Community biomass of abandoned farmland and its effects on soil nutrition in the Loess hilly region of Northern Shaanxi, China

In order to have a basic knowledge of revegetation, one needs to deepen his understanding of the interactive effects of vegetation and soil. In this article, aboveground biomass, soil nutrients and moisture of 36 old-fields with different abandonment ages (from 2 to 45 years after abandonment), aboveground biomass of 4 typical old-fields, and growth characteristics of 7 predominant old-field species were measured. Changing pace, trend and relationship of community aboveground biomass and soil nutrition during the secondary succession were evaluated; effects of soil nutrition on community aboveground biomass were analyzed using multivariable analysis and pathway analysis, and effects of aboveground biomass on soil nutrition were further discussed. The results show that: (1) Soil nutrients, including organic matter, total nitrogen, total phosphorus, total potassium, nitrate nitrogen, ammonium nitrogen, active phosphorus and active potassium, have the same changing pace and trends as the aboveground biomass. In the process of secondary succession, both the soil nutrition and the community aboveground biomass decreased in the earlier abandonment stage of succession and then increased subsequently. (2) On the basis of the correlation of soil nutrients and abandonment ages, effects of vegetation on 0–20 cm organic matter, active phosphorus, 0–20 cm and 20–40 cm nitrate nitrogen nutrition are significant, while on the basis of the correlation of soil nutrition and aboveground biomass, no significant effects were observed. Hereinbefore, aboveground biomass accounts for only a part of vegetation-soil nutrition effects. The effects of biomass on organic matter, total nitrogen, total phosphorous, total potassium, nitrate nitrogen, active potassium and phosphorous are positive, whereas for ammonium nitrogen it is negative. (3) Abandonment ages, total nitrogen, total potassium, active potassium and soil moisture fluctuation have direct positive effects on the aboveground biomass of old-field communities; abandonment and soil moisture fluctuation have lager effects. Each ingredient of soil nutrition has relatively small effect, among which total nitrogen has larger effects than total and active potassium. The changes in aboveground biomass of old-field communities during succession are caused mainly by the changes in coverage and ecological characteristics of community species (the relatively larger direct effects of abandonment ages), and secondly by the soil moisture fluctuation (the relative smaller indirect effect of abandonment ages through soil moisture). (4) As a dependent variable, belowground biomass approaches power function of soil depth and declines in deeper layer. The root/shoot ratio of communities tends to increase in later succession stages, which also has an increasing tendency. These may influence the accumulation of biomass and decomposition of organic matter, and the vegetation-soil effects may be different.     

Community biomass of abandoned farmland and its effects on soil nutrition in the Loess hilly region of Northern Shaanxi, China

In order to have a basic knowledge of revegetation, one needs to deepen his understanding of the interactive effects of vegetation and soil. In this article, aboveground biomass, soil nutrients and moisture of 36 old-fields with different abandonment ages (from 2 to 45 years after abandonment), aboveground biomass of 4 typical old-fields, and growth characteristics of 7 predominant old-field species were measured. Changing pace, trend and relationship of community aboveground biomass and soil nutrition during the secondary succession were evaluated; effects of soil nutrition on community aboveground biomass were analyzed using multivariable analysis and pathway analysis, and effects of aboveground biomass on soil nutrition were further discussed. The results show that: (1) Soil nutrients, including organic matter, total nitrogen, total phosphorus, total potassium, nitrate nitrogen, ammonium nitrogen, active phosphorus and active potassium, have the same changing pace and trends as the aboveground biomass. In the process of secondary succession, both the soil nutrition and the community aboveground biomass decreased in the earlier abandonment stage of succession and then increased subsequently. (2) On the basis of the correlation of soil nutrients and abandonment ages, effects of vegetation on 0–20 cm organic matter, active phosphorus, 0–20 cm and 20–40 cm nitrate nitrogen nutrition are significant, while on the basis of the correlation of soil nutrition and aboveground biomass, no significant effects were observed. Hereinbefore, aboveground biomass accounts for only a part of vegetation-soil nutrition effects. The effects of biomass on organic matter, total nitrogen, total phosphorous, total potassium, nitrate nitrogen, active potassium and phosphorous are positive, whereas for ammonium nitrogen it is negative. (3) Abandonment ages, total nitrogen, total potassium, active potassium and soil moisture fluctuation have direct positive effects on the aboveground biomass of old-field communities; abandonment and soil moisture fluctuation have lager effects. Each ingredient of soil nutrition has relatively small effect, among which total nitrogen has larger effects than total and active potassium. The changes in aboveground biomass of old-field communities during succession are caused mainly by the changes in coverage and ecological characteristics of community species (the relatively larger direct effects of abandonment ages), and secondly by the soil moisture fluctuation (the relative smaller indirect effect of abandonment ages through soil moisture). (4) As a dependent variable, belowground biomass approaches power function of soil depth and declines in deeper layer. The root/shoot ratio of communities tends to increase in later succession stages, which also has an increasing tendency. These may influence the accumulation of biomass and decomposition of organic matter, and the vegetation-soil effects may be different.     

