Even-aged Structure Research Articles

Structural Characteristics of the Pine Stands on Degraded Lands in the South-East of Romania, in the Context of Climate Changes

The present research was carried out in stands of Scots pine and black pine, pure or mixed with deciduous trees, installed on degraded lands from the Curvature Subcarpathian area, Romania, in a representative network of permanent research plots and followed the analysis of the structural diversity and stability indicators of these stands at different ages and in different conditions of degraded lands. The relationships between the quantitative variables with reference to the structure were established by analyzing the significance of the Pearson correlation coefficient (r) and also including datasets of slenderness indexes, which were classed into three domains of vulnerability to abiotic factors (like wind and snow). The compositional diversity of pine stands (pure or mixed with deciduous ones) is different in relation to age and is correlated with the structural diversity. The obtained correlation coefficients (r Pearson) express very strong and significant relationships between biometric parameters (h x Dbh, h x Lc%, Dc x Dbh, and Lc% x Dbh) of the structural diversity (r = 0.800–0.930), which is important for the analysis of the stability and vulnerability of pine forests. The strong correlation between the analyzed variables expresses a weak vulnerability to the action of harmful abiotic factors and the increase in the stability and resilience of the studied stands, especially of over 50 years old. In the old pine stands, the low-vulnerability domain (I < 0.80) is the best represented one, with an average of 64.01% from the total number of trees. At this age, trees with DBH > 22 cm fall into the low-vulnerability category. The explanation is that the stands were affected in their youth by the action of snow and wind, which, combined with the silvotechnical works performed, led to their compositional and structural diversification and increased stability. The young (<45 years) and pure-pine stands with higher consistency (>0.8) and even-aged structure are the most vulnerable to abiotic factors due to the fact that a large number of trees are passing gradually into the higher cenotic classes.

Intelligent Pubescent Oak Forests (Quercus Pubescens Wild.) From Dobroudja Plateau, Romania

Dobrudjea Plateau, located in south-east Romania, is characterized by low altitudes, old rocks, a temperate-continental climate and a silvosteppe and steppe vegetation. Pubescent oak is one of the tree species characteristic for this area. With average dimensions, this tree fulfils numerous ecosystem functions.
 The concept of “Climate-Smart Forestry – CSF” is recent and was adapted in this article for the pubescent oak characteristic for this area; clear and measurable criterions were also identified and applies for this species in order to identify the smart stands.
 Smart pubescent oak forests represent 3% of all this specie’s stands and are more common in the north part of Dobrudjea Plateau. They are characterized by advanced ages (61-70 years), 20%-30% compositions and even-aged structures. The forests are located on relatively small distances from forest roads, at altitudes of 100m - 250 m, and on west and east expositions.
 The present study has showed that smart pubescent oak forests can be established by taking into account 14 site (flora, soil or forest type) and stand conditions (pruning, vitality, average diameter and height, functional group and category, litter). The identification of these stands is extremely important for their protection as well as for applying the appropriate silvicultural measures.

Group-selection silviculture conditionally enhances recruitment of yellow birch in a shade-tolerant hardwood forest

Wide-spread use of single-tree harvest methods has inhibited regeneration of yellow birch in shade-tolerant hardwood forests. Shelterwood harvesting can improve recruitment, but incurs higher costs, longer harvesting cycles, and produces an even-aged structure. Group selection (GS) harvesting provides an alternative method with the benefits of single-tree selection (STS; mixed-ages, shorter cycles), yet produces larger gaps that may favour recruitment of mid/intolerant tree species. Recent GS trial studies have shown promise, but results vary and differences in edaphic conditions and competition dynamics associated with climate, historical management, and season of harvesting may influence responses. We evaluated the yellow birch recruitment efficacy of GS in an Ontario shade-tolerant hardwood forest by comparing change in regeneration as percent ground cover (stems <50 cm) and large stem density (>50 cm) over ten years in STS harvested and unharvested forest relative to two types of GS gaps: “typical” gaps placed in suitable microsites, and indiscriminate “systematic” interval gaps harvested on a grid.Autumn-harvested gaps established 2–4× more yellow birch cover and recruited 7–10× more large stems by year ten than STS and winter harvested gaps; unharvested controls remained unchanged. Typical gaps recruited 3× more stems than systematic gaps in autumn-only. Soil disturbance and seed tree proximity were correlated to establishment of yellow birch cover in year 1, which predicted large stem recruitment by year 10. Winter-harvesting favoured sugar maple cover in year 1, which predicted lower yellow birch recruitment by year 10. These results indicate that autumn-harvested typical gaps optimised germination and growth conditions for yellow birch (light availability, soil disturbance, reduced competition, seed proximity/dispersal). Consequently, GS harvesting in autumn can be considered an effective alternative to shelterwood harvesting for yellow birch recruitment in poorly-represented shade-tolerant hardwood stands.

