Ponderosa Pine Research Articles

Measurement report: Introduction to the HyICE-2018 campaign for measurements of ice-nucleating particles and instrument inter-comparison in the Hyytiälä boreal forest

Abstract. The formation of ice particles in Earth's atmosphere strongly influences the dynamics and optical properties of clouds and their impacts on the climate system. Ice formation in clouds is often triggered heterogeneously by ice-nucleating particles (INPs) that represent a very low number of particles in the atmosphere. To date, many sources of INPs, such as mineral and soil dust, have been investigated and identified in the low and mid latitudes. Although less is known about the sources of ice nucleation at high latitudes, efforts have been made to identify the sources of INPs in the Arctic and boreal environments. In this study, we investigate the INP emission potential from high-latitude boreal forests in the mixed-phase cloud regime. We introduce the HyICE-2018 measurement campaign conducted in the boreal forest of Hyytiälä, Finland, between February and June 2018. The campaign utilized the infrastructure of the Station for Measuring Ecosystem-Atmosphere Relations (SMEAR) II, with additional INP instruments, including the Portable Ice Nucleation Chamber I and II (PINC and PINCii), the SPectrometer for Ice Nuclei (SPIN), the Portable Ice Nucleation Experiment (PINE), the Ice Nucleation SpEctrometer of the Karlsruhe Institute of Technology (INSEKT) and the Microlitre Nucleation by Immersed Particle Instrument (µL-NIPI), used to quantify the INP concentrations and sources in the boreal environment. In this contribution, we describe the measurement infrastructure and operating procedures during HyICE-2018, and we report results from specific time periods where INP instruments were run in parallel for inter-comparison purposes. Our results show that the suite of instruments deployed during HyICE-2018 reports consistent results and therefore lays the foundation for forthcoming results to be considered holistically. In addition, we compare measured INP concentrations to INP parameterizations, and we observe good agreement with the Tobo et al. (2013) parameterization developed from measurements conducted in a ponderosa pine forest ecosystem in Colorado, USA.

Short-term benefits of prescribed fire to bird communities of dry forests

BackgroundLow-severity prescribed fire is an important tool to manage fire-maintained forests across North America. In dry conifer forests of the western USA, prescribed fire is often used to reduce fuel loads in forests characterized historically by mixed- and low-severity fire regimes. Understanding the ecological effects of prescribed fire treatments is important for predicting the impacts of these management actions on wildlife communities. Few studies, however, have estimated small landbird responses to forest treatments at spatial scales relevant to their ecology or have examined potential differences in treatment effects applied within historically mixed- vs. low-severity fire regimes. Therefore, we evaluated prescribed fire treatment effects and relationships with burn severity for avian communities in dry conifer forests dominated by ponderosa pine (Pinus ponderosa) located on seven national forests in the interior western USA. We surveyed birds for 1–4 years and 1–3 years before and after prescribed fire treatments at mixed- and low-severity fire regime locations, respectively, following a before-after, control-impact study design — 8 paired control-treatment units in mixed-severity locations (16 total study units with 320 survey points) and 4 paired control-treatment units in low-severity locations (10 total study units with 278 survey points). Using a Bayesian hierarchical multi-species occupancy model, we investigated responses to prescribed fire treatments by a community of 95 bird species.ResultsWe found statistically supported treatment effects and/or burn severity relationships for 33 species primarily in mixed-severity locations. The data supported positive treatment effects at mixed-severity locations for 9 species (American robin [Turdus migratorius], western bluebird [Sialia mexicana], hairy woodpecker [Dryobates villosus], black-backed woodpecker [Picoides arcticus], American three-toed woodpecker [Picoides dorsalis], house wren [Troglodytes aedon], dusky flycatcher [Empidonax oberholseri], western wood-pewee [Contopus sordidulus], gray flycatcher [Empidonax wrightii]), whose occupancy was more likely after treatment at the most severely burned units, and a negative effect for one species (ruby-crowned kinglet [Corthylio calendula]), whose occupancy was less likely after treatment at the most severely burned units. At low-severity locations, only two species exhibited treatment effects, both negative (red-faced warbler [Cardellina rubrifrons] and lark sparrow [Chondestes grammacus]). We also found supported occupancy relationships with burn severity post-treatment (i.e., regardless of species distribution before treatment) for 29 species, most of which were consistent with their life histories (e.g., patterns of positive relationships for cavity-nesting, bark insectivores and negative relationships for open-nesting, foliage insectivores). Stronger responses to prescribed fire treatments at mixed-severity locations were unexpected because prescribed fire applications were more similar to historical wildfires characteristic of low-severity fire regimes.ConclusionsBird populations in historically low-severity locations may be relatively unresponsive to prescribed fire because fire there is typically more frequent and regular. By comparison, fire events in forests characterized by a mixed-severity regime are less common, potentially eliciting more responses to an infrequent opportunity, even by species that are strongly associated with recently burned forests by wildfire. Our results suggest that fire management activities intended to reduce fuels and lower the risk of high-severity wildfire can also be effective in creating habitat for some fire specialists at least in the short term.

