Shrub Production Research Articles

Host Status of Ornamental Shade Trees and Shrubs to Plant Parasitic Nematodes.

Oregon leads the United States in nursery production of shade trees and is third in deciduous and broadleaf evergreen shrub production. Plant-parasitic nematodes have been implicated in problems with the growth of plants in nurseries and are also of phytosanitary risk. A greenhouse experiment was conducted to evaluate the host status of four trees (Quercus alba, Quercus garryana, Acer campestre, Thuja occidentalis) and two shrubs (Buxus sempervirens, Rhododendron catawbiense) to Meloidogyne incognita, Meloidogyne hapla, and Pratylenchus neglectus. Each plant/nematode treatment was replicated five times, and the experiment was conducted twice. Plants were inoculated with 3,000 eggs of M. incognita or M. hapla and 2,500 individuals of P. neglectus two weeks after planting. After three months, the plants were harvested, and the total density of nematodes in soil and roots for P. neglectus and the total density of second-stage juveniles (J2) in soil and eggs on roots for M. hapla and M. incognita were determined. The final nematode population (Pf) and reproductive factor (RF = Pf/initial population density) were calculated. For M. incognita and M. hapla, all of the ornamental trees and shrubs would be considered as fair to good hosts with RF values > 1. Meloidogyne incognita had the highest Pf (5,234 total J2 and eggs/pot) and RF value (28.4) on A. campestre. For P. neglectus, all of the ornamental trees and shrubs were fair to good hosts, except for B. sempervirens. Buxus sermpervirens was not a host for P. neglectus, with an RF value of almost 0. This is the first report of Q. alba, Q. garryana, and A. campestre as hosts for M. incognita, M. hapla, and P. penetrans. This is also the first report of T. occidentalis and R. catawbiense as hosts for P. penetrans and the non-host status of B. sermpervirens for P. penetrans.

A spatio-temporal analysis of the magnitude and trend of land use/land cover changes in Gilgel Gibe Catchment, Southwest Ethiopia

Analyzing alterations in land use/land cover is crucial for water Scientists, planners, and decision-makers in watershed management. This examination enables the development of effective solutions to mitigate the adverse impacts resulting from such changes. The focus of this research was analyzing alterations in land use/land cover within the Gilgel Gibe Catchment in 1991 – 2021. LULC data of 1991-2021 were derived from multispectral Landsat images. Data were also gathered using field observations and key informant interview. Data of LULC classes (1991–2021) were generated utilizing supervised classification with maximum likelihood algorithm of ENVI 5.1 and ArcGIS 10.5. Change detection analysis and accuracy assessment were done where accuracy levels all the study periods were > 85 %, and the overall Kappa statistics of the periods were > 0.89. Built-up area and cultivated land of the catchment are increasing with increasing magnitude of change; whereas, while forest cover and grazing land of the catchment are shrinking with declining magnitudes of change, shrubland covers and water body are declining with increasing magnitude of change in the catchment. The net increase in degraded land is a reflection of the increasing degradation of natural resources in the catchment. Swift escalation of population and the subsequent raising demand for farmland and forest and shrub (e.g. fuel-wood and construction) products, decline yield, unemployment and lack of alternative income source, and open access and limited conservation of resources are the principal factors for the dramatic shrinkages of grazing, forest, water body and shrubland resources. Thus, concerned bodies should take rehabilitation measures to restore degraded lands, improve production and yield of farmland by increasing improved farm-inputs and irrigation, and create employment and alternative income sources for the youth, women and the poor so as to ensure sustainable rural livelihoods and to curb the impacts on forest, shrubland and other resources.

