Old-growth Temperate Forest Research Articles

Coarse woody debris facilitates oak recruitment in Białowieża Primeval Forest, Poland

While oaks contribute to the ecology and economy of temperate lowland forests, recruitment into larger size classes is generally scarce. Ungulate herbivory is a limiting factor for tree recruitment, thus natural structures protecting against ungulates may be important for recruitment success. We studied oak recruitment in relation to coarse woody debris (CWD) in the Białowieża National Park, Poland, one of the last remaining reference sites for undisturbed temperate lowland forests in Europe that contains the full natural assemblage of large ungulate species and their predators. We compared two contrasting management types: one that excludes all forestry activities (the strict reserve) and one where sanitary cutting and removal of bark-beetle infested Picea abies occurs to prevent further spread.We sampled 4m wide transects (19ha in total, of which 15.8ha in the strict reserve) and recorded sapling height and sapling browsing, distance from, height of and CWD encirclement, distance to and diameter of mature oaks, tree composition, distance to and diameter of nearest trees, canopy openness and cover of herbs, mosses, bare soil and litter in an equal number of plots with and without saplings. We found 161 oak saplings (8.5/ha). CWD was predominantly formed by P. abies. Sapling plots contained more often CWD than plots without saplings. Also, the distance to CWD was smaller and the CWD encirclement was higher in sapling plots, while canopy cover did not differ. Sapling height increased and sapling browsing decreased with increasing presence of CWD. Both CWD and recruitment beyond 50cm were reduced in the managed zone.Our study shows that CWD plays an essential role for the recruitment of oaks in old-growth temperate forest systems, predominantly via protection against ungulate browsing. Sanitary cutting of infested trees, a common management practice in temperate forests, prevents the natural accumulation of CWD and so can be counter-productive for the recruitment of appreciated species.

Evolution of atmospheric carbon dioxide concentration at different temporal scales recorded in a tall forest

Understanding the temporal evolution of CO2 over specific ecosystems can provide additional insight into atmospheric CO2 variability. From 2003 to 2010, CO2 ambient concentrations in an old-growth temperate forest were measured continuously by using an infrared analyzer. The results show that daily cycle and seasonal variation of CO2 were mostly dominated by vegetation activity, whereas the weak turbulent mixing at night contributed frequently to CO2 build-up below the canopy. As a result, CO2 concentrations changed considerably during daytime and nighttime in the forest stand. The monthly means exhibited a seasonal variation characterized by a primary peak in December and a minimum during July to August, with an average seasonal amplitude (the difference of minimum and maximum monthly means) of 60.5 ppmv. By fitting a harmonic model to the monthly means, linear increase trends of 1.7 ppmv yr−1 in the annual mean CO2 concentrations and 0.58 ppmv yr−1 in the amplitude of the seasonal cycle were estimated. The upward trend of annual mean CO2 concentration may be attributed to the dramatic global increase in CO2 emissions during the study period. This study also found that the stratification of CO2 concentrations below the canopy during nighttime was easily disrupted after sunrise, which suggests that forest floor plants are not, as previous assumed, exposed to significantly greater CO2 concentrations than the normal atmospheric concentrations.

Effects of local biotic neighbors and habitat heterogeneity on tree and shrub seedling survival in an old-growth temperate forest

Seedling dynamics play a crucial role in determining species distributions and coexistence. Exploring causes of variation in seedling dynamics can therefore provide key insights into the factors affecting these phenomena. We examined the relative importance of biotic neighborhood processes and habitat heterogeneity using survival data for 5,827 seedlings in 39 tree and shrub species over 2 years from an old-growth temperate forest in northeastern China. We found significant negative density-dependence effects on survival of tree seedlings, and limited effects of habitat heterogeneity (edaphic and topographic variables) on survival of shrub seedlings. The importance of negative density dependence on young tree seedling survival was replaced by habitat in tree seedlings ≥ 4 years old. As expected, negative density dependence was more apparent in gravity-dispersed species compared to wind-dispersed and animal-dispersed species. Moreover, we found that a community compensatory trend existed for trees. Therefore, although negative density dependence was not as pervasive as in other forest communities, it is an important mechanism for the maintenance of community diversity in this temperate forest. We conclude that both negative density dependence and habitat heterogeneity drive seedling survival, but their relative importance varies with seedling age classes and species traits.

