Water and forest productivity

Water availability is a major factor influencing the distribution and productivity of the earth's vegetation, but details of the mechanisms by which its effects are felt are not well understood. This is due in large part to the interactions between water and vegetation, such as through interception and change in leaf-area, which affect rates of canopy photosynthesis and transpiration. Physiological differences among species are not always directly translated to differences among stands, emphasizing the importance of climate and microclimate as controls.

Leaf-area index (L) is a critical integrator of water availability and productivity, and changes in leaf-area, such as occur through thinning and understory control, may have dramatic effects on both. There is increasing evidence that L changes significantly within an annual cycle and from year to year, even in closed-canopy conifer stands. Consequently, the season and year in which a measurement of L is made may explain much of the variability noted before in its response to water availability and effects on productivity. Because carbon, water, and nutrient cycles are so closely coupled, simulation models that represent both direct and indirect relationships are useful tools for understanding and managing forest ecosystems.     

桉树生态问题及发展思路

列举了桉树生态问题争论的主要事件及焦点,阐述了桉树的水分利用、养分消耗和化感作用,在对桉树生态问题进行评价的基础上,提出了正视桉树人工林的生态问题,强化规划、设计、施工监督和质量管理;遗传育种应由单一性状向多性状转变,培育具有节水保肥的新品种和优良无性系;注重桉树菌根等新技术的研发与应用,提高桉树对土壤养分的有效利用和保水能力;采取综合营林措施,维护桉树林的土壤养分平衡;开展固氮菌接种和维持林地的持久生产力等桉树发展思路。     

Forest management effects on in situ and ex situ slash pine forest carbon balance

In this study we analyzed the effect of silviculture on carbon (C) budgets in Pinus elliottii (slash pine) plantations on the southeastern U.S. Coastal Plain. We developed a hybrid model that integrates a widely used growth and yield model for slash pine with allometric and biometric equations determined for long-term C exchange studies to simulate in situ C pools. The model used current values of forest product conversion efficiencies and forest product decay rates to calculate ex situ C pool. The model was validated from a variety of sources, accurately simulating C estimates based on multiple measurement techniques and sites. Site productivity was the major factor driving C sequestration in slash pine stands. On high productivity sites, silvicultural schemes that promote sawtimber-type products are more suitable for increasing C storage (even not taking in account the consequent economical revenues associated with sawtimber production). When rotation length was increased from 22 to 35 years on unthinned and thinned stands, respectively, we estimated net increments of 26 and 20 MgC ha⁻¹ in average C stock of the first five rotations. Even though in situ C pool in slash pine accounts for most of this net increment, C in sawtimber products increased from 8 and 14 to 23 and 24 MgC ha⁻¹, on unthinned and thinned stands, respectively. Thinning effects on net C stock depended on intensity and timing of intervention, mainly due to changes in diameter classes that promote higher proportion of long-lived products. Emissions associated with silvicultural activities, including transportation of logs to the mill, are small compared to the magnitude of net C sequestration, accounting for between 2.2 and 2.3% of gross C stock. This slash pine plantation C sequestration model, based on empirical and biological relationships, is appropriate for use in regional C stock assessments or for C credit verification.     

Boom and bust of a moose population: a call for integrated forest management

There is increasing pressure to manage forests for multiple objectives, including ecosystem services and biodiversity, alongside timber production. However, few forests are currently co-managed for timber and wildlife, despite potential economic and conservation benefits. We present empirical data from a commercial Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) production system in southern Norway in which moose (Alces alces) are an important secondary product. Combining long-term hunting and forestry records, we identified temporal variation in clear-felling over the past five decades, peaking in the 1970s. Herbicide treatment of regenerating stands and a fivefold increase in moose harvest has lead to a reduction in availability of successional forest per moose of >90 % since the 1960s. Field estimates showed that spraying with the herbicide glyphosate reduced forage availability by 60 and 96 % in summer and winter, respectively, 4 years after treatment. It also reduced moose use and habitat selection of young spruce stands compared with unsprayed stands. Together these lines of evidence suggest that forest management led to an increase in moose carrying capacity during the 1970s and a subsequent decline thereafter. This is likely to have contributed to observed reductions in moose population productivity in southern Norway and is counter to sustainable resource management. We therefore call for better integration and long-term planning between forestry and wildlife management to minimise forest damage and the development of large fluctuations in ungulate populations.     

