Use of artificial seedlings to estimate damage of forest seedlings due to litterfall and animals

Abstract. The artificial seedling assay method has been used in several tropical and temperate forests to estimate seedling damage and subsequent mortality due to non‐trophic micro‐disturbances such as litterfall and trampling. However, there has been no evidence presented to support the assumption that artificial seedling damage correlates with natural seedling mortality. In this study we evaluated the use of artificial seedlings in five New Zealand forests by comparing damage rates of artificial seedlings with damage and mortality rates of an equal number of selected natural seedlings. A total of 1200 artificial, and 1200 natural seedlings were monitored monthly for two years. Litterfall damage rates of natural seedlings were correlated with those of artificial seedlings. However, there was no relationship found between artificial and natural seedling damage due to animals, or between artificial seedling damage and natural seedling mortality for either cause. Artificial seedlings should not therefore be used to estimate seedling mortality due to non‐trophic microdisturbance. Monitoring natural seedlings enabled non‐trophic animal damage to be readily detected and provided additional information on animal‐plant interactions. The value of using artificial seedlings is that they provide a measure of the litterfall disturbance potential that is independent of the patchy distribution of natural seedlings within safe sites, and independent of species specific resistance to damage. They therefore provide an indication of the selective pressure on seedlings due to litterfall and are useful for comparing the relative ‘safety’ of different forests and microsites. Monitoring natural seedlings provides a measure of the damage and mortality due to litterfall for a specific seedling size class. Concurrently monitoring artificial and natural seedlings for litterfall disturbance provides more information than the same effort expended on either method alone.     

The influence of macro‐litterfall and forest structure on litterfall damage to seedlings

Abstract Microdisturbance to seedlings is important because it can differentially affect the mortality and recruitment of seedlings of forest tree species and thereby ultimately affect community composition. Microdisturbance due to litterfall has been shown to vary greatly in its influence on seedling survival among and within forests, and yet there have been no previous studies that investigate the cause of these differences. In this study the influence of macro‐litterfall on seedling damage is investigated in five complex temperate forests in New Zealand. Litterfall damage to artificial seedlings in these forests was strongly correlated with macro‐leaf‐fall (leaves > 30 cm × 1.5 cm) dry weight and total macro‐litterfall (leaves and deadwood > 30 cm × 1.5 cm) surface area (R² = 0.99, P < 0.005 for each). Protective vegetation within 2 m of the ground (mostly lianes and woody shrubs) reduced the risk of litterfall damage by up to 84%. Hitherto unexplained differences in litterfall damage to seedlings found among, and within, forests (tropical and temperate) may therefore be due to differences in rates of macro‐leaf‐fall and forest structure. These results are important because they suggest that subtle differences in forest structure, and species composition, may influence regeneration patterns through the litterfall microdisturbance regime.     

Susceptibility of Tree Seedlings to Biotic and Abiotic Hazards in the Understory of a Moist Tropical Forest in Panama

We evaluated temporal patterns of seedling survival of eight Neotropical tree species generated under multiple abiotic and biotic hazards (vertebrates, disease, litterfall) in the forest understory on Barro Colorado Island, Panama. Seedlings were transplanted at first leaf expansion in low densities along a 6-km transect and damage and mortality were recorded for 1 yr. We also planted and monitored small and large artificial seedlings to estimate physical disturbance regimes. During 0–2 mo after transplant, vertebrate consumers of reserve cotyledons caused high mortality of real seedlings, but little damage to artificial seedlings. On real seedlings after 2 mo, disease became an important agent of mortality, despite a decrease in overall mortality rates. Damage by litterfall remained relatively low during the 1-yr study period. Survival ranks among species showed ontogenetic shifts over time, as species changed susceptibility to the mortality agents. Survival after 2 mo was positively correlated with stem toughness, not because species with tough stems were less likely to receive mechanical damage, but because they survived better after receiving mechanical damage. Within each transplant station, artificial seedlings were not good predictors of litterfall damage experienced by real seedlings. Forest-wide litterfall damage level, however, was similar for both real and artificial seedlings ( ca 10%/yr), a moderate level compared to other tropical forests. In conclusion, species traits including biomechanical traits interact to create complex temporal patterns of first year seedling survival, resulting in ontogenetic shifts that largely reflect changes in the relative importance of vertebrate consumers relative to other hazards.     

