Masting in Fagus crenata and its influence on the nitrogen content and dry mass of winter buds

In Fagus, full-mast seeding years are invariably followed by at least one non-mast year. Both flower and leaf primordia develop during the summer within the same winter buds. Flower bud initiation occurs when the N content of developing seeds is increasing rapidly. We hypothesized that competition for nitrogen (N) between developing seeds and buds limits flower primordium formation in mast years and, hence, limits seed production in years following mast years. We tested this hypothesis in three Fagus crenata Blume forests at elevations of 550, 900 and 1500 m. Bud N concentration (N con), amount of N per bud (N bud) and dry mass per bud (DM) were compared between a mast year (2005) and the following non-mast year (2006), and between winter buds containing both leaf and flower primoridia (BF), which were formed during the non-mast year, and winter buds containing leaf primordia only (BL), which were formed in both mast and non-mast years. In addition, leaf numbers per shoot corresponding to the analyzed buds were counted, and the effect of masting on litter production was analyzed by quantifying the amounts of litter that fell in the years 2004 to 2007. The dry mass and N content of BF formed in 2006 by trees at both 550 and 1500 m were 2.1-3.4-fold higher than the corresponding amounts in BL, although the numbers of leaves per current-year shoot in 2007 that developed from the two bud types in the same individuals did not differ significantly. These results indicate that more N and carbohydrate are expended in producing BF than in producing BL. The amount of litter from reproductive organs produced in the mast year was similar to the amount of leaf litter at 900 and 1500 m, but three times as much at 550 m. Leaf numbers per shoot were significantly lower at all elevations in the mast year than in the non-mast years (and the amount of leaf litter at 550 and 1500 m tended to be lower in the mast year than in the non-mast years. In conclusion, preferential allocation of resources to seeds in the mast year reduced the availability of resources for flower primordium formation, and this may have accounted for the poor seed production in the following non-mast year.     

A sixteen-year record of regional and temporal variation in the fruiting of beech (Fagus sylvatica L.) in England (1980-;1995)

Annual production of mast by the beech is highly variable, yetthere are few long-term records of the extent of masting whichmight help to explain the masting phenomenon. In this 16-yearstudy, beech mast has been sampled from 100 trees by 7-min samplescollected from the ground and from low-growing branches at sitesranging from the south to the north of England, and varyingfrom closed canopy beechwood to shelter belts, avenues and isolatedtrees in parks. Variation in production of viable seed is much greater fromyear to year than from north to south. Good masting occurredin 1980, 1982, 1984, 1990 and 1995: in these years at leastone year of very bad masting normally followed. Otherwise, predictionof masting is unreliable. No full mast was found in 1981. Overallthere was very little full mast in five other years, but evenin these years, some sites or some trees produced an appreciableamount. All trees produced empty pericarps as well as full mast, especiallyon lower or shaded branches. Isolated trees produced more emptypericarps than trees in groups; this is likely to result froma lack of cross pollination. It is concluded that ground samplingfor a fixed period affords a rapid and effective method of assessingmasting despite the factors intervening between mast sheddingand collection.     

Masting behaviour and dendrochronology of European beech (Fagus sylvatica L.) in southern Sweden

To identify weather controls of beech diameter growth and masting in southern Sweden, we analyze records of monthly weather, regional masting record, and tree-ring chronologies from five beech-dominated stands. The results indicate a strong weather control of temporal pattern of masting events in southern Sweden over the second half of the 20th century. Negative summer temperature anomaly 2 years prior to a mast year, coupled with positive temperature anomaly in the year immediately preceding the same mast year, is a characteristic weather pattern associated with known mast years. Strong dependence of beech masting behaviour on temperature explains the high degree of regional synchronization of masting events. Growth of beech in southern Sweden is strongly and negatively correlated with previous year's summer temperature and positively – with previous year's October temperature. The present study does not provide a conclusive answer in identifying a full set of direct and indirect effects of climatic variables controlling tree-ring growth, since the negative effect of previous year's summer temperature may be a result of a temperature-controlled increase in the beech nut production in the current year. Consistent and significant negative departures of ring-width index during mast years support the hypothesis about a trade-off between investment of bioassimilates into production of beech nuts and tree-ring growth. Alternative explanation of growth anomalies in mast years, relating such anomaly to a negative impact of previous year's growing season, was not supported by the data. We found a limited effect of masting on diameter growth in the following years, indicating that decline in the overall wood production, associated with heavy masting, is short term and typically occurs in the year of actual masting.     

