Carbon and nitrogen mineralization in soil of leguminous trees in a degraded pasture in northern Rio de Janeiro,Brazil

Use of legume trees can improve soil quality in degraded pastures. The aim of this study was to characterize C and N mineralization kinetics and estimate the potentially mineralizable C and N in soil under Mimosa caesalpiniifolia Benth. and Acacia auriculiformis A. Cunn.ex Benth. secondary forest and pasture in red-yellow latosols in southeast Brazil. We conducted a laboratory aerobic incubation experiment using a completely randomized design of four replicates and four types of plant cover using a modified version of the Stanford and Smith technique(1972) to study C and N mineralization potential.Potentially mineralizable N(N_o) ranged from 135 to170 mg kg-~(1). The predominant form of mineral N for all types of plant cover was N-NO_3~-. M. caesalpiniifolia was the only species that had a positive influence on N mineralization. Neither of the legumes influenced C mineralization in pasture or secondary forest. The model of N mineralization corresponded to a sigmoidal curve while C mineralization corresponded to an exponential curve,revealing that the N and C mineralization processes were distinct. N mineralized by M. caesalpiniifolia(216 kg of N ha~(-1)) was adequate to meet the N requirement for a livestock-forest system.     

湖州市不同森林植被生物量的研究

对浙江省湖州市5种森林植被的生物量进行研究,结果表明:湖州市不同森林植被的平均生物量分别是,毛竹林121 14t/hm2,杉木林111 77t/hm2,马尾松林51 48t/hm2,常绿阔叶林104 95t/hm2,松阔混交林99 42t/hm2。该地区5种森林植被的总生物量为17475213 08t。     

Forest structure in selected South African forests: edaphoclimatic environment, phase and disturbance

Analysing data from 903 permanent sample plots situated in medium-moist and moist forests in the southern Cape, South Africa, we explored factors controlling forest structure. Pronounced subcanopy stem density persistence (well-stocked subcanopy forest matrix) and stem density packing (comparatively high stem densities of relatively large-sized trees) were found in the moist, less seasonal (quasi-tropical) Tsitsikamma forests. These attributes of structure were linked to the prevailing dystrophic, less seasonal conditions and the associated metabolic vertical growth orientation. The cool, moist and seasonal (quasi-temperate) Knysna forests had lower densities of relatively large-sized trees at the canopy level (stem density intolerance). This was attributed to the lateral growth mode and extended persistence of the trees involved. The warm, seasonal (quasi-subtropical) Outeniqua forests, on relatively nutrient-rich soils, had high stem densities at the canopy level relative to the subcanopy stratum; due to a combination of low subcanopy tree persistence, fast ingrowth of trees into the canopy stratum, which were then lost to mortality before they reached large sizes (high canopy tree turnover). Persistence of the multi-species subcanopy forest matrix supported asynchronous establishment and death of individual trees. Typical for tropical-type forests, the development of trees towards maturity (phase) was associated with a spatially fine-grained disturbance regime. A metabolic performance trade-off model was developed and provided an ecophysiological framework for the interpretation of forest structure and its underlying dynamics. This explanatory model indicated causal links between intraspecific metabolic tactics of trees in response to their edaphoclimatic environment and associated attributes of forest structure. Some implications of the findings for tropical forest management are discussed.     

Chrysoporthe puriensis causing canker and mortality in Pleroma mutabile in the Atlantic Forest,Brazil

Fungi of the Cryphonectriaceae family are globally known to be tree pathogens. In Brazil, several species of Chrysoporthe have been found causing stem and branch cankers in Pleroma (= Tibouchina) spp. Recently, Chrysoporthe puriensis was described as a new species causing stem and branch cankers in Pleroma granulosum, Pleroma candolleanum, and Pleroma heteromallum, all native species of the Melastomataceae family. During an investigation to collect isolates of the Cryphonectriaceae family in an important Brazilian biome, the Atlantic Forest, in Serra do Mar, structures typical of Chrysoporthe species were found in a different host, Pleroma mutabile. Fruiting bodies present in the bark of these trees were collected and isolated. The isolates were submitted on morphological characterization and phylogenetic analyses of the internal transcribed spacer (ITS) and β-tubulin gene regions using Maximum likelihood, Bayesian inference and Maximum parsimony methods. The isolates collected, for this study, were identified as C. puriensis. Pathogenicity tests on seedlings of Pleroma species and Eucalyptus clones revealed C. puriensis can infect and cause canker in these plant species as mortality. The results demonstrate the importance of delimiting the C. puriensis collection range to track its dissemination in other hosts. No host specificity was observed in the inoculation tests, suggesting this is an important finding, the pathogen causes diseases and mortality in several plants of the Atlantic Forest. Additionally, the pathogen can affect others hosts, such as Eucalyptus clones in commercial plantations.     

