The effects of gap disturbance on nitrogen cycling and retention in late-successional northern hardwood–hemlock forests

Late-successional forests in the upper Great Lakes region are susceptible to nitrogen (N) saturation and subsequent nitrate (NO₃⁻) leaching loss. Endemic wind disturbances (i.e., treefall gaps) alter tree uptake and soil N dynamics; and, gaps are particular susceptible to NO₃⁻ leaching loss. Inorganic N was measured throughout two snow-free periods in throughfall, forest floor leachates, and mineral soil leachates in gaps (300–2,000 m², 6–9 years old), gap-edges, and closed forest plots in late-successional northern hardwood, hemlock, and northern hardwood–hemlock stands. Differences in forest water inorganic N among gaps, edges, and closed forest plots were consistent across these cover types: NO₃⁻ inputs in throughfall were significantly greater in undisturbed forest plots compared with gaps and edges; forest floor leachate NO₃⁻ was significantly greater in gaps compared to edges and closed forest plots; and soil leachate NO₃⁻ was significantly greater in gaps compared to the closed forest. Significant differences in forest water ammonium and pH were not detected. Compared to suspected N-saturated forests with high soil NO₃⁻ leaching, undisturbed forest plots in these late-successional forests are not losing NO₃⁻ (net annual gain of 2.8 kg ha⁻¹) and are likely not N-saturated. Net annual NO₃⁻ losses were observed in gaps (1.3 kg ha⁻¹) and gap-edges (0.2 kg ha⁻¹), but we suspect these N leaching losses are a result of decreased plant uptake and increased soil N mineralization associated with disturbance, and not N-saturation.     

Effects of forest-pasture edge on C,N and P associated with <Emphasis Type="Italic">Caesalpinia eriostachys</Emphasis>, a dominant tree species in a tropical deciduous forest in Mexico

Forest fragmentation in tropical ecosystems can alter nutrient cycling in diverse ways. We have analysed the effects of the forest-pasture edge on nutrient soil dynamics in a tropical deciduous forest (TDF) in Mexico. In two remnant forest fragments, both larger than 10 ha, litterfall, litter and soil samples associated to the tree Caesalpinia eriostachys were collected at five distances from the pasture edge into the inner forest (10 m in the pasture and 0–10, 30–40, 70–80 and 100–110 m towards the forest interior). We measured the concentrations of carbon (C), nitrogen (N) and phosphorus (P) in litterfall, surface litter and soil, and soil microbial C (C_mic) and microbial N (N_mic). Soil nutrient concentrations and C_mic and N_mic were lower in the pasture soils than in the forest soil samples. Total C and N pools, and C_mic and N_mic in the pasture were lower than in the forest. In contrast, net N immobilization and the increase in N_mic from rain to dry season increased from the edge to the inner forest. Soil P concentration was lower in the pasture and at the first distance class in the forest margin (0–10 m) than in the sites located further into the forest, while litter P concentration had the inverse pattern. Litterfall P was also reduced near the edge and increased towards the forest interior. As a consequence, litterfall C:P and N:P ratios decreased from the edge to the inner forest. These results suggest that the forest–pasture edge disrupts P dynamics within the first 10 m in the forest. Thus, plants' use of nutrients and productivity could be altered in the edge of fragmented forests.     

Comparison between perfect information and passive–adaptive social learning models of forest harvesting

This paper compares perfect information and passive–adaptive social learning models of forest harvesting using a simple Markov chain model for land-use dynamics. A perfect information model assumes that landowners know true utility values of forest conservation and harvesting. In contrast, a passive–adaptive social learning model assumes that landowners do not know true utility values and they learn these values by their past experiences and by exchanging information with others in a society. We determine conditions under which the same consequences expected from perfect information and passive–adaptive social learning models. We found that the outcome from a perfect information model resembles that from passive–adaptive social learning model only when the perfect information model incorporates little discounting for future values. The stability analysis of landscape dynamics predicts a cyclic overexploitation of forest resources in a passive–adaptive social learning model with short-term memory, while instability of landscapes is never expected in a perfect information model. We discuss the role of discounting the future and discounting the past in the context of forest management.     

