Effects of thinning on nutrient content pools in two Pinus sylvestris forests in the western Pyrenees

Abstract

Nutrient content [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg)] in needles, branches and stems before (P0, not thinned) and after thinning (P20 and P30, 20% and 30% of basal area removed, respectively) was studied in 37- and 32-year-old Pinus sylvestris L. forests in the western Pyrenees: Garde and Aspurz. Thinning significantly decreased all nutrient pools in P20 and P30 relative to P0 on both sites, but no significant differences were found between P20 and P30 owing to low statistical power. Thinning increased the differences between the two forests for total above-ground content of P and Mg, and for the content of N, P and K in the 1999 needles cohort. The former result was due in part to the higher concentration of P (needles and branches) and Mg (needles) in Garde. Therefore, the importance of needles relative to the other nutrient pools increased for N and P after thinning. This may have resulted from the fact that the removal of dead trees with low needle biomass was greater in Garde than in Aspurz. Based on the percentage of basal area removed, nutrient removal in Garde for P30 was higher than expected, apparently owing to an increase in branch removal relative to P20. These results indicate that effects of thinning on nutrient pools were influenced by differences in stand structure and nutrient tissue concentrations between sites.     

Nutrients return from leaves and litterfall in a mediterranean cork oak (<Emphasis Type="Italic">Quercus suber</Emphasis> L.) forest in southwestern Spain

The knowledge of the cycle of nutrients is fundamental for the correct comprehension of the tree–soil relationship and for an adequate forest management. In order to analyse the nutrients return from leaves and litterfall in a Mediterranean cork oak forest in southwestern Spain, 12 trees were randomly selected and litterfall collected for 2 years. Samples were taken monthly and separated in different fractions (leaves, twigs, catkins, acorns and miscellaneous), then leaves nutrients were analyzed. Simultaneously, we analyzed the nutrient content of living leaves from the same trees in each season during 1 year. The analyzed nutrients were C, N, P, K, Ca, Mg, Fe, Mn, S, Cu, Zn and Mo. Annual patterns of each nutrient in fallen leaves were characterized and compared with seasonal values of these nutrients in living leaves. Leaves fall has two annual maximum, first and most important in spring around April coinciding with renewal of foliar cover and second around October. Main concentration patterns of N, P and K are related with phenological patterns, in consequence minimum concentration in leaves fall were obtained in periods of growing and maximum litterfall. Concentrations of Ca, Fe and Mn increase with the age of the leaves and maximum concentrations were obtained before periods of maximum litterfall while concentrations of Cu, Mo and Mg stay stable. Seasonal analysis of nutrients in living leaves collected from the same trees in four different periods of the year allowed to corroborate the patterns of leaves fall and the probable osmotic function of K.     

Nutrient cycling and distribution in different-aged plantations of Chinese fir in southern China

The distribution in tree biomass and understorey vegetation and annual biological and geochemical cycling of total nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were measured in young, middle-aged and mature plantations (8-, 14- and 24-years old) of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) in southern China. Although >98% of nutrients occurred in the soil, soil nutrient content decreased with plantation age. Nutrient outputs from the soil exceeded inputs in stands of all ages but the net soil nutrient loss increased significantly for N, P and Ca with plantation age. Comparison of nutrient fluxes showed that the smallest (and hence limiting for nutrient cycling) fluxes were litter decomposition in the young plantation in contrast to canopy fluxes (apart from for Mg) in the middle-aged and mature plantations. Nutrient use efficiency, release of nutrients from litter decomposition and nutrient return, particularly in litterfall, increased significantly with plantation age. These results suggest that, as stand age increases, nutrient cycling in Chinese fir plantations is increasingly dominated by biological processes and becomes less dependent on external nutrient sources in rainfall and the soil. It therefore appears that prolonging the rotation length of Chinese fir plantations by approximately 5 years could be beneficial for maintaining the soil nutrient status for successive plantings.     

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.     

