神农架巴山冷杉天然林凋落量及养分特征

研究了湖北神农架巴山冷杉 (Abies fargesii) 天然林凋落物量、凋落物N、P、K、Ca、Mg的含量及其归还量。结果表明:巴山冷杉天然林的年凋落量为5702.99kg·hm-2;巴山冷杉林的凋落 物组成比较丰富, 主要有落叶、落枝、球花、球果和其他5部分, 其中以落叶为多, 占总凋落量的46.00%;凋落量的月变化模式呈双峰型, 分别在2006年10~11月和2007年4~5月达到峰值;凋落物养分含量的大小顺序为:N>K>Ca>P>Mg;N、P、 K、Ca、Mg的年归还量分别为:39.1063、4.5346、13.4367、5.4965和0.0911kg·hm-2;就凋落物各组分的养分年归 还量而言, 落叶的养分归还量远远大于其余组分的养分归还量, 占总归还量的52.65%。因此, 不论凋落量还是养分归还量, 巴山冷杉林凋落物中的落叶都占绝对优势。     

大熊猫栖息环境的森林凋落物动态研究

本文以王朗自然保护区冷杉、云杉暗针叶林为对象,在定位测定森林凋落量及其动态和枯枝落叶贮量的基础上,研究了凋落物分解速率及其主要营养元素含量的变化,结果表明：(1)地表枯枝落叶总贮量变化在30.0—91.8t／ha,其中未分解层4.9—17.8,半分解层11.5—19.7,腐殖质层13.6—57.3t／ha。(2)森林凋落的枯枝落叶量因林型不同而略有差异,平均为2.8 t／ha·yr,其凋落高峰期分别在生长季开始的5月和生长季末的10月。(3)每年以凋落物形式返回林地的养分,氮为35.5kg／ha、磷为5.7kg／ha、钾为7.0kg／ha、镁为6.8kg／ha、钙为62.9kg／ha。(4)森林各种凋落物的混合物年分解率为0.3041g／g。95%的凋落物被分解需时约10年,在分解一段时间后,凋落物中的氮、钙、镁含量略有上升,钾明显减少,而磷含量变化不大。(5)森林凋落物的混合物腐解过程中,养分释放速率大小的顺序为：K>P>Mg>Ca>N,大熊猫主食竹的凋落叶则为：K>N>Ca>Mg>P。     

不同坡位对琉球松人工林凋落物及其养分归还量的影响

对日本冲绳岛北部不同坡位的琉球松人工林凋落物量及其养分归还量进行了为期3年的观测研究,结果表明,琉球松成林年凋落物量为6．54～8．05Mg·hm^-2·年^-1,其凋落高峰出现在6、7月份．台风干扰对年凋落物量及其季节动态影响显著．凋落物不同组分的养分含量差异明显．年均养分归还总量为113．4～154．6kg·hm^-2·年^-1,其中氮素归还量最大,占42．2％;各养分归还量的大小依次为N>Ca>K>Mg>Na>P．两调查林分由于立地条件的显著差异,年均凋落物量及其相应的养分归还量亦存在明显差异．在立地条件较好的下坡,林分P1的年均凋落物量达8．05Mg·hm^-2·年^-1,高于立地条件相对较差的上坡的林分P2的23．1％;其相应的年养分归还量为：N66、04,P1.63,K17．42,Ca48.31,Mg14.65和N。6、57kg·hm^-2·年^-1,分别高于林分P2的39.7％、48.8％、39．4％、32.9％、24.8％和49.3％．两林分凋落物的养分利用效率分别是N为122和138,P为4934和5945,K为462和523,林分P1明显低于林分P2,这与林分P2的立地条件较差相关．可见,所调查的琉球松林是一种高效的养分利用系统。     