A significant carbon sink in temperate forests in Beijing: based on 20-year field measurements in three stands

Numerous efforts have been made to characterize forest carbon(C) cycles and stocks in various ecosystems. However, long-term observation on each component of the forest C cycle is still lacking. We measured C stocks and fluxes in three permanent temperate forest plots(birch, oak and pine forest) during 2011–2014, and calculated the changes of the components of the C cycle related to the measurements during 1992–1994 at Mt. Dongling, Beijing, China. Forest net primary production in birch, oak, and pine plots was 5.32, 4.53, and 6.73 Mg C ha?1 a?1, respectively. Corresponding net ecosystem production was 0.12, 0.43, and 3.53 Mg C ha?1 a?1. The C stocks and fluxes in 2011–2014 were significantly larger than those in 1992–1994 in which the biomass C densities in birch, oak, and pine plots increased from 50.0, 37.7, and 54.0 Mg C ha–1 in 1994 to 101.5, 77.3, and 110.9 Mg C ha?1 in 2014; soil organic C densities increased from 207.0, 239.1, and 231.7 Mg C ha?1 to 214.8, 241.7, and 238.4 Mg C ha?1; and soil heterotrophic respiration increased from 2.78, 3.49, and 1.81 Mg C ha?1 a?1 to 5.20, 4.10, and 3.20 Mg C ha?1 a?1. These results suggest that the mountainous temperate forest ecosystems in Beijing have served as a carbon sink in the last two decades. These observations of C stocks and fluxes provided field-based data for a long-term study of C cycling in temperate forest ecosystems.     

Present status and rate of carbon sequestration of forest vegetation in Jilin Province,Northeast China北大核心CSCD

