Table 1 Explanatory variables used in this study and their hypothesised link to wood density
From: Variation in wood density across South American tropical forests
Variable | Potential effect on wood density | Source |
|---|---|---|
Mean annual temperature (bio1) | Greater potential for drought stress at higher temperatures, so community-weighted mean wood density expected to increase with temperatures. | Worldclim V259 |
Mean annual precipitation (bio12) | Greater drought stress (and hence expectation for higher wood density) when precipitation lower. | Worldclim V259 |
Maximum cumulative water deficit (MCWD) | Higher wood density expected when moisture availability most limited. | Calculated using data from Worldclim V259 and TerraClimate.60 |
Mean wind speed in the windiest month | Proxy for potential for wind damage. High wind speeds could favour high wood-density species. Alternatively, frequent disturbances77 could favour low wood density pioneers. | Worldclim V263 |
Cloud frequency | Frequent cloud could reduce drought stress from evapotranspiration. | |
Lightning frequency | Potential to cause canopy gaps favouring pioneers.77 Trunk properties influence impacts of lightning strikes.78 | TRIMM LIS Very High Resolution Gridded Climatology.79 |
Soil cation exchange capacity | A proxy for soil fertility (other metrics such as total exchangeable bases would be preferable but are not available in gridded form across the study area). More fertile soils are expected to favour faster life-history strategies, leading to lower average wood density. | SoilGrids62 |
Soil pH | Potential control on tree species distributions, with specialist communities in low or high pH environments. | SoilGrids62 |
Depth to rock | Shallower soils are potentially unstable, and frequent disturbances would be expected to favour pioneer species, which tend to have low wood density. | SoilGrids62 |
Soil texture | Relates to soil stability (more disturbances leads to more low wood density pioneers) and to soil moisture holding capacity. | SoilGrids62 |
Topography - rugosity | More disturbances likely on steeper slopes, which favours pioneers, which tend to have low wood density. | Calculated from SRTM V464 |
Topography - slope | More disturbances likely on steeper slopes, which favours pioneers, which tend to have low wood density. | Calculated from SRTM V464 |
Topography - HAND | Height above nearest drainage relates to soil drainage. Wood density may be lower in soils that retain moisture due to lower drought stress. | Donchyts et al.65 |
Spatial coordinates | Wood density is expected to vary independently of the environment due to biogeographic variation in species distributions. Additionally, spatial coordinates can capture variation in wood density caused by environmental factors not included in the analysis. |
