Forest Ecology and Management

Published by Elsevier
Online ISSN: 0378-1127
Publications
Workflow to determine the dry needle mass of an individual tree.
Comparison of the relationship between leaf area (LA) and crown surface area (CSA) of the lowest and highest dominant height (hdom) concerning different ratios of dominant height to diameter in breast height (dbh).
Article
Since individual tree leaf area is an important measure for productivity as well as for site occupancy, it is of high interest in many studies about forest growth. The exact determination of leaf area is nearly impossible. Thus, a common way to get information about leaf area is to use substitutes. These substitutes are often variables which are collected in a destructive way which is not feasible for long term studies. Therefore, this study aimed at testing the applicability of using substitutes for leaf area which could be collected in a non-destructive way, namely crown surface area and crown projection area. In 8 stands of Norway spruce (Picea abies L. Karst.), divided into three age classes and two thinning treatments, a total of 156 trees were felled in order to test the relationship between leaf area and crown surface area and crown projection area, respectively. Individual tree leaf area of the felled sample trees was estimated by 3P-branch sampling with an accuracy of ±10%. Crown projection area and crown surface area were compared with other, more commonly used, but destructive predictors of leaf area, namely sapwood area at different heights on the bole. Our investigations confirmed findings of several studies that sapwood area is the most precise measure for leaf area because of the high correlation between sapwood area and the leaf area. But behind sapwood area at crown base and sapwood area at three tenth of the tree height the predictive ability of crown surface area was ranked third and even better than that of sapwood area at breast height (R(2) = 0.656 compared with 0.600). Within the stands leaf area is proportional to crown surface area. Using the pooled data of all stands a mixed model approach showed that additionally to crown surface area dominant height and diameter at breast height (dbh) improved the leaf area estimates. Thus, taking dominant height and dbh into account, crown surface area can be recommended for estimating the leaf area of individual trees. The resulting model was in line with many other findings on the leaf area and leaf mass relationships with crown size. From the additional influence of dominant height and dbh in the leaf area model we conclude that the used crown model could be improved by estimating the position of the maximum crown width and the crown width at the base of the crown depending on these two variables.
 
Article
The identification and study of adaptively important genes in forest trees represents a formidable challenge because of their long generation spans. In annual or perennial herbs, formal genetic studies can be employed to identify the quantitative trait loci (QTLs) and/or candidate genes that underlie important traits, and the segregating populations can be transplanted into natural populations to measure the strength and direction of selection. However, the application of these methods to forest trees is difficult, because the creation of appropriate genetic material is extremely time-consuming in long-lived, woody plants, and lifetime fitness estimates are difficult or impossible to obtain. Although QTL mapping should in principle be feasible in wild intraspecific populations (as an alternative to artificial crosses), this approach is less likely to be successful in trees because LD (linkage disequilibrium) will decay quickly in large outbreeding plant populations. Within the present paper, we discuss a modified approach based on natural hybrid zones. We describe the use of wild annual sunflowers (Helianthus spp.) as a model for exploring the hybrid zone approach. Transplanted experimental hybrids allowed us to assess the adaptive value of individual chromosomal blocks in nature, and data on natural Helianthus hybrids suggest that similar approaches are possible in natural hybrid zones. Our results allowed us to test the role of hybridization in the origin of ecological divergence in wild sunflowers. In addition, they have practical implications for identifying adaptively important genes or QTLs in trees. This is exemplified by three temperate forest taxa, Populus (poplars, aspens, cottonwoods), Fraxinus (ash), and Quercus (oak). All three are diploid and important genomic tools are under development. Moreover, all three offer extensive hybrid zones whose likely age can be inferred from fossil data. Age data enables estimates of the size and frequency of chromosomal blocks in hybrids, thereby providing guidance in designing marker-based experiments. We predict that natural hybrid zones will be valuable tools for identifying the QTLs and/or candidate genes responsible for adaptive traits in forest trees.
 
Tukey-boxplots of the maximum variation in the species proportion within 4 consecutive 500-year simulation periods. The first period begins after 1000 simulation-years. The maximum variation was calculated as the maximum value over all tree species of the difference between the highest proportion and the lowest proportion within a specific period. The boxplots show the distribution of the maximum variation over 10 randomly selected sample plots for each of the 18 PNV-types.
The simulated development of the volume per hectare for one plot of the Austrian National Forest Inventory, as an example for the wave form of the volume curve simulated by PrognAus. The dashed rectangle marks the time period which was used to calculate the steady state species proportions.
The proportion of coniferous tree species in the steady state species composition simulated by using PrognAus and the respective plot elevation for 6933 sample plots of the Austrian National Forest Inventory. Note that elevations were grouped into 100 m classes.
Probability of mortality modified after Monserud and Sterba (1999) (for coefficients see Hasenauer, 2000) over the diameter at breast height for Fagus sylvatica, Picea abies, Larix decidua, and “Other broadleaf species” at a BAL of 0 (left), 5 (centre), and 50 m2 ha−1 (right) and a crown ratio of 0.6.
Article
Tree growth models are supposed to contain stand growth laws as so called "emergent properties" which derive from interactions of individual-tree growth and mortality functions. This study investigates whether the evolving tree species composition in a long term simulation by the distance-independent tree growth model PrognAus matches the species composition of the potential natural vegetation type which is expected to occur if one refrains from further management interventions and major disturbances, climate change, and changes in site conditions can be excluded. For this purpose the development of 6933 sample plots of the Austrian National Forest Inventory was predicted for 2500 years. The resulting species proportions, derived from volume per hectare of 15 tree species or species groups, were used to classify every sample plot according to potential natural forest types, following a classification scheme based on expert knowledge. These simulated potential natural vegetation types were compared with expert reconstructions of the sample plots of the Austrian National Forest Inventory. A total of 5789 plots were actually classified with the scheme; in 33% of the cases the classification on the basis of the PrognAus-simulations was identical with the classification by the Austrian National Forest Inventory. A predominantly correct classification was achieved for the subalpine Picea abies-type and the Fagus sylvatica-type although PrognAus showed a tendency to overestimate the proportion of F. sylvatica and P. abies. Weaknesses in the ability to simulate forest types dominated by Quercus spp., Acer spp., and Pinus sylvestris were identified. This shortcoming might be caused by the mortality model which allows a larger diameter at breast height for F. sylvatica or by the ingrowth model whose terms for the consideration of inter-specific competition may lead to a disadvantage of Quercus spp., P. sylvestris, and Abies alba. Moreover, the ingrowth model might be influenced by management effects and the effect of selective browsing.
 
Article
Height:diameter ratios are an important measure of stand stability. Because of the importance of height:diameter ratios for forest management, individual-tree growth models should correctly depict height:diameter ratios. In particular, (i) height:diameter ratios should not exceed that of very dense stands, (ii) height:diameter ratios should not fall below that of open-grown trees, (iii) height:diameter ratios should decrease with increasing spacing, (iv) height:diameter ratios for suppressed trees should be higher than ratios for dominant trees. We evaluated the prediction of height:diameter ratios by running four commonly used individual-tree growth models in central Europe: BWIN, Moses, Silva and Prognaus. They represent different subtypes of individual-tree growth models, namely models with and without an explicit growth potential and models that are either distance-dependent (spatial) or distance-independent (non-spatial). Note that none of these simulators predict height:diameter ratios directly. We began by building a generic simulator that contained the relevant equations for diameter increment, height increment, and crown size for each of the four simulators. The relevant measures of competition, site characteristics, and stand statistics were also coded. The advantage of this simulator was that it ensured that no additional constraint was being imposed on the growth equations, and that initial conditions were identical. We then simulated growth for a 15- and 30-year period for Austrian permanent research plots in Arnoldstein and in Litschau, which represent stands at different age-classes and densities. We also simulated growth of open-grown trees and compared the results to the literature. We found that the general pattern of height:diameter ratios was correctly predicted by all four individual-tree growth models, with height:diameter ratios above that of open-grown trees and below that of very dense stands. All models showed a decrease of height:diameter ratios with age and an increase with stand density. Also, the height:diameter ratios of dominant trees were always lower than that of mean trees. Although in some cases the observed and predicted height:diameter ratios matched well, there were cases where discrepancies between observed and predicted height:diameter ratios would be unacceptable for practical management predictions.
 
