Changes in O horizon mass,thickness and carbon content following fire in northern hardwood forests

This study examines temporal changes in the thickness, mass, and organic carbon content of the O horizon (forest floor) of eight forested plots in northern Michigan, USA. Each plot had experienced a recent burn (prescribed or accidental); burn dates ranged from 1798 to 1980. The climax forest in this region is mixed Pinus-Acer-Betula-Tsuga, whereas the fire successional species are predominantly Populus spp. and Betula papyrifera. O horizon data were fit to logarithmic functions (chronofunctions) that depicted rapid accumulations of mass and thickness in the first years after the fire, followed by decreasing rates of increase after 100 years. Extension of the chronofunctions to 5000 years allowed for a theoretical examination of forest floor conditions, e.g., steady state and time to steady state, after long periods without disturbance. The models predicted greater O horizon thicknesses and slightly lower mass for steady state conditions than have been reported for old-growth stands elsewhere. Steady state accumulations of litter in these mixed, temperate forests requires at least 200 and possibly > 1000 years, which is markedly longer than most other estimates. Although frequent disturbance by fire in these forests would likely preclude such values from being attained, these data provide theoretical maximum values for forest floor conditions in these ecosystems.     

Canopy cover and tree regeneration in old-growth cove forests of the Appalachian Mountains

Relationships between canopy cover and tree regeneration were determined for various species in cove forests of the Great Smoky Mountains. Old-growth stands were sampled with six plots covering a total area of 4.8 ha. Each plot was subdivided into contiguous 10×10 m quadrats. Canopy cover overlying each of the 480 quadrats was characterized with three different indices based on visual estimates of cover. Influences of: (1) overlying cover, (2) proximate openings, and (3) total area of proximate openings on quadrat regeneration densities were determined. Most species reproducing by seed and some species reproducing by vegetative means had higher densities in quadrats with openings, but only the intolerants were highly dependent on gaps. Tsuga canadensis, a very shade-tolerant species, was one of the few species with abundant regeneration beneath dense canopy cover. In general, understory areas near gaps had somewhat higher regeneration densities than other areas with overlying cover. Several shade-tolerant species showed a positive regeneration density response to canopy openings and an ability to regenerate in gaps 0.01–0.03 ha in area. These openings were too small for intolerant species. Many species exhibited a positive response to total size of the proximate opening(s). A sharp increase in regeneration density with area of the opening(s) was evident at approximately 0.04 ha for the shade-intolerant species.     

Fractal properties of forest spatial structure

The definition of fractal dimension of natural objects, which enables to deal with scale dependence of fractal dimension is discussed. Abrupt changes of fractal dimension of spatial structure of terrestrial ecosystems are considered in the context of hierarchical paradigm. On this ground the procedure is proposed for segmentation of a territory, which takes into account the scale dependence of spatial variability of ecological parameters. Using remotely sensed data — normalized difference vegetation index (NDVI) and thermal radiation in the infrared band — fractal dimensions and critical scales are evaluated for different forest types with the help of software, developed for this purpose. The results obtained corroborate the potentialities of fractal approach in ecology. These methods and results can be used for discrimination of remotely sensed data; but further investigations, including detailed comparison of fractal characteristics of remotely sensed forest images with results of on-site field studies are necessary to validate them.     

The fate of nutrients during fires in a tropical savanna

Abstract The nutrient loads contained in the grassy fuel before fires, and of ash subsequently, were compared to determine the fluxes of macronutrients, copper and zinc during fires at Kapalga in Kakadu National Park. The fluxes were estimated in three vegetation types: forest, woodland and open woodland. The magnitudes of the fluxes were greatest in the forest community where grassy fuel loads were highest at about 6.3 t ha^?1. In these sites, 54–94% of all measured nutrients in the fuel were transferred to the atmosphere during the fires. For each nutrient, the proportion transferred to the atmosphere as entrained ash was calculated by assuming that calcium was not volatilized during the fires. If the transfer of entrained ash represents local redistribution only, then rainfall accession and the deposition of these particu-lates should replace most of the losses of all nutrients except nitrogen (N). Estimated rates of biological fixation of N appear to be insufficient to replace the annual losses of N. It is therefore concluded that a regime of annual fires that completely burn the available grassy fuel would deplete N reserves in these savannas, unless there are other sources of biologically fixed N, which are unknown at present.     

天然林内红松种群年龄更替数学模型及研究

本文给出天然林内红松种群年令更替数学模型（1）。通过对（1）进行定性分析,得到主要结论是：系统（1）在第一象限内存在唯一稳定周期解的充要条件是bk-bc-2d＞0其生态意义是天然林内红松幼树与母树随时间变化会产生一个有规律、互为消涨的变化特征。     

Ethnobotany of Atlantic Forest coastal communities: Diversity of plant uses in Gamboa (Itacuruçá island,Brazil)

Local plants are a very important resource for the community of Gamboa, located at Itacuruçá Island, Sepetiba Bay, State of Rio de Janeiro, Brazil Ninety species of plants, belonging to 40 families, are used for a variety of purposes, such as food, construction, handicraft, and medicine. In a survey medicinal uses for plants were the most quoted by the community. Uses of medicinal plants within Gamboa and with other coastal communities are analyzed using diversity indices. Use by different categories of people based on sex, age, and economic activity was compared and significant differences were found among the groups compared, except for economic categories (fishermen and non-fishermen). The theory of island biogeography is shown to be useful for analyzing different levels of resource uses on different islands.     

