Ground Net Primary Production Research Articles

Global pattern and associated drivers of grassland productivity sensitivity to precipitation change

Precipitation is a primary climatic determinant of grassland productivity, with many global change experiments manipulating precipitation. Here we examine the impacts of precipitation addition and reduction treatment intensity and duration on grassland above- (ANPP) and below- (BNPP) ground net primary productivity in a large-scale meta-analysis. We tested, 1) the double asymmetry model of sensitivity, specifically whether the sensitivity of productivity decreases with treatment intensity under increased precipitation and increases with treatment intensity under decreased precipitation, 2) whether the sensitivity of productivity to precipitation change decreases with treatment length, and 3) how the sensitivity of productivity changes with climate conditions. ANPP showed higher sensitivity than BNPP under increased precipitation but similar sensitivity to BNPP under decreased precipitation. The sensitivity of ANPP and BNPP decreased with increasing treatment intensity (e.g., percentage change in precipitation, ΔPPT) and leveled off in the long-term. With increased precipitation, the sensitivity of productivity decreased with increasing treatment length (e.g., experimental duration) and leveled off in the long-term, whereas the sensitivity increased with increasing treatment length under reduced precipitation. Furthermore, the sensitivity of productivity to precipitation change decreased with increasing mean annual precipitation and temperature. Finally, our meta-analysis shows that above- and belowground net primary productivity have asymmetric responses to precipitation change. Together these results highlight the complex mechanisms underlying the impacts of precipitation change, particularly the intensity and duration of such changes, on grassland productivity.

Trends and variations in the activity of global vegetation in response to climate variability between 1987 and 1997

Eleven-year (1987-1997) time series data of remotely sensed vegetation index (NDVI) and meteorological observations (temperature, precipitation, cloud cover and relative humidity) provided a powerful tool to illuminate the response of global terrestrial vegetation to short-and long-term climate variability. NDVI being a sensitive estimator of the amount of photosynthetic active radiation intercepted by the canopy has been treated as a proxy for above ground net primary production (ANPP). Analyses of trends, multiple regression and correlation analyses were employed. The main result indicates a considerable increase (0.7~1.9%/year) of monthly vegetation production in all ecosystems over the investigated period, allied with an analogous increase (0.9~15%/year) in precipitation. Additionally, several direct relationships were also observed on the intra- and inter-annual time scales suggesting that the increase and variation of ANPP in most biomes could be mainly linked to the corresponding increase and variation in precipitation. Overall, the four climate variables play a considerable role in the inter-annual variability of ANPP of global vegetation.

The Resilient Recurrent Behavior of Mediterranean Semi-Arid Complex Adaptive Landscapes

Growing external pressures from human activities and climate change can exacerbate desertification, compromising the livelihoods of more than 25% of the world’s population. The dryland mosaic is defined by land covers that do not behave similarly, and the identification of their recurring or irregular changes over time is crucial, especially in areas susceptible to become desertified. To this aim, the methodological approach of this research is based on the integration of non-linear data analysis techniques, such as recurrence plots (RPs) and recurrence quantification analysis (RQA), applied to the Enhanced Vegetation Index (EVI), which is a functional ecological proxy of above ground net primary production. The research exploits the recurring change detected in vegetation cover over time to gauge the predictable (resilient) behavior of the EVI as well as its chaoticity in a semi-arid Mediterranean region (Apulia, Italy). Interestingly, the results have shown the spatial rendering of recurrence variables, confirming the well-known hot spots of soil degradation and desertification taking place in the region, which are characterized by greater EVI chaoticity, but they have also identified new potential candidate sites. As a result, the susceptibility to land degradation, as measured by the EVI-RQA approach, can help in measuring land desertification with evident operational benefits for landscape planning. The novelty of the research lies in the spatially explicit identification of resilient and less resilient areas to desertification that can support the definition of more targeted interventions and conservation priorities for better planning and sustainable management of Mediterranean drylands.

