OOS 39-4
Depicting floristic patterns in fens, meadows, and grasslands
Meadow and grassland vegetation are typically mapped at a coarse scale, inadequately representing their diverse floristic components and making it difficult to detect changes over time. Is it possible to classify and map complex mosaics of meadow and grassland vegetation at the alliance level? By applying the National Vegetation Classification (NVC) standards to sample, classify and map vegetation in two pilot project areas of California, we assessed fine-scale patterns of annual and perennial herbaceous types as well as shrublands in the Carrizo Plain National Monument and in meadows of the Sierra Nevada.
We used extensive field surveys in combination with high resolution aerial imagery to quantitatively classify and map vegetation. In the Sierra Nevada meadows, we combined hydrology, soils and vegetation data to distinguish fens from adjacent meadow types. We used soil probes to determine peat depth and GPS units to mark stand boundaries, which were mapped with attributes at varying levels within the NVC hierarchy. In the Carrizo Plain, we re-visited plots across years especially in annual-dominated types to address spatial and temporal change in vegetation patterns.
Results/Conclusions
We successfully characterized fine-scale patterns in meadow and grassland complexes by using appropriately timed field data. It was often difficult to differentiate similar herbaceous types and signatures from aerial imagery without numerous, spatially accurate surveys. Other challenges included ecosystem changes that can occur over a short time period, e.g. shrub die-back and compositional changes in annual types.
In meadows, a hierarchical approach was useful for applying standard names (e.g., Group and Macrogroup) when we were unable to map at the alliance level. However, the NVC hierarchy was difficult to apply to the shifts between fen and non-fen vegetation, currently separated at the Formation level. As we apply the standard to complex ecosystems, we are helping to refine the NVC hierarchy and expand our understanding of alliance and higher level concepts.
For the Carrizo Plain, wildlife preferences are strongly correlated with the fine-scale patterns delineated in this mapping effort. For this semi-desert region, absolute cover of saltbush species can be significant in determining wildlife species presence even at levels as low as 4%. Small changes in shrub cover over time could impact wildlife, which highlights the importance of detailed baseline mapping and future re-mapping using a standard classification.