Long-term Research Plots Research Articles

The Influence of Wild Boars on the Growth of Forest Trees and Stands: A Case Study of a Wild Boar Game Preserve/ A vaddisznó hatása a fák és a faállomány növekedésére - egy vaddisznóskert esettanulmánya

AbstractThis research investigated methods for determining and quantifying the impact of wild boars on the increment and growth of forest trees and stands. The influence of wild boars on stand variables was observed in a wild game preserve established in central Slovakia in 2000 practicing intensive wild boar management. Long-term measurements obtained from two long-term research plots of sessile oak trees established in 1969 were used to monitor stand growth. Increments of trees were observed on tree ring cores coming from trees surrounded by differently damaged soil surfaces. Wild boars rooting the soil surface proved to have neither a positive nor negative influence on the mean diameter and height of the forest stands. Analysis of radial increments in 9 trees growing on sites with more intense, deeper, and permanent rooting in the soil profile located near a larger mud bath was also carried out. A more distinctive increment depression was found on one oak near the mud bath and on one beech where deeper soil surface rooting occurred.

Tree species diversity change in natural regeneration of a beech forest under different management

Biodiversity is deemed to play an important role in adaptation of forest ecosystems to climate change. However, there is ongoing research to determine if the best way to preserve or increase biodiversity is through leaving forest ecosystems to their natural-development. In this study we investigated how forest management can influence tree species diversity in a natural regenerating beech-dominated forest ecosystem. For this purpose, long-term research plots were established in 1989 to simulate different intensities of cutting intervention (including clear-cut) in mature forest stands. The natural regeneration was surveyed five times during the period between 2002 and 2012, 14–24years after the initial cutting. In addition to forest density, tree species and diversity indices (Hill E5 and Shannon H′) were used to quantify diversity and temporal change. Results show that management can impact development and diversity of natural regeneration, but this varied with management intensity. Only the initial cutting affected the development of successive young stands, and additional interventions did not lead to further changes in biodiversity. Beech, as the dominant species of the forests in long-term plots, had a high competitive ability however, the proportion of beech regeneration depended on the intensity of the initial cutting: more canopy openness resulted in a lower proportion of regeneration. Since beech is the most competitive species in the region, the most intensive forest management would be required to increase species diversity.

Predicting Tree Mortality for European Beech in Southern Germany Using Spatially Explicit Competition Indices

Individual tree mortality prediction is a key component of single tree-based stand simulators. However, accurate modeling of long-term research plot data is hampered by rare events, variable lengths of observation, and multiple sources of heterogeneity. This study makes use of a result from medicine that demonstrates the equivalence of logistic and Cox proportional hazards regression for modeling survival data in the case of large sample sizes, rare events, and variable interval periods of observation. Pooled logistic regression models are used to model tree mortality across multiple observation periods with random effects to account for heterogeneity due to plots and calendar year. The models are applied to data from 21,051 observation periods (each approximately 5 years) from 9,292 beech trees in a Bavarian long-term forest research plot network. Among the observation periods studied, 604 (2.9%) resulted in a mortality. Indices measuring competition from light, trees of the same species, conifer trees, and shading are significantly associated with mortality, whereas other variables, including dbh, fail to add additional predictive value. Analytic equations for predicting mortality in new trees are provided and yield an area underneath the receiver operating characteristic curve of 91.5%.

Detecting trends in diameter growth of Norway spruce on long-term forest research plots using linear mixed-effects models

The objective of the study was to introduce a simultaneous approach to extracting growth trends from diameter increment series by combining tree- and stand-level information in the framework of mixed-effects modeling. The model results are compared with those of the sequential modeling approach according to Yue et al. Can J For Res 41:1577–1589, (2011). Comprehensive data from periodically repeated tree and stand measurements on 113 Norway spruce long-term forest research stands distributed throughout southwestern Germany as well as annually resolved diameter growth data from stem analysis of 581 sample trees are used for model parameterization. Results provide clear evidence for distinct temporal variation due to environment-related effects after accounting for tree- and stand-level effects on diameter growth of Norway spruce over the past 136 years, with especially high growth levels during the last four decades. Most remarkable is the considerable increase in diameter growth rates following the 1947–1952 growth depression. From the early 1960s onwards, growth rates fluctuated on an elevated level until most recent years. Model comparison reveals that results of the sequential and simultaneous modeling approaches are similar with respect to the course of the time-specific environmental effects on growth. We conclude that the proposed simultaneous modeling approach has the advantages of extracting growth trends at a higher level of precision and being the more parsimonious modeling option.

