Total Aboveground Net Primary Productivity Research Articles

Modeling canopy cover and aboveground net primary production using soil factors in rangelands of Ardabil province, Iran

<p>Canopy cover (CC) and the aboveground net primary production (ANPP) vary under the influence of various environmental factors. They underscore ecological sustainability under different environment-human interactions. Towards this, the present study aimed to model the CC and ANPP of different plant functional types (PFTs) and their total using the soil attributes in the northwest (Ardabil province) rangelands of Iran. According to ecoregions and plant types and environmental factors, sampling was taken at the peak stage of plant growth from 2016 to 2020 using 1-m2 plots. For each transect, a soil sample was taken and transferred to the soil laboratory and the various attributes were measured. Maps of soil attributes were prepared using the inverse distance weighting (IDW) method. Differences in CC and ANPP of PFTs among soil attributes were analyzed using the paired sample t-test. Linear multiple regression was used for modeling the soil attributes. Total CC and ANPP were prepared in two ways (i.e., regression and PFTs maps summing). The accuracy assessment of the maps was calculated by using the criteria of mean absolute error (MAE), mean deviation error (MDE), and root mean squared error (RMSE). The obtained results were acceptable (value < 7). The difference between the modeled and measured mean values of CC was equal to –0.03% for grasses, –0.01% for forbs, +0.03% for shrubs, 0% for total<sub>regression model</sub>, and +0.06 for total<sub>PFTs maps summing</sub>. Additionally, this difference in terms of the ANPP was equal to 0 kg/ha for grasses, +0.02 kg/ha for forbs, –0.09 kg/ha for shrubs, –0.02 for total<sub>regression model</sub>, and +0.02 kg/ha for total<sub>PFTs maps summing</sub>. The present results are applicable to managing the balance between supply and demand of rangeland products and they can be used from carbon management perspectives.</p>

Forage quantity and protein concentration changes across a forest-savanna gradient with management implications for white-tailed deer

White-tailed deer (Odocoileus virginianus) hunting is an important economic activity associated with the management of forests and rangelands in the USA, with over $12.9 billion dollars of related annual expenditures. Reducing tree cover through thinning and prescribed fire both have the potential to increase the quantity and quality of deer forage. We evaluated the long-term impacts of eight different combinations of fire return intervals and tree harvest on forage productivity and protein content of the forage. Based on management regime, study units ranged from savanna to closed-canopy forest. Aboveground net primary production (ANPP) of six functional groups (grass, panicum, forb, legume, woody, sedge) of understory vegetation was measured in October 2019 and 2020 using destructive sampling. Samples for foliar crude protein (CP) concentration were collected in spring, summer, and fall of 2020. Total understory ANPP ranged from 2.9 to 466.3 g m−2 and was up to 566% greater in savanna systems maintained by frequent fire (return interval of three years or less) than in non-burned forest treatments. Annual burning resulted in ANPP dominated by herbaceous plants composed mostly of fire-tolerant grasses (e.g., Andropogon gerardii, Schizachyrium scoparium). Longer fire return intervals or no fire resulted in roughly equal ANPP from understory woody and herbaceous species. Crude protein concentrations were up to 45.7% greater in the woodland and forest units than in the savanna units for seven of the eleven species sampled. The greater CP in the forests was most noticeable in the summer when deer needs for quality forage are substantial. Increased protein concentrations of understory species in the forests, but greater ANPP in the savannas indicate that managing for a mix of savanna and woodland could be ideal for balancing forage quantity with increased forage protein.