Pastoralism in the highest peaks: Role of the traditional grazing systems in maintaining biodiversity and ecosystem function in the alpine Himalaya.

Rangelands cover around half of the planet's land mass and provide vital ecosystem services to over a quarter of humanity. The Himalayan rangelands, part of a global biodiversity hotspot is among the most threatened regions in the world. In rangelands of many developing nations policies banning grazing in protected areas is common practice. In 1998, the Indian state of Sikkim, in the Eastern Himalaya, enacted a grazing ban in response to growing anthropogenic pressure in pastures and forests that was presumably leading to degradation of biodiversity. Studies from the region demonstrate the grazing ban has had some beneficial results in the form of increased carbon stocks and regeneration of some species of conservation value but the ban also resulted in negative outcomes such as reduced household incomes, increase in monocultures in lowlands, decreased manure production in a state that exclusively practices organic farming, spread of gregarious species, and a perceived increase in human wildlife conflict. This paper explores the impact of the traditional pastoral system on high elevation plant species in Lachen valley, one of the few regions of Sikkim where the grazing ban was not implemented. Experimental plots were laid in along an elevation gradient in grazed and ungrazed areas. Ungrazed areas are part of pastures that have been fenced off (preventing grazing) for over a decade and used by the locals for hay formation. I quantified plant species diversity (Species richness, Shannon index, Simpson diversity index, and Pielou evenness index) and ecosystem function (above ground net primary productivity ANPP). The difference method using movable exlosure cages was used in grazing areas to account for plant ANPP eaten and regrowth between grazing periods). The results demonstrate that grazing significantly contributes to greater plant species diversity (Species richness, Shannon index, Simpson diversity index, and Pielou evenness index) and ecosystem function (using above ground net primary productivity as an indicator). The multidimensional scaling and ANOSIM (Analysis of Similarities) pointed to significant differences in plant species assemblages in grazed and ungrazed areas. Further, ecosystem function is controlled by grazing, rainfall and elevation. Thus, the traditional transhumant pastoral system may enhance biodiversity and ecosystem function. I argue that a complete restriction of open grazing meet neither conservation nor socioeconomic goals. Evidence based policies are required to conserve the rich and vulnerable biodiversity of the region.

Effects of manipulated precipitation on aboveground net primary productivity of grassland fields: Controlled rainfall experiments in Inner Mongolia, China

AbstractRecovery from grassland degradation caused by climate change and human disturbance is critical to the sustainable development of drylands. Grassland in China accounts for 13% of the global grassland area, and more than half of it is still recovering from degradation. How climate change will contribute to the recovery of degraded grassland has not been clarified through field experiments. Here, we report the effects of manipulated precipitation regimes on above ground net primary productivity (ANPP) in five grassland fields along a degradation gradient using a 3‐year controlled rainfall manipulation experiment in Inner Mongolia, China. We found that differences of approximately 20–30% in growing season precipitation have limited impacts on the ANPP of grasslands, and the responses can depend crucially on the degradation status indicated by vegetation and soil features. ANPP sensitivity to spring drought increased with increasing degradation level, which was mainly determined by vegetation composition. ANPP was generally insensitive to summer drought except for mature grassland, in which drought led to severe soil water deficit, mainly mediated by soil water holding capacity. Our results suggest that the recovery of degraded grassland is expected to be delayed by increasing drought early in the growing season, and mature grassland would be more vulnerable to extreme summer drought. These findings highlight the negative impacts of seasonal drought on degraded grassland and emphasize the importance of accounting for climate change and degradation status in future grassland ecosystem restoration and management policies.

