Forest Succession Model Research Articles

Spatial simulation of historical landscape patterns in coastal forests of the Pacific Northwest

Concerns about the fragmentation of Pacific Northwest forests are based on the assumption that these landscapes historically contained large, contiguous patches of old growth. However, this supposition appears to conflict with disturbance history research, which shows that wildfire was an important component of pre-settlement forest ecosystems. To better quantify historical forest patterns, a spatial simulation model of wildfire and forest succession was used to simulate pre-settlement landscape dynamics in the Oregon Coast Range, U.S.A. The model was parameterized to simulate fire regimes over 1000 years prior to Euro-American settlement using data from paleoecological, dendro ecological, and historical sources. A simple fire-spread algorithm produced mosaics of variable fire severity and allowed simulated fires to be calibrated to match the shapes of real fires. The simulated landscape was spatially heterogeneous and highly dynamic. Old growth was the dominant patch type occupying a median of 42% of the total area. The relatively long fire return intervals, highly skewed fire size distributions, and mixed severities characteristic of the historical fire regime generated a landscape mosaic with large (> 100 000 ha) patches of old-growth forest, although smaller patches (<100 ha) were the most numerically abundant. Both small and large patches of old forest have important ecological roles in a dynamic ecosystem, and future landscape management efforts should consider the implications of altering these historical patterns.

Forest carbon sequestration and harvests in Scots pine stand under different climate and nitrogen deposition scenarios

In this study, effects of altered rotation length, nitrogen deposition and changing climate on harvest removal and carbon sequestration of forest, as well as on economic profitability of forestry, were assessed. This study was based on simulations with a gap-type forest succession model in the conditions that represent Scots pine stands in southern Finland. Both warmer climatic conditions and increased nitrogen deposition enhanced forest productivity and timber yield. This also shortened the optimum rotations based on mean annual yield and soil expectation value. The highest carbon stock in forests, i.e. the highest mean annual carbon stock in the forest over a rotation period, was achieved with long rotations and higher nitrogen deposition. However, a warmer climate had an opposite effect on the forest carbon stock, because enhanced decomposition of soil organic matter resulted in a lower carbon stock in the forest soil.

Evaluating the potential of the SORTIE forest succession model for spatio-temporal analysis of small-scale disturbances

Ecologists and forest managers both recognize the importance of detailed spatio-temporal knowledge on local small-scale disturbances (SSD) dynamics and impacts. However, a large proportion of the knowledge about SSD is based on temporally short data sets, and on non-spatial analysis. SORTIE, a stochastic and mechanistic spatially explicit and individual-based forest succession model, is particularly well suited for simulating SSD and overcoming traditional field studies limitations. Our main goal is to investigate the potential of SORTIE for spatio-temporal analysis of SSD. More specifically, we intend to evaluate the model sensitivity to initial conditions, and to assess the impact of introduced minor disturbances on the species densities. We hypothesize that SORTIE will generate realistic species dynamics within the range of tested scenarios. We performed simulations over a period of 1000 years using two different initial spatial configurations (Random and Aggregated) and fifteen replicates. For each replicate we extracted, at each time step of 5 years, the species local spatial structure with the use of the Ripley's K statistic. The resulting time series periods and trends were compared between initial condition scenarios by performing phase coherence and regression analysis. In another set of simulations, SSD of different sizes (500, 800 and 1100 m 2) were introduced at two distinct time steps (400 and 600 years). Species density time series were analyzed again in terms of periodicity and trend. Results indicate a sensitivity to initial conditions limited to the first 300 years, and a very similar species local spatial structure between the scenarios after that period. Also, statistical tests revealed that the species densities are not sensitive to single introduced SSD, for all SSD sizes and moments of disturbance. These conclusions suggest that SORTIE can be a valuable complementary tool to SSD field studies.

Evaluating a model of forest succession using fuzzy analysis

In this paper we discuss how to select the optimal policy from a set of possible policies for a model of forest succession, which can be characterized by a set of trees and the corresponding average life-span with each possible tree transition. The transition probabilities are estimated by counting the numbers of sapling trees of each species under a canopy tree. [1]. In our setting the transition matrix is defined by using the linguistic terms and as a consequence, the expected longevity of each tree is fuzzy. We use the Dempster–Shafer theory [8] ('76) together with techniques of Norton [7] ('88) and Smetz [9] ('76) to approximate the transition probabilities.

