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At least 1,153 records · Page 64Linked to original sources
USGS2026

Cross-site comparison of ecosystem nutrient cycling in hardwood and conifer forests on contrasting soils

In the northeastern United States, both hardwood and conifer forests have developed on sites with contrasting soils, allowing an examination of the effect of site and forest type on ecosystem nutrient cycling. We measured biomass production and nutrient fluxes in northern hardwood and conifer stands at three sites differing in soil fertility. We found that leaf, root, and wood concentrations of calcium (Ca), magnesium (Mg), and potassium reflected differences in soil base cation availability, while concentrations of nitrogen (N) and phosphorus (P) were more consistent across sites. Nutrient uptake was calculated as the sum of litterfall, net throughfall (throughfall minus precipitation), root turnover, and accumulation in perennial tissues (wood). We propose a novel metric of nutrient cycling, the nutrient retention fraction (NRF), defined as the proportion of annual nutrient uptake retained in biomass accretion. Because the NRF is unitless, it can be compared across nutrients; Ca and Mg had the highest NRF and P the lowest ( p = 0.05). Across sites and elements, NRFs were lower for conifers (5.0 ± 0.6%) than for hardwoods (7.2 ± 0.5%), associated with their lower productivity. Nutrient-use efficiency (biomass production divided by nutrient uptake) tended to be high where foliar concentrations indicated low availability of that nutrient. Nutrient retention of N and P was higher where availability of the other element was high, which could be a mechanism contributing to N and P co-limitation.

Canadian Journal of Forest Research↗
USGS2006

Factors affecting distribution of wood, detritus, and sediment in headwater streams draining managed young-growth red alder - Conifer forests in southeast Alaska

Factors (riparian stand condition, management regimes, and channel properties) affecting distributions of wood, detritus (leaves and branches), and sediment were examined in headwater streams draining young-growth red alder (Alnus rubra Bong.) - conifer riparian forests (<40 years old) in southeast Alaska. More riparian red alder were found along streams affected by both timber harvesting and mass movement than in streams affected by timber harvesting alone. Young-growth stands produced little large wood material (diameter ???10 cm) and had little effect on altering the size distribution of functional large wood in channels, although more alder wood pieces were found in streams with greater numbers of riparian alder trees. Legacy wood pieces (>40 years old) remained in channels and provided sites for sediment and organic matter storage. Despite various alder-conifer mixtures and past harvesting effects, the abundance of large wood, fine wood, and detritus accumulations significantly decreased with increasing channel bank-full width (0.5-3.5 m) along relatively short channel distances (up to 700 m). Changes in wood, detritus, and sediment accumulations together with changes in riparian stand characteristics create spatial and temporal variability of in-channel conditions in headwater systems. A component of alder within young-growth riparian forests may benefit both wood production and biological recovery in disturbed headwater stream channels. ?? 2006 NRC.

Canadian Journal of Forest Research↗
USGS2010

The role of mosses in ecosystem succession and function in Alaska’s boreal forest

Shifts in moss communities may affect the resilience of boreal ecosystems to a changing climate because of the role of moss species in regulating soil climate and biogeochemical cycling. Here, we use long-term data analysis and literature synthesis to examine the role of moss in ecosystem succession, productivity, and decomposition. In Alaskan forests, moss abundance showed a unimodal distribution with time since fire, peaking 30–70 years post-fire. We found no evidence of mosses compensating for low vascular productivity in low-fertility sites at large scales, although a trade-off between moss and vascular productivity was evident in intermediate-productivity sites. Mosses contributed 48% and 20% of wetland and upland productivity, respectively, but produced tissue that decomposed more slowly than both nonwoody and woody vascular tissues. Increasing fire frequency in Alaska is likely to favor feather moss proliferation and decrease Sphagnum abundance, which will reduce soil moisture retention and decrease peat accumulation, likely leading to deeper burning during wildfire and accelerated permafrost thaw. The roles of moss traits in regulating key aspects of boreal performance (ecosystem N supply, C sequestration, permafrost stability, and fire severity) represent critical areas for understanding the resilience of Alaska’s boreal forest region under changing climate and disturbance regimes.