Microsite heterogeneity in litterfall risk to seedlings

Abstract Litterfall is an important cause of damage and mortality to seedlings in many forest ecosystems. This study is the first to investigate the contribution of variable risk of litterfall damage to microsite heterogeneity. Two hundred artificial seedlings were ‘planted’ in the ground at 2‐m intervals along transects in each of two New Zealand forests, and all plant species with foliage directly above each artificial seedling were recorded. Additional artificial seedlings were planted on the ground underneath treeferns and on their trunks (epiphytically). The artificial seedlings were monitored monthly for damage over 2 years. Three overtopping species that cause litterfall damage, along with one species that impedes litterfall, produced different microsites with a hierarchy of litterfall damage risk to seedlings (2–30% per year). This risk differed significantly among microsites (P < 0.0005). Seedlings differ in resilience to litterfall and, therefore, microsites with different litterfall risks provided the potential for regeneration niche differentiation. More seedlings were damaged beneath Cyathea dealbata (Cyatheaceae), which drops whole fronds, than on its trunks. The reverse was found for Dicksonia fibrosa (Dicksoniaceae), which retains dead fronds as a ‘skirt’. We suggest that shedding whole fronds, or producing a skirt of fronds, are alternative ‘strategies’ that can reduce competition from terrestrial and epiphytic seedlings, respectively.     

Seedling mortality and damage due to non‐trophic animal interactions in a northern New Zealand forest

Abstract The importance of non‐trophic animal damage (biting and uprooting without consumption) and mortality of canopy tree seedlings were investigated in a warm temperate forest, in northern New Zealand. Two hundred seedlings 10‐30 cm in height were monitored at 4‐6‐week intervals for 2 years. Non‐trophic animal damage accounted for more seedling mortality in the first year (37.5% of all mortalities) than any other cause. Of the seedlings damaged in non‐trophic animal interactions 73% were bitten off close to the ground and left uneaten and the remainder were uprooted. In the second year all non‐trophic animal damage and mortality ceased following the control of rabbits (Oryctolagus cuniculus), suggesting that rabbits were the major cause of this damage. Total annual mortality rates (6‐8%) were low. However, measured seedling growth rates indicated an average time for seedlings to grow from 10 to 30 cm of 37 years. Therefore, in the absence of rabbit control, mortality due to non‐trophic animal interactions (3% per year) can have an important cumulative effect. Non‐trophic animal damage found in the present study before rabbits were culled (5% per year) was similar to that reported for two tropical forests, but much less than that reported for some other tropical and temperate forests.     

Regional‐Scale Variation in Litter Production and Seasonality in Tropical Dry Forests of Southern Mexico1

Highly seasonal rainfall creates a pulse of litterfall in the southern Yucatan peninsula region, with cascading effects on the timing of essential nutrient fluxes, microbial dynamics, and vegetation growth. I investigated whether forest age or a regional environmental gradient related to rainfall has a greater effect on patterns of litterfall in this increasingly human‐dominated landscape. Litterfall was sampled in 10–13 stands in each of three locations spanning a rainfall gradient of ca 900–1400 mm/yr. Litter was collected monthly from November 1998 through January 2000 in mature forests and in secondary forests aged 2–25 yr. Despite a substantial precipitation gradient, age was the only significant predictor of annual litter mass. Two‐ to five‐yr‐old forests produced significantly less litter than 12–25‐yr‐old secondary forests (4.6 vs. 6.2 Mg/ha/yr), but the difference between older secondary forests and mature forests (9 percent) was not significant. Litter production increased with rainfall, but not significantly so. The pattern of litterfall was similar across locations and age classes, with a peak during late March or early April. However, litterfall seasonality was most pronounced in the old secondary and mature forests. Litterfall was more evenly distributed throughout the year in forests under 10 yr old. Seasonality of litterfall was also less pronounced at the wettest site, with less disparity between peak litterfall and off‐peak months. Seasonality was not related to soil texture. Forest age and rainfall are important drivers of litterfall dynamics; however, both litter mass and degree of seasonality depended more strongly on forest age. Thus, the impact of land‐use change on litter nutrient cycling is as great, if not greater, than the constraint imposed by the major natural environmental factor affecting tropical dry forests.     