Effect of human disturbance on the structure and regeneration of forests in the Nevado de Toluca National Park, Mexico

Sample plots were established in the principal forest types in the the Nevado de Toluca National Park, Mexico including those dominated by Pinus hartwegii, Abies religiosa, Quercus laurina and Alnus jorullensis. The vertical structure was defined by three strata in the coniferous forests and two strata in the broadleaved forests. Timber harvesting in Abies religiosa and Quercus laurina forests and fires generated by humans in Pinus hartwegii forests impeded the recruitment of saplings. Mature trees were also heavily impacted by logging in Pinus hartwegii forests. On the contrary, Alnus jorullensis forests were increasing due to the disturbance of Pinus and Quercus forests, as well abandoned crop lands within the park. A combination of logging, uncontrolled fire, and grazing appears to be compromising the recruitment of important tree species in this national park. These factors, together with human settlements, have also increased the proportion of early successional species. Changes in forest structure from human disturbance indicate a need to control these activities if conservation goals are not to be compromised.     

Influence of edge and topography on the vegetation in an Atlantic Forest remnant in northeastern Brazil

Like edge effects, variations in topography can influence the physiognomy and structural patterns of the vegetation due to the high dynamics encountered in inclined areas. We evaluated the effect of edges on the structure and physiognomy of the arboreal and woody understory communities in patches of an Atlantic Forest remnant in two distinct topographic positions. Four study situations were laid out (slope edge, top edge, slope interior, and top interior), with ten 10 × 10 m plots each to sample the arboreal components (circumference at breast height ≥15 cm), and ten 5 × 5 m plots (in the corner of each arboreal component plot) to sample the woody understory (circumference at ground level ≥3 cm and with circumference at breast height <15 cm). We investigated physiognomic and structural variables of edge and interior environments in similar topographic positions on both slope and top (level) areas of the same remnant forest. Physiognomic and structural differences between edge and interior vegetation were noted, and these were found to be still more evident when different topographic positions were considered. Physiognomic and structural variations between the edge and interior vegetation were more notable on slopes than on hill tops, indicating greater dynamics in areas with greater topographic inclinations.     

Forest land-use history affects the species composition and soil properties of old-aged hillock forests in Estonia

Decisions regarding forest typology, management and protection are often based on the structures of present-day forests, ignoring their successional history. Forests growing on kames, eskers and various moraine hillocks common in regions with Holocene glaciation are good examples of this approach. In Estonia, these forests locally persist as fragments of continuous primary forest, but usually they are situated on former slash-and-burn areas (bushlands) or reforested agricultural land. Our aim was to elucidate the strength of the effect of long-term land-use history on the present-day vegetation compositions of mature hillock forests and their soil chemistry. It appeared that even the mature secondary hillock forests are still distinct from historically continuous stands in terms of species composition. We discovered connections between stand history and species content in hillock forests as well as transformed soil properties. The carbon and nitrogen contents in the humus horizons of secondary forests are lower while their carbon–nitrogen ratios are higher than in continuous forests. The relationship between vegetation and stand history is demonstrated by the higher proportions of anthropophytic and apophytic species in the herb layer of the secondary forests. The presence of species that are tolerant of anthropogenic impact on the secondary hillock forests floor can also be partly explained by the effect of different species in the tree and shrub layers, gaps in the tree canopy, and the boundary effect caused by the small areas of forest patches, neighboring grasslands or fields. The extinction debt in secondary communities should also be considered.     

