Carbon storage in biomass,litter, and soil of different plantations in a semiarid temperate region of northwest China

? Context

A large area of abandoned land in the semiarid temperate region of China has been converted into plantations over the past decades. However, little information is available about the ecosystem C storage in different plantations.

? Aim and methods

Our objective was to estimate the C storage in biomass, litter, and soil of four different plantations (monospecific stands of Larix gmelinii, Pinus tabuliformis, Picea crassifolia, and Populus simonii). Tree component biomass was estimated using allometric equations. The biomasses of understory vegetation and litter were determined by harvesting all the components. C fractions of plant, litter, and soil were measured.

? Results

The ecosystem C storage were as follows: Picea crassifolia (469 t C/ha)?>?Larix gmelinii (375 t C/ha), Populus simonii (330 t C/ha)?>?Pinus tabuliformis (281 t C/ha) (P?<?0.05), 59.5–91.1 % of which was in the soil. The highest tree and understory C storage were found in the plantation of Pinus tabuliformis (247 t/ha) and Larix gmelinii (1.2 t/ha) respectively. The difference in tree C fraction was significant among tree components (P?<?0.05), following the order: leaf?>?branch?>?trunk?>?root. The highest soil C (SC) was stored in Picea crassifolia plantation (411 t C/ha), while Populus simonii plantation had a higher SC sequestration rate than others.

? Conclusion

C storage and distribution varied among different plantation ecosystems. Coniferous forests had a higher live biomass and litter C storage. Broadleaf forests had considerable SC sequestration potential after 40 years establishment.     

Carbon and nutrient stocks in the litter layer of agroforestry systems in central Amazonia,Brazil

Both second-growth and agroforestry systems (AFs) have the potential for recovering thousands of abandoned pasturelands in Amazon. The AFs may do it faster and, at the same time, produce direct economic benefits for farmers. Improved nutrient recycling may be expected due to distinctive litter production in AFs, but lacks experimental data yet. The stocks of carbon and nutrients of the litter layer under different agroforestry systems (AFs) were investigated at an abandoned pasture site, 60 km north of Manaus. The experimental design consisted of three blocks, with five treatments: four different types of 5-year-old AFs and a secondary forest (CAP). Litter layer was sampled in the wet and dry seasons, sorted according to the predominant plant species and analysed for carbon and nutrient concentrations. The litter layer in the control plots was much larger than in the AFs, and thus, the carbon stocks in the litter layer of the control (wet = 489 g m²; dry = 783 g m²) were larger than in the AFs. However, due to a clearly higher concentration of nutrients in the litter from the AFs, some nutrient stocks were similar or even greater than in the control. The planted timber species and the green manures were important sources of K and Ca to the litter layer while the peach-palm was an important source of Mg. In general, the litter of AFs had lower C:nutrient ratios than the litter in the secondary forest control, indicating a faster nutrient recycling in the AFs.     

Biomass production and carbon stocks in poplar-crop intercropping systems: a case study in northwestern Jiangsu,China

The importance of agroforestry systems in CO₂ mitigation has become recognized worldwide in recent years. However, little is known about carbon (C) sequestered in poplar intercropping systems. The main objective of this study is to compare the effects of three poplar intercropping designs (configuration A: 250 trees ha⁻¹; configuration B: 167 trees ha⁻¹ and configuration C: 94 trees ha⁻¹) and two intercropping systems (wheat–corn cropping system and wheat–soybean cropping system) on biomass production and C stocks in poplar intercropping systems. The experiment was conducted at Suqian Ecological Demonstration Garden of fast-growing poplar plantations in northwestern Jiangsu. A significant difference in C concentration was observed among the poplar biomass components investigated (P ≤ 0.05), with the highest value in stemwood and the lowest in fine roots, ranging from 459.9 to 526.7 g kg⁻¹. There was also a significant difference in C concentration among the different crop components (P ≤ 0.05), and the highest concentration was observed in the corn ear. Over the 5-year period, the total poplar biomass increased with increasing tree density, ranging from 8.77 to 15.12 t ha⁻¹, while annual biomass production among the crops ranged from 4.69 to 16.58 t ha⁻¹ in the three configurations. Overall, total C stock in the poplar intercropping system was affected by configurations and cropping systems, and configuration A obtained the largest total C stock, reaching 16.7 t C ha⁻¹ for the wheat–soybean cropping system and 18.9 t C ha⁻¹ for the wheat–corn cropping system. Results from this case study suggest that configuration A was a relative optimum poplar intercropping system both for economic benefits and for C sequestration.     