Article
In the current context of global deforestation and global warming, a wide range of organisations, with local to international remits, need estimates of forest biomass to assess the state of the World’s forests and their rate of change. The task would be impossible without space-based Earth observation, which allows the rapid generation of extensive data sets describing land surface properties. It is the task of remote sensing scientists to interpret these data into a meaningful source of forest information. Here, a fast and easily automated method for classifying boreal forests in terms of growing stock volume is presented. The work was conducted as part of the SIBERIA project, which has resulted in the recent publication of a map of forest growing stock volume covering 900 000 km2 in Central Siberia. The paper describes the use of satellite-based radar coherence to differentiate categories of forest growing stock volume, the application of this method to classify and map Central Siberian forests, and the characterisation of the forest classes to help in the interpretation. A list of acronyms and abbreviations used in the text is provided in Appendix A.
 
Article
This study was done to identify the species groups of mangrove forest in aerial photographs, to delineate their distribution and to quantify their coverage. Aerial photographs with a scale of 1:40 000 taken in 1983, were used to delineate mangrove forest from Kemaman to Kuantan. The study was conducted in two phases, interpretation of black-and-white panchromatic photographs, and field survey. Results show that there are three mangrove forest types, namely the Rhizophora type, the Avicennia/Sonneratia type, and the mixed-mangrove type. These can be delineated with 90% correct interpretation. An area of 2214 ha is covered by mangrove forest, of which 2% is the Avicennia/Sonneratia type, 24% the Rhizophora type and 74% the mixed-mangrove type. Avicennia/Sonneratia is found to have the highest stand density with 13 348 trees ha−1, followed by Rhizophora with 6697 and mixed-mangrove forest 1997. Thus, it can be concluded that mangrove forest can be delineated, classified and mapped by using this method of study.
 
Article
Establishing white spruce (Picea glauca (Moench) Voss) by planting it under established aspen (Populus tremuloides Michx.), stands has substantial potential as a technique for regenerating boreal mixedwood stands. The presence of an aspen overstory serves to ameliorate frost and winter injury problems and suppresses understory vegetation that may compete with white spruce. In this study we examine the growth of white spruce during the first 10 years after being planted underneath a 39-year-old stand of trembling aspen following thinning and fertilization. Results indicate successful establishment and reasonable growth rates of white spruce planted under thinned and unthinned aspen stands, even with aspen basal area of 51 m2 ha−1. Thinning of overstory aspen to 1000 or 2000 stems ha−1 did not increase light reaching seedlings, but did result in improvements in light above the shrub layer and in diameter and height growth of the underplanted seedlings. However, these increases in growth of underplanted spruce may not justify the expense of thinnings. Fertilization of these stands prior to planting had no effect on spruce growth. Growth of spruce underplanted at this site near Fort Nelson was similar to that at two other stands near Dawson Creek, B.C.Information on treatment effects on light, beam fraction, air temperature, and soil temperature are presented. Measurements of light obtained using LAI-2000 and hemispherical photography were compared with those obtained from hourly PPFD measurements. Results indicate that while both methods provide estimates of transmittance that are highly correlated with those provided by actual light measurements, they provide substantial underestimates of actual light levels.
 
Article
We simulated fuel reduction treatments on a 16,000 ha study area in Oregon, US, to examine tradeoffs between placing fuel treatments near residential structures within an urban interface, versus treating stands in the adjacent wildlands to meet forest health and ecological restoration goals. The treatment strategies were evaluated by simulating 10,000 wildfires with random ignition locations and calculating burn probabilities by 0.5 m flame length categories for each 30 m × 30 m pixel in the study area. The burn conditions for the wildfires were chosen to replicate severe fire events based on 97th percentile historic weather conditions. The burn probabilities were used to calculate wildfire risk profiles for each of the 170 residential structures within the urban interface, and to estimate the expected (probabilistic) wildfire mortality of large trees (>53.3 cm) that are a key indicator of stand restoration objectives. Expected wildfire mortality for large trees was calculated by building flame length mortality functions using the Forest Vegetation Simulator, and subsequently applying these functions to the burn probability outputs. Results suggested that treatments on a relatively minor percentage of the landscape (10%) resulted in a roughly 70% reduction in the expected wildfire loss of large trees for the restoration scenario. Treating stands near residential structures resulted in a higher expected loss of large trees, but relatively lower burn probability and flame length within structure buffers. Substantial reduction in burn probability and flame length around structures was also observed in the restoration scenario where fuel treatments were located 5–10 km distant. These findings quantify off-site fuel treatment effects that are not analyzed in previous landscape fuel management studies. The study highlights tradeoffs between ecological management objectives on wildlands and the protection of residential structures in the urban interface. We also advance the application of quantitative risk analysis to the problem of wildfire threat assessment.
 
Article
Contemporary patterns of genetic variation can be incorporated into theoretical models with the goal of understanding the evolutionary processes that led to these patterns. Neutral processes allow explicit predictions to be made, such that a comparison across loci permits inferences about mutation, migration and drift. Because migration and drift act evenly on all nuclear loci, we can infer that those loci which show discordant patterns of variation may be experiencing either contrasting mutation rates, or locus-specific natural selection. However, in changing environments, populations are frequently out of equilibrium with patterns of migration and drift. This can induce a high locus-to-locus heterogeneity in patterns of variation, mimicking the action of natural selection. Coalescent modeling indicates that even highly contrasting patterns of variation can be consistent with neutral evolution at all loci. The same reasoning can be applied to quantitative traits, provided that genetic variation in traits is explicitly measured. Generally, traits exhibit greater population divergence than do putatively neutral genetic markers, an observation consistent with locally adaptive selection acting on traits. However, the correlation of marker divergence with trait divergence is not strong enough to be predictive. The individual loci underlying quantitative traits (QTLs) are the hardest to study directly in natural populations, and simulations suggest that such loci will exhibit patterns very similar to neutral marker loci, in spite of strong selection on the traits they code for. This can occur because spatially heterogeneous selection imposes a covariance of allele frequencies across populations, so that traits diverge to a greater extent than the allele frequencies at the corresponding QTLs. This holds out the possibility of using simple genetic markers to draw inferences about the distribution and amount of allelic variation (adaptive potential) at QTLs, but such conjecture remains to be empirically confirmed.
 
(a) The proportions of species in each diameter increment group belonging to different categories of adult size. Closed bars, understorey species; cross hatched bars, middle storey, dotted bars, subcanopy species, open bars, canopy emergent species. Diameter increment group codes: (1) very slow growth; (2) slow growth; (3) moderate growth; (4) fast growth; and (5) very fast growth. (b) The proportions of species belonging to each diameter increment group under each of the three silvicultural regimes. Closed bars, very slow growth, vertically hatched bars, slow growth, cross-hatched bars, moderate growth, dotted bars, fast growth, open bars, very fast growth. Managed lowland rain forest at La Tirimbina, northeastern Costa Rica.
Distributions of the number of trees in each diameter increment group belonging to different categories of crown illumination, crown form and diameter at breast height; canopy and emergent species only. Diameter increment groups: (a) very slow growth; (b) slow growth; (c) moderate growth; (d) fast growth; and (e) very fast growth. See text for explanation of formation of diameter increment groups.
Article
Studies of growth rates of trees in managed neotropical forests have rarely employed complete botanical identification of all species, while published information for Central American lowland rain forests largely concerns forests free of recent disturbance. We studied diameter increments of trees in a managed Costa Rican rain forest. The Pentaclethra macroloba-dominated forest was located on low hills with Ultisols in Holdridge's Tropical Wet Forest life zone. The 540 m × 540 m (29.2 ha) experimental area was lightly logged during 1989–1990. The 180 m × 180 m (3.24 ha) experimental plots comprised a 100 m × 100 m (1.0 ha) central permanent sample plot (PSP) with a 40-m wide buffer strip. Post-harvest silvicultural treatments were liberation/refinement (in 1991) and shelterwood (in 1992), applied under a complete randomized block design with three replicates, using logged but untreated plots as controls. All live trees ≥10 cm DBH in the PSPs, were identified to species; data reported are for 1993–1996. Cluster analysis was used to group species on the basis of the median and quartiles of their diameter increment distributions, separating data by silvicultural treatments; five diameter increment groups were established and subdivided on the basis of the adult height of each species (four categories), giving 17 species groups in the final classification. Adult height and silvicultural treatment made a significant contribution to growth rate variation. Median annual increments of the slowest-growing species groups, which featured many under- and middle story species, were ca. 1 mm; those for the fastest growing species, which were mainly canopy and emergents, were ca. 16 mm. All species in the groups of very fast growth were pioneers, whether short or long-lived, though many other pioneer species did not show fast growth. The proportions of species found in groups of moderate, fast or very fast growth were greater in the silviculturally treated plots than in the controls, and one complete diameter increment group, of fast growth, was only represented in the treated plots. Crown form, crown illumination and presence of lianas in the crown, showed significant correlations with diameter increments, though the importance of these latter two variables varied with silvicultural treatment. The very fast growth groups differed from the others in having higher proportions of trees with well-formed, well-illuminated crowns and an irregular diameter distribution with relatively few individuals in the smallest DBH class. Comparison with data from other neotropical forest sites shows that long-lived pioneers such as Vochysia ferruginea and Jacaranda copaia grow fast or very fast at all sites, while non-commercial canopy and emergent species of Chrysobalanaceae and Sapotaceae appear to be uniformly slow-growing. Growth data for the majority of species are, however, published for the first time.
 