Biomass equations for seven different tree species growing in coppice-with-standards forests in Central Germany

With an increasing demand of sustainable raw materials for bioenergy use, coppicing as management approach to increase the biomass production of forests is becoming of greater importance. This study describes the parameterization of biomass equations for six tree species traditionally used in coppices forests, namely sycamore maple (Acer pseudoplatanus L.), field maple (Acer campestre L.), European ash (Fraxinus excelsior L.), European hornbeam (Carpinus betulus L.), downy birch (Betula pubescens Ehrh.), and common hazel (Corylus avellana L.) growing in coppice-with-standard systems in Lower Saxony, Germany. The parameterization was based on measurements of over 950 trees sampled from two forest sites. The sampled trees were felled and separated into three biomass compartments (stem, coarse branches, and fine brushwood) and weighed on site. The dry weight of sub samples from each compartment was measured. Equations were derived for total aboveground biomass, stem biomass, and crown biomass using regression analyses. We either used diameter at breast height as single independent explanatory variable or in combination with tree height. Biomass production of stump sprouts and generatively grown stems was compared for ash and sycamore maple. In the same age classes, it was found that ash stump sprouts had a slightly higher production than seed-grown stems. For sycamore maple, no difference was detected.     

Effects of history of use on secondary forest regeneration in the Upper Parana Atlantic Forest (Misiones, Argentina)

The Upper Parana Atlantic Forest, as with other areas, has been modified due to anthropogenic activities, generating a mosaic of agricultural fields and forests of varying ages and levels of conservation. The objective of this study was to identify structural and floristic patterns in secondary forests generated in abandoned fields with varying historic uses. Changes in vegetation were surveyed using chronosequences from 2 to 70 years. Stands with different land use histories in three areas of northern Misiones, Argentina, were considered. Adults (DBH ≥ 10 cm), saplings (3 ≥ DBH < 10 cm), seedlings (DBH < 3 cm and height ≥ 50 cm) and non-arboreous vegetation (herbaceous plants and shrubs) were surveyed. Data was analyzed using multivariate techniques (TWINSPAN, Detrended Correspondence Analysis, Cluster Analysis, and Kruskal–Wallis test). In the floristic analysis, two main forest groups were identified: one made up of primary forest and oldest secondary forest (>20 years), and another of the youngest secondary forests (<20 years). Basal area and density of individuals (seedlings, saplings, and adults) rapidly increased during the first two decades, and subsequently the adult category reached values comparable to those of mature forests (32 m²/ha and 850 individuals/ha). During the early years of succession, the forests showed floristic and structural differences related to history of use previous to abandonment; abandoned annual crops showed the greatest densities of saplings and seedlings, while abandoned pastures presented only individuals in the seedling category, and at very low densities. In stands analyzed since the beginning of succession, species of several ecological groups were present (pioneer, initial secondary, late secondary), while climax species appeared only in the seedling category, and in abandoned pastures no species of the later groups were recorded. Our results suggest that differences recorded during the early years of regeneration in sites with varying historic uses may be generated mainly by remnant vegetation at the time of abandonment of the fields (grasses and remnant monoculture plants). After 20 years of succession, it was no longer possible to differentiate the forests structurally or floristically, regardless of age or historic use of each stand. Due to their rapid regeneration capacity, the forests studied play an important role from the start of the successional process in heterogeneous anthropogenic landscapes such as that of Misiones, and contribute to maintaining biodiversity while providing numerous environmental services.     

巴西城市森林的发展与管理

巴西是一个发展中的大国，由于城市化的发展，75％的巴西人口居住在城市，人口的激增带来了许多的环境问题。为改善和提高城市环境质量，巴西政府采取了一系列的有效措施发展城市森林，并取得了巨大的成效。总结了巴西发展和管理城市森林的经验，这对于我国在城市化过程中发展城市森林、改善和提高城市环境质量有重要的借鉴意义。     

Biomass and production of fine roots in Japanese forests

To better understand the control of fine-root dynamics in Japanese forests, we reviewed studies conducted in Japan on fine-root biomass and production. Most of the data on fine-root biomass were obtained for conifer plantations in limited regions; the average fine-root biomass of dominant trees ranged from ∼50 g m₋₂ for Pinus species (n = 3) to ∼600 g m₋₂ for Cryptomeria japonica (n = 4) and Chamaecyparis obtusa (n = 3). These values are comparable with or less than those reported for other temperate forests mainly in North America or Europe. Information on fine-root production in Japanese forests remains limited. Fine-root production accounted for ∼30% of the net primary productivity in two deciduous forests, but similar data was not reported for coniferous forests in Japan. In Japanese forests, slope position is a key parameter controlling fine-root biomass that is greater on upper slopes than on lower slopes, probably because soil resource availability decreases upslope. Studies in manipulated soil environments (e.g., removing throughfall to simulate drought) also suggested that fine-root biomass and production were greatly affected by altered soil environments. Physiological control of fine-root dynamics was recently discussed via anatomical analyses of Chamaecyparis obtusa. Findings from Japanese studies generally support data on fine-root biomass and production obtained from other temperate regions. Further attempts to elucidate the influence of slope position (soil resource availability) on fine-root production would be useful to gain a more detailed understanding of the fine-root dynamics in Japanese forests.     

