Managing red pine stand structure to mitigate drought impacts

Reducing forest stand density through silvicultural thinning has demonstrated potential to mitigate drought impacts on growth; however, less has been studied on how changes in stand structure created by different thinning methods influence forest growth responses to drought. This research examined the growth responses to drought of natural-origin red pine in a long-term study contrasting thinning methods. Dendrochronological methods were used to examine growth responses during several drought events among stands where different thinning methods have been applied since 1950. Growth responses to drought were expressed as resistance (maintaining growth during drought), and resilience (regaining pre-drought growth). Results indicate that periodic thinning from above, which resulted in smaller diameters, has the potential to moderate drought-induced growth reductions. Larger tree diameters negatively influenced tree-level resistance and resilience across all treatments; however, the proportion of dominant trees in a stand had contrasting effects on stand-level drought responses. Stands thinned from above exhibited more complex vertical structure and increased stand-level resistance and resilience to drought-induced growth declines because competition is more stratified among smaller diameter trees. Opposite trends were observed in stands thinned from below, where the larger diameters and monolayered structure create greater competition among trees of similar size and crown position. The results of this study highlight the utility in managing for greater structural diversity to mitigate the negative effects of drought in red pine forest ecosystems.     

How do Araucaria angustifolia trees grow in overstocked stands?

The objective of this study was to evaluate growth along the stem of Araucaria angustifolia (Bertol.) Kuntze trees competing in overstocked stands, in order to identify periods when growth and trunk shape are differentiated during the trees' lifespan. The research was carried out in a planted forest of Araucaria angustifolia established in 1946 in the Açungui National Forest in Campo Largo, Paraná, Brazil, when these trees were 65 years old. One thinning was recorded, at some time between 1970 and 1980. Forty-six trees were selected and divided into three development classes (DC) at 65 years of age; these classes considered diameter at 1.30 m (breast height, dbh) with a range of 20 cm (from 10 cm to 70 cm). In addition to dbh, total tree height, and crown height and diameter were measured in the field. From each tree, 14 disks were removed to analyze growth rings and confirm the age of the stand. Some trees in the smallest DC (10 ≤ dbh < 30 cm) were the product of natural regeneration (younger trees that grew after the initial planting). In 63% of the trees, at least one growth ring was missing at breast height. Missing rings at breast height were more common in trees with smaller dbh and crown diameters. The need for more growing space was observed at different periods during the studied lifespan of the trees from three DCs. It resulted in changes in stems shape from conical to cylindrical. Different growth patterns could be observed during the lives of some trees as they outgrew their competition.     

Effects of fire alone or combined with thinning on tissue nutrient concentrations and nutrient resorption in <Emphasis Type="Italic">Desmodium nudiflorum</Emphasis>

This study examined tissue nutrient responses of Desmodium nudiflorum to changes in soil total inorganic nitrogen (TIN) and available phosphorus (P) that occurred as the result of the application of alternative forest management strategies, namely (1) prescribed low-intensity fire (B), (2) overstory thinning followed by prescribed fire (T + B), and (3) untreated control C), in two Quercus-dominated forests in the State of Ohio, USA. In the fourth growing season after a first fire, TIN was significantly greater in the control plots (9.8 mg/kg) than in the B (5.5 mg/kg) and T + B (6.4 mg/kg) plots. Similarly, available P was greater in the control sites (101 μg/g) than in the B (45 μg/kg) and T + B (65 μg/kg) sites. Leaf phosphorus ([P]) was higher in the plants from control site (1.86 mg/g) than in either the B (1.77 mg/g) or T + B plants (1.73 mg/g). Leaf nitrogen ([N]) and root [N] showed significant site–treatment interactive effects, while stem [N], stem [P], and root [P] did not differ significantly among treatments. During the first growing season after a second fire, leaf [N], stem [N], litter [P] and available soil [P] were consistently lower in plots of the manipulated treatments than in the unmanaged control plot, whereas the B and T + B plots did not differ significantly from each other. N resorption efficiency was positively correlated with the initial foliar [N] in the manipulated (B and T + B) sites, but there was no such relation in the unmanaged control plots. P resorption efficiency was positively correlated with the initial leaf [P] in both the control and manipulated plots. Leaf nutrient status was strongly influenced by soil nutrient availability shortly after fire, but became more influenced by topographic position in the fourth year after fire. Nutrient resorption efficiency was independent of soil nutrient availability. These findings enrich our understanding of the effects of ecosystem restoration treatments on soil nutrient availability, plant nutrient relations, and plant–soil interactions at different temporal scales.     

