Spatial and temporal patterns at small scale in Austrocedrus chilensis diseased forests and their effect on disease progression

Austrocedrus chilensis is an endemic conifer of Patagonia that suffers a widespread mortality whose causes are a topic of discussion. Since Phytophthora austrocedrae is the most probable cause, we proposed that the spatial and temporal patterns of disease at small scale should reflect pathogen behavior. We aimed at characterizing the spatial and temporal patterns of diseased trees in different soil types and the effect of microsite variability on diseased trees spatial pattern. The spatial pattern of disease was influenced by soil type and tree density. In clay soils with low disease incidence (ca. 25%), the spatial pattern was random and not influenced by abiotic microsite conditions. When disease incidence increased (ca. 70%), concurring with denser plots, the spatial pattern was clustered, as a result of an infection process, and it was independent of microsite variability. In soils with better drainage conditions, that is, alluvial soils with volcanic ash input and coarse textured volcanic soils, the disease was clustered and associated with flat microtopographies. The progression of the disease at small scale was influenced by soil, precipitation and tree density. The spatial and temporal patterns of disease progression were associated with a contagion process and with environmental variables that affect drainage, coinciding with Phytophthora biology and requirements. Our results concur in pointing at Phytophthora as the cause of A. chilensis disease in the study area. Management practices should be urgently applied in order to minimize the spread of the inoculum.     

Nutrient cycling in Nothofagus pumilio forests along an altitudinal gradient in Tierra del Fuego,Argentina

Nothofagus pumilio (lenga) forests form monocultures from sea level to timberline in Tierra de Fuego, Argentina. Past studies suggested that the life form change from erect forest to krummholz had advantages to forest function. Aboveground net primary productivity (NPP) and organic matter production per unit leaf area and growing season day were higher in krummholz than in adjacent short erect forests at lower elevation. We compared tall erect, short erect, and krummholz lenga stands in terms of the concentration, accumulation, fluxes, turnover, and use-efficiency of nutrients (N, P, K, Ca, and Mg) along an elevation gradient (220–640 m) in Tierra del Fuego (Valle de Andorra, 54°9′S, 68°2′W). With few exceptions, patterns of decreasing values of nutrient concentration, nutrient stock, nutrient flux, and nutrient turnover reversed at the krummholz, which had higher values of these parameters than an adjacent short erect forest at lower elevation. Nutrient cycles accelerated at the krummholz but nutrient use-efficiency of organic matter production and nutrient return to the forest floor decreased. Several functional attributes of krummholz support the notion that this life form has functional advantages at timberline. For example: (1) a shift towards fast turnover compartments for nutrient storage; (2) a switch from high storage of nutrients in stemwood biomass to nutrient storage in branch biomass; (3) faster rates of internal nutrient transfer (recycling and retention); (4) greater dependence on biotic recycling of nutrients; (5) morphological characteristics associated with leaf size, leaf duration, number of leaves, and leaf area to sapwood area ratio. Nutrient cycling attributes measured in Tierra del Fuego span values reported for forests across temperate and boreal latitudes, with krummholz and tall erect forests representing either the low or the high values. Lenga krummholz is different from coniferous krummholz in North America's tundra in that lenga appears to be a nutrient-rich forest that acts as a nutrient sink, while coniferous krummholz scavenge for nutrients on tundra soils and reduce their nutrient pools.     

Effects of nurse shrubs and tree shelters on the survival and growth of two Austrocedrus chilensis seedling types in a forest restoration trial in semiarid Patagonia, Argentina

? Context

Harsh environmental conditions in xeric sites of Andean Patagonia, affect the emergence, survival, and growth of either naturally grown or planted Austrocedrus seedlings.

? Aims

We evaluated the effects of nurse shrubs and tree shelters on the survival and growth of Austrocedrus seedlings as compared to unprotected (control) areas and how differently produced seedling types perform under these treatments.

? Methods

In 2006, two Austrocedrus seedling types (1?+?2?=?S1 and Plug 2?+?1?=?S2) were planted under shrub cover (C1), tree shelter (C2), and control (C3). Soil surface temperature and moisture were measured for each treatment during the first growing season, while seedling survival and height were recorded during 5 years.

