DOI: 10.5061/dryad.1q88j
title: Data from: Canopy closure exerts weak controls on understory dynamics: a 30-year study of overstory-understory interactions

description: Stem exclusion and understory re-initiation are commonly described, but
 poorly understood stages of forest development. It is assumed that
 overstory trees exert strong controls on understory herbs and shrubs
 during the transition from open to closed-canopy forests, but long-term
 observations of this process are rare. We use long-term data from 188
 plots to explore patterns and correlates of variation in understory
 richness and abundance 15-45 yr after clear-cut logging and burning of two
 experimental watersheds in western Oregon, USA. We test whether variation
 in the temporal dynamics of plots can be explained by topoedaphic factors
 that influence resource availability (insolation and soil moisture),
 variation in the pace and intensity of overstory development, or
 characteristics of the vegetation prior to canopy closure. Changes in
 forest structure were substantial over the study period; canopy cover
 increased four-fold, stem density by 75%, and bole biomass by two orders
 of magnitude, although trends were highly variable among individual plots.
 In contrast, understory richness, foliar cover, and biomass declined only
 30-40%, driven by loss of early-seral colonists, not residual forest
 species. Canopy closure occurred earlier on north aspects but declines in
 understory biomass, reflecting loss of colonizing shrubs (without
 concomitant increases in forest shrubs), were limited to south aspects. In
 contrast, variation in effective soil moisture had little influence on the
 pace of decline. Temporal trends were highly asynchronous among plots
 nearly 50% of plots experienced some form of decline, but &gt;35%
 showed no discernible trend. Declines were more likely in plots with
 greater tree influence before or at peak overstory development, but also
 in plots with greater understory development prior to canopy closure.
 Quantile regression models indicated weak relationships between understory
 biomass and overstory structure at most points in time. Our long-term data
 support a model of understory dynamics in which characteristics of the
 pre-closure vegetation are as important as overstory structure in
 determining the timing and nature of decline. Long-term studies are
 critical for elucidating patterns and processes that cannot be inferred
 from short-term experiments or space-for-time substitutions.
description: Plot_Resource_EnvironmentsClassification of sample plots by resource environment. Column headings are: Plot number (first digit is watershed number, 1 or 3); Moisture (soil moisture availability class), and Aspect (aspect class). Moisture = Moist, Mesic, or Xeric. Aspect = Northerly, Southerly, or Intermediate (intermediate aspects were not analyzed for this attribute).Biomass_Herb_ColonistPlot-level estimates of total above-ground biomass over the study period (1979 to 2008) for colonizing herbaceous species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are Mg/ha.Biomass_Herb_ResidualPlot-level estimates of total above-ground biomass over the study period (1979 to 2008) for residual herbaceous species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are Mg/ha.Biomass_Herb_TotalPlot-level estimates of total above-ground biomass over the study period (1979 to 2008) for all herbaceous species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are Mg/ha.Biomass_Shrub_ColonistPlot-level estimates of total above-ground biomass over the study period (1979 to 2008) for colonizing shrub species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are Mg/ha.Biomass_Shrub_ResidualPlot-level estimates of total above-ground biomass over the study period (1979 to 2008) for residual shrub species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are Mg/ha.Biomass_Shrub_TotalPlot-level estimates of total above-ground biomass over the study period (1979 to 2008) for all shrub species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are Mg/ha.Biomass_TotalPlot-level estimates of total above-ground biomass over the study period (1979 to 2008) for all understory species. Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are Mg/ha.Biomass_Total_ColonistPlot-level estimates of total above-ground biomass over the study period (1979 to 2008) for all colonizing species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are Mg/ha.Biomass_Total_ResidualPlot-level estimates of total above-ground biomass over the study period (1979 to 2008) for all residual species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are Mg/ha.Cover_Herb_ColonistPlot-level values of total (summed) cover over the study period (1979 to 2008) of colonizing herbaceous species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are % (values can exceed 100%).Cover_Herb_ResidualPlot-level values of total (summed) cover over the study period (1979 to 2008) of residual herbaceous species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are % (values can exceed 100%).Cover_Herb_TotalPlot-level values of total (summed) cover over the study period (1979 to 2008) of all herbaceous species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are % (values can exceed 100%).Cover_Shrub_ColonistPlot-level values of total (summed) cover over the study period (1979 to 2008) of colonizing shrub species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are % (values can exceed 100%).Cover_Shrub_ResidualPlot-level values of total (summed) cover over the study period (1979 to 2008) of residual shrub species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are % (values can exceed 100%).Cover_Shrub_TotalPlot-level values of total (summed) cover over the study period (1979 to 2008) of all shrub species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are % (values can exceed 100%).Cover_TotalPlot-level values of total (summed) cover over the study period (1979 to 2008) of all understory species. Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are % (values can exceed 100%).Cover_Total_ColonistPlot-level values of total (summed) cover over the study period (1979 to 2008) of all colonizing species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are % (values can exceed 100%).Cover_Total_ResidualPlot-level values of total (summed) cover over the study period (1979 to 2008) of all residual species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are % (values can exceed 100%).Richness_Herb_ColonistRichness over the study period (1979 to 2008) of colonizing herbaceous species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are number of species/plot.Richness_Herb_ResidualRichness over the study period (1979 to 2008) of residual herbaceous species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are number of species/plot.Richness_Herb_TotalRichness over the study period (1979 to 2008) of all herbaceous species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are number of species/plot.Richness_Shrub_ColonistRichness over the study period (1979 to 2008) of colonizing shrub species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are number of species/plot.Richness_Shrub_ResidualRichness over the study period (1979 to 2008) of residual shrub species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are number of species/plot.Richness_Shrub_TotalRichness over the study period (1979 to 2008) of all shrub species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are number of species/plot.Richness_TotalRichness over the study period (1979 to 2008) of all understory species. Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are number of species/plot.Richness_Total_ColonistRichness over the study period (1979 to 2008) of colonizing species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are number of species/plot.Richness_Total_ResidualRichness over the study period (1979 to 2008) of residual species (see Appendix A for species classification). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are number of species/plot.Overstory_CoverPlot-level values of total (summed) tree species cover (foliage &gt;2 m tall) over the study period (1979 to 2008). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1979, 1980, 1983, 1987, 1990, 1994, 1997, 2002, and 2008. Units are % (values can exceed 100%).Overstory_DensityPlot-level values of tree density (&gt;1.4 m tall) over the study period (1980 to 2007). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1980, 1984, 1988, 1991, 1995, 2001, and 2007. Units are trees/ha.Overstory_Bole_BiomassPlot-level estimates of tree (&gt;1.4 m tall) bole biomass over the study period (1980 to 2007). Column headings are: Plot number (first digit is watershed number, 1 or 3); the remainining columns are sampling dates (1980, 1984, 1988, 1991, 1995, 2001, and 2007. Units are Mg/ha.