Influence of initial plant density on sawn timber properties for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)

Mechanical wood properties are increasingly relevant for structural applications and are influenced by growing space availability. Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) has an increasing market share in Europe and is mainly processed to sawn timber. A sample of 164 thinning trees was taken from two Douglas-fir long-term forestry research plots in Germany. The end-use quality of about 2,000 side and center boards was analyzed as a function of initial plant density (1,000, 2,000, and 4,000 trees per hectare) and log position within the stem. Sawn timber quality was described by knottiness, density, modulus of elasticity, and strength. Explanatory parameters were radial position, longitudinal position, and initial plant density. All boards were strength graded visually and by the grading machine GoldenEye-706 using both X-rays for detecting densities and size as well as position of knots and laser interferometry for detecting eigenfrequency (DIN 4074, DIN 2012; EN 14081-2, CEN 2010). High plant density led to better mechanical sawn timber quality. Significant differences were especially observed between 1,000 and 2,000 trees per hectare. The yield of machine strength-graded center boards of strength class C24 increased from 50 to 89 % at low and high initial plant density, respectively. Foresters are able to improve end-product quality by controlling planting density in particular. The roundwood price that foresters get should be based on the proportion of higher strength classes within logs to give incentives for a more quality-oriented forest management.

Long-term fluorometric measurements of photosynthetic processes in Antarctic moss Bryum sp. during austral summer season

Photosynthetic activity pattern of Bryum sp. was monitored for 28days using a chlorophyll a fluorescence measuring system installed in the field. For the study, long-term research plot, a moss-dominated vegetaiton oasis at seashore located close to the J.G. Mendel station (James Ross Island, Antarctica) was selected. In this study, two measuring sites were used: (1) control plot with moss cover and (2) moss located inside open top chamber (OTC). At both sites, effective quantum yield of photosynthetic processes in photosyntem II (FPSII) was measured and relative photosynthetic electron transport rate (ETRrel) evaluated each 15 min. Simultaneously, microclimate of the sites was measured including air and moss surface temperature, relative air humidity and photosynthetically active radiation. The length of photosyntetically active period depended mainly on hydration of moss cushion. Water availability, however, was not limiting in the measuring period (Jan 8 - Feb 18, 2009), because the sites were well suplied by melt water from neighbouring snowfield. Thus, daily courses of ETRrel were dependent on incident PAR. On sunny days, ETRrel reached values over 400. Inhibition of primary photosynthetic processes due to below-zero temperature and resulting freezing of moss cushions appeared two times within the measuring periods thanks to rapid decreases in air temperature. The effect of low air temperature on ETRrel was less apparent in OTC site since moss cushion freezing period was shorter and less pronounced than in control site thanks to OTC-induced shift in air temperature. For future photosynthetic studies in Antarctic mosses, simultaneous measurements of gas exchange- and chlorophyll fluorescence-related parameters is recommended so that the effects of particular limiting factors for photosynthesis and photosynthetic productivity can be distinguished and evaluated.