209 Effects of Biochar in Finishing Beef Cattle Diets on Greenhouse Gas Emissions

Abstract Two experiments were conducted to evaluate impacts of biochar on methane (CH4) and carbon dioxide (CO2) emissions, performance, and carcass characteristics of finishing beef cattle. Experiment 1 (initial BW = 329 kg ± 19 kg) utilized biochar sourced from pistachio shells (VGrid Energy Systems) in a 70% corn, 20% distillers grains, and 5% corn residue diet. Experiment 2 (initial BW = 386 kg ± 19 kg) utilized biochar sourced from ponderosa pine wood waste (Vital Ag) in a 40% corn, 40% Sweet Bran, and 15% corn silage diet. Both experiments evaluated 2 treatments: control (CON) diet containing no biochar and biochar (BIO) replacing 1% of dietary corn. Pen was the experimental unit with 8 steers per pen and 8 replications. Four replications rotated through a two-chamber emissions barn in 5-d cycles to measure CH4 and CO2 emissions. Cattle performance data were analyzed using the MIXED procedure of SAS with treatment and body weight block as fixed effects and emissions data analyzed as repeated measure. There were no statistical differences in experiment 1 for CH4, g/d (P = 0.75) and g/kg of dry matter intake (DMI; P = 0.99) or CO2 as g/d (P = 0.94) and g/kg DMI (P = 0.88). No impact on cattle performance or carcass characteristics were observed (final BW, DMI, average daily gain, gain to feed, hot carcass weight, longissimus muscle area, USDA quality grade, 12th rib fat; P ≥ 0.21). In experiment 2, there were no statistical differences between treatments for CH4, g/d (P = 0.78) and g/kg DMI (P = 0.84) or CO2, g/d (P = 0.50) and g/kg DMI (P = 0.52). Supplementing biochar at 1% of diet DM did not impact CH4 and CO2 emissions from finishing beef cattle. Cattle performance and carcass characteristics were not impacted by biochar in experiment 1.

Cover and density of southwestern ponderosa pine understory plants in permanent chart quadrats (2002-2020).

This data set consists of 101 permanent 1m × 1m (1-m2 ) quadrats located within southwestern ponderosa pine ecosystems near Flagstaff, Arizona, USA. Individual plants in these quadrats were identified and mapped annually for 19 years (2002-2020). The original chart quadrats were established between 1912 and 1927 to determine the effects of domestic livestock grazing on herbaceous plants and pine seedlings. Today these data provide opportunities to examine the effects of climate and land-use change on plant demography, population dynamics, and community processes. We provide the following data and data formats: (1) digitized maps of all plant locations in shapefile and geodatabase format, (2) shapefiles showing annual locations of each individual plant species, (3) annual maps of each quadrat in TIFF and PDF format, (4) annual basal area of each species per quadrat for species mapped as polygons, (5) tabular representation of polygon areas and centroid locations for plant species mapped as polygons, (6) tabular representation of point locations for plant species mapped as points, (7) plot-scale 20 m × 20 m overstory tree canopy cover, tree basal area, parent material, and elevation, (8) quadrat-scale information (e.g., quadrat site and number, coordinates in UTM Zone 12 and latitude/longitude, and descriptive comments for each quadrat), (9) plant species list, (10) summary of plant species observed in each quadrat, (11) summary of quadrats mapped by site and year, and (12) data formatted for use in Integral Projection Models (IPM) and plant population analyses. There are no copyright restrictions; please cite this paper and the associated data set when data are used in publications.

