Vancouver Trees – Vizualizing biodiversity, native and introduced trees

November 22, 2018
By

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Following from the past post, this post is focused on visualizing diversity through the package vegan and also maps showing the presence of native/introduced trees.

The most important code in this post is manipulating Spatial*DataFrames.

The same files will be read in, including the native/introduced status downloaded from USDA PLANTS.

library(rgdal)
library(sp)
library(raster)
library(dplyr)
library(httr)
library(rvest)
library(purrr)
library(tidyr)
# read in  trees df
trees_df<-read.csv("StreetTrees_CityWide.csv", stringsAsFactors = F)
trees_df<-trees_df[trees_df$LATITUDE > 40 & trees_df$LONGITUDE < -100,]
# read in polygons
locmap<-readOGR("cov_localareas.kml", "local_areas_region", stringsAsFactors = F)
## OGR data source with driver: KML 
## Source: "C:\Users\YIHANWU\Documents\Stuff\blogdown-ywu\content\post\cov_localareas.kml", layer: "local_areas_region"
## with 22 features
## It has 2 fields
# read in native/introduced
city_plant_info <- read.csv("vancouver_info.csv")
# extract tree data
trees_df$SCIENTIFIC_NAME <- paste(trees_df$GENUS_NAME, trees_df$SPECIES_NAME)
trees_df$GENUS_NAME <- as.character(trees_df$GENUS_NAME)
trees_df$SPECIES_NM <- as.character(trees_df$SPECIES_NAME)

species_correction <- function(genus, species){
  if(species == "SPECIES"){
    return(genus)
  } else if (length(grep("\\sX$", species)) > 0){
    return(paste(genus," x ", unlist(strsplit(species, " "))[[1]]))
  } else {
    return(paste(genus, species))
  }
}
trees_df$SCIENTIFIC_NAME <- map2_chr(trees_df$GENUS_NAME, trees_df$SPECIES_NAME, species_correction)
head(trees_df)
##   TREE_ID CIVIC_NUMBER       STD_STREET NEIGHBOURHOOD_NAME
## 1     589         4694         W 8TH AV    WEST POINT GREY
## 2     592         1799 W KING EDWARD AV        SHAUGHNESSY
## 3     594         2401         W 1ST AV          KITSILANO
## 5     596         2428         W 1ST AV          KITSILANO
## 6     598         2428         W 1ST AV          KITSILANO
## 7     599         1725        BALSAM ST          KITSILANO
##          ON_STREET ON_STREET_BLOCK STREET_SIDE_NAME ASSIGNED
## 1        BLANCA ST            2400             EVEN        N
## 2 W KING EDWARD AV            1700              MED        N
## 3         W 1ST AV            2400              ODD        N
## 5         W 1ST AV            2400             EVEN        N
## 6         W 1ST AV            2400             EVEN        N
## 7         W 1ST AV            2400             EVEN        N
##   HEIGHT_RANGE_ID DIAMETER DATE_PLANTED PLANT_AREA ROOT_BARRIER CURB
## 1               5     32.0     20180128          B            N    Y
## 2               1      3.0     20100104         30            N    Y
## 3               4     14.0     20180128          B            N    Y
## 5               2     11.0     20180128          B            N    Y
## 6               2      3.0     20180128          B            N    Y
## 7               2     13.5     20180128          B            N    Y
##   CULTIVAR_NAME GENUS_NAME SPECIES_NAME              COMMON_NAME LATITUDE
## 1                    ALNUS       RUGOSA           SPECKLED ALDER 49.26532
## 2                    ABIES      GRANDIS                GRAND FIR 49.24952
## 3                    PINUS        NIGRA            AUSTRIAN PINE 49.27096
## 5                   PRUNUS    SARGENTII SARGENT FLOWERING CHERRY 49.27083
## 6                   PRUNUS    SARGENTII SARGENT FLOWERING CHERRY 49.27084
## 7                    PICEA        ABIES            NORWAY SPRUCE 49.27083
##   LONGITUDE  SCIENTIFIC_NAME SPECIES_NM
## 1 -123.2150     ALNUS RUGOSA     RUGOSA
## 2 -123.1457    ABIES GRANDIS    GRANDIS
## 3 -123.1599      PINUS NIGRA      NIGRA
## 5 -123.1602 PRUNUS SARGENTII  SARGENTII
## 6 -123.1605 PRUNUS SARGENTII  SARGENTII
## 7 -123.1600      PICEA ABIES      ABIES

We can attach the native/introduced status through a dplyr::left_join.

