Model Of Forest Dynamics Research Articles

Asymmetric Competition Can Shape the Size Distribution of Trees in a Natural Tropical Forest

AbstractThe architecture (here, the size distribution combined with the spatial pattern of individuals) of natural forest at demographic equilibrium can be used to infer the demographic processes that drive the forest dynamics. In particular, a constant growth rate and a constant mortality rate for all trees would generate an exponential distribution of their size, whereas the metabolic scaling theory predicts a power distribution. In an undisturbed tropical rainforest in French Guiana, the diameter distribution was significantly steeper than the best-fit exponential distribution and significantly flatter than the best-fit power distribution. A simple individual-based model of forest dynamics with asymmetric competition between trees, where the strength of competition was regulated by a single parameter, was able to predict the observed distribution. Competition drove the forest into a self-organized state with stronger inequalities of size among trees, a lower mean competition index, and a spatial pattern of trees that deviated from complete spatial randomness.

How multiple and interacting disturbances shape tree diversity in European mountain landscapes

The relationship between disturbances and diversity remains uncertain, especially in forest landscapes where large spatial extents need to be considered, dynamics are slow, and disturbance interactions are common. To analyse the individual and combined effects of ungulate browsing and wind disturbance on tree species diversity at the landscape scale. We used a dynamic forest landscape model to simulate the effects of browsing and wind disturbances (i.e., frequency and windthrow size) on tree species diversity in four mountain landscapes in Central Europe. Using boosted regression trees, we analysed the relative importance of each disturbance type for diversity at different layers (i.e., regeneration versus overstorey, and all tree sizes), the shapes of the diversity–disturbance relationships and the combined effect of wind and browsing disturbances on diversity. Across all landscapes, browsing and windthrow were equally important for tree species diversity when considering all forest layers, but no consistent patterns could be observed for the regeneration and overstorey layer. The shape of the disturbance–diversity relationships differed between disturbance types. More frequent and severe windthrow events typically increased diversity almost linearly, while browsing showed a non-linear response with the highest diversity at intermediate browsing pressure. However, these relationships were not consistent across the four landscapes. Tree species diversity can be influenced by both browsing and windthrow disturbances. Forested landscapes are likely to experience multiple disturbances, and their relative influence on diversity needs to consider their different spatial and temporal scales.

Quantifying and modeling water availability in temperate forests: a review of drought and aridity indices

Abstract: Climatic water availability is a major determinant of forest structure and composition, while drought events may severely impact forest dynamics. In recent decades, an increasing number of severe drought events has been reported in forests around the world. In the future, climate models project increasingly dry conditions in many temperate regions. Various tools have been applied to better understand the effects of drought on forests, such as dendrochronological analyses, climatic trend analyses and dynamic models. With these approaches, water availability is often summarized as a single scalar, termed a drought or aridity index. As droughts are complex phenomena, such indices are always associated with a loss of information. Many different such indices exist, and have been developed for various purposes. This review asks whether some of these indices are more suitable than others to quantify water availability in temperate forests. In a first step, the rationale and theoretical background of different drought indices are spelled out and compared among each other. Then, evaluations and intercomparisons of drought indices from the literature are reviewed. The implementation of drought indices in dynamic forest models is also discussed. Finally, two current research questions are identified: the role of dry air for physiological drought, and the suitability of various drought indices under climate change. It appears from this review that indices accounting for evaporative demand generally perform better than indices based on precipitation alone. When comparing sites with different edaphic conditions, indices accounting for soil moisture storage are more suitable. Nevertheless, results from intercomparisons show considerable divergence, and it is not possible to clearly favor one index. Furthermore, a differential response of tree species to different drought indices is often observed, although no clear pattern emerges from this comparison. More intercomparisons of indices, across climates and species, might provide valuable knowledge. Another key finding is that the properties of indices also depend on choices regarding, e.g., the calculation of evaporative demand, or the underlying water balance model. Reporting such methodological details could greatly increase the value of future evaluations of drought indices.