Compensatory dynamics drive grassland recovery from drought

Abstract Grasslands are expected to experience droughts of unprecedented frequency and magnitude in the future. Characterizing grassland responses and recovery from drought is therefore critical to predict the vulnerability of grassland ecosystems to climate change. Most previous studies have focused on ecosystem responses during drought while investigations of post‐drought recovery are rare. Few studies have used functional traits, and in particular bud or clonal traits, to explore the mechanisms underlying grassland responses to and recovery from drought. To address this issue, we experimentally imposed a four‐year drought in a C3‐dominated grassland in northeastern China and monitored recovery for 3 years post‐drought. We investigated the immediate and legacy effects of drought on total above‐ground net primary productivity (ANPP), ANPP of functional groups (rhizomatous grasses, bunch grasses and forbs), and how the legacy effects were driven by plant species diversity, clonal traits and vegetative traits. We found that drought progressively reduced total ANPP over the 4‐year period. The reductions in total ANPP in the first and third drought years were caused by the decrease in ANPP of bunch grasses only, while that of the second year was caused by declines in ANPP of bunch grasses and forbs, and the fourth year decline was linked to all three functional groups. The post‐drought recovery of ANPP, which occurred despite the continued loss of plant species diversity, was mainly driven by rapid recovery of rhizomatous and bunch grasses, which compensated for the slow response by forbs. The rapid post‐drought recovery of these grasses can be attributed to their relatively large, intact bud and shoot densities post‐drought, as well as the recovery of plant height and specific leaf area. The rapid recovery of grasses possibly restricted the growth and distribution of forbs, resulting in reduced forb ANPP and, consequently, lower species diversity during the recovery period. Synthesis. These results highlight the potential for positive legacy effects of drought on ANPP as well as the important and complementary roles of plant reproductive and vegetative traits in mediating ecosystem recovery from drought in a C3‐dominated grassland.

Responses of a semiarid grassland to recurrent drought are linked to community functional composition.

Recurrent droughts are an inevitable consequence of climate change, yet how grasslands respond to such events is unclear. We conducted a 6-year rainfall manipulation experiment in a semiarid grassland that consisted of an initial 2-year drought (2015-2016), followed by a recovery period (2017-2018) and, finally, a second 2-year drought (2019-2020). In each year, we estimated aboveground net primary productivity (ANPP), species richness, community-weighted mean (CWM) plant traits, and several indices of functional diversity. The initial drought led to reduced ANPP, which was primarily driven by limited growth of forbs in the first year and grasses in the second year. Total ANPP completely recovered as the rapid recovery of grass productivity compensated for the slow recovery of forb productivity. The subsequent drought led to a greater reduction in total ANPP than the initial drought due to the greater decline of both grass and forb productivity. The structural equation models revealed that soil moisture influenced ANPP responses directly during the initial drought, and indirectly during the subsequent drought by lowering functional diversity, which resulted in reduced total ANPP. Additionally, ANPP was positively influenced by CWM plant height and leaf nitrogen during the recovery period and recurrent drought, respectively. Overall, the greater impact of the second drought on ecosystem function than the initial drought, as well as the underlying differential mechanism, underscores the need for an understanding of how increased drought frequency may alter semiarid grassland functioning.

How much aboveground net primary production can be used for human activities in the alpine grasslands in the Three Rivers Source Region (TRSR), China?

Sustainable management of grasslands has always been an urgent issue for policy-makers. The three rivers source region (TRSR) contains widely distributed natural grasslands and is sensitive to climate warming. To enable the sustainable development of the human-nature system in the TRSR, we propose a novel indicator based on the allocation of aboveground net primary production (ANPP). The indicator we proposed is the ANPP that can be used for human activities (UANPP). In the study, we simulated the spatial and temporal patterns of the UANPP in the alpine grasslands in the TRSR during 1979–2016 and explored the main driving factors of the UANPP. The results revealed that (a) the annual total UANPP in the TRSR was 13.22 TgC, approximately accounting for 47% of total ANPP. (b) The areas with negative UANPP values accounted for 16% of the entire TRSR, and they were primarily located within the Nature Reserve of the Yangtze and Yellow river source regions, while three-quarters of the area exhibited improvement trends. (c) The regional mean UANPP significantly increased during 1979–2016, at a rate of 0.28 gC m−2 yr−1 (p < 0.01). In the entire TRSR, 87% of the area exhibited increasing trends. (d) The UANPP in most areas of the TRSR was strongly correlated with precipitation, and the effect of human activities on the UANNP increased slightly during the 38 year study period. The UANPP represents the upper limit of human use of nature. These findings provide a reference for policy-makers to make decisions toward human-nature system sustainability while meeting human needs for grassland resources. ANPP allocation between nature and human system is a potentially important tool from the standpoint of sustainable development.

Can grazing by elk and bison stimulate herbaceous plant productivity in semiarid ecosystems?

