Forest ecosystem recovery in the southeast US: soil ecology as an essential component of ecosystem management

The forestry industry in the southeastern United States relies upon soils that are highly eroded and depleted of their original organic matter and nutrient content. Pro-active land management can ensure continued and possibly increased production and revenue through the management and recovery of the soil resource. With an emphasis on loblolly pine (Pinus taeda L.) forests, this review integrates land-use history, pine ecology, silviculture, soil ecological research and the implications for forest management into a single discussion. Promoting soil recovery involves knowledge of ecosystem history and disturbance as well as nutrient cycling mechanisms, pools, fluxes and soil forming factors. Research on the rhizosphere is an area that is needed. Recovery of regional soils may confer benefits of drought and disease resistance. The goal of sustainable forestry is compatible with soil recovery; however, the technology and practices of modern forestry deserve thorough evaluation. Emphasis on the continued production of commodities, the agricultural model, is much different from managing for the functioning of healthy forest ecosystems. Many of the practices and outcomes of intensive forest management, including short rotations, harrowing, subsoiling, and burning or removal of logging slash, seem to be at odds with the goal of soil recovery. Best management practices that foster soil recovery include less intensive stand utilization and reduced soil disturbance. Stem-only harvest and longer rotations permit a recovery of soil biodiversity and an accrual of detritus and soil organic matter. Windrowing and similar techniques have dramatic and lasting effects on soil development. No-tillage agriculture as a model for pine plantations is discussed.     

林火干扰对土壤氮组分及微生物氮循环影响研究进展

林火干扰作为森林生态系统中能量传递和养分循环的重要因子,对于研究火烧迹地植被更新与快速恢复可提供一定的数据理论支撑,而林火干扰对土壤微生境及微生物氮循环的影响机制一直是广大学者研究的热点。文中从火烧强度、恢复时间、火烧木管理方式等3个方面总结国内外林火干扰对土壤氮组分及氮循环的影响研究进展,揭示了林火干扰和全球气候变化对土壤氮循环的短期及长期影响机制,探讨不同生物技术在林火干扰下土壤微生物氮循环基因丰度变化中的应用;提出未来林火干扰对森林生态系统土壤氮循环影响的研究展望:1）全面比较研究不同林火干扰模式对土壤氮组分、微生物氮循环的影响;2）研究评价不同林火干扰模式下土壤氮库的稳定性;3）加强高通量测序、定量PCR技术、宏基因组学、稳定同位素探测等技术在林火干扰与气候变化对森林生态系统影响研究中的应用。研究结果对火烧迹地植被更新、土壤氮库的重建与功能发挥具有重要意义。     

Effects of site preparation and slash management on growth and understory vegetation of Eucalyptus globulus plantations along a rotation time span in Portugal

The removal or maintenance of harvest residues in eucalypt plantations may influence site quality and productivity. Removal of slash from the site may facilitate further management operations and provide a valuable energy resource, but effects on site productivity and sustainability for a rotation time span were not yet assessed under Mediterranean conditions. Therefore, a study was carried out to assess the effects of slash (harvest residues plus forest floor litter) management and soil preparation options on stand productivity and understory vegetation dynamics, hypothesizing that those options influence tree growth, forest floor dynamics and understory biomass and diversity. An experiment was installed in West Central Portugal, consisting on: removal of slash without soil preparation (R); broadcast of harvest residues on the soil surface without soil disturbance (S); as in S, but concentrating the woody debris between tree rows (W); incorporation of slash into the soil by harrowing (I); removal of slash followed by harrowing (RH); and as in I followed by ripping (IS). The experiment was monitored for a rotation time span (140 months). Maintenance of slash followed by deep soil disturbance led to the highest wood production, but differences between treatments were not significant (p > 0.05). Forest floor load and understory biomass were also similar between treatments. Ground vegetation played an important role on nutrient cycling in early rotation stages, such effect being irrespective on slash management options. Incorporation of slash into the soil followed by ripping is probably the best option to match production and environmental sustainability of eucalypt plantations in Mediterranean conditions.     