Leaf traits in relation to crown development, light interception and growth of elite families of loblolly and slash pine

Crown architecture and size influence leaf area distribution within tree crowns and have large effects on the light environment in forest canopies. The use of selected genotypes in combination with silvicultural treatments that optimize site conditions in forest plantations provide both a challenge and an opportunity to study the biological and environmental determinants of forest growth. We investigated tree growth, crown development and leaf traits of two elite families of loblolly pine (Pinus taeda L.) and one family of slash pine (P. elliottii Mill.) at canopy closure. Two contrasting silvicultural treatments -- repeated fertilization and control of competing vegetation (MI treatment), and a single fertilization and control of competing vegetation treatment (C treatment) -- were applied at two experimental sites in the West Gulf Coastal Plain in Texas and Louisiana. At a common tree size (diameter at breast height), loblolly pine trees had longer and wider crowns, and at the plot-level, intercepted a greater fraction of photosynthetic photon flux than slash pine trees. Leaf-level, light-saturated assimilation rates (A(max)) and both mass- and area-based leaf nitrogen (N) decreased, and specific leaf area (SLA) increased with increasing canopy depth. Leaf-trait gradients were steeper in crowns of loblolly pine trees than of slash pine trees for SLA and leaf N, but not for A(max). There were no species differences in A(max), except in mass-based photosynthesis in upper crowns, but the effect of silvicultural treatment on A(max) differed between sites. Across all crown positions, A(max) was correlated with leaf N, but the relationship differed between sites and treatments. Observed patterns of variation in leaf properties within crowns reflected acclimation to developing light gradients in stands with closing canopies. Tree growth was not directly related to A(max), but there was a strong correlation between tree growth and plot-level light interception in both species. Growth efficiency was unaffected by silvicultural treatment. Thus, when coupled with leaf area and light interception at the crown and canopy levels, A(max) provides insight into family and silvicultural effects on tree growth.     

Disturbances and structural development of natural forest ecosystems with silvicultural implications,using Douglas-fir forests as an example

Forest managers need a comprehensive scientific understanding of natural stand development processes when designing silvicultural systems that integrate ecological and economic objectives, including a better appreciation of the nature of disturbance regimes and the biological legacies, such as live trees, snags, and logs, that they leave behind. Most conceptual forest development models do not incorporate current knowledge of the: (1) complexity of structures (including spatial patterns) and developmental processes; (2) duration of development in long-lived forests; (3) complex spatial patterns of stands that develop in later stages of seres; and particularly (4) the role of disturbances in creating structural legacies that become key elements of the post-disturbance stands. We elaborate on existing models for stand structural development using natural stand development of the Douglas-fir—western hemlock sere in the Pacific Northwest as our primary example; most of the principles are broadly applicable while some processes (e.g. role of epicormic branches) are related to specific species. We discuss the use of principles from disturbance ecology and natural stand development to create silvicultural approaches that are more aligned with natural processes. Such approaches provide for a greater abundance of standing dead and down wood and large old trees, perhaps reducing short-term commercial productivity but ultimately enhancing wildlife habitat, biodiversity, and ecosystem function, including soil protection and nutrient retention.     

The interaction between organic layer and forest growth and forest development on former heathland

Heathland soils are characterized by high acidity and poor nutrient contents. Nutrient availability could then be an important factor in forest growth and development on these soils. The hypothesis to be verified was 1. The enduring change in vegetation composition and production is of great influence especially on the development of the organic layer and on the nutrient distribution between this compartment and the mineral soil, and 2. As a result, forest nutrition and water supply will change during forest growth with consequences for forest development itself. In NW Germany heathland forest development are dominated by heathlands as the initial stage of the succession, naturally established pioneering pine dominated woodlands, and oak and beech dominated forests as the terminal stages. In a comparative study, within these stages of forest succession the nutrient and water supply in the organic layer were investigated with regards to the nutrient and water supply in the mineral soil and to the morphology of the organic layer itself. The successional development was associated with an increased productivity and a marked enrichment of organic material and nutrients in the organic layer, whereas the nutrient storage in the mineral soil was unchanged. The nutrient storage in the organic layer in the forested sites amounted to up to 80% of the plant-available nutrients within the organic layer–mineral soil system. The water supply increased too due to higher water storage and increasing root penetration within the organic layer. However, the increase in water supply was less marked than the nutrient enrichment. Especially the beech-dominated broad-leaved forests depend on higher nutrient and water supply of the organic layer. They have better growth conditions in the late stages of succession, due to an intense humus accumulation by the pioneering birch–pine woodlands. Consequently, the development of the organic layer facilitates the change of coniferous woodlands to forests and woodlands dominated by broad-leaved trees. Using pine as first planted tree is recommended to support this development.     

