Foliage Mass Research Articles

Обобщенные модели фитомассы деревьев ивы (род Salix L.): мета-анализ

Climate change has a negative impact on the environment, including forest ecosystems. However, forests are not only passive objects affected by climate change, but also, due to their ability to absorb and accumulate carbon, they themselves can significantly influence this process. Carbon sequestration by forest ecosystems plays an important role in mitigating the effects of climate change. Therefore, it is necessary to know about the amount of carbon stored in forest phytomass, and it is becoming increasingly important to accurately determine the phytomass of forest trees. Due to the absorption of carbon dioxide during plant growth and its release during wood burning, forests are a carbon-neutral energy source. The idea of using phytomass as an energy source to replace fossil fuels is most promising for fast-growing species. These include willows (genus Salix L.), native to Europe, Asia, America and Africa and found from the tundra to the tropics. Willow is successfully used as fuel in many countries, showing excellent growth and productivity even at juvenile stages and, under certain climatic conditions, having the highest capacity among woody plants to convert solar radiation into phytomass. Short-rotation willow plantations represent an ecologically promising energy resource for reducing greenhouse gas levels. Since the development of phytomass models is a laborious process, so-called “generic meta-models” are used. The aim of this study has been to construct generic models of both aboveground phytomass and phytomass fractions (foliage, branches, stem, roots) of willow trees based on meta-analysis of data. In the course of the work, the models have been constructed for assessing the aboveground phytomass of trees both in diameter at the stem base and in diameter at breast height, the information content of which is close to functional, and the biases are only about 2 %. Since each fraction of phytomass has a specific carbon-sequestering capacity and makes a different contribution to the carbon balance, generic models have been developed to estimate the mass of foliage, branches, stems and roots in relation to the aboveground phytomass of trees, explaining from 82 % (for foliage) to 99 % (for stems and roots) of the total variability of phytomass.

Propagating Uncertainty in Predicting Individuals and Means Illustrated with Foliar Chemistry and Forest Biomass

Quantifying uncertainty is important to establishing the significance of comparisons, to making predictions with known confidence, and to identifying priorities for investment. However, uncertainty can be difficult to quantify correctly. While sampling error is commonly reported based on replicate measurements, the uncertainty in regression models used to estimate forest biomass from tree dimensions is commonly ignored and has sometimes been reported incorrectly, due either to lack of clarity in recommended procedures or to incentives to underestimate uncertainties. Even more rarely are the uncertainty in predicting individuals and the uncertainty in the mean both recognized for their contributions to overall uncertainty. In this paper, we demonstrate the effect of propagating these two sources of uncertainty using a simple example of calcium concentration of sugar maple foliage, which does not require regression, then the mass of foliage and calcium content of foliage, and finally an entire forest with multiple species and tissue types. The uncertainty due to predicting individuals is greater than the uncertainty in the mean for studies with few trees—up to 30 trees for foliar calcium concentration and 50 trees for foliar mass and calcium content in the data set we analyzed from the Hubbard Brook Experimental Forest. The most correct analysis will take both sources of uncertainty into account, but for practical purposes, country-level reports of uncertainty in carbon stocks can safely ignore the uncertainty in individuals, which becomes negligible with large enough numbers of trees. Ignoring the uncertainty in the mean will result in exaggerated confidence in estimates of forest biomass and carbon and nutrient contents.

Age-Related Changes in the Ratios of the Components of Aboveground Phytomass of Forest-Forming Species of Eurasia

The assessment of phytomass, as the most important characteristic of forest ecosystems, plays a key role in monitoring the global carbon cycle and assessing the state of forests. In order for the species to achieve optimal productivity at the plant level, some proportionality between the functions and phytomass of its components must be ensured. The theory of optimal phytomass partitioning suggests that plants adapt the size of their organs not only to the external environment, but also to the physiological activity of various tissues. According to this theory, it has been established that the share of the component in the total phytomass (i.e., the relative phytomass of the component) is not constant: if in mature trees the largest share of phytomass falls on the stem and the smallest on the assimilation apparatus, then in seedlings the largest share of phytomass falls not on the stem, but on the assimilation organs. In order to establish the age at which the aforementioned trends change, the author’s database on the phytomass of trees belonging to the forest-forming genera of Eurasia was used. Models of changes in relative phytomasses for four coniferous and four deciduous forest-forming genera have been developed in relation to the age and the aboveground phytomass. Their contributions to the explanation of the variability of relative phytomass components amounted to 57–60 and 40–43%, respectively. It is established that with age the positive dependence of the relative phytomass of the stem upon the aboveground phytomass is replaced by a negative one, and the negative dependence of the relative phytomass of the branches is replaced by a positive one. The negative dependence of the relative foliage mass upon the aboveground phytomass by the age of maturity is leveled. The ages of the change of the positive or negative dependence of the relative phytomass of the components upon the aboveground phytomass by the opposite dependence in the studied age range have been established. However, the ages of the change of these rankings vary greatly in different genera, and further research is needed both to clarify the ages of the named shift and to clarify the reasons for such a significant variation. The obtained results showed that the relative phytomasses of the components change with age and phytomass in their interaction, i.e. there is a synergy of factors.