Aims Forests represent the most important component of the terrestrial biological carbon pool and play an important role in the global carbon cycle. The regional scale estimation of carbon budgets of forest ecosystems, however, have high uncertainties because of the different data sources, estimation methods and so on. Our objective was to accurately estimate the carbon storage, density and sequestration rate in forest vegetation in Jilin Province of China, in order to understand the role of the carbon sink and to better manage forest ecosystems. Methods Vegetation survey data were used to determine forest distribution, size of area and vegetation types regionally. In our study, 561 plots were investigated to build volume-biomass models; 288 plots of shrubs and herbs were harvested to calculate the biomass of understory vegetation, and samples of trees, shrubs and herbs were collected to analyze carbon content. Carbon storage, density and sequestration rate were estimated by two forest inventory data (2009 and 2014), combined with volume-biomass models, the average biomass of understory vegetation and carbon content of vegetation. Finally, the distribution patterns of carbon pools were presented using ArcGIS soft ware. Important findings Understory vegetation biomass overall was less than 3% of the tree layer biomass, varying greatly among different forest types and even among the similar types. The carbon content of trees was between 45.80% 52.97%, and that of the coniferous forests was higher than that of the broadleaf forests. The carbon content of shrub and herb layers was about 39.79% 47.25% and 40%, respectively. Therefore, the vegetation carbon conversion coefficient was 0.47 or 0.48 in Jilin Province, and the conventional use of 0.50 or 0.45 would cause deviation of ±5.26%. The vegetation carbon pool of Jilin Province was at the upper range of regional carbon pool and had higher capacity of carbon sequestration. The value in 2009 and 2014 was 471.29 Tg C and 505.76 Tg C, respectively, and the total increase was 34.47 Tg C with average annual growth of 6.89 Tg C•a1. The corresponding carbon sequestration rate was 0.92 t•hm 2•a1. The carbon density rose from 64.58 t•hm 2 in 2009 to 66.68 t•hm2 in 2014, with an average increase of 2.10 t•hm2. In addition, the carbon storage of the Quercus mongolica forests and broadleaved mixed forests, accounted for 90.34% of that of all forests. The carbon increment followed the order of young > over-mature > near mature > middle-aged > mature forests. The carbon sequestration rate of followed the order of over-mature > young > near mature > middle-aged > mature forests. Both the carbon increment and the carbon sequestration rate of mature forests were negative. Furthermore, spatially the carbon storage and density were higher in the east than in the west of Jilin province, while the carbon increment was higher in northeast and middle east than in the west. The carbon sequestration rate was higher in Tonghua and Baishan in the south, followed by Jinlin in the middle and Yanbian in the east, while Baicheng and Songyuan, etc. in west showed negative values.     

Research on characteristics of biomass distribution in urban forests of Shanghai metropolis based on remote sensing and spatial analysis北大核心CSCD

Aims Monitoring and quantifying the biomass and its distribution in urban trees and forests are crucial to understanding the role of vegetation in an urban environment. In this paper, an estimation method for biomass of urban forests was developed for the Shanghai metropolis, China, based on spatial analysis and a wide variety of data from field inventory and remote sensing. Methods An optimal regression model between forest biomass and auxiliary variables was established by stepwise regression analysis. The residual value of regression model was computed for each of the sites sampled and interpolated by Inverse-distance weighting (IDW) to predict residual errors of other sites not subjected to sampling. Forest biomass in the study area was estimated by combining the regression model based on remote sensing image data and residual errors of spatial distribution map. According to the distribution of plantations and management practices, a total of 93 sample plots were established between June 2011 and June 2012 in the Shanghai metropolis. To determine a suitable model, several spectral vegetation indices relating to forest biomass and structure such as normalized difference vegetation index (NDVI), ratio vegetation index (RVI), difference vegetation index (DVI), soil-adjusted vegetation index (SAVI), and modified soil-adjusted vegetation index (MSAVI), and new images synthesized through band combinations such as the sum of TM2, TM3 and TM4 (denoted Band 234), and the sum of TM3, TM4 and TM5 (denoted Band 345) were used as alternative auxiliary parameters . Important findings The biomass density in urban forests of the Shanghai metropolis varied from 15 to 120 t•hm2. The higher densities of forest biomass concentrated mostly in the urban areas, e.g. in districts of Jing'an and Huangpu, mostly ranging from 35 to 70 t•hm2. Suburban localities such as the districts of Jiading and Qingpu had lower biomass densities at around 15 to 50 t•hm2. The biomass density of Cinnamomum camphora trees across the Shanghai metropolis varied between 20 and 110 t•hm2. The spatial biomass distribution of urban forests displayed a tendency of higher densities in northeastern areas and lower densities in southwestern areas. The total biomass was 3.57 million tons (Tg) for urban forests and 1.33 Tg for C. camphora trees. The overall forest biomass was also found to be distributed mostly in the suburban areas with a fraction of 93.9%, whereas the urban areas shared a fraction of only 6.1%. In terms of the areas, the suburban and urban forests accounted for 95.44% and 4.56%, respectively, of the total areas in the Shanghai metropolis. Among all the administrative districts, the Chongming county and the new district of Pudong had the highest and the second highest biomass, accounting for 20.1% and 19.18% of the total forest biomass, respectively. In contrast, the Jing'an district accounted for only 0.11% of the total forest biomass. The root-mean-square error (RMSE), mean absolute error (MAE) and mean relative error (MRE) of the model for estimating urban forest biomass in this study were 8.39, 6.86 and 24.22%, respectively, decreasing by 57.69%, 55.43% and 64.00% compared to the original simple regression model and by 62.21%, 58.50%, 65.40% compared to the spatial analysis method. Our results indicated that a more efficient way to estimate urban forest biomass in the Shanghai metropolis might be achieved by combining spatial analysis with regression analysis. In fact, the estimated results based on the proposed model are also more comparable to the up-scaled forest inventory data at a city scale than the results obtained using regression analysis or spatial analysis alone.     

