Thinnings using cut-to-length or whole-tree harvesting systems followed by underburning were evaluated for their effects on seedling and sapling demography in a pure, uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) stand containing a minor component of California white fir (Abies concolor var. lowiana [Gord.] Lemm.). Depression of seedling counts due to forest floor disturbance associated with thinning was followed by a recovery largely confined to Jeffrey pine in the whole-tree treatment where final seedling counts exceeded those found initially. The postburn substrate was more favorable for establishment of Jeffrey pine than white fir seedlings, and the largest increase in seedling counts between the initial and final inventories occurred in the burned portion of the whole-tree treatment. Live sapling losses from thinning were greatest in the cut-to-length treatment, while underburning induced complete sapling mortality. Absent treatment, several stand and site variables influenced seedling and sapling abundance, prominent among them a propensity for mahala mat (Ceanothus prostratus Benth.) to elevate counts of white fir within 655 both size classes. These results provide land managers insight into the impacts of six combinations of thinning and burning treatment on natural regeneration in eastern Sierra Nevada Jeffrey pine and similar dry site forest types.
Thinnings using cut-to-length and whole-tree harvesting systems followed by prescribed underburning were assessed for their effects on shrub, forb, and grass understory species in a second-growth Jeffrey pine ( Pinus jeffreyi Grev. & Balf.) stand. Prior to treatment installation, a mixed shrub-dominated understory featuring antelope bitterbrush ( Purshia tridentata [Pursh] DC.) with mules ears ( Wyethia mollis A. Gray) as the only forb and Sandberg bluegrass ( Poa secunda J. Presl) the most prominent among sparse grasses was inventoried such that both percent cover and dry weight by species were revealed. Five growing seasons after thinning and four after underburning, this inventory was repeated. By either abundance measure, bitterbrush was reduced by approximately two-thirds in the cut-to-length treatment and by one-half in the whole-tree treatment in comparison to that in the unthinned control at the final inventory. For the cut-to-length treatment, a similar reduction in mules ears was noted, but that in the whole-tree treatment was somewhat less for this species. Bluegrass was reduced 823 824 W. G. Salverson et al. by approximately one-half in the former treatment and by threefourths in the latter. Prescription fire reduced bitterbrush to less than one-tenth and mules ears to approximately one-half of that in the unburned treatment, but bluegrass prevalence was more than 10× greater in the burned than in the unburned treatment. Among an array of regression models used to evaluate selected variables for their predictive capacity regarding understory plants, abundance of each species noted above among others was negatively correlated with overstory density across treatments.
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