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Papers by Frank Thomas

Basic and Applied Ecology, Nov 1, 2018

Forests are under pressure from accelerating global change. To cope with the multiple challenges ... more Forests are under pressure from accelerating global change. To cope with the multiple challenges related to global change but also to further improve forest management we need a better understanding of (1) the linkages between drivers of ecosystem change and the state and management of forest ecosystems as well as their capacity to adapt to ongoing global environmental changes, and (2) the interrelationships within and between the components of forest ecosystems. To address the resulting challenges for the state of forest ecosystems in Central Europe, we suggest 45 questions for future ecological research. We define forest ecology as studies on the abiotic and biotic components of forest ecosystems and their interactions on varying spatial and temporal scales. Our questions cover five thematic fields and correspond to the criteria selected for describing the state of Europe's forests by policy makers, i.e. biogeochemical cycling, mortality and disturbances, productivity, biodiversity and biotic interactions, and regulation and protection. We conclude that an improved mechanistic understanding of forest ecosystems is essential for the further development of ecosystem-oriented multifunctional forest management in the face of accelerating global change.

IAWA Journal, 2021

Wood density constitutes an integrative trait of water relations and growth. We compared the rece... more Wood density constitutes an integrative trait of water relations and growth. We compared the recently developed blue intensity (BI) method, which has only rarely been applied to tropical conifers, for determining wood density with anatomical analyses in studying the three rarely investigated palaeotropical pine species Pinus kesiya, P. dalatensis and P. krempfii, which co-occur in South-Central Vietnam, but differ in their distribution areas. For species comparisons, we also calculated the hydraulic conductivity of the xylem with the Hagen-Poiseuille equation and the water potential causing 50% loss of hydraulic conductivity () based on the anatomical analyses. We hypothesized (i) that the BI values are correlated with the cell wall fractions, the calculated hydraulic conductivity and the values; and (ii) that the wider occurrence of P. kesiya, which also can grow at drier sites, is reflected by higher wood density, lower hydraulic conductivity, lower (more negative) values and a sm...

Summary Durch Infiltration von Blittem von Phaseolus vulgaris L. cv. Molina kann eine lnterzellul... more Summary Durch Infiltration von Blittem von Phaseolus vulgaris L. cv. Molina kann eine lnterzellultire Waschfliissigkeit gewonnen werden, deren lo- nenzusammensetzung Rbckschlusse auf die Gehalte der Zellwand an ge- losten und austauschbaren lonen erlaubt. Mit der Verwendung geeigneter lnfiltrationsliisungen scheint eine Differenzierung zwischen WFS (Water Free Space) und gesamtem AFS (Apparent Free Space) moglich zu sein. Die gegebene Stickstofform beeinflu5t neben den lonen- Gesamtgehal- ten der Blatter auch die lonenzusammensetzung der Zellwbde: In WFS und gesamtem AFS tendieren Nitrat-emWe im Vergleich zu gemischt emhn Pflanzen zu hoheren Gehalten an zweiwertigen Kationen, die speziell auf h6here Calciumgehalte zuriickgehen. Der pH-Wert der Niihr- losung allein iibt keinen Einflu5 auf die Ionenzusammensetzung aus. Die gefundenen Unterschiede sind moglicherweise auf Kopplung des Calciurntranspom mit der Nitratverlagerung in den SproB zuriickzufiih- ren. Ausgehend von diesem Modell...

