The anthropogenic imprint on temperate and boreal forest demography and carbon turnover.

Aim: The sweeping transformation of the biosphere by humans over the last millennia leaves only limited windows into its natural state. Much of the forests that dominated temperate and southern boreal regions have been lost and those that remain typically bear a strong imprint of forestry activities and past land-use change, which have changed forest age structure and composition. Here, we ask how would the dynamics, structure and function of temperate and boreal forests differ in the absence of forestry and the legacies of land-use change? Location: Global. Time Period: 2001-2014, integrating over the legacy of disturbance events from 1875 to 2014. Major Taxa Studied: Trees. Methods: We constructed an empirical model of natural disturbance probability as a function of community traits and climate, based on observed disturbance rate and form across 77 protected forest landscapes distributed across three continents. Coupling this within a dynamic vegetation model simulating forest composition and structure, we generated estimates of stand-replacing disturbance return intervals in the absence of forestry for northern hemisphere temperate and boreal forests. We then applied this model to calculate forest stand age structure and carbon turnover rates. Results: Comparison with observed disturbance rates revealed human activities to have almost halved the median return interval of stand-replacing disturbances across temperate forest, with more moderate changes in the boreal region. The resulting forests are typically much younger, especially in northern Europe and south-eastern North America, resulting in a 32% reduction in vegetation carbon turnover time across temperate forests and a 7% reduction for boreal forests. Conclusions: The current northern hemisphere temperate forest age structure is dramatically out of equilibrium with its natural disturbance regimes. Shifts towards more nature-based approaches to forest policy and management should more explicitly consider the current disturbance surplus, as it substantially impacts carbon dynamics and litter (including deadwood) stocks.

Model ensembles of ecosystem services fill global certainty and capacity gaps.

Sustaining ecosystem services (ES) critical to human well-being is hindered by many practitioners lacking access to ES models ("the capacity gap") or knowledge of the accuracy of available models ("the certainty gap"), especially in the world's poorer regions. We developed ensembles of multiple models at an unprecedented global scale for five ES of high policy relevance. Ensembles were 2 to 14% more accurate than individual models. Ensemble accuracy was not correlated with proxies for research capacity, indicating that accuracy is distributed equitably across the globe and that countries less able to research ES suffer no accuracy penalty. By making these ES ensembles and associated accuracy estimates freely available, we provide globally consistent ES information that can support policy and decision-making in regions with low data availability or low capacity for implementing complex ES models. Thus, we hope to reduce the capacity and certainty gaps impeding local- to global-scale movement toward ES sustainability.

Ensembles of ecosystem service models can improve accuracy and indicate uncertainty.

Many ecosystem services (ES) models exist to support sustainable development decisions. However, most ES studies use only a single modelling framework and, because of a lack of validation data, rarely assess model accuracy for the study area. In line with other research themes which have high model uncertainty, such as climate change, ensembles of ES models may better serve decision-makers by providing more robust and accurate estimates, as well as provide indications of uncertainty when validation data are not available. To illustrate the benefits of an ensemble approach, we highlight the variation between alternative models, demonstrating that there are large geographic regions where decisions based on individual models are not robust. We test if ensembles are more accurate by comparing the ensemble accuracy of multiple models for six ES against validation data across sub-Saharan Africa with the accuracy of individual models. We find that ensembles are better predictors of ES, being 5.0-6.1% more accurate than individual models. We also find that the uncertainty (i.e. variation among constituent models) of the model ensemble is negatively correlated with accuracy and so can be used as a proxy for accuracy when validation is not possible (e.g. in data-deficient areas or when developing scenarios). Since ensembles are more robust, accurate and convey uncertainty, we recommend that ensemble modelling should be more widely implemented within ES science to better support policy choices and implementation.

Role of forest regrowth in global carbon sink dynamics.