Factors influencing biomass and carbon storage potential of different land use systems along an elevational gradient in temperate northwestern Himalaya

We observed the influence of five different altitudes and prevailing agro ecosystems on biomass and carbon sequestration potential in Kullu district of Himachal Pradesh, India. The study area had five prevailing land uses viz., agriculture, agro-horticulture, horticulture, silvi-pasture, and forest at four elevations representing about 1 °C temperature change. The results showed that maximum total biomass of 404.35 Mg C ha^?1 was accumulated by forest landuse and followed a decreasing trend in the order as forest > silvi-pasture > agro-horticulture > horticulture > agriculture. Similar trends were also seen with respect to biomass carbon (C) density and C-sequestration potential of different land uses. Biomass and carbon density potential enhanced with the increase in the altitudinal ranges from 1100–1400 to 2000–2300 m a.s.l. But, the rate of C-sequestration potential enhanced from 1100 to 2000 m and declined at 2000–2300 m a.s.l. Maximum carbon density (393.29 Mg C ha^?1) of both plant as well as soil was displayed by the forest-based land use systems situated at an altitudinal gradient of 2000–2300 m a.s.l. The rate of C-sequestration was maximum (2.17 Mg ha^?1) in the agro-horticulture at 2000–2300 m a.s.l. This study brings out the potential of different land use systems influenced by varying factors on their C-sequestration potential in western Himalayan elevation gradient, thereby providing useful information for effective management in a climate change mitigation and carbon budget.     

Non-additive effects of litter-mixing on soil carbon dioxide efflux from poplar-based agroforestry systems in the warm temperate region of China

Poplar-based agroforestry systems are one of the most important farming systems on the temperate plains of China, but soil respiration in those systems has seldom been reported. In this study, poplar leaf litter and residues of the two main crops (wheat and peanut) grown in the agroforestry system were amended to form different litter mixing treatments in field experiments at two sites located in Jiangsu Province, China. We measured soil respiration and environmental factors in the different treatments. Soil respiration rates were increased by the addition of plant residues but were strongly influenced by residue quality. During the growing season, soil respiration was negatively related with C/N ratio, while positively related with the initial P concentration of residues (P < 0.05). Poplar leaf litter and crop residues showed non-additive effects on soil respiration when they were mixed. Both air and soil temperature at 10 cm depth explained more than 85 % of the variation of soil respiration at both sites with an exponential model. A significant linear relationship between soil respiration and soil water content at 10 cm depth (W_S) was also observed. The percent of variation in soil respiration explained by a model based on air temperature and soil water content was greater than that explained by a model based on temperature alone. Thus, soil respiration in the studied poplar-based agroforestry systems was driven by both temperature and soil water content. Soil respiration was significantly different between the two sites that had different clay content and C/N ratios. Results from this study are important for us to understand how soil respiration responds to litter mixing or is influenced by biophysical factors in poplar-based agroforestry systems.     