trees_df <- left_join(trees_df, city_plant_info)
## Joining, by = "SCIENTIFIC_NAME"
## Warning: Column `SCIENTIFIC_NAME` joining character vector and factor,
## coercing into character vector

We have to convert the trees_df into a SpatialPointsDataFrame in order to make calculations based on areas of specific size and to plot the data using the sp library. The first step is to identify the longitude and latitude columns. We put those as input into the SpatialPointsDataFrame function, add the entire data frame to the object being created and set a projection. In this case, we use the same projection as our locmap object as the csv file did not specify any projection, and it is unlikely that one data producer would use two different projections.

xy <- trees_df[, c("LONGITUDE", "LATITUDE")]
trees_shp <- SpatialPointsDataFrame(coords = xy, data = trees_df, proj4string = CRS(proj4string(locmap)))

To split Vancouver into smaller plots to calculate biodiversity, I transformed the two Spatial*DataFrames into the same projection. Then I rasterized the Vancouver shapefile and changed the resolution until each cell represents 100 m^2 before turning the raster map back into a SpatialPolygonDataFrame. This was accomplished primarily by first changing the projection system to UTM which is based on meters.

# convert both spatial objects to utm (zone 10)
locmap_utm<-spTransform(locmap, CRS("+proj=utm +zone=10 +datum=WGS84"))
trees_utm<-spTransform(trees_shp, CRS("+proj=utm +zone=10 +datum=WGS84"))
# convert the polygon to raster w/ 100m grids, extend the map grid to the extent of the polygons
raster_map<-raster(extent(locmap_utm))
# using the same conversion for the grid as well
projection(raster_map)<- proj4string(locmap_utm)
# right now, set to 100 meter square girds
res(raster_map)<-100
# now make the raster a polygon
raster_poly<-rasterToPolygons(raster_map)
raster_clip<-raster_poly[locmap_utm,]

So the resulting gridded SpatialPolygonDataFrame, raster_poly contains 15582 100 m^2 polygons. Then it is clipped by the boundaries of the trees spatial object to only have polygons within the limit of the trees dataset.

To attache the trees and their associated data from the SpatialPointsDataSet to raster_clip which is a SpatialPolyon, I used the over function. This “overlays” the data from one spatial object to another.

To get the number of trees in each square polygon, I counted the number of rows in each polygon.

trees_grid<-over(x=raster_clip, y=trees_utm[,c("SCIENTIFIC_NAME", "status")], returnList = T)
tree_metrics<-as.data.frame(sapply(trees_grid, nrow))
names(tree_metrics)<- "Number_of_trees"

The same approach can also be used to find unique tree species within each polygon.

# find unique species in grid
tree_metrics$tree_richness<-sapply(sapply(trees_grid, function(x) unique(x[,1])), length)

vegan can calculate multiple values of diversity, and I chose the Simpson diversity index. In list_diversity, for every polygon, if there are trees in the polygon, Simpson diversity is calculated.

library(vegan)
## Loading required package: permute
## Loading required package: lattice
## This is vegan 2.5-2
# function to use to get diversity from a list of grids
list_diversity <- function(x) {
  # only calculate if there are trees
  if(nrow(x) > 0){
    # makes data frame from the list entry
    freq<-as.data.frame((table(x$SCIENTIFIC_NAME)))
    # makes species the row name
    rownames(freq)<-freq[,1]
    freq[,1]<-NULL
    # get frequency of each species in grid
    t_freq<-as.data.frame(t(freq))
    # computes the species diversity (can change the measure from simpson to others ie Shannon)
    simp<-diversity(t_freq, "simpson")
    return(simp)
  } else {
    return("NA")
  }
}

test<-sapply(trees_grid, list_diversity)
tree_metrics$simp_div<-as.numeric(as.character(test))
## Warning: NAs introduced by coercion

We can loop through the polygons to find the polygons containing trees with “introduced” status.

# get presence absence of introduced
presence_introduced <- function(x){
  if(nrow(x) > 0){
    return(sum(x$status == "I", na.rm=T))
  } else {
    return(NA)
  }
}
test <- sapply(trees_grid, function(x) any(x$status=="I"))
test <- sapply(trees_grid, presence_introduced)
tree_metrics$presence <- test

# now put the calculated data back to the grid shapefile for visualization
[email protected]<-tree_metrics

We can compute some general statistics about the trees in Vancouver. For example, there are 11689 grid squares making up Vancouver with 2654 cells having no trees at all, and 1126 cells only having one unique species and 10713 cells having at least one introduced tree species.

