Abiotic Site Factors Research Articles

Micro-site conditions affect Fennoscandian forest growth

The long tradition of dendroclimatological studies in Fennoscandia is fostered by the exceptional longevity and temperature sensitivity of tree growth, as well as the existence of well-preserved subfossil wood in shallow lakes and extent peat bogs. Although some of the world’s longest ring width and density-based climate reconstructions have been developed in northern Fennoscandia, it is still unclear if differences in micro-site ecology matter, and if so, whether they have been considered sufficiently in previous studies. We developed a Fennoscandia-wide network of 44 Scots pine ring width chronologies from 22 locations between 59°–70 °N and 16°–31 °E, to assess the effects of moist lakeshores and dry inland micro-sites on tree growth. Our network reveals a strong dependency of pine growth on July temperature, which is also reflected in latitude. Differences in forest productivity between moist and dry micro-sites are likely caused by associated effects on soil temperature. While trees at moist micro-sites at western locations exhibit higher growth rates, this pattern is reversed in the continental eastern part of the network, where increased ring widths are found at drier sites. In addition to the latitudinal increase in growth sensitivity to July temperature, pines at moist sites exhibit an increased dependency of summer warmth. The highest temperature sensitivity and growth coherency, and thus greatest suitability for summer temperature reconstructions, is found in those regions where July mean temperatures range between 11.5 and 13.5 °C, and May precipitation totals do not exceed 100 mm. Our study not only provides guidance for the selection of sampling sites for tree ring-based climate reconstructions, but also reveals the effect of micro-site ecology on Fennoscandian forest growth. The manifestation of micro-site effects varies substantially over the Fennoscandian boreal forest and is predominately triggered by the geographical setting of the stand as expressed by differing abiotic site factors.

Which landscape and abiotic site factors influence vegetation succession across seres at a country scale?

AbstractQuestions(1) How much do abiotic site factors and land‐cover categories influence the course of succession across successional series at a country scale? (2) Are there any differences in the abiotic site factors and land‐cover categories which are responsible for driving primary and secondary seres? (3) Which of the factors influence species richness and participation of target species?LocationVarious disturbed sites in the Czech Republic, Central Europe.MethodsThe Database of Successional Series (DaSS) was compiled of 21 different types of succession, comprising 2,846 phytosociological relevés. The stages ranged from 1 to >150 years in age. Abiotic site factors included macroclimate characteristics and substrate; landscape factors comprised various land‐cover categories in a radius of 1 km around each sampled site. Principal Coordinate Analysis of Neighbour Matrices (PCNM) was performed to quantify the effect of abiotic site factors and landscape factors on seral vegetation, also regarding the primary or secondary status of succession. The relationships between number of species, number and proportion of target species and abiotic site and landscape factors were further assessed using generalised linear model analysis.ResultsAll considered abiotic and landscape factors were found to have significant effects on the course of succession. The effects of abiotic site factors appeared to be more important than those of the surrounding landscape structure. Species richness was higher on basic substrates. The proportion of target species increased with increasing woodland area in the surrounding and with a wetter and colder climate, and decreased with urbanisation rate of the landscape.ConclusionNot only local but landscape factors, such as climate and land cover, should be considered in any study of succession, as they substantially influence the general successional pattern. Quantification of the role of these environmental factors may help to decide where a spontaneous restoration is a viable option for the restoration of disturbed sites. The primary or secondary status of succession is less relevant than has usually been supposed.

