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At least 199 records · Page 11Linked to original sources
USGS2018

Landscape-scale variation in canopy water content of giant sequoias during drought

Recent drought (2012–2016) caused unprecedented foliage dieback in giant sequoias ( Sequoiadendron giganteum ), a species endemic to the western slope of the southern Sierra Nevada in central California. As part of an effort to understand and map sequoia response to droughts, we studied the patterns of remotely sensed canopy water content (CWC), both within and among sequoia groves in two successive years during the drought period (2015 and 2016). Our aims were: (1) to quantify giant sequoia responses to severe drought stress at a landscape scale using CWC as an indicator of crown foliage status, and (2) to estimate the effect of environmental correlates that mediate CWC change within and among giant sequoia groves. We utilized airborne high fidelity imaging spectroscopy (HiFIS) and light detection and ranging (LiDAR) data from the Carnegie Airborne Observatory to assess giant sequoia foliage status during 2015 and 2016 of the 2012–2016 droughts. A series of statistical models were generated to classify giant sequoias and to map their location in Sequoia and Kings Canyon National Parks (SEKI) and vicinity. We explored the environmental correlates and the spatial patterns of CWC change at the landscape scale. The mapped CWC was highly variable throughout the landscape during the two observation years, and proved to be most closely related to geological substrates, topography, and site-specific water balance. While there was an overall net gain in sequoia CWC between 2015 and 2016, certain locations (lower elevations, steeper slopes, areas more distant from surface water sources, and areas with greater climate water deficit) showed CWC losses. In addition, we found greater CWC loss in shorter sequoias and those growing in areas with lower sequoia stem densities. Our results suggest that CWC change indicates sequoia response to droughts across landscapes. Long-term monitoring of giant sequoia CWC will likely be useful for modeling and predicting their population-level response to future climate change.

California↗
USGS2019

Bryophyte abundance, composition and importance to woody plant recruitment in natural and restoration forests

Restoration of tropical forests can lead to enhanced ecosystem services and increases in native biodiversity. Bryophytes may be an integral part of the forest restoration process and can serve a critical role in forest functioning. However, the recovery of bryophytes and their ability to facilitate woody plant establishment during restoration remains poorly studied, especially in the tropics. We investigate how bryophyte abundance and community composition, as well as woody plant seedling associations with bryophyte mats and other ground cover types change from under the canopy of intact forest to under trees in restoration corridor plantings in Hawaii. Restoration corridors consisted of corridors of koa (Acacia koa) trees that were planted roughly 30 years ago. Some corridors were planted around remnant ʻōhiʻa trees (Metrosideros polymorpha) that can be several hundred years old. We sampled under ʻōhiʻa in intact forest and both koa and ʻōhiʻa trees in restoration corridors. In restoration corridors, bryophyte abundance was low relative to intact forest and species diversity was a subset of that found in intact forest despite restoration corridors being several decades old. Seedlings strongly associated with bryophytes across all habitats suggesting that bryophytes may significantly enhance forest seedling establishment when present in restoration corridors. Other ground cover types like woody litter and nurse logs also had a positive association with forest seedlings but were rare in restoration corridors. Grass remained a dominant ground cover type in restoration corridors under koa and remnant ʻōhiʻa trees and only a single seedling was ever found growing in this grass. Enhancing bryophyte growth and recovery within restoration plantings through the reduction of grass cover could facilitate native plant establishment.