Climate change and tree harvest interact to affect future tree species distribution changes

Abstract Tree harvest and climate change can interact to have synergistic effects on tree species distribution changes. However, few studies have investigated the interactive effects of tree harvest and climate change on tree species distributions. We assessed the interactive effects of tree harvest and climate change on the distribution of 29 dominant tree species at 270 m resolution in the southern United States, while accounting for species demography, competition, urban growth and natural fire. We simulated tree species distribution changes to year 2100 using a coupled forest dynamic model (LANDIS PRO), ecosystem process model (LINKAGES) and urban growth model (SLEUTH). The distributions of 20 tree species contracted and nine species expanded within the region under climate change by end of 21st century. Distribution changes for all tree species were very slow and lagged behind the changes in potential distributions that were in equilibrium with new climatic conditions. Tree harvest and climate change interacted to affect species occurrences and colonization but not extinction. Occurrence and colonization were mainly affected by tree harvest and its interaction with climate change while extinctions were mainly affected by tree harvest and climate change. Synthesis and applications. Interactive effects of climate and tree harvest acted in the same direction as climate change effects on species occurrences, thereby accelerating climate change induced contraction or expansion of distributions. The overall interactive effects on species colonization were negative, specifically with positive interactive effects at leading edges of species ranges and negative interactive effects at trailing edges. Tree harvest generally did not interact with climate change to greatly facilitate or ameliorate species extinction. Our modelling results highlight the importance of considering disturbances and species demography (e.g. post‐harvest regeneration dynamics) when predicting changes in tree distributions.

Using linear mixed models to evaluate stand level growth rates for dipterocarps and Macaranga species following two selective logging methods in Sabah, Borneo

To understand and predict the dynamics and productivity of the world’s tropical rainforests after logging is a major challenge for ecologists and forest managers. Realistic forest-dynamics models for this biome are largely lacking. Using linear mixed models, we analyse basal area development for the commercially valuable tree species of dipterocarps and the fast-growing pioneer Macaranga spp., following two selective logging methods; supervised logging (SL) and conventional logging (CL) combined with- or without pre-harvest climber cutting (SLC and SL, and CLC and CL, respectively). After logging there was an initial period of about five years before recovery started. During the 18-year study period, the average stand basal area growth rates of the dipterocarp group in the SLC treatment was double that in the CL treatment, revealing a faster recovery. Eighteen years after logging, SL and SLC treatments recovered 93% and 84%, respectively, of the initial standing dipterocarp basal area, compared to 73% and 72% recovery for the CL and CLC treatments. SLC treatments reduced the overall establishment of pioneer species (Macaranga spp.) by about 45% in contrast to CL and CLC treatments. Our study provides a framework for evaluating and comparing growth rates in tropical forests for different logging methods. The results suggest that a combination of directional felling, pre-aligned skid trails and pre-harvest climber cutting can improve future yields in tropical rainforests.

Water limitation can negate the effect of higher temperatures on forest carbon sequestration

Climate change will bring about a consistent increase in temperatures. Annual precipitation rates are also expected to increase in boreal countries, but the seasonal distribution will be uneven, and several areas in the boreal zone will experience wetter winters and drier summers. This study uses the dynamic forest ecosystem model ForSAFE to estimate the combined effect of changes in temperature and precipitation on forest carbon stocks in Sweden. The model is used to simulate carbon stock changes in 544 productive forest sites from the Swedish National Forest Inventory. Forest carbon stocks under two alternative climate scenarios are compared to stocks under a hypothetical scenario of no climate change (baseline). Results show that lower water availability in the future can cause a significant reduction in tree carbon compared to a baseline scenario, particularly expressed in the southern and eastern parts of Sweden. In contrast, the north-western parts will experience an increase in tree carbon stocks. Results show also that summer precipitation is a better predictor of tree carbon reduction than annual precipitation. Finally, the change in soil carbon stock is less conspicuous than in tree carbon stock, showing no significant change in the north and a relatively small but consistent decline in the south. The study indicates that the prospect of higher water deficit caused by climate change cannot be ignored in future forest management planning.

