Second-growth Douglas-fir Forests Research Articles

Soil fungal and prokaryotic community structure exhibits differential short-term responses to timber harvest in the Pacific Northwest

Conventional clear-cut timber harvest is a widespread industrial practice across the Pacific Northwest; however, information regarding how these practices impact soil microbial community structure at the regional scale is limited. With evidence of consistent and substantial impact of harvest on soil microbial functional profiles across the region (despite a range of environmental conditions), the objective of this study was to determine the extent to which harvest also influences the structure of prokaryotic and fungal soil microbial communities, and how generalized these trends are throughout the geographic region. Paired soil samples were collected one year before and after harvest across nine second-growth Douglas-fir forests in the Pacific Northwest. Total community DNA was extracted from the soils, and high-throughput targeted gene sequencing of the 16S rRNA gene for prokaryotes and the internal transcribed spacer (ITS) gene for fungi was performed. Alpha diversity was consistently and significantly higher after harvest; it was moderately so for fungal communities (+14.6%), but only marginally so for prokaryotic communities (+2.0%). Similarly, on average, a greater proportion of the variation in the community structure of fungi (20.1%) at each site was associated with forest harvest compared to that of prokaryotes (13.2%). Overall, the greatest influence of timber harvest on soil microbial communities appeared to be a relative depletion of ectomycorrhizal fungi, with a concomitant enrichment of saprotrophic fungi. Understanding the short-term responses of soil microbial communities across the region, particularly those of tree root-associated symbionts, may aid our understanding of the role soil microbial communities play in ecological succession.

Harvesting Douglas-fir Stands Shifts Soil Microbial Activity and Biogeochemical Cycling

Clear-cutting is a common timber extraction method used across the Pacific Northwest, but the variability in soil microbial community functional response across the range of soil types and stand ages in the region is largely unknown. Our objective was to determine if shifts in soil microbial carbon (C) and nitrogen (N) pools and activities shortly following harvest are similar among similarly treated, but environmentally diverse sites. At nine second-growth Douglas-fir forests, paired soil samples were collected one year before and after clear-cutting. Samples were analyzed for total, extractable, and microbial biomass C and N, and seven extracellular enzyme activities. Total C and N did not change following harvest, but extractable organic C decreased and total extractable N increased. Microbial biomass C generally increased, as did microbial C/N. Activities of β-glucosidase and cellobiohydrolase increased significantly, whereas activities of phenol oxidase and peroxidase decreased. N-acetylglucosaminidase, leucine aminopeptidase, and phosphatase showed site-specific responses. Cumulative respiration during a 3-mo incubation was lower in post-harvest soils. Although the total N leached during the incubation was similar in soils sampled before and after harvest, it was dominated by dissolved organic N pre-harvest and NO₃⁻ post-harvest. Collectively, the changes in soils following harvest were related to shifts in available C and N. Pre-harvest measurements suggested that soil microbial communities may be co-limited by C and N, whereas C limitation was suggested post-harvest. Analyzing short-term microbial responses following harvest may bolster understanding of post-harvest successional processes, which is essential for determining the long-term sustainability of these practices.

Balancing horizontal accuracy and data collection efficiency with mapping-grade GPS receivers