Alaska↗
USGS2010

The role of soil drainage class in carbon dioxide exchange and decomposition in boreal black spruce (Picea mariana) forest stands

Black spruce (Picea mariana (Mill.) B.S.P.) forest stands range from well drained to poorly drained, typically contain large amounts of soil organic carbon (SOC), and are often underlain by permafrost. To better understand the role of soil drainage class in carbon dioxide (CO2) exchange and decomposition, we measured soil respiration and net CO2 fluxes, litter decomposition and litterfall rates, and SOC stocks above permafrost in three Alaska black spruce forest stands characterized as well drained (WD), moderately drained (MD), and poorly drained (PD). Soil respiration and net CO2 fluxes were not significantly different among sites, although the relation between soil respiration rate and temperature varied with site (Qw: WD > MD > PD). Annual estimated soil respiration, litter decomposition, and groundcover photosynthesis were greatest at PD. These results suggest that soil temperature and moisture conditions in shallow organic horizon soils at PD were more favorable for decomposition compared with the better drained sites. SOC stocks, however, increase from WD to MD to PD such that surface decomposition and C storage are diametric. Greater groundcover vegetation productivity, protection of deep SOC by permafrost and anoxic conditions, and differences in fire return interval and (or) severity at PD counteract the relatively high near-surface decomposition rates, resulting in high net C accumulation.

Canadian Journal of Forest Research↗
USGS2011

Geostatistical modeling of riparian forest microclimate and its implications for sampling

Predictive models of microclimate under various site conditions in forested headwater stream - riparian areas are poorly developed, and sampling designs for characterizing underlying riparian microclimate gradients are sparse. We used riparian microclimate data collected at eight headwater streams in the Oregon Coast Range to compare ordinary kriging (OK), universal kriging (UK), and kriging with external drift (KED) for point prediction of mean maximum air temperature (Tair). Several topographic and forest structure characteristics were considered as site-specific parameters. Height above stream and distance to stream were the most important covariates in the KED models, which outperformed OK and UK in terms of root mean square error. Sample patterns were optimized based on the kriging variance and the weighted means of shortest distance criterion using the simulated annealing algorithm. The optimized sample patterns outperformed systematic sample patterns in terms of mean kriging variance mainly for small sample sizes. These findings suggest methods for increasing efficiency of microclimate monitoring in riparian areas.

Canadian Journal of Forest Research↗
USGS2012

The effect of size and competition on tree growth rate in old-growth coniferous forests

Tree growth and competition play central roles in forest dynamics. Yet models of competition often neglect important variation in species-specific responses. Furthermore, functions used to model changes in growth rate with size do not always allow for potential complexity. Using a large data set from old-growth forests in California, models were parameterized relating growth rate to tree size and competition for four common species. Several functions relating growth rate to size were tested. Competition models included parameters for tree size, competitor size, and competitor distance. Competitive strength was allowed to vary by species. The best ranked models (using Akaike’s information criterion) explained between 18% and 40% of the variance in growth rate, with each species showing a strong response to competition. Models indicated that relationships between competition and growth varied substantially among species. The results also suggested that the relationship between growth rate and tree size can be complex and that how we model it can affect not only our ability to detect that complexity but also whether we obtain misleading results. In this case, for three of four species, the best model captured an apparent and unexpected decline in potential growth rate for the smallest trees in the data set.

Canadian Journal of Forest Research↗
USGS1995

Effect of timber harvest on soil carbon storage at Blodgett Experimental Forest, California

Four plots from a mixed conifer forest were similarly cleared, burned, and replanted at various times over 17 years; a plot logged 79 years before sampling was used as a control. The plots had similar slope (2 to 15%, midslope position), aspect (south to southeast), and soil type (Holland series: mesic Haploxeralf; a Gray Brown Luvisol in the Canadian classification system). Twenty sites at each plot were sampled volumetrically by horizon to 20 cm below the organic–mineral soil boundary. Samples were analyzed for bulk density, organic C, and total N. There was an initial loss (15%) of organic C from the soil within 1 to 7 years, likely the result of oxidation (burning and decomposition) and erosion. For 17 years of forest regrowth, the soil continued to lose C (another 15%), probably owing to decomposition of slash material and possibly erosion, despite the slight accumulation of new litter and roots. After 80 years of regrowth, rates of carbon accumulation exceeded rates of loss, but carbon storage had declined and was not likely to recover to preharvest levels. Timber harvest and site preparation dramatically altered soil C and N distribution, in which C/N ratios after site preparation were initially high throughout the upper 20 cm. Subsequently, C/N ratios became lower with depth and with recovery age. Although stocks of C and N varied considerably among the plots and did not change consistently as a function of recovery age, the C/N ratios did vary systematically with recovery age. We hypothesize that the amount of C ultimately stored in the soil at steady state depends largely on N reserves and potentials, which appear to vary with erosion, intensity of burning, and site treatment.

