Mixed Conifer Research Articles

Long-term effects of prescribed fire on large tree growth in mixed conifer forests at Lassen Volcanic National Park, California

Prescribed fire in dry coniferous forests of the western U.S. is used to reduce fire hazards. How large, old trees respond to these treatments is an important management consideration. Growth is a key indicator of residual tree condition, which can be predictive of mortality and response to future disturbance. Using a combination of long-term plot records and dendrochronological samples, we analyzed the effects of prescribed fire treatments from the early 1990 s on forest structure and individual tree growth in mixed-conifer forests of Lassen Volcanic National Park in northern California. Prescribed fire reduced stand live tree basal area and stem density at our sites up to 10 years following fire. Within two prescribed fire burn units and two adjacent unburned stands, we analyzed tree cores from 136 large (mean stem diameter > 70 cm) yellow pine (Pinus jeffreyi and P. ponderosa) and 136 large (mean stem diameter > 50 cm) white fir (Abies concolor). After accounting for annual precipitation, basal area increment for individual trees initially declined up to < 3 years post-fire for white fir and > 10 years post-fire for yellow pine, presumably in response to tree injuries. Growth improved for both species at a site that was burned twice, particularly for white fir. Recent average basal area increment was positively related to crown ratio and negatively associated with an index of local competition. Our findings suggest that forest management, such as prescribed fire and mechanical thinning, may be beneficial in terms of maintaining or improving tree growth among large residual trees. However, managers may want to balance the benefits of these treatments against inadvertent injury and mortality of large trees.

Copiotrophic Bacterial Traits Increase With Burn Severity One Year After a Wildfire

Wildfire and burn severity influence soil microbial communities during post-fire recovery. If post-fire differences in microbial communities affect soil carbon (C) pool dynamics, altered microbial communities could influence the transition of forests from C sources to C sinks during ecosystem recovery. For example, fire may change the abundance of copiotrophic and oligotrophic bacteria, influencing the kinetic rates of soil C pools due to differences in C-acquisition strategies and nutrient requirements. We assessed differences in soil bacterial communities and soil C pool kinetics 1 year after a wildfire in a mixed-conifer forest in northern California, United States. We determined whether differences in bacterial communities and soil C pools were related to copiotrophic versus oligotrophic life history strategies. Specifically, we assessed bacterial community oligotrophy versus copiotrophy based on phyla relative abundances and predicted 16S gene copy numbers. We then determined whether these life-histories were correlated with C pool kinetic rates. We further determined whether C degradation metabolic pathways predicted using PICRUSt2 were related to C pool kinetics. We found that copiotrophic bacteria exhibited greater abundance in burned areas than unburned areas, evidenced by increases in 16S rRNA gene copy number and by taxonomic classifications. Furthermore, the abundance of predicted metabolic pathways associated with fast-cycling C compounds increased with severity, including carbohydrate, alcohol, and amine degradation pathways, suggesting increased copiotrophic metabolic strategies. In contrast, the abundance of metabolic pathways of slow-cycling aromatic C compounds did not change, indicating oligotrophic metabolic strategies did not increase. The kinetic rate of the active C pool was positively related to the copiotrophic metabolic pathway of alcohol degradation, and negatively related to oligotrophic pathways like aromatic compound degradation. The links between C pool kinetics and phylum-level life-strategy classifications were ambiguous. Overall, our results suggest that metabolic life-strategies are related to soil C pool kinetics and could have short- and long-term impacts on soil C persistence during post-fire recovery. In the short-term, increased copiotrophy could increase soil C effluxviarapid cycling of labile C pools. However, over the longer-term lower prevalence of oligotrophic strategies could allow aromatic compounds associated with pyrogenic C to accumulate, increasing stable soil C stocks.