Weusedmapping-gradeglobalpositioningsystem(GPS)receiverstoexaminepost-processedhorizontalmeasurement accuraciesduring nine separate visitstosix sitesthat eachcontained 10 test points withina second-growth Douglas-firforest.OurprimaryobjectivewastocompareGPSaccuraciesresultingfromtwodifferentreceiverconfigurations that vary in productivityand accuracy. A secondaryobjective wasto determine howaccuracies would change with recordinginterval (whether we averaged 1, 5, 10, 30 or 60 positions). We also examined which environment-andGPS-relatedfactorsmostinfluencedGPSaccuracy.Rootmeansquareerror(RMSE)atthe95percent confidencelevel(RMSE95)usingthe‘default’GPSsetting(positiondilutionofprecision(PDOP):6;SNR39;minimum elevation158)was6.0 m,whileRMSE95using ‘maximum’settings(PDOP: 20;SNR33;minimumelevation:58)was 8.0 macrossallsitesandrecordingintervals.Usingdefaultsettings,RMSE95decreasedfrom7.3 mwhenaveraging one position to 4.4 m when averaging 60. For maximum settings, RMSE95 decreased from 9.1 to 6.5 m. Our best models selected basal area, dilution of precision and weather, but not terrain. When using default settings the averagewait timewas 55 sec whencollecting one position and 236 sec whenaveraging60. Using maximum settings,averagewaittimewas8 secwhencollectingoneposition,and74 secwhenaveraging60positions.Theerrors that we report are acceptable for many forestry applications. These results should help users to balance productivity with accuracy when using mapping-grade GPS receivers in second-growth Douglas-fir forests.

Comparison of remote sensing and ground-based methods for determining residue burn pile wood volumes and biomass

Following forest harvest, residues left on site are often piled and burned. Quantification of residue piles is required in many jurisdictions to estimate billable waste, harvest efficiency, smoke emissions, C budgets, and available bioenergy biomass. Piled residues and harvested wood were measured on four blocks of a second-growth Douglas-fir forest in coastal British Columbia. Pile wood volumes were determined by two ground-based methods (a Waste and Residue Survey (WRS) and a geometric equation (EEP) used for smoke emissions) and by two geospatial methods using orthophotography (GIS) and LiDAR. Eight sample piles were disassembled to determine plot densities (PD) and packing ratios (PR). Plot density did not differ between the WRS and GIS method. Packing ratios of the EEP were 50% of that of the LiDAR method. LiDAR pile bulk volume and PR were negatively correlated. Choice of LiDAR digital elevation model had no significant effect on pile bulk volumes. The WRS method underestimated pile areas by 50% and the EEP method overestimated pile bulk volumes by two times. Pile wood volumes from the WRS method (20.0 m3·ha−1 (SE 2.8)) were 30%–50% of those for all other methods (46.1–60.4 m3·ha−1). The EEP method overestimated wood volume if nonspecific PRs were used. The residues to harvest ratio for the WRS method (3.3% (SE 0.45)) was lower than for all other methods (7.5%–9.6%). Total pile wood biomass from LiDAR was 25.4 t dry mass·ha−1 (SE 5.9). Ground-based methods are still required to determine PD or PR. Since their estimation depends on the method used to determine pile area or bulk volume, and may vary with pile size and type, they remain the major source of uncertainty in determining pile wood volumes. However, use of remote sensing techniques to determine the area or bulk volume of all piles in a cutblock can improve estimates of pile wood volumes and biomass.

Herb establishment in a young Pseudotsuga menziesii forest: a seven-year seed addition experiment1

The abundance of old-growth associated herbs in young Pseudotsuga menziesii forests is limited in part by the low availability of propagules of these species, but it remains unclear whether the slow post-logging development of old-growth species in younger forests also reflects a lack of microhabitats suitable for seed germination. This study attempts to fill an almost total lack of knowledge about germination of understory species in second-growth Douglas-fir forests, and in young coniferous forests in general, while providing a preliminary exploration of the relative importance of these two limiting factors. The ability of six common forest herbs to germinate in a 40-year-old Pseudotsuga menziesii stand was tested, and survival and growth were monitored for seven years. Five of the six species germinated well (8–50% germination), while one open-site species failed to germinate. After seven years, survival of four old-growth associated species was ∼10% (of the original seed number), while only 1% of seeds of a disturbance-adapted species were still present as seedlings. For all species, seedlings grew slowly and did not reach reproductive size, forming a seedling bank analogous to that of shade-tolerant tree seedlings. All old-growth associated species showed higher overall seedling numbers or greater survival in gaps than in non-gap microsites, and two species showed higher survival in the more mesic lower part of the watershed. Naturally occurring seedlings were rare and included only easily dispersed species that are forest generalists or characteristic of mature, but not of old-growth forests. I conclude that germination of late-seral herb species in young Pseudotsuga menziesii forests is not strictly microsite limited, but that these species are instead limited by a combination of low propagule availability and low resource levels with concomitant slow growth rates.

