Annual Aboveground Net Primary Production Research Articles

Quantifying the ecological carrying capacity of grasslands in Inner Mongolia.

Quantifying the ecological carrying capacity has emerged as a crucial factor for maintaining ecosystem stability for sustainable development in vulnerable eco-regions. Here, we propose a new framework for ecological carrying capacity quantification suitable for vulnerable eco-regions. We applied this framework to calculate the ecological carrying capacity of Inner Mongolia from 1987-2015 and used a geographical detector to identify the driving factors behind spatial heterogeneity. Our results revealed the following. (1) The above-ground net primary production (ANPP) required to support the ecosystem service of soil conservation (ANPPSC) decreased from northeast to southwest, whereas the distribution pattern of ANPP required to support the ecosystem service of sand fixation (ANPPSF) exhibited a contrary trend. The average annual ANPP required to support the ecosystem service of natural regeneration (ANPPNR) in Inner Mongolia from 1987 to 2015 was 101.27 gCm-2year-1, revealing a similar spatial distribution with ANPP. (2) The total ecological carrying capacity of Inner Mongolian grassland was 78.52 million sheep unit hm-2. The regions with insufficient provisioning service capability accounted for 4.18% of the total area, primarily concentrated in the east and northwest. (3) The average optimal livestock number for grasslands in Inner Mongolia was 1.59 sheep unit hm-2 from 1987-2015, ranging from 0.77 to 1.69 sheep unit hm-2 across different zones. The average ecological carrying capacity of the cold temperate humid, medium-temperate arid, and warm temperate semi-humid regions was less than 1.08 sheep unit m-2, suggesting a need to prohibit grazing in these areas. (4) The primary influencing factors affecting ecological carrying capacity distribution were normalized difference vegetation index (NDVI), precipitation, and soil type. The framework developed herein can help identify sustainable development potential from the ecosystem service perspective and effectively contribute to decision-making in grassland ecosystem management.

Anthropogenic Climate Change Negatively Impacts Vegetation and Forage Conditions in the Greater Four Corners Region

AbstractThe Southwestern U.S. has been in a megadrought for the past two decades, stressing vegetation across the region and leading to poor forage conditions on rangelands. How has human‐induced climate change affected air temperatures and atmospheric evaporative demand in the greater Four Corners region of the Southwest, and what have the corresponding impacts been to vegetative productivity? We address this question via a multi‐step climate change detection and attribution analysis. We first relate evaporative demand (quantified by Vapor Pressure Deficit, or VPD) and precipitation to the Normalized Difference Vegetation Index (NDVI) in six unique plant‐precipitation zones. VPD is strongly negatively related to NDVI, and the strength of this relation is similar in magnitude to precipitation. We then use a large ensemble of climate change simulations to estimate the magnitude of VPD increases attributable to human‐induced climate change. We find that modest increases in air temperatures have led to large increases in VPD, with the influence of climate change about twice the inter‐annual standard deviation by 2020. Finally, we estimate the reductions in NDVI due to increased VPD and present the reductions in terms of total annual Aboveground Net Primary Productivity. We conclude that human‐induced warming has roughly doubled the magnitude of recent vegetation deficits, especially in mid‐precipitation areas (receiving 250–500 mm of precipitation annually), concentrated in New Mexico. These results indicate that increased temperatures from human‐caused climate change are having persistent and damaging impacts on vegetation productivity, with significant implications for ranchers and other land users in the region.

