Abstract Detail



Ecology

Gorchov, David [1].

High Winter Temperatures Facilitate Invasion of Tradescantia fluminensis in the Apalachicola River Floodplain.

Temperature impacts organisms at a finer scale than that represented by weather stations and climate models.  I investigated whether the expansion of a non-native herb, Tradescantia fluminensis Vell. (Commelinaceae) (Small-leaf Spiderwort), up the slopes on the east bank of the Apalachicola River, Florida, was related to topography and/or surface temperature.  These slopes comprise the entire range of the Federally endangered Florida torrey, Torreya taxifolia Arn. (Taxaceae), the rarest tree species in North America.  Cold temperatures were expected to kill T. fluminensis based on Bannister’s (1986) determination that the LT50 (point of 50% damage) of T. fluminensis is -4.2° C.
At multiple points along the upland boundaries of T. fluminensis patches I measured vegetative growth over one year and surface temperature minima during the winter of 2016/17.  Because T. fluminensis has extremely small, shallow, roots, I reasoned that temperature at the soil surface would be relevant to the survival or death of ramets,  Soil surface temperatures were recorded hourly using self-recording temperature data loggers (Thermochron iButton model DS1921G-F5). 
I found that minimum temperatures were colder at higher elevations and greater distances from the floodplain, but did not reach -4.2° C.  Patches expanded upslope an average of 1.2 m/yr.  Patches of T. fluminensis were as close as 2.7 m to T. taxifolia, so the invader could reach the endangered species in 2 yrs.
Temperature minima at the upland limits of T. fluminensis were strongly correlated with, but > 1.3° C warmer than, those at the Wilma, FL, weather station, due to the specific heat of wet soil and perhaps also insulating effects of the canopy and nearby swamp.  Historically, temperatures ≤ -5.5° C (expected to correspond to -4.2° C on slopes) occurred during 2/3 of winters, but the lack of temperatures ≤ -7° C since 2011/12 might account for the expansion of T. fluminensis in recent years.  Temperature did plunge to -5.6°C on 4 January and -6.7°C on 18 January 2018, and on January 19, about 5% of T. fluminensis ramets on slopes showed frost-induced necrosis. Climate models project warmer winter temperatures in the Panhandle, suggesting that such mortality events will be rarer and T. fluminensis will invade further.
In October, 2018, Hurricane Michael caused extensive treefalls on the slopes of the Apalachicola River.  I will attempt to determine how this massive disturbance has affected the spatial distribution and density of T. fluminensis in this area.


1 - Miami University, Department Of Biology, Pearson Hall, Oxford, OH, 45056, United States

Keywords:
climate change
iButton data loggers
frost-induced necrosis
invasive plants
microclimate
Torreya taxifolia.

Presentation Type: Oral Paper
Number: 0003
Abstract ID:222
Candidate for Awards:None


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