Carbon storage of the forests and its spatial pattern in Nei Mongol,China北大核心CSCD

Aims Forest carbon storage in Nei Mongol plays a significant role in national terrestrial carbon budget due to its large area in China. Our objectives were to estimate the carbon storage in the forest ecosystems in Nei Mongol and to quantify its spatial pattern. Methods Field survey and sampling were conducted at 137 sites that distributed evenly across the forest types in the study region. At each site, the ecosystem carbon density was estimated thorough sampling and measuring different pools of soil (0 100 cm) and vegetation, including biomass of tree, grass, shrub, and litter. Regional carbon storage was calculated with the estimated carbon density for each forest type. Important findings Carbon storage of vegetation layer in forests in Nei Mongol was 787.8 Tg C, with the biomass of tree, litter, herbaceous and shrub accounting for 93.5%, 3.0%, 2.7% and 0.8%, respectively. Carbon density of vegetation layer was 40.4 t•hm2, with 35.6 t•hm2 in trees, 2.9 t•hm2 in litter, 1.2 t•hm2 in herbaceous and 0.6 t•hm2 in shrubs. In comparison, carbon storage of soil layer in forests in Nei Mongol was 2 449.6 Tg C, with 79.8% distributed in the first 30 cm. Carbon density of soil layer was 144.4 t•hm2. Carbon storage of forest ecosystem in Nei Mongol was 3 237.4 Tg C, with vegetation and soil accounting for 24.3% and 75.7%, respectively. Carbon density of forest ecosystems in Nei Mongol was 184.5 t•hm2. Carbon density of soil layer was positively correlated with that of vegetation layer. Spatially, both carbon storage and carbon density were higher in the eastern area, where the climate is more humid. Forest reserves and artificial afforestations can significantly improve the capacity of regional carbon sink.     

Forest crown density restoration and influencing factors in the burned area of northern Great Hing′an Mountains of China

Fire in the Great Hing′an Mountains in 1987 affected an area of more than 1.33×10⁶ hm², creating a mosaic of burn severities across the landscape, which strongly affected the postfire vegetation succession. In addition, undulate landform and anthropogenic disturbance inevitably influenced the postfire vegetation succession. In this paper, a typical area was selected for a case study, including two forest farms, covering more than 1.2×10⁵ hm². In order to reveal how the forest changed in 2000 (13 years after the fire) by comparing with 1987 (prefire) and to find out the relationship between the forest succession and the affecting factors, forest crown density was selected as the criterion, and forest type, fire severity, silviculture practice, elevation and topography gradients were designed as the affecting variables. With the support of GIS software, each variable was classified and entered into the multivariate regression model. The result showed that the forest crown density changed notably in 2000 compared with that of the prefire, and all the variables significantly affected the forest crown density. The most important affecting variable was elevation, which was positively correlated with the forest crown density. The next was fire severity, which was negatively related with the forest succession. The effects of topographic factors and silviculture practices on forest crown density were relatively small.     

