Combining napier grass with leguminous shrubs in contour hedgerows controls soil erosion without competing with crops

We established hedges/barriers of calliandra (Calliandra calothyrsus Meissner), leucaena (Leucaena trichandra (Zucc.) Urban)) and napier grass (Pennisetum purpureum Schumach) and combination hedges of either calliandra or leucaena with napier grass on slopes exceeding 5% to study the effect of vegetative barriers on productivity of arable steep-lands in central Kenya. Hedges/barriers were pruned regularly and biomass incorporated into the plots. Hedge plots were monitored for soil fertility, soil losses and maize crop yield changes. Inorganic-N concentration in the tree hedge plots was higher than in the control and napier barrier plots after 20 months. Napier grass barriers were the most effective in reducing erosion losses across the two seasons. The effectiveness of napier grass to significantly reduce soil erosion was detectable in one year old napier barriers. Soil loss from all the other one year old vegetative treatments was similar to soil loss from the control. Seventeen month old combination hedge plots recorded lower soil losses than tree hedges of the same age (P = 0.012). Maize crop yields throughout the trial period were high and similar for leguminous and combination hedge plots, but lower in the napier grass and control plots. Overall, we observed that the combination hedges seemed to provide a win-win scenario of reduction in soil erosion combined with improvement of maize crop yields and soil fertility enhancement. We conclude that vegetative hedges have a potential for improving soil productivity in arable steep-lands of the central highlands of Kenya, and that in adoption of vegetative hedges for this purpose there are trade-offs between soil conservation, soil fertility and maize crop yields to be considered. Throughout the text, tree hedges and leguminous hedges are used interchangeably to imply calliandra and leucaena hedges while use of barrier/s to refer to a treatment is restricted to monospecific grass strips     

Wind protection in a hedged agroforestry system in semiarid Kenya

In semiarid Laikipia (Kenya) severe crop damage and loss of mulch material may be caused by south to south-easterly winds from June to September. Demonstration agroforestry systems which surround farms with live fences had some success in protecting crops, mulch and soil, but great care must be taken, because air may be channelled through or over them. For demonstration purposes, a deliberate gap was made in a two meter high Coleus barbatus live fence to study its effect on wind speed and damage to crops. The effectiveness of protection given by this hedge together with intercropped Grevillea robusta trees was quantified using electrical cup anemometers. The combination of hedges and trees gave protection to a maize/bean intercrop but the biomass distribution was not the most suitable one. This picture was complicated by variable wind direction and interactions between wind and the biomass of hedges and trees. The lowest efficiency of wind reduction occurred closest to the deliberate gap, where also the lowest protection by the Grevillea trees was found. South to south-easterly winds increased the gap effect and caused gradients in tree protection perpendicular to the southern hedge. This gave at times wind speeds even higher than outside the system. Only visually wind effects could be detected. Trees and hedges strongly competed with the crops if not root pruned.This revised version was published online in November 2005 with corrections to the Cover Date.     

Tithonia diversifolia: variations in leaf nutrient concentration and implications for biomass transfer

Green leaf biomass of Tithonia diversifolia is high in nutrients and recognised as a potential source of nutrients for crops. We conducted a field survey in western Kenya to determine the variation in leaf nutrient concentrations in tithonia grown in naturalised hedges and agricultural fields, and to examine whether leaf nutrient concentrations were related to soil nutrient status. Leaf P and K concentrations were higher in naturalised hedges (3.2 g P kg^–1 and 35 g K kg^–1) than in unfertilised fields (2.2 g P kg^–1 and 23 g K kg^–1). The critical level of 2.5 g P kg^–1 for net P mineralisation was exceeded by > 90% of the leaves from hedges, but by only 14% from unfertilised fields. Leaf P and K concentration increased linearly with increasing natural logarithm of anion resin extractable soil P and exchangeable soil K, respectively. However, at the same levels of soil available P and K, field-grown tithonia consistently produced lower leaf P and K concentrations than that grown in hedges. This study indicates that biomass from tithonia planted on nutrient-depleted soils would be a less effective source of P and K, via biomass transfer, than tithonia from naturalised hedges.This revised version was published online in November 2005 with corrections to the Cover Date.     

