Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Frankincense in peril
Bongers, Frans ; Groenendijk, Peter ; Bekele, Tesfaye ; Birhane, Emiru ; Damtew, Abebe ; Decuyper, Mathieu ; Eshete, Abeje ; Gezahgne, Alemu ; Girma, Atkilt ; Khamis, Mohamed A. ; Lemenih, Mulugeta ; Mengistu, Tefera ; Ogbazghi, Woldeselassie ; Sass-Klaassen, Ute ; Tadesse, Wubalem ; Teshome, Mindaye ; Tolera, Motuma ; Sterck, Frank J. ; Zuidema, Pieter A. - \ 2019
Nature Sustainability 2 (2019). - ISSN 2398-9629 - p. 602 - 610.
The harvest of plant parts and exudates from wild populations contributes to the income, food security and livelihoods of many millions of people worldwide. Frankincense, an aromatic resin sourced from natural populations of Boswellia trees and shrubs, has been cherished by world societies for centuries. Boswellia populations are threatened by over-exploitation and ecosystem degradation, jeopardizing future resin production. Here, we reveal evidence of population collapse of B. papyrifera—now the main source of frankincense—throughout its geographic range. Using inventories of 23 populations consisting of 21,786 trees, growth-ring data from 202 trees and demographic models on the basis of 7,246 trees, we find that over 75% of studied populations lack small trees, natural regeneration has been absent for decades, and projected frankincense production will be halved in 20 yr. These changes are caused by increased human population pressure on Boswellia woodlands through cattle grazing, frequent burns and reckless tapping. A literature review showed that other Boswellia species experience similar threats. Populations can be restored by establishing cattle exclosures and fire-breaks, and by planting trees and tapping trees more carefully. Concerted conservation and restoration efforts are urgently needed to secure the long-term availability of this iconic product.
Status of introduction and distribution of fodder seeds and planting materials in selected districts of Amhara, Oromia, SNNP and Tigray Regional States
Tolera, Adugna ; Vernooij, Adriaan ; Berhanu, Tinsae - \ 2019
Wageningen : Wageningen Livestock Research (Wageningen Livestock Research report 1152) - 45
Dairy Input Service Delivery System By Lead Farm To Dairy Farmers For The Improvement Of Dairying In Three Zones Of Oromia, Ethiopia
Tolera, Degu ; Merera, Chala ; Gelmessa, U. ; Lee, J. van der; Ndambi, O.A. - \ 2018
International Journal of Advanced Research and Publications (2018). - ISSN 2456-9992 - p. 12 - 19.
Excessive pruning and limited regeneration: Are Faidherbia albida parklands heading for extinction in the Central Rift Valley of Ethiopia?
Sida, Tesfaye Shiferaw ; Baudron, Frédéric ; Deme, Dejene Adugna ; Tolera, Motuma ; Giller, Ken E. - \ 2018
Land Degradation and Development 29 (2018)6. - ISSN 1085-3278 - p. 1623 - 1633.
Scattered Faidherbia albida trees provide multiple ecological and production benefits across the Sahel. The intensive management and use of this important tree may impede its regeneration. Regeneration bottlenecks were explored and population dynamics modelled. On experimental plots in which seed of F. albida was sown, exposure to the first 2 months of dry season resulted in a quarter of seedling mortality. Exposure to season‐long free grazing and browsing caused significantly greater seedling mortality. Results from monitoring 100 permanent plots scattered over the landscape showed that adult population density was 4.2 ± 0.3 (mean ± SE) trees ha−1 and dominated by old age classes. Sixty percent of the total population were older than 30 years. The mean density for juveniles was 1.4 ± 0.2 (mean ± SE) individuals ha−1. The annual rates of decline were 1.2%, 51.3%, and 63.2% for adults, seedlings, and saplings, respectively. Our model predicted that the F. albida population will start to decline within 1–2 decades to eventually fall below 1 tree ha−1 within 60 years under current management. The model highlighted that the limited seed source, caused by excessive pruning, was the main constraint for recruitment. Appropriate land management policy to ensure adequate seed production would avert current trends in decline of F. albida population.
