Climate Adaptive Silviculture for the City: Practitioners and Researchers Co-create a Framework for Studying Urban Oak-Dominated Mixed Hardwood Forests

Urban forested natural areas are an important component of the forest and tree canopy in northeastern United States urban areas. Although similar to native forests in surrounding regions in structure, composition, and function, these natural areas are threatened by multiple, co-occurring biological and climate stressors that are exacerbated by the urban environment. Furthermore, forests in cities often lack application of formal silvicultural approaches reliant upon evidence-based applied ecological sciences. These include both urban- and climate-adapted silvicultural techniques to increase the resilience and sustainability of native forests in cities. With this in mind, we convened a group of urban forest practitioners and researchers from along a latitudinal gradient in the northeastern United States to participate in a workshop focused on co-developing long-term, replicated ecological studies that will underlie the basis for potential silvicultural applications to urban forests. In this article we review the process and outcomes of the workshop, including an assessment of forest vulnerability, and adaptive capacity across the region, as well as shared management goals and objectives. We discuss the social and ecological challenges of managing urban oak-dominated mixed hardwood forests relative to non-urban forests and identify potential examples of urban- and climate-adapted silviculture strategies created by practitioners and researchers. In doing so, we highlight the challenges and need for basic and long-term applied ecological research relevant to silvicultural applications in cities.

Characterizing Stand and Biomass Tables from Diameter Distribution Models: A Case Study for Mixed-Hardwood Forests in Eastern Tennessee, USA

Accurately assessing forest structure and productivity is critical to making timely management decisions and monitoring plant communities. This study aims to evaluate the prediction accuracy of site-level stand and biomass tables from the diameter distribution models. The efficacy of the single Weibull function and two finite mixture models was compared for six species groups on three mixed-hardwood sites in eastern Tennessee, USA. To evaluate model performance, two types of stand/biomass tables were generated. The first type was constructed from all species on a given site (site-specific), whereas the second type was built for a single species from all sites (species-specific). Results indicate that both types of stand and biomass tables were consistently well quantified by the two-component mixture model in terms of goodness of fit, parsimony and robustness. The two-component mixture model better characterized the complex, multimodal diameter distributions than the single Weibull model, which underpredicted the upper portion of the distributions. The three-component model tends to overfit the data, which results in lower prediction accuracy. Among the three models examined, the two-Weibull mixture model is suggested to construct site-level stand/biomass tables, which provides more reliable and accurate predictions to assess forest structure and product class. Study Implications Compared to pine monocultures, diameter distribution models for upland mixed-hardwood forests in the Southeastern United States have not been widely explored. Mixed-hardwood forests not only supply high-quality timber for domestic and international uses, but also provide various ecosystem services and essential habitats for wildlife. The finite mixture model has been proposed for characterizing the irregular forms of diameter distribution curves, but the reliability of this method has not been explicitly examined for a wide variety of species. This study provided insights for natural resources managers to select appropriate models when modeling stand and biomass tables for mixed-hardwood forests.

Light Detection and Ranging (LiDAR) Assisted Detection of Rock Outcrops in Appalachian Hardwood Forests

The identification of small habitat features embedded within forest ecosystems is a challenge for many wildlife inventory and monitoring programs, especially for those involving rock outcrop specialist taxa. Rock outcrops are often difficult to remotely detect in dense Appalachian hardwood forests, as most outcrops remain hidden under the forest canopy and therefore invisible when relying on aerial orthoimagery to pinpoint habitat features. We investigated the ability for light detection and ranging (LiDAR) point cloud data to identify small rock outcrops during the environmental assessment phase of a proposed management project on the Jefferson National Forest in Virginia, USA. We specifically compared this approach to the visual identification of rock outcrops across the same area using aerial orthoimagery. Our LiDAR-based approach identified three times as many rock outcrop sites as aerial orthoimagery, resulting in the field-verification of four times as many previously-unknown populations of green salamanders Aneides aeneus, a rock outcrop specialist amphibian of high conservation concern, than would have been possible if relying on aerial orthoimagery alone to guide surveys. Our results indicate that LiDAR-based methods may provide an effective, efficient, and low-error approach that can remotely identify below-canopy rock outcrops embedded within Appalachian forests, especially when researchers lack pre-existing knowledge of local terrain and the location of habitat features.