? Results

Survival was not affected by cover type the first year, but it was affected by seedling type (S1?>?S2). After an extremely dry second growing season, seedling survival significantly decreased in relation to either cover or seedling type. Five years after plantation, survival was significantly higher for C1 and C2 (40?C60 %) as compared to C3-S2 (18 %). Seedling height was significantly affected by cover, but not by seedling type.

? Conclusions

The use of nurse shrubs and/or tree shelters is useful in Austrocedrus seedling restoration trials. Seedling morphology appears as relevant for survival in semiarid environments.     

Understory woody vegetation in manmade Mediterranean pine forests: variation in community structure along a rainfall gradient

Natural regeneration that occurs in the understory of Mediterranean pine monocultures provides the basis for the transition of these simply structured systems toward a more complex and sustainable state. However, the course and consequences of this process, and its relationships with environmental and silvicultural variables, are still inadequately understood. We investigated the relationship between rainfall amount and understory woody vegetation (UWV) structure in mature (40–50 year) Pinus halepensis plantations in the Mediterranean zone of Israel, where rainfall ranges from 280 mm/year in the south to 900 mm/year in the north. We measured abundance, diversity and species composition on south- and north-facing slopes, in forest sites distributed along the rainfall gradient. UWV abundance, as measured by cover percentage and height, increased with rainfall amount along the entire gradient (2–113% and 0.1–3.4 m, respectively), more rapidly on north-facing slopes. Species composition varied along the rainfall gradient, with ranges of species occurrences corresponding to those in unforested habitats. The relationship between rainfall and UWV species richness was positive throughout most of the rainfall gradient, possibly with a shift in pattern at the highest rainfall levels. UWV richness increased sharply with increasing abundance, up to a certain point with no further increase in richness as abundance increased further. We concluded that UWV structure in the studied forest environment and climatic range is strongly determined by rainfall and suggested that the design and management of Mediterranean forests should focus more on optimizing water availability for the various components.     

Ecological integrity of remnant montane forests along an urban gradient in the Sierra Nevada

Urban development typically has extensive and intensive effects on native ecosystems, including vegetation communities and their associated biota. Increasingly, urban planning strives to retain elements of native ecosystems to meet multiple social and ecological objectives. The ecological integrity of native forests in an urbanizing landscape is challenged by a myriad of impacts, such as forest management and invasive species. Environmental protection efforts in the Lake Tahoe basin, spanning the California/Nevada border in the Sierra Nevada mountains, over the past half century have resulted in the retention of thousands of parcels of remnant native forest located throughout the urbanizing landscape. The basin landscape provides an opportunity to evaluate the effects of land development on the composition and structure of remnant native forests along a gradient of urbanization. We sampled 118 sites located in remnant forests in the lower montane zone surrounded by 0–70% development. We also sampled forest structure in the landscape surrounding 75 of these sites to evaluate the contribution of remnant forests to the retention of native forest elements in the larger landscape. We characterized plant species composition and cover, vertical structure, and the density of trees, snags, and logs, as well as levels of ground disturbance and human activity. We found that remnant native forests retained much of their compositional and structural character along the development gradient, including large tree density, total canopy cover, and plant species richness. Notable exceptions were reductions in the density and decay stage of snags and logs, and the density of understory trees. We also observed increases in the richness and cover of herb and grass species and increases in the number of exotic plant species. In contrast, structural complexity was reduced in the landscape surrounding forest remnants in all measures except large tree density. We conclude that remnant native forests contribute significantly to maintaining native species in an urbanizing landscape, and that land conservation practices have an important role to play in protecting native forest ecosystems.     

Carbon stock of trees along an elevational gradient in temperate forests of Kedarnath Wildlife Sanctuary

The estimation of carbon density of high altitude forests was carried out at five different sites along an elevational gradient from 1550 m to 3550 m in a part of Kedarnath Wildlife Sanctuary, which is one of the largest protected areas of the Garhwal Himalaya, India. Among the study sites the above ground biomass density (AGBD) ranged from 202.72 Mg·ha-1 (Site 5) to 718.75 Mg·ha-1 (Site 1) and below ground biomass density (BGBD) from 61.00 Mg·ha-1 (Site 5) to 203.04 Mg·ha-1 (Site 1). The total biomass density (TBD) also followed similar trend, where the lowest value (263.73 Mg·ha-1 ) was observed at Site 5 and the highest (921.79 Mg·ha-1 ) at Site 1. The total carbon density (TCD) ranged from 131.86 Mg·ha-1 (Site 5) to 460.89 Mg·ha-1 (Site 1), which indicates that the carbon density of forests reduces with increasing elevation.     

