Colorado mountains
From Long-Term Data to Understanding: Toward a Predictive Ecology
2015 LTER ASM Estes Park, CO - August 30 - September 2, 2015

The impact of microclimate variation on budburst phenology within a mature Douglas-fir tree (Pseudostuga menziesii)

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Becky Miller
Dr. Heather Lintz
Dr. Christoph Thomas

Budburst, the initiation of annual growth in plants, is sensitive to climate variation and is therefore used to monitor physiological responses to climate change. Budburst timing can vary between regions of an individual tree, but this phenomenon it is unaccounted for in current monitoring efforts and may contribute to the difficulty of deriving a coherent signature of budburst within a population or across a landscape. It’s not known what stimulates this variation in timing, termed here budburst diversity, but we hypothesize that diverse microclimates within the individual tree may play a role. In this study, microclimate variation was documented within eight regions of a mature Douglas-fir tree before, during and after budburst by measuring foliar temperature with a thermal infrared camera. The timing of budburst was monitored within the tree crown using time-lapse photography in the visible spectrum. Shortwave radiation, wind speed, air temperature and relative humidity were measured in the crown to evaluate which microclimate variables influenced foliar temperature. One full week lapsed between the first and last region to break bud. Microclimate differences between the eight regions were subtle but evident in conditions that induced convective heat transfer. Spatial distribution within the tree crown may have contributed to microclimate variation and thus affected budburst timing. Additionally, we observed diurnal patterns of foliar temperature that differed from air temperature and where largely driven by vapor pressure deficit. This study demonstrates that variation of budburst timing can be significant within an individual tree, prompting questions of how budburst diversity may contribute to an individual’s budburst phenotype.