Seed rain composition responds to climate change in a subtropical forest

Recent climate change has been shown to alter aspects of forest plant demography, such as growth and mortality, but less attention has been focused on how climate change alters the reproduction of plant populations through time. We hypothesized that the plant seed production would respond to climate change, and that the response would differ according to plant life form and functional traits. We tested this hypothesis by examining climate change from 2005 to 2020 and by determining the temporal trends of seed rain and seed production from plants with different life forms (e.g., herbs, vines, trees, palms) and of tree species with different statures as well as leaf, seed and wood traits during 2014-2020. We also tested the correlation between meteorological variables and time series of seed rain using cross correlation analysis. We found increasing wetness (lower vapor pressure deficit) through time but with decreasing minimum relative humidity, which is a pattern consistent with trends seen in many other parts of the world. During the study period, seed production of shrubs and relative contribution of woody vines to total seed rain decreased, while relative contribution of palms to total seed rain and tree species with more conservative leaf traits increased their contribution to total seed rain. Overall, these trends were well explained by the trends of meteorological variables and the responses of these life forms to climate change in previous studies. Additionally, the increasingly conservative leaf traits were also consistent with shifts in traits following recovery from disturbance. Our results suggest that a trait-based approach may help to unveil trends that are not readily apparent by examining seed counts alone. The compositional change found in the seed rain may indicate future shifts in forest species composition and should be incorporated into future studies of forest modelling and projections under climate change.

Indicators of ecosystem degradation along an elevational gradient in the Mediterranean Andes

Successful restoration measures need a good understanding of how the composition, structure, and functioning of ecosystems change with degradation and what the best indicators of these changes are. To answer these questions, we worked on four ecosystem types in the Mediterranean Andes mountains in central Chile (from sclerophyllous forest to Andean shrublands), which represent an elevational gradient from 700 to 3,250 m. We sampled three plots on each of the three degradation levels (low, medium, and high) for each ecosystem at increasing distances from goat corrals. We measured 35 indicators that describe vegetation (14), soil (15), and ecosystem processes (6) for one growing season. Degradation caused a decrease in shrub cover, shrub productivity, the Normalized Community Structure Integrity Index (CSIIn), litter depth, total soil nitrogen and C/N ratio, and an increase in clay content. Plant species indicating low degradation were consistently native woody species. When comparing ecosystems (i.e., at different elevations) against the type of variable, process-based indicators showed more statistically significant differences. Based on their consistency across ecosystems and ease of measurement, we recommend using shrub cover and litter depth as indicators of degradation. Finally, we concluded that ecosystems are highly degraded when vegetation- and process-based indicators change ∼ 60% or when soil indicators change ∼ 25%. These results could also be used to set goals for restoration projects in these mountain ecosystems.

Productivity and Nutritional Quality of Nitrogen-Fixing and Non-Fixing Shrub Species for Ruminant Production

Fodder shrubs are important dry season feed sources for livestock in semi-arid environments. It has been proposed that a mixture of leguminous with non-leguminous shrubs may increase rates of N cycling and improve biomass and fodder quality. The objective of the present study was to assess the biomass productivity and fodder quality of leguminous shrubs growing a mixture with non-leguminous shrubs. Three shrub species—the legume Leucaena leucocephala (Lam.) and the non-legumes Guazuma ulmifolia (Lam.) and Moringa oleifera (Lam.)—were grown as legume/non-legume mixtures and as monocultures. Total fodder production and quality were estimated over five harvests at three-month intervals. The Leucaena–Guazuma mixture had the largest fodder production (9045 kg ha−1 year−1), followed by the Leucaena monocrop (7750 kg ha−1 year−1). Total nitrogen accumulation in the foliage was also high in the Leucaena–Guazuma mixture, reaching 282 kg ha−1 year−1; the Leucaena monocrop accumulated 244 kg N, while the Moringa monocrop took up only 46 kg N ha−1. The concentration of polyphenols was high in Leucaena and Guazuma, while Moringa had the lowest value. The high survival and excellent growth rates, as well as the high foliage production observed in Leucaena and Guazuma, suggest that they have the potential to provide high-quality fodder for livestock.

Protecting nature's most effective carbon sink: an important role for fungi in peatlands.

This article is a Commentary on Shao et al. (2023), 238: 80–95.

