Estimating forest-grassland dynamics using soil phytolith assemblages and δ13C of soil organic matter

Our objectives were to examine the relationship between contemporary vegetation and Surface soil phytolith assemblages, and use phytoliths and delta C-13 of soil organic matter (SOM) to explore forest-gras land vegetation dynamics. We established plots within three canopy types (open, old-growth. and dense Young Pine) with different grass species compositions in a Pinus ponderosa forest in northern Arizona and collected vegetation data and surface (0-2 cm) and subsurface (2-7 cm) mineral soil samples. Surface soil phytolith as assemblages strongly reflected vegetation at the site scale (within several km(2)). Local vegetation patterns (< 50 m(2)) associated with overstory canopy types were weakly detected, Significantly fewer C-4 grass and ponderosa pine phytoliths were found in subsurface compared to surface soils. Surface delta C-13 values showed no difference among canopy types, Subsurface delta C-13 values were significantly (+ 0.83 %) more enriched in C-13 than surface values. Phytolith assemblages and delta C-13 of SOM reflect long-term accumulation of organic matter in soils and may not mirror contemporary vegetation for many reasons. including spatial shifts in species distribution and productivity. Considering all our phytolith and delta C-13 evidence. we suggest that C-4 grasses were more widely distributed but less abundant. grasses were more spatially continuous, total grass productivity was greater. and species in the genus Koeleria and Bromus were more common in the past.