Mixed Conifer Research Articles

Evaluation of Soil Biodiversity in Alpine Habitats through eDNA Metabarcoding and Relationships with Environmental Features

Soil biodiversity is fundamental for ecosystems, ensuring many ecosystem functions, such as nutrient cycling, organic matter decomposition, soil formation, and organic carbon pool increase. Due to these roles, there is a need to study and completely understand how soil biodiversity is composed through different habitats. The aim of this study was to describe the edaphic soil community of the alpine environments belonging to the Gran Paradiso National Park, thus detecting if there are any correlation with environmental features. We studied soil fauna through environmental DNA metabarcoding. From eDNA metabarcoding, 18 families of arthropods were successfully detected, and their abundance expressed in terms of the relative frequency of sequences. Soil faunal communities of mixed coniferous forests were characterized by Isotomidae, Entomobriydae, Hypogastruridae, and Onychiuridae; while mixed deciduous forests were composed mostly by Isotomidae, Cicadidae, Culicidae, and Neelidae. Calcicolous and acidic grasslands also presented families that were not detected in forest habitats, in particular Scarabaeidae, Curculionidae, Brachyceridae, and had in general a more differentiated soil community. Results of the Canonical Component Analysis revealed that the main environmental features affecting soil community for forests were related to vegetation (mixed deciduous forests, tree basal area, tree biomass, Shannon index), soil (organic layers and organic carbon stock), and site (altitude); while for prairies, soil pH and slope were also significant in explaining soil community composition. This study provided a description of the soil fauna of alpine habitats and resulted in a description of community composition per habitat and the relation with the characteristic of vegetation, soil, and topographic features of the study area. Further studies are needed to clarify ecological roles and needs of these families and their role in ecosystem functioning.

Conifers are a major source of sedimentary leaf wax n-alkanes when dominant in the landscape: Case studies from the Paleogene

Plant wax n-alkanes are valuable paleoclimate proxies because their carbon (δ13C) and hydrogen (δ2H) isotopes track biological and environmental processes. Angiosperms produce higher concentrations of n-alkanes than conifers, with some exceptions. Vegetation source is significant because in similar climates, both taxa produce n-alkanes with unique δ13C and δ2H values due to different physiological strategies. To test whether conifers contribute significantly to sediment n-alkanes and result in distinctive isotopic signatures, we collected sediment samples from a suite of Paleogene paleobotanical sites in North America with high and low conifer abundances. To disentangle the source of sediment n-alkanes, we measured the δ13C values of nonsteroidal triterpenoids (angiosperm biomarkers) and tricyclic diterpenoids (conifer biomarkers) to determine angiosperm and conifer end member δ13C values. We then compared these end member values to n-alkane δ13C values for each site to estimate their major taxon sources. At sites dominated by conifer macrofossils, δ13C values of n-alkanes indicate a conifer source. At mixed conifer and angiosperm sites, conifer contributions increased with increasing n-alkane chain length. At sites where conifers were not as abundant as angiosperms, the δ13C values of n-alkanes indicate a predominant angiosperm source with some sites showing a conifer contribution to n-C33 and n-C35 alkanes. This suggests that conifers in the Paleogene contributed to longer chain n-alkanes (n-C33 and n-C35) even when not the dominant taxa, but this likely differs for other geographic locations and taxa. This new approach allows unique floral information to be extracted when chain length is carefully considered in the absence of other paleobotanical data and necessitates having some paleovegetation constraints when interpreting carbon and hydrogen isotopes of plant wax-derived n-alkanes.

METODY PROWADZENIA ODNOWIEŃ NATURALNYCH SOSNY ZWYCZAJNEJ (PINUS SYLVESTRIS L.) W NADLEŚNICTWIE SKWIERZYNA

For many years, the Skwierzyna Forest District has been a leader among 35 units of the Regional Directorate of State Forests in Szczecin in terms of the area of the obtained natural regeneration of Scots pine. In the Skwierzyna Forest District in the period 2010-2018, 522.93 ha of natural regeneration was recognized, which constitutes 43% of the total regeneration, the habitat of fresh mixed coniferous forest and fresh coniferous forest as optimal for obtaining regeneration of the natural pine. In the spring date of plowing, the forest plow LPz-75 is applied, as the best for obtaining satisfactory self-seeding. The basic method of natural regeneration of pine in the Skwierzyna Forest Inspectorate is the use of a strip-like clear cutting (Ib) in the form of classic narrow sheds, with a cutting width of up to 60 m. It is noteworthy that in the woodcutting the under-eaves undergrowths, arising in forest stands close to the harvest, are left intact and later used within the naturally renovated area.