Trends of Aboveground Net Primary Productivity of Patagonian Meadows, the Omitted Ecosystem in Desertification Studies

The United Nations defines desertification as the loss of productivity in arid and semiarid environments. The extended steppes of Patagonia harbor small meadows whose compounded area is comparatively small, but their aboveground net primary production (ANPP) is up to ten times higher than their surroundings. These meadows then represent a key ecosystem for cattle grazing systems, but there are no descriptions of the trends in their ANPP and, consequently, their carrying capacity, and, as a result, their degradation syndromes. Our objectives were as follows: (1) analyze the trends of mean and spatial heterogeneity of annual ANPP in meadows and neighboring steppes and relate them with precipitation and temperature, (2) evaluate the impact on the livestock carrying capacity of meadows in the region, and (3) evaluate the degradation trends of these meadows, based on a novel description proposed to characterize the trend syndromes of these type of ecosystems. We identified meadow areas across a subcontinental scale in Patagonia, covering a mean annual precipitation range from 129 to 936 mm. We estimated ANPP on a monthly basis from 2000 to 2019 via regional calibrated remote sensing information. In the last two decades, ANPP decreased in 74% of the studied meadow areas, while remaining relatively stable in the nearby steppes. This decrease was relatively higher in the arid end of the analyzed precipitation gradient. Hence, the global carrying capacity for all the studied meadow areas decreased by 8%. Finally, we identified four trend syndromes based on the combination of the ANPP trend and its spatial heterogeneity, calculated as the spatial standard deviation. The predominant trend syndrome, in 55% of the area, was associated with a negative trend of both ANPP and spatial heterogeneity. These results could help prioritize areas where specific management decisions, given the different trend syndromes, could help revert ANPP negative trends.

Precipitation controls the annual net primary productivity in sown pastures across a precipitation gradient in dry subtropical Chaco

Exotic pasture species are increasingly replacing native vegetation in subtropical areas because of their potential to increase forage yields. However, there is a scarce analysis of the relationship between forage yield and mean annual precipitation across regional gradients. We analyzed at a regional scale the temporal relationship between the aboveground net primary productivity (ANPP) and the precipitation for different sown grasses for several growing seasons across Dry Chaco, Argentina. We compiled biomass harvest data for seven cultivars of Megathyrsus maximus and Cenchrus ciliaris at eight different sites across a gradient of mean annual precipitation (MAP; 200 mm–1100 mm). We found positive relationships between ANPP and precipitation for most of the cultivars. The strong relationship between annual ANPP and MAP found implies that the high temporal variability in MAP translates into ANPP variability. The regional slope between annual ANPP and MAP was 11.12 kg DM.ha−1.year−1.mm−1. The ratio between the temporal and the spatial models ranged from 0.26 to 1.35. Precipitation use efficiency ranged between 3.9 and 24.1 kg DM.ha−1.year−1.mm−1. These models are robust enough to estimate the ANPP of specific pastures from MAP data. This represents a breakthrough, in grazing systems planning and defining conservation policies for natural resources.

Identifying critical climate periods for temporal dynamics of aboveground net primary productivity in the Eurasian steppe region

Understanding correlations between aboveground net primary productivity (ANPP) and climate change has remained a long-standing goal in ecology. Annual ANPP experienced significant interannual variations in the Eurasian steppe region (EASR) over past three decades. However, critical climate periods for annual ANPP remain poorly understood. Here, we comprehensively examined ANPP–climate relationships in the EASR on a seasonal scale from 1982 to 2013. Partial correlation coefficients were calculated between annual ANPP and seasonal climatic variables. A multiple linear regression (MLR) model was implemented between annual ANPP and three climatic factors over four seasons. For each climatic variable during each season, the relative importance for the MLR model was determined to identify critical climate periods for annual ANPP. Results demonstrated that (1) seasonal differences could be observed in response of annual ANPP to climatic variables. The influence of precipitation (PRE) on annual ANPP gradually increased from previous-year winter to summer seasons, with a diminishing effect of solar shortwave radiation (SWD), and decreased from summer to autumn with an increasing effect of SWD. Summer TMP imposed the strongest effects, followed by previous-year winter TMP. The influence of TMP exhibited only slight changes between spring and autumn. (2) PRE, TMP and SWD were crucial climatic variables affecting annual ANPP in 41%, 31% and 28%, respectively, of the EASR, especially summer PRE, summer TMP and previous-year winter SWD. The critical climate periods for annual ANPP exhibited large spatial differences in the EASR. (3) Furthermore, the effects of PRE and SWD on annual ANPP increased from the first stage (1982–1995) to the second stage (1996–2007) with a decreasing influence of TMP, and then decreased from the second stage to the third stage (2008–2013) with an increasing influence of TMP. This study could be crucial for improving vegetation productivity predictions and understanding ecosystem-climate feedbacks.

