Quantitative classification and carbon density of the forest vegetation in Lüliang Mountains of China

Forests play a major role in global carbon (C) cycle, and the carbon density (CD) could reflect its ecological function of C sequestration. Study on the CD of different forest types on a community scale is crucial to characterize in depth the capacity of forest C sequestration. In this study, based on the forest inventory data of 168 field plots in the study area (E 111°30′–113°50′, N 37°30′–39°40′), the forest vegetation was classified by using quantitative method (TWINSPAN); the living biomass of trees was estimated using the volume-derived method; the CD of different forest types was estimated from the biomass of their tree species; and the effects of biotic and abiotic factors on CD were studied using a multiple linear regression analysis. The results show that the forest vegetation in this region could be classified into 9 forest formations. The average CD of the 9 forest formations was 32.09 Mg ha⁻¹ in 2000 and 33.86 Mg ha⁻¹ in 2005. Form. Picea meyeri had the highest CD (56.48 Mg ha⁻¹), and Form. Quercus liaotungensis + Acer mono had the lowest CD (16.14 Mg ha⁻¹). Pre-mature forests and mature forests were very important stages in C sequestration among four age classes in these formations. Forest densities, average age of forest stand, and elevation had positive relationships with forest CD, while slope location had negative correlation with forest CD.     

Variation in carbon stocks on different slope aspects in seven major forest types of temperate region of Garhwal Himalaya,India

The present study was undertaken in seven major forest types of temperate zone (1500 m a.s.l. to 3100 m a.s.l.) of Garhwal Himalaya to understand the effect of slope aspects on carbon (C) density and make recommendations for forest management based on priorities for C conservation/sequestration. We assessed soil organic carbon (SOC) density, tree density, biomass and soil organic carbon (SOC) on four aspects, viz. north-east (NE), north-west (NW), south-east (SE) and south-west (SW), in forest stands dominated by Abies pindrow, Cedrus deodara, Pinus roxburghii, Cupressus torulosa, Quercus floribunda, Quercus semecarpifolia and Quercus leucotrichophora. TCD ranged between 77.3 CMg ha⁻¹ on SE aspect (Quercus leucotrichophora forest) and 291.6 CMg ha⁻¹ on NE aspect (moist Cedrus deodara forest). SOC varied between 40.3 CMg ha⁻¹ on SW aspect (Himalayan Pinus roxburghii forest) and 177.5 CMg ha⁻¹ on NE aspect (moist Cedrus deodara forest). Total C density (SOC + TCD) ranged between 118.1 CMg ha⁻¹ on SW aspect (Himalayan Pinus roxburghii forest) and 469.1 CMg ha⁻¹ on NE aspect (moist Cedrus deodara forest). SOC and TCD were significantly higher on northern aspects as compared with southern aspects. It is recommended that for C sequestration, the plantation silviculture be exercised on northern aspects, and for C conservation purposes, mature forest stands growing on northern aspects be given priority.     

Diversity of understory plants in undisturbed and disturbed tropical lowland forests of Little Andaman Island, India

Species richness and density of understory plants were investigated in eight 1 ha plots, distributed one each in undisturbed and disturbed tropical evergreen, semi-evergreen, deciduous and littoral forests of Little Andaman island, India, which falls under one of the eight hottest hotspots of Biodiversity in the world viz. the Indo-Burma. One hundred 1 m⁻² quadrats were established in each 1 ha plot, in which all the understory plants (that include herbs, undershrubs, shrubs and herbaceous climbers) were enumerated. The total density of understory plants was 6,812 individuals (851 ha⁻¹) and species richness was 108 species, representing 104 genera and 50 families. Across the four forest types and eight study plots, the species richness ranged from 10 to 39 species ha⁻¹. All the disturbed sites harbored greater number of species than their undisturbed counterparts. Herbs dominated by species (63%) and density (4,259 individuals). The grass Eragrostis tenella (1,860 individuals; IVI 40), the invasive climber Mikania cordata (803; IVI 20) and the shrub Anaxagorea luzonensis (481; IVI 17.5) were the most abundant species. Poaceae, Asteraceae, Acanthaceae, Orchidaceae and Euphorbiaceae constituted the species-rich families represented by 6 species each. The species-area curves attained an asymptote at 0.8 ha level except in sites DD and DL, indicating 1 ha plot is not sufficient to capture all the understory species in disturbed forests. The alien weeds formed about one-fourth of the species richness (31 species; 28%) and density (1,926 individuals; 28.3%) in the study sites, indicating the extent of weed invasion and the attention required for effective conservation of the native biodiversity of the fragile island forest ecosystem.     