Transforming smallholder dairy farms : The role of lead farms in Ethiopia
Ndambi, O.A. ; Lee, J. van der; Wassink, Gerko ; Tolera, Degu ; Merera, Chala ; Galmessa, Ulfina ; Andeweg, K. - \ 2017
Wageningen University & Research (Practice Brief DairyBISS project ) - 4 p.
Response of woody plant species diversity and tree growth in exclosure to spate irrigation from gullies
Etefa Guyassa, Dinssa ; Frankl, Amaury ; Amanuel, Zenebe ; Abebe, Damtew ; Descheemaeker, K.K.E. ; Tolera, Motuma ; Poesen, J. ; Nyssen, J. - \ 2017
In: Book of abstracts European Conference of Tropical Ecology 2017. - German Society for Tropical Ecology - ISBN 9783000556319 - p. 204 - 204.
From runoff contributor to runoff absorber : spate irrigation on exclosures in Tigray, northern Ethiopia
Etefa Guyassa, ; Frankl, A. ; Abebe, Damtew ; Amanuel, Zenebe ; Jacob, M. ; Tolera, Motuma ; Abebe, Damtew ; Descheemaeker, K.K.E. ; Poesen, J. ; Nyssen, J. - \ 2017
The frankincense tree Boswellia neglecta reveals high potential for restoration of woodlands in the Horn of Africa
Mokria, Mulugeta ; Tolera, Motuma ; Sterck, Frank J. ; Gebrekirstos, Aster ; Bongers, Frans ; Decuyper, Mathieu ; Sass-Klaassen, Ute - \ 2017
Forest Ecology and Management 385 (2017). - ISSN 0378-1127 - p. 16 - 24.
Boswellia neglecta S. Moore is a frankincense-producing tree species dominantly found in the dry woodlands of southeastern Ethiopia. Currently, the population of this socio-economically and ecologically important species is threatened by complex anthropogenic and climate change related factors. Evaluation of tree age and its radial growth dynamics in relation to climate variables helps to understand the response of the species to climate change. It is also crucial for sustainable forest resource management and utilization. Dendrochronological and remote-sensing techniques were used to study periodicity of wood formation and leaf phenology and to assess the growth dynamics of B. neglecta. The results show that B. neglecta forms two growth rings per year in the study area. The growth ring structure is characterized by larger vessels at the beginning of each growing season and smaller vessels formed later in the growing season, suggesting adaptation to decreasing soil moisture deficits at the end of the growing season. Seasonality in cambial activity matches with a bimodal leaf phenological pattern. The mean annual radial growth rate of B. neglecta trees is 2.5 mm. Tree age varied between 16 and 28 years, with an average age of 22 years. The young age of these trees indicates recent colonization of B. neglecta in the study region. The growth rate and seasonal canopy greenness (expressed by Normalized Difference Vegetation Index – NDVI) were positively correlated with rainfall, suggesting that rainfall is the main climatic factor controlling growth of B. neglecta. The observed temporal changes in leaf phenology and vessel size across the growth rings indicate that the species is drought tolerant. Therefore, it can be regarded as a key tree species for restoration of moisture-related limited areas across the Horn of Africa.
Understanding producers' motives for adopting sustainable practices : The role of expected rewards, risk perception and risk tolerance
Trujillo-Barrera, Andres ; Pennings, Joost M.E. ; Hofenk, Dianne - \ 2016
European Review of Agricultural Economics 43 (2016)3. - ISSN 0165-1587 - p. 359 - 382.
Motivation for adoption of sustainability - Risk perception - Risk tolera