Ecological benefits provided by alley cropping systems for production of woody biomass in the temperate region: a review

In temperate Europe alley cropping systems which integrate strips of short rotation coppices into conventional agricultural fields (ACS) are receiving increasing attention. These systems can be used for crops and woody biomass production at the same time, enabling farmers to diversify the provision of market goods. Adding trees into the agricultural land creates various additional benefits for the farmer and society, also known as ecosystem services. However, tree-crop interactions in the temperate region have not been adequately substantiated which is identified as a drawback to the practical implementation of such systems. In order to bridge this gap, the current paper aims to present a comprehensive overview of selected ecosystem services provided by agroforestry with focus on ACS in the temperate region. The literature indicates that compared with conventional agriculture ACS have the potential to increase carbon sequestration, improve soil fertility and generally optimize the utilization of resources. Furthermore, due to their structural flexibility, ACS may help to regulate water quality, enhance biodiversity, and increase the overall productivity. ACS are shown as suitable land use systems especially for marginal sites. Based on the available data collected, we conclude that ACS are advantageous compared to conventional agriculture in many aspects, and therefore suggest that they should be implemented at a larger scale in temperate regions.     

Inventory-based estimates of forest biomass carbon stocks in China: A comparison of three methods

Several studies have reported different estimates for forest biomass carbon (C) stocks in China. The discrepancy among these estimates may be largely attributed to the methods used. In this study, we used three methods [mean biomass density method (MBM), mean ratio method (MRM), and continuous biomass expansion factor (BEF) method (abbreviated as CBM)] applied to forest inventory data to estimate China's forest biomass C stocks and their changes from 1984 to 2003. The three methods generated various estimates of the biomass C stocks: the lowest (4.0–5.9 Pg C) from CBM and the highest (5.7–7.7 Pg C) from MBM, with an intermediate estimate (4.2–6.2 Pg C) from MRM. Forest age class is a major factor responsible for these method-induced differences. MBM overestimates biomass for young-aged forests, but underestimates biomass for old-aged forests; while the reverse is true for MRM. Further, the three methods resulted in different estimates of biomass C stocks for different forest types. For temperate/subtropical mixed forests, MBM generated a 92% higher estimate than CBM and MRM generated a 14% lower than CBM. The degree of the overestimates is closely related with the proportion of young-aged forest within total area of each forest type.     

Babassu palm in the agroforestry systems in Brazil's Mid-North region

Babassu palms (Orbignya spp.) cover nearly 200,000 km² in Brazil, providing cash income, fuel, fibre, edible oil and food to a large number of tenant farm households. Babassu is closely integrated within pastoral and shifting cultivation systems of Mid-North Brazil. In pastures, babassu provides shade for cattle, aids soil moisture retention, produces organic matter, generates supplementary farm income at little cost, and offers year-round employment. On the other hand, the persistence of juvenile palms reduces pasture grass productivity due to plant competition, and therefore there is a trend to eradicate babassu through clearcutting and understorey suppression. At moderate densities of less than 100 individuals per ha, mature babassu palms in cropland do not appear to harm crop productivity. In such cases, palms are thinned and leaves of the remaining ones are cut back, supplying fuel for the burn and nutrients to the soil. However, reduced fallow cycles due to pasture conversion threaten babassu as well as crop productivity.

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Resumo Palmeiras de babaçu (Orbignya spp.) occorrem em quase 200.000 km² no Brazil, proporcionando renda em dinheiro, combustível, fibras, óleo e alimentos para cerca de quinhentas mil famílias de pequenos produtores rurais, a maioria arrendatários ou posseiros. O babaçu aparece integrado dentro de sistemas de produção pastorís e de agricultura migratória no Meio Norte do Brazil. Nas pastagens, o babaçu provê sombra para o gado, ajuda na retenção da umidade no solo, produz matéria orgânica, gera renda suplementar com investimento mínimo, e oferece condições para fixar a força de trabalho durante a entressafra dos produtos agrícolas. A presença de palmeiras juvenís, porém, reduz a produtividade dos pastos devido a competição, o que leva os criadores de gado a erradicar o babaçu, suprimindo tanto as palmeiras juvenís, como as palmeiras adultas.No que diz respeito à agricultura migratória, o babaçu adulto em densidades moderadas, ou seja, até 100 indivíduos por hectare, aparentemente não reduz a produtividade das culturas anuais. Nestes casos, parte das palmeiras são desbastadas e as folhas das restantes cortadas, proporcionando combustível para a queima e nutrientes para o solo. No entanto, a redução nos ciclos de descanso devido à conversão das terras agrícolas em pastagens ameaça a produtividade quer do babaçu quer das próprias culturas.

