Seedling growth response of two tropical tree species to nitrogen deposition in southern China

Seedling growth response of two tropical tree species (Schima superba and Cryptocarya concinna) to simulated N deposition was studied during a period of 11 months. One-year-old seedlings were grown in forest soil treated with N as NH₄NO₃ at Control–no N addition, N5–5, N10–10, N15–15, and N30–30 g N m⁻² year⁻¹. The objective was to examine the effects of N addition on seedling growth and compare this effect between the two tropical tree species of different species-N-requirement. Results showed that both species responded significantly to N addition and exhibited positive effect to lower rate of N addition and negative effect to higher rate of N addition on growth parameters (height and stem base diameter, biomass production, and net photosynthetic rate). The highest values were observed in the N10 plots for S. superba and in the N15 plots for C. concinna, but the lowest values were observed in the N30 plots for both species. However, the reduction in the N30 plots was more pronounced for S. superba than for C. concinna relative to the control plots. Our findings suggest that response of seedling growth of tropical tree species to atmospheric N deposition may vary depending on rate of N deposition and species-N-requirement.     

Interactions between Widely Spaced Young Poplars (Populus spp.) and Introduced Pasture Mixtures

Silvopastoral systems involving poplars are widespread in rural landscapes in a number of regions of New Zealand. The effect of widely spaced trees of Populus nigra × P. maximowiczii, aged 8–11 years, on the growth and botanical composition of understorey pasture mixes was determined over 3 years at a southern North Island hill country site. Pasture mixes comprised existing pasture, and two introduced test swards comprising new grass (Agrostis capillaris, Dactylis glomerata, Lolium perenne) and legume (Lotus uliginosus, Trifolium repens) cultivars. Pasture accumulation beneath trees (6.6 t DM ha⁻¹ year⁻¹) was 23% less than open (unshaded, no trees) pasture (8.6 t DM ha⁻¹ year⁻¹) and differences in accumulation occurred between tree aspects (North and South sides of trees) when trees were foliated. In early spring, North plots produced 11–14% more herbage than South plots whereas in late summer, South plots produced up to 44% more herbage than North plots. Yield of both test swards (6.4 and 8.0 t DM ha⁻¹ year⁻¹) was not significantly different from that of the existing sward (7.4 t DM ha⁻¹ year⁻¹) but productivity varied between swards in spring and summer. One test sward included Lotus uliginosus cv. Grasslands Maku, and the sward produced 30% more DM than the other swards in mid-summer. Dactylis glomerata cv. Grasslands Wana comprised 37% of the DM of swards in which it was sown and was the most successful cultivar, followed by Grasslands Maku. Both cultivars are recommended for silvopastoral systems where pasture is lightly grazed.     

Responses of fine root mass,length, production and turnover to soil nitrogen fertilization in <Emphasis Type="Italic">Larix gmelinii</Emphasis> and <Emphasis Type="Italic">Fraxinus mandshurica</Emphasis> forests in Northeastern China

The responses of fine root mass, length, production and turnover to the increase in soil N availability are not well understood in forest ecosystems. In this study, sequential soil core and ingrowth core methods were employed to examine the responses of fine root (≤1 mm) standing biomass, root length density (RLD), specific root length (SRL), biomass production and turnover rate to soil N fertilization (10 g N m⁻² year⁻¹) in Larix gmelinii (larch) and Fraxinus mandshurica (ash) plantations. N fertilization significantly reduced fine root standing biomass from 130.7 to 103.4 g m⁻² in ash, but had no significant influence in larch (81.5 g m⁻² in the control and 81.9 g m⁻² in the fertilized plots). Similarly, N fertilization reduced mean RLD from 6,857 to 5,822 m m⁻² in ash, but did not influence RLD in larch (1,875 m m⁻² in the control and 1,858 m m⁻² in the fertilized plots). In both species, N fertilization did not alter SRL. Additionally, N fertilization did not significantly alter root production and turnover rate estimated from sequential soil cores, but did reduce root production and turnover rate estimated from the ingrowth core method. These results suggested that N fertilization had a substantial influence on fine root standing biomass, RLD, biomass production and turnover rate, but the direction and magnitude of the influence depended on species and methods.     

