Implications For Silviculture Research Articles

Variability of Water Use Efficiency of Gmelina arborea Plantations in the Tropical Dry Forest of Colombia

Effective forest management strategies to adapt to climate change are essential. Water use efficiency (WUE), which integrates biomass production and water consumption, is a key indicator of forest adaptation. This study evaluated the WUE of Gmelina arborea plantations in the tropical dry forest and identified the main influencing factors, with implications for silviculture and management. Data on total biomass (TB) and total volume (V) were obtained from permanent sample plots in the upper and lower Magdalena River basin in Colombia. WUE was calculated as m3 of V (WUEV) or kg of TB (WUETB) per m3 of evapotranspired water. Significant regional differences were found, with higher WUE in the Caribbean plains (WUETB = 1 kg m−3 and WUEV = 0.0018 m3 m−3) compared to the inter-Andean valleys (WUETB = 0.77 kg m−3 and WUEV = 0.013 m3 m−3). Stand variables had the greatest influence on WUE, showing positive associations with site productivity and stand density measures. Soil variables such as texture, available water, and calcium content, along with a drier climate, were crucial for achieving higher WUE. The study underscores the importance of comprehensive site selection and effective silvicultural practices to maximize WUE and productivity, especially in the context of climate change.

Vulnerability of African Rosewood (Pterocarpus erinaceus, Fabaceae) natural stands to climate change and implications for silviculture in West Africa

Pterocarpus erinaceus is a native tree species of the Guineo-Sudanian and Sudano-Sahelian zones where natural stands are under constant pressure and heavily exploited for timber, animal feeding and others uses. A part from the overexploitation, climate change could also become a serious threat to the species natural distribution. For that purposes, this study aims to assess the vulnerability of P. erinaceus potential niche to climate change within its natural distribution area in West Africa. Niche predictions are based on 6,981 natural occurrence of the species and 19 global bioclimatic variables available through WorldClim. The future niche of the species is predicted according to three concentration pathways (RCPs 2.6, 4.5 and 8.5) of BC model for 2050 and 2070, thanks to Maxent software. P. erinaceus is currently reported from Senegal to Cameroon. Its potential niche covers the Sudano-Sahelian zone and the Dahomey gap on approximately 17.42% of the total area of these countries. In general, the niche of the species is not sensitive to climate change, regardless of the climate scenario and the year. Compared to its initial niche, the niche of the species will increase from 22.33% to 43.61% in 2050 and from 27.12% to 53.61% in 2070. However, this ecological expansion observed mainly in the Gulf of Guinea, will be associated with a considerable decrease in the Sahel and central Nigeria. This study shows the importance of promoting the development of innovative silvicultural strategies for the extension and restoration of natural stands of P. erinaceus in order to meet sustainably the timber needs of the West African region. It helps also to strengthening the roles of natural forests in providing ecosystem services and mitigating climate change effects.

Microsite conditions in a low-elevation Engelmann spruce forest favor ponderosa pine establishment during drought conditions