Wildfire controls on land surface properties in mixed conifer and ponderosa pine forests of Sierra Nevada and Klamath mountains, Western US

This study examines the post-fire biogeophysical and biochemical dynamics after several high-severity wildfires that occurred in mixed conifer and ponderosa pine forest types in the Sierra Nevada and Klamath Mountains regions between 1986 and 2017. We found a consistent pattern of reduced leaf area index (LAI) in the first year after fire, followed by gradual recovery over the subsequent 25 years. Recovery rate varied between forest types. For example, average summer LAI for 16-25 years post-fire was 88% of the pre-fire average for mixed conifers in the Sierra Nevada, 64% for ponderosa pine in the Sierra Nevada, and 83% for mixed conifers in Klamath Mountains (63, 35, and 64% in winter, respectively). The slower recovery of LAI in ponderosa pine could be due to poor species diversity and drier climate. Summer and winter albedo increased progressively until 12 years post-fire in Sierra Nevada, while it continued to increase until 25 years post-fire in Klamath Mountains. Ponderosa pine had the highest summer (0.148 ± 0.001) and winter (0.5 ± 0.0033) albedos. Post-fire changes in evapotranspiration (ET) and gross primary productivity (GPP) were consistent with the changes in LAI. Both summer and winter ET and GPP returned to pre-fire levels by 25 years after fire in mixed conifers of both regions, while the ET and GPP did not recover to pre-fire levels in ponderosa pine. Wildfires increased the land surface temperature (LST) immediately after fire in summer. This effect was significantly higher in mixed conifers of the Sierra Nevada (11 ± 0.03 °C) compared to Klamath Mountains (7 ± 0.01 °C). Our results suggest that reduced ET, consistent with less leaf area and its associated reduced evaporative cooling is the main factor controlling the immediate post-fire warming effect of wildfires in these regions. The findings reported here can be used to understand ecological responses to wildfire in these and nearby ecoregions as they represent mean historical behavior across multiple wildfire events.

Influence of Different Vegetation Types on Soil Physicochemical Parameters and Fungal Communities.

This study assessed the effects of Betula dahurica (BD), Betula platyphylla (BP), Larix gmelinii (LG), Quercus mongolica (QM), and a mixed conifer–broadleaf forest composed of LG and QM (LGQM) on the soil physicochemical parameters and community structure of fungi in the Zhongyangzhan Black-billed Capercaillie Nature Reserve. Fungal community structures were characterized via ITS rRNA sequencing. The effects of soil parameters on the community structure of soil fungi were assessed by Pearson correlation analysis and redundancy analysis (RDA). LGQM exhibited lower C/N, available nitrogen (AN), total phosphorus (TP), and available phosphorus (AP) compared with the QM broadleaf forest. The fungal Shannon and Simpson diversity indices were highest in BP, whereas LG exhibited the highest ACE index. The Basidiomycota, Ascomycota, Mortierellomycota, and Mucoromycota fungal phyla were dominant across all vegetation types. Each of the different vegetation types studied herein exhibited a unique fungal community structure. The RDA results indicated that fungal community structures were primarily shaped by the total N, available N, and available P of soil. Our findings thus indicated that forests restored with different species of trees may exhibit variations in soil quality and characteristics despite sharing the same climate. Furthermore, broadleaved and coniferous forests exhibited a unique fungal community diversity and composition.

Taxonomy and ecology of genus Psyra Walker, 1860 (Lepidoptera: Geometridae: Ennominae) from Indian Himalaya.

The Psyra Walker, 1860, is a typical Sino-Himalayan genus of the subfamily Ennominae, currently known by 18 species/4 subspecies globally and 9 species from India. This study aims to revise the taxonomy and ecology of Indian Psyra by providing a morphology-based diagnostic key, highlighting their altitudinal, habitat and seasonal preferences, and modelling their distribution based on current and future climatic scenarios. Here, we describe a new species, P. variabilis sp. nov. and document 4 species and 1 subspecies as new to India, viz. P. gracilis, P. szetschwana, P. dsagara, P. falcipennis and P. debilis debilis, thus updating the global species count to 19 with 14 species/1 subspecies from India. We also submitted partial mitochondrial COI sequences of P. crypta, P. similaria, P. spurcataria and P. gracilis as novel to the global genetic database and calculated the overall genetic divergence was 5.17% within the genus, suggesting strong monophyly. Being a typical montane genus, most of the species of Psyra were active within 2000–2280 m altitude, 10.55–15.7°C annual mean temperature, 1200–2300 mm annual precipitation and 168–179 NDVI. Psyra species were predominant in wet temperate, mixed coniferous and moist temperate deciduous forests, their abundance and richness being at peak during post-monsoon months of October–November. The major bioclimatic variables influencing the overall distribution of the genus were mean temperature of warmest quarter, temperature seasonality and precipitation of coldest/driest quarter. While two of the modelled species were predicted to lose area occupancy under future climatic scenarios, the narrow-specialist, Trans-Himalayan species P. debilis debilis was projected to gain up to 75% additional area in the years 2041–60. The results of this study will be helpful to identify sites with maximum area loss projection in ecologically fragile Indian Himalaya and initiating conservation management for such climatically vulnerable insect species groups.

