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• 61. [Article] Variation of Surface Air Temperature in Complex Terrain

  Data from three micronetworks with eddy correlation data and three additional micronetworks without eddy correlation data are analyzed to study the spatial variability of surface air temperature in complex ...

  Citation × Citation Citation Abstract Copy Title: Variation of Surface Air Temperature in Complex Terrain Author: Mahrt, L. Data from three micronetworks with eddy correlation data and three additional micronetworks without eddy correlation data are analyzed to study the spatial variability of surface air temperature in complex terrain. A simple similarity relationship is constructed to relate the spatial variation of air temperature along the slope to the thermal forcing and mixing. Mixing is not included in present empirical formulations of the surface air temperature distribution in complex terrain. The development of surface temperature gradients along the slope, resulting from surface heating or cooling, is bounded by a maximum (or saturated) value, where a further increase of temperature gradients is restricted by redistribution of heat by thermally driven slope circulations. Although much of the spatial variation of the surface air temperature is governed by complex three-dimensionality and surface vegetation, a relatively simple relationship is able to account for much of the diurnal and day-to-day variation of the spatial distribution of air temperature. This relationship requires information on the surface heat flux and friction velocity over a reference surface. Required generalizations of the relationship are outlined before it can be applied to an arbitrary site. Title: Variation of Surface Air Temperature in Complex Terrain Author: Mahrt, L. Data from three micronetworks with eddy correlation data and three additional micronetworks without eddy correlation data are analyzed to study the spatial variability of surface air temperature in complex terrain. A simple similarity relationship is constructed to relate the spatial variation of air temperature along the slope to the thermal forcing and mixing. Mixing is not included in present empirical formulations of the surface air temperature distribution in complex terrain. The development of surface temperature gradients along the slope, resulting from surface heating or cooling, is bounded by a maximum (or saturated) value, where a further increase of temperature gradients is restricted by redistribution of heat by thermally driven slope circulations. Although much of the spatial variation of the surface air temperature is governed by complex three-dimensionality and surface vegetation, a relatively simple relationship is able to account for much of the diurnal and day-to-day variation of the spatial distribution of air temperature. This relationship requires information on the surface heat flux and friction velocity over a reference surface. Required generalizations of the relationship are outlined before it can be applied to an arbitrary site. Close

• 62. [Article] A second forecast of temperature conditions in Brownlee Reservoir and in the Snake River below Brownlee Dam

  A graph is presented which shows the average annual temperature depth profile which has been computed and estimated for the Brownlee Reservoir. Forecast computations and estimations are for a median river ...

  Citation × Citation Citation Abstract Copy Title: A second forecast of temperature conditions in Brownlee Reservoir and in the Snake River below Brownlee Dam Author: Oregon State College. School of Science, Burt, Wayne V., U.S. Fish and Wildlife Service A graph is presented which shows the average annual temperature depth profile which has been computed and estimated for the Brownlee Reservoir. Forecast computations and estimations are for a median river flow year. The graph also contains forecasts of the annual temperature cycle for the Snake River below Brownlee Dam. Title: A second forecast of temperature conditions in Brownlee Reservoir and in the Snake River below Brownlee Dam Author: Oregon State College. School of Science, Burt, Wayne V., U.S. Fish and Wildlife Service A graph is presented which shows the average annual temperature depth profile which has been computed and estimated for the Brownlee Reservoir. Forecast computations and estimations are for a median river flow year. The graph also contains forecasts of the annual temperature cycle for the Snake River below Brownlee Dam. Close

• 63. [Article] The thermal regulation, microclimate, and distribution of the mountain beaver, Aplodontia rufa pacifica Merriam

  An investigation was undertaken to determine the role that temperature might play in limiting the distribution of the mountain beaver, Aplodontia rufa. A field study was carried on from August, 1965, through ...

  Citation × Citation Citation Abstract Copy Title: The thermal regulation, microclimate, and distribution of the mountain beaver, Aplodontia rufa pacifica Merriam Author: Johnson, Sheldon Robert An investigation was undertaken to determine the role that temperature might play in limiting the distribution of the mountain beaver, Aplodontia rufa. A field study was carried on from August, 1965, through August, 1966, in the coast mountains of Benton County, Oregon, and consisted of measuring the annual temperature cycle of the burrows in conjunction with air temperatures taken at a height of six cm above the soil surface. A laboratory study was conducted to determine the effects of ambient temperature on body temperature, metabolic rate, thermal conductance, insensible water loss, and heart rate. The burrow system was characterized by a cool and stable microclimate. The temperature above the soil showed a maximum annual fluctuation of 40.5°C, the temperature within the burrows varied 18.3°C, with a weekly variation in burrow temperature of not more than 4°C. Annual range in mean burrow temperature was from 2° to 14°C. The mean body temperature of Aplodontia, over an ambient temperature range of from 4° to 290°C was 37.60°C. Free-living animals had a mean body temperature of 38.0°C. Hyperthermia began at ambient temperatures above 29°C and a lethal body temperature of approximately 42°C was reached after a two hour exposure to temperatures between 32° and 35°C. Aplodontia lacked a thermoneutral zone and minimal metabolic rates were recorded at high ambient temperatures when the animals were hyperthermic. Under conditions of heat stress, mean metabolicrateswere 65 percent of the values predicted by Kleiber's equation. These animals were lethargic, their respiration rates decreased to as low as 18 per minute with minimal heart rates between 60 and 100 beats per minute. The mean minimal recorded heart rates, based on body weight, were 38 percent of that predicted. Aplodontia had a minimal thermal conductance of 0.195 cal/g/hr/°C which could only be increased by a factor of 1.84. Winter animals had an effective insulation L. 23 times that of summer animals. This raised the lower critical temperature of summer animals by 4°C (19° to 23°C). Aplodontia required a six degree thermal gradient to dissipate its minimal heat production. Insensible water loss could only be increased by a factor of 2.3 over the ambient temperature range of 12° to 31.5°C. At the latter ambient temperature, evaporative heat loss accounted for only 22 percent of Aplodontia's total heat loss. The results of this investigation indicated that high environmental temperatures may act as an important limiting factor in the distribution of the mountain beaver which lacks adequate mechanisms to avoid heat stress. Title: The thermal regulation, microclimate, and distribution of the mountain beaver, Aplodontia rufa pacifica Merriam Author: Johnson, Sheldon Robert An investigation was undertaken to determine the role that temperature might play in limiting the distribution of the mountain beaver, Aplodontia rufa. A field study was carried on from August, 1965, through August, 1966, in the coast mountains of Benton County, Oregon, and consisted of measuring the annual temperature cycle of the burrows in conjunction with air temperatures taken at a height of six cm above the soil surface. A laboratory study was conducted to determine the effects of ambient temperature on body temperature, metabolic rate, thermal conductance, insensible water loss, and heart rate. The burrow system was characterized by a cool and stable microclimate. The temperature above the soil showed a maximum annual fluctuation of 40.5°C, the temperature within the burrows varied 18.3°C, with a weekly variation in burrow temperature of not more than 4°C. Annual range in mean burrow temperature was from 2° to 14°C. The mean body temperature of Aplodontia, over an ambient temperature range of from 4° to 290°C was 37.60°C. Free-living animals had a mean body temperature of 38.0°C. Hyperthermia began at ambient temperatures above 29°C and a lethal body temperature of approximately 42°C was reached after a two hour exposure to temperatures between 32° and 35°C. Aplodontia lacked a thermoneutral zone and minimal metabolic rates were recorded at high ambient temperatures when the animals were hyperthermic. Under conditions of heat stress, mean metabolicrateswere 65 percent of the values predicted by Kleiber's equation. These animals were lethargic, their respiration rates decreased to as low as 18 per minute with minimal heart rates between 60 and 100 beats per minute. The mean minimal recorded heart rates, based on body weight, were 38 percent of that predicted. Aplodontia had a minimal thermal conductance of 0.195 cal/g/hr/°C which could only be increased by a factor of 1.84. Winter animals had an effective insulation L. 23 times that of summer animals. This raised the lower critical temperature of summer animals by 4°C (19° to 23°C). Aplodontia required a six degree thermal gradient to dissipate its minimal heat production. Insensible water loss could only be increased by a factor of 2.3 over the ambient temperature range of 12° to 31.5°C. At the latter ambient temperature, evaporative heat loss accounted for only 22 percent of Aplodontia's total heat loss. The results of this investigation indicated that high environmental temperatures may act as an important limiting factor in the distribution of the mountain beaver which lacks adequate mechanisms to avoid heat stress. Close

