Dominant species’ resprout biomass dynamics after cutting in the Sudanian savanna-woodlands of West Africa: long term effects of annual early fire and grazing

Background   

The potential of forest to regenerate after harvesting is a key element for sustainability of the ecosystem. For semi-arid tropical savanna environments, managing resprouts after tree cutting is ideally suited because of the natural ability of many indigenous species to regenerate vegetatively. Regeneration in this ecosystem is, however, prone to many disturbance factors such as fire and grazing by livestock.     

Artificial regeneration with <Emphasis Type="BoldItalic">Quercus ilex</Emphasis> L. and <Emphasis Type="BoldItalic">Quercus suber</Emphasis> L. by direct seeding and planting in southern Spain

 Introduction   

The limited ability of Quercus species to regenerate naturally in Mediterranean forests has led to the development of various artificial regeneration methods; however, there is no general consensus as to what specific method is the best one for this purpose.     

Root spatial distribution and biomass partitioning in <Emphasis Type="Italic">Quercus robur</Emphasis> L. seedlings: the effects of mounding site preparation in oak plantations

In a reforestation field experiment undertaken in southern Sweden and planted with pedunculate oak, three site preparation treatments (herbicide application (H), mounding site preparation (MSP) and combined herbicide and mounding treatment (H + MSP)) were compared to an undisturbed control (C). We analysed root spatial and biomass distribution in 48 harvested seedlings. Compared to the control, both MSP and H treatments resulted in a significantly higher root system biomass (means C: 16.4 g, H: 45.7 g, MSP: 41.4 g, MSP + H: 102.2 g). The proportion of lateral root biomass increased from 38% (C) to 62% (MSP + H), while the two remaining treatments (H, MSP) attained percentages of 48% and 51%, respectively. The treatments did not alter seedlings’ allometry and root:shoot ratio significantly. However, biomass distribution of different root system parts varied among treatments, so that lateral root biomass increased relative to leaf biomass from C to MSP + H variant. Site preparation treatments (MSP, MSP + H) increased the horizontal extension of root biomass, compared to C and H variants. We conclude that mounding site preparation is an efficient method for the reforestation of pedunculate oak stands. Due to the comparative positive effects on root system development, MSP presents an alternative to herbicide treatment, particularly at sites where the use of chemicals is restricted.     

Performance of northern red oak enrichment plantings in naturally regenerating Southern Appalachian hardwood stands

The limited success of methods to naturally regenerate northern red oak (Quercus rubra L.) has increased the use of artificial techniques to improve overall oak composition. Enrichment plantings are often recommended as a means to supplement species composition within the existing natural reproduction. Previous enrichment efforts have often resulted in low survival and poor growth, generally due to poor planting stock quality and a lack of competition control. In this study, high quality northern red oak seedlings were established on four recently harvested sites in western North Carolina using one of four competition control treatments (untreated, year 1 control, year 2 control or a weed mat) in a 1.2 × 1.2 m area around each seedling with or without a soil fertility amendment. The 3 year results show that competition control and fertilization treatments had few positive impacts on survival and growth of the planted seedlings. These results suggest that either the treatment area was insufficient to adequately release the seedlings, or other factors like belowground competition from existing advance reproduction and/or stump sprouts may be important determinants of the overall success of northern red oak enrichment plantings on recently harvested sites.     

Estimating balanced structure areas in multi-species forests on the Sierra Madre Occidental,Mexico

• Introduction   

This study presents a method for estimating the minimum area which exhibits a balanced diameter distribution, and the corresponding number of trees, for different tree species and forest types in the Santiago Papasquiaro region in the State of Durango, Mexico. The balanced structure area is defined as the minimum contiguous area that is required for sustainable management of a multi-sized selection forest. A multi-sized forest represents a balanced structure unit if the relationship between harvest and growth can be maintained, using a defined target diameter distribution and disregarding major natural disturbances. The study is based on 17,577 sample plots in uneven-aged forests, which are selectively harvested by local communities.     

Species and functional diversity of ectomycorrhizal fungal communities on Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) trees on three different sites

• Introduction   

In the present study, we describe the aboveground (epigeous sporocarps) and belowground (ectomycorrhizal root tips and their exploration types) composition of ectomycorrhizal (ECM) fungal species on three 20-year-old Scots pine sites.     