Effects of water availability and fertilization on nitrogen cycling in a stand of Pinus radiata

Nitrogen cycling was studied for four years (1983–1987) in an N-deficient 10-year-old stand of Pinus radiata growing on a yellow podzolic soil which had a low water-holding capacity. Trees were subjected to combinations of irrigation of N-fertilization resulting in a wide range of N uptake and tree growth. Net mineralization, plant uptake and leaching of soil N was monitored using a sequential coring and in-situ incubation technique. Nitrogen concentrations were measuredd monthly in live needles and litterfall. Average rates of weight loss and release of N from decomposing litter were estimated over a 3-year period using a budgeting approach.

Trees responded only to N (not to P, and there was no N×P interaction), but there was a large positive interaction between N supply and water availability. Response to fertilizer averaged + 24% over a 4-year period, but was zero during a growing-season which contained a 4-month drought. Irrigation alone increased growth by 60%, but in combination with high N availability growth increased 2–3 fold. Annual uptake of N ranged from <10 (irrigated plots in years 2 and 3 after enhanced mineralization during the initial year) to 166 kg ha⁻¹ (during a wet growing season following heavy N fertilization). Although soil mineral-N concentrations were elevated for only about 1 year after fertilization, fertilization enhanced rates of N mineralization throughout the soil N mineralization may have resulted from re-mineralization of the large quantity (147 kg soil N mineralization may have resulted from re-mineralization of the large quantity (147 kg ha⁻¹) of fertilizer N immobilized by the soil during the initial 8 months after fertilization, or the N released from decomposition of fine roots having higher N content. Nitrification was negligible in unfertilized soils, but increased markedly 50–100 days after fertilization and resulted in the leaching of about 60 kg N ha⁻¹ during autumn and winter of the first year after fertilization. Fertilized soils have continued to nitrify readily. Irrigation increased rates of weight loss and N release from decomposing litter.

The rate of N uptake by trees markedly affected the concentrations of N in newly emerging and older needles, and the concentration of N in needlefall. The weighted mean concentration of N in annual needlefall ranged from 0.42% in the irrigated-only plot (most N-stressed) to 0.94% in the heavily fertilized plot during the first year after treatment. These weighted concentrations are a useful index of N uptake from the soil and of growth rate where water supply is not limiting. Except for the initial year after heavy N fertilization, annual uptake of N was equivalent to annual soil N mineralization, and N uptake was positively linearly correlated with annual basal-area increment of trees.     

Annual and geographic variation in seed traits of Argentinean populations of southern beech Nothofagus nervosa (Phil.) Dim. et Mil.

Nothofagus nervosa (=N. alpina) is one of the most important native forest tree species of Argentina, with a very small natural distribution area, fast growth and a high wood quality. Its overexploitation in the past seriously affected some populations and made others disappear, making it necessary to implement conservation policies and breeding programs.In order to study the genetic and geographic variation of the species, seeds from a total of 29 populations from the entire natural distribution area in Argentina were harvested, 11 of them during four consecutive years. Annual and geographic covariation of seed production, seed weight and proportion of seeds damaged by insects were analyzed.Significant differences among populations and among years for all studied traits were found. Seed production was highly variable, both among populations and among years. `Partial mast years' seem to occur every two years, whereas the occurrence of `full mast years' has a lower frequency. A significant population × year interaction was found both for the proportion of damaged seeds and for the seed weight. The proportion of seeds damaged by insects was very important, reaching >80% of the total seed produced in some populations. The differences in the quantity of attacked seeds among years are discussed in relation to seed production, insect's life cycle and climatic factors. Seed weight was also variable among populations and years, despite the small natural distribution area of the species in Argentina. Best seed quality, according to lower proportion of damaged seeds and higher seed weight, was observed in the analyzed `full mast year'. This would also imply a better genetic representation of populations with seed samples harvested during these years. A lower proportion of damaged seeds as well as the heaviest seeds were also found among those seeds fallen during the first part of the seed-fall period.The found covariation is discussed in relation to patterns of genetic variation previously found in this species and to the implementation of genetic studies and conservation and breeding programs.     