Evaluation of ecosystem services in a protected mountain area: Soil organic carbon stock and biodiversity in alpine forests and grasslands

Ecosystem services (ES) evaluation is included in the environmental programs and policy strategies of protected natural areas in many countries. Alpine forests and grasslands play an important role in climate regulation but their contribution is still unknown. In this study, we estimated soil organic carbon (SOC) stocks for forest and grassland habitats by collecting samples from 87 plots in Gran Paradiso National Park (western Italian Alps). Results of the LMM show that habitat type affects SOC stock; grasslands and mixed broadleaf forests store higher SOC than mixed coniferous forests, spruce forests and larch forests. We investigate the relationships between biodiversity, SOC stock, OC stock in organic layers, soil types, forests structure and other environmental features using a canonical component analysis and a Pearson correlation matrix. The results show that biodiversity is mainly influenced by the altitude, OC stock in organic layers OH and habitats of coniferous forests. Biodiversity positively correlates to organic layers (Staphylinidae, Formicidae, Orthoptera), forests’ Shannon and evenness indices (Carabidae, Formicidae, Orthoptera, Aranea, Lepidoptera) and forests’ basal areas and stem density (Staphylinidae, Formicidae, Aranea). Further studies are needed to better investigate the relation between biodiversity and habitat features on ecosystem functions and thus on the provision of ES.

Late Pleistocene-Holocene vegetation history and anthropogenic activities deduced from pollen spectra and archaeological data at Guxu Lake, eastern China

This study presents high-resolution pollen and charcoal records from Guxu Lake in the Taihu Lake Basin, eastern China, spanning the last 23,000 years. The sedimentary sequences revealed dynamic terrestrial and lacustrine environments during 23.0-11.7 cal ka BP, the climate was relatively cold and dry, and the vegetation was dominated by evergreen-deciduous broadleaf and coniferous mixed forest. During 11.7-4.4 cal ka BP, the Quercus- and Castanopsis-dominated evergreen-deciduous broadleaf mixed forest expanded, while the Poaceae and Artemisia were still the major terrestrial herbs under warmer and more humid conditions. After this period, the climate became relatively cool and dry again, and the vegetation landscape was comparatively stable, as it remains today. Wild rice likely grew before Neolithic humans occupied this area. The variations in Oryza-type Poaceae pollen spectra and distributions of Neolithic archaeological sites indicate rice agriculture may have first appeared and developed with human occupation in ca. 7.0-4.4 ka BP. During the historical period, beginning approximately 4 ka BP, a clear signal of intensified anthropogenic disturbance is evident from the clearing of forests, high charcoal concentrations and the presence of rice pollen in large quantities. These results suggest more intensified rice farming was widespread, with increasing human impact on the environment.

The linkages of plant, litter and soil C:N:P stoichiometry and nutrient stock in different secondary mixed forest types in the Qinling Mountains, China.

BackgroundCarbon (C), nitrogen (N) and phosphorus (P) stoichiometric ratios are important indicators of ecosystem function and productivity. However, few studies have assessed the nutrient relationship between plant, litter and soil, and the nutrient stock in different secondary mixed forest types.MethodsWe investigated the C, N and P concentrations and stoichiometric ratios in trees, understory plants, litter and soil layers in three different secondary mixed forest types (broadleaf mixed forests (BM), broadleaf-conifer mixed forests (BCM) and coniferous mixed forests (CM)) in the Qinling Mountains.ResultsThe results showed that significant differences in C:N:P stoichiometry were detected in multiple organs in the vegetation layers in the different forest types. Trees, shrubs and herbs all allocated more N and P in leaves and had a higher N:P ratio in leaves than in other organs. The C concentrations, C:N ratios and C:P ratios of all tree organs showed a decreasing order: BM < BCM < CM, while the N and P concentrations showed an increasing order: BM > BCM > CM. For litter and soil, BM had generally higher N and P concentrations than those of BCM and CM. The highest N and P stock was in tree branches-not in the stem, which had the highest biomass (except for P in CM). Compared with other forest types, CM stored more nutrients in the labile litter layer, while BM stored more nutrients in the stable soil layer. The net ecosystem nutrient element stock in BM was generally higher than that in BCM and CM. The C, N and P concentrations and stoichiometry in the plant organs, litter and soil were significantly correlated.ConclusionOur findings demonstrate that nutrient concentrations in plant organs, litter and soil are tightly linked in secondary mixed forests.