Main biotic drivers of tree growth in a developing Juniperus thurifera stand in central Spain

Over the last few decades, abandonment of traditional management practices in Spain has led to widespread stand densification and has favoured the expansion of some forest species that previously exhibited more restricted ranges. Spanish juniper (Juniperus thurifera L.) woodlands are experiencing this phenomenon due to agricultural land abandonment and a decrease in the livestock pressure. Yet the main drivers underlying stand structure and dynamics at this novel scenario are poorly understood. In this study, we investigate the main biotic drivers of tree growth in a high-density stand of the dioecious J. thurifera at an early developmental stage (mean tree age of 32, ca. 50 years after land abandonment). Tree growth was measured by coring 299 individuals of different reproductive classes (male, female and non-reproductive). Neighbourhood models were used to assess the relative importance of tree size and neighbourhood competition on tree growth of each reproductive class in the study plot. We found that tree size had the strongest effect on tree growth, whereas the effect of intraspecific competition was negligible. We observed differences in growth patterns among reproductive classes along trunk diameter sizes. Thus, at smaller sizes, the three reproductive classes presented identical patterns of growth. However, at bigger sizes, females were the fastest growing individuals, followed by males and non-reproductive individuals. Overall, our results suggest that in young J. thurifera monospecific forests, where self-thinning processes may have not undergone yet, tree size and the reproductive class could play a relatively more important role than competition as drivers of tree growth. These findings constitute new information which contributes to understanding growth dynamics at early developmental stages in this dioecious species. Furthermore, our results provide guidelines for silvicultural managing, suggesting that at these young juniper stands thinning would likely not translate into enhanced growth on remnant trees.     

Contribution of a liana species, <Emphasis Type="Italic">Mucuna macrocarpa</Emphasis> Wall., to litterfall production and nitrogen input in a subtropical evergreen broad-leaved forest

Annual amounts of litterfall and nitrogen input by litterfall were measured in a subtropical evergreen broad-leaved forest to examine the contribution of a liana species, Mucuna macrocarpa Wall., to the spatial heterogeneity of litterfall production and nitrogen input. The total litterfall in the study plot was 7.1 t ha⁻¹ year⁻¹. The amount of litterfall varied with topography and was greatest at the valley bottom and decreased toward the ridges. Macuna macrocarpa litterfall was absent on the ridges although it accounted for the largest percentage, 32%, of total leaf litter production in the valley. Nitrogen input by litterfall was 69 kg ha⁻¹ year⁻¹ in the plot. Nitrogen input by litterfall was also largest at the valley bottom and decreased toward the ridges. Leaf litter of M. macrocarpa had approximately twice the nitrogen concentration of litterfall of other species. Macuna macrocarpa accounted for 42% of nitrogen input by leaf litter in the valley. The abundance and the high nitrogen concentration of M. macrocarpa intensified differences in the amount of litterfall and nitrogen input by litterfall between valleys and ridges. It was concluded that a liana species, M. macrocarpa, can contribute to the spatial heterogeneity of litterfall and may subsequently affect nutrient cycling in a subtropical evergreen broad-leaved forest on Okinawa Island.     

Inventory and eddy covariance-based estimates of annual carbon sequestration in a Sitka spruce (<Emphasis Type="Italic">Picea sitchensis</Emphasis> (Bong.) Carr.) forest ecosystem

A comparison was made of annual net ecosystem productivity (NEP) of a closed canopy Sitka spruce forest over 2 years, using either eddy covariance or inventory techniques. Estimates for annual net uptake of carbon (C) by the forest varied between 7.30 and 11.44 t C ha⁻¹ year⁻¹ using ecological inventory (NEP_eco) measures and 7.69–9.44 t C ha⁻¹ year⁻¹ using eddy covariance-based NEP (-NEE) assessments. These differences were not significant due to uncertainties and errors associated with estimates of biomass increment (15–21%) and heterotrophic respiration (12–19%). Carbon-stock change inventory (NEP_ΔC ) values were significantly higher (27–32%), when compared to both NEP_eco- and -NEE-based estimates. Additional analyses of the data obtained from this study, together with published data, suggest that there was a systematic overestimation of NEP_ΔC -based assessments due to unaccounted decomposition processes and uncertainties in the estimation of soil-C stock changes. In contrast, there was no systematic difference between NEP_eco and eddy covariance assessments across a wide range of forest types and geographical locations.     