Site sensitive maximum stand density index models for mixed conifer stands across the Inland Northwest, USA

Density management is a key silvicultural tool for developing management prescriptions that maintain and enhance forest health and productivity, particularly in droughty, fire-prone ecosystems of the Inland Northwest, USA. Within this context, understanding the role of species mixing, climate, topography, and soil properties on maximum stand density is critical for predicting forest stand response to management given a suite of site characteristics and species composition. We assembled a dataset from public and private land management organizations that allowed us to test the role of ecological variables on modifying maximum stand density frontiers. Maximum stand density frontier models were built for selected conifer species using stochastic frontier regression. The influence of species mixing was assessed by including as a covariate basal area proportion of the three conifer species of interest in this study: Pinus ponderosa var. ponderosa, Pseudotsuga menziesii var. glauca, and Abies grandis var. idahoensis. A single, parsimonious model was found to fit each species, with variable coefficients reflecting species adaptation to varying abiotic site factors across the region. Site factors that increased maximum density included cool, moist conditions, soils containing volcanic ash over coarse-textured bedrock, and high tree-species diversity. These observations correspond to regional silvicultural guidance, thereby providing both a site-sensitive, quantitative maximum density measure for mixed species stands, and a tool for evaluating the effect of climate scenarios on future stand carrying capacity.

Predicting site productivity of the timber tree Pterocarpus angolensis

Pterocarpus angolensis is an important timber tree of the miombo woodlands of sub-Saharan Africa. The species only grows in natural mixed forests and little is known about is productivity potential. This study aimed at investigating productivity of P. angolensis on a local scale in Namibia and Angola and on a regional scale in southern Africa. The most commonly accepted productivity indicator is stem diameter increment and this was used to study productivity at a regional scale. Indicators of productivity used at the local scale were basal area, proportional basal area and site form, which were derived from 217 forest inventory plots in Namibia and Angola. The productivity measures were modelled with abiotic site factors; biotic factors were added for the local scale. Results indicated that the most consistent site factors at local and regional scale were not related to climate but to forest cover, with the species having a competitive advantage in more open forests. Mean annual diameter increment in the open forests of Namibia was 0.51 cm after 50 years. Boosted regression tree models at a local scale showed that species presence can be modelled more successfully than species basal area, proportional basal area (correlation of 0.72 vs 0.56 and 0.45, respectively) and site form. The sites with the highest productivity of P. angolensis at the local scale had a temperature seasonality below 34.5 °C, a slope of less than 1.5°, tree cover less than 20% and stand basal area higher than 9 m2 ha−1. The results can assist in establishing a site-dependent growth model for the species and direct forest and fire management towards the most productive areas.

Modelling impacts of acid deposition and groundwater level on habitat quality and plant species diversity

We quantified the effects of the site factors pH and nitrate (NO3) concentration in soil solution and groundwater level on the vegetation of terrestrial ecosystems for the Netherlands in response to changes in atmospheric nitrogen (N) and sulphur (S) deposition and groundwater level over the period 1990–2030. The assessment was made with the SMART2 model, a simple one-layer model including geochemical buffer processes, element cycling by litterfall, mineralisation and uptake, nitrogen transformation processes and element input through deposition, weathering and upward seepage. To assess the effects of changes in abiotic site factors on the vegetation, we developed a simple plant diversity indicator for grassland, heathland and forest, based on the occurrence of target plant species and competing species. Species occurrence was calculated from the preferred ranges of each species for the NO3 concentration and pH in soil solution and mean spring groundwater level. Changes in the plant diversity indicator were assessed from effects of changes in the occurrence of target and competing plant species in response to changes in mean spring groundwater level and in pH and NO3 concentration, as calculated with SMART2. Calculations were made for combinations of five vegetation structure types (three forest types, semi-natural grassland and heathland) and seven soil types (three sandy soils, two clay soils, peat and loess soils) using a 250 × 250 m grid. We used data for atmospheric deposition and groundwater level in the past to assess trends between 1990 and 2010 and evaluated two future scenarios for the period 2010–2030: a Business as Usual and an Improved Environment scenario. Comparison of model predictions on pH and NO3 with measured soil solution concentrations for forest showed a reasonable to good agreement for pH but rather poor for NO3. The largest impacts were found for the combination of the two Improved Environment scenarios. Reductions in N and S deposition and an increase in groundwater level between 1990 and 2030 hardly caused changes in soil pH and only relatively small reductions in NO3 concentration (11–13%). Nevertheless, those changes caused a significant increase in plant diversity indicator.