An Area-Based Matrix Model for Uneven-Aged Forests

In this paper a new concept for modeling uneven-aged forests (UEAF) is presented. The term UEAF in this article encloses all forests that deviate from the even-aged structure. The matrix model is area-based, in that the forest under study is described by a distribution of areas over fixed state-spaces spanned by stem number and volume per hectare classes. Dynamics is introduced as transitions of areas inside the state-space during the simulation. Harvesting activities and the occurrence of calamities are explicitly handled. The model is designed to be suitable for large-scale analyses. The concept was tested in an application to Austrian National Forest Inventory (NFI) data. Results shown, including a comparison to older inventory data, indicate that it is worth further elaborating on the concept and the model. The work will be continued and in the next step the model concept will be applied in several other countries.

Characterizing residual structure and forest recovery following high-severity fire in the western boreal of Canada using Landsat time-series and airborne lidar data

Post-fire regrowth is an important component of carbon dynamics in Canada's boreal forests, yet observations of structural development following fire are lacking across this remote and expansive region. Here, we used Landsat time-series data (1985–2010) to detect high-severity fires in the Boreal Shield West ecozone of Canada, and assessed post-fire structure for >600 burned patches (>13,000ha) using airborne light detection and ranging (lidar) data acquired in 2010. We stratified burned areas into patches of dense (>50% canopy cover) and open (20–50% canopy cover) forests based on a classification of pre-fire Landsat imagery, and used these patches to establish a 25-year chronosequence of structural development for each class. While structural attributes were similar between dense and open patches during the first ten years since fire (YSF), canopy cover (cover above 2m) and stand height (75th height percentile) were significantly higher (p<0.001) for dense patches by the end of the chronosequence (20–25YSF), suggesting that differences in site productivity were driving patches towards pre-disturbance structure. Our results suggest that growing space remained in stands at the end of the chronosequence, and therefore stem exclusion was not yet reached, as canopy cover was significantly lower (p<0.001) for patches at 20–25YSF (mean=41.9% for dense, 18.6% for open) compared to patches with no recorded burns (mean=63.3% for dense, 38.6% for open). The lasting impact of high-severity fire on structure was further confirmed by estimates of stand height, which were approximately half as tall for patches 20–25YSF (4.9m for dense, 4.2m for open) compared to patches with no recorded burns (9.8m for dense, 7.7m for open). Additionally, we assessed the structural complexity of burned stands using measures of canopy roughness (i.e., rumple) and the distribution shape of lidar returns (i.e., skewness and kurtosis), which provided evidence of young, even-aged structure once a new overstory was formed. As forest inventories are not routinely conducted across Canada's northern boreal, the fusion of Landsat time-series and airborne lidar data provides powerful means for assessing changes in forest structure following disturbance over this large forested area.