Management implications of tree growth patterns in miombo woodlands of Zambia

Brachystegia-Julbernardia (miombo) woodlands of east and southern Africa are divided into dry (<1000 mm annual rainfall) and wet (>1000 mm). These woodlands first became established about 14,500 years ago. Since the migration of the Bantu people 5000 years ago, miombo woodlands have experienced widespread degradation and deforestation. There is little long-term data on tree growth and forest productivity for miombo woodlands and yet such data are required for the proper management of these woodlands. This study used tree growth data from 35 temporary plots in regrowth of 5–49 years old, and six permanent sample plots (PSPs) in old growth forest, which were monitored over a 28-year period (1990–2018). These data were used to investigate tree diameter growth and develop models of forest dynamics in wet and dry miombo woodlands. The study found that variations in tree diameter and stand basal area increments are strongly driven by stand age, tree size and density and that growth rates are higher in wet than dry miombo. Overall miombo woodland trees grew slowly at a rate of 0.34–0.50 cm yr−1 in re-growth areas. Most of the species in uneven-aged old-growth stands in dry miombo grew by 0.15 cm yr−1 with no significant annual differences although variations among conspecifics were large. Models predicted tree diameter increments of 0.10–0.24 cm yr−1 for stands of 100 years old. Transitions from one 5-cm diameter class to the next was estimated to take over 20 years and significant shifts in stand tree diameter distribution curves require over 25 years because of the low annual diameter increments. Stand responses to degradation varied from site to site and were driven by the number of saplings transiting into small diameter size classes. On the temporary regrowth plots basal areas averaged 7.1 m2 ha−1 and 9.9 m2 ha−1 in dry and wet re-growth miombo, respectively, with positive increments estimated at 0.40 m2 ha−1 yr−1 in dry miombo and 0.53 m2 ha−1 yr−1 in wet miombo. By contrast, average basal area increment on old-growth PSPs was negative, at −0.26 m2 ha−1 yr−1 over the 1990–2018 period, due to cutting and fire damage. Such drivers of forest degradation need to be controlled, especially in old-growth miombo, to maintain forest health and prevent decline in biomass.

Redefining temperate forest responses to climate and disturbance in the eastern United States: New insights at the mesoscale

AbstractAimClimate and disturbance alter forest dynamics, from individual trees to biomes and from years to millennia, leaving legacies that vary with local, meso‐ and macroscales. Motivated by recent insights in temperate forests, we argue that temporal and spatial extents equivalent to that of the underlying drivers are necessary to characterize forest dynamics across scales. We focus specifically on characterizing mesoscale forest dynamics because they bridge fine‐scale (local) processes and the continental scale (macrosystems) in ways that are highly relevant for climate change science and ecosystem management. We revisit ecological concepts related to spatial and temporal scales and discuss approaches to gain a better understanding of climate–forest dynamics across scales.LocationEastern USA.Time periodLast century to present.Major taxa studiedTemperate broadleaf forests.MethodsWe review regional literature of past tree mortality studies associated with climate to identify mesoscale climate‐driven disturbance events. Using a dynamic vegetation model, we then simulate how these forests respond to a typical climate‐driven disturbance.ResultsBy identifying compound disturbance events from both a literature review and simulation modelling, we find that synchronous patterns of drought‐driven mortality at mesoscales have been overlooked within these forests.Main conclusionsAs ecologists, land managers and policy‐makers consider the intertwined drivers of climate and disturbance, a focus on spatio‐temporal scales equivalent to those of the drivers will provide insight into long‐term forest change, such as drought impacts. Spatially extensive studies should also have a long temporal scale to provide insight into pathways for forest change, evaluate predictions from dynamic forest models and inform development of global vegetation models. We recommend integrating data collected from spatially well‐replicated networks (e.g., archaeological, historical or palaeoecological data), consisting of centuries‐long, high‐resolution records, with models to characterize better the mesoscale response of forests to climate change in the past and in the future.

Eкоморфічний аналіз рослинного покриву територій електричних підстанцій

Досліджено рослинний покрив на територіях енергетичних підстанцій, вста-новлено особливості їх екоморфічної організації та визначено напрямки трансфор-мації рослинного покриву за умов забруднення ґрунту технологічною олією. У ре-зультаті проведеного дослідження встановлено, що на території ділянок електрич-них підстанцій видовий склад угруповань рослин представлений 118 видами. В кон-трольних умовах середнє значення проективного покриття рослинності становить79,68 %. За умов забруднення ґрунту технологічною олією проективне покриття рос-линності значно знижується до рівня 7,16 %. Основними трендами трансформаціїекологічної структури біогеоценотичного покриву за умов забруднення ґрунту тех-нологічною олією є збільшення частки однорічних рудерантів, аридизація режимувологості та збіднення ефективної родючості едафотопу.

