Aboveground Live Carbon Research Articles

Dominant role of the non-forest woody vegetation in the post 2015/16 El Niño tropical carbon recovery.

The extreme dry and hot 2015/16 El Niño episode caused large losses in tropical live aboveground carbon (AGC) stocks. Followed by climatic conditions conducive to high vegetation productivity since 2016, tropical AGC are expected to recover from large losses during the El Niño episode; however, the recovery rate and its spatial distribution remain unknown. Here, we used low-frequency microwave satellite data to track AGC changes, and showed that tropical AGC stocks returned to pre-El Niño levels by the end of 2020, resulting in an AGC sink of Pg C year-1 during 2014-2020. This sink was dominated by strong AGC increases ( Pg C year-1) in non-forest woody vegetation during 2016-2020, compensating the forest AGC losses attributed to the El Niño event, forest loss, and degradation. Our findings highlight that non-forest woody vegetation is an increasingly important contributor to interannual to decadal variability in the global carbon cycle.

A Density Management Diagram for Pitch Pine to Illustrate Tradeoffs between Carbon and Wildfire Risk

Abstract Pitch pine (Pinus rigida Mill.) can be found across a broad range in eastern North America but assumes local dominance only on poor soils in the northeastern United States. Contemporary management goals in the Northeast for areas dominated by pitch pine are focused on noncommercial benefits of forests, such as carbon density, reduced wildfire risk, habitat for rare species, and water provisioning. We present a density management diagram that empirically articulates the size-density limits of even-aged pitch pine stands. Included in the diagram are wildfire risk and carbon density, which are inversely related for most stand sizes. Maximum possible aboveground live tree carbon begins to decline at a quadratic mean diameter greater than 9 in., while crown fire risk remains high along the size-density limit until a quadratic mean diameter above 12 in. is achieved. Study Implications: Modern silvicultural tools that illustrate forest stand conditions have not been developed for pitch pine, but this species occurs in a region with much public attention on forests. We develop and present a density management diagram to show the interplay of different social goals for the forest and how they relate to the maximum size-density relationship. Pitch pine stands with high levels of aboveground live carbon are at high risk of crown fire, particularly in the smaller size classes.

Long-term efficacy of fuel reduction and restoration treatments in Northern Rockies dry forests.

Fuel and restoration treatments seeking to mitigate the likelihood of uncharacteristic high-severity wildfires in forests with historically frequent, low-severity fire regimes are increasingly common, but long-term treatment effects on fuels, aboveground carbon, plant community structure, ecosystem resilience, and other ecosystem attributes are understudied. We present 20-year responses to thinning and prescribed burning treatments commonly used in dry, low-elevation forests of the western United States from a long-term study site in the Northern Rockies that is part of the National Fire and Fire Surrogate Study. We provide a comprehensive synthesis of short-term (<4 years) and mid-term (<14 years) results from previous findings. We then place these results in the context of a mountain pine beetle (MPB; Dendroctonus ponderosae) outbreak that impacted the site 5-10 years post-treatment and describe 20-year responses to assess the longevity of restoration and fuel reduction treatments in light of the MPB outbreak. Thinning treatments had persistently lower forest density and higher tree growth, but effects were more pronounced when thinning was combined with prescribed fire. The thinning+prescribed fire treatment had the additional benefit of maintaining the highest proportion of ponderosa pine (Pinus ponderosa) for overstory and regeneration. No differences in understory native plant cover and richness or exotic species cover remained after 20 years, but exotic species richness, while low relative to native species, was still higher in the thinning+prescribed fire treatment than the control. Aboveground live carbon stocks in thinning treatments recovered to near control and prescribed fire treatment levels by 20 years. The prescribed fire treatment and control had higher fuel loads than thinning treatments due to interactions with the MPB outbreak. The MPB-induced changes to forest structure and fuels increased the fire hazard 20 years post-treatment in the control and prescribed fire treatment. Should a wildfire occur now, the thinning+prescribed fire treatment would likely have the lowest intensity fire and highest tree survival and stable carbon stocks. Our findings show broad support that thinning and prescribed fire increase ponderosa pine forest resilience to both wildfire and bark beetles for up to 20 years, but efficacy is waning and additional fuel treatments are needed to maintain resilience.