Carbon and nitrogen storage in an age-sequence of <Emphasis Type="Italic">Pinus densiflora</Emphasis> stands in Korea

The carbon (C) and nitrogen (N) storage capabilities of Pinus densiflora in six different stand ages (10, 27, 30, 32, 44, and 71 years old) were investigated in Korea. Thirty sample trees were destructively harvested and 12 were excavated. Samples from the above and belowground tree components, coarse woody debris (CWD), forest floor, and mineral soil (0–30 cm) were collected. Tree biomass was highest in the 71-year-old stand (202.8 t ha⁻¹) and lowest in the 10-year-old stand (18.4 t ha⁻¹). C and N storage in the mineral soil was higher in the 71-year-old stand than in the other stands, mainly due to higher soil C and N concentrations. Consequently, the total ecosystem C and N storage (tree+forest floor+CWD+soil) was positively correlated with stand age: increasing from a minimum in the 10 year old stand (18.8 t C ha⁻¹ and 1.3 t N ha⁻¹) to a maximum in the 71-year-old stand (201.4 t C ha⁻¹ and 8.5 t N ha⁻¹). The total ecosystem C storage showed a similar sigmoidal pattern to that of tree C storage as a function of the age-sequence, while N storage in the CWD, forest floor and mineral soil showed no significant temporal trends. Our results provide important insights that will increase our understanding of C and N storage in P. densiflora stands and our ability to predict changes according to stand age in the region.     

Biometric-based estimation of net ecosystem production in a mature Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) plantation beneath a flux tower

Quantification of carbon budgets and cycling in Japanese cedar (Cryptomeria japonica D. Don) plantations is essential for understanding forest functions in Japan because these plantations occupy about 20% of the total forested area. We conducted a biometric estimate of net ecosystem production (NEP) in a mature Japanese cedar plantation beneath a flux tower over a 4-year period. Net primary production (NPP) was 7.9 Mg C ha⁻¹ year⁻¹ and consisted mainly of tree biomass increment and aboveground litter production. Respiration was calculated as 6.8 (soil) and 3.3 (root) Mg C ha⁻¹ year⁻¹. Thus, NEP in the plantation was 4.3 Mg C ha⁻¹ year⁻¹. In agreement with the tower-based flux findings, this result suggests that the Japanese cedar plantation was a strong carbon sink. The biometric-based NEP was higher among most other types of Japanese forests studied. Carbon sequestration in the mature plantation was characterized by a larger increment in tree biomass and lower mortality than in natural forests. Land-use change from natural forest to Japanese cedar plantation might, therefore, stimulate carbon sequestration and change the carbon allocation of NPP from an increment in coarse woody debris to an increase in tree biomass.     

Mid-successional stand dynamics in a cool-temperate conifer-hardwood forest in northern Japan

Stand dynamics was studied over 13 years in a cool-temperate conifer-hardwood forest, northern Japan. A total 30 hardwood species and one conifer, Abies sachalinensis, larger than 1.5 cm DBH were recorded. The total stand density was 1677 trees ha⁻¹ at the beginning, decreasing to 1184 trees ha⁻¹ (30% reduction) over the study period, but the total stand basal area was almost unchanged (about 49 m² ha⁻¹). This large reduction in total density was mainly due to the death of saplings and infrequent recruitment. Number of recruits gradually decreased with time, while that of dead trees was constant. Cause of death of small trees was mainly due to suppression by tall trees. Skewness of the DBH frequency distribution varied among the species. A less skewed frequency distribution (i.e., few number of saplings) was shown by shade-intolerant species such as Populus maximowiczii and Betula maximowicziana, and a more skewed frequency distribution (i.e., large number of saplings) by shade-tolerant species such as Acer mono and Tilia japonica. DBH frequency distribution changed to less skewed patterns with reduction of density in most species during the census period. Rank of shade tolerance positively correlated with tree density and skewness, and negatively correlated with mean DBH. Skewness also positively correlated with recruitment rates. Furthermore, rank of shade tolerance positively correlated with seed size. These results suggest that shade-intolerant species regenerated immediately after disturbances by wide dispersal of small seeds, but their recruitment was interrupted after that. By contrast, shade-tolerant species were able to recruit even after the ceasation of recruitment of shade-intolerant species, but suffered severe mortality due to the increasing shading with the progress of stand development. This study suggests that the stand is still developing, with changes in species composition and size structure, and that species differences in shade tolerance and seed size are important for the stand structural changes.     