     

Evolution of agroforestry in the Xishuangbanna region of tropical China

A review of agroforestry practices in one lowland and one highland community of Xishuangbanna [Yunnan, P.R. China] has been carried out. Multilayer homegardens and taungya for fuelwood in the lowlands, tea shaded by natural forest and shellac production in a swidden farming system in the highlands are described. The extention of these agroforestry systems in Xishuangbanna is analyzed.Farming systems are facing problems related to shifting cultivation and to a rapid development of rubber which induce a negative evolution of these agroforestry systems.New agroforestry patterns based on Chinese research work, with rubber trees or with shade medicinal plants, are in extension in villages and in state farms.

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Résumé Un inventaire des systèmes agroforestiers du Xishuangbanna [Yunnan, R.P. Chine] a été réalisé: jardins à plusieurs étages et production de bois feu par système de taungya dans un village de plaine, thé à l'ombre de forêt naturelle et production de gomme-lacque dans un système d'agriculture sur brûlis dans un village de montagne.Les systèmes de production sont confrontés aux problèmes liés à l'agriculture sur brûlis, et au développement de l'hévéa. Il en résulte des évolutions négatives de ces practiques agroforestières.De nouveaux modèles agroforestiers, à base d'hévéa ou de plantes médicinales d'ombre, se développent dans les villages et dans les fermes d'état á la suite des travaux de la recherche chinoise.

     

Plant growth, biomass production and nutrient accumulation by slash/mulch agroforestry systems in tropical hillsides of Colombia

Planted fallow systems under ‘slash and mulch’ management were compared with natural fallow systems at two farms (BM1 and BM2) in the Colombian Andes. The BM1 site was relatively more fertile than the BM2 site. Planted fallow systems evaluated included Calliandra calothyrsus CIAT 20400 (CAL), Indigofera constricta (IND) or Tithonia diversifola (TTH). During each pruning event slashed biomass was weighed, surface-applied to the soil on the same plot and sub-samples taken for chemical analyses. While Indigofera trees consistently showed significantly greater (p < 0.05) plant height and collar diameter than Calliandra trees at both study sites, only collar diameter in Indigofera was significantly affected at all sampling times by differences between BM1 and BM2. After 27 months, TTH presented the greatest cumulative dry weight biomass (37 t ha^–1) and nutrient accumulation in biomass (417.5 kg N ha^–1, 85.3 kg P ha^–1, 928 kg K ha^–1, 299 kg Ca ha^–1 and 127.6 kg Mg ha^–1) among planted fallow systems studied at BM1. Leaf biomass was significantly greater (P < 0.05) for CAL than IND irrespective of site. However, CAL and IND biomass from other plant parts studied and nutrient accumulation were generally similar at BM1 and BM2. At both sites, NAT consistently presented the lowest biomass production and nutrient accumulation among fallow systems. Planted fallows using Calliandra and Indigofera trees had the additional benefit of producing considerable quantities of firewood for household use. This revised version was published online in June 2006 with corrections to the Cover Date.     

Livestock activities in agroforestry systems in Guadeloupe: systems of production and functions

