How should leaf area, sapwood area and stomatal conductance vary with tree height to maximize growth?

Conventional wisdom holds that the ratio of leaf area to sapwood area (L/S) should decline during height (H) growth to maintain hydraulic homeostasis and prevent stomatal conductance (g(s)) from declining. We contend that L/S should increase with H based on a numerical simulation, a mathematical analysis and a conceptual argument: (1) numerical simulation--a tree growth model, DESPOT (Deducing Emergent Structure and Physiology Of Trees), in which carbon (C) allocation is regulated to maximize C gain, predicts L/S should increase during most of H growth; (2) mathematical analysis--the formal criterion for optimal C allocation, applied to a simplified analytical model of whole tree carbon-water balance, predicts L/S should increase with H if leaf-level gas exchange parameters including g(s) are conserved; and (3) conceptual argument--photosynthesis is limited by several substitutable resources (chiefly nitrogen (N), water and light) and H growth increases the C cost of water transport but not necessarily of N and light capture, so if the goal is to maximize C gain or growth, allocation should shift in favor of increasing photosynthetic capacity and irradiance, rather than sustaining g(s). Although many data are consistent with the prediction that L/S should decline with H, many others are not, and we discuss possible reasons for these discrepancies.     

Difference in shade tolerance affects foliage–sapwood response to thinning by two eucalypts

In eucalypt plantations in subtropical Australia, Eucalyptus dunnii exhibits greater diameter increment after thinning than more shade-tolerant Corymbia citriodora. To elucidate the mechanism underlying this difference, we investigated relationships between tree leaf area and sapwood area following thinning in 11-year-old E. dunnii and C. citriodora plantations. There was no significant difference in specific leaf area (SLA) between thinned and unthinned stands in E. dunnii and C. citriodora, whereas crown zone significantly affected SLA in the two eucalypts. At the whole-tree level non-linear leaf area (A_l)–sapwood area (A_s) relationships were measured in both eucalypts by thinning treatment. A significant increase in A_l/A_s ratio was only observed at the upper crown in thinned E. dunnii. The present results suggested the plastic nature of response of leaf characteristics in both eucalypts grown in different light environments and the species-specific pattern of crown-zone leaf responses to thinning in the two species, i.e. the top of the canopy appears to be driving greater growth response to thinning in the less shade tolerant E. dunnii compared with the more shade-tolerant C. citriodora. It is concluded that different thinning regimes should be applied in shade-tolerant and shade-intolerant eucalypt forests.     

Changes in soil acidity from 1927 to 1982–1984 in a forest area of south‐west Sweden

Reinvestigation of 90 soil profiles sampled for pH measurements in 1927 revealed a general decrease in pH with 0.3–0.9 units (measured electrometrically on field‐moist samples in water with the same ratio soil/water on both occasions). All soil horizons (A₀, A₂, B and the subsoil, C, at 70 cm depth) had become more acid beneath all types of canopy (beech, oak, spruce planted during different periods), but the spruce stands were on average more acid than the hardwoods. In the upper soil horizons (A₀ and A₂), old spruce stands were more acid than the young ones at both samplings, but this effect was small in the B horizon and absent in the C horizon. While the tree species effect and age effect in the spruce stands may be called biological acidification, the acidification of deeper horizons, now often below pH 4.5 and in the aluminium buffer range, seems difficult to explain without assuming an influence of acid deposition.     

Can community forestry contribute to household income and sustainable forestry practices in rural area? A case study from Tshapey and Zariphensum in Bhutan

Community forestry is an emerging success model of state–community partnership for forest management and poverty reduction. Bhutan's initial experience of forest management by user group is promising, but merits further study on how community forests have experienced with harvesting and income generation consistent with national forest policy. This study quantifies whether community forestry contribute to household income with equitable products and income distribution and gender inclusive participation; and community forests are managed applying the principles of sustainable harvest without compromising regeneration and productivity. We applied a combination of social and ecological methods using household interview and forest sampling plots. Our findings revealed that community forestry contributes to household income through harvesting and marketing of large trees, and non-wood forest products where markets are accessible. Household income, however, vary widely between rich and poor households with former capitalizing on commercial and latter on subsistence products. Timber harvesting is consistent with the principles of sustainable harvest without altering species composition, regeneration and productivity. To narrow income inequality, pro-poor approach to community forestry needs to target poor households with income diversification activities and market accessibility. The promising results are context-driven and warrant consolidation from other community forests experiencing harvest in Bhutan.     

Leaf angle responds to nitrogen supply in eucalypt seedlings. Is it a photoprotective mechanism?