Temporal variation in nutrient concentrations of Pinus sylvestris needles

Temporal variation in nutrient concentrations of Scots pine (Pinus sylvestris L.) needles was studied during a three‐year period in three stands of differing stages of development. Concentrations of N, P and K varied significantly between years; this variation was related to differences in needle dry weight. Concentrations of all measured nutrients (N, P, K, Ca, Mg, Mn, Cu, Zn, Fe, B) and Al varied between seasons; this variation was related to nutrient mobility and the annual physiological cycle. Concentrations of the mobile nutrients N, P and K decreased in spring and early summer during shoot and needle elongation and increased in late summer and autumn during needle senescence and litterfall. Concentrations of Mg, Cu, Zn and B followed somewhat similar patterns. The poorly mobile nutrients Ca, Mn and Fe accumulated gradually in needles during each growing season. Needle nutrient concentrations were stable during the nonactive period.     

Effects of silvicultural treatments and seasonal patterns on foliar nutrients in young post-fire Pinus halepensis forest stands

Tree growth and health status appear to be related to foliar nutrient contents. Foliar nutrient concentration might be the result of a complex interaction between soil nutrients and effective availability caused by climate, water and other site and treatment effects. This study examines foliar macronutrient (N, P, K, Ca, Mg) and organic C concentrations in Aleppo pine (Pinus halepensis) needles (between 5 and 18 months old), as well as time course variability (nine dates, from July 1999 to November 2001). Variability was assessed depending on quality site (two sites, Yeste and Calasparra; SE Spain) and seven silvicultural treatments including thinning, scrubbing, pruning and particular combinations of them. Foliar macronutrient concentrations for Aleppo pine in South-eastern Spain were slightly lower (N, P, K,) or higher (Mg, Ca) than the considered as adequate ranges for Aleppo pine and Pinus genera. However, our results agree well with other normal ranges reported for Aleppo pine in Spain and for other North American Pinus species such as P. elliottii, P. taeda and P. palustris. Site, treatment and date (season) affected significantly the foliar macronutrient and C concentration, although the most important was the date, likely due to the two growth periods per year that Aleppo pine has in Mediterranean sites. Silvicultural treatments affected foliar nutrient concentration, so that the concentrations of N, P and K were higher when treatments included thinning than those that did not. The contrary was true for Mg and Ca. However, treatments did not affect the time course of the concentration, i.e., seasonality was not broken due to treatments. Moreover, the effect of the treatments was markedly high along the first year after they were applied but the differences were attenuate 2 years later. Site affected the time course of N, K, Mg and C in a different way: while for N, K and C, at the end of study period, they were higher in Calasparra than in Yeste, for Mg the contrary was true. Nutrient ratios had a different behaviour regarding to single nutrient: although date was significant, we did not appreciate seasonality. In addition, some nutrient ratios were not affected by treatments (N/P, N/K, Ca/Mg,) or by site (N/Ca, K/Ca). Average foliar N concentration and Ca/Mg ratio explained significantly the mean diameter and height growth, so that higher is the foliar N concentration and lower is Ca/Mg, higher is the growth.     

日本北海道北部寒温带森林流域林冠层凋落物及其养分归还量的景观格局(英文)

Within a forested watershed at the Uryu Experimental Forest of Hokkaido University in northern Hokkaido, overstory litterfall and related nutrient fluxes were measured at different landscape zones over two years. The wetland zone covered with Picea glehnii pure stand. The riparian zone was deciduous broad-leaved stand dominated by Alnus hirsuta and Salix spp., while the mixture of deciduous broadleaf and evergreen conifer dominated by Betula platyphylla, Quercus crispula and Abies sachalinensis distributed on the upland zone. Annual litterfall averaged 1444, 5122, and 4123 kg.hm^-2·a^-1 in the wetland, riparian and upland zones, respectively. Litterfall production peaked in September-October, and foliage litter contributed the greatest amount （73.4%-87.6 %） of the annual total litterfall. Concentrations of nutrients analyzed in foliage litter of the dominant species showed a similar seasonal variation over the year except for N in P glehnii and A. hirsuta. The nutrient fluxes for all elements analyzed were greatest on riparian zone and lowest in wetland zone. Nutrient fluxes via litterfall followed the decreasing sequence： N （11-129 kg.hm-2.aq） 〉 Ca （9-69） 〉 K （5-20） 〉 Mg （3-15） 〉 P （0.4-4.7） for all stands. Significant differences were found in litterfall production and nutrient fluxes among the different landscape components. There existed significant differences in soil chemistry between the different landscape zones. The consistently low soil C：N ratios at the riparian zone might be due to the higher-quality litter inputs （largely N-fixing alder）.     