Journal of Plant Ecology, Aug 19, 2016

Aims Along central-Asian rivers in arid regions, lowering of the groundwater level constitutes a ... more Aims Along central-Asian rivers in arid regions, lowering of the groundwater level constitutes a major threat to the riparian forests, whose tree layers are dominated by Euphrates poplar (Populus euphratica). Some of these fragile ecosystems are supplied with additional ('ecological') water for protection and conservation. We investigated interrelationships among groundwater distance, stand structure and above-ground wood production (at the tree and the stand level) in P. euphratica stands along a groundwater gradient (distances of 2.0-12.0 m) that also included a plot supplied with 'ecological water'. Methods We measured the height, diameter at breast height and basal area of poplar trees and determined the annual above-ground wood production for the three most recent years on the basis of tree-ring analyses and allometric regressions at three sites at the upper, middle and lower reaches of the tarim River, Xinjiang, NW china. Important Findings the distribution of age classes differed significantly among the plots: in accordance with their life histories, stands growing at a larger distance to the groundwater harboured a larger fraction of old trees (>80 years) and, in most cases, a smaller fraction of young trees (≤20 years). the annual above-ground wood production per ha was highest on a plot with a short groundwater distance (2.0 m; maximum of the 3-year investigation period: 3.0 t ha −1 a −1) and lowest, at a plot with a large distance to the water table (6.6 m; minimum: 0.23 t ha −1 a −1). However, the plot located close to the groundwater (and to the river) at the middle reaches exhibited a relatively large interannual variation in above-ground wood production, which can be attributed to interannual variations in the river discharge. At the middle and the lower reaches, these interannual variations on plots with the most favourable water supply were even more obvious at the tree level. For the fraction of mature trees (60-99 years old), no significant differences in above-ground wood production were found between the plots with the most and the least favourable water supply. Overall, the productivity at the stand level was most closely correlated with the stand density (number of trees per ha, tree cover percentage). Productivity was negatively related to tree age, whereas groundwater distance alone was not a good predictor of above-ground wood production. In conclusion, vigorous growth of P. euphratica is possible at sites with groundwater distances of up to 12 m. Supply with 'ecological water' may be beneficial to trees growing at groundwater distances not larger than ~6 m. However, allocation of water should focus on stands with a short distance to the groundwater because only under these conditions, natural generative reproduction of the poplars is possible.

Forest Ecology and Management, Oct 1, 2015

ABSTRACT Populus euphratica (Euphrates poplar) is the dominant tree species of the riparian (“tug... more ABSTRACT Populus euphratica (Euphrates poplar) is the dominant tree species of the riparian (“tugai”) forests of Central Asia, which provide important ecosystem services to a rapidly growing population. However, overuse of the forests by wood harvest (pollarding) contributes markedly to their destabilisation. At the upper reaches of the Tarim River (Xinjiang, NW China), we investigated the effects of past pollarding (in the 1970s and 1980s) on the stand structure, tree morphology, stem diameter increment and intrinsic water use efficiency (iWUE) of poplars with different pollarding intensities in the past (‘No Use’, ‘Moderate’, ‘Intense’) growing on three adjacent plots with the same distance to the groundwater level. Compared to the non-used trees, the pollarded poplars (in particular, the intensely used trees) exhibited smaller figures of the following morphological variables: ratio of tree height to diameter at breast height, vertical crown extension, crown projection area, crown volume, and tree-ring width as well as basal area increment (BAI) during the past 24 years; but a higher number of secondary shoots, a higher percentage of hollow stems and a higher degree of hollowness of the stems. The pollarded trees were capable of regenerating to a certain extent, which was obvious from the formation of secondary shoots and, in the intensely pollarded trees, from a lower iWUE (inferred by more negative δ13C isotopic ratios of the tree rings; most probably due to higher rates of gas exchange) as well as from their capability of re-establishing a crown efficiency similar to non-pollarded trees. However, the BAI of the main trunk and the secondary branches of the pollarded trees decreased continuously during the last 24 years of investigation. Whilst moderate intensities of pollarding seem to be sustainable for the riparian P. euphratica forests, intense pollarding reduces the growth increment of the trees and, even more importantly, results in a distinct increase in the percentage of hollow stems, which can render the trees less stable and more susceptible to secondary damaging factors. The significant correlations between BAI and morphological variables of crown projection area and crown volume are promising for developing approaches to assess the productivity of P. euphratica stands on a landscape level using methods of remote sensing.

