Temporal, environmental and spatial changes in the effect of windbreaks on pasture microclimate

Windbreaks modify microclimatic conditions within agricultural systems, however these affects are altered by temporal, environmental and spatial factors often resulting in variation in the reported agricultural benefits. Understanding the climatic conditions and times when windbreaks are most effective will increase our ability to predict impacts of windbreaks on agricultural yields and returns. We examined the effects of windbreaks on paddock microclimate (windspeed, temperature, relative humidity and vapor pressure deficit (VPD)) at fine temporal scales and described the temporal and spatial patterns in the effectiveness of windbreaks in moderating microclimate. We also assessed the climate conditions under which windbreaks have the biggest impact on paddock microclimates to determine the climate conditions where windbreaks are most effective. Microclimate variables were monitored at six distances away from established windbreaks across four pasture/grazing paddocks in the Tasmanian midlands, Australia. Results showed that the effect of windbreaks on paddock microclimate varied; spatially, temporally and with environmental conditions. Temperature, relative humidity and VPD exhibited highly diurnal and seasonal trends in their response to windbreaks, with the largest effects observed in summer and during the afternoon. Environmental conditions also impacted on the magnitude of windbreak effects observed. Windbreaks were most effective at reducing wind when speeds were high, although under these conditions the impact of windbreaks on temperature and relative humidity was reduced. Wind direction was also a key factor, with the largest microclimate changes observed when wind originated from directly behind the windbreak, although plots closely adjacent to windbreaks had microclimate changes when wind came from all directions. This study highlights that when predicting the benefits of windbreaks, it is important to consider spatial and temporal dynamics as well as the environmental conditions of the site.