亚高山暗针叶林凋落物的分解过程

凋落物是森林生态系统的重要组成部分,其分解过程是森林生态系统养分循环的重要环节。准确测定凋落物的分解动态,对研究森林生态系统的格局和过程非常重要。本文的工作在贡嘎山高山生态系统观测试验站开展,对海拔3 000 m的峨眉冷杉(Abies fabri)林进行定位观测,并对峨眉冷杉林凋落物分解过程进行了长期测定。研究结果表明:(1)凋落物的分解速率是阔叶>针叶>枯枝,峨眉冷杉林的阔叶、针叶和枯枝等凋落物分解一半所需要的时间分别为6.8年、10.5年和14.5年,分解95%所需时间分别为29.3年、45.6年和63.1年;(2)无论阔叶还是针叶、枯枝,其有机碳含量均随着时间的推移而下降,而有机碳分解率均随着时间而增高;利用指数衰减模型,获得凋落物有机碳的分解系数是阔叶>针叶>枯枝;(3)在每年凋落物输入峨眉冷杉林林地时,其中的阔叶、针叶和枯枝已经开始分解,当年可释放的有机碳分别为52.18 kg·hm^-2、4.32 kg·hm^-2和0.67 kg·hm^-2,各类凋落物每年有机碳释放总量为61.13 kg·hm^-2,占凋落时有机碳量的6.58%。     

孟加拉吉大港地区丘陵森林有机物积累

在孟加拉吉大港丘陵地区,调查了热带季风气候条件下的3种人工林(7年生大叶相思(Acacia auriculiformis)林、15年生大叶相思林和18年生混交林)和1种天然林的森林凋落物及其对土壤性质的作用.结果表明,总的有机质积累随人工林树龄增加而增加,但是年积累量随之降低.在同一植被类型内,不同坡位新鲜或部分分解的凋落物有机质累计量变化较大,坡底部有机质积累量最高,沿着山坡向上逐渐减少.在15年生大叶相思人工林内,土壤整合有机物积累量变化趋势与新鲜或部分分解有机质积累量变化趋势相反.在7年生和15年生的大叶相思林以及18年龄的阔叶混交人工林内,新鲜、部分分解和完全分解(含土壤整合有机质)有机质总生产速率分别是2554.31、705.79和1028.01kg.ha-1·a-1,新鲜凋落物有机质在3种林分中的生产速率分别是38.23,19.40和30.48 kg·ha-1·a-1.3种人工林和自然林内,平均新鲜凋落物的有机质积累占有机质产出总量的32.45%,部分分解凋落物占13.50%,而全分解整合土壤有机质占54.56%.森林土壤酸度随凋落物分解阶段的深入而增加.     

华北落叶松人工林凋落物组成及动态研究

以阴山山地苏木山林场华北落叶松人工林为研究对象,利用野外调查和数据分析的方法,对凋落物年凋落量、组成、月动态变化及现存量进行研究。结果表明:华北落叶松人工林凋落物年凋落总量为4.74 t·hm~(-2),其中,落叶2.64 t·hm~(-2),落枝1.53 t·hm~(-2),落果0.50 t·hm~(-2),落皮0.07 t·hm~(-2),分别占总凋落量的55.69%、32.28%、10.55%和1.48%。各组分中,落叶在10月份凋落量最大,为1.56 t·hm~(-2),落枝和落果5月份凋落量最大,分别为0.28 t·hm~(-2)和0.10 t·hm~(-2)。林地凋落物现存量为5.04 t·hm~(-2),其中,未分解层3.67 t·hm~(-2),半分解层1.37 t·hm~(-2)。研究结果可为华北落叶松人工林物质循环和林地养分平衡研究提供参考依据。     

四川省茂县四种人工林凋落物研究

对四川省茂县四种人工林的年凋落量、凋落物组成、凋落动态及分解率进行了观测.结果表明:云南松、日本落叶松、连香树、油松这四种人工林的年凋落量依次为6.42、4.87、3.79、3.45 t·hm-2a-1;四种人工林其叶的年凋落量占年总凋落量的比例明显大于其它组分的;四种人工林其叶的凋落集中在10、11月,呈现出明显的温带森林凋落的特征;连香树、日本落叶松、油松、云南松其花的凋落高峰期分别出现在4月、4月、6月和6～7月;日本落叶松和油松、云南松其果的凋落高峰期分别出现在9月和4月;叶鞘和芽鳞分别在8月和7月时出现最大凋落量;其它组分凋落的动态规律不明显;各人工林凋落物的分解率随其阔叶所占总凋落量比例的增加而增加.     