Pollination Potential of Riparian Hardwood Forests—A Multifaceted Field-Based Assessment in the Vistula Valley, Poland

Riparian forests with oaks, ashes and elms, now highly fragmented and rare in Europe, are considered hotspots for ecosystem services. However, their capacity to provide pollination seems to be quite low, although reports from in-situ research supporting this view are scarce. Our goal was therefore to thoroughly assess their pollination potential based on multifaceted field measurements. For this, we selected six test sites with well-developed riparian hardwood forests, located in the agricultural landscape along the middle Vistula River in Poland. We used seven indicators relating to habitat suitability (nesting sites and floral resources) and pollinator abundance (bumblebees and other Apoidea) and propose a threshold value (AdjMax) based on value distribution and Hampel’s test to indicate the level of pollination potential for this type of riparian forest. The obtained AdjMax for bumblebee density was 500 ind. ha−1, for Apoidea abundance—0.42 ind. day−1, while for nectar resources—200 kg ha−1. We demonstrate that the investigated small patches of the riparian hardwood forest have a higher pollination potential than reported earlier for riparian and other broadleaved temperate forests, but the indicators were inconsistent. As forest islands in the agricultural landscape, riparian hardwood forests play an important role in maintaining the diversity and abundance of wild pollinators, especially in early spring when there is still no food base available elsewhere.

Phytosociological analysis of noble hardwood forests (Ostryo-Tilienion platyphylli) in the Karst and its neighbouring regions (SW Slovenia)

In SW Slovenia, at Gora under Železna Vrata and Petnik gorge near Branik – both on the northern edge of the Karst, in the collapse doline Orleška Draga at Sežana and under Brkinski Rob at the contact of the Karst and Brkini Hills, we conducted a phytosociological analysis of the stands whose tree layer is dominated by Tilia platyphyllos, T. cordata, Acer pseudoplatanus, Ulmus glabra, in places also Carpinus betulus and Ostrya carpinifolia, and classified them into three associations, Corydalido ochroleucae-Aceretum pseudoplatani, Paeonio officinalis-Tilietum platyphylli and Fraxino orni-Aceretum pseudoplatani. The latter was described as a new. Also new is a secondary large-leaved lime association Lamio orvalae-Tilietum platyphylli on the sites of montane beech forests (Lamio orvalae-Fagetum) in the Čepovan valley, at the contact of the Dinaric and sub-Mediterranean phytogeographical regions of Slovenia.

Northern Long-Eared Bat (Myotis septentrionalis) Day-Roost Loss in the Central Appalachian Mountains following Prescribed Burning

Before the arrival of white-nose syndrome in North America, the northern long-eared bat (Myotis septentrionalis) was a common cavity-roosting bat species in central Appalachian hardwood forests. Two successive prescribed burns on the Fernow Experimental Forest, West Virginia, in 2008 and 2009, were shown to positively affect maternity colony day-roost availability and condition in the near-term. However, whether immediate benefits were temporary and if burned forests actually experienced an accelerated loss of trees and snags possibly suitable for bats more than background loss in unburned forests became an important question following the species’ threatened designation. In 2016, we revisited 81 of 113 northern long-eared bat maternity colony day-roosts initially discovered in 2007–2009 with the objective of ascertaining if these trees and snags were still standing and thus potentially “available” for bat use. Initial tree or snag stage condition class and original year of discovery were contributory factors determining availability by 2016, whereas exposure to prescribed fire and tree/snag species decay resistance were not. Because forest managers may consider using habitat enhancement to improve northern long-eared bat survival, reproduction, and juvenile recruitment and must also protect documented day-roosts during forestry operations, we conclude that initial positive benefits from prescribed burning did not come at the expense of subsequent day-roost loss greater than background rates in these forests at least for the duration we examined.

