Interannual Invariability of Forest Evapotranspiration and Its Consequence to Water Flow Downstream

Although drought in temperate deciduous forests decreases transpiration rates of many species, stand-level transpiration and total evapotranspiration is often reported to exhibit only minor interannual variability with precipitation. This apparent contradiction was investigated using four years of transpiration estimates from sap flux, interception–evaporation estimates from precipitation and throughfall gauges, modeled soil evaporation and drainage estimates, and eddy covariance data in a mature oak-hickory forest in North Carolina, USA. The study period included one severe drought year and one year of well above-average precipitation. Normalized for atmospheric conditions, transpiration rates of some species were lower in drought than in wet periods whereas others did not respond to drought. However, atmospheric conditions during drought periods are unlike conditions during typical growing season periods. The rainy days that are required to maintain drought-free periods are characterized by low atmospheric vapor pressure deficit, leading to very low transpiration. In contrast, days with low air vapor pressure deficit were practically absent during drought and moderate levels of transpiration were maintained throughout despite the drying soil. Thus, integrated over the growing season, canopy transpiration was not reduced by drought. In addition, high vapor pressure deficit during drought periods sustained appreciable soil evaporation rates. As a result, despite the large interannual variation in precipitation (ranging from 934 to 1346 mm), annual evapotranspiration varied little (610–668 mm), increasing only slightly with precipitation, due to increased canopy rainfall interception. Because forest evapotranspiration shows only modest changes with annual precipitation, lower precipitation translates to decreased replenishment of groundwater and outflow, and thus the supply of water to downstream ecosystems and water bodies.     

Variations in daytime net carbon and water exchange in a montane shrubland ecosystem in southeast Spain

Carbon and water fluxes in a semiarid shrubland ecosystem located in the southeast of Spain (province of Almería) were measured continuously over one year using the eddy covariance technique. We examined the influence of environmental variables on daytime (photosynthetically active photons, F _P >10 μmol m⁻² s⁻¹) ecosystem gas exchange and tested the ability of an empirical eco-physiological model based on F _P to estimate carbon fluxes over the whole year. The daytime ecosystem fluxes showed strong seasonality. During two solstitial periods, summer with warm temperatures (>15 °C) and sufficient soil moisture (>10 % vol.) and winter with mild temperatures (>5 °C) and high soil moisture contents (>15 % vol.), the photosynthetic rate was higher than the daytime respiration rate and mean daytime CO₂ fluxes were ca. −1.75 and −0.60 μmol m⁻² s⁻¹, respectively. Daytime evapotranspiration fluxes averaged ca. 2.20 and 0.24 mmol m⁻² s⁻¹, respectively. By contrast, in summer and early autumn with warm daytime temperatures (>10 °C) and dry soil (<10 % vol.), and also in mid-winter with near-freezing daytime temperatures the shrubland behaved as a net carbon source (mean daytime CO₂ release of ca. 0.60 and 0.20 μmol m⁻² s⁻¹, respectively). Furthermore, the comparison of water and carbon fluxes over a week in June 2004 and June 2005 suggests that the timing—rather than amount—of spring rainfall may be crucial in determining growing season water and carbon exchange. Due to strongly limiting environmental variables other than F _P, the model applied here failed to describe daytime carbon exchange only as a function of F _P and could not be used over most of the year to fill gaps in the data.     

Intraseasonal Variation in Water and Carbon Dioxide Flux Components in a Semiarid Riparian Woodland

Abstract We investigated how the distribution of precipitation over a growing season influences the coupling of carbon and water cycle components in a semiarid floodplain woodland dominated by the deep-rooted velvet mesquite (Prosopis velutina). Gross ecosystem production (GEP) and ecosystem respiration (R _eco) were frequently uncoupled because of their different sensitivities to growing season rainfall. Soon after the first monsoon rains, R _eco was high and was not proportional to slight increases in GEP. During the wettest month of the growing season (July), the system experienced a net carbon loss equivalent to 46% of the carbon accumulated over the 6-month study period (114 g C m⁻²; May–October). It appears that a large CO₂ efflux and a rapid water loss following precipitation early in the growing season and a later CO₂ gain is a defining characteristic of seasonally dry ecosystems. The relative contribution of plant transpiration (T) to total evapotranspiration (ET) (T/ET) was 0.90 for the entire growing season, with T/ET reaching a value of 1 during dry conditions and dropping to as low as 0.65 when the soil surface was wet. The evaporation fraction (E) was equivalent to 31% of the precipitation received during the study period (253 mm) whereas trees and understory vegetation transpired 38 and 31%, respectively, of this water source. The water-use efficiency of the vegetation (GEP/T) was higher later in the growing season when the C4 grassy understory was fully developed. The influence of rain on net ecosystem production (NEP) can be interpreted as the proportion of precipitation that is transpired by the plant community; the water-use efficiency of the vegetation and the precipitation fraction that is lost by evaporation.     

