Relationships between primary productivity, precipitation and phenology in an Ozark oak/hickory woodland from 2000-2020: Making connections with fire management

Background/Question/Methods

Ozark woodlands historically span from Illinois to Oklahoma. These woodland ecosystems are a unique but imperiled ecosystem type as a result of fragmentation, lack of proper management and a changing climate. Management, conservation, and restoration of Ozark woodlands is a priority of both federal and state agencies. The ecosystem services provided by Ozark woodlands include unique plant and animal biodiversity, carbon sequestration, and hydrologic cycling. Management, conservation and restoration of Ozark woodlands requires information on how they respond to changes in precipitation and temperature within and between years, and to highly variable prescribed burning regimes. Primary production and phenology are recognized as key variables for documenting responses of woodlands/forests to management practices, extreme weather events and climate changes. We examined the relationships between primary productivity, precipitation and temperature in an Ozark woodland between 2000-2020. Phenology data from a phenocam were initiated in 2014. The study area is within a 1,200 ha State Conservation Area. The woodlands have three very distinct fire histories: unburned for 60 years or burned every 2-4 years for the past 20 or 40 years. The area is characterized as upland oak-hickory forest with 50% classified as degraded woodland; unburned and 20 year burned areas are considered degraded because overstory cover is between 75-95%. Leaf production was estimated by collecting leaf litter 0.25 m above ground yearly. Precipitation and temperature data were obtained from NOAA county climate data (Taney County, MO). Phenology and greenness/productivity was measured using green chromatic coordinate (GCC) data obtained from a phenocam at the Bull Shoals Field Station. We used five different measures of GCC to examine relationships between temperature, precipitation, phenology and production (yearly, mean, growing season, May-August, and bud break to leaf fall GCC).

Results/Conclusions

We only found significant relationships between annual precipitation and leaf production in woodlands burned for the past 40 years. We found some significant relationships between phenology, annual precipitation and production, most strongly in 40 year burned woodlands. For the past 20 years, woodland leaf production ranges from 80 to 450 g/m2/yr and decomposition ranges from 40-150 g/m2/yr and is highly significantly related to burn history as follows: unburned>20 years burning>40 years burning. Our data are consistent with recent research illustrating that phenology is a robust integrator of the effects of year-to-year climate variability and longer-term climate change on ecosystems. Our data suggest that uniform and consistent burning across the entire woodland would decrease carbon sequestration and turnover.