Radish management and grazing effects on weed control and corn response

AbstractPlanting cover crops (CCs) may improve soil health, protect from soil erosion, interrupt disease and pest cycles, minimize weed infestations, provide grazing opportunities, and increase commodity crop yields. In upstate Missouri, field research (2012 and 2013) evaluated the effect of tillage (reduced and no‐till), planting date (nonseeded, early, and late Sept.) of radish (Raphanus sativus L.), grazing (grazed and nongrazed radish) on winter annual weed control, and radish and corn (Zea mays L.) response. The experiment was a split–split plot design with grazed and nongrazed radish as the main plot, tillage as the subplot, and radish planting time as the sub‐subplot with four replicates. The results of this research during 2011–2012 were under extreme drought and 2012–2013 under flash drought conditions. Early planted radish produced greater tuber and foliage mass and reduced winter annual weed dry weights compared to late planting. Grazing in the autumn during dry years did not affect weed control and corn yield. The use of CCs during drought conditions can help alleviate forage shortages for livestock producers, but early planting of radish is critical for autumn grazing. Late‐planted radish treatments resulted in greater corn grain yield than the early planted radish and nonseeded control in 2013; however, there was no impact of planting date and tillage on corn yield in 2012. When planted early, weed control and winter‐kill characteristics of radish make it a favorable CC prior to corn, but radish growth was poor when planted following typical corn harvest dates in upstate Missouri.

Microwave-assisted drying of Cymbogopon nardus leaves: Kinetics, moisture diffusivity, energy, and emission study

The essential oils extracted from Cymbopogon nardus (C. nardus) leaves have a distinct fragrance containing citronellal, citronellol, and geraniol, which has led to their extensive use in the pharmaceutical and perfume industry. The potential of C. nardus might be limited by the short shelf life due to high moisture content, thus a drying process and kinetics analysis is vastly researched to preserve the beneficial compound longer. A microwave-assisted drying method in the present study was analysed by the calculation of the effective moisture diffusivity, activation energy, CO2 emission, and specific energy consumption (SEC) at various microwave power levels (136, 264, 440, and 616 W) and foliage leaf mass (5, 10, 15, 20, and 25 g). Through ten different drying kinetics model fitting and validated by five statistical parameters, Jena-Das model showed the best fit to the foliage drying at various mass and microwave powers. Effective moisture diffusivity was found to increase with microwave power and decrease with decreasing mass. The drying of C. nardus leaf resulted in Ea = 38.6299 Wg-1 in variation of microwave power and Ea = 9.1592 Wg-1 in variation of foliage mass. The lowest CO2 and SEC emissions were found at power of 616 W. Thus, according to mass variation, the lowest CO2 values are at 5 g mass and 20 g SEC. These findings may encourage the development of material analysis in industrial drying technologies to support the availability and quality of specific products.