A comparative analysis of spatial, temporal, and ecological characteristics of forest fires in seasonally dry tropical ecosystems in the Western Ghats, India

The Western Ghats in India is one of the 25 global hotspots of biodiversity, and it is the hotspot with the highest human density. This study considers variations in the regional fire regime that are related to vegetation type and past human disturbances in a landscape. Using a combination of remote sensing data and GIS techniques, burnt areas were delineated in three different vegetation types and various metrics of fire size were estimated. Belt transects were enumerated to assess the vegetation characteristics and fire effects in the landscape. Temporal trends suggest increasingly short fire-return intervals in the landscape. In the tropical dry deciduous forest, the mean fire-return interval is 6 years, in the tropical dry thorn forest mean fire-return interval is 10 years, and in the tropical moist deciduous forest mean fire-return interval is 20 years. Tropical dry deciduous forests burned more frequently and had the largest number of fires in any given year as well as the single largest fire (9900 ha). Seventy percent, 56%, and 30% of the tropical moist deciduous forests, tropical dry thorn forests, and tropical dry deciduous forests, respectively have not burned during the 7-year period of study. The model of fire-return interval as a function of distance from park boundary explained 63% of the spatial variation of fire-return interval in the landscape. Forest fires had significant impacts on species diversity and regeneration in the tropical dry deciduous forests. Species diversity declined by 50% and 60% in the moderate and high frequency classes, respectively compared to the low fire frequency class. Sapling density declined by ca. 30% in both moderate and high frequency classes compared to low frequency class. In tropical moist deciduous ecosystems, there were substantial declines in species diversity, tree density, seedling and sapling densities in burned forests compared to the unburned forests. In contrast forest fires in tropical dry thorn forests had a marginal positive effect on ecosystem diversity, structure, and regeneration.     

Variation of wood density and hydraulic properties of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) clones related to a heat and drought wave in France

Drought response of three Douglas-fir clones (slow, intermediate and fast growing) inhabiting two different climatic regimes in France was examined. We used the hydraulic conductivity and the percent loss of conductivity due to embolism from stems and branches as well as wood microdensity measurements to determine the role of genetics in the control of embolism in this species. Conductivity and tree-ring’s microdensity variables (ring width: RW, mean ring density: MRD, minimum ring density: MID and maximum ring density: MAD) were compared in growth rings in all three clones during a typical year (2002) vs. an extremely dry year (2003). A new method was developed in order to assess axial hydraulic specific conductivity (K_s) within tree rings. The results show that branches are more resistant to embolism than stems, and that there are significant differences in embolism resistance among the clones between the two sites. K_s varied between years, sites and clones but the site exerted the most significant effect. Lartimache (more humid site during 2003) trees showed substantially higher K_s than those inhabiting Chassenoix (strongly affected by the 2003 heat and drought wave site). Wood analysis showed a significant year effect for all ring variables and a significant clone effect for all ring variables except for MAD, while the site effect was significant for MRD and MAD. The existence of a genetic control for the study traits indicates that Douglas-fir populations introduced in France may have a selection potential to face extreme climate events like the 2003 heat and drought wave.     

History of Peridermium Stem Rust of Scots Pine (Pinus sylvestris L.) in Thetford Forest, East Anglia

‘Peridermium’ stem rust (Peridermium pini (Pers.)Lev.) has been present in Thetford forest for at least 40 years,but has only become a major problem during the last decade.Survey data are presented which show that there has been a dramaticincrease in the disease in crops of Scots pine between 1964,when with less than one per cent of the trees showed symptoms,and 1979, when the figure was 10 per cent. The disease has apparentlyspread outwards from a central focus in the middle of the forest.In four plots the proportion of trees with visible symptomshas increased in five years from an average of 28 per cent to46 per cent. However, only 1–2 per cent of the trees havedied annually, and it appears that many trees with ‘deadtops’ may survive for long periods. The situation in Thetfordseems to contrast with that in north-east Scotland, where limiteddata suggest there has been no appreciable increase in diseaseincidence during recent years. There are only two records ofthe disease on Corsican pine (P. nigra var. maritima (Ait.)Melville) in Thetford.     