Carbon accumulation along a stand development sequence of Nothofagus antarctica forests across a gradient in site quality in Southern Patagonia

Above- and below-ground C pools were measured in pure even-aged stands of Nothofagusantarctica (Forster f.) Oersted at different ages (5–220 years), crown and site classes in the Patagonian region. Mean tissue C concentration varied from 46.3% in medium sized roots of dominant trees to 56.1% in rotten wood for trees grown in low quality sites. Total C concentration was in the order of: heartwood > rotten wood > sapwood > bark > small branches > coarse roots > leaves > medium roots > fine roots. Sigmoid functions were fitted for total C accumulation and C root/shoot ratio of individual trees against age. Total C accumulated by mature dominant trees was six times greater than suppressed trees in the same stands, and total C accumulated by mature dominant trees grown on the best site quality was doubled that of those on the lowest site quality. Crown classes and site quality also affected the moment of maximum C accumulation, e.g. dominant trees growing on the worse site quality sequestered 0.73 kg C tree⁻¹ year⁻¹ at 139 years compared to the best site where 1.44 kg C tree⁻¹ year⁻¹ at 116 years was sequestered. C root/shoot ratio decreased over time from a maximum value of 1.3–2.2 at 5 years to a steady-state asymptote of 0.3–0.7 beyond 60 years of age depending on site quality. Thus, root C accumulation was greater during the regeneration phase and for trees growing on the poorest sites. The equations developed for individual trees have been used to estimate stand C accumulation from forest inventory data. Total stand C content ranged from 128.0 to 350.9 Mg C ha⁻¹, where the soil C pool represented 52–73% of total ecosystem C depending on age and site quality. Proposed equations can be used for practical purposes such as estimating the impact of silvicultural practices (e.g. thinning or silvopastoral systems) on forest C storage or evaluating the development of both above- and below-ground C over the forest life cycle for different site qualities for accurate quantification of C pools at regional scale.     

SOIL NITROGEN MINERALIZATION UNDER NORTHERN HARDWOOD FORESTS ALONG A SULFATE AND NITRATE DEPOSITION GRADIENT IN THE GREAT LAKES REGION

INTRODUCTIoNChangesinsoilNmineralizationratescouIdbeanearlywarningofsoilNavaila-bilityoreventualforestdeclinesinceNisoftenan.importantnutrientforgrowth(Keeneyl98O;Leaetal.l982;Vitouseketal-l982).Nitrogenmineralizationinvolvestwodistinctprocessesfammonification,inwhichNH:isformedfromorganiccom-pounds,andnitrification,theoxidationofNH:toNO3.ManystudiesofatmosphericdepositionimpactsonforestshavetargetedsoilNmineraIizationusingsimulatedaciddepositionundercontrolledlaboratoryconditions(T…     

Fine root morphological adaptations in Scots pine, Norway spruce and silver birch along a latitudinal gradient in boreal forests

Variability in short root morphology of the three main tree species of Europe's boreal forest (Norway spruce (Picea abies L. Karst.), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth)) was investigated in four stands along a latitudinal gradient from northern Finland to southern Estonia. Silver birch and Scots pine were present in three stands and Norway spruce was present in all stands. For three fertile Norway spruce stands, fine root biomass and number of root tips per stand area or unit basal area were assessed from north to south. Principal component analysis indicated that short root morphology was significantly affected by tree species and site, which together explained 34.7% of the total variability. The range of variation in mean specific root area (SRA) was 51-74, 60-70 and 84-124 m(2) kg(-1) for Norway spruce, Scots pine and silver birch, respectively, and the corresponding ranges for specific root length were 37-47, 40-48 and 87-97 m g(-1). The range of variation in root tissue density of Norway spruce, Scots pine and silver birch was 113-182, 127-158 and 81-156 kg m(-3), respectively. Sensitivity of short root morphology to site conditions decreased in the order: Norway spruce > silver birch > Scots pine. Short root SRA increased with site fertility in all species. In Norway spruce, fine root biomass and number of root tips per m(2) decreased from north to south. The differences in morphological parameters among sites were significant but smaller than the site differences in fine root biomass and number of root tips.     