A novel smartphone-based activity recognition modeling method for tracked equipment in forest operations.

Activity recognition modelling using smartphone Inertial Measurement Units (IMUs) is an underutilized resource defining and assessing work efficiency for a wide range of natural resource management tasks. This study focused on the initial development and validation of a smartphone-based activity recognition system for excavator-based mastication equipment working in Ponderosa pine (Pinus ponderosa) plantations in North Idaho, USA. During mastication treatments, sensor data from smartphone gyroscopes, accelerometers, and sound pressure meters (decibel meters) were collected at three sampling frequencies (10, 20, and 50 hertz (Hz)). These data were then separated into 9 time domain features using 4 sliding window widths (1, 5, 7.5 and 10 seconds) and two levels of window overlap (50% and 90%). Random forest machine learning algorithms were trained and evaluated for 40 combinations of model parameters to determine the best combination of parameters. 5 work elements (masticate, clear, move, travel, and delay) were classified with the performance metrics for individual elements of the best model (50 Hz, 10 second window, 90% window overlap) falling within the following ranges: area under the curve (AUC) (95.0% - 99.9%); sensitivity (74.9% - 95.6%); specificity (90.8% - 99.9%); precision (81.1% - 98.3%); F1-score (81.9% - 96.9%); balanced accuracy (87.4% - 97.7%). Smartphone sensors effectively characterized individual work elements of mechanical fuel treatments. This study is the first example of developing a smartphone-based activity recognition model for ground-based forest equipment. The continued development and dissemination of smartphone-based activity recognition models may assist land managers and operators with ubiquitous, manufacturer-independent systems for continuous and automated time study and production analysis for mechanized forest operations.

Tree growth sensitivity to climate varies across a seasonal precipitation gradient

Spatial patterns of precipitation in the southwestern United States result in a complex gradient from winter-to-summer moisture dominance that influences tree growth. In response, tree growth exhibits seasonal-to-annual variability that is evident in the growth of whole tree rings, and in sub-annual sections such as earlywood and latewood. We evaluated the influence of precipitation and temperature on the growth of Pinus ponderosa trees in 11 sites in the southwestern US. Precipitation during the year of growth and the prior year accounted for about half of the climate influence on annual growth, with the other half reflecting conditions 2-4years prior to growth, indicating that individual trees do indeed exhibit multi-year "memory" of climate. Trees in wetter sites exhibited weaker influence of past precipitation inputs, but longer memory of climatic variability. Conversely, trees in dry sites exhibited shorter memory of long-term climatic variability, but greater sensitivity to past precipitation effects. These results are consistent with the existence of complex interactions between endogenous (phenotype) effects and exogenous (climate) effects in controlling climate memory in trees. After accounting for climate, residual variability in latewood growth was negatively correlated with earlywood growth, indicating a potential tradeoff between latewood versus earlywood growth. This study provides new insights that will assist the accurate prediction of woody biomass growth and forest carbon sequestration across a southwestern US precipitation gradient.

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.

