Mixed Forest Research Articles

Dominant Tree Species and Litter Quality Govern Fungal Community Dynamics during Litter Decomposition.

Litter decomposition is a crucial biochemical process regulated by microbial activities in the forest ecosystem. However, the dynamic response of the fungal community during litter decomposition to vegetation changes is not well understood. Here, we investigated the litter decomposition rate, extracellular enzyme activities, fungal community, and nutrient cycling-related genes in leaf and twig litters over a three-year decomposition period in a pure Liquidamabar formosana forest and a mixed L. formosana/Pinus thunbergii forest. The result showed that during the three-year decomposition, twig litter in the mixed forest decomposed faster than that in the pure forest. In both leaf litter and twig litter, β-cellobiosidase and N-acetyl-glucosamidase exhibited higher activities in the mixed forest, whereas phosphatase, β-glucosidase, and β-xylosidase were higher in the pure forest. The fungal α-diversity were higher in both litters in the pure forest compared to the mixed forest, with leaf litter showing higher α-diversity than twig litter. Fungal species richness and α-diversity within leaf litter increased as decomposition progressed. Within leaf litter, Basidiomycota dominated in the mixed forest, while Ascomycota dominated in the pure forest. Funguild analysis revealed that Symbiotroph and ectomycorrhizal fungi were more abundant in the mixed forest compared to the pure forest. In the third-year decomposition, genes related to phosphorus cycling were most abundant in both forests, with the pure forest having a higher abundance of cex and gcd genes. Fungal community structure, predicted functional structure, and gene composition differed between the two forest types and between the two litter types. Notably, the fungal functional community structure during the first-year decomposition was distinct from that in the subsequent two years. These findings suggest that dominant tree species, litter quality, and decomposition time all significantly influence litter decomposition by attracting different fungal communities, thereby affecting the entire decomposition process.

Assessing phylogenetic diversity metrics in terrestrial ecological restoration: global trends and gaps

Phylogenetic diversity (PD) metrics estimate community diversity through evolutionary relationships, yet their potential in restoration ecology remains underutilized. This study reviews the literature on ecological restoration of terrestrial vegetation to evaluate the use of PD metrics, focusing on their application, global trends, and existing research gaps. Most studies were conducted in the United States, China, and Brazil, primarily in temperate broadleaf mixed forests (36.36%) and tropical and subtropical moist broadleaf forests (33.33%). Half of the papers were based on observational studies of restorations, and the other half were experimental studies. Plant PD was the primary focus in 90.09% of papers, with grasses and trees being the most studied life forms. Standardized effect size of the mean pairwise distance and mean nearest taxonomic distance metrics were the most commonly used metrics. The majority of studies used PD as a response variable and restoration indicators (e.g. age, initial seed/seedling mixture, and restoration impact) as explanatory variables. Research bias toward grassland and limited studies in Africa and Oceania were noted. Future studies should broaden geographic coverage in restoration to provide a more comprehensive understanding of PD dynamics globally. Also, efforts should be made to expand the taxonomic scope beyond to capture the full spectrum of biodiversity in restoration assessments.

Relationship Between Evolutionary Diversity and Aboveground Biomass During 150 Years of Natural Vegetation Regeneration in Temperate China.

While the link between plant species diversity and biomass has been well-studied, the impact of evolutionary diversity on community biomass across long timescales or ongoing change remains a subject of debate. We elucidated the association between evolutionary diversity and community aboveground biomass (AGB) using an ideal experimental system with over 150-year history of natural vegetation regeneration. Higher phylogenetic diversity facilitated the sampling effect under the influence of environmental filtering, and caused an increase in AGB. Phylogenetic structure varied from aggregation to dispersion during the later period of vegetation recovery (70-150 years), which was correlated with increases in niche complementarity and increasing AGB. Woody plant evolutionary diversity was used as a key to predict the relationship between vegetation recovery and AGB, with a total explanatory power of ~84.7%. Mixed forests composed of evergreen conifers and deciduous broadleaf forests had higher carbon sequestration potential than that of pure forests, which is advantageous for increasing top-stage AGB. This research expands our knowledge of the causes and effects of biodiversity and ecosystem function dynamics over time and space, which is important for accurately predicting future climate change effects.

