Natural tree regeneration and coarse woody debris dynamics after a forest fire in the western Cascade Range

Abstract

Cover photosPlot number 16 at 7 and 14 years after fire. At 7 years, there is abundant regeneration of Pseudotsuga menziesii under a canopy of snags. At 14 years, the snag canopy is thinning out owing to snag fall and fragmentation; tree, shrub, and herb regeneration mix but trees are the tallest elements.This work was performed under USDA Forest Service PO AG-04T0-P-10-0057. We monitored coarse woody debris dynamics and natural tree regeneration over a 14-year period after the 1991 Warner Creek Fire, a 3631-ha (8,972-ac) mixedseverity fire in the western Cascade Range of Oregon. Rates for tree mortality in the fire, postfire mortality, snag fall, and snag fragmentation all showed distinct patterns by tree diameter and species, with Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) more likely to survive a fire, and to remain standing as a snag, than other common tree species. Natural seedling regeneration was abundant, rapid, and highly variable in space. Densities of seedlings >10 cm height at 14 years postfire ranged from 1,530 to 392,000 per ha. Seedling establishment was not concentrated in a single year, and did not appear to be limited by the abundant growth of shrubs.The simultaneous processes of mortality, snag fall, and tree regeneration increased the variety of many measures of forest structure. The singular event of the fire has increased the structural diversity of the landscape.Keywords: Fire severity, monitoring, coarse woody debris, reforestation, snag recruitment, regeneration. SummaryWe monitored natural tree regeneration and coarse woody debris dynamics over 14 years following the 1991 Warner Creek Fire, a 3,631-ha (8,972-ac) mixed-severity fire in the western Cascade Range of Oregon. The results provide a detailed picture of the variety of natural postfire conditions in westside Cascade forests, and demonstrate how a single mixed-severity fire can increase variety in forest structures.We studied 24 permanent plots representative of the burned area and its mix of fire severities, which ranged from 0.1 to 100 percent of prefire canopy killed. Plots This postfire mortality rate was higher in plots with higher initial fire severity.Much of the new snag volume quickly transferred to the ground via snag fall and fragmentation. Small snags, and A. amabilis snags, were more likely to fall. Larger snags were more likely to fragment.Natural seedling regeneration was abundant, and highly variable in space. Densities of seedlings >10 cm height at 14 years postfire ranged from 1,670 to 392,000 per ha in the higher elevation zone, and from 1,530 to 47,500 per ha in the lower zone. New seedlings were observed over all study visits, in patterns demonstrating that establishment was not concentrated in a single year. The growth of shrubs was abundant but did not appear to be limiting tree regeneration. The mixed-severity fire, followed by variable mortality, snag fall, and tree regeneration, led to an increase in variability, among plots, of several metrics of forest structure. The prominence of P. menziesii ...

Post‐fire tree establishment and early cohort development in conifer forests of the western Cascades of Oregon, USA

“…Establishment trajectories did not vary by aspect in this study (Fig. 4c), nor did seedling density differ between north and south aspects 14 years after the Warner Creek Fire, 24 km southeast of the Fall Creek study area (Brown et al 2013). Although repeated sampling following timber harvest revealed that north aspects reached canopy closure 10 years earlier than south aspects (Halpern and Lutz 2013), post-harvest conditions differ from those after wildfire in several important ways.…”

“…Although repeated sampling following timber harvest revealed that north aspects reached canopy closure 10 years earlier than south aspects (Halpern and Lutz 2013), post-harvest conditions differ from those after wildfire in several important ways. For example, delayed tree mortality (e.g., 55% of trees that were alive the year after the Warner Creek Fire died by year 14) and snags that persist following wildfire provide partial shade that could dampen microclimatic extremes on south aspects (Brown et al 2013). …”

Contenidos De Celulosa Y Lignina En Restos Lignino- Celulósicos De Gran Tamaño (Necromasa) En Un Bosque Templado De Antiguo Crecimiento Del Centro-Sur de Chile

“…Estos valores pueden considerarse como representativos para bosques templados siempreverdes de antiguo crecimiento del sur de Chile, y demuestran mayores aportes de madera muerta al piso forestal, que los bosques simpreverdes de coníferas del hemisferio norte (Carmona et al, 2002). El volumen de RLC depositados en el bosque, representó el 16,4% del volumen fustal (2.394,9 m 3 ha -1 ) de los árboles vivos por ha -1 , reflejando plena dominancia de N. betuloides, especie sombra-intolerante, cuyos restos maderables depositados en el suelo, liberan espacios con acceso a luz, que son colonizados por la regeneración natural (Brown et al, 2013).…”

“…sobre y bajo el piso forestal, ocurre como producto de disturbios naturales (bosques prístinos) y antropogénicos (bosques intervenidos), (Carmona et al, 2002;Schlegel & Donoso, 2008). Bajo condiciones prístinas, los RLC se acumulan en el suelo, cuando el bosque sufre disturbios naturales recurrentes, como actividad volcánica, vientos, nevadas, lluvias torrenciales, derrumbes, o en su defecto ataques de plagas, especialmente en árboles que han llegado al final de su ciclo biológico (Brown et al, 2013), y su presencia es evidente, constituyendo un componente funcional y estructural como hábitat para productores y consumidores (Jia-bing et al, 2005) que tributan a la biogeoquímica del sistema (Heinemann & Kitzberger, 2006).…”

“…Entre las contribuciones de esta necromasa, se destacan la función de sustrato para plántulas de regeneración del bosque, hábitat para meso y microbiota, etc., (Brown et al, 2013). Durante su descomposición se liberan gradualmente nutrientes y formas orgánicas e inorgánicas de carbono (C), (Watkinson et al, 2006), constituyendo uno de los procesos más importantes del reciclaje en ecosistemas terrestres, por el aporte de nutrientes al suelo y la formación de materia orgánica (González-Polo et al, 2013).…”