Growth and yield models for uneven-sized forest stands in Finland

Uneven-sized forestry is gradually gaining popularity and acceptability also in the Nordic countries. This is because of the willingness of the public and some forest owners to avoid clear-fellings and pursue more near-nature forest structures. It has also been realized that the profitability of uneven-sized forestry may be competitive with even-aged forestry. In Finland, management of uneven-sized stands is hampered by the lack of information about the dynamics of such stands, and about the yield and profitability of uneven-sized forestry. This study developed models which allow managers to simulate the growth and yield of uneven-sized stands in Finland, making it possible to predict the yield and analyze the sustainability of different management options. The model set consists of individual-tree diameter increment, height and survival models, and a model for ingrowth. The modeling data consisted of two long-term field experiments of uneven-sized forest management, a set of temporary sample plots measured earlier for growth modeling purposes, and the sample plots of the third National Forest Inventory of Finland. The application area of the models covers all growing sites, all main tree species, and the whole surface area of Finland. According to the models, the sustainable harvest of a fertile (Oxalis-Myrtillus site) uneven-sized Norway spruce forest varies between 5.5 and 7 m³ ha⁻¹ a⁻¹ in Central Finland, depending on the length of the cutting cycle, stand density, and shape of the diameter distribution. It is profitable to harvest large diameter classes more heavily than small ones. Due to the large amount of data the models for diameter increment are highly significant and reliably show the growth level of trees in uneven-sized stands. The weakest models are the ingrowth models, which are based on a clearly smaller data set than the other models.     

Optimizing any-aged management of mixed boreal forest under residual basal area constraints

The current trend of forest management in many countries is reduced use of clear-felling and planting, and increased use of continuous cover management. In Finland, the new forest act of 2014 made all types of cuttings equally allowable on the condition that if the post-cutting residual stand basal area is too low, the stand must be regenerated within certain time frame. Forest landowner can freely choose between evenand uneven-aged management. This study developed a method for optimizing the timing and type of cuttings without the need to categorize the management system as either even-aged or uneven-aged. A management system that does not set any requirements on the sequence of post-cutting diameter distributions is called any-aged management. Planting or sowing was used when stand basal area fell below the required minimum basal area and the amount of advance regeneration was less than required in the regulations. When the cuttings of 200 stands managed earlier with even-aged silviculture were optimized with the developed system, final felling followed by artificial regeneration was selected for almost 50% of stands. Reduction of the minimum basal area limit greatly decreased the use of artificial regeneration but improved profitability, suggesting that the truly optimal management would be to use natural regeneration in financially mature stands. The optimal type of thinning was high thinning in 97–99 % of cases. It was calculated that the minimum basal area requirement reduced the mean net present value of the stands by 12–16 % when discount rate was 3–5 %.     

The minimum temperature for budburst in Betula depends on the state of dormancy

Vegis has put forward the theory that the range of growth-promoting temperatures changes during the induction and the release of dormancy. We have tested the response of buds of Betula pubescens Ehrh. and B. pendula Roth. on temperature during the induction and release of dormancy. Betula seedlings were exposed to dormancy-inducing high-temperature and short-day conditions and subsequently to dormancy-releasing chilling conditions in darkness. To monitor the dormancy status of the seedlings, subsets of them were transferred to five forcing temperatures and their budburst was observed. The results show that the expression of dormancy was temperature dependent, so that the minimum temperature for 100% budburst rose during the induction and dropped during the release of dormancy. These responses may explain previous contradictions between experimental and modelling studies, but that needs to be verified with more extensive experiments, some of which are identified in this study. The results provide further evidence for the concept of gradual change in bud dormancy. They also suggest that global change studies modelling budburst phenology should address the changing expression of bud dormancy.     