Hurricanes,people, and riparian zones: controls on nutrient losses from forested Caribbean watersheds

Studies of nutrient cycling in tropical forests have shifted and broadened their focus in the past 20 years. Early research highlighted the tight retention of nutrients (primarily P) in the soil profile, and the effects of slash and burn agriculture on nutrients in soil and soil water. More recent work includes a wider variety of experimental approaches, nutrients, and disturbance types. Using examples from my own research and from the literature, I examine the impact of catastrophic natural disturbance, human land use, and landscape features near the stream channel (riparian and hyporheic zones) on nutrient losses from tropical forests. These studies show that the effects of catastrophic natural disturbance can be ephemeral, that impacts of human land use can greatly exceed those of natural disturbance, and that landscape features can play a very important role in minimizing nitrogen losses from humid tropical catchments. Future directions for research in tropical forest nutrient cycling are suggested.     

Effects of an exotic conifer (Pinus radiata) plantation on forest nutrient cycling in southeastern Australia

The distribution and movement of N, P, K, Na, Mg, and Ca were studied in southeastern Australia in a 37—year-old Pinus radiata plantation and in a nearby Eucalyptus obliqua — Eucalyptus dives forest of the same age and of the same type as that which had been replaced by the P. radiata plantation. The soil beneath the P. radiata plantation contained significantly less total N and exchangeable K, Mg, and Ca than that beneath the eucalypt forest. No large accumulation of nutrients was found in either the litter or the trees in the P. radiata plantation relative to that in the eucalypt forest. However, there was a slightly greater accumulation of N and K in the P. radiata biomass than in the eucalypt biomass. The annual soil nutrient balance obtained by subtracting outputs (mineral soil leachate + biomass incorporation) from inputs (precipitation + mineral weathering) indicated a more favourable balance for each nutrient in the soil beneath the eucalypts than in the soil beneath the pines. Calculations suggested that these balances could only partially account for the differences in soil nutrient quantities between eucalypt and pine ecosystems. It was hypothesized that these differences are also partially explainable in terms of the nutrient losses accompanying two fires which had occurred in the pine plantation area. Nitrogen balances in this study were incomplete because several potentially important fluxes were not measured.     

An examination of stocking and early growth in the Warra silvicultural systems trial confirms the importance of a burnt seedbed for vigorous regeneration in Eucalyptus obliqua forest

Clearfelling of wet eucalypt forest followed by high intensity burning and aerial sowing, a silvicultural system designed to mimic the natural dynamic of sporadic regeneration following cataclysmic disturbance, has attracted criticism for not maintaining the structural diversity that is associated with natural disturbance. A silvicultural systems trial was established at the Warra Long-Term Ecological Research site in southern Tasmania to explore alternatives to clearfelling in tall wet eucalypt forest. Stocking, density and growth of the seedling regeneration were monitored for up to 3 years after harvesting and regeneration treatments were applied from 1998 to 2007. The treatments were clearfell with understorey islands, a patchfell, stripfell, dispersed retention, aggregated retention, and single-tree/small-group selection. High intensity burning, low intensity burning and no burning were variously applied as part of these treatments.     

Assessing the effects of early silvicultural management on long-term site productivity of fast-growing eucalypt plantations: the Brazilian experience

Eucalyptus is the dominant and most productive planted forest in Brazil, covering around 3.4 million ha for the production of charcoal, pulp, sawtimber, timber plates, wood foils, plywood and for building purposes. At the early establishment of the forest plantations, during the second half of the 1960s, the eucalypt yield was 10 m³ ha^?1 y^?1. Now, as a result of investments in research and technology, the average productivity is 38 m³ ha^?1 y^?1. The productivity restrictions are related to the following environmental factors, in order of importance: water deficits > nutrient deficiency > soil depth and strength. The clonal forests have been fundamental in sites with larger water and nutrient restrictions, where they out-perform those established from traditional seed-based planting stock. When the environmental limitations are small the productivities of plantations based on clones or seeds appear to be similar. In the long term there are risks to sustainability, because of the low fertility and low reserves of primary minerals in the soils, which are, commonly, loamy and clayey oxisols and ultisols. Usually, a decline of soil quality is caused by management that does not conserve soil and site resources, damages soil physical and chemical characteristics, and insufficient or unbalanced fertiliser management. The problem is more serious when fast-growing genotypes are planted, which have a high nutrient demand and uptake capacity, and therefore high nutrient output through harvesting. The need to mobilise less soil by providing more cover and protection, reduce the nutrient and organic matter losses, preserve crucial physical properties as permeability (root growth, infiltration and aeration), improve weed control and reduce costs has led to a progressive increase in the use of minimum cultivation practices during the last 20 years, which has been accepted as a good alternative to keep or increase site quality in the long term. In this paper we provide a synthesis and critical appraisal of the research results and practical implications of early silvicultural management on long-term site productivity of fast-growing eucalypt plantations arising from the Brazilian context.     

