Changes In Forest Composition Research Articles

Life history and habitat explain variation among insect pest populations subject to global change

AbstractPopulation dynamic responses to global change have varied widely among taxa. Most studies of population dynamics of insect pests focus on one or a few species, leaving open the question of whether changes in outbreak patterns are species‐specific or reveal predictable responses to global change, and what factors explain differences among populations. We analyzed 64 multi‐decadal time series of agricultural and forest pest insect populations in the United States. We first characterized populations according to long‐term trends, strength of population regulation, and cycle presence and length. We then asked whether these attributes could be predicted by geography, taxonomy, and life‐history traits. Roughly half of time series exhibited a long‐term trend, and agricultural pests were more likely to be declining, while forest pests were more likely to be increasing. Approximately one quarter of records exhibited periodic oscillations, and we used their statistical properties to infer whether the oscillations were environmentally forced or arose from density dependence. Insects hatching in early spring may be more strongly influenced by environmental forcing, for example, early springs or late spring frosts, than species hatching later. Our findings suggest roles of climate change, forest compositional change, and agricultural practices in driving long‐term change in pest populations.

A multi-sensor approach for improving biodiversity estimation in the Hyrcanian mountain forest, Iran

ABSTRACTModelling tree biodiversity in mountainous forests using remote-sensing data is challenging because forest composition and structure change along elevation. Topographic variations also affect vegetation’s spectral and backscattering behaviour. We demonstrate the potential of multi-source integration to tackle this challenge in a mountainous part of the Hyrcanian forest in Iran. This forest is a remnant of a deciduous broadleaved forest with heterogeneous structure affected by natural and anthropogenic factors. The multi-source approach (i.e. Landsat Enhanced Thematic Mapper Plus (ETM +), Advanced Land Observing Satellite/ Phased Array type L-band Synthetic Aperture Radar (ALOS/PALSAR), and topographic variables) allows us to propose a biodiversity estimation model using partial least square regression (PLSR) calibrated and validated with limited field data. The effective number of species was calculated based on field measurements of the biodiversity in the study area. In order to model species diversity in more homogeneous extrinsic environmental conditions, we divided data into two groups with relatively uniform slope values. In each slope group, we modelled the correlation between observed biodiversity and satellite-derived data. For that, we followed three scenarios: (A) multispectral Landsat ETM + alone, (B) ALOS/PALSAR alone, and (C) inclusion of both sensors. In each scenario, elevation and slope data were also considered as predictors. We observed that in all scenarios, coefficient of determination (R2) in gentler slopes was higher than that in areas with steeper slopes (average difference in R2: ∆R2 = 0.21). The highest correlation was achieved by inclusion of synthetic aperture radar (SAR) and ETM + (R2 = 0.87). The results clearly confirm that the multi-source remote-sensing approach can provide a practical estimate of biodiversity across the Hyrcanian forest and potentially in other deciduous broadleaved forests in complex terrain.

Shifts in tree functional composition amplify the response of forest biomass to climate.

Forests have a key role in global ecosystems, hosting much of the world's terrestrial biodiversity and acting as a net sink for atmospheric carbon. These and other ecosystem services that are provided by forests may be sensitive to climate change as well as climate variability on shorter time scales (for example, annual to decadal). Previous studies have documented responses of forest ecosystems to climate change and climate variability, including drought-induced increases in tree mortality rates. However, relationships between forest biomass, tree species composition and climate variability have not been quantified across a large region using systematically sampled data. Here we use systematic forest inventories from the 1980s and 2000s across the eastern USA to show that forest biomass responds to decadal-scale changes in water deficit, and that this biomass response is amplified by concurrent changes in community-mean drought tolerance, a functionally important aspect of tree species composition. The amplification of the direct effects of water stress on biomass occurs because water stress tends to induce a shift in tree species composition towards species that are more tolerant to drought but are slower growing. These results demonstrate concurrent changes in forest species composition and biomass carbon storage across a large, systematically sampled region, and highlight the potential for climate-induced changes in forest ecosystems across the world, resulting from both direct effects of climate on forest biomass and indirect effects mediated by shifts in species composition.

