DOI: 10.5061/dryad.dr7sqv9w9
title: Climate more important than soils for predicting forest biomass at the continental scale

description: Above-ground biomass in forests is critical to the global carbon cycle as
 it stores and sequesters carbon from the atmosphere. Climate change will
 disrupt the carbon cycle hence understanding how climate and other abiotic
 variables determine forest biomass at broad spatial scales is important
 for validating and constraining Earth System models and predicting the
 impacts of climate change on forest carbon stores. We examined the
 importance of climate and soil variables to explaining above-ground
 biomass distribution across the Australian continent using publicly
 available biomass data from 3130 mature forest sites, in 6 broad
 ecoregions, encompassing tropical, subtropical, and temperate biomes. We
 used the Random Forest algorithm to test the explanatory power of 14
 abiotic variables (8 climate, 6 soil) and to identify the best-performing
 models based on climate-only, soil-only, and climate plus soil. The best
 performing models explained ~50% of the variation (climate-only: R2 = 0.47
 ± 0.04, and climate plus soils: R2 = 0.49 ± 0.04). Mean temperature of the
 driest quarter was the most important climate variable, and bulk density
 was the most important soil variable. Climate variables were consistently
 more important than soil variables in combined models, and model
 predictive performance was not substantively improved by the inclusion of
 soil variables. This result was also achieved when the analysis was
 repeated at the ecoregion scale. Predicted forest above-ground biomass
 ranged from 18 to 1066 Mg ha-1, often under-predicting measured
 above-ground biomass, which ranged from 7 to 1500 Mg ha-1. This suggested
 that other non-climate, non-edaphic variables impose a substantial
 influence on forest above-ground biomass, particularly in the high biomass
 range. We conclude that climate is a strong predictor of above-ground
 biomass at broad spatial scales and across large environmental gradients,
 yet to predict forest above-ground biomass distribution under future
 climates, other non-climatic factors must also be identified.
description: These data are a compilation of Australia-wide forest above
 ground biomass records retrieved from the Biomass Plot Library (TERN
 AusCover, 2017), soil data retrived from the Australian Soil and Landscape
 Grid (Viscarra Rossel, R., et al. 2014), climate data retrieved from
 WorldClim 2.0 (Fick, S. E. and Hijmans, R. J. 2017), forest-type data
 retrieved from Australia's State of the Forest report (ABARES 2013),
 biome data from Australia's ecoregion map (Department of Agriculture
 Water and the Environment 2020), and ecoregion data from the Global
 ecological zones map (Food and Agricultural Organisation of the United
 Nations 2001). Data sets were first processed in ArcGIS
 10.4.1 to spatially join raster data to above-ground biomass point data,
 and then processed in R to remove measurements that were suspected to be
 errors, duplicated site measurements, non-forest, or highly disturbed.  A
 full description of this process is provided in the published manuscript
 and in the supplementary material.
description: Data fields are described as follows: Field Description Original Source 
 ID
 Row index Used in processing
 FID_ Unique
 identifier Biomass Plot Library
 agb_drymass_ha Tree
 AGB /ha Biomass Plot Library 
 State Australian
 State Biomass Plot Library 
 Long Longitude
 Biomass Plot Library 
 Lat Latitude Biomass
 Plot Library E
 Easting Added during processing
 N
 Northing Added during processing
 HEIGHT Forest height
 code Forest extent 2013 (v2) 
 COVER Forest cover
 code Forest extent 2013 (v2) 
 FOR_CAT Forest
 category Forest extent 2013 (v2)
 FOR_TYPE Forest
 type Forest extent 2013 (v2) 
 bio_1 Mean annual
 temperature WorldClim 2.0 
 bio_3 Isothermality
 WorldClim 2.0 
 bio_7 Temperature annual range
 WorldClim 2.0 
 bio_9 Mean temperature of driest
 quarter WorldClim 2.0 
 bio_12 Annual
 precipitation WorldClim 2.0 
 bio_15 Precipitation
 seasonality WorldClim 2.0 
 bio_17 Precipitation of driest
 quarter WorldClim 2.0 
 bio_19 Precipitation of coldest
 quarter WorldClim 2.0 
 awc_0_5 Available water capacity
 (%) Soil and Landscape Grid 
 bdw_0_5 Bulk density (g
 cm<sup>-3</sup>) Soil and Landscape
 Grid cly_0_5
 Clay (%) Soil and Landscape Grid
 ece_0_5 Effective
 cation exchange capacity (me 100 g<sup>-1</sup>)
 Soil and Landscape Grid 
 phc_0_5 pH Soil and
 Landscape Grid 
 pto_0_5 Total phosphorus (%)
 Soil and Landscape Grid 
 Biome Global biome
 classification Global ecological zones map
 Ecoregion World
 ecoregion classification Australia's ecoregion
 map 
 References for data sources are as follows:
 ABARES 2013. Australia national forest inventory - Forest extent
 (2013) v2.0, electronic dataset. - ABARES.
 http://data.daff.gov.au/data/warehouse/9aaf/foa/2013_v2/foa13g9abfs20160212egialb132.zip, Accessed [25 October 2017]. Department of Agriculture Water and the Environment 2020. Australia's ecoregions map. - http://www.environment.gov.au/land/nrs/science/ibra/australias-ecoregions, Accessed [20 March 2020]. Fick, S. E. and Hijmans, R. J. 2017. Worldclim 2: New 1-km spatial resolution climate surfaces for global land areas. - Int. J. Climatol. 37: 4302-4315. Food and Agricultural Organisation of the United Nations 2001. Global ecological zones map. - GeoNetwork. http://www.fao.org/geonetwork/srv/en/resources.get?id=1255&fname=eco_zone.zip&access=private. Accessed [8th October 2018]. TERN AusCover 2017. Biomass Plot Library - National collation of tree and shrub inventory data, allometric model predictions of above and below-ground biomass, Australia. - Dataset. http://www.auscover.org.au/purl/biomass-plot-library, Accessed [17 September 2017]. Viscarra Rossel, R., et al. 2014. Soil and landscape grid national soil attribute maps (3" resolution): Bulk density - whole earth (v1.4); Organic carbon (v1.1); Clay (v1.1); Soil depth (v1.2); Effective cation exchange capacity (v1.3); pH - CaCl2 (v1.3); Available water capactiy (v1.3); Sand (v1.4); Total nitrogen (v1.4); Total phosphorus (v1.4); and Silt (v1.4). - CSIRO Data Collection.  http://www.clw.csiro.au/aclep/soilandlandscapegrid/GetData-DAP.html, Accessed [9th October 2017].