Understanding the motives and risk attitudes of producers to engage in sustainable practices is important for policy-makers who wish to increase the likelihood of adoption and improve the design of incentives. This article examines the underlying motives of producers to adopt sustainable practices. We focus on expected economic, social and personal rewards and analyse the role of producers' financial risk perception and risk tolerance. Results from personal interviews with 164 hog producers show that the adoption of sustainable practices is affected by expected economic rewards but not by social and personal rewards. Further, while perceived risk is a barrier to the adoption of sustainable practices, risk tolerance is a positive moderator of the relationship between economic rewards and adoption. In addition, perceived tax benefits and turnover have a significant positive relationship with adoption, while education and age do not play a role.

Frankincense yield is related to tree size and resin-canal characteristics
Tolera, Motuma ; Sass-Klaassen, Ute ; Eshete, Abeje ; Bongers, Frans ; Sterck, Frank - \ 2015
Forest Ecology and Management 353 (2015). - ISSN 0378-1127 - p. 41 - 48.
Boswellia papyrifera - Frankincense - Path analysis - Resin canals - Tapping - Tree characteristics

Boswellia papyrifera Hochst. is the most important global source of frankincense. Tree numbers are rapidly decreasing in many populations of B. papyrifera in Ethiopia, where most of the internationally traded frankincense comes from. Improper tapping is among the frequently mentioned reasons for this decrease within populations. We still lack sustainable techniques for frankincense tapping, and these techniques are not yet tuned to individual trees since we are unaware how tree characteristics influence frankincense yield. This study investigates the relationships between different tree characteristics and their relation to frankincense yield. We selected 53 trees and measured frankincense yield and their DBH, tree age, number of leaf apices, radial growth, bark thickness, total resin-canal area, and total number of resin canals in a cross-section. Regression and path analysis were used to unravel cause-effect relationships between tree characteristics and frankincense yield. Frankincense yield was independent of the actual radial growth rate, but increased with increasing total resin-canal area in the bark, stem diameter, tree age, and the number of leaf apices. We show that frankincense yield by trees is not only a simple function of tree size. Remarkably, trees that grew slower over their whole life history produced more frankincense, suggesting an intra-specific trade-off in growth rate and frankincense production. Overall, this study thus shows that frankincense production is the result of complex plant trait networks and long term tree life properties. The results contribute to management regimes that minimize the damage to trees, while maximizing benefits in terms of frankincense yield and can also be used for selection and propagation of trees which are well suited for frankincense production.

Chemical composition and in vitro total gas and methane production of forage species from the Mid Rift Valley grasslands of Ethiopia
Bezabih, M. ; Pellikaan, W.F. ; Tolera, A. ; Khan, N.A. ; Hendriks, W.H. - \ 2014
Grass and Forage Science 69 (2014)4. - ISSN 0142-5242 - p. 635 - 643.
feed-intake - production profiles - southern ethiopia - detergent fiber - ruminant feeds - zebu cattle - rumen fluid - fermentation - protein - degradability
There is increasing interest in sustainable land use in the tropics to optimize animal production while also reducing methane (CH4) emissions, but information on nutritive value and CH4-emission potential of tropical forage species is limited. Samples of 24 grasses and five other forages were collected during the main rainy season on randomly positioned quadrats in semi-arid grassland in the Mid Rift Valley of Ethiopia. Samples were pooled by species, analysed for chemical composition and incubated with rumen fluid to determine total gas and CH4-emission potentials using a fully automated in vitro gas production apparatus. Organic matter digestibility (OMD) and metabolizable energy (ME) contents were calculated from chemical composition and gas production data. Large variability was observed among forages for all nutritional variables considered. The grasses Eleusine multiflora, Pennisetum stramineum, Dactyloctenium aegyptium, Eragrostis aspera, Cenchrus ciliaris and Eragrostis cilianensis showed relatively high OMD (68–72%) and ME values (9 1– 10 2 MJ kg 1 dry matter). Melinis repens, E. multiflora and the non-legume forb Zaleya pentandra showed relatively low CH4 to total gas ratios; these species may have potential for use in low CH4-emission forage diets. Acacia tortilis fruits had high content of crude protein and moderate ME values, and may be an ideal feed supplement for the grazing ruminant. Sodium content was below the recommended level for ruminants in all the forage species. Overall, the pasture stand during the main growing season was evaluated as having moderate nutritional quality.
Nutritional status of cattle grazing natural pasture in the Mid Rift Valley grasslands of Ethiopia measured using plant cuticular hydrocarbons and their isotope enrichment
Bezabih, M. ; Pellikaan, W.F. ; Tolera, A. ; Khan, N.A. ; Hendriks, W.H. - \ 2014
Livestock Science 161 (2014). - ISSN 1871-1413 - p. 41 - 52.
n-alkanes - diet selection - compensatory growth - southern ethiopia - mineral status - feed-intake - botanical composition - mammalian herbivores - tropical forages - detergent fiber
The seasonal diet composition, digestibility and nutrient intake of cattle grazing on natural pasture in the Mid Rift valley region of Ethiopia were determined using an improved n-alkanes method. Sixteen local Borana and Arsi cattle (8 bulls and 8 heifers, 175±10 kg weight) were randomly selected from herds at two sites; a moderately grazed ranch and a heavily grazed, communal grassland area. Grazing behaviour was observed and herbage species consumed sampled during five periods (early-dry, dry, short-rainy, main-rainy and end-of-rainy seasons) throughout the year at the two grazing sites. During each period, animals were dosed twice daily with 152±4 mg of C32 and 150±3 mg C36 alkanes for 10 consecutive days, with faeces samples collected in the morning during the last five days to determine dry matter intake (DMI).The proportion of consumed herbage species in the diet was determined using n-alkanes and their carbon isotope enrichments as markers, while the energy and nutrient intakes were derived from the DMI, digestibility, and diet composition of the DM consumed. Marked seasonal variations (P
Dendrochronology and bark anatomy of the frankincense tree
Tolera Feyissa, M. - \ 2013
Wageningen University. Promotor(en): Frans Bongers, co-promotor(en): Ute Sass-Klaassen; Frank Sterck. - S.l. : s.n. - ISBN 9789461736444 - 136
boswellia - dendrochronologie - groei - plantenanatomie - harsgangen - boswellia - dendrochronology - growth - plant anatomy - resin canals