Driving Climatic Factors at Critical Plant Developmental Stages for Qinghai–Tibet Plateau Alpine Grassland Productivity

Determining the driving climatic factors at critical periods and potential legacy effects is crucial for grassland productivity predictions on the Qinghai–Tibet Plateau (QTP). However, studies with limited and ex situ ground samples from highly heterogeneous alpine meadows brought great uncertainties. This study determined the key climatic factors at critical plant developmental stages and the impact of previous plant growth status for interannual aboveground net primary productivity (ANPP) variations in different QTP grassland types. We hypothesize that the impact of climatic factors on grassland productivity varies in different periods and different vegetation types, while its legacy effects are not great. Pixel-based partial least squares regression was used to associate interannual ANPP with precipitation and air temperature at different developmental stages and prior-year ANPP from 2000 to 2019 using remote sensing techniques. Results indicated different findings from previous studies. Precipitation at the reproductive stage (July–August) was the most prominent controlling factor for ANPP which was also significantly affected by precipitation and temperature at the withering (September–October) and dormant stage (November–February), respectively. The influence of precipitation was more significant in alpine meadows than in alpine steppes, while the differentiated responses to climatic factors were attributed to differences in water consumption at different developmental stages induced by leaf area changes, bud sprouting, growth, and protection from frost damage. The prior-year ANPP showed a non-significant impact on ANPP of current year, except for alpine steppes, and this impact was much less than that of current-year climatic factors, which may be attributed to the reduced annual ANPP variations related to the inter-annual carbon circulation of alpine perennial herbaceous plants and diverse root/shoot ratios in different vegetation types. These findings can assist in improving the interannual ANPP predictions on the QTP under global climate change.

Urban net primary production: Concepts, field methods, and Baltimore, Maryland, USA case study.

Given the large and increasing amount of urban, suburban, and exurban land use on Earth, there is a need to accurately assess net primary productivity (NPP) of urban ecosystems. However, the heterogeneous and dynamic urban mosaic presents challenges to the measurement of NPP, creating landscapes that may appear more similar to a savanna than to the native landscape replaced. Studies of urban biomass have tended to focus on one type of vegetation (e.g., lawns or trees). Yet a focus on the ecology of the city should include the entire urban ecosystem rather than the separate investigation of its parts. Furthermore, few studies have attempted to measure urban aboveground NPP (ANPP) using field-based methods. Most studies project growth rates from measurements of tree diameter to estimate annual ANPP or use remote sensing approaches. In addition, field-based methods for measuring NPP do not address any special considerations for adapting such field methods to urban landscapes. Frequent planting and partial or complete removal of herbaceous and woody plants can make it difficult to accurately quantify increments and losses of plant biomass throughout an urban landscape. In this study, we review how ANPP of urban landscapes can be estimated based on field measurements, highlighting the challenges specific to urban areas. We then estimated ANPP of woody and herbaceous vegetation over a 15-year period for Baltimore, MD, USA using a combination of plot-based field data and published values from the literature. Baltimore's citywide ANPP was estimated to be 355.8g m-2 , a result that we then put into context through comparison with other North American Long-Term Ecological Research (LTER) sites and mean annual precipitation. We found our estimate of Baltimore citywide ANPP to be only approximately half as much (or less) than ANPP at forested LTER sites of the eastern United States, and more comparable to grassland, oldfield, desert, or boreal forest ANPP. We also found that Baltimore had low productivity for its level of precipitation. We conclude with a discussion of the significance of accurate assessment of primary productivity of urban ecosystems and critical future research needs.