Species richness and community composition of mat-forming ectomycorrhizal fungi in old- and second-growth Douglas-fir forests of the HJ Andrews Experimental Forest, Oregon, USA

We investigated the species identity of mat-forming ectomycorrhizal (EM) fungi associated with old- and second-growth Douglas-fir stands. Using molecular analyses of rhizomorphs and EM root tips, we characterized 28 unique internal transcribed spacer sequences and considered them proxies for mat-forming EM species. In both stand age classes, one Athelioid species in the genus Piloderma dominated our sample of the mat-forming fungal community. In second-growth stands, the second most frequently encountered mat-forming EM species belonged to the genus Hysterangium. In old-growth stands, several Ramaria species were associated with a frequently encountered mat morphology but no species dominated the community. After using rarefaction analysis to standardize sampling effort, the total species richness did not differ statistically between old- and second-growth habitats. Both an abundance of infrequently encountered species and incomplete sampling of the mat-forming EM community may have limited our ability to detect potential differences in species richness. Several frequently encountered Piloderma species appear to have broad (holarctic) distributions and diverse host associations and their potential importance in forest ecosystems warrants further study.

Overstory Response to Alternative Thinning Treatments in Young Douglas-fir Forests of Western Oregon

An increase in land dominated by young second-growth Douglas-fir forests in the Pacific Northwest has coincided with heightened concerns over loss of old-growth habitat. In search of options for managing young forests to provide late-successional forest structures, the Young Stand Thinning and Diversity Study was designed to test the effectiveness of modified thinning in acceleration of late-successional structural characteristics. Thinning treatments included: a control, a light thin (typical of standard commercial thins), a heavy thin (densities lower than typically prescribed), and a light thin with gaps (stands thinned lightly with the addition of 0.2 hectare patch cuts evenly spaced throughout the stand). Early response (maximum of 5–7 years post-treatment) of overstory vegetation was examined. Average growth of Douglas-fir increased in all thinned stands, but growth of the largest Douglas-fir trees was only accelerated in the heavy thin. After thinning, the canopy of all thinned treatments was initi...

Effects of conifer basal area on understory herb presence, abundance, and flowering in a second-growth Douglas-fir forest

Although overstory trees exert competitive effects on understory plants, it is not clear how this competition affects the distribution and performance of herb species. This study seeks to clarify the relationship between understory herb performance and overstory basal area in second-growth Pseudotsuga menziesii (Mirb.) Franco stands. Data on 11 understory herb species were collected in a 100-ha watershed. Statistical models were constructed to control for the effects of slope, aspect, soil type, and distance from the central stream or peripheral ridge lines. Presence of old-growth associated and forest generalist herbs was positively associated with conifer basal area, as well as with north-facing aspects and proximity to the stream channel. Presence of release herbs, subordinate forest species that respond positively to canopy disturbance, was largely independent of measured variables. Abundance of individual species showed weak and inconsistent relationships with conifer basal area. In contrast, flowering of almost all species was negatively related to conifer basal area. Regression tree models suggested that conifer basal area may have stronger negative effects farther from the moist environments along stream channels. I conclude that patterns of presence of slow-growing forest species may be determined primarily by past events, while flowering better reflects current stand conditions.

