Floristic Monitoring at Van Vleck Mitigation Bank
The picture above was taken earlier this month while Westervelt Ecological Services (WES) completed annual floristic monitoring at our Van Vleck Mitigation Bank.
The 775 acre site is located in eastern Sacramento County and provides offsite mitigation for impacts to vernal pool habitats and associated grassland species in the greater Sacramento area. The preserved landscape is comprised of rolling mima mound topography and annual grasslands. It supports wetlands, a majority of which are vernal pools and vernal swales, while the upland serves as foraging habitat for Swainson’s hawk (Buteo swainsonii). The vernal features support a broad diversity of native flora and fauna, including rare plants and the federally listed threatened vernal pool fairy shrimp (Branchinecta lynchi).
In addition to preserving the existing wetlands on the Bank, Westervelt Ecological Services (WES) has created additional vernal pools, vernal swales, and seasonal wetlands. As a result, WES has to complete annual floristic monitoring on a portion of the preserved and constructed pools.
The floristic monitoring is performed by systematically sampling a subset of the constructed pools and comparing their function to the existing vernal pools on the property. Approximately 20% of the constructed pools (“Sample Pools”) are monitored during each monitoring year. Sample Pools were selected upon completion of construction and prior to the initiation of year one monitoring. These sample locations remain unchanged during the duration of the monitoring period. Sample Pools were selected to achieve an accurate representation of all constructed pools on the Bank, including characteristics such as: depth, acreage, and position within the landscape.
Through comparison of the constructed pools with reference pools, the ecological development of constructed habitats can be evaluated against a representative climax vegetation community.
A minimum of ten percent (10%) of existing, natural vernal pools were selected as reference pools (“Reference Pools”). Reference pools were subjectively selected based upon acreage, depth, and position within the landscape. This produces an accurate representation of the characteristics present across the vernal pool landscape; not just the extremes. Reference pools were monitored at the same time as constructed pools on the Bank.
The first round of floristic monitoring was during the peak phenology, in the spring of year 2 (WY 2010/2011). Floristic monitoring was collected using the relevé sampling method. Data were collected within 10 m2 plots, subjectively selected within the pool to sample representative vegetation that characterized the pool. All species within the plot were identified and their absolute cover within the plot was recorded. Other plot-specific data recorded included total herb cover (%), bare soil (%), rocks/cobbles (%), open water (%), algal matting (%), thatch (%), and litter.
Supplemental floristic monitoring was conducted again in year 2 using the California Rapid
Assessment Monitoring (CRAM) method. Detailed CRAM methods for vernal pools can be
found in the CRAM for Wetlands User Manual (Collins et. al. 2008), and in the CRAM field
book for Vernal Pool systems (version 5.0.3; last updated March 30, 2009 available online at
For more information, contact Westervelt Ecological Services.