Tropical moist <Emphasis Type="Italic">Polylepis</Emphasis> stands at the treeline in East Bolivia: the effect of elevation on stand microclimate,above- and below-ground structure,and regeneration

We studied Polylepis forests along an elevational transect between 3,650 and 4,050 m a.s.l. at the treeline of the moist eastern cordillera in Bolivia to examine changes in above- and below-ground stand structure, leaf and root morphology, and regeneration in relation to stand microclimate. Field measurements and model predictions indicated relatively cold growth conditions of the Polylepis forests. Tree height, stem diameter, and basal area of the stands decreased markedly while stem density increased with elevation. Leaf morphology differed between the two occurring Polylepis species, and trees at the treeline had smaller leaves with higher specific leaf area. In contrast, fine root biomass increased from 37 g m⁻² at the lowermost stand to 234 g m⁻² at the treeline. Trees of the uppermost stand had higher specific root surface area and a much higher number of root tips per unit dry mass. Thus, root surface area and total number of root tips per unit ground area increased conspicuously from the lowermost stand to the treeline. Density of young growth inside the forest increased towards the treeline, while density in the open grassland decreased with elevation. Young growth originated from sexual reproduction at the lower forest but was comprised exclusively of root suckers at the treeline stand. We conclude that both the marked change in carbon allocation towards the root system, as well as the changes in root morphology with elevation indicate an adaptation to reduced nutrient supply under cold conditions of these Polylepis stands at the treeline in E Bolivia.

Tree species composition and diversity in natural temperate forests of the North-Western Himalayas

The present study was undertaken in the natural temperate Himalayan forests of Himachal Pradesh, India, to assess the tree species composition and diversity. For this purpose, six major forest types (FT) viz., FT1- Upper Himalayan Pinus roxburghii forest, FT2- Quercus leucotrichophora forest, FT3- Low-level P. wallichiana forest, FT4- Moist C. deodara forest, FT5- Western Mixed Coniferous Forest, FT6- Pinus gerardiana forest were selected. Detailed sampling was carried out in these forest types, and the sample plots in each forest type were laid out using the stratified random approach. Tree stem density varied from 191.11 N ha^?1 (FT6) to 441.11 N ha^?1 (FT2), whereas the tree total basal cover varied from 20.01 m² ha^?1 (FT6) to 47.59 m² ha^?1 (FT5). The diversity indices reflected that a total of 21 tree species (16 genera, 11 families) were identified, with tree species richness ranging from 3 (FT6) to 9 (FT1 & FT5). The forest type FT5 recorded the maximum Shannon index of diversity (2.36), Simpson Index of diversity (0.75), Margalef's Index of richness (1.37), pielou equitability (0.74), menheink index of species richness (0.49), whereas the highest Shannon Index of diversity (0.73) and species heterogeneity (0.85) in FT6 forest type. Furthermore, dominance-diversity (d-d) curves drawn that all the six forest types showed geometric curves reveals that one or two tree species are dominant in a particular forest type. Simultaneously, the research area's species diversity, tree stem density, and tree total basal cover were equivalent to those seen in other sections of Western Himalayas.     