Warming climate in U.S. forests may limit future viability of dominant high-elevation species at their lower elevation range limits but favor more drought-adapted sympatric species, potentially contributing to species distribution changes. Adaptive management may address future uncertainty in species distributions by facilitating regeneration of multiple species with contrasting silvics. However, the success of this approach will depend on suitable microsite conditions, the effects of which are not well understood across species and forest types. These concerns are present in the southern Rocky Mountain region, where current and future climate may restrict Engelmann spruce regeneration but benefit sympatric species like ponderosa pine. We used a planting experiment to systematically evaluate microsite conditions which support critical first-season survival and root growth of these contrasting species in a low-elevation spruce forest during a droughty 2018 growing season. Our assessment targeted species responses to variation in canopy cover generated by different silvicultural regeneration treatments, with and without additional shelter from coarse woody debris. We also considered microsite variables of seedling size, vegetation and litter cover, soil moisture and depth, and competition from established tree regeneration. Survival of ponderosa pine was nearly twice that of Engelmann spruce, but the relative effects of microsite variables were similar. Coarse woody debris shelter improved the probability of survival by approximately 357%, though the effect was stronger for spruce. Influences of canopy cover were minimal and opposite our expectations; spruce was marginally inhibited by canopy cover, while pine was positively influenced by more dense canopy. Smaller seedling heights improved the probability of survival for both species by 179% compared to mean seedling heights. Pine root growth was 150% greater in open versus dense canopy microsites and limited in coarse woody debris shelter. We discuss likely site and physiological factors underlying these results. This study provides insight into the factors which define suitable microsites for first-season establishment for these species in rapidly changing low-elevation spruce forests, especially during drought conditions. We discuss implications for adaptive management and silviculture, concluding that regeneration efforts which seek to improve forest resilience to climate-related changes in species viability could consider more drought-adapted, sympatric species as viable supplements to moisture-dependent species at their current lower range limits.

Role of green alder in boreal conifer growth: competitor or facilitator?

Sustainable forest management implies successful regeneration after disturbances. Low N availability and competition can, however, limit tree establishment in boreal ecosystems. To develop silviculture strategies that maintain productivity in such context, we established a field trial in northern Québec, Canada. We evaluated if a companion N2-fixing species ( Alnus alnobetula) promotes or hinders Picea mariana and Pinus banksiana establishment over six growing seasons. We tested if Alnus has a facilitation effect through nutritional processes and a competition effect through light interception. Foliar stable nitrogen isotope ratio ( δ15N = 15N/14N, ‰) results confirmed that Alnus obtains a substantial part of its N through biological fixation and represents an N source in this system. Although we did not observe increased foliar N concentrations in either conifer species in the presence of Alnus, Pinus growth was nonetheless higher in presence of Alnus, whereas no difference was observed for Picea. In the plots where Alnus cohabited with the conifers, the former had a negative impact on seedling growth, suggesting a significant competition for light. Overall, the net effect of Alnus was positive for Pinus and neutral for Picea. Our results have significant implications for silviculture in N-limited systems, especially in the context of climate change that imposes increased levels of stress on regeneration.

Tree species mixing can increase maximum stand density

Mixed-species stands are on the advance in Europe. They fulfil many functions better than monocultures. Recent papers show that mixed stands can have higher yields, but it remains open whether mixed stands simply grow faster along the same self-thinning lines as pure stands or have higher maximum stand densities. We analyzed the effect of species mixing on maximum density based on triplets of pure and mixed stands at approximately maximum density. Most considered mixtures include Norway spruce (Picea abies (L.) H. Karst.). We show that (i) in mixed stands, maximum density is, on average, 16.5% higher than in neighbouring pure stands, and (ii) species mixtures with Norway spruce exceed densities of pure stands by 8.8%, on average. For individual species mixtures, we find a significant density effect of +29.1% for Norway spruce mixed with European larch (Larix decidua Mill.) and +35.9% for Scots pine (Pinus sylvestris L.) in association with European beech (Fagus sylvatica L.). No significant links with stand variables such as age and mean tree size and site fertility were found. The results indicate that species mixing substantially increases stand density, indicating a higher carrying capacity caused by a higher supply and use efficiency of resources. The implications for inventory, silviculture, and forest modelling are discussed.

A Review of the Characteristics of Small-Leaved Lime (Tilia cordata Mill.) and Their Implications for Silviculture in a Changing Climate

Tilia cordata Mill. is a minor European broadleaved species with a wide but scattered distribution. Given its scarcity and low value in the wood market, it has received little attention from researchers and forest managers. This review summarizes the main aspects of T. cordata ecology and growth. Its main limiting factor is its need for warm summer temperatures to ensure successful seed production. It has a height growth pattern relatively similar to that of Acer pseudoplatanus L., with a slight delay in the early stages. Yield tables report great productivity, especially in eastern Europe. T. cordata used to be a major species in Europe, in contrast to its present distribution, but it is very likely to receive renewed interest in the future. Indeed, with the potential change of competition between species in some regions and the need for important diversification in others, T. cordata may play an important role in forest adaptation to climate change, especially owing to its wide ecological tolerance and its numerous ecosystem services. It is necessary to increase our knowledge about its regeneration and its responses to environmental and silvicultural factors, to establish clear management recommendations.