We examined the adjustment of leaf angle (L theta) and foliar chlorophyll and xanthophyll chemistry in Eucalyptus nitens (Deane and Maiden) Maiden seedlings maintained in various nitrogen (N)-supply treatments over a 6-month period. Adjustment of L theta toward the vertical was greatest under conditions of foliar N deficiency and became incrementally more horizontal with increasing foliar N concentration. Photochemical efficiency (Fv/Fm) and quantum yield were lower in seedlings with low foliar N (low-N seedlings) in winter, but not in autumn. Low-N seedlings generally had low area-based chlorophyll concentrations and high xanthophyll-cycle conversion ratios, particularly during months of low temperature. Under mild temperature conditions, high concentrations of zeaxanthin and antheraxanthin were associated with lower electron transport rates (ETR). Incident light, Fv/Fm, ETR and total chlorophyll concentration were negatively correlated with L theta, with horizontal leaf orientation measured as 0 degrees and vertical leaf orientation as 90 degrees . Xanthophyll conversion ratio was positively correlated with L theta. Adjustments in L theta may play a role in photoprotection of E. nitens seedlings by assisting the leaf to balance its utilization and dissipation of energy.     

Forestland-cover changes in China’s tropical area: Historical patterns,implications, and policy options—a case study from Xishuangbanna

To effectively conserve tropical forested areas, it is useful to study and understand historical land-cover changes and local people’s attitudes toward the current land-uses. Using forest inventory data, and data collected from a survey of 145 households, we explored the forestland-cover changes, within the past 50 yr, in Xishuangbanna, China, and assessed the local residents’ perceptions toward the existing forestland management schemes. Our analysis showed that although forestland coverage has increased during the time-period studied, the increase can be mostly attributed to the expansion of rubber plantations. Forest degradation continues to be an issue in the area studied. The government’s attempts to mitigate the effects of rubber monocultures, by promoting environment-friendly plantations, have been proven challenging, which was mainly due to locals’ unfavorable view of the plan. Also, because of the recent decreasing prices of dry rubber, many locals have lost their interest in managing the forest plots they own, hindering further the successful implementation of the plan. Considering these challenges, and the strong negative effects of rubber monocultures on biodiversity, we argue that the current incentives should be further strengthened to promote more efficiently the government’s “Environment-Friendly Ecological Rubber Plantations” plan, and the joint management of the locals’ forest plots.     

Nutrient release from litter and humus in coniferous forest soils—a mini review

In northern coniferous forests nutrient release from litter occurs primarily in late stages of decomposition when mainly extensively lignified parts remain. An important regulating factor in these stages is the turnover rate of lignin and related compounds. Two factors which influence the decomposition rate of lignin are 1) nitrogen concentration which retards decomposition and 2) concentration of celluloses which increase the turnover rate. The amount and composition of humus which is formed may be dependent on the initial lignin concentration of the litter, which in its turn varies among species. These results from studies in northern coniferous forests are discussed in an ecosystem context.     

Understory dynamics after disturbance accelerate succession from spruce to beech-dominated forest—the Siggaboda case study

??Context

It is assumed that climate change will favour European beech (Fagus sylvatica L.) to Norway spruce (Picea abies [L.] Karst.) at its northern range margins due to climate change and induced disturbance events.

??Aims

An old-growth mixed forest of spruce and beech, situated near the northern beech margin, was studied to reveal effects of disturbances and response processes on natural forest dynamics, focussing on the understory.

??Methods

We carried out analyses on understory dynamics of beech and spruce in relation to overstory release. This was done based on a sequence of stand and tree vitality inventories after a series of abiotic and biotic disturbances.

??Results

It became apparent that beech (understory) has a larger adaptive capacity to disturbance impacts and overstory release (68 % standing volume loss) than spruce. Understory dynamics can play a key role for forest succession from spruce to beech-dominated forests. Disturbances display an acceleration effect on forest succession in the face of climate change.

??Conclusion

Beech is poised strategically to replace spruce as the dominant tree species at the study area. Due to an increasing productivity and a lower risk of stand failure, beech may raise into the focus of forestry in southern Sweden.     

Manipulation of conventional forest management practices to increase forest growth—results from the Skogaby project

Above ground dry mass production and N accumulation on an areal basis in stems, branches and needles as well as in litterfall in a Norway spruce stand in south Sweden treated with unlimited availability of water and nutrients (fertilisation with irrigation) or of water (irrigation) during a 6 year experimental period are presented. Fertilisation was made in liquid form on a weekly basis during the vegetation period with 100 kg N ha⁻¹ year⁻¹ during each year. The fertiliser also included a balanced composition of P, K, Ca, Mg and S as well as of micronutrients. Irrigation was carried out as soon as a 20 mm water storage deficit developed. It is concluded that there is a large potential to improve Norway spruce production through liquid fertilisation with irrigation. Stem and branch production of Norway spruce was almost doubled due to this treatment. Also, stand needle dry mass and litterfall were markedly increased in comparison with the control. Water and N availability were the two most limiting growth factors. During the experimental period, irrigation had a greater effect on growth than N addition. The gross N uptake increased by 450 kg ha⁻¹ as a result of 600 kg ha⁻¹ fertiliser addition. Needle retention was increased for irrigated trees but needle litterfall remained unchanged. Changing the forest management of Norway spruce to intensive cultivatation results in transitional carbon sequestration in both stand and soil compared with an untreated ecosystem. The largest long-term environmental value is, however, achieved if this cultivated renewable biomass is used as a substitute for fossil fuels. Wood utilisation options of intensively cultivated Norway spruce are discussed.     

