Accumulated Heat Load Research Articles

The Impact of Climate Variability on Cattle Heat Stress in Vanuatu

Heat stress is a climate extreme that impacts cattle health, fertility, feed intake, production, and well-being. In Vanuatu, the beef industry is crucial to local livelihoods and the nation’s economy, thus the objective of this study was to examine the impact of heat stress on cattle health and production. This study uses the Heat Load Index (HLI) and Accumulated Heat Load (AHL) as proxies to assess the impact of heat stress on cattle in Vanuatu over a 30-year period (1994–2023), using the fifth generation of the European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis of the global climate (ERA5) data. The analysis examines historical patterns of heat stress in cattle across Vanuatu, identifying more instances of heat stress occurring during the wet season due to characteristically elevated temperatures, humidity, and low wind speeds. Findings also suggest that El Niño events may increase the intensity and duration of heat stress events. These insights inform the development of an Early Warning System for heat stress in cattle, establishing a crucial foundation for targeted adaptation strategies aimed at enhancing the resilience and sustainability of Vanuatu’s beef industry to climate variability and change.

Design and Simulation of eVTOL Aircraft Thermal Management System

Abstract Vertical Take-off and Landing (VTOL) aircraft with hybrid or fully-electric propulsion systems are becoming popular for Urban Air Mobility (UAM) applications. However, they face challenges such as limited power and energy density, stringent operating temperature constraints, and the generation of low-grade waste heat. These issues emphasize the need for effective Thermal Management Systems (TMS) design. In light of the above, this paper aims to design the TMS for a parallel hybrid electric XV-15 aircraft, a widely known civil tiltrotor concept. The TMS is integrated into the aircraft system to assess its impact on energy efficiency and emissions at both aircraft and mission levels. This study considers current state of the art technology and expected advancements over the next two decades to identify the benefits of electrification. In the designed TMS, liquid cooling cold plates serve as the main heat acquisition and cooling system for each electric component. An air-coolant heat exchanger is also incorporated to dissipate the accumulated heat load. The study conducts a comparative analysis to determine the optimal TMS design point. It involves a comparison between two design scenarios: one focused on the cruise condition, which constitutes a significant portion of the flight mission, and another designed specifically for peak heat load conditions. This ensures a holistic evaluation of the TMS's performance across various flight phases, balancing efficiency and resilience to peak demands. Finally, the energy efficiency and emission penalty associated with the TMS integration are quantified and discussed in the study.

Tissue specific responses to oxidative fuel source preference during heat stress in lactating dairy cows

Prolonged exposure to high environmental temperatures results in an accumulated heat load that induces a heat stress (HS) response in dairy cattle. Heat stress compromises dairy farm profitability by reducing milk yield, altering milk composition, and hindering reproductive performance. The ability to alternate between carbohydrate and lipid sources for energy production is termed metabolic flexibility (Met Flex). The objective of this study was to evaluate the Met Flex of mammary, muscle, and liver tissue in lactating dairy cows under HS and thermoneutral (TN) conditions. Sixteen Holstein cows were assigned to 1 of 2 treatment groups: pair feeding in a TN environment (PFTN) or HS. All cows experienced a 4 d TN period with ad libitum intake followed by a 4 d treatment period. Heat stress cows were exposed to a temperature humidity index (THI) ranging from 76 to 80 and the PFTN cows were exposed to a THI of 64. Milk production and health data were recorded twice daily. Semitendinosus biopsies were obtained on d 4 of each period and post-mortem mammary and liver samples were obtained on d 4 of period 2. All tissue samples were assayed for Met Flex. Activity of mitochondrial (Mit) enzymes were assessed in skeletal muscle only. Four d of HS decreased milk yield, altered milk composition, and increased respiration rate and rectal temperatures. No differences in Met Flex were observed in mammary or liver tissue during period 2. However, HS, but not PFTN conditions, lowered Met Flex of skeletal muscle by 18.3% when compared with TN ad libitum feed intake conditions of period 1. No treatment differences were observed in skeletal muscle Mit enzyme activity indicating the decrease in Met Flex occurred independently of changes in Mit function. The reduction in Met Flex of skeletal muscle during HS may contribute to reduced milk yield and warrants further investigation.