Effect of tree species mixing on the size structure, density, and yield of forest stands

An increasing number of studies provide evidence that mixed-species stands can overyield monocultures. But it is still hardly understood, how the overyielding at the stand level emerges from the tree, canopy, and size structure. Analyses of 42 triplets with 126 mixed and mono-specific plots in middle-aged, two-species stands of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies [L.] Karst.), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), and European beech (Fagus sylvativa L.) in Central Europe revealed that mixed-species compared with mono-specific stands can have (1) higher tree numbers, higher right skewness and kurtosis of the size distribution, higher inequality of tree sizes, and thereby higher stocking densities and sum of crown projection areas, (2) growth–size relationships with stronger size asymmetry of growth and higher inequality of size growth, and (3) higher stand productivity coupled with higher maximum stand density, canopy space filling, and size asymmetry. These differences depend on the species assemblage. They suggest a deeper entrance of light into the canopy as well as a higher light interception and light-use efficiency as main causes of the overyielding and overdensity. We discuss implications for research and silviculture and draw conclusions for designing and managing resource-efficient production systems.

Economic performance of uneven-aged forests analysed with annuities

For this study, 18 permanent research plots in Switzerland with an area between 0.5 and 2.5 ha that have been installed between 1905 and 1931 were analysed using annuities. The plots cover a wide range of uneven-aged forest-types from pure Norway spruce to classical single-tree selection (plenter) forests dominated by Silver fir in different elevations (575–1810 m a.s.l). The areas have been managed according to an uneven-aged silvicultural system and growth and yield characteristics have been assessed on a single-tree basis every 5–11 years. Net revenues of timber harvesting were computed as a time series from the installation of the plots until today and transformed into net present values and subsequently into annuities for each assessment interval. Three types of annuities: (1) for cutting cycles; (2) forward; (3) backward for the whole assessment period were calculated together with internal rates of return. The results display that annuities were usually positive with an interest of 2 per cent. High elevation (>1400 m) Norway spruce dominated forests as well as heavily overstocked (>900–1000 m3 ha−1) plots showed the lowest or even negative annuities. The reduction of overstocks lead in the mid-term to an increase, but resulted in a short-term decrease of the annuities. For many of the research plots, especially those in higher elevations, there is a trend towards an increase of the annuities over time. The highest annuities were found in Silver fir dominated selection forests with a growing stock close to or slightly above an equilibrium structure. The backward calculation of the annuities improved for some plots the problem of the strong influence of the value of the initial growing stock. Implications for uneven-aged silviculture as well as for the analysis of the economic performance of uneven-aged and even-aged forests and the application of annuities are discussed in the paper.

Changing perspectives on regeneration ecology and genetic diversity in western quaking aspen: implications for silviculture

A conventional view of regeneration ecology of quaking aspen ( Populus tremuloides Michx.) in western North American holds that reproduction is strictly vegetative and, except on some marginal sites, only successful following high-severity disturbance. This view has strongly influenced silvicultural treatment of western aspen and has led to low expectations concerning genetic diversity of stands and landscapes. However, recent discoveries are fundamentally altering our understanding of western aspen regeneration ecology and genetics. For example, there are clearly multiple pathways of aspen regeneration and stand development. Research on a variety of fronts indicates that seedling establishment is common enough to be ecologically important and that genetic diversity is substantially greater than previously thought. We review conventional understanding of western aspen and put this into the context of silvicultural practice. We then review recent developments in aspen research and assess the silvicultural implications of these insights.