Tree species composition in European pristine forests: Comparison of stand data to model predictions

The degree of general applicability across Europe currently achieved with several forest succession models is assessed, data needs and steps for further model development are identified and the role physiology based models can play in this process is evaluated. To this end, six forest succession models (DISCFORM, ForClim, FORSKA-M, GUESS, PICUS v1.2, SIERRA) are applied to simulate stand structure and species composition at 5 European pristine forest sites in different climatic regions. The models are initialized with site-specific soil information and driven with climate data from nearby weather stations. Predicted species composition and stand structure are compared to inventory data. Similarity and dissimilarity in the model results under current climatic conditions as well as the predicted responses to six climate change scenarios are discussed. All models produce good results in the prediction of the right tree functional types. In about half the cases, the dominating species are predicted correctly under the current climate. Where deviations occur, they often represent a shift of the species spectrum towards more drought tolerant species. Results for climate change scenarios indicate temperature driven changes in the alpine elevational vegetation belts at humid sites and a high sensitivity of forest composition and biomass of boreal and temperate deciduous forests to changes in precipitation as mediated by summer drought. Restricted generality of the models is found insofar as models originally developed for alpine conditions clearly perform better at alpine sites than at boreal sites, and vice versa. We conclude that both the models and the input data need to be improved before the models can be used for a robust evaluation of forest dynamics under climate change scenarios across Europe. Recommendations for model improvements, further model testing and the use of physiology based succession models are made.

Net primary productivity following forest fire for Canadian ecoregions

Recent modelling results indicate that forest fires and other disturbances determine the magnitude of the Canadian forest carbon balance. The regeneration of post-fire vegetation is key to the recovery of net primary productivity (NPP) following fire. We geographically co-registered pixels classed using the Boreal Ecosystem Productivity Simulator, a process-based model with AVHRR (advanced very-high resolution radiometer) satellite estimates of leaf-area index and land cover type, with polygons from a recent database of large Canadian fires. NPP development with time since fire was derived for the first 15 years following the disturbance in the boreal and taiga ecozones. About 7 × 106 ha were analysed for over 500 fires occurring between 1980 and 1994. NPP increases linearly through this period, at rates that depend on ecoregion. A longer data set for the Boreal Plains ecozone of Alberta shows that NPP levels off at about 20-30 years and remains constant for 60 years. The NPP trajectories can be used as spatial averages to support models of forest carbon balance and succession through the most fire-prone regions of Canada.

Net primary productivity following forest fire for Canadian ecoregions

Recent modelling results indicate that forest fires and other disturbances determine the magnitude of the Canadian forest carbon balance. The regeneration of post-fire vegetation is key to the recovery of net primary produc- tivity (NPP) following fire. We geographically co-registered pixels classed using the Boreal Ecosystem Productivity Simulator, a process-based model with AVHRR (advanced very-high resolution radiometer) satellite estimates of leaf- area index and land cover type, with polygons from a recent database of large Canadian fires. NPP development with time since fire was derived for the first 15 years following the disturbance in the boreal and taiga ecozones. About 7 × 10 6 ha were analysed for over 500 fires occurring between 1980 and 1994. NPP increases linearly through this period, at rates that depend on ecoregion. A longer data set for the Boreal Plains ecozone of Alberta shows that NPP levels off at about 20-30 years and remains constant for 60 years. The NPP trajectories can be used as spatial averages to sup- port models of forest carbon balance and succession through the most fire-prone regions of Canada.

Error Propagation in a Forest Succession Model: The Role of Fine-Scale Heterogeneity in Light

Error Propagation in a Forest Succession Model: The Role of Fine-Scale Heterogeneity in Light

Modeling successional patterns of high-elevation forests under changing herbivore pressure – responses at the landscape level