Accumulative Heat Stress in Ruminants at the Regional Scale under Changing Environmental Conditions

Environmental heat stress is implicated in various animal health issues in ruminants, including reproduction rates, mortality rates, and animal physical quality. During extremely hot weather, there is often no overnight equilibration of animal temperature with its cooling effect, and the accumulated heat load becomes an important factor in animal health for ruminants such as sheep. Using the heat load index (HLI), a heat load model is used as an indicator of heat stress on an hourly basis and annually, using downscaling models for temperature, humidity, solar radiation, and wind speed, in both spatial and temporal cases, across several example sites in regional Victoria. Analysis is provided on the performance of the downscaling models and various adaptation and mitigation options are discussed and tested. These options include using different tree planting patterns to modify solar radiation exposure and wind effects, with mixed results because adding shading structures may also diminish the effect of wind-based cooling. The modelling experiments indicated that (1) heat stress is likely to increase under future climate conditions and could represent a serious threat to the health of small ruminants; (2) adaptation measures by means of tree planting to provide shade may not be sufficient to alleviate projected heat stress; and (3) other adaptation measures will need to be considered. Indicative results for heat stress under potential future environments are provided for 2030, 2050, and 2070. Also discussed is the performance of wind speed modelling, and the effect of heat stress on animal growth and ram fertility.

Assessing Heatwaves and Their Association with North African Dust Intrusions in the Algarve (Portugal)

Heatwaves are an extreme meteorological event in which affected populations may also be exposed to deteriorated air quality conditions due to the increase in air pollutant concentrations, such as PM10 (particulate matter < 10 µg/m3). In order to identify heatwaves (1973–2019) in the region of Faro (Algarve) during the hot season (April–September), the Excess Heat Factor (EHF) index was applied. The Mann–Kendall test revealed an upward trend in three heatwave metrics in Faro, and the trend of accumulated heat load (EHF load) was also positive as would be expected, but its signal was not statistically significant. An inventory of North African dust events (2006–2019) was made, and their simultaneous occurrence with heatwaves was assessed, pointing to only 20% of dust events of the Sahara occurring simultaneously with heatwave days. A cluster analysis was conducted on daily geopotential height fields at 850 hPa level over the 2006–2019 period, and four distinct patterns were identified as the most prominent synoptic circulations promoting both heatwave conditions and North African dust over the Algarve.

Characteristics of Cowsheds in Vietnamese Smallholder Dairy Farms and Their Associations with Microclimate—A Preliminary Study

