Cacao-fruit tree intercropping effects on cocoa yield, plant vigour and light interception in Côte d’Ivoire

A major challenge for cocoa producers in Côte d’Ivoire is to seek alternative shade trees or crop associations to adapt their planting devices and techniques to the shortage of forests. The recent tendency developed by farmers is to plant simplified orchards combining cacao and fruit trees. An on-farm trial was set up in a 5-year-old cocoa farm to compare a cacao monocrop planted at densities of 1,115 trees ha^?1 with cacao intercropped with orange or avocado trees, both at 44 trees ha^?1. Observations were done on incident light received by the cacao, vigour, growth and cocoa yields. On average, the cacaos received 100 % light in the monocrop, 89.6 % under orange trees and 80.6 % of incident light under avocado trees. They yielded 64.0 pods tree^?1 year^?1 in the monocrop (equivalent to 2.54 kg dry cocoa beans tree^?1), 30.3 pods tree^?1 when combined with orange trees and 28.3 pods tree^?1 with avocado trees. The two combinations allowed cocoa yields equivalent to those observed in the region (0.58 kg dry cocoa beans tree^?1). Vigour and yield were very highly correlated with the incident light received. Both the yield and the incident light are a logistic function of the planting distance from the shade tree. The inflexion point of the logistic functions corresponds to the minimum planting distance between the cacao and the intercropped fruit trees. On this basis, we suggest that the cacaos should not be planted closer than 6.50 ± 0.2 m to the orange or avocado trees.     

Effect of shading by baobab (Adansonia digitata) and néré (Parkia biglobosa) on yields of millet (Pennisetum glaucum) and taro (Colocasia esculenta) in parkland systems in Burkina Faso, West Africa

An experiment was conducted in Nobéré, Burkina Faso to assess the effect of shade of two indigenous fruit trees, Adansonia digitata (Baobab) and Parkia biglobosa (Néré), on a shade-tolerant crop called taro (Colocasia esculenta) in comparison with millet (Pennisetum glaucum) a shade-intolerant crop. Photosynthetically active radiation (PAR) and performance of crops under trees and in the open field were assessed during three cropping seasons. Millet performed better under baobab (806.1?±?121.48?kg?ha^?1) compared to the control plot (595.8?±?83.43?kg?ha^?1) and néré (320.2?±?59.91?kg?ha^?1). In contrast, the yield of taro was higher under néré (4124.0?±?469.05?kg?ha^?1) compared to the control plot (2336.9?±?617.04?kg?ha^?1) and baobab (2738.3?±?595.61?kg?ha^?1). There was a strong relationship between the amount of PAR intercepted by trees and crop yields under trees. As PAR decreased the yield of millet decreased whereas the yield of taro increased. Hence, it was concluded that parkland productivity could be enhanced by cropping taro under néré where light reduction was 83, 56 and 18% in zones A, B and C, respectively. An efficient association of baobab with crops could be the production of taro in zone A and millet in zones B and C where PAR reduction was 62, 38 and 15%, respectively.     

Ontogenetic changes in water-use efficiency (δC) and leaf traits differ among tree species growing in a semiarid region of the Loess Plateau,China

On the Loess Plateau, China, several planted tree species such as Populus hopeinsis and Robinia pseudoacacia suffer occasional diebacks in the top shoots, reducing growth rates after maturation. However, this does not usually occur in other species, e.g., Ulmus pumila and Zizyphus jujuba. We compared stable carbon isotope ratios (δ¹³C) as indicators of leaf water-use efficiency (WUE), leaf mass per unit area (LMA), and leaf area- and mass-based nitrogen content (N_area and N_mass) by tree height (1, 5, and 10 m) in P. hopeinsis, R. pseudoacacia, U. pumila, and Z. jujuba. In P. hopeinsis and R. pseudoacacia, leaf δ¹³C and N_area were significantly lower in 10-m trees than in 1-m saplings, indicating that leaf WUE and photosynthetic rates of both species decreased with tree height. In contrast, δ¹³C in Z. jujuba varied little with tree height. The δ¹³C of 10-m-tall U. pumila trees was significantly higher than that of 1-m plants, demonstrating an increase in WUE with tree height. Decreasing WUE, leaf N_area, and N_mass with height increases in P. hopeinsis and R. pseudoacacia may be related to water and nutrient limitations for these species in semiarid regions. In contrast, stable or increasing δ¹³C with tree height in U. pumila and Z. jujuba may account (to some extent) for successful production of these species under identical environmental conditions. Diameter growth rate also decreased with maturity in P. hopeinsis and R. pseudoacacia, but increased or was stable for U. pumila and Z. jujuba. The differences in leaf WUE and LMA among species with tree maturity may be related to species’ growth patterns and susceptibility to drought stress, and are likely to be important new criteria for plantation species selection on the Loess Plateau.     