Contrasting responses of woody and grassland ecosystems to increased CO2 as water supply varies.

Experiments show that elevated atmospheric CO2 (eCO2) often enhances plant photosynthesis and productivity, yet this effect varies substantially and may be climate sensitive. Understanding if, where and how water supply regulates CO2 enhancement is critical for projecting terrestrial responses to increasing atmospheric CO2 and climate change. Here, using data from 14 long-term ecosystem-scale CO2 experiments, we show that the eCO2 enhancement of annual aboveground net primary productivity is sensitive to annual precipitation and that this sensitivity differs between woody and grassland ecosystems. During wetter years, CO2 enhancement increases in woody ecosystems but declines in grass-dominated systems. Consistent with this difference, woody ecosystems can increase leaf area index in wetter years more effectively under eCO2 than can grassland ecosystems. Overall, and across different precipitation regimes, woody systems had markedly stronger CO2 enhancement (24%) than grasslands (13%). We developed an empirical relationship to quantify aboveground net primary productivity enhancement on the basis of changes in leaf area index, providing a new approach for evaluating eCO2 impacts on the productivity of terrestrial ecosystems.

Interactions among climate, topography, soil structure and rangeland aboveground net primary production

Aboveground Net Primary Production (ANPP) of rangeland ecosystems is driven by interactions among multiple environmental factors. This study aimed to model the combined effects of precipitation, elevation, and soil conditions on ANPP variation along an elevation gradient. Ground surveys and vegetation sampling were conducted in 2016 through 26 sampling sites along two elevation profiles in the rangelands of Moghan-Sabalan, Ardabil Province, Iran. At each sampling site, the ANPP of each plant functional type (PFT; grasses, forbs, and shrubs) was measured, and soil samples were taken from 0–15 to 15–30 cm depth. Regression analysis and structural equation modeling (SEM) were used to investigate the factors affecting both total and PFT ANPP. Soil variables were the best predictors of grass (R2 = 0.51), forb (R2 = 0.61), shrub (R2 = 0.71), and total (R2 = 0.76) ANPP. The SEM interpretation suggested that precipitation is the most important direct driver of ANPP with R2 values of 0.20 (Total), 0.30 (Shrubs), 0.26 (Grasses), and 0.10 (Forbs). Whereas soil factors were good predictors in the regression models, the SEM models demonstrated that soil factors were generally unimportant compared with climate, likely owing to the close links between soil-forming factors and climate. The results make it possible to estimate annual ANPP combined with climate forecasts and leads to more accurate estimates of future grazing capacity by policy makers and stakeholders.

Global Rangeland Primary Production and Its Consumption by Livestock in 2000–2010

Livestock grazing occupies ca. 25% of global ice-free land, removing large quantities of carbon (C) from global rangelands (here, including grass- and shrublands). The proportion of total livestock intake that is supplied by grazing (GP) is estimated at >50%, larger than the proportion from crop- and byproduct-derived fodders. Both rangeland productivity and its consumption through grazing are difficult to quantify, as is grazing intensity (GI), the proportion of annual aboveground net primary productivity (ANPP) removed from rangelands by grazing livestock. We develop national or sub-national level estimates of GI and GP for 2000–2010, using remote sensing products, inventory data, and model simulations, and accounting for recent changes in livestock intake, fodder losses and waste, and national cropland use intensities. Over the 11 study years, multi-model average global rangeland ANPP varied between the values of 13.0 Pg C in 2002 and 13.96 Pg C in 2000. The global requirement for grazing intake increased monotonically by 18%, from 1.54 in 2000 to 1.82 Pg C in 2010. Although total global rangeland ANPP is roughly an order of magnitude larger than grazing demand, much of this total ANPP is unavailable for grazing, and national or sub-national deficits between intake requirements and available rangeland ANPP occurred in each year, totaling 36.6 Tg C (2.4% of total grazing intake requirement) in 2000, and an unprecedented 77.8 Tg C (4.3% of global grazing intake requirement) in 2010. After accounting for these deficits, global average GI ranged from 10.7% in 2000 to 12.6% in 2009 and 2010. The annually increasing grazing deficits suggest that rangelands are under significant pressure to accommodate rising grazing demand. Greater focus on observing, understanding, and managing the role of rangelands in feeding livestock, providing ecosystem services, and as part of the global C cycle, is warranted.