Twenty-five years of progress in understanding pollination mechanisms in palms (Arecaceae).

With more than 90 published studies of pollination mechanisms, the palm family is one of the better studied tropical families of angiosperms. Understanding palm-pollinator interactions has implications for tropical silviculture, agroforestry and horticulture, as well as for our understanding of palm evolution and diversification. We review the rich literature on pollination mechanisms in palms that has appeared since the last review of palm pollination studies was published 25 years ago. Visitors to palm inflorescences are attracted by rewards such as food, shelter and oviposition sites. The interaction between the palm and its visiting fauna represents a trade-off between the services provided by the potential pollinators and the antagonistic activities of other insect visitors. Evidence suggests that beetles constitute the most important group of pollinators in palms, followed by bees and flies. Occasional pollinators include mammals (e.g. bats and marsupials) and even crabs. Comparative studies of palm-pollinator interactions in closely related palm species document transitions in floral morphology, phenology and anatomy correlated with shifts in pollination vectors. Synecological studies show that asynchronous flowering and partitioning of pollinator guilds may be important regulators of gene flow between closely related sympatric taxa and potential drivers of speciation processes. Studies of larger plant-pollinator networks point out the importance of competition for pollinators between palms and other flowering plants and document how the insect communities in tropical forest canopies probably influence the reproductive success of palms. However, published studies have a strong geographical bias towards the South American region and a taxonomic bias towards the tribe Cocoseae. Future studies should try to correct this imbalance to provide a more representative picture of pollination mechanisms and their evolutionary implications across the entire family.

A review of European ash (Fraxinus excelsior L.): implications for silviculture

Summary European ash (Fraxinus excelsior L.) is common throughout much of Europe and is a valuable broadleaved tree due to its ecological characteristics, outstanding wood properties and high economic value. It is a fast growing species, associated with several forest types and with a scattered distribution in many different forest communities. In this review, we sum up essential characteristics of European ash, relevant to the further development of silvicultural practices. The paper covers site requirements, regeneration and stand establishment, growth dynamics and wood quality, and health and robustness. The review also highlights implications for silviculture and summarizes new information on ash dieback, a phenomenon which is observed in many European countries. Ash grows best on fertile, pH-neutral, deep, freely drained soils and such sites should be favoured if the aim is for high quality timber. Ash grows well at wide spacing which can result in enlarged ring width and increased latewood percentage, making the wood denser and stronger. Relatively short rotations may be recommended, depending on site, to avoid black heart: for example, a harvesting diameter of 60 cm can be reached within 60–75 years at 60–80 ash crop trees per ha. Universal recommendations are therefore for wide spacing with heavy, regular thinning in order to get a large diameter within a relatively short rotation. The necessity for pruning depends on the stand density at establishment and the subsequent thinning regime.

A review of growth and stand dynamics of Acer pseudoplatanus L. in Europe: implications for silviculture

1 Sycamore (Acer pseudoplatanus L.) is a widespread but minor species throughout Europe but 2 there is a growing interest in using it more widely because of its potentially high economic 3 and ecological values. Silvicultural recommendations for exploiting the potential of the 4 species to the full should aim at producing high quality timber on short rotations. This can be 5 achieved in a number of ways including the creation of mixed-species and structurally diverse 6 stands that will simultaneously increase ecological values. This review synthesises existing 7 knowledge on growth and development of sycamore that may be used as a basis for 8 developing silvicultural recommendations. Sycamore regenerates easily, although competing 9 ground vegetation, damage by browsers and bark stripping by grey squirrels may endanger 10 production of valuable timber. Existing yield models show that sycamore grows rapidly for 11 the first 20-25 years and then slows considerably. Because of its relative scarcity, there has 12 been limited interest in the species for growth model development and this has restricted its 13 inclusion in forest growth simulators. This review shows that there is currently a lack of 14 detailed knowledge about the responses of sycamore to various environmental, ecological and 15 silvicultural factors and this hinders the understanding and management of this valuable 16 broadleaved tree. 17