ROOST CHARACTERISTICS OF BATS IN THE PINE RIDGE REGION OF NEBRASKA

Protecting day roosts is imperative to the persistence and survival of local populations of tree-roosting bats. The Pine Ridge region of Nebraska represents the largest area of coniferous forests in the state and possesses the greatest diversity of bats in Nebraska. In this study, we examined roost characteristics primarily for 4 species in need of conservation in the region: Fringed Myotis (Myotis thysanodes), Long-legged Myotis (Myotis volans), Little Brown Myotis (Myotis lucifugus), and Hoary Bat (Aeorestes cinereus). With a limited understanding of roost characteristics for other species in the region, we also collected some roost data for the Big Brown Bat (Eptesicus fuscus) and Western Small-footed Myotis (Myotis ciliolabrum). We tracked 42 bats with an emphasis on lactating females. Fringed Myotis, Big Brown Bats, and Western Small-footed Myotis typically roosted in cracks and crevices of dead trees. Long-legged Myotis roosted only in rock crevices at our western-most study site and only large, dead Ponderosa Pines (Pinus ponderosa) at our eastern-most site. Little Brown Myotis roosted in human-made structures in large colonies. Hoary Bats roosted in foliage of live hardwoods and conifers. Conservation of dead Ponderosa Pines, particularly those with large diameters and exfoliating bark, will provide roost structures for most crevice-roosting bats in the region. Our limited data for Hoary Bats suggest that roost-tree use is variable, as individuals roosted in both live hardwoods and conifers. Exclusive use of buildings throughout the region by female Little Brown Myotis implies timber harvests and wildfires might not greatly affect roosts for reproductive females. We demonstrated that roost characteristics vary among species and between nearby populations of the same species, representing important information for making informed habitat management decisions in a region with limited forests in northwestern Nebraska.

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.

Root system architecture of Pinus ponderosa three decades after copper root pruning in a container nursery

Root system architecture of Pinus ponderosa three decades after copper root pruning in a container nursery

Combustion of Aboveground Wood from Live Trees in Megafires, CA, USA

Biomass combustion is a major biogeochemical process, but uncertain in magnitude. We examined multiple levels of organization (twigs, branches, trees, stands, and landscapes) in large, severe forest fires to see how combustion rates for live aboveground woody parts varied with tree species, size, and fire severity in Ponderosa pine (Pinus ponderosa Dougl. ex Laws.) and mixed conifer-dominated forests of the Sierra Nevada, California, USA. In high severity fire patches, most combustion loss was from branches < 2 cm diameter; in low to moderate severity patches, most was from bole charring. Combustion rates decreased as fire severity declined and with increasing tree size. Pinus species had little branch combustion, leading them to have ≈50% the combustion rate of other taxa. Combustion rates could be 100% for small branch segments and up to 57% for small tree aboveground woody biomass in high severity fire patches. However, combustion rates are very low overall at the stand (0.1%–3.2%) and landscape level (0.6%–1.8%), because large trees with low combustion rates comprise the majority of biomass, and high severity fire patches are less than half of the area burned. Our findings of low live wood combustion rates have important implications for policies related to wildfire emissions and forest management.

Competitive Hierarchy Processes Support Mixed Species Regeneration in Strip-Cuts in the British Columbia Interior

Competitive exclusion can lead to a loss of species diversity within small forest gaps. Thus, it poses a potential concern for mixed species regeneration following strip-cut harvesting in the species rich interior moist forests of British Columbia. In this study, we compare nine tree species widely used in reforestation for their growth rates along a light/gap-position gradient in 50 m wide east-west oriented strip-cuts. Data after 15 growing seasons reveal that a crossover of species’ growth patterns along the light gradient can be linked to their shade tolerance ranking, and competitive hierarchy processes can be observed between species. The growth of two shade-intolerant (lodgepole pine and ponderosa pine), and two moderately tolerant (Douglas fir and white pine) species did surpass the growth of other more tolerant species under high light conditions in this study. Thus, we conclude that maintaining shade-intolerant species within 50 m wide strip-cuts is feasible, but species need to be planted in locations that suit their light requirements.

Not Only Severe Events: Moderate Dry Periods Impact the Hydraulic Functioning and Survival of Planted Ponderosa Pine Seedlings