Reassessing the Diversity of the Arthropod-Pathogenic Genus Pandora Batko (Entomophthoromycotina; Erynioideae)

The fungal order Entomophthorales occurs worldwide, with most species infecting arthropods as pathogens. Species in this order can cause epizootics and change the behavior of infected hosts. Molecular data are available only for 20% of the known species, and distributions of species are seldom summarized. Significant diversity of hosts, poor molecular data availability, and poor resolution of the phylogenetic relationships within this fungal order suggest that the diversity of these fungi is not sufficiently described. The subfamily Erynioideae includes 111 arthropod pathogens, divided among six genera, with the genus Pandora being one of the most diverse genera. Sequences of 18S, 28S, and ITS for two species are used to place these Pandora species in a phylogenic tree of the subfamily; this tree also supports our synonymy of the genus Furia with Pandora. Among the two species specifically covered in this paper, Pandora gloeospora was observed during epizootics occurring in mushroom flies (Diptera: Sciaridae) on Agaricus bisporus cultures in Pennsylvania, Delaware, and Maryland (US) mushroom farms and also in Florida on Pleurotus sp. Outside the US, P. gloeospora was found infecting several Nematocera (Diptera) in Europe (France) and Asia (China). Pandora sylvestris n. sp. was collected during epizootics occurring in larvae of hickory tussock moths, Lophocampa caryae (Lepidoptera: Erebidae), in hardwood forests in Michigan and Vermont.

Wildlife damage to forest stands in the context of climate change – a review of current knowledge in the Czech Republic

Abstract Wildlife damage to forests has become an increasingly serious problem in recent years, and its impact is exacerbated by ongoing climate change. Rising temperatures, prolonged droughts, uneven precipitation distribution, and other factors affect forest ecosystems, which, in turn, affect cloven-hoofed animal populations, their food preferences, and ultimately, the extent of damage they cause. Based on 133 references, this review article focuses on the relationships between wildlife damage and climate change and presents possible strategies to address this issue in the Czech Republic. Wildlife damage includes not just browsing and fraying in natural and artificial regeneration but also damage to trees from bark stripping and the lesser-known rooting of seedlings. Concerning tree species, browsing is most damaging to silver fir (Abies alba Mill.) and sycamore maple (Acer pseudoplatanus L.). The enticement to wildlife increases as the proportion of the tree species in the stand decreases. Browse damage is more severe at the edge of the stand. Bark stripping and secondary rot cause the most damage to the production quality of Norway spruce (Picea abies [L.] Karst.). Total wildlife damage increases with elevation. Combined with the progress of climate change, game-induced damage significantly restricts close-to-nature forest management practices and limits the use of adaptive measures in response to climate change. In addition, mixed forests with species that attract wildlife and the rapid increase in the number of clearings following bark beetle salvage logging significantly increase game pressure. This is primarily the result of the overpopulation of native and introduced game species and the considerable inconsistency between forest and hunting management practices, with the latter not respecting the principle of ecologically tolerable game damage.

Bryophytes in managed lowland forests of Slovakia (Central Europe): looking into species diversity across different forest types

AbstractThe majority of the woodland area in Central Europe is composed of managed forests. Although the species diversity and composition, particularly in older forests, may be similar to those of natural or close-to-nature forests, intensive forestry and other human activities have adverse impacts on biodiversity. The present study focused on bryophyte diversity in managed lowland forests, as these have received less attention compared to other types of forests. Our research targeted the area located within the Borská nížina Lowland in south-western Slovakia. In total, 37 forest sampling plots (SPs) were selected, representing five different forest types, namely Quercus, Fraxinus, Robinia, Pinus, and mixed forests. Multivariate statistical analyses were conducted across these forest types to demonstrate variations in bryophyte species richness, composition, and functional traits. Overall, 60 species of bryophytes were identified, of which five were liverworts and 55 were mosses. Epiphytes were the most abundant substrate group in deciduous and mixed stands, while epigeic species prevailed in Pinus forests. Considering environmental factors, the bryophyte diversity was influenced mostly by the forest type and area size of SPs. Clear differences in species composition were observed when comparing coniferous and deciduous stands, as well as non-native Robinia forests and native tree stands. Overall, intensive forest management results in a high concentration of hemerophilous and nitrophilous species, along with the absence of rare and threatened mosses and liverworts. Nevertheless, by adhering to proper management methods, even managed forests can provide suitable habitats for various bryophytes.