SoCal EcoServe: an online mapping tool to estimate wildfire impacts in southern California

Background Wildfires in Mediterranean-type climate regions have numerous impacts on the ecosystem services provided by native shrublands, however, quantifying these impacts is challenging. Aims We developed a reproducible method to quantify fire impacts on ecosystem services and created a tool for resource managers in southern California. Methods The SoCal EcoServe tool consists of two components: a desktop tool and an online mapping tool. We used the Alisal Fire of 2021 as a case study and quantified: aboveground live carbon storage using pre- and post-fire biomass data; water runoff, groundwater recharge and sediment erosion retention by integrating data on burn severity into hydrological and sediment erosion models; and estimated recreation services and biodiversity using pre-fire data. Key results We estimated the Alisal Fire resulted in an immediate post-fire reduction in carbon storage of 25%, of which 20% was estimated to be permanently lost. Water runoff increased by 21%, groundwater recharge 7-fold, and sediment erosion increased 24-fold. Conclusions The EcoServe tool provides an initial approximation of wildfire impacts that can support damage assessments post-fire, track carbon storage and help identify priorities for post-fire restoration. Implications We intend the tool to be used by USDA Forest Service resource managers of shurblands in southern California. However, it can provide the framework for future work in shrublands throughout the western USA.

Modeling Above-Ground Carbon Dynamics under Different Silvicultural Treatments on the McDonald–Dunn Research Forest

Forest management decisions affect carbon stock and rates of sequestration. One subject of debate is the rotation age that will optimize sequestration over extended periods. Some argue that shorter rotations facilitate greater sequestration rates due to the accelerated growth rates of younger trees compared to mature or old-growth trees. Others maintain that frequent harvesting will not allow forest carbon to rebound after each subsequent rotation, and thus more extended periods between clearcutting is the superior choice. These contrasting viewpoints are mirrored regarding the impact of thinning treatments, in that either thinning will enhance forest carbon uptake by facilitating improved and sustained r growth of residual trees or removing any above-ground biomass will outweigh the yields. This study aims to compare the different suites of management decisions and identify practical combinations of rotation ages and thinning applications that will optimize carbon sequestration while meeting other objectives over a 240-year projection timeframe. Stand development under different harvest rotations and thinning specifications was modeled using a Forest Vegetation Simulator (FVS). We found that site productivity was the primary determinant in stand-above-ground carbon dynamics under various management scenarios. Thus, the optimal rotation age/thinning treatment combinations differed between site classes. High productivity stands were estimated to sequester the most above-ground live carbon with 60-year rotations with a low-intensity thin at age 40. Moderately productive stands performed the best with 80-year rotations when two low-intensity thinning treatments were applied between harvests. For high and moderate productivity stands, estimates of gross carbon increased when two low or moderate-intensity thinning treatments were applied within 80- or 120-year rotations. High-intensity thinning treatments reduced total carbon sequestered over the 240-year projection timeframe for all productivity levels and rotation ages, except for low productivity stands under 120-year rotations.

Growth response, climate sensitivity and carbon storage vary with wood porosity in a southern Appalachian mixed hardwood forest

Disturbance regimes are often a complex suite of interacting agents that drive forest dynamics. Changes to any one or many of the agents will potentially affect future forest services such as productivity and carbon storage potential. Differences in sensitivity to disturbance events between diffuse-porous and ring-porous tree species, however, are currently unclear despite having important ecological and management implications. We used a dendroecological approach to identify whether diffuse and ring-porous species differ in their disturbance history, response to climate influence, and carbon storage potential in a mature Quercus-Carya stand in the Appalachian Mountains, USA. Several major abrupt growth increases indicating disturbance were identified during the history of the stand in the 1860s, 1930s, and 1960s. While both functional groups showed sensitivity to climate variables, growth reductions following drought events were more often significant for ring-porous species compared to diffuse-porous species. The decadal growth responses to drought events were similar among functional groups, and age classes, but indicated reduced growth following successive events. For the inventory year of 2015, the stand-wide aboveground live carbon content was 96.2 Mg C ha−1, with 58.3 Mg C ha−1 captured in ring-porous species and 37.9 Mg C ha−1 captured in diffuse-porous species. Our results suggest that understanding how different species and functional groups respond to forest disturbance and climate variability is critical for evaluating future management scenarios and prediction of climate change feedbacks.