The population dynamics and productivity of <Emphasis Type="Italic">Acacia pennatula</Emphasis> in the pasturelands of the Nature Reserve Mesas de Moropotente,Estelí, Nicaragua

Acacia pennatula trees are the most conspicuous woody species in the pasturelands of the Nature Reserve Mesas de Moropotente, Estelí, Nicaragua. Cattle ranchers keep A. pennatula because it produces fence posts, forage (pods) and firewood. A population projection matrix model was developed to: (1) estimate the sustainable harvest (H) of fence posts at different tree population densities, (2) explore the range of recruitment (R), and survival and growth of both saplings and small poles compatible with current population density, and (3) determine how much carbon is stored in the soil-pasture-tree system. Acacia pennatula trees take 40 years to reach H size (D₃₀ ≥ 30 cm). Estimated sustainable H from current tree population density is 1.8l7 trees ha⁻¹ year⁻¹, yielding 2.8 large and 11.2 regular size fence posts ha⁻¹ year⁻¹. This annual output easily satisfies the needs of a typical 100 ha cattle ranch in the study area. Current population density is congruent with very low R (<100 saplings ha⁻¹ year⁻¹), very low survival rates (<0.30%) and/or retarded D₃₀ growth of saplings and small poles. Total carbon in tree biomass was only 37 Mg ha⁻¹. Cattle ranchers have learned to harness the invasive nature of the species to obtain valuable tree products for farm use or sale.     

Biomass of a man-made forest of timber tree species in the humid tropics of West Java, Indonesia

Biomass of a mature man-made forest in West Java, Indonesia, was estimated to evaluate the carbon sequestration potential of plantation forest in the humid tropics. Twenty plots, each 0.25 ha in area and containing one to six planted species over 40 years of age and with closed canopies, were selected. Trunk dry mass was estimated from trunk diameter, tree height, and bulk density. Maximum trunk diameter (122 cm) was observed in a 46-year-old Khaya grandifoliola C. DC. tree, and the tallest tree (51 m) was a 46-year-old Shorea selanica (DC.) Blume. The largest trunk biomass (911 Mg ha⁻¹) was achieved in the plot composed of two Khaya spp. Among the plots composed of indigeneous Dipterocarpaceae species, the largest trunk biomass was 635 Mg ha⁻¹. These trunk biomasses were larger than those reported from primary rainforests in Southeast Asia (e.g., 403 Mg ha⁻¹ in East Kalimantan, 522 and 368 Mg ha⁻¹ in Peninsular Malaysia). The large biomass in this forest suggests that, given favorable conditions, man-made forests can accumulate the quantities of atmospheric carbon that were lost by the logging of primary forests in the humid tropics.     

Tamarack and Black Spruce Growth on a Boreal Fen in Central Alberta 9 Years after Drainage

Tree growth was measured before, and 9 years after draining a boreal fen that supported a 50- to 60-year-old stand of tamarack (Larix laricina (Du Roi) K. Koch) and black spruce (Picea mariana (Mill.) B.S.P.). Treatments consisted of a series of ditches spaced 30, 40 or 50 m apart, and an undrained control. Nine years after drainage, the diameter, height, basal area, and volume growth of tamarack had increased by 2–5 times that on the control site. Black spruce growth on the drained site was 1.6–5 times that on the control. Tamarack average volume growth (1.20 m³ ha⁻¹ year⁻¹) on the drained site was superior to that of black spruce (0.21 m³ ha⁻¹ year⁻¹). In general for both species, there were no significant differences in growth between trees on the different ditch spacings. This result was attributed to the water table being low enough that adequate aeration zones existed across the strips between ditches on all spacings. Regeneration after treatment was greater on the drained than on the control plots, particularly in the disturbed areas near the ditches where new tamarack seedlings reached densities between 9400 and 12,000 stems ha⁻¹. There was no relationship between increased tree growth and tree distance from the ditches for both species, probably because the water table had been lowered sufficiently so that inadequate substrate aeration was no longer a limiting factor.     