羊草群落的水分利用

羊草(Leymus chinensis (Trin.)Tzvel.)群落的土壤水分具有明显的成层性:0～40 cm是根系集中分布层,受降水和蒸散的直接影响,称为蒸散与降水相互作用层;40～120 cm贮水变化滞后于根系层贮水和群落蒸散的季节变化,称为主要贮水层;120 cm以下称为水分相对稳定/平衡层.1996年属平水年,生长季末土壤水盈余18 mm;1998年属丰水年,在连续强降雨时发生渗漏,生长季末土壤水亏缺15 mm.蒸腾-蒸散比(T/ET)不仅反映群落的繁茂和活力,而且反映植物对环境水资源的利用状况.1998年8月T/E7值较小(0.5),6月达0.7,7月受降水少影响而有所降低(0.6),8月水分利用效率达到最大(0.9),9月降到0.6.水分利用效率(WUE)在良好的水分条件下(1998年),主要受植物自身生长速度的限制,其季节变化与生长大周期吻合.深入分析WUE和T/E的内涵,提出蒸散效率(ETE)的概念,能更好地反映植物对环境水资源利用的状况或程度,具有实际意义.     

Increasing precipitation event size increases aboveground net primary productivity in a semi-arid grassland

Water availability is the primary constraint to aboveground net primary productivity (ANPP) in many terrestrial biomes, and it is an ecosystem driver that will be strongly altered by future climate change. Global circulation models predict a shift in precipitation patterns to growing season rainfall events that are larger in size but fewer in number. This “repackaging” of rainfall into large events with long intervening dry intervals could be particularly important in semi-arid grasslands because it is in marked contrast to the frequent but small events that have historically defined this ecosystem. We investigated the effect of more extreme rainfall patterns on ANPP via the use of rainout shelters and paired this experimental manipulation with an investigation of long-term data for ANPP and precipitation. Experimental plots (n = 15) received the long-term (30-year) mean growing season precipitation quantity; however, this amount was distributed as 12, six, or four events applied manually according to seasonal patterns for May–September. The long-term mean (1940–2005) number of rain events in this shortgrass steppe was 14 events, with a minimum of nine events in years of average precipitation. Thus, our experimental treatments pushed this system beyond its recent historical range of variability. Plots receiving fewer, but larger rain events had the highest rates of ANPP (184 ± 38 g m⁻²), compared to plots receiving more frequent rainfall (105 ± 24 g m⁻²). ANPP in all experimental plots was greater than long-term mean ANPP for this system (97 g m⁻²), which may be explained in part by the more even distribution of applied rain events. Soil moisture data indicated that larger events led to greater soil water content and likely permitted moisture penetration to deeper in the soil profile. These results indicate that semi-arid grasslands are capable of responding immediately and substantially to forecast shifts to more extreme precipitation patterns.     

Ecohydrology and the Partitioning AET Between Transpiration and Evaporation in a Semiarid Steppe

Water availability defines and is the most frequent control on processes in arid and semiarid ecosystems. Despite widespread recognition of the importance of water in dry areas, knowledge about key processes in the water balance is surprisingly limited. How water is partitioned between evaporation and transpiration is an area about which ecosystem ecologists have almost no information. We used a daily time step soil water model and 39 years of data to describe the ecohydrology of a shortgrass steppe and investigate how manipulation of soil and vegetation variables influenced the partitioning of water loss between evaporation and transpiration. Our results emphasize the overwhelming importance of two environmental factors in influencing water balance processes in the semiarid shortgrass steppe; high and relatively constant evaporative demand of the atmosphere and a low and highly variable precipitation regime. These factors explain the temporal dominance of dry soil. Annually and during the growing season 60–80% of the days have soil water potentials less than or equal to −1.5 MPa. In the 0–15 cm layer, evaporation accounts for half of total water loss and at 15–30 cm it accounts for one third of the loss. Annual transpiration/actual evapotranspiration (T/AET) ranged from 0.4–0.75 with a mean of 0.51. The key controls on both T/AET and evaporation/actual evapotranspiration in order of their importance were aboveground biomass, seasonality of biomass, soil texture, and precipitation. High amounts of biomass and late timing of the peak resulted in the highest values of T/AET.     