Litterfall Dynamics Under Different Tropical Forest Restoration Strategies in Costa Rica

In degraded tropical pastures, active restoration strategies have the potential to facilitate forest regrowth at rates that are faster than natural recovery, enhancing litterfall, and nutrient inputs to the forest floor. We evaluated litterfall and nutrient dynamics under four treatments: plantation (entire area planted), tree islands (planting in six patches of three sizes), control (same age natural regeneration), and young secondary forest (7–9‐yr‐old natural regeneration). Treatments were established in plots of 50 × 50 m at six replicate sites in southern Costa Rica and the annual litterfall production was measured 5 yr after treatment establishment. Planted species included two native timber‐producing hardwoods (Terminalia amazonia and Vochysia guatemalensis) interplanted with two N‐fixing species (Inga edulis and Erythrina poeppigiana). Litter production was highest in secondary forests (7.3 Mg/ha/yr) and plantations (6.3), intermediate in islands (3.5), and lowest in controls (1.4). Secondary forests had higher input of all nutrients except N when compared with the plantation plots. Inga contributed 70 percent of leaffall in the plantations, demonstrating the influence that one species can have on litter quantity and quality. Although tree islands had lower litterfall rates, they were similar to plantations in inputs of Mg, K, P, Zn, and Mn. Tree islands increased litter production and nutrient inputs more quickly than natural regeneration. In addition to being less resource intensive than conventional plantations, this planting design promotes a more rapid increase in litter diversity and more spatial heterogeneity, which can accelerate the rate of nutrient cycling and facilitate forest recovery.     

Nutrient accessions in a mixed conifer–angiosperm forest in northern New Zealand

Nutrient accessions in litterfall are described for a mixed conifer (mostly Agathis australis D.Don (Lindl.), New Zealand kauri) and angiosperm temperate forest in northern New Zealand to determine the relative contributions to nutrient cycling of the conifer and angiosperm components of the forest. Concentrations for many nutrients were significantly lower in conifer litterfall fractions than for equivalent angiosperm fractions. Angiosperm leaves had concentrations of N and P twice those found in conifer leaf fall. Despite a large contribution to litterfall from weight, conifer reproductive parts (mostly cone scales) were very low in nutrients (especially N, P and Ca). Whereas angiosperm litterfall constituted < 45% of total litterfall by weight, nutrient accessions from the angiosperm component accounted for 45–60% of total nutrient accessions and the conifer fraction for only 30–45%, almost the exact reverse of their contributions to litterfall by weight. Of the macronutrients, P (3 kg ha^–1 year^–1) showed the lowest rate of accession in litterfall while Ca (84 kg ha^–1 year^–1) showed the highest. Faunal detritus, although < 1% of total litterfall by weight, contributed 10% of total P and 4% of total N reaching the forest floor via the litterfall pathway each year. The C:N and C:P ratios in litterfall and litterstore were all well above the levels at which mineralization is likely to occur. Based on the estimated residence times, long‐term immobilization was more likely for N than for P. The annual pattern of nutrient accessions differed for the two components, with angiosperm accessions highest in spring and summer, and conifer accessions highest in autumn, due largely to a peak in litterfall of reproductive parts at that time of year. It is argued that differences in litter quality, decomposition rates and spatial and temporal patterns of litterfall for angiosperm versus conifer components of the forest, in conjunction with long‐term disturbance regimes, may contribute to conifer–angiosperm coexistence.     

Dynamics of composition and structure in an old Sequoia sempervirens forest

Abstract. Dynamics of a Sequoia sempervirens forest in northern California were studied with long‐term plot data (1.44 ha) and recent transect data. The study was conducted in an old stand (> 1100 yr) on alluvial flats. Over three decades (1972–2001), changes in the composition and structure of the tree stratum were minor. Sequoia maintained a broad distribution of stem diameters throughout the period. Annual rates of Sequoia mortality (0.0029) and ingrowth (0.0029) were low, reflecting the great longevity of Sequoia and the slow canopy turnover of the study forest. Transect data also indicated a low frequency of canopy gap disturbance (≤ 0.4% of total land area per yr), but gap size was potentially large (> 0.1 ha) and the fraction of area in gaps (ca. 20%) was similar to other temperate forests. Regeneration quadrats sampled along transects, in gap centers, and on logs revealed that Sequoia regeneration is elevated at gap edges. The longevity of Sequoia and its response to gap disturbances ensure that it will remain a dominant species in the study forest.     