Tree diversity and conservation value of Ngovayang’s lowland forests,Cameroon

The Ngovayang Massif of southern Cameroon is a range of small hills near the Atlantic coast, in the Lower Guinea floristic region. This region is known to harbor forests with high levels of biodiversity and endemism, but this Massif is botanically poorly known. We assessed tree species diversity, floristic composition and level of endemism of the Ngovayang forest, comparing it with other sites in Central Africa. Five 1-ha permanent plots within old-growth lowland forests of the Ngovayang Massif were censused. A total of 2,658 individuals with dbh ≥ 10 cm were recorded, belonging to 293 species, 170 genera and 60 families. The mean number of stems was 532 ± 75 stems ha⁻¹. Taking into account other data available, the list of vascular plants known in the Massif reaches a total of 450 species. We found 47 species of high conservation value, including Cameroon endemics and other rare and threatened species. Species richness and endemism are comparable to those of the richest known sites in Central African forests. The forests of Ngovayang were found to be particularly rich in Fabaceae-Caesalpinioideae. Topographic heterogeneity, high precipitation and atmospheric humidity owing to the proximity of the ocean, and permanence of a forest cover during past geological times probably all contribute to explaining the Massif’s high tree diversity and endemism. This study highlights the botanical importance of the poorly studied Ngovayang forest within the Lower Guinea region, justifying efforts for improved assessment of this value and for the development of suitable national conservation strategies.     

Laurel forests in Tenerife,Canary Islands

 Stand structure and leaf area distribution of a laurel forest in the Agua García mountains of Tenerife are described. The site is situated at 820 m a.s.l., faces NNE, and has a humid mediterranean climate. Summer droughts are mitigated by relatively high air humidity and clouds. The natural mixed hardwood forest is composed of six major tree species: Laurus azorica (Seub.) Franco, Persea indica (L.) Spreng, Myrica faya Ait., Erica arborea L. and two species of Ilex (I. platyphylla Webb & Berth. and I. canariensis Poivet.). The experimental stand had a density of 1693 trees ha^– 1, a basal area of 33.7 m²ha^– 1, and a cumulated volume of above-ground parts of trees of 231 m³ ha^– 1 with a corresponding dry mass of 204 ton ha^– 1. Diameters at breast height ranged from 6 to 46 cm. Mean concentration of plant dry mass per volume was 1.17 kg m^– 3. The vertical pattern of leaf area distribution in individual trees for all tree species was characterized by a Gaussian-like curve. Stand leaf area index was 7.8. These evergreen, broad-leaved (laurisilva or lucidophyllous) forests represent a relic forest that was widespread in the Mediterranean region some 20 million years ago. Our data illustrate some of the structural characteristics of this historically widespread forest type. Received: 2 December 1994 / Accepted: 6 November 1995     

Soil moisture condition and soil nitrogen dynamics in a pure Alnus japonica forest in Korea

This study was conducted to examine the influences of soil-moisture conditions on soil nitrogen (N) dynamics, including in situ soil N mineralization, N availability, and denitrification in a pure Alnus japonica forest located in Seoul, central Korea. The soil N mineralization, N availability, and denitrification were determined using the buried bag incubation method, ion exchange resin bag method, and acetylene block method, respectively. The annual net N mineralization rate (kg N ha⁻¹ year⁻¹) and annual N availability (mg N bag⁻¹) were 40.26 and 80.65 in the relatively dry site, −5.43 and 45.39 in the moist site, and 7.09 and 39.17 in the wet site, respectively. The annual net N mineralization rate and annual N availability in the dry site were significantly higher than those in the moist and wet sites, whereas there was no significant difference between the moist and wet sites. The annual mean denitrification rate (kg N ha⁻¹ year⁻¹) in the dry, moist, and wet sites was 2.37, 2.76, and 1.59, respectively. However, there was no significant difference among sites due to the high spatial and temporal variations. Our results indicate that soil-moisture condition influenced the in situ N mineralization and resin bag N availability in an A. japonica forest, and treatments of proper drainage for poorly drained sites would increase soil N mineralization and N availability and consequently be useful to conserve and manage the A. japonica forest.     

Effects of population density on forest structure and species richness and diversity of trees in Kampong Thom Province, Cambodia

This study examined differences in stand structure, tree species richness, and tree species diversity in relation to population density in Kampong Thom Province, Cambodia. Tree data were obtained from a 1997 forest inventory involving 60 clusters (540 plots) systematically distributed over 30% of the provincial forest area. Spatially referenced population data were obtained from the 1998 national population census. The average number of trees per cluster was 356/ha, the average basal area, 23 m²/ha, the average stand volume, 217 m³/ha, and the average aboveground biomass, 273 Mg/ha for all trees of DBH 10 cm and larger. The average species richness per cluster was 37 species, while average species diversity was measured as 0.916 using Simpson’s index and 2.98 by Shannon’s index. Significant negative correlations were generally found between population density surrounding clusters and tree density, basal area, stand volume, aboveground biomass, and species richness and diversity for three examined diameter classes (DBH of 10–30, ≥30, and ≥10 cm). As the distance from clusters for calculating population density increased, the correlation levels increased up to 5 or 7 km, depending on the variables and diameter class, and then stayed relatively constant for stand structure variables and decreased for species richness and diversity. The results indicate that evidence of disturbance was more pronounced at higher population density up to around 5 to 7 km. We suggest that introduction of greater controls on human disturbance should be a high priority for resource management and conservation in Kampong Thom Province and, presumably, Cambodia as a whole.     