Presence of Access Roads Results in Reduced Growing Season Carbon Uptake in Adjacent Boreal Peatlands

AbstractWe conducted a 2‐year study to examine the impacts of resource access roads on carbon (C) exchange in two forested boreal peatlands (a bog and a fen). Along six transects (perpendicular to the road), at 2, 6, and 20 m from the edge of the road on both sides of the road (RI areas), we measured understory CO2 fluxes bi‐weekly from May to August 2016 and 2017 and compared this to measurements at reference areas at least 50 m from the road. Furthermore, we estimated aboveground biomass and net primary productivity of overstory shrubs and trees and combined that with understory fluxes to estimate annual net ecosystem carbon balance, and road‐induced C emissions. Overall, at the bog, the RI areas were sources of C in both 2016 (89.9 g C m−2 y−1) and 2017 (108.9 g C m−2 y−1) while reference areas were sinks. However, at the fen, both RI areas (−744.7, −310.9 g C m−2 y−1 in 2016 and 2017, respectively) and reference areas were sinks of C. Averaged across both peatlands, the estimated road‐induced C losses were ∼7.97 and 7.40 Mg C for each km of the road in 2016 and 2017, respectively. However, areas connected by culverts showed lower road‐associated impact on C emissions. Therefore, we suggest that industries and infrastructure developers align the road parallel to the local water flow direction, when possible, consider the hydrogeological setting during road design to reduce hydrologic impacts, and increase hydrological flows between up‐ and downstream by adequate culverts.

Sediment-Based Growing Media Provides a Window Opportunity for Environmentally Friendly Production of Ornamental Shrubs

Sediments remediated with a nature-based solution approach (NBS-sediments) can represent a suitable and affordable alternative to peat as a constituent of growing media for ornamental plant production based on the combination of advanced production efficiency and rational green use of resources, including peat and water. In a greenhouse experiment, the effect of different growing media containing NBS-remediated sediments on two-year-old container grown cherry laurel (Prunus laurocerasus cv. ‘Novìta’) under standard and induced restrictive irrigation was evaluated. Six ternary mixes with different proportion (45:30:25 and 30:20:50 v/v) of peat:pumice:sediment (PE:TS25, PE:TS50), coconut fiber:pumice:sediment (CF:TS25, CF:TS50) and wood fiber:pumice:sediment (WF:TS25, WF:TS50) were tested in comparison to the standard peat:pumice blend (60:40 v/v), commonly used for pot ornamental crops ad used as control (PE, control). Pots were drip irrigated with 200 and 250 cc daily water volume (DWV). Cherry laurels grown in the control showed the lowest sign of stress, maintaining the highest net CO2 assimilation and transpiration rates, however stomatal conductance was reduced compared to PE:TS mixes. On the other hand, photosynthetic performance was strongly depressed by WF:TS25 and WF:TS50 under reduced DWV compared to the control, due to the combined effect of physical properties of the used matrices and reduced water availability. Nevertheless, final biomass production of plants grown on sediment-based growing media was similar to that of control, indicating that photosynthetic performance of plants fully recovered during the cultivation period. Differences in final plant development were negligible when compared to quality standards of marketing categories. Thus, appropriately blended NBS-sediment-based growing media can be used on a larger scale to produce rustic outdoor ornamentals.

Near‐Surface Hydrology and Soil Properties Drive Heterogeneity in Permafrost Distribution, Vegetation Dynamics, and Carbon Cycling in a Sub‐Arctic Watershed

