Under drought conditions, arbuscular mycorrhizal (AM) fungi alter water relationships of plants and improve their resistance to drought. In a factorial greenhouse experiment, we tested the effects of the AM symbiosis and precipitation regime on the performance (growth, gas exchange, nutrient status and mycorrhizal responsiveness) of Boswellia papyrifera seedlings. A continuous precipitation regime was imitated by continuous watering of plants to field capacity every other day during 4 months, and irregular precipitation by pulsed watering of plants where watering was switched every 15 days during these 4 months, with 15 days of watering followed by 15 days without watering. There were significantly higher levels of AM colonization under irregular precipitation regime than under continuous precipitation. Mycorrhizal seedlings had higher biomass than control seedlings. Stomatal conductance and phosphorus mass fraction in shoot and root were also significantly higher for mycorrhizal seedlings. Mycorrhizal seedlings under irregular watering had the highest biomass. Both a larger leaf area and higher assimilation rates contributed to higher biomass. Under irregular watering, the water use efficiency increased in non-mycorrhizal seedlings through a reduction in transpiration, while in mycorrhizal seedlings irregular watering increased transpiration. Because assimilation rates increased even more, mycorrhizal seedlings achieved an even higher water use efficiency. Boswellia seedlings allocated almost all carbon to the storage root. Boswellia seedlings had higher mass fractions of N, P, and K in roots than in shoots. Irregular precipitation conditions apparently benefit Boswellia seedlings when they are mycorrhizal. Electronic supplementary material The online version of this article (doi:10.1007/s00442-012-2258-3) contains supplementary material, which is available to authorized users.

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Arbuscular mycorrhizal fungi enhance photosynthesis, water use efficiency, and growth of frankincense seedlings under pulsed water availability conditions

Positioning non-timber forest products on the development agenda

1. In the Horn of Africa, frankincense (an aromatic hardened wood resin) is obtained by tapping Boswellia papyrifera. World-wide, frankincense is of great economic and social importance as an important element of incense and perfumes. The production is declining as a result of poor natural regeneration of the Boswellia woodlands, possibly as a result of the low production of viable seeds. We hypothesize that this is because of the current intensive tapping regime, which might favour allocation of carbohydrates for synthesis of resin at the expense of allocation for generative growth. 2. Investigations were carried out at sites in different agro-ecological zones with annually tapped trees and with trees that had not been tapped for several years. Seed viability and germination success were determined for 200 randomly collected seeds in each site. For three stands, the sexual reproduction (number of flowers, fruits and seeds) was determined for different sized trees subjected to three experimental tapping intensities (no, normal and heavy tapping). 3. At the stand level, non-tapped trees produced three times as many healthy and filled seeds as tapped trees. Germination success was highest in stands with non-tapped trees (> 80%) and lowest for those with tapped trees (<16%). 4. At the tree level, sexual reproduction decreased with increasing tapping regime irrespective of tree size. Overall, large trees tended to produce slightly heavier seeds than small trees, and seeds from non-tapped trees were heavier than those from tapped trees. In the stands where tapping was prohibited changes in tapping regimes had the greatest effect on sexual reproduction. Trees subjected to annual tapping always showed the lowest sexual reproduction. 5. Synthesis and applications. Tapping for frankincense results in limited flower and fruit production, and low production of mainly non-viable seeds in B. papyrifera. We argue that tapping causes competition for carbohydrates between frankincense production, and fruit and seed setting. Consequently, the current tapping regimes will cause tree exhaustion and eventually a decline in vitality. Tapping may potentially reduce natural regeneration of the species. New tapping regimes are suggested that include periods of time in which tapping is prohibited in order for trees to recover and replenish their stored carbon pool, and a reduction in the number of tapping points per tree. This is important in view of the long-term sustainability of frankincense production, an internationally highly valued resource.

The effect of tapping for frankincense on sexual reproduction in Boswellia papyrifera

Biotechnological approaches for cocoa waste management: A review.

