minimum temperature was 1.9ºC (3.5ºF) and 2/3 of the stations were classified into the correct zone.

The influence of flesh colour and growing locality on polyphenolic content and antioxidant activity in potatoes

Compounds contained in potato tubers that may act as antioxidants have been attracting increased attention. The main antioxidants in potatoes are polyphenolic compounds. The total polyphenolic (TP) content and antioxidant activity (AA) in potato tubers of four yellow-fleshed cultivars and two purple-fleshed cultivars from the 2004 harvest were tested. The total polyphenolic content was determined using the Folin-Ciocalteau reagent (FC) and the antioxidant activity, with the DPPH method using stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH·). Significant differences were found in total polyphenolic content between the yellow-fleshed cultivars Karin, Impala, Ditta, and Saturna. Significant differences between yellow and purple-fleshed potatoes were found: the yellow-fleshed cultivars had an average of 2.96 g gallic acid equivalents (GAE) per kg DM, the purple-fleshed cultivars 4.68 g GAE per kg DM. Significant differences in AA between the yellow and purple-fleshed cultivars were determined (yellow-fleshed in an average of 139.3 mg equivalents of ascorbic acid [EAA] per kg DM, purple-fleshed 332.3 mg EAA per kg DM) as well as between the purple-fleshed cultivars Valfi (298 mg EAA per kg DM) and Violette (366 mg EAA per kg DM). The major antioxidants in purple-fleshed cultivars were anthocyanidins petunidin (Valfi 92% rel) and malvidin (Violette 85% rel). Cv. Violette contained three times higher content of anthocyanidins than cv. Valfi. Among four experimental localities, the higher situated potato-growing region of Stachy (locality with the lowest average annual and daily minimum temperatures and the highest sum of precipitation in the vegetative period) differed significantly from other localities by a higher TP content, AA and yield in the analyzed cultivars. A high positive correlation between antioxidant activity and total polyphenolic content with R = 0.8648, R 2 = 0.7478 ( P = 0.0001) was found.

Heat Waves in Southern California: Are They Becoming More Frequent and Longer Lasting?

Los Angeles is experiencing more heat waves and also more extreme heat days. These numbers have increased by 3.09°F (1.72°C) per century and 22.8 per century occurrences, respectively. Both have more than tripled over the past 100 years as a consequence of the steady warming of Los Angeles. Our research explores the daily maximum and minimum temperatures from 1906 to 2006 recorded by the Department of Water and Power (DWP) downtown station and Pierce College, a suburban valley location. The average annual maximum temperature in Los Angeles has warmed by 5.0°F (2.8°C), while the average annual minimum temperature has warmed by 4.2°F (2.3°C). The greatest rate of change was during the summer months for both maximum and minimum temperature, with late fall and early winter having the least rates of change. There was also an increase in heat wave duration. Heat waves lasting longer than six days occurred regularly after the 1970s but were nonexistent from the start of 1906 until 1956, when the first six-day heat wave was recorded. While heat days have increased dramatically in the past century, cold days, where minimum temperature is below 45°F (7.2°C), show a slight decreasing trend.

The climate of the coast and fog zone in the Tarapacá Region, Atacama Desert, Chile