Mammalian browsing impact on regenerating <Emphasis Type="Italic">Eucalyptus</Emphasis> seedlings in a large commercially managed native forest estate

Excessive browsing by herbivorous mammals can adversely effect both forestry operations and ecosystem structure and function, and effective management of the problem across large forest estates requires the spatial extent of browsing impact to be determined. We conducted a browsing impact survey within 1.3 million ha of commercially managed Eucalyptus forest, and hypothesised that browsing impact would be related to variables reflecting habitat suitability for a major browsing species, the swamp wallaby (Wallabia bicolor Desmarest), at both large and small spatial scales. A simple spatial analysis showed that browsing severity varied across the landscape, but was high in a number of districts (30,000–100,000 ha land management units) grouped in a similar part of the surveyed area, identifying this region as a focus for management and research. Ordinal logistic regression showed that browsing impact was related to (a) the location of districts and (b) the number of times post-harvest regeneration had been attempted, with browsing impact generally worse in areas where regeneration had occurred twice. The latter result was consistent with our original hypothesis, as multiple regeneration attempts promote high quality habitat patches for wallabies. In most heavily browsed districts browsing severity varied substantially between harvested sites, suggesting that processes operating at the site scale were important. Our results describe the spatial extent of browsing within the surveyed area, and identify high risk localities and states, but additional data are required to understand the processes regulating browsing impact.     

Alley cropping of maize with calliandra and leucaena in the subhumid highlands of Kenya: Part 2. Soil-fertility changes and maize yield

Although N-rich leaf biomass of multipurpose trees is known to be a good source of N to crops, integrating such trees into crop production systems is a major challenge in the development of viable agroforestry systems. An approach to integrating calliandra (Calliandra calothyrsus Meissner) and leucaena (Leucaena leucocephala (Lam.) de Wit), two promising agroforestry tree species, into maize (Zea mays L.) production system was investigated in the subhumid highlands of central Kenya during four maize-growing seasons from 1994 to 1996. The experiment consisted of maize plots to which tree prunings obtained from hedgerows grown either in situ (alley cropping) or ex situ (biomass transfer from outside) were applied. When alley-cropped with leucaena, maize produced significantly higher yields compared to maize monoculture (both non-fertilized and fertilized) treatments, but when alley-cropped with calliandra, the yield of maize was less than that of the monocropped unfertilized control. Application of ex situ grown calliandra and leucaena prunings with or without fertilizer resulted in higher maize grain yield than in the nonfertilized and fertilized treatments. Yields of calliandra alley- cropped maize were 11% to 51% lower than those of nonalley-cropped treatments receiving calliandra prunings from ex situ grown trees; the decrease was 2% to 17% with leucaena, indicating that calliandra hedges were more competitive than leucaena hedges. The alley-cropped prunings-removed treatments produced the lowest maize yields. The study showed that, in the subhumid tropical highlands of Kenya, inclusion of calliandra hedges on cropland adversely affected maize yields. On the other hand, alley cropping with leucaena was advantageous. This revised version was published online in June 2006 with corrections to the Cover Date.     

Manipulating phenology and water relations in <Emphasis Type="Italic">Senna spectabilis</Emphasis> in a water limited environment in Kenya

The effect of shoot pruning on leaf phenology, stem wood anatomy and sap flow was investigated on Senna spectabilis (DC.) Irwin and Barneby in Machakos, Kenya. Unpruned trees (single stem) were compared to hedges (two to four stems), pruned 4 times a year during two rainy seasons (April–June, 1997 and November, 1997–January, 1998) separated by a dry season (July–October 1997). Trees attained peak leaf area of 55 m² plant⁻¹ during the rainy seasons, and shed all their leaves naturally during the dry season. Maximum hedge leaf area was 4 m² plant⁻¹ between pruning events and 5.2 m² plant⁻¹ during the dry season. Pruning induced multiple stems and narrow xylem vessels with low hydraulic conductivity. Average cross sectional area of conducting wood per plant was at least 1.8 times greater in trees than in hedges. Xylem lumen diameter at 5 mm depth below the cambium was significantly (P < 0.001) larger in trees (53.6 ± 6.21 μm) than that in hedges (36.2 ± 8.21 μm). Maximum sap flow occurred in the wet season for trees (4800 g d⁻¹ plant⁻¹) and in the dry season for hedges (1400 g d⁻¹ plant⁻¹). Wet season pruning suppressed crown expansion and modified the natural phenology of senna, reducing transpiration rate and therefore soil water depletion, causing crowns to grow. This enhanced the ecological combining ability of senna managed as hedges with annual crops.     

Within gender differences in tree management: Is gender distinction a reliable concept?