Although the existence of a large carbon sink in terrestrial ecosystems is well-established, the drivers of this sink remain uncertain. It has been suggested that perturbations to forest demography caused by past land-use change, management, and natural disturbances may be causing a large component of current carbon uptake. Here we use a global compilation of forest age observations, combined with a terrestrial biosphere model with explicit modeling of forest regrowth, to partition the global forest carbon sink between old-growth and regrowth stands over the period 1981-2010. For 2001-2010 we find a carbon sink of 0.85 (0.66-0.96) Pg year-1 located in intact old-growth forest, primarily in the moist tropics and boreal Siberia, and 1.30 (1.03-1.96) Pg year-1 located in stands regrowing after past disturbance. Approaching half of the sink in regrowth stands would have occurred from demographic changes alone, in the absence of other environmental changes. These age-constrained results show consistency with those simulated using an ensemble of demographically-enabled terrestrial biosphere models following an independent reconstruction of historical land use and management. We estimate that forests will accumulate an additional 69 (44-131) Pg C in live biomass from changes in demography alone if natural disturbances, wood harvest, and reforestation continue at rates comparable to those during 1981-2010. Our results confirm that it is not possible to understand the current global terrestrial carbon sink without accounting for the sizeable sink due to forest demography. They also imply that a large portion of the current terrestrial carbon sink is strictly transient in nature.

Implications of accounting for management intensity on carbon and nitrogen balances of European grasslands.

European managed grasslands are amongst the most productive in the world. Besides temperature and the amount and timing of precipitation, grass production is also highly controlled by applications of nitrogen fertilizers and land management to sustain a high productivity. Since management characteristics of pastures vary greatly across Europe, land-use intensity and their projections are critical input variables in earth system modeling when examining and predicting the effects of increasingly intensified agricultural and livestock systems on the environment. In this study, we aim to improve the representation of pastures in the dynamic global vegetation model LPJ-GUESS. This is done by incorporating daily carbon allocation for grasses as a foundation to further implement daily land management routines and land-use intensity data into the model to discriminate between intensively and extensively used regions. We further compare our new simulations with leaf area index observations, reported regional grassland productivity, and simulations conducted with the vegetation model ORCHIDEE-GM. Additionally, we analyze the implications of including pasture fertilization and daily management compared to the standard version of LPJ-GUESS. Our results demonstrate that grassland productivity cannot be adequately captured without including land-use intensity data in form of nitrogen applications. Using this type of information improved spatial patterns of grassland productivity significantly compared to standard LPJ-GUESS. In general, simulations for net primary productivity, net ecosystem carbon balance and nitrogen leaching were considerably increased in the extended version. Finally, the adapted version of LPJ-GUESS, driven with projections of climate and land-use intensity, simulated an increase in potential grassland productivity until 2050 for several agro-climatic regions, most notably for the Mediterranean North, the Mediterranean South, the Atlantic Central and the Atlantic South.

Characterization of a novel human endogenous retrovirus, HERV-H/F, expressed in human leukemia cell lines.

We have identified and characterized a human endogenous retrovirus (HERV) gag transcript in the human pre-B cell leukemia line Reh. The transcript was found to be a splice product of a structurally intact HERV element located on chromosome 6q13. Its primer binding site is complementary to phenylalanine (F) tRNA, common for the HERV-F family, but the overall genome sequence is closely related to the HERV-H family. The retroviral sequence was therefore designated HERV-H/F. The HERV element shows a distinct mRNA expression pattern among hematopoietic cancer cell lines with expression in some leukemia-derived cell lines of B-lymphoid and myeloid origin. No expression was observed in normal human tissues, indicating a cancer-specific expression pattern. The 5' long terminal repeat (LTR) was tested for promoter activity in HERV-H/F expressing and nonexpressing cell lines. The cell specificity of the LTR-mediated reporter gene expression did not conclusively correlate with endogenous virus expression, indicating that the transcription regulation of this gene is not alone dependent on cell-specific activity of transcription factors.

Full-length HERV-H elements with env SU open reading frames in the human genome.

Human endogenous retroviruses (HERVs) are estimated to represent at least 1% of the human genome. An HERV-H env SU sequence (HERV-H19) was used to screen the high-throughput (htgs) and nonredundant (nr) databases for other HERV-H SU open reading frames (ORFs) and thus possible functional proteins. Using PCR with primers derived from HERV-H19 SU, we also obtained several new sequences with ORFs from a human DNA sample. In a phylogenetic analysis, ORF-containing sequences clustered with HERV-H sequences from chromosomes 1 and 2. SU ORF- and non-SU ORF-containing elements had about the same difference between 5' and 3' long terminal repeats (LTRs) (about 4%), indicating a similar time of integration. SU ORF sequences had a moderately high number of synonymous-versus-nonsynonymous mutations, which indicates a selection for maintenance of the HERV-H SU ORFs.