SPECIES AND STATUS OF BAMBOO KNOWN FOR THE CONICAL HAT OF NORTHWESTERN LAYA: A UNIQUE CULTURE IN GASA, BHUTAN

Montane bamboo is of very importance to the indigenous people inhabiting mountains of the Himalayas, and is a necessary component of highaltitude temperate forest ecosystems. Particularly, in Laya it is commonly used for weaving conical hat and other implements. Thamnocal amusspathiflorus (Trin.) Munro bamboo was documented as a main element of the conical hat making, displaying the highest altitude frost hardy bamboos in mixed coniferous forest. The cluster analysis specified major habitat of 60% significance (p-value ≤ 0.72) indicating a strong influence of bamboo density with associated species composition and other ecological factors. Unregulated harvesting of young culms and the harvesters repeatedly congregating in the same site resulted in unhealthy clump. Its narrow distribution pattern might threaten to population decline or total wipe off and also remote cause possibly by the spread of secondary forest tree species such as Picea spinulosa &amp; Abies dens a that have gradually taken over areas previously occupied by the bamboo forest. Seventy percent of Laya pinter viewed agreed with the decline inthe production and use of conical hats. The element of this unique culture is under constant threat, for it was challenged by various factors including the stereotypical believes of the people.

Forest Above-Ground Biomass Inversion Using Optical and SAR Images Based on a Multi-Step Feature Optimized Inversion Model

Forest biomass change monitoring is essential for climate change. Synthetic aperture radar (SAR) and optimal remote sensing (RS) data are two very helpful data sources for forest biomass monitoring and estimation. During the procedure of biomass estimation using RS technique, optimal features selection and estimation models used are two critical steps. This paper therefore focuses on building an operational and robust method of biomass retrieval using optical and SAR RS data. First, random forest (RF) algorithms are used for reducing time-consuming and decreasing computational burden; then, an iterative procedure was embedded in K-nearest neighbor (KNN) algorithms for the best optimal feature selection and combination; last, the best feature combinations and KNN models were applied for forest biomass estimation. Moreover, forest type effects and RS feature source effects were considered. The results showed that feature combination of two optical images and the SAR image showed highest estimation accuracy by using the proposed algorithm (R2 = 0.70 for Forest-1, R2 = 0.72 for Forest-2, and R2 = 0.71 for Forest-3; RMSE = 16.18 Mg/ha for Forest-1, RMSE =17.66 Mg/ha for Forest-2, and RMSE = 18.67 Mg/ha for Forest-3, where Forest-1 is natural pure forests of Yunnan Pines, Forest-2 is natural mixed coniferous forests, and Forest-3 is the combination of Forest-1 and Forest-2). With the comparative analysis of proposed algorithm and different non-parametric algorithms, traditional nonparametric algorithms performed better in Forest-1, but worse in Forest-2 and Forest-3, while the proposed algorithm performed no obvious difference in three forest types and using five feature groups. The results revealed that the proposed algorithm was robust in biomass estimation, with almost no feature source and forest structure dependent for biomass estimation.