Altitudinal changes in carbon storage of temperate forests on Mt Changbai, Northeast China

A number of studies have investigated regional and continental scale patterns of carbon (C) stocks in forest ecosystems; however, the altitudinal changes in C storage in different components (vegetation, detritus, and soil) of forest ecosystems remain poorly understood. In this study, we measured C stocks of vegetation, detritus, and soil of 22 forest plots along an altitudinal gradient of 700–2,000 m to quantify altitudinal changes in carbon storage of major forest ecosystems (Pinus koraiensis and broadleaf mixed forest, 700–1,100 m; Picea and Abies forest, 1,100–1,800 m; and Betula ermanii forest, 1,800–2,000 m) on Mt Changbai, Northeast China. Total ecosystem C density (carbon stock per hectare) averaged 237 t C ha⁻¹ (ranging from 112 to 338 t C ha⁻¹) across all the forest stands, of which 153 t C ha⁻¹ (52–245 t C ha⁻¹) was stored in vegetation biomass, 14 t C ha⁻¹ (2.2–48 t C ha⁻¹) in forest detritus (including standing dead trees, fallen trees, and floor material), and 70 t C ha⁻¹ (35–113 t C ha⁻¹) in soil organic matter (1-m depth). Among all the forest types, the lowest vegetation and total C density but the highest soil organic carbon (SOC) density occurred in Betula ermanii forest, whereas the highest detritus C density was observed in Picea and Abies forest. The C density of the three ecosystem components showed distinct altitudinal patterns: with increasing altitude, vegetation C density decreased significantly, detritus C density first increased and then decreased, and SOC density exhibited increasing but insignificant trends. The allocation of total ecosystem C to each component exhibited similar but more significant trends along the altitudinal gradient. Our results suggest that carbon storage and partitioning among different components in temperate forests on Mt Changbai vary greatly with forest type and altitude.     

Alternative pathways of liana communities in the forests of northwestern Argentina

Liana dynamics in secondary and mature forests are well known in tropical areas dominated by native tree species. Outside the tropics and in secondary forests invaded by exotic species, knowledge is scarce. In this study, we compare liana communities between secondary and mature forests dominated by native species in a subtropical montane area of Sierra de San Javier, Tucuman, Argentina. Additionally, we evaluate changes of liana communities in secondary forests with increasing densities of Ligustrum lucidum and Morus alba, two of the most invasive exotic trees of the area. We surveyed liana species richness and density in three 30-year secondary patches, four 60-year secondary patches, and four mature patches dominated by native tree species, to analyze changes in liana communities with forest age. Within each patch, we sampled 10–25 20 × 20 m quadrats. Additionally, we surveyed liana density and species richness in secondary forest patches with different densities of L. lucidum and M. alba. In native-dominated forests, liana species richness increased and showed a tendency of increasing basal area from 30-year secondary forests to mature forests. Liana density was highly variable, and most of the species were shared between native-dominated secondary and mature forests. Liana density and species richness decreased with L. lucidum density, whereas in secondary forests highly dominated by M. alba, lianas increased in density. Overall, lianas followed different pathways influenced by native forest succession and exotic tree invasions.     