Species Interactions in the Dynamics of Even- and Uneven-Aged Boreal Forests

Many boreal tree stands are neither clearly even-aged nor clearly uneven-aged. The stands may undergo a series of stages, during which an even-aged stand is transformed into two-storied mixed stand, and finally to multistoried or uneven-aged stand structure. The species composition often changes during the succession of stand stages. This study developed models for stand dynamics that can be used in different stand structures and species compositions. The model set consists of species-specific individual-tree diameter increment and survival models, and models for ingrowth. Separate models were developed for Scots pine, Norway spruce, and hardwood species. The models were used in a growth simulator, to give illustrative examples on species influences and stand dynamics. Methods to simulate residual variation around diameter increment and ingrowth models are also presented. The results suggest that mixed stands are more productive than one-species stands. Spruce in particular benefits from an admixture of other species. Mixed species improve diameter increment, decrease mortality, and increase ingrowth. Pine is a more beneficial admixture than birch. Simulations showed that uneven-aged management of spruce forests is sustainable and productive, and even-aged conifer stands growing on medium sites can be converted into uneven-aged mixed stands by a series of strong high thinnings.     

Critical night length for bud set and its variation in two photoperiodic ecotypes of Betula pendula

We studied the variation in critical night length for bud set in two photoperiodic ecotypes (two latitudinally distant stands) of silver birch (Betula pendula Roth) in three phytotron experiments. Seeds from 21 open-pollinated mother trees in a southern (Tuusula, 60 degrees N) and a northern (Kittil?, 67 degrees N) Finnish stand were germinated and grown for 4 weeks in a 24-h photoperiod in a greenhouse and then moved to different night length treatments at 18 degrees C for 4 to 6 weeks. Night lengths from 5 to 8.5 h were used for southern origin seedlings and from 1 to 4.5 h for northern origin seedlings. At the end of the treatments, apical bud set was observed and the percentage of seedlings with bud set calculated for each treatment and tree progeny. The critical night lengths (CNL) for 50% bud set were determined separately for seedlings from each mother tree by regression analysis. In both ecotypes, the mean percentage of seedlings with bud set was lowest for the shortest night lengths and increased rapidly as night lengths increased. Mean CNL with its 95% confidence interval for the southern and northern ecotypes was 6.3 +/- 0.2 and 3.1 +/- 0.3 h, respectively. The CNL of the two ecotypes differed significantly in three experiments. Within-ecotype variance of the CNL was significantly higher in the northern ecotype (0.484) than in the southern ecotype (0.150). Significant differences in CNL were detected between individual mother trees of the southern ecotype, but not between mother trees of the northern ecotype. The ranking of individual mother trees, based on CNL, differed in the three experiments.     

Spice crops agroforestry systems in the East Usambara Mountains,Tanzania: growth analysis

A scarcity of cultivation land calls for more intensive and productive land use in the East Usambara Mountains in NE Tanzania. Spice crops could generate cash in higher parts of the mountains, but the present cultivation methods are depleting the valuable forest resources. The trial was established at the end of 2000 to find out how the two popular cash crops, cardamom (Elettaria cardamomum (L.) Maton.) and black pepper (Piper nigrum L.), normally grown under the natural forest, will produce in intensive agroforestry system with two multipurpose farm trees, Grevillea robusta A.Cunn. and nitrogen fixing Gliricidia sepium Jacq. Results from 6 years showed that cardamom produced better with grevillea than in natural forest; 5.5 times more in the fourth year than the average in the area. The Land Equivalent Ratios for black pepper and cardamom showed that pepper intercropped with grevillea produced 3.9 times more than in monoculture whereas cardamom intercropped with grevillea and pepper produced 2.3 times more than in monoculture. Gliricidia improved the nitrogen and organic matter content of the soil over the levels found in natural forest. Soil acidity was, however, preventing the plants from using the available mineral nutrients more effectively.     