The Potential Impact of Small-Scale Physical Disturbance on Seedlings in a Papuan Rainforest1

Physical disturbance, such as falling debris, is an important cause of mortality to rain forest seedlings. I used artificial seedlings to quantify physical disturbance in a rain forest at the Crater Mountain Biological Research Station in Papua New Guinea. Single (N= 418) and clustered artificial seedlings (N= 428) were placed on eight transects spanning varied topography to assess the area's disturbance regime, to test if ground slope affected disturbance, and to test if clustering affected the incidence of damage. Two transects showed a significant departure from random in the spatial distribution of damaged seedlings within the transect, suggesting that some areas of experience more disturbance than others. Artificial seedlings on level ground experienced damage less often than artificial seedlings on slopes; disturbance increased with ground slope. Artificial seedlings in dry washes experienced the greatest probability of damage. Artificial seedlings in clusters experienced significantly less damage than single ones, suggesting clustered seedlings might be less vulnerable to damage than lone seedlings. The disturbance rate at this site (34.7% damaged in one year) was markedly lower than that measured at the La Selva Biological Reserve in Costa Rica (82.4%).     

Fine root and litterfall dynamics of three Korean pine (Pinus koraiensis) forests along an altitudinal gradient

Background and aims

Fine root and aboveground litterfall, two large fluxes of nutrients and carbon in the forest ecosystems, are key processes to be considered in efforts of measuring, modeling and predicting soil carbon sequestration.

Methods

We used sequential coring and litter trap to measure seasonal dynamics of fine root and litterfall in three Korean pine dominated forests along an altitudinal gradient in the Changbai Mountain during the 2012 growing season.

Results

Fine root biomass decreased significantly while necromass increased remarkably with altitude. Patterns and amounts of fine root production and mortality varied among forest types. Litterfall decreased significantly with altitude, whereas forest floor mass increased. Carbon inputs through fine root mortality and litterfall decreased significantly with altitude while carbon storage of fine root mass did not differ among forest types and carbon storage of forest floor mass was significantly larger in higher altitudinal forests due to lower turnover rates.

Conclusions

This study provided an insight into the variations of fine root and litterfall dynamics among three Korean pine forests which were associated with different vegetation traits and environmental conditions, and also the quantification of carbon fluxes through fine root mortality and litterfall for estimating carbon budget of temperate forest.     

50 years of change in a Swedish boreal old-growth Picea abies forest

Abstract. Changes in the tree layer (> 1.3m) and sapling layer (< 1.3m, including seedlings) of a Swedish boreal old-growth Picea abies (Norway spruce) forest from the 1930s to the 1980s were studied in permanent plots. The plots were established in 1938–1939 and re-analysed in 1983–1988. Regeneration, mortality, turnover rate in the tree layer and amount of decomposing logs as well as the time required for complete decomposition of logs were investigated using the detailed data from the 1930s. Ca. 25 % of the trees present during the first analysis were no longer alive. This mortality was balanced by recruitment from the sapling layer. The rate of mortality suggests a turnover time for the tree layer of ca. 200 yr. The number of spruces in the sapling layer has increased by ca. 85 %, hypothetically in response to an increase in amount of decomposing wood that can serve as nurse logs and stumps. The mean time for total decomposition was calculated as ca. 200 yr. Spruce regeneration on logs does not occur until the log is at least ca. 50 yr old. The survival pattern in the sapling layer suggests a high mortality rate at the seedling stage (≤ 1 yr) and a low mortality rate at the sapling stage. In conclusion, it is suggested that the amount of coarse woody debris available for regeneration, the occurrence of seedlings, and seedling mortality constitute concurrent factors through which climatic fluctuations, in a long-term perspective, direct stand recruitment and density. As a consequence, these boreal forests will be kept in a dynamical equilibrium.     