Hawaii↗
USGS2019

Finding the sweet spot: Shifting climate optima for maple syrup production in North America

Climate change is affecting the benefits society derives from forests. One such forest ecosystem service is maple syrup, which is primarily derived from Acer saccharum (sugar maple), currently an abundant and widespread tree species in eastern North America. Two climate sensitive components of sap affect syrup production: sugar content and sap flow. The sugar in maple sap derives from carbohydrate stores influenced by prior year growing season conditions. Sap flow is tied to freeze/thaw cycles during early spring. Predicting climate effects on syrup production thus requires integrating observations across scales and biological processes. We observed sap at 6 sugar maple stands spanning sugar maple’s latitudinal range over 2¬–6 years to predict the role of climate variation on sugar content and sap flow. We found that the timing of sap collection advanced by 4.3 days for every 1 °C increase in March mean temperature, sap volume peaked at a January-May mean temperature of 1 °C, and sap sugar content declined by 0.1 °Brix for every 1 °C increase in previous May-October mean temperature. Using these empirical relationships, we projected that the sap collection season midpoint will be 1 month earlier and sap sugar content will decline by 0.7 °Brix across sugar maple’s range by the year 2100 in an RCP 8.5 climate change scenario. The region of maximum sap flow is expected to shift northward by 400km, from near the 43rd parallel to the 48th parallel by 2100. Our findings suggest climate change will have profound effects on syrup yield across most of sugar maple’s range; drastic shifts in the timing of the tapping season accompanied by flat to moderate increases in syrup yield per tap in Canada contrast with declines in syrup yield and higher frequencies of poor syrup production years across most of the U.S. range.

Forest Ecology and Management↗
USGS2019

Whitebark pine (Pinus albicaulis) growth and defense in response to mountain pine beetle outbreaks

Whitebark pine (Pinus albicaulis) is a critical forest species of Northern Rocky Mountain upper subalpine ecosystems, yet little is known about the physiological response of whitebark pine to disturbance (e.g. fire, bark beetles, and pathogens) across a range of diverse environmental gradients. Resin–based defenses have long been recognized as the primary mechanism by which conifers respond to attack by bark beetles and pathogens and several studies have linked resin duct properties to survivorship during periods of increased beetle activity. However, to our knowledge, no studies have compared axial resin ducts in the secondary xylem of whitebark pine across pairs of living and dead whitebark pine trees to better understand survivorship following multiple disturbances including mountain pine beetle and white pine blister rust. We found a clear distinction in growth and defense characteristics between live and dead whitebark pine. Across our study sites on the Flathead Indian Reservation in northwestern Montana, live whitebark pine produced larger resin ducts with a greater annual investment in resin–based defenses than whitebark pine that died. Resin duct size, duct area, and relative duct area were all greater in live whitebark pine (by 56%, 48%, and 57%, respectively) and these were the most important variables influencing whitebark pine survivorship. In contrast, whitebark pine that had died grew faster over time (22% larger ring widths) than their live counterparts and also produced more resin duct structures (20% more ducts on average). Whitebark pine at our study sites exhibit differing strategies in the allocation of resources toward growth and defense, with the majority of survivors of recent disturbance investing more in defensive structures than growth. Our results support the idea that maintaining genetic variability and the associated suite of differing physiological traits promotes diverse response strategies to a complex array of biophysical and biological stressors that might leave a species vulnerable to extinction across its range.

Northern Rocky Mountain↗
USGS2019

Influence of forest harvest severity and time since perturbation on conservation of North American birds

I calculated avian conservation scores, based on published quantitative assessment of bird presence (typically relative abundance) and regional Partners in Flight conservation concern score of each species. I related these avian conservation scores to severity of forest perturbation (i.e., % retention) and number of years since perturbation for forest stands within North America. I characterized avian response to perturbation by comparing avian conservation score on perturbed stands with that of paired unperturbed reference stands. Positive avian response to perturbation, representative of improved avian conservation status, was found when forest retention was >20% of coniferous forests or 25%–75% of hardwood forests. Positive avian response was greatest ~10 years after perturbation that retained 58% of conifer forests or 49% of hardwood forests. Increased avian conservation scores following perturbation may last for up to 23 years after perturbation but occur and diminish sooner with greater forest retention. Average annual avian response, over 23 years post-perturbation, was greatest when 30%–50% of hardwood stands were retained and when 50%–70% of conifer stands were retained.

