Maximum Mean Annual Increment Research Articles

Upland black spruce stand development 17 years after cleaning and precommercial thinning

Density management is often used by silviculturists to guide stand composition and development. We examined the effects of cleaning (hardwood removal) and four levels of precommercial thinning (0, 20, 35 and 50% basal area removal) on stand development in a dense, 24-year-old upland black spruce (Picea mariana [Mill.] BSP) plantation near Beardmore, Ontario. Immediately before treatment, stand densities and basal areas for all species and for black spruce averaged 7375 and 6415 stems ha-1, and 27.9 and 20.5 m2 ha-1, respectively. Seventeen years after treatment, black spruce total stand volume (VT) was higher in the cleaned, unthinned plots (243 m3 ha-1) than in the untreated controls (171 m3 ha-1) while total stand volume increment of all species combined was similar in these two treatments. Compared with cleaning alone, thinning cleaned plots from below increased quadratic mean diameters (DQ) by up to 9% but decreased VT by up to 28%. At plantation age 41, increases in black spruce densities of 1000 stems ha-1 resulted in mean decreases of 0.6 cm in DQ and mean increases of 43 m3 ha-1 in VT. Endemic black spruce stem mortality rates decreased with thinning intensity, with mortality concentrated in the smallest size classes. In some plots, mortality was increased by wind or snow damage, and by root rots. Height increment of dominant trees was unaffected by thinning. Projected yields at age 55 (the physical rotation age—the age at which maximum mean annual increment occurs) suggest the heaviest precommercial thinning could increase quadratic mean diameter from 16.1 to 17.7 cm, but decrease merchantable stand volume from 292 to 225 m3 ha-1. Results indicate that total black spruce fibre yields and product value on these sites will be maximized in denser stands. Cleaning appears to offer greater benefits for black spruce fibre production than precommercial thinning. Key words: black spruce, precommercial thinning, cleaning, density management, projected yields

Growth and recruitment after mountain forest selective cutting in irregular spruce forest. A case study in Northern Norway

During the last thirty years the interest for the use of selective cutting in the sub-alpine spruce forests of Norway has increased. However, there have been very few investigations on the post harvesting development after such cuttings. Four plots in irregular Norway spruce (Picea abies (L.) Karsten) dominated forests on semi-fertile sites in Northern Norway have been the subjects of a case study. We performed a reconstruction of the stand development by means of biometric assessments and ring widths measurements of all standing trees. Tree ages, stand structure, growth and recruitment were examined. Even though a hypothetical reverse J-curve for the present diameter distribution was identified, the four plots were even-aged. Growth reactions indicate that most of the present sawtimber trees were established after heavy dimension cuttings in the late 19th century. The recruitment situation is characterized as satisfying in one of four plots. The post harvesting mean volume increment on the plots have been about two thirds of the potential yield estimated from site indices and maximum mean annual increment in regular stands. Managing strategies for irregular spruce forest stands are briefly discussed.

Quantity and quality of harvestable biomass from Populus short rotation coppice for solid fuel use—a review of the physiological basis and management influences

Woody biomass from poplar and aspen ( Populus sp.) short rotation coppice (SRC) has good combustion properties compared to non wood solid bio fuels and fossil solid fuels. This review compiles and discusses relevant literature on fuel quality and yield for Central European conditions. The most problematic quality parameter of woody biomass from Populus SRC is its high water content at harvest time (55–60%). Storing unchipped material on the field during summer is an efficient tool to lower it. In order to control other quality parameters—mainly nitrogen (N), potassium (K) and heavy metal contents but also yield—one has to take into account the physiological background of SRC. Important features are species/clone, age of sprouts, growth pattern, site and nutrient cycling. Maximum mean annual increment (MAI) occurs later than in willows. Therefore rotations should be longer than in willow: at least 6–7 years for poplars and,—due to differences in growth pattern,—10 to 12 years for aspen. Both results in MAIs of 10– 12 o.d.t. ha −1 yr −1 and reduced nutrient concentrations due to a lower share of branches and twigs in the harvested biomass. However, with elongated rotations costs rise because yet no automated (and thus cheap) harvest methods for large stem diameters were developed. Although sometimes ignored poplars are demanding concerning site characteristics. Basic requirements are good water (minimum 350 mm rainfall during growing season) and nutrient supplies, deep soils and favourable climatic conditions (average air temperature between June and September at least 14°C). Only aspen are partly suited for poorer conditions. For Populus-SRC in general weed control during establishing phase is essential.