神农架常绿落叶阔叶混交林凋落物养分特征

凋落物是联结陆地生态系统植物与土壤养分的重要媒介,了解凋落物养分特征有助于理解陆地生态系统物质循环的机理。该研究于2015年收集了神农架地区常绿落叶阔叶混交林的新鲜凋落物及现存凋落物,测定其不同器官中大量元素(C、N、P、K、Ca、Mg)的含量,据此分析其养分含量、养分归还量、养分储量及化学计量比的特征。结果发现:该常绿落叶阔叶混交林新鲜凋落物的C、K养分含量显著高于现存凋落物,N、P、Ca、Mg养分含量显著低于现存凋落物;其凋落物大量元素的养分归还量及养分储量大小顺序均为C Ca N Mg K P,分别为1569.84、52.44、34.82、6.24、5.24、1.30 kg hm~(-2) a~(-1)及1835.29、87.87、51.17、12.12、3.90、1.95 kg hm~(-2) a~(-1);其新鲜凋落物及现存凋落物的C∶N∶P分别为1307.33∶27.73∶1及976.48∶26.77∶1,新鲜凋落物的C∶N、C∶P显著高于现存凋落物,N∶P无显著区别。研究表明,新鲜凋落物与现存凋落物养分含量之间的差异与不同元素在分解过程中的可淋溶性及生物固持等因素有关。该地区常绿落叶阔叶混交林凋落物养分归还量及养分储量相对于亚热带阔叶林平均水平较低;且显著低于喀斯特地区同类型森林,主要与其凋落物产量、降水量及植被类型有关。该森林生态系统新鲜凋落叶与中国及全球范围内阔叶树种凋落叶相比C∶N较低,C∶P、N∶P较高,这可能是由于该地区N沉降及P限制现象较为严重所致。     

中亚热带4种森林凋落物量、组成、动态及其周转期

为研究亚热带次生林保护对森林生态系统养分循环等功能过程的影响。采用凋落物直接收集法,比较湘中丘陵区3种次生林(马尾松+石栎针阔混交林、南酸枣落叶阔叶林、石栎+青冈常绿阔叶林)和杉木人工林的凋落物量、组成特征及其周转期。结果表明:4种林分年凋落物量在414.4—818.2 g m-2a-1之间,3种次生林显著高于杉木人工林,3种次生林两两之间差异不显著,落叶对林分凋落物量的贡献最大,占林分凋落物量的59.9%—66.6%。杉木人工林和南酸枣落叶阔叶林的凋落物量月动态变化呈"双峰型",马尾松+石栎针阔混交林、石栎+青冈常绿阔叶林呈"不规则型"。优势树种的凋落物量对其林分凋落物量的贡献随林分树种多样性的增加而下降,杉木、马尾松凋落物量的月动态与其林分凋落物量的月动态基本呈一致变化趋势,但南酸枣、青冈、石栎没有一致的变化趋势。杉木人工林凋落物分解率最低(0.31),周转期最长(3.2 a),南酸枣落叶阔叶林分解率最高(0.45),周转期最低(2.2 a),凋落物的分解速率和周转随林分树种多样性增加而加快。可见,次生林凋落物量大,且分解快,周转期短,有利于养分归还和具有良好地力维持的能力。     

雷州半岛桉树人工林凋落物量和养分循环研究

为了解雷州半岛地区桉树人工林凋落物量和养分归还特征,对不同林龄人工林凋落物量和养分动态连续12个月进行监测。结果表明,桉树人工林的凋落物总量为5 a9 a7 a,5 a生桉树人工林的凋落物总量显著高于7和9 a生林分,且7和9 a生林分间没有显著差异。不同林龄桉树人工林凋落物总量具有明显的季节变化,均呈双峰型,峰值出现在雨季初期和末期。林分结构因子同凋落物量相关性不显著,但气候因子中的月均温与凋落物量存在显著正相关关系。不同林龄桉树人工林的养分年循环量由凋落物量和凋落物养分含量共同决定,氮、磷、钾元素的养分年归还总量为9 a7 a5 a,且彼此间达到显著差异。凋落物养分元素归还高峰期集中在雨季前后,以冬季养分归还量较低。因此,为增加桉树人工林产量且利于人工林地力恢复,桉树人工林应适当增加种植年限,且采伐季节选择在冬季。     

