António Fabião

Fine-root dynamics, soil moisture and soil carbon content in a Eucalyptus globulus plantation under different irrigation and fertilisation regimes

The minirhizotron technique was used to study the temporal dynamics of fine-roots over a 10 month period in a E~caZyprus plantation in central Portugal. Four treatments were applied: a control without irrigation or fertilisation (C), fertilisation twice per year (F), irrigated without fertilisation (I), and irrigated and fertilised once each week with fertiliser in the irrigation water (IL). In I and IL a drip-tube system was used, and fertiliser rates were adjusted based on the estimated plant nutrient demand. Soil moisture content was measured during the same period at 5 cm depth intervals down to 90 cm depth. Soil carbon content was measured at planting, 30 months after planting and 54 months after planting. Interrelations between fine-root dynamics, soil moisture, and soil carbon content are discussed. Fine-root counts peaked in late autumn in all treatments and declined thereafter until March. Fine-root growth in spring and summer seemed to be dependent on water supply; i.e. with an ample water supply (within rows, close to the drip-tubes in I and IL), root counts increased almost linearly between April and November. In the non-irrigated treatments (C and F, as well as between rows in I and IL), no marked increase in root counts occurred until late August, when it increased immediately after a heavy rain. Root growth in I was shallowest during spring and summer, while in F it was shallowest during autumn and winter. In general, treatment means of root counts were highest in IL, somewhat lower in I, and considerably lower in C and F. In addition to irrigation effects, treatment differences in soil water content were enhanced by differences in soil carbon content, which in turn could be attributed to root turnover, as reflected by the temporal dynamics of root counts. The carbon flow from the trees to the soil, which was probably associated mainly with root death, was highest in IL. Thus this treatment should have enhanced soil fertility.

Development of root biomass in an Eucalyptus globulus plantation under different water and nutrient regimes

The distribution along the soil profile of Eucalyptus globulus root biomass was followed in a plantation in central Portugal at 1, 2 and 6 years after planting, using an excavation technique. The experimental design consisted of a control (C) and 3 treatments: application of solid fertilizers twice a year (F), irrigation without the application of fertilizers (I) and irrigation combined with liquid fertilizers (IL). Below- and above-ground biomass decreased as follows: IL>I>F>C. So, water stress limited growth more severely than nutrient stress. The roots rapidly colonized the top soil volume (0–20 cm depth) during the first year after planting. Fine root biomass 6 years after planting was 2.2, 1.8 and 1.6 times higher in IL treatment than it was respectively in control, and in F and I treatments. The distribution of fine roots along the soil profile 6 years after planting was more even in IL compared to the other treatments. However, fine roots in the top soil were more concentrated along the tree rows in the irrigated treatments than in the others. The proportion of below-ground biomass relative to the total tree biomass and the root/shoot ratio were higher in C than in the treatments at early growth stages. This pattern was not so clear 6 years after planting, due to the increased proportion of the tap root relative to total biomass, especially in the IL treatment.

Growth dynamics of superficial roots in Portuguese plantations of Eucalyptus globulus Labill. studied with a mesh bag technique

SummaryThe variation in growth of the fine roots of blue gum (Eucalyptus globulus labill. ssp.globulus) in the 0–40 cm soil layer was studied from March 1982 to March 1983 at Quinta do Furaduoro, Óbidos, Portugal. A mesh bag method was used; bags of nylon net were inserted into a clay soil and a sandy soil and filled with root-free soil. They were resampled after 2, 4, 6 and 12 months in both places and, in a separate series in the sandy soil every second month throughout the year.The ingrowth of roots was high during the winter months but there was also a surprisingly high ingrowth during the spring-early summer period. There was also some root growth during the driest part of the yearviz. July–September.The amount of fine roots reached a maximum of about 260 g dw m−2 after about 6 months in the sandy soil, whereas it took at least 12 months to reach the somewhat higher level of 450 g dw m−2 in the clay soil. At that level the decomposition of dead roots was expected to equal the formation of new roots. Dead roots appeared after only 2 months. There was a higher proportion of dead roots in the clay soil than in the sandy soil, 35% as compared with 20% on an average, which indicates a slower decomposition or a higher mortality at equal decomposition rates in the clay than and in the sandy soil. The present data gives an indication of a minimum fine root production in mature Eucalyptus stands of at least 600 g dw m−2 yr−1.

Root mass in plantations of Eucalyptus globulus in portugal in relation to soil characteristics

Abstract Root mass (living and dead roots) in two stands of blue gum (Eucalyptus globulus Labill.), near the town of Obidos in west‐central Portugal, was measured using an excavation method. One stand, at Alto do Vilao (AV), was 18 years old and was located on a sandy loam—clay loam. The other stand, at Bom Sucesso (BS), was 12 years old and was located on a sandy soil. AV was planted after superficial ploughing, while BS was planted after superficial ploughing followed by the creation of deep furrows in rows. Total root mass was significantly higher at BS (23 t ha−1) than at AV (12 t ha−1). At BS total root mass was significantly higher within tree rows than between rows. The difference between the stands at AV and BS can probably be explained by differences in bulk density of the soil, since the less dense soil at BS may have allowed roots to penetrate a greater soil volume. The difference between within‐and between‐row estimates of root mass at BS can probably be explained by deeper soil preparation, w...