Population dynamics has greater effects than climate change on tree species distribution in a temperate forest region

AbstractAimPopulation dynamics and disturbances have often been simplified or ignored when predicting regional‐scale tree species distributions in response to climate change in current climate‐distribution models (e.g., niche and biophysical process models). We determined the relative importance of population dynamics, tree harvest, climate change, and their interaction in affecting tree species distribution changes.LocationCentral Hardwood Forest Region of the United States.Major taxa studiedTree species.MethodsWe used a forest dynamic model, LANDIS PRO that accounted for population dynamics, tree harvest, and climate change to predict tree species’ distributions at 270 m resolution from 2000 to 2300. We quantified the relative importance of these factors using a repeated measures analysis of variance. We further investigated the effects of each factor on changes in species distributions by summarizing extinction and colonization rates.ResultsOn average, population dynamics was the most important factor affecting tree species distribution changes. Tree harvest was more important than climate change by 2100 whereas climate change was more important than harvest by 2300. By end of the 21st century, most tree species expanded their distributions irrespective of any climate or harvest scenario. By 2300, most northern, some southern, and most widely distributed species contracted their distributions while most southern species, some widely distributed species, and few northern species expanded their distributions under warmer climates with tree harvest. Harvest accelerated or ameliorated the contractions and expansions for species that were negatively or positively affected by climate change.Main conclusionsOur results suggest that population dynamics and tree harvest can be more important than climate change and thus should be explicitly included when predicting future tree species’ distributions. Understanding the underlying mechanisms that drive tree species distributions will enable better predictions of tree species distributions under climate change.

Impacts of shaded agroforestry management on carbon sequestration, biodiversity and farmers income in cocoa production landscapes

Conversion of shaded agroforests to unshaded monocultures endangers the resilience of tropical landscapes. Landscape-scale impacts of alternative shade managements have rarely been assessed. This study explored plantation- and landscape-level impacts of different shade management strategies on aboveground biomass, functional group diversity, and economic potential of cocoa production in northern Ecuador. We simulated several cocoa shade management scenarios, using the dynamic forest model LANDIS-II: (i) ‘baseline’ projections representing the current mosaic of traditional agroforests, planted agroforests, and unshaded monoculture plantations; (ii) ‘traditional’ agroforestry shaded by native fruit and timber trees; (iii) ‘planted’ agroforests shaded by planted fruit trees; and (iv) ‘monoculture’ unshaded plantations. The impacts of setting aside 20, 30, and 40% of cocoa plantations for natural regeneration was tested for the monoculture scenario. Traditional agroforests shaded by native trees stored up to 7% more aboveground biomass and had higher abundances of rare functional groups compared to monocultures after 50 years of simulation. Smaller effects were found for planted agroforests. Shaded plantations and land set aside for natural regeneration reduced forest fragmentation at the landscape level. The estimated yield gap for monoculture and shaded plantations could not be compensated by additional revenues for carbon storage at current carbon market price. Improving payment-for-ecosystem services and certification schemes are needed to incentivize smallholders to maintain substantial non-cocoa tree cover that may provide an environmental-friendly way to improve economic potential and food security for smallholders, while supporting biomass and functional group diversity at the landscape level.

Calibration of forest 137Cs cycling model ”FoRothCs” via approximate Bayesian computation based on 6-year observations from plantation forests in Fukushima

Predicting the environmental fate of 137Cs in forest ecosystems along with the concentrations of 137Cs in tree parts are important for the managements of radioactively contaminated forests. In this study, we calibrate the Forest RothC and Cs model (FoRothCs), a forest ecosystem 137Cs dynamics model, using observational data obtained over six years from four forest sites with different levels of 137Cs contamination from Fukushima Prefecture. To this end, we applied an approximate Bayesian computation (ABC) technique based on the observed 137Cs concentrations (Bq kg−1) of five compartments (leaf, branch, stem, litter, and soil) in a Japanese cedar plantation. The environmental decay (increment) constants of the five compartments were used as the summary statistics (i.e., the metric for model performance) to infer the five parameters related to 137Cs transfer processes in FoRothCs. The ABC technique successfully reconciled the model outputs with the observed trends in 137Cs concentrations at all sites during the study period. Furthermore, the estimated parameters are in agreement with the literature values (e.g., the root uptake rates of 137Cs). Our study demonstrates that model calibration with ABC based on the trends in 137Cs concentrations of multi compartments is useful for reducing the prediction uncertainty of 137Cs dynamics in forest ecosystems.