Forest Ecology and Management↗
USGS2020

Climate relationships with increasing wildfire in the southwestern US from 1984 to 2015

Over the last several decades in forest and woodland ecosystems of the southwestern United States, wildfire size and severity have increased, thereby increasing the vulnerability of these systems to type conversions, invasive species, and other disturbances. A combination of land use history and climate change is widely thought to be contributing to the changing fire regimes. We examined climate-fire relationships in forest and woodland ecosystems from 1984 – 2015 in Arizona and New Mexico using 1) an expanded satellite-derived burn severity dataset that incorporates over one million additional burned hectares when compared to MTBS data, and 2) climate variables including temperature, precipitation, and vapor pressure deficit (VPD). Regional climate-fire relationships were assessed by correlating annual area burned, area burned at high and low severity, and percent high severity with fire season (May-August) and water-year (October-September) climate variables. We also analyzed relationships between climate and high-severity fire at the scale of the individual fires using a hurdle model. We found that increasing temperature and VPD and decreasing precipitation were associated with increasing area burned regionally, and that area burned at high severity had the strongest relationships with climate metrics. The relationship between climate and fire activity in the Southwest appears to be strengthening since 2000. VPD-fire correlations were consistently as strong as, or stronger than, temperature or precipitation variables alone, both regionally and at the scale of the individual fires. Notably, at the scale of the individual fires, temperature and precipitation were not significant predictors of fire activity. Thus, our results support the use of VPD as a more integrative climate metric to forecast fire activity. We suggest that the strong relationship between VPD and fire activity may be useful to assess the likelihood of high-severity fire occurrence through continued development of the high-severity fire threshold model we present. The link between increasing aridity and increasing wildfire activity suggests a future with more fire in Southwest forests and woodlands with projected warming, underscoring the urgency of restoration in dry forests to reduce the likelihood of uncharacteristic, large high-severity fires.

Arizona, New Mexico↗
USGS2020

Carbon stock trends of baldcypress knees along climate gradients of the Mississippi River Alluvial Valley using allometric methods

Carbon stock trends of the knees of Taxodium distichum likely vary across climate gradients of the southeastern United States and contribute an unknown quantity of “teal” carbon to inland freshwater wetlands. Knee metrics (e.g., density, height, biomass) were measured in mixed T. distichum swamps across the Mississippi River Alluvial Valley (MRAV) from Illinois to Louisiana. Based on their geometric similarity to a cone, the biomasses of field knees were estimated by relating the volume of their measured field dimensions to lab-measured water displacement volume and biomass via volume/mass regressions (biomass (g) = 7.2230149 + 0.292902 × volume). Knees had greater height in flooded conditions (maximum height = 163 cm; Goose Lake, Arkansas), and also in climate normal environments of mid-range precipitation and temperature (p < 0.0001). Overall, knee biomass ha−1 was 7.5 times greater in flooded vs. not flooded conditions (34.6 ± 7.3 vs. 4.6 ± 1.0 Mg ha−1, respectively). The overall mean of knee carbon biomass stock was substantial (flooded vs. not flooded conditions: 18.1 ± 3.7 Mg C ha−1 to 2.9 ± 0.7 Mg C ha−1, respectively; knee/tree live standing biomass: 17.9–5.2%, respectively). Clearly, T. distichum knees should not be ignored in blue (teal) carbon discussions of wetlands. Because knees respond to climate normal conditions, hotter/drier environments in the MRAV could lead to a decline in the contribution of knee carbon stock in the southeastern United States.

