Disturbance is central to maintaining diversity in forest ecosystems. In the dry forests of the western United States, over a century of fire exclusion has altered the fire regimes of these forests, resulting in high fuel loads and a loss of plant diversity. Mechanical thinning and prescribed fire are widely used to restore structural complexity and species diversity in many western U.S. forests. While studies have shown that the reintroduction of fire into these forests initially promotes plant diversity, there is limited information on the persistence of this effect. We evaluated the effects of thinning and burning treatments on the understory plant community fifteen years after treatment in an old-growth, Sierran mixed-conifer forest. Using a full-factorial design, including three levels of thinning and two levels of burning, we found mechanical thinning and prescribed fire reduced litter depths and increased the availability of bare ground, resulting in an initial increase in herb cover. However, fifteen years after treatment, litter depths and shrub cover increased, resulting in a more homogenous understory community and a loss of herb cover. Overall, our results suggest that while thinning and burning treatments initially promote herbaceous plant cover, these effects are short lived in the absence of a second disturbance.

These data are the supporting vegetation data for:

Goodwin, MJ, MP North, HSJ Zald, MD Hurteau. 2018. The 15-year post-treatment response of a mixed-conifer understory plant community to thinning and burning treatments. Forest Ecology and Management 429:617-624.

The Understory Vegetation data contain gridpoint data for all 402 gridpoints for each measurement year.

The measurement years include: 2001, 2002, 2003, 2004 and 2006 (2, 3, 4 and 6 years post-treatment), 2011, 2012 and 2013 (11, 12 and 13 years post-treatment),
and 2016 and 2017 (16 and 17 years post-treatment).

The following variables were assessed at each gridpoint:

Percent cover of all species present (recorded in columns with species code)

Total Plant Cover

Percent cover of bareground (bare ground = mineral soil)

Percent cover of rock (any exposed rock larged than a marble)

Average litter depth (average of three litter depth measurements)

Percent cover of sticks (any piece of wood larger than 2 cm diameter (approx. the size of an index finger) and smaller than 7 cm in diameter)

Percent cover of Coarse Woody Debris decay class 1 to 3 (any piece of wood larger than 7 cm in diameter with wood still intact. You could step on it or poke it with a ruler and not sink into the wood)

Percent cover of Coarse Woody Debris decay class 4 and 5 (any piece of wood larger than 7 cm in diameter with wood beginning to fall apart. If you stepped on it or poked it, it would fall apart)

Cover values were recorded as follows:

0.1-0.9 % cover – record by 0.1 (0.1, 0.2, 0.3 etc.). 0.1 indicates a species is present.  Use this value even if the % cover is less than 0.1

1-10 % cover-record as whole numbers (1,2,3 etc.)

10-100% cover- record as a multiple of 5 (15,20,25 etc.)

The Treatment Codes refer to the following Treatments:

BC = Burn/Understory Thin
BN = Burn Only
BS = Burn/Overstory Thin
UC = Understory Thin
UN = Control
US = Overstory Thin