Variation of wood color parameters of Tectona grandis and its relationship with physical environmental factors

? Context

Teak??s wood color is considered an important attribute in the marketing phase and it has been influenced by environmental setting, stand conditions and management, plant genetic source, and age. However, there is a lack of understanding about how the environmental factors might affect the teak??s wood color planted in short-rotation forest plantations.

? Aims

The aim of this study is to understand the relationship, gathered from generated information, between edaphic and climatic variables and their effects in the wood color variation of Tectona grandis from trees in forest plantations.

? Methods

Twenty-two plots were grouped in five cluster sites that shared similar climatic and soil conditions. Data about soil??s physical?Cchemical properties and climatic variables were collected and analyzed. Representative trees were harvested next to each plot in order to obtain a wood sample per tree at a diameter breast height. Wood color was measured using standardized CIELab??s chromaticity system.

? Results

After comparing the wood change color index (?E*) in the five studied clusters, it was found that heartwood produced from drier and fertile sites had more yellowish-brown color. The heartwood b* color index resulted with significant correlations (R?>?0.5, P?<?0.05) among nine climatic and eight edaphic variables.

? Conclusion

It was concluded that climatic variables should be considered as the first-order causal variables to explain wood color variation. Hence, darker b* wood color was associated with dry climates; also, with deeper and fertile sites.     

Low pre-death growth rates of oak (<Emphasis Type="Italic">Quercus robur</Emphasis> L.)—Is oak death a long-term process induced by dry years?

• Background and purpose   

A complex interplay between biotic and abiotic factors is believed to be responsible for several oak declines in pedunculate oak (Quercus robur L.). This study aims to clarify the temporal process of oak declines, as well as identifying individual tree and environmental variables that affects growth rate and that may increase the risk of mortality. The study was performed in southern Sweden at three sites.     

Pattern of genotype–environment interaction in <Emphasis Type="Italic">Picea glauca</Emphasis> (Moench) Voss in Alberta,Canada

• Introduction  

Genotype-environment interaction (GEI) among 19 white spruce provenances planted on eight sites in Alberta, Canada, was analyzed using type B correlations (r _p ) and the additive main effects and multiplicative interaction (AMMI) model. The objectives were to quantify the extent of crossover interaction for height and diameter; evaluate the age-trends in GEI for height and diameter; and examine the role of provenance and test site climate in causing GEI.     

Nutrient concentration and allometric models for hybrid eucalyptus planted in France

Context

Short rotation coppice (SRC) of hybrid Eucalyptus has been developed in France for almost 30 years for the production of pulp and paper and, since a few years, for energy purposes. In the traditional pulp production, only the stems are harvested, whereas the whole biomass may be harvested for energy purposes. Thus, a range of different harvest scenarios need to be considered with higher plantation densities or younger age of harvest for example.

Aims

The objective of this study was to build models to estimate biomass and nutrient content of eucalyptus at different ages and so to estimate the production and the nutrient exportation of a SRC, depending on the different harvest scenarios.

Methods

Over 250 trees were sampled in 16 stands at ages from 1 to 15 years. For each tree, biomass of different compartments and nutrient contents were recorded.

Results

A complete set of equations for the four compartments (wood, bark, branches, and leaves) of aboveground biomass and for nutrient concentration was set up.

Conclusion

Biomass and its allocation to different compartments and nutrient concentrations depended on the dimension and/or the age of the tree. In particular, nutrient concentration decreased with increasing tree diameter.     

Effect of species grouping and site variables on aboveground biomass models for lowland tropical forests of the Indo-Malay region

Key message

This study assessed the effect of ecological variables on tree allometry and provides more accurate aboveground biomass (AGB) models through the involvement of large samples representing major islands, biogeographical zones and various succession and degradation levels of natural lowland forests in the Indo-Malay region. The only additional variable that significantly and largely contributed to explaining AGB variation is grouping based on wood-density classes.

Context

There is a need for an AGB equation at tree level for the lowland tropical forests of the Indo-Malay region. In this respect, the influence of geographical, climatic and ecological gradients needs to be assessed.

Aims

The overall aim of this research is to provide a regional-scale analysis of allometric models for tree AGB of lowland tropical forests in the Indo-Malay region.