California↗
USGS2022

Understory plant communities show resistance to drought, hurricanes, and experimental warming in a wet tropical forest

Global climate change has led to rising temperatures and to more frequent and intense climatic events, such as storms and droughts. Changes in climate and disturbance regimes can have non-additive effects on plant communities and result in complicated legacies we have yet to understand. This is especially true for tropical forests, which play a significant role in regulating global climate. We used understory vegetation data from the Tropical Responses to Altered Climate Experiment (TRACE) in Puerto Rico to evaluate how plant communities responded to climate warming and disturbance. The TRACE understory vegetation was exposed to a severe drought (2015), 2 years of experimental warming (4°C above ambient in half of the plots, 2016–2017 and 2018–2019), and two major hurricanes (Irma and María, September 2017). Woody seedlings and saplings were censused yearly from 2015 to 2019, with an additional census in 2015 after the drought ended. We evaluated disturbance-driven changes in species richness, diversity, and composition across ontogeny. We then used Bayesian predictive trait modeling to assess how species responded to disturbance and how this might influence the functional structure of the plant community. Our results show decreased seedling richness after hurricane disturbance, as well as increased sapling richness and diversity after warming. We found a shift in species composition through time for both seedlings and saplings, yet the individual effects of each disturbance were not significant. At both ontogenetic stages, we observed about twice as many species responding to experimental warming as those responding to drought and hurricanes. Predicted changes in functional structure point to disturbance-driven functional shifts toward a mixture of fast-growing and drought-tolerant species. Our findings demonstrate that the tropical forest understory community is more resistant to climatic stressors than expected, especially at the sapling stage. However, early signs of changes in species composition suggest that, in a warming climate with frequent droughts and hurricanes, plant communities might shift over time toward fast-growing or drought-tolerant species.

Bosque experimental de Luquillo, Luquillo Experime↗
USGS2023

Mortality thresholds of juvenile trees to drought and heatwaves: Implications for forest regeneration across a landscape gradient

Tree loss is increasing rapidly due to drought- and heat-related mortality and intensifying fire activity. Consequently, the fate of many forests depends on the ability of juvenile trees to withstand heightened climate and disturbance anomalies. Extreme climatic events, such as droughts and heatwaves, are increasing in frequency and severity, and trees in mountainous regions must contend with these landscape-level climate episodes. Recent research focuses on how mortality of individual tree species may be driven by drought and heatwaves, but how juvenile mortality under these conditions would vary among species spanning an elevational gradient—given concurrent variation in climate, ecohydrology, and physiology–remains unclear. We address this knowledge gap by implementing a growth chamber study, imposing extreme drought with and without a compounding heatwave, for juveniles of five species that span a forested life zones in the Southwestern United States. Overall, the length of a progressive drought required to trigger mortality differed by up to 20 weeks among species. Inclusion of a heatwave hastened mean time to mortality for all species by about 1 week. Lower-elevation species that grow in warmer ambient conditions died earlier ( Pinus ponderosa in 10 weeks, Pinus edulis in 14 weeks) than did higher-elevation species from cooler ambient conditions ( Picea engelmannii and Pseudotsuga menziesii in 19 weeks, and Pinus flexilis in 30 weeks). When exposed to a heatwave in conjunction with drought, mortality advanced significantly only for species from cooler ambient conditions ( Pinus flexilis : 2.7 weeks earlier; Pseudotsuga menziesii : 2.0 weeks earlier). Cooler ambient temperatures may have buffered against moisture loss during drought, resulting in longer survival of higher-elevation species despite expected drought tolerance of lower-elevation species due to tree physiology. Our study suggests that droughts will play a leading role in juvenile tree mortality and will most directly impact species at warmer climate thresholds, with heatwaves in tandem with drought potentially exacerbating mortality especially of high elevation species. These responses are relevant for assessing the potential success of both natural and managed reforestation, as differential juvenile survival following episodic extreme events will determine future landscape-scale vegetation trajectories under changing climate.