The interception effect of heavy metals in different types of Chinese fir plantations.

The aim of this research is to investigate the interception effect of heavy metals, such as zinc (Zn), copper (Cu), lead (Pb), arsenic (As), and cadmium (Cd) in different ages of Chinese fir plantations. The study was conducted in 21-year-old (CF21, near mature stand) and 29-year-old (CF29, old stand) pure Chinese fir forest stands (CF) as well as a mixed coniferous and broad-leaved forest stand (MF) in Huitong from November 2016 to October 2017. The study results revealed the variation ranges of interception of Cu, Zn, Cd, As, and Pb by the research forest stands were respectively, 3.436-36.778mg·m-2·month-1, 7.458-98.763mg·m-2·month-1, 0.003-0.608mg·m-2·month-1, 0.094-4.471mg·m-2·month-1, and 1.251-23.141mg·m-2·month-1. Compared with the different ages of CF, the average monthly interception of Cu, Zn, Cd, As, and Pb in CF21 were respectively, higher 6.0%, - 3.3%, 59.0%, 1.4%, and 3.4% than those in CF29. However, seasonal changes of that in CF of different ages were those in CF21 > in CF29 in summer and autumn, and those in CF21 < in CF29 in winter and spring. Compared in different forest types, the average monthly interception of Cu, Zn, Cd, As, and Pb in MF was respectively, higher 20.2%, 5.8%, 185.2%, 2.6%, and 12.3% than those in CF. Furthermore, the seasonal flux of heavy metal retention in the forest ecosystems was higher during winter and spring than in summer and in autumn. This study provided an important information regarding the dynamics of heavy metal interception in forest ecosystems.

Canopy Opening and Site Preparation Effects on Conifer and Understory Establishment and Growth after an Uneven-Aged Free Selection Regeneration Harvest in the Northern Rocky Mountains, USA

Research Highlights: Forest management is trending toward creating multi-aged forest structures and diverse vegetative compositions. The challenge is successfully designing and implementing treatments that create these diverse forests. Regeneration establishment is the most important step when applying a silvicultural system because it determines future treatments and optimizes management options. This study provided the minimum canopy openings that favor the establishment of shade-tolerant and shade-intolerant tree species to inform the implementation of uneven-aged management. Background and Objectives: A replicated study was implemented in 2007 in moist mixed-conifer forests to design, apply, and test two silvicultural concepts, canopy opening size and site preparation. Our objective in 2015 was to evaluate tree regeneration establishment and growth and understory vegetation in relation to these two silvicultural concepts. Materials and Methods: Canopy opening sizes as measured by lidar ranged from 15% to 100%; and through the application of prescribed fire, mastication, pile and burn, or no site preparation, different combinations of forest floor substrates were created. We stratified our study area into five canopy opening classes and four site preparation treatments. Using this stratified sampling scheme, we located 65 plots and measured tree species, abundance, 5-year height growth, and vegetative lifeforms. Results: The pile and burn site preparation favored the establishment of all six tree species. The canopy opening size of 55% to 92% favored the regeneration of both shade-tolerant and shade-intolerant species. Grand-fir 5-year height growth was significantly influenced by site preparation and canopy opening, and western white pine 5-year height growth was only influenced by canopy opening. Treatments did not influence vegetative richness. Conclusions: This study provided key treatment parameters in designing the regeneration step for uneven-aged management strategies with the goal of creating vegetative diversity and establishing shade-intolerant tree species in moist mixed-conifer forests.