Root turnover in a beech and a spruce stand of the Belgian Ardennes

The theoretical basis of fine root turnover estimation in forest soils is discussed, in relation to appropriate experimental techniques of measurement. After sequential coring, the correct expression is the sum of significant positive increments of live and dead roots of the various diameter categories, to which the transfer of dead roots to organic matter derived from roots, OMDR, has to be added. This should not be confounded with dead root mineralization. The transfer rates should first be estimated in root dimensions and not in weight of dry matter. The measurements were carried out in a 120 year old beech (Fagus sylvatica L.) stand and a 35 year old Norway spruce (Picea abies Karst) stand, in the Eastern Ardennes, Belgium. The turnover rate of fine roots (diam. <5 mm) was 4393 kg ha⁻¹ year⁻¹ (root dry weight), including 711.2 kg ha⁻¹ year⁻¹ for dead root transfer to OMDR, for beech. For spruce, turnover rate was 7011 kg ha⁻¹ year⁻¹ (root dry weight), including 1498 kg ha⁻¹ year⁻¹ for dead root transfer to OMDR. Under beech, there was a slight root density increase in spring. No seasonal fluctuations were observed under spruce, but a strong irreversible drop in live root growth was found in the later season 1980–1981, corresponding to a decrease of tree height growth and trunk radius increment. Turnover rates were further expressed in dry weight and in amounts of elements (kg ha⁻¹ year⁻¹) (Ca, Mg, K, Na, Al, N, P, S). Correlative relations between root dimensions and dry weight and element concentrations show that the derived values, and in particular root specific density (dry weight volume⁻¹) vary according to species, root category, and seasonal sampling. Various schemes of seasonal variations of root growth, described in Europe, show that the major dependance on general climate is obscured by environmental factors (soil, exposure, species). It is suggested that root density fluctuation approach the steady state on an annual basis under mild Atlantic conditions.     

Native tree regeneration in native tree plantations: understanding the contribution of Araucaria angustifolia to biodiversity conservation in the threatened Atlantic Forest in Argentina

Deforestation is a global process that has strongly affected the Atlantic Forest in South America, which has been recognised as a threatened biodiversity hotspot. An important proportion of deforested areas were converted to forest plantations. Araucaria angustifolia is a native tree to the Atlantic Forest, which has been largely exploited for wood production and is currently cultivated in commercial plantations. An important question is to what extent such native tree plantations can be managed to reduce biodiversity loss in a highly diverse and vulnerable forest region . We evaluated the effect of stand age, stand basal area, as a measure of stand density, and time since last logging on the density and richness of native tree regeneration in planted araucaria stands that were successively logged over 60 years, as well as the differences between successional groups in the response of plant density to stand variables. We also compared native tree species richness in planted araucaria stands to neighbouring native forest. Species richness was 71 in the planted stands (27 ha sampled) and 82 in native forest (18 ha sampled) which approximate the range of variation in species richness found in the native forests of the study area. The total abundance and species richness of native trees increased with stand age and time since last logging, but ecological groups differed in their response to such variables. Early secondary trees increased in abundance with stand age 3–8 times faster than climax or late secondary trees. Thus, the change in species composition is expected to continue for a long term. The difference in species richness between native forest and planted stands might be mainly explained by the difference in plant density. Therefore, species richness in plantations can contribute to local native tree diversity if practices that increase native tree density are implemented.     

Density effects and self-thinning in even-aged pure stands ofEucalyptus camaldulensis Dehn

The competition density effect and changes of mean total tree weight (w) and stand density (ρ) during course of self-thinning were examined in even-aged pure stands ofEucalyptus camaldulensis Dehn. which were planted in the tropical monsoon region. The level of competition was controlled by changing the initial stand density from 625 trees ha⁻¹ to 40,000 trees ha⁻¹. Hozumi's model was used to describe thew-ρ trajectory with aging of each stand and thew-ρ relation between stands of different densities at each time. The higher density produced trees of smaller mean tree sizes. The higher the density, the sooner self-thinning began. The growth curve ofE. camaldulensis followed the logistic growth curve where both maximum size and intrinsic growth rate change with time. Mean intrinsic growth rate was maximized at initiation of growth after lag time and then gradually decreased as time progressed. Hozumi's model was considered to be the best model with wide applicability for describing and comparing the growth characteristics during the course of self-thinning among different species, especially in tropical forest plantations, in which many diverse species were used for reforestation.     