海南麻竹林凋落物及养分动态研究

研究了海南麻竹林凋落物量及其养分动态.结果表明:麻竹林凋落物全年总量为6 862.8 kg·hm-2.N、P、K、Ca、Mg的年归还量分别为74.847、3.264、25.921、45.924、11.902kg·hm-2,大小顺序为:N＞Ca＞K＞Mg＞P,养分总的年归还量是161.858kg·hm-2·a-1.凋落物分解失重率达95%的分解期为11.59个月,每年产生的凋落物全部归还于土壤.     

模拟N沉降对滇中亚高山典型森林凋落物分解及土壤微生物的影响

[目的]模拟N沉降下凋落物分解及土壤微生物特征,为研究森林生态系统碳、氮循环对氮沉降的响应机制提供依据。[方法]以滇中亚高山常绿阔叶林、华山松(Pinus armandii)林、高山栎(Quercus semicarpifolia)林和云南松(Pinus yunnanensis)林凋落物为研究对象,采用凋落物袋法,于2018年2月至2019年1月,通过模拟N沉降和原位分解实验,研究不同模拟N沉降下(CK, 0;LN, 5;MN, 15;HN, 30 g·m~(-2)·a~(-1))凋落物碳氮、土壤微生物量碳(MBC)、微生物量氮(MBN)及土壤微生物数量变化特征。[结果]分解1年后,不同N沉降处理下,常绿阔叶林和高山栎林凋落物C含量均显著增加(0.40%～8.16%),华山松林和云南松林凋落物C含量呈LN减少(2.67%),HN增加(4.09%);各林分凋落物N含量均显著增加(1.45%～69.01%),C/N则显著降低(0.34%～37.92%);相同N沉降下土壤微生物量随土层的加深而减小,N沉降对土层垂直分布格局影响不显著;N沉降对常绿阔叶林和高山栎林土壤MBC和MBN的影响表现为抑制,对华山松林和云南松林表现为低N促进,高N抑制;4种林分土壤MBC/MBN介于5.31～11.26之间,N沉降对不同林分不同土层的MBC/MBN影响存在差异,但均受到高N的抑制作用。[结论]滇中亚高山4种典型森林凋落物分解主要受森林类型影响,N沉降次之;土壤微生物量和数量主要受森林类型影响,土壤深度次之,N沉降最小。     

川西亚高山针叶林与针阔混交林凋落量及养分归还动态

本文选择川西亚高山针叶纯林和针阔混交林作为研究对象,并于2007年7月～12月采用收集框法研究了森林凋落物量以及N、P、K养分归还量。结果表明,混交林凋落量(2 090.47 kg·hm-2)比针叶林凋落量(1 189.59kg.hm-2)高出43%,林分凋落动态和归还动态呈单峰型,其高峰都出现在10月份。混交林中阔叶对凋落量的贡献达69%。同时,阔叶的养分归还量大于针叶的养分归还量。混交林和针叶林养分归还量都表现为N﹥K﹥P,针阔混交林凋落物养分归还量大于针叶林。在川西亚高山地区针阔混交林比针叶纯林具有更强的自肥能力。     

施氮条件下森林凋落物分解早期的碳和氮动态

通过13周实验室培养试验,研究了施氮和树种对森林凋落物早期分解过程中碳和氮动态的影响,新鲜凋落物样品包括针叶（红松）和两种阔叶（蒙古栎和紫椴）,采自长白山北坡阔叶红松林。试验共包括3个施氮梯度（0、30和50kg·ha^-1．a^-1 NH4NO3）。以质量减少和呼吸速率表征的凋落物分解速率随可溶性氮的增加而显著增加,阔叶凋落物质量减少和累积CO2—C释放量比针叶凋落物高,不同物种之间凋落物沥出物中溶解性有机碳（DOC）浓度变化较大,但施氮处理对DOC的影响不大。除了施氮率,施氮处理和物种对凋落物沥出物中溶解性有机氮（DON）浓度都没有显著影响。有52—78％的外加氮滞留在凋落物中,氮滞留率与凋落物质量减少呈正相关（R^2=0．91,P〈0．05）,这表明易分解凋落物覆盖的森林地面比分解较慢的凋落物覆盖的森林地面有更高的N汇潜力。图3表1参40。     

