短周期杉木人工林不同林龄土壤肥力综合评价

为探讨不同生长发育阶段林地土壤肥力状况及地力衰退趋势,分析影响地力衰退的主要影响因子,以不同林龄(2、4、6、8和11 a)杉木短周期小径材培育人工林的土壤样本为研究对象,检测土壤有机质、全氮、全钾、全磷、水解性氮、速效钾、有效磷、有效铁、交换性钙、交换性镁含量和pH值共11个土壤肥力指标,分析不同林龄土壤养分差异及其变化趋势。结果表明:除土壤pH值外,土壤主要肥力指标的变化幅度较大,有机质、全氮、水解性氮、速效钾、有效磷含量在不同土层和不同林龄间均存在极显著差异(P<0.01);随着林龄的增长,林地土壤有机质和氮磷肥消耗较大,其中,表土层(0~20 cm)有机质、水解性氮、有效磷含量到11 a主伐时的降幅均超过30%,但不同林龄间各肥力指标差异不显著;采用改进后的Nemerow法计算的土壤肥力综合指数为0.412~0.530,土壤肥力等级为Ⅲ级(P_综<0.9),土壤肥力较低,相比较而言,土壤中有机质和氮肥含量较充足,而交换性阳离子极为贫乏;有机质、速效钾、水解性氮、有效磷含量与综合肥力指数呈显著或极显著正相关(R_偏~2>0.8),是影响土壤肥力的主要因子;土壤肥力综合指数随林龄增大而降低,11 a主伐期比造林初期(2 a)下降22.26%,但不同林龄间各单项肥力指数及综合肥力指数均不存在显著差异(P>0.08)。在该栽培模式的超短经营周期内,随着林龄增大及林木生长对土壤养分的消耗,林地土壤肥力出现一定程度的退化现象,但并未达到显著水平,有必要通过提高整地质量、改良土壤、林粮间作、增施有机肥及氮磷钾肥等措施适度增加土壤肥力,维持林地长期生产力。     

杉木土壤肥力观测及叶片营养分析

土壤肥力变化是造林地环境评价的主要内容之一。本研究通过对杉木造林地土壤的肥力观测分析,为杉木造林地的环境评价和防止杉木人工林地土壤肥力衰退,改善营林措施提供重要参考。１试验地基本情况试验地位于云南省东部罗平县八大河乡,东经１０４°４０′,北纬２４°２...     

南亚热带杉木人工成熟林密度对土壤养分效应研究

[目的]研究5种不同密度林分土壤剖面养分含量的变化规律。[方法]以广西大青山37年生杉木密度试验林为研究对象,测定了A(1 667株·hm-2)、B(3 333株·hm-2)、C(5 000株·hm-2)、D(6 667株·hm-2)、E(10 000株·hm-2)5种密度下0 100 cm土层土壤养分含量。利用单因素方差分析和多重比较判断不同密度和不同土层土壤养分含量的差异。[结果]表明:(1)杉木人工成熟林大多数土层土壤有机质、全氮、碱解氮、全磷、有效性铁含量在A、B等低密度林分中最高,并且在0 30 cm的土壤中,随密度的增加表现出总体下降的变化趋势,而土壤pH值与全钾、速效钾随密度的增加而上升,交换性钙与交换性镁含量受密度影响不明显;(2)土壤有机质、全氮、碱解氮、有效磷、速效钾、交换性钙、交换性镁和有效性铁含量均随土层深度的增加而明显下降,0 30 cm表层土壤的降幅较大,密度对不同土壤深度养分含量的变化具有一定影响。[结论]初植密度对杉木人工成熟林土壤养分含量影响明显,低初植密度更有利于杉木人工林土壤肥力的长期维持,南亚热带杉木林密度对土壤养分的影响深度可达60 cm。     

Effects of Lime and Wood Ash on Soil-solution Chemistry,Soil Chemistry and Nutritional Status of a Pine Stand in Northern Germany