The impact of teleconnections on the temporal dynamics in aboveground net primary productivity of the Mongolian Plateau grasslands

AbstractTemporal dynamics in aboveground net primary productivity (ANPP) are significant for environmental protection and economic development in the Mongolian Plateau grasslands (MPGs). Climate control of ANPP's temporal variations has intensified in response to local meteorological conditions, while the contributions of large‐scale atmospheric circulations to ANPP variations are poorly understood in the MPGs. First, we explored the temporal dynamics in annual ANPP, and then, we analyzed correlations among annual ANPP, local meteorological variables, and three different teleconnections during 1982–2015 in this study. Our analytical results indicated that (a) ANPP exhibited an increasing trend during the entire study period. However, the increasing trend did not persist, and two reversals occurred in 1998 and 2007. (b) ANPP variations were primarily influenced by summer precipitation in most regions and by summer precipitation and temperature together in other regions of the MPGs. (c) The Atlantic Multidecadal Oscillation (AMO) in winter negatively dominated annual ANPP variations by influencing summer precipitation and summer temperature in central Mongolia. The North Atlantic Oscillation (NAO) in winter exerted strong positive impacts on ANPP variations by influencing summer precipitation in Inner Mongolia, China. The East Atlantic Western Russia (EAWR) in spring controlled annual ANPP variations by influencing summer precipitation in western and eastern Mongolia. (d) The winter AMO, winter NAO and spring EAWR significantly dominated the annual ANPP variations in 49.78% of the MPGs, with values of 18.90, 9.81 and 21.07%, respectively. (e) Reversals of the winter AMO, winter NAO and spring EAWR between negative and positive phases resulted in two reversals of ANPP trends. This study will improve our understanding of the role of large‐scale atmospheric circulations in regulating ANPP variations and will be valuable in guiding the development of grazing land management in Mongolia and Inner Mongolia, China.

Annual aboveground carbon uptake enhancements from assisted gene flow in boreal black spruce forests are not long-lasting

Assisted gene flow between populations has been proposed as an adaptive forest management strategy that could contribute to the sequestration of carbon. Here we provide an assessment of the mitigation potential of assisted gene flow in 46 populations of the widespread boreal conifer Picea mariana, grown in two 42-year-old common garden experiments and established in contrasting Canadian boreal regions. We use a dendroecological approach taking into account phylogeographic structure to retrospectively analyse population phenotypic variability in annual aboveground net primary productivity (NPP). We compare population NPP phenotypes to detect signals of adaptive variation and/or the presence of phenotypic clines across tree lifespans, and assess genotype‐by‐environment interactions by evaluating climate and NPP relationships. Our results show a positive effect of assisted gene flow for a period of approximately 15 years following planting, after which there was little to no effect. Although not long lasting, well-informed assisted gene flow could accelerate the transition from carbon source to carbon sink after disturbance.

Timing of drought in the growing season and strong legacy effects determine the annual productivity of temperate grasses in a changing climate

