Spatial variation in species richness under contrasting topographies and grazing regimes

One of the important components of biodiversity is species richness. Species richness is usually reported as the total number of species found for a defined area, but with little consideration of spatial variation of species within this area. The objective of this study was to determine whether species richness was spatially variable, and the extent this variation might be influenced by slope and grazing management. Species occurrence was recorded in F increments along 33.3 ft transects within established pasture in central Iowa. Measurements were made on two slope classes (flat and steep), for three grazing managements (ungrazed, rotationally grazed and continuously grazed), and at two orientations (down slope and across slope) and for 4 replicates. Data were integrated for each transect to determine botanical composition. Biodiversity was calculated using Shannon's index. Data were analyzed using the two-term least quadrat variance method (TTLQV). There was clear evidence of spatial pattern in species richness in every plot measured. Continuously grazed plots and steep sites tended to have more complex structure (secondary structure in addition to primary structure), larger block sizes, and a more intense (or defined) spatial pattern than for other treatments. These patterns are of interest since they almost certainly affect interactions among plant species, grazing animals, and even possibly spread of pests and disease.