Natural disturbance impacts on trade-offs and co-benefits of forest biodiversity and carbon.

With accelerating environmental change, understanding forest disturbance impacts on trade-offs between biodiversity and carbon dynamics is of high socio-economic importance. Most studies, however, have assessed immediate or short-term effects of disturbance, while long-term impacts remain poorly understood. Using a tree-ring-based approach, we analysed the effect of 250 years of disturbances on present-day biodiversity indicators and carbon dynamics in primary forests. Disturbance legacies spanning centuries shaped contemporary forest co-benefits and trade-offs, with contrasting, local-scale effects. Disturbances enhanced carbon sequestration, reaching maximum rates within a comparatively narrow post-disturbance window (up to 50 years). Concurrently, disturbance diminished aboveground carbon storage, which gradually returned to peak levels over centuries. Temporal patterns in biodiversity potential were bimodal; the first maximum coincided with the short-term post-disturbance carbon sequestration peak, and the second occurred during periods of maximum carbon storage in complex old-growth forest. Despite fluctuating local-scale trade-offs, forest biodiversity and carbon storage remained stable across the broader study region, and our data support a positive relationship between carbon stocks and biodiversity potential. These findings underscore the interdependencies of forest processes, and highlight the necessity of large-scale conservation programmes to effectively promote both biodiversity and long-term carbon storage, particularly given the accelerating global biodiversity and climate crises.

Evaluating nature-based solutions for climate mitigation and conservation requires comprehensive carbon accounting.

Nature-based solutions (NbS) can address climate change, biodiversity loss, human well-being and their interactions in an integrated way. A major barrier to achieving this is the lack of comprehensiveness in current carbon accounting which has focused on flows rather than stocks of carbon and led to perverse outcomes. We propose a new comprehensive approach to carbon accounting based on the whole carbon cycle, covering both stocks and flows, and linking changes due to human activities with responses in the biosphere and atmosphere. We identify enhancements to accounting, namely; inclusion of all carbon reservoirs, changes in their condition and stability, disaggregated flows, and coverage of all land areas. This comprehensive approach recognises that both carbon stocks (as storage) and carbon flows (as sequestration) contribute to the ecosystem service of global climate regulation. In contrast, current ecosystem services measurement and accounting commonly use only carbon sequestration measured as net flows, while greenhouse gas inventories use flows from sources to sinks. This flow-based accounting has incentivised planting and maintaining young forests with high carbon uptake rates, resulting, perversely, in failing to reveal the greater mitigation benefit from protecting larger, more stable and resilient carbon stocks in natural forests. We demonstrate the benefits of carbon storage and sequestration for climate mitigation, in theory as ecosystem services within an ecosystem accounting framework, and in practice using field data that reveals differences in results between accounting for stocks or flows. Our proposed holistic and comprehensive carbon accounting makes transparent the benefits, trade-offs and shortcomings of NbS actions for climate mitigation and sustainability outcomes. Adopting this approach is imperative for revision of ecosystem accounting systems under the System of Environmental-Economic Accounting and contributing to evidence-based decision-making for international conventions on climate (UNFCCC), biodiversity (CBD) and sustainability (SDGs).

Fish Performance Indicators Adjacent to Oil Sands Activity: Response in Performance Indicators of Slimy Sculpin in the Steepbank River, Alberta, Adjacent to Oil Sands Mining Activity.

Since 2009, the Canadian and Alberta governments have been developing monitoring plans for surface water quality and quantity of the lower Athabasca River and its tributaries (2010-2013). The objectives of the present study to the fish monitoring program were to 1) assess the current status of fish in a tributary of the lower Athabasca River, 2) identify existing differences between upstream reference and within the oil sands deposit exposure sites, and 3) identify trends/changes in fish performance indicators relative to historical studies. The present study examines the fish performance indicators in slimy sculpin (Cottus cognatus) in the Steepbank River, Alberta, in terms of growth, gonad size, condition, and hepatic 7-ethoxyresorufin-O-deethylase (EROD) activity as an indicator of exposure to oil-sands-related compounds. The sampling program followed historical sampling methods (1999-2000) to provide comparable data over time with an additional upstream site (n = 2) added as development progressed. Consistent changes were documented in sculpin collected from downstream sections of the Steepbank River within the oil sands deposit (n = 2) in 2010 through 2013. Sculpin demonstrated increased liver size with corresponding induction of EROD activity consistent with historical data and reductions in energy investment relative to reproductive development and gonadal steroid production capacity. There was no consistent evidence of changes in fish performance indicators with increased surface mining development, particularly adjacent to the Steepbank River Mid site. Although physical development in the Steepbank watershed has increased over the last 15 yr, these results are consistent with historical data suggesting that the magnitude of the response in the aquatic environment adjacent to the development has not changed. Environ Toxicol Chem 2020;39:396-409. © 2019 SETAC.