KOMPOSISI FUNCTIONAL SPECIES GROUP PADA SISTEM SILVIKULTUR TEBANG PILIH TANAM JALUR DI AREA IUPHHK-HA PT. SARPATIM, KALIMANTAN TENGAH Composition of Functional Species Group at Silviculture System of Tebang Pilih Tanam Jalur in IUPHHK-HA Area

Forest management can have an impact on changes in forest structure and composition of plant species. Functional species Group (FSG) may explain the unity of the trees species that are selected in a group in a forest management activities so that it can help in explaining the characteristic of biodiversity such as the quality of habitat and ecosystem processes. The purpose of this research is to know the composition of forest vegetation that the production system are managed with a Silviculture system of TPTJ as seen from the forest structure and composition of the type that belongs to FSG for the stands and natural regeneration in log over area (LOA) and KPPN (The Conservation of Germplasm Area) IUPHHK-HA PT. Sarmiento Parakantja Timber (Sarpatim), Central Kalimantan. Analysis of the composition of the stands type and structure used terraced path in the area of TPTJ and KPPN. The results showed that the types of climax on an entire swath of observations, generally have greater proportion than the group of pioneers, the number of the climax type is 100 while pioneer type is 59. The structure of the stands form a J reverse curve, it show that the composition of vegetation recovery on log over areas managed by using TPTJ and KPPN Silviculture system has balance characteristic of uneven age forest. The value of diversity is high (H'>3). Most of tree and stands community have different communities (ID>50%).Key words: LOA, FSG, TPTJ, stand structure, composition of species

Peat bog and alluvial deposits reveal land degradation during 16th‐ and 17th‐century colonisation of the Western Carpathians (Czech Republic)

AbstractWallachian (shepherd) colonisation of the upper parts of the Carpathians, the second largest mountain range in Europe, provides a unique opportunity to study human‐induced ecological changes and subsequent sediment mobilisation within slope and fluvial systems. The Wallachians came to the nearly pristine landscape in the Czech part of the Western Carpathians during the 16th to 17th century bringing large‐scale deforestation and grazing to the upper parts of its ridges. Despite the importance of this event, there is a lack of high‐resolution multiproxy reconstructions to help decipher the relative influence of anthropogenic and climate factors on this landscape. Here, we provide an approximately 2.1‐kyr record obtained from a peat bog where, using chronological, sedimentological, and pollen analyses, we were able to differentiate between environmental conditions before, during, and after colonisation. Prior to colonisation, climate deterioration following the onset of Little Ice Age caused changes in forest composition and erosion events (causing a ~ad 0–1500 gap in the record). Abrupt human‐induced deforestation detected in the pollen record, together with the abundant fine‐grained minerogenic content of peat deposits between ad ~1640 and ad 1870, corresponds to increased run‐off and sheet erosion on slopes, enhanced by Little Ice Age climate deterioration. The sedimentary record in alluvial deposits downstream indicates that the colonisation of the mountain slopes in this region not only had a local effect on soil degradation, but it also increased the net aggradation of overbank deposits within valley floors. After reforestation, net aggradation was replaced by river incision into alluvia.

Wildfire‐mediated vegetation change in boreal forests of Alberta, Canada

AbstractClimate‐induced vegetation change may be delayed in the absence of disturbance catalysts. However, increases in wildfire activity may accelerate these transitions in many areas, including the western boreal region of Canada. To better understand factors influencing decadal‐scale changes in upland boreal forest vegetation, we developed a hybrid modeling approach that constrains projections of climate‐driven vegetation change based on topo‐edaphic conditions coupled with weather‐ and fuel‐based simulations of future wildfires using Burn‐P3, a spatial fire simulation model. We evaluated eighteen scenarios based on all possible combinations of three fuel assumptions (static, fire‐mediated, and climate‐driven), two fire‐regime assumptions (constrained and unconstrained), and three global climate models. We simulated scenarios of fire‐mediated change in forest composition over the next century, concluding that, even under conservative assumptions about future fire regimes, wildfire activity could hasten the conversion of approximately half of Alberta's upland mixedwood and conifer forest to more climatically suited deciduous woodland and grassland by 2100. When fire‐regime parameter inputs (number of fire ignitions and duration of burning) were modified based on future fire weather projections, the simulated area burned was almost enough to facilitate a complete transition to climate‐predicted vegetation types. However, when fire‐regime parameters were held constant at their current values, the rate of increase in fire probability diminished, suggesting a negative feedback by which a short‐term increase in less‐flammable deciduous forest leads to a long‐term reduction in area burned. Our spatially explicit simulations of fire‐mediated vegetation change provide managers with scenarios that can be used to plan for a range of alternative landscape conditions.

