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Planted forests, although only seven per cent of the world's forest resources, have superseded naturally regenerating forests as the principal source of industrial wood products. Lessening the pressure for wood production, tree planting has released natural forests to be managed for other purposes - carbon sinks, soil and water protection, conservation of biological diversity, recreation and amenity. Representing a complement, but not an alternative, to natural forests, planted forests have become increasingly important for reducing worldwide deforestation, loss of forest ecosystems and forest degradation. Examining the significance of this rapidly emerging world resource, chapters consider the strengths and weaknesses of planted forests, management objectives for their use and aspects of ownership and policy. Data from key production countries are used to evaluate the implications and sustainability of planted forests as a source of forest products as well as social and ecological issues.

Forests occupy one third of the world’s land area and govern carbon (C) transfers and influence nitrogen (N) content in the biosphere. Afforestation leads to soil changes of specific dynamics, often accompanied by acidification. Especially at higher altitudes this effect is accelerated and increased with the stand age since forestation. The change in soil C and N content following afforestation is controlled by a number of factors, including: previous land use (grasslands, cropland, etc.), tree species, soil cultivation method, soil properties (clay content, pH), stand age, site management, topography, and climate. In the Czech Republic, large area changes in land use took place in the last centuries – forests covering roughly 20% in the 18th century currently occupy almost 34%, with still increasing tendencies. This paper compares basic soil properties (soil reaction, total soil organic carbon as well as total nitrogen contents) of the agricultural land and land afforested 40–60 years ago. The results confirmed the key role of afforestation in the change of soil organic matter dynamics after establishing new forests on the former agricultural lands in the uppermost mineral soil part of the Orlické hory Mts. region in the Czech Republic. During that time, comparatively substantial changes in soil organic matter and nitrogen were registered. Afforestation considerably increased organic matter content in the studied A-horizons of different land use types. Soil development resulted in a high production of C and N pools under the forest stands, contrary to agricultural land. In general, afforestation caused significant soil acidification. The common tendency of higher acidity of forest soils compared to agricultural ones was documented in the studied case as well. The general tendencies of soil reaction and soil organic matter dynamics at the studied sites are comparable to those in other regions of the Czech Republic.

Afforestation in the tropics may sequester soil C and has been proposed as a management tool to aid in controlling rising levels of atmospheric CO2. We measured changes in soil C following afforestation of sugarcane fields with fast-growing Eucalyptus saligna (Sm.) plantations in Hawaii. Using stable C isotopes, we estimated the contributions to changes in total soil C that were due to the loss of C from the prior cane cultivation, and to the gain of C from the new Eucalyptus plantations. Total soil C 10-13 yr after afforestation was 114 and 113 Mg/ha, respectively, in the Eucalyptus and cane plantation. Eucalyptus increased total soil C in the 0-10 cm layer by 11.5 Mg/ha, but that was offset by a loss of 10.1 Mg/ha of cane-derived C from the 10-55 cm layer. The net effect on soil C of afforestation of cultivated lands depends not only on new C gained, but also on C lost from the previous management.

Afforested lands are different from natural forests in terms of hydrologic conditions, runoff generation potential, and sediment generation rate. These differences emerge due to changes in soil structure and vegetation density, litter amount, trees heights, and so on. In this study, a comparison has been made between natural forests and afforested lands in Kasilian – a watershed located in Mazandaran province, Northern Iran. To achieve this purpose, harmonious units have been defined by overlay analysis of these layers in GIS environment: slope, aspect, Digital Elevation Model (DEM) and soil. Then, the location of couple plots was defined by field studies in the harmonious units. The plot locations were selected in a way that runoff generation was a function of tree species and tree conditions, assuming that rainfall intensity is equal in all areas. Initial loss and runoff volume were measured in even plots after rainfall. Then, the initial loss parameter in a rainfall-runoff model was applied to compare runoff volume and peak discharge in the afforested lands and natural forests. The rainfall-runoff model was presented using GIS and HEC-HMS model. The results showed that reforested lands have lower infiltration, lower initial loss, and higher runoff due to lower density, canopy, litter, and soil compaction. Furthermore, the runoff generation potential of reforested lands is several times higher than that of natural forests.