Fine-scale genetic structure of Nothofagus pumilio (lenga) at contrasting elevations of the altitudinal gradient

Montane forests provide the natural framework to test for various ecological settings at distinct elevations as they may affect population demography, which in turn will affect the spatial genetic structure (SGS). We analyzed the fine-scale SGS of Nothofagus pumilio, which dominates mountain areas of Patagonia, in three pairs of sites at contrasting elevations (low- vs. high-elevation). Within a total area of 1ha fresh leaf tissue from 90 individuals was collected at each of the six studied stands following a spatially explicit sampling design. Population genetic diversity parameters were analyzed for all sampled individuals using five polymorphic isozyme loci, and a subset of 50 individuals per stand were also screened for five microsatellite loci. The SGS was assessed on 50 individuals/stand, using the combined datasets of isozymes and microsatellites. Most low-elevation stands consisted of older individuals with complex age structures and genetically diverse plots. In contrast, high-elevation stands and one post-fire low-elevation population yielded even-aged structures with evidence of growth suppression, and were genetically homogeneous. All stands yielded significant SGS. Similarly to mature stands of the non-sprouter congener Nothofagus dombeyi, multi-age low-altitude N. pumilio yielded significant SGS weakened by competing species of the understory and the formation of seedling banks. Alike the sprouter Nothofagus antarctica, high-altitude stands produced significant SGS as a consequence of occasional seedling establishment reinforced by vegetative spread.

Influence of fire intensity on structure and composition of jack pine stands in the boreal forest of Quebec: Live trees, understory vegetation and dead wood dynamics

North American jack pine ( Pinus banksiana Lamb.) stands are generally characterized by an even-aged structure resulting from high intensity fires (HIF). However, non-lethal fires of moderate intensity (MIF), which leave behind surviving trees, have also been reported. The objectives of this study were two-fold: (1) assess the concurrent dynamics of live trees, understory vegetation and different types of coarse woody debris (CWD) during succession after HIF; and (2) document how MIF affects stand structure component dynamics compared to HIF. Stands affected by both HIF and MIF were selected. Tree characteristics and age structure, understory biomass, and CWD volume were assessed. Our results suggest that the structural succession of jack pine stands following HIF comprises three stages: young stands (<48 years), premature and mature stands (58–100 years) and old stands (>118 years). Canopy openness and jack pine density significantly decreased with time since HIF, while black spruce density and CWD volume significantly increased. The highest structural diversity was measured in the premature and mature stands. Compared to HIF, MIF increased mean jack pine basal area, decreased average stand density, delayed the replacement of jack pine by black spruce replacement in the canopy, decreased CWD volume, and significantly increased bryophytes mass. MIF increased the diversity of live trees and generally decreased CWD structural diversity. The study confirms the diversity of natural disturbance magnitude and successional processes thereby initiated. Thereafter, it appeared to be relevant for adjustment of disturbance emulating forest-management systems.

Canopy disturbance and tree recruitment over two centuries in a managed longleaf pine landscape

Disturbance history was reconstructed across an 11300ha managed longleaf pine (Pinus palustris Mill.) landscape in southwestern Georgia, USA. Our specific objectives were to: (i) determine forest age structure; (ii) reconstruct disturbance history through the relationship between canopy disturbance, tree recruitment and growth; and (iii) explore the relationship between canopy disturbance and climate. Age structure, canopy disturbance events and initial growth patterns at coring height were examined by randomly sampling 1260 trees in 70 1.3ha plots. Principal component analysis was used to group plots with similar age structures to gain insight into the dynamics between canopy disturbance and recruitment. Disturbance events were detected by large and rapid increases in radial growth. We tested the following hypothesis to investigate whether these growth increases could have been triggered by improved climatic conditions: precipitation and drought are positively correlated to radial growth releases. Only four stands (comprising <6% of the study area) had an even-aged structure. Further, tree recruitment prior to European settlement indicates that longleaf pine naturally recruited into areas 1.3ha or less, supporting early-20th century observations that the primary longleaf pine forest was uneven-aged. Contrary to our hypothesis, growing season precipitation and drought was significantly and negatively correlated with canopy disturbance (radial growth releases), which indicates that a reconstruction of disturbance history could proceed with some confidence. Most trees sampled were recruited at coring height from 1910 to 1935. Of the 67 canopy disturbances detected from 1910 to 1935, the average growth release ranged from 139 to 277% per half decade suggesting the occurrence of large canopy disturbances. Rapid initial growth patterns of young trees during these years show evidence of reduced overstory competition and support the detected disturbance intensity. Our reconstruction of stand dynamics is markedly similar to independent records of local oral and written history, which gives an additional set of evidence that the disturbance detection methodology used can be useful in open-canopied forests. Stands with multiple cohorts reveal a mix of continuous minor and major canopy disturbances leading to continual tree recruitment, suggesting their applicability as models for long-term forest management. The significant relationship between climate and disturbance in our data suggests that with the expected warming over the next 100 years, climatic impacts on stand dynamics should be incorporated into long-term longleaf pine forest restoration and management.