Siberian carbon sink reduced by forest disturbances

Siberian forests are generally thought to have acted as an important carbon sink over recent decades, but exposure to severe droughts and fire disturbances may have impacted their carbon dynamics. Limited available forest inventories mean the carbon balance remains uncertain. Here we analyse annual live and dead above-ground carbon changes derived from low-frequency passive microwave observations from 2010 to 2019. We find that during this period, the carbon balance of Siberian forests was close to neutral, with the forests acting as a small carbon sink of $$+ 0.02_{ + 0.01}^{ + 0.03}$$ PgC yr−1. Carbon storage in dead wood increased, but this was largely offset by a decrease in live biomass. Substantial losses of live above-ground carbon are attributed to fire and drought, such as the widespread fires in northern Siberia in 2012 and extreme drought in eastern Siberia in 2015. These live above-ground carbon losses contrast with ‘greening’ trends seen in leaf area index over the same period, a decoupling explained by faster post-disturbance recovery of leaf area than live above-ground carbon. Our study highlights the vulnerability of large forest carbon stores in Siberia to climate-induced disturbances, challenging the persistence of the carbon sink in this region of the globe. Carbon sequestration by Siberian forests has been low over the past decade due to disturbances that have decreased live biomass and increased dead wood, according to passive microwave observations.

Examining k-Nearest Neighbor Small Area Estimation Across Scales Using National Forest Inventory Data

National forest inventories (NFI), such as the one conducted by the United States Forest Service Forest Inventory and Analysis (FIA) program, provide valuable information regarding the status of forests at regional to national scales. However, forest managers often need information at stand to landscape scales. Given various small area estimation (SAE) approaches, including design-based and model-based estimation, it may not be clear which is most appropriate for the user’s application. In this study, our objective was to assess the uncertainty in tree aboveground live carbon (ALC) estimates for differing modes of SAE across multiple scales to provide guidance for appropriate scales of application. We calculated means and variances for ALC with design-based (Horvitz-Thompson), model-assisted (generalized regression), and model-based (k-nearest neighbor synthetic) estimators for estimation units over a range of sizes for 30 subregions in California, United States. For larger areas (10,000–64,800 ha), relative efficiencies greater than one indicated that the generalized regression estimator (GREG) generated estimates with less error than the Horvitz-Thompson estimator (HT), while the bias-adjusted synthetic estimator relative efficiency compared to either the Horvitz-Thompson or model-assisted estimators exceeded one for areas 25,000 ha and smaller. Variance estimates from the unadjusted synthetic estimator underestimated the total error, because the estimator ignores bias and thus only addresses model variance. Across scales (250–64,800 ha, 0–27 plots per area of interest), 93% of the variation in the synthetic estimator’s relative standard error was explained by forest area, forest dominance, and regional variation in forest landscapes. Our results support model-assisted estimation use except for small areas where few plots (&amp;lt;10 in the current study) are available for generating estimates in spite of biases in estimates. However, users should exercise caution when interpreting model-based estimates of error as they may not account for model mis-specification, and thus induced bias. This research explored multiple scales of application for SAE procedures applied to NFI data regarding carbon pools, potentially supporting a multi-scale approach to forest monitoring. Our results guides users in developing defensible estimates of carbon pools, particularly as it relates to the limits of inference at a variety of spatial scales.

