Although nitrogen deposition and tropospheric ozone have impacted California forests for decades, broad scale studies of these impacts on forest growth and mortality are lacking. Because of the summer-dry climate over most of the state, forest responses to air pollution are expected to differ from more mesic climates. In this study, data from US Forest Service Forest Inventory and Analysis (FIA) permanent (remeasured) plots were combined with modelled atmospheric N and S deposition and an ozone exposure index to evaluate tree growth and mortality responses in California. Seven of 18 species exhibited significantly greater carbon increment (CI) in tree boles as N deposition increased, though the magnitude of the effect was quite small in most California forests. However, increases in CI were substantial in the coastal ecosections of central and northern California where precipitation and fog exposure are greatest. Redwood (Sequoia sempervirens (D. Don) Endl.) trees exhibited the strongest CI response to N deposition. Our model results imply a mean CI increase of 4.2 kg ha−1 yr−1 of C per kg ha−1 yr−1 of N deposition statewide versus 13.6 in the Central and Northern California Coast ecosections, where > 50% of the trees are redwood or tanoak (Lithocarpus densiflorus (Hook. & Arn.) Rehd.). Increased carbon sequestration rates in response to N deposition in these California coastal regions were similar to increases reported for Europe and global estimates. Nitrogen and S deposition significantly increased the odds of top damage and trees with crown damage exhibited higher mortality, although the effect was small. Elevated ozone exposure was associated with significantly larger rates of overall tree growth. However, for ozone-sensitive ponderosa pine at moderate ozone levels (ozone index values of ca. 20–30 ppb) and moderately-elevated N deposition (15–25 kg ha−1 hr−1), CI begins to decline, before increasing at higher pollution levels, presumably because of the fertilizing effect of N deposition; although data are limited for these more polluted conditions. Sulfur deposition in California forests was low, ranging from 0.3 to 3.1 kg ha−1 yr−1, but was associated with positive growth response in seven coniferous species. The combined effect of N and S deposition and ozone exposure statewide is a net increase in bole CI. However, aridity reduces the stimulatory growth effect of N deposition, and alters the threshold, capacity and sometimes the direction (e.g., S deposition) of the CI response to deposition, factors that need to be considered in global change models.
Large-scale, high-severity wildfires are a major challenge to the future social-ecological sustainability of fire-adapted forest ecosystems in the American West. Managing forests to mitigate this risk is a collective action problem requiring landowners and stakeholders within multi-ownership landscapes to plan and implement coordinated restoration treatments. Our research question is: how can we promote collective action to reduce wildfire risk and restore fire-resilient forests in the American West? To address this question we draw on collective action theory to produce an environmental public good (fire-resilient forests), and empirical examples of collective action from six projects that are part of the US Forest Service–Natural Resources Conservation Service Joint Chiefs’ Landscape Restoration Partnership. Our findings are based on qualitative, semi-structured interviews conducted with 104 individuals who were purposively selected to represent the diverse stakeholders involved in these projects. Fostering collective action to restore fire-resilient forests entails getting as many landowners (especially large landowners) to participate in wildfire risk reduction as possible to increase its areal extent; and landowner coordination in planning and implementing strategically designed restoration treatments to optimize their effectiveness. We identify factors that enabled and constrained landowner participation and coordination in the Joint Chiefs’ projects. Based on our findings and theory about when collective action will emerge, we specify a suite of practices to promote collective action for wildfire risk reduction across property boundaries, emphasizing incentives and enabling conditions. These include proactive education and outreach targeting landowners; multi-stakeholder processes with broad landowner representation to develop coordinated management approaches; financial and technical assistance to support fuels treatments on all ownerships within similar time frames; strong partnerships; and using common forestry professionals to plan and implement treatments on different ownerships (especially private lands). Our findings can inform cross-boundary management for landscape-scale conservation and restoration in other contexts.