宽阔水太阳山阔叶混交林森林凋落物量动态研究

针对宽阔水太阳山阔叶混交林凋落物的数量、组成及季节动态进行了研究,结果表明:宽阔水太阳山阔叶混交林森林凋落物年凋落量为5192.34kg/hm~2,其中枝凋落量为1025.74kg/hm~2,占年凋落量的19.75%;叶凋落量为3329.87kg/hm~2,占年凋落量的64.13%。峰值出现在5月(810.53kg/hm~2),占年凋落物量的15.61%,低谷出现在3月(298.54kg/hm~2)和6月(274.33kg/hm~2),分别占年凋落量的5.75%和5.28%,表现出总凋落物量随季节发生动态变化。     

油松人工林下真菌群落对凋落物分解的影响

为探究真菌群落在凋落物分解进程中的影响,以在油松人工林中分离纯化而来的3株真菌Irpex lacteus(白囊耙齿菌)、Collybia subnuda(金钱菌属)和Trametes hirsuta(毛栓菌)为供试菌株,经组合形成不同真菌群落,以油松针叶、蒙古栎阔叶凋落物及两者混合形成3种类型分解基质,通过发酵纯培养的方法,测定了底物有机质量损失及发酵过程中羧甲基纤维素酶(CMCase)活性变化,并验证了酶活性与底物降解的关系。结果表明:凋落物类型和真菌组合均显著影响凋落物分解,且两者之间存在交互作用;真菌多样性提高了凋落物的分解速率;凋落物混合产生了正面非加性效应,且这种效应主要由阔叶引起。质量损失率和纤维素酶活性呈现类似的规律,即同一凋落物类型下,组合菌群大于或等于单一菌群;同一真菌群落下,阔叶混合针叶。     

Red alder leaf decomposition and nutrient release in alder and conifer riparian patches in western Washington,USA

Current management practices encourage conversion of red alder (Alnus rubra) riparian forests to conifers in the Pacific Northwest U.S. Patches of young naturally regenerated conifers are commonly present in alder dominated riparian areas and an understanding of the soil processes in these patches will be helpful in guiding future riparian management. Study objectives were to: (1) determine decomposition rates of red alder leaves in riparian alder and conifer patches, (2) relate decomposition rates to environmental factors and litter chemistry, and (3) determine nutrient release from decomposing alder leaves in these patches. Study sites were riparian areas adjacent to Brown and Le Bar creeks in the Skokomish River basin, Olympic National Forest, Washington. Red alder leaves were placed in litterbags in red alder and conifer riparian patches along each stream in November 2000 and collected after 1 and 3 years. There was rapid mass loss of alder leaves in the first year in both patch types, but decomposition was significantly faster (p < 0.05) in alder patches (43.2% mass remaining, k = 0.855 year⁻¹) than in conifer patches (48.4% mass remaining, k = 0.734 year⁻¹). There was little mass loss after the first year and no significant difference in decomposition rates. After 3 years mass remaining was 44.2% (k = 0.283 year⁻¹) and 47.8% (k = 0.48 year⁻¹) in alder and conifer patches, respectively. Decomposition rate differences were attributed more to the effects of the different litters in each patch and the influence on soil microbial and faunal communities than differences in soil temperature and moisture. The forest floor was deeper in conifer patches (3.7 cm) than alder (1.8 cm) patches. This was ascribed to slower decomposition rates in conifer patches, greater litterfall in conifer patches, and/or removal of alder surface litter by flooding. Alder patches were lower in elevation (0.8 m above bankfull width) than conifer patches (2.2 m). Forest floor and soil C and N concentrations and pHs were not significantly different in alder and conifer patches. Nutrient release from decomposing alder leaves was not significantly different in conifer and alder patches, although there was a trend for C, N, P, K, and Ca to be lost faster from leaves in alder patches than conifer patches in the first year. Red alder litter input to riparian conifer patches will initially decompose rapidly and provide nutrients, particularly N and P to conifers, as well as enhancing soil C since long-term decomposition rates are slow.     