Combining multiple feature selection methods and structural equation modelling for exploring factors affecting stand biomass of natural coniferous-broad leaved mixed forests

Recognition of biotic and abiotic factors affecting biomass of natural mixed forests is of great importance for forest carbon estimation and management. When estimating stand biomass using models, different variable selection methods often yield inconsistent results, and there is lack of systematic analysis. This study aimed to combine multiple feature selection methods with structural equation modelling (SEM) to identify a set of variables affecting stand biomass more reasonably. Eight methods were applied for feature selection based on data from 286 permanent sample plots in natural coniferous-broad leaved mixed forests in northeast China. These methods included Pearson correlation analysis, two methods derived from principal component analysis (PCA), stepwise regression, redundancy analysis (RDA), generalized additive model (GAM), random forest (RF), and boosted regression tree (BRT). A total of 56 candidate variables were considered, covering stand, biodiversity, climate and soil features. Significant variability was observed in the variables selected, however, there were 6 variables consistently identified across all methods, including tree species diversity (N_Sp_Div), stand structural diversity (N_ Size_ Div), nearest taxon index (NRI), community weighted mean based on dry matter mass of leaves (CWM.LDMC), soil pH, and degree-days above 18 °C (DD18). Then, these variables were included in the SEM with stand average age and additive stand density index (aSDI) to explore the direction and magnitude of their impacts on stand biomass. The SEM results showed that aSDI and average age had the greatest positive effects on stand biomass, and structural diversity also had a significant positive effect. DD18 affected stand biomass both directly and indirectly, with the total negative effect. Soil pH indirectly affected stand biomass via aSDI. Our findings demonstrated that combining multiple feature selection methods with SEM was an effective approach for understanding multiple factors affecting stand biomass, and provided valuable insights for forest biomass estimation and carbon management.

Positive impact of large wild herbivore exclusion on silver fir regeneration: A case study from the Poľana Mountains, Central Slovakia

Abstract In forest ecosystems, the browsing activity of large wild herbivores (LWH) often leads to reduced tree and plant diversity, diminished biomass production, and challenges in achieving forest management objectives. Our case study focuses on assessing the impact of LWH browsing during the initial stages of forest growth by comparing fenced plots (F plots) with excluded LWH and control plots (C plots) with the presence of LWH. The experiment took place at the Hukavský Grúň research site in the Poľana Mts., characterized by a high red deer (Cervus elaphus L.) population. Fifteen F plots and fifteen C plots, all situated within mixed maternal forests, were established in the 2023 growing season. Thus, circular plots with a radius of 2.5 m were utilized, and comprehensive data were collected on young trees (excluding those under 10 cm in height), covering tree species, positions, heights, and stem diameters. Species-specific allometric relations were employed to calculate the aboveground biomass of each tree, contributing to the overall biomass stock on a plot basis. A comparison between F and C plots revealed a prevalence of silver fir (Abies alba Mill.) in F plots, while European beech (Fagus sylvatica L.) dominated C plots. F plots exhibited higher tree species diversity (4.5 species), contrasting with the lower diversity (2.0 species) and absence of silver fir in C plots. The F plots also demonstrated greater tree density and sizes, resulting in substantial differences in aboveground biomass stocks. Browsing in C plots predominantly affected tree height rather than stem diameter, leading to a bigger height-to-diameter ratio in F plots compared to C plots. We suggest that fencing as a method to exclude LWH might be economically expensive and provide a temporary solution limited by the functionality of the fence. Therefore, the primary strategy for safeguarding the future of silver fir may lie in regulating LWH populations to a reasonable threshold.