Diversity and spatio-temporal dynamics of dead wood in a temperate near-natural beech forest (<Emphasis Type="Italic">Fagus sylvatica</Emphasis>)

The diversity, spatial patterns and temporal dynamics of dead wood were examined within the near-natural beech forests (Fagus sylvatica) of Serrahn (North-eastern Germany). Data were collected in an 8 ha sample plot and in two permanent plots (0.36 and 0.25 ha) that had been established at the end of the 1960s. The mean volume of dead wood was 94 m³ ha⁻¹, amounting to 14% of the total volume of all trees. The dead wood displayed a large variation in dead wood type, tree size and decay class. Standing dead wood accounted for about one-third of the total dead wood volume. The densities of standing dead trees were about 10% of the densities of the living trees over a wide range of diameters. The overall spatial distribution of dead trees exhibited a random pattern. Among the different dead wood types, standing entire dead trees and uprooted trees deviated from this pattern by displaying a significantly aggregated pattern. In the permanent plots a high mortality of overstorey trees was observed (1.3% year⁻¹) and the average amount of dead wood increased greatly from 2.9 to 111.6 m³ ha⁻¹ over the 35-year observation period. The near-natural beech forests of Serrahn have experienced a long period of low human interference. Nevertheless, our results suggest that the structure and dynamics of dead wood are strongly affected by the last major disturbance events that took place at the end of the Middle Ages. Information about the forest history is therefore a basic requirement when interpreting the results obtained in near-natural forests.     

Influence of characteristics and extension of a forest road network on the supply cost of forest woodchips

A forest road network in northeastern Italy was explored by field investigations to evaluate the cost of covering annual demand of woodchips according to three scenarios. The first scenario (A) considered the current extent of the forest road network (mainly tractor road) and the associated qualitative characteristics; the second scenario (B) evaluated the possibility of increasing the availability of the technical amount of forest biomass by extending the forest road network by three tractor roads (3.9 km); the third scenario (C) considered the impact on woodchip supply of converting 9.3 km of tractor forest road into truck forest road. At a woodchip price of 60 € t⁻¹, the cost–supply curve of scenario C indicated a woodchip amount of 2886 t year⁻¹, which was 561 t year⁻¹ greater than scenario A and 161 t year⁻¹ greater than scenario B.     

Carbon accumulation in aboveground and belowground biomass and soil of different age native forest plantations in the humid tropical lowlands of Costa Rica

Generic or default values to account for biomass and carbon accumulation in tropical forest ecosystems are generally recognized as a major source of errors, making site and species specific data the best way to achieve precise and reliable estimates. The objective of our study was to determine carbon in various components (leaves, branches, stems, structural roots and soil) of single-species plantations of Vochysia guatemalensis and Hieronyma alchorneoides from 0 to 16 years of age. Carbon fraction in the biomass, mean (±standard deviation), for the different pools varied between 38.5 and 49.7% (±3 and 3.8). Accumulated carbon in the biomass increased with the plantation age, with mean annual increments of 7.1 and 5.3 Mg ha⁻¹ year⁻¹ for forest plantations of V. guatemalensis and H. alchorneoides, respectively. At all ages, 66.3% (±10.6) of total biomass was found within the aboveground tree components, while 18.6% (±20.9) was found in structural roots. The soil (0–30 cm) contained 62.2 (±13) and 71.5% (±17.1) of the total carbon (biomass plus soil) under V. guatemalensis and H. alchorneoides, respectively. Mean annual increment for carbon in the soil was 1.7 and 1.3 Mg ha⁻¹ year⁻¹ in V. guatemalensis and H. alchorneoides. Allometric equations were constructed to estimate total biomass and carbon in the biomass which had an R ²aj (adjusted R square) greater than 94.5%. Finally, we compare our results to those that could have resulted from the use of default values, showing how site and species specific data contribute to the overall goal of improving carbon estimates and providing a more reliable account of the mitigation potential of forestry activities on climate change.     