Litter decomposition can detect effects of high and moderate levels of forest disturbance on stream condition

Considerable research efforts have been devoted to determining what forest management practices most affect stream ecosystems, and how those impacts might be mitigated. Recent studies have stressed the relevance of litter decomposition to assess the conditions of headwater streams affected by riparian and upland forest harvest. Here we specifically examined whether litter decomposition can detect ecological effects of clearcutting to stream edges on headwater streams eight years after logging and if large (30 m) and narrow (10 m) riparian reserves (8-year post-harvest), and selection logging at 50% removal of basal area of riparian trees (1-year post-harvest), are effective protection measures for streams. We measured decomposition rates of red alder (Alnus rubra) leaf litter in sixteen stream reaches, including reference reaches in a 70-year-old forest. We further examined assemblages of two main litter consumer groups, shredder invertebrates in riffles and aquatic hyphomycete fungi developing on decaying alder leaves. Alder decay rate was significantly lower in clearcut reaches than in reference reaches, and we found no evidence that any alternative riparian management practices examined in this study were able to mitigate against such an effect of logging. In unlogged reaches, rapid litter decomposition (0.0050–0.0118 day⁻¹) was associated with high density and diversity of shredders (up to ten taxa). Slower litter decomposition in wide and narrow reserve reaches (0.0019–0.0054 day⁻¹) and clearcut reaches (0.0024–0.0054 day⁻¹) was attributed to lower density and richness of shredders. By contrast, the low decay rate in recently established thinned reaches (0.0031–0.0049 day⁻¹) was not associated with a numerical response of shredders. Smothering of submerged leaves by sediments may have caused the reduction in alder decay rate in thinned reaches. Across all forest treatments fungal biomass or diversity remained fairly similar. Our findings suggest that stream ecosystems are extremely sensitive to small changes in riparian and upland forest cover. We propose that litter decomposition as a key ecosystem function in streams could be incorporated into further efforts to evaluate and improve forestry best management practices.     

Exotic tree leaf litter accumulation and mass loss dynamics compared with two sympatric native species in south Florida,USA

The exotic tree Melaleuca quinquenervia (melaleuca) forms dense forests usually characterized by low plant diversities and dense litter biomass accumulations on forest floors of ecologically sensitive ecosystems, including portions of the Florida Everglades. We quantified litter accumulation in mature melaleuca stands and compared decomposition rates of melaleuca leaves with a sympatric native plant, either Cladium jamaicense (sawgrass) in sawgrass marshes or Pinus elliottii (slash pine) in pine flatwoods habitats that varied in soil types. Total litter accumulation in mature melaleuca forests prior to June 1997 ranged from 12.27 to 25.63 Mg ha⁻¹. Overall, melaleuca leaves decomposed faster in organically rich versus arenaceous soils. Decomposition rates were lower for melaleuca leaves than for sawgrass in both melaleuca-invaded and uninvaded sawgrass marshes. In arenaceous soils of pine flatwoods, melaleuca leaf and pine needle decomposition rates were similar. Complete mineralization of sawgrass leaves occurred after 258 weeks, whereas melaleuca leaves had up to 14% and pine foliage had up to 19% of the original biomass remaining after 322 weeks. Total carbon (C) in intact decomposing leaves varied slightly, but total nitrogen (N) steadily increased for all three species; the greatest being a fourfold in sawgrass. Increases in N concentrations caused decreases in the C/N ratios of all species but remained within an optimal range (20–30) in sawgrass resulting in higher decomposition rates compared to melaleuca leaves and pine needles (C/N ratio >30). Slower decomposition of melaleuca leaves results in denser litter layers that may negatively affect recruitment of other plant species and impede their establishment in invaded communities.     

Decomposition of Scots pine fine woody debris in boreal conditions: Implications for estimating carbon pools and fluxes