Lime and wood ash may be useful to improve acidic forest soils. A field experiment was conducted in a pine stand on a sandy podzol at Fuhrberg, Germany, which involved an application of dolomitic lime (3 t ha^-1) with three replications or wood ash (4.8 t ha^-1) without replications on the forest floor. During the 2 yr study period, lime affected the soil solution composition only slightly. Ash had a marked effect on solution chemistry of the mineral soil at 10 cm and the pH values dropped temporarily from 3.7 to 3.1. Nineteen months after the treatments, exchangeable calcium in the organic layer and mineral soil increased by 222 (lime addition) or 411 kg ha^-1 (ash addition) and exchangeable magnesium increased by 101 (lime addition) or 39 kg ha^-1 (ash addition). After ash addition, no marked change in heavy metal content was found below 4 cm of the organic layer. In the ash treatment, the potassium concentration of the 1-yr-old pine needles increased from 5.6 to 5.9 g kg^-1. This study suggests that ash from untreated wood may be recommended for amelioration of forest soils.     

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。     

华北土石山区刺槐和栓皮栎人工林土壤微生物数量和微生物量碳、氮研究

正截止到2014年,全国水土流失面积已高达294.91万km2,占国土总面积的30.72%[1-2]。水土流失造成生态环境脆弱,植被破坏促使水土流失加剧是区域环境恶化的主要原因之一[3]。众多研究表明,植被恢复可有效地减少水土流失,是遏制生态环境恶化、改善脆弱生态系统的有效措施[4-6]。在森林生态系统中,土壤微生物对土地利用的变化、管理措施、耕作和肥力水平等外界条件的变化十分敏感,     

思茅松人工林幼林期林地土壤肥力状况的研究

对思茅松人工林幼林期(1~4年生)林地土壤肥力的定位监测结果表明:营造思茅松人工林,只要合理施肥,就能有效地维护其林地土壤的肥力。其经营过程中施用尿素能够显著提高思茅松人工林林地土壤的养分含量,改善其土壤的化学性质;施用过磷酸钙和硫酸钾对思茅松人工林林地土壤肥力的影响不显著,但当其施用量达到一定水平时也能防止林地土壤的退化。     

Effect of land-use conversion from forest to cocoa agroforest on soil characteristics and quality of a Ferric Lixisol in lowland humid Ghana

Soil fertility decline caused by deforestation, soil degradation and low input use has become a primary factor limiting sustainable utilization of soil resources in cocoa agroforestry systems on acid soils in lowland humid Ghana. Changes in and responses of soil physico-chemical properties and soil quality to land-use change was investigated along a chronosequence of farm fields on a Ferric Lixisol in the Ashanti region of Ghana. Soil bulk density increased significantly only in the top 0–10 cm soil layer. Concentrations and stocks of soil organic carbon (SOC) and total N decreased significantly in the top 0–10 and 10–20 cm soil depths. By 30 years after forest conversion, cocoa system had re-accumulated up to 38.8 Mg C ha^?1 or 85 % of initial forest carbon stock values. Total porosity (%) decreased significantly in shaded-cocoa fields in comparison with the natural semi-deciduous forest. An assessment of soil deterioration using degradation indices (DIs) revealed that total soil quality (0–20 cm) deteriorated significantly (DI = –60.6) in 3-year-old of cocoa system but improved in 15 and 30-year-old systems. Available P stocks declined consistently while soil exchangeable Ca, K and Mg stocks as well as cation exchange capacity (CEC) and base saturation remained more or less stable with a tendency to improve. The inclusion of leguminous shade trees during early plantation development, development of mechanisms for the integration of cover crops and enhancement of farmer capability in improved farm management are required to maintain high C and nutrient base, minimize soil quality degradation during plantation development phase and sustain long-term productivity.     