Simulation of succession in a neotropical forest: High selective logging intensities prolong the recovery times of ecosystem functions

There is increasing concern, to what extent production forests in the Neotropics are sustainably managed. The implementation of effective forest management strategies that are ecologically beneficial plays thus a central role to prevent forest degradation. However, to identify effective forest management strategies, there is a need for methods supporting the decision-making process.The main objective of our study is to analyze the mid- and long-term impacts of different management intensities, such as varying the minimum stem diameter of harvestable commercial trees, on the dynamic and structure of a species-rich tropical lowland forest of French Guiana. Therefore, we have applied the management module of a dynamic forest model and analyzed simulation experiments for undisturbed forest growth and selective logging.For the first time we were able to quantify the mean recovery times of multiple ecosystem functions and properties (biomass, gross primary production, leaf area index, Shanon diversity, timber volume) after selective logging.Accordingly, we validated simulation results (biomass, number of trees harvested) of selective logging with forest inventory data from the last 32 years. The forest model reliably reproduces the observed pre-logging biomass, tree-size distribution, and logging intensity (10 trees/ha, 39 m3/ha). In addition, it became clear how strongly management with higher logging intensities influences the forest in the long term: (1) the mean recovery times of the investigated ecosystem functions were significantly extended. With very intensive logging (116 m3/ha), the average recovery time of forest biomass was almost twice as long as in a moderate simulation scenario (tint 138 a, tmod 77 a). Similar patterns were observed for other ecosystem functions, e.g. timber volume (tint 158 a, tmod 62 a). (2) Additionally, the functional composition shifted, as up to 30% pioneer tree species in particular invaded the forest.This innovative use of forest growth models may help in the development of ecologically reasonable forest management strategies.

Recent rising temperatures drive younger and southern Korean pine growth decline

The Earth has experienced an unequivocal warming, with the warmest period of the past 150 years occurring in the last three decades. Korean pine (Pinus koraiensis), a key tree species in northeast Asia, is predicted to be particularly vulnerable to climate change. Here, we use dendrochronological methods to test whether the observed growth decline of Korean pine in northeast China is related to climate warming and whether climate-growth responses varied with age. A total of 628 cores from 401 trees across 16 sites were sampled over the entire distribution area of Korean pine in China. Samples were divided into three age classes: younger (50–130 years), middle (131–210 years), and older trees (>210 years), and measured by the ring-width index and basal area increment (BAI). Results showed a significant decline in BAI in most sites coinciding with an increase of temperature in the growing season and a decrease in precipitation since the 1980s. Meanwhile, we found that temperature-induced growth decline was significantly related to tree age. The BAI of younger trees decreased significantly and sharply (0.44 cm2 year−1, P < 0.0001), while old trees either decreased slightly or stabilized (0.04 cm2 year−1, P = 0.33). Tree growth in the southernmost locations was more likely to decline, what was most likely a result of forest-stand age. The age-related growth decline induced by climate warming might be explained by tree species traits, differences in growth rates between age classes and their relation to stress, changes in root system, competition/stand structure or physiological mechanisms. Our results might also predict that early stand process-thinning is exacerbated by warming and drying. This research informs that the age effect of growth response to rising temperature should be considered in forest management under climate change, and particularly models of future carbon cycle patterns and forest dynamics.

Effects of species biological traits and environmental heterogeneity on simulated tree species distribution shifts under climate change

Demographic processes (fecundity, dispersal, colonization, growth, and mortality) and their interactions with environmental changes are not well represented in current climate-distribution models (e.g., niche and biophysical process models) and constitute a large uncertainty in projections of future tree species distribution shifts. We investigate how species biological traits and environmental heterogeneity affect species distribution shifts. We used a species-specific, spatially explicit forest dynamic model LANDIS PRO, which incorporates site-scale tree species demography and competition, landscape-scale dispersal and disturbances, and regional-scale abiotic controls, to simulate the distribution shifts of four representative tree species with distinct biological traits in the central hardwood forest region of United States. Our results suggested that biological traits (e.g., dispersal capacity, maturation age) were important for determining tree species distribution shifts. Environmental heterogeneity, on average, reduced shift rates by 8% compared to perfect environmental conditions. The average distribution shift rates ranged from 24 to 200myear−1 under climate change scenarios, implying that many tree species may not able to keep up with climate change because of limited dispersal capacity, long generation time, and environmental heterogeneity. We suggest that climate-distribution models should include species demographic processes (e.g., fecundity, dispersal, colonization), biological traits (e.g., dispersal capacity, maturation age), and environmental heterogeneity (e.g., habitat fragmentation) to improve future predictions of species distribution shifts in response to changing climates.