Mississippi River Alluvial Valley↗
USGS2020

Long term persistence of aspen in snowdrift-dependent ecosystems

Quaking aspen (Populus tremuloides) forests throughout the western United States have experienced significant mortality in recent decades, much of which has been influenced by climate variability, especially drought. In the western portion of its range, where most precipitation arrives during winter as snowfall and summers are dry, snowdrifts that persist into the growing season provide soil moisture recharge that sustain many aspen groves that are important locations of biodiversity within the landscape. There is growing concern that reduced snowpack due to climate change may reduce the long-term persistence and productivity of aspen communities in these regions. In this study, we evaluated the potential for climate change and drought to reduce or eliminate isolated aspen communities in southwestern Idaho. We used a landscape simulation model integrated with inputs from an empirically derived biogeochemical model of growth, and a species distribution model of regeneration to forecast how changes in climate, declining snowpack, and competition with a conifer species is likely to affect aspen occupancy over the next 85-years. We found that simulated reductions in snowpack depth (and associated increases in climatic water deficit) caused a reduction in aspen persistence; aspen occupancy was reduced under all high emissions climate scenarios. Douglas-fir (Pseudotsuga menziesii) occupancy also declined under all future climates. Aspen regeneration declined over the course of all simulations, with an ensemble ratio of mortality/establishment increasing over the course of both low and high emissions climate scenarios. Climate-induced mortality of aspen clones increased in frequency under all climate scenarios and, under the most severe emissions scenarios, contributed to a substantial decline of aspen cover. Our research suggests that snowbanks will be an important determinant of long-term persistence of aspen under changing climate in the region.

Forest Ecology and Management↗
USGS2020

Rethinking foundation species in a changing world: The case for Rhododendron maximum as an emerging foundation species in shifting ecosystems of the southern Appalachians

“Foundation species” are widespread, abundant species that play critical roles in structuring ecosystem characteristics and processes. Ecosystem change in response to human activities, climate change, disease introduction, or other environmental conditions may promote the emergence of new foundation species or the decline of previously important foundation species. We present rhododendron ( Rhododendron maximum ) as an example of an emerging foundation species in riparian forest and headwater stream ecosystems of the southern Appalachian Mountains and use its example to propose a dynamic approach to recognizing foundation species. As other species have declined, rhododendron has increased in abundance, biomass, and ecosystem importance, and now dominates the riparian zones and mesic uplands of much of the region. Rhododendron structures, stabilizes, and modulates functions within both terrestrial and aquatic ecosystems. Studies of forest ecosystem response to environmental conditions indicate that rhododendron may increase the resistance and resilience of its associated ecosystems to predicted anthropogenic stress, including climate change, nitrogen enrichment, and invasive species. A more dynamic conception of foundation species as dependent on ecosystem states will help ecologists to focus on ecosystem processes and services, rather than on historically dominant species, for restoration strategies.

Alabama, Georgia, North Carolina, South Carolina, ↗
USGS2020

Small gradients in salinity have large effects on stand water use in freshwater wetland forests

Salinity intrusion is responsible for changes to freshwater wetland watersheds globally, but little is known about how wetland water budgets might be influenced by small increments in salinity. We studied a forested wetland in South Carolina, USA, and installed sap flow probes on 72 trees/shrubs along a salinity gradient. Species investigated included the trees baldcypress ( Taxodium distichum [L.] Rich.), water tupelo ( Nyssa aquatica L.), swamp tupelo ( Nyssa biflora Walt.), and the shrub waxmyrtle ( Morella cerifera (L.) Small). This study improves upon past reliance on greenhouse seedling studies by adding measurements of trees/shrubs along a salinity gradient, and better describes the role of low salinity on water use in freshwater wetland forests. We measured patterns of water use related to salinity, atmospheric conditions and season, and hypothesized that salinity would influence wetland forest water use through two mechanisms: salinity disturbances would yield stands with species and size classes that transpire less and individual trees with less conductive xylem tissue (i.e., sapwood). Both hypotheses held. At salinity concentrations ranging from fresh to 3 psu, forest structural changes alone resulted in stand water use reductions from 494 mm year -1 in freshwater stands to 316 mm year -1 in stands of slightly higher salinity. Tree sapwood function (inferred from radial sap flux profiles) also changed along this gradient and reduced sap flow rates by an additional 13.3% per unit increase in salinity (psu). Thus, stand water use was further reduced to 190 mm year -1 on saline sites. We found that forest structure is not the only change that affects water use in salinized watersheds; individual tree eco-physiological responses to salinity, manifesting in different radial sap flow profiles, are important as well.