Identifying suitable areas for plenter forest management

Plenter forests, also known as uneven-aged or continuous cover forests enhance forest resilience and resistance against disturbances compared to even-aged forests. They are considered as an adaptation option to mitigate climate change effects. In this study, we present a conceptual approach to determine the potentially suitable area for plenter forest management within central European mixed species forests and apply our approach to the case study area in Styria, the south-eastern Province of Austria. The concept is based on ecological and technical-economic constraints and considers expected future climate conditions and its impact on plenter forest management. For each 1 ha forest pixel, we assess the ecological conditions for plenter forest management according to the autecological growth conditions of silver fir, and at least one additional shade tolerant tree species. The technical-economic constraints are defined by slope (≤ 30%) and distance to the next forest road (≤ 100 m) to ensure cost-efficient harvesting. The results show that under current climate conditions 28.4% or 308,349 ha of the forests in Styria are potentially suitable for plenter forest management. For the years 2071 to 2100 and under the climate change scenario RCP 4.5, the potential area decreases to 286,098 ha (26.3% of the total forest area) and for the scenario RCP 8.5 to 208,421 ha (19.1% of the total forest area). The main reason for these changes is the unfavourable growing conditions for silver fir in the lowlands, while in the higher elevations silver fir is likely to expand. Our results may serve forest managers to identify areas suitable for plenter forests and assist in the transformation of even-aged pure forests to uneven-aged forests to increase resistance, resilience, and biodiversity under climate change.

Seasonal changes in the abundance and distribution of large terrestrial mammals in old Oyo National Park, Nigeria

Seasonal distribution of large terrestrial mammals in African protected areas is shaped by factors such as food and water availability, breeding cycles, and predation risks. This study utilised encounter rates derived from diurnal distance sampling to examine seasonal variations in the abundance and distribution of these mammals within Old Oyo National Park, Nigeria. Notably, the abundance and distribution in the Marguba range, characterised by mixed open savanna woodland, differed significantly between the dry and wet seasons, as well as among various sub-habitats and ranges during the dry season. The impact of key factors—(1) resource availability (food and water) and/or (2) poaching threat—remains critical and potentially influential in driving these seasonal differences. Further investigation to ascertain the effect of poaching and determine the impact of other controlling factors is crucial. Understanding the effects of these factors is essential for the effective and sustainable management and conservation of large terrestrial mammals in the study area.

Vegetation and environmental changes on the Northeast China Plain during warm periods since MIS 3

Understanding past terrestrial ecosystem responses to climate changes is vital for future predictions, but research in densely populated plains is limited due to insufficient materials. This study focuses on vegetation and environmental changes in the Northeast China Plain since Marine Isotopic Stage (MIS) 3 using pollen analysis from core WCZK03. The findings reveal significant shifts in vegetation that correspond to climatic events. During MIS 3 (52–29 cal ka BP), the region was predominantly a lake environment with vegetation transitioning from grassland dominated by Poaceae, Chenopodiaceae and Artemisia to conifer-broadleaf mixed forests as the climate ameliorated. The Last Glacial Maximum (29–17 cal ka BP) was characterized by loess deposits, followed by drought-tolerant grassland (17.0–11.3 cal ka BP) dominated by Artemisia and Chenopodiaceae in the plain. The onset of the Holocene witnessed the expansion of conifer and broad-leaved deciduous forests in hilly areas and the retreat of grassland in the plain. The sedimentary sequence shows transitions from fluvial-lacustrine deposits to loess-like and black soil deposits, showing significant environmental changes. This study suggests that changes in vegetation on the Northeast China Plain were closely related to regional climate patterns and were more responsive to climate changes than the surrounding mountainous areas.