Carbon Sequestration by the Above Ground Biomass Pool in the South West Mau Forest of Kenya, 1985 - 2015

Forests are important for regulation of the global carbon balance. Increase in forest biomass enhances atmospheric carbon sequestration while decrease in forest biomass contributes to carbon dioxide emissions. World over, forest biomass has been declining due to forest loss and degradation. The South West Mau has experienced significant forest loss since 1964. The decline is posited to have significant impacts on carbon sequestration, carbon storage, carbon dioxide emissions and status of atmospheric carbon dioxide. This study assessed interannual trend and variability as well as change point detection in carbon sequestration in South West Mau Forest, Kenya between 1985 and 2015. Above ground biomass carbon sequestration was quantified based on the Carnegie-Ames-Stanford Approach (CASA) and carbon fraction for tropical climate domain. Carbon sequestration dynamics were characterized by increase-decrease cycles of approximately 3 years and low interannual variability (CV= 9.13). It emerged that South West Mau Forest was a net carbon emitter with a carbon sequestration balance of -588.40 Kg/ha between 1985 and 2015. Keywords: Forest, Carbon sequestration, Carnegie-Ames-Stanford Approach, Above ground net primary production DOI: 10.7176/JEES/10-8-05 Publication date: August 31 st 2020

High Below-Ground Productivity Allocation of Alpine Grasslands on the Northern Tibet.

The allocation of net primary production (NPP) between above- and belowground components is a key step of ecosystem material cycling and energy flows, which determines many critical parameters, e.g., the fraction of below ground NPP (BNPP) to NPP (fBNPP) and root turnover rates (RTR), in vegetation models. However, direct NPP estimation and partition are scarcely based on field measurements of biomass dynamics in the alpine grasslands on the Northern Tibetan Plateau (NTP). Consequently, these parameters are unverifiable and controversial. Here, we measured above- and belowground biomass dynamics (monthly from May to September each year from 2013 to 2015) to estimate NPP dynamics and allocations in four typical alpine grassland ecosystems, i.e., an alpine meadow, alpine meadow steppe, alpine steppe and alpine desert steppe. We found that NPP and its components, above and below ground NPP (ANPP and BNPP), increased significantly from west to east on the NTP, and ANPP was mainly affected by temperature while BNPP and NPP were mainly affected by precipitation. The bulk of BNPP was generally concentrated in the top 10 cm soil layers in all four alpine grasslands (76.1% ± 9.1%, mean ± SD). Our results showed that fBNPP was significantly different among these four alpine grasslands, with its means in alpine meadow (0.93), alpine desert steppe (0.92) being larger than that in the alpine meadow steppe (0.76) and alpine steppe (0.77). Both temperature and precipitation had significant and positive effects on the fBNPP, while their interaction effects were significantly opposite. RTR decreased with increasing precipitation, but increased with increasing temperature across this ecoregion. Our study illustrated that alpine grasslands on the NTP, especially in the alpine meadow and alpine desert steppe, partitioned an unexpected and greater NPP to below ground than most historical reports across global grasslands, indicating a more critical role of the root carbon pool in carbon cycling in alpine grasslands on the NTP.

Response of southern African vegetation to climate change at 1.5 and 2.0° global warming above the pre-industrial level

Climate change has severely impacted southern African vegetation over the last decades. Recent studies have shown that limiting the global warming level to well below 2 °C above pre-industrial level may reduce the catastrophic effects of anthropogenic climate change. However, there is limited knowledge on the response of vegetation to climate change at different global warming levels. This study examines how southern African vegetation may respond to climate change at 1.5 °C and 2 °C warming. An ensemble of climate projections from the CESM model were analyzed to evaluate the potential changes in timing and magnitude of vegetation index and parameters across southern African biomes for a global warming of 1.5 °C and 2 °C under the RCP8.5 scenario. The results show that the spatial pattern of the Normalized Difference Vegetation Index (NDVI) are well captured by the ensemble mean. However, the model overestimates NDVI over the east coast of South Africa while it underestimates it over Angola. The strong relationship between the NDVI and other vegetation parameters (e.g. net primary production, leaf area cover) over southern Africa, suggests that vegetation productivity is projected to decline over Mozambique, Namibia, Botswana, Zimbabwe and Zambia at 1.5 °C and 2 °C warming. However, vegetation productivity is projected to likely increase over some parts of Madagascar and South Africa. The results further show that there is a similarity in the response of vegetation parameters at 1.5 °C and 2 °C warming. The difference in projected changes of the above ground net primary production, soil carbon and surface run-off is negligible between 1.5 °C and 2 °C warming. While the model ensemble members show a range in the magnitude of changes, they all project an increase in below ground net primary production, soil carbon and photosynthesis over the southern African biomes while projecting a decline in canopy transpiration over all the biomes. Furthermore, the CESM projects an increase in drought intensity as temperature increases over the southern African biomes. The projected changes in the drought intensity appears more pronounced with the Standardized Precipitation Evapotranspiration Index (SPEI) than with the Standardized Precipitation Index (SPI). The results of the study is important in informing policy makers for climate change mitigation and adaptation efforts in southern Africa. For effective mitigation and adaptation strategy, there is a need to translate the results to make them more accessible to inform policy through the use of appropriate engagement platforms such as multi-stakeholder partnerships and workshops.