We describe an ecological risk assessment for determining the potential long-term impacts of browsing by red deer, roe deer and chamois on the stand dynamics of mountain forests in xeric parts of Central Europe. The assessment is performed by applying a forest succession model of the FORET/JABOWA type which was supplemented with an empirically based browsing subroutine to simulate the effects of browsing by red and roe deer, and chamois. The following scenarios are assumed: (1) no browsing; (2) actual browsing intensity as determined in field trials; (3) browsing intensity twice as high as in scenario (2); and (4) browsing intensity three times as high as in scenario (2). The simulations for two different forest sites in the subalpine region of Eastern Switzerland revealed that heavy browsing can alter development and composition of the observed forests. The extent of this alteration was influenced not only by high browsing intensity, but also by the selection of tree species which were browsed on a particular site at the same time. Taking into account all the uncertainties of the model approach, we conclude from our preliminary studies that, in the regions considered, even strong herbivore pressure (2–3 times today's values) is not a major threat for the survival of the forest as a biological resource, i.e. the long-term total woody biomass is not altered significantly and the changes in the successional pathways are not dramatic. High browsing intensities, however, alter the forest structure considerably. We found that heavily browsed forests tend to be more open, mortality is higher and trees reach an intermediate and adult size quicker. This shortened development cycle of the stands may have implications for forest functions. The risk assessment yields critical values for mean browsing intensity, `MBI', ( Pinus cembra/ Pinus mugo: 30%; Picea abies: 50%; and Larix decidua: 40%), below which successional patterns and forest structures with browsing are not significantly different from forest succession without browsing.

Aggregation of Individual Trees and Patches in Forest Succession Models: Capturing Variability with Height Structured, Random, Spatial Distributions

Individual based, stochastic forest patch models have the potential to realistically describe forest dynamics. However, they are mathematically intransparent and need long computing times. We simplified such a forest patch model by aggregating the individual trees on many patches to height-structured tree populations with theoretical random dispersions over the whole simulated forest area. The resulting distribution-based model produced results similar to those of the patch model under a wide range of conditions. We concluded that the height- structured tree dispersion is an adequate population descriptor to capture the stochastic variability in a forest and that the new approach is generally applicable to any patch model. The simplified model required only 4.1% of the computing time needed by the patch model. Hence, this new model type is well-suited for applications where a large number of dynamic forest simulations is required.

Forest biomass from combined ecosystem and radar backscatter modeling

Above-ground woody biomass is an important parameter for describing the function and productivity of forested ecosystems. Recent studies have demonstrated that synthetic aperture radar (SAR) can be used to estimate above-ground standing biomass. To date, these studies have relied on extensive ground-truth measurements to construct relationships between biomass and SAR backscatter. In this article we discuss the use of models to help develop a relationship between biomass and radar backscatter and compare the predictions with measurements. A gap-type forest succession model was used to simulate growth and development of a northern hardwood-boreal transitional forest typical of central Maine, USA. Model results of species, and bole diameter at breast height (dbh) of individual trees in a 900 m 2 stand were used to run discontinuous canopy backscatter models to determine radar backscatter coefficients for a wide range of simulated forest stands. Using model results, relationships of copolarized backscatter to forest biomass were developed and applied to airborne SAR (AIRSAR) image over a forested area in Maine. A relationship derived totally from model results was found to underestimate biomass. Calibrating the modeled backscatter with limited AIRSAR backscatter measurements improved the biomass estimation when compared to field measurements. The approach of using a combination of forest succession and remote sensing models to develop algorithms for inferring forest attributes produced comparable results with techniques using only measurements. Applying the model derived algorithm to SAR imagery produced reasonable results when mapped biomass was limited to 15 kg/m 2 or less.

Application of a forest succession model to a continentality gradient through Central Europe

The forest succession model FORSKA was applied to a west-east transect across Central Europe using points from a global climate data set. Climate change experiments were undertaken for two general circulation model scenarios and two different site classes. The simulated climate changes lead to reduced forest productivity and a changed species composition on most sites. Under current climate, the broad scale pattern of the climatically driven distribution of forest communities is quite realistically reproduced. However, the resolution of climate data imposes limitations on the simulation of forest dynamics in subcontinental climate, because climate variability and extreme events are not well represented.

Development of a MIOMBO woodland dynamics model in Zambezian Africa Using Malawi as a case study

A patch model was developed to characterize the effects of climate on succession of miombo dry forests of Zambezian Africa using Malawi as a case study. The model, called MIOMBO, is based on the FORSKA Version 1 gap model of forest succession by Prentice and Leemans (1990). The FORSKA model was modified to include the effects of moisture and fire; and how these affect processes of establishment, survival, growth and development. The impacts that four different GCM scenarios for a CO2 doubling might have on dynamics of a number of miombo species were analyzed. Preliminary results show a gradual increase in the basal area of the more mesic species. This result is consistent with what might be expected with increased precipitation. Tree growth and development data with associated detailed climatic data are lacking and severely limit the ability to define quantitatively how species are influenced by given levels of environmental factors (such as climate and nutrient factors), and how they might respond to seasonal changes in climate variability.