AbstractDiscontinuous permafrost environments exhibit strong spatial heterogeneity at scales too small to be driven by weather forcing or captured by Earth System Models. Here we analyze effects of observed spatial heterogeneity in soil and vegetation properties, hydrology, and thermal dynamics on ecosystem carbon dynamics in a watershed on the Seward Peninsula in Alaska. We apply a Morris global sensitivity analysis to a process‐rich, successfully tested terrestrial ecosystem model (TEM), ecosys, varying soil properties, boundary conditions, and weather forcing. We show that landscape heterogeneity strongly impacts soil temperatures and vegetation composition. Snow depth, O‐horizon thickness, and near‐surface water content, which vary at scales of O(m), control the soil thermal regime more than an air temperature gradient corresponding to a 140 km north–south distance. High shrub productivity is simulated only in talik (perennially unfrozen) soils with high nitrogen availability. Through these effects on plant and permafrost dynamics, landscape heterogeneity impacts ecosystem productivity. Simulations with near‐surface taliks have higher microbial respiration (by 78.0 gC m−2 yr−1) and higher net primary productivity (by 104.9 gC m−2 yr−1) compared to runs with near‐surface permafrost, and simulations with high shrub productivity have outlying values of net carbon uptake. We explored the prediction uncertainty associated with ignoring observed landscape heterogeneity, and found that watershed net carbon uptake is 60% larger when heterogeneity is accounted for. Our results highlight the complexity inherent in discontinuous permafrost environments and demonstrate that missing representation of subgrid heterogeneity in TEMs could bias predictions of high‐latitude carbon budget.

Impact of ambient temperature, precipitation and seven years of experimental warming and nutrient addition on fruit production in an alpine heath and meadow community

Alpine and polar regions are predicted to be among the most vulnerable to changes in temperature, precipitation, and nutrient availability. We carried out a seven-year factorial experiment with warming and nutrient addition in two alpine vegetation communities. We analyzed the relationship between fruit production and monthly mean, maximum, and min temperatures during the fall of the pre-fruiting year, the fruiting summer, and the whole fruit production period, and measured the effects of precipitation and growing and thawing degree days (GDD & TDD) on fruit production. Nutrient addition (heath: 27.88 ± 3.19 fold change at the end of the experiment; meadow: 18.02 ± 4.07) and combined nutrient addition and warming (heath: 20.63 ± 29.34 fold change at the end of the experiment; meadow: 18.21 ± 16.28) increased total fruit production and fruit production of graminoids. Fruit production of evergreen and deciduous shrubs fluctuated among the treatments and years in both the heath and meadow. Pre-maximum temperatures had a negative effect on fruit production in both communities, while current year maximum temperatures had a positive impact on fruit production in the meadow. Pre-minimum, pre-mean, current mean, total minimum, and total mean temperatures were all positively correlated with fruit production in the meadow. The current year and total precipitation had a negative effect on the fruit production of deciduous shrubs in the heath. GDD had a positive effect on fruit production in both communities, while TDD only impacted fruit production in the meadow. Increased nutrient availability increased fruit production over time in the high alpine plant communities, while experimental warming had either no effect or a negative effect. Deciduous shrubs were the most sensitive to climate parameters in both communities, and the meadow was more sensitive than the heath. The difference in importance of TDD for fruit production may be due to differences in snow cover in the two communities.

Influence of various types of light on growth and physicochemical composition of blueberry (Vaccinium corymbosum L.) leaves

It is important to use light that has a positive effect on plants. For plant growers, achieving the lowest possible cost of shrub production is crucial. We investigated the influence of light (white and violet LEDs as well as fluorescent white and red light) on the rooting and growth of blueberry cuttings (V. corymbosum L.) 'Aurora' and 'Huron'. Blueberry cuttings (4 cm tall) were planted into boxes with peat, which were placed in a phytotron at 22 °C and illuminated for 16 hours a day. The plants died under the red fluorescent light source and, therefore, we discontinued its use. The other three light sources had a positive effect on plant growth and development. The light source had little effect on the content of macroelements in the leaves. Plants grown under white fluorescent and white LED light did not significantly differ in the height (22.0-25.8 cm), proline (4.67-7.23 μmol g-1), and polyphenol content (4987-5212 mg 100 g-1). In both cultivars, the violet LED light reduced plant growth and increased the content of polyphenols (6,448 mg 100 g-1) and proline (8.11-9.06 μmol g-1) in the leaves, which may indicate abiotic stress. 
 During the rooting of highbush blueberry cuttings, it is advisable to use white LED light. It has a positive economic impact on crop production due to low electricity consumption and it benefits the environment by eliminating mercury. The plant quality is similar to that of fluorescent white light.

