Prescribed fire is an important management practice used to control woody encroachment and invasive species in grasslands. To use this practice successfully, managers must understand the seasonal windows within which prescribed fire can be applied and how fire behavior could potentially vary among these windows. To characterize prescribed fire windows within the northern Great Plains of North America, we collected data from 20 remote weather stations positioned across North Dakota and northwestern Minnesota, USA, from station inception to 2015. We performed an hourly analysis for each station to determine if air temperature (2 to 43 °C), relative humidity (25 to 80%), and wind speed (6.44 to 24.12 km h− 1) conditions were within acceptable ranges for at least six contiguous precipitation-free hours from 0800 to 1800 h. We summarized acceptable conditions over five half-season windows and then used the Rothermel fire spread equation to simulate fire behavior within these half-season windows based on average, minimum, and maximum conditions for seasonally appropriate live herbaceous to fine dead fuel ratios. While the number of acceptable prescribed fire days did not change from early spring (21 March) to early fall (6 November), the number of acceptable days for conducting spring fires decreased and the number of acceptable days for conducting late summer to early fall fires increased over the study period. The change in spring acceptability reflected an increase in the number of days with air temperatures below acceptable minimum temperature and outside of acceptable wind conditions to conduct operations. Predicted rate of fire spread was highest and most sensitive to the season of the year, fuel curing status, and site invasion status when fire spread was simulated at the upper end of acceptable wind speed and at the lower end of fuel moisture conditions. Prescribed fire planning needs to take into account the timeframe during which fire windows exist within a year, and how these conditions affect fire behavior. In the northern Great Plains, there is ample opportunity for grassland managers to use summer and fall prescribed fires, and managers should expect to get variable fire behavior results when prescribed fires are applied in more extreme conditions throughout the year.

中文翻译：

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美国大平原北部规定的火灾天气窗口的季节性和预测的火灾行为

处方火是一种重要的管理措施，用于控制草原上的木本性侵犯和入侵物种。为了成功地使用这种做法，管理人员必须了解可以在其中应用规定的火灾的季节性窗口，以及这些窗口之间的火灾行为可能如何变化。为了表征北美洲大平原北部规定的防火窗，我们从站点开始到2015年从位于北达科他州和美国明尼苏达州西北部的20个远程气象站收集了数据。我们对每个站点进行了每小时分析，以确定是否有空气温度（2至43°C），相对湿度（25至80％）和风速（6.44至24.12 km h-1）条件在0800至1800 h的至少六个连续无降水小时内处于可接受的范围内。我们总结了五个半季节窗口内的可接受条件，然后使用Rothermel火灾蔓延方程，根据季节性合适的活用草本燃料与精细死燃料比的平均，最小和最大条件，模拟了这些半季节窗口内的火灾行为。尽管从3月21日早春至11月6日初秋，规定的防火天数没有变化，但春季大火的可接受天数减少了，夏末至秋季初的火天可接受的天数减少了在研究期间有所增加。弹簧可接受性的变化反映了气温低于可接受的最低温度并且在可接受的风力条件之外进行操作的天数增加。当在可接受的风速上限和燃料湿度条件下限模拟火势蔓延时，预测的火势蔓延率最高，并且对一年中的季节，燃料固化状态和站点入侵状态最为敏感。规定的防火计划需要考虑一年之内存在防火窗的时间表，以及这些条件如何影响防火行为。在大平原北部，草原管理者有充分的机会使用夏季和秋季规定的火种，并且当全年在更极端的条件下使用规定的火种时，管理者应期望获得可变的火势结果。在可接受的风速上限和燃油湿度条件下限模拟火势蔓延时的位置和现场入侵状态。规定的防火计划需要考虑一年之内存在防火窗的时间表，以及这些条件如何影响防火行为。在大平原北部，草原管理者有充分的机会使用夏季和秋季规定的火种，并且当全年在更极端的条件下使用规定的火种时，管理者应期望获得可变的火势结果。在可接受的风速上限和燃油湿度条件下限模拟火势蔓延时的位置和现场入侵状态。规定的防火计划需要考虑一年之内存在防火窗的时间表，以及这些条件如何影响防火行为。在大平原北部，草原管理者有充分的机会使用夏季和秋季规定的火种，并且当全年在更极端的条件下使用规定的火种时，管理者应期望获得可变的火势结果。