Thinning Effects on Stand Structure and Carbon Content of Secondary Forests

In, this study, we analysed the effects of thinning on stand structure and carbon stocks for a mixed conifer and broadleaf natural secondary forests in the Small Khingan Mountains, China. Stand structure and carbon stocks were assessed in trees from unthinned control (CK), lightly thinned (LT), moderately thinned (MT) and heavily thinned (HT) treatments. Results showed that the heavier the thinning, the larger the crown area became. Under the MT treatment, trees tended to be evenly distributed when compared to trees under the other treatments. All the trees of the LT and HT treatments were mixed strongly compared to those of the CK treatment. As the thinning intensitiy increased, the distributions of size differentiation and crowding degree gradually decreased. As a result, the competitive pressure diminished, and more dominant trees emerged. In addition, there was a significant positive correlation between individual tree carbon stock and canopy under all treatments. Carbon tends to accumulate in individuals with a random distribution, sparse spacing, strong mingling index and large competitive advantage. However, the results varied slightly under the HT treatment. Individuals in a dominant position occupied abundant resources and great niche space.

Development of Tools to Age Grand Fir to Aid in Collaborative Restoration of Federal Lands in Eastern Oregon

Abstract The USDA Forest Service is working closely with collaborative stakeholder groups to accelerate the pace and scale of restoration in fire-prone mixed conifer forests of eastern Oregon. Collaboratively planned restoration projects are typically designed to conserve older trees established before fire exclusion policies and other management practices began to alter forest landscapes beginning in the late 1800s. Tools exist for accurately estimating the age of common species including ponderosa pine, Douglas-fir, and western larch. There are no existing tools available for aging grand/white fir, although an important objective of many restoration projects in mixed conifer stands is to retain older grand/white fir while removing younger individuals that have infilled into stands in the absence of fire to enhance resilience of stands to future climate and disturbance regimes. This article describes the development of tools to age grand fir on the Malheur National Forest by taking simple field measurements of morphological characteristics. Bark fissure depth, height to live foliage, and diameter at breast height were the strongest noncorrelated tree morphological characteristics associated with tree age. Crown class had no predictive power for estimating tree age. A variety of methods are presented that can estimate the age of grand fir with reasonable accuracy and are appropriate for different management objectives. Additional field testing and continued experimentation with different tree aging methods within an adaptive management framework is recommended. Study Implications: Shade tolerant grand fir has expanded dramatically in mixed conifer stands of eastern Oregon in the absence of frequent fire. Collaboratively designed restoration projects in mixed conifer stands usually call for the removal of younger grand fir while maintaining older grand fir that contribute to stand- and landscape-scale biodiversity. It can be difficult to estimate the age of grand fir based on morphological clues because of highly variable growth forms in this species. However, several easy-to-use grand fir aging tools promise to facilitate restoration by making reasonably accurate estimates of tree age.

Land management explains major trends in forest structure and composition over the last millennium in California’s Klamath Mountains

SignificanceWe provide the first assessment of aboveground live tree biomass in a mixed conifer forest over the late Holocene. The biomass record, coupled with local Native oral history and fire scar records, shows that Native burning practices, along with a natural lightning-based fire regime, promoted long-term stability of the forest structure and composition for at least 1 millennium in a California forest. This record demonstrates that climate alone cannot account for observed forest conditions. Instead, forests were also shaped by a regime of frequent fire, including intentional ignitions by Native people. This work suggests a large-scale intervention could be required to achieve the historical conditions that supported forest resiliency and reflected Indigenous influence.

Tree species composition, stand structure and distribution patterns across three Kashmir Himalayan forests, India

ABSTRACT Himalayan ecosystems provide a unique opportunity to analyze the determinants of species richness across large elevation gradients. Understanding forest diversity and structure is fundamental to set conservation priorities. A quantitative assessment of tree species was conducted in Kashmir Himalayan forests to ascertain their composition, stand structure and distribution in 143 plots of 50 × 50 m2. Altogether, 13 species were recorded, ranging from five in subalpine (SA) forests to 10 in mixed conifer (MC) forests. There was a compositional dissimilarity among forest types. Pinus wallichiana was the most important species in low-level blue pine (BP) forests, whereas Abies pindrow prevailed in mid-elevation MC and high-elevation SA forests. Pinaceae contributed around 98% of stems and was the most speciose family, followed by Sapindaceae and Betulaceae. Stand density and basal area differed among forest types and were significantly correlated with elevation and slope. The tree diameter class distribution displayed an approximate reverse J-shaped pattern indicating the influence of disturbance. As the first two axes of the canonical correspondence analysis explained more than 93% of the inertia in the species-environment relation, elevation and slope are the main drivers of species distribution. Information about these forest attributes could provide better ecological insights for sustainable forest management.