Evaluation of rainwater harvesting and shrub establishment methods for sustainable watershed management in northern Afghanistan

Watershed rangelands in Northern Afghanistan provide various ecosystem services that support the local people’s livelihoods, but they are now highly degraded essentially due to the continuous high grazing pressure and recurrent droughts. Effects of shrub establishment method enhanced by water harvesting techniques to rehabilitate degraded rangelands have not been well addressed. The main goal of this study was to evaluate the impact of direct seeding and transplanting of seedlings in combination with semi-circular bunds on growth, yield, and survival rate of four shrub species (Atriplex halimus, Atriplex nummularia, Atriplex lentiformis, and Maireana brevifolia) under semi- arid conditions of Sayyad village, Khulm watershed. Survival rate (%), plant height, width, and plant length (cm) and plant cover (%) were measured for each plant over five occasions. A non-destructive reference unit was used to estimate biomass production. The results showed that growth attributes and biomass production of shrubs were consistently greater in the transplanting compared to direct seeding. On average, the plant length, width, height, volume, cover, and biomass production of transplanted shrubs were greater than direct-seeded shrubs by 24.3%, 8.6%, 8.7%, 121.5%, 13.8% and 34.1%, respectively. Biomass production of transplanted seedlings was the highest for A. nummularia (1313.5 g DM/plant) and A. halimus (800 g DM/plant). There was a strong correlation between plant biomass production and plant volume (R2Plant volume = 0.88) for the shrub A. nummularia, indicating that plant volume is a key variable for assessing biomass production for this species. Additionally, the survival rate of M. brevifolia was 100% in both planting methods, suggesting that based on better survival this halophytic plant has great potential when restoring degraded rangelands. Collectively, on the basis of better growth rates, yield, and survival, transplanting A. nummularia and A. halimus may enhance shrub establishment and contribute to the rehabilitation of sloping semi-arid degraded areas of Northern Afghanistan.

Occurrence of Crown Gall Disease on Japanese Spindle (Euonymus japonicas var. Green Rocket) Caused by Agrobacterium rosae in Iran.

Crown gall disease caused by diverse Agrobacterium species is one of the main biotic constraints in the ornamental plants industry in Iran (Mafakheri et al. 2017). In August 2019, Japanese spindle (Euonymus japonicus var. Green Rocket) plants showing crown gall symptoms were observed in a commercial greenhouse in Tehran, Iran. Infected plants were characterized by a visible overgrowth on their stems and crown. Bacterial isolation from the gall tissues was performed on nutrient agar (NA) and 1A media as described by Moore et al. (2001). The six resulted bacterial strains (A.E1 to A.E6) were evaluated using PCR primer pair F8360/F8361 amplifying a 453 bp DNA fragment in recA gene and confirmed as Agrobacterium sp. (Shams et al. 2013). Pathogenicity of the strains was evaluated in two independent assays on Japanese spindle plantlets as well as 10-15 day old tomato (Solanum lycopersicum cv. Sunseed 6189) and sunflower (Helianthus annuus cv. Armavirski) plants in greenhouse conditions using the needle prick method as described previously (Mafakheri et al. 2019). The reference strain A. radiobacter ICMP 5856 and sterile distilled water were used as positive and negative controls, respectively. Crown gall symptoms appeared 20-25 days post inoculation on the Japanese spindle plantlets as well as tomato and sunflower plants inoculated with the strains isolated in this study, while the negative control plants remained asymptomatic. Koch's postulates were accomplished by re-isolating on NA medium and PCR-based identification of the inoculated strains from the symptomatic plants. The representative strain A.E1 was subjected to multilocus sequence analysis (MLSA) using the sequences of four housekeeping genes (i.e. atpD, gyrB, recA, and rpoB) as described previously (Mafakheri et al. 2019). MLSA results revealed that the strain A.E1 is phylogenetically closely related to A. rosae. The sequences were deposited into GenBank under the accession numbers MT007962 to MT007965 for atpD, gyrB, recA, and rpoB, respectively. Further, the strain A.E1 was subjected to whole genome sequencing using Illumina HiSeq X platform. DNA extraction was performed using NucleoSpin Microbial DNA kit (Macherey-Nagel, Germany), DNA libraries were obtained with Nextera XT DNA Library Prep Kit (Illumina, USA), and de novo sequence assembly was performed using SPAdes genome assembler. The resulting whole genome sequence was deposited into the GenBank database under the accession number JAFJZW000000000. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values were calculated among all the type strains of Agrobacterium species/genomospecies using standard criteria as detailed previously (Osdaghi et al. 2020; Chen et al. 2021). The strain A.E1 had 97% ANI and 72% dDDH values with A. rosae strain NCPPB 1650, suggesting that the bacterial strains isolated from Japanese spindle in Iran belong to A. rosae. This is the first report of A. rosae causing crown gall disease on Japanese spindle in Iran. The new crown gall disease could negatively affect the ornamental shrub production industry in central Iran unless strict sanitary measures are taken into the account in the nurseries in these areas. Further nationwide surveys and samplings are warranted to elucidate the economic impact of the pathogen on ornamental plant industry in the country.