Boswellia papyrifera(Burseraceae) trees grow in drylands south of the Sahara. In Ethiopia, it grows in seasonally dry Combretum-Terminalia woodlands. It is a source of frankincense, an economically important olio-gum resin used for cultural and religious ceremonies throughout the world and as raw material in several industries. Ethiopia is a major exporter of frankincense. Currently, the populations of this species are threatened by farmland expansion, fire, overgrazing, improper tapping techniques and possibly also by climate change. Focussing on tree ring analyses and resin-production related bark anatomical features, this study had two objectives.

The first objective was to quantify the status of B. papyrifera populations with respect to radial stem-growth dynamics and size and age structure. Based on analysis of wood structure and crossdating of tree-rings series, it is shown that B. papyriferaforms annual growth rings and that the average age of sampled B. papyrifera trees is 76 years.More importantly, it is shown that the B. papyrifera populations lack trees that recruited over the last 55 years (1955-2010), and that the remnant trees established continuously between 1903 and 1955. This lack of successful recruitment for such a long period of time is attributed to continuous disturbances, such as fire and grazing accompanying new settlements of people into the area over the past decades. Radial growth patterns over decades suggest effects of heavy disturbances that the trees were experiencing. Remarkably, B. papyrifera trees showed a 2-3 year cycle in annual radial growth, and responded significantly to climate. As expected, radial growth increased with rainfall. An increase in ring width with maximum temperature may reflect radiation limits on growth. Radial growth decreased with increasing minimum temperatures, which may reflect temperature impacts on respiration. Overall, the predicted increase in temperature and rainfall for Ethiopia may not pose a direct threat for this species.

The second objective of this study was to describe the resin-secretory structure in the bark of B. papyrifera. The aim was to understand the relationship between structure and functioning of the secretory system with special reference to implications for frankincense yield and improvements of current tapping techniques. Resin canals of B. papyrifera form a three-dimensional network within the inner bark. In the wood, only few radial resin canals were encountered. The intact resin-producing and transporting network is on average limited to the inner 6.6 mm of the inner bark. Within the inner bark, the density of non-lignified axial resin canals decreases from the vascular cambium towards the outer bark. We also show that whole tree properties, such astotal resin-canal area in the bark, stem diameter, tree age, and the number of leaf apices impact frankincense yield.

Finally, this study provides recommendations for improving the existing tapping practice, aiming at maximization of frankincense yield at minimum damage costs to the trees. The new insights can also be used for selection and propagation of trees which are well suited for frankincense production. The information generated in this study is vital for planning sustainable management of the remnant trees and populations of B. papyrifera and the widely demanded frankincense.