• 64. [Article] Developmental anatomy of Phaseolus vulgaris L. as influenced by temperature

  Bush snap beans (Phaseolus vulgaris L.) cvs 'G5O' (Gallatin 50) and 'OSU58' (Oregon 58) were used for anatomical and morphological studies of their responses to three levels of temperature. The plants ...

  Citation × Citation Citation Abstract Copy Title: Developmental anatomy of Phaseolus vulgaris L. as influenced by temperature Author: Wivutvongvana, Manee Bush snap beans (Phaseolus vulgaris L.) cvs 'G5O' (Gallatin 50) and 'OSU58' (Oregon 58) were used for anatomical and morphological studies of their responses to three levels of temperature. The plants were grown in a controlled chamber under a 16-hour photoperiod at 60°/50°, 70°/60° and 80°/70°F (day/night temperature), respectively. The leaf primordia were initiated in spiral phyllotaxy. They were oriented perpendicular to their particular stipule primordia. Decussate phyllotaxy or a mixture between decussate and spiral phyllotaxy within the same plant was observed under stress condition. Low temperature decreased the number of leaf primordia per plant and delayed the initiation. Initiation of the axillary bud primordia was delayed by low temperature when compared with medium and high temperatures. The axillary bud of the uppermost leaf was the first triad primordium of the plant. It was observed at seven to nine days after planting at medium or high temperature, and at 17 and 14 days at low temperature in 'G5O' and 'OSU58', respectively. The initiation of the triad primordia of the terminal raceme of the main shoot and the primordium of the uppermost leaf of the lateral branches were also delayed by low temperature. The initiation in 'G50' was more affected by low temperature than'OSU58'. The development of the primordia was delayed by low temperature in both cultivars with the development in 'G50' being more affected than in 'OSU58'. This delay was observed in the primordium of the uppermost leaf and the first primordium of the terminal raceme of the main shoot. The opening of flowers followed the sequence of floral initiation and development. Regardless of temperature, the first flower to open was the triad of the uppermost leaf. The first triad of the terminal raceme also opened with the first group, or in some cases, with the second group. The second group of opened flowers was of the non-leaf and the one-leaf branches. The third group was the upper triad of the terminal raceme, the two-leaf branch and the branches of the first node. The time required for opening of flowers of the second and the third group was longer than the first one. Overlapping of the two later groups was observed in 'OSU58' at high and low temperatures. Seed germination and growth of seedlings were markedly delayed by low temperature. The number of nodes was decreased. The time requirement for the first flower to open was significantly lengthened as well as the duration of flowering. The pattern of flowering was changed. Concentrated flowering within a short period was observed at medium and high temperatures, whereas uniform flowering within a long period was seen at low temperature. Different responses were observed in the number of opened flowers per plant and the percentage of pod set as a function of temperature, The highest number of opened flowers in 'G50' was observed at medium temperature, whereas highest percentage of pod set was obtained at low temperature. 'OSU58' showed reversed responses from 'G50'. High temperature decreased the percentage of pod set in both cultivars. Title: Developmental anatomy of Phaseolus vulgaris L. as influenced by temperature Author: Wivutvongvana, Manee Bush snap beans (Phaseolus vulgaris L.) cvs 'G5O' (Gallatin 50) and 'OSU58' (Oregon 58) were used for anatomical and morphological studies of their responses to three levels of temperature. The plants were grown in a controlled chamber under a 16-hour photoperiod at 60°/50°, 70°/60° and 80°/70°F (day/night temperature), respectively. The leaf primordia were initiated in spiral phyllotaxy. They were oriented perpendicular to their particular stipule primordia. Decussate phyllotaxy or a mixture between decussate and spiral phyllotaxy within the same plant was observed under stress condition. Low temperature decreased the number of leaf primordia per plant and delayed the initiation. Initiation of the axillary bud primordia was delayed by low temperature when compared with medium and high temperatures. The axillary bud of the uppermost leaf was the first triad primordium of the plant. It was observed at seven to nine days after planting at medium or high temperature, and at 17 and 14 days at low temperature in 'G5O' and 'OSU58', respectively. The initiation of the triad primordia of the terminal raceme of the main shoot and the primordium of the uppermost leaf of the lateral branches were also delayed by low temperature. The initiation in 'G50' was more affected by low temperature than'OSU58'. The development of the primordia was delayed by low temperature in both cultivars with the development in 'G50' being more affected than in 'OSU58'. This delay was observed in the primordium of the uppermost leaf and the first primordium of the terminal raceme of the main shoot. The opening of flowers followed the sequence of floral initiation and development. Regardless of temperature, the first flower to open was the triad of the uppermost leaf. The first triad of the terminal raceme also opened with the first group, or in some cases, with the second group. The second group of opened flowers was of the non-leaf and the one-leaf branches. The third group was the upper triad of the terminal raceme, the two-leaf branch and the branches of the first node. The time required for opening of flowers of the second and the third group was longer than the first one. Overlapping of the two later groups was observed in 'OSU58' at high and low temperatures. Seed germination and growth of seedlings were markedly delayed by low temperature. The number of nodes was decreased. The time requirement for the first flower to open was significantly lengthened as well as the duration of flowering. The pattern of flowering was changed. Concentrated flowering within a short period was observed at medium and high temperatures, whereas uniform flowering within a long period was seen at low temperature. Different responses were observed in the number of opened flowers per plant and the percentage of pod set as a function of temperature, The highest number of opened flowers in 'G50' was observed at medium temperature, whereas highest percentage of pod set was obtained at low temperature. 'OSU58' showed reversed responses from 'G50'. High temperature decreased the percentage of pod set in both cultivars. Close