万木林自然保护区2种天然林及杉木人工林凋落量及养分归还

通过对福建建瓯万木林自然保护区内以观光木(Tsoongiodendron odorum,TSO)和细柄阿丁枫(Altingia gracilipes,ALG)为建群种的2种天然林及杉木(Cunninghamia lanceolata,29年生)人工林凋落量与养分归还为期3a(2000~2002年)的研究表明,3种林分年均凋落量(t.hm-2)范围从杉木人工林的4.63t.hm-2到观光木林的6.74t.hm-2,叶所占比例范围为62%~69%。细柄阿丁枫林凋落量每年只出现1次峰值(3月份或4月份),观光木林的出现2次(3月份、6~8月份),而杉木林的则出现3次(3月份或4月份、6~8月份和11~12月份)。3种林分Ca和Mg年归还量大小排序与按总凋落量的不同。除杉木人工林的Ca年归还量最大外,其余养分年归还量均以观光木天然林的最大。通过凋落物各组分的养分归还中,落叶是养分归还的主体。与针叶树人工林相比,天然林的凋落量大、养分归还量高,具有良好维持地力的能力。因此,保护和扩大常绿阔叶林资源已成为南方林区实现森林可持续经营的重要措施之一。     

雪灾对古田山常绿阔叶林建群种养分含量及归还量的影响

在古田山国家级自然保护区24hm2长期监测样地设置凋落物收集框,对常绿阔叶林的养分归还量进行动态监测。2008年初南方发生特大雪灾,为研究雪灾对建群种甜槠和木荷凋落叶中主要养分含量、归还量的影响提供了契机。结果表明:(1)虽然建群种凋落叶中碳含量受雪灾影响不显著,但雪灾导致其凋落量明显下降,因此碳的归还量在灾后明显减少。(2)建群种凋落叶氮含量在雪灾前后有显著差异,表现为灾前<灾后;但因受凋落量的影响,其归还量仍表现为灾前>灾后。(3)建群种凋落叶磷含量在雪灾前后存在极显著差异(P<0.01),表现为灾前<灾后,导致其归还量也表现为灾前<灾后。     

不同海岸距离上木麻黄凋落叶金属元素含量及归还量动态特征

精确估算生态系统内部环境梯度引起的养分循环差异, 对评估其生态功能十分重要。为探讨不同距海生境对木麻黄(Casuarina equisetifolia)凋落叶金属元素含量及养分归还动态的影响, 以福建省惠安赤湖国有防护林场木麻黄凋落叶为研究对象, 按照离海由近及远的顺序设置5个距离(T₁到T₅), 收集凋落叶测定金属元素含量。结果表明: 1)海岸梯度环境对木麻黄凋落叶各元素含量及归还量具有显著影响, 由基干林带向林内元素含量、归还量呈线性规律, 总体上近海高于远海, 按照离海由近及远元素含量逐渐降低, 铁(Fe)、铜(Cu)、锌(Zn)和锰(Mn)在T₄后上升, 归还量变化趋势与含量相似。2)凋落叶元素含量在不同月份存在显著差异, Na、Fe、Cu、Zn具有相似性, 6月、11月存在明显低谷; Mn在2至4月下降后波动上升。归还量总体表现为钠(Na)、Cu相似, 5、8、次年1月出现峰值;Mn、Fe、Zn相似, 5、8、11、次年1月出现峰值。3)土壤Na含量按照离海由近及远逐渐降低, 其他元素波动变化, 各距离之间差异不明显。4)凋落叶Na-Fe含量存在显著正相关关系, Na-Zn、Fe-Cu、Fe-Zn含量存在极显著正相关关系; 土壤与凋落叶相同元素含量间存在正相关关系, Na和Cu达到显著水平。究其原因, 叶片元素含量差异受叶凋落时间差异造成的重吸收差异影响大; 月间差异因植物生命活动对元素需求量存在差异; 归还量差异与凋落叶量及元素含量有关。     