竹木混交林改为毛竹纯林经营后的林分生长动态

对分别在１９７４年和１９８４年实施清除混交乔、灌木，把原竹木混交林改为毛竹纯林经营的两片毛竹林分内，于１９８５年各设立固定标准地２０块，自１９８５年至１９９５年对改造后处于自然肥力条件下的林分不同生长阶段的毛竹纯林的生长指标，进行为期１１ａ的观测，结果表明：在竹木混交林改成毛竹纯林后的较长经营期中，各生长因子的变化过程表现出明显的阶段性，即：新 竹个体数量增长和粗度下降期（１－４ａ），主要特征是林     

A comparison of the medieval and the current fire regimes in managed pine forests of Catalonia (NE Spain)

We compared the fire regimes in Mediterranean pine forests during two periods, 1370–1466 and 1966–1996 A.D. Medieval fire regime was estimated from the ‘claveria’ books of the Tortosa city, which record the city expenditures, including those for fighting fires that were burning in the city forest. We used the amount spent as an estimate of fire magnitude. Current fire regime was estimated for the same area from the local environment agency data bank, which includes date, location and burned area. The mean number of recorded fires per year, which mostly occurred in summer, is not significantly different between the two periods. Time-since-fire distributions of both periods fitted the negative exponential model, and they were not significantly different. The probability of fire occurring within 1-year interval was 0.44 for the 1379–1466 period and 0.46 for the 1966–1996 period. In both cases, small fires were more abundant, although there are some differences in the medieval series, 13% of all documented fires accounted for 47% of the suppression effort, whereas in the 20th century series, one single fire accounted for 88% of the area burned. Analysis of extreme fire also indicates that in the medieval series the largest fire per year needed one or less days of suppression effort in 58% of the years, whereas in the current period, fires were smaller than 1 ha in 78% of the years. We found that fire suppression in the Middle Ages was associated with forest exploitation. Although we cannot compare the two data sets accurately, there is not evidence of differences in fire frequency between the medieval and the current periods. Differences in fire magnitude distributions of both series of records may be explained by the different purposes and technical resources involved in the fire suppression practices.     

Composition, structure and dynamics of Dysart Woods, an old-growth mixed mesophytic forest of southeastern Ohio

Dysart Woods is a 23 ha old-growth remnant of mixed mesophytic vegetation located in southeastern Ohio, USA. A designation of mixed mesophytic for this forest has historically been difficult, in part due to the abundance of white oak (Quercus alba); however, the dominance of a variety of other hardwoods prevents a simple oak forest designation. Using two 0.35 ha plots on opposing north- and south-facing slopes, we describe the structure and composition of the overstory, understory, and soils, 30 years after their first examination. In 1970, the woods was dominated by beech (Fagus grandifolia), white oak, and sugar maple (Acer saccharum) — historically, the three most abundant species in this region. At that time, white oak was only present in the largest size classes, was not regenerating, and was predicted to decline in importance through succession. These patterns continue today suggesting that inferences made via overstory–understory relations in regards to forest succession are relatively robust over this time period. Beech and maple have increased in importance; white oak has decreased in importance due to mortality in the larger size classes and decreasing density due to regeneration failure. Coarse woody debris distributions correlated strongly with living stem species’ composition and structure implying an equilibrium balance. CWD volume and frequency were dominated by Quercus spp. A detailed analysis of forest health showed that all oak species were in severe decline. The oaks are in a disease decline spiral affiliated with a variety of pre-disposing and inciting factors which include their advanced age (>300 years), their large size (> 100 cm DBH), topography, chronic air pollution, drought, and Armillaria root rot fungus. Ca:Al molar ratios in the soil are also extremely low (<1.0) and may be having an additional detrimental effect. All other canopy species appear to be healthy. One of the unusual features of this woods is its relatively diverse and high coverage (up to 90%) understory layer. The herbaceous community was sampled throughout the growing season and found to be markedly dissimilar among sample times and habitat productivity (aspect, soil quality, and light). The role of these factors has not been as well studied for herb communities as it has for tree communities. There appears to be a relatively strong linkage between the overstory regeneration and understory coverage. While a variety of woody seedlings were discovered, most were of shade tolerant species. Only a few small seedlings of white oak were discovered, with none advancing past 30 cm in height, indicating strong competition in the understory. Furthermore, this small remnant forest patch is surrounded by an agricultural and second-growth forest matrix with many non-indigenous plants — none of which have been able to enter the woods, suggesting strong equilibrium stability of these old-growth patches. The hardwood forests of the hills region has been heavily impacted by various human cultures for thousands of years. Dendrochronological analysis of a full basal slab cut from a wind-thrown white oak revealed a fairly active period of fire following European settlement. A lack of fire during the early 1600s to mid 1700s suggests that pre-Anglo fire frequency may have been negligible. There is clearly a continued role for the preservation and study of these old-growth remnants. They remain integrally important as we attempt to understand and better manage our remaining anthropogenically disturbed landscape.     