Topographic variation in tree group and gap structure in Sierra Nevada mixed-conifer forests with active fire regimes

In Sierra Nevada mixed-conifer forests, heterogeneity in overstory tree spatial patterns is an important ecological characteristic associated with resilience to frequent fires. Regional managers often emphasize this heterogeneity as a key component of forest treatments. There is a lack of information about how the dimensions of fire-resilient tree spatial patterns might vary with topography, which is an important influence on forest structure. We mapped, analyzed, and compared overstory tree spatial patterns across three topographic slope positions (ridges, mid-slopes, and valleys) in unlogged stands with multiple recent lower/mixed-severity burns. Using analysis of Individual trees, Clumps of trees, and Openings (ICO), we found significant differences in a number of spatial pattern metrics, including stand-level tree density and maximum clump size (highest in valleys), forest opening size (largest on ridges), and species composition (percent shade-intolerant stems highest on ridges). We found notably non-significant differences in within-clump tree densities at all spatial scales. Additionally, stand-level averages for forest structure across topography did not consistently capture spatial patterns for individual trees or smaller clump sizes, but often matched trends for clumps and openings in the largest size classes. As “megafires” become more common, prescribed fire and thinning treatments will be used more often to increase forest resilience. By quantifying variable tree spatial patterns across topographic positions in frequent-fire forests, we provide general guidelines for marking prescriptions that may increase resilience of treated forests to increasing fire intensity.

Butterfly diversity in Gidakom Forest Management Unit, Thimphu, Bhutan

This study was carried out to establish the diversity and distribution of butterflies in Gidakom Forest Management Unit (GFMU), Thimphu, Bhutan. A survey was conducted from June 2016 to July 2017 in three locations within GFMU: Jamdo, Chimithanka, and Jedekha. A total of 90 species belonging to 52 genera and five families of butterflies were recorded. Nymphalidae was dominant with 38 species, followed by Lycaenidae with 19, Pieridae with 15, Papilionidae with 11, and Hesperiidae with seven species. Diversity of butterfly species was highest in farmland associated with pockets of forest cover in the lower valley, and a decreasing trend was observed towards higher elevations. The maximum species richness (83 species) was recorded from Chimithanka between 2500m &amp; 2900m, where agriculture is associated with patches of forest, streams, forest edges, and open scrub land. Butterfly diversity was lowest at Jedekha above 2,900m (37 species), an area dominated by mixed conifer forest with little agriculture.

Effects of post-fire management on dead woody fuel dynamics and stand structure in a severely burned mixed-conifer forest, in northeastern Washington State, USA

The increasing amount of high-severity wildfire in historical low and mixed-severity fire regimes in western US forests has created a need to better understand the ecological effects of different post fire management approaches. For three different salvage prescriptions, we quantified change in stand structural metrics (snag densities and snag basal areas), dead woody fuel loadings, tree regeneration survival, and percentage change in vegetation cover before and after post-fire logging 1 year after the 2015 Stickpin Wildfire on the Colville National Forest in northeastern Washington State, USA. In a generalized randomized block design three salvage logging prescriptions were randomly assigned within each block: no treatment control (C); standard salvage retention (SSR; thin to 3.4 m2/ha basal area); and mimic green tree thinning (GTR; thin to 10.3 m2/ha basal area). SSR reduced average snag basal area 73–83% to 4.1–8.8 m2/ha (68–674 trees ha−1). GTR reduced average snag (standing dead trees) basal area 41–71% to 6.5–15.9 m2/ha (90–794 trees ha−1). There were mixed results for the change in dead woody fuel loadings depending on fuel size class. In general, fine (FWD) and coarse woody (CWD) debris tended to increase immediately post-treatment in logged areas relative to the controls but did not exceed management loading threshold for providing acceptable risk of fire hazard. Treated stands had a significant increase in FWD relative to controls, including the individual 1-, 10-, and 100-hr fuel size classes. The treatment effect differed by experimental block. The 1000-hr sound class did not have a significant treatment effect. Changes in surface fuel loading were inconsequential to modeled wildfire behavior metrics (rate-of-spread, flame lengths). The Fire and Fuels Extension to Forest Vegetation Simulator (FFE-FVS) modeling projected CWD accumulation in the controls exceeded total accumulation in both treatments. Future fuel loadings may affect reburn severity as our simulated wildfire 20 years after harvesting caused significant mortality (89%) to regenerating forest. Almost all blocks showed a decrease in seedling counts pre and post-logging, including the control plots. This study provides empirical data on the effects of different post-fire management strategies that can inform environmental analyses for future post-fire management decision and address social concerns associated with this often-controversial practice (Roccaforte et al., 2012).