Application of the model forsum to the Solling spruce site

forsum, a forest succession model of the jabowa/foret type, was applied to the Solling spruce site. Reconstruction of the forest development for the last 100 years showed good agreement with real forest development for that site. One model experiment performed on the site was designed to explore the long-term effects of the management stop in 1966 on the spruce site. The invasion of other species takes place some 300 years from now and the vegetation slowly develops towards a beech-dominated forest. Finally, potential development of species composition was evaluated using the IPCC-‘business-as-usual’ climate scenario with a an increase of the mean annual temperature by 0.3°C/decade until the end of the 21st century. According to the model predictions Picea abies would disappear from the Solling site and be replaced by a Luzulo Fagetum forest type with Acer platanoides, Quercus petraea and Fagus sylvatica. forsum successfully combines long-term (e.g., succession) and short-term (e.g., hydrology) processes, giving the opportunity to simulate forest ecosystem processes more adequately. Forest succession models can be used to evaluate climate change impacts on forest ecosystems, even though some parameters are highly uncertain or are even unknown. Further research efforts are needed to fill the knowledge gaps and to improve model accuracy and reliability, especially plant physiological aspects with respect to a changed and a changing environment.

Successional status of trees in gallery forest along the river Rhine

Abstract. 20 alluvial forest stands of different ages along the river Rhine in central Alsace, France, are described. A natural complex landscape occurs which is formed by erosion activity of the river. Recent human impact (canal construction, cutting) has affected river hydrology: flooding is eliminated over large areas and the underground water levels are stabilized. The forest vegetation varies in species diversity and structure, from young pioneer to older, mid‐successional forests. The forests were classified into four associations: Salici‐Populetum nigrae, Ligustro‐Populetum nigrae, Fraxino‐Populetum albae and Querco‐Ulmetum minoris. The first three communities are ‘softwood’ because of the dominance of Salix and Populus, the fourth, dominated by Quercus robur, Fraxinus excelsior and Ulmus minor, is ‘hardwood’.Differences in structure, species composition and diversity in 10 widely varying stands in 30‐yr and 150‐yr old forests are quantified and interpreted in relation to the processes and gradients (moisture and texture) involved.A model of forest succession is developed as follows: Whatever the topographic level, Salix and Populus species are the most competitive in colonizing bare sediments. Under natural conditions, pioneer softwoods are generally replaced by hardwoods in less than 100 yr. Old Querco‐Ulmetum is basically the terminal stage of the alluvial succession. Old softwood forests result from an interruption of the natural course of succession. Softwoods may be an intermediate or late‐successional phase depending on the interruption. Successional processes change according to hydrological and edaphic gradients. Allogenic processes of flooding are fundamental in the space‐time species pattern. Allogenic processes are responsible for the high species and community diversity.

Potential effects of climatic change on some western Canadian forests, based on phenological enhancements to a patch model of forest succession

We enhanced the forest patch model, Zelig, to explore the implications of 2×CO2 climate change scenarios on several forest regions in British Columbia and Alberta, Canada. In addition to the processes and phenomena commonly represented in individual-based models of forest stand dynamics, we added some species-specific phenology and site-specific frost events. The consideration of bud-break heat sum requirements, growing season limits, and chilling requirements for the induction of dormancy and cold hardiness slightly improved the ability of Zelig to predict the present composition of B.C. forests. Simulations of the predicted effects of future climatic regimes (based on the averaged predictions of four general circulation models) include some major shifts in equilibrial forest composition and productivity. Lowland temperate coastal forests are predicted to be severely stressed because indigenous species will no longer have their winter chilling requirements met. High-elevation coastal forests are expected to increase in productivity, while interior subalpine forests are expected to remain stable in productivity but will gradually be replaced by species currently characteristic of lower elevations. Dry, interior low-elevation forests in southern B.C. are likely to persist relatively unchanged, while wet interior forests are expected to support dramatic increases in yield, primarily by western hemlock. Northern interior sub-boreal forests are likewise expected to increase in productivity through enhanced growth of lodgepole pine. Conversely, the precipitous collapse of spruce stands in the true boreal forests of northeastern B.C. is expected to be associated with reduced productivity as they are replaced by pine species. Boreal-Cordilleran and Moist Boreal Mixedwood forests in Alberta are less likely to undergo compositional change, while becoming somewhat more productive. We believe these model enhancements to be a significant improvement over existing formulations, but the resulting predictions must still be viewed with caution. Model limitations include: (1) the current inability of climate models to predict future variation in monthly temperature and precipitation; (2) sparse information on the phenological behaviour of several important tree species; and (3) a poor understanding of the degree to which growth is constrained by different suboptimal climatic events.