Journal of Arid Land, Sep 27, 2018

Many riparian (Tugai) forests growing along rivers in arid and hyper-arid regions of Central Asia... more Many riparian (Tugai) forests growing along rivers in arid and hyper-arid regions of Central Asia are dominated by the Euphrates poplar (Populus euphratica). Besides generative reproduction, which is only possible upon flooding events and at a distance to the groundwater of less than 2 m, this phreatophytic tree species also reproduces vegetatively by forming clones that can cover land surface areas of several hectares. Along a gradient of groundwater distances, we investigated whether the fraction of clones in P. euphratica stands (1) increases with increasing distance to the water table; (2) is higher if supplied with water via river cutoffs ; and (3) approaches 100% at a short distance to the groundwater, but at high salt concentrations in the upper soil layers, which would prevent germination and establishment of seedlings. AFLP (Amplified Fragment Length Polymorphism) analyses were conducted on leaf samples taken from mature P. euphratica trees growing at the fringes of the Taklimakan Desert in stands with different distances (2-12 m) to the groundwater at two plots at the middle and the lower reaches of the Tarim River and in a stand close to Ebinur Lake, Xinjiang, China. Genetic diversity was large among plots, but considerably smaller within plots. We found the highest genetic diversity (caused by regeneration from seeds) at plots that have a short distance to the groundwater or are supplied with additional water. There was no significant relationship between groundwater distance and clonal fraction. All investigated trees at the saline Ebinur Lake site belonged to one single clone. Our results demonstrate that the genetic pattern of this widespread species is not easily predictable even over small distances as it is a result of a complex interplay of stand history and dispersal of propagules (pollen, seeds, and vegetative diaspores) by wind and water. In conservation and restoration schemes, P. euphratica stands with a high genetic diversity and stands that grow at short distances to the water table and are regularly subjected to flooding (which favors generative over clonal reproduction) should be prioritized.

Plants

Against the background of climate change, we studied the effects of a severe summer drought on bu... more Against the background of climate change, we studied the effects of a severe summer drought on buds of European beech (Fagus sylvatica L.) saplings and on leaves formed during the subsequent spring in trees attributed to different drought-damage classes. For the first time, we combined assessments of the vitality (assessed through histochemical staining), mass and stable carbon isotope ratios (δ13C) of buds from drought-stressed woody plants with morphological and physiological variables of leaves that have emerged from the same plants and crown parts. The number, individual mass and vitality of the buds decreased and δ13C increased with increasing drought-induced damage. Bud mass, vitality and δ13C were significantly intercorrelated. The δ13C of the buds was imprinted on the leaves formed in the subsequent spring, but individual leaf mass, leaf size and specific leaf area were not significantly different among damage classes. Vitality and δ13C of the buds are suitable indicators of...

Die Beschreibungen des pflanzlichen Wasser- und Kohlenstoffhaushalts und der damit verbundenen ze... more Die Beschreibungen des pflanzlichen Wasser- und Kohlenstoffhaushalts und der damit verbundenen zentralen Lebensvorgange der Pflanzen nehmen in diesem Kapitel einen besonderen Raum ein. Besonders betont werden dabei die Zusammenhange zwischen Struktur und Funktion des Pflanzenkorpers und seiner Elemente. Erganzend werden Methoden zur Messung von Stoffwechselvorgangen vorgestellt. Komplettiert werden diese Darstellungen durch eine Ubersicht uber den Mineralstoffhaushalt der Pflanzen. Vor dem Hintergrund der beschriebenen Mechanismen werden Angepasstheiten von Pflanzen an die zentralen Standortsfaktoren Licht, Temperatur, Feuchtigkeit und Bodenfaktoren einschlieslich anthropogener Umweltveranderungen und die Eignung von Pflanzenarten als Bioindikatoren dargestellt.

Aufgrund geologischer, klimatischer und astronomischer Phanomene traten im Verlauf der Erdgeschic... more Aufgrund geologischer, klimatischer und astronomischer Phanomene traten im Verlauf der Erdgeschichte mehrmals deutliche Veranderungen der Umweltbedingungen auf, die sich in Form von Aussterbeereignissen und Evolutionsprozessen auch auf Pflanzen und die Vegetation auswirkten. Anthropogene Veranderungen von Vegetation und Okosystemen in Form von Landnutzungsanderungen in prahistorischer und historischer Zeit werden im Zusammenhang mit Ressourcenverbrauch und Nachhaltigkeit dargestellt. Besonders hervorgehoben werden Prozesse der Degradation von Boden und Vegetation und der Eutrophierung. Als Folgen der Industrialisierung werden Folgen der Emissionen von Schadgasen fur die Pflanzen und des Anstiegs der atmospharischen CO2-Konzentration sowie des damit einhergehenden Klimawandels hervorgehoben. Berucksichtigt werden auch Okosystemdienstleistungen fur die Menschen und Masnahmen zum Schutz von Pflanzen und ihren Lebensraumen einschlieslich nachhaltiger Landwirtschaft.