Biomass increment and mortality losses in tropical secondary forests of Hainan,China

Secondary forests, created after heavy logging,are an important part of China's forests. We investigated forest biomass and its accumulation rate in 38 plots in a tropical secondary forest on Hainan Island. These secondary forests are moderate carbon sinks, averaging1.96–2.17 t C ha-1 a-1. Biomass increment is largely by medium-sized(10–35 m) trees. Tree mortality accounts for almost 30% of the biomass and plays a negligible role in biomass accumulation estimates. Mortality rate is highly dependent on tree size. For small trees and seedlings, it is related to competition due to elevated irradiance after logging. Regarding prospective biomass and rates of accumulation, recovery is not as rapid as in secondary forests of cleared land. Therefore, tropical forests are susceptible to logging operations and need careful forest management.     

Forest regeneration composition and development in upland, mixed-oak forests

Advance regeneration in 52 mature mixed-oak stands was analyzed and described. Red maple (Acer rubrum L.) was the most abundant species in the study area. Among oak (Quercus) species, northern red oak (Q. rubra L.) was the most abundant within the Allegheny Plateau physiographic province, whereas chestnut oak (Q. montana L.) was the most abundant within the Ridge and Valley physiographic province. Sixteen stands, for which data are available through the fourth growing season following harvest, were used to describe stand development. Cumulative height, a composite measure of size and density, was used to describe early stand development. Black gum (Nyssa sylvatica Marsh.) and black birch (Betula lenta L.) had dramatic increases in stand density and cumulative height after overstory removal. Cumulative height of northern red oak and chestnut oak showed a faster positive response to overstory removal than red maple. Oak retained its dominance in cumulative height for at least 4 years after harvest. Red maple nevertheless remained the most abundant tree species after overstory removal. Our results suggest that the principal advantage of red maple regeneration is its ability to accumulate in large numbers prior to harvest.     

The response of understory herbaceous plants to nitrogen fertilization in forests of different land-use history

Forests growing on former agricultural land often have reduced frequencies of many native forest herbs compared with forests that were never cleared for agriculture. A leading explanation for this pattern is that many forest herbs are dispersal limited, but environmental conditions may also hinder colonization. We examined the response of six forest herb taxa (Arisaema triphyllum, Cimicifuga racemosa, Disporum lanuginosum, Osmorhiza spp., Polygonatum spp., and Prenanthes altissima) to nitrogen (N) fertilization in forests with and without an agricultural history to investigate how N availability affects plant performance. The study was conducted in the southern Appalachian Mountains in western North Carolina, USA. There was a significant interaction between land-use history and N treatment for several species. In A. triphyllum and Osmorhiza spp., N fertilization increased aboveground biomass or leaf area more in the post-agriculture site than in the reference site. However, in the reference site, N fertilization depressed aboveground biomass or leaf area in the same taxa, as well as in C. racemosa. The foliar N concentration of these three taxa was elevated in fertilized plots regardless of land-use history, and there was no indication that the light environment differed among plots. These results suggest that some plants growing in post-agricultural stands may be N limited, whereas undisturbed stands in this region appear to be approaching N saturation. Thus, environmental conditions, and particularly N availability, may be an obstacle to the restoration of forest herb communities.     

Dendrochronology-based fire history of mixed-conifer forests in the San Jacinto Mountains,California

The growing public awareness of the increasing number of large wildfires across forested landscapes, coupled with needs of resource base management has accelerated research into forest reference conditions and the historical role of fire in coniferous ecosystems. This work investigates historical fire regimes of mixed-conifer forests in the San Jacinto Mountains of southern California using fire-scar dendrochronology. As such this is the first reconstruction of fire history in the mixed-conifer forests of southern California using landscape-scale systematic-based fire-scar dendrochronology. The pre-historical fire size, seasonality, and frequency within these forests are reconstructed and demonstrated graphically, employing systematic sampling and Geographical Information System (GIS) reconstruction. A 250 m grid system was overlaid upon a 270 ha sample location, and fire-scar samples were collected from each of the grid intersection points. Fire-scar dendrochronology resulted in a 653 years long chronology, indicating a point mean fire return interval of 5.2 years, and an area wide grand mean fire interval of 32.2 years. The majority of fires occurred within latewood or at the ring boundary. Graphic modelling of fire events indicate three-quarters of all fires sampled were less than 6.25 ha in size, but burned over 50% of the area sampled during the period; only a small portion of fires were larger than 18 ha within the sample area. Use of systematic sampling is an important step in modeling long-term frequency and effects of fire on a landscape level, and is invaluable to the long-term management planning.     