巨尾桉林地土壤化学性质变化分析

通过对福建省长泰县一块巨尾桉林地18 a经营前后土壤各种养分指标的比较,揭示桉树林地长期经营对土壤肥力的影响,结果表明：土壤有机质、养分全量及交换性钙、镁、碱解氮等都有不同程度提高,而速效钾、pH值和速效磷等有所降低,分析认为杂交桉主要靠杂交优势而非靠消耗地力获得增产,杂交桉林地养分循环良好,土壤有机质增加,土壤供肥潜力提高;现有速效钾、pH值为林地正常值,18 a前测定的为炼山造林后的样品数据,草木灰（K2CO3）渗入土壤所致,速效磷降低为杂交桉对其需求量较大所致;建议在桉树人工林经营过程中应注意补充磷肥和钙肥。     

巨桉(Eucalyptus grandis)植被和其相邻的山地雨林中土壤营养的评价

A study was conducted to evaluate the status of soil nutrients under E. grandis plantation in comparison with that in its adjacent submontane rain forest. Twenty sequare plots, with an area of 20 m×20 m for each, were established in both of E. grandis plantation and its adjacent sub-montane rain forest, independently. Soil samples were collected from each square plot, at five points (at the four corners and at the center) of each plot. The collected soil samples were mixed to make a composite and representative sample for each plot, independently. The analyses were done in a soil laboratory following appropriate methods. The analysis result indicated that there were no significance differences between E. grandis plantation and its adjacent sub-montane rain forest in the level of major soil nutrients (total N, available P, exchangeable K, Ca and Mg), pH and total carbon of soils (p < 0.05). There were significance differences between two sites of forest soils in percentage of clay particles, and exchangeable Na content. E. grandis plantation was found improving soil nutrients and total carbon as compared with that of its adjacent submontane rain forest.     

Vegetation community and soil characteristics of abandoned agricultural land and pine plantation in the Qinling Mountains,China

In order to determine the changes in the characteristics of the vegetation and soil following agricultural abandonment and compare the effects of different restoration approaches on ecosystem recovery, we studied the vegetation community and soil characteristics (nutrients, bulk density, water content and pH) of Pinus tabulaeformis plantations and abandoned croplands in different successional stages in the Foping National Nature Reserve, located in the Qinling Mountains, northwest China. The results indicated that natural vegetation and habitat could be restored via natural regeneration. These spontaneous restoration forests were characterized by high diversity, high soil fertility and rich unique species. The soil organic matter, total carbon, total nitrogen, available potassium, community cover, depth of litter, depth of humus and soil water content increased significantly with years after abandonment, while the total potassium, total phosphorus, available phosphorus, soil pH did not seem to change significantly with abandonment time. The soil mineral nitrogen (NH₄-N + NO₃-N) tended to increase during the first 50 years after abandonment and then decreased. The pine plantations tended to show a low level of biodiversity in tree and herb layer, but the shrub layer (including sapling) composition and diversity were similar to secondary forests. Although the pine plantation showed lower soil fertility, they did not seem to result in the habitat-degradation.     

马尾松人工幼林土壤肥力变化及其综合评价研究

通过分析广西环江县桉树林及砍伐后种植马尾松和荒地的土壤化学性质,运用灰色关联分析方法,研究和评价马尾松和荒地取代桉树后土壤肥力变化状况。研究结果显示:取代桉树林后,4.0a马尾松和荒地的土壤碱解N、有效P、速效K、交换性Ca和有效Zn有所提高,土壤pH值有所改善,而全N、全P、全K、交换性Mg和有效Cu有所减少。0～20cm层土壤有机质和有效B有所降低,20～40cm层的反而有所提高。不同林龄马尾松和荒地的土壤综合肥力普遍较差。造林4年后,同土层马尾松林的土壤综合肥力低于荒地。除4.0a荒地0～20cm层的土壤综合肥力基本无变化外,其他4.0a马尾松和荒地土壤综合肥力都有不同程度退化,而以4.0a马尾松20～40cm层的土壤肥力退化最严重。研究结果可为马尾松人工幼林的配方施肥提供理论依据。     

Enrichment planting of Picea glauca in boreal mixedwoods: can localized site preparation enhance early seedling survival and growth?