Potential use of wood ash in South African forestry: a review

The use of landfills as a disposal method for wood ash is costly, environmentally detrimental and is pitted against increasingly stern environmental regulations. Literature has shown that wood ash has the potential to be used as a forest fertiliser and the effects tend to be highly site-specific. Wood ash contains a combination of carbonates, hydroxides and other calcium-containing minerals that are responsible for the liming effect observed following application to soils. In addition, it contains significant magnesium and potassium concentrations, but little nitrogen and sulphur. The phosphorus availability of wood ash varies considerably and in effect can limit soil phosphorus uptake and may affect subsequent nutrient balance in plants. Short-rotation forestry practices and whole-tree harvest systems can induce periodic or persisting nutrient deficiencies and acidify the soil. This may affect the ability of a site to sustain adequate nutrient levels over successive rotations. Utilising wood ash as a soil amendment can offset or correct some nutrient deficiencies and imbalances induced by intensively managed plantation forests. This review covers the international literature on ash applications to forest land, including the effect of ash-beds remaining after slash burning (as a useful analogy for the effects of wood ash on soil properties and tree growth). The results show that ash applications to forest land can be done safely and can potentially stimulate microbial activity and improve pine and eucalypt growth. Safe ash application rates should be determined after consideration of (1) soil buffer capacity and ash alkalinity (expressed as calcium carbonate equivalence) and (2) an evaluation of the concentrations of heavy metals existing in soils and present in the available ash, particularly from cadmium, chromium, lead and arsenic.     

森林不同组分对降水的生态效应研究进展

森林是一个复杂的生态系统, 森林水文学是近年来研究的热点.大气降水作为森林生态系统养分来源之一, 是目前研究森林生态系统养分循环不可或缺的因子.典型的森林生态系统一般通过乔木层、灌草层、凋落物层和土壤层等组分对降水进行分配.文中系统阐述了国内外研究者关于森林生态系统各组分对降水生态效应的研究进展, 同时对森林降水中营养物质的输入和输出研究作了简述, 指出目前相关研究中存在的问题和今后努力的方向, 旨在为今后的研究提供参考.     

桉树人工林养分循环研究成果分析

本文主要介绍了桉树人工林养分循环的意义与研究现状。从地球化学循环和生物小循环（养分含量、养分积累和分布、凋落物、养分循环特征）两方面阐述桉树人工林养分循环的研究内容,分析说明桉树人工林养分循环研究存在的问题及发展趋势,并提出几点建议。     

Impact of wildfire intensity and logging on fungal and nitrogen-cycling bacterial communities in British Columbia forest soils

Wildfire and logging are common disturbances in the forests of northwestern North America, causing changes in soil chemistry and microbiology, including fungal and nitrogen-cycling bacterial communities. These organisms play key roles in nutrient cycling, and affect the regeneration of tree seedlings after disturbance. We studied the effects of wildfire and logging on fungal and nitrogen-cycling communities in the rhizosphere of 16 month-old Douglas-fir seedlings as they regenerated in burned and logged soils. Seeds were planted against root windows that were set up vertically in the soil, with a removable front panel used to access the seedling rhizosphere soil surface. Windows were established in control, lightly burned, and severely burned plots, as well as two types of logged plots (clearcut and screefed clearcut). Soil scrapings from the root window–soil interface were taken and the structure of fungal and nitrogen-cycling communities was resolved using length-heterogeneity PCR (LH-PCR) of fungal nuclear ribosomal RNA genes, and terminal restriction fragment length polymorphism (T-RFLP) analysis of nifH and nosZ genes. We found striking differences in the community structure of fungal, denitrifying, and N-fixing communities in response to burning and logging. With the exception of clearcut and screefed clearcut, which were generally similar, each treatment had a unique impact on community structure for these genes. Burning and logging also impacted the relative richness and evenness of these communities. Fungal relative richness and evenness increased in response to logging and severe burning, while denitrifier relative richness and evenness increased in all disturbance treatments, and N-fixing bacterial relative richness and evenness decreased in response to burning. The greatest differences in microbial community structure, relative richness, and evenness were found in the comparisons of lightly burned and logged treatments. The results suggest that the presence of an intact forest floor influences soil microbial communities less than the presence of living trees.     