Decline of soil nitrogen mineralization and nitrification during forest conversion of evergreen broad-leaved forest to plantations in the subtropical area of Eastern China

We examined soil nitrogen (N) mineralization and nitrification rates, and soil and forest floor properties in one native forest: evergreen broad-leaved forest (EBLF), one secondary shrubs (SS), and three adjacent plantation forests: Chinese fir plantation (CFP), bamboo plantation (BP) and waxberry groves (WG) in Tiantong National Forest Park, Eastern China. All forests showed seasonal dynamics of N mineralization and nitrification rates. Soil N mineralization rate was highest in EBLF (1.6 ± 0.3 mg-N kg⁻¹ yr⁻¹) and lowest in CFP (0.4 ± 0.1 mg-N kg⁻¹ yr⁻¹). Soil nitrification rate was also highest in EBLF (0.6 ± 0.1 mg-N kg⁻¹ yr⁻¹), but lowest in SS (0.02 ± 0.01 mg-N kg⁻¹ yr⁻¹). During forest conversion of EBLF to SS, CFP, BP and WG, soil N mineralization rate (10.7%, 73%, 40.3% and 69.8%, respectively), soil nitrification rate (94.9%, 32.2%, 33.9% and 39%, respectively), and soil N concentration (50%, 65.4%, 78.9% and 51.9%, respectively) declined significantly. Annual soil N mineralization was positively correlated with total C and N concentrations of surface soil and total N concentration of forest floor, and negatively correlated with soil bulk density, soil pH and C:N ratio of forest floor across the five forests. Annual soil nitrification was positively correlated with total C concentration of surface soil and N concentration of forest floor, and negatively correlated with soil bulk density and forest floor mass. In contrast, annual soil nitrification was not correlated to pH value, total N concentration, C:N ratio of surface soil and total C concentration and C:N ratio of forest floor.     

Altered leaf-litter decomposition rates in tropical forest fragments

The effects of forest fragmentation on leaf-litter decomposition rates were investigated for the first time in an experimentally fragmented tropical forest landscape in Central Amazonia. Leaf-litter decomposition rates were measured at seven distances (0–420 m) along forest edge-to-interior transects in two 100-ha fragments, two continuous forest edges, and at an identical series of distances along two deep continuous forest transects, as well as at the centers of two 1-ha and two 10-ha fragments. Decomposition rates increased significantly towards the edge of 100-ha forest fragments. Litter turnover times were 3–4 times faster within 50 m of the edge of 100-ha fragments than normally found in deep continuous forest. In contrast, there was no significant change in the rate of leaf-litter decomposition from the interior to the edge of continuous forest. It is difficult to account for these very different edge responses. Decomposition rates were not correlated with air temperature differentials, evaporative drying rates, litter depth, biomass or moisture content, or with total invertebrate densities, either within individual edge transects or across all sites. The difference in edge response may be due to chance, particularly the patchy removal of vast quantities of litter by litter-feeding termites, or may be a real, area-dependent phenomenon. Clearly, however, forest fragmentation increases the variability and unpredictability of litter decomposition rates near forest edges. In addition to edge effects, decomposition rates were strongly affected by decreasing fragment area. While sites at the centers of 10-ha and 100-ha forest fragments and continuous forest had equivalent decomposition rates, rates were markedly lower at the centers of 1-ha fragments. Litter turnover times were 2–3 times slower in 1-ha fragments than in continuous forest, and up to 13 times slower than at 100-ha edges. Litter structure and nutrient cycling dynamics are inevitably altered by forest fragmentation. Received: 16 October 1997 / Accepted: 14 April 1998     

Modelling Recolonization of Second-Growth Forest Stands by the North American Red Squirrel Tamiasciurus hudsonicus

In this paper, we present a model for source–sink population dynamics where the locations of source and sink habitats change over time. We do this in the context of the population dynamics of the North American red squirrel, Tamiasciurus hudsonicus, within a forest environment subject to harvesting and regrowth. Harvested patches of forest are initially sinks, then eventually become source habitat again as the forest regrows. At the same time, each harvested patch is gradually recolonized by squirrels from other forest patches. We are interested in the interaction of forest harvesting dynamics with squirrel population dynamics. This depends on the harvesting schedule, and on the choices squirrels make when deciding whether to settle in a mature forest patch or in a recently harvested patch. We find that the time it takes for a second-growth forest patch to be recolonized at the mature forest level is longer than the time required for the habitat quality to be restored to the mature forest level. We also notice that recolonization pressure decreases squirrel populations in neighbouring patches. The connectivity between forest patches and the cutting schedule used also affect the time course of recolonization and steady-state population levels.     