Abstract. The frequency of extreme weather events, such as droughts, is assumed to increase and lead to alterations in ecosystem productivity and thus the terrestrial carbon cycle. Although grasslands typically show reduced productivity in response to drought, the effects of drought on grassland productivity have been shown to vary strongly. Here we tested, in a 2-year field experiment, if the resistance and the recovery of grasses to drought varies throughout a growing season and if the timing of the drought influences drought-induced reductions in annual aboveground net primary production (ANPP) of grasses. For the experiment we grew six temperate and perennial C3 grass species and cultivars in a field as pure stands. The grasses were cut six times during the growing season and subject to 10 week drought treatments that occurred either in the spring, the summer or the fall. Averaged across all grasses, drought-induced losses in productivity in spring were smaller (−20 % to −51 %) than in summer and fall (−77 % to −87 %). This suggests a higher resistance to drought in spring when plants are in their reproductive stage and their productivity is the highest. After the release from drought, we found no prolonged suppression in growth. In contrast, post-drought growth rates of formerly drought-stressed swards outperformed the growth rates of the control swards. The strong overcompensation in growth after the drought release resulted in relatively small overall drought-induced losses in annual ANPP that ranged from −4 % to −14 % and were not affected by the timing of the drought event. In summary, our results show that (i) the resistance in growth rates of grasses to drought varies across the season and is increased during the reproductive phenological stage when growth rates are highest; (ii) that the positive legacy effects of drought indicate a high recovery potential of temperate grasses to drought; and (iii) that the high recovery can compensate for immediate drought effects on total annual biomass production to a significant extent.

Big landscapes meet big data: Informing grazing management in a variable and changing world

On the Ground • Rangeland-based livestock raising is the only agricultural production system that maintains native plant communities, providing ecosystem services in the same space as food and fiber production. • Annual aboveground net primary productivity (ANPP) underlies forage production and multiple ecosystem services. ANPP is highly variable in rangelands in the western United States, across the landscape, from year to year, and within a growing season. Variability is also increasing as the climate changes. • Grazing management decisions that determine when, where, and how much of ANPP is consumed by livestock, including stocking rate decisions, can ultimately determine rangeland health and the future sustainability of livestock production and provision of ecosystem services. • Yet managers' access to data on available forage and its variability is limited, and existing field methods to quantify forage production accurately require extensive sampling and are prone to errors or bias. • A variety of remotely sensed data sources exist to help characterize forage availability and how it has varied spatially and temporally over the last 30 or more years, as well as other datasets that can estimate available forage and inaccessible terrain for livestock. • We discuss the need for a state-of-the-art decision support tool that integrates available remote-sensing data on forage availability with land managers’ knowledge of local needs and information for managers to access to the depth and breadth of information they need to sustainably manage grazing under variable and changing conditions. • Such a decision support tool could help land managers better manage rangeland ecosystems with flexible stocking rates and adaptive grazing management opportunities that adjust to variations in ANPP, leading to increased regional and site-specific rangeland resilience.

Lagged precipitation effect on plant productivity is influenced collectively by climate and edaphic factors in drylands

Lagged precipitation effect explains a large proportion of annual aboveground net primary productivity in some dryland ecosystems. Using satellite-derived plant productivity and precipitation datasets in the Northern Hemisphere drylands during 2000–2018, we identify 1111 pixels mainly located in the Tibetan Plateau, the western US, and Kazakhstan where productivities are significantly correlated with previous-year precipitation (hereafter, the lagged type). Differences in climatic and edaphic factors between the lagged and unlagged (pixels where productivities are not correlated with previous-year precipitation) types are evaluated. Permutational multivariate analysis of variance shows that the two types differ significantly regarding six climatic and edaphic factors. Compared to unlagged type, water availability, soil organic carbon, total nitrogen, field capacity, silt content and radiation are more sensitive to changes in precipitation in lagged type. Water availability is the most important factor for distinguishing the two types, followed by soil organic carbon, total nitrogen, field capacity, soil texture, and radiation. Our study suggests that the altered sensitivities of several climatic and edaphic factors to precipitation collectively affect the lagged effect of precipitation on productivity in drylands.