Functional–structural water flow model reveals differences between diffuse- and ring-porous tree species

A functional–structural (FS) model of tree water flow is applied for single trees in an old-growth temperate broad-leaved forest stand. Roots, stems and branches are represented by connected porous cylinder elements that are divided into the inner heartwood cylinders surrounded by xylem and phloem. Xylem water flow is simulated by applying a non-linear Darcy water flow in porous media driven by the water potential gradient according to the cohesion–tension theory. The flow model is based on physiological input parameters such as the hydraulic conductivity, stomatal response to leaf water potential and root water uptake capability and, thus, can reflect the different properties of the two diffuse-porous tree species Fagus sylvatica and Tilia cordata and the ring-porous species Fraxinus excelsior. The structure of the canopy is obtained by applying an automatic tree skeleton extraction algorithm from point clouds obtained by terrestrial laser scans allowing an explicit representation of the water flow path in the stem and branches.Supported by measurements of stem sap flow, the model reveals differences of the simulated stomatal closure due to low branch xylem water contents between the tree species. The diffuse-porous species reduced the transpiration by the stomatal closure only at hot days with a high potential transpiration. For the ring-porous ash the simulated reduction is much higher with a mean value of all trees over the observation period of 0.72. The model gives insights to the mechanism that lead to the stomatal closure and can spot the axial xylem hydraulic conductance along the flow pathway as the limiting factor of leaf water supply at days with moist soil water conditions.

Local-Scale Drivers of Tree Survival in a Temperate Forest

Tree survival plays a central role in forest ecosystems. Although many factors such as tree size, abiotic and biotic neighborhoods have been proposed as being important in explaining patterns of tree survival, their contributions are still subject to debate. We used generalized linear mixed models to examine the relative importance of tree size, local abiotic conditions and the density and identity of neighbors on tree survival in an old-growth temperate forest in northeastern China at three levels (community, guild and species). Tree size and both abiotic and biotic neighborhood variables influenced tree survival under current forest conditions, but their relative importance varied dramatically within and among the community, guild and species levels. Of the variables tested, tree size was typically the most important predictor of tree survival, followed by biotic and then abiotic variables. The effect of tree size on survival varied from strongly positive for small trees (1–20 cm dbh) and medium trees (20–40 cm dbh), to slightly negative for large trees (>40 cm dbh). Among the biotic factors, we found strong evidence for negative density and frequency dependence in this temperate forest, as indicated by negative effects of both total basal area of neighbors and the frequency of conspecific neighbors. Among the abiotic factors tested, soil nutrients tended to be more important in affecting tree survival than topographic variables. Abiotic factors generally influenced survival for species with relatively high abundance, for individuals in smaller size classes and for shade-tolerant species. Our study demonstrates that the relative importance of variables driving patterns of tree survival differs greatly among size classes, species guilds and abundance classes in temperate forest, which can further understanding of forest dynamics and offer important insights into forest management.

Mass dynamics of coarse woody debris in an old-growth deciduous forest of Gwangneung, Korea

We investigated the mass dynamics of coarse woody debris (CWD) in an old-growth deciduous forest dominated by Quercus serrata, Carpinus laxiflora, and C. cordata in a 1 ha permanent plot of the Gwangneung Experiment Forest, Korea, from 2002 through 2010. CWD mass varied from 16.8 to 34.2 Mg ha−1, and the ratio of CWD mass to stand biomass varied from 0.06 to 0.13. The mean CWD mass input and loss rates were 4.81 Mg ha−1 yr−1 and 2.28 Mg ha−1 yr−1, respectively. A large heterogeneity of CWD mass, as represented by the spatial coefficient of variation (127.2%) and annual coefficient of variation (178.5%), might be inherent in the old-growth temperate forest, which consisted of large biomass trees. The decay rate constant, as estimated from the wood density change, was 0.049yr−1. However, the large variation of annual CWD mass input could cause the overestimation of decay rate constant (0.167 yr−1) as calculated from the ratio of CWD mass input to CWD mass. According to the CWD decay class classification, class II (72.8%) comprised the majority of CWD mass. The proportion of CWD mass to total CWD mass was 57.5% for Q. serrata, 25.0% for C. laxiflora, and 10.4% for C. cordata, respectively, and corresponded to the proportion of stem biomass to total stem biomass. These data support the stability of the current status in this old-growth deciduous forest as representing the climax stage. Due to the relatively short-term measurement of CWD mass compared with the whole life span of CWD, additional long-term studies with various approaches are required to enhance the knowledge of CWD mass dynamics in this forest.

