DOI: 10.5061/dryad.g1jwstqrq
title: Feedbacks between forest structure and an opportunistic fungal pathogen

description: Abiotic stresses, physiological dysfunction, forest stand dynamics, and
 primary tree attackers (native and non-native) are all recognized as
 important contributors to both anomalous tree mortality and background
 tree mortality, and thus as important influences on biogeochemical cycling
 and habitat for associated terrestrial organisms. Opportunistic and latent
 tree pathogens and insect pests have largely been left out of this
 discussion, probably because they are difficult to monitor and their
 effects sometimes more diffuse, yet they play important roles in tree
 mortality scenarios. We know very little about the influence of biotic
 gradients, e.g., forest dynamics and forest structure, on the occurrence
 and effects of these opportunistic biotic enemies. To better understand
 the influence of an important biotic gradient—forest structure as
 represented by tree density and competition—on the occurrence and
 distribution of a typical opportunistic pathogen, we analyzed the
 relationship between tree neighborhood competition and soil-dwelling
 rhizomorphs of the fungus Armillaria gallica in regenerating (20-yr-old)
 and mature (80-100-yr-old) hardwood-dominated forest stands in central
 Missouri following a severe drought. We detected A. gallica, rhizomorphs
 in twice as many sampling sites in young (dense) plots as in mature (open)
 plots, and by contrast, found a twofold occurrence of other saprophytic
 fungi in the soil of mature plots compared to young plots. Mean tree
 density and competition index were significantly higher in subplots where
 A. gallica was found than in those with no A. gallica detections, and the
 pattern of A. gallica occurrence tracked closely with the occurrence of
 dense “hotspots” of competition in the plots. Synthesis. Early stages of
 forest structure and succession—potentially through initial inputs of
 disturbance-produced woody biomass, increased host connectivity and
 competition-influenced host tree susceptibility to fungal
 colonization—provide important feedbacks to A. gallica foraging, which in
 turn influences forest development. The recognition that tree density and
 competition influence A. gallica foraging suggests that in order to
 achieve a more comprehensive understanding of forest growth, development,
 and biogeochemical cycling, it may be necessary to increase life-history
 studies and basic occurrence surveys for opportunistic tree pathogens and
 insect pests.
description: Methods for field data collection are detailed in the paper.
 Field data were recorded on paper, transcribed to Excel- and text-format
 spreadsheets, and proofread before analysis using standard open-source
 statistics applications and GIS software. 
description: Besides the Readme file appended to this submission, each Excel
 spreadsheet contains an extra tab with definitions needed to understand
 header data (i.e., variable data collected in the field) on the primary
 data tab. There is also a supplementary rich text format file with a list
 of tree species included in this study, which is helpful to understand the
 "species" data header.