Climate‐Driven Limits to Future Carbon Storage in California's Wildland Ecosystems

AbstractEnhanced ecosystem carbon storage is a key component of many climate mitigation pathways. The State of California has set an ambitious goal of carbon neutrality by 2045, relying in part on enhanced carbon sequestration in natural and working lands. We used statistical modeling, including random forest and climate analog approaches, to explore the climate‐driven challenges and uncertainties associated with the goal of long‐term carbon sequestration in forests and shrublands. We found that seasonal patterns of temperature and precipitation are strong controllers of the spatial distribution of aboveground live carbon. RCP8.5 projections of temperature and precipitation are estimated to drive decreases of 16.1% ± 7.5% in aboveground live carbon by the end of the century, with coastal areas of central and northern California and low/mid‐elevation mountain areas being most vulnerable. With RCP4.5 projections, declines are less severe, with 8.8% ± 5.3% carbon loss. In either scenario, increases in temperature systematically cause biomass declines, and the spread of projected precipitation across 32 CMIP5 models contributes to substantial uncertainty in the magnitude of that decline. Projected changes in the environmental niche for the 20 most biomass‐dominant tree species revealed widespread replacement of conifers by oak species in low elevation regions of central and northern California, with a corresponding decline in carbon storage depending on expected migration rates. The spatial patterns of vulnerability we identify may allow policymakers to assess where carbon sequestration in aboveground biomass is an appropriate part of a climate mitigation portfolio, and where future climate‐driven carbon losses may be a liability.

Bedrock type drives forest carbon storage and uptake across the mid-Atlantic Appalachian Ridge and Valley, U.S.A.

Lithology influences forest carbon storage and productivity yet is often overlooked for forests of the eastern United States, a large and important carbon sink. This research explores the influence of two common lithologies of the Ridge and Valley physiographic province in the Appalachian Mountains, shales and sandstones, on live aboveground carbon storage, carbon uptake, forest community composition and their interrelationships. We couple forest inventory data from 565 plots from Pennsylvania state agencies with a suite of GIS derived landscape metrics including measures of climate, topography and soil physical properties to identify biotic and abiotic drivers of live forest carbon dynamics in relation to lithology.Forests growing on shale bedrock store more live aboveground carbon compared to forests on sandstone when controlling for stand age, which ranged from 20 to 200 years. Furthermore, forests in the dominant ages (81–120 years) store more live aboveground carbon (108.1 Mg/ha vs. 86.5 Mg/ha) and uptake live aboveground carbon at a faster rate (1.32 Mg/ha/yr vs 0.85 Mg/ha/yr) on shale compared to sandstone respectively. Overall forest communities on both lithologies are dominated by oaks (Quercus spp.), however northern red oak (Q. rubra) is more dominant at shale sites compared to chestnut oak (Q. prinus), which dominates on sandstone. Most species in the forest tend to be more productive on shale, which may account for differences in carbon pools and fluxes across the landscape. Tree species richness is higher in sites on shale bedrock, but biodiversity-productivity relationships within lithologic classifications fail to account for differences in forest productivity. Modeled live aboveground carbon storage points to topography (elevation and aspect) and soil physical properties (% clay and available water capacity) as important influences on forest productivity that related back to lithology. Incorporating lithology into forest management strategies that are focused on a variety of ecosystem services can aid future site selection, and we demonstrate that forests on shale bedrock grow faster, store more carbon and have higher species diversity. The results presented here highlight the potential for underlying bedrock to exert differential influences on forest ecosystem structure and function across a region.

Partitioning main carbon pools in a semi-deciduous rainforest in eastern Cameroon