Climate change alters interannual variation of grassland aboveground productivity: evidence from a 22-year measurement series in the Inner Mongolian grassland

Climate change is known to influence interannual variation in grassland aboveground net primary productivity (ANPP), or seasonal biomass, but direct, long-term ground observations are rare. We present a 22-year (1982–2003) measurement series from the Inner Mongolia grassland, China, to examine the effect of climate change on interannual variations in ANPP and monthly aboveground biomass (MAB). ANPP exhibited no increase over 1982–2003 but there was an association with previous-year precipitation. MAB in May increased by 21.8% from 47.8 g m⁻² (averaged for 1982–1984) to 58.2 g m⁻² (2001–2003), whereas there was no significant variation in June, July and August, and a decrease of 29.7% in September. The MAB increase in May was correlated with increases in precipitation and temperature in the preceding months. These findings suggest that the effects of climate change on grassland production vary throughout the growing season, with warmer and wetter springs resulting in increased biomass early in the growing season, and drier falls causing a decrease in biomass late in the growing season.     

羊草群落的水分利用

羊草(Leymus chinensis (Trin．)Tzvel．)群落的土壤水分具有明显的成层性：O-40cm是根系集中分布层,受降水和蒸散的直接影响,称为蒸散与降水相互作用层;40-120cm贮水变化滞后于根系层贮水和群落蒸散的季节变化,称为主要贮水层;120cm以下称为水分相对稳定／平衡层。1996年属平水年,生长季末土壤水盈余18mm;1998年属丰水年,在连续强降雨时发生渗漏,生长季末土壤水亏缺15mm。蒸腾-蒸散比(T/ET)不仅反映群落的繁茂和活力,而且反映植物对环境水资源的利用状况。1998年8月T/ET值较小(0．5),6月达O．7,7月受降水少影响而有所降低(O．6),8月水分利用效率达到最大(O．9),9月降到O．6。水分利用效率(WUE)在良好的水分条件下(1998年),主要受植物自身生长速度的限制,其季节变化与生长大周期吻合。深入分析WUE和T/ET的内涵,提出蒸散效率(ETE)的概念,能更好地反映植物对环境水资源利用的状况或程度,具有实际意义。     

Harvesting rate of the termite,Drepanotermes tamminensis (Hill) within native woodland and shrubland of the Western Australian wheatbelt

The Western Australian termite,Drepanotermes tamminensis (Hill), harvests various plant materials according to biomass availability. The main litter components harvested by this termite in a woodland dominated byEucalyptus capillosa are bark and leaves of the major tree species, while in shrubland dominated byAllocasuarina campestris, shoots of this species are taken. Harvesting mainly occurs during the autumn (April–May) and spring (September–October) seasons. The commencement and duration of harvesting appears to depend partly on weather conditions, with harvesting taking place at temperatures between 15 and 25°C after periods of rain. This species of termite harvests approximately 15.6 g m⁻² year⁻¹ and 3.2 g m² year⁻¹ (dry weight of plant material) in the woodland and shrubland, respectively.     

Winter production of CO2 and N2O from alpine tundra: environmental controls and relationship to inter-system C and N fluxes

Fluxes of CO₂ and N₂O were measured from both natural and experimentally augmented snowpacks during the winters of 1993 and 1994 on Niwot Ridge in the Colorado Front Range. Consistent snow cover insulated the soil surface from extreme air temperatures and allowed heterotrophic activity to continue through much of the winter. In contrast, soil remained frozen at sites with inconsistent snow cover and production did not begin until snowmelt. Fluxes were measured when soil temperatures under the snow ranged from –5°C to 0°C, but there was no significant relationship between flux for either gas and temperature within this range. While early developing snowpacks resulted in warmer minimum soil temperatures allowing production to continue for most of the winter, the highest CO₂ fluxes were recorded at sites which experienced a hard freeze before a consistent snowpack developed. Consequently, the seasonal flux of CO₂ –C from snow covered soils was related both to the severity of freeze and the duration of snow cover. Over-winter CO₂ –C loss ranged from 0.3 g C m⁻² season⁻¹ at sites characterized by inconsistent snow cover to 25.7 g C m⁻² season⁻¹ at sites that experienced a hard freeze followed by an extended period of snow cover. In contrast to the pattern observed with C loss, a hard freeze early in the winter did not result in greater N₂O–N loss. Both mean daily N₂O fluxes and the total over-winter N₂O–N loss were related to the length of time soils were covered by a consistent snowpack. Over-winter N₂O–N loss ranged from less 0.23 mg N m⁻² from the latest developing, short duration snowpacks to 16.90 mg N m⁻² from sites with early snow cover. These data suggest that over-winter heterotrophic activity in snow-covered soil has the potential to mineralize from less than 1% to greater than 25% of the carbon fixed in ANPP, while over-winter N₂O fluxes range from less than half to an order of magnitude higher than growing season fluxes. The variability in these fluxes suggests that small changes in climate which affect the timing of seasonal snow cover may have a large effect on C and N cycling in these environments. Received: 5 April 1996 / Accepted: 25 November 1996     