Simple SummaryAppropriately designed cowsheds could help improve the microclimate within Vietnamese tropical smallholder dairy farms to minimise the risk of heat stress in the cows. Currently, these farmers build cowsheds on whatever land is available based on self-accumulated experiences without careful consideration of heat stress. This study characterised heat stress abatement strategies by identifying the housing parameters most associated with the cowshed microclimate across four climatically contrasting dairy regions of Vietnam. During the daytime, the microclimate inside the cowsheds was found to be relatively hot in highland and very hot in lowland regions. Although there were seven typical cowshed types defined, none were more effective than the others in improving cowshed microclimate. Increasing altitude, eave roof height and floor area per cow, and using the roof soakers together with fans, were most associated with improving microclimate, as indicated by decreasing temperature, decreasing temperature-humidity index and increasing air speed. These cowshed parameters should be prioritised for future research into the amelioration of heat stress of the cows in tropical smallholder dairy farms.In smallholder dairy farms (SDFs), farmers often build cowsheds using local materials and based on self-accumulated experience without due consideration to reducing the risk of heat stress. This study aimed to characterise the heat stress abatement strategies and microclimate within SDF cowsheds from four typical dairy regions of Vietnam (south lowland, south highland, north lowland and north highland) and identify the housing parameters most associated with the microclimate. The study was conducted on 32 SDFs (eight SDFs per region) in autumn 2017. Twelve housing management variables, illustrating cowshed design and heat stress abatement methods of each SDF, were collected. Six microclimate parameters, collected within the cowshed, were temperature (AT), humidity, air speed (AS), heat load index (HLI), Temperature-humidity index (THI) and accumulated heat load units (AHLU) during a day (06:00 h to 18:00 h). Factor analysis and cluster analysis was applied to group cowsheds of SDFs into clusters where SDFs in the cluster had the same cowshed characteristics. Multivariable linear models were applied to define the parameters most likely to inform future research into heat stress mitigation on SDF. Averaged from 08:00 h to 18:00 h, microclimate inside the cowsheds was considered hot (HLI > 79) in the highland and very hot (HLI > 86) in the lowland regions. Cows in the lowland regions accumulated high heat load (AHLU > 50) by 18:00 h. Cowsheds of SDFs varied widely and grouped into seven cowshed types, but no type was more effective than others in reducing heat stress conditions within cowsheds. Using roof soakers together with fans decreased AT and HLI by 1.3 °C and 3.2 units, respectively, at 14:00 h compared to 11:00 h. Each 100 m increase in altitude was associated with decreases of 0.4 °C in AT, 1.3 units in HLI and 0.8 units in THI (p < 0.001). Each meter increase in the eave height of the cowshed roof was associated with decreases of 0.87 °C in AT, 3.31 units in HLI and 1.42 units in THI, and an increase of 0.14 m/s in AS (p < 0.05). The cowshed parameters that should be prioritised for future research into the amelioration of heat stress in SDF cows include using the roof soakers together with fans, increasing altitude, eave roof height and floor area per cow.

Heat load increases the risk of clinical mastitis in dairy cattle

The study was aimed at assessing heat load-related risk of clinical mastitis (CM) in dairy cows. Records of CM for the years 2014 and 2015 were obtained from a large conventional dairy farm milking about 1,200 Holstein cows in central Italy. A case of CM was defined by the presence of clinical signs and veterinary confirmation. Quarter milk samples were collected and bacteriological investigated for each CM. Etiological agents were identified and classified as environmental or contagious pathogens. Hourly weather data from the nearest weather station were used to calculate heat load index (HLI). Upper and lower thresholds of HLI, at which the animal accumulates or dissipates heat, were settled and used to measure heat load balance through the accumulated heat load (AHL) model. Zero and positive values of AHL indicate periods of thermo-neutral and heat accumulation, respectively. Each case of CM was associated with HLI-AHL values recorded 5 d before the event. The risk of CM was evaluated using a case-crossover design. A conditional logistic regression model was used to calculate the odds ratio and 95% confidence intervals of CM recorded in thermo-neutral (AHL = 0) or heat load (AHL > 0) days, pooled or stratified for pathogen type (environmental or contagious). Classes of AHL as low (<6.5), medium (6.6-34.9), and high (>35) were included in the model. Other variables included in the model were milk yield as liters (<20, 20-30, and >30), days in milk (<60, 60-150, and >150), and parity (1, 2-3, and >3). A total of 1,086 CM cases were identified from 677 cows. Escherichia coli, Streptococcus spp., and Streptococcus uberis were the environmental pathogens isolated with the highest frequency; Staphylococcus aureus prevailed within contagious species. The analysis of pooled data indicated a significant effect of heat load on the occurrence of CM in the contagious pathogen stratum. Higher milk yield, middle and late stage of lactation, and older parity increased the risk of CM under heat load conditions. However, the association between pathogen type and these factors was not clear because the model provided significant odds ratios within all pathogen categories. The present study provided the first evidence of an association between HLI and CM in dairy cattle and suggested the ability of the AHL model to assess the risk of mastitis associated with heat load.