Gender is often a useful distinction for analysis and project design, but in some cases it is too narrowly applied to capture some of the fundamental differences among female producers. Evaluating agroforestry practices in the Siaya and South Nyanza districts of Kenya, the authors argue that, in designing agroforestry interventions and assessing policy or program impacts, there is a need to go beyond simple gender distinctions and look at additional stratifiers such as the individual producer's access to resources, including use rights and control over the benefits from and use of a particular resource. Furthermore, the study reveals some of the difficulties in separating activities and effects by gender in households where agroforestry decisions are often joint. The results of their study show that species choice, tree product marketing and use, and the employment or soil conservation and fertility management practices arenot clearly differentiated by gender, but rather, more variable across the marital status of women.     

沙障固沙原理的研究

提出了不以粗糙度而以障内沙面蚀积强度作为沙衡量沙障固沙效能的综合标志，主张通过障埂占位，通过对障埂高度和障梗间距的调节控制风沙流的蚀积机制，在此基础上推导了控蚀公式，并以Ｋ值等于１／１０作为沙障成败优劣的判断标准，对指导治沙实践具有较强的可操作性。     

北京市引进植物的区系分析

通过问卷和野外调查,对北京市引进植物的组成、地理区系及空间分布进行了统计分析。结果表明:1)北京市引进植物共有965种(包括品种),隶属于86科,179属,其中境内引进植物占总数的62%,境外引进植物占总数的38%,中国特有种8个;2)引进植物属的区系分布以北温带分布、东亚和北美间断分布及泛热带分布为主,科的区系分布多以世界分布、泛热带分布为主;3)优势科为蔷薇科、豆科、禾本科、菊科等9个,占总种数的55.97%;4)北京市引进植物有61%用于风景观赏,有16%生态防护与风景观赏并用;5)空间分布以海淀区、朝阳区、昌平区引进植物种类较多,主要分布在公园和苗圃。     

深圳市游憩资源现状及建设对策研究

文中采用问卷调查的方式结合对游憩资源的空间分布研究,对深圳市目前游憩资源的供给能力、使用状况、服务能力以及公众满意度与影响原因进行分析,结果表明:1)深圳总体的游憩资源类型供给能力排序为滨海风光类 > 都市观光类 > 休闲娱乐类 > 人文历史类 > 自然郊野类,同时各区的供给能力及其对总体资源供给能力的贡献不相同,盐田海滨风光类供给能力强且贡献最大,南山、福田、罗湖都市观光类供给能力强且对贡献相对次之,龙岗自然资源供给能力最强但贡献较小;2)海滨风光、都市观光、自然郊野游憩资源具有较高的吸引力与使用度;3)深圳总体自然郊野游憩资源的服务压力最大,其次为都市观光、滨海风光、休闲娱乐、人文历史,同时不同区的游憩资源本地服务能力存在差异;4)公众对深圳总体游憩地的满足度还不够高,主要源自建设内容与形式、特色创新、亲和融入性、体验参与性、方便可达性5个方面存在的问题。最后基于这一结果归纳出各区游憩资源开发提升的主题并提出多样丰富性、特色创新性、亲和融入性、体验参与性、方便可达性5项建设原则。     

What do farmers think? Farmer evaluations of hedgerow intercropping under semi-arid conditions

Results from farmer evaluations of exploratory on-farm trials with hedgerow inter-cropping in a semi-arid region of Kenya (the Yatta Plateau of Machakos District) are presented. Hedgerows ofCassia siamea, Gliricidia sepium andLeucaena leucocephala, which were managed by eight farmers to enhance soil fertility, were established in the mid-1980s. Although trial farmers appear convinced of the ability of the technology to increase crop yields, reduce erosion and provide firewood, most did not feel that the short-term risks (i.e. reduction in crop productivity) and the extra labour required were worth the long-term benefits. Hence, few of the eight farmers were willing to extend their hedges. The discussion suggests that in the risky production environment of the Yatta Plateau, where crop yields fluctuate constantly with the amount of rainfall, soil fertility is not of urgent concern to farmers. A participatory case study approach, which emphasizes farmers' opinions, preferences and ideas elicited through regular farmer evaluation exercises, as distinct from on-farm technology testing for validation, is recommended for on-farm research on new and complex agroforestry technologies. This approach permits between understanding of some of the complex socio-economic factors affecting the adoption of hedgerow intercropping and is the most cost-effective way to gather in-depth and contextual information on farmer decision-making and management of externally introduced agroforestry technologies.     