Ancient trees and modern wildfires: Declining resilience to wildfire in the highly fire-adapted giant sequoia

Ancient giant sequoias Sequoiadendron giganteum (Lindl.) J. Buchholz are highly valued trees with limited distribution. They are the most massive trees on earth, and they have exceptional longevity (>3,000 years). Given their extraordinary resilience to wildfire, insects, and disease, most managers hoped giant sequoias would be resistant to anthropogenic change. However, the warming climate and fire exclusion-caused fuel build-up has dramatically increased the amount of high-intensity wildfire in giant sequoia groves since 2015. To better understand recent wildfire effects on large, legacy giant sequoia trees, we surveyed high- and moderate-severity fire areas in groves that burned in three wildfires between 2015 and 2017. Within areas classified as high severity via remote sensing, ∼84% of the 162 large sequoias (>1.2 m diameter at breast height) were killed; in moderate severity, ∼28% of the 239 large sequoias were killed. These rates varied between fires but overall were at the lower end of the mortality range that has been documented in Sierra Nevada mixed-conifer forests. Across all three fire areas, we found large sequoia mortality was linked with presence of significant prior fire damage to the lower tree bole (i.e., fire scars or “catfaces”), lower crown ratios, and lower elevations. At Black Mountain Grove, we tracked trees through time and found total crown damage and the presence of fire scars were the best predictors of mortality by year three, where large sequoias sustained up to ∼ 85% crown damage before succumbing to injury. There, 52 of 204 trees were dead one-year postfire, with 71 dead by year three. Overall, these fires caused significant and concerning mortality levels of these ancient trees, and yet the impact on sequoia groves between 2015 and 2017 was dwarfed in comparison to the more recent 2020 Castle Fire, 2021 Windy Fire and 2021 KNP Complex Fire. With the push to increase forest and fuel treatments to reduce catastrophic fire risk across the Western U.S., more immediate triage to protect irreplaceable resources is needed as fire activity rapidly increases. Our study suggests that prioritizing management action that creates fire resilience in unburned groves, and maintains the fuel reduction benefits accrued by past treatments and lower severity wildfires, will be critical to avoid continued losses of these exceptional, irreplaceable old growth forests.

Cumulative Severity of Thinned and Unthinned Forests in a Large California Wildfire

Studies pertaining to fire severity in commercially thinned versus unthinned forests are based on a comparison of tree mortality between the two categories. Commercial thinning is widely conducted on public and private forestlands as a fire management approach designed to reduce fire severity and associated tree mortality. However, tree mortality from thinning itself, prior to the occurrence of the wildfire, is generally not taken into account, which leaves a potentially important source of tree loss, with its associated forest carbon loss and carbon emissions, unreported. This study investigated the “cumulative severity” of commercially thinned and unthinned forests in a large 2021 wildfire, the Antelope fire, occurring within mixed-conifer forests on public lands in northern California, USA. Using published data regarding the percent basal area mortality for each commercial thinning unit that burned in the Antelope fire, combined with percent basal area mortality due to the fire itself from post-fire satellite imagery, it was found that commercial thinning was associated with significantly higher overall tree mortality levels (cumulative severity). More research is needed, in other large forest fires, to determine whether the finding, that commercial thinning killed more trees than it prevented from being killed, is common elsewhere.

Have western USA fire suppression and megafire active management approaches become a contemporary Sisyphus?