Repackaging precipitation into fewer, larger storms reduces ecosystem exchanges of CO2 and H2O in a semiarid steppe

General circulation models predict that precipitation will become more extreme, i.e. rainfall events of larger size but reduced frequency. Studies in North American grasslands have shown that such repackaging of precipitation into fewer, larger events enhanced above ground net primary productivity (ANPP), likely due to deeper soil moisture infiltration favoring plant water use over evaporation. However, ANPP responses in other regions remain poorly understood, and responses of carbon and water exchanges with the atmosphere remain unknown. Here we manipulated rainfall in a steppe ecosystem of northern China over 4 years to investigate how temporal packaging of precipitation impacts ANPP, evapotranspiration (ET), net ecosystem CO2 exchange (NEE) and the component fluxes gross primary productivity (GPP) and ecosystem respiration (RE). Experimental plots received precipitation equivalent to the 60-year growing-season average of 240 mm, variously packaged into 6, 10, 16, or 24 events representing extreme (P6) to historical average (P24) rainfall frequency. Extraordinarily extreme frequency (6 large events) reduced NEE, GPP, RE, ET and water use efficiency (WUE = |NEE|/ET). The average NEE, GPP and RE declined 35%, 45% and 48% respectively in the P6 treatment as compared to P16, which showed maximum ET and CO2 exchange. After peaking in the 16-event treatment, GPP and WUE in P24 were not distinguishable from P6. These peaks suggest that P16 was optimal for photosynthesis, with sufficiently frequent rain to maintain unregulated plants and adequately deep soil moisture infiltration to favour transpiration, with associated carbon uptake, over evaporation. Path analysis indicated the lower CO2 fluxes were influenced by reduced soil water content and leaf area index and higher soil temperature, with ET regulating the effects of these microclimatic drivers. ANPP showed a monotonic but non-significant decline with decreasing precipitation frequency, consistent with reduced CO2 fluxes. We found an increase in ANPP of xerophyte plants partially compensated for the ANPP decline in the dominant eurytopic xerophyte plants. Our results suggest that extreme temporal repackaging of precipitation into few events with correspondingly long dry intervals may reduce the capacity of steppe ecosystems to assimilate atmospheric CO2, although community diversity may moderate impacts.

Comparative productivity of alternative cellulosic bioenergy cropping systems in the North Central USA

