Regional Sediment Deficits in the Dutch Lowlands: Implications for Long-Term Land-Use Options (8 pp)

Background, Aim and Scope   Coastal and river plains are the surfaces of depositional systems, to which sediment input is a parameter of key-importance. Their habitation and economic development usually requires protection with dikes, quays, etc., which are effective in retaining floods but have the side effect of retarding sedimentation in their hinterlands. The flood-protected Dutch lowlands (so-called dike-ring areas) have been sediment-starved for up to about a millennium. In addition to this, peat decomposition and soil compaction, brought about by land drainage, have caused significant land subsidence. Sediment deficiency, defined as the combined effect of sediment-starvation and drainage-induced volume losses, has already been substantial in this area, and it is expected to become urgent in view of the forecasted effects of climate change (sea-level rise, intensified precipitation and run-off). We therefore explore this deficiency, compare it with natural (Holocene) and current human sediment inputs, and discuss it in terms of long-term land-use options. Materials and Methods: We use available 3D geological models to define natural sediment inputs to our study area. Recent progress in large-scale modelling of peat oxidation and compaction enables us to address volume loss associated with these processes. Human sediment inputs are based on published minerals statistics. All results are given as first-order approximations. Results: The current sediment deficit in the diked lowlands of the Netherlands is estimated at 136 ± 67 million m3/a. About 85% of this volume is the hypothetical amount of sediment required to keep up with sea-level rise, and 15% is the effect of land drainage (peat decomposition and compaction). The average Holocene sediment input to our study area (based on a total of 145 km3) is ~14 million m3/a, and the maximum (millennium-averaged) input ~26 million m3/a. Historical sediment deficiency has resulted in an unused sediment accommodation space of about 13.3 km3. Net human input of sediment material currently amounts to ~23 million m3/a. Discussion: As sedimentary processes in the Dutch lowlands have been retarded, the depositional system's natural resilience to sea-level rise is low, and all that is left to cope is human countermeasure. Preserving some sort of status quo with water management solutions may reach its limits in the foreseeable future. The most viable long-term solutions therefore seem a combination of allowing for more water in open country (anything from flood-buffer zones to open water) and raising lands that are to be built up (enabling their lasting protection). As to the latter, doubling or tripling the use of filling sand in a planned and sustained effort may resolve up to one half of the Dutch sediment deficiency problems in about a century. Conclusions: Conclusions, Recommendations and Perspectives. We conclude that sediment deficiency – past, present and future – challenges the sustainable habitation of the Dutch lowlands. In order to explore possible solutions, we recommend the development of long-term scenarios for the changing lowland physiography, that include the effects of Global Change, compensation measures, costs and benefits, and the implications for long-term land-use options. Recommendations and Perspectives: -     

Radiata pine plantations in Chile

The landscape of the southcentral part of Chile is dominated by fast-growing plantations of radiata pine (Pinus radiata D. Don), and in lesser extent bluegum eucalyptus (Eucalyptus globulus Labill.), Italian poplar, and willows. Radiata pine was first introduced in 1885 as an ornamental species. During 1940–1960 it was used to control erosion in the Coastal Range. Finally, since the 1960s it has been used for commercial plantations. The present extent of the plantation resource is 1,694,104 ha, of which 80.9 percent is radiata pine. During 1991, 1992, and 1993, this species was planted at rates of 75,416 ha, 81,868 ha, and 71,411 ha, respectively. Even though the soils are eroded to different degrees, exhibit a variety of nutritional disorders, and contain some physical restrictions, the productivity of radiata pine ranges from 18 m³/ha/yr to 35 m³/ha/yr. Additional stress comes from some potentially serious pests; for example, the European pine shoot moth, Rhyacionia buoliana, has presented a real threat to radiata pine. The main products obtained from radiata pine are exported to Japan, Korea, Middle and Far East countries, and Europe. Sawlogs, sawntimber, pulpwood, clearwood, and wood chips are some of the products comprising sales in 1994 of U.S.$1,564 billion. The purpose of this paper is to show how radiata pine silviculture has changed since the last part of the 1980s in Chile. Also we want to show how forestry activities have produced a profound and positive change in the social and economic environment that surrounds the areas where the industry’s main production areas exist. This revised version was published online in June 2006 with corrections to the Cover Date.     

Relative importance of water and nutrients on the growth of coast Douglas fir in the Pacific Northwest

The Douglas-fir region in northwestern North America is characterized by abundant moisture supply during winter, extended dry periods during the growing-season and significant differences in water availability. Many soils have low fertility and native tree species respond to nitrogen fertilization, especially Pseudotsuga menziesii (Mirb.) Franco (coast Douglas fir). Although irrigation of commercial forests in this region is currently impractical, questions arising about the relative importance of water and nutrients were examined using long-term growth data from three studies.

At Pack Forest, fertilization within irrigation doubled growth rates, and no positie growth responses were measured from irrigation. Short-term (5 years) irrigation with sewage effluent containing many nutrients resulted in a six-fold increase in biomass production for poplar and three-fold for Douglas fir as compared to irrigation with equal volumes of river water.

Volume growth in 12- to 65-year-old stands in southwestern Oregon was increased by fertilization at about 70% of the location; annual gain averaged 2.73 m³ ha⁻¹ for 5–12 years. Response was not related to annual precipitation, which ranhed from 81 to 279 cm, nor other moisture-related variables. Absolute and relative volume response showed highest correlation with soil carbon: nitrogen ratio.

Compared with nutrition, moisture does not seem to be a major limiting factor for growth in the Douglas-fir region of the Pacific northwest.     

Nitrogen balances in forest ecosystems of the Pacific Northwest

In order to understand the role of nitrogen in the forests of the Pacific Northwest, especially Douglas-fir, a great number of studies have been initiated to evaluate both static and dynamic aspects of the nitrogen balance. This paper presents a summary of many of these past results covering 20 yr research with the specific intent of defining the nitrogen economy of these systems and the long- and short-term changes that are occurring. Variations of nitrogen in both soils and vegetation are discussed with some sampling techniques applicable to coniferous forests given. It appears that the soil total nitrogen, in different soils, varies several fold more than the nitrogen in the forest crops of these soils. The dynamics of nitrogen transfer within the ecosystem, together with gains and losses from the system, are presented.     

Sustainable management of native and exotic plantations in Australia

The emphasis of plantation management changes as the resource and the market develop. This is especially the case when a plantation program is developing a new timber resource, is not the case with many of the Pinus radiata (D. Don) plantings in the southern hemisphere. Australia establishes and manages plantations of both exotic conifer and native hardwood (Eucalyptus spp.) plantations, and these vary in their stage of development. The tenure and objectives in establishment have varied, but some key aspects of the resources may be analyzed. Optimization of production per unit area was not a prime objective during the developmental stages of many exotic pine plantations. Currently, with increased commercial emphasis, this has changed to a greater focus on increased value through Site Specific Management and tree improvement through which gains of at least 20 percent are expected during the first stages. With a key objective of sustainability, questions regarding impacts of soils, water, and biological changes need consideration and are being addressed. The eucalypt plantation resource in Australia is smaller in extent than is the pine resource, but of increasing importance, especially as the plantations are perceived to be more environmentally and ecologically acceptable than exotic conifers. In the past, questions of productivity, especially in relation to impacts of natural pests and diseases, have been raised. Sustainability of all plantations is a critical aspect, however, for specific issues there are different emphases with different species. For example, the relatively, high removal of calcium in smooth barked Eucalyptus plantations is seen as important in long term forest management. This revised version was published online in June 2006 with corrections to the Cover Date.