Frontiers in Forests and Global Change↗
USGS2021

Watershed and estuarine controls both influence plant community and tree growth changes in tidal freshwater forested wetlands along two U.S. mid-Atlantic rivers

The tidal freshwater zone near the estuarine head-of-tide is potentially sensitive to both sea-level rise and associated salinity increases as well as changing watershed inputs of freshwater and nutrients. We evaluated the vegetation response of tidal freshwater forested wetlands (TFFW) to changes in nontidal river versus estuarine controls along the longitudinal gradient of the Mattaponi and Pamunkey rivers in the Mid-Atlantic USA. The gradient included nontidal freshwater floodplain (NT) and upper tidal (UT), lower tidal (LT), and stressed tidal forest transitioning to marsh (ST) TFFW habitats on both rivers. Plot-based vegetation sampling and dendrochronology were employed to examine: (1) downriver shifts in plant community composition and the structure of canopy trees, understory trees/saplings/shrubs and herbs, tree basal-area increment (BAI) and (2) interannual variability in BAI from 2015 dating back as far as 1969 in relation to long-term river and estuary monitoring data. With greater tidal influence downstream, tree species dominance shifted, live basal area generally decreased, long-term mean BAI of individual trees decreased, woody stem mortality increased, and live herbaceous vegetative cover and richness increased. Acer rubrum , Fagus grandifolia , Ilex opaca , and Fraxinus pennsylvanica dominated NT and UT sites, with F. pennsylvanica and Nyssa sylvatica increasingly dominating at more downstream tidal sites. Annual tree BAI growth was positively affected by nontidal river flow at NT and UT sites which were closer to the head-of-tide, positively influenced by small salinity increases at LT and ST sites further downstream, and positively influenced by estuarine water level throughout the gradient; nutrient influence was site specific with both positive and negative influences. The counterintuitive finding of salinity increasing tree growth at sites with low BAI is likely due to either competitive growth release from neighboring tree death or enhanced soil nutrient availability that may temporarily mitigate the negative effects of low-level salinization and sea-level increases on living TFFW canopy trees, even as overall plant community conversion to tidal marsh progresses.

Virginia↗
USGS2001

Salmonberry and salal annual aerial stem production: The maintenance of shrub cover in forest stands

Annual sprouting of aerial stems and ramets enables populations of salmonberry (Rubus spectabilis Pursh), salal (Gaultheria shallon Pursh), and probably other forest shrubs to maintain dense covers (>20 000 stems/ha). We studied annual stem production of salmonberry on cut (all stems cut within 15 cm of the ground) and uncut (stems were not treated) plots for 8 years and salal for 5 years in the understories of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), alder, and riparian stands, as well as clearcuts, which are all common stand types in western Oregon. Mean salmonberry stem production on uncut plots ranged from 4.7 stemsA?ma??2A?yeara??1 (95% CI 2.9a??7.4) in alder stands and clearcuts to 1.6 stemsA?ma??2A?yeara??1 (95% CI 1.0a??2.6) in conifer stands. Mean salal production was greater, ranging from 58 stemsA?ma??2A?yeara??1 (95% CI 25a??135) to 8.6 stemsA?ma??2A?yeara??1 (95% CI 3.7a??20.1) on uncut plots in clearcuts and unthinned Douglas-fir stands, respectively. Annual production of both species was somewhat greater on cut plots. Most stems produced in early spring die by December, but enough are recruited to replace mortality of older stems. Stem density was maintained for 8 years for salmonberry and 5 years for salal on both cut and uncut plots. Based on length of rhizomes and bud density we estimate that only 1a??5% of the buds in the rhizomes are needed to support this annual stem production. Although these species sprout vigorously after their aerial stems are killed, disturbance is not necessary for maintaining a dense cover. It appears that, once established, salal, salmonberry, and probably other clonal forest shrubs can maintain a dense cover that can interfere with establishment of trees and other shrubs in canopy gaps or other openings.