林窗效应研究综述

森林群落常发生一些小规模的内源干扰,从而形成林窗。林窗的形成对推动森林群落的演替更新和生态系统发展至关重要。林窗面积的大小与树木的倒伏方式和林冠冠幅及大小有关。林窗面积及林窗内位置的不同,导致其小气候和土壤理化性质等环境因子发生改变,进而影响到林窗内树种更新和物种组成、林窗植被的物种多样性及其微生物和土壤动物的种类、数量等方面。未来林窗研究重点应该放在次生林和人工林的林窗效应,林窗对森林生态系统碳储量影响机制,林窗凋落物分解因子间的相互关系、作用机理和养分循环,不同树种的林窗与最适更新面积的关系,林窗的边缘效应,林窗的土壤动物和微生物动态及过程。     

关于我国人工林长期生产力的保持

为了保持我国人工林的长期生产力和提高森林质量,达到可持续经营的目的。作者在以往研究工作的基础上,广泛收集了国内外有关成果与资料,概括论述了我国人工林森林生产力的现状、不能保持生产力的原因与机理以及长期保持人工林生产力的技术对策。按第八次清查的全国森林资源数据,每公顷蓄积量为89.79 m^3,其中天然林为104.6 m^3,人工林为52.76 m^3,人工林森林生产力明显低于天然林;我国优势树种人工林每公顷蓄积量也不高,如杉木为69.8 m^3,马尾松为56.2 m^3,落叶松为58.6 m^3,这些数据比日本2002年3月公布的人工林相似树种的数据低很多,如日本针叶树蓄积量为227.97 m^3·hm^-2,柳杉为295.83 m^3·hm^-2,落叶松为189.88 m^3·hm^-2。关于年生长量,按全国第七次资源清查的中龄林与近熟林的数据做统计:杉木人工林5.2~4.2 m^3·hm^-2,马尾松为3.2~1.8 m^3·hm^-2,柏木为3.4~3.2 m^3·hm^-2;但按作者掌握的我国重点或示范性、试验性小面积人工林生长量看,却很高,按我国编制的速生丰产林标准的生长量数据看比较高。我国大面积人工林生产力不高,短周期经营的杨树、桉树人工林也不高,主要原因是:(1)纯林化与针叶化严重。按第八次全国森林资源统计,纯林占人工林的85%,而且针叶化明显,人工乔木林10个优势树种中针叶林比例高达56.9%。人工纯林结构简单,生物多样性低,生物学上缺乏稳定性。人工纯林特别是针叶纯林,抗性低,抗自然灾害和大气污染能力均差,人工纯林维护地力的能力也弱。(2)集约育林的技术措施:立地控制技术未得到推广,适地适树适品种原则在育林中未能认真贯彻;密度、植被、地力控制技术也执行不力,大面积上的人工林仍属于粗放经营;连作引起林地土壤理、化、生物特性恶化,土壤质量衰退,导致林木生长不良,林分生产力逐代下降;造林作业造成水土流失,如杉木造林,传统的育林技术未得到明显改进,福建尤溪炼山后进行的3年观测结果表明,炼山和水土流失损失的有机质高达989.35 kg·hm^-2,养分586.26 kg·hm^-2。桉树在砖红壤进行的机耕整地,水土流失也很严重,不合理的造林作业,最终导致土壤质量与森林生产力下降。短周期培育人工林带来了2个重要问题,一是对林地肥力要求高,二是如何利用无性系才能保持长期生产力。短周期经营采用的无性系,生长速度快,生长量大,轮伐期短,养分需求量大,如刚果12号W5无性系,通常利用地上部分,以5~7 a的轮伐期计,消耗的养分达571.75 kg·hm^-2,我国培养短周期人工林的土壤质量本底原本普遍不高,如果采取连作,土壤有机质养分会明显下降,土壤质量衰退,并对其功能产生危害。我国杨树、桉树等人工林要达到短周期持续经营,还需要实行多无性系造林。我国人工林长期生产力保持的技术对策,应采取先进的集约育林措施,包括遗传控制、立地控制、密度控制、植被控制与地力控制。     