Fine root dynamics in three central Himalayan high elevation forests ranging from closed canopied to open-canopied treeline vegetation

Fine root biomass, rates of dry matter production and nutrients dynamics were estimated for 1 year in three high elevation forests of the Indian central Himalaya. Fine root biomass and productivity were higher in closed canopied cappadocian maple forest (9.92 Mg ha⁻¹ and 6.34 Mg ha⁻¹ year⁻¹, respectively), followed by Himalayan birch forest (6.35 Mg ha⁻¹ and 4.44 Mg ha⁻¹ year⁻¹) and Bell rhododendron forest (6.23 Mg ha⁻¹ and 2.94 Mg ha⁻¹ year⁻¹). Both fine root biomass and productivity declined with an increase in elevation. Across the sites, fine root biomass was maximal in fall and minimal in summer. In all sites, maximum nutrient concentration in fine roots was in the rainy season and minimum in winter. Fine root biomass per unit basal area was positively related with elevation, Bell rhododendron forest having the largest fine root biomass per unit of basal area (0.53 Mg m⁻²) and cappadocian maple the least (0.18 Mg m⁻²). The production efficiency of fine roots per unit of leaf biomass also increased with elevation and ranged from 1.13 g g⁻¹ leaf mass year⁻¹ in cappadocian maple forest to 1.28 g g⁻¹ leaf mass year⁻¹ in Bell rhododendron forest. Present fine root turnover estimates showed a decline towards higher elevations (0.72 year⁻¹ in cappadocian maple and 0.58 year⁻¹ in Bell rhododendron forest) and are higher than global estimates (0.52).     

Structure and Function of <Emphasis Type="Italic">Populus deltoides</Emphasis> Agroforestry Systems in Eastern India: 1. <Emphasis Type="Italic">Dry matter dynamics</Emphasis>

Agroforestry systems based on poplar (Populus deltoides) are becoming popular in eastern and northern parts of India. Therefore studies on the structure and function of the systems are important. The investigations included allometric equations for above- and belowground tree components, crop and plantation floor biomass and litter fall estimation at Pusa, Bihar, India. Biomass, floor litter mass, litter fall and net primary productivity (NPP) of plantations increased with an increase in age of trees whereas, crop biomass for any specific crop interplanted with poplar decreased with the age of the plantation. The total plantation biomass increased from 12.08 to 90.59 Mg ha⁻¹ and NPP varied from 5.69 to 27.9 Mg ha⁻¹ year⁻¹. The biomass accumulation ratio ranged from 2.1 to 3.2. Total annual litter fall was in between 1.95 and 10.00 Mg ha⁻¹ year⁻¹, of which 92–94% was contributed by leaf litter. Compartmental models were developed for dry matter distribution in agroforestry systems involving young (3-year-old) and mature (9-year-old) poplar trees interplanted with various crops, the crops being grown in two rotations maize (Zea mays) – wheat (Triticum aestivum) – turmeric (Curcuma domestica) and pigeonpea (Cajanus cajan) – turmeric. This study substantiates the potential of Populus deltoides G₃ under agroforestry combinations.     

