Impacts of thinning on structure,growth and risk of crown fire in a Pinus sylvestris L. plantation in northern Spain

We studied the combined effects of thinning on stand structure, growth, and fire risk for a Scots pine thinning trial in northern Spain 4 years following treatment. The thinning treatments were: no thinning, heavy thinning (32–46% of basal area removed) and very heavy thinning (51–57% of basal area removed). Thinning was achieved via a combination of systematic and selective methods by removing every seventh row of trees and then by cutting suppressed and subdominant trees in the remaining rows (i.e., thinning from below). Four years after thinning, mean values and probability density distributions of stand structural indices showed that the heavier the thinning, the stronger the tendency towards random tree spatial positions. Height and diameter differentiation were initially low for these plantations and decreased after the 4-year period in both control and thinned plots. Mark variograms indicated low spatial autocorrelation in tree diameters at short distances. Diameter increment was significantly correlated with the inter-tree competition indices, and also with the mean directional stand structural index. Two mixed models were proposed for estimating diameter increment using a spatial index based on basal area of larger trees (BALMOD) in one model versus spatial competition index by Bella in the other model. As well, a model to estimate canopy bulk density (CBD) was developed, as this variable is important for fire risk assessment. Both heavy and very heavy thinning resulted in a decrease of crown fire risk over no thinning, because of the reduction in CBD. However, thinning had no effect on the height to crown base and thus on the flame length for torching. Overall, although thinning did not increase size differentiation between trees in the short term, the increase in diameter increment following thinning and the reduction of crown fire risks support the use of thinning. Also, thinning is a necessary first step towards converting Scots pine plantations to more natural mixed broadleaved woodlands. In particular, the very heavy thinning treatment could be considered a first step towards conversion of overstocked stands.     

A nutrient balance model (NuBalM) to predict biomass and nitrogen pools in Pinus radiata forests

Forest managers are increasingly required to enhance the productivity and profitability of plantation management while simultaneously reducing the negative ecological effects associated with forest operations. NuBalM (from Nutrient Balance Model) is presented here as a decision support tool that has the potential to assist forest managers in meeting these requirements in Pinus radiata D. Don (radiata pine) plantations. NuBalM incorporates nutrient dynamics and allocation into projections of growth, allowing management techniques to be optimised for productivity and nutrient pool retention over single or multiple rotations.NuBalM was developed using data from biomass, nutrient allocation and soil nutrient dynamics studies conducted in New Zealand radiata pine plantations. The capability of NuBalM to predict stem wood mass based on nitrogen supply and demand was tested against data from multiple trial sites established to examine the effects of variations in stocking, thinning and fertilization regimes. NuBalM satisfactorily predicted stem wood masses across a range of stand ages, with the exception of a trial examining ultra-high applications of nitrogen fertilizer. With the exclusion of the data from this trial, the predicted stem wood masses underestimated the observed figures by a mean value of 1.1 ± 1.0 t ha⁻¹ (95% CI, n = 92).The utility of NuBalM as a tool to predict biomass allocation in radiata pine and nitrogen pools in the forest floor and soil was assessed using comprehensive biomass, nutritional and site data collected from two radiata pine trial sites subjected to differences in organic matter removal at site establishment. NuBalM performed acceptably, generating accurate estimates of stem mass (mean overestimate of 5.5 ± 7.4 t ha⁻¹, 95% CI, n = 6) and total above ground biomass (mean overestimate of 3.1 ± 9.6 t ha⁻¹, 95% CI, n = 6). The effects of organic matter removal and fertilization on total nitrogen pools were also predicted with a reasonable degree of accuracy (mean overestimate of 52 ± 53 kg N ha⁻¹, 95% CI, n = 9).From these results we conclude that NuBalM can be utilised to provide projections of productivity and nitrogen pools in radiata pine plantations, and enables the effects of various management practices to be predicted with a reasonable degree of confidence.     

Changes in the canopies of Pinus sylvestris and Picea abies under alkaline dust impact in the industrial region of Northeast Estonia

Studies were carried out in 1999, 2005 and 2007 in the area of Kunda cement plant in Northeast Estonia on sample plots 3 km W and 2.5 and 5 km E of Kunda. As control stands, two plots for pine and spruce were established in Lahemaa National Park (34-38 km W of Kunda). The selected pine and spruce stands were 75-85-year-old Myrtillus site type, of 0.7-0.8 density and II quality class, with moderately dense or sparse understorey. The values concerning needle density and number of needle scars were higher for shoots formed in the period of higher pollution than for the shoots grown under a considerably lower pollution load. Although the cement dust pollution has notably decreased from year to year, the number of needle pairs per 1 cm of the shoot was 1.8-2.1 times greater in the shoots formed in 1998 than in those formed in 2003, whereas the changes were statistically reliable. Possibly the low temperatures at the time of shoot and needle formation affected the density of needles on all sample plots, and thus the number of needles on shoots formed in 2003 was many times smaller. After the significant fall in the pollution load since 1996 the length growth of needles intensified around Kunda cement plant, at the same time no changes occurred in the length growth of needles in the control area. As compared to the data from 1998, the length growth of pine needles had improved, especially 2.5 and 5 km E from the cement plant, needles being respectively 1.5 and 1.1 cm longer than 6 years ago. The stimulation of the growth of pine and spruce needles 2.5 and 5 km E of the cement plant may be a sign of a positive effect of reduced doses of cement dust in soil. The greater length of pine and spruce needles is the reason for the larger biomass of the needles.