Influence of different forest conversion strategies on ground vegetation and tree regeneration in pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) stands: a case study in NE Germany

The conversion of anthropogenic into more natural, self-regenerating forests is one of the major objectives of forestry throughout Europe. In this study, we present investigations on permanent plots with different silvicultural treatment in NE German pine stands. Management of old-growth pine stands on acidic and nutrient-poor sandy sites differs in fencing, thinning, and planting of certain tree species. The investigations were carried out on the community, population, and individual level of the pine forest ecosystems. Thus, vegetation changes, size and height of tree populations, and height increment of tree individuals were observed over a time span of 6 years. Special attention was paid to short-lived tree species such as, e.g., Frangula alnus and Sorbus aucuparia, as well as to Fagus sylvatica as one of the most typical forest tree species of Central Europe. Vegetation changes are interpreted as a consequence of natural regeneration of formerly degraded forest sites, involving an increase in nutrient availability. High browsing pressure can be considered as a key factor for the inhibition of tree seedlings and growth of saplings. Some Sorbus aucuparia individuals, however, succeeded in growing out of the browsing height also in unfenced stands. Few found specimens of Fagus sylvatica proved that this species is able to establish spontaneously on these relatively dry, acidic sites under continental climate influence. Such natural regeneration processes, also including spontaneous rejuvenation of trees, can be integrated into silviculture as passive forest conversion management. An active management like thinning of stands, planting of trees, and fencing can accelerate forest conversion with regard to height growth and species number of trees.     

Long-term management impacts on carbon storage in Lake States forests

We examined carbon storage following 50+ years of forest management in two long-term silvicultural studies in red pine and northern hardwood ecosystems of North America’s Great Lakes region. The studies contrasted various thinning intensities (red pine) or selection cuttings, shelterwoods, and diameter-limit cuttings (northern hardwoods) to unmanaged controls of similar ages, providing a unique opportunity to evaluate long-term management impacts on carbon pools in two major North American forest types. Management resulted in total ecosystem carbon pools of 130-137 Mg ha⁻¹ in thinned red pine and 96-177 Mg ha⁻¹ in managed northern hardwoods compared to 195 Mg ha⁻¹ in unmanaged red pine and 224 Mg ha⁻¹ in unmanaged northern hardwoods. Managed stands had smaller tree and deadwood pools than unmanaged stands in both ecosystems, but management had limited impacts on understory, forest floor, and soil carbon pools. Total carbon storage and storage in individual pools varied little across thinning intensities in red pine. In northern hardwoods, selection cuttings stored more carbon than the diameter-limit treatment, and selection cuttings generally had larger tree carbon pools than the shelterwood or diameter-limit treatments. The proportion of total ecosystem carbon stored in mineral soil tended to increase with increasing treatment intensity in both ecosystems, while the proportion of total ecosystem carbon stored in the tree layer typically decreased with increasing treatment intensity. When carbon storage in harvested wood products was added to total ecosystem carbon, selection cuttings and unmanaged stands stored similar levels of carbon in northern hardwoods, but carbon storage in unmanaged stands was higher than that of thinned stands for red pine even after adding harvested wood product carbon to total ecosystem carbon. Our results indicate long-term management decreased on-site carbon storage in red pine and northern hardwood ecosystems, but thinning intensity had little impact on carbon storage in red pine while increasing management intensity greatly reduced carbon storage in northern hardwoods. These findings suggest thinning to produce different stand structures would have limited impacts on carbon storage in red pine, but selection cuttings likely offer the best carbon management options in northern hardwoods.     

藜蒴大面积人工造林技术初报

文章介绍了藜蒴大面积人工造林技术,包括种子的采集贮藏方法、播种育苗的一系列措施、造林抚育的一整套技术。     

Regulation of ponderosa pine foliar physiology and insect resistance mechanisms by basal area treatments

We compared foliar physiology and several measures of tree resistance to insect attack among ponderosa pine (Pinus ponderosa var. scopulorum Engelm.) trees growing in thinned stands. Measurements were made in a second-growth ponderosa pine forest in northern Arizona where the basal area treatments (6.9, 18.4, 27.6, 78.2 m(2) ha(-1)) have been experimentally maintained by frequent thinnings for 32 years before our measurements began in 1994. Most of the physiological characteristics measured were affected by the basal area treatments. As stand basal area increased from 6.9 to 78.2 m(2) ha(-1), predawn water potential, midday water potential, net photosynthetic rate, resin production, phloem thickness, and foliar toughness decreased. Foliar nitrogen concentration was greatest in trees in the intermediate basal area treatments. Our results show that the physiological condition of second-growth ponderosa pine can be manipulated by silvicultural control of stand basal area, and support the hypothesis that high stand basal area increases tree stress and decreases tree resistance to insect attack.     