Article
The impact of forest management on genetic diversity and mating was examined in European beech (Fagus sylvatica L.). Ten beech stands located in Europe were studied in pair-wise plots, differing in management intensity. The stands were genotyped with four highly polymorphic microsatellite loci. Comparison for genetic diversity measures between the stands with limited management and the high management-intensity stands (mostly shelter wood system) revealed no significant differences for allelic richness (A), effective number of alleles (Ae), number of rare alleles (Arare), neither for observed (Ho) nor expected heterozygosity (He). In all stands a significant excess of homozygotes was found, which is in agreement with previous isozyme publications. However, the increase in the inbreeding coefficient (Fis) in the stands with limited management was significantly higher than in the highly managed stands. Expectedly a low, but significant, differentiation among all stands was found (Fst = 0.058) which still reveals a clear geographic structure.The results indicate that the shelter wood system has no or minimum impact on the genetic diversity in European beech.
 
Article
Rain forest logging is spreading in eastern Amazonia, and logging practices are careless, resulting in much unnecessary damage. We considered the technical feasibility, efficiency and profitability of `best' logging practices in this region by comparing planned and unplanned logging operations in side-by-side plots. We also calculated the medium-term economic performance of `best' forestry practices under a selective harvest regime by comparing net present value for 20- and 30-year cutting cycles, with and without forest management. The cost to plan logging operations was estimated at US$72/ha or approximately US$1.80–2.05/m3 for harvests of 35–40 m3/ha (typical of study region). More than 90% of this cost was in tree mapping, vine cutting, and planning logging maneuvers (e.g., skid trail layout, felling angle determinations, etc.). The careful planning of tree felling operations resulted in a 15% increase in productivity (m3 felled/work h) over the unplanned operation. The machine time (min/m3 harvested) necessary to open logging roads and log landings was 37% less in the planned operation than in the unplanned operation, and the productivity of skidding logs to landings (m3 hauled/h) was 27% greater in the planned operation, using wheeled skidders compared to standard bulldozer-based operations in unplanned extraction. Moreover, in the absence of planning, 26% of the volume of timber that was felled was wasted: 7% lost to poor felling techniques and 19% lost simply because felled trees were never found by tractor operators. In the planned area, only 1% of the felled timber was wasted. Overall, increased work productivity and reduced waste in the planned logging operation resulted in financial benefits of US$3.7/m3, which was about two times the cost of planning. In addition to short-term economic benefits, carefully planned logging operations reduce damage to the forest, leaving a well-stocked stand. Good stocking, combined with the application of silvicultural treatments following logging, should result in greater timber production in managed forests. With management, we estimate that 68% more timber volume could be extracted over a 30-yr period than without management. Using discount rates ranging from 6 to 20%, our estimates of the net present value of timber extraction with forest management were 38 to 45% higher than without management. Although forest management appears to be economically attractive, there are various barriers to its widespread application in the region. Information on the technical aspects of forest management has not been transferred to land owners. Forestry regulations are not enforced. Additionally, any investment in forested land is perceived as risky because of frequent disputes over land ownership. Overcoming these barriers will require, at the very least, the implementation of a regional forest-use policy that is sensitive to both local economic conditions and forest ecology.
 
Article
Short rotation coppice culture systems are characterized by a high stool and shoot density, and by rotation durations between 2 and 3 years for species showing an extremely fast growth such as poplar. With the objective to study the long-term biomass production evolution and dynamic of such systems, a high-density plantation with 17 poplar (Populus) clones belonging to six parentages was established in April 1996 and coppiced in December 1996, January 2001, and February 2004. At the end of each growing season, stool survival, shoot diameter, and the number of shoots per stool were measured. Biomass production was estimated directly by harvesting a number of shoots or indirectly via allometric power equations. Stool survival rates differed among parentages and from year to year irrespective of number of rotations; the highest rates were for P. nigra and the lowest rates were for P. deltoides × P. nigra and P. deltoides × P. trichocarpa parentages. In the second and third rotations, the P. trichocarpa × P. deltoides hybrids showed very high mortality rates. The number of shoots per stool varied among rotations and parentages, and shoot elimination was parentage specific. The number of shoots per stool increased with increasing rotation number, while they decreased from year to year within each rotation. A single general allometric equation linking shoot diameter to shoot biomass could be used to estimate biomass production for most years and most clones. Exceptions were found for the year 2001 and for clone Hazendans. Biomass production differed among parentages and among rotations. The different parentages also differed in their strategy of biomass accumulation. Although P. nigra had the highest biomass production over 11 years, the parentage ranking of biomass production shifted over rotations. The P. trichocarpa × P. deltoides hybrids showed high biomass production in the first rotation, but low in the second and third rotations. Biomass production increased from year to year within one rotation, while it decreased with rotation number. Among the parentages examined, P. nigra and P. trichocarpa were the best performing ones and the best adapted to the multiple coppice rotations.
 
Article
Data from a spacing study in an 11-year-old plantation of Terminalia superba were examined with response models. Analysis of variance of the latin-square design with four spacings indicated significant effects of spacing on survival and mean diameter, as well as basal area, height and volume growth. Response model analysis showed that a planting density of 2391 trees ha−1 maximizes basal area growth and 2331 trees ha−1 maximizes volume growth, but the largest mean diameter is produced by planting 232 trees ha−1. Guides are provided for the forest manager's use in determining trade-offs between maximum timber production and space between trees to grow agricultural crops within the Taungya system.
 
Article
Nitrogen and water status were manipulated experimentally by thinning, residue management and application of N and P fertiliser. The experiment was thinned in November 1988, residue treatments were installed in December 1988 and fertiliser was applied in September 1989. Basal area increment (m2 ha−1) increased in response to thinning, the quantity of residue retained, and with the rate of N fertiliser. There was no response to P nor any N×P interaction. Nitrogen uptake in 1989–1990 was highly correlated with tree growth in thinned treatments over the next 3 years. The positive growth response to N uptake was mediated primarily through increased leaf area index (LAI). Thus LAI in 1991 was highly correlated with N uptake in 1989–1990 and with subsequent growth. Growth per unit N uptake or per unit leaf area were much lower in the unthinned treatment where predawn needle water potentials (Ψ) were consistently more negative than the thinned treatments. Combining Ψ with N uptake or LAI in a simple linear model explained 96% and 94%, respectively of the variation in tree growth for all treatments. Annual growth increments in thinned treatments not fertilised with N were correlated with current N uptake. In N fertilised treatments, growth was highly correlated with N uptake in the year after fertiliser application but was then independent of subsequent N uptake. Foliar N concentrations in June 1990 were highly correlated with N uptake and subsequent growth in thinned treatments. However, treatment concentration differences declined with time while differences in growth remained due to differences in LAI. Consequently, the correlation between foliar N concentration and growth was substantially reduced. An index of canopy N content (LAI×foliar N concentration) was no better correlated with growth than LAI alone. Litter N concentrations (maxima, minima or mean annual weighted) in thinned treatments were correlated with tree growth in the subsequent year. Regression coefficients were initially low but increased up to a maximum of 0.90 for growth in 1990–1993. Stem growth in both thinned and unthinned treatments could be explained by combining foliar or litter N concentrations with Ψ in a simple linear relationship. Litter N concentrations could not be used to estimate N uptake.
 
Article
The influence of initial stand density and genetic population on corewood dynamic stiffness of 11-year-old Pinus radiata [D. Don] was investigated at a field trial in Canterbury, New Zealand. Corewood dynamic stiffness was determined on standing trees using the stress wave method over the lower stem (0.2–2.0 m) of 182 trees, from an experiment which included three contrasting genetic populations (GF1, GF27 and clonal) grown at 833 and 2500 stems ha−1.Stiffness was significantly influenced by planting density (P < 0.001), and genetic population (P < 0.01). Planting density had the largest influence on stiffness, with values in the high-density plots exceeding values in the low-density plots by on average 1.7 GPa or 34%. Gains in stiffness attributable to genetic population averaged 0.8 GPa or 15%. Stiffness was not significantly influenced by the interaction between planting density and genetic population.There was a significant (P < 0.01) negative relationship between tree diameter at breast height (DBH) and stiffness, for all genetic populations, which explained 57%, 56% and 14% of the variation in stiffness for the clones, GF27 and GF1, respectively. Although correction for variation in DBH reduced variation in stiffness, residual variation in stiffness between planting densities and genetic population were still significant after the effect of DBH had been removed. These findings highlight the importance of planting density in regulating stiffness, and strongly suggest that effects of planting density and genetic population on stiffness are independent.
 