Environmental factors determining spontaneous recovery of industrially mined peat bogs: A multi-site analysis

Peat is still mined in many parts of the World. What to do with the peatlands after the peat mining has stopped is a question for restoration ecologists and to leave a disturbed site to spontaneous regeneration could be one option. The main question of our study was whether it is an effective means of restoration and under which circumstances. Spontaneous succession was studied in 11 industrially mined peatlands, which encompassed successional stages of different age. Vegetation samples (109), 5m×5m in size, were recorded in the stages using visual estimation of percentage cover of all present vascular plants. The age, abiotic environmental characteristics (position of water table, water pH, and substratum chemistry), as well as biotic characteristics (proportion of land cover categories up to 100m, 300m and 1km from each sample, and the distance to the nearest undisturbed peatland vegetation) were assessed for each sampled successional stage. Other characteristics were related to the whole localities (altitude, average annual temperature, and precipitation). The data were analyzed by multivariate statistics. The environmental variables, except K-content and land cover up to 100m, exhibited some significant effects on the vegetation patterns. External, i.e., landscape factors, had together a larger effect on the course of succession than abiotic site factors. The most important particular factors included ground water level, substrate pH, and presence of undisturbed peatland vegetation in the surroundings. Also important was geographic location predominantly reflecting site altitude. Spontaneous recovery of the peatland vegetation was more successful on those sites where the water table was intentionally increased. The increase of the water table after peat extraction and preservation of the original undisturbed peatland vegetation in the area neighbouring a mined site during the process of peat extraction are recommended to promote spontaneous recovery of the peatlands.

Relating microbial community structure to functioning in forest soil organic carbon transformation and turnover.

Forest soils store vast amounts of terrestrial carbon, but we are still limited in mechanistic understanding on how soil organic carbon (SOC) stabilization or turnover is controlled by biotic and abiotic factors in forest ecosystems. We used phospholipid fatty acids (PLFAs) as biomarker to study soil microbial community structure and measured activities of five extracellular enzymes involved in the degradation of cellulose (i.e., β-1,4-glucosidase and cellobiohydrolase), chitin (i.e., β-1,4-N-acetylglucosaminidase), and lignin (i.e., phenol oxidase and peroxidase) as indicators of soil microbial functioning in carbon transformation or turnover across varying biotic and abiotic conditions in a typical temperate forest ecosystem in central China. Redundancy analysis (RDA) was performed to determine the interrelationship between individual PFLAs and biotic and abiotic site factors as well as the linkage between soil microbial structure and function. Path analysis was further conducted to examine the controls of site factors on soil microbial community structure and the regulatory pathway of changes in SOC relating to microbial community structure and function. We found that soil microbial community structure is strongly influenced by water, temperature, SOC, fine root mass, clay content, and C/N ratio in soils and that the relative abundance of Gram-negative bacteria, saprophytic fungi, and actinomycetes explained most of the variations in the specific activities of soil enzymes involved in SOC transformation or turnover. The abundance of soil bacterial communities is strongly linked with the extracellular enzymes involved in carbon transformation, whereas the abundance of saprophytic fungi is associated with activities of extracellular enzymes driving carbon oxidation. Findings in this study demonstrate the complex interactions and linkage among plant traits, microenvironment, and soil physiochemical properties in affecting SOC via microbial regulations.

OldPinus ponderosagrowth responses to restoration treatments, climate and drought in a southwesternUSlandscape