Canadian Journal of Forest Research↗
USGS2005

Research for the development of best management practices for minimizing horse trail impacts on the Hoosier National Forest

This research investigates horse trail impacts to gain an improved understanding of the relationship between various levels of horse use, horse trail management alternatives, and subsequent horse trail degradation. A survey of existing horse trails on the Hoosier National Forest was used to collect data on use-related, environmental and management factors to model horse trail impacts. Results are analyzed to identify which factors are most easily manipulated by managers to effectively avoid and minimize horse trail impacts. A specific focus includes evaluating the relative effect of trail use level, surfacing, grade, and water control on indices of erosion and trafficability such as trail cross sectional area, estimated erosion, muddiness, and incision. Overall, the Hoosier National Forest horse trails could be significantly improved by relocating or closing inherited trails that directly ascend slope or are excessively steep, reducing the distance between water control structures, and by applying gravel to harden trail surfaces and reduce soil erosion. A set of Best Management Practices for trails are included as a product of this work, with recommendations based on this research.

U.S. Forest Service, Final Research Report↗
USGS2008

δ 15 N patterns of Douglas-fir and red alder riparian forests in the Oregon Coast Range

We used naturally occurring stable isotopes of N to compare N dynamics in near-stream and upslope environments along riparian catenas in N-fixing red alder (Alnus rubra) and Douglas-fir (Pseudotsuga menziesii) forests in the Coast Range of western Oregon. Based on the existing literature, we expected soil δ 15 N to be enriched closer to streams owing to inputs of isotopically heavy, marine-derived N by spawning salmon, higher rates of denitrification near the stream, or both. However, it has been unclear what effect red alder might have on soil δ 15 N patterns near streams. We found a consistent −1‰ δ 15 N signature in red alder foliage, and δ 15 N of total N in soils under red alder averaged 2.2‰ along sampling transects extending 20 m upslope from the stream. Surprisingly, δ 15 N of total N in soil under Douglas-fir was progressively depleted nearer to streams, opposite from the pattern expected from N losses by denitrification or N inputs from anadromous salmon. Instead, δ 15 N of total N in soil under Douglas-fir converged toward soil δ 15 N values typical of red alder sites. We consider that the historic presence of red alder may have contributed a legacy of lower soil δ 15 N nearer to streams on sites that are currently dominated by young Douglas-fir forest.

Oregon↗
USGS1989

Disturbance-mediated accelerated succession in two Michigan forest types

In northern lower Michigan, logging accelerated sugar maple ( Acer saccharum ) dominance in a northern white cedar ( Thuja occidentals ) community, and clear-cutting and burning quickly converted certain sites dominated by mature jack pine ( Pinus banksiana ) to early-succesional hardwoods, including Prunus, Populus , and Quercus . In both forest types the succeeding hardwoods should continue to increase in the future at the expense of the pioneer conifer species. In the cedar example, sugar maple was also increasing a an undisturbed, old-growth stand, but at a much reduced rate than in the logged stand. Traditionally, disturbance was through to set back succession to some earlier stage. However, out study sites and at least several other North American forest communities exhibited accelerated succession following a wide range of disturbances, including logging fire, ice storms, wind-throw, disease, insect attack, and herbicide spraying.

Michigan↗
USGS2016

Foreword: The dynamics of change in Alaska’s boreal forests: Resilience and vulnerability in response to climate warming

Long-term research by the Bonanza Creek (BNZ) Long Term Ecological Research (LTER) program has documented natural patterns of interannual and successional variability of the boreal forest in interior Alaska against which we can detect changes in system behavior. Between 2004 and 2010 the BNZ LTER program focused on understanding the dynamics of change through studying the resilience and vulnerability of Alaska's boreal forest in response to climate warming. The overarching question in this endeavor has been “How are boreal ecosystems responding, both gradually and abruptly, to climate warming, and what new landscape patterns are emerging?”