Altering Rainfall Timing and Quantity in a Mesic Grassland Ecosystem: Design and Performance of Rainfall Manipulation Shelters

Global climate change is predicted to alter growing season rainfall patterns, potentially reducing total amounts of growing season precipitation and redistributing rainfall into fewer but larger individual events. Such changes may affect numerous soil, plant, and ecosystem properties in grasslands and ultimately impact their productivity and biological diversity. Rainout shelters are useful tools for experimental manipulations of rainfall patterns, and permanent fixed-location shelters were established in 1997 to conduct the Rainfall Manipulation Plot study in a mesic tallgrass prairie ecosystem in northeastern Kansas. Twelve 9 x 14–m fixed-location rainfall manipulation shelters were constructed to impose factorial combinations of 30% reduced rainfall quantity and 50% greater interrainfall dry periods on 6 x 6–m plots, to examine how altered rainfall regimes may affect plant species composition, nutrient cycling, and above- and belowground plant growth dynamics. The shelters provided complete control of growing season rainfall patterns, whereas effects on photosynthetic photon flux density, nighttime net radiation, and soil temperature generally were comparable to other similar shelter designs. Soil and plant responses to the first growing season of rainfall manipulations (1998) suggested that the interval between rainfall events may be a primary driver in grassland ecosystem responses to altered rainfall patterns. Aboveground net primary productivity, soil CO₂ flux, and flowering duration were reduced by the increased interrainfall intervals and were mostly unaffected by reduced rainfall quantity. The timing of rainfall events and resulting temporal patterns of soil moisture relative to critical times for microbial activity, biomass accumulation, plant life histories, and other ecological properties may regulate longer-term responses to altered rainfall patterns.     

Can water responses in Stipa tenacissima L. during the summer season be promoted by non-rainfall water gains in soil?

This article reports on quantified soil water gains and their possible effects on summer water relationships in a semiarid Stipa tenacissima L. grasslands located in SE Spain. We believe that the net soil water gains detected using minilysimeters could be from soil water vapour adsorption (WVA). Our study of high water-stress showed stomatal conductance (21.8–43.1 mmol H₂O m⁻² s⁻¹) in S. tenacissima leaves unusual for the summer season, and the evapotranspiration from S. tenacissima grassland, estimated by a multi-source sparse evapotranspiration model, closely corresponding to total WVA. This highlights the importance of summer soil WVA to stomatal conductance and vital transpiration in S. tenacissima. This study measured pre-dawn leaf water potential (ψ) response to sporadic light rainfall, finding that a light summer rainfall (1.59 mm day⁻¹) was sufficient to vary ψ in S. tenacissima from −3.8 (close to the turgour loss point) to −2.7 MPa. We hypothesize that soil WVA can supply vegetation with water vital to its survival in seasons with a severe water deficit, giving rise to a close relationship between soil water dynamics and plant water response.     

The influence of temperature and nitrogen source on growth and nitrogen uptake of two polar-desert species,Saxifraga caespitosa and Cerastium alpinum