Carbon sequestration of naturally regenerated Aleppo pine stands in response to early thinning

Sustainable forest management ought to include the production of non-use value, mainly in forests with low value of direct production. Predictions on climate change points out increase in aridity and changes in fire regime (increasing fire risk, recurrence and severity), particularly in the Mediterranean Basin. However, we have to question whether this implies a decrease in forest resilience and productivity. In summer 1994, large forest fires burned a huge surface of Aleppo pine stands in Spain. In areas naturally regenerated, we carried out early thinning and sampled 18 plots. In winter 2008 and 2009, we inventoried all pine trees in sampling plots, recording total height, diameter and canopy cover for scaling-up results to stand-level estimation. In addition, we destructively sampled 54 individual pine trees, selecting various thinning and dating treatments, to measure and estimate biomass and partitioning. The date of thinning influenced allometric relationships, earlier thinning stimulated the productivity of individual pine saplings, increasing the three components of carbon intake. Although, the total net carbon value was lower in almost all thinned plots (at least for short periods after thinning), differences were actually found depending on the cutting age and thinning severity. Control and thinned plots (mainly those thinned earlier and heavier) showed similar amounts of carbon but comprised in a low number of living trees with high productivity. Thus, productivity and carbon storage assessment should be monitored, in the long-term, to check prediction of proposed models for evaluation on early treatments.     

Carbon sequestration in Spanish Mediterranean forests under two management alternatives: a modeling approach

Management implications associated with two different silvicultural strategies in two Spanish pine forests (Scots pine stands in northern Spain and Mediterranean Maritime pine stands in Central Spain) were explored. Whole-stand yield, growth models and individual tree equations were used to estimate carbon stock in forests under different silvicultural alternatives and site indexes. Each alternative was evaluated on the basis of the land expectation value (LEV). Results reveal the appropriateness of implementing carbon payments, because it can clearly complement traditional management objectives in economic terms. Longer rotations on the poorest sites result in a positive economic return by introducing carbon output. The proportion of carbon stock in the final harvest relative to total fixed carbon is always higher in long rotation scenarios. However, short rotation systems produce the highest values of carbon MAI regardless of site index. The impact of carbon price is higher on the Maritime pine stands than on Scots pine stands. For both the species, changes in the discount rate have a minor impact on Carbon LEV. Notwithstanding, the proportion of total LEV due to carbon is greater when the discount rate increases.     

Impacts of changing climate on the productivity of Norway spruce dominant stands with a mixture of Scots pine and birch in relation to water availability in southern and northern Finland

A process-based ecosystem model was used to assess the impacts of changing climate on net photosynthesis and total stem wood growth in relation to water availability in two unmanaged Norway spruce (Picea abies) dominant stands with a mixture of Scots pine (Pinus sylvestris) and birch (Betula sp.). The mixed stands were grown over a 100-year rotation (2000-99) in southern and northern Finland with initial species shares of 50, 25 and 25% for Norway spruce, Scots pine and birch, respectively. In addition, pure Norway spruce, Scots pine and birch stands were used as a comparison to identify whether species' response is different in mixed and pure stands. Soil type and moisture conditions (moderate drought) were expected to be the same at the beginning of the simulations irrespective of site location. Regardless of tree species, both annual net canopy photosynthesis (P(nc)) and total stem wood growth (V(s)) were, on average, lower on the southern site under the changing climate compared with the current climate (difference increasing toward the end of the rotation); the opposite was the case for the northern site. Regarding the stand water budget, evapotranspiration (E(T)) was higher under the changing climate regardless of site location. Transpiration and evaporation from the canopy affected water depletion the most. Norway spruce and birch accounted for most of the water depletion in mixed stands on both sites regardless of climatic condition. The annual soil water deficit (W(d)) was higher on the southern site under the changing climate. On the northern site, the situation was the opposite. According to our results, the growth of pure Norway spruce stands in southern Finland could be even lower than the growth of Norway spruce in mixed stands under the changing climate. The opposite was found for pure Scots pine and birch stands due to lower water depletion. This indicates that in the future the management should be properly adapted to climate change in order to sustain the productivity of mixed stands dominated by Norway spruce.     