Male flowering of birch: Spatial synchronization, year-to-year variation and relation of catkin numbers and airborne pollen counts

The magnitude of flowering of many forest tree species varies intermittently and extensively from year to year. Besides its great consequences for the reproductive biology of plant species, the phenomenon has manifold implications for silviculture, ecological interactions and public health. In order to characterise the male flowering and pollen flow of birch ( Betula), and to understand the proximal causes contributing to them, we studied the annual variability and spatial synchronization of male catkin numbers of silver birch ( Betula pendula Roth.) and downy birch ( Betula pubescens Ehrn.) stands, and the relation of catkin numbers to airborne pollen counts during 18 years in Finland in northern Europe. Years with either low or abundant catkin production of both species tended to occur at the same time over a large geographic area. The longest distance between two stands in our study was 500 km, and all correlations between annual catkin amounts were still positive at this distance. Years with abundant and low male catkin crops were correlated among stands of the same birch species as well as among stands of silver birch and downy birch. The association between annual airborne pollen sums and catkin numbers was positive, but interestingly, marked differences were also detected.

Seed dispersal and its implications for silviculture of African mahogany ( Entandrophragma spp.) in undisturbed forest in the Central African Republic

The study of seed dispersal has received considerable attention in tropical ecology with emphasis placed on its role in the maintenance of species diversity. Since seeds of numerous high-value tropical timber trees are nominally or actively wind dispersed, the subject is also of interest to tropical foresters. In central Africa, up to 70% of harvested timber trees are wind dispersed, including African mahoganies of the genus Entandrophragma. The dual goals of managing many remote areas in central Africa for both biodiversity and timber production values has led to the consideration of low impact logging techniques. In the Central African Republic, increasing light downwind of Entandrophragma has been proposed as a way of increasing regeneration and recruitment of these trees. Mean wind direction at the time of dehiscence of Entandrophragma angolense and Entandrophragma cylindricum was compared with compass orientation of seed shadows for five individuals in mature, undisturbed forest. Mean wind direction was found to be toward the northeast for morning, afternoon, and daily winds and was significantly different from the orientation of seed shadows for all trees. Mean branch direction did not vary significantly from a random pattern, but matched the direction of the seed shadow better than wind direction did. It is concluded that harvesting interventions aimed at increasing light downwind of Entandrophragma will not necessarily benefit seedlings of the species at the study site and further silvicultural research is needed to determine appropriate management interventions, particularly in remote areas of Africa where conservation values are important.

Effects of Previous High N Addition on Nutrient Conditions in Above-ground Biomass of a Picea abies Stand in Sweden

Deposition of air pollutants, together with intensified harvesting practices, has led to concern about the declining base cation status and the acidifying effects in the soil, with possible implications for silviculture. The aim of this study was to analyse the effects of a previous high N addition on the nutritional status in the above - ground part of a tree stand. We sampled various biomass fractions in a highly productive Norway spruce (Picea abies (L.) Karst.) stand in the province of Värmland, western Sweden. The experimental plots had been fertilized with urea four times at intervals of 5 yrs, the last time being 13 yrs before our study. The total amount of N added was in the range 480 - 2400 kg ha?1. Despite the high N addition and an insignificant growth increase following N input, there were no obvious residual changes of nutrient concentrations in the above - ground parts of trees.