In the Atacama Desert, the narrow littoral plain and the adjacent mountain range have a unique climate. This area is locally called the “coastal desert with abundant cloudiness”, and extends from the coastline up to an elevation of 1000 m. The climate is designated as being BWn according to Köppen's Climate Classification as adapted for Chile. In the original classification the acronym (Bn) is used for foggy environments. Toward the east a “normal desert” climate (BW) is found. This is known as one of the most extreme deserts of the world. In the BWn areas there are meteorological differences between low and high elevation zones. The climate of the coastal plains and the mountains is described in this paper in order to show that there is an area where the climate differs from those classified as BWn and BW in the Chilean Climate Classification. This area is located between 650 and 1200 m a.s.l. and contains several fog oases or lomas vegetation, rich in biodiversity and endemism. The weather is warmer near sea level, with an annual average temperature of 18 °C. At high elevation sites like Alto Patache, the temperature decreases at a rate of 0.7 °C for every 100-m increase in altitude. The average annual minimum temperature often approaches 1 °C in winter, while the mean annual temperature range is significant (8.3 °C in Los Cóndores). The mean monthly relative humidity in Alto Patache is over 80%, except during the summer months. During autumn, winter and spring high elevation fog is present in the study area at altitudes ranging from 650 m up to 1060 m, giving annual water yields of 0.8 to 7 L m − 2 day − 1 . If vegetation is used as an indicator, the foggy zone lies between 650 m a.s.l. and 1200 m a.s.l. About 70% of the mountain range experiences the foggy climate, as opposed to the coastal plains that are characterized by a cloudy climate.

Temperature as an Indicator of Landform Influence on Atmospheric Processes

Potential land surface-atmosphere interactions were observed on satellite imagery in the lower reaches of the alluvial valley of the Mississippi River. Monthly temperature data were used to determine if a measurable relationship between the land surface and resulting atmospheric processes can be similarly found in the long-term record throughout the entire year. Comparison of temperatures inside the valley with those outside the valley revealed that annual average minimum temperature in the valley is warmer by 1°C than outside the valley. Analyses of seasonal temperature showed that average maximum temperature in the valley is warmer by 0.5°C in summer and colder by 0.5°C in winter. Average minimum temperature in the valley is consistently over 1°C warmer in all seasons. Monthly temperature analyses showed that average maximum temperature in the valley is colder from November-March and warmer from May-October, while average minimum temperature is consistently warmer in the valley in all months. Average temperature range in the valley is consistently smaller than outside the valley. Statistically significant results indicate that days are hotter in summer and colder in winter, and that nights are warmer all year in the valley. Soil type differences and consequently differing soil moisture regimes are suggested as possible causal mechanisms.

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

AbstractAlthough 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.

A Comparison of Local and Regional Trends in Surface and Lower-Tropospheric Temperatures in Western North Carolina

Abstract Temperature time series for stations in western North Carolina are used to evaluate the potential for an urban signal in the local temperature trend, and to compare a homogeneous temperature record from a mountain-top station to two versions of the lower-tropospheric, satellite-derived temperatures from the Microwave Sounding Unit (MSU). Results regarding the urban signal are in agreement with the conclusion from previous investigations that after a location is urbanized, the local temperature trend is consistent with trends derived from surrounding, more rural stations. With respect to the mountain top and lower-tropospheric temperature comparison, the magnitudes of the two MSU-derived trends for the western North Carolina area are closer to the average annual minimum temperature trend than to the annual average maximum temperature trend.