Conserving forest biodiversity has become a significant global concern. A change in forest composition, compared to pre-industrial values, is an important biodiversity issue. In this regard, there is a significant decrease in Picea glauca densities at the landscape level in boreal mixedwoods of northeastern Canada, compared to pre-industrial abundance. Enrichment planting is considered a promising silvicultural approach for improving P. glauca stocking and re-establishing its natural co-dominance with Abies balsamea. However, optimal enrichment scenarios must be identified, notably regarding site preparation treatments that can enhance planted seedling survival and growth while protecting Abies advance regeneration. We established a field trial in Quebec (Canada), laid out as a complete block split-plot design. Picea glauca and P. mariana seedlings (main plot) were planted according to 3 “microsite” treatments (subplot): (1) planting in the humus layer; (2) planting in the mineral soil, with minimal humus disturbance; and (3) planting in a microsite mechanically-prepared using modified brushsaws. After 3 growing seasons, P. mariana seedlings were taller than P. glauca seedlings, but had smaller ground-level diameters. Seedlings planted in the mineral soil had overcome the initial height difference they had with seedlings planted in the humus and mechanically-prepared microsites, with no interaction with species. Ground-level diameter was similar for seedlings planted in the humus and mechanically-prepared microsites, but smaller for seedlings planted in the mineral soil. Water potentials, available light, and foliar nutrient concentrations were not influenced by treatments or species; survival was >90 %. Our results indicate that P. glauca can be established through enrichment planting in boreal mixedwoods. Localized site preparation is not required to limit initial plantation stress in this ecosystem.     

Characteristics of carbon and nitrogen of soil microbial biomass and their relationships with soil nutrients in Cunninghamia lanceolata plantations

The soil microbial biomass and nutrient status under the native broadleaved forest and Cunninghamia lanceolata plantations at the Huitong National Research Station of Forest Ecosystem (in Hunan Province, midland of China) were examined in this study. The results showed that after the native broadleaved forest was replaced by mono-cultured C. lanceolata or C. lanceolata, soil microbial biomass and nutrient pool decreased significantly. In the 0–10 cm soil layer, the concentrations of soil microbial carbon and nitrogen in the broadleaved forest were 800.5 and 84.5 mg/kg, respectively. These were 1.90 and 1.03 times as much as those in the first rotation of the C. lanceolata plantation, and 2.16 and 1.27 times as much as those in the second rotation of the plantation, respectively. While in the 10–20 cm soil layer, the microbial carbon and nitrogen in the broadleaved forest were 475.4 and 63.3 mg/kg, respectively. These were 1.86 and 1.60 times as much as those in the first rotation, and 2.11 and 1.76 times as much as those in the second rotation, respectively. Soil nutrient pools, such as total nitrogen, total potassium, NH₄ ⁺-N, and available potassium, also declined after the C. lanceolata plantation replaced the native broadleaved forest, or Chinese fir was planted continuously. Less litter and slower decay rate in pure Chinese fir plantation were the crucial factors leading to the decrease of soil microbial biomass and nutrient pool in this area. Human disturbance, especially slash-burning and site preparation, was another factor leading to the decrease. There were significant positive correlations between soil microbial carbon and nitrogen and soil nutrients. To improve soil quality and maintain sustainable productivity, some measures, including planting mixed conifer with hardwood, preserving residues after harvest, and adopting scientific site preparation, should be taken. Translated from Chinese Journal of Applied Ecology, 2006, 17(12): 2,292–2,296 [译自: 应用生态学报]     

Development of bioavailable pools of base cations and P after afforestation of volcanic soils in Iceland