Fifty-Five Years of Change in a Northwest Georgia Old-Growth Forest

ABSTRACT Old-growth forests provide unique insight into historical compositions of forests in the eastern United States. Plots established within a mixed forest community within Marshall Forest in Rome, Georgia, in 1960 (and remeasured in 1989) were reassessed to determine changes in forest composition. The community has experienced approximately 10% increase in basal area since the previous measurement period. However, changes in species importance have occurred. Chestnut oak (Quercus montana), mockernut hickory (Carya tomentosa), white oak (Quercus alba), and flowering dogwood (Cornus florida) have all decreased in importance, while pignut hickory (Carya glabra), winged elm (Ulmus alata), yellow poplar (Liriodendron tulipifera), and red maple (Acer rubrum) have all increased in importance. Additionally, there are no Pinus spp. saplings in the study area, indicating seedlings are not being recruited into the midstory. These changes indicate continued succession to a composition increasingly dominated by ...

Dominant effect of increasing forest biomass on evapotranspiration: interpretations of movement in Budyko space

Abstract. During the last 6 decades, forest biomass has increased in Sweden mainly due to forest management, with a possible increasing effect on evapotranspiration. However, increasing global CO2 concentrations may also trigger physiological water-saving responses in broadleaf tree species, and to a lesser degree in some needleleaf conifer species, inducing an opposite effect. Additionally, changes in other forest attributes may also affect evapotranspiration. In this study, we aimed to detect the dominating effect(s) of forest change on evapotranspiration by studying changes in the ratio of actual evapotranspiration to precipitation, known as the evaporative ratio, during the period 1961–2012. We first used the Budyko framework of water and energy availability at the basin scale to study the hydroclimatic movements in Budyko space of 65 temperate and boreal basins during this period. We found that movements in Budyko space could not be explained by climatic changes in precipitation and potential evapotranspiration in 60 % of these basins, suggesting the existence of other dominant drivers of hydroclimatic change. In both the temperate and boreal basin groups studied, a negative climatic effect on the evaporative ratio was counteracted by a positive residual effect. The positive residual effect occurred along with increasing standing forest biomass in the temperate and boreal basin groups, increasing forest cover in the temperate basin group and no apparent changes in forest species composition in any group. From the three forest attributes, standing forest biomass was the one that could explain most of the variance of the residual effect in both basin groups. These results further suggest that the water-saving response to increasing CO2 in these forests is either negligible or overridden by the opposite effect of the increasing forest biomass. Thus, we conclude that increasing standing forest biomass is the dominant driver of long-term and large-scale evapotranspiration changes in Swedish forests.

Timing of major forest compositional changes and tree expansions in the Retezat Mts during the last 16,000 years

This paper focuses on the Late Glacial (LG) and Holocene regional and local establishment times of several tree and shrub species in the Retezat Mountains (South Carpathians) using pollen, stomata and plant macrofossil records from four lakes situated at different altitudes. We used the empirical and rational pollen percentage limits to infer the local presence and population expansion/recession times. Our results show that Pinus mugo and P. sylvestris spread first at 15,100 cal yr BP in the mountain. P. mugo arrived at high altitudes (1740 m) already at 13,600 cal yr BP. The expansion of Larix decidua was weakly recorded in the pollen diagrams, but the plant macrofossil and stomata records suggested its Late Glacial expansion mainly on the northern slope and local presence since 14,900 cal yr BP at 1740 m. The species likely went extinct in the Late Holocene (around 3330 cal yr BP). The expansion of Picea abies and Ulmus commenced earlier on the southern slope, from 15,200 to 14,400 cal yr BP respectively, compared to the northern slope, where these species expanded from 14,300 to 13,850 cal yr BP. The following step was the expansion of Quercus at 13,900 cal yr BP. Following the Younger Dryas decrease of temperate deciduous taxa and P. abies, their expansion on the northern flank was in the order of P. abies (11,750), Ulmus (11,600), Quercus (11,100), Corylus (10,600), Carpinus betulus (7100), Abies alba (5100) and Fagus sylvatica (5000 cal yr BP). Timing of the Early Holocene tree expansions on the southern flank is ambiguous due to uncertainties in the Early Holocene age-depth model of Lake Lia; however, the mid-Holocene expansion of C. betulus and A. alba were well-dated in both southern slope pollen records to 7700 and 6100 cal yr BP, respectively, and we inferred several hundred years earlier expansion on the southern flank that can be explained by climatic differences. Higher solar radiation results in longer growing seasons and milder winters on the southern flank, which likely facilitated the earlier spread of these trees.For several woody taxa studied in this paper, last glacial maximum refugial populations can be inferred either locally in the mountain (P. abies, P. mugo, P. sylvestris, L. decidua) or in the region (Quercus, Ulmus, C. betulus, F. sylvatica) on the basis of their pollen presence since at least 15,700–16,000 cal yr BP and early increase during the LG.We compared the pollen inferred population expansion times of several tree taxa along a south-north transect in the Romanian Carpathians, and found that the Early Holocene high altitude expansion of A. alba (10,650–9400 cal yr BP) is exceptional in the region. We also demonstrated that the Holocene mass expansion of Quercus and C. avellana started earliest in the Retezat, and at least two centuries later in other sites in the Romanian Carpathians. We also demonstrated that certain tree species had preference for survival and/or early expansion on the northern slopes (A. alba, L. decidua, F. sylvatica), while others on the southern slopes (C. avellana, C. betulus).

