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 >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.
Plot_Resource_Environments
Classification 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_Colonist
Plot-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_Residual
Plot-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_Total
Plot-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_Colonist
Plot-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_Residual
Plot-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_Total
Plot-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_Total
Plot-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_Colonist
Plot-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_Residual
Plot-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_Colonist
Plot-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_Residual
Plot-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_Total
Plot-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_Colonist
Plot-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_Residual
Plot-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_Total
Plot-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_Total
Plot-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_Colonist
Plot-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_Residual
Plot-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_Colonist
Richness 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_Residual
Richness 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_Total
Richness 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_Colonist
Richness 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_Residual
Richness 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_Total
Richness 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_Total
Richness 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_Colonist
Richness 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_Residual
Richness 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_Cover
Plot-level values of total (summed) tree species cover (foliage >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_Density
Plot-level values of tree density (>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_Biomass
Plot-level estimates of tree (>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.