Mapping soil CO 2 efflux in an old-growth forest using regression kriging with estimated fine root biomass as ancillary data

Efflux of carbon dioxide (CO 2) from the soil to the atmosphere is one of the most important pathways of carbon in forests. However, its accurate determination is difficult because of the multiplicity of sources and considerable spatial and temporal variability. Although the contribution of root and rhizosphere respiration varies between 10% and 90% of soil CO 2 efflux (depending on vegetation and season), it is usually at the higher end of that range in temperate forests. The relationship between estimated fine root biomass (FRB) and soil CO 2 efflux was investigated within an old-growth temperate deciduous forest in the Hainich National Park in central Germany. A heuristic model for estimating FRB, originally developed for Norway spruce was adapted and modified to predict relative FRB for two broad-leaved tree species ( Fagus sylvatica L. and Fraxinus excelsior L.). The model is based on easily assessable aboveground parameters of stand structure, such as tree species, diameter at breast height (dbh), and tree location. It relies on the assumption that FRB decreases with a decrease in tree diameter; this decrease is species-specific. Location and dbh were recorded for 3478 trees, and soil CO 2 efflux, moisture, and temperature were measured biweekly from August 2005 until June 2007 at 76 randomly distributed measurement locations within an area of 6 ha. The adapted FRB prediction model was parameterized for each tree species using data from 24 soil cores derived in the same forest close to the study site. Since highly significant model fits between predicted and measured FRBs were observed for beech ( R 2 = 0.90) and ash ( R 2 = 0.78), the parameterization of the model was considered successful. However, this did not allow the prediction of annual or seasonal soil CO 2 efflux rates using regression kriging with the map of modeled total FRB as ancillary data. Significant model fits could only be established when the estimated FRB of ash-dominated locations was used as ancillary data in regression kriging to predict monthly averages of hourly soil CO 2 efflux rates for June, August, and September 2006. Considering the often found low spatial variation in total FRB, species-specific estimates of FRB may offer the opportunity to address seasonal and spatial variations in the contribution of root and rhizosphere respiration to soil CO 2 efflux. The extrapolation of pointwise soil CO 2 efflux measurements by regression kriging using maps of modeled FRB as ancillary data may be an interesting approach if it is possible to include further ancillary data on abiotic variables such as soil carbon and soil moisture.

Importance of root derived carbon for soil organic matter storage in a temperate old-growth beech forest – Evidence from C, N and 14C content

High carbon uptake of old-growth forests contradict the assumption that old-growth forests are carbon neutral and suggest their Kyoto relevance. As tree biomass is unlikely to store additional carbon in the long term we investigated carbon and nitrogen stock changes in the soil. Therefore we performed paired soil sampling in the years 2000 and 2004 at the National Park Hainich, Germany. In the upper 0–20 cm soil layer 498 g SOC m −2 was lost in 4 years, but interestingly in 20–60 cm soil depth 1155 g m −2 of SOC was stored, resulting in an accumulation rate of 164 g m −2 per year. In the same time nitrogen was accumulated at a rate of 32 g N m −2 per year. While in 0–20 cm preferential carbon was respired, in the deeper soil layers organic matter with a C/N ratio of microbial organisms was gained. Most interestingly 14C measurements indicate that gained and lost carbon is of recent carbon age. Our findings suggest that soil organic matter even in deeper soil horizons is very dynamic and that possibly root driven carbon input can significantly change soil organic matter stocks in all depth segments simultaneously. In consequence old growth forests still have a high soil organic matter storage potential as their roots sustain a long-lived permanent storage structure.