Unexpected ecological advances made possible by long‐term data: A Coweeta example

In the 1970s, Forest Service and academic researchers clearcut the forest in Watershed 7 in the Coweeta Basin to observe how far the perturbation would move the ecosystem and how quickly the ecosystem would return to its predisturbance state. Our long‐term observations demonstrated that this view of resistance and resilience was too simplistic. Forest disturbance triggered a chain of ecological dynamics that are still evolving after 40 years. Short‐term pulses in dissolved inorganic nitrogen (DIN) (3 years) and streamflows (4 years) were followed by several years in which the system appeared to be returning to predisturbance conditions. Then however, changes in forest composition triggered a regime change in DIN dynamics from biological to hydrological control as well as persistent high stream DIN levels mediated by climatic conditions. These forest composition changes also led to later reductions in streamflow. These long‐term observations of streamflows, stream DIN concentrations, stream DIN exports, and stand composition have substantially advanced our understanding of forest ecosystem dynamics; and they demonstrate the value of long‐term observational data in revealing ecosystem complexities and surprises, generating new hypotheses, and motivating mechanistic research. Shorter observational records from this experiment would have produced incomplete or erroneous inference. WIREs Water 2018, 5:e1273. doi: 10.1002/wat2.1273This article is categorized under: Science of Water > Hydrological Processes Science of Water > Water Quality Water and Life > Nature of Freshwater Ecosystems

Impacts of different land management histories on forest change.

Many western North American forest types have experienced considerable changes in ecosystem structure, composition, and function as a result of both fire exclusion and timber harvesting. These two influences co-occurred over a large portion of dry forests, making it difficult to know the strength of either one on its own or the potential for an interaction between the two. In this study, we used contemporary remeasurements of a systematic historical forest inventory to investigate forest change in the Sierra Nevada. The historical data opportunistically spanned a significant land management agency boundary, which protected part of the inventory area from timber harvesting. This allowed for a robust comparison of forest change between logged and unlogged areas. In addition, we assessed the effects of recent management activities aimed at forest restoration relative to the same areas historically, and to other areas without recent management. Based on analyses of 22,007 trees (historical, 9,573; contemporary, 12,434), live basal area and tree density significantly increased from 1911 to the early 2000s in both logged and unlogged areas. Both shrub cover and the proportion of live basal area occupied by pine species declined from 1911 to the early 2000s in both areas, but statistical significance was inconsistent. The most notable difference between logged and unlogged areas was in the density of large trees, which declined significantly in logged areas, but was unchanged in unlogged areas. Recent management activities had a varied impact on the forest structure and composition variables analyzed. In general, areas with no recent management activities experienced the greatest change from 1911 to the early 2000s. If approximating historical forest conditions is a land management goal the documented changes in forest structure and composition from 1911 to the early 2000s indicate that active restoration, including fire use and mechanical thinning, is needed in many areas.

