27.39 Plot the means. Starting from the data in Table 27.5, you can calculate the mean plant biomass for each treatment in each year as follows: DATA MASSMEAN YEAR 2001 2002 2003 2004 2005 Winter 132.58 203.33 205.17 223.58 332.84 Spring 257.69 388.85 315.39 299.54 289.66 Control 81.67 180.31 136.65 201.07 257.37

(a) Plot the means for each of the three treatments against year, connecting the yearly means for each treatment by lines to show the pattern over time. Use the same plot for all three treatments, with a different color for each treatment. From this plot, you can get an overall picture of the experiment’s results.

(b) Across all fi ve years, does more water in the wet season increase plant growth? What about more water in the dry season? Which seasonal addition of water has the larger effect?

(c) One-way ANOVAs comparing the mean plant biomass separately in each year fi nd signifi cant differences in three years and no signifi cant difference in two years. Based on your plot, in which three years do you think the treatment means differ signifi cantly?

(d) In 2005, there were unusual late rains during the spring. How does the effect of this natural rainfall show up in your plot? (You see that it would not be wise to do an experiment like this in just one year.)