AbstractPlant communities in rangeland ecosystems vary widely in the degree to which they can compensate for losses to herbivores. Ecosystem‐level factors have been proposed to affect this compensatory capacity, including timing and intensity of grazing, and availability of soil moisture and nutrients. Arid ecosystems are particularly challenging to predict because of their high degree of temporal variability in moisture inputs. We used a replicated herbivore exclusion experiment to evaluate herbaceous plant responses to grazing by large ungulates to test current theory and identify constraints on plant compensation in a dryland ecosystem. We measured nitrogen (N) yield and herbaceous production in three plant communities: meadows, willow‐associated herbaceous communities, and riparian communities. We implemented grazing exclusion treatments from 2005 to 2008 in areas with elk and bison and areas with only elk. Grazing by large ungulates increased herbaceous production and N yield in herbaceous riparian communities. In willow communities, herbaceous plants displayed equal compensation in response to grazing in total aboveground production and N yield. Our results support the idea that plant compensation in this semiarid system is contingent on soil moisture availability, wherein the most productive sites (that received substantial moisture inputs from subsurface flow) exhibited overcompensation. Although the herbaceous riparian communities we studied are isolated patches of productive grassland in an otherwise shrub‐dominated and minimally productive semiarid landscape, grazing by a combination of bison and elk removed only 44%–53% of aboveground net primary productivity (ANPP) during the growing season, and 25%–38% of production over winter. Consumption by ungulates was a positive linear function of herbaceous production, similar to reported patterns from other temperate and tropical grazing ecosystems. The slope of this relationship was affected by the analytical method used to calculate ANPP and consumption rates, but, regardless of the method, was lower or similar to reported slopes for other intensively grazed systems (Yellowstone, Serengeti, Laikipia) that have sustained high ungulate densities for decades to centuries. Given that the vegetation communities exhibited equal or overcompensation in terms of total herbaceous ANPP in both years, elk and bison population levels during our study period did not appear to occur at densities leading to degradation of herbaceous communities.

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.

LPDynR: A new tool to calculate the land productivity dynamics indicator

The United Nations Sustainable Development Goal 15 (Life on Land), adopted the indicator 15.3.1 to measure the Land Degradation Neutrality. This indicator is based on three sub-indicators: (1) Trends in Land Cover, (2) Land Productivity and (3) Carbon Stocks. The Land Productivity sub-indicator refers to the total above-ground Net Primary Production and reflects changes in health and productive capacity of the land. It can be calculated using the Land Productivity Dynamics approach, which performs a combined assessment of the long term tendency of change of land productivity and its current level relative to homogeneous land areas.Here, we present the R-based tool LPDynR, which implements the Land Productivity Dynamics approach for the calculation of the Land Productivity sub-indicator. LPDynR ingests vegetation-related indices derived from time series of remote sensed imagery. The final indicator is a 5-class map, ranging from declining to increasing land productivity. As an example of LPDynR functionalities and applicability, we present a case study for Europe. First, we show the general way to calculate the indicator for the entire time series (2000–2019), explained in a step by step process. Secondly, we show how to alternatively calculate the indicator based only on the long term tendency of change, but we evidence the added value of including the current level of productivity to refine the final indicator. Finally, we present some code for the calculation of “partial indicators” in terms of time scale along the observation period, which may help the user to understand the land productivity dynamics within the time series, as well as to assess the stability of the final product. While the indicator shows a general positive dynamics across Europe during the period 2000–2019, some of the partial maps show more negative trends, demonstrating the highly fluctuating character of vegetation.

Above‐ground net primary productivity in regenerating seasonally dry tropical forest: Contributions of rainfall, forest age and soil

Abstract Identifying factors controlling forest productivity is critical to understanding forest‐climate change feedbacks, modelling vegetation dynamics and carbon finance schemes. However, little research has focused on productivity in regenerating tropical forests which are expanding in their fraction of global area have an order of magnitude larger carbon uptake rates relative to older forest. We examined above‐ground net primary productivity (ANPP) and its components (wood production and litterfall) over 10 years in forest plots that vary in successional age, soil characteristics and species composition using band dendrometers and litterfall traps in regenerating seasonally dry tropical forests in northwestern Costa Rica. We show that the components of ANPP are differentially driven by age and annual rainfall and that local soil variation is important. Total ANPP was explained by a combination of age, annual rainfall and soil variation. Wood production comprised 35% of ANPP on average across sites and years, and was explained by annual rainfall but not forest age. Conversely, litterfall increased with forest age and soil fertility yet was not affected by annual rainfall. In this region, edaphic variability is highly correlated with plant community composition. Thus, variation in ecosystem processes explained by soil may also be partially explained by species composition. These results suggest that future changes in annual rainfall can alter the secondary forest carbon sink, but this effect will be buffered by the litterfall flux which varies little among years. In determining the long‐term strength of the secondary forest carbon sink, both rainfall and forest age will be critical variables to track. We also conclude that detailed understanding of local site variation in soils and plant community may be required to accurately predict the impact of changing rainfall on forest carbon uptake. Synthesis. We show that in seasonally dry tropical forest, annual rainfall has a positive relationship with the growth of above‐ground woody tissues of trees and that droughts lead to significant reductions in above‐ground productivity. These results provide evidence for climate change—carbon cycle feedbacks in the seasonal tropics and highlight the value of longitudinal data on forest regeneration.

