# Climate Effects on Tallgrass Prairie Responses to Continuous and Rotational Grazing
## 3 Results
### The Dynamics of EVI Values in the Continuous Versus Rotational Grazing Paddocks  
The average growing season EVI is a good indicator of vegetation production during the growing season. The initial condition of average growing season EVI values (Figure 5) varied largely during the prior year (2008) and the first year of the experiment (2009). After that, climate was the major driver in affecting the average growing season EVI. The growing season average EVI values were larger than 0.5 in wet years (2013 and 2015). In severe drought years (2011 and 2012), all treatments had low average EVI values. Treatment differences were larger in moderate drought years (2014 and 2016). Even though 2012 was a drier and hotter year than 2016, the average EVI in 2012 and 2016 were comparable because of early greening up of vegetation and more growth by May in 2012 (Figure 2). The average growing season EVI in Rb was consistently larger than in Cb. However, the average growing season EVI in Ra could be similar to, higher, or lower than Ca in different years.  
The maximum growing season EVI indicates the peak vegetation growth during the growing season. Rep a consistently had larger growing season maximum EVI values than rep b during the study period (Figure 6 top), indicating higher photosynthesis capability in rep a than rep b. Maximum EVIs were largest in wet years (2013 and 2015) and lowest in severe drought years (2011 and 2012), showing the significant control of climate conditions on maximum productivity in all treatments. The maximum EVI values in 2012 were higher than those in 2016 because peak EVI occurred before severe drought in 2012. The maximum EVI values only tended to converge in very wet or dry years, otherwise they had large ranges. The maximum EVI values in Rb were larger than in Cb in majority of cases. The differences in maximum EVI between Ra and Ca were smaller than between Rb and Cb.  
The minimum growing season EVI can represent the low photosynthesis capability caused by climate or other stresses on vegetation. The growing season minimum EVI (Figure 6 bottom) converged more than maximum EVI, with larger differences in moderate drought years (2014 and 2016). In contrast to what it was observed in maximum EVI, the minimum EVI was much lower in 2012 than in 2016, suggesting a collapse of vegetation condition because of the severe summer drought. The minimum EVI values in both rotational grazing treatments were larger than their counterparts (Rb larger than Cb and Ra larger than Ca) in most years.  
Figure 5: Growing season average EVI from Landsat 7 for different treatments in rep a and rep b. Solid lines are for rep a and dashed lines are for rep b. Solid and hollow shapes represent continuous grazing and rotational grazing.  
The growing season standard deviation of EVI (\(\sigma_{\text{EVI}}\)) shows the variation of vegetation production during the growing season. Rep a had larger growing season \(\sigma_{\text{EVI}}\) than rep b (Figure 7). Ca had larger \(\sigma_{\text{EVI}}\) than Ra in most years while the differences between Cb and Rb were small throughout the years. Ca usually had the largest \(\sigma_{\text{EVI}}\) because of its mixture of grass, brush, and trees, which had different seasonality.