施肥方式对紫色土土壤异养呼吸的影响

Recent studies have shown that soil respiration is the critical importance in determining the carbon balance of terrestrial ecosystems. Respiration from soils is comprised of both the heterotrophic respiration of microorganisms( soil bacteria,fungi,and fauna) and autotrophic respiration from roots and mycorrhizae. Precise assessment of these components is important for calculating the carbon budgets of vegetation and the turnover rate of soil organic matter,as well as for understanding sources and sinks of carbon in terrestrial ecosystems in the face of global climate change. Although soil heterotrophic respirations have received considerable attention in recent decades,much less is known about the effects of various natural or artificial factors such as temperature,precipitation or fertilization etc. on it. The field study was conducted at a sloping cropland in Yanting Agro-ecological Station of Purple Soil,Chinese Academy of Science under Chinese Ecosystem Research Network( CERN),situated at N31°16°,E105°28',with the altitude of 400 to 600 meters in the middle of Sichuan Basin,where a set of long-term research plots is located. Three plots were randomly assigned to oneof the following treatments: conventional chemical fertilizer( NPK),organic manure( pig slurry,OM) and crop residue with chemical fertilizer( RSDNPK). Total nitrogen for each fertilization treatment was applied at the same rate with 130 and150 kgN /hm2 for wheat and maize seasons,respectively. The results showed that soil heterotrophic respiration exhibited pronounced seasonal variations that clearly reflected those of soil temperature,with minimum values in winter and maximum values in summer. There was a pulse of soil heterotrophic respiration induced by fertilization at the 5th day after fertilization. The peak rate for OM treatment was 2356. 8 mgCO2m-2h-1and it was significantly higher than that for both RSDNPK and NPK treatments( P0. 01). Meanwhile,the respiration rate and the annual cumulative CO2 emission in OM and RSDNPK treatments were higher than those in NPK treatment. During wheat growing season,average respiration rate for NPK,OM and RSDNPK treatments were 212. 9,285. 8 and 305. 8 mgCO2m-2h-1,respectively,which were all lower than that in maize growing season. The cumulative soil CO2 emissions from NPK,OM and RSDNPK were 255. 1,342. 3and 369. 5 gC /m2 for wheat season,and 344. 7,542. 8 and 376. 9 gC /m2 for maize season,while 599. 8,885. 1 and 746. 4gCm-2for the whole year,respectively. The results implied that lower C /N ratio organic material was the primary driving force for increasing soil heterotrophic rate and cumulative soil CO2 emissions. The values of temperature sensitivity( Q10)for soil heterotrophic respiration in wheat season and maize season were also measured. The results showed that Q10 values in wheat season always higher than that in maize season at all plots. During the whole experiment time,the magnitudes of Q10 both followed the order of OM NPK RSDNPK,which was clearly reflected that Q10 was sensitive to lower C /N organic materials. Q10 values obtained from soil temperature at soil surface( 0 cm) and soil 5 cm depth in OM and RSDNPK were2. 64,2. 77 and 1. 88,1. 99,respectively. It indicated that the Q10 values for soil heterotrophic respiration rates were higher at lower temperatures and lower at higher temperature.

Assessment of the Norway spruce plantation growth on a mountain forest site disturbed by windrowing and ameliorated by green alder

Mechanized windrowing in the top region of the Orlické hory Mts. has disturbed hundreds of hectares of immission clearcuts during eighties. The soil surface on the Velká Deštná Mountain was disturbed in 1987. One year later the Forest Research Station at Opočno established on this place the long-term research plot. Degree and extent of soil surface disturbance were recorded. Besides other experiments, the experimental Norway spruce plantation was established on three strips: control strip, strip treated by fertilizers or limestone (1991), and strip ameliorated byAlnus viridisplantation (1992). The effect of site degradation by mechanized windrowing has been indicated by young spruce growth for a long time period. The assessment of 17 years old spruce growth on the control strip shows significantly greater height increment on negligibly disturbed sites comparing to that on remarkably and very remarkably disturbed sites. Amelioration of spruce trees brings perspective outcomes on the strip biologically amended byAlnus viridis. High atmospheric depositions especially of nitrogen compounds, fungal disease by Ascocalyx abietina, climatic fluctuations, and high values of groundlevel ozone have brought new problems into spruce plantation performance since 1999. Nevertheless, it has been more substantially reduced by green alder.

Variability in solar radiation and temperature explains observed patterns and trends in tree growth rates across four tropical forests

The response of tropical forests to global climate variability and change remains poorly understood. Results from long-term studies of permanent forest plots have reported different, and in some cases opposing trends in tropical forest dynamics. In this study, we examined changes in tree growth rates at four long-term permanent tropical forest research plots in relation to variation in solar radiation, temperature and precipitation. Temporal variation in the stand-level growth rates measured at five-year intervals was found to be positively correlated with variation in incoming solar radiation and negatively related to temporal variation in night-time temperatures. Taken alone, neither solar radiation variability nor the effects of night-time temperatures can account for the observed temporal variation in tree growth rates across sites, but when considered together, these two climate variables account for most of the observed temporal variability in tree growth rates. Further analysis indicates that the stand-level response is primarily driven by the responses of smaller-sized trees (less than 20 cm in diameter). The combined temperature and radiation responses identified in this study provide a potential explanation for the conflicting patterns in tree growth rates found in previous studies.