Polar-desert plants experience low average air temperatures during their short growing season (4–8 °C mean July temperature). In addition, low availability of inorganic nitrogen in the soil may also limit plant growth. Our goals were to elucidate which N sources can be acquired by polar-desert plants, and how growth and N-uptake are affected by low growth temperatures. We compared rates of N-uptake and increases in mass and leaf area of two polar-desert species (Cerastium alpinum L. and Saxifraga caespitosa L.) over a period of 3 weeks when grown at two temperatures (6 °C vs. 15 °C) and supplied with either glycine, NH₄ ⁺ or NO₃ ⁻. At 15 °C, plants at least doubled their leaf area, whereas there was no change in leaf area at 6 °C. Measured mean N-uptake rates varied between 0.5 nmol g⁻¹ root DM s⁻¹ on glycine at 15 °C and 7.5 nmol g⁻¹ root DM s⁻¹ on NH₄ ⁺ at 15 °C. Uptake rates based upon increases in mass and tissue N concentrations showed that plants had a lower N-uptake rate at 6 °C, regardless of N source or species. We conclude that these polar-desert plants can use all three N sources to increase their leaf area and support flowering when grown at 15 °C. Based upon short-term (8 h) uptake experiments, we also conclude that the short-term capacity to take up inorganic or organic N is not reduced by low temperature (6 °C). However, net N-uptake integrated over a three-week period is severely reduced at 6 °C. This revised version was published online in June 2006 with corrections to the Cover Date.     

Transpiration of Pinus rotundata on a wooded peat bog in central Europe

Transpiration of a central European endemic tree species, Pinus rotundata Link, growing on a wooded peat bog in the Třeboň Basin, Czech Republic, was studied in 1999–2000. Transpiration was measured by sap flow techniques (heat field deformation method) on individual trees and scaled up to stand level. The radial patterns of sap flow density showed narrow peaks in the outer part of the xylem, sapwood accounted for 47–60% of the xylem radius and 72–84% of the xylem basal area. Adult trees tolerated well both short-term flooding during the growing season and drawdown of the water table to a depth of 60 cm below ground level. The maximum and mean daily transpiration rates were 3.0 and 1.8 mm per day, and were thus similar to published data for Scots pine. The seasonal total transpiration (25 April–20 October 2000, 180 days) amounted to 322 mm, or 62% of the potential evapotranspiration over this period. This canopy transpiration was compensated by 319 mm of precipitation. The difference between the accumulated precipitation and the accumulated transpiration (derived from seasonal sap flow measurements) closely mimicked the seasonal course of the water table.     

Diurnal and seasonal changes in the intensity of photosynthesis in stems of lilac (Syringa vulgaris L.)

It has been demonstrated that during the whole year the stems are photosyntheticaly active and capable of assimilating atmospheric CO₂. The intensity of photosynthesis varies. During the vegetation period the registered net photosynthesis lasted up to 13 hours per day, and in the leafless period for 2–3 hours a day. Photosynthesis was registered also at temperatures below zero (−3 °C) as a reduced CO₂ evolution in light in comparison with darkness. The maximal net photosynthesis values during the vegetation period amounted to 6 up 8 μmol (CO₂)·m⁻²·s⁻¹, and in the leafless period 0.5 – 1 μmol (CO₂)·m⁻²·s⁻¹, and they were close to being up to twice as big as the values obtained of darkness respiration. An increase of the photosynthetic activity of stems preceded the spring development of the leaves.     

Vegetation control effects on untreated wood,crude cellulose and holocellulose δ<Superscript>13</Superscript>C of early and latewood in 3- to 5-year-old rings of Douglas-fir

The stable carbon (C) composition of tree rings expressed as δ¹³C, is a measure of intrinsic water-use efficiency and can indicate the occurrence of past water shortages for tree growth. We examined δ¹³C in 3- to 5-year-old rings of Douglas-fir (Pseudotsuga menziesii (Mirb) Franco) trees to elucidate if decreased water supply or uptake was a critical factor in the observed growth reduction of trees competing with understory herb and shrub vegetation compared to those growing without competition. We hypothesized that there would be no differences in δ¹³C of earlywood in trees growing in plots with competing vegetation and those in plots receiving complete vegetation control during 5 years because earlywood formed early in the growing season when soil water was ample. We also hypothesized that δ¹³C in latewood which was formed during the later half of the growing season when precipitation was low, would be greater (less negative) in trees in plots without vegetation control. We then separated early and latewood from rings for three consecutive years and analyzed their δ¹³C composition. No significant differences in earlywood δ¹³C in years 3–5 were observed for trees in the two vegetation control treatments. δ¹³C of untreated latewood separated from wood cores was greater in 4- and 5-year-old rings of trees growing with competing vegetation compared to trees growing without vegetation competition (i.e., −25.5 vs. −26.3‰ for year 4, and −26.1 vs. −26.8‰ for year 5). Results suggest that water shortages occurred in Douglas-fir trees on this coastal Washington site in the latewood-forming portion of the growing season of years 4 and 5 in the no-vegetation control treatment. We also compared δ¹³C from untreated wood, crude cellulose extracted with the Diglyme–HCl method, and holocellulose extracted with toluene–ethanol to see if the extraction method would increase the sensitivity of the analysis. δ¹³C values from the two extraction methods were highly correlated with those from untreated samples (r ² = 0.97, 0.98, respectively). Therefore, using untreated wood would be as effective as using crude cellulose or holocellulose to investigate δ¹³C patterns in young Douglas-fir.     

