DOI: 10.5061/dryad.37qc017
title: Data from: New regionally modelled soil layers improve prediction of vegetation type relative to that based on global soil models

description: Aim: High-resolution spatial soil data are crucial to species distribution
 modelling for fundamental research and conservation planning. Recent
 globally-modelled soil layers (e.g. SoilGrids) have transformed
 distribution modelling, but may fail to represent regional soil
 characteristics accurately. We hypothesize that in the Cape biodiversity
 hotspot of South Africa, the use of global soil layers has led to
 underestimation of the importance of edaphic factors as determinants of
 species’ and vegetation distributions. We present a series of new,
 regionally-modelled layers to address this deficiency. Location: Greater
 Cape Floristic Region (GCFR, South Africa) Methods: We georeferenced
 edaphic characteristics from literature and other sources and used boosted
 regression trees (BRT) to associate edaphic characteristics with
 spatially-explicit topographic, climatic, soil texture and biotic
 variables. Multinomial BRTs were used to predict mapped vegetation types
 from the collated edaphic and other data. Results: BRTs reliably predicted
 pH (92% of variance), Na (87%), K (85%), electrical conductivity (81%) and
 P (73%), but were less accurate for total N (55%) and total C (61%), for
 which data were sparser. Soil clay and pH values differed markedly in
 range and in spatial variation from those in SoilGrids. Using our new
 edaphic layers, we were able to accurately predict spatial distributions
 of vegetation types within the GCFR (multi-class AUC = 0.96). The
 multinomial BRT predicted vegetation less well when based on SoilGrids
 data alone (AUC = 0.84). Main conclusions: The more faithful
 representation of soil properties in our model is attributable both to its
 use of ca. 10-fold more samples, and to its regional focus. Our model of
 edaphic characteristics captures important edaphic variability that is
 vital for understanding plant and consequently faunal distributions, with
 wide-ranging conservation implications. Ongoing development of global
 syntheses of soil data requires more samples, especially in areas with
 high spatial heterogeneity and extreme edaphic conditions.
description: Collated and
 georeferenced GCFR soil dataSoil chemical data for
 the Greater Cape Floristic Region (GCFR) collated from sources and
 geo-referenced. The variables in this file include the latitude and
 longitude of each point, the pH measured in water (pH_H2O), pH measured in
 extracts (pH_extract, mostly 1 M KCl), Cation exchange capacity (CEC;
 cmol(+)/kg; H+ (cmol(+)/kg), Total exchangeable cations (cmol(+)/kg),
 Extractable K (cmol(+)/kg), Extractable Na (cmol(+)/kg), Extractable P
 (mg/kg), total P (mg/kg), Organic C (%), total C(%) and total
 N(%).GCFR_soil.csvGCFR soil pHpH values were obtained from collated data and also AFSP. Data from pH measured in water were corrected to KCl extract values using linear regression of known KCL and water extracts. The raster layer represents the modeled interpolation of this pH (CRS EPSG:4326 - WGS 84 - Geographic) in GeoTIFF format. Note that there are some voids (NA values) within the geographic area modeled.pH.tifGCFR soil electrical conductivity (EC, mS/m)The raster layer represents the modeled interpolation of electrical conductivity (EC) (CRS EPSG:4326 - WGS 84 - Geographic) in GeoTIFF format. Units are mS/m. Note that there are some voids (NA values) within the geographic area modeled.EC_mS_m.tifGCFR soil extractable K (cmol(+)/kg)The raster layer represents the modeled interpolation of extractable K (CRS EPSG:4326 - WGS 84 - Geographic) in GeoTIFF format. Units are cmol(+)/kg soil. Note that there are some voids (NA values) within the geographic area modeled.Ext_K_cmol_kg.tifGCFR soil extractable Na (cmol(+)/kg)The raster layer represents the modeled interpolation of extractable Na (CRS EPSG:4326 - WGS 84 - Geographic) in GeoTIFF format. Units are cmol(+)/kg soil. Note that there are some voids (NA values) within the geographic area modeled.Ext_Na_cmol_kg.tifGCFR soil extractable P (mg/kg)The raster layer represents the modeled interpolation of extractable P (CRS EPSG:4326 - WGS 84 - Geographic) in GeoTIFF format. Units are mg/kg soil. Note that there are some voids (NA values) within the geographic area modeled.Ext_P_mg_kg.tifGCFR soil total C (%)The raster layer represents the modeled interpolation of total C (CRS EPSG:4326 - WGS 84 - Geographic) in GeoTIFF format. Units are % (w/w) soil. Note that there are some voids (NA values) within the geographic area modeled. Total C includes organic and inorganic C.Total_C_%.tifGCFR soil total N (%)The raster layer represents the modeled interpolation of total N (CRS EPSG:4326 - WGS 84 - Geographic) in GeoTIFF format. Units are % (w/w) soil. Note that there are some voids (NA values) within the geographic area modeled.Total_N_%.tif