Field-Based Radiometry to Estimate Tidal Marsh Plant Growth in Response to Elevated CO2 and Nitrogen Addition

Plant growth is one of the most important variables to measure in long-term research plots, but the negative effects of labor-intensive and destructive sampling can restrict frequent assessment of plant biomass. Here, we used field-based, active radiometry to assess plant biomass in an ongoing, experimental manipulation of atmospheric CO2 and soil nitrogen availability in a tidal wetland. We compared the ability of several radiometric vegetation indices (VIs) to predict total plant biomass and that of two plant functional groups, sedges and grasses. All VIs estimated total biomass better in July than in October, when senescence had begun. All VIs correlated strongly and positively to grass biomass (average r = 0.83) and weakly or negatively to sedge biomass (r = −0.30). Modified soil-adjusted vegetation index (MSAVI2) performed well through space (average July total biomass r = 0.83) and time (across four sampling times r = 0.83) and predicted CO2 and nitrogen treatment effect sizes. In conjunction with conventional biomass measurements field-based, active radiometry provides (1) a frequent estimate of biomass that can reveal plant responses to environmental stimuli that would otherwise escape detection, and (2) a viable alternative to frequent destructive sampling for assessing growth of fine-stemmed species such as Spartina patens and Distichlis spicata.

Comparison of selected Nordic stand growth models for Norway spruce, Scots pine and birch

Abstract Thirteen Nordic stand growth models have been validated by use of a test data set from long-term research plots in Norway. The evaluated data was from time-series of even-aged, pure stands of Norway spruce, Scots pine and birch (silver birch and downy birch). In selected models from Finland, Norway and Sweden measures of site productivity, mean tree size and various stand characteristics are represented. Different models display both strengths and weaknesses in their predicting ability. Several measures of precision and bias have been calculated and the models are ranked due to their performance. We observed site quality, stand density and average tree size as the three main components in the models. Basal area increment model for spruce from Sweden had the lowest standard deviation with 23%. The mean R2 between residuals and stand characteristics from this model was also low (1.3%), which indicates that independent variables are well included. For Scots pine and birch, Finnish volume increment models showed the best fit to the Norwegian test data, with a R2 between residuals and stand characteristics of 2.8 and 6.7%, respectively. Several of the models from Sweden and Finland predicted the growth as well as stand models frequently in use in Norway. The results indicated that similar forest conditions and traditional even-aged forest management practice in the Nordic countries could be seen as a suitable basis for developing a joint family of growth models. By careful recalibration of existing models, a reasonable accuracy could be achieved and the prediction bias could be reduced.

Nitrogen and phosphorus status and their influence on aboveground production under increasing nitrogen deposition in three successional forests

Compared with temperate ecosystems, tropical ecosystems will respond differently to increasing nitrogen (N) deposition due to indirect effects on the availability of phosphorus (P). Data in this study were collected from the long-term research plots and controlled experiments in a succession series, including 50-year-old pine forest (PF), 80-year-old mixed pine and broadleaved forest (MF), and more than 400-year-old monsoon evergreen broadleaved forest (MEBF), in southern China to study growth patterns and biogeochemical processes. The results showed that soil total N and available N were significantly higher in MEBF than in the other two forests. Soil available P was significantly lower in MEBF than in PF though the total P was the same. The N/P ratios in living leaves were increasing with succession stages. The standing biomass and productivity of MEBF have been declining over the last 30 years. Our findings suggest that the high N stock in soil pools through atmospheric deposition and self-accumulation in MEBF would require more available P to prevent deficiency that would limit plant growth. However, as more organic matter accumulated and thus, more P was bound in MEBF, there was much less available P in soils. These processes result in significantly higher N/P ratios in living leaves of the old-growth forest, which may be responsible for the decline.

