Y axis won't start at 0 in ggplot
ggplot automatically extends the axes slightly to make sure there is room for points to plot. You can turn this behaviour off with the expand argument
ggplot(sub1, aes(x=YR,y=Freq)) +
geom_bar(stat='identity') +
annotate("text",x=3,y=14.9,label="Population status",cex=10) +
scale_y_continuous(expand = c(0, 0), limits = c(0, 15))