Late-Holocene vegetation change reveals the environment of ancient people and the origin of Huashan cliff paintings in Guangxi, southwestern China

Human activities in the historical period were determined by the natural environment and social characteristics. The Zuojiang Huashan Rock Art Cultural Landscape in Guangxi is the most important World Heritage for prehistorical culture in southwestern China. However, knowledge about the natural environment and associated historic human–climate interactions during the period of cliff painting creation remains scarce, which has been an obstacle to understanding the process of regional civilization. Here, we report a pollen record from the core distributing region of Huashan cliff paintings to interpret the natural environment and climate changes, and further to discuss how and why ancient people create these giant cliff paintings based on the relationships of human–climate interactions. Pollen results imply an existence of a mixed broad-leaf and conifer forest in the woodland landscape at Huashan region before 1860 cal. yr BP, after which pine forests were more prevalent. During the cliff painting period from 2370 to 2115 cal. yr BP, broad-leaf and conifer trees dominated the tree layer and provided the key source materials for painting. It can be reasonably assumed that people used stake or ladder to climb the cliffs and created the cliff paintings during a humid climate condition from 2560 to 2000 cal. yr BP. Furthermore, the humid climate during 2700 and 2400 cal. yr BP had been interrupted by short-term drought episodes. These turbulent climate episodes probably played the role of disasters and impacted on the human activities, leading to the social–political tensions and the out-break of war. During the Qin and Han Dynasties, social–political changes relieved the pressure from natural climate changes and led to a more stable society, in which the creating of cliff paintings was gradually fading. Our results manifest the necessity to analyze the natural environment and social–political background in combination in this study on ancient human activities.

Using Satellite Imagery to Evaluate Bark Beetle-Caused Tree Mortality Reported in Aerial Surveys in a Mixed Conifer Forest in Northern Idaho, USA

Bark beetles cause significant tree mortality in western North America. The United States Forest Service coordinates annual insect and disease surveys (IDS) by observers in airplanes to map and quantify the tree mortality caused by beetles. The subjective nature of these surveys means that accuracy evaluation is important for characterizing uncertainty. Furthermore, the metric reported for quantifying tree mortality recently changed (2012–2018 depending in region) from killed trees per acre to percent tree mortality within damage polygons, posing challenges for linking older and newer records. Here we evaluated IDS severity estimates in a beetle-affected forest in northern Idaho, USA using fine-resolution satellite imagery, which permitted greater areal coverage than field data. We first used well-established methods to map beetle-caused tree mortality in two WorldView-2 (WV2) images with a high accuracy relative to field observations. Trees-per-acre measurements within collocated IDS polygons were then converted to percent mortality using three methods and evaluated with the WV2 maps. The overall accuracies for the three methods ranged from 35–38% (for methods that used five percent-mortality classes) and 49–56% (three classes). When IDS and WV2 estimates of mortality severity that were within ±15% of each other were considered accurate, overall accuracies were 71–78%. Within the aerial survey damage polygons, the total mortality area tended to be overestimated relative to WV2. WV2 imagery identified ~50% more mortality across the study region compared with the IDS methods, with most of the difference occurring where damage was low severity or in wilderness areas. Severity of Douglas-fir beetle-caused tree mortality was estimated the most accurately, whereas severity of mountain pine beetle-caused tree mortality was estimated the least accurately. Future studies that control for temporal ambiguity between IDS and satellite imagery, as well as IDS spatial error, might provide better assessments of IDS severity accuracy. Our study increases the usefulness of the rich aerial survey database by providing estimates of uncertainty in the IDS database of tree mortality severity.