Fine-root dynamics in a young hinoki cypress (<Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>) stand for 3 years following thinning

Fine roots play a key role in carbon and nutrient dynamics in forested ecosystems. Fine-root dynamics can be significantly affected by forest management practices such as thinning, but research on this topic is limited. This study examined dynamics of fine roots <1 mm in diameter in a 10-year-old stand of hinoki cypress (Chamaecyparis obtusa) for 3 years following thinning (65% in basal area). Fine-root production and mortality rates were estimated using a minirhizotron technique in combination with soil coring. In both thinned and un-thinned control plots, fine-root elongation occurred from early spring to winter (March to December) and fluctuated seasonally. In the thinned and the control plots, the annual fine-root production rates were estimated to be 101 and 120 g m⁻² year⁻¹, respectively, whereas the estimated annual fine-root mortality rates were 77 and 69 g m⁻² year⁻¹, respectively. At 3 years after thinning, live fine-root biomass was significantly smaller in the thinned plot (143 g m⁻²) than in the control plot (218 g m⁻²), whereas dead fine-root biomass was not (147 and 103 g m⁻², respectively). Morphological and physiological indices of fine roots such as diameter, specific root length, and root tissue density of the live fine roots was similar in both plots. These results suggested that thinning tended to decrease biomass and production of fine roots, but the effects on characteristics of fine roots would be less evident.     

Biomass production of Eucalyptus boundary plantations and their effect on crop productivity on Ethiopian highland Vertisols

In recent years, Eucalyptus globulus planted along field boundaries has come to dominate the central highland landscape of Ethiopia. Although evidence is scanty, there is a perception that this practice adversely affects crop productivity. An on-farm trial was conducted on Pellic Vertisol at Ginchi to determine the production potential of eucalypt boundaries and their effect on the productivity of adjacent crops of tef (Eragrostis tef) and wheat (Triticum sp.). The experiment comprised three stand ages, four field aspects and six distances from the tree-crop interface, using a split-split plot design with three replicates. Wood production rates ranged between 168 kg ha⁻¹ y⁻¹ (four years old) and 2901 kg ha⁻¹ y⁻¹ (twelve years). Thus eucalypt boundaries planted on a hectare of land would satisfy 50 to 75% of the annual biomass energy requirement of a rural household of five persons. Significant depression of tef and wheat yields occurred over the first 12m from the tree line: the reduction was 20 to 73% for tef and 20 to 51% for wheat, equivalent to yield losses of 4.4 to 26% and 4.5 to 10% per hectare respectively. Nevertheless, in financial terms, the tree component adequately compensated for crop yield reduction and even generated additional income. Therefore, eucalypt boundaries have great potential to satisfy the rising demand for wood, without requiring a major change in land use on the highland Vertisols. The greater availability of wood will reduce the demand for dung and crop residues for fuel, and thus may contribute to improved soil management on croplands while relieving the increasing pressure on indigenous forest and woodlands.     

Large-scale structural variation and long-term growth dynamics of Juniperus thurifera trees in a managed woodland in Soria, central Spain

? Juniper woodlands have a great conservational and productive importance in Spain. However, basic traits of their structural variation and growth dynamics are unknown.

? To characterize the structural variation and assess both height and radial growth patterns, we sampled and measured stem cross-sections every 0.5 m in height from 107 Spanish juniper (Juniperus thurifera L.) trees, which were selected based on a 350 m regular grid over a whole woodland of 3 300 ha in area. We used dendroecological techniques and spatial analysis to study tree structure and growth.

? Structural traits such as bole diameter and height were mainly determined by tree life-related parameters such as tree age and growth rate variation, while abiotic factors such as altitude played a minor role in determining structural variation. Over the last 300 years, juniper establishment has been continuous in time but discontinuous in space. Large-scale spatial heterogeneity of tree establishment, and the presence of an early growth suppression and abrupt growth changes in junipers > 100 years old are consequences of an intense management that almost ceased in the late 19th century.

? Abrupt growth releases and suppressions were synchronic among different age classes, and coincided with documentary records on livestock decrease and key historical changes in land use. Growth patterns suggest that juniper is a brow sing-tolerant species that is able to survive large periods of intense browsing pressure.