连续年龄序列桉树人工林凋落物量及养分通量

在福建漳州地区,对连续年龄序列(2、3、4、5、6年生)的尾巨桉(Eucalyptus grandis ×E.urophylla)人工林凋落物量及其养分通量进行了研究.结果表明:不同林龄(2、3、4、5和6年生)的年凋落物总量分别为2796.65、3098.10、4489.13、4200.72和3692.40 kg·hm-2,呈现先期增加,4年生后出现缓慢下降的趋势.各年龄段林分凋落物量均显示出明显的季节动态,其中3、4和6年生林分呈单峰型,前二者出现在6月,后者出现在4月;而2和5年生林分则出现2个峰值,前一个峰值出现在4月,后一峰值出现在6月.在凋落物的组成中,落叶占总凋落物量的84.86%～90.04%,其次分别为碎屑物(5.01%～6.70%)、落枝(2.95%～4.52%)、树皮(2.64%～3.62%)和落果(0.30%～0.55%).凋落物各组分中,主要养分元素含量大小顺序为N>Ca>K>Mg>P.各龄级桉树人工林凋落物中5种元素的年通量的大小顺序表现为:4年生(133.20 kg·hm-2)>5年生(124.98 kg·hm-2)>6年生(97.56 kg·hm-2)>3年生(90.51 kg·hm-2)>2年生(86.01 kg·hm-2).     

The management of rice straw,fertilisers and leaf litters in rice cropping systems in Northeast Thailand.

The maintenance of soil organic matter (SOM) and the balancing of nutrient flows into and out of the rainfed rice cropping systems in Northeast Thailand is of paramount importance to arresting the decline in soil fertility and crop yields. A system where small applications of leaf litters from locally grown trees are applied annually to rice paddy soils prior to transplanting is described. The annual application of 1500 kg/ha of Cajanus cajan, Acacia auriculiformis, Phyllanthus taxodifolius and Samanea saman for five seasons resulted in increases in rice grain yield of 48, 35, 32 and 23% above the no-leaf litter control, respectively. Average annual nutrient inputs from the leaf litters, in kg/ha, ranged from 62.7 N, 3.9 P, 17.9 K, and 3.5 S for Cajanus cajan to 24.5 N, 1.5 P, 8.1 K and 2.0 S for Acacia auriculiformis. Nutrient balances, determined by the difference between the inputs (fertiliser and added leaf litters) and outputs (grain and straw) indicated net positive N and P balances of up to 457 and 60 kg/ha. respectively, after five seasons of leaf litter applications. Sulfur and potassium balances resulted in net deficits of up to −3 and −52 kg S and K/ha, respectively, where no leaf litter was applied and rice straw was removed following harvest. Calculated apparent nutrient recoveries reflected the decomposition rate of the added residues and were highest for P and K, reflecting their higher soil residual value than mobile nutrients such as N and S. Sustainable farming systems will require that crop yields are stable through the maintenance of soil fertility and the balance of nutrients in the system. This revised version was published online in June 2006 with corrections to the Cover Date.     

Structure and function of shisham forests in central Himalaya,India: nutrient dynamics