• 65. [Article] The influence of climate change and restoration on stream temperature

  Water temperature is an essential property of a stream. Temperature regulates physical and biochemical processes in aquatic habitats. Various factors related to climatic conditions, landscape characteristics, ...

  Citation × Citation Citation Abstract Copy Title: The influence of climate change and restoration on stream temperature Author: Diabat, Mousa Water temperature is an essential property of a stream. Temperature regulates physical and biochemical processes in aquatic habitats. Various factors related to climatic conditions, landscape characteristics, and channel structure directly influence stream temperature. Numerous studies indicate that increased average air temperature during the past century has led to stream warming across the world. The trend of stream warming was also present in spring-fed watersheds, where summer flow has decreased. In addition, anthropogenic practices that alter the natural landscape and channel structure, such as forest management, agriculture, and mining contributed to stream warming. For example, deforested and unshaded stream reaches or dredged channels were warmer than shaded reaches and meandering streams. Stream temperatures in North American lotic habitats are of a specific concern due to their significant economic, cultural, and ecological value. With climate projections indicating that air temperature will only continue to rise throughout the 21st century, cold- or cool-water organisms, especially fishes, will be affected. Therefore, there is a strong need to better understand the impacts of changing climate, riparian landscape, and channel structure on a stream's heat budget. This may assist in restoring the historic thermal regime in impacted sites and mitigating the impacts of future climate change. This study looks into the relative influences of the different factors on a stream's heat budget with three manuscripts: one on stream temperature response to diel timing of air warming, one on stream temperature response to changes in air temperature, flow, and riparian vegetation, and one on stream temperature response to air warming and channel reconstruction. I used the software Heat Source version 8.05 to simulate stream temperature for all three analyses along the Middle Fork John Day River, Oregon USA. Two of the manuscripts were applied to an upper 37 km section of the Middle Fork John Day River (presented in chapter 2 and 3), where the third manuscript was applied to a 1.5-km section. The sensitivity analysis of stream temperature response to diel timing of air warming (Chapter 2: Diel Timing of Warmer Air under Climate Change Affects Magnitude, Timing, and Duration of Stream Temperature Change) was based on scenarios representing uniform air warming over the diel period, daytime warming, and nighttime warming. Uniform warming of air temperature is a simple representation of increases in the average daily or monthly temperatures generated by the 'delta method'. The delta method relies on adding a constant value to the air temperature time-series data. This constant value is the difference (delta) between base case average air temperatures and the projected one. Scenarios of daytime or nighttime warming represent conditions under which most of the warming of the air occurs during the daytime or the nighttime, respectively. I simulated the stream temperature response to warmer air conditions of +2 °C and +4 °C in daily average for all three cases of air warming conditions. The three cases of different diel distributions of air warming generated 7-day average daily maximum stream temperature (7DADM) increases of approximately +1.8 °C ± 0.1 °C at the downstream end of the study section relative to the base case. In most parts of the reach, the three distributions of air warming generated different ranges of stream temperatures, different 7DADM values, different durations of stream temperature changes, and different average daily temperatures. Changes of stream temperature were out of phase with imposed changes of air temperature. Therefore, nighttime warming of air temperatures would cause the greatest increase in maximum daily stream temperature, which typically occurs during the daytime. The sensitivity analysis of the relative influences of changes in air temperature, stream flow, and riparian vegetation on stream temperature (Chapter 3: Assessing Stream Temperature Response to Cumulative Influence of Changing Air Temperature, Flow, and Riparian Vegetation). This study summarized stream temperature simulation in 36 scenarios representing possible manifestations of 21st century climate conditions and land management strategies. In addition to existing conditions (base case) of flow, air temperature, and riparian vegetation, scenarios consisted of: two air temperature increases of 2 °C and 4 °C, two stream flow variations of +30% and -30%, three spatially uniform riparian vegetation conditions that create averages of effective shade 7%, 34%, and 79%, in addition to 14% for base case conditions. Results suggest that variation in riparian vegetation was the dominant factor influencing stream temperature because it regulates incoming shortwave radiation, the largest heat input to the stream, while variation in stream flow has a negligible influence. Results indicated that increasing the effective shade along the study section, particularly in the currently unshaded sections, could mitigate the influence of increasing air temperature, and would reduce stream temperature maxima below current values even under future climate conditions of warmer air. With the small influence it had, increasing stream flow reduced the 7DADM under low shade conditions. However, increasing stream flow showed counterintuitive results as it contributed to increasing stream temperature maxima when the stream was heavily shaded. The applied study examined the stream temperature response to restoration practices and their potential to mitigate the influence of warmer air conditions (Chapter 4: Estimating Stream Temperature Response to Restoring Channel and Riparian Vegetation and the Potential to Mitigate Warmer Air Conditions). This study focused on a 1.5 km section along the upper part of the Middle Fork John Day River that was modified due to past anthropogenic activities of mining for gold and timber harvest. Currently, the riparian vegetation of the study site is mostly shrubs and stands of short trees. Restoration designs call for the restoration of both the channel structure and replanting the riparian vegetation. Simulation results showed that the 7DADM was higher in the restored channel than the existing channel with both conditions of low and high effective shade conditions. However, a combined restoration practice of channel reconstruction and medium effective shade conditions reduced stream temperature maxima more than restoring riparian vegetation alone. In addition, results showed that restoring riparian vegetation was sufficient to mitigate the influence of warmer air on stream temperature, while restoring the channel alone is not. Heat budget analysis showed that heat accumulation during the daytime increased in the restored channel, which was longer, narrower, and deeper than the existing channel. It is important to emphasize that stream temperature is one of many goals that restoration activities aim to improve. Furthermore, differences in 7DADM among the different scenarios of restoration are negligible. Such small differences could hardly be measure. While this study examined a short section of 1.5 km, longer stream sections may increase the differences in 7DADM. Primary conclusions of this study are: 1) daily maxima of stream temperature will increase in response to increased air temperature regardless of the distribution of air warming during the diel cycle; 2) nighttime air warming caused a greater increase in stream temperature maximum than daytime warming; 3) riparian vegetation was the dominant factor on stream's heat budget, more than air temperature or stream flow; 4) restoring riparian vegetation mitigated the influence of warmer air; 5) restoring channel structure alone was not sufficient to lower temperature maxima; and 6) restoration project was most successful in improving degraded stream temperature when combined with channel reconstruction and improved riparian