Fire suppression policies and “active management” in response to wildfires are being carried out by land managers globally, including millions of hectares of mixed conifer and dry ponderosa pine (Pinus ponderosa) forests of the western USA that periodically burn in mixed severity fires. Federal managers pour billions of dollars into command-and-control fire suppression and the MegaFire (landscape scale) Active Management Approach (MFAMA) in an attempt to contain wildfires increasingly influenced by top down climate forcings. Wildfire suppression activities aimed at stopping or slowing fires include expansive dozerlines, chemical retardants and igniters, backburns, and cutting trees (live and dead), including within roadless and wilderness areas. MFAMA involves logging of large, fire-resistant live trees and snags; mastication of beneficial shrubs; degradation of wildlife habitat, including endangered species habitat; aquatic impacts from an expansive road system; and logging-related carbon emissions. Such impacts are routinely dismissed with minimal environmental review and defiance of the precautionary principle in environmental planning. Placing restrictive bounds on these activities, deemed increasingly ineffective in a change climate, is urgently needed to overcome their contributions to the global biodiversity and climate crises. We urge land managers and decision makers to address the root cause of recent fire increases by reducing greenhouse gas emissions across all sectors, reforming industrial forestry and fire suppression practices, protecting carbon stores in large trees and recently burned forests, working with wildfire for ecosystem benefits using minimum suppression tactics when fire is not threatening towns, and surgical application of thinning and prescribed fire nearest homes.

Tree growth responses to extreme drought after mechanical thinning and prescribed fire in a Sierra Nevada mixed-conifer forest, USA

An estimated 128 M trees died during the 2012–2016 California drought, largely in the southern Sierra Nevada Range. Prescribed burning and mechanical thinning are widely used to reduce fuels and restore ecosystem properties, but it is unclear if these treatments improve tree growth and vigor during extreme drought. This study examined tree growth responses after thinning, prescribed burning, and extreme drought at the Teakettle Experimental Forest, a historically frequent fire mixed-conifer forest in the southern Sierra Nevada of California, USA. Mechanical thinning (no thin, understory thin, and overstory thin) and prescribed burning (unburned, fall burning) were implemented in 2000–2001. Using annual growth data from increment cores, over 10,000 mapped and measured trees, and lidar-derived metrics of solar radiation and topographic wetness, we had two primary questions. First, what were the growth responses to thinning and prescribed burning treatments, and did these responses persist during the 2012–2016 drought? Second, what tree-level attributes and environmental conditions influenced growth responses to treatments and drought?Thinning increased residual tree growth and that response persisted through extreme drought 10–15 years after treatments. Growth responses were higher in overstory versus understory thinning, with differences between thinning types more pronounced during drought. Species-specific growth responses were strongest with overstory thinning, with sugar pine (Pinus lambertiana) and incense-cedar (Calocedrus decurrens) having higher growth responses compared to white fir (Abies concolor) and Jeffery pine (Pinus jeffreyi). For individual trees, factors associated with higher growth responses were declining pretreatment growth trend, smaller tree size, and post-treatment low neighborhood basal area. Growth responses were initially not influenced by topography, but topographic wetness became important during extreme drought. Mechanical thinning resulted in durable increases in residual tree growth rates during extreme drought over a decade after thinning occurred, indicating treatment longevity in mitigating drought stress. In contrast, tree growth did not improve after prescribed burning, likely due to fire effects that reduced surface fuels, but had little effect on reducing tree density. Thinning treatments promoted durable growth responses, but focusing on stand-level metrics may ignore important tree-level attributes such as localized competition and topography associated with higher water availability. Mechanical thinning was effective at improving growth in trees that had been experiencing declining growth trends, but was less effective in improving growth responses in large old trees of higher ecological importance.