Dieses einfuhrende Kapitel gibt einen kurzen Uberblick uber die Entstehung und Entwicklung (pflan... more Dieses einfuhrende Kapitel gibt einen kurzen Uberblick uber die Entstehung und Entwicklung (pflanzen-)okologischer Fragestellungen bis zu den Arbeitsgebieten der modernen Pflanzenokologie und nennt historisch wichtige Personlichkeiten und die mit ihnen verbundenen Errungenschaften in diesem Bereich. Vor dem Hintergrund okologischer Grundprinzipien werden die Ebenen pflanzenokologischer Forschung und wichtige Forschungsmethoden dargestellt. Darauf aufbauend werden die Anforderungen an eine wissenschaftliche Hypothese und das Standardverfahren ihrer Uberprufung kurz beschrieben. Dazu werden zentrale Begriffe und Verfahren der Statistik summarisch prasentiert. Auf der Basis statistischer Methoden werden abschliesend wesentliche Kriterien der Planung und Durchfuhrung okologischer Untersuchungen benannt.

Proceedings of the National Academy of Sciences, 2020

Significance Climate change increases the frequency of drought events and leads to higher variabi... more Significance Climate change increases the frequency of drought events and leads to higher variability in precipitation. Drought impairs rhizosphere (root and the root-associated microbiome) functioning in trees and leads to a reduced assimilate supply belowground. It remains unclear if rhizosphere and thus whole-tree functioning can quickly recover after drought release. We show that rhizosphere metabolic activity in previously drought-exposed 100-y-old Scots pine increased in response to subtle soil moisture increases (induced by light rainfall). As a consequence of this activity change, the belowground allocation of new assimilates was immediately stimulated. Even light rainfall events can lead to a fast recovery of rhizosphere functioning and the increased C and energy demand is instantly met by altered whole-tree assimilate allocation.

Forest Ecology and Management, 2019

Upon the occurrence of acidic deposition-driven damage to forests at the beginning of the 1980s, ... more Upon the occurrence of acidic deposition-driven damage to forests at the beginning of the 1980s, large-scale liming has been applied to acidic forest sites in Germany. Due to possible negative consequences on soil chemistry and on (soil) fauna and flora, this measure was discussed highly controversially right from the beginning and is disputed until today. In investigations of liming effects on the forest understory vegetation, very few studies covered a time period of more than two decades with intermittent relevés. We analyzed relevés of the herbal understory on limed and control plots in one pine (Pinus sylvestris), one oak (Quercus robur), two European beech (Fagus sylvatica) and five Norway spruce (Picea abies) stands at permanent observation sites in southwestern Germany. These relevés had been repeatedly conducted during approximately 25 years. The number of herbal plant species was generally low. An increase in the herb layer's plant cover with time was found at six out of the nine study sites and was mainly due to spreading of two grass species (Milium effusum, Deschampsia flexuosa) and of the subshrub Vaccinium myrtillus, which might have benefitted from continuous nitrogen deposition. Only two species (Agrostis stolonifera, Stellaria media) with a main distribution in open landscapes were found in the years of investigation and their occurrence was restricted to only four sites and some few years. Across all sites, the average Ellenberg indicator values of nutrient (nitrogen) supply (N-values) were significantly increased on the limed plots ten years after liming, and at Year 10, the N-values of the limed plots were significantly higher than that of the control, presumably due to increased decomposition rates after liming. At the spruce sites, the average Ellenberg indicator values of soil reaction (R-values) of the limed plots 10 years after liming were significantly higher than at the beginning (Year 0) and at the end of the investigation (2013). We found no significant differences among the Ellenberg indicator values of light condition (L-values). In conclusion, liming had a significant, but only transient effect on the composition of the understory species. Therefore, our results do not support arguments against liming of acidic forests that are based on long-term changes in the herbal flora. In managed forests for wood production on acidic soils, liming can continue contributing to buffer the soils against ongoing acidification and accompanying cation leaching caused by anthropogenic deposition of nitrogen.

Grundzüge der Pflanzenökologie, 2018

Der Bau der Pflanzen steht in unmittelbarer Wechselwirkung mit ihrem Funktionieren und ihren Anpa... more Der Bau der Pflanzen steht in unmittelbarer Wechselwirkung mit ihrem Funktionieren und ihren Anpassungsleistungen an die Umwelt. Daher ist ein Grundverstandnis der pflanzlichen Strukturen wichtig, um okophysiologische und okologische Prozesse von der Ebene der Einzelpflanze bis zum Okosystem zu verstehen. Dieses Kapitel vermittelt einen Uberblick uber die wichtigsten organischen Stoffgruppen und Strukturen der Pflanzen sowie deren Evolution bis hin zur nacheiszeitlichen Verbreitung der Vegetationsformen Mitteleuropas, unter Einschluss von Methoden zur Rekonstruktion von Klima und Vegetation. Wesentliche Anpassungsleistungen an das Leben auf Landoberflachen werden besonders berucksichtigt. Das Kapitel schliest ab mit einer Darstellung der pflanzlichen Wuchs- und Lebensformen.