Forest crown density restoration and influencing factors in the burned area of northern Great Hing′an Mountains of China

Fire in the Great Hing′an Mountains in 1987 affected an area of more than 1.33×10⁶ hm², creating a mosaic of burn severities across the landscape, which strongly affected the postfire vegetation succession. In addition, undulate landform and anthropogenic disturbance inevitably influenced the postfire vegetation succession. In this paper, a typical area was selected for a case study, including two forest farms, covering more than 1.2×10⁵ hm². In order to reveal how the forest changed in 2000 (13 years after the fire) by comparing with 1987 (prefire) and to find out the relationship between the forest succession and the affecting factors, forest crown density was selected as the criterion, and forest type, fire severity, silviculture practice, elevation and topography gradients were designed as the affecting variables. With the support of GIS software, each variable was classified and entered into the multivariate regression model. The result showed that the forest crown density changed notably in 2000 compared with that of the prefire, and all the variables significantly affected the forest crown density. The most important affecting variable was elevation, which was positively correlated with the forest crown density. The next was fire severity, which was negatively related with the forest succession. The effects of topographic factors and silviculture practices on forest crown density were relatively small.     

Response of land use/coverage change to hydrological dynamics at watershed scale in the Loess Plateau of China

In this study Qiaozidong and Qiaozixi watersheds in Loess Plateau were selected as the case to investigate the effects of land use/coverage change on hydrological dynamics. The results showed that the runoff coefficient of controlled watershed reduced by about 50%, 85%, 90%, respectively, in wet, normal and dry years in comparison with that of uncontrolled watershed. The average runoff coefficient reduced by 73.6% during the period of 1995–2004 compared with that in the previous period of 1986–1994 for land use in controlled watershed. And the impacts of land use and vegetation changes on runoff were strengthened in response to the increasing rainfall. Additionally, the impacts of land use/coverage change on runoff yield are characterized by seasonal fluctuation. The maximum monthly runoff reduction in the both watersheds occurred in May, which was consistent with the period of the maximum land coverage appeared. Finally, when the rainfall intensity reached a certain threshold, the variance of flood peak in two watersheds reduced, which showed that the effects of forest on flood weakened. The flood peak discharge frequencies indicated that peak discharge would respond to the land use and vegetation change obviously on condition that there were the same frequencies of rainfall intensity in the earlier and later periods.     

Response of land use/coverage change to hydrological dynamics at watershed scale in the Loess Plateau of China

In this study Qiaozidong and Qiaozixi watersheds in Loess Plateau were selected as the case to investigate the effects of land use/coverage change on hydrological dynamics. The results showed that the runoff coefficient of controlled watershed reduced by about 50%, 85%, 90%, respectively, in wet, normal and dry years in comparison with that of uncontrolled watershed. The average runoff coefficient reduced by 73.6% during the period of 1995–2004 compared with that in the previous period of 1986–1994 for land use in controlled watershed. And the impacts of land use and vegetation changes on runoff were strengthened in response to the increasing rainfall. Additionally, the impacts of land use/coverage change on runoff yield are characterized by seasonal fluctuation. The maximum monthly runoff reduction in the both watersheds occurred in May, which was consistent with the period of the maximum land coverage appeared. Finally, when the rainfall intensity reached a certain threshold, the variance of flood peak in two watersheds reduced, which showed that the effects of forest on flood weakened. The flood peak discharge frequencies indicated that peak discharge would respond to the land use and vegetation change obviously on condition that there were the same frequencies of rainfall intensity in the earlier and later periods.     