Impact of Ice-Storms and Subsequent Salvage Logging on the Productivity of Cunninghamia lanceolata (Chinese Fir) Forests

The impacts of ice-storms on forests have received growing attention in recent years. Although there is a wide agreement that ice-storms significantly affect forest structure and functions, how frequent ice-storms and subsequent salvage logging impact productivity of subtropical coniferous forests in the future still remains poorly understood. In this study, we used the Ecosystem Demography model, Version 2.2 (ED-2.2), to project the impact of salvage logging of ice-storm-damaged trees on the productivity of Cunninghamia lanceolata-dominated coniferous forest and C. lanceolata-dominated mixed coniferous and broadleaved forests. The results show that forest productivity recovery is delayed in coniferous forests when there is no shade-tolerant broadleaved species invasion after ice-storms, and C. lanceolata could continue to dominate the canopy in the mixed coniferous and broadleaved forests under high-frequency ice-storms and subsequent salvage logging. The resistance and resilience of the mixed coniferous and broadleaved forests to high-frequency ice-storms and subsequent salvage logging were stronger compared to coniferous forests. Although conifers could continue to dominate the canopy under shade-tolerant broadleaved species invasion, we could not rule out the possibility of a future forest community dominated by shade-tolerant broadleaf trees because there were few coniferous saplings and shade-tolerant broadleaf species dominated the understory. Our results highlight that post-disaster forest management should be continued after high-frequency ice-storms and subsequent salvage logging in C. lanceolata forests to prevent possible shade-tolerant, late successional broadleaf trees from dominating the canopy in the future.

Persistent composition legacy and rapid structural change following successive fires in Sierra Nevada mixed conifer forests

Mixed conifer forests in the Sierra Nevada, California, USA, face threats from frequent high-severity reburns caused by fuel accumulation and increasingly dry, hot conditions associated with climate change. Stand replacing fire and establishment of expansive shrub patches may result in positive feedbacks causing landscapes to convert to persistent shrubland or grassland. Our objective was to examine changes in mixed conifer forest density and species composition after successive fires across a range of initial and reburn severities. We resampled 134 field plots 5–6 years after the Chips Fire reburned stands initially burned by the Storrie and Rich fires on the Lassen and Plumas National Forests. Generalized Linear Models and post-hoc margins analyses were used to examine the interaction effects of initial and reburn fire severities on changes in conifer tree and seedling densities, percent cover of shrubs, and changes in species composition evaluated using fire tolerance index. We found that successive fires with severities less than high-severity significantly reduced tree densities to values within or close to the natural range of variation for mixed conifer stands. Despite these changes in density, species composition did not shift toward increasing dominance of fire tolerant species; mature trees and seedlings of true firs and other fire intolerant species remained dominant after successive low and moderate severity fires. Seedling establishment pulses were associated with sampling years with abundant precipitation, and unburned, unchanged, and low-severity plots in the reburn sample had significant increases in seedling densities across the range of initial burn severities. Shrub cover increased significantly with only a few reburn severity interactions, but declined significantly with repeated high-severity fire. Although two low- to moderate-severity fires may reduce tree densities to within the natural range of variation, they may not shift species composition towards historical patterns. Selective thinning in areas that burned at low- to moderate-severity may be necessary to restore historical species composition in Sierra Nevada mixed conifer forests.

Late Pleistocene palaeoenvironments and a possible glacial refugium on northern Vancouver Island, Canada: Evidence for the viability of early human settlement on the northwest coast of North America

Multi-proxy palaeoecological analyses of lake cores from two sites on northern Vancouver Island reveal previously undocumented non-arboreal environments in the region during the late Pleistocene. Radiocarbon, pollen, sedimentary ancient DNA (sedaDNA), diatom, and grain size analyses indicate that Topknot Lake on the west coast of northern Vancouver Island was not glaciated in the last 18,500 years, extending into the hypothesized regional glacial maximum. A cold herb-shrub coastal tundra existed at the site from ca. 17,500–16,000 cal BP with species including willows (Salix), grasses (Poaceae), sedges (Cyperaceae), heathers (Ericaceae), and sagebrush (Artemisia). SedaDNA analysis also supports the presence of rare non-arboreal taxa at Topknot Lake during this interval including Jacob's-ladder (Polemonium), bistort (Bistorta), and wild berries (Rubus). After ca. 16,000 cal BP and through the terminal Pleistocene, pine (Pinus), alder (Alnus), and ferns formed open forests under cool and dry conditions. At Little Woss Lake in the mountains of north-central Vancouver Island, fir (Abies) stands dominated from ca. 14,200–14,100 cal BP, then were replaced by open pine woodland with alder and ferns from ca. 14,100–12,000 cal BP. SedaDNA corroborates these plant taxa as well as indicating grizzly bear (Ursus arctos horribilis) and Chinook salmon (Oncorhynchus tshawytscha) in and around the basin by ca. 14,100 cal BP. Mixed conifer forests of pine, western hemlock (Tsuga heterophylla), and alder spread into the island's interior ca. 12,000–11,100 cal BP during the Pleistocene-Holocene transition. The records from these two lakes demonstrate the diachronous development of postglacial ecosystems on northern Vancouver Island. Furthermore, these data provide key evidence for environments that could have supported human populations on the northwest coast of North America for several millennia during the terminal Pleistocene.