shade. Title: The influence of climate change and restoration on stream temperature Author: Diabat, Mousa Water temperature is an essential property of a stream. Temperature regulates physical and biochemical processes in aquatic habitats. Various factors related to climatic conditions, landscape characteristics, and channel structure directly influence stream temperature. Numerous studies indicate that increased average air temperature during the past century has led to stream warming across the world. The trend of stream warming was also present in spring-fed watersheds, where summer flow has decreased. In addition, anthropogenic practices that alter the natural landscape and channel structure, such as forest management, agriculture, and mining contributed to stream warming. For example, deforested and unshaded stream reaches or dredged channels were warmer than shaded reaches and meandering streams. Stream temperatures in North American lotic habitats are of a specific concern due to their significant economic, cultural, and ecological value. With climate projections indicating that air temperature will only continue to rise throughout the 21st century, cold- or cool-water organisms, especially fishes, will be affected. Therefore, there is a strong need to better understand the impacts of changing climate, riparian landscape, and channel structure on a stream's heat budget. This may assist in restoring the historic thermal regime in impacted sites and mitigating the impacts of future climate change. This study looks into the relative influences of the different factors on a stream's heat budget with three manuscripts: one on stream temperature response to diel timing of air warming, one on stream temperature response to changes in air temperature, flow, and riparian vegetation, and one on stream temperature response to air warming and channel reconstruction. I used the software Heat Source version 8.05 to simulate stream temperature for all three analyses along the Middle Fork John Day River, Oregon USA. Two of the manuscripts were applied to an upper 37 km section of the Middle Fork John Day River (presented in chapter 2 and 3), where the third manuscript was applied to a 1.5-km section. The sensitivity analysis of stream temperature response to diel timing of air warming (Chapter 2: Diel Timing of Warmer Air under Climate Change Affects Magnitude, Timing, and Duration of Stream Temperature Change) was based on scenarios representing uniform air warming over the diel period, daytime warming, and nighttime warming. Uniform warming of air temperature is a simple representation of increases in the average daily or monthly temperatures generated by the 'delta method'. The delta method relies on adding a constant value to the air temperature time-series data. This constant value is the difference (delta) between base case average air temperatures and the projected one. Scenarios of daytime or nighttime warming represent conditions under which most of the warming of the air occurs during the daytime or the nighttime, respectively. I simulated the stream temperature response to warmer air conditions of +2 °C and +4 °C in daily average for all three cases of air warming conditions. The three cases of different diel distributions of air warming generated 7-day average daily maximum stream temperature (7DADM) increases of approximately +1.8 °C ± 0.1 °C at the downstream end of the study section relative to the base case. In most parts of the reach, the three distributions of air warming generated different ranges of stream temperatures, different 7DADM values, different durations of stream temperature changes, and different average daily temperatures. Changes of stream temperature were out of phase with imposed changes of air temperature. Therefore, nighttime warming of air temperatures would cause the greatest increase in maximum daily stream temperature, which typically occurs during the daytime. The sensitivity analysis of the relative influences of changes in air temperature, stream flow, and riparian vegetation on stream temperature (Chapter 3: Assessing Stream Temperature Response to Cumulative Influence of Changing Air Temperature, Flow, and Riparian Vegetation). This study summarized stream temperature simulation in 36 scenarios representing possible manifestations of 21st century climate conditions and land management strategies. In addition to existing conditions (base case) of flow, air temperature, and riparian vegetation, scenarios consisted of: two air temperature increases of 2 °C and 4 °C, two stream flow variations of +30% and -30%, three spatially uniform riparian vegetation conditions that create averages of effective shade 7%, 34%, and 79%, in addition to 14% for base case conditions. Results suggest that variation in riparian vegetation was the dominant factor influencing stream temperature because it regulates incoming shortwave radiation, the largest heat input to the stream, while variation in stream flow has a negligible influence. Results indicated that increasing the effective shade along the study section, particularly in the currently unshaded sections, could mitigate the influence of increasing air temperature, and would reduce stream temperature maxima below current values even under future climate conditions of warmer air. With the small influence it had, increasing stream flow reduced the 7DADM under low shade conditions. However, increasing stream flow showed counterintuitive results as it contributed to increasing stream temperature maxima when the stream was heavily shaded. The applied study examined the stream temperature response to restoration practices and their potential to mitigate the influence of warmer air conditions (Chapter 4: Estimating Stream Temperature Response to Restoring Channel and Riparian Vegetation and the Potential to Mitigate Warmer Air Conditions). This study focused on a 1.5 km section along the upper part of the Middle Fork John Day River that was modified due to past anthropogenic activities of mining for gold and timber harvest. Currently, the riparian vegetation of the study site is mostly shrubs and stands of short trees. Restoration designs call for the restoration of both the channel structure and replanting the riparian vegetation. Simulation results showed that the 7DADM was higher in the restored channel than the existing channel with both conditions of low and high effective shade conditions. However, a combined restoration practice of channel reconstruction and medium effective shade conditions reduced stream temperature maxima more than restoring riparian vegetation alone. In addition, results showed that restoring riparian vegetation was sufficient to mitigate the influence of warmer air on stream temperature, while restoring the channel alone is not. Heat budget analysis showed that heat accumulation during the daytime increased in the restored channel, which was longer, narrower, and deeper than the existing channel. It is important to emphasize that stream temperature is one of many goals that restoration activities aim to improve. Furthermore, differences in 7DADM among the different scenarios of restoration are negligible. Such small differences could hardly be measure. While this study examined a short section of 1.5 km, longer stream sections may increase the differences in 7DADM. Primary conclusions of this study are: 1) daily maxima of stream temperature will increase in response to increased air temperature regardless of the distribution of air warming during the diel cycle; 2) nighttime air warming caused a greater increase in stream temperature maximum than daytime warming; 3) riparian vegetation was the dominant factor on stream's heat budget, more than air temperature or stream flow; 4) restoring riparian vegetation mitigated the influence of warmer air; 5) restoring channel structure alone was not sufficient to lower temperature maxima; and 6) restoration project was most successful in improving degraded stream temperature when combined with channel reconstruction and improved riparian shade. Close

• 66. [Article] The influence of environmental and physical factors on the thermal patterns of headwater streams

  A case study was performed in 2000 and 2001 to characterize the thermal pattern of four morphologically similar eastern Oregon streams and to identify the physical and environmental factors that expressed ...