AbstractQuestionsDo landscape‐scale thin and burn restoration treatments have a long‐term, landscape‐scale impact on oldPinus ponderosagrowth? Is there a relationship between oldP. ponderosagrowth and climatic factors, in particular, drought, before and after restoration treatments?LocationNorthwesternArizona,USA.MethodsWe looked at oldP. ponderosagrowth across the landscape in both an area ‘treated’ by thin and burn restoration treatments, and a neighbouring untreated area. We re‐visited each oldP. ponderosalocated on permanent 0.1‐ha plots installed across the landscape prior to treatment implementation and recorded tree status, diameter, aspect, slope and competition from neighbouring trees. Growth was analysed from shallow increment cores taken from each tree at breast height (1.37 m). Comparisons of growth between the treated and untreated areas were carried out using regional proxy and instrumental Palmer drought severity index values and instrument precipitation data.ResultsWe found significant differences in precipitation and temperature between the treated and untreated areas, indicating a drier, less advantageous climate in the untreated area. Old trees in the treated area responded less negatively in diameter growth to treatments; both treatment and abiotic site factors were important in predicting post‐treatment growth. All old trees grew slowly during drought years; however, old trees in the treated area grew better after three recent drought years than old trees in the untreated area.ConclusionsOldP. ponderosadiameter growth increased following restoration, though not immediately. Old trees in the treated area also grew better in the years after drought than old trees in the untreated area. Restoration, or similar treatments removing small, neighbouring trees may be critical in maintaining oldP. ponderosain the landscape, particularly under future climate change and increasing drought frequency in the westernUSA.

The South Hesse Oak Project (SHOP): Species- and site-specific efficiency of the photosynthetic apparatus of Mediterranean and Central European Oaks

In three experimental sites in Southern Hesse, differing in management procedures, one- to three-year-old saplings of Quercus robur, Q.pubescens, and Q.ilex were planted to study their performance under Central European climate conditions. Toward the end of the growth period (mid–late September 2011), during a very dry period, we measured JIP transients of photosystem II chlorophyll fluorescence induction curves to evaluate the effects of abiotic site factors on the photosynthetic apparatus by comparing them to data from well-watered saplings measured before the onset of senescence processes. In all three sites, Q. robur saplings in September showed the strongest deviation from the measurements in August, followed by Q. pubescens. Q. ilex, in general, was nearly unaffected by September climate conditions or performed better than plants measured in August. Differences in the behavior between species and sites could be explained by the species’ different drought susceptibility and by differential induction of early leaf senescence (in Q. robur and Q. pubescens). We conclude that measurement of the JIP transient is a feasible method in forestry to compare adverse microclimatic site effects and genetically fixed reactions of the photosynthetic apparatus in the field.

Abiotic and biotic factors used to assess decline risk in red pine (Pinus resinosa Ait.) plantations

This study was conducted to assess causes of unprecedented rates of mortality in maturing, commercial-sized red pine(Pinus resinosa Ait.) plantations in southern Ontario, Canada. Concentrated and diffuse mortality as well as windthrowof living trees were observed in many plantations, while others seemed disease-free. Nine sites exhibiting recent mortality(diseased) plus three not exhibiting disease (healthy) were selected. In sample plots at each site, abiotic site factors, hostcharacteristics, and insect pests and fungal pathogens were assessed. Tree mortality was attributed to Armillaria root disease,annosus root rot, black pineleaf scale, drought, and iron deficiency. The single abiotic factor that distinguishedhealthy sites from diseased sites was C soil horizon pH, which averaged 8.35 on diseased sites compared to 6.55 on healthysites. Rooting was also deeper on healthy sites than on diseased sites. We suggest that an alkaline C horizon may result inshallower rooting and greater susceptibility to drought stress, rendering trees less resistant to root disease pathogens andinsect pests. The pH of the C horizon and the depth of the A and B horizons may be useful as indicators of the likelihoodof red pine mortality and to guide the choice of management objectives for plantations. Key words: red pine mortality, root disease, calcareous soil, rooting depth, Armillaria

Determinants of soil organic matter chemistry in maritime temperate forest ecosystems