Understorey light conditions and regeneration with respect to the structural dynamics of a near-natural temperate deciduous forest in Denmark

Suserup Skov is a near-natural temperate mixed deciduous forest dominated by Fagus sylvatica L. (beech) and Fraxinus excelsior L. (ash) with some Quercus robur L. (oak), and Ulmus glabra Huds. (elm). The forest dynamics in Suserup Skov can be described by the forest cycle, a sequential shift between a series of developmental phases: innovation, aggradation, early biostatic, late biostatic, and degradation phases. Climax microsuccession from ash to beech occurs as an integral part of the forest cycle. The spatial match to the forest cycle is a shifting mosaic of the same phases. The light conditions at the forest floor and the regeneration of beech and ash were studied with regard to the mosaic-cycle. The relative light intensity (RLI) and the variation in RLI (CV-RLI) were measured in patches representing different phases of the mosaic-cycle. RLI and CV-RLI were compared between phases by analyses of variance, the RLI-model as well as the CV-RLI-model were statistically highly significant. RLI was below 2% in all phases of the forest cycle, except in gaps (degradation and innovation phases). In gaps RLI increased to about 10%, making regeneration of ash and beech possible. CV-RLI was higher under ash dominated canopies than under beech-dominated canopies. Regeneration of ash and beech did not survive at RLI below 2%. At RLI above 3%, regeneration of both ash and beech developed successfully. Successful establishment and development of ash and/or beech regeneration only occurred in gaps. Advance regeneration of both beech and ash occurred under smaller, often temporary, canopy gaps. In an examined gap, ash established first, responding with rapid height growth at increasing light levels. Beech was established at the next mast year. Under the ash plants RLI was above 3%, which made the establishment and development of a beech understorey possible. The studied gap represents the beginning of a successional shift from ash to beech within the forest cycle. The results have practical implications for nature-based silviculture, especially concerning choice of regeneration strategy and management of stand structures in order to improve the conditions for regeneration.

A decline‐model interpretation of genetic and habitat structure in oak populations and its implications for silviculture

SummaryOak decline is attributable to predisposing conditions of both biotic and abiotic origin, arid to numerous insects, pathogens, and abiotic events that act as intermediate or ultimate agents of mortality. The precise causal factors vary with circumstances, but the fundamental role of the tree genotype in the process appears to be one of predisposition. Trees are predisposed to oak decline when they are genetically incapable of surviving the stresses natural to the habitats they occupy. Quercus rubra is discussed as a ease study for which there is a considerable amount of genetic and ecological information. This species is characterized by (1) unusual sensitivity in growth to small‐scale environmental heterogeneity and (2) unusually high levels of within‐population variation in growth rate. Using growth rate as the best‐available surrogate measure of ecological fitness, it is clear that high levels of genetic variability are important, even necessary, for the ecological success of populations of this species. Differential adaptation of genotypes to microsites within even very small areas is likely. To minimize susceptibility to oak decline, forest practices should favour (1) the maintenance of high levels of genetic variation, (2) the use of local provenances in artificial regeneration, and (3) large seedling populations. A further implication is that high rates of seedling mortality in plantations may be normal and even desirable for long‐term forest health.

Species Diversity Research in Bornean Forests with Implications for Conservation Biology and Silviculture.

The majority of tree species in tropical rain forests are rare on a local scale. A major problemin ecology is to investigate how these species can persist at such low local density. A related probleminvolves the demographic factors preventing any of the more common species from achieving dominancein the forest such as happens in the temperate zone. To investigate this topic tree populations in threecontrasting mixed dipterocarp forests in Sarawak have been measured at five-year intervals to gain information on rates of tree growth, recruitment and survival. The strengths and weaknesses of our methodology are contrasted with alternative experimental designs to highlight the best approaches for investigations of biodiversity. We have compared the demographic patterns of rare, occasional and commonspecies by combining species into abundance classes. For locally common species we have been able toevaluate population stability using regression analysis of changes in population size over four successiveintervals of five years. Using such approaches, long-term demographic studies can suggest the degree oftemporal stability of rainforest communities and give practical suggestions for preserving tree species innature reserves. These studies are also being used to provide baseline data for comparison with selec-tively logged forests and to assist in effective forest management planning. Such efforts are importantbecause logging and agricultural activities are currently having a major impact on Sarawak’s forests.