The value enhancement of Guadeloupe's private forests (48% of the total) is a major challenge for the territory in terms of agroecological transition combined with diverse ecosystem services (ES). In many Latin American regions, agroforestry systems (AFS) include a significant proportion of livestock, but very few are described in Guadeloupe. In this study, AFS including livestock activities were classified through semi-open interviews (n?=?50) based on two dimensions: the agricultural region and the farmer’s main production strategy. Results showed that, on average, AFS are family farming systems (more than 30%) and the percentage of farmers with multiple activities is high (77%). Mixed tree-crop-livestock systems are very frequent, with 1/3rd of the sub-units devoted to animal husbandry. Farmers preferably raise small ruminants, backyard animals, and large herbivores (20 to 25% of answers each), and to a lesser extent raise pigs and keep bees (12% each). Mixed animal units exist (50%) with between two and six species. More than 80% of farmers use their farm resources (pastures, natural fodder trees or crop by-products) to feed their animals. Even though self-consumption remains widespread (50% of responses), 80% of the farmers want to give a more economic orientation to their activities. The other responses (16%) concerned socio-cultural functions. Several ES are described and are discussed here at different levels (farm, territory, society). In conclusion, in the forested area of Guadeloupe, there is a potential for the development of efficient livestock farming using an agroecological approach. Complete mixed systems (tree-crop-livestock) should be promoted for the provision of multiple ES.

     

Willows rapidly affect microclimatic conditions and forage yield in two temperate short-rotation agroforestry systems

Temperate short-rotation agroforestry systems are promising solutions for environmentally and economically sound production of crops and woody biomass. Accurate estimates of microclimatic conditions and tree-crop interactions in these systems are clearly needed to improve their adoption and management, especially in northeastern North America. The objective of this study was to determine the effects of a windbreak and an alley cropping system that were planted with strips of short-rotation willow on microclimate and forage crop yields. Microclimatic conditions (wind speed, air temperature, air relative humidity, light availability, soil moisture, snow depth) and forage yields were measured at different distances from the willow strips in these two agroforestry systems and in agricultural control plots between the third (2020) and fourth years (2021) after experiment establishment. Willow strips significantly reduced wind speed in both experiments, despite their relatively short stature (260 cm, June 2021). Wind speed reduction was greatest (50 and 58% in alley cropping and windbreak systems, respectively) close to the willow strips (5 m), intermediate at 20 m (22% in both systems), and negligible at 50 m (windbreak system). A significant increase in daytime air temperature that reached almost 1 °C was measured close to the willow strips in the agroforestry systems, compared to control plots. Higher soil moisture was measured close to the windbreak. In both agroforestry systems, snow depth was significantly greater near the willow strips. In both systems, forage yield close to the willow strips was not different from that at any other measured distances and in the control plots, which suggests that no competition for resources occurred between the willows and the forage crop during the study. In July 2021, forage yield within the windbreak (0–50 m from the willow strip) was 44% greater than that in the control plots. The alley cropping system had significant negative (-12%, June 2020) and positive (+?13%, September 2021) effects on forage yield, possibly as a result of temporal variation in climatic conditions. Results of this study stress the importance of better understanding of intra- and inter-annual forage crop variability within agroforestry systems.

     

Allometric tree biomass models of various species grown in short-rotation agroforestry systems

Biomass equations for tree species and the early stages of growth used in short-rotation coppices and agroforestry systems are still lacking. Further, discussion about the structure and parameters of biomass equations are still ongoing. Yield estimations should be precise, while keeping efforts low. To determine the influence of tree species, farming system, and tree position (inner and outer row) on allometric relationships, we derived biomass equations for various tree species from organic and conventional silvoarable agroforestry systems with an alley-cropping configuration. The allometric equations were based on the power relationship between aboveground dry biomass and stem base diameter (SBD) as a single variable or in combination with tree height (H) and were calculated by log-linear mixed-effect regression. Equations span the third and fourth growth year of the first rotation and were validated on the fourth year. Neither farming system nor row position influenced allometric relationship, although biometric variables varied between trees from inner and outer rows. A general model across species explained 95% (\(R_{\text{cond}}^{2}\)) of the variation for tree dry weight or 97% (\(R_{\text{cond}}^{2}\)) with H as covariate. Yet, for the sake of precision, species-specific equations were necessary. The best fitting equation with only SBD as predictor had species-specific allometric factors and a general exponent across species. However, predicted yields were biased by 8–31%. Thus, functions incorporating H are recommended, as compensation for variances in height-diameter relationships due to the ontogenetic stage, site differences, or social status of the tree reduced the bias of biomass estimation (<10%).     