Madagascar's highland region once was covered with an evergreen forest dominated by about 20 endemic tree species. This has been permanently replaced by a floristically impoverished steppe vegetation on ferrolitic soils. Human intervention has caused this deforestation, aided by a notable failure of highland forests to spontaneously regenerate. Beginning about A.D. 600, Indonesian settlers began removing forests in this region to create swidden fields. After A.D. 1000, zebu cattle introduced from Africa provided a strong motive for islanders to increase grassland at the expense of forest. By A.D.1600 the highland forest cover had mostly disappeared except for localized tract, patches, and strips. The historical record and contemporary observations point to the importance of fire in destroying the forest. This landscape conversion has had devastating outcomes. Tree and humus removal has led to massive erosion, floods, water shortages, and faunal extinctions or endangerments. Agricultural and pastoral production on upland soils is marginal. Re-establishment of long-term ecological stability to this region would require an end to burning as a form of pasture management, changes in communal land tenure, and reforestation of the highlands with native tree species. /// Les montagnes de Madagascar étaient dans le passé couvertes d'une forêt sempervirente dominée par 20 essences endémiques. Cette forêt a été remplacée en permanence par une végétation de steppe á flore appauvrie sur des sols ferralitiques. L'intervention humaine est à l'origine de cette déforestation, combinée avec un manque remarquable de régénération spontanée. Au début du VIIe siècle, les immigrants indonésiens ont commencé à détruire les forêts de la région dans le but de pratiquer l'agriculture sur brûlis. Au XIe siècle, l'introduction du zébu africain a beaucoup encouragé les habitants à augmenter les pâturages au détriment des forêts. Vers la fin du XVe siècle, la couverture forestière des montagnes avait pratiquement disparu, à part de petites étendues localisées. Le dossier historique et les observations contemporaines ont mis en évidence le rôle du défrichement par incendie dans la destruction des forêts. Cette conversion du paysage a produit des effets désastreux. La disparition des arbres et de l'humus a entraîné une érosion massive, des inondations, des pénuries d'eau et des extinctions ou menaces d'extinction de la faune. La productivité agricole et pastorale sur les sols de montagne est marginale. Le rétablissement de la stabilité écologique à long terme de cette région nécessiterait le renoncement à l'incendie comme forme de gestion des pâturages, un changement de régime foncier communal et la reforestation avec des essences indigènes. /// Früher war das Hochland von Madagaskar stark bewaldet und von hauptsächlich immergrünen endemischen Arten gab es mehr als zwanzig. Gegenwärtig sind die eisenhaltigen Böden nur mit einer dürftigen Steppenvegetation bewachsen. Die Entwaldung ist Folge von anthropogenen Eingriffen, und sie wird verstärkt durch die Tatsache, daß sich Hochlandwald sehr langsam regeneriert. Die Abholzung begann um etwa 600 a.D., als indonesische Siedler mit Brandfeldbau begannen. Ab etwa 1000 a.D. wurde Zebu Vieh aus Afrika eingeführt, was die Inselbewohner motivierte, die Entwaldung noch stärker zugunsten von Grassland voranzutreiben. Dies führte dazu, daß ab etwa 1600 a.D. der Waldbestand des Hochlandes bis auf vereinzelte, lokal begranzte Flächen verschwunden war. Alte Aufzeichnungen und neuere Beobachtungen zeigen, daß Waldbrand und nicht Abholzung dann den Wald endgültig vertilgt haben. Solch gravierende Land-schaftsveränderungen hatten verheerende Folgen. Der fehlende Baumbewuchs und der damit verbundene Verlust an Humusboden führte zu starker Erosion, Überschwemmungen, und Wassermangel und gefährdete außerdem die Tierwelt bis hin zum Aussterben einzelner Arten. Hochlandböden bringen der Land- und Weidewirtschaft nur noch geringe Erträge. Konsequenzen, die langsichtig zu ökologischer Stabilität führen, erfordern daß Brandfeldbau abgeschafft wird, daß Gemeindeland anders verwaltet wird, und daß das Hochland mit endemischen Baumarten aufgeforstet wird.

It may be possible to sequester carbon in forests and forest products, but to date global trends in land management have resulted in a release of terrestrial carbon to the atmosphere. Over 100 PgC were released between 1850 and 1980, and during the 1980s global changes in land use (predominantly deforestation) caused a net release of 1.6 PgC yr-1, about 25% of the total emissions of carbon dioxide from human activities and about 15% of the enhanced radiative forcing. Management practices that could change this release of terrestrial carbon to an accumulation include (i) a halt to deforestation; (ii) an expansion in the land area of forests; (iii) an increase in the stocks of carbon in existing forests; (iv) more efficient harvest and greater use of wood in long-lasting products; and (v) the substitution of wood fuels for fossil fuels. However, the rate of global warming needs management as well. Unless the warming is gradual enough to avoid widespread mortality of forests, the additional releases of carbon caused by the warming itself, through increased respiration, decay, and fires, may cancel the intended effects of forest management.