Effect of rainfall on Artemisia ordosica Krasch anual net primary production and allocation in sandy land in China

The adjustment of aboveground biomass allocation is an important part of plant growth adaptation strategies. Due to global climate change, rising temperatures are causing changes in global air circulation patterns. Therefore, more extreme drought and flood events will happen in the future. Xerophytic shrubs are the main vegetation types of dryland ecosystems and are expected to be sensitive to changes in rainfall, which would inevitably affect the stability of the ecosystem. We conducted field experiments to simulate the effects of rainfall on Artemisia ordosica Krasch annual net primary productivity (ANPP) and allocation in the Mu Us Desert in northern China. This study examined six different rainfall levels: natural rainfall level (control); natural rainfall level reduced by 30%, 50%, and 70% (−30%, −50%, −70% treatment); and natural rainfall level increased by 30% and 50% (+30%, +50% treatment). The plant height, cover/volume, size/number of vegetative and reproductive twigs, and dry weight of vegetative and reproductive twigs were measured. The results showed the following: (1) Twig size and number are more sensitive to rainfall changes than the cover/volume of this species. (2) Rainfall has a significant influence on shrub ANPP (maximum ANPP was reached at + 30% treatment, and the minimum value was reached at −70% treatment). (3) With the increase or decrease of rainfall, A. ordosica number of twigs increased, and the length became shorter. (4) Rainfall had a significant effect on ANPP allocation (vegetative growth and reproductive growth). With the increase or decrease of rainfall, vegetative growth and reproductive growth of A. ordosica showed a trade-off strategy. Under the condition of adding rainfall, vegetative twig ANPP increased significantly. Under severe drought stress (-70% treatment), ANPP decreased significantly. Adding or subtracting rainfall caused a significant decrease in the vegetative twig ANPP ratio and a significant increase in the reproduction twig ANPP ratio. Our results highlight the sensitivity of twig size and number as indicators of shrub production estimation and the mechanism underpinning desert shrub ANPP response to global environmental changes.

Effects of grazing disturbance of spatial distribution pattern and interspecies relationship of two desert shrubs

Grazing significantly affects the distribution, growth, and productivity of shrubs. In this study, we evaluated the effects of grazing disturbance on the spatial distribution patterns and interspecific relationships of two desert shrubs, Ammopiptanthus mongolicus and Sarcozygium xanthoxylon. Three types of grazing conditions were considered, including enclosed area (EA), seasonal rotational grazing area (SRGA), and grazing area (GA) (100 m × 100 m), in the West Ordos Nature Reserve of Inner Mongolia, China. The results showed that A. mongolicus and S. xanthoxylon populations were uniformly distributed at a small scale, and the distribution in EA and SRGA became gradually random. In GA, A. mongolicus population showed aggregated distribution but S. xanthoxylon population showed random distribution at a small scale. Moreover, both A. mongolicus and S. xanthoxylon populations at the 5–7 m scale showed random distribution. At the small and intermediate scales, the two species showed positive interspecific relationships of GA. However, no interspecific relationship was noted between the two species in EA and SRGA. A significant positive relationship (P < 0.01) was noted between the two species at 2–9 m and a negative relationship (P < 0.01) at 13–17 m scales in GA. Positive relationship (P < 0.01) was noted between the two species at 6–13 m scales and a significant negative relationship (P < 0.01) at 14–24 m scales in SRGA. The two species of desert shrubs showed positive interspecific relationships at the small scale, and they showed negative relationships as the interspecific competition intensified in the presence of grazing disturbance. When the grazing intensity exceeds a certain threshold, the interspecific relationships become weak. Therefore, moderate grazing would facilitate interspecific competition and species succession, whereas excessive grazing would disrupt natural competition causing desertification ultimately.