南亚热带7种林分凋落叶养分含量的年动态变化

2006-05-2007-04对广西凭祥市7种主要林分凋落叶的N,P,K,Ca及Mg含量进行分析.结果表明:林分凋落叶的N,P,K,ca及Mg含量全年月份动态变化趋势较为一致;在林木生长旺盛的高温雨季4-9月,林分凋落叶的N及P养分含量较高,而K的含量较低;在林木生长缓慢或休眠的干旱低温季10月至翌年3月,凋落叶N及P养分的含量较低,而K的含量较高,说明林分凋落叶的N与P含量与林木生长量成正相关,而K与生长量成负相关;Ca随月份的变化较小,但不同林分之间的差异较大;Mg随月份的变化较大;西南桦凋落叶N含量最高(14.44 g·kg-1),火力楠最低(5.11 g·kg-1);次生林凋落叶P含量最高(1.20 g·kg-1),马尾松最低(仅0.53 g·kg-1);K也以次生林最高(5.16 g·kg-1),马尾松最低(1.71 g·kg-1);Ca以杉木最高(达11.10 g·kg-1),马尾松最低(仅3.76g·kg-1);Mg以次生林最高(3.03 g·kg-1),马尾松最低(1.18 g·kg-1);7种林分凋落叶的N,P,K,Ca与Mg的最高与最低含量比值都超过2.     

Influence of nitrogen and phosphorus fertilizers on amount and nutrient content of litterfall in a regrowth eucalypt forest

The effects of fertilizer treatment on nutrient transfers to the forest floor were examined in regrowth Eucalyptus diversicolor F. Muell. forest. Dry weight and nutrient content of leaf litterfall and total litterfall were measured for 3 years in a stand to which two levels of N (0, 200 kg ha^-1 year^-1) were applied each year at each of three levels of a single initial application of P (0, 30, 200 kg ha^-1). Annual accessions of litter to the forest floor were significantly increased by additions of both N (by 17%, 18% and 21% in the 3 years) and 200 kg P ha^-1 (by 8%, 8% and 4% in the 3 years) but there was no interaction between effects of N and P treatments. Fertilizer application also had a significant effect on the nutrient content of leaf litterfall and total litterfall. Concentration of N in leaf litterfall was 9% to 23% greater on plots treated with N fertilizer compared to untreated plots. The amounts of N in litterfall were about 30% greater on N-treated compared to untreated plots. On plots treated with 200 kg P ha^-1, P concentrations in leaf litter were 50% to 100% greater than in litter from plots receiving no P. Application of 200 kg P ha^-1 increased the amounts of P in annual litterfall by 32% to 87%. The greatest increase in P accessions occurred soon after fertilizer treatment. The amounts of Ca, K, and Na in litterfall were also significantly increased by fertilizer application. For Ca and K this was due partly to increases in element concentrations in litterfall following application of treatments. The effect of fertilizers on internal recycling of plant nutrients and on litter accumulation and nutrient dynamics in forest floor litter is discussed.     

Biomass production,nutrient cycling and distribution in age-sequence Chinese fir(Cunninghamia lanceolate) plantations in subtropical China

Biomass production and nutrient(N, P, K, Ca and Mg) accumulation, distribution and cycling were quantified in young, mature and over-mature(10-, 22-, and34-year old) Chinese fir [Cunninghamia lanceolate(Lamb.) Hook] plantations in southern China. Total stand biomass of young, mature and over-mature stands was 38,104 and 138 t ha-1respectively. Biomass production increased significantly with age. Stem wood represented the highest percentage of stand biomass, accounting for 41,55 and 63 % in the young, mature and over-mature plantations respectively. Nutrients concentration was highest in live needles and branches, and lowest in stem wood. The plantations accumulated more N, followed by K, Ca, Mg,and P. Nutrient return amount, nutrient utilization efficiency, nutrient turnover time, the ratio of nutrient returnand uptake increased with stand age, which implies that young Chinese fir deplete soil nutrients to maintain growth,and efficiently utilize nutrients to decrease dependence on soil nutrients as they age. Harvesting young Chinese fir plantations would therefore lead to high nutrient loss, but prolonging the rotation length could improve soil recovery,and help sustain productivity in the long-term. Improved nutrient return through litterfall as stands get older may also be beneficial to nutrient pool recovery.     