Juvenile tree survival will increasingly shape the persistence of ponderosa pine forests in the western United States. In contrast to severe pulse disturbances that induce widespread adult and juvenile tree mortality, moderate periods of low rainfall and warm temperatures may reduce forest persistence by killing juvenile trees at the seedling stage. Intensification of these periods in a changing climate could therefore increasingly restrict both natural regeneration and artificial regeneration of planted seedlings. We conducted a controlled field experiment at a single site in the Front Range of Colorado, USA, to determine the responses and survival of 3 Colorado subpopulations of <1 year old potted ponderosa pines to moderately dry conditions, variation in small rainfall events based on observed patterns, and shaded and unshaded microsite environments. Near surface soil moisture increased slightly following small rainfall events, but declined over the 45-day experimental period. Seedling transpiration and associated canopy cooling declined after ∼13 days, and further declines in transpiration and canopy cooling suggest that the majority of trees in lower rainfall treatments experienced hydraulic dysfunction between days ∼20–30. After 45 days, mortality across all subpopulations and treatments, inferred by relative water loss, exceeded 90–95%. Despite some uncertainty pertaining to the stress tolerance of nursery grown versus naturally germinated conifers, our results show that planted ponderosa pine seedlings <1 year old are unlikely to survive moderate dry periods of 20+ days relying on small rainfall events. Although microsite conditions and soil moisture availability shaped tree hydraulic functioning early in the experiment (days 1–13), later functioning was shaped predominately by the legacy of rainfall treatments. Our results illustrate the importance of moderate dry events that occur consistently as part of seasonal variation in climate, and show how their intensification may constitute a sustained press that limits opportunities for natural and artificial regeneration.

Soil moisture response to seasonal drought conditions and post‐thinning forest structure

AbstractProlonged drought conditions in semi‐arid forests can lead to widespread vegetation stress and mortality. However, the distribution of these effects is not spatially uniform. We measured soil water potential at high spatial and temporal resolution using 112 sensors distributed across a ponderosa pine forest in northern Arizona, USA, during two abnormally dry years with below‐average total precipitation. We used the data to assess the effects of fore‐summer drought period on the timing, magnitude, and extent of drying throughout the top 100 cm of the soil profile. Additionally, we use high spatial resolution terrestrial lidar measurements of forest structure to develop relationships between soil drying and fine‐scale forest structure. We find that increasing drought from 2019 to 2020 caused significantly earlier onset of soil dying at all depths (25, 50 and 100 cm) and more days below a critical drying threshold for ponderosa pine. Additionally, our results show that significantly drier soils are found in areas with higher stand‐level basal area, canopy cover and tree density, and shorter trees. Our results from the unprecedented spatial and temporal resolution data suggest that tailored restoration thinning with specific tree density and size parameters can be used to increase and prolong the availability of deep soil water to trees during drought.

Wildfire and forest thinning shift floral resources and nesting substrates to impact native bee biodiversity in ponderosa pine forests of the Colorado Front Range

In fire-adapted ponderosa pine forests of western North America, fire suppression policies during much of the 19th century gradually resulted in high stem densities undesirable for fire risk management. To restore desirable forest structures, regional ecosystem management efforts often focus on reducing stand densities and re-introducing fire disturbances. However, it remains unclear whether these practices benefit insect species important for ecosystem function, including native bees. Bee community assemblages were sampled across the growing season in 39 ponderosa pine stands for two years in central Colorado to model effects of fire and thinning disturbances on bee populations. Four key findings emerged: (1) overall native bee diversity consisted of 5 families (Andrenidae, Apidae, Colletidae, Halictidae, and Megachilidae), 30 genera, and at least 70 unique bee species. Predominant genera were bumblebees (Bombusspp.), mason bees (Osmiaspp.), and digger bees (Anthophoraspp.), accounting for 50%, 9%, and 5 % of all captures, respectively. (2) Average bee abundance did not vary among burned, thinned, or non-treated control stands, though bee species richness and diversity were highest in stands affected by high severity wildfire. (3) Bee community composition differed among disturbance types, and there was turnover in the ratios of Bombus: Osmia species between control and burned stands. (4) Representation of bee nesting strategies at sample sites also differed due to fire and thinning disturbances, but these effects were moderated by seasonality. We link variation in forest structure to bee assemblages using linear models and show that presence of coarse woody debris has positive effects on overall forest bee abundance, richness, and diversity. Ponderosa pine forests in central Colorado provide habitat for a diverse assemblage of native bee species, and thinning operations are not associated with reductions in bee diversity, and fire disturbances were associated with enhanced bee foraging and nesting habitats. Bee community composition and associated life histories vary across disturbance types and unique bee assemblages are associated with different disturbance histories. Accordingly, maintaining a mosaic of thinning treatments and promoting wildland fire use that results in a gradient of burn severities may increase floral resources and nesting opportunities and can help to maximize overall bee biodiversity at a landscape scale.

