Reduction In Volume Growth Research Articles

Ertragskundliche Aspekte und Strukturdynamik der Buchen-Lichtwuchsdurchforstung

Effects of heavy selective thinnings in beech stands with regard to stand productivity and structural diversity Based on thinning trials in beech stands initiated in the early 1970s, the effects of selective thinnings in favour of 100 to 120 future crop trees were analysed with regard to volume productivity and the stands' structural diversity. The results show that these kinds of thinnings reduce volume productivity by approximately 6% compared to the maximum volume growth. The reduction in volume growth is mostly caused by the fact that the strongly released crop trees have reduced their height growth for the benefit of a lateral crown expansion, while basal area growth was not affected. Calculations indicate that silvicultural systems working with only 50 future crop trees per hectare may decrease the maximum volume production by about 12%. Furthermore, the results show that the intense crown releases caused by selection thinnings increase the horizontal and vertical diversity of beech stands, since the trees in the understorey profit from better light conditions. The indices calculated for diameter and height diversity of the selection thinning plots approach the values being typical for single tree selection forests (“Plenterwälder”). Already after three to four consecutive selection thinnings, the beech stands' diameter distributions displayed an exponentionally decreasing shape typical for single tree selection forests close to equilibrium. Growth simulations revealed that it might even be possible to directly transform beech stands by selection thinnings into single tree selection structures. However, presumably negative effects on timber quality to be expected under single tree selection structures should be considered as a critical aspect with regard to theoretically possible transformation.

Impact of armillaria root disease and the effect of thinning in a late‐rotation Pinus radiata plantation

SummaryIn a search for alternative methods for managing armillaria root disease in Pinus radiata plantations in New Zealand, a thinning trial was established in a 1985 planted stand infested by Armillaria novae‐zelandiae. The incidence of chronic (non‐lethal) infection rose significantly following a first thinning at age 7 years that provided additional inoculum in the form of colonized stumps. However, this effect diminished before age 19 years when the small stumps had decomposed and, contrary to expectations, a further increase in infection did not follow a second thinning at age 13.5 years, despite a high incidence of larger colonized second thinning stumps. Apparently the increased vigour and associated resistance in the released older trees was sufficient to counter any increase in inoculum potential following treatment. It therefore now appears that thinning may not be detrimental to the final crop volume in contemporary diseased second‐rotation plantations. However, this treatment furnishes no disease control benefit, and should still be deployed judiciously in heavily infested stands. There was a small, but significant reduction in volume growth on the more severely infected trees during the first 13 years in this trial, but on the larger trees later in the rotation at age 19 years there was no difference in stem volume between infection severity categories. A previous assessment based only on the earlier data therefore overestimates the impact of Armillaria in present and future pine plantations in New Zealand. Nevertheless, its widespread distribution and its demonstrated pathogenicity indicate that forest owners should be conscious of the presence of Armillaria during plantation management.

Analysing effects of thinning on stand volume growth in relation to site conditions: A case study for even-aged Sitka spruce (Picea sitchensis (Bong.) Carr.)

This study challenges all-else-equal assumptions in the analysis of thinning effects and more specifically those regarding local variation in forest site productivity. It is demonstrated that considerable variation may occur in site productivity in apparently homogeneous forest stands, whether thinned or unthinned, and that this may not be reflected in height, but rather in basal area growth. To account for such variation, the suggestion is to include an unbiased pre-treatment measure of site productivity, such as total volume production prior to first thinning, as a covariate in the analysis. In a wider perspective, the study further challenges two general site productivity hypothesis, namely, the general assumption that stand volume growth correlates well with stand height (the site index hypothesis, i.e. that site productivity can be estimated based on stand height) and the assumption that, for a given species, total volume production at a given stand height is identical for all site classes (Eichhorn's rule). The thinning response pattern for even-aged Sitka spruce is quantified for different site types based on two thinning experiments in Denmark and six comparable experiments in Great Britain, Norway and Sweden. The effect of thinning from below on stand volume growth is strongly site dependent, but heavy thinning usually leads to a reduction in volume growth as compared with an unthinned stand growing under similar site conditions. For some sites, typically those with stable and ample water supply and a deeply developed root system, stand volume growth is maximized through light thinning. For some other sites, typically those with a high ground water table and a shallow root system, thinning reduces stand volume growth and considerably so with increasing thinning grade. There seems to be a gradient in the reduction, so that it is lessened with increasing rooting depth and with increasing stability of water supply. Due to site-dependent variation in the relation between height growth and stand volume growth as well as site-dependent variation in thinning response pattern, it is recommended to establish and maintain unthinned observation plots in managed stands to ensure reliable growth and yield prognoses. Such plots can serve as a reference for thinning practices as well as a standard for potential volume growth. This recommendation could also hold for other species and in other parts of the world.