Tropical forests contribute to climate change mitigation by absorbing carbon from the atmosphere and storing this in biomass and soil organic matter. However, there is still considerable uncertainty about the above- and belowground quantity and distribution of carbon stocks in African forests. Here, we evaluate how different carbon pools (aboveground live biomass, aboveground dead biomass, belowground biomass) contribute to total carbon stocks, and how different carbon components (e.g. large trees, understorey trees, coarse woody debris, roots, soil organic carbon etc.) contribute to carbon pools and total carbon stocks. We evaluated data of extensive inventories within 30 1-ha plots spanning the terra-firme semi-deciduous forest in eastern Cameroon. Hence, the plots were placed at a mean distance of 1 km from the nearest plot and we analyzed the data using variation partitioning, linear regressions and correlation tests. We found that the terra-firme semi-deciduous forests store 283.97 ± 51.42 Mg C ha−1. The aboveground biomass pool, with a carbon stock of 180.99 ± 25.8 Mg C ha−1, mostly explained variation in total carbon stocks (R2 = 0.79). From all aboveground biomass components, carbon in large trees was most strongly correlated with total carbon stocks. The second most important carbon pool was belowground carbon (on average 85.06 ± 16.86 Mg C ha−1; R2 = 0.78), mainly explained by coarse root carbon. Carbon in dead biomass had only a small contribution to total carbon stocks (R2 = 0.04). Hence, our results indicate that aboveground live biomass is a good predictor for variation in total carbon storage within this semi-deciduous terra-firme forest. However, aboveground live carbon and belowground carbon and their interactions explained most of the variation in total carbon stock, indicating that a whole-ecosystem approach is necessary for a full understanding of the carbon cycle.

Aboveground Live Carbon Storage in Woody Agroforestry Systems of Sokoru District, Jimma Zone, Southwest Ethiopia

There is a growing interest in the role of different types of land use systems in stabilizing the atmospheric CO₂ concentration, reducing the CO₂ emissions and on increasing the carbon sink of forestry and agroforestry systems. Agroforestry has potential to mitigate climate change and help farmers to adapt the impacts of climate change. Different types of agroforestry systems such as homegarden, cropland and pastureland have great role in storing carbon and stabilizing the climate change by absorbing CO₂ from the atmosphere. The main objective of this study was to investigate aboveground live carbon storage in agroforestry of Sokoru District, Jimma Zone. The study was conducted from February to May, 2018. Descriptive statistics and one way ANOVA were used to analyze the population density, above ground live biomass, carbon storage, tree height and diameter at breast height and basal area for each tree was calculated. Aboveground live biomass of each tree was determined by using the revised nondestructive equation. The amount of carbon stored in each tree was estimated at 50% of the aboveground live biomass hence 5.54 t, and in homegarden, 9 t in cropland and 3.47 t pastureland carbon was stored. From three land use types the highest amount of carbon was stored in cropland followed by homegarden and pastureland. Eventually, the study revealed that the woody species found in different agroforestry system of the study area have great role in carbon storage and CO₂ sequestration. Thus all stakeholders should focus on conservation of trees and shrubs found agricultural landscapes.

Trade-offs between carbon stocks and biodiversity in European temperate forests.

Policies to mitigate climate change and biodiversity loss often assume that protecting carbon-rich forests provides co-benefits in terms of biodiversity, due to the spatial congruence of carbon stocks and biodiversity at biogeographic scales. However, it remains unclear whether this holds at the scales relevant for management, and particularly large knowledge gaps exist for temperate forests and for taxa other than trees. We built a comprehensive dataset of Central European temperate forest structure and multi-taxonomic diversity (beetles, birds, bryophytes, fungi, lichens, and plants) across 352 plots. We used Boosted Regression Trees (BRTs) to assess the relationship between above-ground live carbon stocks and (a) taxon-specific richness, (b) a unified multidiversity index. We used Threshold Indicator Taxa ANalysis to explore individual species' responses to changing above-ground carbon stocks and to detect change-points in species composition along the carbon-stock gradient. Our results reveal an overall weak and highly variable relationship between richness and carbon stock at the stand scale, both for individual taxonomic groups and for multidiversity. Similarly, the proportion of win-win and trade-off species (i.e., species favored or disadvantaged by increasing carbon stock, respectively) varied substantially across taxa. Win-win species gradually replaced trade-off species with increasing carbon, without clear thresholds along the above-ground carbon gradient, suggesting that community-level surrogates (e.g., richness) might fail to detect critical changes in biodiversity. Collectively, our analyses highlight that leveraging co-benefits between carbon and biodiversity in temperate forest may require stand-scale management that prioritizes either biodiversity or carbon in order to maximize co-benefits at broader scales. Importantly, this contrasts with tropical forests, where climate and biodiversity objectives can be integrated at the stand scale, thus highlighting the need for context-specificity when managing for multiple objectives. Accounting for critical change-points of target taxa can help to deal with this specificity, by defining a safe operating space to manipulate carbon while avoiding biodiversity losses.