Alaska↗
USGS2001

Erosion and sediment delivery following removal of forest roads

Erosion control treatments were applied to abandoned logging roads in California, with the goal of reducing road-related sediment input to streams and restoring natural hydrologic patterns on the landscape. Treatment of stream crossings involved excavating culverts and associated road fill and reshaping streambanks. A variety of techniques were applied to road benches, which included decompacting the road surface, placing unstable road fill in more stable locations, and re-establishing natural surface drainage patterns. Following treatment and a 12-year recurrence-interval storm, some road reaches and excavated stream crossings showed evidence of mass movement failures, gullying, bank erosion and channel incision. Post-treatment erosion from excavated stream crossings was related to two variables: a surrogate for stream power (drainage area × channel gradient) and the volume of fill excavated from the channel. Post-treatment erosion on road reaches was related to four explanatory variables: method of treatment, hillslope position (upper, mid-slope or lower), date of treatment, and an interaction term (hillslope position × method of treatment). Sediment delivery from treated roads in upper, middle and lower hillslope positions was 10, 135 and 550 m 3 of sediment per kilometre of treated roads, respectively. In contrast, inventories of almost 500 km of forest roads in adjacent catchments indicate that untreated roads produced 1500 to 4700 m 3 of sediment per kilometre of road length. Erosion from 300 km of treated roads contributed less than 2 per cent of the total sediment load of Redwood Creek during the period 1978 to 1998. Although road removal treatments do not completely eliminate erosion associated with forest roads, they do substantially reduce sediment yields from abandoned logging roads.

Earth Surface Processes and Landforms↗
USGS2017

Predicting redox-sensitive contaminant concentrations in groundwater using random forest classification

Machine learning techniques were applied to a large (n > 10,000) compliance monitoring database to predict the occurrence of several redox-active constituents in groundwater across a large watershed. Specifically, random forest classification was used to determine the probabilities of detecting elevated concentrations of nitrate, iron, and arsenic in the Fox, Wolf, Peshtigo, and surrounding watersheds in northeastern Wisconsin. Random forest classification is well suited to describe the nonlinear relationships observed among several explanatory variables and the predicted probabilities of elevated concentrations of nitrate, iron, and arsenic. Maps of the probability of elevated nitrate, iron, and arsenic can be used to assess groundwater vulnerability and the vulnerability of streams to contaminants derived from groundwater. Processes responsible for elevated concentrations are elucidated using partial dependence plots. For example, an increase in the probability of elevated iron and arsenic occurred when well depths coincided with the glacial/bedrock interface, suggesting a bedrock source for these constituents. Furthermore, groundwater in contact with Ordovician bedrock has a higher likelihood of elevated iron concentrations, which supports the hypothesis that groundwater liberates iron from a sulfide-bearing secondary cement horizon of Ordovician age. Application of machine learning techniques to existing compliance monitoring data offers an opportunity to broadly assess aquifer and stream vulnerability at regional and national scales and to better understand geochemical processes responsible for observed conditions.

Water Resources Research↗
USGS2026

Evaluating seedling traits, maintenance and effective costs to support tropical forest restoration practices

While large-scale restoration is essential, tropical forest restoration often depends on small-scale practitioners and landowners who produce, plant and maintain trees. Their collective impact on restoring forest diversity and function is substantial, making it critical to address the constraints they face through efficient, effective techniques. We used generalized linear mixed models to evaluate how seedling traits, weeding maintenance and a fertilizer application influenced the 5-year survival of 1796 seedlings from 11 tree species planted in Monteverde, Costa Rica. Estimates of annual survival increased with seedling age (time after planting) and leaf count at planting. Weeding effects varied by species, improving survival in 7 of 10 species and reducing survival in one. All species reached >80% annual survival after 2 years regardless of maintenance, and seedlings planted with ≥25 leaves showed increased survival that decreased the need for weeding. Weeding is costly: all effective costs per 4-year surviving seedlings were higher with weeding than without and varied by species. Costs were calculated by species, treatment and seedling leaf counts when planted (5, 10, 15, 25, 35, 45). Beyond the 2-year threshold, where mortality is highest, weeding effort and costs no longer appear justified. A single fertilizer application did not improve survival in either of the species tested. Practical implications . These findings support landowner restoration by giving restoration technicians accessible tools to improve seedling survival—increasing leaf counts before planting—and reducing post-planting weeding costs by targeting only species for which it benefits and limiting weeding to 2 years.

Los Llanos, Monteverde↗