Heat Mitigation Strategies for Finishing Beef Cattle During the Summer in the Southeastern United States Reduces Heat Load and Improves Weight Gain, but does not Influence Meat Quality

ObjectivesThe objective of this research was to determine the effect of heat mitigation strategies on meat quality when finishing cattle under heat stress conditions.Materials and MethodsForty-five Angus crossbred steers (446 ± 23 kg) were blocked by weight and randomly assigned to 1 of 3 finishing environments: shaded with fan (CWF), shaded without fan (CNF), or outside no shade (OUT). For 92 d steers were individually fed a corn-based total mixed ration and were weighed every 3 wk. Environmental monitors (Kestrel Instruments) were used to quantify heat load index (HLI) and accumulated heat load units (AHLU). When the first treatment group averaged 613 kg all steers were harvested. Carcass quality and yield data were collected 24 h postmortem. Strip loins were removed from the right side of each carcass at 24 h postmortem, vacuum packaged, and aged (2 ± 1°C) for 5 d. Strip loins were then fabricated into 2.54-cm steaks anterior to posterior. The first steak was designated for proximate analysis, followed by two steaks for slice shear force (14 and 21 d aging), two steaks for other analyses, and the remaining 7 steaks were randomly assigned to shelf life (SL) for 6 d following 28 d of wet aging. Steaks were vacuum packaged and held (2 ± 1°C) for their respective days of aging. After 28 d, shelf life steaks were opened, placed in Styrofoam trays with PVC overwrap, and placed in retail display cases (1 ± 2°C). Steaks were frozen (–20°C) once they reached their assigned day of wet aging or simulated shelf life. Objective color L* (lightness), a* (redness), b* (yellowness), and isobestic wavelengths were recorded daily (± 2 h). Hue, chroma, DE, and deoxymyoglobin (%Dmb), oxymyoglobin (%Omb), and metmyoglobin (%Mmb) were calculated. Data were analyzed using a mixed model (JMP v.13; SAS) and means were separated using LSmeans at a = 0.05.ResultsEnvironmental monitors showed that CWF and CNF had lower HLI and AHLU (P &lt; 0.01) than OUT. Final weights were greater for CWF than OUT (P = 0.02) while CNF was similar (P ≥ 0.17) to both. Similar results were observed for hot carcass weights where CWF &gt; OUT (P = 0.03), and CNF was similar to both (P ≥ 0.23). Treatment differences were not observed for USDA yield grade (P = 0.38), dressing percent (P = 0.93), kidney pelvic heart fat (P = 0.89), ribeye area (P = 0.47), backfat thickness (P = 0.49), marbling score (P = 0.71), overall maturity (P = 0.92), or subjective lean color (P = 0.16). No differences in fat color scores were observed between CNF and OUT (P = 0.95) while CWF were whiter (P ≤ 0.04) than both. Protein analysis showed CWF had more protein than OUT (P = 0.01) while CNF was similar to both (P ≥ 0.90). No differences were observed for lipid content (P = 0.99), ash (P = 0.39), or moisture (P = 0.92). Treatment nor day of aging effected slice shear force (P = 0.45 and P = 0.53, respectively). While treatment differences were not observed for a*, b*, hue, chroma and DE (P = 0.51, P = 0.65, P = 0.18 P = 0.57, and P = 0.57, respectively). Treatment values for L* were lighter for CNF than CWF (P = 0.04), while OUT was similar to both (P ≥ 0.14). There were no differences for %Dmb, %Omb, and %Mmb (P = 0.24, P = 0.32, and P = 0.39, respectively) among the treatments.ConclusionResults indicate that heat stress mitigation is a viable method to improve weight, however, does not impact the quality of the meat.