The growth potential of downy birch (Betula pubescens (Ehrh.)) in Ireland

Birch in Ireland has long been regarded a timber species of minor importance, and it is noted more often for its invasiveness in young coniferous forests and clearfelled areas than for its potential as a commercial forestry species. While research on other native hardwood species such as oak or ash has been ongoing for a number of years, very little is known about the Irish birch resource. The lack of quantitative data relating to height growth, diameter growth and volume increment of birch in this country is of particular concern. The objective of this study was to examine the growth potential of birch in Ireland. Following a field survey, eight well‐stocked, unthinned birch stands were selected for inclusion in the study. All of the selected stands were determined to be downy birch. Following analysis of sample tree disc sections, two stands were excluded (because of indistinct annual rings) and the study was restricted to the six remaining stands. A total of 100 sample trees were felled at the six sites. Tree ring data were collected from a total of 1333 sample tree disc sections. Using these ring data, the historic patterns of radial growth at breast height, height growth and volume growth of the six stands were reconstructed, examined and analysed in detail. The results showed that for well‐stocked, unthinned, even‐aged stands the period of maximum radial growth, and therefore diameter growth, occurred between the ages of 5 and 20 years. The fastest growing tree achieved a diameter of 25 cm in 32 years. It is suggested that for the stands included in this study, the lack of management, in particular the lack of adequate thinning, will have resulted in excessive crown competition and consequently reduced diameter growth. Maximum height increment occurred before the age of 20 years and fast growing trees achieved a height growth of > 1 m per year during this period. The results showed that a well‐stocked, unthinned downy birch stand can achieve a standing volume (under‐bark) of 200 m 3 ha −1 in 42 years. While some of the stands included in the study had not reached the age of maximum mean annual increment, comparison with the Forestry Commission yield models showed that stands of downy birch in Ireland can achieve a yield class of 8 and, given the correct thinning regime, total recovered volume production could possibly be raised to that equivalent with yield class 10.

Assessment of the impact of climate change on the growth of Sitka spruce in Scotland

A regression model developed to predict the general yield class (GYC, maximum mean annual volume increment) of Sitka spruce (Piceasitchensis (Bong.) Carrière) from a range of site factors has been used to assess the potential impact of climate warming on the growth of Sitka spruce in Scotland. The model was interfaced with a geographic information system to predict and map the GYC of Sitka spruce across Scotland under a number of climate change scenarios. GYC was predicted to increase by 2.8 m3•ha−1•year−1 per °C rise in temperature when a uniform temperature increase was assumed during the year. A more likely assumption is a greater warming during winter months, and under such a scenario the increase in mean GYC was predicted to be 2.4 m3•ha−1•year−1•°C−1 because of a negative correlation between growth rate and mean winter temperature. When assessed in terms of land area capable of supporting a GYC greater than 18 m3•ha−1•year−1 (a value likely to provide an internal rate of return of approximately 6%), this area was predicted to almost double within the next 20 years with a similar increase occurring during the subsequent 40 years.

Predicting spacing effects on growth and optimal rotations of tropical multipurpose trees

Abstract In order to improve our ability to analyze growth of tropical fast-growing trees, we developed a simple model (MPTGro) to predict development of even-aged stands from allometric equations of leaf area and total biomass. and a competition index based on wood production per unit leaf area, or net assimilation rate (E). In this study we (1) tested te model assumption that our competition index is valid across plant spacings, (2) tested the performance of MPTGro on two species of tropical multipurpose trees, and (3) applied the model to optimize rotations based on tree size, biomass allocation, or annual biomass increment. Measurements of E and stand leaf area index (LAI) at three-month intervals in spacing trials of Acacia auriculiformis and Leucaena diversifolia supported the assumption that a single relationshp between E and LAI would explain growth at a variety of planting densities. Increasing plant density in the simulations decreased time unitl maximum mean annual increment (MAI) and diameter at maximum MAI, but increased leaf: wood biomass ratio at maximum AMI