     

Nitrogen budget of a rehabilitated forest on a degraded granitic hill

Rehabilitated forests established about 100 years ago on denuded lands in a hilly granitic area are widespread in the Kyoto–Osaka area, the second largest megalopolis in Japan. From 2001 to 2003, we monitored the annual nitrogen (N) budget of a rehabilitated forest watershed dominated by Quercus serrata and Ilex pedunculosa. The ion concentrations of bulk rain in the watershed were similar to those of other watersheds in Japan. The annual bulk rain input of N ranged from 5.1 to 6.3 kg N ha⁻¹ year⁻¹, and the N deposition from throughfall and stem-flow ranged from 7.5 to 8.2 kg N ha⁻¹ year⁻¹. Estimated annual outputs of N from the stream ranged from 3.3 to 10.6 kg N ha⁻¹ year⁻¹. These results indicate that the amount of N deposition in this area is less than that in urban Tokyo (>10 kg N ha⁻¹ year⁻¹), but the N output of the watershed is comparable with that of the Tokyo area. We discuss the characteristics of N dynamics in rehabilitated forests, focusing on the biogeochemical processes of this watershed.     

Ecological studies on subtropical evergreen broad-leaved forest in Okinawa, Japan: Litter production and nutrient input

Patterns of litterfall and nutrient input in a subtropical evergreen broad-leaved forest in northern Okinawa, Japan, were studied during May, 1996–April, 1999. The mean annual rate of litterfall in the five sampling plots ranged from 6.84 to 8.93 Mg ha⁻¹ yr⁻¹, of which 63.3–68.5% were leaves; 22.4–29.1% woody parts (including branches < 5.0 cm in diameter and bark); 2.8–5.0% sexual organs and 4.6–6.3% miscellaneous material. Significant differences were found among plots and among years. Significantly monthly differences pronounced seasonal patterns in litterfall were observed. Total litterfall and leaf litter showed negative correlations with relative basal area of the dominant species,Castanopsis sieboldii; and showed positive correlations with mean height of the stands. The dominant species,C. sieboldii produced an average of 2.36 Mg ha⁻¹ yr⁻¹ of leaf litter, which covered 30.5% of the annual litter production, and the nutrient input from those litterfall contributed 32.3, 28.3, 30.2, 22.2, 32.5, and 30.5% of total N, P, K, Ca, Mg, and Na, respectively. Nutrient use efficiency in litter production was high, especially for P and K compared with other broad-leaved forests in Japan indicating that P and K may be limiting in Okinawan evergreen broad-leaved forest.     

Tree size dependence of litter production, and above-ground net production in a young Hinoki (Chamaecyparis obtusa) stand

The study was carried out in a 9-year-old hinoki cypress (Chamaecyparis obtusa (Sieb. et Zucc.) Endl.), stand over a span of three years from July 1992 to June 1995, primarily to predict litter production from exteral tree dimensions by combining open-top clothtrap and clipping methods. Litter production was virtually concentrated in October and November. Stem cross-sectional area at the crown base was proved to be the reliable predictor of litter production, and that single regression model was evolved irrespective of year. The regression model had proportional constants of 2.696 × 10⁻² and 3.540 × 10⁻² kg cm⁻² year⁻¹ for leaf litter and total litter production, respectively. Utilizing the model, leaf litter production of the stand was assessed to be 5.04, 5.12, and 4.99, and total litter production to be 6.48, 6.58, and 6.40 Mg ha⁻¹ year⁻¹ for the first, second and third year, respectively. Biomass increment was 6.67, 7.80, and 7.70, tree mortality was 0.15, 0.13, and 0.41, and insect grazing was 0.09, 0.05, and 0.002 Mg ha⁻¹ year⁻¹ for the first, second and third year, respectively. Above-groud net production was therefore 13.39, 14.55, and 14.51, Mg ha⁻¹ year⁻¹, and biomass accumulation ratio (biomass/net production) was 1.86, 2.21, and 2.76 year for the first, second and third year, respectively. Considering data from earlier studies and the results of this study, biomass accumulation ratio,BAR (year), of hinoki stands was best related to above-ground biomass,y (Mg ha⁻¹), using the power function:BAR=0.112y ^0.936. Excluding seedling stands, leaf efficiency (above-ground net production per unit leaf mass) of hinoki stands was 0.91±0.02 (SE) Mg Mg⁻¹ year⁻¹, irrespective of stand biomass or age.