Stem respiration of Norway spruce trees under elevated CO2 concentration

Measurements of stem respiration were conducted for a period of four years (1999–2002) in 14-year old Norway spruce (Picea abies [L.] Karst) trees exposed to ambient (CA) and elevated CO₂ concentration (CE; ambient plus 350 μmol mol⁻¹). Stem respiration measurements of six trees per treatment were carried out 2–3 times per month during the growing season. Stem respiration in CE treatment was higher (up to 16 %) than in CA treatment. Temperature response of stem respiration (Q₁₀) for the whole experimental period ranged between 1.65–2.57 in CA treatment and 2.24–2.56 in CE treatment. The mean stem respiration rate normalized to 10 °C (R₁₀) in CA and CE treatments ranged between 1.67–1.95 and 2.19–2.72 μmol(CO₂) m⁻² s⁻¹, respectively. Seasonal variations in stem respiration were related to temperature and tree growth.     

Variations in water temperatures and levels in the St. Lawrence River (Québec,Canada) and potential implications for three common fish species

The implications for fish populations of long- (multi-decadal, 1919–2007), medium- (inter-annual) and short- (seasonal, daily) term variations in water temperatures and levels were examined in the St. Lawrence River (SLR). The effects of the seasonal thermal regime of the SLR and its tributaries on the thermal budgets of resident and migrating fish were contrasted. Over the 1919–2007 period, the mean annual water level in Montreal declined significantly; for a discharge of 8,000 m³ s⁻¹, levels dropped steadily by about 3.6 cm year⁻¹ between 1955 and 1982, coinciding with the period of major shoreline alteration and channel excavation. Between 1960 and 2007, the annual water temperature of the SLR rose by 1.3°C (0.027°C year⁻¹); none of the 10 coldest years and six of the 10 warmest years were observed since 1981. Temperature differences between the warmest and coolest years were greatest in spring and fall (by about 2.5°C); fish growing season (>5°C) was longer by 5 weeks and represented 20% more degree-days for the warmest years. In comparison with its tributaries, SLR water was slower to warm up in the spring but remained warmer in the fall: fish migrating seasonally between water masses could thus enhance or reduce their thermal budgets by 1–2°C daily. Northern pike recruitment years (year-class strength index [YCSI] values above the time series median) were best with June water levels >4.9 m IGLD85 (International Great Lakes Datum of 1985), combined with June air temperatures >18.6°C. For yellow perch, water temperatures >16.2°C in June alone explained six out of the eight best recruitment years in the time series. Conversely, an episode of massive carp mortality in 2001 exemplifies the inherent risk of using shallow flooded habitats for spawning when rapidly dropping levels coincide with hot, sunny weather. The effects of water temperature and level, singly and in combination, thus appear to be critical variables in determining successful fish recruitment in shallow riparian areas—areas which constitute the most important yet the most elusive fish spawning and nursery habitats.     

A study of the macro-environment at BenCat in southern Vietnam

Based on the meteorological data over a period of 4 years (1980–3), the macro-environment of BenCat Farm situated in the southern part of Vietnam (27 m above mean sea-level, 11° N and 106° E) was categorized as a “monsoon tropical climate”, due to heavy rainfall (annual mean 2028.96 mm) and about 32% wet days (annual mean 116.52 days) together with high air temperature (annual mean daily temperature 28.58, max. 32.33 and min 24.85° C). April was the hottest (monthly mean >35°C) and January the coldest month (monthly mean <22° C) of the year. The maximum number of wet days were during September and October (mean 18 days.month), whereas the minimum number of wet days were during January and February (mean <1 day/month). The months of December and January at Ben-Cat buffalo farm were categorized as the “comfortable (moderate-Dry) period” as the mean daily temperature was <27° C, while the remaining 10 months of the Calender year (February–November) were categorized as the “hot period” (mean daily temperature >27° C). On the basis of rainfall and the number of wet days, the hot period was further subdivided into a “hot-dry period” (February–April, mean of 1.67 wet days/month and mean rainfall 19.43 mm/month) and a “hot-humid period” (May–November, mean of 15.57 wet days/month and mean rainfall 276.28 mm/month).