While the influence of climate, vegetation, management and abiotic site factors on total carbon budgets and turn-over is intensively assessed, the influences of these ecosystem properties on the chemical complexity of soil organic matter (SOM) remains poorly understood. This study addresses the chemical composition of NaOH-extracted SOM from maritime temperate forest sites in Flanders (Belgium) by pyrolysis-GC/MS. The studied forests were chosen based on dominant tree species ( Pinus sylvestris, Fagus sylvatica, Quercus robur and Populus spp.), soil texture and soil-moisture conditions. Differences in extractable-SOM pyrolysis products were correlated to site variables including dominant tree species, management of the woody biomass, site history, soil properties, total carbon stocks and indicators for microbial activity. Despite of a typical high intercorrelation between these site variables, the influence of the dominant tree species is prominent. The extractable-SOM composition is strongly correlated to litter quality and available nutrients. In nutrient-poor forests with low litter quality, the decomposition of relatively recalcitrant compounds (i.e. short and mid-chain alkanes/alkenes and aromatic compounds) appears hampered, causing a relative accumulation of these compounds in the soil. However, if substrate quality is favorable, no accumulations of recalcitrant compounds were observed, not even under high soil-moisture conditions. Former heathland vegetation still had a profound influence on extractable-SOM chemistry of young pine forests after a minimum of 60 years.

Nutritional imbalance caused by nitrogen excess is correlated with the occurrence of watermark disease in white willow

Willows in the Flemish region are threatened by the watermark disease, a wood disease caused by the bacterium Brenneria salicis (Hauben et al. Syst Appl Microbiol 21:384–397, 1998). Affected trees are observed to grow at specific sites which seem more sensitive to periodical watermark symptom development than other sites. In this study we aim at revealing abiotic site factors that could play a role in triggering the watermark disease. During three consecutive years we analyzed stands of young isogenic willows (Salix alba L. cv. Lichtenvoorde), which were planted on four different sites in an agricultural environment. These test sites were chosen, based on the occurrence/absence of watermark disease in the old willows that grow on these sites. Two sites had old willow pollards with clear watermark symptoms, and on the two other sites the old willows were unaffected. Differences in abiotic characteristics between the sites were analysed and their effects on the nutrient status in willow were measured in the isogenic willows that were newly planted. Brenneria salicis-specific multiplex PCR revealed the presence of this pathogenic bacterium in both the old and the freshly planted young willows. At each site, the physical and chemical characteristics of soil and groundwater were investigated; the young tree growth was monitored and nutritional status of the willow plantings was assessed by foliar analysis. Physical soil properties including soil type and profile water availability, and chemical soil analysis were unable to explain differences between healthy and affected sites. Diseased sites, however, had significantly higher N concentrations and traces of herbicides in the groundwater. In young trees, foliar levels of N and S were always greater at the affected sites, while P contents were lower. Dry mass based N concentration in the leaves of the newly planted trees increased systematically over the years, but more at affected than at healthy sites. Also, chlorophyll content was significantly greater at the affected sites. Growth rate of the young isogenic trees was twice as fast at the diseased sites. The presented data suggest that application of fertilisers in agriculture causes an imbalance in the nutritional status of Salix alba L. Excess nitrogen makes this species fast-growing, reflected by an average foliar N:P ratio >10, and more susceptible for watermark disease, indicated by an average foliar N:Ca ratio exceeding 1.5.

Biotic and abiotic influences on wind disturbance in forests of NW Pennsylvania, USA

Forests in northwestern Pennsylvania experienced a severe windstorm in July 2003. The storm damaged some forests and left others in its path intact. This varied impact raised the question of whether biotic and abiotic stand characteristics influenced storm damage. To answer this question we investigated data on windthrow severity, vegetation characteristics, and physiographic variables provided by the three largest landowners affected by the storm. These local forest managers provided stand level data on 258,000 ha, about half of the storm swath, of which about 5000 ha (2%) experienced moderate or severe blowdown. The study includes over 1002 disturbance patches, 60% of which were under 3 ha. We used classification tree analysis, a non-parametric method of statistical inquiry, to identify the variables that were most useful in predicting storm damage. Our model used biotic and abiotic site factors to correctly predict affected and unaffected stands 89% of the time (kappa value 0.63). The most predictive biotic variables were stand structure and stand age. Predictive abiotic variables included mean elevation, the range of elevations across the stand, and topographic position relative to neighboring stands. Results show that windthrow was more likely in older stands, stands at the highest elevations, and in flatter stands at lower elevations. Except for red maple stands on wet sites, which were disproportionately affected, forest type was not a useful predictor of the storm's impact.