The structure and function of Shisham (Dalbergia sissoo Roxb.) forests were investigated in relation to nutrient dynamics in 5- to 15-year-old stands growing in central Himalaya. Nutrient concentrations and storage in different layers of vegetation were in the order: tree > shrub > herb. Forest soil, litter and vegetation accounted for 80.1-91.9, 1.0-1.5 and 7.0-18.4%, respectively, of the total nutrients in the system. There were considerable reductions (trees 32.8-43.1; shrubs 26.2-32.4; and herbs 18-8-22-2%) in nutrient concentrations of leaves during senescence. Nutrient uptake by the vegetation as a whole and also by the different components, with and without adjustment for internal recycling, was investigated. Annual transfer of litter nutrients to the soil from vegetation was 74.8-108.4 kg ha(-1) year(-1) N, 56.8-4 kg ha(-1) year(-1) P and 38.7-46.9 kg ha(-1) year(-1) K. Turnover rate and time for different nutrients ranged between 56 and 66 % year(-1) and 1.5 and 1.8 years, respectively. The turnover rate of litter indicates that over 50% of nutrients in litter on the forest floor are released, which ultimately enhances the productivity of the forest stand. The nutrient use efficiency in Shisham forests ranged from 136 to 143 kg ha(-1) year(-1) for N, 1,441 to 1,570 kg ha(-1) year(-1) for P and 305 to 311 kg ha(-1) year(-1) for K. Compared with natural oak forest (265 kg ha(-1) year(-1) and an exotic eucalypt plantation (18 kg ha(-1) year(-1), a higher proportion of nutrients was retranslocated in Shisham forests, largely because of higher leaf tissue nutrient concentrations. This indicates a lower nutrient use efficiency of Shisham compared with eucalypt and oak. Compartment models for nutrient dynamics have been developed to represent the distribution of nutrients pools and net annual fluxes within the system.     

Latitudinal Patterns and Climatic Drivers of Leaf Litter Multiple Nutrients in Chinese Broad-Leaved Tree Species: Does Leaf Habit Matter?

Leaf litter nutrients play a key role in nutrient cycling in forest ecosystems, yet our current knowledge of the ways in which climate controls leaf litter nutrients remains uncertain, especially for broad-leaved tree species in China. We performed a meta-analysis of geographic patterns of leaf litter nutrients of Chinese broad-leaved tree species in relation to climatic variables and leaf habit (as a discrete classification of tree species). We found that mean leaf litter carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were 458.36, 10.11, 0.72, 6.37, 14.22 and 2.59 mg^?1 g, respectively. Leaf litter nutrients did not diverge between leaf habits where they coexisted. These leaf litter nutrients displayed significant latitudinal trends, partly driven by climatic factors and a shift in leaf habit. Mean annual precipitation explained the largest amount of total variation in leaf litter C, N, P and K, and mean annual temperature was the most important predictor for leaf litter Mg, whereas leaf habit was the largest contributor to total variation in leaf litter Ca. We further found that the relationships between climate and leaf litter nutrients were distinguishable for evergreen and deciduous broad-leaved tree species. Collectively, our study differed from previous studies that evaluated leaf litter nutrients and only focused on N and P, and substantiated that leaf litter nutrients in forest ecosystems were affected by climate and leaf habit, but the strengths of the influences of these factors were strongly contingent on leaf litter nutrient identity. Therefore, alteration of climate would directly and indirectly (via a shift in species composition) affect latitudinal patterns of leaf litter nutrients and thus the associated nutrient flux and ecosystem functioning. Our study also underlined the need to include multiple nutrients to explore the influence of climate on leaf litter nutrient stoichiometry.     

Tropical forest restoration in Costa Rica: the effect of several strategies on litter production, accumulation and decomposition