Few long-term studies have been conducted on changes in soil nutrients after afforestation in Iceland, a country with a young history of forest management. While fertilization was shown to improve survival of seedlings in the first years after planting on the nutrient limited soils, knowledge about the nutrients status of the soils that develop under maturing forest stands is still scarce. In a chronosequence study, the development of base cations and Olsen-phosphorus (Olsen-P) in the mineral soil was followed in six forest stands of two different tree species of increasing age (14–97 years): native birch (Betula pubescens) and introduced Siberian larch (Larix sibirica). A treeless heathland was included to present soil conditions prior to forest establishment. The sites are part of the largest forest area in Iceland, located in the east of the country. Results revealed an effect of stand age on all soil nutrients investigated except for potassium (K). Olsen-P increased in 0–10 cm depth of the mineral soil, indicating a better availability and thus improved P supply in maturing forest stands. Calcium (Ca) and magnesium (Mg) concentrations decreased with stand age in 0–10 and 10–20 cm soil depth, while sodium (Na) decreased only in the upper soil layer. Only Olsen-P and K concentrations were higher in the upper soil layer as compared to 10–20 cm depth. This indicates a higher biotic control as opposed to the geochemical control of the other base cations.     

鼠茅草间作对油茶林地土壤养分及酶活性的影响

[目的]探索油茶林间作鼠茅草对土壤质量的影响,为油茶林地的科学经营提供参考。[方法]采用随机定点取样法,测定分析鼠茅草腐解过程中油茶林地0~20 cm耕作层土壤含水量、养分含量及酶活性指标的动态变化。[结果]鼠茅草间作对油茶林地0~20 cm耕作层土壤含水量、养分含量及酶活性影响显著。与对照相比,7—10月鼠茅草间作的土壤含水量平均增幅达39.62%;鼠茅草间作不仅显著提高了油茶林地0~20 cm耕作层土壤有机质、全氮、全磷及全钾含量,而且也提高了土壤中的水解性氮、有效磷与速效钾的含量,其中,有效磷增幅最显著,在8月下旬为对照组的9倍;鼠茅草间作对油茶林地土壤脲酶、酸性磷酸酶与过氧化氢酶的活性影响显著,对蔗糖酶活性影响不显著。[结论]鼠茅草间作经营一定程度上提高了油茶林地土壤肥力水平,对油茶林地土壤改良和可持续生产具有积极的作用。     

Export of Nutrients in Plant Biomass Following Harvest of Eucalypt Plantations in Kerala,India

Abstract

Pools of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were examined in the soil and above-ground plant biomass at the end of a 7 year rotation at two E. tereticornis lowland sites and two E. grandis highland sites in Kerala, India. Potential export rates of these nutrients were also examined for different biomass removal scenarios from the plantations. Pools of nutrients were measured in the above-ground components of the tree crop, forest floor and understorey, and in soil down to 1 m depth. At harvest, large quantities of biomass and nutrients are removed from eucalypt plantation sites, with the quantities of nutrients exported unlikely to be replaced through natural atmospheric and weathering inputs. Between 24 Mg ha^-1 and 115 Mg ha^-1 of biomass was exported in stem wood across the sites, and this increased to 40-145 Mg ha^-1 in scenarios where all of the branches, bark and understorey were also exported. Stem wood had the lowest concentration of nutrients and had a relatively low export of nutrient per kg of biomass. On average, 54 kg, 12 kg and 65 kg of N, P and K were removed per hectare in stem wood only, equivalent to 0.46%, 0.17%, and 6.7%, respectively, of above- and below-ground (to 1 m depth) site pools. Export increased to 194 kg, 30 kg, and 220 kg of N, P and K per hectare if the branches, bark and understorey were also removed (equivalent to 1.6%, 0.5% and 24.7% of above- and below-ground site pools down to 1 m depth). Export of Ca and Mg was also high, with an average of 88 kg and 11 kg of Ca and Mg removed per hectare if only the stem wood was taken (3.12% and 1.34% of total above-ground and exchangeable below-ground to 1 m depth), increasing to 501 kg ha^-1 and 66 kg ha^-1 if the branches, bark and understorey were also removed (21.7% and 11.3% of total above-ground and available below-ground to 1 m depth). Removals of this magnitude represent a significant proportion of site nutrient pools and have the potential to reduce future plantation productivity unless steps are taken to promote retention of biomass and nutrients on site and/or replacement of nutrients through fertilizer application.     