Test of a system to predict productivity of eucalypt plantations in Tasmania

Summary A test was undertaken of a system which predicts eucalypt plantation wood volume yields in Tasmania from a set of eight topographic, climatic and soil variables measured at a site. The system was tested in 32 plots located in plantations of E. globulus and E. nitens in northern Tasmania. When the system predicted that a site had high productivity (maximum mean annual increment ≤20 m3ha−1yr−1), there was a fairly high probability (≈80%) that the site indeed had that productivity. However, when it predicted lower productivity, it incorrectly predicted a substantial proportion of sites (≈50%) as being of lower productivity when they were in fact of high productivity. It was shown that, on average, the system underestimated productivity by 7%. In practice, the system could be used to predict average productivity over a region within a range bounded by -4% to +18% of the prediction (95% prediction interval). The system had a similar predictive ability to two other systems developed in Australia to esti...

Analytical model of stemwood growth in relation to nitrogen supply.

We derived a simplified version of a previously published process-based model of forest productivity and used it to gain information about the dependence of stemwood growth on nitrogen supply. The simplifications we made led to the following general expression for stemwood carbon (c(w)) as a function of stand age (t), which shows explicitly the main factors involved: c(w)(t) = eta(w)G*/ micro (w)(1 - lambdae(- micro (w)t) - micro (w)e(-lambdat)/lambda - micro (w)), where eta(w) is the fraction of total carbon production (G) allocated to stemwood, G* is the equilibrium value of G at canopy closure, lambda describes the rate at which G approaches G*, and micro (w) is the combined specific rate of stemwood maintenance respiration and senescence. According to this equation, which describes a sigmoidal growth curve, c(w) is zero initially and asymptotically approaches eta(w)G*/ micro (w) with the rate of approach dependent on lambda and micro (w). We used this result to derive corresponding expressions for the maximum mean annual stem-wood volume increment (Y) and optimal rotation length (T). By calculating the quantities G* and lambda (which characterize the variation of carbon production with stand age) as functions of the supply rate of plant-available nitrogen (U(o)), we estimated the responses of Y and T to changes in U(o). For a plausible set of parameter values, as U(o) increased from 50 to 150 kg N ha(-1) year(-1), Y increased approximately linearly from 8 to 25 m(3) ha(-1) year(-1) (mainly as a result of increasing G*), whereas T decreased from 21 to 18 years (due to increasing lambda). The sensitivity of Y and T to other model parameters was also investigated. The analytical model provides a useful basis for examining the effects of changes in climate and nutrient supply on sustainable forest productivity, and may also help in interpreting the behavior of more complex process-based models of forest growth.

Sustainable stemwood yield in relation to the nitrogen balance of forest plantations: a model analysis.

We used an existing analytical model of stemwood growth in relation to nitrogen supply, which we describe in an accompanying paper, to examine the long-term effects of harvesting and fire on tree growth. Our analysis takes into account the balance between nitrogen additions from deposition, fixation, and fertilizer applications, and nitrogen losses from stemwood harvesting, regeneration burning, leaching and gaseous emissions. Using a plausible set of parameter values for Eucalyptus, we conclude that nitrogen loss through fire is the main factor limiting sustainable yield, defined as the maximum mean annual stemwood volume increment obtained in the steady state, if management practices are continued indefinitely. The sustainable yield is 30 m(3) ha(-1) year(-1) with harvesting only, 15 m(3) ha(-1) year(-1) with harvesting and regeneration burning, and 13 m(3) ha(-1) year(-1) with harvesting, fire, leaching and gaseous emissions combined. Our approach uses a simple graphical analysis that provides a useful framework for examining the factors affecting sustainable yield. The graphical analysis is also useful for extending the application of the present model to the effects of climate change on sustainable yield, or for interpreting the behavior of other models of sustainable forest growth.

Single rotation vs coppice systems for short-rotation intensive culture plantations—optimality conditions for volume production

Short rotation intensive culture plantations can be managed under a single rotation or coppice system. This paper shows the optimality conditions that must exist in order to maximize volume production of short rotation coppice stands. The results indicate the importance of equating the current annual increment of the stand to its mean annual increment whether managing with a single rotation or a series of coppice rotations over a cycle of time. The mathematical conditions for having the coppice system rather than the single rotation for volume production are also derived. These conditions indicate the average of the mean annual increments for the coppice harvests must be greater than the maximum mean annual increment of the single rotation. Finally, an example illustrates an application of the optimality conditions to a set of hypothetical data.