Supercooling and Cold Hardiness in Sour Cherry Germplasm: Flower Buds

Flower buds of two sweet cherry (Prunus avium L.), 12 sour cherry (Prunus cerasus L.) and one ground cherry (P. fruticosa Pall.) were collected monthly from Aug. 1990 to Mar. 1991, and subjected to freeze tests to determine the level of cold hardiness. LT50 values (temperatures at which 50% of the flower buds were killed) summed over all months were significantly correlated (r = 0.6844, P ≤ 0.01) to the flower bud low temperature exotherms (LTEs). Correlation of LTEs to LT50 values was highest, r = 0.85, P ≤ 0.01 for the acclimation and midwinter period, November to February collections. During this period the average LT50 occurred before and within 2.5 °C of the LTE, indicating tissue injury before the LTE occurrence. During deacclimation, represented by the March collection, the LT50 began within 2.0 °C, on average, of the LTE, and in 11 of 12 cultivars and seedlings preceded the LTE. In March, the correlation of LTEs to LT50 values was less, r = 0.69, P ≤ 0.05, indicating possible changes flower bud deep supercooling. LTE values were selected as a measure of flower bud hardiness in sour cherry. Exotherms were not detected in the flower buds of all germplasm tested on all evaluation dates, but were the best means of separating selections. While LTE analyses expressed significant differences in November, December, and March at P ≤ 0.01, the LT50 analyses expressed differences only in December and February at P ≤ 0.05. The relationship between ambient temperatures and floral tissue hardiness indicated that November and March are two critical times for flower bud injury. November injury would occur in years when sudden low temperatures occur without sufficient pre-exposure to freezing temperatures. March injury would occur in years when sudden freezing temperatures follow warm days. This type of injury would be most pronounced in southern genotypes. Spring freeze injury could be significantly reduced by the selection of cultivars and seedlings that have delayed deacclimation. Exotherm occurrence and bud volume were correlated (r = 0.95, P ≤ 0.05). In January, when exotherms were least prevalent, they were generally present only in the five cultivars and seedlings with large bud volumes. The LTEs in midwinter, occurred within 3 °C of the reported average annual minimum temperature for the northern range of Prunus commercial production (Zone 6). The results of the principal component analysis of flower bud LTEs indicated that other selection criteria as flowering time might have played a more significant role in the hardiness range of sour cherry than simply geographic origin. The first principal component (PC1), which accounted for 77% of the total variance was used to separate among cultivars and seedlings. Selections at the positive end of PC1 had flower buds that were more cold susceptible than selections at the negative end of PC. This concurs with other research showing that flower bud hardiness is related more to commercial range (i.e., the range of commercial production) than to geographic distribution.

Provenance tests as Indicators of growth response to climate change in 10 north temperate tree species

Thirteen series of multilocation provenance test plantations, representing 10 tree species common to eastern North America, were analyzed to determine the effect of variation in average annual minimum temperature on height growth of trees from known seed source locations. Regressions were developed to predict provenance height, based on the temperature differentials between seed source locations and provenance locations. Regression equations for 12 of the 13 provenance test series were sigificant (p < 0.01) and accounted for an average of 29% of the height variation among provenances. For 8 of the 10 species examined, an increase in average annual minimum temperature is projected to result in a decline in tree height growth, relative to an adapted source.

Evidence of a physiological basis for the boreal-deciduous forest ecotone in North America

The observed northern limit of the deciduous forest formation in North America is shown to agree closely with the reported −40°C average annual minimum temperature isotherm. This indicates that supercooling as a means of resisting freezing stresses may set a physiological limit on the northern expansion of the deciduous forest formation.

Cold hardiness and supercooling along an altitudinal gradient in andean giant rosette species.

Factors affecting supercooling capacity and cold hardiness were investigated in leaves of ten giant rosette species of the genus Espeletia (Compositae). These species grow along a 2,800-4,200 m elevation gradient in the Venezuelan Andes. In this high tropical environment, freezing frequently occurs every night, particularly above 3,300 m, but lasts for only a few hours. Supercooling capacty is linearly related to leaf water potential (Ψ L ) in all species; however supercooling is more responsive to Ψ L changes in Espeletia species from high paramos. The rate of change in the species-specific supercooling point and the rate of change of average annual minimum temperature along the elevation and climatic gradient follow the same trend (approximately -0.6 K per 100 m elevation). At a given elevation, the expanded leaves of the different species tend to supercool 8-10 K below minimum air temperatures. Experimentally-induced freezing was accompanied by the formation of intracellular ice and tissue damage. The relative apoplastic water content (RAWC) of the leaves, which may influence the ice nucleation rate or the facility by which ice propagates, was determined by pressure-volume methods. Species from higher sites tend to exhibit lower RAWC (2%-7%) than species from lower sites (7%-36%). A causal relationship between supercooling capacity and RAWC is suggested. In the high tropical Andes, the temperature oxotherm plateau of Espeletia leaves seems to be sufficiently fow to avoid freezing.