Application of Two Forest Succession Models at Sites in North East Germany

In order to simulate potential impacts of climate change on forests, two succession models were applied to sites in the north east German lowlands. The models, which had been developed for alpine (FORECE) and boreal (FORSKA) forests differ from each other in the way they represent tree growth processes and the impact of environmental factors on establishment and growth. Both models were adjusted and compared with each other at sites that are situated along an ecological gradient from maritime to subcontinental climate. These sites are extending the former environmental space of model application towards water-limited conditions, which under a predicted climatic change may have increasing importance for European forests. First results showed that FORECE was unrealistically sensitive to changes in soil moisture. On the other hand, FORSKA generally simulated very low biomasses. Since the structure of

Disturbance and the Population Dynamics of Liriodendron Tulipifera: Simulations with a Spatial Model of Forest Succession

I Population dynamics of Liriodendron tulipifera throughout the successional sere were investigated with a spatial simulator of forest community dynamics. The simulations were complemented by data from Appalachian cove forests at different stages of development. Gap size was a key consideration in simulation of Liriodendron recruitment; seed regeneration of this shade-intolerant species was unlikely except in large gaps (> 0.04 ha). 2 In simulations of long-term forest development (800 years) without exogenous disturbance, Liriodendron was a dominant species in early succession (50-150 years), but it was absent or present at low levels in stands > 500 years of age. The simulated basal area levels of Liriodendron approximated actual levels in cove forests having a disturbance regime characterized by a very low frequency of severe, large-scale events. 3 The idea that canopy gap size distributions change over the course of forest development was supported by the simulations. Given that intolerant species require large gaps for successful establishment, it was clear that temporal patterns of large gap formation affected the dynamics of such species. Intolerants were unable to regenerate during the stem exclusion phase, but they could regenerate during the subsequent understorey reinitiation and old-growth phases having large gaps. 4 Certain simulated disturbances imposed on old forests elevated Liriodendron basal area. Components of the disturbance regime included patch size, return interval, severity and spatial dispersion. The largest increases in Liriodendron basal area resulted from disturbance patches > 0.04 ha. Gaps, 0.1 ha in size, formed at intervals < 100 years by the mortality of c. 25% of the canopy trees in a stand, were sufficient to maintain the high levels of Liriodendron observed in some primeval forests of eastern North America.

Development of a simulation model of the forest–tundra transition zone of northeastern Canada

A forest succession model has been adapted to simulate the dynamics of subarctic spruce–lichen woodland of northeastern Canada. Most adaptations concern the simulation of seed regeneration of subarctic forest communities growing on moderately to well drained sites. The yearly seed production in Piceamariana (Mill.) B.S.R stands is controlled by temperature and stand structural characteristics. In addition to the seed input, the model considers the influence of seedbed properties on the establishment of seedlings. Overall, this model simulates the entire regeneration dynamics in a more realistic way than in most other gap models where successional processes are driven by resource constraints on tree growth. The model produces realistic predictions about the pattern of early post-fire age structure, and the biomas and density dynamics of black spruce populations. Simulations under a climate-warming scenario suggest that physiognomic change in subarctic spruce–lichen woodland would be more pronounced in areas subjected to moderately frequent forest fires than in those where the fire frequency is very low.

Modelling forest ecosystem dynamics using multitemporal multispectral scanner (MSS) data

An empirical model of forest succession was developed using MSS data. Images from 1976 and 1987 were classified and registered to assess vegetation change. Data were analyzed to determine the proportion of each landscape class that changed, and these proportions were used to develop a Markov Model. The simulation model was run to produce forest cover for 99 years. MSS data were classified into six classes with an overall accuracy of 93%. The landscape composition remained relatively constant, but over half the individual units changed, indicating a dynamic equilibrium. Results of the Markov model show a theoretical climax community that stabilizes rapidly. Over 60% of the area was composed of conifer, supporting the concept of a conifer dominated climax. However, continuous levels of other classes were maintained, indicating an inherently heterogeneous landscape.