Litter production, seasonal pattern and nutrient return in seven natural forests compared with a plantation in southern China

The amount and pattern of litterfall and its nutrient returnwere studied in seven natural forests of Schima superba Gardn.and Champ. (SCS), Castanopsis fabri Hance (CAF), Tsoongiodendronodorum Chun (TSO), Cinnamomum chekiangense Nakai (CIC), Altingiagracilipes Hemsl. (ALG), Castanopsis carlesii (Hemsl.) Hayata(CAC) and Pinus massoniana D. Don (PIM), and compared with thatof an adjacent 29-year-old plantation of Chinese fir (Cunninghamialanceolata Lamb.) (CUL) in Jianou, Fujian, China. Mean annualtotal litterfall over 3 years of observations varied from 4.63Mg ha^–1 in the CUL to 8.85 Mg ha^–1 in the PIM; ofthis litterfall, the leaf contribution ranged from 62 to 73per cent. Litterfall in the CAF, ALG and CAC showed an unimodaldistribution pattern, while for the five other forests, thelitterfall pattern was multi-peak. The rank order of the eightforests, according to nutrient return mass with the exceptionof P, was different from the order when rank was according tototal mass of litterfall. The highest annual N, K and Ca returnsfrom total litterfall were noticed in the TSO, the CAF and theCUL, respectively. The amounts of P and Mg potentially returnedto the soil were the highest in the PIM. The leaf fraction providedgreater potential returns of N, P, K, Ca and Mg to the soilthan other litter fractions. The results of this study demonstratethat natural forests have a greater capability for maintainingsite productivity than the monoculture coniferous plantation,due to higher amount of above-ground litter coupled with greaternutrient returns; therefore conservation of natural forestsis recommended as a practical measure in forest management torealize sustainable development of forestry in mountainous areasof southern China.     

降雨在杉木和马尾松人工林养分循环中的作用

本文对杉木和马尾松林内、外雨树干茎流及迳流所含各种养分物质量进行了测定,其结果表明:林内雨的各种养分物质浓度显著地高于林外雨。林外雨的各养分物质含量是 N>Ca>K>Mg>P,杉木林内雨的各种养分物质量是 K>N>Ca>Mg>P。皆伐迹地迳流中养分流失量显著地高于林地的流失量。雨水养分含量与降雨量存在着半对数函数关系。由降雨输入的养分量显著地大于迳流输出的养分量。林内雨和树干茎流淋溶的养分量占还原养分总量的 48—53％。林内雨和树干淋溶的K、Mg、N的养分量超过凋落物归还的养分量。     

Biomass production,nutrient cycling and distribution in age-sequence Chinese fir (<Emphasis Type="Italic">Cunninghamia lanceolate</Emphasis>) plantations in subtropical China

Biomass production and nutrient (N, P, K, Ca and Mg) accumulation, distribution and cycling were quantified in young, mature and over-mature (10-, 22-, and 34-year old) Chinese fir [Cunninghamia lanceolate (Lamb.) Hook] plantations in southern China. Total stand biomass of young, mature and over-mature stands was 38, 104 and 138 t ha^?1 respectively. Biomass production increased significantly with age. Stem wood represented the highest percentage of stand biomass, accounting for 41, 55 and 63 % in the young, mature and over-mature plantations respectively. Nutrients concentration was highest in live needles and branches, and lowest in stem wood. The plantations accumulated more N, followed by K, Ca, Mg, and P. Nutrient return amount, nutrient utilization efficiency, nutrient turnover time, the ratio of nutrient return and uptake increased with stand age, which implies that young Chinese fir deplete soil nutrients to maintain growth, and efficiently utilize nutrients to decrease dependence on soil nutrients as they age. Harvesting young Chinese fir plantations would therefore lead to high nutrient loss, but prolonging the rotation length could improve soil recovery, and help sustain productivity in the long-term. Improved nutrient return through litterfall as stands get older may also be beneficial to nutrient pool recovery.     

Local basal area affects needle litterfall,nutrient concentration,and nutrient release during decomposition in <Emphasis Type="Italic">Pinus halepensis</Emphasis> Mill. plantations in Spain

Key message

Stand density has a positive effect on C, K and Mg concentration in needle litterfall and a negative one on C, N, Ca, K, Mg, P, S, Zn, and Cu release from needle litter. Consequently, forest management practices such as thinning decrease nutrient concentration in needle litterfall and accelerate nutrient release from decomposing needles in Pinus halepensis plantations in Spain.