Biofuels from lignocellulosic feedstocks have the potential to improve a wide range of ecosystem services while simultaneously reducing dependence on fossil fuels. Here, we report on the six-year production potential (above ground net primary production, ANPP), post-frost harvested biomass (yield), and gross harvest efficiency (GHE=yield/ANPP) of seven model bioenergy cropping systems in both southcentral Wisconsin (ARL) and southwest Michigan (KBS). The cropping systems studied were continuous corn (Zea mays L.), switchgrass (Panicum virgatum L.), giant miscanthus (Miscanthus×giganteus Greef & Deuter ex Hodkinson & Renvoize), hybrid poplar (Populus nigra×P. maximowiczii A. Henry ‘NM6’), a native grass mixture (5 sown species), an early successional community, and a restored prairie (18 sown species). Overall the most productive cropping systems were corn>giant miscanthus>and switchgrass, which were significantly more productive than native grasses≈restored prairie≈early successional≈and hybrid poplar, although some systems (e.g. hybrid poplar) differed significantly by location. Highest total ANPP was observed in giant miscanthus (35.2±2.0Mgha−1yr−1) at KBS during the sixth growing season. Six-year cumulative biomass yield from hybrid poplar at KBS (55.4±1.3 Mgha−1) was high but significantly lower than corn and giant miscanthus (65.5±1.5, 65.2±5.5Mgha−1, respectively). Hypothesized yield advantages of diversity in perennial cropping systems were not observed during this period. Harvested biomass yields were 60, 56, and 44% of ANPP for corn, perennial grass, and restored prairie, respectively, suggesting that relatively simple changes in agronomic management (e.g. harvest timing and harvest equipment modification) may provide significant gains in bioenergy crop yields. Species composition was an important determinant of GHE in more diverse systems. Results show that well-established, dedicated bioenergy crops are capable of producing as much biomass as corn stover, but with fewer inputs.

Carbon and nitrogen dynamics in a Pinus densiflora forest with low and high stand densities

Aims understanding carbon ( c) and nitrogen (N) dynamics and their dependence on the stand density of an even-aged, mature forest provides knowledge that is important for forest management. this study investigated the differences in ecosystem total c and N stor age and flux between a low-density stand (D) and a high-density stand (HD) and examined the effects of stand density on above ground net primary productivity (

Above-Ground Net Primary Production from Vascular Plants Shifts the Balance Towards Organic Matter Accumulation in Restored Sphagnum Bogs

The organic matter accumulation potential of a restored bog was estimated over 2 years as a balance be- tween losses to decomposition and inputs through above- ground net primary productivity (AGNPP) in five micro- habitats of increasing complexity (relating to the moss car- pet thickness and the number of vegetation functional groups). Decomposition and accumulation rates variations were hypothesized to lead to higher organic matter accumu- lation potential in the more complex micro-habitats. In general, for a given litter type, the mass losses and decom- position rates were rather homogeneous between micro- habitats, but, they were correlated to the cover of particular species: Eriophorum vaginatum with slower decomposition rates, and Ledum groendlandicum or Kalmia angustifolia with higher rates. Therefore, the abundance of some peatland species, rather than the habitat complexity itself, was a driver of decomposition rates. While the Sphagnum AGNPP did not compensate for decomposition losses, the organic matter accumulation potential was tipped towards a sink (positive) by the contribution of vascular species to the AGNPP. The organic matter accumulation potentials are much improved by the presence of Sphagnum, but from a restoration perspective, promoting the growth of vascular peatland species might also be a key to achieving a positive balance of organic matter accumulation.

Fine root dynamics along an elevational gradient in tropical Amazonian and Andean forests

AbstractThe key role of tropical forest belowground carbon stocks and fluxes is well recognised as one of the main components of the terrestrial ecosystem carbon cycle. This study presents the first detailed investigation of spatial and temporal patterns of fine root stocks and fluxes in tropical forests along an elevational gradient, ranging from the Peruvian Andes (3020 m) to lowland Amazonia (194 m), with mean annual temperatures of 11.8°C to 26.4 °C and annual rainfall values of 1900 to 1560 mm yr‐1, respectively. Specifically, we analyse abiotic parameters controlling fine root dynamics, fine root growth characteristics, and seasonality of net primary productivity along the elevation gradient. Root and soil carbon stocks were measured by means of soil cores, and fine root productivity was recorded using rhizotron chambers and ingrowth cores. We find that mean annual fine root below ground net primary productivity in the montane forests (0–30 cm depth) ranged between 4.27±0.56 Mg C ha‐1 yr‐1 (1855 m) and 1.72±0.87 Mg C ha‐1 yr‐1 (3020 m). These values include a correction for finest roots (<0.6 mm diameter), which we suspect are under sampled, resulting in an underestimation of fine roots by up to 31% in current ingrowth core counting methods. We investigate the spatial and seasonal variation of fine root dynamics using soil depth profiles and an analysis of seasonal amplitude along the elevation gradient. We report a stronger seasonality of NPPFineRoot within the cloud immersion zone, most likely synchronised to seasonality of solar radiation. Finally, we provide the first insights into root growth characteristics along a tropical elevation transect: fine root area and fine root length increase significantly in the montane cloud forest. These insights into belowground carbon dynamics of tropical lowland and montane forests have significant implications for our understanding of the global tropical forest carbon cycle.