An Analysis of Vegetation Restoration on Opencast Oil Shale Mines in Estonia

We compared four types of 30‐year‐old forest stands growing on spoil of opencast oil shale mines in Estonia. The stand types were: (1) natural stands formed by spontaneous succession, and plantations of (2) Pinus sylvestris (Scots pine), (3) Betula pendula (silver birch), and (4) Alnus glutinosa (European black alder). In all stands we measured properties of the tree layer (species richness, stand density, and volume of growing stock), understory (density and species richness of shrubs and tree saplings), and ground vegetation (aboveground biomass, species richness, and species diversity). The tree layer was most diverse though sparse in the natural stands. Understory species richness per 100‐m² plot was highest in the natural stand, but total stand richness was equal in the natural and alder stands, which were higher than the birch and pine stands. The understory sapling density was lower than 50 saplings/100 m² in the plantations, while it varied between 50 and 180 saplings/100 m² in the natural stands. Growing stock volume was the least in natural stands and greatest in birch stands. The aboveground biomass of ground vegetation was highest in alder stands and lowest in the pine stands. We can conclude that spontaneous succession promotes establishment of diverse vegetation. In plantations the establishment of diverse ground vegetation depends on planted tree species.     

Succession of vegetation after a high-intensity fire in a pine forest with lichens

This paper presents the results of 20-year studies into the impact made by an experimental high-intensity fire on ecosystem components and postfire succession in a middle-taiga pine forest. About 44% of forest fuel loads burned down during the fire, and the emission of carbon was more than 18 t C/ha. As a result of the fire impact, trees died within 3 years after the fire, and this resulted in a significant accumulation of fuel loads. Twenty years after the fire, the biomass of forest fuel loads surpassed the prefire values 4 times, which led to the possibility of the origin of a repeated high-intensity fire. The initial stage of postfire succession in the pine forest is determined by forest vegetation conditions and takes place with the replacement of dominant grass and shrubs. The agrochemical and hydrothermal soil indicators were revealed to be changed after the fire, and this promoted improved conditions for the origin and development of natural regeneration sufficient for the formation of forest stand.     

南亚热带水土流失地区人工加速植被演替过程

水土流失地区植被在自然条件下从阳生草本到乔灌草复合植被的演替过程常常需要很长的时间,选取适当树种人工造林可以省略先锋物种强阳生草本的发育时间,提早诱发灌木和草本植物发育,大大加速植被恢复演替过程。通过对广东惠州市惠阳区上杨试验站等南亚热带典型水土流失地区的研究发现：自然封育状态下,水土流失地区植被恢复和演替缓慢,25。后植被覆盖度只有35％,且主要以阳生性耐贫瘠的灌木及草本为主,土壤侵蚀仍然比较严重。选择大叶相思树人工造林加速了植被演替进程,控制了水土流失,12a左右植被覆盖度就达90％左右。造林23a左右,林地遮蔽涵养水分和控制侵蚀作用下迅速生长多种当地物种,形成了乔、灌、草、藤、竹多层复合植被。在南亚热带季风气候地区,自然封育状态下严重水土流失区植被恢复至较稳定的次生林阶段需要60a左右的时间;人工造林加速植被演替只需要20a。植树造林是该地区植被恢复发育及控制水土流失的有效措施。     

城市土地利用是否会降低区域碳吸收能力?——台州市案例研究

城市土地利用显著改变了原有生态系统的结构和功能,特别是建成区植被的碳吸收和碳储存能力。该研究通过实地调查和测量,估算城市建成区内乔木、灌木、草坪的生物量和净初级生产力(net primary productivity,NPP),该方法考虑了园林管理(如修剪或割草)对建成区碳吸收和碳储存的影响。结果表明,台州城市树木个体生物量年增量是野外森林中同类树木的近2倍;乔木修剪量占乔木NPP的1/3。目前台州市建成区的植被碳吸收能力为2.1×103kgC.hm–2.a–1(其中乔木的贡献为64%,灌木为9%,草坪为27%),低于本地野外森林同面积的碳吸收能力;通过与野外常绿阔叶林比较发现,增加台州建成区的绿化覆盖率(从23%提高到46%)即可补偿因城市扩张引起的植被碳吸收能力的损失。     