Modelling water yields in response to logging and Representative Climate Futures.

Natural and human disturbance along with climate change pose major challenges for resource management. This is relevant in natural forests, where conflict can occur between water provision and industrial logging. As a result, conversion of old forests to young, fast-growing stands through logging can dramatically reduce streamflow and water yield. We modelled changes in stream run-off and hence water yield from a forest catchment in response to clearcut logging and compared this with projected climate change (using a Representative Climate Futures [RCFs] approach). We focused on the Thomson Catchment, which is the largest single catchment for the city of Melbourne, south-eastern Australia. Within this catchment, we targeted our analysis at montane ash-type eucalypt forests, as these receive the most rainfall and are subject to clearcutting. We used several forest management scenarios to model changes in water yield over time. For our analysis of projected climate change, we employed a range of RCFs that represent 'consensus', 'wettest' and 'driest' scenarios to model the impacts of multiple Representative Concentration Pathways (RCPs). Our initial spatial analysis revealed that 42% of the ash-type eucalypt forests in the Thomson Catchment have been logged. Under historical and continued logging, stream runoff decreases by 40,211 ML by 2090 compared with a hypothetical baseline if logging had ceased in 1995 and 34,059 ML if logging continues beyond 2019. These losses exceed the projected impacts of climate change under the consensus and wettest scenarios, but the driest scenarios are projected to exceed these losses, consisting of 49,998 ML and 69,474 ML for RCP 4.5 and RCP 8.5, respectively. We suggest logging be excluded from the Thomson Catchment because of decreasing stream flows due to climate change and an increasing water demand due to human population growth. This study provides a quantitative approach for highlighting how resource conflicts can be magnified under climate change.

Putting biodiversity into the national accounts: Creating a new paradigm for economic decisions.

Economics has long taken precedence over the environment in both governmental and business decision making, with the System of National Accounts and the indicator GDP coming to represent much that is wrong with the current environmental conditions. Increasing recognition of the environmental damage human activity causes and that human well-being depends on biodiversity and ecosystems means that new systems to measure and sustainably manage the world are needed. Integrating the environment into national accounts has been suggested as a way to improve information but so far impact on decision making is limited. This outlook needs to change. Using examples from Australia and Botswana, we show how integrating information on biodiversity, resource use and the economy via accounting can help create a new decision-making paradigm and enable a new policy framing with spending on biodiversity conservation and sustainability seen as an investment, not a cost.

Ecosystem accounts define explicit and spatial trade-offs for managing natural resources.

Decisions about natural resource management are frequently complex and vexed, often leading to public policy compromises. Discord between environmental and economic metrics creates problems in assessing trade-offs between different current or potential resource uses. Ecosystem accounts, which quantify ecosystems and their benefits for human well-being consistent with national economic accounts, provide exciting opportunities to contribute significantly to the policy process. We advanced the application of ecosystem accounts in a regional case study by explicitly and spatially linking impacts of human and natural activities on ecosystem assets and services to their associated industries. This demonstrated contributions of ecosystems beyond the traditional national accounts. Our results revealed that native forests would provide greater benefits from their ecosystem services of carbon sequestration, water yield, habitat provisioning and recreational amenity if harvesting for timber production ceased, thus allowing forests to continue growing to older ages.

Under What Circumstances Do Wood Products from Native Forests Benefit Climate Change Mitigation?

Climate change mitigation benefits from the land sector are not being fully realised because of uncertainty and controversy about the role of native forest management. The dominant policy view, as stated in the IPCC's Fifth Assessment Report, is that sustainable forest harvesting yielding wood products, generates the largest mitigation benefit. We demonstrate that changing native forest management from commercial harvesting to conservation can make an important contribution to mitigation. Conservation of native forests results in an immediate and substantial reduction in net emissions relative to a reference case of commercial harvesting. We calibrated models to simulate scenarios of native forest management for two Australian case studies: mixed-eucalypt in New South Wales and Mountain Ash in Victoria. Carbon stocks in the harvested forest included forest biomass, wood and paper products, waste in landfill, and bioenergy that substituted for fossil fuel energy. The conservation forest included forest biomass, and subtracted stocks for the foregone products that were substituted by non-wood products or plantation products. Total carbon stocks were lower in harvested forest than in conservation forest in both case studies over the 100-year simulation period. We tested a range of potential parameter values reported in the literature: none could increase the combined carbon stock in products, slash, landfill and substitution sufficiently to exceed the increase in carbon stock due to changing management of native forest to conservation. The key parameters determining carbon stock change under different forest management scenarios are those affecting accumulation of carbon in forest biomass, rather than parameters affecting transfers among wood products. This analysis helps prioritise mitigation activities to focus on maximising forest biomass. International forest-related policies, including negotiations under the UNFCCC, have failed to recognize fully the mitigation value of native forest conservation. Our analyses provide evidence for decision-making about the circumstances under which forest management provides mitigation benefits.