Litter quality and environmental effects on Scots pine (Pinus sylvestris L.) fine woody debris (FWD) decomposition were examined in three forestry-drained peatlands representing different site types along a climatic gradient from the north boreal (Northern Finland) to south (Southern Finland) and hemiboreal (Central Estonia) conditions. Decomposition (percent mass loss) of FWD with diameter ≤10 mm (twigs) and FWD with diameter >10 mm (branches) was measured using the litter bag method over 1–4-year periods. Overall, decomposition rates increased from north to south, the rate constants (k values) varying from 0.128 to 0.188 year⁻¹ and from 0.066 to 0.127 year⁻¹ for twigs and branches, respectively. On average, twigs had lost 34%, 19% and 19%, and branches 25%, 17% and 11% of their initial mass after 2 years of decomposition at the hemiboreal, south boreal and north boreal sites, respectively. After 4 years at the south boreal site the values were 48% for twigs and 42% for branches. Based on earlier studies, we suggest that the decomposition rates that we determined may be used for estimating Scots pine FWD decomposition in the boreal zone, also in upland forests. Explanatory models accounted for 50.4% and 71.2% of the total variation in FWD decomposition rates when the first two and all years were considered, respectively. The variables most related to FWD decomposition included the initial ash, water extractives and Klason lignin content of litter, and cumulative site precipitation minus potential evapotranspiration. Simulations of inputs and decomposition of Scots pine FWD and needle litter in south boreal conditions over a 60-year period showed that 72 g m⁻² of organic matter from FWD vs. 365 g m⁻² from needles accumulated in the forest floor. The annual inputs varied from 5.7 to 15.6 g m⁻² and from 92 to 152 g m⁻² for FWD and needles, respectively. Each thinning caused an increase in FWD inputs, up to 510 g m⁻², while the needle inputs did not change dramatically. Because the annual FWD inputs were lowered following the thinnings, the overall effect of thinnings on C accumulation from FWD was slightly negative. The contribution of FWD to soil C accumulation, relative to needle litter, seems to be rather minor in boreal Scots pine forests.     

Effects of CO2 enrichment on the photosynthetic light response of sun and shade leaves of canopy sweetgum (Liquidambar styraciflua) in a forest ecosystem

To investigate whether sun and shade leaves respond differently to CO2 enrichment, we examined photosynthetic light response of sun and shade leaves in canopy sweetgum (Liquidambar styraciflua L.) trees growing at ambient and elevated (ambient + 200 microliters per liter) atmospheric CO2 in the Brookhaven National Laboratory/Duke University Free Air CO2 Enrichment (FACE) experiment. The sweetgum trees were naturally established in a 15-year-old forest dominated by loblolly pine (Pinus taeda L.). Measurements were made in early June and late August 1997 during the first full year of CO2 fumigation in the Duke Forest FACE experiment. Sun leaves had a 68% greater leaf mass per unit area, 63% more leaf N per unit leaf area, 27% more chlorophyll per unit leaf area and 77% greater light-saturated photosynthetic rates than shade leaves. Elevated CO2 strongly stimulated light-saturated photosynthetic rates of sun and shade leaves in June and August; however, the relative photosynthetic enhancement by elevated CO2 for sun leaves was more than double the relative enhancement of shade leaves. Elevated CO2 stimulated apparent quantum yield by 30%, but there was no interaction between CO2 and leaf position. Daytime leaf-level carbon gain extrapolated from photosynthetic light response curves indicated that sun leaves were enhanced 98% by elevated CO2, whereas shade leaves were enhanced 41%. Elevated CO2 did not significantly affect leaf N per unit area in sun or shade leaves during either measurement period. Thus, the greater CO2 enhancement of light-saturated photosynthesis in sun leaves than in shade leaves was probably a result of a greater amount of nitrogen per unit leaf area in sun leaves. A full understanding of the effects of increasing atmospheric CO2 concentrations on forest ecosystems must take account of the complex nature of the light environment through the canopy and how light interacts with CO2 to affect photosynthesis.     

Litter decomposition and nutrients dynamics in <Emphasis Type="Italic">Nothofagus antarctica</Emphasis> forests under silvopastoral use in Southern Patagonia

The role of environmental variables on litter decomposition and its nutrient release in Nothofagus antarctica forest in Patagonia is poorly understood. Moreover, in these forests under silvopastoral use there are few antecedents. Litter decomposition and nutrient release of grasses and tree leaves were evaluated under different crown cover and two site quality stands during 480 days. Organic matter decomposition varied with crown cover for both types of litter, achieving mean values of 23 and 34% for maximal and minimal crown cover, respectively. Total transmitted radiation was the main environmental factor explaining 61 and 49% of the variation of grass and tree leaves decay rates, respectively. N, P, and Ca were mineralized during first 60 days in decomposing tree leaves and then immobilized without differences between crown cover. The K was immobilized during the evaluated period. In decomposing grass leaves the results varied according to site quality and time. There was a tendency of nutrient mineralization at the first 120 days and then immobilization. The removal of trees for silvopastoral use of N. antarctica may increase litter decomposition by changing the microclimate, but nutrients release or immobilization was mainly affected for their concentration in decomposing material.     