Sub-continental-scale carbon stocks of individual trees in African drylands

The distribution of dryland trees and their density, cover, size, mass and carbon content are not well known at sub-continental to continental scales1–14. This information is important for ecological protection, carbon accounting, climate mitigation and restoration efforts of dryland ecosystems15–18. We assessed more than 9.9 billion trees derived from more than 300,000 satellite images, covering semi-arid sub-Saharan Africa north of the Equator. We attributed wood, foliage and root carbon to every tree in the 0–1,000 mm year−1 rainfall zone by coupling field data19, machine learning20–22, satellite data and high-performance computing. Average carbon stocks of individual trees ranged from 0.54 Mg C ha−1 and 63 kg C tree−1 in the arid zone to 3.7 Mg C ha−1 and 98 kg tree−1 in the sub-humid zone. Overall, we estimated the total carbon for our study area to be 0.84 (±19.8%) Pg C. Comparisons with 14 previous TRENDY numerical simulation studies23 for our area found that the density and carbon stocks of scattered trees have been underestimated by three models and overestimated by 11 models, respectively. This benchmarking can help understand the carbon cycle and address concerns about land degradation24–29. We make available a linked database of wood mass, foliage mass, root mass and carbon stock of each tree for scientists, policymakers, dryland-restoration practitioners and farmers, who can use it to estimate farmland tree carbon stocks from tablets or laptops.

ENVIRONMENTAL EFFECTS ON FOLIAGE FORMATION IN A TREE STAND AND METHODS FOR CALCULATING ITS MASS

The article reveals the role of environmental factors in foliage formation. For a given value of region-averaged climatic characteristics, the stand productivity depends on the forest site conditions, which predetermine the forest type and soil fertility. An increase (decrease) in the productivity of the stand is accompanied by a decrease (increase) in the specific mass of foliage. Changes in the specific mass of foliage when the productivity of the stand changes by 1 stand quality class in south Karelian conditions amount to an average of 5–20 % for a middle-aged stand, depending on the tree species. In a predominantly forested area, the growth and development of a tree stand of each forest type are constrained by energy availability. Changes in the specific mass of foliage are related to this factor. As the radiation balance grows in the north-to-south direction, the share of foliage in the stand increases, and the quality class of the forest type is improved accordingly. Greater changes happen in tree stands growing in better site conditions. As a result of these changes it may be that within the same stand quality class there will be more foliage in a stand growing under poorer site conditions but at higher radiation balance values. The quality class reaches a maximum where the radiation balance is 1400–1600 MJ/(m2 year). As a rule, the methods of calculating foliage mass use the tree stand valuation characteristics as the main parameters. To develop a foliage mass estimation method unified for different climatic and site characteristics in the given forest zone one should take into account the environmental factors and the forest type.

Belowground resource utilization in monocultures and mixtures of Scots pine and Norway spruce

Mixed forests have been recommended to replace monocultures, often being more productive and resilient ecosystems. Those benefits of species mixing have been suggested to be attributed to lower competition (above- and belowground) due to potential separation of resource acquisition strategies, yet a mechanistic understanding of belowground processes has largely been missing. We applied an isotopic-labelling technique using 15N and 2H at ~5 cm soil depth to study acquisition of two important resources, nitrogen (N) and water, in a replicated field experiment including mature Scots pine and Norway spruce monocultures and their mixture in boreal Sweden. Based on the isotopic data, we modelled distance-dependent N and water uptake and described the horizontal reach of active rooting areas around trees. The active root area for both N and water uptake in monocultures of both species was approximately 6–10 m2. Substantially wider areas were observed inside the mixture for N acquisition (27 m2 for pine and 21 m2 for spruce). Water was mainly acquired from within a 12–15 m2 area in mixture. The mixture and the pine monocultures exhibited similar recovery of the added 15N (3.8–4.5%) and its uptake per unit of foliage mass. The recovery of 15N for the spruce monocultures was generally lower (2.1%) but no difference was noted in the uptake per unit of foliage mass between spruce monoculture and mixture. No differences were found for recovery of 2H between the stand types. Mixing pine and spruce did not improve the resource uptake in comparison with the estimated theoretical mixture (according to the normalized basal area in monocultures). However, the mixing revealed significant differences between tree species whereas pines inside the mixture recovered 11.3-fold more 15N than accompanying spruce. Root overlap of 3–11 trees on 1 m2 was observed in all stand types, far exceeding the degree of canopy overlap. We discuss this overlap in terms of competition between individual trees. Spruces have proportionally larger horizontal rooting area relative to their aboveground size than pines. Scots pine and Norway spruce mixing in this type of boreal forest does not significantly enhance resource acquisition but leads to compensatory partitioning of growth, suggesting fierce interspecific competition, rather than niche separation.

