By Celeste Dodge, MS, Systems Ecologist
Water is the driving force behind ecosystems, determining which plants can thrive and what types of habitat they can provide for animals. In Mediterranean climates like Northern California’s, the extreme shift in seasonal water availability is largely to thank for the incredible amount of biodiversity we enjoy, as many species have adapted to our region’s unique climatic conditions. As much needed rainfall is only just beginning to alleviate a historic drought, we are reminded of how delicate this water balance truly is.
Pepperwood is studying the relationship between water availability and vegetation so our region’s land and water managers can better prepare for what is expected to be a more arid future for California. The work we are conducting at our preserve gives organizations like the Sonoma County Water Agency and the US Geological Survey key data on not just variations in weather, but also how our soils, plants and animals are responding to these changing conditions.
As part of our Sentinel Site monitoring network, Pepperwood is expanding our capacity to measure water on our preserve. We now have a team of 20 volunteers monitoring 21 rain gauges at remote locations across the preserve, with the goal of improving the span and accuracy of our rainfall monitoring. Four of the rain gauges are located at weather stations in Martin Creek, Double Ponds, Rogers Canyon and at Bechtel house. Rain gauges at these stations will help improve the accuracy of existing electronic rain sensors called tipping bucket gauges, which are susceptible to underestimating rainfall amounts, particularly during high intensity storms.
The other 17 of these rain gauges are located at a selection of our 50 long term forest monitoring plots. Installed by the UC Berkeley Ackerly Lab, these plots span the preserve and allow us to track key indicators of forest health including growth rates of both young and mature trees within the plots. This biological data is analyzed alongside climate data collected at the same plots so we can determine the effects of long term climate trends and extreme weather events—like the recent drought—on plant life.
By recording rainfall under the canopy at the forest monitoring plots, we are getting a pretty good sense of the environmental conditions experienced by seedlings in our forests. Total rainfall at these site varies by as much as 40% and is controlled by both canopy and topographic effects. At one site where there are particularly strong canopy effects, the rainfall we have measured thus far amounts to only 20% of the rainfall out our wettest location. We may decide to move our forest plot gauges out from under the canopy to a nearby grassland area to better understand the effects of topography alone next season. This will also make our data more valuable to forecasters. A nationwide citizen science project called the Community Collaborative Rain Hail and Snow Network collects backyard rain gauge data along these lines and uses it retroactively to improve weather models.
In addition to the new rain gauges, some of the forest monitoring plots are already equipped with instruments that collect data on leaf wetness, temperature, and humidity. Data from these instruments is relayed across the preserve by a wireless mesh network, a series of antennas that transmit across the preserve to a central computer.
But measuring the amount of rain that falls is only one piece of the puzzle. We also need to determine what happens when it hits the ground. Pepperwood is one of only four sites in the entire Bay area equipped with soil moisture probes, which allow us to gain vital insights into the amount of water available to plants in the soil throughout the year. We currently have two sets of probes installed, and our goal is to install 10 sets of probes at two depths at our mesh network antennas before this year’s spring dry-down occurs. This will give us a better sense of the heterogeneity of the preserve’s hydrology, and will enable forecasters to better predict potential flood or mudslide events.
Pepperwood’s ever-expanding Sentinel Site monitoring work is generating a wealth of data to help our region’s land and water managers better prepare for the climate challenges that lay ahead.