Seasonal thaw and landscape position determine foliar functional traits and whole-plant water use in tall shrubs on the low arctic tundra.

Climate warming is driving tundra shrub expansion with implications for ecosystem function and regional climate. Understanding associations between shrub ecophysiological function, distribution and environment is necessary for predicting consequences of expansion. We evaluated the role of topographic gradients on upland shrub productivity to understand potential constraints on shrub expansion. At a low arctic tundra site near Inuvik, Northwest Territories, Canada, we measured sap flow, stem water potential and productivity-related functional traits in green alder, and environmental predictors (water and nutrient availability and seasonal thaw depth) across a toposequence in alder patches. Seasonal thaw reduced stem sap flow whereas topographic position predicted stem water potential and productivity-related functional traits. Upslope shrubs were more water-limited than those downslope. Shrubs in drainage channels had traits associated with greater productivity than those on the tops of slopes. The effect of thaw depth on sap flow has implications for seasonal water-use patterns and warming impacts on tundra ecohydrology. Topographic variation in functional traits corresponds with observed spatial patterns of tundra shrub expansion along floodplains and concave hillslopes rather than in upland areas. Green alder is expanding rapidly across the low arctic tundra in northwestern North America; thus, anticipating the implications of its expansion is essential for predicting tundra function.

Fine root production, turnover of Reaumuria songarica and soil carbon and nitrogen in Alxa steppe desert of NW China

Variations of fine root production and turnover of the dominant shrubs associated with soil carbon (C) and nutrients are of key importance for evaluating desert ecosystem sustainability. Here we examined fine root production and turnover rate of Reaumuria songarica in Alxa steppe desert of northwestern China through sequential coring, ingrowth cores, and mesh‐bag methods, and then assessed soil C and nitrogen (N) stock and its correlation with fine root and leaf litter input. Results showed that fine root production and turnover rate were closely related to soil water content. Fine root production density and turnover rate of R. songarica were 386.8 g m−2 and 2.4 yr−1, respectively. Annually, fine root and leaf litter of R. songarica input 126.3 g C m−2 and 4.7 g N m−2 to soil. Soil organic C and N under shrub canopies increased substantially, which promoted the heterogeneity of soil properties and is considered as an important mechanism underlying the restoration of degraded sandy lands.

Short-term effect of thinning on the carbon budget of young and middle-aged Scots pine (Pinus sylvestris L.) stands

Thinning is the main silvicultural method for improving stand growth and wood quality, however, despite the relevance and extensive use of thinning in forest management, its effect on stand carbon (C) balance is still poorly studied at the ecosystem level. The present case study estimated the two-year post-thinning effect on the C balance of a pole stand and a middle-aged Scots pine stand growing on mesotrophic sandy soils. Moderate thinning from below reduced the stand C storage by 21–24%, however, the amount of C accumulated in woody biomass, which was removed by logging, is expected to recover in both stands in the following four years. The reduced biomass of the trees contributed to the decreased annual net primary production (NPP) of the stand by 9–11%. The absolute value of net ecosystem production decreased by 0.9 and 0.7 t C ha−1 yr−1 in the pole and the middle-aged stand, respectively; still, both thinned plots maintained their C sink status. The production of the herbaceous understorey as well as the production of needles increased in the younger stand after thinning, but this could not compensate for C loss at the stand level. The effect of thinning on the production of mosses and dwarf shrubs was not expressed in either stand, probably due to the too short post-thinning period. Thinning did not significantly affect either total soil respiration or the heterotrophic respiration (Rh). However, it increased the contribution of Rh to total soil respiration, which can be attributed to decreased fine root biomass and root respiration, while the aboveground litterfall was not significantly changed after thinning. Fine root production, which accounted for the main belowground litter input, was significantly lower in both thinned plots. Moderate thinning in the pole and the middle-aged Scots pine stand did not change the ecosystem into a C source and the induced C loss will be compensated during a short post-thinning period.