Factors related to amphibian occurrence and abundance in headwater streams draining second-growth Douglas-fir forests in southwestern Washington

Forested headwaters of the US Pacific Northwest are an important habitat resource for a varied amphibian fauna. Factors related to occupancy and relative abundance for many of these species are poorly known, adding uncertainty to conservation decisions in managed forestlands. We sampled occurrence and abundance of amphibians in 40 perennial headwater streams traversing 50–65-year-old second-growth forests in the coast range of southwestern Washington. Streams were divided among basalt ( n=18) and marine sediment ( n=22) lithologies. Our samples resulted in collections of 1141 amphibians of six taxa — three stream-breeders and three woodland salamanders. Stream-breeding taxa included larval and neotenic giant salamanders ( Dicamptodon spp.), Columbia torrent salamanders ( Rhyacotriton kezeri) and larval tailed frogs ( Ascaphus truei). Pacific giant salamanders ( D. tenebrosus) and/or Cope’s giant salamanders ( D. copei) occupied 95% of sampled streams, accounting for 57% of total amphibians collected. Streams traversing basalt lithology had almost twice the giant salamander abundance of marine sediment streams. Adjusting for lithology, giant salamanders increased in abundance with increasing pool frequencies in combination with increasing large woody debris (LWD) accumulations in adjacent riparian areas, and decreased with increasing accumulations of large (>60 cm diameter) woody debris in the channel. Torrent salamanders occupied 53% of sampled streams. The likelihood of habitat occupancy by torrent salamanders increased as channel gradient increased and basin area decreased. When adjusted for basin area, torrent salamander abundance increased as the proportion of the active channel with flowing water decreased, and at more northerly aspects. Larval tailed frogs larva were found in 13% of sampled streams, exclusively occupying basalt streams at elevations >300 m. At least one of the three species of woodland salamanders ( Plethodon spp.) occupied habitats adjacent to 93% of sampled streams. Western red-backed salamanders ( P. vehiculum) were most ubiquitous, occupying habitats adjacent to 85% of sampled streams. Dunn’s salamanders ( P. dunni) occupied habitats adjacent to 58% of sampled streams, likelihood of occurrence increasing with increasing gradient of the steepest sideslope. Van Dyke’s salamanders ( P. vandykei) occupied habitats adjacent to three streams, all of which traversed basalt lithologies on north-facing slopes. Our results suggest that habitat quality for headwater amphibians in this region is strongly influenced by landform characteristics, including basin lithology. These associations provide managers an opportunity to improve headwater amphibian conservation strategies by prioritizing stream segments with respect to their likely amphibian fauna.

Amphibians in Managed, Second-Growth Douglas-Fir Forests

Few studies have been conducted on amphibian communities in managed, second-growth Douglas-fir (Pseudotsuga menziesii) forests in the Pacific Northwest. My objectives were to investigate patterns of amphibian species richness, biomass, and abundance, and explore habitat relationships in different age classes of second-growth Douglas-fir forests managed primarily for timber production. I sampled terrestrial amphibian populations occurring in 4 distinct age classes of managed forest in western Washington with pitfall traps from 1992 to 1994. Although these forests were devoid of residual old growth, and all stands were at least in their second rotation, they contained the same assemblage of amphibian species occurring in unmanaged Douglas-fir forests in this region. Terrestrial amphibian communities in managed forests were structured differently than in unmanaged forests, however, with higher proportions of northwestern salamanders (Ambystoma gracile) and western redback salamanders (Plethodon vehiculum), and a much lower proportion of tailed frogs (Ascaphus truei). Contrary to several previous studies, I found no evidence that variation in amphibian abundances was strongly influenced by the amount of coarse woody debris on the forest floor. Further research is needed to elucidate the effects of intensive timber management on coarse woody debris and its role in the persistence of terrestrial amphibian populations in managed forests. Because rotation-age stands (the oldest age class) had the highest amphibian species richness, total biomass, and total abundance, and contained significantly higher abundances of the ensatina (Ensatina eschscholtzii) and red-legged frog (Rana aurora) than all younger age classes, silvicultural strategies that increase the percentage of rotation-age forest conditions within managed landscapes are likely to enhance the long-term habitat quality of intensively managed forest landscapes for terrestrial amphibians.

