Altering arrays to add/remove entries at each time-step in R - arrays

Question

This question, probably has a simple solution but I cannot think of how to do it...
So I have a script as follows:
# ------------------ MODEL SETUP ----------------------------------------# simulation length
t_max <- 50
# arena
arena_x <- 100
arena_y <- 100
# plant parameters
a <- 0.1
b <- 0.1
g <- 1
# list of plant locations and initial sizes
nplants <-dim(plantLocsX)[1]*dim(plantLocsX)[2]
iterations<-5
totalBiomass<-matrix(0,nrow=iterations,ncol=1)
# starting loop
sep <- 10
# Original matrix
plantLocsX <- matrix(rep(seq(0,arena_x,sep), arena_y/sep),
nrow=1+arena_x/sep,
ncol=1+arena_y/sep)
plantLocsY <- t(plantLocsX)
plantSizes <- matrix(1,nrow=nplants,ncol=1)
# Plot the plants
radius <- sqrt( plantSizes/ pi )
symbols(plantLocsX, plantLocsY, radius, xlim = c(0,100), ylim=c(0,100), inches=0.05, fg = "green",
xlab = "x domain (m)", ylab = "y domain (m)", main = "Random Plant Locations", col.main = 51)
# Calculate distances between EACH POSSIBLE PAIR of plants
distances <- matrix(0,nrow=nplants,ncol=nplants)
for (i in 1:nplants){
for (j in 1:nplants){
distances[i,j] <- sqrt( (plantLocsX[i]-plantLocsX[j])^2 + (plantLocsY[i]-plantLocsY[j])^2 )
}
}
# ------------------ MODEL RUNNING ---------------------------------------
I need to alter the arrays containing plant locations and plant sizes so that at each time step, entries are removed and added (simulating mortality/reproduction, respectively). The "distances" must be updated with plant locations and sizes after each iteration...I can only think of complex ways to do this: destructing and constructing new matrices at each time step to fit the new number of elements but there must be functions to make this simpler....any advice?
Many thanks!!