The effect of Maya traditional harvesting on the leaf production, and demographic parameters of Sabal palm in the Yucatán Peninsula, Mexico

Palm leaves are an important resource for family households. The effect of harvest on leaf production, growth and fecundity of wild individual palm trees has been studied, but little is known about palm harvest in agro-forestry systems. In the Maya area of the Yucatán Peninsula, Mexico, leaves of the xa’an palm (Sabal yapa, and Sabal mexicana) have been used since pre-Hispanic days for thatching the roofs of traditional Maya houses. The Maya have introduced xa’an palms in homegardens and the care they provide them improves their growth. Maya householders agree on what they consider to be the best harvest intensity for xa’an, recommending one or two harvest events per year, and leaving one or two leaves in each event; however, there is not ecological information documenting whether the traditional harvesting practices are the most adequate to maintain or increase leaf production, and their effect on the growth and fecundity of the palm trees. In Maxcanú, Yucatán, we studied eight family homegardens with S. yapa and S. mexicana. The selected individuals from each homegarden (n = 252) underwent six harvest treatments for 2 years C: control, no harvest, Al: annual harvest, leaving three leaves on the palm, Am: annual harvest leaving two leaves, Ah: annual harvest leaving one leaf, Sl: two harvests per year leaving three leaves, Sm: two harvests per year leaving two leaves. Treatments Ah and Sm simulated the traditional harvest method, and the remaining treatments simulated higher or lower harvest intensities and frequencies. Leaf production was higher in individual palms under higher harvest intensities and frequencies (Ah, Sl and Sm), but palm growth and leaf size were not affected by harvest. Number of inflorescences per palm differed between treatments and between homegardens during the first year only, but we could not find a clear pattern of variation. Production of new leaves was affected by initial palm size and initial leaf number. Removing mature leaves while leaving the young ones, as well as the intensity and frequency, with which traditional harvest is practiced, stimulate palms to compensate the defoliation effects by producing new leaves. This practice is based on empirical Maya knowledge that enables the manipulation of micro-environmental conditions and the development of sustainable harvesting strategies for the xa’an palm in traditional agro-forestry systems.     

不同种源杉木树轮α纤维素δ13C对年气候因子的响应

[目的]通过对不同地理种源杉木α纤维素中的稳定碳同位素(δ^13C)与气候因子的相关性分析,筛选出影响杉木树轮δ^13C的主导气候因子,解释不同种源差异性响应,为种源层面上区域杉木的培育提供理论参考。[方法]以广西柳州的杉木试验林场的30个种源为研究材料,提取并测量α纤维素中δ^13C,利用相关分析和逐步回归分析方法,对杉木树轮δ^13C与当年、前1年、前2年的降水、平均温度、最低气温、最高气温、平均相对湿度、最小相对湿度、日照时数及湿润度指数进行分析。[结果]不同种源杉木(1987-2013)树轮δ^13C值的变幅为-20.997‰^-25.910‰,表现出较强的一阶自相关,相关系数为0.181~0.866。大部分种源杉木树轮的δ^13C与平均温度、最高气温、最低气温呈显著正相关(p<0.05),与日照时数呈不显著正相关,与平均相对湿度、最小相对湿度呈极显著负相关(p<0.01),而与降水及湿润度指数的相关性不统一。逐步回归分析结果发现,30个杉木种源中有26个种源与当年最小相对湿度呈线性关系。[结论]最小相对湿度是影响不同种源杉木树轮α纤维素中δ^13C的主导气候因子,而对降水的依赖性很小。杉木不同种源树轮δ^13C对气候因子的响应存在明显的滞后效应。研究有效的填补了种源层面上树轮稳定碳同位素对气候响应研究的不足,也为杉木培育及经营管理提供了参考。     