Observations of Weasels in Second-Growth Douglas-Fir Forests in the Puget Trough, Washington

Mustela frenata and M. erminea are common mammalian predators in Pacific Northwest forests, yet very little is known about their ecology in this region. Forty-five Mustela spp. were captured in >200,000 trap nights. Mustela erminea were most often captured in thinned stands with dense understory but little coarse woody debris; M. frenata were most often captured in unthinned stands with little understory development but high levels of coarse woody debris. Management history may influence Mustela spp. abundance and diversity. Eight M. frenata dens were located; 2 were in arboreal stick nests. Evidence from 4 yr of small mammal research in second-growth Pseudotsuga menzeisii stands, including recovery of 58 radio transmitters placed on Glaucomys sabrinus, suggests that Mustela spp. are important predators of G. sabrinus in the Puget Trough. Our knowledge of wildlife ecology in Pacific Northwest forests is rapidly growing. Substantial information has been accumulated on game animals, threatened species, management indicator species, and vertebrate communities (Szaro and others 1988, Ruggiero and others 1991). However, little information exists on species without special legal status or species that are not sampled effectively with techniques used for study of vertebrate communities, such as weasels (Mustela spp.). Two weasels, M. frenata (long-tailed weasel) and M. erminea (short-tailed weasel), are sympatric in the Pacific Northwest (Ingles 1965). Incidental records of road-killed M. frenata suggest they are relatively abundant in some areas of the Puget Trough (Buchanan 1987). Little is known, however, of the ecological roles played by M. frenata or M. erminea in this region. Weasels are predators and, sometimes, prey; they consume small to medium-sized mammals and birds and, in turn, can be preyed upon by larger predators (for example, owls, hawks, and canids; Fagerstone 1987). Mustelids prey on a variety of species (King 1983, 1989); the size of prey seems related to the size of the species of mustelid. Both M. frenata and M. erminea exhibit sexual dimorphism, with males much larger than females (King 1989). M. erminea are small (males are 70 to 206 g, females are 28 to 85 g; Fagerstone 1987), and can easily enter the burrows of small prey, thus M. erminea specialize in preying on small rodents, particularly microtines (Erlinge 1981, King 1989). The larger M. frenata (males are 160 to 450 g, females are 80 to 250 g; Fagerstone 1987) also prey on microtines but seem to be less specialized; they hunt above ground more often, and they prey on larger species (for example, squirrels and lagomorphs) than do M. erminea (Fagerstone 1987). Weasels have been shown to be arboreal, but most observations of arboreal activity describe escape behavior or pursuit of prey (Nams and Beare 1982). In areas of sympatry, M. erminea are reported to be more abundant than M. frenata (Fagerstone 1987). We have been live-trapping arboreal and forest-floor small mammals in the Puget Trough for 4 yr (Carey and others, in press b). We recorded incidental captures and occurrences of weasels during live-trapping, and during radio-telemetry studies of Glaucomys sabrinlls (northern flying squirrels). Our objectives here are to summarize our records of weasel captures and weasel predation in the Puget Trough, and speculate on the role M. frenata and M. erminea play in the region's forest ecosystems.

Influence of ectomycorrhizal mat soils on lignin and cellulose degradation

The ectomycorrhizal fungus Hysterangium setchellii (Fisher) forms extensive hyphal mats at the soillitter interface with the roots of the host tree Douglas fir Pseudotsuga menziesii [(Mirb.) Franco]. Microbial biomass, and lignin and cellulose decomposition rates were measured seasonally for 1 year, using 14C techniques in ectomycorrhizal mat soils and adjacent non-mat soils in a second-growth Douglas fir forest. The microbial biomass and cellulose degradation rates were 3–6 times higher in ectomycorrhizal mat soils than in adjacent nonmat soils. Lignin degradation rates were higher in ectomycorrhizal mat soils than adjacent non-mat soils. Our data suggest that the ectomycorrhizal fungus H. setchellii provides a microenvironment with increased microbiological activity which results in faster lignin and cellulose decomposition.