Density Management in the 21 st Century: West Side Story PNW-GTR-880 Riparian Buffers and Thinning in Headwater Drainages in Western Oregon: Aquatic Vertebrates and Habitats

Abstract Th e Density Management and Riparian Buff er Study (DMS) of western Oregon is a template for numerous research projects on managed federal forestlands. Herein, I review the origins of Riparian Buff er Study component and summarize key fi ndings of a suite of associated aquatic vertebrate projects. Aquatic vertebrate study objectives include characterization of headwater fauna and habitats, and examination of the eff ects on headwater-dwelling species of combined buff er-andthinning treatments in years 1, 2, 5, and 10 post-treatment. Some treatment eff ects have emerged, with negative eff ects on bank amphibian counts occurring in treatments with the narrowest buff ers 10 years post-thinning. Nevertheless, all taxa appear to be persisting at sites. Instream amphibians, in particular, appear to be highly resilient to the types of disturbances resulting from the thinning and buff er treatments of the DMS

The ecological and behavioral dynamics of breeding in three sympatric anuran amphibians

Breeding ecology and behavior were investigated in a field study of three sympatric anuran amphibians in the Oregon Cascade Mountains: the western toad (Bufo boreas), the Cascades frog (Rana cascadae) and the Pacific treefrog (Hyla regilla). A comprehensive study of the western toad mating system was conducted at three populations during five years (15 explosive-breeding aggregations). Two size-dependent pairing patterns (a large male mating advantage and size assortative mating) occurred variably among aggregations and among breeding days within aggregations. Body size variation and the degree of sexual size dimorphism explained much of the mating pattern variability. Field observations and experiments suggest nonrandom mating resulted from male-male exploitative competition for mates and passive female choice of mates. Density and sex ratio had little affect on pairing behavior. Sporadic mass-predation on breeding toads was associated with pair-separations and may have influenced pairing patterns. Toads showed sex and site differences in multiyear breeding schedules, recapture/survival rates, and yearly and multiyear cumulative mating success. The opportunity for selection on toads was partitioned into 3 selection episodes: adult survival, mating success, and fertility. The largest contributors to selection opportunity were mating success for males, and clutch size (fertility) for females. At some aggregations, the opportunity for sexual selection on males was the lowest recorded for anurans. Temporal and spatial synchrony of breeding occurred with Cascade frogs and Pacific treefrogs. During two years, interspecific interactions resulted in the displacement of treefrogs by Cascade frog males from the warmer areas of the ice-covered pond

Near-Term Effects of Repeated-Thinning with Riparian Buffers on Headwater Stream Vertebrates and Habitats in Oregon, USA

We examined the effects of a second-thinning harvest with alternative riparian buffer management approaches on headwater stream habitats and associated vertebrates in western Oregon, USA. Our analyses showed that stream reaches were generally distinguished primarily by average width and depth, along with the percentage of the dry reach length, and secondarily, by the volume of down wood. In the first year post-harvest, we observed no effects of buffer treatment on stream habitat attributes after moderate levels of thinning. One of two “thin-through” riparian treatments showed stronger trends for enlarged stream channels, likely due to harvest disturbances. The effects of buffer treatments on salamanders varied among species and with habitat structure. Densities of Plethodon dunni and Rhyacotriton species increased post-harvest in the moderate-density thinning with no-entry buffers in wider streams with more pools and narrower streams with more down wood, respectively. However, Rhyacotriton densities decreased along streams with the narrowest buffer, 6 m, and P. dunni and Dicamptodon tenebrosus densities decreased in thin-through buffers. Our study supports the use of a 15-m or wider buffer to retain sensitive headwater stream amphibians.Keywords: Amphibians, Plethodon, Rhyacotriton, Pacific Northwest, Dicamptodon, Timber harvest, Salamander

Effects of riparian buffer width on wood loading in headwater streams after repeated forest thinning