  Citation × Citation Citation Abstract Copy Title: The influence of environmental and physical factors on the thermal patterns of headwater streams Author: Carr, Craig A. A case study was performed in 2000 and 2001 to characterize the thermal pattern of four morphologically similar eastern Oregon streams and to identify the physical and environmental factors that expressed significant and functionally viable relationships with stream temperature (daily maximum, daily minimum and daily rate of heating). Stream and environmental attributes were measured at various locations along each stream to provide a data set comprised of variables representing daily stream temperatures (minimum, maximum and rates of heating), daily air temperatures (minimum and maximum), shade, elevation, elevation change and length. Data from the 20 hottest days were analyzed using analysis of variance and regression-based path analysis. With the exception of those reaches that were influenced by groundwater or subsurface flow, downstream reaches consistently experienced increases in the daily maximum stream temperature. The most significant parameter with respect to daily maximum stream temperature appeared to be reach elevation; expressed through reach location in the watershed. Maximum air temperature also positively influenced maximum stream temperature however, only on streams that expressed significant variation in maximum air temperature. The dominant influence of groundwater on maximum stream temperature was also apparent. Significant reach level variation in daily minimum stream temperatures was not observed in this study, however most streams did record increases in the downstream direction. Daily minimum air temperature was consistent across all streams in expressing the most significant relationship with daily minimum stream temperature. With the exception of groundwater influenced reaches, all streams exhibited obvious downstream increases in the daily rate of stream heating. Daily minimum air temperature consistently exhibited a significant negative association with the rate of heating and a relationship was also implied between reach elevation, maximum stream temperature and minimum stream temperature and this stream temperature response. Groundwater and subsurface flow, when present, also appeared to influence the daily rate of stream heating. Resource management activities should have little impact on the parameters found, on these streams, to be associated with stream temperature. Location in the watershed and climatic influence through both minimum and maximum air temperatures emerged as the dominant factors with respect to stream thermal patterns. Title: The influence of environmental and physical factors on the thermal patterns of headwater streams Author: Carr, Craig A. A case study was performed in 2000 and 2001 to characterize the thermal pattern of four morphologically similar eastern Oregon streams and to identify the physical and environmental factors that expressed significant and functionally viable relationships with stream temperature (daily maximum, daily minimum and daily rate of heating). Stream and environmental attributes were measured at various locations along each stream to provide a data set comprised of variables representing daily stream temperatures (minimum, maximum and rates of heating), daily air temperatures (minimum and maximum), shade, elevation, elevation change and length. Data from the 20 hottest days were analyzed using analysis of variance and regression-based path analysis. With the exception of those reaches that were influenced by groundwater or subsurface flow, downstream reaches consistently experienced increases in the daily maximum stream temperature. The most significant parameter with respect to daily maximum stream temperature appeared to be reach elevation; expressed through reach location in the watershed. Maximum air temperature also positively influenced maximum stream temperature however, only on streams that expressed significant variation in maximum air temperature. The dominant influence of groundwater on maximum stream temperature was also apparent. Significant reach level variation in daily minimum stream temperatures was not observed in this study, however most streams did record increases in the downstream direction. Daily minimum air temperature was consistent across all streams in expressing the most significant relationship with daily minimum stream temperature. With the exception of groundwater influenced reaches, all streams exhibited obvious downstream increases in the daily rate of stream heating. Daily minimum air temperature consistently exhibited a significant negative association with the rate of heating and a relationship was also implied between reach elevation, maximum stream temperature and minimum stream temperature and this stream temperature response. Groundwater and subsurface flow, when present, also appeared to influence the daily rate of stream heating. Resource management activities should have little impact on the parameters found, on these streams, to be associated with stream temperature. Location in the watershed and climatic influence through both minimum and maximum air temperatures emerged as the dominant factors with respect to stream thermal patterns. Close

• 67. [Article] The influence of contemporary forest harvesting on summer stream temperatures in headwater streams of Hinkle Creek, Oregon

  Stream temperature is a water quality parameter that directly influences the quality of aquatic habitat, particularly for cold-water species such as Pacific salmonids. Forest harvesting adjacent to a stream ...