Species richness and composition of Curculionidae (Coleoptera) in a conifer plantation, secondary forest, and old-growth forest in the central mountainous region of Japan

Weevil (Curculionidae, Coleoptera) species richness and composition were investigated and compared among larch [Larix kaempferi (Lamb.) Carriére] plantations, secondary forests, and old-growth forests in the central mountainous region of Japan. In addition, to assess the effects of forest-management practices, namely thinning and long-rotation logging schedules (long rotation), the weevil assemblages of recently thinned middle-aged and long-rotated larch plantations were compared with those of middle-aged larch plantations. Malaise traps were set in 44 stands of these forest types, and weevils were separated and identified. Several environmental factors other than forest type were also examined. Weevil species richness and diversity indices [Shannon-Wiener diversity index (H) and Simpsons index of diversity (D)] were higher in the secondary forest than in the larch plantation. Because of its wide distribution and higher weevil species richness, the secondary forest contributed to maintaining weevil diversity in this region. Old-growth forest had higher diversity indices (H and D) than did the larch plantation. The secondary forest had the highest number of species in total. Though the number of individuals was the highest in larch plantation, species richness, H and D of the plantation were generally low. Weevil community structure and species composition differed among the three forest types, but the difference in weevil composition between the larch plantation and the other two forest types was the largest. Forest type is probably the most important factor for determining the differences in weevil assemblage, and further, both dominant tree type (coniferous trees versus broad-leaved trees) and the number of mature tree species seem to be important factors for weevil species composition. Among forest management practices, long rotation caused diversity indices (H and D) to increase while thinning appeared to cause only minor changes in the weevil assemblages. Because species richness and species composition of Curculionidae well reflected the differences in forest types and some other environmental factors investigated, this family seems suitable for diversity research in forests. Further research on biodiversity with the use of this family should, therefore, be expected.     

Modelling the distribution of diameter growth along the stem in Scots pine

This paper presents an empirical model for the distribution of diameter growth along the stem in Scots pine (Pinus sylvestris L.) and for the consequent stem form over time. First, the distribution of annual mass growth in the stem is determined as a function of the total annual growth in stem mass, current stem mass and the distribution of the latter along the stem. Second, the distribution of diameter growth is obtained by converting the fraction of annual growth in the stem mass at a given height in the stem into the thickness of the annual ring at the same height. Application of the model to Scots pine data sets including both young and mature trees not used in parameter estimation showed that the model was capable of reconstructing the distribution of diameter growth from the stem butt to the apex and from the pith to the stem surface at any height in the stem in both young and mature trees. The resulting empirical model was also linked to a physiological, process-based model in order to study its performance in a simulated stand. Simulations representing trees grown in unthinned and thinned Scots pine stands with trees of different status (from dominant to suppressed) showed that the response in tree growth to thinning in terms of the distribution of diameter growth along the stem was quite realistic relative to measured data.     