Frankincense tree recruitment failed over the past half century
Tolera Feyissa, M. ; Sass, U.G.W. ; Eshete, A. ; Bongers, F. ; Sterck, F.J. - \ 2013
Forest Ecology and Management 304 (2013). - ISSN 0378-1127 - p. 65 - 72.
annual growth rings - long-term growth - dry-forest trees - boswellia-papyrifera - pterocarpus-angolensis - population-dynamics - age-determination - acacia-erioloba - seed predation - tropical trees
Boswellia papyrifera (Burseraceae) trees grow in dry woodlands south of the Sahara and produce frankincense, the economically important olio-gum resin used for cultural and religious ceremonies throughout the world and as raw material in several industries. Across its distribution area, this species is threatened by farmland expansion, fire, improper tapping and overgrazing. Most of its populations lack saplings and small-sized trees (e.g.
Nutrition of grazing cattle in the Mid Rift Valley of Ethiopia: use of an improved n-alkane method to estimate nutrient intake
Derseh, M.B. - \ 2013
Wageningen University. Promotor(en): Wouter Hendriks, co-promotor(en): Wilbert Pellikaan; A. Tolera. - S.l. : s.n. - ISBN 9789461734686 - 160
rundvee - begrazing - weiden - merkers - voedingsstoffenopname (mens en dier) - voedselsamenstelling - voedingswaarde - verteerbaarheid - ruwvoer (roughage) - diervoeding - ethiopië - cattle - grazing - pastures - markers - nutrient intake - food composition - nutritive value - digestibility - roughage - animal nutrition - ethiopia

Nutrient intake is an important factor that determines the performance of production animals. In free ranging animals, direct measurement of nutrient intake is difficult to conduct, and it is frequently estimated indirectly by the aid of markers. The aim of this thesis was to investigate the potential of using cuticular n-alkanes and their carbon isotope enrichments (δ13C) as markers to study the nutritional ecology of grazing animals under tropical conditions. In addition, this improved method was used to determine the seasonal patterns of nutrient intake and diet composition of grazing cattle in the Mid Rift Valley grasslands of Ethiopia. The first focus of the thesis was to quantify the interspecies variability in the n-alkane profile and δ13C values of alkanes among commonly available pasture species in the Mid Rift Valley of Ethiopia. The analysis showed that the variability is sufficiently large to allow n-alkane and their δ13C values to be used as diet composition markers, with a combined use of the two increasing the discriminatory power. Faecal recovery of dosed and natural alkanes in cattle consuming low-quality tropical roughages was investigated in an indoor balance study. The recovery of synthetic alkanes dosed in the form of molasses boluses was considerably higher than adjacent natural odd-chain alkanes, and correction appears necessary when intake is estimated with the double n-alkane method. The next focus of the thesis was to generate information on the nutritive value of pasture species and nutritional status of grazing cattle in the region. Large variability was observed in the nutritive value and methane production potential of pasture species as evaluated in vitro, with scope for selection of genotypes with high nutritive value and low methane production potential for a sustainable pastureland management. The nutritional status of grazing cattle measured using a combination of n-alkanes, their δ13C values and visual observations showed that diet composition and nutrient intake of the animals is highly dependent on rainfall patterns, with a cyclic positive (wet period) and negative (dry period) energy and nutrient balance observed over the grazing seasons. Energy intake was more limiting than crude protein for body weight gain in most of the grazing seasons. While mature and non-producing animals appeared to tolerate nutritional restriction in the dry period and regain lost body condition in the following wet periods, young animals before the age of puberty may need supplementary feeding. Furthermore, concentrate supplementation of finishing animals needs to coincide with the onset of the wet season to take advantage of compensatory growth. In conclusion, the n-alkanes method coupled with isotope enrichment in n-alkanes and visual observations as used in the present study can provide realistic nutritional data for free-ranging cattle which correlates well with changes in body conditions.