Regional and local patterns of ectomycorrhizal fungal diversity and community structure along an altitudinal gradient in the Hyrcanian forests of northern Iran

• Altitudinal gradients strongly affect the diversity of plants and animals, yet little is known about the altitudinal effects on the distribution of microorganisms, including ectomycorrhizal fungi. • By combining morphological and molecular identification methods, we addressed the relative effects of altitude, temperature, precipitation, host community and soil nutrient concentrations on species richness and community composition of ectomycorrhizal fungi in one of the last remaining temperate old-growth forests in Eurasia. • Molecular analyses revealed 367 species of ectomycorrhizal fungi along three altitudinal transects. Species richness declined monotonically with increasing altitude. Host species and altitude were the main drivers of the ectomycorrhizal fungal community composition at both the local and regional scales. The mean annual temperature and precipitation were strongly correlated with altitude and accounted for the observed patterns of richness and community. • The decline of ectomycorrhizal fungal richness with increasing altitude is consistent with the general altitudinal richness patterns of macroorganisms. Low environmental energy reduces the competitive ability of rare species and thus has a negative effect on the richness of ectomycorrhizal fungi. Because of multicollinearity with altitude, the direct effects of climatic variables and their seasonality warrant further investigation at the regional and continental scales.

Synergistic effects of nitrogen amendments and ethylene on atmospheric methane uptake under a temperate old-growth forest

An increase in atmospheric nitrogen (N) deposition can promote soil acidification, which may increase the release of ethylene (C2H4) under forest floors. Unfortunately, knowledge of whether increasing N deposition and C2H4 releases have synergistic effects on soil methane (CH4) uptake is limited and certainly deserves to be examined. We conducted some field measurements and laboratory experiments to examine this issue. The addition of (NH4)2SO4 or NH4Cl at a rate of 45 kg N ha−1 yr−1 reduced the soil CH4 uptake under a temperate old-growth forest in northeast China, and there were synergistic effects of N amendments in the presence of C2H4 concentrations equal to atmospheric CH4 concentration on the soil CH4 uptake, particularly in the NH4Cl-treated plots. Effective concentrations of added C2H4 on the soil CH4 uptake were smaller in NH4+-treated plots than in KNO3-treated plots. The concentration of ca 0.3 µl C2H4 L−1 in the headspace gases reduced by 20% soil atmospheric CH4 uptake in the NH4Cl-treated plots, and this concentration was easily produced in temperate forest topsoils under short-term anoxic conditions. Together with short-term stimulating effects of N amendments and soil acidification on C2H4 production from forest soils, our observations suggest that knowledge of synergistic effects of NH4+, rather than NO3−, amendments and C2H4 on the in situ soil CH4 uptake is critical for understanding the role of atmospheric N deposition and cycling of C2H4 under forest floors in reducing global atmospheric CH4 uptake by forests. Synergistic functions of NH4+-N deposition and C2H4 release due to soil acidification in reducing atmospheric CH4 uptake by forests are discussed.

Comparison of conventional eight-point crown projections with LIDAR-based virtual crown projections in a temperate old-growth forest

Sight-based field measurements of tree crown projection area and canopy height are common praxis in forest science but difficult to validate. We quantified their measurement errors based on the virtual representation of an 11-species old-growth forest provided by high-resolution terrestrial LIDAR (light detection and ranging) measurements. Based on the expectations (a) that violations of the triangulation theory are the main error source of height measurements, and (b) that approximations of tree crowns with fixed angles are not flexible enough for irregular crown shapes in natural stands, we investigated the relative accuracies of triangulation measurements of height of crown base (B T) vs. tree height (H T) and of different crown projection methods. B T (±0.52 m) showed lower measurement errors than H T (±2.4 m). Larger deviations between field-measured and virtually executed crown projections could partly be attributed to structural differences of the crowns that were two-dimensionally quantified as space capture index (SCI). The largest deviations between both methods occurred on suppressed tree crowns and tall Quercus robur trees in the stand. Because of the method-inherent underestimation of crown projections with fixed angular grid, we propose the use of flexible angles by trained operators.