Dynamic forest vegetation models for predicting impacts of climate change on forests: An Indian perspective

Understanding climate change vulnerability of Indian forests has received wider attention in recent years and a number of assessments with different approaches have emerged over time. These assessments have mostly used climate-sensitive vegetation models to explain the climate change impacts. In these studies, trees constituting a particular forest are often clubbed together into small number of groups having similar functional traits referred as Plant Functional Types (PFTs). Most of the Forest Vegetation Models (FVMs) are still in their developmental stage and there have been attempts at various levels to develop more versatile and precise models. Several developing countries, including India, still lag behind in developing dynamic vegetation models (DVMs), which could be appropriate for the local applications to predict the impact on forests at regional level. This is restrained mainly because of the lack of long-term observations with respect to various interacting biotic, abiotic and climatic (or environmental) variables in a forest ecosystem, like water and nitrogen use efficiency, response to elevated concentration of CO2, nutrient cycling, net primary productivity, etc. The observations on influence of the environmental variables on forest ecosystems are available in discrete form. Existing FVMs integrate observations more appropriately for their place of origin for which they have been developed. Different types of forests in different climatic zones are supposed to respond differently to climatic changes. Hence, it is imperative that models are developed for the specific biogeographic regions in order to predict the influences more accurately. It may not be wise to use existing FVMs in their pristine form for all of the region without considering the regional influences. Various challenges associated with the usage of the generic models of external origin with special reference to Integrated Biosphere Simulator (IBIS) model - being widely used and accepted in Indian policy documents- is presented in this paper. We also discuss on the need for developing a regional FVM for climate change impact studies, so that the impact prediction is more precise and reliable.

Sensitivity of forest water balance and physiological drought predictions to soil and vegetation parameters – A model-based study

A global sensitivity analysis was conducted on a dynamic water balance model with 19 parameters describing canopy structure, stomatal regulation and soil characteristics, to quantify the importance of vegetation and soil properties in coupled models of hydrology and forest dynamics. Main outputs were total evaporation, as well as a physiological drought index calculated from actual and potential transpiration. Parameter sensitivity was assessed at ten temperate to sub-alpine locations, covering both water-limited and energy-limited sites.Varying parameter values within plausible ranges led to differences of several hundreds of mm/year in predicted long-term evaporation. Root zone storage is the most important parameter at drier stations, whereas canopy and stomatal parameters become more important where soil moisture is less limiting. Physiological drought also depends strongly on root zone properties, while canopy structure only matters at the drier sites. Stomatal sensitivity to dry air substantially contributed to drought stress at the more humid sites.

Analysis of ecological thresholds in a temperate forest undergoing dieback.

Positive feedbacks in drivers of degradation can cause threshold responses in natural ecosystems. Though threshold responses have received much attention in studies of aquatic ecosystems, they have been neglected in terrestrial systems, such as forests, where the long time-scales required for monitoring have impeded research. In this study we explored the role of positive feedbacks in a temperate forest that has been monitored for 50 years and is undergoing dieback, largely as a result of death of the canopy dominant species (Fagus sylvatica, beech). Statistical analyses showed strong non-linear losses in basal area for some plots, while others showed relatively gradual change. Beech seedling density was positively related to canopy openness, but a similar relationship was not observed for saplings, suggesting a feedback whereby mortality in areas with high canopy openness was elevated. We combined this observation with empirical data on size- and growth-mediated mortality of trees to produce an individual-based model of forest dynamics. We used this model to simulate changes in the structure of the forest over 100 years under scenarios with different juvenile and mature mortality probabilities, as well as a positive feedback between seedling and mature tree mortality. This model produced declines in forest basal area when critical juvenile and mature mortality probabilities were exceeded. Feedbacks in juvenile mortality caused a greater reduction in basal area relative to scenarios with no feedback. Non-linear, concave declines of basal area occurred only when mature tree mortality was 3–5 times higher than rates observed in the field. Our results indicate that the longevity of trees may help to buffer forests against environmental change and that the maintenance of old, large trees may aid the resilience of forest stands. In addition, our work suggests that dieback of forests may be avoidable providing pressures on mature and juvenile trees do not pass critical thresholds.