Context

Silvicultural practices usually include stand density reduction resulting in changes in litterfall and litter decomposition rates. Little is known about the effect on nutrient concentrations in litterfall and nutrient release during decomposition even when this is the main path of nutrient return to soils.

Aims

The aims of the study are to evaluate the seasonal pattern of nutrient concentration in litterfall, to study how nutrients are released from needle litterfall during decomposition, and to assess whether local basal area of the stand affects nutrient concentration of litterfall and nutrient release during litter decomposition.

Methods

Eight plots were established on each of four stands covering the widest range in local basal area. A littertrap and 15 litterbags were placed on each plot. Periodically, needle litterfall and litter contained in the litterbags were analyzed for C, N, Ca, K, Mg, P, S, Fe, Cu, Mn, and Zn.

Results

Local basal area had a positive effect on C, K, and Mg concentration in needle litterfall and a negative effect on the release of all the nutrients studied but Fe and Mn during the first 2 years of litter decomposition.

Conclusion

Density management of stands has an impact on nutrient cycling, reducing nutrient concentration in needle litterfall, and accelerating nutrient release during decomposition.

     

Variation in the amount and quality of litterfall in a Pinus sylvestris L. stand growing on a bog

The amount and nutrient content of the above-ground litterfall was followed for 9 years in an unfertilized, PKMgB and NPKMgB fertilized Scots pine stand growing on a drained ombrotrophic bog in eastern Finland. The annual litterfall on unfertilized plots was 1995 kg ha⁻¹, of which needles accounted for 74%. The effective temperature sum (threshold value + 5°C) explained 99% of the annual variation in the amount of needle litterfall when the data from one atypical year were excluded from the analysis. Nutrient concentrations were, except for Fe, higher in needle litter than in the other litterfall fractions. Nitrogen, P and K concentrations were low in autumn, and those of Ca and Mn high, possibly owing to variation in the mobility of elements during senescence. The annual litterfall input of N to the soil was 12.4 kg ha⁻¹, and the corresponding values for P and K were 0.08 kg ha⁻¹ and 1.81 kg ha⁻¹, respectively. Fertilization reduced needle litterfall in the first year after treatment, but had no effect thereafter. The amount of other litterfall fractions was not affected by fertilization in any of the 9 years of the study. Nitrogen, P, K and B concentrations increased in the needle litter after both fertilization treatments. The results indicate long-term cycling of fertilizer nutrients on the site.     

沙地柏对毛乌素沙地3种生境中养分资源的反应

为了揭示沙地柏对毛乌素沙地不同生境中养分资源的适应性反应 ,分析了固定沙地、流动沙地和滩地中土壤养分状况、生物量和养分在植株不同结构中的分配以及植株对不同养分的利用和重吸收效率。结果表明 :(1) 3种生境中的氮、磷、钾、钙和镁含量存在不同程度差异 ;(2 )生物量、氮和磷在叶片中分配比率随氮和磷含量的降低而增大 ,而在根中的分配恰好相反 ;(3)氮和磷重吸收效率、钾利用效率和重吸收效率、钙和镁利用效率随相应养分含量的降低而增大 ,氮和磷利用效率随氮和磷可利用性的降低而降低 ;(4)叶片和根系对养分内循环的贡献恰好相反 ;(5 )根分布对不同养分异质性的影响存在差异。     

A comparison of litterfall and element fluxes in even aged Norway spruce,sitka spruce and beech stands in Denmark