Role of thinning intensity in creating mixed hardwood and conifer forests within a Cryptomeria japonica conifer plantation: A 14-year study

For managers of conifer plantations, conversion to mixed hardwood and conifer forests is an important management goal. However, the extent to which thinning intensity affects stand volume and timber quantity and quality remains unclear. We investigated the growth of conifer and hardwood trees over 14 years (at 5 and 9 years after the first and second thinning operations, respectively) under unthinned (Control), 33% thinned (Weak), and 67% thinned (Intensive) treatments in a Cryptomeria japonica plantation. The diameter growth of both conifers and hardwoods, stand volume of hardwoods, and relative increment of stand volume of conifers increased with greater thinning intensity in the order of Control < Weak < Intensive, whereas the reverse was observed for the stand volume of conifers, dead conifer trees, and total yield of stand volume (i.e., gross production). These results suggest that intensive thinning can create large conifers and hardwoods, but reduces gross production. Mean annual tree ring width (ATRW), consistency of ATRW value, and mean crown ratio increased with increasing thinning intensity in the order of Control < Weak < Intensive, while height-to-diameter ratio (i.e., slenderness) showed the opposite trend. These findings suggest that timber quality (e.g., wood density, stiffness, visual grading) was better under Weak than under Intensive thinning. However, the production of large conifer timbers with homogeneous ATRW may offset reductions in quality. This study suggests that intensive thinning is a reliable method for rapidly creating mixed hardwood–conifer forests at the canopy level and producing large timbers of both conifer and hardwood species, whereas weak thinning is suitable for producing high-quality conifer timbers and maintaining net primary production, although repeated thinning is necessary.

Co‐designed management scenarios shape the responses of seasonally dry forests to changing climate and fire regimes

Abstract Climate change is altering disturbance regimes and recovery rates of forests globally. The future of these forests will depend on how climate change interacts with management activities. Forest managers are in critical need of strategies to manage the effects of climate change. We co‐designed forest management scenarios with forest managers and stakeholders in the Klamath ecoregion of Oregon and California, a seasonally dry forest in the Western US subject to fire disturbances. The resultant scenarios span a broad range of forest and fire management strategies. Using a mechanistic forest landscape model, we simulated the scenarios as they interacted with forest growth, succession, wildfire disturbances and climate change. We analysed the simulations to (a) understand how scenarios affected the fire regime and (b) estimate how each scenario altered potential forest composition. Within the simulation timeframe (85 years), the scenarios had a large influence on fire regimes, with fire rotation periods ranging from 60 years in a minimal management scenario to 180 years with an industrial forestry style management scenario. Regardless of management strategy, mega‐fires (&gt;100,000 ha) are expected to increase in frequency, driven by stronger climate forcing and extreme fire weather. High elevation conifers declined across all climate and management scenarios, reflecting an imbalance between forest types, climate and disturbance. At lower elevations (&lt;1,800 m), most scenarios maintained forest cover levels; however, the minimal intervention scenario triggered 5 × 105 ha of mixed conifer loss by the end of the century in favour of shrublands, whereas the maximal intervention scenario added an equivalent amount of mixed conifer. Policy implications. Forest management scenarios that expand beyond current policies—including privatization and aggressive climate adaptation—can strongly influence forest trajectories despite a climate‐enhanced fire regime. Forest management can alter forest trajectories by increasing the pace and scale of actions taken, such as fuel reduction treatments, or by limiting other actions, such as fire suppression.

Forest characteristics, population structure and growth trends of Pinus yunnanensis in Tianchi National Nature Reserve of Yunnan, southwestern China