Methods

A dataset of 1300 harvested trees (5 cm ≤ trunk diameter ≤ 172 cm) was collected from a wide range of succession and degradation levels of natural lowland forests through direct measurement and an intensive literature search of principally grey publications. We performed ANCOVA to assess possible irregular datasets from the 43 study sites. After ANCOVA, a 1201-tree dataset was selected for the development of allometric equations. We tested whether the variables related to climate, geographical region and species grouping affected tree allometry in the lowland forest of the Indo-Malay region.

Results

Climatic and major taxon-based variables were not significant in explaining AGB variations. Biogeographical zone was a significant variable explaining AGB variation, but it made only a minor contribution on the accuracy of AGB models. The biogeographical effect on AGB variation is more indirect than its effect on species and stand characteristics. In contrast, the integration of wood-density classes improved the models significantly.

Conclusion

Our AGB models outperformed existing local models and will be useful for improving the accuracy on the estimation of greenhouse gas emissions from deforestation and forest degradation in tropical forests. However, more samples of large trees are required to improve our understanding of biomass distribution across various forest types and along geographical and elevation gradients.

     

A review of the development of Mediterranean pine–oak ecosystems after land abandonment and afforestation: are they novel ecosystems?

Context

Mediterranean landscapes are composed of different interacting vegetation patches. Pine and oak ecosystems form contiguous patches within these landscapes, in pure stands, or as mixed pine?Coak ecosystems. During the nineteenth century, pine forest distribution in the Mediterranean Basin increased dramatically as a result of large-scale re-forestation and spontaneous forest regeneration. At the same time, secondary succession of abandoned agricultural land allowed development of pine and oak ecosystems. Consequently, a pine?Coak mosaic has developed, which created opportunities for cross-colonization, i.e. species colonization from one ecosystem in the reciprocal system. Pines shed their wind-dispersed seeds and colonize Mediterranean oak vegetation. Oaks regenerate in different ecosystems, including pine forest understories.

Research question

This paper reviews fire-free landscape-scale dynamics of pine?Coak Mediterranean mosaics and analyze how landscape-scale interactions are leading to pine?Coak ecosystems by different processes.

Results

Published information from the Mediterranean Basin illustrates pathways of pine?Coak ecosystems formation. Using Mediterranean literature, I try to elucidate the factors that (1) control colonization potential and (2) modulate the resistance to colonization, in different habitats, land uses, and landscape settings.

Conclusion

Management implications for these mixed pine?Coak ecosystems are suggested. The question of whether they are novel ecosystems is discussed.     

Effects of vegetation control on nutrient removal and Fagus orientalis, Lipsky regeneration in the western Black Sea Region of Turkey

Dense Rhododendron ponticum (L.) understories of eastern beech (Fagus orientalis Lipsky) stands in the Black Sea Region (BSR) of Turkey create challenging forest vegetation management problems relative to beech regeneration. Rhododendron traditionally is controlled in Turkish forests with grubbing and bulldozing. The effects of these practices on nutrient removal and natural beech regeneration have not been quantitatively studied. Two woody vegetation control treatments (bulldozing and hand-grubbing) were installed during late summer, 2002 in three mature beech stands with dense rhododendron understories in the Düzce Forest Management Directorate, in the Turkish western BSR. Aboveground biomass of each vegetation component, total aboveground vegetation biomass, nutrient concentrations, organic matter (OM) removal, and total amount of OM nutrients were determined for each woody vegetation control treatment. Soil bulk density and nutrient content, and beech seedling biomass, nutrient content, and natural regeneration also were studied. One year after treatment, the machine site preparation by bulldozing (MSP) that removed understory vegetation and attached roots, reduced mean forest floor OM content by about 84%, when compared to hand-grubbing. Mean soil C, N, K and Mg concentrations on the bulldozed sites were 36, 27, 50 and 55% less, respectively, than those on the grubbed sites. Total C and Mg amounts at the 5–10 cm soil depth were 24 and 47% lower, respectively, for mechanical site preparation (MSP) sites, when compared to grubbed sites. Overall, soil bulk density did not differ significantly between the grubbing and MSP treatments. Frequent passes on designated transects on MSP sites resulted in a significant (P < 0.01) one-third increase in bulk density of the first 20 cm soil depth, when compared to grubbed sites. No natural beech regeneration occurred on untreated control sites. Mineral soil exposure on the MSP sites increased beech seedling germination substantially. One year after treatment, the mean number of naturally regenerated seedlings for MSP sites was 2.5 times greater than for grubbed sites. Woody control treatments had significant effects upon beech seedling chemistry, with N, P, K, Ca and Mg concentrations averaging 35, 47, 12, 33 and 25% lower, respectively, for MSP sites, when compared to grubbed sites. However, mean seedling biomass and nutrient content were significantly greater (P < 0.05) on MSP sites. Long-term effects from windrowing on MSP site residues, associated topsoil and nutrients need to be evaluated.     