Future forest landscapes of the Carpathians: vegetation and carbon dynamics under climate change

Climate change will alter forest ecosystems and their provisioning of services. Forests in the Carpathian Mountains store high amounts of carbon and provide livelihoods to local people; however, no study has yet assessed their future long-term dynamics under climate change. Therefore, we selected a representative area of 1340 km2 to investigate the effects of changing climate and disturbance regimes on (i) the spatial dynamics of the dominant tree species and forest types and (ii) the trajectories of the associated aboveground live carbon (ALC). We simulated 500 years of change under four Representative Concentration Pathway (RCP) scenarios, incorporating wind and bark beetle disturbances using the LANDIS-II forest change model. Our simulations revealed a lagged adaptation of the forest landscape to climate change. While Picea abies dominance declined in all scenarios, Carpinus betulus expanded at low elevations and Acer pseudoplatanus at mid-elevations. We also found a slow but continuous expansion of Quercus petraea and Q. robur at low elevations and of Fagus sylvatica at mid and high elevations. This change in species composition was accompanied by a significant reduction of ALC: on average over the simulation period, unmitigated climate change reduced ALC between − 2.1% (RCP2.6) and − 14.0% (RCP8.5), while disturbances caused an additional reduction of ALC between − 4.5% (RCP2.6) and − 6.6% (RCP8.5). Therefore, foresighted management strategies are needed to facilitate vegetation adaptation to climate change, with the goal of stabilizing carbon storage and maintaining economic value of future Carpathian forests.

The role of traditional coffee management in forest conservation and carbon storage in the Jimma Highlands, Ethiopia

Ethiopia has lost 90% of its forest extent. Remnant patches in the southwest are often semi-forest coffee (SFC), a system whereby coffee is managed beneath the canopy. Here, we (1) quantify aboveground live carbon (AGC) stored by trees in SFC and other land use types in the Jimma Highlands; and (2) determine coffee farmers’ preference for canopy shade trees, and the resulting differences in carbon storage. We surveyed twenty coffee farmers and assessed thirty-one 1-ha vegetation plots across a 23.6-km transect. The most preferred shade species were Albizia gummifera, Acacia abyssinica, Millettia ferruginea and Cordia africana, which together accounted for 42% AGC in SFC and 12% in natural forests. These species had broad size class distributions, while the least preferred had scant representation in lower size classes. SFC stores significantly more AGC (61.5 ± 25.0 t ha−1, mean ± SE) than woodland, pasture and cropland, significantly less than plantation and slightly less than natural forest (82.0 ± 32.1 t ha−1). If SFC was converted to cropland, then 59.5 t ha−1 would be released, at a social cost of US$2892–4225 ha−1. Carbon-payment schemes (e.g. REDD+) may, therefore, play a role in conserving these forests and associated biodiversity and livelihoods into the future.

Live aboveground carbon stocks in natural forests of Colombia

Emission factors are essential in order to accurately account and report land use and land use change emissions due to deforestation at a national level, in accordance with the United Nations Framework Convention on Climate Change reporting guidelines. Nonetheless, in many tropical countries its availability is still scarce, especially in Colombia where a National Forest Inventory is lacking. Here, we estimate the amount of carbon stored in the live aboveground biomass of the forests of Colombia, using data from 4981 sampling forest plots of various sizes established between 1990 and 2014. Our study included an analysis of the influence of the choice of allometric model and the carbon density estimation method employed in the estimation. We found that the most conservative total mean value for the entire country was 226.9±4.5Mgha−1, obtained by using a previous set of allometric equations developed for the natural forest of Colombia and an inverse-variance weighting that accounts for the variation in plot size, which represents a potential stock of 6.44±0.13Pg of carbon. Thus, our study provides a method to utilize existing sample data to assess forest carbon stocks at national level, make available conservative carbon stocks estimates for the natural forests of Colombia, and reports enhanced and adequate information subject to national capabilities and policies in the context of results-based payments for reducing emissions from deforestation and forest degradation and the conservation.