Effect of grazing exclusion on soil and vegetation characteristics in desert steppe rangelands: a case study from north-western Iran

This case study examined the effect of grazing exclusion on the soil and vegetation characteristics to provide support for the restoration of the degraded desert steppe rangelands of the Arshagh ecoregion. Six sampling sites were selected (three overgrazed and three not grazed sites) from the ecoregion. Vegetation sampling (1 m2 area at 10 intervals) was carried out along 18 pieces of 90 m long transects. Soil samples were collected from the plots at the beginning, middle, and end of each transect from 0–15 cm depths and then combined to get one sample per transect. Differences between vegetation and soil properties of the grazing exclusion and overgrazed sites were analyzed using the t-test statistic. Species richness index (2.32), the diversity index (1.87), and plant cover (69.46%) were maximum at sites after 20-years of grazing exclusion. All species of plant functional types at the exclusion sites were significantly (p < 0.05) different from those at the overgrazed site. Total aboveground net primary production was greater at the exclusion sites (56.50 g/m2) than at the overgrazed sites. Soil pH was significantly (p < 0.05) higher at the exclusion site than at the overgrazed sites. Electrical conductivity was significantly higher at the overgrazed sites than at the exclusion sites. These results imply that livestock exclusion plays an important role in such vegetation parameters as the diversity, cover and soil properties of degraded rangeland ecosystems. Moreover, grazing exclusion in Arshagh rangelands may be a promising management option for the restoration of such rangelands.

Estimating Aboveground Net Primary Production (ANPP) Using Landsat 8-Based Indices: A Case Study From Hir-Neur Rangelands, Iran

Aboveground Net Primary Production (ANPP), an indicator of ecosystems’ ability to capture and convert solar energy, is critical to evaluate and manage ecosystem carbon balance index including rangelands. Measuring ANPP over a large area is difficult at it varies with different factors including climate and anthropogenic, while satellite-based information shows strong opportunity. The aim of this study was to estimate the ANPP of Plant Functional Types (PFTs) using Landsat-8 imagery over the rangelands of Hir-Neur from Ardabil Province, Iran as a case study area. Landsat-8 Operational Land Imager (OLI) satellite images were collected on 9th June 2017 aligning with the field sampling of PFTs ANPP. Eleven sampling sites with 10 plots at each site (locations recorded with a Global Positioning System, GPS) were selected along a transect with elevation gradient and the ANPP of PFTs were recorded. Twenty-two vegetation indices were calculated from the Landsat-8 imagery and the index values were extracted for the sampling plots. Correlation between derived indices and field collected ANPP data were calculated. Predictive relationships between PFTs and total ANPP and satellite indices were developed using a 3rd-order polynomial model and the model was used to map the whole study area. The best estimation of PFTs and total ANPP was obtained using the Vegetation Index (VI3) for grasses (R2=0.47), Iron Oxide (IO) for forbs (R2=0.51), and Renormalized Difference Vegetation Index (RDVI) for shrubs (R2=0.50). The Difference Vegetation Index (DVI) was the best estimator for the total ANPP (R2=0.49). The overall accuracies of the maps were acceptable (MAE, MDE, RMSE <0.5). Results showed a difference when using PFTs for ANPP estimation in comparison with direct ANPP estimation. Thus, direct estimation of ANPP from the satellite based indices would be more accurate. This study also showed promising capabilities of the indices based on PFTs and total ANPP for estimating aboveground biomass, supply-demand balance and carbon balance at the study area and elsewhere with similar ecological conditions. This study also showed opportunity to select the most appropriate vegetation indices for the estimation of PFTs and the total ANPP.