Resin secretory structures of Boswellia papyrifera and implications for frankincense yield
Tolera, M. ; Menger, D. ; Sass, U.G.W. ; Sterck, F.J. ; Copini, P. ; Bongers, F. - \ 2013
Annals of Botany 111 (2013)1. - ISSN 0305-7364 - p. 61 - 68.
timber forest product - northern ethiopia - norway spruce - metema district - bark anatomy - tree size - conifers - biosynthesis - canals - plants
Frankincense, a gum-resin, has been tapped from Boswellia papyrifera trees for centuries. Despite the intensive tapping and economic interest of B. papyrifera, information on the resin secretory structures, which are responsible for synthesis, storage and transport of frankincense, is virtually absent. This study describes the type, architecture and distribution of resin secretory structures of B. papyrifera and its relevance for the ecophysiology and economic use of the tree. The type and architecture of resin secretory structures present in bark and wood was investigated from transversal, tangential and radial sections of bark and wood samples. The diameter and density (number of resin canals mm(2)) of axial resin canals were determined from digital images of thin sections across the different zones of inner bark. Resin canals form a three-dimensional network within the inner bark. Yet, the intact resin-conducting and producing network is on average limited to the inner 66 mm of the inner bark. Within the inner bark, the density of non-lignified axial resin canals decreases and the density of lignified resin canals increases from the vascular cambium towards the outer bark. In the wood, only radial resin canals were encountered. Frankincense tapping techniques can be improved based on knowledge of bark anatomy and distribution and architecture of resin secretory structures. The suggested new techniques will contribute to a more sustainable frankincense production that enhances the contribution of frankincense to rural livelihoods and the national economy.
Estimation of feed intake and digestibility in cattle consuming quality tropical roughage diets using molasses-based n-alkane boluses
Derseh, M.B. ; Pellikaan, W.F. ; Tolera, A. ; Hendriks, W.H. - \ 2012
Animal Feed Science and Technology 177 (2012)3-4. - ISSN 0377-8401 - p. 161 - 171.
dry-matter intake - herbage intake - vegetation communities - detergent fiber - sheep - markers - accuracy - pasture - validation - nutrition
A feeding experiment was conducted to measure the faecal recovery rates of n-alkanes and to evaluate molasses-based alkane boluses for feed intake and digestibility estimations in cattle consuming low-quality tropical roughages. The experiment was performed in a cross-over design with four experimental diets, four 21-day feeding runs and eight bulls. The animals received a measured amount of the experimental diets that resulted in little refusal throughout the experiment. After seven days of adaptation, the animals were dosed with molasses-based alkane boluses (each containing 200 g C32 and 150 g C36) twice daily at 07:00 and 18:00 h. Concurrent with the alkane dosing, faecal spot samples were taken twice daily until the end of each run. In addition, total faecal collections were performed over the last 5 days of each run. The mean faecal recovery rate of both natural and dosed n-alkanes ranged between 0.61 and 0.86, with the recovery showing an upward trend with increasing carbon-chain length. The recovery rate of dosed alkanes was considerably higher than that of adjacent odd-chain alkanes. Whilst diets did not differ (P=0.23) in the recovery of even-chain n-alkanes, an effect of diet (P=0.01) was observed in the recovery of odd-chain n-alkanes. The faecal concentration of dosed alkanes reached equilibrium 3.30 days into the alkane dosing. On the assumption of similar faecal recovery of adjacent n-alkanes, intake was underestimated by 12% (P
Evaluation of n-alkanes and their carbon isotope enrichments (d13C) as diet composition markers
Derseh, M.B. ; Pellikaan, W.F. ; Tolera, A. ; Hendriks, W.H. - \ 2011
Animal 5 (2011)1. - ISSN 1751-7311 - p. 57 - 66.
plant wax components - chain fatty alcohols - cuticular wax - mammalian herbivores - domestic herbivores - herbage intake - sheep - selection - pasture - cattle
Plant cuticular n-alkanes have been successfully used as markers to estimate diet composition and intake of grazing herbivores. However, additional markers may be required under grazing conditions in botanically diverse vegetation. This study was conducted to describe the n-alkane profiles and the carbon isotope enrichment of n-alkanes of common plant species from the Mid Rift Valley rangelands of Ethiopia, and evaluate their potential use as nutritional markers. A total of 23 plant species were collected and analysed for long-chain n-alkanes ranging from heptacosane to hexatriacontane (C27 to C36), as well as their carbon isotopic ratio (13C/12C). The analysis was conducted by gas chromatography/combustion isotope ratio mass spectrometry following saponification, extraction and purification. The isotopic composition of the n-alkanes is reported in the delta notation (d13C) relative to the Vienna Pee Dee Belemnite standard. The dominant n-alkanes in the species were C31 (mean ± s.d., 283 ± 246 mg/kg dry matter) and C33 (149 ± 98 mg/kg dry matter). The carbon isotopic enrichment of the n-alkanes ranged from -19.37‰ to -37.40‰. Principal component analysis was used to examine interspecies differences based on n-alkane profiles and the carbon isotopic enrichments of individual n-alkanes. Large variability among the pasture species was observed. The first three principal components explained most of the interspecies variances. Comparison of the principal component scores using orthogonal procrustes rotation indicated that about 0.84 of the interspecies variances explained by the two types of data sets were independent of each other, suggesting that the use of a combination of the two markers can improve diet composition estimations. It was concluded that, while the n-alkane profile of the pasture species remains a useful marker for use in the study region, the d13C values of n-alkanes can provide additional information in discriminating diet components of grazing animals
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