Allometric relationships of frequently used shade tree species in cacao agroforestry systems in Sulawesi, Indonesia

Shade trees play an important role within agroforestry systems by influencing radiation and wind regimes as well as nutrient and hydrological cycling. However, there is a lack of quantitative assessments of their functions. One of the reasons is the rare information on structural characteristics of shade tree species. Therefore, the aim of this study is to provide basic information on the structure of frequently used shade tree species for the implementation of models simulating the ecosystem processes in agroforestry systems. The investigation of the shade trees was conducted at two cacao agroforestry sites on Sulawesi, Indonesia. The measurements of the main structural parameters: diameter at breast height, tree height, trunk height, crown length and crown radius were carried out for the shade tree species Aleurites moluccana, Cocos nucifera and Gliricidia sepium. For data collection, the National Forest Inventory Field Manual Template by FAO (2004) was applied. Based on this information allometric functions were derived for the correspondent shade tree species. The best significant relationships were obtained for the height-crown length relationship of the dicotyledonous tree species’ A. moluccana and G. sepium with a coefficient of determination r² = 0.925 and r² = 0.738, respectively, and the height-crown length relationship of the monocotyledonous palm C. nucifera with r² = 0.663. The transferability tests ‘analysis of covariance’ and ‘homogeneity of slopes’ have shown that the obtained allometric functions are also applicable to other cacao agroforestry systems of the region.     

Pine wilt disease: a short review of worldwide research

This article summarizes the results of the research papers presented at the International Symposium on pine wilt disease (IUFRO Working Party Meeting 4.04.03) held in July 2009, at Nanjing, China. The general topics covered were on pine wilt disease (PWD), its causal organism, the pinewood nematode (PWN) Bursaphelenchus xylophilus, plus other PWN-associated microorganisms that play a significant role in PWD such as bacteria (e.g. Pseudomonas fluorescens). Most of the papers that are reviewed are based on work on PWD-PWN in East Asia and Russia. Specific topics covered include: 1) the fundamental conceptions of PWD development, 2) pathogenicity, 3) host-parasite relationships including the histopathology of diseased conifers and the role of toxins from bacteria-nematode ecto-symbionts, 4) PWN life cycle and transmission, 5) B. xylophilus dissemination models, 6) associations (with other nematodes), 7) diagnostics, 8) quarantine and control of the PWN and 9) biocontrol of the PWN.     

Nitrogen-fixing legume tree species for the reclamation of severely degraded lands in Brazil

The main challenges faced in the reclamation of severely degraded lands are in the management of the systems and finding plant species that will grow under the harsh conditions common in degraded soils. This is especially important in extremely adverse situations found in some substrates from mining activities or soils that have lost their upper horizons. Under these conditions, recolonization of the area by native vegetation through natural succession processes may be extremely limited. Once the main physical and chemical factors restrictive to plant growth are corrected or attenuated, the introduction of leguminous trees able to form symbioses with nodulating N?-fixing bacteria and arbuscular mycorrhizal fungi constitutes an efficient strategy to accelerate soil reclamation and initiate natural succession. These symbioses give the legume species a superior capacity to grow quickly in poor substrates and to withstand the harsh conditions presented in degraded soils. In this article we describe several successful results in Brazil using N?-fixing legume tree species for reclamation of areas degraded by soil erosion, construction and mining activities, emphasizing the potential of the technique to recover soil organic matter levels and restore ecosystem biodiversity and other environmental functions.     

Loss of hydraulic conductivity due to water stress in intact juveniles of Quercus rubra and Populus deltoides

Despite many studies of the percent loss of hydraulic conductivity in excised branches, there is doubt as to whether cutting stems in air introduces unnatural embolism into the xylem at the cut surface. To address this question, hydraulic conductivity was measured in seedlings of northern red oak (Quercus rubra L.) and rooted scions of eastern cottonwood (Populus deltoides Bartr. ex Marsh.) that had been droughted in pots. Results indicate that in situ dehydration produced a very similar vulnerability curve (% loss of conductivity versus water potential) to those previously obtained by bench-top dehydration of excised branches of eastern cottonwood and red oak. In eastern cottonwood cuttings, conductivity loss increased sharply below water potentials of -1.0 MPa, with 100% loss of conductivity occurring by -2.0 MPa, whereas conductivity loss in red oak seedlings was more gradual, i.e., increasing below -1.5 MPa and sustaining 100% loss of conductivity by about -4.0 MPa.     