This Special Issue addresses the intersections of outdoor recreation, nature-based tourism, and sustainability. Outdoor recreation and nature-based tourism provide essential benefits to individuals, communities, and society and thereby contribute to sustainability. Equitable provision of opportunities, cultural variations in desired experiences, barriers to outdoor recreation, and diverse perceptions of both nature and recreation add to the complexity in outdoor recreation and nature-based tourism service delivery. Outdoor recreation and nature-based tourism occur within a socioecological system with feedback loops to changing social, economic, technological, and ecological conditions. On a global scale, climate change and other disturbance factors are impacting ecosystems and opportunities, increasing the importance of adaptation strategies for longer-term planning. Population growth and regional shifts in demographics and distribution (e.g., urbanization), as well as socioeconomic trends, affect who engages in outdoor recreation and nature-based tourism, opportunities sought, nature access, and governance of outdoor services. Overall the complexity of sustainable outdoor recreation and tourism may suggest a need for different approaches to service delivery, culture change among service providers and managers of natural spaces, and novel approaches to inclusive governance and shared stewardship. Given the clear importance of outdoor recreation and nature-based tourism to society, we invite you to consider this initial introduction to our assembled collection, which is meant to advance our understanding of the intersections of outdoor recreation, nature-based tourism, and sustainability.
Exposure of nontarget wildlife to anticoagulant rodenticides (AR) is a global conservation concern typically centered around urban or agricultural areas. Recently, however, the illegal use of ARs in remote forests of California, USA, has exposed sensitive predators, including the federally threatened northern spotted owl (Strix occidentalis caurina). We used congeneric barred owls (S. varia) as a sentinel species to investigate whether ARs pose a threat to spotted owls and other old-forest wildlife in northern regions of the Pacific Northwest. We analyzed the liver tissue from 40 barred owls collected in Oregon and Washington and confirmed exposure to ≥1 AR compounds in 48% of the owls examined. Brodifacoum, an extremely toxic second-generation AR, was the most common compound detected (89% of positive cases), followed by bromadiolone (11%), difethialone (11%), and warfarin (5%). Brodifacoum was also detected in one barred owl and one spotted owl opportunistically found dead (liver concentrations were 0.091 and 0.049 μg/g, respectively). We found no evidence that exposure varied with proximity to developed and agricultural areas, or among different study areas, age-classes, and sexes. Rather, exposure was ubiquitous, and the rates we observed in our study (38–64%) were similar to or greater than that reported previously for barred owls in California (40%). Together these studies indicate widespread contamination in forested landscapes used by spotted owls and other wildlife of conservation concern. Owls collected in older forests may have been exposed via illegal use of ARs, highlighting a mounting challenge for land managers and policy makers.
Public officials and stakeholders who want to advance watershed protection may want to consider how ballot referendum design can serve as a nudge in voting behaviors. We extend the research literature on voter preferences by using behavioral economics theory to provide new insights into voter behaviors towards watershed conservation referendums. We drew upon observations from 76 separate watershed protection referendums, conducted in the eastern U.S. from 1991 to 2013, and evaluated the wording of the ballot statement to determine their potential influence on voter support and the psychology of voting. Data were fitted to weighted least squares regression models to allow for broader inferences about voting behaviors. We found shorter ballot referendums with broad or vague descriptions of expected benefits and fewer descriptions of funding mechanisms likely increased the perceived odds of a favorable outcome and subsequently increased likelihood of a yes vote.
This is a guide for the collection of reference samples of trees to enable the identification of species and/or geographical origin of woody material. It is an update of the sampling section of the GTTN standards and guidelines (Ekué 2014) and builds further on a discussion initiated during a workshop held in Hamburg at the Thünen Institute for Wood Research in 2014. If you are looking for support on how to collect test samples, see the UNODC guide (UNODC 2016). To enable the implementation of the different laws regulating the trade in illegal wood, reference databases for various timber tracking tools are urgently needed for at least the most traded and endangered tree species. The Global Timber Tracking Network (GTTN) is building a central database where not only the reference data can be stored but which will also function as a sample locator. Having a common sampling guide will facilitate meaningful exchange of samples. In addition, to optimise the use of wood/wood product identification (taxonomic identity or geographic origin) in support of law enforcement, the guide anticipates upcoming developments to combine (Paredes Villanueva 2018) different timber identification methods (Dormontt et al. 2015, Lowe et al. 2016) such as wood anatomy (Koch and Schmitt 2015, Helmling et al. 2018), DNA-based methods (Jolivet and Degen 2012, Blanc-Jolivet et al. 2018, Chaves et al. 2018), stable isotopes (Paredes-Villanueva et al. in preparation, Vlam et al. 2018), DART TOFMS (Lancaster and Espinoza 2012, Espinoza et al. 2015, Deklerck et al. 2017, Paredes-Villanueva et al. 2018) and NIRS (Pastore et al. 2011, Bergo et al. 2016, Snel et al. 2018). This sampling guide is written to make sharing of samples between researchers specialised in different timber tracking methods possible, as samples should ideally come from the same location in the tree, from the same individual and from well-identified trees when combining methods.