Photosynthetic capacity and nitrogen partitioning in foliage of the evergreen shrub Daphniphyllum humile along a natural light gradient

We examined the effects of leaf age and mutual shading on the morphology, photosynthetic properties and nitrogen (N) allocation of foliage of an evergreen understory shrub, Daphniphyllum humile Maxim, growing along a natural light gradient in a deciduous Fagus crenata-dominated forest in Japan. Seedlings in high-light environments were subject to greater mutual shading and 1-year-old foliage survival was lower than in seedlings in low-light environments, indicating that the survival rates of foliage were related to the degree of mutual shading. Although specific leaf area (SLA) in current- and 1-year-old foliage was curvilinearly related to daily photosynthetic photon flux (PPF), SLA was unaffected by leaf age, indicating that foliage in D. humile may not acclimate morphologically to annual changes in light caused by mutual shading. Light-saturated net photosynthetic rates (Pmax) were correlated with daily PPF in current-year foliage. In addition, a strong, positive relationship was found between nitrogen concentration per unit leaf area and Pmax. In contrast, the relationship among PPF, N and photosynthetic parameters in 1-year old foliage was weak because of the strong remobilization of N from older leaves to current-year foliage in plants growing in high light. However, the relationship between daily PPF and both photosynthetic N-use efficiency and the ratio of maximum electron transport rate to maximum carboxylation rate did not differ between current-year and 1-year-old foliage, suggesting that these responses help maintain a high photosynthetic efficiency even in older foliage. We conclude that D. humile maximizes whole-plant carbon gain by maintaining a balance among photosynthetic functions across wide ranges of leaf ages and light environments.     

The potential of transforming simple structured pine plantations into mixed Mediterranean forests through natural regeneration along a rainfall gradient

The aim was to study the potential for using natural regeneration as a basis for transformation of simply structured conifer plantations into mixed Mediterranean forests. We studied the variation along a rainfall gradient, in the natural regeneration of tree species in the understory of planted 40- to 50-year-old Aleppo pine (Pinus halepensis) forests. The study was conducted within the Mediterranean zone of Israel, which extends from the semiarid northern Negev desert (rainfall ca. 300 mm yr⁻¹) in the south to the humid Upper Galilee in the north (ca 900 mm yr⁻¹). Cover and height, density, and species composition of regenerating trees were measured on south- and north-facing slopes in forest sites of comparable silvicultural history (site preparation methodology, planting density and thinning regime) distributed along the rainfall gradient. Altogether, 12 species of regenerating native broadleaved trees were found in the understory of the various forest sites. Surface cover, density and species richness increased linearly along the entire rainfall gradient, on both north- and south-facing slopes, ranging from zero in the driest forest sites up to 85% cover, 7980 trees ha⁻¹ and 4.5 species per 200 m², respectively, in the most humid ones. Species composition of regenerating trees was also related to rainfall amount, through changes in the relative importance of species along the rainfall gradient. The effect of topographic aspect on tree regeneration was inconsistent, i.e., the interaction Rainfall × Aspect was significant. Nevertheless, the general trend showed better regeneration on north-facing slopes. Most of the regenerating trees in the understory were small, i.e., less than 100 cm in height, with no clear effect of rainfall amount and topographic aspect on the relative abundance of height classes. Regeneration by Aleppo pine was highly variable among and within the different forest sites and ranged from 0 to 1565 trees ha⁻¹, with no clear relationships with rainfall amount and topographic aspect. In light of our results we propose that the future structure of forests should vary with respect to annual rainfall amount within possible silvicultural scenarios.     

Growth response to climate and drought change along an aridity gradient in the southernmost Pinus nigra relict forests

Context

Tree populations at the rear edge of species distribution are sensitive to climate stress and drought. However, growth responses of these tree populations to those stressors may vary along climatic gradients.

Aims

To analyze growth responses to climate and drought using dendrochronology in rear-edge Pinus nigra populations located along an aridity gradient.