Accounting for biomass carbon stock change due to wildfire in temperate forest landscapes in Australia.

Carbon stock change due to forest management and disturbance must be accounted for in UNFCCC national inventory reports and for signatories to the Kyoto Protocol. Impacts of disturbance on greenhouse gas (GHG) inventories are important for many countries with large forest estates prone to wildfires. Our objective was to measure changes in carbon stocks due to short-term combustion and to simulate longer-term carbon stock dynamics resulting from redistribution among biomass components following wildfire. We studied the impacts of a wildfire in 2009 that burnt temperate forest of tall, wet eucalypts in south-eastern Australia. Biomass combusted ranged from 40 to 58 tC ha(-1), which represented 6-7% and 9-14% in low- and high-severity fire, respectively, of the pre-fire total biomass carbon stock. Pre-fire total stock ranged from 400 to 1040 tC ha(-1) depending on forest age and disturbance history. An estimated 3.9 TgC was emitted from the 2009 fire within the forest region, representing 8.5% of total biomass carbon stock across the landscape. Carbon losses from combustion were large over hours to days during the wildfire, but from an ecosystem dynamics perspective, the proportion of total carbon stock combusted was relatively small. Furthermore, more than half the stock losses from combustion were derived from biomass components with short lifetimes. Most biomass remained on-site, although redistributed from living to dead components. Decomposition of these components and new regeneration constituted the greatest changes in carbon stocks over ensuing decades. A critical issue for carbon accounting policy arises because the timeframes of ecological processes of carbon stock change are longer than the periods for reporting GHG inventories for national emissions reductions targets. Carbon accounts should be comprehensive of all stock changes, but reporting against targets should be based on human-induced changes in carbon stocks to incentivise mitigation activities.

Re-evaluation of forest biomass carbon stocks and lessons from the world's most carbon-dense forests.

From analysis of published global site biomass data (n = 136) from primary forests, we discovered (i) the world's highest known total biomass carbon density (living plus dead) of 1,867 tonnes carbon per ha (average value from 13 sites) occurs in Australian temperate moist Eucalyptus regnans forests, and (ii) average values of the global site biomass data were higher for sampled temperate moist forests (n = 44) than for sampled tropical (n = 36) and boreal (n = 52) forests (n is number of sites per forest biome). Spatially averaged Intergovernmental Panel on Climate Change biome default values are lower than our average site values for temperate moist forests, because the temperate biome contains a diversity of forest ecosystem types that support a range of mature carbon stocks or have a long land-use history with reduced carbon stocks. We describe a framework for identifying forests important for carbon storage based on the factors that account for high biomass carbon densities, including (i) relatively cool temperatures and moderately high precipitation producing rates of fast growth but slow decomposition, and (ii) older forests that are often multiaged and multilayered and have experienced minimal human disturbance. Our results are relevant to negotiations under the United Nations Framework Convention on Climate Change regarding forest conservation, management, and restoration. Conserving forests with large stocks of biomass from deforestation and degradation avoids significant carbon emissions to the atmosphere, irrespective of the source country, and should be among allowable mitigation activities. Similarly, management that allows restoration of a forest's carbon sequestration potential also should be recognized.

Mechanisms linking plant productivity and water status for a temperate Eucalyptus forest flux site: analysis over wet and dry years with a simple model.