Stand age structural dynamics of North American boreal forests and implications for forest management

SuMMARY The age structure of a stand provides an understanding of important ecological processes taking place during stand development. The age of trees has been estimated by historical records, estimation from tree size, ring counting at breast height and ground level, pith node counting, and dendrochronological cross dating. Each of these methods has inherent advantages and limitations. In the fire-driven boreal forest, stand age structure has been found to shift from a relatively even-aged structure, where all trees establish immediately after fire with a similar height and diameter, to one that is uneven-aged, where trees vary in height and diameter as time since fire increases. The age structure dynamics differ with stand species composition and influenced by non-stand replacing disturbances. Traditional forest management can shift the age structure at both the stand and landscape level, but silvicultural systems and forest management planning techniques are available to mimic natural age structural patterns.

A forest planning problem solved via a linear fractional goal programming model

We present a linear fractional goal programming model to a timber harvest scheduling problem in order to obtain a balanced age class distribution of a forest plantation in Cuba. The forest area of Cuba has been severely reduced due to indiscriminate exploitation and natural disasters (fires, hurricanes, etc.). Thus, in this particular case, the main goal is to organize and regulate the forest. This involves a significant change from its current distribution by ages to obtain a more even-aged structure over a planning horizon of 25 years which coincides with the rotation age. This has been formalized as fractional goals which take into account the evolution of the forest and ensure attaining a balanced age class distribution in a progressive and flexible way. The proposed model aims at achieving this new distribution while bearing in mind the economic aspects of the forest as well as other factors. In order to test its potential we have applied the model to a Cuban plantation belonging to the forestry company “Empresa Forestal Integral Pinar del Río”. We obtained several solutions that provided a regulated forest while respecting the economic and other targets of the decision-makers.

Benefit-Cost Analysis of Modesto's Municipal Urban Forest

This study answers the question: Do the accrued benefits from Modesto's urban forest justify an annual municipal budget that exceeds $2 million? Results indicate that the benefits residents obtain from Modesto's 91,179 public trees exceeded management costs by a factor of nearly 2. In fiscal year 1997-1998, Modesto spent $2.6 million for urban forestry ($14.36/resident, $28.77/tree), and 74% of this amount was for mature tree care. Total annual benefits from Modesto's urban forest were $4.95 million ($27.12/ resident, $54.33/tree). Net benefits for FY 1997- 1998 were $2,329,900 ($12.76/resident, $25.55/tree). Annual air-pollutant uptake was 154 metric tonnes (3.7 lb/tree), with an implied value of $1.48 million ($16/ tree). Aesthetics and other benefits had an estimated value of $1.5 million ($17/tree). Building shade and cooler summer temperatures attributed to street and park trees saved 110,133 MBtu, valued at $870,000 (122 kWh/tree, $10/ tree). Smaller benefits resulted from reductions in stormwater runoff (292,000 m3 or 845 gal/tree, $616,000 or S7/tree) and atmospheric carbon dioxide (13,900 t or 336 lb/tree, $460,000 or $5/tree). Due to the population's relatively even-aged structure and heavy reliance on mature Modesto ash for benefits, management strategies are needed that may reduce net benefits but increase diversity and stability.