Article
Root system architecture and field performance of 90 twelve-year-old lodgepole pine (Pinus contorta var. contorta Dougl.) saplings, initially raised in containers for one year (1979) before planting, were compared with 60 naturally regenerated lodgepole pine saplings of the same age. The naturally regenerated saplings were significantly taller, and leader increments for 1989–1990 and 1990–1991 indicated that they performed better than the planted saplings during the two most recent growing seasons. Planted saplings displayed root morphologies which differed markedly from their natural counterparts; these included poor structural lateral root symmetry, fewer first order lateral roots, a greater distance from the ground surface to the first structural lateral root, and a greater root collar diameter and concentration of lateral roots 10 cm below the groundline. In addition, root stocks of planted saplings possessed remnants of vertical container shaping and a number of deformed roots that were either constricted, coiled and/or kinked. Naturally regenerated saplings illustrated elaborate sinker root development, and an assortment of self-grafted roots which were not observed on planted saplings. Possible effects of containerization on root morphology are discussed in relation to difficulties which may arise from artificial regeneration of cut-over sites.
 
Article
Rainforest fragments in central Amazonia have been found to experience a marked loss of above-ground biomass caused by sharply increased rates of tree mortality and damage near fragment margins. These findings suggest that fragmentation of tropical forests is likely to increase emissions of CO2 and other greenhouse gases above and beyond that caused by deforestation per se. We estimated committed carbon emissions from deforestation and fragmentation in Amazonia, using three simulated models of landscape change: a `Rondônia scenario,' which mimicked settlement schemes of small farmers in the southern Amazon; a `Pará scenario,' which imitated large cattle ranches in the eastern Amazon; and a `random scenario,' in which forest tracts were cleared randomly. Estimates of carbon emissions for specific landscapes were from 0.3 to 42% too low, depending on the amount and spatial pattern of clearing, when based solely on deforestation. Because they created irregular habitat edges or many forest perforations which increased tree mortality, the Rondônia and random-clearing scenarios produced 2–5 times more fragmentation-induced carbon emissions than did the Pará scenario, for any given level of clearing. Using current estimates of forest conversion, our simulations suggest that committed carbon emissions from forest fragmentation alone will range from 3.0 to 15.6 million t/year in the Brazilian Amazon, and from 22 to 149 million t/year for tropical forests globally.
 
Article
In tropical forest areas with highly weathered soils, organic matter plays an important role in soil functioning and forest sustainability. When forests are clear-cut, the soil begins almost immediately to lose organic matter, triggering a series of soil degradation processes, the extent and intensity of which depends on soil management. Depending on the level of soil degradation, the rate at which the system can re-establish itself can be slow and may require the use of degraded land restoration techniques. This study aimed at evaluating the potential of pioneer leguminous nitrogen-fixing trees to recuperate degraded land. The area studied – located in the coastal town of Angra dos Reis in the State of Rio de Janeiro, Brazil – was planted with seven species of fast-growing leguminous nitrogen-fixing trees in 1991. The nutrient concentrations (Ca, Mg, P and K) and N and C stocks in the soil and litter were determined, in addition to the free- and occluded-light fractions of soil organic matter. Soil samples were also collected from two reference areas: (1) an area of undisturbed native forest; and (2) a deforested area spontaneously colonised by Guinea grass (Panicum maximum). The nutrient stocks in the litter of the restored area were similar to those found in native forest. The recuperation technique used was able to re-establish the soil C and N stocks after 13 years. C and N increased by 1.73 and 0.13 Mg ha−1 year−1, respectively. The free-light fraction was highest in the recuperated area and lowest in the deforested area. The occluded-light fraction of the recuperated area was higher than that of the native forest only in the 0–5 cm layer. Both the free-light and occluded fractions were higher in the native forest and recuperated areas than in the deforested area. Since the free-light and the occluded-light fractions are the result of litterfall and decomposition, these results – combined with the data of litter stocks and soil C and N stocks – indicate that the use of legume trees was efficient in re-establishing the nutrient cycling processes of the systems. These results also show that recovering degraded land with this technique is effective in sequestering carbon dioxide from the atmosphere at high rates.
 
Article
Influences on forest stand development were assessed using tree age and long-term mortality data in ten 0.4 ha permanent plots established in 1935. The stand originated following a major fire in the 1840s with a period of rapid invasion (1851–1870). This was followed by slower filling to full stand closure (1871–1900), recruitment suppression (1901–1930), reinitiation of hemlock recruitment (1931–1950), and continued slow recruitment (1951-present). Recruitment re-initiation was apparently associated with natural stand thinning and not with major disturbance. Large blowdown patches occurred in two plots in the 1960s, but the primary effect was release of hemlock advance regeneration rather than recruitment of new individuals. From 1935 to 1983 annual mortality (calculated from 5–10-years remeasurements) was 0.5–1.2% for both species. At this rate, continued thinning will likely allow a gradual transition to an all-aged forest, as population turnover time is short relative to frequency of intermediate or major disturbance.
 
Article
The effects of ash fertilization and prescribed burning on the P, K, Ca, Mg, Mn, S, Fe, Al, Cu, Zn, Cd, Cr, Ni and 137Cs concentrations in lingonberry (Vaccinium vitis-idaea L.) berries were investigated in a 100-year-old Scots pine (Pinus sylvestris L.) stand growing on a dry site in central Finland. The treatments were control, prescribed burning and three ash-fertilizer doses of 1000, 2500 and 5000 kg ha−1. The size of the plots was 30 × 30 m, and there were four replications per treatment. Lingonberries were collected two (1991) and seven (1996) growing seasons after the treatments. Ash fertilization had no effect on the heavy metal concentrations in the berries. Potassium was the only macronutrient whose concentration in the berries significantly increased after ash fertilization (5000 kg ha−1). Prescribed burning increased the berry Cd concentrations, which, however, remained low even after prescribed burning. The berry 137Cs concentrations decreased as a result of ash fertilization and prescribed burning. The reduction in 137Cs concentrations caused by ash fertilization may be an important finding especially for areas where the picking and consumption of berries has to be restricted as a result of radioactive fallout.
 
Article
The region immediately adjacent to established roots of mature trees has been termed the “reoccurring rhizosphere” and it has been hypothesized that organic matter input from fine root turnover, root exudates and sloughing may result in a build up of the soil carbon in this region. The “reoccurring rhizosphere” for first-, second- and third-order roots of select loblolly pines (Pinus taeda L.) were examined on sandy, loamy sand and sandy loam soils. A significant carbon build up next to the root orders was confirmed for the sandy and loamy sand soils. The carbon build up was substantial (55% increase) next to the first-order roots of the sandy soil. However, the sandy loam soil did not display a significant amount of carbon build up next to the root orders. Extraction of the soil samples with supercritical freon-22 showed that the additional carbon in the “reoccurring rhizosphere” was highly soluble. Approximately 60% of the total soil carbon was extracted from the sandy and loamy sand soils, while approximately 40% was extracted from the sandy loam soil. A qualitative comparison of the extracts by liquid state nuclear magnetic resonance showed that the “reoccurring rhizosphere” region had a higher relative proportion of labile materials (i.e. carbohydrates, proteins, etc.) than the bulk soil. This information coupled with the high solubility in supercritical freon-22 suggests that the carbon build up in the “reoccurring rhizosphere” region of loblolly pines may be transient in nature.
 
Article
Only a few growth and yield programs allow users to model the effects of hardwood competition on yields from pine plantations. Several of these programs were developed with the assumption that reducing hardwood competition would consistently produce a Type 2 growth response where pine volume gains increase over time. However, the actual response is not always a Type 2 response. To determine growth response types resulting from woody control treatments, plot volume data were analyzed from 14 trials (on 13 sites) measured over a period of 2 decades (The COMProject). The “age-shift” method of growth analysis and regression analyses were used to classify the types of responses. After 20 years, stand volumes of loblolly pine (Pinus taeda L.) were increased after woody control at 13 of 14 trials when compared to no controls. At four trial locations the age gain ranged from 0.7 to 1.6 years and the growth response was classified as a pseudo-Type 1 response (i.e., pine growth was increased while the total above-ground biomass of the mixed-stand was not altered by the species shift). At nine trial locations a true Type 2 response was observed (i.e., increase in total above-ground biomass of the pine dominated mixed-stand) and the age gain ranged from 0.9 to 5.1 years. At a site in Louisiana, woody control on two similar blocks resulted in a reduction in both early and mid-rotation pine volumes (termed a Type E response) while two other blocks resulted in an early reduction that changed to a mid-rotation volume increase (termed a Type F response). Thus, four types of growth response were associated with woody control treatments.
 