Climate Impacts on Tree Growth in the Sierra Nevada

Rising temperatures and aridity may negatively impact tree growth, and therefore ecosystem services like carbon sequestration. In the Sierra Nevada in California, annual variation in precipitation is high, and forests have already been impacted by several recent severe droughts. In this study, we used growth census data from long-term plots in the Sierra Nevada to calibrate an annual climate-dependent growth model. Our results highlight a high diversity of responses to climate, although the effects of climate are small compared to those of tree size and competition. Some species grow less during dry years (Pinus contorta and Calocedrus decurrens) but, surprisingly, other species exhibit higher growth during dry years (Pinus monticola, Abies magnifica, Pinus jeffreyi, Quercus kelloggii). These results emphasize the need for growth models to take into account species variability, as well as spatial heterogeneity, when studying mixed conifer forests. So far, temperatures have increased in California, and tree growth of some species may drastically decrease in the Sierra Nevada if warming continues, leading to changes in forest structure and composition as well as potential changes in wood production and carbon sequestration.

Likelihood of changes in forest species suitability, distribution, and diversity under future climate: The case of Southern Europe.

Forest conservation strategies and plans can be unsuccessful if the new habitat conditions determined by climate change are not considered. Our work aims at investigating the likelihood of future suitability, distribution and diversity for some common European forest species under the projected changes in climate, focusing on Southern Europe. We combine an Ensemble Platform for Species Distribution Models (SDMs) to five Global Circulation Models (GCMs) driven by two Representative Concentration Pathways (RCPs), to produce maps of future climate‐driven habitat suitability for ten categories of forest species and two time horizons. For each forest category and time horizon, ten maps of future distribution (5 GCMs by 2 RCPs) are thus combined in a single suitability map supplied with information about the “likelihood” adopting the IPCC terminology based on consensus among projections. Then, the statistical significance of spatially aggregated changes in forest composition at local and regional level is analyzed. Finally, we discuss the importance, among SDMs, that environmental predictors seem to have in influencing forest distribution. Future impacts of climate change appear to be diversified across forest categories. A strong change in forest regional distribution and local diversity is projected to take place, as some forest categories will find more suitable conditions in previously unsuitable locations, while for other categories the same new conditions will become less suited. A decrease in species diversity is projected in most of the area, with Alpine region showing the potentiality to become a refuge for species migration.

The Uncertain Role of Biogenic VOC for Boundary-Layer Ozone Concentration: Example Investigation of Emissions from Two Forest Types with a Box Model

High levels of air pollution including ground level ozone significantly reduce humans’ life expectancy and cause forest damage and decreased tree growth. The French Vosges and the German Black Forest are regions well-known for having the highest tropospheric ozone concentrations at remote forested sites in Central Europe. This box model study investigates the sensitivity of atmospheric chemistry calculations of derived ozone on differently resolved forest tree composition and volatile organic compound emissions. Representative conditions were chosen for the Upper Rhine area including the Alsatian Vosges/France and the Black Forest/Germany during summer. This study aims to answer the following question: What level of input detail for Alsace and Black Forest tree mixtures is required to accurately simulate ozone formation? While the French forest in Alsace—e.g., in the Vosges—emits isoprene to a substantially higher extent than the forest at the German site, total monoterpene emissions at the two sites are rather similar. However, the individual monoterpene structures, and therefore their reactivity, differs. This causes a higher ozone production rate for Vosges forest mixture conditions than for Black Forest tree mixtures at identical NOx levels, with the difference increasing with temperature. The difference in ozone formation is analyzed in detail and the short-comings of reduced descriptions are discussed. The outcome serves as a to-do-list to allow accurate future ozone predictions influenced by the climate adaptation of forests and the change in forest species composition.