Practical Field Methods of Estimating Canopy Cover, PAR, and LAI in Michigan Oak and Pine Stands

Abstract With the increased use of variables such as canopy cover, photosynthetically active radiation (PAR) and overstory leaf area index (LAI) in forestry research, relationships between these variables and traditional forestry variables must be defined before recommended levels of these research variables can be achieved by forestry practitioners on the ground. We measured basal area, canopy cover, Ozalid percent full light, PAR, and overstory LAI in thinned and unthinned plots within oak and pine stands with the objectives of: (1) determining the relationships between these variables in two common forest types, (2) investigating the feasibility of using basal area to estimate and achieve recommended levels of canopy cover, PAR, and LAI in the field, and (3) examining the possibility of using direct canopy cover and Ozalid light measurements for estimating PAR and LAI. Very strong relationships (r² &gt; 0.90 and P &lt; 0.0001) were indicated between basal area and canopy cover, PAR, and LAI. Direct canopy cover and Ozalid light measurements were also strongly related to PAR and LAI. It is likely that the even-aged structure of the stands studied contributed to these results. The strength of the relationships between the measures examined suggest that practical variables such as basal area could potentially be used by forestry practitioners to estimate and achieve recommended levels of canopy cover, PAR, and LAI in similar oak and pine stands. The possibility also exists for strong relationships between these variables in other stand types that resemble those studied in terms of overstory structure. North. J. Appl. For. 16(1):25-32.

Vegetative Structure and Composition of Southern Appalachian Riparian Forests

HEDMAN, CRAUG W. (Southlands Experiment Forest, International Paper, Bainbridge, GA 31717) AND DAvID H. VAN LEAR (Department of Forest Resources, Clemson University, Clemson, SC 29634-1003). Vegetative structure and composition of Southern Appalachian riparian forests. Bull. Torrey Bot. Club 122: 134-144. 1995.-Vegetative characteristics of twelve Southern Appalachian riparian forests were sampled as part of a larger study which examined functional attributes of riparian zones. Riparian forests were representative of the mixed mesophytic forest, eastern hemlock forest, and transitions between these types. Earlyand mid-successional stages were generally dominated by an overstory of pioneering shade-intolerant species and had an even-aged structure. The diameter distribution of these relatively young stands of mixed species was typically inverse J-shaped. Late-successional and old-growth stages were dominated by shade-tolerant or moderately tolerant overstory species and were uneven-aged. Diameter distribution in these older stands approximated a rotated sigmoid curve. Rhododendron (Rhododendron maximum L.) was the dominant understory species and controlled understory and midstory composition. Characterization of riparian forests in different stages of succession will help understanding of vegetative processes and forms the basis of subsequent ecological studies of riparian functional dynamics.

Progression of damping-off epidemics in Glycine populations of even-age and mixed-age structure

Development of damping-off epidemics, caused by a random distribution of Pythium aphanidermatum in soybean populations, was quantified in even-aged and mixed-aged populations of Glycine max and Glycine soja (progenitor of cultivated species). Age structures were created to mimic naturally occurring even- and mixed-aged structures of G. max and G. soja, respectively. Damping-off epidemics developed more rapidly in populations of G. max than G. soja, in mixed-aged than even-aged populations of G. max, and even-aged than mixed-aged populations of G. soja. Diseased soybeans were distributed less uniformly, both temporally and spatially, and epidemics were longer in mixed-aged than even-aged structures and in populations of G. soja than G. max. Incidence of preemergence disease was greater near the inoculum source. Seedlings that damped-off after emergence and (or) those that remained symptomless were peripheral to the inoculum source. Epidemic development was dependent upon plant species and the temporal and spatial distribution of susceptible plants and virulent pathogen. Key words: Glycine max, Glycine soja, Pythium aphanidermatum, soybean, survivorship analysis.