Article
In the early 1980s, nitrogen (N) deposition was first postulated as a cause of N saturation and spruce mortality across the northeastern US. In 1988, a series of high elevation spruce-fir forest N addition plots were established on Mt. Ascutney (southeastern) Vermont to test this hypothesis. The paired plots each received, in addition to ambient N deposition, 15.7 kg N ha−1 year−1 (low N addition), 31.4 kg N ha−1 year−1 (high N addition) or no N addition (control) from 1988 to 2002. Over the years, potential and annual in situ forest floor net N mineralization and net nitrification, foliar and forest floor elemental concentrations, and basal area growth by species were measured on each plot. Live basal area decreased by 18% on the low N addition plots, and by 40% on the high N addition plots between 1988 and 2002, while the control plots had a 9% increase in basal area over the same time period. Initially, none of the plots had measurable rates of in situ nitrification, but by 2002, 21% of the mineralized N was being annually nitrified on the high N addition plots, compared to no net nitrification on the control plots. We also observed a significant increase in forest floor N concentration on the high N plots from 1988 to 2000. Reductions in live basal area, and increased net nitrification suggest that we induced late stage N saturation on the high N addition plots. The low N addition plots exhibited symptoms of mid-stage N saturation, with a smaller reduction in live basal area and net N mineralization, and a smaller increase in net nitrification compared to the high N addition plot values. Other correlations between forest floor and vegetation composition and function, and N saturation will be discussed in the paper.
 
Article
The effects of forest management on soil carbon (C) and nitrogen (N) are important to understand not only because these are often master variables determining soil fertility but also because of the role of soils as a source or sink for C on a global scale. This paper reviews the literature on forest management effects on soil C and N and reports the results of a meta analysis of these data. The meta analysis showed that forest harvesting, on average, had little or no effect on soil C and N. Significant effects of harvest type and species were noted, with sawlog harvesting causing increases (+18%) in soil C and N and whole-tree harvesting causing decreases (−6%). The positive effect of sawlog harvesting appeared to be restricted to coniferous species. Fire resulted in no significant overall effects of fire on either C or N (when categories were combined); but there was a significant effect of time since fire, with an increase in both soil C and N after 10 years (compared to controls). Significant differences among fire treatments were found, with the counterintuitive result of lower soil C following prescribed fire and higher soil C following wildfire. The latter is attributed to the sequestration of charcoal and recalcitrant, hydrophobic organic matter and to the effects of naturally invading, post-fire, N-fixing vegetation. Both fertilization and N-fixing vegetation caused marked overall increases in soil C and N.
 
Article
Non-native trees have been introduced to Britain and native trees have been redistributed for over 2000 years, but most species were introduced in the last 400 years, and the ecological consequences have not yet been fully manifested. Introduction has been followed by various forms of adaptation to British conditions: (i) genetic changes in the trees themselves, (ii) assimilation into forest communities, (iii) colonisation by native plants, animals and fungi and (iv) gradual cultural acceptance. Nevertheless, some naturalised shrubs are widely regarded as ecologically damaging in semi-natural vegetation (e.g. Rhododendron ponticum, Acer pseudoplatanus), and the introduction of non-native conifers has allowed forestry to expand over moorland with substantial ecological effects.
 
Plot of 5-year periodic annual height increment by initial diameter at breast height using the coefficients derived for Eq. (1). 
Plot of 5-year periodic annual height increment by initial diameter at breast height and site index (SI) for managed even-aged stands of ponderosa pine throughout the western United States using the coefficients in Table 4. 
Ranking of variables based on change in the size of the standard error of prediction without the variable in question
Article
A height increment model is developed and evaluated for individual trees of ponderosa pine throughout the species range in western United States. The data set used in this study came from long-term permanent research plots in even-aged, pure stands both planted and of natural origin. The data base consists of six levels-of-growing stock studies supplemented by initial spacing and other permanent-plot thinning studies for a total of 310 plots, 34,263 trees and 122,082 observations. Regression analysis is the most commonly used statistical method in forest modeling. However, research studies with repeated measurements are common in forestry and other biological disciplines. We choose the mixed models instead of the regression analysis approach because it allows for proper treatment of error terms in a repeated measures analysis. The model is well behaved and possessed desirable statistical properties. Our goal is to present a single height increment model applicable throughout the geographic range of ponderosa pine in the United States and by using only data from long-term permanent plots on sites capable of the productivity estimated by Meyer [Meyer, W.H., 1938. Yield of Even-aged Stands of Ponderosa Pine. US Department of Agriculture Technical Bull. 630].
 
Article
Forests in Europe currently receive inorganic nitrogen deposition (wet and dry) ranging from less than 1 to more than 75 kg N ha−1 year−1. A survey of nitrogen output from 65 forested plots and catchments throughout Europe indicated a three-stage response to these inputs. Below a deposition threshold of about 10 kg N ha−1 year−1 no significant nitrogen leaching occurred from the forests; at intermediate levels of 10–25 kg N ha−1 year−1 leaching occurred at some sites; above 25 kg ha−1 year−1 significant leaching occurred at all sites. NITREX sites followed this larger European pattern. Among 41 different variables tested in the survey, output-N (seepage or runoff) was most highly correlated with input-N (r2=0.69), followed by input-SO4, soil pH (negative correlation), percent slope, bedrock type and latitude (negative correlation). The latter three, however, were highly intercorrelated with input-N. A combination of input-N and soil pH explained 87% of the variability in output-N (N = 20) and predicted output-N successfully from NITREX sites and other European test sites.
 
Article
Biological N2 fixation by understorey legumes Acacia melanoxylon and Acacia mucronata in a mixed eucalypt forest was estimated by both natural 15N abundance and 15N-enriched isotope dilution methods over a period of 27 months following a prescribed fire. A native grass, Poa sieberiana, and opportunistic non-fixing species were used as reference plants. The natural 15N abundance, method was considered to provide accurate estimates of N2 fixation because of uniformity in natural 15N enrichment and high δ15N values in soil and reference plants. Estimates of N2 abundance method. Estimates of N2 fixed by A. melanoxylon and A. mucronata increased from 2.0 and 1.4 mg per plant after 1 year to 26 mg per plant and 57 mg per plant after 27 months, respectively. Accretion of N to the forest ecosystem from N2 fixation by these Acacia species was low (5 and 116 g ha−1 after 27 months) due to low plant densities following prescribed fire.Labelled S (35S) was applied to the plots at sowing with labelled N (N/S=10/1). Legumes accumulated significantly less dry matter and total S compared with the reference plants, although total N uptake was similar. Reference plants accumulated more labelled S and generally more labelled N than the legumes, and ratios of labelled to unlabelled S for all species were higher than ratios of labelled to unlabelled N derived from soil sources. Equal ratios of labelled to unlabelled S between legumes and reference plants did not correspond with equal ratios of soil-derived labelled to unlabelled N. These results therefore cast doubt on the validity of the concept of labelling with 35S to assess the accuracy of reference plants to estimate the isotopic composition of soil-derived legume N.
 
Article
The importance of surface litter as a sink for atmospheric N deposition on forests was investigated using tracers to quantify the effects of N input rate and litter age on retention of N inputs by forest litter. The study was conducted in plots receiving ambient (0.8 g N m⁻² per year) and chronically elevated N inputs (ambient+5 g NH4NO3-N m⁻² per year) in both a hardwood forest and a red pine plantation. Plots ( m) were part of the Chronic Nitrogen Amendment Study at the Harvard Forest, Massachusetts, USA. To allow estimates of N sink strength in litter cohorts of two different ages, litterbags containing oak leaves, maple leaves, pine needles, or maple wood chips were placed in the plots in years 1 and 3 of fertilizer additions. Uptake of N inputs into decomposing litter was estimated using tracers applied as or during years 4 and 5 of fertilizer additions. Thus additions occurred to litters in their fourth and fifth years of decay (set out in year 1 of N additions) and to litters in their second and third years of decay (set out in year 3 of N additions).
 
