南平溪后杉木林取代杂木林后土壤肥力变化的研究

 本文对福建省南平溪后70年生杉木丰产林与杂木林的土壤肥力进行对比研究。结果表明：与前茬杂木林相比,70年生杉木林下土体较紧实,土壤有机质和营养元素含量降低,土壤酶活性和氧化代谢能力减弱。目前70年生杉木丰产林之所以仍保持较高的土壤肥力水平,主要是杉木林林冠疏开后林下植物多样性提高及生物量增加的缘故。     

山杨林林分密度效应动态模拟

 本文用林窗模型研究了小兴安岭南坡山杨林林分密度动态过程,在给定林分初始条件后,模拟了林分密度、断面积、生物量、叶面积指数和生产力150年的变化。用林分密度效应的3/2法则和产量恒定法则检验模拟林分,结果表明模拟林分密度发展与理论预测相符合。通过本文的研究既检验了林窗动态模型又印证了林分密度效应理论。     

林分随机生长模型与Richard模型

本文从一般的假设出发,很自然导出连续状态空间的树木直径分布生长方程,证明此方程解的存在性,并给出一个例子说明Richards方程是直径分布生长方程的一个特解的二阶矩．     

Interference of shape Choricarpia leptopetala by shape Lantana camara with nutrient enrichment in mesic forests on the Central Coast of NSW

Suppression of Choricarpia leptopetala (F. Muell.) Domin., an early native coloniser of mesic forests, by Lantana camara L. was evaluated using field-based variable density and substitution experiments. Sites were located in disturbed areas within wet sclerophyll forest and warm temperate rainforest near Lake Macquarie on the Central Coast of NSW. In the variable density experiment, C. leptopetala growth was significantly suppressed by 36.4% from 3.3 to 2.1 g plant^-1 in the presence of equal proportions of L. camara at a total density of 20 seedlings m^-2, only when nutrients (60 g m^-2 of a slow release NPKS fertiliser) were added to the soil surface. Lantana camara growth significantly increased by 14.6% from 4.1 to 4.7 g plant^-1 when nutrients were added. At a density of 40 seedlings m^-2, growth of C. leptopetata was suppressed by 37.5% from 3.2 to 2.0 g plant^-1 in the zero nutrient treatment with equal proportions of L. camara, and was further suppressed by 40.0% from 2.0 to 1.2 g plant^-1 with the addition of nutrients. Lantana camara growth significantly increased by 43.7% from 2.3 to 3.3 g plant^-1 when nutrients were added. Pure stands of C. leptopetala did not respond significantly to nutrient addition at either density. In the substitution experiment (with a constant density of 20 seedlings m^-2), C. leptopetala growth was significantly suppressed by 44.1% from 3.4 to 1.9 g plant^-1 when L. camara reached 75% of stand composition in the zero nutrient treatment and by 43.2% from 3.7 to 2.1 g plant^-1 when it reached 50% of stand composition in the nutrient addition treatment.The results link interference and suppression of native colonisers by exotic invaders with demonstrated increases in resource availability following ecosystem disturbance. Lantana camara is able to take better advantage of increased resource availability than C. leptopetala, thereby accumulating more biomass and suppressing the growth of C. leptopetala. Suppression of C. leptopetala also increased when the density of L. camara was increased. Consequently, the negative effect of the invading species on the indigenous species is both nutrient-addition and density dependent. Models describing interference in ecosystem recovery following disturbance need to include interference processes associated with weed invasion that disadvantage indigenous species.Nomenclature: Harden (1990).     

Natural regeneration of forest related to the spatial structure of trees: A study of two forest communities in Western Carpathians,southern Poland

The existence of a relationship between the spatial pattern of trees and the distribution of young individuals beneath the canopy has been tested in the beech (Fagus sylvatica) and spruce (Picea abies) — fir (Abies alba) forests in the mountainous region, using two different methods. The first method was the analysis of spatial pattern of individuals, the second one was based on calculating sums of influences of all trees occurring within analysed plot on a given point on the forest floor. Results of spatial pattern analyses were surprisingly consistent: almost all mature trees and seedlings didplayed a random pattern of spatial arrangement. However, there is a clear, although statistically insignificant tendency towards uniformity of spatial pattern with increasing sizes of analysed trees. Results of comparing sums of influences on regularly distributed points with sums of influences on seedlings or saplings revealed no tendency in forest regeneration to concentrate in places, where the sums were smaller than the average for a plot. This, coupled with the dominance of random spatial pattern of trees, suggests, that viewed on a small spatial scale, influence of competition among forest trees on their spatial arrangement is obscured by other factors, which are not closely related to the distribution of individuals.     

Analysis of stand density effects on canopy structure: a conceptual approach

Summary A few assumptions were used to generate a series of specific, quantitative predictions for the relationships between stand density and various dimensional measures of canopy structure. The predictions, each indicating an increase in mean crown size as density decreased, appeared to be reasonable and intuitive. Predictions were compared to data for two conifer species with different crown forms, Pinus contorta var. latifolia and Abies lasiocarpa. Results of these comparisons were mixed — the linear, directly measured dimensions were consistent with predicted relationships, but dimensions calculated from the linear measures were not. Re-examination of the original assumptions indicated that the model should account for crown shyness (engagement/disengagement) to adequately reflect the influence of stand density on canopy structure. The results also indicated a strong association between stand height and measures of mean crown size. Mean crown size of lodgepole pine was altered much more by density than was mean crown size of subalpine fir, due primarily to the different relative shade tolerances of the two species. Some of the observed differences between species may also reflect the range of densities examined and uneven spacing in the unmanaged natural stands.     