贵州黔南州林地土壤养分分析及资产价值评价

通过对研究地黔南州林地土壤养分的定量分析探讨黔南地区林地土壤的养分状况及养分价值,旨为科学评价林地土壤养分价值,为科学营林、合理利用森林土壤资源提供依据。研究表明:不同的植被类型,土壤养分的含量不同;有林地土壤的养分含量明显高于无林地土壤;土壤养分总量针阔混交林高于阔叶林,阔叶林高于针叶林;林地土壤营养物质的总储量为7277.59万t,相当于14581.05万t标准化肥,价值为472.19亿元。     

采伐对森林土壤功能的影响

采伐作为森林经营主要的措施之一,直接或间接地影响了森林土壤功能演变。合理采伐能改善森林土壤功能,进而促进森林的恢复、更新和演替,维持森林资源的可持续性。文中在介绍土壤功能概念及分类的基础上,综述了森林土壤功能（水分和养分循环、碳存储、缓冲与过滤、植物生产和动植物栖息地功能）对采伐方式和强度的响应,并探讨了研究中亟待解决的问题,以期为维护和增强土壤功能,更好地经营森林提供参考。     

海岸带木麻黄林生态系统过程与可持续管理

木麻黄为我国东南沿海防护林体系的主栽树种,如何维持和提高其环境调控功能成为当前沿海防护林经营的重要科学问题。文中概述了海岸带木麻黄林生态系统的物质循环、能量流动和防护功能以及育林措施对森林生态系统的影响等国内外研究成果,指出木麻黄人工林具有生产力高、光能利用率高和适应性强的特点;在探讨干扰与木麻黄林生态系统退化之间关系的基础上,提出加强木麻黄海岸防护林的恢复重建与生态系统管理等建议。     

Long-term impact of prescribed burning on the nutrient status and fuel loads of rehabilitated bauxite mines in Western Australia

Alcoa World Alumina Australia has been rehabilitating bauxite mines in the jarrah (Eucalyptus marginata) forest of Western Australia for more than 35 years. It is a requirement of Alcoa’s completion criteria that rehabilitated areas can be incorporated into the prescribed burning program implemented in the surrounding forest. Rehabilitated areas may be more susceptible to nutrient losses following burning because of their relatively young age and reliance on N fixation from a legume understorey. The objective of this study was to assess the impact that prescribed burning has on the nutrient pools within rehabilitated ecosystems 5 and 8 years after fire, and compare these responses to unburnt rehabilitated areas and the unmined forest. The nutrient status of sites established in previous studies were assessed five (burnt and unburnt forest, 1989 and 1992 rehabilitation) and 8 (spring, autumn and unburnt 1981/1982 rehabilitation) years after burning. Soil, litter and understorey samples were collected and analysed for nutrient content. Burning 1981/1982 rehabilitation in either season 8 years earlier had no long-term negative effect on the nutrient status of the rehabilitation compared to the unburnt controls. Spring burning increased the nitrogen status of the rehabilitated areas by 52 kg ha⁻¹ compared with the unburnt control. Sites rehabilitated in 1989 and burnt 5 years ago showed similar post-fire recovery of nitrogen status to that of the burnt native forest sites (77–85%), while 1992 rehabilitation sites had only recovered 52% of the of the nitrogen of the unburnt sites. Therefore, the impact of burning on nitrogen status was greatest in the 5-year-old rehabilitation and least in the 12–13-year-old sites. Phosphorus was less affected by burning than nitrogen largely because the majority of P is bound in the soil in the jarrah forest. It is recommended that rehabilitated sites are burnt under low intensity in spring when they are 12–15-year-old to ensure rapid post-fire recovery of nutrients.     