Damage to artificial seedlings across a disturbed Afromontane forest landscape

Seedling mortality is an important demographic bottleneck for forest regeneration, yet the factors influencing recruitment are often poorly characterized across space and time. In African highlands, where extensive patches of previously disturbed forests remain in persistent shrub‐dominated states, patterns of damage to seedlings have not been examined in detail. We used artificial seedlings to determine how (non‐herbivory‐related) damage varies across a fragmented forest landscape in the Bwindi Impenetrable National Park, Uganda. A total of 848 artificial seedlings were established in 106 plots, each with 8 seedlings, across a gradient of environmental factors, including habitat type, topographic position, distance to water, and distance to human activity. We divided damage into that due to vertebrates, plant debris, and unknown agents. From our 16,960 monthly stem assessments, 1,289 damage events were recorded. The mean “seedling” damage per year (± 1 SE) was 59.5 ± 2.3%. Damage was significantly more frequent in sites dominated by short herbs (66.1 ± 3.0) than in sites dominated by shrubs (60.1 ± 2.6) and ferns (47.9 ± 2.7). The mean percentage of damage by each class of agents was 45.8 ± 2.1% for vertebrates, 21.4 ± 2.1% for plant debris, and 3.8 ± 0.6% for unknown agents. These rates surpass those reported in other montane forests, likely reflecting the density of large vertebrates in our site. Our results indicate that most damage to artificial seedlings arises from larger vertebrates but that most spatial variation in this damage reflects the impacts of falling plant debris. These damage processes appear sufficient to constrain the regeneration of tree species in areas where forest cover is patchy and fragmented.     

Litterfall dynamics in a mixed conifer-angiosperm forest in northern New Zealand

Litterfall in a mixed conifer-angiosperm temperate forest in northern New Zealand was traced for 5 years to determine the patterns of litter production and turnover for conifer and angiosperm components of the forest. Basal area and above-ground biomass was shared approximately equally between conifer (mostly Agathis australis; New Zealand kauri) and angiosperm species (plus tree ferns). The five-year mean annual litterfall, excluding macro-litter, was 7.76± 0.39(SEM) t ha^?1 and ranged from 6.77±0.70 t ha^?1 in 1983–4 to 8.79±1.00 t ha^?1 in 1987–8. Mean monthly litterfall showed a strong seasonal pattern with low rates in winter and early spring, increasing to a peak in early autumn. There were major differences in the nature and timing of litterfall between the conifer and angiosperm fractions. Angiosperm leaf litter reached a maximum in early summer, while conifer litterfall showed highest rates for leaves, twigs and cone scales in late summer-autumn. Conifer reproductive structures (strobili and cone scales) contributed from 13 to 21% of total litterfall, a value high relative to other temperate forests. However, conifer leaf turnover was low relative to that for the angiosperms. Size of the microlitter store was 16.16±1.97 t ha^?1 prior to conifer cone fall, and 18.70±2.02 t ha^?1 following it, and conifer litter made up 76–78% of the total litter store. The estimated mean annual decomposition constant, k, was 0.39 overall, 0.33 for conifer leaf litter and 0.71 for angiosperm leaf litter, values which agree well with previously published rates for decomposition in this forest stand. Differences in the costs of biomass production and rates of turnover, as measured by litterfall and decomposition, may help to explain the functional coexistence of conifers and angiosperms in mixed forests.     

Dynamics of forests with Araucariaceae in the western Pacific

Abstract. Several species of Araucaria and Agathis (Araucariaceae) occur as canopy emergents in rain forests of the western pacific region, often representing major components of total stand biomass. New data from permanent forest plots (and other published work) for three species (Araucaria hunsteinii from New Guinea, A. laubenfelsii from New Caledonia, and Agathis australis from New Zealand) are used to test the validity of the temporal stand replacement model proposed by Ogden (1985) and Ogden & Stewart (1995) to explain the structural and compositional properties of New Zealand rain forests containing the conifer Agathis australis. Here we propose the model as a general one which explains the stand dynamics of rain forests with Araucariaceae across a range of sites and species in the western Pacific. Forest stands representing putative stages in the model were examined for changes through time in species recruitment, growth and survivorship, and stand richness, density and basal area. Support for the model was found on the basis of: 1. Evidence for a phase of massive conifer recruitment following landscape-scale disturbances (e.g. by fire at the Huapai site, New Zealand for Agathis australis); 2. Increasing species richness of angiosperm trees in the pole stage of forest stand development (i.e. as the initial cohort of conifers reach tree size; >10 cm DBH); 3. A high turnover rate for angiosperms (<100 yr), and low turnover for conifers (≥ 100 yr) in the pole stage, but similar turnover rates for both components (50–100 yr) as forests enter the mature to senescent phase for the initial conifer cohort; 4. Very low rates of recruitment for conifers within mature stands, and projected forest compositions which show increasing dominance by angiosperm tree species; 5. A low probability of conifer recruitment in large canopy gaps created by conifer tree falls during the initial cohort senescent phase, which could produce a second generation low density stand in the absence of landscape scale disturbance; 6. Evidence that each of the three species examined required open canopy conditions (canopy openness > 10 %) for successful recruitment. The evidence presented here supports the temporal stand replacement model, but more long-term supporting data are needed, especially for the phase immediately following landscape level disturbance.     

