Bryoid Layer Response to Soil Disturbance by Fuel Reduction Treatments in a Dry Conifer Forest

Bryoid Layer Response to Soil Disturbance by Fuel Reduction Treatments in a Dry Conifer Forest Amanda Hardman and Bruce McCune1 ABSTRACT. .Weinvestigated the response of the bryoid layer, bryophyte and lichen communities on the soil surface, three years after fuel reduction treatment (logging and burning) in the central Blue Mountains of eastern Oregon. Both treatment and control areas had been decimated by spruce budworm and drought before the fuel reduction treatments. Treatments reduced overstory and understory woody vegetation, litter, and coarse woody debris and disturbed the soil surface. In the untreated stands minor local disturbances had created bare mineral soil over about 1% of the ground area, about half of that was from burrowing rodents. Fuel reduction treatments disturbed an additional 23% of the ground area, beyond the 1% disturbed in untreated sites. Over half of the recently disturbed treatment areas had been colonized by pioneering short mosses. Bare soil from rodent disturbances covered about 10 times more area in treated sites than in untreated sites, increasing from 0.4% to 5.5% cover. The bryoid layer responded to the treatments by changes in species composition, rather than species richness. Treated areas had more cover of small acrocarpous pioneer bryophytes (i.e., Funaria hygrometrica, Ceratodon purpureus, and especially Bryum caespiticium), whereas cover of larger pleurocarps, such as Brachythecium and Rhytidiadelphus was reduced by soil disturbance. We infer that pioneer bryophytes perform a valuable ecosystem service in these dry forests by rapidly colonizing and stabilizing the soil surface, reducing its vulnerability to erosion by wind and water. KEYWORDS. .Biotic crusts, Brachythecium, Bryum caespiticium, Ceratodon purpureus, ecosystem services, Funaria hygrometrica, lichen, logging, Pacific Northwest, Rhytidiadelphus, rodents. In the last few decades forests in much of western crusts, the thin living skin on the surface of the soil. North America have experienced an onslaught of Biotic soil crusts can include any association of disturbances, including insects, disease, fire, and mosses, lichens, liverworts, microfungi, logging. Although researchers have studied many cyanobacteria, algae, and other microscopic ecosystem responses to these disturbances, we are organisms found at the soil surface and in the upper relatively ignorant about the responses of biotic few mm of soil in exposed habitats. Biotic crusts grade into a "bryoid layer" (Achuff & La Roi 1977), a particularly appropriate term for bryophyte- dominated surface layers. Arid and semi-arid environments often host persistent, highly-developed biotic crusts that are frequently dominated by lichens Belnap et al. 2001). Free-living, and both lichen- and or cyanobacteria, and tend to increase in cover with moss-associated cyanobacteria fix N2 (DeLuca et al. time since disturbance. In recently deforested areas in 2002), providing a significant input, particularly in moister climates, the bryoid layer is often initially nitrogen-poor environments. Schlatterer and Tisdale dominated by short-lived mosses whose cover usually ( 1969) found a positive relationship between biotic diminishes with time since disturbance. crusts and the growth of perennial bunchgrass Many studies have demonstrated important species; this also seems possible in open, dry forests. functions of biotic crusts in arid and semi-arid Finally, moss cover can alter moisture and environments (reviewed by Belnap & Lange 2001). temperature at the soil surface, affecting seed Many of these roles should also apply to bryoid layers germination. A few studies have found a positive in other environments. In particular, the bryoid layer relationship between biotic crusts and the can colonize recently disturbed soils, potentially germination of perennial bunchgrasses (Schlatterer & stabilizing the soil surface. This may be especially Tisdale 1969; St. Clair et al. 1984), though this true when hot fires kill canopies and root systems of relationship has been questioned by others (Prasse & higher plants, opening the soil surface to erosion by Bornkamm 2000; West 1990). In some cases intact wind and water. biotic crusts may reduce establishment of invasive Soil stabilization results from various properties species (Serpe et al. 2006). of the bryoid layer. The protonemata, or juvenile The Blue Mountains of northeastern Oregon stages of a bryophyte, bind soil particles as they grow have a long history of logging, fire suppression, and over and through the soil. Mature mosses trap cattle grazing (Langston 1995). Twentieth-century airborne soil particles (Danin & Ganor 1991). Moss forest management led to dense forests that are prone colonies in the Blue