South Carolina↗
USGS2021

Seed production patterns of surviving Sierra Nevada conifers show minimal change following drought

Reproduction is a key component of ecological resilience in forest ecosystems, so understanding how seed production is influenced by extreme drought is key to understanding forest recovery trajectories. If trees respond to mortality-inducing drought by preferentially allocating resources for reproduction, the recovery of the stand to pre-drought conditions may be enhanced accordingly. We used a 20-year annual seed capture data set to investigate whether seed production by three tree genera commonly found in the Sierra Nevada ( Abies , Pinus , and Calocedrus ) was correlated with variation in local weather, which included an extreme drought spanning multiple years. We tested whether average seed production differed during the drought years, and whether annual seed counts could be explained by three weather variables: spring temperature, annual precipitation, and summer climatic water deficit (CWD). We fit models testing for four separate effects: (1) a priming year model (weather 1 year prior to reproductive bud initiation), (2) a bud initiation model (weather in the year of reproductive bud initiation), (3) a pollination year model (weather in the year of pollination), and (4) maturation year model (weather in the year of seed maturation). For genera with two-year reproductive cycles, the pollination and maturation models were combined. We found support for the summer CWD Abies maturation year model, which suggested higher seed outputs immediately following dry summer conditions. The spring temperature pollination year model was selected for Pinus , which suggested that seed output is higher following warm spring weather during pollination. The annual precipitation priming year model was selected for Calocedrus , which showed a negative association between seed production and wetter conditions two years prior to seed production. More parent tree basal area resulted in higher seed output for all genera, though the confidence intervals overlapped 0 for Calocedrus . Permutation tests sugested there was no systematic difference in mean seed production during the drought after accounting for live tree basal area, regardless of genus. These results highlight the variability in response across genera, and suggest that the influence of seed production on forest recovery following drought-related mortality may depend on affected species and the timing of the mortality event within the masting cycle. A greater understanding of species-level masting to drought stress is needed to more precisely predict community-level recovery following drought.

California↗
USGS2021

Mammal species composition and habitat associations in a commercial forest and mixed-plantation landscape

Commercial forest plantations of fast-growing species have been established globally to meet increasing demands for timber, pulpwood, and other wood products. Industrial plantations may contribute to tropical forest conservation by reducing exploitation of primary and secondary natural forests. Whether such plantations can support critical elements of biodiversity, including provision of habitat and movement corridors for species of conservation concern, is an important question in Southeast Asia. Our objectives were to investigate relationships between habitat gradients and community attributes of medium-sized to large mammals in a mixed plantation mosaic in Bengkoka Peninsula, Sabah, East Malaysia. Data on mammals were collected using 59 remote camera stations deployed for a minimum of 21 days (24-hour sampling occasions) in three major land-use types: natural forest, Acacia plantations, and non- Acacia plantations (oil palm, rubber, young Eucalyptus pellita ). We used sample-based rarefaction to evaluate variation in species richness with land use. We used generalized linear models and ordination analyses to evaluate whether variation in mammal detections and species composition was associated with habitat gradients. We recorded >22 mammal species over 1572 sampling occasions. Natural forest area was positively associated with mammal species richness and detections of threatened mammals. Overall detections of mammals increased with decreasing elevation, but decreased within, and close to, Acacia plantations. Detections of threatened mammals increased with greater proportions of natural forest and Acacia and increasing proximity to roads. Sample-based rarefaction indicated that species richness of mammals in Acacia and natural forest was considerably higher than observed. Both natural forest and Acacia plantations shared similar values for species richness and diversity, but non- Acacia plantations scored lower in both metrics. Mammal species composition differed among different types of land use. Smaller generalists used non- Acacia plantation forests. A variety of other mammals including some threatened species used natural forest, Acacia , or a combination of the two. Acacia plantations possess attributes supporting a diversity of mammal species, including those we defined as threatened based on IUCN criteria. However, this is likely a function of the habitat mosaic with natural forest in the study area and the mangrove forests on the fringes of the peninsula serving as refuges of mammal diversity. Retention and restoration of natural and mangrove forests may therefore enhance the conservation potential of industrial Acacia plantations. Additionally, controlled road access in conjunction with anti-poaching operations and strengthening public awareness are essential to reduce the threat of overexploitation.