Effects of fire on sward structure and grazing in western Serengeti, Tanzania

Fire is one of the major ecological factors that determines structure and function of grassland and savanna ecosystems through its effects on soil nutrient pools, floristic composition and primary production, and foraging behaviour and distribution of populations of wildlife species. Therefore, some wildlife protected area authorities in African savannas have a fire management scheme to cater for a variety of purposes such as, to prevent bush encroachment into grassland, to increase production of quality forage, to control wild fires from outside the protected areas and their spread, and to keep animals in tourist areas for visitors’ enjoyment. The responses to fire of ecosystem processes can be quantified but the outcomes are generally complex depending on the nature of the fire regime, primarily the frequency and timing of the fire events. For example, while ash after fire may have a fertilising effect that will facilitate seedling establishment and increase the growth and production, there is evidence that in East Africa, fire may lead to the dominance of a few species over several other species. Fire may also lead to loss of nutrients, for example nitrogen, through volatilisation. Such variaty in responses to fire makes the use of fire as a tool in the management of wildlife and protected areas usually controversial. Therefore, the main challenge of management is to strike a fire management regime as close as possible to a natural fire regime in this ecosystem.In the Serengeti ecosystem, fire has been regarded to have a critical role on herbivores and their forage resources. Thus, burning has been a management tool in protected areas and a common practice of range management by pastoralists. Herdsmen use fire to improve the pasture quality for cattle. Removal of old or dead grass material by fire enhances sprouting of plants, which improves, at least for a short-term, the quality of the sward. In the Serengeti National Park, early dry-season burns had been executed by the Serengeti Ecological Monitoring Program Department from end of May to mid August without clear understanding about grassland responses to the prescribed burns.The perceived importance of fire to the management and conservation of Serengeti ecosystem has driven this thesis to focus on the effects of fire on large herbivores and their forage resources in the Serengeti National Park. To accomplish that, the thesis examines the relationships between burning and 1) above ground net primary productivity in relation to sward structure and precipitation (Paper I), 2) forage quality, i.e. the concentration of macronutrients (N, P, K, Na, Mg and Ca), in vitro organic matter digestibility and levels of acid detergent fibre per phytomass component (Paper II), and 3) the temporal and spatial patterns of herbivores’ consumption (Paper III), and 4) the patch selection by ungulate species, individually and/or grouped in diet groups (Paper IV).The result of the early dry season burns is a significantly higher daily above ground net primary production (ANPP) on burnt plots at early post-fire stages, coinciding with the dry season (July-September) and during the short rainy period (October-December). Though not significantly different, it was also high on burnt plots at the end of the main rain period (March – May), but higher on non-burnt plots in December-February, and in early dry season, June- July of the subsequent year.Results from this area with high diversity of large herbivore species show that grazing herbivores switch between burnt and non-burnt patches by trading off between forage quantity and quality along growing season. The quality on burnt areas appears to be governed by enhanced concentrations of macronutrients, increased digestibility and reduced concentration of acid detergent fibres. The above quality variables are linked to increased ratio between live and total phytomass. Quality of forage explains the preference by grazing animals for burnt areas during some periods, and in non-burnt areas due to high phytomass in other periods.Selection for non-burnt or burnt patches or against patches burnt more than once in a period of three years by some species of ungulates and/or diet groups are also indicative that quality and/or quantity of forage in the respective patch underlay patch choice. The cause of temporal variation in selectivity of the patches needs further investigation. However, it is unequivocal that maintenance of mosaic of burnt and non-burnt areas with adequate provision of forage amount and quality all year round is of paramount importance.