Litterfall was investigated in three even-aged Norway spruce (Picea abies), sitka spruce (Picea sitchensis) and beech (Fagus sylvatica) stands on a nutrient poor-soil in Southern Denmark. Dry weights and N, P, K, S, Mg, Ca, Na, Al, and Fe concentrations and fluxes were examined in litterfall fractions. Foliage litter amounted to 90% of total litterfall. The tree stands showed a similar mean annual litterfall. In the spruce stands, annual litterfall was correlated negatively with the current year increment and positively with the previous year increment. Annual litterfall in beech was constant during the 6 study years whereas Norway spruce and sitka spruce showed large fluctuations between years caused by drought, spruce aphid infestations and probably sea salt stress. Norway spruce responded with a long lasting elevated needle loss. Sitka spruce responded to infestations with premature needle loss during short periods. The presence of a large syrphid (Coccinellidae) population was important in regulating aphid (Elatobium abietinum) population density. The between-year variation in element concentrations of litterfall was small whereas variations during the year were large. Interspecific levels were recognized: Norway spruce>beech>sitka spruce. High concentrations in Norway spruce were ascribed to a combination of drought, sea salt stress and elevated transpiration. In sitka spruce, aphid infestations reduced the litterfall N content. Sitka spruce showed the smallest amount of base cation fluxes with litterfall. In contrast, spruce and beech exhibited even litterfall element fluxes. Litterfall studies revealed reduced vitality in the non-native spruce stands and underlined the perception of a healthy stand of native beech.     

Nutrient content of standing crop and biological cycling in Pinus patula ecosystem

Nutrient contents were estimated in different components of Pinus patula trees growing in six stands ranging from 8 to 34 years of age in the Darjeeling hills, India. The highest concentrations of most nutrients were found in the leaves but the maximum nutrient pool was contained in the bole which accounted for about 58 to 85% of the total aerial contents of different elements. Among the nutrients, N concentration (2.2%) was the highest, followed by Ca Mg K P Na. Nutrient contents in the standing crop increased with stand age and were nearly 2102 kg Ca, 1911 kg N, 875 kg Mg, 478 kg K, 285 kg P and 82 kg Na per ha in above-ground biomass of the 34-year-old stand. The annual uptake of N is highest but its accumulation in the standing stock is lower than that of Ca in the 34-year-old stand. The uptake and storage of Mg closely resembled those of K. Nutrient return and release were also determined to establish biological cycling in the 34-year-old P. patula ecosystem. Litter is resistent to decay and the forest floor retained a very rich nutrient store over the mineral soil. Turnover rates and times for nutrient fluxes showed the higher efficiency of the return pathway and the greater stability of the soil pool.     

Variation in nutrient concentrations of Pinus sylvestris stems

Spatial and temporal variation of N, P, K, Ca, Mg, Mn, Zn, B and Al concentrations in Scots pine (Pinus sylvestris L.) bark and stemwood was studied in three stands at different stages of development. Concentrations of the mobile nutrients N, P and K increased in stemwood and inner bark towards the youngest tissues vertically towards the top of the stem, and horizontally from the pith to the youngest annual rings. The concentrations of Ca, Mg, Mn and Zn were greatest in the oldest tissues and decreased horizontally towards the youngest annual rings. There was a slight increase of most nutrients near the divide between sapwood and heartwood. Seasonal nutrient variation was greatest in the inner bark. The highest nutrient concentrations occurred in winter and spring. Concentrations also varied with stand age, especially in the inner bark, being lowest in the oldest stand.     

Changes in nutrient concentrations and nutrient release in decomposing needle litter in monocultural systems of Pinus contorta and Pinus sylvestris—a comparison and synthesis

Scots pine (Pinus sylvestris) and lodgepole pine (Pinus contorta) needle litters were compared in terms of nutrient composition and its change during decomposition. Initial nutrient composition differed between the species, with lodgepole pine needle litter having significantly higher concentrations of P, Mg and Mn. However, no difference was found for concentrations of N, Ca or K. Increases in concentrations of N, P and K during decomposition were significant in both litter types. For Ca the pattern of concentration changes followed a quadratic function as decomposition proceeded. Concentrations of Mg and Mn decreased in lodgepole pine needle litter. In Scots pine litter there was also an initial decrease, but it was followed by an increase in most incubations. For both Mg and Mn, changes in concentrations during decomposition differed significantly between species. In the late decomposition stages, concentrations of Mg and Mn became similar in both litter types. Nutrient concentrations generated by the models were compared with those of the humus (F and H) layer in the stands. The model was quite accurate in predicting concentrations of N and P for both species and the concentration of Mg for lodgepole pine. By contrast, it was not accurate in predicting concentrations of Ca and Mn. Nutrient release was estimated for the two species using both measured litterfall data and long‐term estimates, and regression models were used to predict concentration changes. Rates of release of P, Mg and Mn in the lodgepole pine stands were found to be about twice as high compared with those in Scots pine. Calcium was also released to a greater extent although the difference was not significant.