  Citation × Citation Citation Abstract Copy Title: The influence of contemporary forest harvesting on summer stream temperatures in headwater streams of Hinkle Creek, Oregon Author: Kibler, Kelly Maren Stream temperature is a water quality parameter that directly influences the quality of aquatic habitat, particularly for cold-water species such as Pacific salmonids. Forest harvesting adjacent to a stream can increase the amount of solar radiation the stream receives, which can elevate stream temperatures and impair aquatic habitat. Oregon Forest Practice Rules mandate that forest operators leave Riparian Management Areas (RMAs) adjacent to streams in order to minimize the water quality impacts from forest harvesting. However, RMAs that contain overstory merchantable conifers are not required for small non-fish-bearing streams in Oregon, thus there is potential for increases in stream temperature to occur in headwater streams after harvesting. There is concern that increases in stream temperatures and changes to onsite processes in non-fish-bearing, headwater streams may propagate downstream and impair habitat in fish-bearing streams. The objectives of the following work are to assess the effects of contemporary forest management practices on stream temperatures of small non-fish-bearing headwater streams and to develop new knowledge regarding the physical processes that control reach-level stream temperature patterns. Summer stream temperatures were measured for five years in six headwater streams in the Hinkle Creek basin in southern Oregon. After four years, four of the streams were harvested and vegetated RMAs were not left between the streams and harvest units. The watersheds of the two remaining streams were not disturbed. Post-harvest stream temperatures were monitored for one year in all six streams. Each harvested stream was paired with one unharvested stream and regression relationships for maximum, minimum and mean daily stream temperatures were developed. Changes to temperatures of harvested streams were detected by comparing the mean pre-harvest regression relationship to the mean post-harvest relationship. Change detection analyses that considered the mean response among all four harvested streams indicated that maximum daily stream temperatures did not increase after harvesting, but that minimum and mean daily temperatures decreased significantly after harvesting. Additionally, diel stream temperature fluctuations were significantly greater one year after harvesting. Pre- and post-harvest surveys of canopy closure in the harvested and unharvested streams were completed in order to compare levels of stream shading before and after harvest. The post-harvest survey quantified canopy closure from remaining overstory vegetation as well as from logging slash that partially covered the harvested streams. The surveys indicated that mean overstory canopy closure in the harvested streams decreased by 84% as a result of the harvest, but as the logging slash provided considerable cover, total canopy closure decreased by only 20%. It is possible that the logging slash effectively attenuated solar radiation and prevented extreme temperature increases in the harvested streams. However, it is likely that streamflow increased after harvesting and that the increased streamflow also prevented increases to maximum temperatures and contributed to lower minimum and mean stream temperatures. Title: The influence of contemporary forest harvesting on summer stream temperatures in headwater streams of Hinkle Creek, Oregon Author: Kibler, Kelly Maren Stream temperature is a water quality parameter that directly influences the quality of aquatic habitat, particularly for cold-water species such as Pacific salmonids. Forest harvesting adjacent to a stream can increase the amount of solar radiation the stream receives, which can elevate stream temperatures and impair aquatic habitat. Oregon Forest Practice Rules mandate that forest operators leave Riparian Management Areas (RMAs) adjacent to streams in order to minimize the water quality impacts from forest harvesting. However, RMAs that contain overstory merchantable conifers are not required for small non-fish-bearing streams in Oregon, thus there is potential for increases in stream temperature to occur in headwater streams after harvesting. There is concern that increases in stream temperatures and changes to onsite processes in non-fish-bearing, headwater streams may propagate downstream and impair habitat in fish-bearing streams. The objectives of the following work are to assess the effects of contemporary forest management practices on stream temperatures of small non-fish-bearing headwater streams and to develop new knowledge regarding the physical processes that control reach-level stream temperature patterns. Summer stream temperatures were measured for five years in six headwater streams in the Hinkle Creek basin in southern Oregon. After four years, four of the streams were harvested and vegetated RMAs were not left between the streams and harvest units. The watersheds of the two remaining streams were not disturbed. Post-harvest stream temperatures were monitored for one year in all six streams. Each harvested stream was paired with one unharvested stream and regression relationships for maximum, minimum and mean daily stream temperatures were developed. Changes to temperatures of harvested streams were detected by comparing the mean pre-harvest regression relationship to the mean post-harvest relationship. Change detection analyses that considered the mean response among all four harvested streams indicated that maximum daily stream temperatures did not increase after harvesting, but that minimum and mean daily temperatures decreased significantly after harvesting. Additionally, diel stream temperature fluctuations were significantly greater one year after harvesting. Pre- and post-harvest surveys of canopy closure in the harvested and unharvested streams were completed in order to compare levels of stream shading before and after harvest. The post-harvest survey quantified canopy closure from remaining overstory vegetation as well as from logging slash that partially covered the harvested streams. The surveys indicated that mean overstory canopy closure in the harvested streams decreased by 84% as a result of the harvest, but as the logging slash provided considerable cover, total canopy closure decreased by only 20%. It is possible that the logging slash effectively attenuated solar radiation and prevented extreme temperature increases in the harvested streams. However, it is likely that streamflow increased after harvesting and that the increased streamflow also prevented increases to maximum temperatures and contributed to lower minimum and mean stream temperatures. Close

• 68. [Article] Soil organic carbon response to six years of warming : assessing the impacts of altered diurnal temperature range

  There is a growing consensus that anthropogenic warming will impact soil organic matter (SOM). Globally, soil contains 2-3 times more carbon (C) than plants, and like plants, temperature induced change ...

  Citation × Citation Citation Abstract Copy Title: Soil organic carbon response to six years of warming : assessing the impacts of altered diurnal temperature range Author: Murphey, Virginia L. W. There is a growing consensus that anthropogenic warming will impact soil organic matter (SOM). Globally, soil contains 2-3 times more carbon (C) than plants, and like plants, temperature induced change of SOM could have significant climate repercussions. Although, the majority of warming experiments have increased day and night temperatures equally, there is evidence of greater increase in global minimum temperatures compared to midday maxima, resulting in an altered mean diurnal temperature range (DTR). Here, intact grassland mesocosms (Terracosm facility, Corvallis OR) were used to assess soil organic C (SOC) changes resulting from altered DTR over a six year period. We assessed the response of SOC to a mean temperature increase of 3.5°C with three temperature treatments: symmetric (SYM) warming of +3.5°C, asymmetric (ASYM) warming of +5°C/ +2°C at minimum and maximum daily temperature, respectively, and control treatments that were kept at ambient (AMB) temperatures. After six years of warming SOC was surprisingly unaltered by increased temperature and was more strongly influenced by plant dynamics than expected. The strongest temperature response was from soil respiration (reported as In-situ cumulative soil C mineralization) with at least 33% higher cumulative C mineralization in warming treatments. In agreement with the soil respiration response, light fraction C (<1.8g/cm³) was depleted in warming treatments (8-10% less C than AMB) at shallow depths. However, laboratory cumulative soil C mineralization, a measure of most easily degraded SOC, had a lack of response to temperature, and actually had trends for greater C in warming treatments. This response was further validated by increased soil water dissolved organic C (DOC) concentration in warming treatments. An increase in these measures suggested that plants were more influential than temperature for highly labile SOC. Aggregates, an important part of SOC allocation and sequestration, had a differential response to SYM and ASYM treatments but this was likely more directly caused by root dynamics than temperature treatment. Due to varying responses of SOC indicators, C budgets were used to assess total ecosystem C balance. We found that under AMB conditions soil was an atmospheric C sink and under both SYM and ASYM conditions soil was an atmospheric C source, with ASYM having a higher source potential than SYM. Overall, SOC responded to both temperature increase via soil respiration and differentially to temperature treatments based on plant response. We expect that a reduced diurnal temperature range could affect soil C differently than mean temperature increase, if plant differences are sustained. Title: Soil organic carbon response to six years of warming : assessing the impacts of altered diurnal temperature range Author: Murphey, Virginia L. W. There is a growing consensus that anthropogenic warming will impact soil organic matter (SOM). Globally, soil contains 2-3 times more carbon (C) than plants, and like plants, temperature induced change of SOM could have significant climate repercussions. Although, the majority of warming experiments have increased day and night temperatures equally, there is evidence of greater increase in global minimum temperatures compared to midday maxima, resulting in an altered mean diurnal temperature range (DTR). Here, intact grassland mesocosms (Terracosm facility, Corvallis OR) were used to assess soil organic C (SOC) changes resulting from altered DTR over a six year period. We assessed the response of SOC to a mean temperature increase of 3.5°C with three temperature treatments: symmetric (SYM) warming of +3.5°C, asymmetric (ASYM) warming of +5°C/ +2°C at minimum and maximum daily temperature, respectively, and control treatments that were kept at ambient (AMB) temperatures. After six years of warming SOC was surprisingly unaltered by increased temperature and was more strongly influenced by plant dynamics than expected. The strongest temperature response was from soil respiration (reported as In-situ cumulative soil C mineralization) with at least 33% higher cumulative C mineralization in warming treatments. In agreement with the soil respiration response, light fraction C (<1.8g/cm³) was depleted in warming treatments (8-10% less C than AMB) at shallow depths. However, laboratory cumulative soil C mineralization, a measure of most easily degraded SOC, had a lack of response to temperature, and actually had trends for greater C in warming treatments. This response was further validated by increased soil water dissolved organic C (DOC) concentration in warming treatments. An increase in these measures suggested that plants were more influential than temperature for highly labile SOC. Aggregates, an important part of SOC allocation and sequestration, had a differential response to SYM and ASYM treatments but this was likely more directly caused by root dynamics than temperature treatment. Due to varying responses of SOC indicators, C budgets were used to assess total ecosystem C balance. We found that under AMB conditions soil was an atmospheric C sink and under both SYM and ASYM conditions soil was an atmospheric C source, with ASYM having a higher source potential than SYM. Overall, SOC responded to both temperature increase via soil respiration and differentially to temperature treatments based on plant response. We expect that a reduced diurnal temperature range could affect soil C differently than mean temperature increase, if plant differences are sustained. Close