Methods

Tree-ring width chronologies were built for the twentieth century and related to monthly climatic variables, a drought index (Standardized Precipitation–Evapotranspiration Index), and two atmospheric circulation patterns (North Atlantic and Western Mediterranean Oscillations).

Results

Growth was enhanced by wet and cold previous autumns and warm late winters before tree-ring formation. The influence of the previous year conditions on growth increased during the past century. Growth was significantly related to North Atlantic and Western Mediterranean Oscillations in two out of five sites. The strongest responses of growth to the drought index were observed in the most xeric sites.

Conclusion

Dry conditions before tree-ring formation constrain growth in rear-edge P. nigra populations. The comparisons of climate-growth responses along aridity gradients allow characterizing the sensitivity of relict stands to climate warming.     

Restoration of bottomland hardwood forests across a treatment intensity gradient

Large-scale restoration of bottomland hardwood forests in the Lower Mississippi Alluvial Valley (USA) under federal incentive programs, begun in the 1990s, initially achieved mixed results. We report here on a comparison of four restoration techniques in terms of survival, accretion of vertical structure, and woody species diversity. The range of treatment intensity allowed us to compare native recolonization to direct seeding and planting of Quercus nuttallii Palmer, and to an intensive treatment of interplanting two species that differed in successional status (early successional Populus deltoides Bartram ex Marsh. ssp. deltoides, with the mid-successional Q. nuttallii). Native recolonization varied in effectiveness by block but overall provided few woody plants. All active restoration methods (planting and direct seeding) were successful in terms of stocking. Populus grew larger than Quercus, reaching canopy closure after 2 years and heights after 2 and 5 years of 6 and 12.7 m, respectively. Planted Quercus were significantly larger than direct seeded Quercus in all years, but only averaged 1.4 m in height after 5 years. Interplanting did not seem to facilitate development of the Quercus seedlings. The early success of the interplanting technique demonstrated that environmental benefits can be obtained quickly by more intensive efforts. Native recolonization can augment active interventions if limitations to dispersal distance are recognized. These results should provide landowners and managers with the confidence to use techniques of varying intensity to restore ecosystem functions.     

Nitrogen mineralization along an altitudinal gradient: Interactions of soil temperature, moisture, and substrate quality

Net soil N mineralization was measured in situ for 2 consecutive years along a 2000-m altitudinal gradient encompassing six vegetation types in northern California. Both anaerobic and aerobic field incubations showed that soil temperature and moisture strongly controlled N release. In sealed container studies, N mineralization per unit of total Kjeldahl N ( ) had a Q₁₀ rate of 2 and varied between 5 and 38 g N/kg when moisture was abundant (anaerobic incubation). However, aerobic mineralization rates fell to between 2 and 22 g N/kg because of summer drought. Aerobic rates were greatest at mid-elevations (the mixed-conifer forest), and were reduced by cold temperatures at higher elevations and by soil drought at lower. The lowest rate found for any site was in a pine plantation scalped of topsoil a decade previously, during site preparation. Open-container incubations involving intact, 15-cm soil cores and ion-exchange resins produced mineralization rates correlated with potential growing days, but not with rates from sealed containers. The forest floor accounted for nearly all the net N mobilized on the coldest site, but only one-half to one-third of the N mobilized on warmer sites. Open containers have important advantages in assessing soil N dynamics.     

苏州太湖湖滨带不同水分梯度土壤氮的时空变异特征

选择苏州渔阳山保存较为良好典型的太湖湖滨带作为试验地,并根据距离水体的远近,将湖滨带从近水体到高岗地分别设置三个实验区,探讨了湖滨带土壤全氮、有效氮、微生物生物量氮的时间和空间变异特征。结果表明:太湖湖滨带土壤有效氮含量近水区中水区远水区,土壤湿度和水淹作用对土壤氮素含量具有影响作用;土壤有效氮呈明显季节波动秋季春季夏季,在植物生长旺盛季节维持较低水平;土壤有效氮随土层深度的增加逐渐减少;土壤有效氮与土壤全氮、土壤微生物生物量氮呈显著正相关关系。沿水分梯度土壤有效氮受土壤全氮、土壤微生物生物量氮、土壤湿度、植被类型以及人类活动影响。     

Nutrients, moisture and productivity of established forests

The response of a forest to nutrient and moisture stresses is reflected in nutritional, physiological, and structural changes that include efficiency of nutrient use, translocation and cycling of nutrients, transpiration, retention of foliage, below-ground and above-ground allocation of carbon, as well as the structural development of the forest stand and its growth characteristics. This article reviews the relationship of forest ecosystems to nutrient and moisture stresses and addresses the means by which productivity can be enhanced by altering nutrient and moisture regimes.