Decomposition and accumulation of litter after fire in sub-alpine eucalypt forests

Accession, decomposition and accumulation of litter were studied in three sub-alpine eucalypt forest communities (dominated by overstoreys of Eucalyptus delegatensis, E. pauciflora or E. dives) located in the Brindabella Range. Australian Capital Territory, at an elevation of 1100–1250 m. The sites had either been protected from fire for more than 20 years or been burnt by low-intensity prescribed fires. After a prescribed burn, the rate of decomposition of abscised leaves was reduced by 22% in E. delegatensis forest and by 34% in E. pauciflora forest, but was little affected in the drier E. dives community. Lowered decomposition was apparently due to greater aridity after fire, a consequence of removal of the shading understorey and reduction in the depth and hence mulching effect of the titter layer. Litter accumulates rapidly after prescribed burning, reaching a mass of 10–12 t ha^?1 within 4–5 years in all communities. Such quantities are dangerous from a fire control viewpoint. The quasi steady-state mass of accumulated litter ranges from about 17 t ha^?1 in E. dives and E. pauciflora forests to about 25 t ha^?1 in old-growth E. delegatensis forests. The rapid re-accumulation of litter after fire is not the result of any significant change in litterfall rate, but is due to a marked reduction in the total amount of litter decomposing—and this reduction is more a consequence of a decrease in the weight of the forest floor than to any fire-induced lowering of the rate of litter decomposition. The rapid build-up of litter is a consequence of the relatively high rates of litterfall (3.4–5.0 t ha^?1 year^?1) and low rates of litter decomposition (k = 0.19–0.32 year^?1) in these forests. In most cases the pattern of litter accumulation was well described by an exponential equation of the form X_t= X_ss (1—e_-kt), where X_t is the weight (t ha_?1) of litter accumulated at time t (year). X_ss is the weight of litter accumulated under steady-state conditions, and k is a decomposition rate constant (year^?1). Marked temporal variations in annual litterfall and mass of accumulated litter were found at specific forest sites which had been unburnt for more than 4.5 years. Variation from the long-term mean was greater for litterfall (31–37%) than for accumulated litter (14–26%). The maximum error when calculating decomposition rate (k) as the ratio of annual litterfall: accumulated titter, when based on single measurements of these parameters, ranged from 43 to 69% of that based on long-term measurements. Decomposition rates of the entire titter layer, calculated for periods of 22–79 months, and based on measurements of litter input and change in mass of accumulated titter, were positively correlated with the average number of days per month during each period that the litter layer remained moist (>approx. 60% ODW). The implications of these findings for fire management planning in sub-alpine and other eucalypt forests are briefly discussed.     

Litter Decomposition and Nutrient Release in a Tropical Seasonal Rain Forest of Xishuangbanna,Southwest China1

We studied litter decomposition and nutrient release in a tropical seasonal rain forest of Xishuangbanna, Southwest China. The monthly decay rates (k) of leaf litter ranged from 0.02 to 0.21/mo, and correlated with rainfall and soil moisture. Annual k values for leaf litter (1.79/yr) averaged 4.2 times of those for coarse wood (2.5–3.5 cm in diameter). The turnover coefficients of forest floor mass (annual litterfall input/mean floor mass) were: 4.11/yr for flowers and fruits, 2.07/yr for leaves, and 1.17/yr for fine wood (≤2 cm in diameter), with resident time decreasing from fine woods (0.85 yr) to leaves (0.48 yr) and to flower and fruits (0.24 yr). Nutrient residence times in the forest floor mass were ranked as: Ca (1.0 yr) > P (0.92 yr) > Mg (0.64 yr) > N (0.36 yr) > K (0.31 yr). Our data suggest that rates of litter decomposition and nutrient release in the seasonal rain forest of Xishuangbanna are slower than those in typical lowland rain forests, but similar to those in tropical semideciduous forests.     

Response of forest tree seedlings to simulated litterfall damage.