Effects of past and current disturbance on carbon cycling in grassland mesocosms

In species rich grasslands, management factors may affect carbon storage both directly (e.g. defoliation) and indirectly, by altering plant community structure. We set up a mesocosm experiment to separate these direct and indirect effects. Monoliths were sampled from two plots of a semi-natural, species-rich pasture at Theix (France), which had been subjected to contrasted disturbance levels, high versus low grazing, for 14 years. These monoliths were placed in transparent enclosures in natural light and temperature conditions. At the start of the experiment, half of the monoliths in each disturbance treatment were shifted to the opposite disturbance regime. Above and below ground CO 2 fluxes were then measured continuously over 2 years. The net below ground carbon storage was positively correlated ( P < 0.001) with net ecosystem productivity (NEP) and was negatively correlated ( P < 0.001) with above ground net primary productivity. The net canopy photosynthesis, net ecosystem productivity and net below ground carbon storage were significantly higher for ecosystems previously adapted to a low rather than a high disturbance regime, irrespective of the disturbance level during the mesocosm experiment. In contrast, above ground net primary productivity (ANPP) was significantly enhanced by a high disturbance level during the experiment. ANPP and NEP showed a faster response to an increase rather than a decrease in disturbance level during the experiment. Grassland ecosystems adapted to frequent disturbance by grazing and cutting stored less carbon compared to ecosystems adapted to a low disturbance regime.

The estimation of above ground Net primary production of boreal deciduous forest in Northern Japan

The estimation of above ground Net primary production of boreal deciduous forest in Northern Japan

Erosion of upland hillslope soil organic carbon: Coupling field measurements with a sediment transport model

Little is known about the role of vegetated hillslope sediment transport in the soil C cycle and soil‐atmosphere C exchange. We combined a hillslope sediment transport model with empirical soil C measurements to quantify the erosion and temporal storage of soil organic carbon (SOC) within two grasslands in central California. The sites have contrasting erosional mechanisms: biological perturbation (Tennessee Valley (TV)) versus clay‐rich soil creep (Black Diamond (BD)). The average SOC erosion rates from convex slopes were 1.4–2.7 g C m−2 yr−1 at TV and 5–8 g C m−2 yr−1 at BD, values that are &lt;10% of above ground net primary productivity (ANPP) at both sites. The eroded soil accumulates on depositional slopes. The long term SOC accumulation (or C sink) rates are ∼1.9 g C m−2 yr−1 in the TV hollow and 1.7–2.8 g C m−2 yr−1 in the BD footslope. We found that the hillslope C sink is driven primarily by the burial of in situ plant production rather than preservation of eroded SOC, a finding that differs from existing hypotheses. At TV, the net sequestration of atmospheric C by long‐term hollow evacuation and refilling depends on the fate of the C exported from the zero order watershed. This study suggests that erosion and deposition are coupled processes that create a previously unrecognized C sink in undisturbed upland watersheds, with a potential to substantially affect the global C balance presently, and over geological timescales.