Aboveground Net Primary Production at Acacia mangium Plantation in Northern Vietnam

Net primary production (NPP) is an important index for understanding carbon cycling in forest ecosystems. In this study, aboveground NPP at Acacia mangium plantation was estimated basing on allometry for aboveground biomass increment (ΔM) and litter trap technique for litterfall (Lf). The experiment was conducted in two plots of 300 m2 each (15 × 20 m), established at a 21-month old plantation. Data were collected five times of 3-month intervals in a total duration of 357 days. The results indicated that Lf and ΔM were seasonal-dependent. Litterfall was highest (4.06 g m-1 day-1) during Sep-Jan (late rainy season, early winter) and lowest (1.10 g m-1 day-1) during Mar-Jun (early rainy season, early summer). While, ΔM was highest (13.51 g m-1 day-1) during Jun-Sep (rainy season, summer) and lowest (3.10 g m-1 day-1) during Jan-Mar (dry season, winter). Total Lf in a duration of 357 days was 9.69 tons ha-1 and ΔM was 27.71 tons ha-1, leading to total aboveground NPP of the present study plantation of 37.40 tons ha-1. It is concluded that aboveground NPP of acacia plantation was much higher than other forests of different types and ages around the world. Such difference indicates the importance of acacia plantation in soil nutrient cycling through litterfall decomposition and carbon sequestration through aboveground biomass increment.

Testing nitrogen and water co-limitation of primary productivity in a temperate steppe

Primary productivity in the temperate steppe is assumed to be co-limited by nitrogen (N) and water availability, but empirical evidence is scarce. We examined the N and water limitation status of primary productivity from the species scale to community scale under the framework of resource co-limitation. We compared the responses of aboveground net primary productivity (ANPP) at different ecological levels to factorial N and water addition in two years in a temperate steppe of northern China. Water addition significantly enhanced total ANPP by 46%, with stronger effects in the dry year. Total ANPP was sub-additively co-limited by N and water availability, being more sensitive to water addition than to N addition in the dry year and equally sensitive to both resources in the year with normal precipitation. The responses of total ANPP to resource additions were largely driven by the changes of grasses rather than the forbs. Species level ANPP showed conservative responses to resource additions. Our results highlight the hierarchical patterns of limitation status in primary productivity at different biological organization levels in this temperate steppe. The sub-additive limitation by N and water in this ecosystem deserves more attention in modelling the dynamics of ecosystem carbon cycle under global change scenarios.

Ecosystem effects of integrating human-made runoff-harvesting systems into natural dryland watersheds

Runoff-harvesting systems (RHSs) design to collect runoff water and nutrients from small rocky watersheds into ponds bounded by soil dikes (termed limans) that are used as an afforestation grove. Our study aimed at quantifying the influence of RHSs using two indicators: soil quality (SQ) and aboveground net primary productivity (ANPP) in a small watershed scale. The SQ index was estimated by 13 physical, chemical, and biological soil properties. ANPP was evaluated by a spaceborne-derived vegetation index of total biomass (woody and annual) and field measurements of annuals. The study was conducted in four small RHS watersheds, as well as in a reference watershed without a liman, located in the Negev Desert, Israel. Our findings are: (1) there is a significantly higher soil organic matter, total water content, and phosphorus values in all the limans than in the other locations (upstream and downstream area); and (2) significantly higher SQ and total ANPP values in the limans than in the downstream areas, amplifying the overall watershed fertility and enhance ecosystem services. We conclude that integrating RHS as a fertility island, be adjusted their size and location, can be essential techniques to sustain ecosystem services and maintain the natural ecosystem in the watershed.

Analysis of spatial and temporal patterns of aboveground net primary productivity in the Eurasian steppe region from 1982 to 2013.