A methodological approach for the assessment of basic crown parameters in Scots pine stands

Among other measurement techniques applied for the assessment of leaf area index, direct methods are still valued as the most accurate measures and often implemented as calibration tools. Even though more attention has been given to indirect measurements of tree crown properties in forest ecosystems over the last decades, the present study was designed to discuss the direct (destructive) and indirect (non-destructive) methods used for the assessment of crown measures in the stands defoliated from 20 to 90%. The stands with similar stand characteristics and representing relatively wide range of defoliation served as an appropriate target for the assessment of foliage mass variations.
 Overall, this study showed that the foliage mass or its surface area and defoliation at the stand level can be determined by the conventional methods used for the assessment of defoliation in forest monitoring programme as well as the PAR transmission methods. The findings showed that needle surface area decreased with the increase of tree defoliation; however, the changes of branch and stem surface areas were insignificant. Otherwise, the branch and shoot area contribute significantly to the total vegetation surface area at least in Scots pine stands. This study also strengthened the idea that the indirect measurement of vegetation area index underestimated vegetation area index at least in Scots pine stands defoliated less than 60%. The multivariate regression models were developed using tree diameter at breast height and tree crown defoliation ranges to estimate needle surface area. Keywords: Pinus sylvestris, crown defoliation, needle area index, regression model

The importance of accounting for enhanced emissions of monoterpenes from new Scots pine foliage in models - A Finnish case study

Models to predict the emissions of biogenic volatile organic compounds (BVOCs) from terrestrial vegetation largely use standardised emission potentials derived from shoot enclosure measurements of mature foliage. In these models, the potential of new foliage to emit BVOCs is assumed to be similar, or up to twice as high, as that of mature foliage, and thus new conifers foliage is predicted to have a negligible to minor contribution to canopy BVOC emissions during spring time due to the small foliage mass of emerging and growing needles. Extensive observations have, however, recently demonstrated that the potential of new Scots pine needles to emit several different BVOCs can be up to about 500 times higher than that of the corresponding mature foliage. Thus, we build on these discoveries and investigate the potential impact of considering these enhanced emissions from new Scots pine foliage on estimates of monoterpene emissions and new atmospheric aerosol particle formation and their subsequent growth. We show that the importance of taking the enhanced monoterpene emission potential of new Scots pine foliage into account decreases as a function of season, tree age and latitude, and that new foliage could be responsible for the majority of the whole tree's foliage emissions of monoterpenes during spring time, independently of tree age and location. Our results suggest that annual monoterpene emission estimates from Finland would increase with up to ~25% if the enhanced emissions from new Scots pine foliage were also considered, with the majority being emitted during spring time where also new particle formation has been observed to occur most frequently. We estimate that our findings can lead to increases in predictions of the formation rates of 2 nm particles during spring time by ~75–280% in northern Finland and by ~130–870% in southern Finland. Likewise, simulated growth rates of 2–3 nm particles would increase by ~65–180% in northern Finland and by ~110–520% in southern Finland if the enhanced emissions of monoterpenes from new Scots pine foliage were explicitly considered. Since only one measurement study (Aalto et al., 2014), on which our work builds, has so far found highly pronounced emissions of monoterpenes from new Scots pine foliage compared to those of mature, we conclude that more spring time measurements of new conifers foliage are required for improving emission algorithms in biogenic emission models. • In models, emission potentials of new and mature foliage are assumed to be similar. • VOCs emissions from new vs mature pine foliage can differ by 2–3 orders of magnitude. • Accounting for new foliage emissions significantly impacts annual emission estimates. • Enhanced springtime emissions can lead to enhanced aerosol formation and growth.

Can crown variables increase the generality of individual tree biomass equations?

Crown variables and height can improve biomass predictions and may help to quantify how tree biomass is influenced by inter-tree competition (stand density, species composition), climate, edaphic conditions, and age. Tree biomass is influenced by tree age, stand structural characteristics, and climatic and edaphic site factors. However, most allometric equations for predicting tree biomass do not quantify these effects and when these characteristics are included as variables, they typically only reflect the average or current conditions even though tree allometry is the result of past growing conditions as well. An alternative to using site and stand characteristics is to use tree variables that have been influenced by site and stand structure for the whole lifetime of the tree. The objective of this study was to compare stem diameter-only equations that predict above-ground biomass or foliage mass with equations that also contain a climatic variable (aridity index) and stand variables, such as age and basal area (as a proxy for competition), or equations containing another tree size variable, such as crown diameter, crown length and tree height. This was done using 348 trees from 24 sites and 10 Eucalyptus species in southern Australia. Stand basal area and age were significant in 2 of 23 final equations and the aridity index was not significant in any equations. Adding another tree size variable to the diameter-only equations reduced the bias and increased the precision in 6 of the final equations. This study shows that the addition of crown variables (or height) to diameter-only biomass equations can quantify some of the effects that site and stand structural characteristics have on biomass. Variables such as crown diameter and height could also be useful because they are easier to measure accurately using remote sensing methods than stem diameters and related stand structural characteristics, such as basal area.