Radial growth changes following hemlock woolly adelgid infestation of eastern hemlock

? Context

Hemlock woolly adelgid (Adelges tsugae) is an invasive insect that is defoliating and killing eastern hemlock (Tsuga canadensis) in the USA.

? Aims

We quantified changes in tree-ring growth rates and wood anatomy for living trees infested with hemlock woolly adelgid across six sites from Massachusetts (42°41′N) to Georgia (34°53′N) to identify growth responses of eastern hemlock that had survived infestation.

? Methods

Annual ring widths from infested eastern hemlocks were cross-dated and measured. Growth rates before and after infestation were compared. Two infested trees from Virginia were cut, and thin sections were prepared to identify changes in cell properties.

? Results

At three sites, trees experienced a significant decrease in radial growth after hemlock woolly adelgid arrival; however, the other three sites showed no change or increase in growth. Latewood produced after hemlock woolly adelgid infestation had significantly smaller cells with reduced cell wall thickness compared to latewood prior to infestation.

? Conclusion

At half the sites where hemlock woolly adelgid infested eastern hemlock trees were sampled, radial growth increased or remained unchanged. This unexpected response may be due to reduced competition due to mortality of other eastern hemlocks or physiological compensatory responses of increased photosynthetic rate and increased water use efficiency experienced by eastern hemlock infested with hemlock woolly adelgid.     

Indications that site preparation increases forest ecosystem carbon stocks in the long term

Mechanical site preparation (MSP) causes a mixing disturbance of the soil, which may increase decomposition of soil organic matter and subsequent carbon (C) dioxide emissions to the atmosphere. MSP also promotes the establishment and growth of tree seedlings, and hence ecosystem C fixation. However, there are uncertainties regarding the net effects of MSP on C stocks at the ecosystem scale. To assess decennial effects of MSP on ecosystem C stocks, C stocks in soil, ground vegetation and trees at three experimental forest sites with Pinus contorta, Pinus sylvestris and Picea abies in Sweden were sampled and measured for ca. 25 years in a control and after three MSP treatments: disc trenching, mounding and ploughing. After 25 years, all of the MSP treatments resulted in larger ecosystem C stocks than the control treatment due to positive effects on the tree biomass C stock. The tree C stock was highest after ploughing, intermediate after mounding or disc trenching and lowest in untreated control plots at all experimental sites. The MSP treatments did not affect the soil C stocks down to 30?cm. We recommend mounding or disc trenching to promote C sequestration as they disturb sites’ ecological, aesthetic and recreational values less than ploughing.     

Synergistic use of very high-frequency radar and discrete-return lidar for estimating biomass in temperate hardwood and mixed forests

• Introduction   

Accurate estimation of aboveground biomass is essential to better understand the carbon cycle in forest ecosystems.     

Segregation of <Emphasis Type="Italic">Eucalyptus tereticornis</Emphasis> Sm. clones for properties relevant to solid wood products

Introduction   

Wood quality is an important criterion in the selection of superior genotypes when breeding for solid wood.     

Shrub island effects on a high-altitude forest cutover in the eastern Tibetan Plateau

• Context  

The roles of woody-plant islands are well documented in low-altitude regions, but research related to such shrub effects in high-altitude regions is scant.     

A survey of root pressure in 53 Asian species of bamboo

Introduction  

Root pressure is a potentially important mechanism for dissolving embolisms in previously cavitated vessels, but the occurrence of root pressure is not a universal property in plants.