Cocoon predation on diprionid sawflies: the effect of forest fertility

Predation by small mammals is thought to be one of the main regulators of outbreaking sawfly species. It has been suggested that predation may be lower in poor and dryish forests, and this is the reason why outbreaks often begin from this type of environment. We studied experimentally how fertility of the forest site affects cocoon predation experienced by two sawfly species, the common pine sawfly Diprion pini (Linnaeus) and the European pine sawfly Neodiprion sertifer (Geoffroy). We applied a fertilization treatment to selected pine-dominated barren forest sites in Finland, and 2–4 years later monitored predation on the sawfly cocoons in fertilized and control areas. The results did not support the idea that forest fertility was related to cocoon predation. We also could not verify that small mammal abundance was related to fertility of the forest. The most obvious pattern we observed was that the two sawfly species differed dramatically in predation experienced. N. sertifer has its cocoon phase in mid-summer and experienced only moderate predation (37%) whereas D. pini, with its cocoon phase in autumn, suffered from very heavy predation (96%). Our observations suggest that if predation is important in controlling the population dynamics of the species, its impact depends more on the sawfly species and season than on the fertility of the forest site. Received: 1 March 1998 / Accepted: 25 May 1998     

Plant Functional Types of Woody Species Related to Fire Disturbance in Forest–Grassland Ecotones

The study of plant functional types (PFTs) has been widely emphasized when analysing plant community changes in relation to variations in climate and disturbance regime. In this study, we search for PFTs of woody species near forest–grassland boundaries in South Brazil where, due to climate, forests tend to expand over grassland but are being restricted by frequent fires. We aimed at answering the questions: (i) which plant functional types of forest woody species can establish in adjacent grassland subject to fire disturbance and (ii) which plant functional types of forest and grassland woody species are related to short-term community dynamics in frequently burned grassland. Traits were assessed in woody plants in 156 plots (6.75 m²) arranged in 12 transects across forest–grassland boundaries with different fire history in their grassland part. The analysis used a recursive algorithm to search for traits and PFTs maximally associated to spatial distance from forest limit in one analysis, and elapsed time since last fire in another. As a result, nine PFTs of forest woody species were identified that best described community patterns associated to distance from forest. Resprouting ability characterized forest plants able to colonize grasslands. PFT diversity was higher in border plots than inside forest or grassland. Four PFTs of forest and grassland woody species best described woody species community patterns in the grassland associated to elapsed time since fire. Taller individuals of single-stemmed shrubs predominated in late post-fire recovery (3–4 years), while shorter multi-stemmed shrubs in recently burned areas (3 months to 1 year). PFTs of forest trees occurred in border plots or, as established adults, in grassland, remaining unaffected by fire. We conclude that easily measurable structural plant traits, such as those used in our study, are sufficient to evaluate post-fire community dynamics. Forest PFTs in burned grassland are restricted to those with resprouting ability to survive recurrent fire events. Establishment success is highest on protected sites with lesser or low-intensity fire.     

Studies on the dynamic properties of terrestrial ecosystems based on a simulation model II. Tropical rainforest dynamics and stability as influenced by stem mortality

Further analysis of tropical rainforest dynamics and stability in relation to stem mortality has been conducted using a microcomputer model developed in a previous study (Oikawa, 1985). By simulation experiments covering a period of 100 years, the effects of changing stem mortality (δc) upon a tropical rainforest were investigated. Increasing stem mortality ranging from a standard value (3%yr⁻¹) to a 4-fold value (12%yr⁻¹) brings about decreases in stem biomass and thus total living biomass, and a contrasting increase of stem litterfall flux at the steady state of the forest ecosystem. At the same time, the decreased stem biomass at the steady state is predicted to result in increases of gross production (P _g) and net production (P _n), and an improvement in production efficiency of the model rainforest expressed as theP _n/P_g ratio. similar simulation experiments predict that the improved production efficiency in the forest with a 4-fold stem mortality is able to enhance tolerance to less productive environments such as a prolonged dry season or a reduced incident light flux density. On the other hand, the standard stem mortality (δ_c=3%yr⁻¹), which was estimated as a probable value for the Pasoh forest, West Malaysia, is considered to approximate the lower threshold necessary for attaining forest stability. Based on the results obtained, the significance of δ_c for the dynamics and stability of a tropical rainforest ecosystem is discussed in relation to the competition and tolerance of trees. In addition, the effectiveness of the simulation approach adopted here is emphasized. Titles are tentative translations by the author for original titles in Japanese.     