Habitat associations of saplings and adults in an old-growth temperate forest in the Changbai mountains, northeastern China

Species-habitat association analysis is useful to detect spatial arrangement of individual plants, to discover rules about the distribution of species and to generate hypotheses about the possible underlying process controlling observed structures. Quantifying methods were used to classify habitats in terms of topographical variables in a mixed temperate broad-leaved Korean pine forest of the Changbai mountains in northeastern China. All of the 625 20 m × 20 m quadrats of the plot could be unambiguously assigned to one of three habitat categories (low-plateau, high-plateau and slope). Torus-translation tests were used to estimate species-habitat associations. Many species are clearly distributed in a biased fashion with respect to habitats. Fifteen (55.6%) out of 27 species showed strong positive or negative association with specific habitats. We compared species-habitat associations at the sapling and adult stages. Adjusted density values indicated few species exhibit extremely strong habitat associations. Only 9 out of 26 species had adjusted densities > 3 in the habitat for which they had strong positive affinity. Few species show the same associations at the small tree and large tree stages. Only 3 out of 22 occurring associations with a specific habitat appeared to have a consistent habitat association at the two stages. These results suggest that species-habitat associations exist in the 25-ha plot of the temperate forest of the Changbai mountains. Owing to limitations in our statistical methodology, we partly underestimated associations by ignoring rare species. Regeneration niches can contribute to co-existence, but regeneration niches due to habitat associations play a limited role in species co-existence, since most species show a similar trend in habitat associations at the sapling and adult stages. We should pay more attention to shifts in habitat associations, i.e. niche shifts at different stages of existence.

Complementary Models of Tree Species–Soil Relationships in Old-Growth Temperate Forests

Ecosystem-level studies identify plant–soil feedbacks as important controls on soil nutrient availability, particularly for nitrogen and phosphorus. Although site- and species-specific studies of tree species–soil relationships are relatively common, comparatively fewer studies consider multiple co-existing species in old-growth forests across a range of sites that vary in underlying soil fertility. We characterized patterns in forest floor and mineral soil nutrients associated with four common tree species across eight undisturbed old-growth forests in Oregon, USA, and used two complementary conceptual models to assess tree species–soil relationships. Plant–soil feedbacks that could reinforce site-level differences in nutrient availability were assessed using the context-dependent relationships model, whereby relative species-based differences in each soil nutrient diverged or converged as nutrient status changed across sites. Tree species–soil relationships that did not reflect strong feedbacks were evaluated using a site-independent relationships model, whereby forest floor and surface mineral soil nutrient pools differed consistently by tree species across sites, without variation in deeper mineral soils. We found that the organically cycled elements carbon, nitrogen, and phosphorus exhibited context-dependent differences among species in both forest floor and mineral soil, and most often followed a divergence model, whereby species differences were greatest at high-nutrient sites. These patterns are consistent with theory emphasizing biotic control of these elements through plant–soil feedback mechanisms. Site-independent species differences were strongest for pools of the weatherable cations calcium, magnesium, potassium, as well as phosphorus, in mineral soils. Site-independent species differences in forest floor nutrients were attributable to one species that displayed significantly greater forest floor mass accumulation. Our findings confirm that site-independent and context-dependent tree species-soil relationships occur simultaneously in old-growth temperate forests, with context-dependent relationships strongest for organically cycled elements, and site-independent relationships strongest for weatherable elements with inorganic cycling phases. These models provide complementary explanations for patterns of nutrient accumulation and cycling in mixed-species old-growth temperate forests.

Wood distribution along streams draining old-growth floodplain forests in Congaree National Park, South Carolina, USA

We measured wood volume and other characteristics along a series of instream and floodplain transects in and around Congaree National Park, South Carolina. Seven transects were surveyed at most sites; one within the bankfull channel, and three on each bank, at 10, 50, and 100 m lateral distances, respectively, from the channel. Along each transect we measured piece dimensions, location along transect, orientation, and decay category. We also characterized channel width, drainage area, vegetation type, average forest basal area, and inundation category for each transect. Forest transects > 100 m from a channel were also surveyed. Instream wood loads for unmanaged channels draining old-growth forests were 102–178 m 3/ha, which is lower than most instream wood loads documented for old-growth temperate forests. We attribute the lower wood loads to the combined effects of high transport capacity and rapid decay. Floodplain wood loads are lowest close to the channel but increase with distance, reaching comparable values (up to 172 m 3/ha) at distances > 100 m from a channel. Channel geometry does not appear to exert the significant influence on instream wood loads that has been documented for more laterally constrained channels. Channel-spanning jams are uncommon and appear to be transient features.