Species-area relationship at different succession stages of monsoon evergreen broad-leaved forest in south subtropical area of Yunnan Province

Based on the investigation data of monsoon evergreen broad-leaved forest at its different succession stages (primary, CP; 15 years of succession, CF; and 30 years of succession, CT) in Pu' er of Yunnan Province, this paper studied the species-area relationship of this forest at each succession stage. It was found that in the communities at each succession stage, the number of total species, trees, shrubs, and lianas had a significant correlation with sampling area, with the area explained over 94% of the total variation. The Z value of the total species (0.334) and trees (0.394) was the lowest at CT, whereas that of shrubs (0.437) and lianas (0.326) was the lowest at CF. No significant differences were observed in the intercepts of the species-area curve of total species, trees, shrubs, and lianas among different succession stages, but the coefficient of determination (R2) of the species-area curve of total species and lianas was the highest at CP. The richness of trees and shrubs at CF explained 99.9% of the variance of Z value, but the richness of total species, trees, shrubs, and lianas at CP and CT had no significant correlations with the Z value.     

Tree–Shrub Interactions During Early Secondary Forest Succession in Uganda

Abstract One of the greatest challenges for ecologists this century will be restoring forests on degraded tropical lands. This restoration will require understanding complex processes that shape successional pathways, including interactions between trees and other plants. Shrub species often quickly invade disturbed tropical lands, yet little is known about whether they facilitate or inhibit subsequent tree recruitment and growth. We examined how shrubs and other vegetation (e.g., vines, grasses, herbs) affect tree recruitment, survival, and growth during the first 6 years of forest succession in Kibale National Park, Uganda. The study was undertaken in two recently logged exotic softwood plantations. We studied the successional trajectories in two recently logged areas that varied in their initial densities of trees and shrubs. Analyses suggested tree seedling presence and density were not strongly related to shrub density or height during succession. Tree sapling presence and density were positively significantly related to shrub density and height. We found little response in the tree community to experimental shrub removal, and although removal of all nontree vegetation temporarily enhanced tree growth, the effect disappeared after 2 years. Some early‐successional trees benefited from reduced competition, whereas some mid‐successional trees benefited from the presence of other vegetation. Some specific tree species responded strongly to vegetation removal. We interpret our findings in light of designing manipulations promoting forest restoration for biodiversity conservation and conclude with four tentative guidelines: (1) manage at the species level, not the community level; (2) increase facilitation for seedlings, reduce competition for saplings; (3) be cautious of assumptions about plant interactions; and (4) be adaptable and creative with new strategies when manipulations fail.     

南亚热带季风常绿阔叶林不同演替阶段物种-面积关系

通过对云南普洱地区季风常绿阔叶林演替15年、30年及原始林群落的调查,探讨了不同演替阶段群落的物种-面积关系.结果表明:不同演替阶段群落中,取样面积与总物种数,乔木、灌木和藤本物种数均具有极显著相关关系,其变化解释率均超过94%;演替30年群落中总物种和乔木的物种累积速率(Z)最低(0.334和0.394),演替15年群落中灌木和藤本的Z值最低(0.437和0.326);不同演替阶段中总物种、乔木、灌木和藤本的物种-面积曲线截距无显著变化,但原始林中总物种和藤本物种-面积曲线的决定系数(R2)显著高于演替15年和30年群落.演替15年群落中,初始乔木及灌木物种丰富度解释了Z值变化的99.9%,而其他演替阶段群落中初始乔木、灌木、藤本及总物种丰富度与Z值均无显著相关性.     