Article
We used isotope mass balances to track the fates of ecosystem-scale tracer additions to control non-fertilized and nitrogen (N)-fertilized plots in oak-dominated hardwood and red pine-dominated pine over nine growing seasons. The plots used in our tracer study are the same as of those used in the Chronic Nitrogen Amendment study (see Magill et al., this volume) at the Harvard Forest in central Massachusetts, USA. Nitrogen tracers were added monthly during growing seasons (April–October) of fertilization years 4 and 5 (1991 and 1992) as either or to control and to N-fertilized plots (low N treatment, receiving additions of 5 g N m−2 per year as NH4NO3). Seven years after the end of additions (1999), tracer recoveries were highest in organic soil, ranging from 34 to 83% of additions across ion form, N loading rate and forest type. Mineral soil (0–20 cm depth) was the second largest sink, with tracer recoveries ranging from 15 to 34% of additions. Tree biomass (foliage, woody tissue, plus fine roots) accumulated 7–16% of tracer additions. Patterns of recoveries after 7 years differed from recovery patterns at the end of the 2-year labeling period. At the end of labeling in 1992, recoveries in tree biomass were higher under chronic N fertilization than under ambient atmospheric N loading (control plots), higher with than additions, and higher in hardwoods than in pines. Seven years after the end of labeling, recoveries in trees were still higher with than with labeling, and trees in control plots continued to accumulate tracers. In contrast, tracer recoveries in trees on the chronically fertilized plots were lower after 7 years than at the end of the labeling period. This was due mainly to transfers of tracer from leaf and root tissue to other ecosystem pools during the years since labeling. Wood produced during the 2-year labeling period and the 7-year post-labeling interval continued to accumulate tracers in control and chronically fertilized plots in both forest types. However, recoveries were low in woody tissues (wood formed from 1990 through 1999 plus bark), ranging from 1.1 to 6.1% of additions across forest types and treatments. Our comparisons of tracer recoveries at the end of a 2-year labeling period and at 7 years following the end of labeling suggest that soils are the dominant sinks for N deposition on temperate forests and that N does not contribute substantially to enhanced carbon uptake into tree biomass.
 
Article
As part of four European ecosystem manipulation experiments in coniferous forests, field-scale 15N tracer experiments have been carried out. The experiments involved a year-long addition of 15NH4+ and/or 15NO3− to throughfall at experimental plots with different N inputs. The fate of this applied 15N in the important ecosystems pools (trees, ground vegetation, forest floor and mineral soil), as well as in drainage was measured. About 10–30% of added 15N was taken up by the trees and 10–15% was retained in the mineral soil. Both retention efficiencies were found to be constant with N input. The part of 15N retained in the organic layer was relatively high (20–45% of applied) at low N inputs (0–30 kg N ha−1 yr−1) but low (10–20%) at high N inputs (30–80 kg N ha−1 yr−1). An inverse relationship between N input and the loss of 15N in drainage was found: drainage losses increased as a function of N input. These results suggest that increased N inputs exceed the capacity of the microbial population to retain throughfall-N in the organic layer, with the result that N leaching increases.
 
Article
Chronic atmospheric nitrogen deposition can alter the rate of internal nitrogen cycling and increase the magnitude of N leaching losses in forested ecosystems. As fractionation of nitrogen in favour of the lighter 14N occurs during various transformations associated with N-enrichment and nitrogen loss, it has been proposed that the 15N signal of vegetation may provide a useful tool in evaluating the past and current N status of forested ecosystems. A series of coniferous forests across a European nitrogen deposition gradient within the NITREX project provided an opportunity to test the relationships between nitrogen supply from atmospheric deposition and the relative 15N-enrichment of vegetation to soil, across a large geographical area. Most δ15N values for above- and below-ground tree components, soil at four depths, bulk precipitation and/or throughfall water and soil solution or outflow water values were within those observed elsewhere except for a few notable exceptions. There was a significant positive relationship between the δ15N enrichment of the tree foliage relative to the soil horizons (or the enrichment factor), and nitrogen flux in the throughfall if Aber forest, N. Wales, was excluded from the regression analysis. An unusually high enrichment factor at the Aber site indicated that a the high rate of N cycling at the site was in excess of that predicted from current N deposition. This was attributed to the effect of ploughing and tree planting on the relatively N- and clay-rich mineral horizons at Aber compared to other sites. Highly significant relationships (P < 0.01) between enrichment factors and parameters describing internal rates of N cycling, such as litterfall N flux and nitrification rates in upper soil horizons, supported this conclusion. There appears to be a strong link between the rate of N cycling and the δ15N enrichment factor, rather than N deposition or nitrate leaching per se. These results confirm the potential use of the δ15N enrichment factor to identify sites influenced by nitrogen deposition. However, consideration should be taken of other site characteristics and land management practises which also influence soil N dynamics and N cycling.
 
Article
This paper reports plant and soil distribution of 15N 1 and 8 years after fertilizer application near Spillimacheen in the British Columbia interior. The experiment was originally established to test the efficacy of fertilization on snow; 15N-urea, 15NH4NO3 and NH415NO3 were applied at 100 kg N ha−1 to 11-year-old lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) in January 1981. After one growing season (October 1981), eight of the 16 plots were destructively sampled. Total recovery of 15N in plot trees was low, from 1.9 to 10.1%. Recovery in understorey was comparable (2.4–3.4%), and 30.6–73.2% of 15N was retained in the soil in organic form. The remaining eight plots were sampled in August 1988. There was a significant growth response to fertilization, amounting to a 34% increase in stem volume for fertilized (ammonium nitrate or urea) versus control trees after eight growing seasons. Approximately two-thirds of the 15N recovered in 1981 could still be accounted for in plant biomass and soil. There had been little additional 15N uptake by plot trees, but more continuing uptake by understorey. About one-fifth of 15N recovered in 1988 was found outside the plot boundaries. The results are consistent with the hypotheses that (i) tree response to fertilization is largely the result of the increase in photosynthetic capacity generated by the first year of uptake, (ii) fertilizer N, once immobilized in the soil, has low availability to crop trees, and (iii) the N mineralized is subject to losses, presumably by leaching and denitrification. Strategies are needed for maximizing the uptake of N in the first growing season. Further research is recommended to determine what factors limit the uptake of available N by trees, and to quantify natural levels of leakage of mineral N from the ecosystem due to denitrification and leaching.
 
Article
Stable isotopes of nitrogen are potentially a valuable tool for regional assessments of nitrogen saturation because they provide an integrated measure of the past nitrogen cycling history of a site. We measured δ15N of soil and litter, as well as net nitrification potential, at three sites across a nitrate-loss gradient in the White Mountains, New Hampshire to test the hypotheses: (1) that δ15N in soil and litter increase across a spatial gradient of nitrate loss; and (2) that δ15N in soil and litter is elevated when nitrification is elevated. δ15N was found not to vary significantly among the three sites. Patterns of leaf litter and forest floor δ15N, however, were strongly influenced by species composition in individual plots. Beech litter had significantly higher δ15N than yellow birch, sugar maple, and red maple. The conifer-dominated plots had significantly lower δ15N in both the organic soil horizons and in litter than did the hardwood-dominated plots. When we adjusted for spatial heterogeneity in mineral soil δ15N values by using an enrichment factor, δ15Nfoliar − δ15NBs, in place of absolute soil δ15N values, a positive relationship was found with net nitrification for hardwoods. δ15N may also be a useful tool for evaluating species differences in nitrogen cycling and nitrogen uptake. The distinct pattern we observed of decreasing δ15N across the continuum from hardwood-dominated to conifer-dominated sites may suggest that local drivers (for example, nitrification rate) regulate the absolute value of foliar δ15N, while species-driven factors (e.g., timing and type of uptake) control the foliar δ15N value of one species relative to another in the same plot.
 
Article
A large-scale tracer study was initiated at the Harvard Forest in 1991 in two forest types (red pine and mixed hardwoods) as a means to test hypotheses concerning long-term dynamics in ecosystem-level N cycling and carbon–nitrogen interactions. Here we describe the application of a biogeochemical process model TRACE, with the ability to simulate tracer redistributions, to help interpret the field study and explore its ramifications. We had three main goals: (1) to compare field results of 8-year time series in and redistributions against previous model predictions; (2) to gain insight into ecosystem C/N interactions through an iterative set of model changes and direct model-data comparisons; and finally (3) to forecast temporal dynamics in the future effects of elevated N inputs on altered C storage in the regionally representative hardwood forest.
 
Article
The uptake of fertiliser-nitrogen and retention within the soil was determined after one growing season in a 2-year-old Pinus radiata plantation on coastal sand dunes at Christchurch, New Zealand. Applications of 15N-labelled urea enriched at 2.33 atom % excess were applied at different frequencies and in different seasons to single-tree root-isolated plots (area, 7 m2). A single application of 90 g N per tree in spring was compared with either three by 30 or nine by 10 split applications. Applications of 30 g N per tree in either autumn, spring or summer were also compared.
 