Photosynthetic utilization efficiency of absorbed photosynthetically active radiation by Scots pine and birch forest stands in the southern Taiga

Absorption and utilization of photosynthetically active radiation (PAR) were investigated in Scots pine (Pinus sylvestris L.) and birch (Betula pendula Roth.) stands that were 41 years old at the end of the experimental period. Canopy depth of the Scots pine stand was about half that of the birch stand (6.5 versus 11.0 m), but absorption of PAR was similar in the two stands. The Scots pine forest canopy, with a leaf area index of 8.9, absorbed 90% of the incoming PAR (APAR), whereas the birch forest canopy, with a leaf area index of 5.9, absorbed 92% of APAR. During maximum foliage development, the upper Scots pine canopy absorbed more PAR than the upper birch canopy (75 versus 66%). The upper, middle and lower layers of the Scots pine canopy contained 37, 48 and 15% of the total needle surface area, respectively. The corresponding distribution of foliage surface area in the three layers of the birch canopy was 50, 30 and 20%, respectively. Measurements of photosynthetic rate were combined with estimates of leaf area index and stand phytomass to determine rates of primary production on a sunny day, a cloudy day, and on an annual basis. The energy equivalents of short- and long-term carbon gain were used with determinations of APAR to calculate photosynthetic utilization efficiency. Throughout the growing season, photosynthetic utilization efficiency of APAR in the upper canopy layer of the Scots pine forest was almost twice that in the lower canopy layer. In the birch forest, photosynthetic utilization efficiency was greater in the lower canopy layer than in the upper canopy layer. In all cases, utilization efficiency was higher in the birch stand than in the Scots pine stand (52 versus 29 J kJ(-1)). Taking account of respiration of the non-photosynthetic parts of each stand (night respiration of needles or leaves; respiration of branches, trunk and roots), estimated utilization efficiency of APAR for net primary production was 11 J kJ(-1) for Scots pine and 19 J kJ(-1) for birch. Solar conversion ratios, expressed as whole-plant net primary productivity per unit of APAR for the growing season, were 0.81 g MJ(-1) for Scots pine and 0.93 g MJ(-1) for birch.     

Numerical modeling of water balance for temporary landfill cover in North Germany

At the end of waste disposal in 2005, a temporary mineral system was constructed to cover the waste body of the municipal landfill in Rastorf (N Germany). The aim of this study was to evaluate the effectiveness of this temporary cover system in limiting the infiltration of surface water into the waste body. The numerical modeling for the hydrological year 2012 was performed in FEFLOW 6.0. The required input data for modeling were achieved by laboratory measurements of the saturated hydraulic conductivity and the water retention characteristics of the mineral layers. The assumed initial and boundary conditions were based on in‐situ measurements of matrix potential and volumetric water content at three different measuring points by tensiometers, FDR sensors and observed meteorological conditions. The model was applied according to Darcy's and Richards' equations for variably saturated flow. Our results allowed assessing the components of water balance for a temporary cover system, especially water seepage into the waste body. The correlation between the measured and modeled volumetric soil water content in the layered temporary cover system was observed (R² = 0.56 to 0.90). Deviations between the measured and modeled values are superficially related to the soil´s heterogeneity. In conclusion, the measured and modeled water balance parameters indicate that the temporary coverage system remains effective in limiting the infiltration rate. However, our studies revealed that the calculated and measured water seepage exceeded the values allowable by the German regulations. Additional studies have to assess variations in the soil water characteristics caused by weather‐related wetting and drying cycles and influence of waste settlement changing the profile of slope.     

The effect of four calcium‐based amendments on soil aggregate stability of two sandy topsoils

The structural stability of soil is a physical characteristic that affects soil degradation processes. Calcium‐based amendments, such as calcium carbonate, calcium sulfate, and calcium oxide/hydroxide, have been shown to improve the stability of soil aggregates. This study seeks to determine which calcium‐based soil amendments, and at what concentration, are the most efficient in improving aggregate stability of sandy topsoils derived from granitic and metamorphic parent materials, and to analyze the mechanisms involved. In the pot experiment, soils amended with CaCO₃, CaCl₂, and CaSO₄ did not present significant differences in aggregate stability compared to the control or among each other. In contrast, Ca(OH)₂ soil amendment brought the greatest stability to the soil aggregates. A dose of 1% Ca(OH)₂ significantly increased the stability of soil aggregates. This effect is due to the reaction of Ca(OH)₂ with atmospheric CO₂ which leads to the formation of CaCO₃, a delayed reaction not showed by the other soil amendments tested. Likewise, the greater solubility of Ca(OH)₂ compared to CaCO₃ exerts a greater aggregation effect on soil. Thus, the mechanism of action of Ca(OH)₂ is related to cementation, rather than flocculation. Future studies should be carried out to demonstrate the effectiveness of Ca(OH)₂ under field conditions.