Primary production in forests of the mangrove palm Nypa fruticans

We investigated the forest structure, leaf demography, leaf allometry and growth of the erect canopy of the mangrove palm Nypa fruticans in four river systems distributed over 10 degrees of latitude in the tropics of northeast Australia and Papua New Guinea to obtain estimates of aboveground biomass (AGB) and annual aboveground net primary production (ANPP). In the four river sites Nypa mean leaf and tree densities ranged from 6538 to 12,200 leaves ha−1, and 1526 to 3550 trees ha-1 and differed significantly among sites, with the lowest densities at the lowest latitude site. AGB ranged from 36.5 to 55.7 Mg ha−1 and also differed among sites with the lowest AGB at the lowest latitude site. The mean plastochron increased with increasing periods of cooler air temperatures. Mean litter production per tree (range, 6.0–16.2 kg year−1) was least in the low latitude site and mean total productivity per tree (range, 13.9–25.1 kg year−1) did not differ significantly across sites. ANPP was lowest in the low latitude site and ranged from 23.8 to 60.9 Mg ha−1 year−1. This placed Nypa forests in the mid to high range of global estimates of ANPP. Rates of litter production at three sites (range, 25.7–37.5 Mg ha−1 year−1) was much greater than for litterfall in any other mangrove forest. ANPP estimated using a combination of demographic data and leaf allometry compares well with previous estimates using a light interception method to predict productivity. The complex pattern of differences in forest structure, growth and ANPP across latitudes likely represent differences in catchment land use, successional stages of forests, river discharge and variation in the length of the dry season.

Lake Drainage in Permafrost Regions Produces Variable Plant Communities of High Biomass and Productivity.

Climate warming, increased precipitation, and permafrost thaw in the Arctic are accompanied by an increase in the frequency of full or partial drainage of thermokarst lakes. After lake drainage, highly productive plant communities on nutrient-rich sediments may develop, thus increasing the influencing greening trends of Arctic tundra. However, the magnitude and extent of this process remain poorly understood. Here we characterized plant succession and productivity along a chronosequence of eight drained thermokarst lakes (khasyreys), located in the low-Arctic tundra of the Western Siberian Lowland (WSL), the largest permafrost peatland in the world. Based on a combination of satellite imagery, archive mapping, and radiocarbon dating, we distinguished early (<50 years), mid (50–200 years), and late (200–2000 years) ecosystem stages depending on the age of drainage. In 48 sites within the different aged khasyreys, we measured plant phytomass and productivity, satellite-derived NDVImax, species composition, soil chemistry including nutrients, and plant elementary composition. The annual aboveground net primary productivity of the early and mid khasyrey ranged from 1134 and 660 g·m−2·y−1, which is two to nine times higher than that of the surrounding tundra. Late stages exhibited three to five times lower plant productivity and these ecosystems were distinctly different from early and mid-stages in terms of peat thickness and pools of soil nitrogen and potassium. We conclude that the main driving factor of the vegetation succession in the khasyreys is the accumulation of peat and the permafrost aggradation. The soil nutrient depletion occurs simultaneously with a decrease in the thickness of the active layer and an increase in the thickness of the peat. The early and mid khasyreys may provide a substantial contribution to the observed greening of the WSL low-Arctic tundra.

An Assessment of Production Trends on the Great Plains from 1984 to 2017

Throughout the Great Plains, aboveground annual net primary productivity (ANPP) is a critical ecosystem service supporting billions of dollars of commerce and countless stakeholders. Managers and producers struggle with high interannual change in ANPP, which often varies 40% between years due to fluctuating precipitation and drought. To quantify ANPP trends and evaluate interannual and spatial variation, we created the Rangeland Production Monitoring Service (RPMS), a spatially explicit database with automatic annual updates of ANPP for all rangelands in the conterminous United States. The RPMS establishes relationships between normalized difference vegetation index (NDVI) from remote sensing data and ANPP from soil ecological site descriptions. These relationships were applied to NDVI data in each year from 1984 to present, although the present assessment focuses on the period from 1984 to 2017. Validation metrics include an r2 of 89% between predicted and observed ANPP at three locations in the Great Plains. For this special issue, we assess data from the RPMS to quantify trends and variation of ANPP in the Great Plains region for four major grassland types, smaller-scale ecological subsections, and national grassland units. Significant (α ≤ 0.05) increases in ANPP since 1984 were observed across all major grassland types in the Great Plains, particularly the northern mixed-grass prairie, which also had the greatest interannual variation (21%) from 1984 to 2017. Corresponding significant increases (P < 0.1) in growing season precipitation were found in all grassland types except the shortgrass steppe. Spatial variation decreases from west to east and tallgrass prairie exhibited the lowest temporal and spatial variation of 8% and 21%, respectively, from 1984 to 2017. Grazing allotments in the National Grasslands exhibit differential recovery after drought ranging from about 15% to 350%.