Shifts in Foliage Biomass and Its Vertical Distribution in Response to Operational Nitrogen Fertilization of Douglas-Fir in Western Oregon

Nitrogen (N) fertilization is a commonly applied silvicultural treatment in intensively managed coast Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) plantations. Field trials were established in a randomized complete block design by Stimson Lumber Company (Gaston, Oregon), to test the economic viability of N fertilization on their ownership and to better understand Douglas-fir growth responses. The 23 stands comprising the trials were Douglas-fir dominated, had a total age of 16–24 years, had been precommercially thinned, and had a density of 386–1021 trees ha−1. Fertilizer was applied aerially at a rate of 224 kg N ha−1 as urea during the 2009–2010 dormant season. In the dormant season of 2016–2017, seven growing seasons following application, 40 trees were felled and measured with the objective of assessing crown attributes and aboveground allometrics. Branch-level foliage mass equations were developed from 267 subsampled branches and were applied to the 40 felled sample trees on which the basal diameter and height of all live branches were measured, allowing estimation of both the total amount of foliage and its vertical distribution. A right-truncated Weibull distribution was fitted to data, with the truncation point specified as the base of live tree crown. The resulting tree-level parameter estimates were modeled as functions of tree-level variables. Stand-level factors not explicitly measured were captured through the use of linear and nonlinear mixed-effects models with random stand effects. Fertilization resulted in more total crown foliage mass in the middle crown-third and caused a downward shift in the vertical distribution of foliage, with implications for feedback responses in crown development and photosynthetic capacity. Defining the morphological responses of Douglas-fir crowns to nitrogen fertilization provides a framework for studying influences on stand dynamics and should ultimately facilitate improved site-specific predictions of stem-volume growth.

Physiological Mechanisms of Foliage Recovery after Spring or Fall Crown Scorch in Young Longleaf Pine (Pinus palustris Mill.)

We hypothesized that physiological and morphological responses to prescribed fire support the post-scorch foliage recovery and growth of young longleaf pine. Two studies conducted in central Louisiana identified three means of foliage regrowth after fire that included an increase in the gas exchange rate of surviving foliage for 3 to 4 months after fire. Saplings also exhibited crown developmental responses to repeated fire that reduced the risk of future crown scorch. Starch reserves were a source of carbon for post-scorch foliage regrowth when fire was applied in the early growing season. However, the annual dynamics of starch accumulation and mobilization restricted its effectiveness for foliage regrowth when fire was applied late in the growing season. As such, post-scorch foliage regrowth became increasingly dependent on photosynthesis as the growing season progressed. Additionally, the loss of foliage by fire late in the growing season interrupted annual starch dynamics and created a starch void between the time of late growing season fire and mid-summer of the next year. The occurrence of drought during both studies revealed barriers to foliage reestablishment and normal stem growth among large saplings. In study 1, spring water deficit at the time of May fire was associated with high crown scorch and poor foliage and stem growth among large saplings. We attribute this lag in stem growth to three factors: little surviving foliage mass, low fascicle gas exchange rates, and poor post-scorch foliage recovery. In study 2, May fire during a short window of favorable burning conditions in the tenth month of a 20-month drought also reduced stem growth among large saplings but this growth loss was not due to poor post-scorch foliage recovery. Application of this information to prescribed fire guidelines will benefit young longleaf pine responses to fire and advance efforts to restore longleaf pine ecosystems.