Aims: Pinus yunnanesis is commercially, culturally and economically important, but there is a lack of ecological data on its role in stand dynamics. Our aims are to clarify the structure, composition, regeneration and growth trends of primary mature P. yunnanensis forests. Study area: The Tianchi National Nature Reserve in the Xuepan Mountains, Yunlong County, northwestern Yunnan, China. Methods: We investigated forests containing P. yunnanensis, measured tree ages and analyzed the data. Results: Six forest types were identified: (1) coniferous forest: Pinus yunnanensis (Type 1); (2) mixed coniferous and evergreen broad-leaved forest: P. yunnanensis-Lithocarpus variolosus (Type 2); (3) mixed coniferous and deciduous broad-leaved forest: P. yunnanensis-Quercus griffithii (Type 3); (4) mixed evergreen broad-leaved and coniferous forest: Castanopsis orthacantha-P. yunnanensis-Schima argentea (Type 4); (5) mixed coniferous, evergreen and deciduous broad-leaved forest: Pinus yunnanensis-Schima argentea-Quercus griffithii (Type 5); (6) mixed coniferous and evergreen broad-leaved forest: Pinus armandii-Quercus rehderiana-Pinus yunnanensis (Type 6). The size- and age-structure and regeneration patterns of P. yunnanensis were highly variable within these six forest types. P. yunnanensis regeneration was well balanced in forest Type 1 as compared to the other five types. All six forest types were identified as rare and old-growth with P. yunnaensis trees reaching ages of more than 105 years (a maximum age of 165 years with a diameter 116 cm at breast height) except for the Type 4 forest (a 90-year-old stand). Growth rates of P. yunnanensis, based upon ring width measurements, were high for the first 10 years, then declined after the 10th year. In contrast, basal area increment (BAI) increased for the first 25 years, plateaued, and only declined as trees became older. Trees in the older age classes grew more quickly than younger trees at the same age, a consequence of either site quality or competitive differences. The BAI of P. yunnanensis in all age classes in the Tianchi National Nature Reserve was much higher than those of the secondary and degraded natural P. yunnanensis forests of other areas. Conclusions: The P. yunnanensis forests of the Tianchi area appear to be some of the last remnants of primeval and old-growth forests of this species. These forests are structurally diverse and contain a rich diversity of overstory, mid-story, and understory species. Taxonomic reference: Editorial Committee of Flora Republicae Popularis Sinicae (1959–2004) for vascular plants. Abbreviations: BA = basal area; BAI = basal area increment; DBH = diameter at breast height; H = height; RBA = relative basal area.

Successful seedling establishment of arbuscular mycorrhizal-compared to ectomycorrhizal-associated hardwoods in arbuscular cedar plantations

Thinning is an effective method to create mixed hardwood-conifer forests, as it results in successful hardwood recruitment. However, it remains unclear to what extent mycorrhizal association (AM, or arbuscular mycorrhizae vs. ECM, ectomycorrhizae) affects hardwood recruitment. In this study, we explored which hardwood mycorrhizal type was more advantageous to recruit into a Cryptomeria japonica (AM conifer) plantation. We compared seedling recruitment success (i.e. seedling emergence, survival, and growth) between AM and ECM hardwoods during five years after thinning at various levels: 67% thinned (intensive), 33% thinned (weak) and un-thinned treatments (control). We also investigated the percent colonization of mycorrhizal fungi for the seedlings of the most dominant AM (Cornus controversa) and ECM (Quercus serrata) hardwoods in both the C. japonica plantation and an adjacent forest dominated by ECM tree species (e.g. Q. serrata, Alnus hirsuta var. sibirica, Castanea crenata). During the five years, seedling emergence and survival were greater in AM than ECM for most of the different emergence cohorts, resulting in a greater number of individuals for AM rather than ECM hardwoods for all thinning intensities. Vertical growth of the seedlings was also greater for AM than ECM species, particularly for early emerging cohorts in both the weak and intensive treatments. Percent colonization of AM fungi to AM seedlings was greater in the AM conifer plantation than in the adjacent ECM-dominant forest. In contrast, percent colonization of ECM fungi to ECM-type seedlings was lower in the plantation compared to the adjacent forest. These results suggest that AM hardwoods could easily be recruited to AM conifer plantations, probably due to the fact that AM-type seedlings could easily become associated with AM fungi in the same mycorrhizal-type plantation. Growth of the AM seedlings was enhanced, which was likely to be due to the sharing of AM fungi, which translocate nutrients via hyphal networks. In contrast, recruitment of ECM-type seedlings was strongly inhibited, probably due to the lack of colonization of the ECM fungi in the AM-type plantation. This study demonstrates that mycorrhizal associations play an important role in recruitment success of hardwoods into AM conifer plantations. Thus, when forest managers intend to convert conifer plantations to mixed hardwood and conifer forests, they should consider the role of mycorrhizal fungal type in future species composition.