Article
The long-term fate of fertilizer N in forest ecosystems is poorly understood even though such information is critical for designing better forest fertilization practices. We studied the distribution and recovery of 15N (4.934 atom% excess)-labelled fertilizer (applied as urea at 200 kg N ha−1) 10 years after application to a 38–39-year-old Douglas-fir (Pseudotsuga menzeisii (Mirb.) Franco) stand in coastal British Columbia. The urea was applied in the spring (May 1982) or fall (November 1982). Sampling was conducted in October 1992, and we found that after 10 years, there were few differences between the fall and spring fertilizer applications in total N and 15N distribution within the tree and forest ecosystem. On average total fertilizer-N recovery was 59.4%; about 14.5% of the applied-N was recovered in the trees including coarse roots, with foliage containing 41% of the labelled-N recovered in the aboveground tree biomass. Tissue 15N remained mobile and could be transferred to new growth. Soil recovery was 39.8%, which had decreased from 57.0% at a previous 1-year sampling, with an average loss of 3.0% per year from the mineral soil and 3.7% from the litter layers. However, it appears that there was little continuing tree uptake. While short-term effects of fall vs. spring urea application were previously reported, there were no long-term effects on either stand productivity or fertilizer use efficiency, suggesting that if fertilization is properly done, timing of fertilization is not a critical issue in terms of maximizing fertilizer use efficiency for the coastal Douglas-fir forest we studied. Our results also highlight the high capacity of this ecosystem to retain externally applied inorganic N over the long-term, the importance of maximizing nitrogen uptake in the first year, and also of the continuing need to develop new approaches to overcome the generally low efficiency of forest N fertilization.
 
Article
A field study was carried out to investigate the impacts of windrowed harvesting residues on denitrification, immobilisation and leaching of 15N-labelled nitrate applied at 20 kg N ha−1 to microplots in second-rotation hoop pine (Araucariacunninghamii) plantations of 1–3 years old in southeast Queensland, Australia. The PVC microplots were 235 mm in diameter and 150 mm long, and driven into the 100 mm soil. There were three replications of such microplots for each of the six treatments which were areas just under and between 1-, 2- and 3-year-old windrows of harvesting residues. Based on gaseous N losses estimated by the difference between the recoveries of bromide (Br) applied at 100 kg Br ha−1 and 15N-labelled nitrate, denitrification was highest (23% based on 15N loss) in the areas just under the 1-year-old windrows 25 days after a simulated 75 mm rainfall and following several natural rainfall events. There was no significant difference in 15N losses (14–17%) among the other treatments. The 15N immobilisation rate was highest for microplots in the areas between the 1-year-old windrows and generally higher for microplots in the areas just under the windrows (30–39%) than that (26–30%) between the windrows. Direct measurement of 15N gas emissions confirmed that the highest denitrification rate occurred in the microplots under the 1-year-old windrows although the gaseous 15N loss calculated by gas emission was only about one-quarter that estimated by the 15N mass balance method. A significant, positive linear relationship (P<0.05) existed between the gaseous 15N losses measured by the two methods used. The research indicates that considerable mineral N could be lost via denitrification during the critical inter-rotation period and early phase of the second rotation. However, the impacts of windrowed harvesting residues on N losses via denitrification might only last for a period of about 2 years.
 
Article
Growth and survival of 16 provenances of Eucalyptus microtheca were studied to assess their adaptability to regularly irrigated conditions. A further aim of the study was to find out which climatic variables in the natural habitat of E. microtheca contribute to adaptation to prevailing conditions.The study area was located in Bura, Tana River District, Kenya. The trial was irrigated at approximately 7 week intervals throughout the experimental period, 1984–1992. The total water input during the experiment was equal to about 5500 mm of rainfall (680 mm year−1).Survival rate ranged from 60 to 100%, and mean annual increment (MAI) from 0.8 to 23.5 m3 ha−1 at 8 years of age. Statistically significant differences between provenances were found in MAI and basal area. The eastern Australian provenances (New South Wales and Queensland) exhibited better growth rate than the northern (Northern Territory) and western (Western Australia) ones. Out of nine climatic variables tested, precipitation of the driest quarter was the best predictor for basal area growth at the age of 8 years.The results indicate that the growth capacity of provenances can be attributed to the precipitation of the driest quarter in their natural habitats in Australia. The frequent mild water stress that occurs in habitats of the eastern provenances may contribute to their prodigal water-use strategy. These provenances have physiological and morphological adaptations that assist quick water harvesting, enabling the plant to maintain a high daily gas exchange rate. The long, dry period that occurs in habitats of the western and northern Australian provenances may contribute towards their conservative water-use strategy. These provenances have mechanisms that enable the plant to conserve water and maintain good water status throughout the day.The provenances could be divided into two categories at the age of 1 year, suggesting that approximate ranking can be carried out at an early stage, thus speeding up final provenance testing. However, the best provenance could be detected as late as 5 years of age, emphasising the importance of long lasting experiments in provenance selection.We conclude that the eastern Australian provenances are most suitable for regularly irrigated conditions owing their great capacity to harvest available water very quickly. Western and northern provenances may be most suitable for areas where long drought periods dominate.
 
Article
Woody debris that is accumulated on the forest floor could potentially be a relatively long-term carbon (C) sink in forest ecosystems. For a 16-year old Pinus radiataD. Don. plantation in Australia, we quantified the dry mass, C and nitrogen (N) stored in woody debris (including dead logs, branches and twigs) relative to the loss of soil C that followed afforestation of the native pasture onto which the plantation had been established. This debris derived mainly from forest management (thinning and pruning) 8 years earlier. The line intersect technique was used on ten 10 m × 12 m plots to estimate the mass of woody debris on the forest floor in 10 diameter classes. There was 6.1 Mg ha−1 of oven dry woody debris, containing 3.1 Mg C ha−1 and 12.9 kg N ha−1, on the forest floor. The largest diameter class (>50 mm) contributed most of the debris’ mass. We also estimated rates of decomposition, and C and N release from the woody debris and calculated its half-life and “life time” (95% disappearance). The overall decay rate constant (k) for all woody debris was 0.069 year−1. The overall half-life and lifetime was 10 and 43 years, respectively. Almost half (42%) of the original C in woody debris was released in the 8 years of decay, but only 12% of the original N was released. Decay rate varied with size class with the largest diameter (>50 mm) decaying the fastest, the smallest diameter class (<5 mm) decaying the second fastest, and the intermediate size-classes being the slowest to decay. Although N was slowly released from the woody debris, this pool was an effective C sink per unit-N involved because of its high C:N ratio. The C stored in the pool offset 22% of the observed soil C-stock reduction 16 years after land use change from pasture to pine plantation.
 
Article
Non-native plant abundance, vascular and non-vascular diversity and plant community succession were studied 10 and 15–16 years after stand initiation at two mixedwood boreal sites in northwestern Canada. At Inga Lake, five silvicultural treatments (untreated, plowed-and-inverted, rotocleared-and-mixed, burned-windrow, repeated vegetation control) created a gradient from pure broadleaf to pure white spruce (Picea glauca [Moench] Voss) overstories. At Iron Creek, four treatments (untreated, mounded, plowed-and-inverted, vegetation control) produced a narrower range of conifer:broadleaf ratios. Both experiments were randomized block designs with 4–5 replications. Univariate ANOVA, stepwise regression and multivariate ANOVA by canonical redundancy analysis were used to address three questions: (1) did non-native species diminish over time?; (2) how was understory diversity related to overstory composition?; and (3) did highly dissimilar plant communities diverge or converge over time? Non-native cover declined three- to six-fold between the two sampling dates. Non-vascular richness generally doubled over the 5–6-year sampling interval. Understory diversity increased with treatment severity and frequency and was positively correlated with conifer overstory abundance. At Inga Lake, there was successional convergence among all treatments. Convergence was most rapid on severely burned windrows where plants originated mainly from seed, and slowest on rotocleared-and-mixed sites with a dense turf of Calamagrostis canadensis (Michx.) Beauv. At Iron Creek, the vegetation control treatment diverged slightly from untreated communities after recent manual cutting. Our results demonstrate the strong resilience of these boreal mixedwood plant communities and suggest ways that silvicultural intervention can modify stand composition and diversity to address a variety of ecosystem management goals.
 