Long-term effects of potassium chloride, wood ash, and EDTA on 137Cs soil-plant transfer in a mixed forest of Ukraine

We conducted a 10-year field experiment to study the effects of potassium chloride, wood ash, zinc, and manganese on reducing 137Cs uptake by young leaves and green shoots of common dwarf shrubs and tree species near the Chornobyl Nuclear Power Plant. A field experiment had four treatments: a control with no fertilisation, and three fertilised treatments: potassium fertiliser (KCl), a combination of potassium fertiliser and wood ash (KCl + Ash), and a solution providing zinc and manganese (EDTA). There was approximately 30 % decrease in 137Cs uptake by most of the studied plants species growing on plots fertilised with KCl compared to unfertilised plots during intermediate (2014–2016) and late (2018–2021) periods. Combining KCl with wood ash was found to be the most effective countermeasure, reducing 137Cs uptake by up to 60% in most species, while treatment with EDTA was less effective. Generally, the decline in 137Cs uptake by plants over the study years following treatments with fertilisers was more pronounced than in the control, indicating the efficiency of fertilisation in reducing 137Cs uptake by forest plants. Our research suggests that a combination of potassium chloride and wood ash can still effectively reduce 137Cs transfer in most common forest species, even years after the accident.

Temperature Sensitivity of Peatland Soils Respiration Across Different Terrestrial Ecosystems

Sequential (S) and equal-time (ET) methods were applied to assess the temperature sensitivity of respiration of peat soils in different terrestrial ecosystems: southern tundra, northern taiga, and mixed coniferous–broadleaved forests. The Q10 values varied widely (1.3–4.8) and in case of the ET method decreased from northern to temperate latitudes. In the cold range (5–15°С), Q10 increased from the southern tundra (3.5) to the northern taiga (4.8) and then sharply decreased in the zone of mixed forests (2.5). Meanwhile, warm range (15–25°С) showed a clear decline of Q10 from northern to temperate latitudes: southern tundra (2.6) > northern taiga (1.6) > coniferous–broadleaved forests (1.3). Application of the S method resulted in low variability of Q10 values. Our results demonstrate a higher temperature sensitivity of the respiration of peat soils in northern latitudes as compared to that in the temperate zone. The Q10 values obtained in this study can be useful for calibration of regional carbon cycle datasets that consider the contribution of peat soils.

Mycorrhizal Types Regulate Tree Spatial Associations in Temperate Forests: Ectomycorrhizal Trees Might Favour Species Coexistence.

In temperate mixed forests, dominant ectomycorrhizal (EM) tree species usually coexist with diverse arbuscular mycorrhizal (AM) understorey tree species. Here, we investigated the spatial associations between AM and EM trees in two > 20 ha temperate forest mega-plots to better understand the observed 'EM-dominant versus AM-diverse' coexistence. Overall, we found that positive spatial associations (e.g., facilitation) were mostly related to EM trees, while negative spatial associations (e.g., inhibition) were mainly related to AM trees. Because adult EM trees tended to facilitate surrounding AM and EM saplings and other EM adults in these two forests, facilitation hotspots that stabilize AM-EM tree coexistence should be centred around EM tree species rather than around AM tree species. Together, we propose a novel EM-stabilization mechanism, which emphasises how, despite some species-specific variation, EM tree species foster 'EM-dominant versus AM-diverse' coexistence in temperate mixed forests by facilitating other trees.

Land Use Optimization from the Perspective of Multiple Stakeholder Groups: A Case Study in Yongsheng County, Yunnan Province, China

With China’s rapid economic development in recent years, enhancing the sense of well-being among citizens has become a critical objective. However, the interests of various stakeholder groups are often overlooked in decision-making surrounding land use. In this study, Yongsheng County, Yunnan Province serves as a case study for land use scenario simulations. The equivalent factor method is combined with Participatory Rural Appraisal (PRA) to investigate the relationship between ecosystem multifunctionality (EMF) and the equity index of multiple stakeholder groups in various land use scenarios. We also explore whether an optimal combination of land use types exists. The results indicate that (1) The current ecosystem service value in Yongsheng County is primarily driven by climate regulation and biodiversity conservation, with a relatively high functional value index but a comparatively low equity index; (2) Different stakeholder groups mainly prioritize food production and ecosystem services impacting food production, such as water resource provision and climate regulation; (3) A land use allocation pattern of 20% farmland, 4% water bodies, 21% mixed forest, 20% coniferous forest, and 35% grassland appears to provide the optimal EMF index while simultaneously achieving the optimal equity index across stakeholder groups. This research may offer valuable insights for optimizing land use planning while taking into account the well-being of diverse stakeholder groups. It also may have practical implications for the formulation of innovative land use management strategies.