Mid-term Impacts of Silvicultural Treatments on Soils and Understory Plant Diversity in Temperate Hardwood Forests of Quebec, Canada.

Background: Short-term effects of silvicultural treatments on soil properties and understory vegetation in temperate hardwood forests are well documented, but few studies have examined longer term effects of treatment intensity. We hypothesized that short-term effects of silvicultural treatments on understory plant diversity do persist over the medium-term (20 years after treatment); the magnitude of these effects would be proportional to the intensity of canopy and soil disturbance.Methods: Soil properties (pH, total C and N, extractable P, exchangeable bases) and understory community diversity indices were measured in six experimental sites along a longitudinal gradient that covered different climatic and edaphic conditions in the yellow birch-sugar maple bioclimate domain. Reference condition, i.e. control forest with no anthropogenic disturbance for at least 80 years (CON) were compared to twenty years old regeneration treaments representing a gradient of canopy and soil disturbance intensity: single-tree selection cuts (SIN); group-selection cuts (GRP); and group-selection cuts with scarification (GRPS). Results: Geographic location of sites explained more variation in soil properties and community composition than did treatments. Species richness in both group-selection treatments was higher than that in CON forests. However, understory plant equitability and beta diversity among sites in GRP and GRPS were lower than in SIN and CON forests. More intense treatments (GRP and GRPS) increased the relative occurrence of vegetatively reproducing heliophilic plants, a trait syndrome associated with adaptations to disturbed environments. These treatments also contributed to the medium-term persistence of recalcitrant competitor species (e.g., Rubus idaeus, Prunus pensylvanica) whereas soil scarification appears to have negative sustained effects on species known to be sensitive to regeneration treatments (e.g. Monotropa uniflora, Dryopteris spinulosa).Conclusion: Of the treatments studied, single-tree selection cutting appears to be the most appropriate silvicultural treatment for maintaining soil functions and heterogeneous understory plant communities with compositions and structures similar to natural forests, while more intense treatments rather maintain and expand species that are better adapted to a wider range of environmental conditions, including open environments.

Influence of individual tree characteristics, spatial structure and logging history on tree-related microhabitat occurrence in North American hardwood forests

Background Tree-related microhabitats (hereafter, “TreMs”) are key components of forest biodiversity but they are still poorly known in North American hardwood forests. The spatial patterns of living trees bearing TreMs (hereafter, “TreM-trees”) also remain to be determined. As logging practices can lead to a loss of TreM-trees and of their associated biodiversity, it is essential to identify the factors explaining TreM occurrence to better integrate them into forest management. We therefore inventoried TreMs in 4 0.5-ha survey strips in northern hardwood forests in Quebec, Canada, while recording the spatial location of each tree. Two strips were located in unmanaged old-growth forests, and 2 were in forests managed under selection cutting. All 4 stands were dominated by sugar maple (Acer saccharum Marsh.) and American beech (Fagus grandifolia Ehrn.). Beech bark disease, an exotic pathology, was observed in all the strips. Results Large diameter at breast height and low tree vigor were the main characteristics explaining the presence of TreMs at the tree scale. TreM-trees presented slight spatial aggregation patterns. These aggregates, however, were not well-defined and were generally constituted by a large number of trees bearing few different types of TreMs. Two TreM classes (broken branch or top and woodpecker lodge) also presented a spatial aggregation. Logging practices had no significant effect on TreM occurrence. Beech bark disease increased the frequency of senescent beeches. The impact of this pathology on TreMs was however mitigated by the small size of infected trees and probably by the short time elapsed since its appearance. Conclusion The factors explaining the presence and abundance of TreMs on trees has so far been little studied in North American hardwood forests. Our results highlight that TreM-tree characteristics in the surveyed forests are consistent with those of previous studies conducted in other forest types and regions (e.g., Europe or Northwestern America). To our knowledge, this study is also the first to identify a spatial aggregation of TreM-trees and of specific TreM classes. It will be nevertheless necessary to determine whether the small impact of logging activities we observed results from current or past management practices.