Changes in soil macroarthropod communities in relation to forest maturation through three successional stages in the Canadian boreal forest

The edaphic macroarthropod communities of three sites representative of the forest succession in the Lake Duparquet region (situated in the southern part of the boreal forest, Abitibi, Quebec, Canada) were studied. A 47-year-old deciduous forest, a 144-year-old mixed forest, and a 231-year-old coniferous forest form a successional forest gradient with a vegetation composition that is a function of the time elapsed since the last forest fire. Along with forest succession, there is a reduction in macroarthropod community biodiversity. There is a negative gradient for mean total abundance (237–41 individuals), total richness (63–23 species), density (1792–661 individuals/m²), diversity (H′ = 1.478–1.007) and equitability (J = 0.821–0.739). These community changes affect saprophagous organisms more than predators. Certain species or taxa show preferences for a particular forest type, such as larval Diptera for the deciduous forest. A comparison of these results with the literature suggests an inverse preference as to habitat choice between microarthropods (Acarina and Collembola) and macroarthropods. From a conservation point of view, macroarthropod biodiversity will be favored by the protection of all forest types since each environment possesses a particular community structure and species. Received: 17 April 1995 / Accepted: 1 April 1996     

Simulation of the effects of deer browsing on forest dynamics

I introduced forest dynamics to a deterministic herbivore-vegetation model to examine the effects of vertically stratified forest structure on the dynamics of the herbivore–vegetation system, the resilience and stable states of vegetation, and the interactions between deer populations and vegetation. I constructed a model based on data from field studies performed in Hokkaido, northern Japan. Three phases of state were identified for a given deer density: (1) understory vegetation is maintained with a equilibrium proportion of canopy gaps in the absence of deer; (2) if the equilibrium proportion of canopy gaps is greater than that in the equilibrium state in the absence of deer, the understory vegetation can be maintained; and (3) the understory vegetation cannot be maintained. At the boundary between phases 2 and 3, the herbivore population level had discontinuous effects on vegetation. When the deer density was held below the threshold, forest vegetation had resilience to recover to the equilibrium stable state at the given deer density, although the equilibrium canopy gap ratio and vegetation biomass differed with deer density. However, the forest vegetation–herbivore system could not be maintained in a stable state without artificial deer population management if food limitation was the only mechanism to keep the deer population at low levels. The deer population must be kept below the boundary between phases 1 and 2 to maintain the forest regeneration processes. The level cannot be determined by observing the deer population; careful observation of forest regeneration processes is required.     

Identifying spatial patterns in the tropical rain forest structure using hemispherical photographs

This work emphasises the usefulness of hemispherical photography for identifying spatial patterns in the tropical rain forest structure. Structural variability was investigated at a local (intra-site) scale, in relation to the forest mosaic, and at a regional (inter-sites) scale, for its implication in forest typology. Four primary forest sites, from 0.6 to 1 ha, were investigated in Central Sumatra, Indonesia.In a first instance, a qualitative analysis of the forest 3-D structure was found to be very helpful in the interpretation of quantitative results related to forest dynamics. The quantitative analysis was undertaken through the assessment of three structural characteristics: (1) the canopy openness (CO), or visible sky as seen from all directions of the hemisphere, (2) the spherical variance (SV), which quantifies the spatial dispersion of gaps and, (3) the plant area index (L_p), defined as half the surface area of canopy elements per unit ground area. At the local scale, maps of the CO values gave an indication about disturbance location and extent, providing an interesting document for studies on forest dynamics. At the regional scale, between-sites comparisons of CO, SV and L_p values added new information on forest structural differences when compared to dendrometric measurements. These results emphasised the fact that rain forest may exhibit high structural variability, even within a same bioclimatic region and a narrow altitude range. Hemispherical photographs could be a quick means of further investigating this spatial variability and it's relation to physical environment, thus providing information that is crucial for the refining of forest typology in the area.     