A simple process-based model was applied to a tall Eucalyptus forest site over consecutive wet and dry years to examine the importance of different mechanisms linking productivity and water availability. Measured soil moisture, gas flux (CO2, H2O) and meteorological records for the site were used. Similar levels of simulated H2O flux in 'wet' and 'dry' years were achieved when water availability was not confined to the first 1.20 m of the soil profile, but was allowed to exceed it. Although the simulated effects of low soil and atmospheric water content on CO2 flux, presumably via reduction in stomatal aperture, also acted on transpiration, they were offset in the dry year by a higher vapour-pressure deficit. A sensitivity analysis identified the processes that were important in wet versus dry years, and on an intra-annual timeframe. Light-limited productivity dominated in both years, except for the driest period in the dry year. Vapour-pressure deficit affected productivity across more of each year than soil moisture, but both effects were larger in the dry year. The introduction of a reduced leaf area tended to decrease sensitivity in the dry year. Plant hydraulic architecture that increases plant available water, maximises productivity per unit water use and achieves lower sensitivity to low soil moisture levels should minimise production losses during dry conditions.

Linking leaf and tree water use with an individual-tree model.

We tested the ability of a model to scale gas exchange from leaf level to whole-tree level by: (1) measuring leaf gas exchange in the canopy of 10 trees in a tall Eucalyptus delegatensis RT Baker forest in NSW, Australia; (2) monitoring sap flow of the same 10 trees during the measurement week; and (3) using an individual-tree-based model (MAESTRA) to link the two sets of measurements. Photosynthesis and stomatal conductance components of the model were parameterized with the leaf gas exchange data, and canopy structure was parameterized with crown heights, dimensions and leaf areas of each of the measurement trees and up to 45 neighboring trees. Transpiration of the measurement trees was predicted by the model and compared with sap flow data. Leaf gas exchange parameters were similar for all 10 trees, with the exception of two smaller trees that had relatively low stomatal conductances. We hypothesize that these trees may have experienced water stress as a result of competition from large neighboring trees. The model performed well, and in most cases, was able to replicate the time course of tree transpiration. Maximum rates of transpiration were higher than measured rates for some trees and lower than measured rates for others, which may have been a result of inaccuracy in estimating tree leaf area. There was a small lag (about 15-30 minutes) between sap flow and modeled transpiration for some trees in the morning, likely associated with use of water stored in stems. The model also captured patterns of variation in sap flow among trees. Overall, the study confirms the ability of models to estimate forest canopy transpiration from leaf-level measurements.

δ13C of organic matter transported from the leaves to the roots in Eucalyptus delegatensis: short-term variations and relation to respired CO2.

Post-photosynthetic carbon isotope fractionation might alter the isotopic signal imprinted on organic matter (OM) during primary carbon fixation by Rubisco. To characterise the influence of post-photosynthetic processes, we investigated the effect of starch storage and remobilisation on the stable carbon isotope signature (δ13C) of different carbon pools in the Eucalyptus delegatensis R. T. Baker leaf and the potential carbon isotope fractionation associated with phloem transport and respiration. Twig phloem exudate and leaf water-soluble OM showed diel variations in δ13C of up to 2.5 and 2‰, respectively, with 13C enrichment during the night and depletion during the day. Damped diel variation was also evident in bulk lipids of the leaf and in the leaf wax fraction. δ13C of nocturnal phloem exudate OM corresponded with the δ13C of carbon released from starch. There was no change in δ13C of phloem carbon along the trunk. CO2 emitted from trunks and roots was 13C enriched compared with the potential organic substrate, and depleted compared with soil-emitted CO2. The results are consistent with transitory starch accumulation and remobilisation governing the diel rhythm of δ13C in phloem-transported OM and fragmentation fractionation occurring during respiration. When using δ13C of OM or CO2 for assessing ecosystem processes or plant reactions towards environmental constraints, post-photosynthetic discrimination should be considered.

Interaction between sapwood and foliage area in alpine ash (Eucalyptus delegatensis) trees of different heights.

In native stands of Eucalyptus delegatensis R. T. Baker, sapwood area (As) to foliage area (Af) ratios (As:Af) decreased as tree height increased, contradicting the common interpretation of the Pipe Model Theory as well as the generally observed trend of increasing As:Af ratios with tree height. To clarify this relationship, we estimated sapwood hydraulic conductivity theoretically based on measurements of sapwood vessel diameters and Poiseuille's law for fluid flow through pipes. Despite the observed decrease in As:Af ratios with tree height, leaf specific conductivity increased with total tree height, largely as a result of an increase in the specific conductivity of sapwood. This observation supports the proposition that the stem's ability to supply foliage with water must increase as trees grow taller, to compensate for the increased hydraulic path length. The results presented here highlight the importance of measuring sapwood hydraulic conductivity in analyses of sapwood-foliage interactions, and suggest that measurements of sapwood hydraulic conductivity may help to resolve conflicting observations of how As:Af ratios change as trees grow taller.