EVAPORATION PATTERNS IN FORESTS OF DIFFERENT AGES, SITE CONDITIONS, AND PRODUCTIVITY LEVELS

The paper analyzes the factors behind evaporation from a forest: foliage and solar irradiance. The patterns of foliage formation and its changes with age in forests of varying productivity are demonstrated. The limiting factor for stand growth and development in each type of forest is the energy resources available. The average radiation balance of a region being given, the stand productivity depends on the characteristics of the locality, which influence soil fertility and predetermine the forest type. The southwards enhancement of the quality class of a forest type with a rise in the radiation balance is associated with the growing share of foliage and intensification of biochemical processes. The share of foliage mass in the total biomass of the tree stand depends on the forest site conditions, quality class, and energy supply. Previously designed techniques have been applied to calculate age-related patterns of evaporation from forest sites of varying habitat conditions and productivity in middle and southern taiga. As the radiation balance grows, physical evaporation from forest areas increases, and the growing share of foliage in the tree stand’s total biomass enlarges transpiration by the stand in every forest type and quality class. Alteration of site conditions entails a change in the age-related pattern of evaporation and transpiration by the stand. Enhancement of site conditions and quality characteristics leads to an increase in evaporation in young and middle-aged forests, however in mature and over-mature forests this trend may be broken. The greatest evaporation and transpiration by the stand are observed at an age when current biomass increment is the highest and the amount of foliage is at maximum. According to our calculations, the age of maximum annual total evaporation and transpiration varies from 50 to 100 years depending on the forest site conditions

Variability of summer apple tree varieties in 2019 by indicators of vegetative organs

The article presents the results of a study of annual shoots of large-fruited apple varieties, characterized by early ripening and consumer maturity, in the Botanical Garden named after Vs. M. Krutovsky. The leaf area, weight of 1 cm2 of leaf and 1 running centimeter of shoot in absolutely dry state are calculated. A significant positive correlation was revealed between the indicators of the area of the sheet and the mass of 1 cm2 of sheet in absolutely dry state, and between the mass of 1 linear cm shoot and 1 cm2 leaf. Using the regression method, it is possible to reduce labor costs for determining phytomass without resorting to additional measurements of the supply of dry foliage mass and to determine the increase in the mass of branches even in leafless periods. In Siberia, it is recommended to use the most promising varieties of apple trees in terms of photosynthetic activity and productivity for cultivation.

Crown architecture, crown leaf area distribution, and individual tree growth efficiency vary across site, genetic entry, and planting density

We examined crown architecture and within crown leaf area distribution effects on Pinus taeda L. growth in North Carolina (NC), Virginia (VA), and Brazil (BR) to better understand why P. taeda can grow much better in Brazil than in the southeastern United States. The NC, VA, and BR sites were planted in 2009, 2009, and 2011, respectively. At all sites, we planted the same two genetic entries at 618, 1236, and 1854 trees ha−1. In 2013, when trees were still open grown, the VA and NC sites had greater branch diameter (24%), branch number (14%), live crown length (44%), foliage mass (82%), and branch mass (91%), than the BR site. However, in 2017, after crown closure and when there was no significant difference in tree size, site did not significantly affect these crown variables. In 2013, site significantly affected absolute leaf area distribution, likely due to differences in live crown length and leaf area, such that there was more foliage at a given level in the crown at the VA and NC sites than at the BR site. In 2017, site was still a significant factor explaining leaf area distribution, although at this point, with crown closure and similar sized trees, there was more foliage at the BR site at a given level in the crown compared to the VA and NC sites. In 2013 and 2017, when including site, genetic entry, stand density, and leaf area distribution parameters as independent variables, site significantly affected individual tree growth efficiency, indicating that something other than leaf area distribution was influencing the site effect. Better BR P. taeda growth is likely due to a combination of factors, including leaf area distribution, crown architecture, and other factors that have been identified as influencing the site effect (heat sum), indicating that future work should include a modeling analysis to examine all known contributing factors.

Impact of Different Shading Levels on Growth, Yield and Quality of Potato (Solanum tuberosum L.)

In agroforestry systems (AFS), trees shade the understory crop to a certain extent. Potato is considered a shade-tolerant crop and was thus tested under the given total solar irradiance and climatic conditions of Southwestern Germany for its potential suitability in an AFS. To gain a better understanding of the effects of shade on growth, yield and quality; a three-year field experiment with different artificial shading levels (12%, 26% and 50%) was established. Significant changes in growth occurred at 50% shading. While plant emergence was not affected by shade, flowering was slightly delayed by about three days. Days until senescence also showed a delay under 50% shade. The number of tubers per plant and tuber mass per plant were reduced by about 53% and 69% under 50% shade. Depending on the year, tuber dry matter yield showed a decrease of 19–44% at 50% shade, while starch content showed no significant differences under shade compared to unshaded treatment. The number of stems per plant, plant height and foliage mass per plant as well as tuber fraction, black spot bruise and macronutrient content were unaffected. Overall, potato seems to tolerate shading and can therefore be integrated in an AFS, and can cope with a reduced total irradiance up to 26%.