Triterpene saponins from the roots of Dipsacus asper and their protective effects against the Aβ(25-35) induced cytotoxicity in PC12 cells

Three new triterpene saponins, named asperosaponin A-C (1-3), together with seven known triterpene saponins (4-10) were isolated from the roots of Dipsacus asper. The structures of compounds 1-3 were elucidated on the basis of detailed spectroscopic analysis and chemical methods. Compounds 1-3, 6-10 had significantly protective effects in PC12 cells against the Aβ(25-35) induced cytotoxicity. All the compounds isolated showed no cytotoxic activity against three human cancer cell lines, A-549, Bel-7402 and BGC-823.     

Intratree Variability of Tensile Strength Parallel to Grain in Chinese Fir and I-214 Poplar from Plantation

The variation of tensile strength parallel to grain in Chinese fir and I-214 poplar wood from plantations was studied in this paper. Aaccording to the national standards The Testing Methods for Physical and Mechanical Properties of Wood (GB 1927 to 1943 ? 1991), the small clear wood samples were cut and tested, which represent the south and north of trees with heights of 1.3, 3.3, 5.3 and 7.3 m. The results showed: the tensile strength parallel to grain of the north wood was higher than that of south wood. ANOVA shows that the tensile strength parallel to the grain with height is of significant difference (at 0.05 level).     

Fifteen Years of Forest Community Management in Niger: from a Technician’s Dream to Social Reality

Forest management policies in tropical countries have undergone a paradigm shift in the 1980s. International environmental policies have recommended redirecting natural resource management from state control to approaches giving responsibilities to local people. In Niger, forest cooperatives and firewood rural markets characterized the transition in forest policies toward the integration of rural people in forest management. Forest management principles have been progressively adapted to the social and ecological context, since the establishment of the first cooperatives in 1986. Changes in forest policies concerned two fronts: forest management governance and forest management technical instruments. In this paper, the impact of governance and technical instruments on forest management is studied in two types of firewood rural markets found in Niger. Both rural markets have been designed to bring about a governance shift in favour of rural people. In one type of rural market, rigorous technical instruments were added, consisting in a rotational system among several plots to be harvested in the forest. This paper shows that in the implementation of rural markets, the shift is mainly on governance of forest management, and not so much on technical instruments. The general management principles remain based on scientific knowledge and are not enforced by rural people. These principles have been shown to be inappropriate with regard to Sahelian people’s representation of space, but because they are scientific, they cannot be questioned. The study suggests that sustainable forest management will be better served by interesting rural people in the rural markets, and thereby promoting their appropriation of forest resources, than by defining rigorous technical rules.     

Why does leaf nitrogen decline within tree canopies less rapidly than light? An explanation from optimization subject to a lower bound on leaf mass per area

A long-established theoretical result states that, for a given total canopy nitrogen (N) content, canopy photosynthesis is maximized when the within-canopy gradient in leaf N per unit area (N(a)) is equal to the light gradient. However, it is widely observed that N(a) declines less rapidly than light in real plant canopies. Here we show that this general observation can be explained by optimal leaf acclimation to light subject to a lower-bound constraint on the leaf mass per area (m(a)). Using a simple model of the carbon-nitrogen (C-N) balance of trees with a steady-state canopy, we implement this constraint within the framework of the MAXX optimization hypothesis that maximizes net canopy C export. Virtually all canopy traits predicted by MAXX (leaf N gradient, leaf N concentration, leaf photosynthetic capacity, canopy N content, leaf-area index) are in close agreement with the values observed in a mature stand of Norway spruce trees (Picea abies L. Karst.). An alternative upper-bound constraint on leaf photosynthetic capacity (A(sat)) does not reproduce the canopy traits of this stand. MAXX subject to a lower bound on m(a) is also qualitatively consistent with co-variations in leaf N gradient, m(a) and A(sat) observed across a range of temperate and tropical tree species. Our study highlights the key role of constraints in optimization models of plant function.     

Indigenous knowledge in a ‘modern’ sustainable agroforestry system—a case study from eastern Brazil

The case of an agroforestry farm in the coastal mountain area of the federal state of Bahia, Brazil, is used to highlight benefits of the integration of traditional knowledge into a scientifically based farming system. Special attention is given to the selection, combination and management of the crops cultivated. Working hypotheses on the rationale of some major measures are suggested and discussed from a synecological point of view. The results show that under the site conditions the forest garden provides cocoa yields without external inputs at a level which, in the surrounding cocoa plantations, can only be attained by the use of considerable amounts of fertilizer and pesticides.