Short-term changes in the soil carbon stocks of young oil palm-based agroforestry systems in the eastern Amazon

The current expansion of the oil palm (Elaeis guineensis Jacq.) in the Brazilian Amazon has mainly occurred within smallholder agricultural and degraded areas. Under the social and environmental scenarios associated with these areas, oil palm-based agroforestry systems represent a potentially sustainable method of expanding the crop. The capacity of such systems to store carbon (C) in the soil is an important ecosystem service that is currently not well understood. Here, we quantified the spatial variation of soil C stocks in young (2.5-year-old) oil palm-based agroforestry systems with contrasting species diversity (high vs. low); both systems were compared with a ~10-year-old forest regrowth site and a 9-year-old traditional agroforestry system. The oil palm-based agroforestry system consisted of series of double rows of oil palm and strips of various herbaceous, shrub, and tree species. The mean (±standard error) soil C stocks at 0–50 cm depth were significantly higher in the low (91.8 ± 3.1 Mg C ha^?1) and high (87.6 ± 3.3 Mg C ha^?1) species diversity oil palm-based agroforestry systems than in the forest regrowth (71.0 ± 2.4 Mg C ha^?1) and traditional agroforestry (68.4 ± 4.9 Mg C ha^?1) sites. In general, no clear spatial pattern of soil C stocks could be identified in the oil palm-based agroforestry systems. The significant difference in soil carbon between the oil palm area (under oil palm: 12.7 ± 2.3 Mg C ha^?1 and between oil palm: 10.6 ± 0.5 Mg C ha^?1) and the strip area (17.0 ± 1.4 Mg C ha^?1) at 0–5 cm depth very likely reflects the high input of organic fertilizer in the strip area of the high species diversity oil palm-based agroforestry system treatment. Overall, our results indicate a high level of early net accumulation of soil C in the oil palm-based agroforestry systems (6.6–8.3 Mg C ha^?1 year^?1) that likely reflects the combination of fire-free land preparation, organic fertilization, and the input of plant residues from pruning and weeding.     

Biological nitrogen fixing capacity and biomass production of different understorey pastures in a Pinus radiata-pasture agroforestry system in New Zealand

Quantitative field measurements of biological nitrogen fixation (BNF) and biomass production by four different understorey pastures in a Pinus radiata-pasture agroforestry system were determined over a period of one year. The trees were two years old at the beginning of this study and the understorey pastures were being cut and removed for silage. The BNF was determined using the ¹⁵N dilution technique. Pastures of ryegrass+clover, cocksfoot+clover, phalaris+clover and lucerne were used. Substantial amounts of BNF were found (71 to 230 kg N ha^–1 year^–1) with lucerne showing the highest N fixation. However, lucerne derived only 71 to 72% of its N from the atmosphere (%Ndfa) during the spring/summer period compared to 83–97% with clovers, thus the net N demand from the soil was substantially higher with lucerne. This caused increased N stress to the trees. Clover in ryegrass+clover pasture fixed more N than the other grass+clover pastures. Although pasture position in relation to trees did not affect annual pasture total DMY and %Ndfa, pastures north of tree row grew better than those in other positions. Trees significantly affected the BNF of legumes and the botanical composition of pastures with highest BNF and legume production occurring in pastures midway between two rows of trees. These results suggest that it would be advantageous to evaluate different legumes and grasses for tolerance of shade and moisture stress in future studies. As the trees studied were only 1.5 to 3 m in height, their effects on BNF, seasonal pasture biomass production and botanical composition are expected to increase with tree dominance in the ecosystem with time. Amounts of N fixed were related to the productivity (i.e. dry matter and N yield) and seasonal persistence of the legumes. The productivity was high in spring and summer and low in autumn and winter.     