The tree mortality regime in temperate old-growth coniferous forests: the role of physical damage

Aspects of the tree mortality regime were characterized for old-growth conifer forests in Mount Rainier National Park, Washington, USA, using individual tree (stems ≥5 cm diameter at breast height (dbh)) records from a network of permanent forest research plots. Average annual forest-wide mortality rates of trees ≥15 cm dbh never exceeded 1% on a stem-density or basal-area basis; mortality was slightly higher for stems <15 cm dbh. Physical agents of mortality (uprooting, stem breakage, and crushing by falling debris) accounted for approximately 40% and 45% of mortality events in trees <15 and ≥15 cm dbh, respectively. These physical processes were chronic sources of mortality: they were not associated with a single or few disturbance events. Preexisting decay fungi were associated with trees that died proximately due to stem breakage (41%) and uprooting (22%), consistent with a predisposing role of decay fungi in trees that die due to mechanical damage. Given the importance of physical processes in the tree mortality regime, we suggest that a richer mechanistic understanding of the causes and consequences of tree mortality in natural forests will be achieved with models that consider the physical, as well as the physiological, attributes of trees and forests.

Respiration of downed logs in an old-growth temperate forest in north-eastern China

Carbon dioxide (CO2) flux from coarse woody debris is an important source of carbon emission in forests with large amounts of coarse woody debris (CWD). Respiration from downed logs of Korean pine (Pinus koraiensis Sieb. et Zucc.) and Amur linden (Tilia amurensis Rupr.) and their response to meteorological factors were investigated using the closed static chamber–gas chromatography technique in an old-growth temperate forest in Changbai Mountain region, north-eastern China. On a yearly timescale, daily respiration rates (R log) varied over two orders of magnitude (8.7–252.3 mg Ckg−1), and were significantly correlated with wood water content and temperature (p<0.05). The temperature-dependent empirical exponential models for each decay class explained more than 67% of the observed variations in R log. More decayed wood had a greater water content and pore space than less decayed wood, and these differences were probably responsible for the observed difference in respiration rate among decay classes. The annual carbon loss rate due to respiration was estimated to be 28.0±3.7 g Cm−2, which contributed only about 3% of total carbon loss from forest floor, but net carbon flux from downed logs accounted for up to 15% of net ecosystem exchange in this old temperate forest. Downed logs represent a small, but substantial carbon flux that is expected to increase over the next several decades in old-growth forest.

Wood retention and transport in tropical, headwater streams, La Selva Biological Station, Costa Rica

Wood in tropical streams has the potential to be more mobile than wood in otherwise similar temperate streams because of the warm and humid conditions that promote decay and the more frequent and flashier floods of the tropics. To test this hypothesis, we monitored all large wood pieces for 2.3 years in 10 50-m-long reaches of old-growth headwater streams in La Selva Biological Station, Costa Rica. Annual wood retention rates for pieces ranged from 0.55 to 0.91 among the sites, and retention rates by volume ranged from 0.67 to 0.99. Assuming steady state wood load, which is reasonable for La Selva, these rates are equivalent to mean residence times of 2.2–10.6 years for pieces, and 3.0–83.2 years for a volume of wood. Calculating mean residence time from the weighted average of retention rates gives an average residence time of 4.9 years for a piece of wood and 6.9 years for a volume of wood. These values are less than those reported for old-growth temperate forests, supporting our hypothesis. Mobility of individual pieces was best predicted by piece length relative to stream width ( l r, higher l r led to lower mobility), channel gradient ( s, higher s led to higher mobility), and piece integration into the channel (unattached pieces were 2.6 times more mobile than attached, ramp, or bridge pieces). Temporal variation in retention rates was well explained by variation in peak flow. All four of these factors have also been observed to influence mobility in the temperate zone. The higher mobility of wood in our study site relative to the temperate rainforest of the Pacific Northwest may be explained by the flashy and frequent floods, the high decay rate, or the branching morphology of the native trees; but differentiating the role of these factors, particularly flow and decay, will be complicated by their covariation across climates.