Journal of Arid Environments, 2017

Populus euphratica is a constitutive tree species of the mostly monospecific forests along Centra... more Populus euphratica is a constitutive tree species of the mostly monospecific forests along Central-Asian rivers. In the hyper-arid climate along the Tarim River, Xinjiang, NW China, these trees are phreatophytes with continuous access to the groundwater. Those poplar stands are often moderately to completely defoliated by Lepidopteran larvae in spring. In a P. euphratica stand at the middle reaches of the Tarim River, which grew close to the river and to the water table, we tested whether severe defoliation significantly reduces the trees' radial stem increment and their production of above-ground wood biomass even at ample water supply by the river. Tree-ring analyses and allometric regressions revealed a drastic decrease in radial stem increment and annual above-ground wood production upon complete defoliation even in a period of ample water supply, which otherwise would have allowed maximum productivity. The loss of above-ground production by herbivory amounted to approximately 44% relative to the high production rate of the year before complete defoliation. During the recent decade, however, only the amount of river discharge e but not the estimated intensity of defoliation e was (marginally) significantly correlated with the stem increment. We conclude that in P. euphratica forests growing close to the river and to the groundwater, tree growth is mainly related to the amount of river discharge, but can be significantly reduced in years with complete defoliation. Therefore, defoliation events should be considered in assessing the productivity of these riparian forests.

Flora, 2017

Populus euphratica, a constitutive tree species of the Central-Asian riparian forests, forms extr... more Populus euphratica, a constitutive tree species of the Central-Asian riparian forests, forms extremely heterophyllous leaves. Along gradients of salinity and water supply from the soil in arid regions of NW China, we tested whether specific leaf area (SLA), a pivotal plant functional trait, is related to other morphological variables and to the productivity of the trees as well as to important physiological variables (foliar concentrations or ratios of sodium (Na +), nutrients and stable isotopes of carbon (␦ 13 C) and oxygen (␦ 18 O)). We evaluated our data at the leaf, tree and stand level. Under the arid climate of the study area, we found large morphological variation among the leaves, which, however, converged to a range of SLA (4.7-12.5 m 2 kg −1 across 95% of the total sample size) that is small when compared to temperate deciduous forest trees of more humid regions. Correlations between SLA and morphological variables (leaf area, number of teeth at the leaf margin, ratio of blade width to blade length) were weak. However, SLA exhibited a significantly negative correlation with foliar ␦ 13 C, and a positive one, with tree height, annual above-ground wood production (AAWP) and (marginally) with stand density. SLA increased with increasing water supply from the soil within a given site but not across sites. Foliar Na + was negatively related to potassium concentration and, at two out of three study sites, positively to ␦ 18 O, but not to SLA, tree morphology, AAWP and stand density. AAWP was not related to nutrient concentrations. We conclude that in P. euphratica, a permanent phreatophyte in the study region, SLA constitutes an acclimatization not only to the water supply from the soil but also-and probably even more importantly-to the local transpirational demand; and that SLA is related to biomass production through optimization of the water use efficiency.

Dendrochronologia, 2017

Intra-annual analysis of wood samples by examination of xylem structure offers the possibility to... more Intra-annual analysis of wood samples by examination of xylem structure offers the possibility to reveal structural adaptations in the xylem of trees to varying climatic conditions with a high temporal resolution. Additionally, it can help closing the gap between annual tree ring width measurements and ecophysiological field studies. Typically, two approaches for intra-annual wood analyses are used: densitometry (x-ray or high frequency measurements) and analyses of microscopic images of cross-sections. While densitometry has recently become the most commonly used method, it requires expensive measurement devices, which are not necessarily part of standard laboratory equipment and accordingly not affordable for a significant number of researchers. We therefore present a new plugin for visualizing intra-annual density fluctuations (IADF) and, more specifically, for analyzing the theoretical volumetric flow rate with an adapted Hagen-Poiseuille law for elliptic conduits per pixel-column. The implemented algorithm represents an alternative for intra-annual analysis of microscopic cross-section images. The plugin has been developed for Fiji, a common package based on the open-source image processing program ImageJ to avoid the use of commercial programs for anatomical analyses.