Rapid 21st century climate change projected to shift composition and growth of Canada’s Acadian Forest Region

Abstract The impact of climate change on forests is expected to vary globally and regionally. Canada’s Acadian Forest Region lies in the transition between the North American boreal and temperate forest biomes and may be particularly sensitive to changes in climate because many of its component species are currently at their southern or northern climatic range limits. Although some species may be lost, others may exhibit major productivity boosts—affecting the goods and services we derive from them. In this study, we use a well-established forest ecosystem simulation model, PICUS, to provide the first exploration of the impact of climate change on the composition and growth of the Acadian Forest Region for the period 2011 to 2100 under two radiative forcing scenarios, RCP 2.6 and RCP 8.5. In the short term (2011–2040), little to no changes in forest composition or growth were projected under either forcing scenario compared with current forest conditions (simulated for 1981–2010 baseline climate); however, by mid-century, PICUS projected increasing departures from the baseline simulations in both composition and growth, with the greatest changes occurring under RCP 8.5 during the late 21st century (2071–2100). Our study indicates that under rapid 21st century warming, Canada’s Acadian Forest Region will begin to lose its boreal character (i.e., “deborealize”) as key tree species fail to regenerate and survive. Furthermore, increased growth and establishment by warm-adapted, temperate tree species may be unable to keep pace with the rapid loss of boreal species. This potential “lag effect” may lead to a temporary decrease in forest growth and wood supply during the late 21st century.

You'd better walk alone: Changes in forest composition affect pollination efficiency and pre-dispersal cone damage in Iberian Juniperus thurifera forests.

Changes in land-use patterns are a major driver of global environmental change. Cessation of traditional land-use practices has led to forest expansion and shifts in forest composition. Consequently, former monospecific forests maintained by traditional management are progressing towards mixed forests. However, knowledge is scarce on how the presence of other tree species will affect reproduction of formerly dominant species. We explored this question in the wind-pollinated tree Juniperus thurifera. We hypothesised that the presence of heterospecific trees would have a negative effect on cone production and on the proportion of cones attacked by specialised predators. We assessed the relative importance of forest composition on cone production, seed development and pre-dispersal cone damage on nine paired pure and mixed J.thurifera forests in three regions across the Iberian Peninsula. The effects of forest composition on crop size, cone and seed characteristics, as well as damage by pre-dispersal arthropods were tested using mixed models. Cone production was lower and seed abortion higher in mixed forests, suggesting higher pollination failure. In contrast, cone damage by arthropods was higher in pure forests, supporting the hypothesis that presence of non-host plants reduces damage rates. However, the response of each arthropod to forest composition was species-specific and the relative rates of cone damage varied depending on individual tree crops. Larger crop sizes in pure forests compensated for the higher cone damage rates, leading to a higher net production of sound seeds compared to mixed forests. This study indicates that ongoing changes in forest composition after land abandonment may impact tree reproduction.

Tracking senescence‐induced patterns in leaf litter leachate using parallel factor analysis (PARAFAC) modeling and self‐organizing maps

AbstractIn autumn, the dissolved organic matter (DOM) contribution of leaf litter leachate to streams in forested watersheds changes as trees undergo resorption, senescence, and leaf abscission. Despite its biogeochemical importance, little work has investigated how leaf litter leachate DOM changes throughout autumn and how any changes might differ interspecifically and intraspecifically. Since climate change is expected to cause vegetation migration, it is necessary to learn how changes in forest composition could affect DOM inputs via leaf litter leachate. We examined changes in leaf litter leachate fluorescent DOM (FDOM) from American beech (Fagus grandifolia Ehrh.) leaves in Maryland, Rhode Island, Vermont, and North Carolina and from yellow poplar (Liriodendron tulipifera L.) leaves from Maryland. FDOM in leachate samples was characterized by excitation‐emission matrices (EEMs). A six‐component parallel factor analysis (PARAFAC) model was created to identify components that accounted for the majority of the variation in the data set. Self‐organizing maps (SOM) compared the PARAFAC component proportions of leachate samples. Phenophase and species exerted much stronger influence on the determination of a sample's SOM placement than geographic origin. As expected, FDOM from all trees transitioned from more protein‐like components to more humic‐like components with senescence. Percent greenness of sampled leaves and the proportion of tyrosine‐like component 1 were found to be significantly different between the two genetic beech clusters, suggesting differences in photosynthesis and resorption. Our results highlight the need to account for interspecific and intraspecific variations in leaf litter leachate FDOM throughout autumn when examining the influence of allochthonous inputs to streams.