Foliar respiration acclimation to temperature and temperature variableQ10alter ecosystem carbon balance

AbstractThe response of respiration to temperature in plants can be considered at both short‐ and long‐term temporal scales. Short‐term temperature responses are not well described by a constantQ10of respiration, and longer‐term responses often include acclimation. Despite this, many carbon balance models use a staticQ10of respiration to describe the short‐term temperature response and ignore temperature acclimation.We replaced static respiration parameters in the ecosystem model photosynthesis and evapo‐transpiration (PnET) with a temperature‐driven basal respiration algorithm (Rdacclim) that accounts for temperature acclimation, and a temperature‐variableQ10algorithm (Q10var). We ran PnET with the new algorithms individually and in combination for 5 years across a range of sites and vegetation types in order to examine the new algorithms' effects on modeled rates of mass‐ and area‐based foliar dark respiration, above ground net primary production (ANPP), and foliar respiration–photosynthesis ratios.TheRdacclimalgorithm adjusted dark respiration downwards at temperatures above 18°C, and adjusted rates up at temperatures below 5°C. TheQ10varalgorithm adjusted dark respiration down at temperatures below 15°C. Using both algorithms simultaneously resulted in decreases in predicted annual foliar respiration that ranged from 31% at a tall‐grass prairie site to 41% at a boreal coniferous site. The use of theRdacclimandQ10varalgorithms resulted in increases in predicted ANPP ranging from 18% at the tall‐grass prairie site to 38% at a warm temperate hardwood forest site.The new foliar respiration algorithms resulted in substantial and variable effects on PnETs predicted estimates of C exchange and production in plants and ecosystems. Current models that use static parameters may over‐predict respiration and subsequently under‐predict and/or inappropriately allocate productivity estimates. Incorporating acclimation of basal respiration and temperature‐sensitiveQ10have the potential to enhance the application of ecosystem models across broad spatial scales, or in climate change scenarios, where large temperature ranges may cause static respiration parameters to yield misleading results.

Vulnerability of the Asian Typical Steppe to Grazing and Climate Change

The vulnerability of grassland vegetation in Inner Mongolia to climate change and grazing was examined using an ecosystem model. Grazing is an important form of land use in this region, yet there are uncertainties as to how it will be affected by climate change. A sensitivity analysis was conducted to study the effects of increased minimum and maximum temperatures, ambient and elevated CO2, increased or decreased precipitation, and grazing on vegetation production. Simulations showed that herbaceous above ground net primary production was most sensitive to changes in precipitation levels. Combinations of increased precipitation, temperature, and CO2 had synergistic effects on herbaceous production, however drastic increases in these climate scenarios left the system vulnerable to shifts from herbaceous to shrub-dominated vegetation when grazed. Reduced precipitation had a negative effect on vegetation growth rates, thus herbaceous growth was not sustainable with moderate grazing. Shifts in temporal biomass patterns due to changed climate have potentially significant implications for grazing management, which will need to be altered under changing climate to maintain system stability.

Land use changes and trends in Human Appropriation of Above Ground Net Primary Production (HANPP) in India (1961–98)

Land use change has the potential to influence energy flows, standing crop and biomass turnover at a variety of scales. To understand and quantify the impact of land use change on natural systems, interdisciplinary approaches and concepts linking biophysical and socioeconomic factors are needed. One such approach for analysing the socioeconomic energy flows from land use changes is Human Appropriated Net Primary Production (HANPP). HANPP is defined as the difference between the net primary production of potential vegetation and the actual net primary production remaining in vegetation after harvest. In this study, we used HANPP to quantify the energy flows consequent upon land use/land cover change from 1961 to 1998 in India. Data from the Food and Agricultural Organization Statistics (FAOSTAT) covering land use/land cover estimates, crop production, harvest and fertilizer use data have been used to analyse the trends in HANPP. Land use changes between 1961 and 1998 indicate a small increase in agricultural areas from 58.2% to 60.8% and in forest and woodland areas from 19.0% to 23.2%. Actual above ground net primary production of vegetation increased from 1280.58 to 1818.23 Tg, an increase of approximately 1.4 times over 37 years. Although population increased exponentially, human appropriation of photosynthetic products did not rise as much due to increases in forest cover and agricultural production. Although the HANPP concept is a useful approach to analyse the trends in photosynthetic products brought about by land use changes and harvesting, more robust indicators are needed to understand the impacts associated with these changes. We discuss the relevance of the HANPP analysis results by focusing on land use/land cover change and exploring the inter‐linkages between energy flows and environment.