• 69. [Article] Temperature and the bioenergetics of Cichlasoma bimaculatum

  One means of evaluating the temperature requirements of an animal is to determine changes temperature causes in the uses and losses of energy and materials in the food the animal consumes. To develop energy ...

  Citation × Citation Citation Abstract Copy Title: Temperature and the bioenergetics of Cichlasoma bimaculatum Author: Sethi, Hari Singh One means of evaluating the temperature requirements of an animal is to determine changes temperature causes in the uses and losses of energy and materials in the food the animal consumes. To develop energy budgets for cichlids (Cichlasoma bimaculatum) at different temperatures (20, 24, 28, 32 and 36 C) data were obtained on food intake, growth (total, fat, and protein), fecal losses, maintenance requirements, and other uses and losses of energy and materials including specific dynamic action, activity, and nitrogen excretion. Starvation experiments were conducted to provide information on the metabolic cost of existence and on adjustments in body composition in the absence of food. Energy expenditure during starvation, estimated from heat of combustion data, was found to increase linearly with temperature over 4, 13 and 20 days of starvation. The caloric cost of existence per fish per day was greatest during the first four days at all temperatures and decreased as starvation was prolonged to 20 days. Caloric losses, and dry weight losses showed essentially the same thing. Protein catabolism increased regularly with temperature and decreased slightly with duration of starvation. Fat catabolism did not vary significantly with temperature but decreased markedly as starvation was prolonged. Food intake, growth, and food conversion efficiency varied greatly with changes in temperature. Cichlids were fed ad libitum on small aquatic worms of the genus Tubifex. For food consumption as well as growth, the optimum temperature dropped from 32 to 28 to 24 C as the experimental period was extended from 5 to 12 to 19 days. Optimum growth in dry weight and calories occurred at the same temperatures. Growth of cichlids through time at 20 and 28 C was nearly linear; at 24 C the curve was exponential. At 32 and 36 C, the growth curves rose and then declined. When the fish were held separately during the experiment, food conversion efficiency of cichlids was highest at 20 C and decreased with increasing temperature. Efficiencies decreased with duration of the experiment. When fish were held in groups during the experiment, efficiency was low at both high and low temperatures. The guts of the cichlids were found to contain food up to 30 hours after an ad libitum meal at all temperatures. They were reasonably empty after 36 hours. Thus, no significant correlation was found between temperature and the length of time necessary for the guts to empty. Food material not absorbed was measured by wet combustion. Percentages of absorption of unrestricted rations were found to be 83, 84, 88, 85 and 69 at 20, 24, 28, 32 and 36 C. Percentages of food absorption were much higher on the restricted ration than on the unrestricted ration. Absorption appears to have been optimal at 28 C. Specific dynamic action (SDA) was estimated at different temperatures by taking the difference between oxygen consumption of unfed and fed cichlids at the same levels of activity. SDA represented 22, 20, 19, 33 and 33 percent of the food consumed at 20, 24, 28, 32 and 36 C, when the fish were swimming at 4 cm/second. SDA was generally complete within 36 hours after feeding. Graphs showing energy and material intake, utilization, loss, and scope for growth at each temperature during different experimental periods were developed both in terms of calories per fish per day and calories per gram of fish per day. The evidence suggests that the optimum temperature for growth of this cichlid is near 24 C. Title: Temperature and the bioenergetics of Cichlasoma bimaculatum Author: Sethi, Hari Singh One means of evaluating the temperature requirements of an animal is to determine changes temperature causes in the uses and losses of energy and materials in the food the animal consumes. To develop energy budgets for cichlids (Cichlasoma bimaculatum) at different temperatures (20, 24, 28, 32 and 36 C) data were obtained on food intake, growth (total, fat, and protein), fecal losses, maintenance requirements, and other uses and losses of energy and materials including specific dynamic action, activity, and nitrogen excretion. Starvation experiments were conducted to provide information on the metabolic cost of existence and on adjustments in body composition in the absence of food. Energy expenditure during starvation, estimated from heat of combustion data, was found to increase linearly with temperature over 4, 13 and 20 days of starvation. The caloric cost of existence per fish per day was greatest during the first four days at all temperatures and decreased as starvation was prolonged to 20 days. Caloric losses, and dry weight losses showed essentially the same thing. Protein catabolism increased regularly with temperature and decreased slightly with duration of starvation. Fat catabolism did not vary significantly with temperature but decreased markedly as starvation was prolonged. Food intake, growth, and food conversion efficiency varied greatly with changes in temperature. Cichlids were fed ad libitum on small aquatic worms of the genus Tubifex. For food consumption as well as growth, the optimum temperature dropped from 32 to 28 to 24 C as the experimental period was extended from 5 to 12 to 19 days. Optimum growth in dry weight and calories occurred at the same temperatures. Growth of cichlids through time at 20 and 28 C was nearly linear; at 24 C the curve was exponential. At 32 and 36 C, the growth curves rose and then declined. When the fish were held separately during the experiment, food conversion efficiency of cichlids was highest at 20 C and decreased with increasing temperature. Efficiencies decreased with duration of the experiment. When fish were held in groups during the experiment, efficiency was low at both high and low temperatures. The guts of the cichlids were found to contain food up to 30 hours after an ad libitum meal at all temperatures. They were reasonably empty after 36 hours. Thus, no significant correlation was found between temperature and the length of time necessary for the guts to empty. Food material not absorbed was measured by wet combustion. Percentages of absorption of unrestricted rations were found to be 83, 84, 88, 85 and 69 at 20, 24, 28, 32 and 36 C. Percentages of food absorption were much higher on the restricted ration than on the unrestricted ration. Absorption appears to have been optimal at 28 C. Specific dynamic action (SDA) was estimated at different temperatures by taking the difference between oxygen consumption of unfed and fed cichlids at the same levels of activity. SDA represented 22, 20, 19, 33 and 33 percent of the food consumed at 20, 24, 28, 32 and 36 C, when the fish were swimming at 4 cm/second. SDA was generally complete within 36 hours after feeding. Graphs showing energy and material intake, utilization, loss, and scope for growth at each temperature during different experimental periods were developed both in terms of calories per fish per day and calories per gram of fish per day. The evidence suggests that the optimum temperature for growth of this cichlid is near 24 C. Close