Comparative growth and yield of layer- and seed-origin black spruce (Piceamariana) stands in Quebec

Stem analysis was used to compare the height, diameter at breast height, and volume growth of seven merchantable black spruce (Piceamariana (Mill.) B.S.P.) stands regenerated after harvesting from advance growth of layer origin with the growth of three merchantable black spruce stands regenerated after fire from seed. The year of harvesting in the second-growth stands was precisely determined using synchronous growth release after logging, scars left by the logging operation, and historical records. The year of the fires in seed-origin stands was determined using fire scars and historical records. Fire-origin stands showed typical even-aged structure, and logged, second-growth stands showed an uneven-aged structure associated with an asymmetric curve. When compared with seed-origin stands, layer-origin stands showed a significantly greater total height 30 years after the stand origin because of the initial height of the layers. However, annual height increments were similar between the two origin types at 30 years. The mean diameter increment at 30 years was significantly higher in the second-growth stands. The mean annual specific volume increment values for the entire period of growth were slightly higher for the fire-origin stands. Layers that were small at the time of logging (&lt;1 m) had a higher specific volume increment after logging compared with the medium (1–2 m) and tall layers (&gt;2 m). There was a significant negative correlation between the height, diameter, and age of the layers at the time of logging and both the mean specific volume increment and the mean annual height increment 30 years after logging. In the second-growth stands, the number of merchantable trees and volume increment increased gradually because of the uneven structure of the stands. In contrast, in the seed-origin stands, the trees attained merchantable size at around 30 years after the fire, and the merchantable volume rose rapidly after this. The layer-origin populations had a significant advantage over the seed-origin populations because of the initial height and diameter of the layers at the time of logging. All seven layer-origin stands achieved, or were predicted to achieve, higher merchantable volumes than the seed-origin stands at 40 years. Our results indicate that the second-growth stands growing on mesic sites have the potential to produce merchantable forests comparable to the yield tables available for black spruce provided that the number of stems per hectare is adequate.

Presettlement forest structure as a factor in urban forest development

Characteristics of presettlement forests at Menlo Park and South Lake Tahoe, CA were compared with the present characteristics of the urban forests in these cities. Urbanization of forest types in both cities led to decreased tree density (in Menlo Park from 279 to 43/ha; in South Lake Tahoe from 761 to 373/ha), decreased tree cover (in Menlo Park from 92 to 34%; in South Lake Tahoe from 57% to 19%). In contrast, urbanization of the oak savannas at Menlo Park has resulted in an increase in tree density (from 4 to 35/ha) crown cover (from 14 to 25%) and the number of species (from 3 to 130). The number of tree species has increased in both cities as a result of urbanization of presettlement forests (in Menlo Park from 5 to 145; in South Lake Tahoe from 1 to 6). The uneven-aged structure of presettlement oak savannas at Menlo Park has been modified to an all-aged structure as a result of tree planting and the mortality of older age classes. The all-aged structure of the presettlement oak forest at Menlo Park was not changed in the transition to the present urban forest. At South Lake Tahoe the even-aged structure of the presettlement Jeffrey pine forest has been modified into a uneven-aged structure by tree planting. Presettlement forest age structure is recognized as the most significant characteristic for the identification of possible management problems in the urban forest.

Comparative stand development in an old-growth Douglas-fir (Pseudotsugamenziesii var. glauca) forest in western Montana

The composition, structure, and reproductive dynamics of two old-growth Douglas-fir (Pseudotsugamenziesii var. glauca (Beissn.) Franco) stands, located on opposing north and south aspects, were analyzed to reconstruct their past developmental patterns. Results indicate that the north aspect stand developed an even-aged structure initially and shifted to an uneven-aged structure over time. The theory of monospecific dominance by the climax species is supported on the north aspect as Douglas-fir maintains the highest importance value of all species present. The competitive exclusion principle appears inappropriate in this case as lodgepole pine (Pinuscontorta Dougl.), an intolerant, seral dominant, is reproducing successfully under the old-growth canopy. The south aspect stand has developed an uneven-aged structure and maintains it as harsh environmental conditions limit reproductive success to favorable microsites, precluding complete canopy closure.