Ambrosia beetle (Coleoptera: Curculionidae: Scolytinae) responses to ice storm damage in mesic, mixed deciduous forests in southeast Ohio, United States

Ambrosia beetle (Coleoptera: Curculionidae: Scolytinae) responses to ice storm damage in mesic, mixed deciduous forests in southeast Ohio, United States

Studies to assess natural resource recovery and evaluate monitoring methods for restored bottomland hardwood forests.

The Natural Resource Damage Assessment and Restoration process assesses natural resource injury due to oil or chemical spills and calculates the damages to compensate the public for those injuries. Ecological restoration provides a means for recovering resources injured or lost due to contamination from oil or chemical spills by restoring the injured site after remediation, or acquiring or reconstructing equivalent resources off site to replace those lost due to the spill. In the case of restored forests, once restoration is implemented, monitoring of forest ecology helps keep recovery on track, with the maturation of forest vegetation, recovered soil conditions, and development of microbial, fungal, and faunal communities, necessary for ecologically functioning forests. This series of papers focuses on applying methods for monitoring restoration progress in forest vegetation and soils, and amphibian, avian, and mammalian communities, assessing strengths and weaknesses of different methods, and evaluating levels of effort needed to obtain accurate indications of forest ecological condition. Integr Environ Assess Manag 2024;00:1-5. © 2024 The Author(s). Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Ectomycorrhizal fungi and the nitrogen economy of Nothofagus in southern Patagonia.

Subantarctic Nothofagus forests are the southernmost forests in the world, with negligible atmospheric nitrogen (N) deposition. Most paradigms about the role of ectomycorrhizal (ECM) fungi in N cycling and plant N uptake at high latitudes have been tested in boreal coniferous forests, while in the southern hemisphere, ECM hosts are primarily angiosperms. Using ITS1 meta-barcoding, we characterized ECM and saprotrophic fungal communities in evergreen and deciduous Nothofagus forests forming monodominant and mixed stands in the archipelago of Tierra del Fuego (Chile and Argentina). We assessed the N economy of Nothofagus by correlating host species with fungal relative abundances, edaphic variables, net N mineralization, microbial biomass N and the activity of eight extracellular soil enzymes activities. The N economy of deciduous N. pumilio forests was strikingly similar to boreal coniferous forests, with the lowest inorganic N availability and net N mineralization, in correlation to higher relative abundances of ECM fungi with enzymatic capacity for organic N mobilization (genus Cortinarius). In contrast, the N economy of evergreen N. betuloides forests was predominantly inorganic and correlated with ECM lineages from the family Clavulinaceae, in acidic soils with poor drainage. Grassy understory vegetation in deciduous N. antarctica forests likely promoted saprotrophic fungi (i.e., genus Mortierella) in correlation with higher activities of carbon-degrading enzymes. Differences between Nothofagus hosts did not persist in mixed forests, illustrating the range of soil fertility of these ECM angiosperms and the underlying effects of soil and climate on Nothofagus distribution and N cycling in southern Patagonia.