Forest Ecology and Management↗
USGS2021

Floodplain forest tree seedling response to variation in flood timing and duration

The regeneration process is a sensitive period within life cycles of floodplain tree species and can strongly influence forest community composition. Yet, fundamental information remains limited on the relationship between regeneration processes and the flood disturbances that, together, construct floodplain forest landscapes. In a controlled greenhouse experiment we tested the effects of complete submergence on six temperate floodplain forest species to understand how flood timing and duration influence seedling survival. Groups of overcup oak ( Quercus lyrata ), Nuttall oak ( Quercus texana ), willow oak ( Quercus phellos ), sugarberry ( Celtis laevigata ), green ash ( Fraxinus pennsylvanica ), and American elm ( Ulmus americana ) seedlings were submerged for either 5, 15, 25, or 0 days (control) at the ages of 3-weeks, 6-weeks, and 9-weeks post-emergence. All species demonstrated a higher sensitivity to flooding at age 3-weeks compared to 6- and 9- weeks, indicating substantial changes in seedling resilience within the first months following emergence. Additionally, the heavier-seeded Q. lyrata , Q. texana, and Q. phellos were less or equally vulnerable to flooding compared to the lighter-seeded C. laevigata, F. pennsylvanica, and U. americana across all age groups, especially at 3-weeks post-emergence. The results of this study have implications for understanding woody species regeneration ecology and changes in floodplain forest composition, particularly in the context of hydrologic modifications.

Forest Ecology and Management↗
USGS2022

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 western USA as future projections show hotter, drier climates potentially resulting 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 forest structure, either overly dense forests due to fire suppression or forests restored to lower densities, interacts with 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, 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.

Arizona↗
USGS2022

A forested wetland at a climate-induced tipping-point: 17-year demographic evidence of widespread tree recruitment failure

Regeneration and survival of forested wetlands are affected by environmental variables related to the hydrologic regime. Climate change, specifically alterations to precipitation patterns, may have outsized effects on these forests. In Tennessee, USA, precipitation has increased by 15% since 1960. The goal of our research was to assess the evidence for whether this change in precipitation patterns resulted in shorter growing seasons and recruitment failure in common canopy trees for a forest wetland. In 2001 and 2018, the density of Quercus lyrata (overcup oak), Liquidambar styraciflua (sweetgum), Quercus phellos (willow oak), and Betula nigra (river birch) seedling, sapling and adult density were mapped in an area of 2.3 ha within a seasonally flooded karst depression. Overall, the percentage of the growing season experiencing inundation was 26% greater in the deep than in shallow areas between 2001 and 2018. Saplings and small adults of all four species were restricted to shallow areas, and their abundance has declined substantially. Overcup oak and sweetgum individuals that were recruited into the adult life history stage were repelled from the deep zone. Overcup oak and sweetgum adults experienced lower mortality across the 2.3-ha study area (11% and 26%, respectively) relative to willow oak (56%) and river birch (64%) over the 17-year study. Growing-season inundation showed no relation to mortality in adult sweetgum and willow oak, a positive relation to mortality among adult river birch across size classes and among small adult overcup oak, and an inverse relation to mortality among large adult overcup oak. In shallow regions, overcup oak and sweetgum adults had greater basal area increment relative to the intermediate and deep regions of the pond. Results of hydrologic modeling for the study area, based on rainfall and temperature records covering 1855–2019, show ponding durations after 1970 considerably longer than the historical baseline, across ponding-depth classes. Our results strongly suggest that climate change is a driving factor suppressing tree regeneration since 1970 in this seasonally flooded karst depression.