To explore the importance of the Eurasian steppe region (EASR) in global carbon cycling, we analyzed the spatiotemporal dynamics of the aboveground net primary productivity (ANPP) of the entire EASR from 1982 to 2013. The ANPP in the EASR was estimated from the Integrated ANPPNDVI model, which is an empirical model developed based on field‐observed ANPP and long‐term normalized difference vegetation index (NDVI) data. The optimal composite period of NDVI data was identified by considering spatial heterogeneities across the study area in the Integrated ANPPNDVI model. EASR's ANPP had apparent zonal patterns along hydrothermal gradients, and the mean annual value was 43.78 g C m−2 yr−1, which was lower than the global grasslands average. Compared to other important natural grasslands, EASR's ANPP was lower than the North American, South American, and African grasslands. The total aboveground net primary productivity (TANPP) was found to be 378.97 Tg C yr−1, which accounted for 8.18%–36.03% of the TANPP for all grasslands. In addition, EASR's TANPP was higher than that of the grasslands in North America, South America, and Africa. The EASR's TANPP increased in a fluctuating manner throughout the entire period of 1982–2013. The increasing trend was greater than that for North American and South American and was lower than that for African grasslands over the same period. The years 1995 and 2007 were two turning points at which trends in EASR's TANPP significantly changed. Our analysis demonstrated that the EASR has been playing a substantial and progressively more important role in global carbon sequestration. In addition, in the development of empirical NDVI‐based ANPP models, the early–middle growing season averaged NDVI, the middle–late growing season averaged NDVI and the annual maximum NDVI are recommended for use for semi‐humid regions, semi‐arid regions, and desert vegetation in semi‐arid regions, respectively.

Forest composition and growth in a freshwater forested wetland community across a salinity gradient in South Carolina, USA

Tidal freshwater forested wetlands (TFFW) of the southeastern United States are experiencing increased saltwater intrusion mainly due to sea-level rise. Inter-annual and intra-annual variability in forest productivity along a salinity gradient was studied on established sites. Aboveground net primary productivity (ANPP) of trees was monitored from 2013 to 2015 on three sites within a baldcypress (Taxodium distichum) swamp forest ecosystem in Strawberry Swamp on Hobcaw Barony, Georgetown County, South Carolina. Paired plots (20×25-m) were established along a water salinity gradient (0.8, 2.6, 4.6PSU). Salinity was continuously monitored, litterfall was measured monthly, and growth of overstory trees ⩾10cm diameter at breast height (DBH) was monitored on an annual basis. Annual litterfall and stem wood growth were summed to estimate ANPP. The DBH of live and dead individuals of understory shrubs were measured to calculate density, basal area (BA), and important values (IV). Freshwater forest communities clearly differed in composition, structure, tree size, BA, and productivity across the salinity gradient. The higher salinity plots had decreased numbers of tree species, density, and BA. Higher salinity reduced average ANPP. The dominant tree species and their relative densities did not change along the salinity gradient, but the dominance of the primary tree species differed with increasing salinity. Baldcypress was the predominant tree species with highest density, DBH, BA, IV, and contribution to total ANPP on all sites. Mean growth rate of baldcypress trees decreased with increasing salinity, but exhibited the greatest growth among all tree species. While the overall number of shrub species decreased with increasing salinity, wax myrtle (Morella cerifera) density, DBH, BA, and IV increased with salinity. With rising sea level and increasing salinity levels, low regeneration of baldcypress, and the invasion of wax myrtle, typical successional patterns in TFFW and forest health are likely to change in the future.

Simulation of the Grazing Effects on Grassland Aboveground Net Primary Production Using DNDC Model Combined with Time-Series Remote Sensing Data—A Case Study in Zoige Plateau, China

Measuring the impact of livestock grazing on grassland above-ground net primary production (ANPP) is essential for grass yield estimation and pasture management. However, since there is a lack of accurate and repeatable techniques to obtain the details of grazing locations and stocking rates at the regional scale, it is an extremely challenging task to study the influence of regional grazing on the grassland ANPP. Taking Zoige County as a case, this paper proposes an approach to quantify the spatial and temporal variation of grazing intensity and grazing period through time-series remote sensing data, simulated grassland ANPP through the denitrification and decomposition (DNDC) model, and then explores the impact of grazing on grassland ANPP. The result showed that the model-estimated ANPP while considering grazing had a significant relationship with the field-observed ANPP, with the coefficient of determination (R2) of 0.75, root mean square error (RMSE) of 122.86 kgC/ha, and average relative error (RE) of 8.77%. On the contrary, if grazing activity was not considered in simulation, a large uncertainty was found when the model-estimated ANPP was compared with the field observation, showing R2 of 0.4, RMSE of 211.51 kgC/ha, and average RE of 32.5%. For the whole area of Zoige County in 2012, the statistics of the estimation showed that the total regional ANPP was up to 3.815 × 105 tC, while the total regional ANPP, without considering grazing, would be overestimated by 44.4%, up to 5.51 × 105 tC. This indicates that the grazing parameters derived in this study could effectively improve the accuracy of ANPP simulation results. Therefore, it is feasible to combine time-series remote sensing data with the process model to simulate the grazing effects on grassland ANPP. However, some issues, such as selecting proper remote sensing data, improving the quality of model input parameters, collecting more field data, and exploring the data assimilation approaches, still should be considered in the future work.