Defining Canada's old-growth forests — problems and solutions

Conceptual and working definitions of old-growth forests are proposed for Canada. Conceptually, old-growth forests are defined in terms of stand age, structure, species composition, anthropogenic influence, and landscape ecology. Working definitions based on stand age in relation to age of maximum mean annual increment and site class are formulated for Canada's inventoried timber-productive forests. The difference between stand age and the age of maximum mean annual increment is proposed as a measure of old-growthness. Recommendations are made for improving Canada's forest inventory database to help acquire ecological definitions of old-growth forests and monitor and maintain Canada's old-growth heritage. Key words: old-growth forests, stand composition, anthropogenic influence, biodiversity, landscape ecology

Relationships between soil characteristics and yield for Norway spruce on fen peat in central Ireland

A site-productivity model for Norway spruce on fen peat in central Ireland was derived by stepwise regression of measured soil data on yield class (the expected maximum mean annual volume increment for the crop, expressed in cubic metres per annum per hectare). Soil C/N ratio, soil air space and hydrogen ion concentration explained 73% of the observed variation in yield class. The results indicated that the yield class of Norway spruce on fen was correlated with the physical properties of the peat and that, assuming adequate inputs of P and K, this species will be most productive on poorly decomposed, well-drained fen which exhibits a botanical composition indicative of relatively poor nutrition at the time of peat formation.

Growth and yield of Casuarina equisetifolia plantations on the coastal sand dunes of Senegal as a function of microtopography

Casuarina equisetifolia Forst. & Forst. plantations, established to stabilize sand dunes on the north coast of Senegal and thus protect inland agricultural areas, were sampled to determine if growth and yield were affected by microtopography. Microtopographical position, classified as interdune depressions, flanks, or summits, was found to have a highly significant effect on height, diameter, and volume growth. Maximum mean annual height increment was attained at Age 6 years (1.6 m year −1) in interdune depressions, at Age 7.5 (1.3 m year −1) on flanks, and at Age 8.5 (1.1 m year −1) on summits. Diameter distributions showed that the interdune depressions had a greater percentage of large diameter trees than flanks or summits. Maximum mean annual volume increment was 4.2 m 3 ha −1 year −1 at Age 18 years for the interdune depressions, 2.0 m 3 ha −1 year −1 at Age 29 for flanks, and 1.7 m 3 ha −1 year −1 at Age 30 for summits. Thus, different rotation lengths can be recommended for specific microsites depending on microtopographical position and on whether fiber production or soil amelioration is the dominant management objective.

Hybrid poplar spacing/productivity relations in short rotation intensive culture plantations

It is often argued that in short rotation intensive culture plantations, biomass productivity increases with narrower tree spacings. Biomass productivity and tree spacing relations were studied for up to 16 years in northern Wisconsin hybrid poplar plantations. Maximum mean annual biomass increment was 12.8 Mg ha −1 yr −1 for Populus clone NE-41 planted at a l m 2 spacing. Productivity differences related to spacing were found to be minor. Productivity was influenced mainly by clone, irrigation and disease. A hypothesis is proposed that time to canopy closure is linearly related to time to maximum mean annual biomass productivity. Wide spacing and wide-crown trees that permit wider tree spacing allow longer rotations, which can lower costs and increase flexibility in management.

Willow coppice systems in short rotation forestry: Effects of plant spacing, rotation length and clonal composition on biomass production

Above ground biomass production was determined for ten Salix clones grown in pure and mixed stands at a square spacing of 1 m and seven rotation periods (1 to 6 and 8 years), and of one clone grown at four square spacings (0.5, 0.6, 0.7 and 1 m), with rotation cycles of 1 to 5 years. Most clones reached a maximum mean annual increment (8 to 14 tons dry matter ha −1 yr −1) under a rotation period of 4 to 5 years. Densely spaced stands exhibited a higher production than wider spacings during the first harvests under the shortest rotation periods. Neither in later harvests of short cycles (1 to 3 years) nor in any harvests of longer cycles (> 3 years) did spacing affect biomass production. Some clones suffered from leaf rust and grazing by roe deer. Clone mixtures showed a higher biomass production in the later stages due to the compensatory effect of the successful clones which, when growing in mixtures, could fill out the gaps left by individuals that suffered from impacts other than competition. We conclude that extremely short rotations (1 to 2 years) are unsuitable for Swedish conditions, and that 4- to 6-year rotations perform best. In such longer rotations, biomass production of stands with 2 × 10 4 plants per hectare equals the production of denser stands.