Age and growth of a fire prone Tasmanian temperate old-growth forest stand dominated by Eucalyptus regnans, the world's tallest angiosperm

Forests are key components of the global carbon cycle, with deforestation being an important driver of increased atmospheric carbon dioxide. Temperate old-growth forests have some of the highest above ground stores of carbon of any forest types on Earth. Unlike tropical forests, the ecology of many temperate forests is dominated by episodic disturbance, such as high intensity fire. An exemplar of a particularly carbon dense temperate forest system adapted to infrequent catastrophic fires is the Eucalyptus regnans forests of south eastern Australia. Knowledge of the growth and longevity of old-growth trees is crucial to understanding the carbon balance and fire regimes of these forest systems. In an old-growth E. regnans stand in the Styx Valley in southern Tasmania we used dendrochronological techniques and radiocarbon dating to determine the age and stem growth of E. regnans and Phyllocladus aspleniifolius, an understorey rainforest conifer. Our analysis revealed that an even-aged cohort of E. regnans and P. aspleniifolius established in 1490–1510AD, apparently after a stand-replacing fire. The stem growth rates of E. regnans in the first 100 years were very rapid compared to the co-occurring P. aspleniifolius. That the longevity of E. regnans is >500 years challenges the suggested 350–450 year timeframe proposed for the widely held model of succession from eucalypt to rainforest. These forests not only have the potential to store vast amounts of carbon, but can also maintain these high carbon densities for a long period of time. Estimates of the capacity of these forests to sequester and store carbon should explicitly consider past harvesting and fire regimes and the potential increases in the risk of fire associated with climate change.

Spatial distributions of species in an old-growth temperate forest, northeastern China

Studying spatial distributions of species can provide important insights into processes and mechanisms that maintain species richness. We used the relative neighborhood density Ω based on the average density of conspecific species in circular neighborhoods around each species to quantify spatial distributions of species with ≥10 individuals in a fully mapped 25 ha temperate plot at Changbaishan, northeastern China. Our results show that spatial aggregation is a dominant pattern of species in the Changbaishan temperate forests. However, the percentage of significantly aggregated species decreases with spatial scale, especially for rare species. Rare species are more aggregated than intermediate and common species. The aggregation intensity declines with increasing size class (diameter at breast height), i.e., species become more regularly spaced as species grow, which is consistent with the predictions of self-thinning and Janzen–Connell spacing effects. Species functional traits (canopy layer, seed dispersal ability, shade tolerant, etc) also havea significant effect on the spatial distributions of species. Our results partially conform to the prediction that better dispersal reduces aggregation. Consequently, dispersal limitation, self-thinning, Janzen–Connell spacing effects, and habitat heterogeneity may primarily contribute to spatial distributions of species in the temperate forests.

Effects of abiotic and biotic factors and stochasticity on tree regeneration in a temperate forest community

How deterministic or stochastic is tree regeneration in a temperate forest? To answer this question, we analyzed the relative effects of abiotic and biotic factors on seed and seedling demography of tree species in an old-growth temperate forest, Ogawa Forest Reserve, Japan. The working hypothesis was that seed and seedling demography of trees would be controlled more deterministically in comparison with tropical forests and that the magnitude of deterministic effects of the abiotic and biotic factors would depend on regeneration traits relating to seed dispersal ability. We examined 5 abiotic factors (litter and humus cover, vegetation cover, light level, soil moisture, and relative elevation) and 2 species-specific biotic factors (distance from the nearest conspecific adult and density of conspecific seeds or seedlings) to quantify their contribution to the spatial variation in seedling emergence and survival for 18 principal tree species in the community. The results showed that conspecific seed density had a negative effect on seedling emergence for almost all species, as suggested by the Janzen- Connell model. On the other hand, various factors were detected for seedling survival of each species. We also found that regeneration traits relating to seed dispersal ability were significantly correlated with some of the abiotic factors. However, the 7 factors tested were less important than expected; seed and seedling demography appeared to be determined rather stochastically in this stable forest community. Even in a temperate forest, seed and seedling demography appeared to be rather stochastic, and niche partitioning among species during these stages was of limited importance.