DOI: 10.5061/dryad.n8pk0p35w
title: Fine-scale variation in soil properties promotes local taxonomic diversity of hybridizing oak species (Quercus spp.)

description: Although many tree species frequently hybridize and backcross, management
 decisions in forestry and nature conservation are usually concentrated on
 pure species. Therefore, understanding which environmental factors drive
 the distribution and admixture of tree species on local stand scale is of
 great interest to support decision making in the establishment and
 management of resilient forests. We extensively sampled a mixed stand of
 hybridizing white oaks (Quercus petraea and Q. pubescens) near Lake
 Neuchâtel (Switzerland), where limestone and glacier moraine geologies
 coexist in proximity, to test whether micro-environmental conditions can
 predict taxonomic distribution and genetic admixture. We collected DNA
 from bud tissue, individual soil samples and extracted high-resolution
 topographic data for 385 oak trees. We used 50 species-discriminatory
 single nucleotide polymorphism (SNP) markers to determine the taxonomic
 composition and admixture levels of individual trees and tested their
 association with micro-environmental conditions. We show that the trees’
 taxonomic distribution can be explained mainly by geographic position,
 soil pH and potential rooting depth, a proxy for soil water availability.
 We found that admixed individuals tend to grow in habitats being
 characteristic for the more drought-tolerant species Q. pubescens rather
 than in intermediate habitats. Using in-situ measurements, we are the
 first to show that fine-scale variation in soil properties related to pH
 and water availability potentially drives the distribution of hybridizing
 tree species in a mixed stand. Micro-environmental variation therefore
 promotes local taxonomic diversity, facilitates admixture and adaptive
 introgression, and contributes to the resilience of forests under
 environmental change. Consequently, species such as white oaks should be
 managed and protected as a species complex rather than as pure species.
description: # Fine-scale variation in soil properties promotes local taxonomic
 diversity of hybridizing oak species (Quercus spp.)
 [https://doi.org/10.5061/dryad.n8pk0p35w](https://doi.org/10.5061/dryad.n8pk0p35w) ## Description of the data and file structure The dataset 2025_EVA_data.xlsx contains (consists of 8 spreadsheets) all environmental, topographic, and geographic variables and taxonomic data (STRUCTURE *Q*-values) for the 385 sampled trees. The datasets 2025_EVA_test_individuals.stru and 2025_EVA_training_individuals.stru contain the STRUCTURE input files resulting from the kompetitive allele specific PCR (KASP) genotyping for the 385 sampled trees and the training individuals, respectively. Please contact the corresponding author if there are any questions regarding the data. ### Files and variables #### File: 2025\_EVA\_data.xlsx ##### Variables Some empty cell scan be found in the data file (because, e.g., soil measurements were not possible in the corresponding soil depth) and are not filled with "n/a" due to possible interference with the analysis scripts which can be found on the GitLab page linked at the bottom of this file. * ID (Tree ID) * Q_robur (STRUCTURE *Q*-values *Quercus robur*) * Q_petraea (STRUCTURE *Q*-values *Quercus petraea*) * Q_pubescens (STRUCTURE *Q*-values *Quercus pubescens*) * lon (longitude; m East; Swiss LV95) * lat (latitude; m North; Swiss LV95) * alt (altitude; m above sealevel) * slp (slope; degrees) * asp (northness) * tri (topographic ruggedness index) * hoc (horizontal curvature; degrees per m) * vec (vertical curvature; degrees per m) * tpi (topographic positioning index) * twi (topographic wetness index) * mpi (morphometric protection index) * ddg (downslope distance gradient; degrees) * pti (potential total insolation; kWh per square m) * prd (potential rooting depth; cm) * lid (lime depth; cm) * tph (topsoil pH) * sph (deep soil pH) * DBH (diameter at breast height; cm) ## Access information Other publicly accessible locations of the data and analysis scripts: [https://gitlabext.wsl.ch/felix.zimmermann/2025_eva_quercus_taxonomic_diversity](https://gitlabext.wsl.ch/felix.zimmermann/2025_eva_quercus_taxonomic_diversity)