Response of understory vegetation to long-term occupancy by introduced Pinus species in temperate deciduous hardwood forests

In many temperate regions of the world, conifer species have been planted to stabilize soils and promote site recovery on former hardwood sites that were cleared for agriculture. In many areas of eastern North America, these conifer plantings consisted of introduced (non-native) Pinus species planted on abandoned agricultural land once dominated by mesophytic hardwood species. These plantings constitute a shift in overstory composition away from native hardwood species with nutrient-rich litter that decomposes more quickly towards Pinus species with recalcitrant litter that may alter soil chemistry and nutrient availability. To examine how edaphic conditions associated with long-term introduced Pinus species occupancy are related to forest regeneration and herbaceous-layer diversity and composition, we sampled a total of 97 plots in planted Pinus echinata and Pinus strobus stands and naturally regenerated hardwood stands growing on two ecological landtype phases (ELTPs) of southern Indiana, USA forests, Fagus-Acer saccharum/Arisaema Mesic Ridges, and Acer saccharinum/Boehmeria Bottomlands. We collected vegetation data and analyzed soil samples to examine herbaceous-layer species distribution across gradients using non-metric multidimensional scaling (NMS) ordination. Two-way ANOVA was used to examine differences in individual species and species functional groups across stand types (P. echinata, P. strobus, and native hardwoods) and ELTPs. Our results show that differences in soil chemistry resulting from Pinus spp. occupancy were associated with differences in the composition and distribution of herbaceous-layer species in ordination space. Species across stand types and ELTPs were distributed across dominant gradients related to litter depth, cation exchange capacity, cation content, and soil aluminum concentration. Hardwood sites had significantly greater herbaceous-layer cover (139.6 ± 8.0 %) than P. echinata (48.5 ± 6.2 %) or P. strobus sites (81.7 ± 7.7 %), as well as greater herbaceous-layer species richness and diversity (mean species richness was 46.9 ± 2.1 on hardwood stands vs. 33.3 ± 1.6 and 36.4 ± 2.0 on P. echinata and P. strobus stands, respectively). Pinus echinata stands contained a greater density of woody regeneration, including Quercus spp. (201 ± 48 saplings ha−1) and Fagus grandifolia stems (415 ± 82 saplings ha−1), both of which occurred in greater density than Acer saccharum (163 ± 93 saplings ha−1) and A. rubrum (70 ± 64 saplings ha−1). Our results suggest that pine occupancy has created divergent successional trajectories in comparison to hardwood stands. These differing trajectories may offer both challenges and opportunities for restoration efforts. For example, the greater abundance of Quercus reproduction under P. echinata on ridges, combined with less productive soils, may allow Quercus stems to be promoted into the canopy with less competition from mesophytic competitors.

Fire history in northern Sierra Nevada mixed conifer forests across a distinct gradient in productivity

BackgroundUnderstanding the role of fire in forested landscapes is fundamental to fire reintroduction efforts, yet few studies have examined how fire dynamics vary in response to interactions between local conditions, such as soil productivity, and more broadscale changes in climate. In this study, we examined historical fire frequency, seasonality, and spatial patterning in mixed conifer forests across a distinct gradient of soil productivity in the northern Sierra Nevada. We cross-dated 46 different wood samples containing 377 fire scars from 6 paired sites, located on and off of ultramafic serpentine soils. Forests on serpentine-derived soils have slower growth rates, lower biomass accumulation, and patchier vegetation than adjacent, non-serpentine sites. Due to these differences, we hypothesized that historical fire frequency and spatial extent would be reduced in mixed conifer forests growing on serpentine soils.ResultsFire scars revealed a history of frequent fire at all of our sites (median composite interval: 6–22.5 years) despite clear differences in soil productivity. Fire frequency was slightly shorter in more productive non-serpentine sites, but this difference was not consistently significant within our sample pairs. While fires were frequent, both on and off of serpentine, they were also highly asynchronous, and this was largely driven by differing climate–fire relationships. Fires in more productive sites were strongly associated with drought conditions in the year of the fire, while fires in less productive serpentine sites appeared to be more dependent on a cycle of wet and dry conditions in the years preceding the fire. Widespread fires that crossed the boundary between serpentine and non-serpentine were associated with drier than normal years.ConclusionsIn our study, fine-scale variation in historical fire regime attributes was linked to both bottom-up and top-down controls. Understanding how these factors interact to create variation in fire frequency, timing, and spatial extent can help managers more effectively define desired conditions, develop management objectives, and identify management strategies for fire reintroduction and forest restoration projects.