Tree establishment and management on farms in the drylands: evaluation of different systems adopted by small-scale farmers in Mutomo District,Kenya

Agroforestry systems in Sub-Saharan African drylands are complex and heterogeneous in nature even under similar biophysical conditions. This can be attributed to household needs and socioeconomic status which influence the species and utility of the adopted trees. This has an impact on the trees establishment and management system through planting or Farmer Managed Natural Regeneration (FMNR). This study evaluates how trees for different utilities are managed and which socioeconomic factors influence these decisions. The study used primary data collected in Mutomo District, Kenya through a household survey based on a structured questionnaire. A paired sample t-test was done to assess the preferred mode of adopting trees for different utilities while factor analysis was used to characterize the households as either planting trees or practicing FMNR. Multiple linear regression using household regression factor scores as independent variables and socioeconomic indicators as dependent variables was done to ascertain which socioeconomic factors affect tree adoption. The results show that trees planted were mostly exotic species valued for their nutrition and commercial value, while FMNR was used for subsistence products and environmental services. Household size, livestock levels and mobility had a positive correlation with tree planting, while income, access to markets and roads had an inverse correlation. Access to natural woodland, distance to the nearest motorable road and land size had a positive correlation with tree protection. It is hoped that this knowledge will act as a reference point when designing agroforestry projects in similar areas to ensure they are more aligned to specific site and household conditions.     

广州市垂直绿化植物资源调查与应用现状分析

对广州市越秀、天河、荔湾和海珠 4 个区 106 个样点的立体绿化情况进行调查与统计分析,得到共有 80 个样点应用了立体绿化景观,立体绿化应用率为 75.47%,其中天河区的应用率最高,为 88.46%,荔湾区的应用率最低,为 66.67%。应用植物种类共 42 科 72 属 86 种,包括草本植物 45 种,木本植物 24 种,藤本植物 17 种,种数应用最多的科是天南星科和百合科,使用频率较高的种是鹅掌藤 Heptapleurum arboricola、光叶子花 Bougainvillea glabra、肾蕨 Nephrolepis cordifolia、使君子 Quisqualis indica 和绿萝Epipremnum aureum 等,植物种类应用较为集中、单一。立体绿化景观设计类型以棚架、桥体和墙面绿化为主,立柱和斜坡绿化较少;植物栽培形式主要有绿篱式、悬挂式、攀爬式、模块式等。     

Analysis of spatio-temporal changes in forest biomass in China

Forests play a central role in the global carbon cycle.China's forests have a high carbon sequestration potential owing to their wide distribution,young age and relatively low carbon density.Forest biomass is an essential variable for assessing carbon sequestration capacity,thus determining the spatio-temporal changes of forest biomass is critical to the national carbon budget and to contribute to sustainable forest management.Based on Chinese for-est inventory data (1999-2013),this study explored spatial patterns of forest biomass at a grid resolution of 1 km by applying a downscaling method and further analyzed spatio-temporal changes of biomass at different spatial scales.The main findings are:(1) the regression relationship between forest biomass and the associated influencing factors at a provincial scale can be applied to estimate biomass at a pixel scale by employing a downscaling method;(2) for-est biomass had a distinct spatial pattern with the greatest biomass occurring in the major mountain ranges;(3) forest biomass changes had a notable spatial distribution pattern;increase (i.e.,carbon sinks) occurred in east and southeast China,decreases (i.e.,carbon sources) were observed in the northeast to southwest,with the largest biomass losses in the Hengduan Mountains,Southern Hainan and Northern Da Hinggan Mountains;and,(4) forest vegetation functioned as a carbon sink during 1999-2013 with a net increase in biomass of 3.71 Pg.     

Tree species diversity in relation to environmental variables and disturbance gradients in a northeastern forest in Bangladesh

Biodiversity has become an issue of global attention because of growing awareness of its importance and its rapid depletion worldwide. Diversity of tree species in relation to environmental and disturbance gradients was examined in three managed forests. Trees were randomly sampled in a survey of 75 circular plots(radius = 13 m)with 5 subplots(radius = 1 m). Generalized linear model analysis was used with a Poisson distribution log link function to understand the effects of variables(organic matter, organic carbon, nitrogen, potassium, pH, elevation and disturbance) on tree species richness. Canonical correspondence analysis was used to explore ecological relationships among plots. Our result found that the stand characteristics was an important influencing factor in the three forests. Our result showed that the variables had a highly positive influence on tree species richness in the three forests. In ordination, the selected variables governed the richness of tree species. Our study can help identify the most important factors that drive tree species richness in the three managed forests in Bangladesh and in similar ecosystems and inform forest management decisions for conservation according to ecological importance.     