How do invasive trees impact shrub layer diversity and productivity in temperate forests?

• Key messageInvasive tree species alter taxonomic diversity and functioning of forest shrub layers: Prunus serotina increases shrub layer biomass two to three times but decreases its biodiversity, Robinia pseudoacacia slightly increases shrub layer biomass and has no effect on its biodiversity, while Quercus rubra both biomass and biodiversity of the shrub layer.• ContextAlthough the impact of invasive trees on understory biodiversity is known, very little data exist about their influence on shrub layer biodiversity and productivity.• AimsTo assess impacts of Prunus serotina Ehrh., Quercus rubra L., and Robinia pseudoacacia L. on shrub layer aboveground biomass, species composition, and alpha diversity.• MethodsWe measured stand structures in a set of 168 study plots established in Wielkopolski National Park (W Poland), and we compared biomass and diversity metrics using generalized mixed-effects linear models.• ResultsWe found the lowest aboveground biomass of shrub layers in Q. rubra forests. P. sylvestris forests invaded by P. serotina had two to three times higher aboveground biomass than non-invaded forests. R. pseudoacacia forests had 27.8% higher shrub layer biomass than Quercus-Acer-Tilia forests. We found negative impacts of Q. rubra and negligible impacts of R. pseudoacacia on shrub layer alpha diversity metrics. However, the effect of Q. rubra was similar to native F. sylvatica. P. serotina negatively affected functional diversity, but its effects were lower in rich P. sylvestris forests than in poor P. sylvestris forests.• ConclusionThe introduction of alien tree species alters ecosystem services and species diversity of shrub layers. The direction and magnitude of these alterations are alien species-specific and context-dependent. Therefore, their management should account for their impacts.

Topographical Controls on Hillslope‐Scale Hydrology Drive Shrub Distributions on the Seward Peninsula, Alaska

AbstractObservations indicate shrubs are expanding across the Arctic tundra, mainly on hillslopes and primarily in response to climate warming. However, the impact topography exerts on hydrology, nutrient dynamics, and plant growth can make untangling the mechanisms behind shrub expansion difficult. We examined the role topography plays in determining shrub expansion by applying a coupled transect version of a mechanistic ecosystem model (ecosys) in a tundra hillslope site in the Seward Peninsula, Alaska. Modeled biomass of the dominant plant functional types agreed well with field measurements (R2 = 0.89) and accurately represented shrub expansion over the past 30 years inferred from satellite observations. In the well‐drained crest position, canopy water potential and plant nitrogen (N) uptake was modeled to be low from plant and microbial water stress. Intermediate soil water content in the mid‐slope position enhanced mineralization and plant N uptake, increasing shrub biomass. The deciduous shrub growth in the mid‐slope position was further enhanced by symbiotic N2 fixation primed by increased root carbon allocation. The gentle slope in the poorly drained lower‐slope position resulted in saturated soil conditions that reduced soil O2 concentrations, leading to lower root O2 uptake and lower nutrient uptake and plant biomass. A simulation that removed topographical interconnectivity between grid cells resulted in (1) a 28% underestimate of mean shrub biomass and (2) over or underestimated shrub productivity at the various hillslope positions. Our results indicate that land models need to account for hillslope‐scale coupled surface and subsurface hydrology to accurately predict current plant distributions and future trajectories in Arctic ecosystems.