Temporal changes of forest species composition studied by compositional data approach

Abstract: Many ecological data are compositional and different quantitative techniques have been used to analyze such data, albeit some of them being methodologically wrong. The aim of this contribution is to apply the compositional data approach to forestry data and demonstrate the strengths of this method for percentage or relative data with infrequent zero values. Basal areas of three dominant tree species (Abies alba, Picea abies, Fagus sylvatica) in 119 forest compartments in some of the Omphalodo-Fagetum forests in Slovenia in 1954 and 2004 were used to investigate the dynamics of forest species composition over a 50-year period. For the investigated period some additional data about geomorphology and harvesting rates within the compartments were used as explanatory variables of compositional change. The species composition of each forest compartment was subjected to several methods within a compositional analysis framework: descriptive, ternary diagram-based graphical presentations, significance of compositional differences between management classes, significance of perturbation differences (the indicator of forest compositional change) and relation of the compositional change with the explanatory variables by means of compositional linear model. Results indicated that the silver fir was the dominant species in both years, but a clear reduction in silver fir proportion was observed after 50 years. The perturbation differences indicated comparatively large relative increase in the proportion of Norway spruce between 1954 and 2004. Subsequently, the perturbation differences were subjected to isometric log-transformation (ilr) and two derived ilr coordinates were further used as dependent variables in the multivariate linear model. The initial stand structure correlated well with the perturbation differences. These were also significantly correlations with salvage cutting, a consequence of silver fir decline in the 1954-2004 period. This study demonstrated that the compositional data approach can be successfully used to study forest dynamics yielding some insights into data which are not possible or even not valid using some alternative methods.

14C mean residence time and its relationship with thermal stability and molecular composition of soil organic matter: A case study of deciduous and coniferous forest types

Soil organic matter (SOM) plays a critical role in the global terrestrial carbon cycle, and a better understanding of soil processes involved in SOM stability is essential to determine how projected climate-driven changes in soil processes will influence carbon dynamics. We used 14C signature, analytical thermal analysis, and ultrahigh resolution mass spectrometry to determine the influence of deciduous and coniferous forest vegetation type and soil depth on the stability of soil C. The 14C mean residence time (MRT) of the illuvial B horizon soils averaged 1350years for the deciduous soils and 795years for the coniferous soils. The difference of MRT between mineral soils by forest type may be due to the saturation of extractable Fe and Al minerals binding sites by SOM in the coniferous soils, allowing greater transport of modern SOM from the O horizon down the soil profile, as compared with the non-saturated minerals in the deciduous soil profile. The molecular mass distribution of the deciduous water-extractable aromatic SOM fraction was shifted to a lower mass range in the lower portion of B horizon soil compared with the upper portion, indicating preferential sorption of the higher mass aromatic fraction. The shift in the mass distribution of the aromatic fraction in the coniferous soil was much less than in the deciduous soil, which supports the view that the extractable metal minerals had reached saturation. We conclude that greater transport of modern O horizon SOM to the lower mineral B horizons in the coniferous soil profile resulted in its radiocarbon enrichment and shorter estimated MRT. Our findings highlight the importance of forest vegetation type, soil depth and transport mechanisms on SOM stability, and suggest important ecological implications for changes in forest composition on the terrestrial C cycle.

Ecology of forest insect invasions

Forests in virtually all regions of the world are being affected by invasions of non-native insects. We conducted an in-depth review of the traits of successful invasive forest insects and the ecological processes involved in insect invasions across the universal invasion phases (transport and arrival, establishment, spread and impacts). Most forest insect invasions are accidental consequences of international trade. The dominant invasion ‘pathways’ are live plant imports, shipment of solid wood packaging material, “hitchhiking” on inanimate objects, and intentional introductions of biological control agents. Invading insects exhibit a variety of life histories and include herbivores, detritivores, predators and parasitoids. Herbivores are considered the most damaging and include wood-borers, sap-feeders, foliage-feeders and seed eaters. Most non-native herbivorous forest insects apparently cause little noticeable damage but some species have profoundly altered the composition and ecological functioning of forests. In some cases, non-native herbivorous insects have virtually eliminated their hosts, resulting in major changes in forest composition and ecosystem processes. Invasive predators (e.g., wasps and ants) can have major effects on forest communities. Some parasitoids have caused the decline of native hosts. Key ecological factors during the successive invasion phases are illustrated. Escape from natural enemies explains some of the extreme impacts of forest herbivores but in other cases, severe impacts result from a lack of host defenses due to a lack of evolutionary exposure. Many aspects of forest insect invasions remain poorly understood including indirect impacts via apparent competition and facilitation of other invaders, which are often cryptic and not well studied.