A GIS-based simulation program to predict multi-species size-structure dynamics for natural forests in Hokkaido, northern Japan

A simulation program that runs on a geographic information system (GIS) was developed to predict the multi-species size-structure dynamics of forest stands. Because important characteristics of a forest stand, including woody biomass accumulation, carbon storage, commercial value of timber, and functions for environmental conservation, can be inferred from the size structures of the component populations, management plans can be made from the predictions of the size-structure dynamics. For example, the simulation can incorporate various forms of thinning; forest managers can then try several thinning plans in simulated forest stands and choose the appropriate plan that achieves the best results. Using GIS to predict the size-structure dynamics of forest stands is of practical importance, because GIS has been used widely in forest management and can easily handle spatial distributions of environmental information (e.g., climate, geology, soils) that may influence tree performance. To predict size-structure dynamics, the program numerically solves a continuum equation that describes size-structure dynamics based on growth and mortality rates of individual trees. When predicting size-structure dynamics of a forest stand, the program obtains the environmental information of the stand from a database stored in the GIS and calculates environmental factors such as warmth index and potential evapotranspiration/precipitation ratio that influence growth and mortality rates. The simulation program calculates growth and mortality rates using published growth and mortality models that incorporate the effects of size of the individual, competition between trees, and abiotic environmental factors. To demonstrate the effects of abiotic environmental factors on the multi-species size-structure dynamics, sensitivity analyses were conducted. The size-structure dynamics varied in a way that was predictable from the responses of the growth and mortality rates to variations in the abiotic environmental factors. To demonstrate the size-structure dynamics in different locations, five test runs of the simulation program were also performed using the same initial size-structure and five different sets of abiotic environmental conditions from five locations. At the end of the simulation, the predicted size structures differed because the growth and mortality rates differed among the five locations. Finally, the response of the size structure to thinning was clarified. The result showed how the size structure of a component species in a forest stand is dependent on the presence of other species.     

Oak woodland restoration: testing the effects on biodiversity of mycetophilids in southern Sweden

The effect of harvesting biofuel and woodland restoration on biodiversity is debated. To evaluate the effects of partial cutting on more organism groups, we used pairwise experimental and undisturbed control stands in a large landscape. On average 26% of the basal area including 50–95% of the understorey was harvested at each of 15 oak-rich forest sites. Our earlier results of partial cutting suggested a positive short-term effect for vascular plants and beetles and no or minor negative effects for fungi. Here we analyse the response of mycetophilids (Diptera: Sciaroidea excl. Sciaridae), a neglected but species-rich insect group that was strongly disfavoured by clear-cutting in previous studies. Increased deadwood (slash) caused increase in the number of individuals of mycetophilids associated with wood or wood fungi. The rarefaction species numbers of mycetophilids declined after the treatment, but the absolute number of species was not affected. Our results indicate that a 25% harvest can be compatible with conservation of vascular plants, fungi, saproxylic and herbivorous beetles and mycetophilids in temperate hardwood stands of the type studied. However, more studies are needed to determine what level(s) of stand thinning can be tolerated by different taxa in landscapes with small fragmented conservation stands.     

间伐强度对杉木－火力楠混交林生长影响的研究初报

对杉木-火力楠混交林进行4种间伐强度试验表明,间伐6年后各林分的杉木、火力楠胸径净生长量比对照分别增加70-139、11-25%,树高增加46-90、7-10%,村积生长增加54-140、10-43%,林分蓄积量增加49-75m³·ha^-1,平均冠高增加2-6、8-13%,第1活枝高下降0.5-3、35-48%.冠幅杉木下降1-2%、火力楠增加1-8%.可以认为,以间伐强度为30和40%2种方式较好,间伐后林分定型株数约保留在1600-2200株·ha^-1之间为宜。     

Old holm oak coppices . . . new sylvopastoral practices

In the south of France, holm oak (Quercus ilex L.) woodlands, particularly coppices, are currently used by livestock farmers. For this vegetation, a grazing allowance is available, based on the relationship between various layers. As far as livestock is concerned, such woodlands can be utilized for many purposes, e.g. stock feeding during critical periods and to provide flexibility to the pasture grazing sequence. Furthermore, the related grazing intake patterns determine the level of holm oak utilization. Practices integrating both wood and livestock production provide a new perspective to the management of these woodlands in that the presence of livestock promotes specific operations which can lead to more diversified forestry. The renewal of both wood and pastoral resources depends on: (i) the initial level of integration of these two activities and (ii) subsequent technical operations. In the present paper a midterm management scenario is developed which describes the likely development of woodlands with multiple use and periodic thinning.