Wood production, litter fall and humus accumulation in a Czech thinning experiment in Norway spruce ( Picea abies (L.) Karst.)

This paper reports results from a thinning experiment in even-aged Norway spruce, located on former agricultural land at Vitkov in the Czech Republic. The experiment is part of a European-wide series, established under the auspices of IUFRO. Site productivity at Vitkov is high. The experiment includes five treatments with four (pseudo) replications in two blocks. The treatments comprise four thinning regimes and an unthinned control. The thinning regimes were defined based on two levels of simulated mechanization, two different selection principles (thinning pre-dominantly from below or crown thinning), three different sequences of thinning operations (early, late or depending on available assortments), and two different rack widths (3.5 or 5.0 m). All treatments, except the unthinned control, include an early, heavy thinning and aim for a final crop of 400 pre-selected trees per ha. In the unthinned control, stem number is being reduced only through natural mortality. After 29 years of observations, from age 8 to 37 years, the experiment demonstrates a reduction of 14–23% in stand volume growth due to thinning. Following an initial, heavy thinning, subsequent thinnings result in a larger reduction in volume growth if they are carried out shortly after the first thinning. The reduction in volume growth increases slightly with increasing rack width. Assortment thinnings (crown thinning) lead to the largest reduction in stand volume growth, but this pattern seems to depend on site or other local conditions. At an age of 39 years, litter fall in an unthinned control and a thinned plot ranged from 8500 to 8700 kg ha −1 (dry weight), with foliar litter accounting for 7100–7800 kg ha −1. The dry weight of biomass accumulated in the holorganic L-, F-, and H-horizons ranged from 80,000 to 100,000 kg ha −1. The organic horizons accumulated 720–950 kg ha −1 of nitrogen, with an annual return of nitrogen through litter fall at 75 kg ha −1. The biomass in the organic horizons contained 20,000 kg ha −1 of carbon. There were no differences between litter fall in the unthinned control and the thinned plot, but a lower content of biomass and nutrients (except calcium) in the thinned plot. This supports the theory of faster decomposition and cycling of nutrients in organic horizons of thinned stands, as compared to unthinned stands of even-aged Norway spruce.

The zone of influence of paddock trees and the consequent loss in volume growth in young Eucalyptus dunnii plantations

Old paddock trees, retained in young eucalypt plantations for biological conservation, can be assumed to have a circular zone of influence within which the growth of the young trees is reduced. We used a set of non-linear simultaneous equations to model the radius of the zone of influence of old paddock trees and the consequent loss in stand volume growth of young trees in 4-year old Eucalyptus dunnii plantations. For paddock trees with crown radii of 5, 10 and 15 m and a suppression intensity of 0.5, the predicted radius of the zone of influence was 9.04, 23.8 and 42.0 m, and the predicted loss in stand volume growth was 1.3, 8.7 and 27.0% per hectare, respectively. The reduction in volume growth is expected to increase with time because the discrepancies in size between trees in and outside the zone of influence will increase as stands grow and competition for resources intensifies. The reduction in merchantable stand volume is expected to be even greater since some trees within the zone of influence are not expected to reach merchantable size by the end of the rotation. To minimise the loss of productivity while maintaining biodiversity, other alternatives such as offsetting removal of paddock trees by planting more trees in designated retention areas may need to be formulated.

Observations on Growth of Paraquat-Treated Slash Pine

Abstract Research in use of paraquat to stimulate oleoresin formation in southern pines has resulted in substantial effort to develop commercial application techniques for increasing resin production. Currently there is some concern over the extent to which paraquat treatment affects the subsequent growth and yields of treated trees. In the present study low concentrations of paraquat cation (0.25 percent) injected into two tangential bore holes at the root collar caused no significant reduction in volume growth of 18-year-old slash pine during the two-year posttreatment period prior to harvest. Paraquat concentrations twice this high (0.5 percent), but injected into a single radial bore hole, resulted in approximately 13-percent growth reduction over the same period of time, indicating that higher concentration and lower volume treatments should be avoided. Both the mode of application and concentration used are important variables to consider in developing techniques to enhance oleoresin production without significant loss in volume growth.