岭南垛基果林湿地土壤碳组分特征

岭南垛基果林湿地是珠三角地区典型的湿地类型之一,其对土壤碳汇的贡献值得关注。为探讨果林种植类型对土壤有机碳的影响,对广州垛基果林湿地内种植黄皮(Clausenalansium)(HP),龙眼(Dimocarpuslongan)(LY)、杨桃(Averrhoa carambola)(YT),龙眼和黄皮间种(LH),杨桃、龙眼和黄皮间种(YLH)共5种种植类型下的表层(0～20 cm)土壤碳组分进行研究。结果表明,不同的植被类型对土壤的总有机碳(SOC)、可溶性有机碳(DOC)、微生物生物量碳(MBC)、易氧化有机碳(ROC)、惰性碳(NLC)含量都有影响,LY的SOC含量最高(22.6 g/kg),显著高于YLH (P<0.05),且NLC含量显著高于LH和YLH (P<0.05)。NLC含量与土壤养分呈正相关,与土壤容重呈负相关。YT的MBC含量显著高于LY、HP、LH (P<0.05),且MBC/SOC显著高于HP、LY(P<0.05)。YLH模式下,土壤DOC含量和DOC/SOC显著高于其他植被类型(P<0.05)。LH的ROC/SOC显著高于HP和L...     

鼎湖山森林群落演替之研究

鼎湖山森林群落在自然状态下遵循一定的客观规律向更优化的气候顶极群落演变。本文分析其1955年至1989年(35年)来的演替结果,总结出鼎湖山森林群落演替的进程和模式,进一步应用植物群落演替系统的线性模型和非线性模型对演替进程进行定量研究,并做出相应的演替进程的数量预测。     

Scale dependence of vegetation-environment correlations: A case study of a North Carolina piedmont woodland

Abstract. Vegetation and its correlation with environment has been traditionally studied at a single scale of observation. If different ecological processes are dominant at different spatial and temporal scales, the results obtained from such observations will be specific to the single scale of observation employed and will lack generality. Consequently, it is important to assess whether the processes that determine community structure and function are similar at different scales, or whether, how rapidly, and under what circumstances the dominant processes change with scale of observation. Indeed, early work by Greig-Smith and associates (Greig-Smith 1952; Austin & Greig-Smith 1968; see Greig-Smith 1979; Kershaw & Looney 1985; Austin & Nicholls 1988) suggested that plant-plant interactions are typically important at small scales, but that the physical environment dominates at large scales. Using a gridded and mapped 6.6 ha portion of the Duke Forest on the North Carolina piedmont for a case study, we examined the importance of scale in vegetation studies by testing four hypotheses. First, we hypothesized that the correlation between vegetation composition and environment should increase with increasing grain (quadrat) size. Our results support this hypothesis. Second, we hypothesized that the environmental factors most highly correlated with species composition should be similar at all grain sizes within the 6.6-ha study area, and should be among the environmental factors strongly correlated with species composition over the much larger extent of the ca. 3500 ha Duke Forest. Our data are not consistent with either portion of this hypothesis. Third, we hypothesized that at the smaller grain sizes employed in this study (< 256 m²), the composition of the tree canopy should contribute significantly to the vegetation pattern in the under-story. Our results do not support this hypothesis. Finally, we predicted that with increased extent of sampling, the correlation between environment and vegetation should increase. Our data suggest the opposite may be true. This study confirms that results of vegetation analyses can depend greatly on the grain and extent of the samples employed. Whenever possible, sampling should include a variety of grain sizes and a carefully selected sample extent so as to ensure that the results obtained are robust. Application of the methods used here to a variety of vegetation types could lead to a better understanding of whether different ecological processes typically dominate at different spatial scales.     

Seed removal,seed dispersers,and the allocation of tissues in Myrtaceae seeds

To avoid seed predation, plants may invest in protective seed tissues. Often related to seed size, allocation in seeds' physical defenses can also be influenced by dispersers. We explore the relationships between seed traits (seed mass and hardness) and seed removal in 22 Myrtaceae species of the Brazilian Atlantic Forest, a dominant and diverse fleshy-fruited taxon dispersed by birds, rodents, and other mammals. Our goal is to understand how seed traits influence seed removal rates, and whether dispersers can affect tissue allocation in the seed coat. Seeds were exposed to field removal experiments. In the laboratory, total seed mass and seed coat mass were obtained. To evaluate the influence of seed traits on removal, we performed Kruskal–Wallis and Simple Linear Regression tests. We assessed seed coat and seed mass covariation through standardized major-axis allometric regressions. Harder seeds were larger than softer ones. Seed traits affect removal rates, as tougher and heavier seeds had lower removal. Seed mass significantly predicts seed coat proportion in seven of the 14 species tested. Bird-dispersed species tend to exhibit lower proportions of seed coat as seed mass increases, whereas rodent-dispersed species apparently present the opposite trend, with seed coat proportion increasing with seed mass. Such difference may be caused by the contrasting seed predation pressure represented by birds and rodents. Energy allocation for defense, expressed in seed coat proportion, is greater in large seeds, as these are mostly dispersed by rodents whose propensity to cache and disperse seeds is greater for large and well-protected seeds.