Structure and dynamics of a beech forest in a fully protected area in the northern Apennines (Sasso Fratino, Italy)

Sasso Fratino Nature Reserve (National Park of Casentino Forests, northern Apennines) is a quite rare example of natural Apennine forest. The Reserve was established in 1959, aiming to protect a forest, although not a virgin one, low-intensively disturbed in the past by comparison with other neighbouring stands. Causes of such a low disturbance are the very limited accessibility of the area due to the very steep slopes characterising the site morphology, as well as historical features. The forest is a pure beech stand from 1250 m a.s.l. upwards, below this altitude is a mixed beech and silver fir forest. The study focuses on the understanding of the processes driving the evolution of the forest in the absence of human activities. To achieve this goal, 9 permanent, long-term research plots were established at different altitudes, in order to investigate on forest dynamics and regeneration processes. Simplified (single-layer) stand structures are more frequent where canopy gaps are absent. Two-layered structures are the result of the occurrence of canopy gaps, which allow the settlement, and subsequently the establishment, of a lower regeneration layer. Where the gap dimensions allow canopy closure, this kind of structure persists. When the gaps are quite large, the regeneration layer reaches the top layer and the structure stand tends, once more, toward a single-layer. Multilayered structures are extremely rare at plot level and become evident only at a wider scale. Our surveys indicate also a high variability of tree diameter distribution patterns in the forest stands. Such variability could be strictly related to the heterogeneity of site characteristics as well as to the effects of disturbance factors (both natural and anthropic). Concerning altitude, we observed an increase both of site index (dominant height) and species diversity in the regeneration layer, moving from higher (1500 m) to lower (900 m) altitudes. As a whole, our observations show that the dynamics of forest vegetation in the reserve is mostly affected by the interruption of tree canopy continuity. This implies substantial local variations of PAR in space and in time, which determine favourable ecological conditions for: (a) survival and growth of beech seedlings, or release of advanced beech regeneration; and (b) release of advanced silver fir regeneration (fir, more shade tolerant than beech, regenerates mainly in locations and conditions where the broadleaf saplings cannot survive for lack of light). The knowledge of the mechanisms of vegetation dynamics in the Reserve can be used to form the basis of close-to-nature silvicultural choices in similar stands in order to increase functionality and stability. Periodical monitoring of RNI will allow the investigation of the evolutionary trends of the forest stands.

Results of the measurement in large scale and long-term ecological research plots in Iwanazawa during 1994-2009

Results of the measurement in large scale and long-term ecological research plots in Iwanazawa during 1994-2009

Result of a measurement in large scale and long-term ecological research plot 15 years after establishment

Result of a measurement in large scale and long-term ecological research plot 15 years after establishment

Trockenperioden seit 1900 und Waldwachstum: eine Analyse langfristiger Datenreihen | Drought periods since 1900 and growth of forest stands: an analysis of long-term data series

Drought during the vegetation period has en effect on tree growth. Using daily precipitation data and growth records from long-term research plots, we investigated what can be defined as “drought” and how strong its effect is. Dry or humid periods are defined as the deviation from the long-term daily mean of precipitation. Such periods must last at least 60 days to be considered as being decisive for tree growth. The drought values are used together with other site and stand parameters as explaining variables in a model for the basal area increment for Norway spruce (Picea abies [L] H. Karst.), silver fir (Abies alba Mill.), European beech (Fagus sylvatica L.) and oak (Quercus L), based on data from long-term growth and yield plots which are located in the neighbourhood of precipitation measurement stations. These models explain 55 to 89% of the variance. In drought situations basal area increment drops clearly for spruce and beech, for fir only weakly and oak shows no reaction. Furthermore, we checked if there happened additional or compulsory felling after drought periods and if the basal area growth changed significantly compared to the growth in the period before. For both it is not the case, despite distinct drought periods in the last century, especially in the 40s with the extreme year of 1947. Therefore we do not expect dramatic changes for the investigated species in similar drought situations under the prerequisite that the other conditions do not change essentially.

Individual tree diameter increment model for managed even-aged stands of ponderosa pine throughout the western United States using a multilevel linear mixed effects model