10 Finishing beef cattle under cover reduces heat load and improves efficiency during the summer

Abstract Heat-stress in finishing cattle presents a significant risk to efficiency and economic viability. The project objective was to quantify the effects of long-term heat stress when finishing cattle during the summer in the southeastern United States. Forty-five Angus crossbred steers (446±23 kg) were blocked by weight and randomly assigned to environmental finishing treatments including: covered with fan (CWF), covered without fan (CNF), or outside without shade (OUT). For 92 d steers were individually fed a typical feedlot ration. Environmental data were continuously recorded including: black globe temperature (BG), heat load index (HLI), and accumulated heat load units (AHLU). Feed intake was recorded daily, and steers were weighed every 20–25 days. When the first treatment averaged 613-kg all steers were slaughtered, and carcass data were collected. Data were analyzed as a Mixed Model (JMP V13; SAS Inst.) and means were separated (Least Squares Means). Average maximal BG was lower for covered finishing than OUT (P &lt; 0.01) however for HLI CWFCNF&gt;OUT, while G:F was similar (P = 0.22) between CWF and CNF, which were greater (P &lt; 0.01) than OUT. Hot carcass weights were heavier for CWF than OUT (P &lt; 0.01) and CNF was similar to both (P ≥ 0.11). There was no difference for USDA Yield Grade (2.6; P = 0.44), or marbling score (Modest20; P = 0.76). Steers finished under cover were more efficient than steers finished in open dry-lots. The addition of cooling fans further improved steer gains over those that were covered without fans.

124 Finishing beef cattle under cover reduces heat load and improves efficiency during the summer

Abstract Heat-stress in finishing cattle presents a significant risk to efficiency and economic viability. The project objective was to quantify the effects of long-term heat-stress when finishing cattle during the summer in the southeastern United States. Forty-five Angus crossbred steers (446±23 kg) were blocked by weight and randomly assigned to environmental finishing treatments including: covered with fan (CWF), covered without fan (CNF), or outside without shade (OUT). For 92 d steers were individually fed a typical feedlot ration. Environmental data were continuously recorded including: black globe temperature (BG), heat load index (HLI), and accumulated heat load units (AHLU). Feed intake was recorded daily, and steers were weighed every 20–25 days. When the first treatment averaged 613-kg all steers were slaughtered, and carcass data were collected. Data were analyzed as a Mixed Model (JMP V13; SAS Inst.) and means were separated (Least Squares Means). Average maximal BG was lower for covered finishing than OUT (P &lt; 0.01); however, for HLI CWFCNF&gt;OUT, while G:F was similar (P = 0.22) between CWF and CNF which were greater (P &lt; 0.01) than OUT. Hot carcass weights were heavier for CWF than OUT (P &lt; 0.01) and CNF was similar to both (P ≥ 0.11). There was no difference for USDA Yield Grade (2.6; P = 0.44), or marbling score (Modest20; P = 0.76). Steers finished under cover were more efficient than steers finished in open dry-lots. The addition of cooling fans further improved steer gains over those that were covered without fans.

Evaluating rumen temperature as an estimate of core body temperature in Angus feedlot cattle during summer.

This study was conducted to determine the relationship between rectal temperature (TREC) and rumen temperature (TRUM) and to assess if TRUM could be used as a proxy measure of core body temperature (TCORE) in feedlot cattle. Eighty Angus steers (388.8 ± 2.1kg) were orally administered with rumen temperature boluses. Rumen temperatures were recorded at 10-min intervals over 128days from all 80 steers. To define the suitability of TRUM as an estimation of TCORE, TREC were obtained from all steers at 7-day intervals (n= 16). Eight feedlot pens were used where there were 10 steers per pen (162m2). Shade was available in each pen (1.8m2/animal; 90% solar block). Climatic data were recorded at 30-min intervals, including ambient temperature (TA; °C); relative humidity (RH; %); wind speed (WS; m/s) and direction; solar radiation (SR; W/m2); and black globe temperature (BGT; °C). Rainfall (mm) was recorded daily at 0900h. From these data, temperature humidity index (THI), heat load index (HLI) and accumulated heat load (AHL) were calculated. Individual 10-min TRUM data were converted to an individual hourly average. Pooled mean hourly TRUM data from the 128-day data were used to establish the diurnal rhythm of TRUM where the mean minimum (39.19 ± 0.01°C) and mean maximum (40.04 ± 0.01°C) were observed at 0800h and 2000h respectively. A partial correlation coefficient indicated that there were moderate to strong relationships between TRUM and TREC using both real-time (r= 0.55; P< 0.001) and hourly mean (r= 0.51; P< 0.001) TRUM data. The mean difference between TREC and TRUM was small using both real-time (0.16 ± 0.02°C) and hourly mean TRUM (0.13 ± 0.02°C) data. Data from this study supports the hypothesis that TRUM can be used as an estimate of TCORE, suggesting that TRUM can be used to measure and quantify heat load in feedlot cattle.