Litterfall is an important cause of seedling mortality in many forests ranging from wet tropical to boreal. However, there is a lack of studies that investigate differences between species in seedling resilience to litterfall damage. We selected seedling pairs of seven tree species and simulated litterfall damage by pinning one of each pair to the ground. The mortality and growth rates varied significantly between species for pinned individuals, but were similar for unpinned seedlings. The mortality of pinned Nestegis cunninghamii and Prumnopitys ferruginea was significantly greater than that of unpinned individuals (P < 0.05). However, contrary to expectations, the growth rates of pinned Hedycarya arborea and Nothofagus menziesii were much greater than for those left unpinned (P < 0.05). In general, seedling resilience to the bending damage differed substantially between species. N. cunninghamii and P. ferruginea suffered high mortalities and did not increase growth rates in response to damage, whereas, H. arborea and N. menziesii suffered few mortalities and regained height quickly. Other study species demonstrated intermediate resilience. This study demonstrates that some species are more likely to survive in high-risk litterfall regimes than are others. Given that litterfall risk can vary greatly between microsites, these results suggest that litterfall can contribute to regeneration niche differentiation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Structure,dynamics and disturbance regime of temperate broad-leaved forests in Japan

Abstract. Structure, diversity and dynamics of five Japanese temperate old-growth forests were compared, differing from each other in, i.a., climate, dominant tree type, topography, disturbance regime. The forests were Aya, Ogawa, Kanumazawa Riparian, Kanumazawa upland and Senju. A permanent plot (1–6 ha) was established in each forest and trees were censused several times at intervals of two years. Mean annual recruitment rates and mortality rates in these forests were both in the range of 0.5 to 4.6 %/yr at the community level. Analyses of the structure and dynamics of populations showed that the underlying process was different among the forests. Some forests experienced compositional shifts in their canopies, others had a constant canopy composition but appeared to lack effective regeneration in recent years. The recruitment rate appeared to be strongly affected by competitive undergrowth vegetation such as dwarf bamboo which has been controlled by natural disturbance or human impact. It is likely that the forests with mostly low recruitment rates had a low species diversity. The current variation in structure, diversity and dynamics of the studied forests might have been determined not only by physical conditions (e.g. climate) but also by chance factors (e.g. disturbance, outbreak of deer population).     

川西亚高山森林不同恢复途径物种组成和群落结构动态变化

川西亚高山森林作为西南林区主体,是长江上游的生态屏障,该区域植被恢复方式主要为人工恢复和自然恢复,比较不同恢复方式下森林的物种组成和群落结构动态变化,对于川西亚高山森林恢复与重建有重要的意义,可以为制定合理的森林管理策略提供科学依据。基于茂县山地生态系统定位研究站不同恢复模式形成的的华山松人工林、油松人工林和自然恢复的次生林野外调查数据,分析了2005-2020年乔、灌、草三个层次的群落结构特征和多样性。结果表明:(1)不同恢复途径下,乔木层物种数都呈现增加趋势,华山松人工林、油松人工林、自然恢复的次生林乔木层物种数分别增加了11种、7种、8种;(2)华山松人工林中华山松重要值从48.06%降低到31.1%,乡土阔叶树种四川蜡瓣花进入乔木层,2020年重要值增大至21.62%,油松人工林中油松重要值逐渐降低,从43.59%降至29.76%;自然恢复的次生林中,乡土树种锐齿槲栎逐渐成为第一优势种,2020年重要值增至19.9%。(3) 华山松人工林、油松人工林和自然恢复的次生林中,温带区系成分分别占总属数的71.43%,80.77%和84%,温带区系特征明显。(4)华山松人工林和油松人工林乔木层径级结构均为偏正态分布;而自然恢复的次生林径级分布呈倒"J"形,以小径级个体为主。(5)不同林型的乔木层高度在15年间呈现增加的趋势,具体表现为油松人工林>华山松人工林>自然恢复的次生林。(6)乔木层Shannon-wiener指数和 Simpson指数均表现为自然恢复的次生林显著大于两个人工林,丰富度指数和均匀度指数表现为油松人工林最大;灌木层4个多样性指数均表现为油松人工林最大;草本层的丰富度指数、Shannon-wiener 指数和 Simpson 指数均表现为油松人工林较大,均匀度指数没有显著差异。结论:人工林恢复速度大于自然恢复的次生林,但自然恢复的次生林更新能力更强,且更有利于多样性的保存。两个人工林逐渐由常绿针叶林演替为以常绿针叶树为主的针阔混交林,自然恢复的次生林演替为以常绿阔叶树为主的针阔混交林。