Landscape-scale forest restoration decreases vulnerability to drought mortality under climate change in southwest USA ponderosa forest

Drought-induced tree mortality is predicted to increase in dry forests across the globe as future projections show hotter, drier climates. This could potentially result in large-scale tree die-offs, changes in species composition, and loss of forest ecosystem services, including carbon storage. While some studies have found that forest stands with greater basal areas (BA) have higher drought mortality, many have not evaluated the extent to which forests restored to lower densities via restoration activities affect drought mortality. The southwestern USA is particularly susceptible to tree mortality due to the predicted increases in temperature, drier soils, and forests with high density. Our objective was to evaluate how ponderosa pine mortality is expected to be influenced by the Four Forests Restoration Initiative (4FRI), a large-scale forest restoration effort ongoing in northern Arizona, USA, that will reduce stand BA by approximately 40%. Specifically, we modeled drought mortality in three time periods, one contemporary (1970–2010), and two future (2020–2059 and 2060–2099) under three restoration scenarios: no thinning, 4FRI thinning, and a BA reduction beyond the 4FRI plan (4FRI-intensive). We estimated mortality using 11 climate models under two emissions scenarios. Without thinning, our model predicted that by mid-century (2020–2059), changes in climate could increase annual ponderosa pine mortality rates by 45–57% over contemporary rates. However, with thinning, mid-century mortality was predicted to remain near or below contemporary rates and these rates are 31–35% (4FRI) and 46–51% (4FRI-intensive) less than the mid-century scenarios without thinning. Our study shows that while climate change is likely to increase tree mortality rates, large-scale forest restoration projects, such as 4FRI, have the potential to ameliorate the effects of climate change and keep mortality rates near contemporary levels for decades.

The Effects of Crown Scorch on Post-fire Delayed Mortality Are Modified by Drought Exposure in California (USA)

Accurately predicting the mortality of trees that initially survive a fire event is important for management, such as planning post-fire salvage, planting, and prescribed fires. Although crown scorch has been successfully used to predict post-fire mortality (greater than one-year post-fire), it remains unclear whether other first-order fire effect metrics (e.g., stem char) and information on growing conditions can improve such predictions. Droughts can also elevate mortality and may interact, synergistically, with fire effects to influence post-fire tree survival. We used logistic regression to test whether drought exposure, as indicated by summarized monthly Palmer Drought Severity Index (PDSI) over ten-years could improve predictions of delayed mortality (4–9 years post-fire) at the individual tree level in fire-affected forest inventory and analysis (FIA) plots in California (USA). We included crown scorch, bark thickness, stem char, soil char, slope, and aspect in the model as predictors. We selected the six most prevalent species to include in the model: canyon live oak, Douglas-fir, Jeffrey pine, incense-cedar, ponderosa pine, and white fir. Mean delayed mortality, based on tree count, across all FIA plots across all tree species and plots was 17%, and overall accuracy was good (AUC = 79%). Our model performed well, correctly predicting survivor trees (sensitivity of 0.98) but had difficulty correctly predicting the smaller number of mortality trees (specificity of 0.27) at the standard probability=0.5 mortality threshold. Crown scorch was the most influential predictor of tree mortality. Increasing crown scorch was associated with greater risk of delayed mortality for all six species, with trees exhibiting over 75% crown scorch having a probability of dying that exceeded 0.5. Increasing levels of stem char and soil char (first order indicators) were associated with increasing mortality risk but to less effect than crown scorch. We expected that greater drought exposure would increase delayed post-fire mortality, but we found that increasing drought exposure (median and minimum PDSI) was associated with a modest decrease in post-fire mortality. However, we did find that trees with high levels of crown scorch were less likely to survive with increasing drought exposure (median PDSI). Delayed mortality risk decreased as terrain slope increased. Taken together, our results suggest that trees with substantial crown damage may be more vulnerable to delayed mortality if exposed to drought and that crown scorch is an effective post-fire mortality predictor up to 10 years post-fire.

