I'm trying to make a CCA plot of some environmental and macrofaunal data. My code looks like this:
library(dplyr)
library(vegan)
library(ggvegan)
all_abun <- abundance
env_PLI <- environment
env_vectors <- env_PLI[, c(1, 3:14)]
abun_GEMAX <- all_abun %>% filter(method == "GEMAX") %>% select(-`Limapontia spp.`)
abun_df <- abun_GEMAX[, 7:29]
site_CCA <- cca(abun_df ~ NH4_inv_PW + C_1cm + PLI + season_year, data = env_PLI)
autoplot(site_CCA)
Now, the variable season_year has two levels, "autumn 2016" and "summer 2017". For some reason the CCA feels obliged to add those into the resulting graph, even though it doesn't do the same thing to any other variable.
How do I stop it from doing that, so I can just have a graph that says "season_year" without "autumn 2016" and "summer 2017" sitting there as well?