Tree population changes in a tropical dry evergreen forest of south India over a decade (1992–2002)

Changes in species composition and density of trees >10 cm gbh in a tropical dry evergreen forest in Puthupet, south India are interpreted for the period between 1992 and 2002. A 1-ha plot was inventoried in 1992 and was recensused in 2002. During the 10-year interval tree taxa diversity as well as stand density increased, but the basal area value decreased. Tree species richness increased by 21% (from 24 to 29 species) by an addition of eight species and local extinction of three species. The tree density increased just by eight individuals (from 1330 stems ha⁻¹ in 1992 to 1338 ha⁻¹ in 2002), but the basal area decreased by 8% (from 37.5 to 34.5 m² ha⁻¹). Many species (11 numbers) have increased in abundance rather than decreased. Many surviving species seem to have considerable stability in abundance at the local scale. The density of smaller stems (10 29 cm gbh) increased by 15.3%, while that of the larger trees decreased drastically (81.6%). Ninety percent of the missing stems were from the middlestorey of the forest. Tree density changes among the three ecological guilds revealed a decrease in stem density and an increase in basal area in the lowerstorey; while the middlestorey exhibited a reverse trend. Family-wise, tree density changes revealed that the majority of families (67%) showed an increase in stem density. Long-term studies on tree population changes are essential to estimate tree mortality and recruitment rates, which will provide a greater insight in tropical forest dynamics.     

Litterfall dynamics in carbonate and deltaic mangrove ecosystems in the Gulf of Mexico

From 1996 to 2002, we measured litterfall, standing litter crop, and litter turnover rates in scrub, basin, fringe and riverine forests in two contrasting mangrove ecosystems: a carbonate-dominated system in the Southeastern Everglades and a terrigenous-dominated system in Laguna de Terminos (LT), Mexico. We hypothesized that litter dynamics is driven by latitude, geomorphology, hydrology, soil fertility and soil salinity stress. There were significant temporal patterns in LT with litterfall rates higher during the rainy season (2.4 g m⁻² day⁻¹) than during the dry season (1.8 g m⁻² day⁻¹). Total annual litterfall was significantly higher in the riverine forest (12.8 Mg ha⁻² year⁻¹) than in the fringe and basin forests (9.7 and 5.2 Mg ha⁻² year⁻¹, respectively). In Southeastern Everglades, total annual litterfall was also significantly higher during the rainy season than during the dry season. Spatially, the scrub forest had the lowest annual litterfall (2.5 Mg ha⁻² year⁻¹), while the fringe and basin had the highest (9.1 and 6.5 Mg ha⁻² year⁻¹, respectively). In LT, annual standing litter crop was 3.3 Mg ha⁻¹ in the fringe and 2.2 Mg ha⁻¹ in the basin. Litter turnover rates were significantly higher in the fringe mangrove forest (4.1 year⁻¹) relative to the basin forests (2.2 year⁻¹). At Southeastern Everglades there were significant differences in annual standing litter crop: 1.9, 3.3 and 4.5 Mg ha⁻¹ at scrub, basin and fringe mangrove sites, respectively. Furthermore, turnover rates were similar at both basin and fringe mangrove types (2.1 and 2.0 year⁻¹, respectively) but significantly higher than scrub mangrove forest (1.3 year⁻¹). These findings suggest that litter export is important in regulating litter turnover rates in frequently flooded riverine and fringe forests, while in infrequently flooded basin forests, in situ litter decomposition controls litter turnover rates.     

Stand density and species richness affect carbon storage and net primary productivity in early and late successional temperate forests differently

How stand density and species richness affect carbon (C) storage and net primary productivity (NPP) changes with forest succession is poorly understood. We quantified the C storage of trees and the aboveground NPP in an early successional secondary birch forest (birch forest) and a late successional mixed broadleaf-Korean pine (Pinus koraiensis) forest (mixed forest) in northeastern China. We found that: 1) tree C storage in the mixed forest (120.3 Mg C ha^?1) was significantly higher than that in the birch forest (78.5 Mg C ha^?1), whereas the aboveground NPP was not different between the two forest types; and 2) only stand density had a positive linear relationship with tree C storage and aboveground NPP in the birch forest. In the mixed forest, both tree C storage and aboveground NPP were significantly affected by the combination of the stand density and species richness. The tree C storage to stand density and species richness relationships were hump-shaped. The aboveground NPP increased with increasing stand density, but its relationship to species richness was hump-shaped. We conclude that the effect of stand density and species richness on tree C storage and aboveground NPP was influenced by forest stand succession, and such effects should be considered in studying stand density- and species richness- ecosystem function (e.g., C storage and NPP) relationships in temperate forest ecosystems.