Canopy Temperature Is Regulated by Ecosystem Structural Traits and Captures the Ecohydrologic Dynamics of a Semiarid Mixed Conifer Forest Site

AbstractPlant canopy temperature (Tc) is partly regulated by evaporation and transpiration from the canopy surface and can be used to infer changes in stomatal regulation and vegetation water stress. In this study, we used a thermal Unmanned Aircraft Systems in conjunction with eddy covariance, sap flow, and spectral reflectance data to assess the diurnal characteristics of Tc and water stress status over a semiarid mixed conifer forest in Arizona, USA. Diurnal Tc dynamics were closely related to tree sap flow and changes in spectral reflectance associated with stomatal regulation. Consistent with previously reported deviations, we found that on average Tc was 1.8°C lower than the above canopy air temperature (Ta). However, the relationship between Tc and Ta varied significantly according to tree density and tree height classes, with taller and denser trees exhibiting relatively low |Tc‐Ta| (2.4 and 2.1°C cooler canopies, respectively) compared to shorter and less‐dense tree stands (1.7 and 1.5°C cooler canopies, respectively). We used these data to evaluate space‐borne diurnal measurements of Tc and water stress from the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) mission. We found that ECOSTRESS observations of Tc accurately tracked seasonal shifts in diurnal surface temperatures and vegetation water stress, and that site‐level observations of heterogeneity in forest composition and structure could be applied to separate the processes of canopy transpiration and soil evaporation within the ECOSTRESS footprint. This study demonstrates how proximal and satellite remote sensing approaches can be combined to reveal the diurnal and seasonally dynamic nature of Tc and water stress.

Role of forest site type in determining bacterial and biochemical properties of soil

• The biological properties of the soil are determined by the site type. • The tested soils are significant differences in microbiological activity. • Soil from fresh mixed boron is the most fertile soil. The aim of the present study was to investigate the effect of forest site type on the bacterial and biochemical properties of the soil. Data for counts, diversity, and composition of bacterial communities, as well as soil enzymatic activity, was used for the assessment. A determination of the relationships between the parameters was also performed. Soil samples were collected in the Stare Jabłonki Forest Division (north-eastern Poland, Central Europe) from four sites: fresh coniferous forest (Fc), fresh mixed coniferous forest (Fm), fresh mixed forest (Mf), and moist mixed forest (Mm). The tested soils showed significant differences in enzyme activity and microflora. Organotrophic bacteria and actinobacteria proliferated the most in soil from fresh mixed coniferous forest. Organotrophic bacteria grew faster than actinobacteria in the soil, indicating that the former were represented by r-strategists, and the latter – by K-strategists. The soil sampled from site Fc2 (fresh coniferous forest) had the highest values of the diversity index. Alphaproteobacteria (phylum Proteobacteria ) were the dominant bacterial class in the soils, followed by Actinobacteria (phylum Actinobacteria ) and Acidobacteriia (phylum Acidobacteria ). Phyla Proteobacteria , Actinobacteria, and Acidobacteria were most abundantly represented by genera Rhodoplanes, Mycobacterium , and Candidatus Solibacter , respectively. According to the biochemical soil quality index (BA), the soil sampled from site Fc2 (fresh mixed coniferous forest) was the most fertile. The study demonstrates that microbial and biochemical parameters of the soil can serve as an accurate indicator of the status and health of forest ecosystems.