Juniperus procera Hocht. ex. Endl. in Ethiopian forestry

The distribution, importance and growth potential of Juniperus procera Hocht. ex Endl., an indigenous conifer in the Ethiopian highlands, were analyzed. As a termite- and fungi-resistant local timber J. procera has been highly valued for the construction of houses and larger buildings such as churches. Decimation of natural forests over the past 100 years, which is continuing, has halted the utilization of J. procera. By analyzing the few remaining J. procera stands of various ages between 10 and 200 years, its growth potential was calculated as maximum mean annual increment (MAI) of 7.5 m 3 ha −1 year −1 at the age of 55 years. The most rapid volume growth occurs at the ages of 15–50 years. The dominant height reaches about 45 m at ages between 100 and 150 years. Favoring J. procera in planting instead of Cupressus lusitanica Mill. is a way to diversify species selection, and to supply durable timber of high local and national preference. The relatively low yield potential of J. procera compared with exotics calls for national or international inputs for plantation establishment.

Production/Harvesting Options for Agroforestry Plantations in the San Joaquin Valley, California

Harvesting costs and annual equivalent worths of stumpage were simulated for several product/harvesting combinations for short rotation trees grown in agroforestry plantations. Optimal rotation ages were near the point of maximum mean annual volume increment of 10 years for the example situation. Production of firewood for local consumption had higher worth than production of firewood for urban markets, fuel chips, or pulp chips. Methods using whole tree transport were not competitive with systems that produced firewood or chips on-site.

Shade shoot structure and productivity of evergreen conifer stands

The current annual increment (wood volume) of stands of evergreen conifers on a research site in Sweden, was found to be significantly correlated with the maximum ratio of shoot to leaf silhouette area of shade‐acclimated shoots (R max). Neither the slope nor the intercept of the regression was significantly different from that published earlier relating maximum mean annual increment of British stands to R max . Moreover, a strong correlation between wood volumen increment and R max also occurs when data from four countries are combined. Wood density was not significantly correlated with R max. Harvest index for stand grown conifers more than 25 year old, was also not correlated with R max. Estimated net biomass production (excluding fine roots) was significantly correlated with R max (R 2 = 0.82, F = 17.7). These new analyses could not be used to disprove the hypothesis that variation in shade shoot structure of evergreen conifers has a measurable effect on maximum biomass production.

Analytical model of carbon storage in the trees, soils, and wood products of managed forests.

The carbon balance between managed forests and the atmosphere depends critically on the frequency and intensity of harvesting, and the lifetime of harvested products. To assess more quantitatively the nature of this dependence, a theoretical analysis, previously applied to carbon storage in trees and wood products only, is extended here to include the carbon in forest floor detritus and soil. A dimensionless combination of the parameters of the model, alpha, with critical value alpha(c), is identified such that for alpha < alpha(c), the conversion of old-growth forest to managed forest releases carbon to the atmosphere in the long term. Parameter alpha is given by the combination f(t)D/T(*), where f(t) is the fraction of old-growth forest carbon stored in trees, D is the residence time of harvested biomass (wood products and slash debris) within the system, and T(*) is the rotation period for maximum sustained yield (maximum mean annual increment). The critical value alpha(c), typically in the range 0.5-0.7, is derived for a variety of forest types. Parameter alpha determines the degree to which the carbon accumulated in harvested biomass offsets the loss of carbon in trees due to felling and in soils due to reduced litter input. When alpha > alpha(c), long-term carbon storage is optimized by harvesting for maximum sustained yield.

Preliminary Yield Tables for Oak Coppice

The growth of oak coppice was investigated by measuring temporary sample plots on 16 sites in southern England and Wales. Very variable height growth with age was apparent and, as a result, site index classes were determined. A yield model was produced based on the dominant height of stands, which could be related to age by using the site index classes. The age of maximum mean annual increment ranged from over 55 years on the poorest sites to only 25 years on the most productive. The mean annual increments {MAIs) at a rotation age of 30 years varied between 1.8 and 7.4 M 3 ha −1 y −1 to 7 cm top diameter and averaged 4 m 3 ha −1 y −1 . The MAIs are similar to those expected from conventionally spaced plantation oak but occur at much earlier ages.