印度喜马拉雅库蒙地区阔叶林下草本植物的生物量

在喜马拉雅库蒙地区（Kumaun Himalaya）中部的不同海拔高度设立研究地点,集中研究由白橡（Quercus leucotrichophora）、石斛（Quercus floribunda）、高山栎（Quercus semicarpifolia）组成的阔叶林下的草本植物群落动态及植物生物量。随着海拔高度的上升,3种森林的林分密度及生物量明显下降。在所有研究样地中,白橡林密度和生物量最大。在两个不同方位研究地,草本植物平均密度明显不同,表现为在西向坡地的草本植物密度较大。在各研究地点,总生物量随着海拔高度明显下降（p〈0.05）,且白橡树林的总生物量最高。     

P transformations in cacao agroforests soils in the Atlantic forest region of Bahia,Brazil

Little is known about the phosphorus (P) fractions and P lability of agroforest soils in tropical regions, particularly those of cacao (Theobroma cacao L.) agroforests. We hypothesized that the effect of P fertilization on the distribution of P fractions in the soil based on the source-sink relationship differs for different cacao agroforestry systems. The cacao agroforestry systems studied were the following: open cacao-cabruca, closed cacao-cabruca, cacao + erythrina, mixed cacao + rubber tree, and cacao + rubber tree intercropping. A natural forest and an unfertilized pasture were used as reference systems. The P fractions were determined using the Hedley sequential extraction method, and the P transformation processes were evaluated via structural equation modeling. The impact of low P fertilizer input on the P fractions varied according to the specific environmental conditions of each cacao production system. Consequently, there was high dissimilarity among all of the cacao sites. In all of the cacao agroforestry systems, there was an increase in inorganic P (Pi), especially the labile fraction (resin-Pi and NaHCO₃-Pi), but organic P (Po) increased only in the cacao + erythrina system and in the rubber tree planting row of the cacao + rubber tree intercropping system. As a result, the fitted structural models indicated that the inter-relationships of the geochemical processes were more important for determining the P availability than the biological processes. However, the Po concentrations and relative proportion were high in all of the cacao agroforestry systems, thereby revealing the high potential of supplying P to plants via the mineralization process in the eventual removal of mineral fertilization.     

Fire history of coniferous riparian forests in the Sierra Nevada

Fire is an important ecological process in many western U.S. coniferous forests, yet high fuel loads, rural home construction and other factors have encouraged the suppression of most wildfires. Using mechanical thinning and prescribed burning, land managers often try to reduce fuels in strategic areas with the highest fuel loads. Riparian forests, however, are often designated as areas where only limited management action can take place within a fixed-width zone. These highly productive forests have developed heavy fuel loads capable of supporting stand-replacing crown fires that can alter wildlife habitat and ecosystem function, and contribute to stream channel erosion. Objectives of this study were to determine whether adjacent coniferous riparian and upland forests burned historically with different frequencies and seasonalities, and whether these relationships varied by forest, site, and stream characteristics. We measured dendrochronological fire records in adjacent riparian and upland areas across a variety of forest, site and stream conditions at 36 sites in three sampling areas in the northern Sierra Nevada.     

川西米亚罗林区林场水平森林生物量研究

利用川西米亚罗林区森林资源清查数据,以森林蓄积量和森林生物量之间的关系模型为基础,对川西林业局301林场的森林生物量进行了估算,并对研究地区不同林龄及森林类型的森林生物量进行了分析。研究结果表明:1)研究区域林分总生物量为3 041 229t,林分单位面积平均生物量为87.13 t/hm2,低于全国生物量及四川省生物量的平均值,主要由于占绝对优势的云、冷杉林所处立地条件差,生物量较低造成;2)林分年龄结构不合理,成、过熟林面积较大(占69%);3)水土保持林的生物量在所有森林类型中所占比例最高(占80%)。