西双版纳辣木生长发育及物候观测初报

在西双版纳栽培条件下,辣木生长发育快,定植当年即可开花结果,而且一年四季均可开花结果;每年雨季(5～9月)为生长高峰期;花量大但座果率平均为3%;豆荚长度多为30～50cm,占豆荚总数的73%,其种子数占种子总数的75%;败育率平均15%。不同品种其生长量有较大差异。     

Early gains from planting large-diameter seedlings and intensive management are additive for loblolly pine

A seedling size/intensive management study with Pinustaeda L. was established in 1993 on two sites in the CoastalPlain of Georgia and South Carolina. Each site contained a 2 × 2split-plot study involving two seedling sizes and two levels ofestablishment intensity. Ideotype ``B' seedlings averaged 5.0 mmin diameter (at the root collar) and were 43 cm tall. Ideotype``A' seedlings averaged 8.5 mm in diameter and were 50 cm tall. ``Standard' establishment practices included herbicides(hexazinone and sulfometuron) and fertilizer (DAP) appliedduring the first year. The ``intensive' management involved twoherbicide applications during the first year and two during thesecond year, fertilizer during the first and third years, andinsecticide applications during the first two years (for controlof tip moth, Rhyacionia frustrana Comstock).Intensive management did not affect survival but planting largerseedlings increased survival slightly on one site. However,treatments affected early growth at both sites. On both sites,fourth-year plot-volumes were increased with greaterestablishment intensity and larger seedlings but there was nointeraction between stock size and establishment intensity. Early growth gains were greatest when both intensive managementand larger seedlings were combined. Depending on site, thiscombination resulted in 21% to 51% more volume (at age 4) thanthe next best treatment (standard seedlings with intensivemanagement).     

Forest growth response to changing climate between 1961 and 1990 in Austria

Using 30 years of climate records from 20 weather stations, we investigate the magnitude of temperature and precipitation change, and change in the length of the growing season between 1961 and 1990. Special attention is paid to the period between 1981 and 1990, because recent research suggests that, during this time span, forest productivity may have increased in the northern latitudes. In order to understand the importance of changes in climate on forest growth, we use the ecosystem model FOREST-BGC as a diagnostic tool to predict the annual net primary production (NPP). The results of our study indicate: no change in precipitation between 1961 and 1990; a significant (α = 0.05) increase in mean annual temperature of 0.72°C, mean annual minimum temperature (0.80°C), winter temperature (2.36°C) as well as an increase in the length of the temperature-controlled growing season by 11 days, resulting in a significant increase in diameter increment obtained from 1179 cores of Norway spruce across Austria. The trends in NPP are consistent with observed increment rates validating the use of biogeochemical modeling as a diagnostic tool to search for possible causes on changing environmental conditions.     

Comparative mast seed production in unmanaged and shelterwood white pine (Pinus strobus L.) stands in central Ontario