Agroforestry diffusion and secondary forest regeneration in the Brazilian Amazon: further findings from the Rondônia Agroforestry Pilot Project (1992–2002)

In July 1992 the Rondônia Agroforestry Pilot Project (RAPP) was launched in two agricultural municipalities (Nova União and Alto Paraiso) in the western Brazilian Amazon State of Rondônia. The purpose of the RAPP was to assess the conditions under which colonist farmers in the western Amazon would integrate agroforestry plantings into their small-scale farming systems and to assess the performance of those plantings over time. An experimental group consisting of 50 small-scale farmers was selected to participate. Plots were designed to accommodate between 3 and 25 different species, each producing one or more commodities with local market potential (hardwood, fruits, nuts, latexes, oils). Farmers planted seedlings typically on a 1-ha plot, located and designed by each farmer with the advice of a professional Brazilian extensionist. During the first phase of the project (1992–1998), the growth performance of the seedlings and changes in household characteristics were monitored on an annual basis. By 2002, 32 (64.0%) of the original 50 agroforest plots were found in place. This paper updates the research findings based on a 2002 follow-up visit to these 32 farms. In addition to growth performance, the authors’ found that 17.95% of the farms in the neighboring control group had planted trees and other agroforest crops between 1992 and 2002, compared to only 5.38% of farms outside the project area, suggesting spontaneous diffusion. The authors also found a potentially synergistic relationship between agroforestry and secondary forest regeneration with the use of satellite image analysis. The experience of the RAPP indicates that colonist farmers in Amazonia can be successful managers of agroforest plots with minimal external inputs over the long-term (10 years).     

Spatial variability of nutrient stocks in the humus and soils of a forest massif (Fougères, France)

In this study, the spatial distribution of nutrient stocks (K, Ca, Mg and P) was examined in humus and soils at the forest massif scale (Fougères forest, France). A random stratified sampling plan including 100 sampling points was used and three potential variation factors of nutrient stocks were tested: age of stand, type of stand (broad-leaved or coniferous trees) and type of soil. Sampling classes were then compared and the variation factors were examined. Results demonstrated that nutrient stocks in the humus were not influenced by the cited factors and only the type of soil influenced nutrient stocks in soils. In fact, stocks of exchangeable elements in soils were much higher in Colluviosols-Fluviosols which show redoximorphic characteristics, and available phosphorus stocks were lower than in Alocrisols-Neoluvisols. Moreover, a low variability of nutrient stocks was observed in Alocrisols-Neoluvisols as opposed to Colluviosols-Fluviosols, which may suggest the existence of other variation factors not taken into account in this study (hydromorphic gradient, type and age of stand in hydromorphic zones).     

Seasonal dynamics of foliar δ~(13)C and nutrient concentration of Chinese chastetree and spine jujube in foothill rock outcrop habitat of the southern Taihang Mountains,Central China

In this study, in situ investigation was conducted on Chinese chastetree(Vitex negundo var. heterophylla)and spine jujube(Ziziphus jujuba var. spinosa) during early, developed, and closing succession stages. Monthly data were recorded for foliar δ¹³C values and foliar N, P,and K concentrations from May to October. Foliar δ¹³C values declined with time and differences by succession stage varied by species. Older spine jujube displayed higher foliar N concentration while foliar P concentration was inversely related with N. Chinese chastetree had lower foliar K concentration than spine jujube. Foliar C/N ratio declined during the dry season and increased in the wet season. Foliar N/P ratio increased during the dry season and declined to its initial level until October, when it increased again. Foliar δ¹³C value was positively correlated with foliar N concentration. Foliar P and K concentrations were positively correlated to each other. In conclusion, the two shrubs had contrasting strategies of water use efficiency during their succession, but water use efficiency of both species was promoted by N availability and limited by P availability.     

Characterizing long-term forest disturbance history and its drivers in the Ning-Zhen Mountains,Jiangsu Province of eastern China using yearly Landsat observations (1987–2011)

Forest losses or gains have long been recognized as critical processes modulating the carbon flux between the biosphere and the atmosphere. Timely, accurate and spatially explicit information on forest disturbance and recovery history is required for assessing the effectiveness of existing forest management. The major objectives of our research focused on testing the mapping efficacy of the vegetation change tracker (VCT) model over a forested area in China. We used a new version of VCT algorithm built upon the Landsat time series stacks (LTSS). The LTSS consisted of yearly image acquisitions to map forest disturbance history from 1987 to 2011 over the Ning-Zhen Mountains, Jiangsu Province of east China. The LTSS consisted of TM and ETM+ scenes with different projections due to distinct data sources (Beijing remote sensing ground station and the USGS EROS Center). The validation results of the disturbance year maps showed that most spatial agreement measures ranged from 70 to 86 %, comparable with the VCT accuracies reported for many places in USA. Very low accuracies were identified in 1995 (38.3 %) and 1992 (56.2 %) in the current analysis. These resulted from the insensitivity of the VCT algorithm to detect low intensity disturbances and also from the mis-registration errors of the image pairs. Major forest disturbance types existing in our study area were identified as agricultural expansion (39.8 %), urbanization (24.9 %), forest management practice (19.3 %), and mining (12.8 %). In general, there was a gradual decreasing trend in forest cover throughout this region, caused principally by China’s economic, demographic, environmental and political policies and decisions, as well as some weather events. While VCT has largely been used to assess long term changes and trends in the USA, it has great potential for assessing landscape level change elsewhere throughout the world.