Data on tree traits and shade generation in a South African forest-savanna mosaic

Forests and mesic savannas can both exist under the same climatic conditions across the tropics and subtropics but differ greatly in ecosystem function. Grass fuels are one key difference: flammable grasses promote fire in savanna but are shade intolerant and thus excluded from forest. While fire suppression via shading is widespread in forests, the extent to which shade results from the traits of individual forest trees versus from a high density of trees remains poorly understood. We examined whether individual or ecosystem-level traits are responsible for excluding shade-intolerant grasses (and hence fire) in forest understory in southern Africa using a simple mathematical model linking tree traits to ecosystem function via their impact on shade and grass-exclusion. To parameterize the model, we used trait data collected along a Leaf Area Index (LAI) gradient spanning across a savanna-forest mosaic in Hluhluwe iMfolozi Park, South Africa. We contrasted two versions of the model, one based on individual tree functional traits and another that also incorporated tree neighbor density, and evaluated which model better predicted measured LAI. This dataset includes trait data and model-predicted shade values for individual trees in savanna and forest habitats, as well as grass biomass and cover data collected from transects in savanna and forest habitats to contextualize tree shade effects on grass. # Data on tree traits and shade generation in a South African forest-savanna mosaic Dataset DOI: [10.5061/dryad.8w9ghx438](doi.org) ## Description of the data and file structure Data include field-collected trait data and model-predicted individual and collected shade values from savanna and forest trees in an African forest-savanna mosaic, in Hluhluwe-iMfolozi Park, South Africa. Data also include grass biomass and cover values from transects reflecting savanna and forest habitat conditions. ### Files and variables #### File: TeamShade_GrassTransects.csv **Description:** Grass data from 40-m transects established in savanna and forest habitats ##### Variables * Site: Unique site codes * Grass_Biomass: Average grass biomass at the transect level, in grams per square meter * Grass_cover: Average grass cover at the transect level, as a percent * Habitat: S for savanna, F for forest, T for thicket ("intermediate-light habitat" in the associated manuscript) #### File: TeamShade_IndividualTrees.csv **Description:** Field-collected trait values of individual trees and associated model-predicted shade values. Note: one individual (RP-S5) has some missing values, denoted as NA, because of a missing hemispherical canopy photo. ##### Variables * ID: Unique tree ID code. First two letters correspond to species; S, F, or T denotes savanna, forest, or thicket habitat. * Species: Tree species name * Genus: Tree genus * Lat: Latitude, in degrees * Long: Longitude, in degrees * Altitude: Altitude, in kilometers * Place: Habitat code: S for savanna, F for forest, T for thicket ("intermediate-light habitat" in the associated manuscript) * Date: Data of data collection, as m/dd/yy * Time: Time of data collection * DBH: Diameter at breast height (of the widest stem for multi-stemmed trees), in cm * Height: Height in meters * Canopy1: Widest canopy diameter, in meters * Canopy2: Canopy diameter perpendicular to the widest canopy diameter, in meters * Grass_DPM: Grass measurement from a disc pasture meter, in cm * Grass_Percent_cover: Grass cover, as a percent * LAI: Leaf area index, calculated by CIMES software based on processed hemispherical canopy photos taken underneath tree * fractional_direct: Prediction of fraction of direct light transmitted through the canopy, by CIMES software based on processed hemispherical canopy photos taken underneath tree * CanopyOpenness: Fraction of canopy that is open (where crown fill = 1 - [canopy openness]), calculated from image analysis of hemispherical canopy photos and used in shade modeling. * NeighborMetric: Number of adjacent neighbors used in shade modeling (0 for savanna trees and 5 for forest trees) * Canopy.radius: Hypothetical canopy radius in meters for a circular tree canopy of equivalent canopy area, used in shade modeling * IndividualTreeShade_percent: Model-predicted shade, as a percent, for this tree if it had no neighbors * CollectiveShade_percent: Model-predicted shade, as a percent, for this tree with its actual number of neighbors * Height.of.savanna.congeneric: For forest trees only - height of paired savanna congeneric in meters, for calculation of hypothetical "short forest tree" shade values. NA for savanna and thicket trees. * Shade.of.short.forest.tree: For forest trees only - model-predicted shade, as a percent, for the hypothetical scenario of a tree with the canopy diameter and crown fill of a forest tree, but the shorter height of a savanna tree. NA for savanna and thicket trees. ## Code/software Data can be viewed in any program that can open CSV files. Associated R code can be found in Zenodo ([zenodo.org](zenodo.org)). ## Access information Other publicly accessible locations of the data: * N/A Data was derived from the following sources: * N/A