Changes in rainfall distribution promote woody foliage production in the Sahel

Dryland ecosystems comprise a balance between woody and herbaceous vegetation. Climate change impacts rainfall timing, which may alter the respective contributions of woody and herbaceous plants on the total vegetation production. Here, we apply 30 years of field-measured woody foliage and herbaceous mass from Senegal and document a faster increase in woody foliage mass (+17 kg ha−1 yr−1) as compared to herbaceous mass (+3 kg ha−1 yr−1). Annual rainfall trends were partitioned into core wet-season rains (+0.7 mm yr-1), supporting a weak but periodic (5-year cycles) increase in herbaceous mass, and early/late rains (+2.1 mm yr−1), explaining the strongly increased woody foliage mass. Satellite observations confirm these findings for the majority of the Sahel, with total herbaceous/woody foliage mass increases by 6%/20%. We conclude that the rainfall recovery in the Sahel does not benefit herbaceous vegetation to the same extent as woody vegetation, presumably favoured by increased early/late rains.

Expanding networks of field hedges in densely populated landscapes in the Sahel

Changing woody plant density across agricultural landscapes of the Sudano-Sahelian region is a debated issue. This paper reports the results of an investigation on the contribution of field hedges to overall woody plant density. Hedges separating individual cropped parcels were studied within village agropastoral territories in the Dantiandou district in western Niger. In 1992, field hedges were mapped over the study area using aerial photography and in 2016, using high resolution Google Earth imagery. In 1992, field hedge length was equal to 1006 km within 435 km2 of croplands, equivalent to 2.3 km km−2. In 2016, 17.5% of these hedges had disappeared, but 1591 km of new hedges were observed resulting in an increased density of hedges to 5.6 km km−2. In 24 years, hedges had increased at a mean annual rate of 3.7% likely associated with the splitting of crop fields by inheritance.The composition and productivity of hedges were also monitored in 1996, 2010 and 2015. All trees (maximum height ≥ 4 m), shrubs (<4 m) and tussock perennial grasses were recorded within twelve field hedge samples of 200 m each. Field measurements were used to estimate basal area, crown area, foliage mass and wood mass of each woody plant within the sampled hedges. No significant trends were found between 1996 and 2015 in woody plant density, basal area, crown cover, wood and foliage masses across all monitored hedges. However, overall means hide a slight decrease in tree contributions, while shrub contributions first increased and then decreased. They also mask contradictory trends among sites most likely related to different rates of shrub coppicing and tree cutting. The woody species composition of the hedges is poor with an increase of Combretum glutinosum to the detriment of Guiera senegalensis over the study period.Multiplying the hedge sample statistics by the changing lengths of field hedges in the study area provides estimates of the contribution of the hedge woody plants to the woody plant population at a landscape scale. Between 1992 and 2016, field hedges contributed to increases of woody plant density by 3.9%, basal areas by 5.4%, crown cover by 2.7%, leading to 6.1% annual increase in foliage mass and 8.8% increase in wood mass.

Distribution of epicormic branches and foliage on Douglas-fir as influenced by adjacent canopy gaps

The influence of adjacent canopy gaps on spatial distribution of epicormic branches and delayed foliage (originating from dormant buds) was investigated in 65-year-old coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco). Sample trees were selected across a broad range of local densities (adjacent canopy gap sizes) from a repeatedly thinned stand in which gaps had been created 12 years prior to our study. Lengths and stem locations of original and epicormic branches were measured within the south-facing crown quadrant, along with extents to which branches were occupied by sequential (produced in association with terminal bud elongation) and (or) delayed foliage. Epicormic branches, while prevalent throughout crowns, contributed only 10% of total branch length and 2% of total foliage mass. In contrast, delayed foliage occupied over 75% of total branch length, accounted for nearly 39% of total foliage mass, and often overlapped with sequential foliage. Canopy gap size did not influence original or epicormic branch length or location. On original branches, larger gaps may have modestly negatively influenced the relative extent of sequential foliage on branches and (or) slightly positively influenced delayed foliage mass. Delayed foliage appears to contribute substantially to Douglas-fir crown maintenance at this tree age, but canopy gap size had a minor influence, at least in the short term.