Climate and pH as determinants of vegetation succession in Central European man‐made habitats

AbstractQuestions: (1) What are the most important abiotic environmental variables influencing succession in central European man‐made habitats? (2) How do these variables interact with one another and with variation in community properties?Location: Central, western and southern parts of the Czech Republic. Habitats included old fields, urban sites, spoil heaps after coal mining, sites at water reservoirs, extracted sand pit and peatland and reclaimed sites in areas deforested by air pollution.Methods: We investigated vegetation patterns on 15 succes‐sional seres, sampled by the same methods. Time of succession over which the data were available ranged from 12 to 76 years. The cover of vascular plant species (in %) was estimated in 5 m × 5 m plots. The relationships between vegetation characteristics (species composition, total cover, cover of woody species, species number and rate of dominant species turnover) and 13 abiotic site factors, including climatic and soil variables, were tested using CCA ordination and regression models.Results: Substratum pH, the only substratum characteristic, and climate were the environmental variables significantly affecting the vegetation patterns in the course of succession. The rate of succession, measured as the turnover of dominant species, was significantly more rapid in lowland than in mountain climates. On alkaline soils, species numbers in succession increased towards warmer climates. However, acid soils prevented any increase in species numbers, regardless of the climate. Surprisingly, forms of nitrogen and contents of C, P and cations did not exhibit any significant effect on the vegetation characteristics studied.Conclusions: Our approach, to compare a number of seres, can contribute not only to our understanding of succession, but also to help restoration projects to predict vegetation change because the crucial environmental variables, as identified by this study, are easy to measure.

Climate and pH as determinants of vegetation succession in Central European man-made habitats

Questions: (1) What are the most important abiotic environmental variables influencing succession in central European man-made habitats? (2) How do these variables interact with one another and with variation in community properties? Location: Central, western and southern parts of the Czech Republic. Habitats included old fields, urban sites, spoil heaps after coal mining, sites at water reservoirs, extracted sand pit and peatland and reclaimed sites in areas deforested by air pollution. Methods: We investigated vegetation patterns on 15 successional seres, sampled by the same methods. Time of succession over which the data were available ranged from 12 to 76 years. The cover of vascular plant species (in %) was estimated in 5 m × 5 m plots. The relationships between vegetation characteristics (species composition, total cover, cover of woody species, species number and rate of dominant species turnover) and 13 abiotic site factors, including climatic and soil variables, were tested using CCA ordination and regression models. Results: Substratum pH, the only substratum characteristic, and climate were the environmental variables significantly affecting the vegetation patterns in the course of succession. The rate of succession, measured as the turnover of dominant species, was significantly more rapid in lowland than in mountain climates. On alkaline soils, species numbers in succession increased towards warmer climates. However, acid soils prevented any increase in species numbers, regardless of the climate. Surprisingly, forms of nitrogen and contents of C, P and cations did not exhibit any significant effect on the vegetation characteristics studied. Conclusions: Our approach, to compare a number of seres, can contribute not only to our understanding of succession, but also to help restoration projects to predict vegetation change because the crucial environmental variables, as identified by this study, are easy to measure.

Comparison of linear and nonlinear overstory-understory models for ponderosa pine

Linear and nonlinear regression models of total understory biomass in relation to overstory canopy cover and several abiotic site factors were tested using data from 31 ponderosa pine ( Pinus ponderosa Dougl.) sites along the Front Range of Colorado and Wyoming. At the forest level, site factors were insignificant in explaining understory biomass. Canopy cover, however, was a significant predictor. The relationship between canopy cover ( X) and grass production ( Y) was best expressed by the nonlinear model, Y = A B X . Total understory production could be predicted with equal precision using simple linear and nonlinear regressions with canopy cover. In this case, the simple linear model captured the interaction of the nonlinear grass response and a suspected quadratic relationship between shrub production and overstory cover as well as any other model.