Comparison of the erosion control potential of agroforestry systems in the Himalayan region

The great erosion control potential of agroforestry systems is generally recognized. However, insufficient data are available to be able to give absolute quantitative values for the erosion control potential of specific agroforestry systems or to compare their potential. To obtain such quantitative erosion data, long-term standard erosion measurements should be done in specific agroforestry systems. Such measurements may become very costly because the data need to be collected in a wide range of agroforestry systems on different sites over a long time. A further constraint is the reliability of such information: erosion figures may not be comparable because of discrepancy between the scale of measurement and the scale of the agroforestry system and the occurrence of different kinds of erosion. The methodology presented here enables a quick comparative estimation of the erosion (surface erosion, gully erosion and mass movement) control potential of different agroforestry systems. The erosion control value of agroforestry systems is related to their protective functions: the cover, barrier and soil reinforcement functions. The methodology involves identifying which features influence these different functions within a specific agroforestry system and subsequently evaluating the efficacy. The applicability of this methodology is demonstated with examples from various agroforestry systems in the Himalayan region.     

Allometric estimation of above-ground biomass and leaf area in managed Grevillea robusta agroforestry systems

Non-destructive methods for determining the biomass and leaf area of individual trees throughout their growing cycle are an essential tool in agroforestry research, but must be capable of providing reliable estimates despite the influence that management strategies such as pruning may have on tree form. In the present study, allometric methods involving measurements of the diameter of all branches provided reliable estimates of canopy leaf area and biomass for grevillea trees (Grevillea robusta A. Cunn.; Proteaceae) grown as poles, but proved unsuitable for routine measurements because of their time-consuming nature. An alternative, less laborious method based on measurements of trunk cross-sectional area immediately below the first branch of the canopy provided satisfactory allometric estimates of leaf area and canopy biomass. Trunk biomass was determined from measurements of tree height and diameter at breast height using established methodology based on the assumption that trunk volume may be calculated using a quadratic paraboloid model; biomass was determined as the product of trunk volume and the specific gravity of the wood. The theoretical basis, development and validation of allometric methods for estimating tree growth are discussed and their wider applicability to other agroforestry systems is assessed. This revised version was published online in June 2006 with corrections to the Cover Date.     

The agroforestry potential of combined production systems in north-eastern Mexico

In the semi-arid to sub-humid north-east of Mexico, no definite agroforestry practices were in use before the Spanish conquest, but present systems and practices offer a good basis for conversion to ecologically sustainable and productive multicrop systems which incorporate trees. In the mountains and on the coastal plain of the Gulf of Mexico, sub-humid tropical tree crops are found in mixture with semi-arid, mediterranean and even temperate species. Irrigation systems are energy and labour intensive and can be improved. Of special interest for farmers without access to finance, are non-irrigated systems mostly derived from the low dry forest (matorral), which yield crops, fruit and wood for different purposes and also serve for depasturing cattle. These latter practices have high potential for development and optimization.Integrated Expert, Agroforestry, CIM, Germany F.R., GTZ Project No. 81.9008.4     

N,P,and K characteristics of different age groups of temperate coniferous tree species in northwestern China

This study chose dominant tree species including Picea crassifolia,Pinus armandii and Pinus tabuliformis which are distributed in Qilian Mountains,Xiaolongshan Mountains,and Bailongjiang River.According to the different tree species,ages and components,we sampled leaves,branches,stems,and roots,and measured the contents of Nitrogen,Phosphorus,Potassium,along with soil fertility.The changes of N,P,and K contents in the different tree species were studied,and the relationship between nutrient content and environmental factors was analyzed.The results indicated that the content of P in all three species was the lowest(0.039–0.28 g kg~(-1)),while N content was the highest(0.095–1.72 g kg~(-1)).As the terminal organ of nutrient transport,the nutrient content of leaves was the highest.P.armandii(0.45 g kg~(-1)) had a higher nutrient concentration than P.tabulaeformis(0.19 g kg~(-1)) and P.crassifolia(0.29 g kg~(-1)).The nutrient content of each species was highest in a young forest,but lowest in a mature forest.The nutrient content of all three tree species was significantly affected by soil nutrient content,and negatively correlated with available soil nutrients.