The effect of two growth forms of Norway spruce on stand development and radiation interception: a model analysis

Summary Development of tree and canopy structure, and interception of photosynthetically active radiation (PAR) were studied in two model stands of Norway spruce consisting of trees with rapid versus slow site capture. The tree models were derived using Burger's (1953) sample tree material, from which two subpopulations of dominant trees were selected using the rate of horizontal site capture of the tree crowns as the criterion of division. The development of stand structure and interception of PAR were simulated in the two model canopies. The simulation period covered the period from tree age 15–80 years. The average development of the trees in the two subpopulations proved to be very different. The rapidly expanding trees were characterized by low mean within-crown needle area density and a long crown. The slowly expanding trees were smaller but had a higher mean within-crown needle area density. Up to approximately 40 years of age the stand of rapidly expanding trees contained more leaf area and intercepted more radiation than the stand of slowly expanding trees, when canopy cover was held constant. After 40 years of age this relationship was reversed due to the subsequent decline of leaf area in the stand of rapidly expanding trees and the increase in leaf area in the stand of slowly expanding trees. The biological relevancy and silvicultural implications of the simulated patterns of tree and stand development are discussed.     

Amelanchier alnifolia vegetation in eastern Idaho,USA and its environmental relationships

Fifteen shrub stands of Amelanchier alnifolia vegetation were studied using Braun-Blanquet procedures, tabulated, and ordered by Twinspan, Decorana, and field experience into 5 groups of stands. The stands occurred on the lower slopes of the southwestern Teton and southeastern Big Hole mountains of eastern Idaho and in-and outside a U.S. Forest Service exclosure above the Hoback River in adjacent Wyoming. The ecology of this Amelanchier vegetation as a whole and of the 5 groups of stands is discussed using Jenny's factors of soil formation (1941, 1958, 1980) as a framework. Plant indicator values (Ellenberg 1979, 1988) which rank species on their occurrences in relation to light, temperature, continentality of climate, water availability, soil reaction (pH), and soil nitrogen supply, were independently assigned to the 121 species of vascular plants encountered in the described stands.     

Structure and floristics of secondary and old-growth forest stands in lowland Costa Rica

We characterized stand structure and floristic composition of woody life forms in three, 16–18 yr old secondary stands that regenerated after pasture abandonment, and three nearby old-growth stands of tropical rain forest in lowland Costa Rica. Basal area and stem density for each of four plant size classes (seedlings, saplings, treelets, trees) were similar among stand types, but density of adult canopy palms (individuals 10 cm DBH), was lower in the secondary stands. We estimate that 15% of the basal area of stems 10 cm DBH correspond to remnant trees in our secondary stands. The observed rapid woody regrowth compared to other published studies in the lowland neotropics, can be attributed to moderate land use and possibly, to the influence of nutrient-rich volcanic soils in the study area. Overall, plant species richness was lower in the secondary stands, but this difference was less pronounced in the smallest size classes (seedlings, saplings). Median percent similarity of all pairwise stand comparisons showed that floristic composition of saplings (stems 1 m tall and 5 cm DBH) was more similar between secondary and old-growth stands than for trees (stems 10 cm DBH). Because the potential value of secondary forests in conserving woody plant diversity appears highest for the young size classes, we suggest that further studies on floristic composition, especially those addressing the dynamics of the understory component, are needed to refine our understanding of the role of this natural resource in the maintenance of plant biodiversity in disturbed landscapes.     

Spatial and temporal patterns of root distribution in developing stands of four woody crop species grown with drip irrigation and fertilization

In forest trees, roots mediate such significant carbon fluxes as primary production and soil CO₂ efflux. Despite the central role of roots in these critical processes, information on root distribution during stand establishment is limited, yet must be described to accurately predict how various forest types, which are growing with a range of resource limitations, might respond to environmental change. This study reports root length density and biomass development in young stands of eastern cottonwood (Populus deltoidies Bartr.) and American sycamore (Platanus occidentalis L.) that have narrow, high resource site requirements, and compares them with sweetgum (Liquidambar styraciflua L.) and loblolly pine (Pinus taeda L.), which have more robust site requirements. Fine roots (<1 mm), medium roots (1 to 5 mm) and coarse roots (>5 mm) were sampled to determine spatial distribution in response to fertilizer and irrigation treatments delivered through drip irrigation tubes. Root length density and biomass were predominately controlled by stand development, depth and proximity to drip tubes. After accounting for this spatial and temporal variation, there was a significant increase in RLD with fertilization and irrigation for all genotypes. The response to fertilization was greater than that of irrigation. Both fine and coarse roots responded positively to resources delivered through the drip tube, indicating a whole-root-system response to resource enrichment and not just a feeder root response. The plastic response to drip tube water and nutrient enrichment demonstrate the capability of root systems to respond to supply heterogeneity by increasing acquisition surface. Fine-root biomass, root density and specific root length were greater for broadleaved species than pine. Roots of all genotypes explored the rooting volume within 2 years, but this occurred faster and to higher root length densities in broadleaved species, indicating they had greater initial opportunity for resource acquisition than pine. Sweetgum’s root characteristics and its response to resource availability were similar to the other broadleaved species, despite its functional resemblance to pine regarding robust site requirements. It was concluded that genotypes, irrigation and fertilization significantly influenced tree root system development, which varied spatially in response to resource-supply heterogeneity created by drip tubes. Knowledge of spatial and temporal patterns of root distribution in these stands will be used to interpret nutrient acquisition and soil respiration measurements. The US Government has the right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper. Mention of a commercial or proprietary product does not constitute endorsement or recommendation by the USDA Forest Service.