Biogeochemistry, 2016

Biological nitrogen fixation is a key ecosystem function incorporating new nitrogen (N) during pr... more Biological nitrogen fixation is a key ecosystem function incorporating new nitrogen (N) during primary successions. Increasing evidence from tropical and northern temperate forests shows that phosphorus (P) and molybdenum (Mo) either alone or in combination limit the activity of free-living diazotrophs. In this study, we evaluated the effects of Mo, P, and carbon (C) addition, either singly or in combination, and moisture, on diazotrophic activity in a post-volcanic forest chronosequence in south-fentral Chile. Diazotrophic activity, both free-living (associated with fine litter) and symbiotic (associated with the moss Racomitrium lanuginosum and the cyanolichens Pseudocyphellaria berberina and P. coriifolia), was evaluated by incubation of samples and subsequent acetylene reduction assays conducted in the field and laboratory, in winter, spring and autumn of two consecutive years. Results showed that diazotrophic activity varied with the season of the year (lowest during the drier spring season), successional stage (highest in the maximal stage), and N-fixer community type (highest in symbiotic diazotrophs). In general, C?P?Mo limitation was documented for heterotrophic diazotrophs and P?Mo limitation for symbiotic diazotrophs. Limitation of diazotrophic activity was not associated with soil nutrient and C status in the chronosequence. Strong inhibition of diazotrophic activity by high N addition and by low moisture suggests that reductions in precipitation expected for south-central Chile under climate change, as well as increasing inputs of reactive N from atmospheric deposition due to increasing use of N fertilizers, may drastically alter the composition and functional role of cryptogamic assemblages in native forests.

Chinese Journal of Plant Ecology, 2003

Earth System Dynamics Discussions, 2014

The Tarim River Basin, located in Xinjiang, NW China, is the largest endorheic river basin of Chi... more The Tarim River Basin, located in Xinjiang, NW China, is the largest endorheic river basin of China and one of the largest in whole Central Asia. Due to the extremely arid climate with an annual precipitation of less than 100 mm, the water supply along the Aksu and Tarim River solely depends on river water. This applies for anthropogenic activities (e.g. agriculture) as well as for the natural ecosystems so that both compete for water. The on-going increase of water consumption by agriculture and other human activities in this region has been enhancing the competition for water between human needs and nature. Against this background, 11 German and 6 Chinese universities and research institutes formed the consortium SuMaRiO (<a href="www.sumario.de"target="_blank">www.sumario.de</a>), which aims at gaining a holistic picture of the availability of water resources in the Tarim River Basin and the impacts on anthropogenic activities and natural ecosystem...

Journal of Plant Nutrition and Soil Science, 2011

Intercropping is an important and widespread land-management system in the tropics. At two agricu... more Intercropping is an important and widespread land-management system in the tropics. At two agricultural sites in Central Kenya differing in elevation and soil type Haplic Nitisols (eutric) and Vitric Gleysols (eutric, epiclayic, endoclayic), we investigated the vertical root distributions using the trench wall profile method in single-crop systems of maize (Zea mays L.) and in intercropping systems of maize and legumes (common bean, Phaseolus vulgaris L.; pigeon pea, Cajanus cajan [L.] Millsp.) to test for possible differences in the use of water and nutrient resources. The physico-chemical soil properties of the sites were similar and imposed no restrictions to the vertical growth of the roots into soil depths of 1.4 m. The vertical distributions of the fine roots (∅ 0.5-2 mm) and very fine roots (∅ < 0.5 mm) were quantified by calculating the parameter b which was computed from the cumulative fraction (Y) of the root densities along the depth (d) of the soil profiles (Y = 1b d). We found no consistent differences between the single-crop and the intercropping systems in the rooting depth down to 1.4 m. However, higher b values for fine roots of the intercropping systems were indicative of a more homogeneous vertical root distribution than in the single-crop fields. In the intercropping fields, 50% of the total number of fine roots were distributed over the uppermost 36 cm of the soil, whereas in the single-crop fields, 50% of the fine roots were concentrated in the uppermost 15-21 cm. Medium-sized roots (∅ > 2-5 mm) were detected in the intercropping fields only. The more homogeneous root distribution in the intercropping fields likely indicates a more efficient use of the limited resources nutrients and water.