Tennessee↗
USGS2024

Forest age is a primary trait filter for saproxylic beetles in the southeastern United States

Many forests throughout the world consist of regenerating mature stands. Although these forests differ in many respects from old-growth (with a history of minimal human disturbance), they typically develop similar structural attributes over time. As a result, older mature forests may be of particular conservation value if they contain resources and microhabitats benefitting saproxylic (deadwood dependent) species. Species’ response to forest age may be driven by traits that relate to ecological functions or habitat preferences, such that species with less compatible traits for a local forest environment are “filtered” out. Thus, forest age may influence species’ distributions and the trait composition of assembled communities.

Georgia↗
USGS2025

Determining the effects of reduced water availability on seed germination of five bottomland hardwood tree species

Globally, floodplain forests are experiencing shifts in species composition associated with drier conditions and disruptions of flood pulse hydrology. The specific processes behind these shifts in composition are not fully understood, but differential effects of drought on regeneration processes such as seed germination may be partially responsible. To determine how reduced water availability impacts seed germination of different floodplain tree species, a lab-controlled germination experiment was conducted. Seeds from tree species common to floodplain forests of the southeastern and southcentral United States whose abundance have been altered by drier hydrogeomorphic conditions were examined. These seeds included desiccation resistant, or orthodox, seeds of sugarberry ( Celtis laevigata ) and green ash ( Fraxinus pennsylvanica ), and desiccation sensitive, or recalcitrant, acorns of overcup oak ( Quercus lyrata ), water oak ( Quercus nigra ), and willow oak ( Quercus phellos ). Seeds of each species were incubated with one of eight osmotically adjusted water solutions ranging in water potential from 0.0 MPa to −1.4 MPa. This reduction in water potential decreases the water available to the seeds for germination. After four weeks, seed germination of all species decreased with reduced water potential; however, desiccation tolerance did not correspond with the ability to germinate under lower water potential. Orthodox seeds only germinated in higher water potential treatments. Sugarberry reached 30 % germination in only the control 0.0 MPa treatment while green ash reached 30 % germination in treatments as low as −0.4 MPa. In contrast, recalcitrant acorns continued to germinate under lower water potentials. Water oak maintained 30 % or greater germination under all treatments and willow oak reached 30 % down to −0.8 MPa. Overcup oak was the only species to not respond to water potential treatment. With respect to maximum germination, sugarberry and green ash reached maximum germination an average of 9 days sooner than the oak species. The results of this study agree with others that demonstrate that seed germination success is sensitive to environmental water conditions and that species specific differences in germination traits are linked to broader life history strategies that are adaptive to common environmental conditions in their range.

Forest Ecology and Management↗
USGS2025

Effects of restoration thinning on live tree carbon in northern secondary coastal redwood forests

At Redwood National and State parks restoration efforts are underway to promote the recovery of forests following a history of intense logging. Unmanaged secondary forests at the parks have high stem density with slow stand development. Restoration thinning treatments of these stands are designed to promote the representation of redwood and improve the growth of residual trees. Restoration treatments, by definition, remove live tree carbon, so there is a potential conflict with restoration and carbon sequestration goals. We used data from 151 monitoring plots to determine early treatment effects (mostly ≤ 10 years following treatments) on live tree forest carbon in thinned and unthinned stands. Aboveground live tree carbon in untreated secondary forests was primarily related to stand age. Both treated and untreated stands accumulated carbon over time, with evidence that treated stands had a slightly faster rate of carbon accumulation. For a subset of plots where we had sufficient replicates of thinning prescriptions, we found thinning resulted in reductions in live tree aboveground carbon, particularly for heavy thinning, but with plots accumulating live tree carbon stocks similar to pre-treatment levels within 6–10 years. Stand projections suggested that both thinned and unthinned stands have the capacity to greatly increase aboveground live tree carbon in coming decades, with thinned stands accumulating aboveground live tree carbon at a slightly faster pace.

California↗