Ecophysiological and morphological responses to shade and drought in two contrasting ecotypes of Prunus serotina

Photosynthesis (A), water relations and stomatal reactivity during drought, and leaf morphology were evaluated on 2-year-old, sun- and shade-grown Prunus serotina Ehrh. seedlings of a mesic Pennsylvania seed source and a more xeric Wisconsin source. Wisconsin plants maintained higher A and leaf conductance (g(wv)) than Pennsylvania plants during the entire drought under sun conditions, and during the mid stages of drought under shade conditions. Compared to shade plants, sun plants of both sources exhibited a more rapid decrease in A or % A(max) with decreasing leaf water potential (Psi). Tissue water relations parameters were generally not significantly different between seed sources. However, osmotic potentials were lower in sun than shade plants under well-watered conditions. Following drought, shade plants, but not sun plants, exhibited significant osmotic adjustment. Sun leaves had greater thickness, specific mass, area and stomatal density and lower guard cell length than shade leaves in one or both sources. Wisconsin sun leaves were seemingly more xerophytic with greater thickness, specific mass, and guard cell length than Pennsylvania sun leaves. No source differences in leaf structure were exhibited in shade plants. Stomatal reactivity to sun-shade cycles was similar between ecotypes. However, well-watered and droughted plants differed in stomatal reactivity within and between multiple sun-shade cycles. The observed ecotypic and phenotypic variations in ecophysiology and morphology are consistent with the ability of Prunus serotina to survive in greatly contrasting environments.     

Colonization and decomposition of leaf litter by ligninolytic fungi in Acacia mangium plantations and adjacent secondary forests

Colonization of leaf litter by ligninolytic fungi and relationships between mass loss and chemical qualities of surface leaf litter were examined in Acacia mangium plantations and adjacent secondary forests in southern Sumatra Island, Indonesia. Leaves were collected from eight A. mangium plantations of different ages and three secondary forests. Partly decomposed leaves beneath the surface leaf litter were used to measure the bleached area which indicated colonization by ligninolytic fungi. Surface leaf litter was used to measure initial chemical content and subjected to the pure culture decomposition test. The bleached area was greater in secondary forests than in A. mangium plantations. Nitrogen content was higher in all the A. mangium plantations than in the secondary forests, and acid unhydrolyzable residue (AUR) content was generally higher in the A. mangium plantations than in the secondary forests. The bleached area of leaf litter was negatively correlated with nitrogen content of surface leaf litter at all sites, indicating an inhibition of the colonization by ligninolytic fungi of leaves with higher nitrogen content. In a pure culture decomposition test inoculating a ligninolytic fungus to surface leaf litter, mass loss of leaves was negatively correlated with AUR content of surface leaf litter. Mass loss of leaves and AUR was not significantly related to nitrogen content. These results suggested that higher nitrogen content in A. mangium leaf litter had a negative effect by colonization of ligninolytic fungi, but the effect of high N in A. mangium leaf litter on the decomposition of leaf litter and AUR remained unsolved.     

Breakdown and macroinvertebrate colonization of needle and leaf litter in conifer plantation streams in Shikoku,southwestern Japan

Breakdown and macroinvertebrate colonization of conifer needles (Cryptomeria japonica) and deciduous broadleaves (Euptelea polyandra) were investigated using litter bags in two study sites in streams flowing through a conifer plantation of C. japonica in Shikoku, southwestern Japan (one site with conifer canopy and another with mixed conifer and broadleaved canopy). Breakdown rates and macroinvertebrate densities were compared between litter species (conifer needle vs broadleaf) and between the two sites (conifer vs mixed canopy) to determine (1) whether breakdown rate of broadleaves is higher than conifer needles, (2) whether macroinvertebrates prefer broadleaves to conifer needles, and (3) whether the difference in riparian canopy is reflected in macroinvertebrate abundance. The results indicated that breakdown rates of broadleaves were higher than those of conifer needles, suggesting poorer quality of the latter as food for macroinvertebrates. Differences in macroinvertebrate density between needles and broadleaves were generally consistent with those in breakdown rates: broadleaves tended to have higher densities than needles, suggesting that conifer needles were not preferred by macroinvertebrates. However, total macroinvertebrate density in the conifer site was not significantly different from that in the mixed site, although the dominant shredder taxon differed (conifer site: gammarids; mixed site: lepidostomatids). Although conifer needles are low-quality food for macroinvertebrates, this may offer some advantages. Conifer needles remain on the streambed for longer periods owing to their lower breakdown rates, being a constantly available resource. In addition, accumulations of conifer litter may effectively trap and retain particulate organic matter.