Considerable research has focused on optimizing productivity by minimizing nutrient and moisture stresses. Research involved in nutrient additions has led to the use of commercial fertilizers to improve forest productivity. The results suggest that many forests are deficient in N and P and, to a lesser extent, S, K, Mg and trace elements. The duration of response for most nutrient additions is, however, relatively brief and the efficiency of the tree in using fertilizer is relatively poor. Long-term correction of nutrient deficiencies is seldom achieved with chemical fertilizers. However, N added through symbiotic fixation or, on a more limited scale, through addition of municipal and industrial waste by-products, can provide an excellent long-term growth response.

It is seldom feasible to change the moisture regime of a forest ecosystem through irrigation. However, field trials involving irrigation have demonstrated that moisture stress can limit productivity. There are various ways of minimizing moisture stress without irrigation, including mulching, removing ground-cover vegetation, and changing the spatial characteristics of the forest cover.

Research trials show that forest ecosystems will respond to moisture and nutrient additions; however, these responses and interactions between nutrients and moisture are typically poorly understood, and many questions remain unanswered: Does fertilization increase moisture-use efficiency of a forest or simply improve the nutrition of the site? Does improving the moisture regime of a site improve productivity primarily by decreasing moisture stress or by increasing nutrient availability and the rate of nutrient uptake? Is there a synergism in growth response with the addition of both nutrients and moisture? The linkages between nutrients and moisture appear inseparable and confound experimentation in this field. Answers to these questions and issues need to be found for the future development of plantation forestry.     

日本水源林建设的一个典型剖析

森林是具有保水功能的绿色水库,其贮水量是水库的１３．３倍,水库只能贮存年总流量的４０％,有３０％需要营建水源涵养林来产现。水源林建设需要资金,建立“水源林基金”是最重要的保证。水源林基金要体现“受益者负担”的原则。基金主要髟于森林所有者进行造林及营要的补助,用于市、镇、村庄造林及营林的借款,用于水源林科学知识的普及等。     

北京市高保护价值森林信息查询系统

介绍了ArcGIS Server的基本知识和体系结构,阐述了ArcGIS Server的运行机制,分析了分布式环境下服务器端的配置和管理方法,针对基于ArcGIS Server开发的Web应用相关问题,结合数据库管理技术,对ArcGIS Server框架(ADF)进行了深入研究,使用Windows平台下的.NET ADF,并结合北京市高保护价值森林资源,开发了一个高保护价值森林资源信息查询系统。     

Diversity and biomass of different functional groups of herbaceous species along an altitudinal gradient in the semi-arid Zagros mountain forests of Iran

The response of diversity and biomass of herbaceous functional groups along an altitudinal gradient in mountainous forests of southern Zagros, Khuzestan Province, Iran was studied by sampling vegetation in 30 circular 1000-m~2 plots in herb layer of the forest floor within 646–2447 m asl(lowland: 1000 m asl, midland:1000–2000 m asl, highland: 2000 m asl). The most important herbaceous functional groups were classified based on two aspects of growth form: annuals–perennials,grasses–forbs. Then the relationship between the diversity,richness, evenness, biomass and elevation was analyzed.The results showed that the annual functional group in the low-and midland classes, and perennial functional group in the lowland class had the highest species diversity and evenness in annual and perennial functional groups,respectively(p 0.01). The perennials in the highland class had the maximum total, above-and belowground dry biomass(p 0.01). On the other hand, the forb functional group in the lowland class had the greatest species diversity, richness, and evenness(p 0.01) and in the highland class had the maximum total dry, above-and belowgrounddry biomass in the grass and forb functional groups(p 0.01). Increasing the diversity, richness, and species evenness resulted in a decrease in the plant dry biomass.