Tropical forest restoration strategies have the potential to accelerate the recovery of the nutrient cycles in degraded lands. Litter production and its decomposition represent the main transfer of organic material and nutrients into the soil substrate. We evaluated litter production, accumulation on the forest floor, and its decomposition under three restoration strategies: plantation (entire area planted with trees), island (trees planted in patches of three different sizes) and control (natural regeneration) plots. We also compared restoration strategies to young secondary forest (7-9 yr). Restoration treatments were established in 50 x 50m plots in June 2004 at six sites in Southern Costa Rica. Planted tree species included two native timber species (Terminalia amazonia and Vochysia guatemalensis) interplanted with two N fixers (Erythrina poeppigiana and Inga edulis). Litter was collected every 15 days between September 2008 and August 2009 in 12 0.25m2 litter traps distributed within each plot; litter that accumulated on the soil surface was collected at four locations (0.25m2 quadrats) within each plot in February and May 2009. Total litter production in plantation (6.3Mg/ha) and secondary forest (7.3Mg/ha) did not differ, but were greater than in islands (3.5Mg/ha) and control (1.4 Mg/ha). Plantation had greatest accumulation of litter on the soil surface (10.6 Mg/ha) as compared to the other treatments (SF = 7.2; I = 6.7; C = 4.9). Secondary forest was the only treatment with a greater annual production of litter than litter accumulation on the soil surface. Carbon storage in litter was similar between plantation and secondary forest, and significantly greater than the other treatments. No differences were found for carbon concentration and storage in the soil among treatments. There was also high variability in the production and accumulation of litter and carbon among sites. Active restoration treatments accelerated the production of litter and carbon storage in comparison to areas under natural recovery. However, the nutrient cycle has not necessarily been restored under these conditions, as high litter accumulation on the soil surface indicates a low decomposition rate, which slows nutrient return to the soil.     

Leaf litter nitrogen concentration as related to climatic factors in Eurasian forests

Aim The aim of this study is to determine the patterns of nitrogen (N) concentrations in leaf litter of forest trees as functions of climatic factors, annual average temperature (Temp, °C) and annual precipitation (Precip, dm) and of forest type (coniferous vs. broadleaf, deciduous vs. evergreen, Pinus, etc.). Location The review was conducted using data from studies across the Eurasian continent. Methods Leaf litter N concentration was compiled from 204 sets of published data (81 sets from coniferous and 123 from broadleaf forests in Eurasia). We explored the relationships between leaf litter N concentration and Temp and Precip by means of regression analysis. Leaf litter data from N₂‐fixing species were excluded from the analysis. Results Over the Eurasian continent, leaf litter N concentration increased with increasing Temp and Precip within functional groups such as conifers, broadleaf, deciduous, evergreen and the genus Pinus. There were highly significant linear relationships between ln(N) and Temp and Precip (P < 0.001) for all available data combined, as well as for coniferous trees, broadleaf trees, deciduous trees, evergreen trees and Pinus separately. With both Temp and Precip as independent variables in multiple regression equations, the adjusted coefficient of determination () was evidently higher than in simple regressions with either Temp or Precip as independent variable. Standardized regression coefficients showed that Temp had a larger impact than Precip on litter N concentration for all groups except evergreens. The impact of temperature was particularly strong for Pinus. Conclusions The relationship between leaf litter N concentration and temperature and precipitation can be well described with simple or multiple linear regression equations for forests over Eurasia. In the context of global warming, these regression equations are useful for a better understanding and modelling of the effects of geographical and climatic factors on leaf litter N at a regional and continental scale.     

Insect outbreaks alter nutrient dynamics in a southern African savanna: patchy defoliation of Colophospermum mopane savanna by Imbrasia belina larvae

Invertebrate herbivore outbreaks have important impacts on system biogeochemical cycling, but these effects have been poorly documented in African savanna ecosystems. In semi‐arid African savannas, outbreaks of the lepidopteran Imbrasia belina (mopane worm) affect discrete patches of the dominant Colophospermum mopane trees; larvae may completely defoliate trees for up to six weeks during each of the early and late growing seasons. We studied the impact of mopane worm outbreaks on the availability of nitrogen (N), phosphorus (P), and potassium (K) within mopane savanna by quantifying major nutrient pools in defoliated and non‐defoliated savanna patches, including leaves, leaf litter, worm frass, and the soil beneath trees. Within an outbreak area, approximately 44 percent of trees were infested, supporting ~29,000 worms/ha, leading to ~640 kg/ha dry weight frass deposition at 1.4 g of frass/day‐individual (fourth or fifth instar), compared with an average 1645 kg/ha dry weight of leaf on trees most of which should be deposited by litterfall at the end of the growing season. Frass had twofold higher P, 10 percent higher K, but equivalent N content than litter. Taking frass and litter deposition together, the N, P, and K contents added due to the outbreak event at our study site were 0.88, 5.8, and 2.8 times those measured in non‐outbreak patches, a pattern which was reflected in the nutrient contents of soil surfaces beneath defoliated trees. Invertebrate herbivory appears to be an important driver for mopane savanna but has been largely neglected.     