Complex mountain terrain and disturbance history drive variation in forest aboveground live carbon density in the western Oregon Cascades, USA

Forest carbon (C) density varies tremendously across space due to the inherent heterogeneity of forest ecosystems. Variation of forest C density is especially pronounced in mountainous terrain, where environmental gradients are compressed and vary at multiple spatial scales. Additionally, the influence of environmental gradients may vary with forest age and developmental stage, an important consideration as forest landscapes often have a diversity of stand ages from past management and other disturbance agents. Quantifying forest C density and its underlying environmental determinants in mountain terrain has remained challenging because many available data sources lack the spatial grain and ecological resolution needed at both stand and landscape scales. The objective of this study was to determine if environmental factors influencing aboveground live carbon (ALC) density differed between young versus old forests. We integrated aerial light detection and ranging (lidar) data with 702 field plots to map forest ALC density at a grain of 25m across the H.J. Andrews Experimental Forest, a 6369ha watershed in the Cascade Mountains of Oregon, USA. We used linear regressions, random forest ensemble learning (RF) and sequential autoregressive modeling (SAR) to reveal how mapped forest ALC density was related to climate, topography, soils, and past disturbance history (timber harvesting and wildfires). ALC increased with stand age in young managed forests, with much greater variation of ALC in relation to years since wildfire in old unmanaged forests. Timber harvesting was the most important driver of ALC across the entire watershed, despite occurring on only 23% of the landscape. More variation in forest ALC density was explained in models of young managed forests than in models of old unmanaged forests. Besides stand age, ALC density in young managed forests was driven by factors influencing site productivity, whereas variation in ALC density in old unmanaged forests was also affected by finer scale topographic conditions associated with sheltered sites. Past wildfires only had a small influence on current ALC density, which may be a result of long times since fire and/or prevalence of non-stand replacing fire. Our results indicate that forest ALC density depends on a suite of multi-scale environmental drivers mediated by complex mountain topography, and that these relationships are dependent on stand age. The high and context-dependent spatial variability of forest ALC density has implications for quantifying forest carbon stores, establishing upper bounds of potential carbon sequestration, and scaling field data to landscape and regional scales.

Bioenergy harvest, climate change, and forest carbon in the Oregon Coast Range

AbstractForests provide important ecological, economic, and social services, and recent interest has emerged in the potential for using residue from timber harvest as a source of renewable woody bioenergy. The long‐term consequences of such intensive harvest are unclear, particularly as forests face novel climatic conditions over the next century. We used a simulation model to project the long‐term effects of management and climate change on above‐ and belowground forest carbon storage in a watershed in northwestern Oregon. The multi‐ownership watershed has a diverse range of current management practices, including little‐to‐no harvesting on federal lands, short‐rotation clear‐cutting on industrial land, and a mix of practices on private nonindustrial land. We simulated multiple management scenarios, varying the rate and intensity of harvest, combined with projections of climate change. Our simulations project a wide range of total ecosystem carbon storage with varying harvest rate, ranging from a 45% increase to a 16% decrease in carbon compared to current levels. Increasing the intensity of harvest for bioenergy caused a 2–3% decrease in ecosystem carbon relative to conventional harvest practices. Soil carbon was relatively insensitive to harvest rotation and intensity, and accumulated slowly regardless of harvest regime. Climate change reduced carbon accumulation in soil and detrital pools due to increasing heterotrophic respiration, and had small but variable effects on aboveground live carbon and total ecosystem carbon. Overall, we conclude that current levels of ecosystem carbon storage are maintained in part due to substantial portions of the landscape (federal and some private lands) remaining unharvested or lightly managed. Increasing the intensity of harvest for bioenergy on currently harvested land, however, led to a relatively small reduction in the ability of forests to store carbon. Climate change is unlikely to substantially alter carbon storage in these forests, absent shifts in disturbance regimes.