How cyclical and predictable are Central European temperate forest dynamics in terms of development phases?

AbstractQuestionsRecently there have been vital discussions about the validity of the European patch‐mosaic conceptual model of forest dynamics – the traditional concept of a shifting patch‐mosaic of development stages and phases, also known as the forest cycle concept. Here we try to answer the fundamental questions of this debate: (1) how much do forest dynamics proceed along a predictable path (in a chronological sequence: growth—optimum—breakdown); or (2) vice versa, are the patches rather a result of disturbances and/or other stochastic growth and mortality patterns?LocationFive long‐term research plots in four different study sites of Central European natural temperate forests.MethodsThe long‐term evolution of forest development phases was analysed with a GIS‐based, spatially explicit, fully reproducible method enabling accurate verification of the functionality of the model forest cycle. We analysed long‐term transitions among forest development phases from the 1970s through the 1990s to 2000s. Observed phase‐to‐phase transitions were compared to a random transition model. We identified preferential pathways within the forest cycle model as well as the proportion of cyclic/acyclic transitions.ResultsIn total, across all sites and observation periods, about 65% of all observed phase‐to‐phase transitions were realized through preferential pathways, about 28% of observed transitions went along pathways of random frequency and only about 7% of observed transitions were realized through uncommon development pathways. On the other hand, less than 40% of all observed transitions might be classified as cyclic (following the model cycle), and thus more than 60% of the transitions were acyclic (moving across or backward in the model cycle). The overall pattern of all observed transitions resembled a complex web rather than a simple repeating cycle.ConclusionsAlthough in all sites we documented signs of the cyclic and predictable development anticipated by the forest cycle concept, the predominance and stochastic nature of multiple acyclic development pathways gave rise to reasonable doubts on the legitimacy and usability of the concept for descriptions of forest dynamics. On the other hand, the verification of the concept may contribute significantly to our understanding of the complexity of forest dynamics.

Linking lidar and forest modeling to assess biomass estimation across scales and disturbance states

Light detection and ranging (lidar) is currently the state-of-the-art remote sensing technology for measuring the 3D structures of forests. Studies have shown that various lidar-derived metrics can be used to predict forest attributes, such as aboveground biomass. However, finding out which metric works best at which scale and under which conditions requires extensive field inventories as ground-truth data. The goal of our study was to overcome the limitations of inventory data by complementing field-derived data with virtual forest stands from a dynamic forest model. The simulated stands were used to compare 29 different lidar metrics for their utility as predictors of tropical forest biomass at different spatial scales. We used the process-based forest model FORMIND, developed a lidar simulation model, based on the Beer-Lambert law of light extinction, and applied it to a tropical forest in Panama. Simulation scenarios comprised undisturbed primary forests and stands exposed to logging and fire disturbance regimes, resulting in mosaics of different successional stages, totaling 3.7 million trees on 4200ha. The simulated forest was sampled with the lidar model. Several lidar metrics, in particular height metrics, showed good correlations with forest biomass, even for disturbed forest. Estimation errors (nRMSE) increased with decreasing spatial scale from <10% (200-m scale) to >30% (20-m scale) for the best metrics. At the often used 1-ha scale, the top-of-canopy height obtained from canopy height models with fine to relatively coarse pixel resolutions (1 to 10m) yielded the most accurate biomass predictions, with nRMSE<6% for undisturbed and nRMSE<9% for disturbed forests. This study represents the first time dynamic modeling of a tropical forest has been combined with lidar remote sensing to systematically investigate lidar-to-biomass relationships for varying lidar metrics, scales and disturbance states. In the future, this approach can be used to explore the potential of remote sensing of other forest attributes, e.g., carbon dynamics, and other remote sensing systems, e.g., spaceborne lidar and radar.