Mountains appear to accumulate to insect outbreaks and catastrophic fire (Hessburg et soil; local soils are developed from volcanic ash, al. 2005; Mutch et al. 1993). Furthermore, reduced unstable where disturbed, and easily transported by species diversity may result from fire exclusion in wind. The bryoid layer reduces wind erosion by these fire-adapted ecosystems (Metlen & Fiedler lowering friction threshold velocities (Belnap & 2006; Vavra et al. 2004). Many of the forests in this Gillette 1997; Leys & Eldridge 1998; Williams et al. region incurred heavy canopy mortality and fuel 1995). Rhizoids, or the root-like structures of a moss, buildup from spruce budworm infestations and also stabilize soil by forming a fine filamentous drought in the 1990s. Research on lichen and matrix near the soil surface. Lichen rhizines and bryophyte community response to these changes, as rhizohyphae act similarly, trapping soil particles. well as to prescribed fire and timber extraction, is Algae, cyanobacteria, and fungi bind soil through the almost nonexistent in western North America. To secretion of polysaccharides (Belnap & Lange 2001; help to fill this gap, we studied the effects of fuel Mazor et al. 1996). Mosses reduce rainsplash- reduction treatments (logging and burning) on the sheetwash erosion by physically intercepting the extent, species richness, and composition of the impact of raindrops (Tchoupopnou 1989); bryoid layer in insect-decimated forests. We also presumably other cryptogram covers do the same. measured soil disturbance by the treatments and the Cryptogam cover can increase rainwater infiltration response of the bryoid layer to that disturbance. This in disturbed soils (Eldridge 1993). Although we did contributes to our basic understanding of ecosystem not measure soil stability per se in this study, the services provided by the bryoid layer in these dry substantial evidence cited above supports an forests. assumption that the conversion of bare soil to bryophyte cover will increase stability of the soil STUDY AREA surface. Starkey Experimental Forest is in the central Biotic crusts can increase above- and below- Blue Mountains of eastern Oregon about 40 km west ground development of vascular plants in arid soils of La Grande, 450 15' N 1180 38' W. Starkey is a by increasing soil fertility (Pendleton et al. 2003; primary research facility for studies of elk, Cervus canadensis, and the influence of herbivory, fire, and logging on the landscape (Rowland et. al. 1997). The region is semi-arid but Pacific maritime air masses provide an average annual precipitation of 550 mm at the higher forested elevations, over half of that as snow. Temperatures recorded on site from 1989- 1995 averaged -7.2 °C in December, and 25.4 °C in August (U.S. Forest Service, unpublished data in Clark et al. 2000). The study sites lie on broad plateaus of basalt at 1350-1470 m in elevation. Soils in forested areas are mostly Andisols, predominately well drained Olot silt loams, which are moderately susceptible to erosion by wind and water (USDA 1985). Abies grandis, Larix occidentalis, Pinus ponderosa, and Pseudotsuga menziesii dominate in the Experimental Forest (nomenclature: Hitchcock & Cronquist 1973). Stand density varies from open similar as possible to each other in elevation, grasslands to closed forests, but all six sites that we topography, soils, and vegetation. An eighth pasture studied were formerly closed forests, apart from a few at each site lay outside of the exclosure and was open grassy, thin-soil inclusions. Mountain pine beetles to free-roaming ungulates. Fuel reduction treatments (Dendroctonus ponderosae) in the early 1970s, and consisting of partial removal of standing live, severe spruce budworm (Choristoneura occidentalis) standing dead, and down wood followed by on-site infestations that began in the 1980s, combined with burning were applied in 2001-2002 to three of the six prolonged drought, caused heavy tree mortality and sites before construction of the exclosures. Burns fuel loads. were in broadcast slash rather than piles. These Our study was part of a larger study of the treatments left only scattered live trees (stand basal influence of ungulates on the development of forest area 4.2-9.6 m2/ha; McCune et al. 2008). The vegetation (M. Wisdom et al. 2005, unpublished remaining three had not been harvested or burned in study plan). A companion study at the same sites over forty years and had abundant snags and documented reductions in the forage lichen Bryoria crisscross jumbles of downed wood. fremontii after insect outbreaks and fuel reduction Sampling was carried out in summer months treatments (McCune et a1. 2008). The Pacific from 2004 to 2006, 3-4 yr after treatments were Northwest Research Station has constructed

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