Aboveground live carbon stock changes of California wildland ecosystems, 2001–2010

The balance between ecosystem emissions of carbon to the atmosphere and removals from the atmosphere indicates whether ecosystems are exacerbating or reducing climate change. Forest ecosystems in the State of California, USA, contain carbon that reaches the highest densities (mass per unit area) in the world, but it has been unresolved whether California ecosystems currently comprise a net sink or source of carbon. The California Global Warming Solutions Act of 2006 established greenhouse gas reduction targets for fossil fuel-burning sectors and ecosystems, underscoring the importance of tracking ecosystem carbon. Here, we conduct statewide spatial inventories of the aboveground live carbon stocks of forests and other terrestrial ecosystems of California, excluding agricultural and urban areas. We analyzed biomass data from field measurements of the Forest Inventory and Analysis program, published biomass information and remote sensing data on non-forest vegetation, and spatial distributions of vegetation types, height, and fractional cover derived by the Landfire program from Landsat remote sensing at 30m spatial resolution. We conducted Monte Carlo analyses of the uncertainty of carbon stock change estimates from errors in tree biomass estimates, remote sensing, and estimates of the carbon fraction of biomass. The carbon stock in aboveground biomass was 850±230 Tg (mean±95% confidence interval) in 2010. We found a net aboveground live carbon stock change of −69±15 Tg from 2001 to 2010, a rate of change of −0.8±0.2%y−1. Due to slow decay of some dead wood, all of the live carbon stock change does not immediately generate emissions. Wildfires on 6% of the state analysis area produced two-thirds of the live carbon stock loss. This suggests that increased tree densities from a century of fire suppression have allowed the accumulation of fuel for carbon losses in recent wildfires. Remote sensing errors in vegetation classification accounted for most of the uncertainty in the carbon stock change estimates. Improvements are also needed to track spatial patterns of growth and dead wood. Our results establish the beginning of a time series for the state greenhouse gas inventory and provide information on the role of forest conservation and management in California in mitigating global climate change.

Late-successional and old-growth forest carbon temporal dynamics in the Northern Forest (Northeastern USA)

Comprehensive data on the capacity and rates of change for carbon pools in managed and unmanaged forests is essential for evaluating climate change mitigation options being considered by policy makers at regional and national levels. We currently lack real and long-term data on forest carbon dynamics covering a wide range of forest management practices and conditions. Because of this, selecting the best policies for conserving forest carbon must rely on forest growth and yield models such as US Forest Service (USFS) Forest Vegetation Simulator (FVS) to predict the future forest carbon impacts of management actions. FVS may underestimate the capacity of older stands to accumulate carbon because the model relies on USFS Forest Inventory and Analysis data that lack data from late-successional and old-growth (LSOG) stands. Improving these models will increase the likelihood of selecting policies that successfully use forests to reduce atmospheric carbon. From 1995 to 2002, Manomet Center for Conservation Sciences conducted research on 65 10m by 50m permanent plots to evaluate forest structure (standing live and dead trees, and down coarse woody material) in LSOG stands across northern Maine. We re-measured these plots in 2011 to assess long-term carbon sequestration trends in LSOG stands of common forest types in the Northern Forest region for above ground alive, standing dead, and coarse woody material carbon pools. Late-successional (LS) and Old-growth (OG) aboveground live carbon (C) stocks were very high relative to regional mean C stocks (2.0–2.5 times the mean), LS plots were accumulating aboveground live C at a positive rate (0.61Mgha−1 year−1), while C stocks on OG plots are declining (−0.54Mgha−1 year−1). This change is driven by the presence of beech bark fungus (Nectria sp.) that is leading to mortality in larger diameter American beech (Fagus grandifolia) trees. We also found that the Northeast Variant of the Forest Vegetation Simulator is not a reliable predictor of aboveground live carbon accumulation rates in Northeastern LS and OG stands. This work provides important baselines for understanding the role of older forests and forest management within climate change mitigation strategies in the northeastern US. Late-successional and old-growth forests can play an important role in mitigating climate change, but understanding and quantifying natural disturbance risk to forest carbon stocks is critical for successful implementation of mitigation strategies. Further, regional forest carbon models will need calibration to accurately predict carbon accumulation rates in older forests.