Historical forest changes in the western United States

Changes in factors such as temperature, precipitation, fire regimes, ozone, atmospheric CO2, and nitrogen deposition may have altered forest growth over the past century. Determining changes in forest growth over long intervals is complicated by constantly changing growing conditions due to tree maturation, stand self-thinning, disturbance, and other factors. Because a comprehensive review is lacking, results from publications examining forest growth trends in the western United States over the past 100 years were evaluated. Across the region, upper elevational forest ecotones have been expanding upward in many but not all locations, possibly due to warming and reduced snowpack. Across most of the region, both growth increases and decreases are localized and spatially dispersed. For the inland West, historical photography and long-term inventory data show clear densification and expansion of ponderosa pine (Pinus ponderosa) and mixed conifer forest across the region, mostly due to reduced fire incidence. However, a recent drought, probably linked to ocean cycles and exacerbated by warming, has caused a growth setback and mortality, especially in the Southwest. Forest densification due to altered fire regimes does not equate to enhanced growth per se. Aspen (Populus tremuloides) dieback has been noted due to recent drought and local conifer mortality caused by drought has also been documented in several locations. Regeneration after recent fires appears to be inadequate in many localities. Except for local increased growth at some high elevation and coastal sites and possible periodic drought effects in the Southwest, it is difficult to detect any growth trends with available data.

Effectiveness of Restoration Treatments for Reducing Fuels and Increasing Understory Diversity in Shrubby Mixed-Conifer Forests of the Southern Rocky Mountains, USA

Exclusion of natural surface fires in warm/dry mixed-conifer forests of the western U.S. has increased potential for stand-replacing crown fires and reduced resilience of these systems to other disturbances, such as drought and insect attack. Tree thinning and the application of prescribed fire are commonly used to restore more resilient ecological conditions, but currently, there is a lack of long-term data with which to evaluate restoration treatment effectiveness in forest types where resprouting shrubs dominate understory communities. At a mixed-conifer site in southwestern Colorado, we compared forest structure and understory vegetation responses to three restoration treatments (thin/burn, burn, and control) over 10 years in a completely randomized and replicated experiment. Forest density, canopy cover, and crown fuel loads were consistently lower, and crown base height was higher, in thin/burn than burn or controls, but the effects diminished over time. Ten years following treatment, &gt;99% of all plant species within both treatments and the control were native in origin. There were no differences between treatments in understory richness, diversity, cover, or surface fuels, but graminoid cover more than doubled in all treatments over the 15-year monitoring period. Similarly, there was more than a 250% increase post-treatment in shrub density, with the greatest increases in the thin/burn treatment. In addition, we saw an increase in the average shrub height for both treatments and the control, with shrub stems &gt;80 cm becoming the dominant size class in the thin/burn treatment. Conifer seedling density was significantly lower in thin/burn compared with burn and control treatments after 10 years. Taken together, these conditions create challenges for managers aiming to reestablish natural fire patterns and sustain mixed-conifer forests. To limit the dominance of resprouting shrubs and facilitate conifer regeneration after overstory thinning and prescribed fire, managers may need to consider new or more intensive approaches to forest restoration, particularly given current and projected climate change.

Bacterial, fungal, and archaeal community assembly patterns and their determining factors across three subalpine stands at different stages of natural restoration after clear-cutting

The knowledge regarding how different soil microbial groups change in subalpine forest areas after clear-cutting is limited. To bridge this gap, we studied the change patterns of the different soil microbial community assemblies and their determining factors in subalpine areas. Field measurements and sampling were conducted in three stands at different stages of natural restoration (BF, broadleaf forest; MF, mixed coniferous and broadleaf forest; and PCF, primeval coniferous forest) after clear-cutting in western Sichuan Province, China. Three soil microbial group (bacteria, fungi, and archaea) community assemblies, edaphic properties, soil nematodes, tree diameter at breast height, plant richness, and understory vegetation biomass were examined and statistically analyzed. The α-diversity of the three microbial groups in the BF and MF stands was significantly higher than that in the PCF stand. The difference between the stands was greater than the difference within the stands for all three microbial groups. The changes in the three microbial groups were all significantly associated with shifts in soil carbon, soil total nitrogen, soil available nitrogen, and tree species composition. The bacterial and archaeal communities were also closely related to the bacterivore number. Acidobacteria, Actinobacteria, Bacteroidetes, Planctomycetes, Basidiomycota, Ascomycota, and Thaumarchaeota were the main phyla that responded to environmental variation. The three soil microbial groups all showed regular trends across the three different stands. The changes in the soil microbial community assembly were mainly attributed to the differences in soil nutrients, tree species composition, and feeding traits of soil nematodes.