Assessing precipitation, evapotranspiration, and NDVI as controls of U.S. Great Plains plant production

AbstractProductivity throughout the North American Great Plains grasslands is generally considered to be water limited, with the strength of this limitation increasing as precipitation decreases. We hypothesize that cumulative actual evapotranspiration water loss (AET) from April to July is the precipitation‐related variable most correlated to aboveground net primary production (ANPP) in the U.S. Great Plains (GP). We tested this by evaluating the relationship of ANPP to AET, precipitation, and plant transpiration (Tr). We used multi‐year ANPP data from five sites ranging from semiarid grasslands in Colorado and Wyoming to mesic grasslands in Nebraska and Kansas, mean annual NRCS ANPP, and satellite‐derived normalized difference vegetation index (NDVI) data. Results from the five sites showed that cumulative April‐to‐July AET, precipitation, and Tr were well correlated (R2: 0.54–0.70) to annual changes in ANPP for all but the wettest site. AET and Tr were better correlated to annual changes in ANPP compared to precipitation for the drier sites, and precipitation in August and September had little impact on productivity in drier sites. April‐to‐July cumulative precipitation was best correlated (R2 = 0.63) with interannual variability in ANPP in the most mesic site, while AET and Tr were poorly correlated with ANPP at this site. Cumulative growing season (May‐to‐September) NDVI (iNDVI) was strongly correlated with annual ANPP at the five sites (R2 = 0.90). Using iNDVI as a surrogate for ANPP, we found that county‐level cumulative April–July AET was more strongly correlated to ANPP than precipitation for more than 80% of the GP counties, with precipitation tending to perform better in the eastern more mesic portion of the GP. Including the ratio of AET to potential evapotranspiration (PET) improved the correlation of AET to both iNDVI and mean county‐level NRCS ANPP. Accounting for how different precipitation‐related variables control ANPP (AET in drier portion, precipitation in wetter portion) provides opportunity to develop spatially explicit forecasting of ANPP across the GP for enhancing decision‐making by land managers and use of grassland ANPP for biofuels.

Grazing Abandonment Delays the Effect of Temperature on Aboveground Net Primary Production in Atlantic Grasslands

We used an Atlantic grassland system on the Iberian Peninsula to ascertain whether monthly climate variability explains variation in monthly aboveground net primary production (ANPP) and to test whether climate-ANPP relationships depend on grazing regime. In 2005, large herbivores (beef cattle, dairy sheep, and horses) were excluded through fencing three 2 500-m2 plots, each located in a different location; adjacent grazed plots of equal size were established. ANPP was measured monthly during the next three growing periods (2006−2008), and locally measured climate data were obtained from a public database. Because between-site variation in annual ANPP was not significant, we used data averaged across sites to test for the effect of monthly climate variability on monthly ANPP by means of dynamic regression. Enhanced ANPP was found after grazing abandonment, probably due to the sudden dominance of productive graminoids. Variation in monthly rainfall did not contribute to explain monthly ANPP under grazing or grazing exclusion. Simultaneous mean monthly air temperature explained monthly ANPP under grazing. By contrast, the effect of temperature on ANPP under grazing exclusion was delayed by 1 mo. We suggest that this delay can be explained by the development of a thick organic layer (litter) that insulated the soil in the grazing exclusion plots. However, changes in floristic composition and, consequently, in phenology might also have contributed to the differential response.