杉木人工林土壤养分及酸杆菌群落结构变化

【目的】研究浙江开化杉木人工林连栽过程中土壤养分及寡营养细菌酸杆菌群落变化规律,揭示不同类型杉木林地导致土壤肥力变化的酸杆菌分子生态学机制,为该地区杉木人工林林分结构调整、土壤资源的科学管理以及构建健康土壤生态系统提供科学依据。【方法】以马尾松林(对照)、马尾松林皆伐后的一代杉木林、杉木林迹地自然更新二代林土壤为研究对象,测定不同深度土层(0～20 cm, 20～40 cm)的土壤pH、束缚水含量、有机碳及主要速效养分含量,比较分析土壤肥力水平,同时进行土壤细菌16S rDNA高通量测序分析了优势酸杆菌群的结构变化。【结果】1)马尾松林改植杉木后土壤酸化显著,碱解氮、有效磷及速效钾含量显著降低(P<0.05),不同林地肥力水平大致规律表现为马尾松林>杉木一代林>杉木连栽林。2) 3种森林类型的土壤细菌中酸杆菌门均占明显优势(32.68%～49.17%),且连栽后的杉木连栽林0～20 cm土层酸杆菌占比显著高于马尾松林0～20 cm土层(P<0.05)。3)共检测出18个酸杆菌类群,其中Gp2在各个样地中均为绝对优势菌群,占酸杆菌群的47.74%～68.80%,Gp1占21.69%～29.72%,其次是Gp3占13.30%～22.41%。酸杆菌类群中Gp2优势加强,同时Gp3具有由优势菌属转变为次优势菌属的趋势。Gp1和Gp10相对丰度分别与土壤pH呈显著负相关(P=0.035)和显著正相关(P=0.035),Gp2相对丰度与土壤有效磷呈显著负相关(P=0.010)。【结论】马尾松林改植杉木及杉木人工林连栽过程中土壤肥力水平降低,而土壤寡营养细菌酸杆菌相对丰度提高,酸杆菌群落作为土壤优势菌群随土壤环境变化而不断调整,这预示着酸杆菌在杉木人工林土壤物质循环中起非常重要作用。     

马尾松两种林型土壤养分特征及其与凋落物质量的关系

【目的】研究土壤养分和地被层凋落物养分含量的差异,为马尾松人工林营林措施及地力维持提供科学依据。【方法】以鼎湖山两种典型林型(马尾松纯林和马尾松-黧蒴混交林)为研究对象,对比分析0~60 cm土层的土壤养分含量及地被层凋落物养分含量的差异,探索凋落物质量如何影响土壤养分。【结果】1)林型对土壤有机质、全氮和硫酸根含量有显著影响(P<0.05),对土壤全磷、交换性K+、Ca2+和Mg2+有极显著影响(P<0.01),混交林土壤养分含量(除硝态氮含量和交换性H+含量以外)均高于纯林。2)相同林型不同土层间土壤养分含量差异极显著(P<0.01),其中,土壤有机质和全氮含量随土层的加深而递减,且主要聚集在0~10 cm土层,表聚效应十分明显。3)纯林凋落物有机碳、全氮、C/N和全磷等含量高于混交林;相同林型不同分解层凋落物有机碳、全钙和全镁含量有显著差异(P<0.05),均表现为未分解层>半分解层>腐殖质层。4)土壤养分与地被层凋落物质量的RDA分析表明,0~10 cm土层土壤养分与腐殖质层有机碳呈极显著负相关(P<0.01),与腐殖质层C/N呈显著负相关(P<0.05);在10~20 cm土层,土壤养分与腐殖质层有机碳呈极显著负相关(P<0.05)。【结论】纯林的土壤养分低于混交林的主要原因是纯林凋落物具有较高的C/N和有机碳含量。     

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.