Grassland plant community spatial patterns driven by herbivory intensity

Heterogeneity is a critical driver in rangeland ecosystems and can be used to direct and quantify management success across landscapes. Plant community dynamics and patterns are frequently examined in relation to herbivory, but most patterns are discussed either in a single dimension, or across species, but at small spatial scales within individual communities. Therefore, we designed a study to measure plant community spatial patterns across similar topographic position and soil type in pastures with three different herbivory intensities. We assessed plant community spatial patterns in the northern mixed-grass prairie near Streeter, ND, USA (46°45′N, 99°28′W) in pastures moderately or intensively grazed or non-grazed exclosures established for 25 years. Plant species composition and abundance were recorded along 50-m transects in three replicate pastures for each grazing intensity (n = 3) at mid-summer twice separated by 10 years. Fine and coarse-scale diversity were similar between the moderately and intensively grazed pastures and greater than the non-grazed exclosures in both years (p ≤ .05). Plant species composition was similar among the three grazing intensities and years. Plant community heterogeneity was highest for moderately grazed pastures followed by intensively and non-grazed exclosures respectively. Similarly, patch size was smallest for moderate pastures followed by intensive pastures and non-grazed exclosures for both years. However, while patch size in both moderate and intensive pastures was similar across years respectively, patch size in non-grazed exclosures increased over time. Land management activities varying the disturbance intensities or timing of disturbance can influence specific species composition and relative abundance among species groups. Grazing intensity influenced both fine- and coarse-scale plant community patterns and created different, but stable, plant community patch sizes over time. Based on these results, the ecological cost of inactivity in managing grasslands may have profound consequences on plant community stability and the wildlife that depend on them.