A diameter increment model is developed and evaluated for individual trees of ponderosa pine throughout the species range in the United States using a multilevel linear mixed model. Stochastic variability is broken down among period, locale, plot, tree and within-tree components. Covariates acting at tree and stand level, as breast height diameter, density, site index, and competition indices are included in the model as fixed effects in order to explain residual variability. The data set used in this study came from long-term permanent research plots in even-aged, pure stands both planted and of natural origin. The data base consists of six levels-of-growing stock studies supplemented by initial spacing and other permanent-plot thinning studies for a total of 310 plots, 34,263 trees and 153,854 observations. Regression analysis is the preferred technique used in growth and yield modeling in forestry. We choose the mixed effects models instead of the regression analysis approach because it allows for proper treatment of error terms in a repeated measures analysis framework. Regional growth and yield models exist for ponderosa pine. However, data collection and analysis procedures differ. As a result, comparisons of growth responses that may be due to geographic variation of the species are not possible. Our goal is to present a single distance-independent diameter increment model applicable throughout the geographic range of ponderosa pine in the United States and by using only data from long-term permanent plots on sites capable of the productivity estimated by Meyer [Meyer, W.H., 1938. Yield of Even-Aged Stands of Ponderosa Pine. US Department of Agriculture Technical Bulletin 630].

Glyphosate Susceptibility in Common Lambsquarters (Chenopodium album) is Influenced by Parental Exposure

Field studies were carried out at two sites in 2005 using common lambsquarters seed collected from long-term research plots near Scottsbluff, NE; Fort Collins, CO; and Torrington, WY, to determine the effect of herbicide selection pressure on glyphosate susceptibility. Parental herbicide exposure influenced the level of glyphosate susceptibility exhibited by a subsequent generation. Common lambsquarters selected from historical plots receiving continuous and exclusive use of glyphosate exhibited lower mortality in response to 420 g ae ha−1glyphosate compared with selections from nonglyphosate treatment histories. Selections from rotating glyphosate treatment histories demonstrated an intermediate tolerance response. Differences in response were also influenced by environmental conditions.

Sustainability in multi-aged stands: an analysis of long-term plenter systems

Long-term research plots in multi-aged stands managed with the plenter system were assessed to evaluate sustainability of the plenter system in Central Europe. Plots primarily consisted of Norway spruce (Picea abies (L.) Karst., silver fir (Abies alba Mill.) or European beech (Fagus sylvatica L.) and were measured for seven to 16 measurement intervals over 60–91 years. Sustainability was assessed with four types of criteria: stand density, tree species diversity, basal area increment, and stand structure. Comparable even-aged stands were also analysed to compare and evaluate the performance of the measures of sustainability. Measures of species diversity, increment and stand structural diversity generally experienced increasing trends over time in these even-aged stands. Basal area generally increased and trees ha-1 decreased in multi-aged stands following similar patterns as in even-aged stands. These results suggest that the plenter system is still evolving and is not the model of sustainability often assumed. Many of the measures used have potential as indicators of sustainability in multi-aged stands.

Linking Increasing Drought Stress to Scots Pine Mortality and Bark Beetle Infestations

In the dry Swiss Rhone Valley, Scots pine forests have experienced increased mortality in recent years. It has commonly been assumed that drought events and bark beetles fostered the decline, however, whether bark beetle outbreaks increased in recent years and whether they can be linked to drought stress or increasing temperature has never been studied.In our study, we correlated time series of drought indices from long-term climate stations, 11-year mortality trends from a long-term research plot, and mortality probabilities modeled from tree rings (as an indicator of tree vitality) with documented occurrences of various bark beetle species and a buprestid beetle, using regional Forest Service reports from 1902 to 2003 and advisory cases of the Swiss Forest Protection Service (SFPS) from 1984 to 2005. We compared the historical findings with measured beetle emergence from a 4-year tree felling and breeding chamber experiment.The documented beetle-related pine mortality cases increased dramatically in the 1990s, both in the forest reports and the advisory cases. The incidents of beetle-related pine mortality correlated positively with spring and summer temperature, and with the tree-ring-based mortality index, but not with the drought index. The number of advisory cases, on the other hand, correlated slightly with summer drought index and temperature, but very highly with tree–ring—based mortality index. The tree-ring-based mortality index and observed tree mortality increased in years following drought. This was confirmed by the beetle emergences from felled trees. Following dry summers, more than twice as many trees were colonized by beetles than following wet summers.We conclude that increased temperatures in the Swiss Rhone Valley have likely weakened Scots pines and favored phloeophagous beetle population growth. Beetles contributed to the increased pine mortality following summer drought. Among the factors not addressed in this study, changed forest use may have also contributed to increased beetle populations and Scots pine mortality, whereas air pollution seems to be of lesser importance.