Using nonparametric modeling approaches and remote sensing imagery to estimate ecological welfare forest biomass

The spatial distribution of forest biomass is closely related with carbon cycle, climate change, forest productivity, and biodiversity. Efficient quantification of biomass provides important information about forest quality and health. With the rising awareness of sustainable development, the ecological benefits of forest biomass attract more attention compared to traditional wood supply function. In this study, two nonparametric modeling approaches, random forest (RF) and support vector machine were adopted to estimate above ground biomass (AGB) using widely used Landsat imagery in the region, especially within the ecological forest of Fuyang District in Zhejiang Province, China. Correlation analysis was accomplished and model parameters were optimized during the modeling process. As a result, the best performance modeling method RF was implemented to produce an AGB estimation map. The predicted map of AGB in the study area showed obvious spatial variability and demonstrated that within the current ecological forest zone, as well as the protected areas, the average of AGB were higher than the ordinary forest. The quantification of AGB was proven to have a close relationship with the local forest policy and management pattern, which indicated that combining remote-sensing imagery and forest biophysical property would provide considerable guidance for making beneficial decisions.     

Crown area allometries for estimation of aboveground tree biomass in agricultural landscapes of western Kenya

Classical allometries determine biomass from measurements of diameter at breast height or volume. Neither of these measurements is currently possible to be derived directly from remote sensing. As biomass estimates at larger scales require remotely sensed data, new allometric relations are required using crown area and/or tree height as predictor of biomass, which can both be derived from remote sensing. Allometric equations were developed from 72 trees semi-randomly selected for destructive sampling in three 100?km² sentry sites in western Kenya. The equations developed fit the data well with about 85?% of the observed variation in aboveground biomass explained by crown area. Addition of height and wood density as second predictor variables improved model fit by 6 and 2?% and lowered the relative error by 7 and 2?%, respectively. The equation with crown area in combination with height and wood density estimated representative aboveground biomass carbon to be about 20.8?±?0.02?t?C?ha^?1; which is about 19?% more than the amount estimated using an allometry with diameter at breast height as predictor. These results form the basis for a new generation of allometries using crown area as a predictor of aboveground biomass in agricultural landscapes. Biomass predictions using crown area should be supported by height and wood density and the application of crown area equations for remote sensing based up-scaling should consider crown interactions with competing or coexisting neighboring trees.     

An improved low-input method for establishing calliandra hedgerows on small-scale farms in western Kenya

Direct seeding methods for nitrogen (N)-fixing tree-legumes by small-scale farmers were developed and studied in humid and sub-humid areas of western Kenya. We focused on the first six months of establishment of calliandra (Calliandra calothyrsus Meissner) multipurpose hedgerows. Direct seeding became effective, reliable, and significantly better than for zero-control treatments when improving A) water uptake by scratching the hard seeds with a sandal against a hard, rough surface, B) phosphorus (P) nutrition by mixing 150 g/m of kitchen wood-ash (1.3% P) into a 10 cm deep, 20 wide cm soil band 5 cm below the seeds, and C) root nodulation by transferring 100 g/m Rhizobium-colonised soil, or 0.5 crushed, incubated nodule, from a calliandra hedge. The field germination was 90% after two weeks, and the hedges were green and about 2 m tall in the dry season six months later. This revised version was published online in June 2006 with corrections to the Cover Date.     

南京市六合区基于0.5m分辨率影像的林地落界及分析

林地落界是为了掌握林地的现有状况,为林地的保护利用规划提供重要的基础数据。高空间分辨率的遥感影像很大幅度地提高了室内林地落界的精度。该文是以高空间分辨率遥感影像为底图,在目视解译的方法上,结合二类调查基础数据,通过建立高清影像的判读解译标志,提取六合区林地,得到南京市六合区林地分布图,与基于中分辨率影像,采用面向对象的方法提取的林地分布图比较,并选取六合区龙袍镇为对象,分析比较了本次林地落界数据和二类调查数据的林地变化率和林地小班的差值变化。结果表明:0.5 m分辨率的影像能够达到将林地落实到田间地块的目的;六合区龙袍镇林地落界由林地到非林地变化率是15%,林地小班差值D的均值为0.24,说明利用高空间分辨率的遥感影像作为目视解译的底图,在林地地类识别和落界精度上都有较大的提高。