Mean Simpson’s index of diversity is 0.5382804

knitr::kable(head(sort(table(trees_df$SCIENTIFIC_NAME[trees_df$status=="N"]), T), 10), caption = "Most common native tree species")
Table 1: Most common native tree species
Var1 Freq
ACER RUBRUM 6800
ULMUS AMERICANA 2079
FRAXINUS AMERICANA 1912
LIQUIDAMBAR STYRACIFLUA 1468
FRAXINUS PENNSYLVANICA 1458
GLEDITSIA TRIACANTHOS 1366
QUERCUS PALUSTRIS 1324
QUERCUS RUBRA 1287
THUJA PLICATA 791
LIRIODENDRON TULIPIFERA 711
knitr::kable(head(sort(table(trees_df$SCIENTIFIC_NAME[trees_df$status=="I"]), T), 10), caption = "Most common introduced tree species")
Table 2: Most common introduced tree species
Var1 Freq
PRUNUS SERRULATA 12035
PRUNUS CERASIFERA 11258
ACER PLATANOIDES 10680
CARPINUS BETULUS 4219
FAGUS SYLVATICA 3560
ACER CAMPESTRE 3043
MAGNOLIA KOBUS 2273
AESCULUS HIPPOCASTANUM 2053
ACER PSEUDOPLATANUS 1903
PYRUS CALLERYANA 1805

And also the proportion of introduced to native trees.

library(ggplot2)
## Warning: package 'ggplot2' was built under R version 3.5.1
ggplot(trees_df[!is.na(trees_df$status),]) + geom_bar(aes(x=status)) + theme_classic() + labs(x="USDA PLANT status", y = "Number of vancouver Trees") + scale_x_discrete(labels = c("Introduced", "Native", "Waif"))

We can then visualize Vancouver for the number of trees.

library(viridis)
## Loading required package: viridisLite
spplot(raster_clip, "Number_of_trees", col.regions=c("grey10", viridis(64)), col="transparent")

And species richness within each cell, this time using red to green scale from colorRamps.

spplot(raster_clip, "tree_richness", col.regions=c("grey10", rev(colorRamps::green2red(18))), col="transparent", main = "Species Richness")

And lastly, all cells with an introduced tree species.

spplot(raster_clip, "presence", col.regions=c("grey10", colorRamps::green2red(20)), col="transparent")

sessionInfo()
## R version 3.5.0 (2018-04-23)
## Platform: x86_64-w64-mingw32/x64 (64-bit)
## Running under: Windows 10 x64 (build 17134)
## 
## Matrix products: default
## 
## locale:
## [1] LC_COLLATE=English_Canada.1252  LC_CTYPE=English_Canada.1252   
## [3] LC_MONETARY=English_Canada.1252 LC_NUMERIC=C                   
## [5] LC_TIME=English_Canada.1252    
## 
## attached base packages:
## [1] stats     graphics  grDevices utils     datasets  methods   base     
## 
## other attached packages:
##  [1] viridis_0.5.1     viridisLite_0.3.0 ggplot2_3.0.0    
##  [4] vegan_2.5-2       lattice_0.20-35   permute_0.9-4    
##  [7] tidyr_0.8.1       purrr_0.2.5       rvest_0.3.2      
## [10] xml2_1.2.0        httr_1.3.1        dplyr_0.7.5      
## [13] raster_2.6-7      rgdal_1.3-2       sp_1.3-1         
## 
## loaded via a namespace (and not attached):
##  [1] tidyselect_0.2.4 xfun_0.3         colorspace_1.3-2 htmltools_0.3.6 
##  [5] yaml_2.1.19      mgcv_1.8-23      rlang_0.2.2      pillar_1.2.3    
##  [9] glue_1.2.0       withr_2.1.2      bindrcpp_0.2.2   bindr_0.1.1     
## [13] plyr_1.8.4       stringr_1.3.1    rgeos_0.3-28     munsell_0.5.0   
## [17] blogdown_0.8     gtable_0.2.0     evaluate_0.10.1  labeling_0.3    
## [21] knitr_1.20       parallel_3.5.0   highr_0.7        Rcpp_0.12.17    
## [25] backports_1.1.2  scales_0.5.0     gridExtra_2.3    digest_0.6.15   
## [29] stringi_1.1.7    bookdown_0.7.17  grid_3.5.0       rprojroot_1.3-2 
## [33] tools_3.5.0      magrittr_1.5     lazyeval_0.2.1   tibble_1.4.2    
## [37] cluster_2.0.7-1  pkgconfig_2.0.1  MASS_7.3-49      Matrix_1.2-14   
## [41] assertthat_0.2.0 rmarkdown_1.10   R6_2.2.2         colorRamps_2.3  
## [45] nlme_3.1-137     compiler_3.5.0

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