High-severity fire reduces early successional boreal larch forest aboveground productivity by shifting stand density in north-eastern China

Climate warming is predicted to increase fire activity across the Eurasian boreal larch forest in the 21st century, which could have serious consequences on carbon storage. Quantifying the effects of fire disturbance on forest structure and aboveground net primary productivity (ANPP) could aid in our ability to predict future carbon storage on a regional and biome level. In this study, we examined the spatial heterogeneity of forest structure and ANPP on sites of varying fire severity and topographic position in a recently burned landscape in the Great Xing’an Mountains, China. Results indicated that after 11 years of vegetation regrowth, fire severity significantly affected forest regeneration ANPP. Spatial heterogeneities in forest regeneration ANPP were explained by both tree sapling density and understorey vegetation abundance. Although understorey vegetation productivity on average contributed 50% of total ANPP after fire, the increase in understorey productivity with fire severity could not offset the decrease in tree productivity in severely burned stands where tree sapling density was limited. Our results suggest that high-severity fire can decrease forest regeneration ANPP by altering forest structure in the early post-fire successional stage and that this shift in forest structure may influence future forest productivity trajectories over an extended period.

Climatic controls of aboveground net primary production in semi-arid grasslands along a latitudinal gradient portend low sensitivity to warming.

Although climate models forecast warmer temperatures with a high degree of certainty, precipitation is the primary driver of aboveground net primary production (ANPP) in most grasslands. Conversely, variations in temperature seldom are related to patterns of ANPP. Thus forecasting responses to warming is a challenge, and raises the question: how sensitive will grassland ANPP be to warming? We evaluated climate and multi-year ANPP data (67 years) from eight western US grasslands arrayed along mean annual temperature (MAT; ~7-14 °C) and mean annual precipitation (MAP; ~250-500 mm) gradients. We used regression and analysis of covariance to assess relationships between ANPP and temperature, as well as precipitation (annual and growing season) to evaluate temperature sensitivity of ANPP. We also related ANPP to the standardized precipitation evaporation index (SPEI), which combines precipitation and evapotranspiration to better represent moisture available for plant growth. Regression models indicated that variation in growing season temperature was negatively related to total and graminoid ANPP, but precipitation was a stronger predictor than temperature. Growing season temperature was also a significant parameter in more complex models, but again precipitation was consistently a stronger predictor of ANPP. Surprisingly, neither annual nor growing season SPEI were as strongly related to ANPP as precipitation. We conclude that forecasted warming likely will affect ANPP in these grasslands, but that predicting temperature effects from natural climatic gradients is difficult. This is because, unlike precipitation, warming effects can be positive or negative and moderated by shifts in the C3/C4 ratios of plant communities.

Belowground bud banks of tallgrass prairie are insensitive to multi‐year, growing‐season drought

In tallgrass prairie plant communities, new shoots are recruited from belowground bud banks, often in response to disturbance. We explored the contribution of belowground bud banks to grassland stability when perturbed by severe drought. We sought to quantify changes in bud bank density and demography, assess the contribution of the bud bank to aboveground net primary productivity, and compare shifts in above‐ and belowground plant community structure in response to drought. We experimentally reduced precipitation 76% from ambient levels for two years, and compared responses of drought plots to ambient and irrigated controls during the two years of drought and two years of recovery. We measured belowground bud bank density and aboveground shoot density, canopy cover, and aboveground net primary productivity. While aboveground net primary productivity and C4 grass flowering shoot density declined during drought, bud bank density was insensitive to drought. Rapid resilience of the aboveground plant community following cessation of drought appears to be mediated by the resistance of bud banks to drought. Shoot density, but not bud bank density, was positively correlated with total aboveground net primary productivity. Furthermore, proportional reductions in aboveground net primary productivity increased as shoot density increased. Plant community structure shifted both above‐ and belowground in response to precipitation treatments. Our results suggest that the response of perennial grasslands to drought may be mediated by the stable belowground bud bank, with shifts in abundance of individual species maintaining overall bud bank density and ecosystem function.