A survey was carried out for 20 forested and five moorland catchments in northern and central Wales to determine the relative importance of vegetation type, plantation age and nitrogen deposition on nitrate losses to stream water. Plantations ranged from 10 to 55-yrs of age and inorganic-N inputs in throughfall from 9 to 25 kg N ha-1yr-1. Samples of throughfall, soilwater below the rooting zone and streamwater were collected every 4 weeks and inorganic-N input-output fluxes calculated for each site. Inorganic-N inputs in throughfall, although variable, tend to increase with stand age. Inorganic-N outputs were less than 5 kg N ha-1yr-1in stands of less than 30 yrs, regardless of inorganic-N inputs, but increased with inputs to more than 30 kg N ha-1yr-1beyond 30 yrs of age. Soil net-nitrogen mineralization and nitrification rates in the organic horizons generally decreased with stand age on a per unit area basis and were therefore not responsible for the increase in nitrate-leaching losses in the older stands. Tree uptake appears to be the most important control for inorganic-N leaching losses until stands reach maturity, thereafter, nitrogen deposition appears to determine leaching losses. Stands more than 30-yrs old have characteristics similar to those described for nitrogen-saturated sites, acting as net sources of inorganic-N rather than as net sinks with elevated stream nitrate concentrations throughout the year. Inclusion of dissolved organic-N fluxes in the input-output budgets alters this relationship such that only the very oldest stands (> 50 yrs old) act as net sources of total dissolved nitrogen.

A numerical experiment was performed to explore the nature of and mechanisms for the effect of large-scale afforestation in the sub-Saharan area on the climate. This sensitivity study, which consists of several short-term integrations of a climate model, suggests that afforestation would enhance the rainfall in the region and would have the largest impact during dry years. While the rainfall increased in the afforestation area, it decreased to the south of that region. It was found that this land surface change altered the surface energy balance and induced a circulation change that led to a change in rainfall. The influences of different vegetation species and the extent of the afforestation area on the rainfall were tested and are discussed. Reducing the afforestation area by about 50% still resulted in a positive simulated rainfall anomaly. A detailed analysis of the surface energy balance is presented. A comparison between the effects of afforestation and desertification is also made.

Vesicular-arbuscular mycorrhizae can be indispensable for establishment and growth of tree seedlings in infertile lowland wet tropical soils. Persistence of mycorrhizal fungi after disturbance, however, is problematic to assess. We used a greenhouse bioassay employing Psidium guajava L. and Allium cepa L. to estimate the most probable number of mycorrhizal fungus propagules in two Costa Rican soils (Oxic Dystropepts) with different vegetation histories. We collected soils at the La Selva Biological Station from sites in secondary forest, abandoned pasture, and plots kept bare of vegetation for four and six years. Both bioassay hosts yielded positively correlated estimates of mycorrhiza propagule numbers. Median propagule estimates per 100 gm dry soil for the pasture site are 57 and 63; these estimates significantly exceed those for the other sites which range from 0.2 to 10 for bare plots and were estimated to be 0.6 and 10 for secondary forest. These bioassay estimates are positively correlated (Pearson r = 0.66 and 0.72) with counts of whole spores in these soils, but not with counts of sporocarps, spore clusters, or the most numerous, spores apparently empty of cytoplasmic contents or parasitized. Growth of both bioassay hosts in pasture soil significantly exceeded growth in soils from the other three sites in accord with the bioassays and whole spore counts.

Results are presented from a fertilization experiment with wood bark ash (0, 1, 2, 5, 10, 20 Mg ha⁻¹) applied to prevent and cure visible nutrient disorders of young Scots pine established on a peatland field. 13 years after fertilization, dieback of trees and other symptoms of nutrient disorders were substantially reduced or even eliminated, especially where higher doses had been applied. The volume of the growing stock was more than 70 m³ ha⁻¹ for the highest dose while control plots produced less than 15 m³ ha⁻¹. Vegetation characteristics changed following ash treatments with high ash doses favouring grasses and low ash doses promoting mosses. Some major changes in soil and foliar nutrient concentrations were evident due to ash fertilization. K and B, however, were clearly the most limiting nutrients that could be cycled where high doses of ash were used. This was particularly the case with a dose of 20 Mg ha⁻¹. Decomposition of the topsoil was at its highest on plots with ash doses of 5 and 10 Mg ha⁻¹ ash and at its lowest when the dose was 2 Mg ha⁻¹. This was partly due to differences in the C/N ratio of the soil. All decomposition parameters indicated a high degree of humification in the topsoil. High N content (of organic material), low C/N in the soil and optimum levels of foliar N concentrations suggested sufficient N mineralization for tree growth to have occurred in the soil.