Winter habitat selection by wild boar <Emphasis Type="Italic">Sus scrofa</Emphasis> in southeastern Poland

Research was conducted on habitat selection by the wild-boar population in the Carpathian foothills, southeastern Poland. In two forest districts (Bircza and Krasiczyn) with a total area of forests of 47,000 ha, 21 line transects were designated (total length, 284 km). In February 2001, tracks that wild boar left during the day were counted on five subsequent days. Using a car mileage meter and forest maps, the locations of tracks in seven forest types, forest meadows and agricultural fields situated inside the forests were determined. The Bailey’s test was applied to calculate the boars’ preference for each forest type and non-forest areas. Spatial distribution of 284 wild-boar tracks shows that the animals do indeed prefer European beech–hornbeam Fagus silvatica–Carpinus betulus forest and avoid silver fir Abies alba forest. The hypothesis raised is that in the European beech–hornbeam forests, there are foraging areas and bedding sites crucial for the animals.     

Impact of game hunting by the Kayapó of south-eastern Amazonia: implications for wildlife conservation in tropical forest indigenous reserves

Indigenous forest reserves represent approximately one fifth of Brazilian Amazonia and pose enormous challenges for sustainable natural resource management by native Amazonians. In collaboration with the Kayapó Indians of A’Ukre of southeastern Amazonia, we obtained a game harvest profile of over 1360 forest vertebrates consumed at this village over a 20-month period, including 743 mammals, 361 forest tortoises and 256 birds from a minimum of 42 game species. This amounted to a total of 13,775 kg of game animals harvested over the entire study (mean = 26.2 kg d⁻¹). We also obtained some 450 km of line transect census data of midsized to large-bodied vertebrates within the core hunting catchment of this village and in an unhunted but otherwise comparable site upriver of A’Ukre. Population density estimates of 16 of the 18 species censused were significantly depressed by hunting by central place foragers within the village catchment, and a number of harvest-sensitive prey species showed clear evidence of local depletion. For the time being, however, we can conclude that hunting was sustainable at the landscape scale largely because source-sink dynamics in the context of low village catchment density is made possible by large surrounding tracts of primary forest that remain unharvested or underharvested.     

Role of the EXPO ’70 forest project in forest restoration in urban areas

The forest-restoration project of EXPO ’70 Commemorative Park, Japan, is an epoch-making attempt to restore a nature-oriented forest park in an urban area in which large-scale land reclamation had occurred. The objective of this paper is to review the concept, planning, and design, and the outcome so far, and discuss current aspects of creating a core natural habitat in the city of Osaka. Innovative planning policy and design methods have been used for construction of the forest-restoration project of EXPO Park. Unexpected troubles have occurred, however. After approximately 10 years severe effects of poor drainage and soil compaction on the establishment of the forest have been revealed by intensive monitoring. Partial redevelopment and soil-amendment work has therefore been conducted. These improvements seemed to have resulted in “a self-sustaining forest”, the original objective of the planning policy. After approximately 25 years, however, a second intensive monitoring program has revealed that the status of nature restoration is generally favorable in quantity but not in structure of forest communities or biodiversity. The major issues identified are excessive tree density with a single foliage layer caused by the single generation of immature forest stand, and ecological isolation from the source of nature. The EXPO forest is currently in the “Second Generation” stage; this involves management, including artificial gap regeneration, and soil seed bank introduction, with careful monitoring. The project is expected to be an ideal example of a core habitat of nature-oriented forest in urban areas achieved by adaptive management.     

Methane oxidation rates in forest soils and their controlling variables: a review and a case study in Korea

Methane is one of the strongest of the greenhouse gases, being 30-fold more radiatively active than carbon dioxide on a molar basis. In addition, its atmospheric concentrations have increased by 1% per year since the Industrial Revolution. As such, the dynamics of methane is of great importance for the prediction of global climatic changes caused by increasing concentrations of greenhouse gases in the atmosphere. One of the most important biological sinks for methane is forest soils, where methanotrophic bacteria oxidize methane to carbon dioxide. Based on data mined from a review of the literature, we determined that the mean methane oxidation rate was 1.90 mg CH₄ m⁻² day⁻¹ and that the main variables controlling this rate were soil water content and inorganic nitrogen in the soils. In contrast, the effects of temperature and pH are minimal. In addition to reviewing the literature, we monitored methane oxidation rates in a temperate forest soil in Korea on a monthly basis for a year, using a static chamber method. The mean oxidation rate was 1.96 mg CH₄ m⁻² day⁻¹ and was positively correlated with nitrate concentration in the soil.     