Experimental study on thermodynamic vent system with different influence factors

Summary A ground experiment is established to investigate the pressure control performance of thermodynamic vent system (TVS) with HCFC123. Different influence factors, including tank pressure control bands, circulation volume flow rates, and heat loads, are investigated separately. The variations of tank pressure and fluid temperature are analyzed in different operation process. To compare the performance of TVS with that of direct venting, the tank heat leakage is solved with a quasi-steady heat transfer model. With the actual penetration heat into tank determined, the performance comparison is made between direct venting and TVS. The results show that the increase rate of tank pressure rises with the heat load during the pressurization process. While the bulk fluid is still subcooled, great tank pressure control and fluid cooling could be obtained by increasing the circulation flow rate in the mixing injection process. With the cold capacity generated by the throttling process, both the vapor and liquid should be well cooled. For the case of No.3 to 4, as the refrigeration capacity of TVS could not eliminate the accumulated heat load timely, the fluid has a temperature increase in the early stage of throttling process. While for the case of No.6, with the fluid being cooled sufficiently, both the vapor and liquid have received great temperature control. Compared with the direct venting, the recovery ratio of venting gas loss generated by TVS ranges from 30% to 145%, which shows the TVS has a large advantage on exhaust saving.

Effect of heat stress on rumen temperature of three breeds of cattle.

Thirty-six steers (12 of each Angus, Charolais, and Brahman) with an initial BW of 318.5±6.7kg were used in a 130-day study. Two treatments were imposed: un-shaded and shaded (3m2/animal; 90% solar block shade cloth). On day 1, steers were administered with rumen temperature boluses. Rumen temperatures (T RUM) were obtained at 10min intervals over the duration of the study to determine differences in T RUM between Bos indicus and Bos taurus cattle. Six feedlot pens (162m2) were used with six steers (2/breed) per pen with three pens/treatment. Ambient dry bulb temperature (T A; °C), relative humidity (RH; %), wind speed (WS; m/s) and direction, and solar radiation (SR; W/m2) were recorded at 10min intervals. Rainfall (mm) was collected daily at 0900h. From these data, black globe temperature (BGT; °C), temperature humidity index (THI), heat load index (HLI), and accumulated heat load (AHL) were calculated. Individual T RUM were converted to an hourly average and then mean hourly T RUM were converted to a mean within hour T RUM across the 130days. Rumen temperatures were analyzed using an autoregressive repeated measures model. The model analyzed the effect of breed (P<0.0002), treatment (P=0.3543), time of day (hour, h; P<0.0001), breed × treatment (P<0.3683), breed × h (P<0.0001), treatment × h (P<0.0001), breed × treatment × h (P=0.0029), pen within treatment (P=0.0195), and animal × breed × treatment within pen (P=0.1041). Furthermore, there were breed × treatment × hour differences in T RUM (P=0.0036), indicating that Bos indicus and Bos taurus regulate T RUM differently.