Influence of soil and organic residue management on biomass and biodiversity of understory vegetation in a Eucalyptus globulus Labill. plantation

The objective of this study was to assess the effect of different options of soil preparation and management of harvesting debris on biodiversity and biomass of understory vegetation in plantations of Eucalyptus globulus of Central Portugal. The experiment consisted of six treatments in a replanted area and four treatments in a coppice area with five replicates, following a randomised block design. Surveys of vegetation were performed for 6 years. The proportion of soil cover by plant species was estimated and the Shannon‐Wiener diversity and equitability indexes determined for each treatment and year. After the 2nd year, the understory vegetation was randomly sampled for above-ground biomass determination. Within the planted area, the removal of slash without soil preparation induced the highest number of species during the experimental period. A similar trend was observed in the coppice area, but less regularly. Significant differences in the proportion of soil cover only occurred within the planted area in the first year, when slash removal without soil preparation induced the highest understory cover. Species diversity was not clearly affected by treatments: significant differences only occurred occasionally and were apparently related to differences in the number of species. Therefore, differences in the equitability index between treatments never were significant. Removal of slash without soil disturbance and broadcast of slash over the soil usually shared the highest biodiversity. Differences between treatments in the amount of understory biomass were never statistically significant during the experimental period. Tendency for a negative influence of soil mobilisation on the amount of understory biomass was observed within the planted area, as well as a similar effect of the treatments consisting of broadcast of slash over the soil surface in the coppice area. In parallel to tree development and canopy closure biomass of that vegetation along the study period was reduced, especially in the planted area. # 2002 Elsevier Science B.V. All rights reserved.

Effect of Water and Nutrient Supply on Root Distribution in an Eucalyptus Globulus Plantation

Water and nutrients were supplied to anEucalyptus globulus plantation in a controlled experiment in west central Portugal. The trees were planted in a sandy soil at a spacing of 3 × 3 m. The experiment consisted of four treatments: irrigation, irrigation plus fertilization, fertilization without irrigation, and a rain fed and unfertilized control. The quantification of root biomass was carried out 13 mo after planting. When the plantation was 31 mo old, a trench was dug in the soil to uncover the distribution of the roots of individual trees. In the irrigated treatments root biomass was higher than in the control and in the fertilized plots. Differences in fine and coarse root distribution along the soil profile were also observed. In both irrigated treatments roots were concentrated along tree rows, where the irrigation tubes were dripping water or water plus nutrients.

Sustainability of forest soils

Forest soils play an important role in sustaining stand productivity and forest values by regulating water uptake, root environment and nutrient cycling processes. A judicious management of soils forms an important component of sustainable forest management (SFM). An international symposium was held at Vila Real, Portugal, from 18 to 22 September 2000 to address some of the pertinent soil management issues in relation to forest productivity and other forest values. These issues included: (1) changes in the nutrient and water-related processes and properties of forest soils with forest management, (2) soil changes in relation to forest productivity and biodiversity and the development and use of simple and practical methods of measuring such soil changes (soil indicators), (3) site factors, site classification and stand productivity and (4) soil management and ameliorative measures. It is now generally realized that management of forests on a sustained basis needs appropriate care and maintenance of their soil resource and, in most cases, the replacement of lost nutrients. Recent international activities such as Montreal process have given further credential to the judicious use of soil resource under forests. Use of forest plantations to sequester CO2 and to produce biofuels as an alternative or substitute for fossil fuels is expected to provide additional research activities in the field of forest soils. Papers included in this issue can be grouped into four following themes:

Early growth of invasive acacias as a potential biomass-for-energy source under Mediterranean conditions

Most of the short rotation energy coppices used in Northern and Central Europe may be of limited value under Mediterranean climates. Abandoned acacia stands with an invasive behaviour, of environmental concern in many Mediterranean countries, may perform better as biomass producers under summer drought than those coppices. Seedlings of invasive Acacia dealbata, A. melanoxylon and A. pycnantha were planted to test for early growth performance under rain-fed and irrigated conditions. Rooted cuttings of an E. globulus clone were also established as a reference for biomass production. Plants were harvested after one year, sorted by biomass components and oven-dried. Above-ground dry weight was calculated on an area basis, accounting for survival. A. dealbata and A. melanoxylon showed low survival and biomass production, even irrigated, whereas A. pycnantha had better survival and growth performance than eucalypt, even in rain-fed plots, suggesting potential for the harvest of this drought-adapted species as a biomass source.

Biomass and Net Primary Productivity of Portuguese Forests

In Portugal, as elsewhere, after the energy crisis, forests started to be regarded with a new interest. Due to this attitude arose the necessity of more information concerning our forest resources and we have recently begun an effort to acquire this knowledge. The present paper reflects the first steps in this direction.