DOI: 10.5061/dryad.d9d83q1
title: Data from: Testing conceptual models of early plant succession across a disturbance gradient

description: 1.Studies of succession have a long history in ecology, but rigorous tests
 of general, unifying principles are rare. One barrier to these tests of
 theory is the paucity of longitudinal studies that span the broad
 gradients of disturbance severity that characterize large, infrequent
 disturbances. The cataclysmic eruption of Mount St. Helens (Washington,
 USA) in 1980 produced a heterogeneous landscape of disturbance conditions,
 including primary to secondary successional habitats, affording a unique
 opportunity to explore how rates and patterns of community change relate
 to disturbance severity, post‐eruption site conditions, and time. 2.In
 this novel synthesis, we combined data from three long‐term (ca. 30‐year)
 studies to compare rates and patterns of community change across three
 ‘zones’ representing a gradient of disturbance severity: primary
 successional blast zone, secondary successional tree blowdown/standing
 snag zone, and secondary successional intact forest canopy/tephra deposit
 zone. 3.Consistent with theory, rates of change in most community metrics
 (species composition, species richness, species gain/loss, and rank
 abundance) decreased with time across the disturbance gradient.
 Surprisingly, rates of change were often greatest at intermediate‐severity
 disturbance and similarly low at high‐ and low‐severity disturbance. There
 was little evidence of compositional convergence among or within zones,
 counter to theory. Within zones, rates of change did not differ among
 ‘site types’ defined by pre‐ or post‐eruption site characteristics
 (disturbance history, legacy effects, or substrate characteristics).
 4.Synthesis. The hump‐shaped relationships with disturbance severity runs
 counter to the theory predicting that community change will be slower
 during primary than during secondary succession. The similarly low rates
 of change after high‐ and low‐severity disturbance reflect differing sets
 of controls: seed limitation and abiotic stress in the blast zone vs.
 vegetative re‐emergence and low light in the tephra zone. Sites subjected
 to intermediate‐severity disturbance were the most dynamic, supporting
 species with a greater diversity of regenerative traits and seral roles
 (ruderal, forest, and non‐forest). Succession in this post‐eruption
 landscape reflects the complex, multi‐faceted nature of volcanic
 disturbance (including physical force, heating, and burial) and the
 variety of ways in which biological systems can respond to these
 disturbance effects. Our results underscore the value of comparative
 studies of long‐term, ecological processes for testing the assumptions and
 predictions of successional theory.
description: Mount St. Helens Plant
 Species Composition DataThis file contains
 community percent cover data for blast, blowdown, and tephra zone plots at
 Mount St. Helens for years 1980-2016. Portions of this dataset have been
 published previously in del Moral 2010 (Ecological Archives E091-152) and
 Fischer et al. 2018 (Dryad Digital Repository.
 https://doi.org/10.5061/dryad.j2k54s8). Contact the authors directly with
 any questions and clarifications.MSHDataWithoutBlastZone.csv