Forested riparian buffer zones are used in conjunction with upland forest management, in part, to provide for the recruitment for large wood to streams. Small headwater streams account for the majority of stream networks in many forested regions. Yet, our understanding of how riparian buffer width influences wood dynamics in headwater streams is relatively less developed compared to larger fish-bearing streams. The effects of riparian buffer width on instream wood loading after thinning can be difficult to discern due to the influence of basin characteristics and reach-scale geomorphology on wood recruitment, breakage and redistribution. We assessed the relationships between instream wood loading, geomorphology and riparian buffer width in small headwater streams after upland thinning. Then we examined the distances between pieces of stream wood and their sources, or the distance from which wood volumes were recruited to these streams. Data were collected along 34 stream reaches at six different sites in a replicated field experiment, comparing three no-harvest streamside buffer treatments (∼6-m, 15-m minimum, and ∼70-m widths). At each site, second-growth forests were thinned first to 200 trees per ha [tph] and ∼10 years later to 85 tph, alongside an unthinned reference unit (∼400 tph). We measured wood loading (m³/100 m) four times: (1) prior to thinning; (2) year 5 post-1st thinning; (3) immediately prior to the 2nd thinning; and (4) year 1 post-2nd thinning. The majority of wood volume was in late stages of decay, most likely biological legacies from the previous forest stand, and distributed along the streambank. Surprisingly, wood volume in early stages of decay was higher in stream reaches with a narrow 6-m buffer than in stream reaches with larger 15- and 70-m buffers and the unthinned reference units. Additionally, wood volume increased with drainage basin area. Only 45% of wood in late stages of decay could be associated with a particular source. Yet, 82% and 85% of sourced wood in early and late stages of decay, respectively, originated from within 15 m of streams. Expected continue low rates will likely result in declining volumes of wood in late stages of decay. Thinning and directional felling of logs into to streams could be used to augment wood volumes in the near term, and accelerate the development of large-diameter logs for future inputs. However, the relationship between instream wood loading and basin area suggests that instream wood loading depends on management across the entire watershed.Keywords: Forest management, Stream management zone, Pacific Northwest, Density management, Coarse woody debris, Best management practice

Host Identity Matters in the Amphibian-Batrachochytrium dendrobatidis System: Fine-Scale Patterns of Variation in Responses to a Multi-Host Pathogen

Species composition within ecological assemblages can drive disease dynamics including pathogen invasion, spread, and persistence. In multi-host pathogen systems, interspecific variation in responses to infection creates important context dependency when predicting the outcome of disease. Here, we examine the responses of three sympatric host species to a single fungal pathogen, Batrachochytrium dendrobatidis, which is associated with worldwide amphibian population declines and extinctions. Using an experimental approach, we show that amphibian species from three different genera display significant differences in patterns of pathgen-induced mortality as well as the magnitude and temporal dynamics of infection load. We exposed amphibians to one of four inoculation dose treatments at both larval and post- metamorphic stages and quantified infection load on day 8 and day 15 post-inoculation. Of the three species examined, only one (the Pacific treefrog; Pseudacris regilla) displayed "dose-dependent" responses; survival was reduced and infection load was elevated as inoculation dose was increased. We observed a reduction in survival but no differences in infection load across pathogen treatments in Cascades frogs (Rana cascadae). Western toads (Anaxyrus boreas) displayed differences in infection load but no differences in survival across pathogen treatments. Within species, responses to the pathogen varied with life history stage, and the most heavily infected species at the larval stage was different from the most heavily infected species at the post-metamorphic stage. Temporal changes in infection load were species and life history stage-specific. We show that variation in susceptibility to this multi-host pathogen is complex when viewed at a fine-scale and may be mediated through intrinsic host traits

Management of Riparian Buffers: Upslope Thinning with Downslope Impacts

We examined the potential of using upslope density management to influence growth and drought tolerance of trees in untreated downslope riparian forests. Increment cores from Douglas-fir trees in three mature stands in western Oregon, USA, were collected and measured. Trees responded to an apparent edge effect up to 15 m downslope of thinned areas but not downslope of gaps. Growth responses in riparian trees were not affected by slope or potential solar radiation (as a function of location and topography). In addition, in a retrospective analysis of tree growth and allocation patterns (represented by the ratio of earlywood to latewood) and climate after treatment over a 12-year period, trees in our study area did not appear to be water limited and did not show a strong correlation with regional drought metrics. We hypothesize that vegetation layers in these riparian forest stands responded differentially to additional resources becoming available as a result of thinning, with overstory trees in riparian areas responding downslope of thinned uplands and subdominant canopy layers responding downslope of gaps. Our study demonstrates that managers can affect riparian forests with upland treatments to a limited spatial extent, which may be the only option in areas where direct riparian management is restricted due to concerns for other ecosystem services.Keywords: riparian management, western Oregon, thinning, climate, drought, riparian zon