辽宁西部地区油松水土保持纯林改造与评价

辽宁省西部营造有大量用于水土保持的油松人工纯林。如何改造这些低效的纯林是生产实践中面临的一个严重问题。根据近自然林业思想,通过实践提出了带状皆伐栽植阔叶树,块状皆伐栽植阔叶树和林中空地、林缘等栽植阔叶树改造现有的油松纯林具体方法。论述了改造的对象和树种选择等问题,并详细介绍了每种方法的关键技术及其应用条件。通过实际调查和对比分析,对经过带状改造的油松林进行了评价。结果表明,16年后,采用上述方法改造的油松林具有明显的分层结构,林下植物物种多样性增加了23．5％-52．9％,土壤脲酶、磷酸酶和蔗糖酶活性比对照分别提高了6％-142％,46％-99％和31％-200％,松毛虫危害得到有效控制,水土保持功能也得到提高。图2表3参37。     

Physiology and genetics of tree growth response to moisture and temperature stress: an examination of the characteristics of loblolly pine (Pinus taeda L.)

Water stress and temperature impose fundamental limits to forest productivity. Stresses caused by fluctuating or extreme temperatures or limited water availability vary both seasonally and from year to year. The role of these stresses should be considered when investigating the causes of declines in forest productivity. Forest growth, or carbon gain, can be related quantitatively to three components: leaf area, rate of net photosynthesis and rate of respiration. This paper examines effects of temperature and water supply on these components with particular reference to loblolly pine (Pinus taeda L.), a species of economic importance in the southeastern United States where declines, of unknown cause, in forest productivity have been reported.     

Seasonal nutrient dynamics in white pine and white spruce in response to environmental manipulation

Seasonal retranslocation in white pine (Pinus strobus L.) and white spruce (Picea glauca (Moench) Voss) was examined in response to silvicultural treatments (scarification, annual fertilization application, and annual control of competing vegetation with herbicide) that changed both environmental conditions and the growth rate of the trees. Four years after plantation establishment and initial treatment, nutrient accumulation in current-year needles of white pine and retranslocation from 1-year-old needles were increased following the vegetation control treatment, which increased resource availability (nutrients, water and light) and, hence, growth rate. Nutrient accumulation also increased in current-year white spruce needles following the same treatment, whereas retranslocation decreased in 1-year-old white spruce needles. Correlations of retranslocation (N, P and K) with growth rate (shoot biomass increment) showed a strong positive relationship for white pine and a negative relationship for white spruce. Retranslocation of K was correlated with foliar and soil K concentrations; the availability of this nutrient was also significantly reduced by vegetation control. A general theory for the control of nutrient retranslocation in conifers, which is not based exclusively on either sink strength or soil nutrient availability, is proposed. We conclude that retranslocation response is species specific and related to the potential phenotypic growth response to changing environmental conditions and to short-term imbalance in the supply versus the demand for nutrients.     

The response of ground vegetation to structural change during forest conversion in the southern Black Forest

The aim of this study is to investigate the effects of forest conversion on forest floor vegetation. ‘Ecological’ forest conversion, as defined by an interdisciplinary southern Black Forest project group, describes the transformation of even-aged spruce (Picea abies L. H. Karst.) stands to structured continuous cover forests consisting of spruce (Picea abies), silver fir (Abies alba Mill.) and beech (Fagus sylvatica L.). In order to analyse the conversion process, four conversion stages were defined in a conceptual forest development model. Four forest districts deemed to be representative of the southern Black Forest region were selected for the study. The ground vegetation was initially classified independently from the stand structures. Subsequently, the relationship between stand structures, as determined by development stage, and ground vegetation was analysed. It was revealed that forest conversion modified the ground vegetation. The main factors influencing ground vegetation were the influence of broadleaves, predominately beech (F. sylvatica), on the canopy composition and litter coverage on the one hand; and the canopy coverage of spruce, the proportion of needle litter and the associated light penetration on the other. The prevalence of moss and vascular plant species preferring acidic sites found in spruce forests decreased during the transition process, whereas, species requiring a moderate base supply increased in abundance. The continuous cover forest representing the final stage of conversion increasingly contained a mixture of ground vegetation species normally associated exclusively with either conifer or deciduous forest. Due to the fact that there is an associated ground vegetation specific to the different stages of forest conversion in stands dominated by Norway spruce or European beech and a mixture in the latest conversion stages, large-scale forest conversion should be avoided in favour of management promoting a diversity of silvicultural goals and treatments in neighbouring stands. Only a variety of treatments ensures the maintenance of floristic diversity in the long-term.