Litter fall and nutrient cycling in karri (Eucalyptus diversicolor F. Muell.) forest in relation to stand age

Annual litter fall, nutrient concentrations in litter components and annual weight of nutrients in litter fall have been estimated for karri forest stands aged 2, 6, 9 and 40 years and in mature forest. The weight of litter falling annually increases with stand age, ranging from 1.13 t/ha in 2-year-otd regeneration to 9.45 t/ha in mature forest. This increase is due mainly to greater amounts of twigs, bark and fruit falling in older stands. Leaf fait is relatively independent of stand age once the canopy of regenerating stands closes and the understorey has developed. Concentrations of N, P, K, S and Mn in karri leaf litter differ significantly between sites and the differences appear to be related to stand age. Highest levels of these elements are found in karri leaf litter from the youngest stand and the concentrations decrease with increasing stand age. The amounts of annual litter fall and of nutrients cycling in litter are among the largest reported for Australian forests. In particular cycling of Ca, K and Mg in mature karri forest is greater than has been reported for any other eucalypt forest. Karri forest understorey plays a key rote in nutrient cycling in these ecosystems, contributing 30–70% of the weight of many of the nutrients in the leaf component of titter. Understorey leaf material is particularly important in the cycling of N, S and the micro-nutrients Cu and Zn.     

Herbivory differentially alters plant litter dynamics of evergreen and deciduous trees

Here we propose that herbivore-induced changes in leaf litter quality can modify aboveground litterfall dynamics differentially in evergreen and deciduous trees. Because aboveground plant litterfall is an important source of nutrients in terrestrial ecosystems, any factor that alters plant litter quality can have large "afterlife" effects on the decomposition rate of that litter and the subsequent rate of nutrient release. Two contrasting patterns emerge from the literature and are corroborated by our two experimental case studies. First, in evergreens, herbivory commonly results in premature leaf abscission, improved litter "quality" and an acceleration of litter decomposition. Second, in deciduous trees, herbivory commonly results in the induction of secondary compounds that decelerates decomposition. We argue that these broad patterns reflect predictable differential responses to herbivores that can have important consequences for terrestrial nutrient cycling and productivity and that warrant more attention in the literature.     

Leaf-litter and changing nutrient levels in a seasonally dry tropical hardwood forest,Belize, C.A.

Summary Total above ground plant biomass in a 45 year old seasonally dry tropical hardwood forest was estimated to be approximately 56,000 kg/ha oven dry weight. Nutrients immobilized in the standing vegetation were: N, 203 kg/ha; P, 24 kg/ha; K, 234 kg/ha; Ca, 195 kg/ha; Mg, 47 kg/ha; Na, 9 kg/ha; Mn, 1 kg/ha; Cu, 0.5 kg/ha; Zn, 3 kg/ha; Fe, 4 kg/ha. Total nutrients returned each year through the litter were: N, 156 kg/ha; P, 9 kg/ha; K, 59 kg/ha; Ca, 373 kg/ha; Mg, 32 kg/ha; Na, 5 kg/ha; Mn, 1 kg/ha; Al, 21 kg/ha; Zn, 0.3 kg/ha; Fe, 9 kg/ha. Half of the nutrients immobilized in the standing vegetation were found in the leaves and are returned annually to the soil. Although litter fall is interrupted during the year, the mean nutrient content of the litter was high –5.2%.A decomposition rate of 0.48 percent per day was considered high for a seasonally dry tropical hardwood forest. Fluctuations in soil nutrient levels showed a sharp increase at the start of the rainy season. Later during the dry season nutrient levels decreased to concentrations similar to what they were just prior to the rainy season. Soil organic matter levels were very high –20% in the top 12 cm.