Edge effects on palm diversity in rain forest fragments in western Ecuador

At the edges of tropical rain forest fragments, altered abiotic and biotic conditions influence the structure and dynamics of plant communities. In Neotropical rain forests, palms (Arecaceae) are important floristic and ecological elements. Palms’ responses to edge effects appear to be idiosyncratic and to depend on the level of disturbance at edges. This paper explores how variation in forest structure at the edges of two old-growth forest fragments in a tropical rain forest in western Ecuador affects palms of different species, life-forms, and size classes. We investigate (1) how edge effects influence the relative proportion of palm adults and juveniles, (2) how distance from the forest edge affects palm density and species richness, (3) how altered forest structure along edges affects palm density. We found that at edges (1) palm communities had a lower proportion of adults relative to juvenile individuals compared to continuous forests, (2) the density of two species of palms and the overall species richness of the palm community tended to decrease toward the edges within forest fragments, and, (3) altered forest structure decreased the density of adult palms. Hence, edge effects on palms were controlled by the degree of modification of the forest structure, and by species responses to edge-related disturbance.     

Core area analysis at semi-deciduous forest islands in the Comoé National Park,NE Ivory Coast

For the protection of forest-interior species in both natural forest islands and anthropogenic forest fragments knowledge on the size of forest-core areas is a central issue. In an intact mosaic of semi-deciduous forests and savanna in the Comoé National Park 31 forest islands were selected (2.1–146.1 ha). Values for the depth-of-edge influence (DEI) of the study area recently published range from 0 m up to nearly 150 m. Thus, core-area analysis was carried out for this range in 5 m steps. For a DEI of 55 m—e.g. computed for tree-species composition of large trees—half of the total forest area can be considered as core area, but only 9 of the studied forest islands still contained a relative core area (rCA) of more than 50%. From non-linear regression it was estimated that for a DEI of 55 m an rCA of 50% can be expected for forest islands with a size of 36.6 ± 7.6 ha. This value increased exponentially with increasing DEI. The GIS-based core-area analysis presented in this paper proved to be suitable to give a well interpretable overview on rCA with respect to varying DEI, and we recommend to incorporate this type of analysis in existing GIS-tools. As the presented study is the first sound core area analysis at forest islands in West Africa, data contribute to a better understanding of this field of ecology that is of high relevance for planners and decision makers to protect biodiversity.     

东灵山地区落叶阔叶林长期动态的模拟

用林窗模型研究了暖温带辽东栎林的长期动态变化。用森林经营历史和实际调查数据求得模型的参数。经过与实际数据检验证明所得模型能合理地预测辽东栎林的物种组成动态变化。通过对辽东栎交生裸地的模拟,可以得到：辽东栎种群在森林动态变化过程中呈现波动的形式,波动的周期为１１０ａ左右,叶面积指数的动态变化过程与林分的竞争状况有密切的关系,生产力的变化有着明显的无规律性,变化极水稳定,在３０ａ进有一个变化的高峰期,     

Structure and dynamics in seasonal dry evergreen forest in northeastern Thailand

Abstract. Studies of tropical forest dynamics have often been based on one large-scale permanent plot, representative of a given forest type. Broad classifications of tropical forest types are expected to include a wide range of stand structures, dynamics patterns and species compositions – a range which cannot be represented in a single plot. To demonstrate this problem two 1-ha permanent plots, dominated by Hopea ferrea and Shorea henryana (both Dipterocarpaceae), respectively, were established in 1987 in seasonal dry evergreen forest at the Sakaerat Environmental Research Station in northeastern Thailand. In 1997 the plots were remeasured as to patterns of recruitment, mortality and growth. The Hopea plot was relatively static with low mortality, recruitment and growth. The Shorea plot was very dynamic with high rates of growth, mortality and recruitment. If the current trends continue, the plots are likely to further diverge. Even if the study of a large forest plot provides a good insight into tropical forest dynamics, it is necessary to consider the entire local pattern of variation.