A new heat load index for feedlot cattle1

The ability to predict the effects of extreme climatic variables on livestock is important in terms of welfare and performance. An index combining temperature and humidity (THI) has been used for more than 4 decades to assess heat stress in cattle. However, the THI does not include important climatic variables such as solar load and wind speed (WS, m/s). Likewise, it does not include management factors (the effect of shade) or animal factors (genotype differences). Over 8 summers, a total of 11,669 Bos taurus steers, 2,344 B. taurus crossbred steers, 2,142 B. taurus x Bos indicus steers, and 1,595 B. indicus steers were used to develop and test a heat load index (HLI) for feedlot cattle. A new HLI incorporating black globe (BG) temperature ( degrees C), relative humidity (RH, decimal form), and WS was initially developed by using the panting score (PS) of 2,490 Angus steers. The HLI consists of 2 parts based on a BG temperature threshold of 25 degrees C: HLI(BG>25) = 8.62 + (0.38 x RH) + (1.55 x BG) - (0.5 x WS) + e((2.4-WS)), and HLI(BG<25) = 10.66 + (0.28 x RH) + (1.3 x BG) - WS, where e is the base of the natural logarithm. A threshold HLI above which cattle of different genotypes gain body heat was developed for 7 genotypes. The threshold for unshaded black B. taurus steers was 86, and for unshaded B. indicus (100%) the threshold was 96. Threshold adjustments were developed for factors such as coat color, health status, access to shade, drinking water temperature, and manure management. Upward and downward adjustments are possible; upward adjustments occur when cattle have access to shade (+3 to +7) and downward adjustments occur when cattle are showing clinical signs of disease (-5). A related measure, the accumulated heat load (AHL) model, also was developed after the development of the HLI. The AHL is a measure of the animal's heat load balance and is determined by the duration of exposure above the threshold HLI. The THI and THI-hours (hours above a THI threshold) were compared with the HLI and AHL. The relationships between tympanic temperature and the average HLI and THI for the previous 24 h were R(2) = 0.67, P < 0.001, and R(2) = 0.26, P < 0.001, respectively. The R(2) for the relationships between HLI or AHL and PS were positive (0.93 and 0.92 for HLI and AHL, respectively, P < 0.001). The R(2) for the relationship between THI and PS was 0.61 (P < 0.001), and for THI-hours was 0.37 (P < 0.001). The HLI and the AHL were successful in predicting PS responses of different cattle genotypes during periods of high heat load.

Ecosystem Thermal Buffer Capacity as an Indicator of the Restoration Status of Protected Areas in the Northern Ethiopian Highlands

Abstract Restoration status of forest rehabilitation areas can be assessed by comparing their ecosystem characteristics with those of a reference system, most often what is considered the natural climax vegetation. However, comprehensive measurements needed for a traditional vegetation description are often hard or impractical in complex (sub)tropical ecosystems. Therefore, an alternative approach is the identification of simple indicators of ecosystem integrity. The use of such indicators can speed up the availability of resource inventories and thus contribute to the accelerated implementation of successful rehabilitation practices. Thermal buffer capacity (TBC) of ecosystems has been previously proposed as an overall indicator of ecosystem integrity. In this article, sequential surface‐temperature measurements are proposed as a method for TBC assessment of different land‐use types. Surface temperatures of seven land units in central Tigray (northern Ethiopia), each with a uniform land‐use type (degraded and bushy grazing land, enriched and non‐enriched rehabilitation area, and forest), were measured with a hand‐held infrared thermometer in the rainy and the dry season. Surface‐temperature models were derived by means of quadratic regression. Cross‐correlation functions were calculated for all possible pairs of land‐unit time‐series data. Instantaneous heat‐up rates, average TBC, and accumulated heat load were calculated. Repeated‐measures analysis of variance was used to test the effect of aspect and protection status on TBC. Kruskal–Wallis one‐way analysis of variance by ranks for small samples was used to test the significance of differences in heat‐up rates and heat load among land‐use groups. Time lags between land‐unit surface temperatures are caused by differences in aspect rather than land‐use type. Protection status and aspect have a significant effect on the average TBC. Results clearly demonstrate a differentiation between protected (low heat‐up rate) and non‐protected areas (high heat‐up rate). Overall ranking suggests that the remnant forest has the highest TBC of all surveyed land‐use types, followed by the enriched protected area. Results of this study show that TBC quickly responds to area closure and can therefore be used to monitor the development of protected areas. It is strongly recommended that a detailed monitoring strategy for protected areas on the basis of this technology be devised, validated, and finally transferred to the local communities.