Optimal management of uneven-aged Norway spruce stands

An optimization model is specified to analyze forest management without any restrictions on the forest management system. The data on forest growth comes from unique field experiments and is used to estimate a nonlinear transition matrix or size-structured model for Norway spruce. The objective function includes detailed harvesting cost specifications and the optimization problem is solved in its most general dynamic form. In optimal uneven-aged management, stand density is shown to be dominated by limitations in natural regeneration. If the goal is volume maximization, even-aged management with artificial regeneration (and thinnings from above) is superior to uneven-aged management. After including regeneration and harvesting costs, the interest rate, and the price differential between saw timber and pulpwood, uneven-aged management becomes superior to even-aged management. However, in the short term the superiority is conditional on the initial stand state.     

Effects of defoliation on carbohydrate status,nodules and spring growth in white clover in a sub-arctic climate

Abstract

In order to improve the basis for utilizing white clover (Trifolium repens L) in northern agriculture, we studied the effects of defoliation intensity on spring growth in a sub-arctic climate in relation to carbohydrate and nodule status. White clover plants (cv Snowy) were studied in a pot experiment in the field on the coast of northern Norway from spring 2001 until spring 2002. The experiment was repeated with some modifications from spring 2002 until spring 2003. During the growing season from summer to autumn, the plants were totally stripped of leaves down to the stolon, cut at four or seven cm height or left undisturbed. The plants were sampled destructively in autumn, early spring and late spring and sorted into leaves, stolons and roots. The plant material was weighed and analysed for carbohydrate reserves and nodule number. Defoliation during the growing season resulted in reduced concentration of reserve carbohydrates in autumn and reduced winter survival of the stolons. The most severe defoliation treatment reduced the herbage growth in spring. In contrast, the two milder defoliation treatments had no effect on herbage growth during spring or on total plant dry matter and nodule status in late spring. In conclusion, moderate defoliation during the growing season had no effect on herbage growth the following spring nor on carbohydrate, nodule or dry matter status of the plant in late spring. Moderate defoliation increased spring growth and thereby also the nitrogen demand of the plants. This probably enhanced nodule formation and development of inactive to active nodules.     

Effect of vegetation cover on soil erosion in a mountainous watershed

We applied the Revised Soil Loss Equation (RUSLE) to assess levels of soil loss in a Geographic Information System (GIS). In this study, we used the k-NN technique to estimate vegetation cover by integrating Landsat ETM+ scenes and field data with optimal parameters. We evaluated the root mean square errors and significance of biases at the pixel level in order to determine the optimal parameters. The accuracy of vegetation cover estimation by the k-NN technique was compared to that predicted by a regression function using Landsat ETM+ bands and field measurements as well as to that predicted by the Normalized Difference Vegetation Index (NDVI). We used a regression equation to calculate the cover management (C) factor of the RUSLE from vegetation cover data. On the basis of the quantitative model of soil erosion, we explored the relationship between soil loss and its influencing factors, and identified areas at high erosion risk. The results showed that the k-NN method can predict vegetation cover more accurately for image pixels at the landscape level than can the other two methods examined in this study. Of those factors, the C-factor is one of the most important affecting soil erosion in the region. Scenarios with different vegetation cover on high-risk areas showed that greater vegetation cover can considerably reduce the loss of soil erosion. The k-NN technique provides a new method to estimate the C-factor for RUSLE erosion mapping. The quantitative model of different vegetation cover scenarios provides information on how vegetation restoration could reduce erosion.     

Development of Cold Tolerance in White Clover (Trifolium repens L.) in Relation to Carbohydrate and Free Amino Acid Content

Abstract

Development of cold tolerance in white clover (Trifolium repens L.) genotypes originating from various parts of Norway and grown outdoors at Tromso, latitude 69°39′N, has been studied. Stolon samples for an artificial freezing test and for chemical analysis were collected three times during the autumn. Generally, the most northern genotypes were more cold tolerant than the southern ones. Cold tolerance increased significantly from September to November in all genotypes. Content of dry matter, soluble carbohydrates, sucrose and proline in stolons increased during the hardening process. These changes were similar in both northern and southern genotypes of white clover.