Heterogeneous isotope effects decouple conifer leaf and branch sugar δ18O and δ13C.

Isotope ratios of tree-ring cellulose are a prominent tool to reconstruct paleoclimate and plant responses to environmental variation. Current models for cellulose isotope ratios assume a transfer of the environmental signals recorded in bulk leaf water to carbohydrates and ultimately into stem cellulose. However, the isotopic signal of carbohydrates exported from leaf to branch may deviate from mean leaf values if spatial heterogeneity in isotope ratios exists in the leaf. We tested whether the isotopic heterogeneity previously observed along the length of a ponderosa pine (Pinus ponderosa) leaf water was preserved in photosynthetic products. We observed an increase in both sugar and bulk tissue δ18O values along the needle, but the increase in carbohydrate δ18O values was dampened relative to the trend observed in leaf water. In contrast, δ13C values of both sugar and bulk organic matter were invariant along the needle. Phloem-exported sugar measured in the branch below the needles did not match whole-needle values of δ18O or δ13C. Instead, there was a near-constant offset observed between the branch and needle sugar δ13C values, while branch δ18O values were most similar to δ18O values observed for sugar at the base of the needle. The observed offset between the branch and needle sugar δ18O values likely arises from partial isotope oxygen exchange between sugars and water during phloem loading and transport. An improved understanding of the conditions producing differential δ13C and δ18O isotope effects between branch phloem and needle sugars could improve tree-ring-based climate reconstructions.

Growth Response of Ponderosa Pine to Intensive Cultural Treatments Varies with Site Quality and Plantation Age

Abstract Long-term forest experiments provide valuable knowledge in managing forests for productivity and other ecosystem services. California’s “Garden of Eden” experiment was established to determine growth potential of Pinus ponderosa plantations in response to intensive cultural treatments. We examined the 20-year growth-response of tree volume to intensive cultural treatments consisting of combinations of herbicide on competing vegetation (H), fertilization (F), and insecticide (I). We found that both H and F treatments synergistically increased tree growth at intermediate and lower-quality sites. Growth increased by 1.5–2.1 times with F, 2.1–2.5 times with H, and 2.3–3.8 times with HF treatments versus control (range = 39.3–109.2 m3 ha−1). Across the highest productive site, H and F effects on volume seemed additive at younger ages, but largely dissipated by age 20, with volume increasing by 1.6, 1.2, and 1.6 times relative to control in F, H, and HF treatments, respectively. However, 20-year mean annual increment was 21.7 m3 ha−1 yr−1 for the F treatment, the highest volume reported for ponderosa pine in California. The results underscore how site-specific cultural treatments, especially H and F, may widely enhance plantation productivity and boost stand development. Study Implications In Mediterranean climates, competing vegetation control is essential for ponderosa pine planation establishment and early growth, especially at intermediate and poor-quality sites. At higher-productivity sites, fertilization enhances stand growth and development, although fertilization’s beneficial effects on growth do not appear until canopy closure. Precommercial thinning in herbicide and fertilization treatments will not reduce overall stand growth 10 years postthinning. Intensively managed plantations appear to have a higher maximum stand density index compared to natural stands or unmanaged plantations. Therefore, these cultural treatments can be used to rapidly reforest areas after disturbances and subsequently promote larger trees on reforested landscapes.

Culturally Modified Trees: Peeled and Scarred Ponderosa Pine Trees in the Zuni Mountains, New Mexico, USA

Modification of forest trees can occur from a variety of factors. Both cultural and natural processes can injure trees and many injuries can be dated dendrochronologically. Distinguishing between types of injuries, however, is important for understanding past human land-use practices and delineating different activities or processes that impact the forest. In the Zuni Mountains of New Mexico, USA, we have identified trees intentionally peeled for their cambial layer and unintentionally damaged trees whose scars resemble cambium-peeled trees. Both detailed attribute recording and dendrochronological dating were used to identify past exploitation of this ponderosa pine forest.