群落结构和叶面积指数在具茨山植被次生演替中的变化

采取3S(GIS,RS和GPS)技术和野外作业相结合的方法,研究了河南省具茨山人为干扰后植被次生演替过程。在此基础上,从宏观和微观尺度对不同演替阶段典型群落的结构变化和植被叶面积指数(LAI)动态进行分析。结果表明:乔木阶段的植被LAI均值为4.1～5.5;灌木阶段为3.0～3.7;草本阶段为1.0～1.5。部分灌木林在生长季的LAI和盖度高于乔木林。随着演替进行,群落结构也发生很大变化,乔木种类和数量逐步上升。植被系统的复杂度和稳定性不断增强,其发挥的生态功能和生态服务价值随之提高。     

Succession following the catastrophic eruption of Ksudach volcano (Kamchatka, 1907)

Ksudach Volcano, southern Kamchatka Peninsula, erupted in 1907 and impacted over 2000 km² of forests with air-fall pumice deposits. We identified three impact zones. In Zone I, deposits deeper than 100 cm destroyed all vegetation. Two early successional stages occur, a lichen-dominated desert and isolated patches of a pioneer herb stage. Zone II is defined by pumice deposits 30 to 100 cm deep. Deposits of 70 to 100 cm destroyed all vegetation, but left scattered snags. Here primary succession dominates recovery, but its rate varies. Isolated trees survived in deposits of 30 to 70 cm and primary and secondary successional stages form a complex mosaic termed an intermediate succession. In Zone II, the primary stages found in Zone I are joined by a dwarf shrub-herb stage and a secondary birch forest stage. Zone III occurs where thinner deposits permitted some vegetation to survive in all locations. Secondary succession dominates in deposits of 10 to 30 cm. Trees suffered damage, but survived deposits of 20 to 30 cm, while other vegetation layers were eliminated. Deposits of 10 to 20 cm eliminated mosses and lichens and but only reduced the number of dwarf shrubs and herbs. Deposits of less than 10 cm damaged herb, moss and lichen layers but did not eliminate any species. All sampled vegetation remains in a pre-climax state, having yet to recover fully from earlier eruptions. Reconstructed vegetation maps for before 1907 and for ca. 1925 are compared to the map of vegetation in 1994. Based on degree of soil formation, vegetation recovery and colonization rates at different pumice depths, and the current vegetation, we estimate that full recovery of the soil-vegetation system will take more than 2000 years.     

Individual and combined effects of disturbance and N addition on understorey vegetation in a subarctic mountain birch forest

Questions: What are the effects of repeated disturbance and N‐fertilization on plant community structure in a mountain birch forest? What is the role of enhanced nutrient availability in recovery of understorey vegetation after repeated disturbance? How are responses of soil micro‐organisms to disturbance and N‐fertilization reflected in nutrient allocation patterns and recovery of understorey vegetation after disturbance? Location: Subarctic mountain birch forest, Finland. Methods: We conducted a fully factorial experiment with annual treatments of disturbance (two levels) and N‐fertilization (four levels) during 1998–2002. We monitored treatment effects on above‐ground plant biomass, plant community structure and plant and soil nutrient concentrations. Results: Both disturbance and N‐fertilization increased the relative biomass of graminoids. The increase of relative biomass of graminoids in the disturbance treatment was over twice that of the highest N‐fertilization level, and N‐fertilization further increased their relative biomass after disturbance. As repeated disturbance broke the dominance of evergreen dwarf shrubs, it resulted in a situation where deciduous species, graminoids and herbs dominated the plant community. Although relative biomass of deciduous dwarf shrubs declined with N‐fertilization, it did not cause a shift in plant community structure, as evergreen dwarf shrubs remained dominant. Both disturbance and N‐fertilization increased the N concentration in vascular plants, whereas microbial biomass N and C were not affected by the treatments. Concentrations of NH₄⁺, dissolved organic N (DON) and dissolved organic C (DOC) increased in the soil after N‐fertilization, whereas concentrations of NH₄⁺ and DON decreased after disturbance. Conclusions: Disturbances caused by e.g. humans or herbivores contribute more to changes in the understorey vegetation structure than increased levels of N in subarctic vegetation. Fertilization accelerated the recovery potential after repeated disturbance in graminoids. Microbial activities did not limit plant growth.