Article
The long-term development of stand characteristics and tree spatial patterns (TSP), their mutual relation, and linkage to site and tree species were studied in the Boubín primeval forest (protected since 1858). Surveys were carried out in 1851, 1961/1964, 1972, 1984/1989, 1996 and 2010 on one to six research plots sized 0.58–1.00 ha. To see how results from these surveys could be generalized, results were also compared with whole-area data sets (46 ha) from 1972 to 2010.The proportion of Abies alba continually decreased, from 20% in 1851 to 2–3% in 2010. This decrease started no later than at the beginning of the 20th century. In contrast, the proportion of Fagus sylvatica slightly increased. The sum of dead and living wood volume was stable during the 159 year period, with deviations of only up to 5%. From 1961/64 to 2010, the number of living trees continually decreased, but the mean-tree volume and volume of dead wood increased. The distribution of dead wood always differed from the distribution of living trees.A random TSP was always most common, which seems to be typical for this type of forest. This was true even when A. alba was gradually forced out from the stand structure. Nevertheless, the pronounced decrease of A. alba found during the 1961/64 survey compared with 1851 was reflected in a tendency towards clustering, as gaps from A. alba dieback gradually closed. In these gaps, competitive pressure was lower, resulting in more clustered distributions. Regular distribution was recorded only rarely. F. sylvatica maintained a random or clustered TSP over long periods, depending on site conditions. On water-affected plots, it had a consistently higher tendency towards clustering. The only step change in TSP occurred due to Hurricane Emma in 2008. Otherwise, the most marked TSP changes over time were found for Picea abies, in which there was a gradual trend from clustered to random, connected with a decreasing number of individuals.The main reason for the decline of A. alba and the decreased number of living trees from 1961/64–2010 was the on-going effect of a high stock of red deer at the turn of the 19th and 20th centuries. The decreasing trend in the number of living trees showed no marked change, even 60 years after the game pressure was strongly reduced. However, the vertical structure became increasingly homogenized due to the long-term absence of severe abiotic and/or biotic disturbances.Highlights► Abies alba decline started at the beginning of the 20th century at the latest. ► The sum of living and dead trees remained stable for almost 160 years. ► Tree spatial pattern (TSP) development differed for both tree species and sites. ► TSP was stable over 50 years, but not for the entire 160 year period studied. ► Game pressure in the past was the principal factor in forest development.
 
Article
Forest management must take into account in its management schemes very different goals such as timber production, protection from natural hazards, and biological conservation. In this paper we propose a new management principle based on the basic ecological characteristics of forests that could help the integration of these goals. We discuss the factors influencing species richness in forests and relate changes in species richness to the history of forest management. A closer look at hypotheses about possible links between disturbances and species richness reveals that dominance reduction is considered to be the main effect of disturbance events on species richness. We therefore propose dominance reduction as a management principle for forests in central Europe that are actively managed. This, we claim, is a way to maintain biodiversity in an integrative management approach. Three types of disturbances are distinguished: endogenous, exogenous, and human-induced disturbances. This distinction allows a connection to be made between natural and anthropogenic impacts on forests, thus overcoming the negative connotation disturbance events have. Planning forest management according to the principle of dominance reduction will facilitate the search for new ways to integrate the different needs society wants to have fulfilled by forests.
 
Article
We describe the fire regime in the Gaspesian mixedwood boreal forest in order to improve our knowledge of the maritime fire regime through time and the role of climate on changes in fire cycle. We also investigated the importance of coarse scale spatial factors, such as topography, altitude, soil-type and vegetation-type. Fire history was reconstructed for a 6480-km2 area using Quebec Ministry of Natural Resource archival data and aerial photographs combined with dendrochronological data, collected using a random sampling strategy. Physiographic features were not found to significantly influence the fire cycle, but an increase in the cycle (from 89 to 176 years p ≤ 0.0001) was observed since the end of Little Ice Age (LIA) (1850). Relative agreement between the archival data (1920–2003) and the semi-parametric survival analysis approach for the 1850–2003 period provides greater confidence in our determination of a fire cycle situated between 170 and 250 years. An analysis of fluctuations in the Canadian forest fire Weather Index system, calculated for the period 1920–2003, showed a statistically significant decrease in extreme values. Given such a long fire cycle and in the context of forest management based on natural disturbance, even-aged management under short rotations should be questioned in these mixedwood boreal forests.
 
Article
The autumn gum moth Mnesampela privata Guenée is a major defoliator of Australia’s commercially important pulpwood plantation species, Eucalyptus globulus Labill. However, little is known about genetic variability of E. globulus to M. privata oviposition preference. We examined oviposition preference by exposing juvenile foliage sprigs of different genetic origins to gravid female moths in cage bioassays. Foliage sprigs were collected from 40 E. globulus families grown in a common environment field trial in southern Tasmania. These families were derived from open-pollinated seed collected in native stands and represented four geographic races of E. globulus. Significant differences in the level of oviposition was detected between foliage sprigs from the different races, with those from the Furneaux race receiving over twice as many egg batches compared to those from either the Strzelecki Ranges or northeastern Tasmania races. The southern Tasmania race received an intermediate egg load. No significant variability in oviposition preference was identified between different localities within races or between different open-pollinated families within localities. Selections from both the Strzelecki Ranges and Furneaux races comprise a large component of the Australian E. globulus breeding population. There is therefore likely to be significant genetic variation for M. privata oviposition preference within the breeding population and by screening before deployment gains in plantation productivity in areas subject to M. privata outbreaks may be possible.
 
Article
Harvesting and repeated burning are frequently used to restore shortleaf pine-bluestem ecosystems within the Ouachita Mountains of Oklahoma and Arkansas, USA. These practices have been shown to adequately restore much of the habitat for bird and mammal species that utilize this ecosystem. However, there have been only limited studies to quantify the impact of restoration activities on soil chemistry and nutrient availability in this region. We compared soil chemistry and foliar nutrient concentrations for a 3-year period in three shortleaf pine-hardwood stands that had restoration activities for at least 17 years with soil chemistry and foliar nutrient concentrations in three stands that have had no restoration activities. Mineralizable N, total N, C, Ca, and pH of the surface soil were higher in the restored stands than in the stands without restoration activities. The magnitude of the increases in nutrient concentrations and pH appeared to reflect the combined impacts of harvesting and prescribed burning in the restored stands. Foliar concentrations of N, P, K, and Ca were significantly higher in the restored stands for at least 1 year following the most recent prescribed fire. However, only K concentrations were greater in the restored stands during the entire 3 year study. An increase in nutrient availability within the restored stands suggests that surface soil fertility and productivity may have increased with shortleaf pine-bluestem restoration activities.
 
List of tree species studied with Latin names and most important uses
Stump sprouting results 3 years after an overstory removal cut
Article
While carrying out an overstory removal/natural regeneration study, the number of sprouts from the trees that were cut down were recorded. Seventeen species with average diameters from 9 to 36 cm were studied. The number of sprouts varied from 1 to 6, and sprout heights from 1.0 m to 5 m, 3 years after the original trees were cut. Overall, the number of sprouts and the height of the sprouts increased as the parent tree diameter increased. This information can be very useful in managing the forest for products other than timber. Firewood, medicinal plants, construction materials, edible fruits, and forages are among the different uses of the observed species. Specific stands might be coppiced to satisfy some of the most immediate needs of the region's inhabitants.
 
Article
Forest harvesting and regeneration may cause changes in soil and solution chemistry that adversely affect forest productivity and environmental quality. The objective of this study was to assess soil carbon (C), nitrogen (N), and base cation cycling 17 years following whole-tree harvesting in a low-elevation red spruce (Picea rubens)-balsam fir (Abies balsamea) watershed (regenerating watershed) in central Maine, USA. Results for forest floor and mineral soil nutrient concentrations and pools were compared to an adjacent non-harvested 77–85-year-old spruce-fir watershed (reference watershed) and to preharvest conditions obtained 17 years earlier. The total soil (forest floor + mineral soil) exchangeable magnesium (Mg) pool was 32% and 44% lower (P ≤ 0.05), respectively, in the regenerating and reference watersheds compared to the preharvest condition. Nitrogen and exchangeable potassium (K) contents in the forest floor, however, were 26% and 65% lower (P ≤ 0.05), respectively, for the preharvest condition compared to the reference watershed; no differences (P > 0.05) occurred between the reference and regenerating watersheds. Mineral soil exchangeable calcium (Ca) and sodium (Na) concentrations and contents, effective cation exchange capacity (CECe), and base saturation were at least twice as high (P ≤ 0.05) in the regenerating compared to the reference watershed or preharvest conditions. Changes in the N and Mg pools indicate that atmospheric deposition may be a concern for Mg depletion and N saturation at this site. However, Ca depletion does not appear to be occurring at this site as a result of either acid deposition or whole-tree harvesting, although there are indications that the reference watershed may be in the initial stages of altered Ca cycling, which may lead to depletion.
 
Top-cited authors
Andreas Rigling
  • Swiss Federal Institute for Forest, Snow and Landscape Research WSL
Jorge Castro
  • University of Granada
Nate McDowell
  • Pacific Northwest National Laboratory
Patrick Gonzalez
  • University of California, Berkeley
Jong-Hwan Lim
  • Korea Forest Research Institute