Impact of land-use type and bark- and leaf-harvesting on population structure and fruit production of the baobab tree (Adansonia digitata L.) in a semi-arid savanna, West Africa

This paper reviews the present condition of cocoa growing in West Africa where some six million ha are planted with cocoa which provide about 70 percent of the total world production. Cote d’Ivoire and Ghana are the largest producers, followed by Nigeria and Cameroon. In the beginning of the 21st century the cocoa production increased from about 2,000,000 tons to about 3,000,000 tons in 2010 and subsequent years. While in this period expansion of the cocoa area (at the expense of forest land) contributed to increased production, nowadays more cocoa has to come from higher yield per ha which is very low at present. This paper highlights at first cocoa growing in each of the cocoa producing countries and then deals with the common constraints and options to higher yields, especially those in Cote d’Ivoire and Ghana. The major causes of low yield are a high incidence of pests and diseases, the old age of cocoa farms and lack of soil nutrients. Concerns about declining output due to aging and diseased trees have urged the government of Cote d’Ivoire and Ghana to launch large rehabilitation and replanting schemes which provide farmers with improved planting materials, plant protection chemicals and fertilizers. As owners of small farms do not earn enough income from their cocoa to purchase external inputs, the traditional mixed planting of cocoa and forest and fruit trees and some oil palms is discussed as an alternative to a high input approach. This low input low output system is sustainable but not the way forward to higher yields. It is thought that in the short run higher cocoa prices and improved management including pest and disease control and to a certain extent fertilizer use offer scope for a larger cocoa output. In the more distant future the predicted climatic change and increased land use for food production will reduce the size of the cocoa area and affect the leading position of West Africa on the world cocoa market. This review shows that at present the conditions for sustainable production are not met and concludes that important structural changes in the cocoa sector are needed to reach this goal. These changes concern the economic viability of cocoa on small farms, extensive land use and the ecological impact of the current cocoa growing practice. The implementation of these changes requires area specific programs with as their common goal increased economic and environmentally sustainable cocoa production on less land.

Cocoa production in West Africa, a review and analysis of recent developments

Aim We determined the present and past distribution, and the abundance, of Boswellia papyrifera in Eritrea, and the environmental and land-use factors determining its distribution limits. Location Eritrea, in the Horn of Africa. Methods In 1997 a Boswellia field survey was conducted in 113 village areas covering four administrative regions. Species occurrence was related to rainfall, air temperature and length of growing period. Additionally, the relationship between the abundance of Boswellia trees and selected physical and chemical soil factors, topography and land-use types was determined for five study areas (with a total of 144 plots) situated along an altitude gradient of 800-2000 m a.s.l. Results The geographical distribution of B. papyrifera was limited to the south-western and southern parts of the country between 800 and 1850 m altitude receiving a mean annual rainfall of 375-700 mm, with a growing period of 45-100 days. Species abundance was affected by, in order of importance: altitude, land-use intensity and soil organic matter. Most trees were found in hilly areas; tree density increased from the foot slope to the hill summit; no trees occurred in valleys. Land-use intensity, especially agriculture, fallow and grazed areas, had a profound negative effect on tree abundance. Natural regeneration of the species was promoted in areas where grazing by livestock was not allowed or regulated. Main conclusions The distribution of B. papyrifera in Eritrea has decreased during past decades, mainly due to an increasing human population, resulting in the conversion of woodlands into agricultural fields and increasing livestock pressure hindering natural regeneration. Consequently, Boswellia trees are found mainly in hilly areas on steep slopes with shallow soils of low fertility. The species appears to be able to adapt to these harsh growing conditions: in adjacent countries it was also found in comparable growth habitats.

Marius Wessel

Papers

Cocoa production in West Africa, a review and analysis of recent developments

The effect of tapping for frankincense on sexual reproduction in Boswellia papyrifera

Distribution of the frankincense tree Boswellia papyrifera in Eritrea: the role of environment and land use