不同造林措施对桉树人工林地土壤养分的影响

针对桉树人工林地力退化问题,通过比较两种造林措施下桉树人工林地土壤肥力特征发现,皆伐和造林时的人为活动对浅土层(0～20 cm)的土壤有松动作用,在一定程度上降低土壤容重,部分提高土壤持水量和孔隙度,但造林后林地土壤物理特性变差,炼山+机械挖桩造林措施对林地土壤物理性质破坏作用要明显高于伐根催腐造林;与皆伐前相比,两种造林措施均导致了林地土壤pH向酸性化方向发展;伐根催腐造林使得林地土壤有机质含量、全N、全K、Ca和Mg含量均较皆伐前大,炼山措施导致大量养分烧失和流失,故其最小;土壤微量元素中除了Cu以炼山造林地最大外,Fe、Mn、Zn、B均以伐根催腐造林地最大。     

Patterns of litterfall and return of nutrients across anthropogenic disturbance gradients in three subalpine forests of west Himalaya, India

The study was conducted to improve our understanding of the effects of forest disturbance on litterfall and patterns of nutrient return in three subalpine forest ecosystems (i.e. Betula utilis-dominated, Abies pindrow-dominated, and Acer mixed broadleaf) of Indian west Himalaya. Total litterfall (t ha⁻¹ yr⁻¹) ranged between 2.6–3.6 and 2.1–2.6 for pristine and degraded stands, respectively. Whereas total litterfall decrease from pristine to degraded stand was about 25–30% in B. utilis and Acer mixed-broadleaf forests, the level of disturbance did not affect total litterfall in A. pindrow (coniferous) forest. Nutrient (N, P, and K) concentrations in litter components of the forests studied also varied across forest types and disturbance intensities. For pristine stands, among all the forests, return of total nutrients via litterfall was higher. The study revealed that patterns of litterfall and nutrient return in the forests studied were sensitive to intensity of disturbance, although sensitivity varied among forest types and nutrient contents. Increased intensity of disturbance greatly affected the total annual amount of nutrient return in broadleaf forests. Maximum impact was recorded in B. utilis forest with a significant decline in nutrient return from pristine to degraded stands (i.e. 64% for N, 38% for P, and 67% for K). Corresponding values for decline in Acer mixed forest were 17, 13, and 33% for N, P, and K, respectively, whereas in A. Pindrow forest N return was 15% higher and P return was 33% lower. This study indicates that the litterfall and litter nutrient concentrations in these forests are sensitive to the intensity of disturbance, which affects the amount of nutrient return. This will have a strong bearing on forest nutrient cycling.     

Spatial variability in microclimate in a mixed-conifer forest before and after thinning and burning treatments

In the western United States, mechanical thinning and prescribed fire are common forest management practices aimed at reducing potential wildfire severity and restoring historic forest structure, yet their effects on forest microclimate conditions are not well understood. We collected microclimate data between 1998 and 2003 in a mixed-conifer forest in California's Sierra Nevada. Air and soil temperatures, relative humidity, photosynthetically active radiation (PAR), wind speed, soil heat flux, and soil volumetric moisture were measured at the center of 18 four-ha plots. Each plot was assigned one of six combinations of thinning and burning treatments, and each treatment was thus given three replications. We found that spatial variability in microclimate, quantified as standard deviations among monthly values of each microclimatic variable across different locations (n ≤ 18), was significantly high and was influenced primarily by elevation and canopy cover. The combination of thinning and burning treatments increased air temperature from 58.1% to 123.6%. Soil temperatures increased in all thinned plots. Air moisture variables indicated that treatments made air drier, but soil moisture increased in the range 7.9–39.8%, regardless of treatment type. PAR increased in the range 50.4–254.8%, depending on treatment type. Treatments combining thinning and burning increased wind speed by 15.3–194.3%. Although soil heat flux increased dramatically in magnitude in some plots, overall treatment effects on G were not statistically significant. We discussed the significance and implications of the spatial variability of microclimate and the treatment effects to various ecological processes and to forest management.