The effect of the seed cut of the uniform shelterwood silvicultural system on white pine seed production, seed characteristics, and seed viability during 2 mast seeding events was examined in operationally harvested second growth, white pine-dominated forest stands in central Ontario. Seed traps placed along transects in unmanaged and shelterwood stands in each of 3 blocks were used to monitor seed production in 2000 and 2006 (4 and 10 years after harvesting). During these 2 mast seed years between 386,000 and 2,730,600 seed ha^?1 were produced among study stands. Total seed production expressed on a per hectare and unit pine basal area basis did not differ by harvest treatment or among blocks in either year. Variability in seed production among stands was primarily due to differences in stand structure, with seed production positively related to white pine basal area. Seed characteristics were largely similar between harvested and unmanaged stands and between seed years. Seed viability was relatively high in both years, with seed from shelterwoods germinating slightly slower than those from unmanaged stands. Seed quality, as estimated by laboratory germination performance, was higher in 2006 than 2000, likely due to improved seed development and maturation in the warmer, wetter growing season of 2006. Our results suggest that the seed cut of the uniform shelterwood system applied to second growth white pine stands is unlikely to adversely affect white pine seed production, seed quality, or potential for natural regeneration during mast seeding events.     

Progress and prospects of community forestry in developing and developed countries

Community forestry is practiced in various countries throughout the world, with respect to both native forests and plantations, for livelihood and forest protection purposes and also for urban amenity values. While forests have been managed to some extent by communities for thousands of years, modern models of community forestry have been practiced widely for only about 30 years. Community forestry takes many forms; there is no unique definition or categorisation, although a number of characteristics are frequently present. There is in general, involvement of a local community in forest planning as well as management, for a form of forestry which is usually relatively small-scale, motivated by multiple objectives, and receiving some financial support and organisational assistance by government and non-government organisations. Where plantations are established, these may be managed as common property, individual property rights may apply, or there may be a combination of both. Analysis of the specific research studies included in this issue reveals that community forestry systems have been refined over time as experience is gained in program designs, and notable successes have been achieved. However, ‘the jury is still out’ on whether community forestry has lived up to the optimistic expectations of its proponents.     

A shifting cultivation land use system under population pressure in Zambia

The status of chitemene shifting cultivation, in northern Zambia was investigated and reviewed. This paper presents results concerning (a) changes in soil nutrients under chitemene shifting cultivation, (b) the relationship between population density and deforestation and (c) how the chitemene shifting cultivation system has survived under conditions of overpopulation relative to the critical population density.In the chitemene shifting cultivation system crops are grown in a small ash garden made by burning a pile of wood cleared from a larger area. The burning increased soil NH₃–N content by 40–50%, with a further increase of 15% after 262 mm of rainfall. In contrast, the soil in unburnt plots lost up to 30% NH₃–N. The content of other major nutrients, such as, P,K, Ca, Mg, and Na also increased in the top soil immediately after burning. The increase in soil NH₃–N after burning is attributed to the reduction in microbacterial activity. These soil nutrient changes appear essential in the production of finger millet.However, the growing rural population in the chitemene shifting cultivation region of northern Zambia has caused deforestation which has resulted in the reduction of (a) the length of the fallow period from 25 years to 12 years, (b) the per person woodland requirement of m 1.1 ha to 0.53 ha and (c) the frequency of clearing new chitemene gardens from yearly to once in two years. These responses to diminishing wood resources have artificially increased the population carrying capacity from 2.4 to 18.7 persons per km². This has enabled the survival of the chitemene shifting cultivation land use system in northern Zambia.     

Effect of clear-felling on runoff in two small watersheds in Central Sweden

Small watersheds were used in a study of the effect of clear-felling on runoff from coniferous forest areas in Central Sweden. After a 3-year calibration period, two watersheds were clear-felled (on one of them the slash was left and on the other slash was removed) and a third was left as a reference.Runoff under forested conditions was 271 and 246 mm year^?1, respectively for the treated watersheds, while the precipitation measured 732 mm year^?1 as a mean for the investigated period. Clear-felling resulted in an increase in runoff of 119 and 75% (371 and 215 mm per year), respectively. The increase occurred during the period of snowmelt (April–May) and the period without snow (June–October). During winter (November–March) a very small increase in runoff was noted. The effect of clear-felling on runoff appears to be greater than has been reported from most other Scandinavian investigations.The increase in runoff during snowmelt is probably due to an increased snow accumulation in the clear-felled area as compared to the forest. The increased runoff for the period without snow is explained by reduced transpiration from the vegetation and reduced evaporation caused by an increased aerodynamic resistance.No effects of slash removal could be detected, probably because of the natural variation between the two treated watersheds.