DNA repair and resistence to UV-B radiation in western spotted frogs

assessed DNA repair and resistance to solar radiation in eggs of members of the western spotted frog complex (Rana pretiosa and R. luteiventris), species whose populations are suffering severe range reductions and declines. Specifically, we measured the activity of photoreactivating enzyme (photolyase) in oocytes of spotted frogs. In some species, photoreactivation is the most important mechanism for repair of UV-damaged DNA. Using field experiments, we also compared the hatching success of spotted frog embr yos at natural oviposition sites at three elevations, where some embr yos were subjected to ambient levels of UV-B radiation and others were shielded from UV-B radiation. Compared with other amphibians, photolyase activities in spotted frogs were relatively high. At all sites, hatching success was unaffected by UV-B. Our data support the interpretation that amphibian embr yos with relatively high levels of photolyase are more resistant to UV-B radiation than those with lower levels of photolyase. At the embr yonic stage, UV-B radiation does not presently seem to be contributing to the population declines of spotted frogs.Peer reviewe

Heterogeneous Occupancy and Density Estimates of the Pathogenic Fungus Batrachochytrium dendrobatidis in Waters of North America

Biodiversity losses are occurring worldwide due to a combination of stressors. For example, by one estimate, 40% of amphibian species are vulnerable to extinction, and disease is one threat to amphibian populations. The emerging infectious disease chytridiomycosis, caused by the aquatic fungus Batrachochytrium dendrobatidis (Bd), is a contributor to amphibian declines worldwide. Bd research has focused on the dynamics of the pathogen in its amphibian hosts, with little emphasis on investigating the dynamics of free-living Bd. Therefore, we investigated patterns of Bd occupancy and density in amphibian habitats using occupancy models, powerful tools for estimating site occupancy and detection probability. Occupancy models have been used to investigate diseases where the focus was on pathogen occurrence in the host. We applied occupancy models to investigate free-living Bd in North American surface waters to determine Bd seasonality, relationships between Bd site occupancy and habitat attributes, and probability of detection from water samples as a function of the number of samples, sample volume, and water quality. We also report on the temporal patterns of Bd density from a 4-year case study of a Bd-positive wetland. We provide evidence that Bd occurs in the environment year-round. Bd exhibited temporal and spatial heterogeneity in density, but did not exhibit seasonality in occupancy. Bd was detected in all months, typically at less than 100 zoospores L⁻¹. The highest density observed was ~3 million zoospores L⁻¹. We detected Bd in 47% of sites sampled, but estimated that Bd occupied 61% of sites, highlighting the importance of accounting for imperfect detection. When Bd was present, there was a 95% chance of detecting it with four samples of 600 ml of water or five samples of 60 mL. Our findings provide important baseline information to advance the study of Bd disease ecology, and advance our understanding of amphibian exposure to free-living Bd in aquatic habitats over time

Mapping the Global Emergence of Batrachochytrium dendrobatidis, the Amphibian Chytrid Fungus

The rapid worldwide emergence of the amphibian pathogen Batrachochytrium dendrobatidis (Bd) is having a profound negative impact on biodiversity. However, global research efforts are fragmented and an overarching synthesis of global infection data is lacking. Here, we provide results from a community tool for the compilation of worldwide Bd presence and report on the analyses of data collated over a four-year period. Using this online database, we analysed: 1) spatial and taxonomic patterns of infection, including amphibian families that appear over-and under-infected; 2) relationships between Bd occurrence and declining amphibian species, including associations among Bd occurrence, species richness, and enigmatic population declines; and 3) patterns of environmental correlates with Bd, including climate metrics for all species combined and three families (Hylidae, Bufonidae, Ranidae) separately, at both a global scale and regional (U. S. A.) scale. These associations provide new insights for downscaled hypothesis testing. The pathogen has been detected in 52 of 82 countries in which sampling was reported, and it has been detected in 516 of 1240 (42%) amphibian species. We show that detected Bd infections are related to amphibian biodiversity and locations experiencing rapid enigmatic declines, supporting the hypothesis that greater complexity of amphibian communities increases the likelihood of emergence of infection and transmission of Bd. Using a global model including all sampled species, the odds of Bd detection decreased with increasing temperature range at a site. Further consideration of temperature range, rather than maximum or minimum temperatures, may provide new insights into Bd-host ecology. Whereas caution is necessary when interpreting such a broad global dataset, the use of our pathogen database is helping to inform studies of the epidemiology of Bd, as well as enabling regional, national, and international prioritization of conservation efforts. We provide recommendations for adaptive management to enhance the database utility and relevance