The simplest way to analyse a number count is to graph the data with the month or year of the count on the x axis and the number of plants recorded on the y axis. This will graphically illustrate the extent to which a plant population is changing.
At this point you will realise the major limitation of a number count in that it is hard to attribute causes to the changes that you can observe in the numbers of plants between years. They maybe caused because of natural fluctuations in population numbers or as a result of a good or bad growing season or good or bad management of the site. To determine what is causing the changes in your plant population additional monitoring maybe necessary.