This guide is intended for scientists, to provide all the information needed to get the most out of sampling campaigns for timber identification purposes. This information should allow setting up a sampling protocol adapted to the specific goal of the research project, the conditions of the sampling area and the background of the people who will do the sampling. Note that this guide is to collect reference samples and hence relatively high amounts of samples from different individuals are needed to take the variability of a species into account. Once reference data have been developed for a tree species for one or more identification methods, however, only one sample of an unidentified wooden object is often sufficient to determine its identity
Atmospheric nitrogen and sulfur pollution increased over much of the United States during the twentieth century from fossil fuel combustion and industrial agriculture. Despite recent declines, nitrogen and sulfur deposition continue to affect many plant communities in the United States, although which species are at risk remains uncertain. We used species composition data from >14,000 survey sites across the contiguous United States to evaluate the association between nitrogen and sulfur deposition and the probability of occurrence for 348 herbaceous species. We found that the probability of occurrence for 70% of species was negatively associated with nitrogen or sulfur deposition somewhere in the contiguous United States (56% for N, 51% for S). Of the species, 15% and 51% potentially decreased at all nitrogen and sulfur deposition rates, respectively, suggesting thresholds below the minimum deposition they receive. Although more species potentially increased than decreased with nitrogen deposition, increasers tended to be introduced and decreasers tended to be higher-value native species. More vulnerable species tended to be shorter with lower tissue nitrogen and magnesium. These relationships constitute predictive equations to estimate critical loads. These results demonstrate that many herbaceous species may be at risk from atmospheric deposition and can inform improvements to air quality policies in the United States and globally.
Slow ecological processes challenge conservation. Short-term variability can obscure the importance of slower processes that may ultimately determine the state of a system. Furthermore, management actions with slow responses can be hard to justify. One response to slow processes is to explicitly concentrate analysis on state dynamics. Here, we focus on identifying drivers of Northern Spotted Owl (Strix occidentalis caurina) territorial occupancy dynamics across 11 study areas spanning their geographic range and forecasting response to potential management actions. Competition with Barred Owls (Strix varia) has increased Spotted Owl territory extinction probabilities across all study areas and driven recent declines in Spotted Owl populations. Without management intervention, the Northern Spotted Owl subspecies will be extirpated from parts of its current range within decades. In the short term, Barred Owl removal can be effective. Over longer time spans, however, maintaining or improving habitat conditions can help promote the persistence of northern spotted owl populations. In most study areas, habitat effects on expected Northern Spotted Owl territorial occupancy are actually greater than the effects of competition from Barred Owls. This study suggests how intensive management actions (removal of a competitor) with rapid results can complement a slower management action (i.e., promoting forest succession).
Coastal Alaska forests consist of 2.6 million hectares of productive timberland and constitute the largest terrestrial carbon reservoir in the state. It has become increasingly urgent to understand potential climate-induced changes in forest structural and species composition in this region. Based on in situ data from 544 permanent sample plots (PSPs) for calibration and 244 PSPs for validation, we developed a climate-sensitive density-dependent, species-, and size-specific matrix model (CSMatrix-AK), to predict fine-scale dynamics of coastal Alaska forests from the present to Year 2100 under three climate scenarios – Representative Concentration Pathway (RCP) 4.5, RCP6.0, and RCP8.5. With post-sample validation, we showed that the CSMatrix-AK model was more accurate than other existing models for the region. Under low-intensity and high-frequency stochastic shocks which represented natural disturbances typical for the region, we projected a gradual decline of Sitka spruce, a major commercial species in the region, and a significantly lower level of total stand basal area under all three climate scenarios. The results suggest that timber industry, landowners and managers, policymakers, and local communities will need to prepare for substantial impacts of climate change on Coastal Alaska forests and the regional forestry sector. Our CSMatrix-AK model provides a useful tool to better inform the stakeholders of such changes and lays the foundation for adaptive forest management to sustain forests and associated ecosystem services in the region.