• 70. [Article] Thermal ecology of the garter snakes Thamnophis sirtalis concinnus (Hallowell) and Thamnophis ordinoides (Baird & Girard)

  In recent years, studies dealing with temperature regulation, temperature sensitivity, and physiological responses to temperature in lizards and other reptiles have increased tremendously. It is notable ...

  Citation × Citation Citation Abstract Copy Title: Thermal ecology of the garter snakes Thamnophis sirtalis concinnus (Hallowell) and Thamnophis ordinoides (Baird & Girard) Author: Stewart, Glenn R. In recent years, studies dealing with temperature regulation, temperature sensitivity, and physiological responses to temperature in lizards and other reptiles have increased tremendously. It is notable that snakes have been largely ignored in such studies. This no doubt is due to their less direct relationship to ancestral endotherms. However, problems in the ecology of snakes themselves may be elucidated by studies of this kind. The present study deals with two species of garter snakes ( Thamnophis sirtalis concinnus and Thamnophis ordinoides) which are abundant in Oregon's Willamette Valley. The species sirtalis is the most wide ranging snake in the United States. It is commonly found near permanent water, though occasionally it is encountered in rather dry situations. In contrast to sirtalis, the monotypic species ordinoides is a strictly terrestrial northern Pacific Coast form, which typically is associated with areas of dense vegetation. T. s. concinnus is often seen basking on mild days of the coldest winter months (November-February) while T. ordinoides rarely emerges during these months. The distinct differences in habitat preference and winter behavior exhibited by these snakes suggest differences in thermal preferences and critical levels. To examine this possibility, and the responses of the snakes to thermal acclimation, comparative data on the following variables have been sought: 1) Body temperature of snakes in the field and its relationship to environmental temperatures; 2) body temperature of snakes in a thermal gradient box; 3) critical thermal maximum and minimum; 4) metabolic rate; 5) the effect of thermal acclimation on items two, three, and four. While more investigations are needed to confirm and clarify the results of this study, some tentative conclusions may be stated here: 1) T. s. concinnus and T. ordinoides are diurnal, heliothermic snakes which consistently maintain body temperatures higher than the air and substrate temperatures. 2) T. s. concinnus is more tolerant of seasonally extreme temperatures than T. ordinoides. 3) T. s, concinnus prefers slightly higher body temperatures than T. ordinoides. 4) If temperature tolerances and preferred temperatures are heritable characteristics developed in the phylogeny of the species, these differences probably are primarily related to the difference in distribution of each species as a whole, and secondarily to differences in habitat preference and habit which have resulted from competetive interactions with other species. 5) There are sexual differences in the preferred temperatures of both species, the most significant of which is the relatively high preferred temperature of pregnant females. 6) Initially, the preferred temperatures of both species are inversely related to acclimation temperature. Later, they may be directly related to acclimation temperature. 7) The critical thermal maxima and minima are similar in both species and are directly related to acclimation temperature. However, reacclimation affects the original response differently in the two species. 8) Both species exhibit typical metabolic rate responses to thermal acclimation. 9) Since metabolic rate responses are the same in both species, the greater cold tolerance of T. s. concinnus cannot be attributed to a greater ability to compensate for low temperature. Title: Thermal ecology of the garter snakes Thamnophis sirtalis concinnus (Hallowell) and Thamnophis ordinoides (Baird & Girard) Author: Stewart, Glenn R. In recent years, studies dealing with temperature regulation, temperature sensitivity, and physiological responses to temperature in lizards and other reptiles have increased tremendously. It is notable that snakes have been largely ignored in such studies. This no doubt is due to their less direct relationship to ancestral endotherms. However, problems in the ecology of snakes themselves may be elucidated by studies of this kind. The present study deals with two species of garter snakes ( Thamnophis sirtalis concinnus and Thamnophis ordinoides) which are abundant in Oregon's Willamette Valley. The species sirtalis is the most wide ranging snake in the United States. It is commonly found near permanent water, though occasionally it is encountered in rather dry situations. In contrast to sirtalis, the monotypic species ordinoides is a strictly terrestrial northern Pacific Coast form, which typically is associated with areas of dense vegetation. T. s. concinnus is often seen basking on mild days of the coldest winter months (November-February) while T. ordinoides rarely emerges during these months. The distinct differences in habitat preference and winter behavior exhibited by these snakes suggest differences in thermal preferences and critical levels. To examine this possibility, and the responses of the snakes to thermal acclimation, comparative data on the following variables have been sought: 1) Body temperature of snakes in the field and its relationship to environmental temperatures; 2) body temperature of snakes in a thermal gradient box; 3) critical thermal maximum and minimum; 4) metabolic rate; 5) the effect of thermal acclimation on items two, three, and four. While more investigations are needed to confirm and clarify the results of this study, some tentative conclusions may be stated here: 1) T. s. concinnus and T. ordinoides are diurnal, heliothermic snakes which consistently maintain body temperatures higher than the air and substrate temperatures. 2) T. s. concinnus is more tolerant of seasonally extreme temperatures than T. ordinoides. 3) T. s, concinnus prefers slightly higher body temperatures than T. ordinoides. 4) If temperature tolerances and preferred temperatures are heritable characteristics developed in the phylogeny of the species, these differences probably are primarily related to the difference in distribution of each species as a whole, and secondarily to differences in habitat preference and habit which have resulted from competetive interactions with other species. 5) There are sexual differences in the preferred temperatures of both species, the most significant of which is the relatively high preferred temperature of pregnant females. 6) Initially, the preferred temperatures of both species are inversely related to acclimation temperature. Later, they may be directly related to acclimation temperature. 7) The critical thermal maxima and minima are similar in both species and are directly related to acclimation temperature. However, reacclimation affects the original response differently in the two species. 8) Both species exhibit typical metabolic rate responses to thermal acclimation. 9) Since metabolic rate responses are the same in both species, the greater cold tolerance of T. s. concinnus cannot be attributed to a greater ability to compensate for low temperature. Close