Tree Basal Area Growth Research Articles

Differential modulation of crown allometry and stem growth at gap edges in five European tree species by drought conditions

BackgroundIn Central Europe, forests are increasingly affected by various disturbances, resulting in an increasing gap formation in the canopy. In order to support goal-oriented management, more knowledge is required about the acclimation of the crown and its effects on the basal area growth of trees at the edge of a gap. MethodsThis work compared trees' growth and crown structure at the edge of a transient gap, with a gap size of more than 80 ​m2, with trees in the stand that were at least 30 ​m away from the gap. A total of 249 European beeches (Fagus sylvatica L.), Norway spruces (Picea abies L. Karst), Scots pines (Pinus sylvestris L.), oaks (Quercus spp.; Quercus petraea (Matt.) Liebl., Quercus robur L.), and silver firs (Abies alba Mill.) were examined on long-term experimental plots in southern Germany. Various crown measures were developed and calculated using high-resolution terrestrial laser scanning (TLiDAR) to capture the three-dimensional crown structures. Growth responses to edge conditions were measured based on tree rings. Using linear mixed models, we predict the basal area increment of edge trees relative to trees in the stand under wet and dry soil moisture conditions after the gap formation. ResultsWe identified i) species-specific acclimation of the crown of edge trees after the gap formation, ii) under wet soil moisture conditions a growth increase of 25%–45% for beech, pine, and oak edge trees and growth losses of 5%–60% for spruce and fir and iii) coniferous tree species benefited from the edge position regarding their basal area increment under dry soil moisture conditions and deciduous tree species grew regardless of the soil moisture conditions at the edge of a gap. ConclusionGaps have a species-specific effect on the habitus and growth of edge trees and can have both positive and negative impacts on silviculture.

Modelling individual tree maximum basal area growth rates of five tall eucalypt species growing in even-aged forests

Inventory plot data were available providing over 87,000 individual tree basal area growth rates from even-aged native forests of three ash eucalypts (Eucalyptus regnans, E. obliqua, and E. delegatensis), from temperate regions, and two other species from more sub-tropical climes (E. grandis and E. pilularis). Models were developed relating maximum observed growth rates for these species in relation to tree size when, presumably, trees were under ideal environmental conditions and without competition from neighbours for site growth resources. These maximum growth rates increased with increasing tree size to a maximum of their own and then declined as tree size (hence age) increased further. The tree sizes, at which these maximum growth rates reached their maxima, were much greater for the ash eucalypts than for the other two species. It is hypothesised that the ash eucalypts may have evolved physiological characteristics that make them more efficient in compensating for the well-known physiological constraints imposed on growth rates as trees grow to great heights and ages.

Varying growth response of Central European tree species to the extraordinary drought period of 2018 – 2020

Droughts have intensified in Central Europe and will likely become a major driver of forest ecosystem change in the future. Regional studies are needed to understand drought impacts on forests and to provide guidance for adaptive management. In this study, we have investigated the effects of an extraordinary drought period in 2018 – 2020 on tree growth in the State of Bavaria (Germany). We (i) assessed overall changes in tree growth compared to pre-drought conditions, (ii) mapped the spatial configuration of drought and its impact on growth across ecoregions, (iii) quantified the standardized drought effect for the most abundant tree species, and (iv) analyzed the inter- and intraspecific variability in growth responses to drought.Covering a large environmental gradient, we compared 3,462 tree basal area growth records at 200 inventory plots with the pre-drought period of 2006 – 2017. We analyzed drought impacts on tree growth using nonparametric randomization tests and linear quantile mixed models (LQMMs).Median annual tree growth declined by 41.3% during drought. Decreases in growth were statistically significant for 13 out of 20 species. Growth reductions were most distinct in northwestern ecoregions of Bavaria. After controlling for other covariates of tree growth, the most abundant conifers, Picea abies [Karst.] and Pinus sylvestris [L.], were overall more susceptible than the common broadleaves, Fagus sylvatica [L.], Quercus robur [L.], and Quercus petraea [Matt.]. Yet, all species exhibited a high intraspecific variation in drought response.Altering tree species composition is a key strategy to adapt forest ecosystems. Our study reveals high potential to mitigate future drought impacts by admixing P. abies- and P. sylvestris-dominated forests with more drought-adapted broadleaved tree species. In addition, the high intraspecific variability in drought susceptibility indicates potential to promote provenances or individuals with low drought sensitivity to reduce the local loss of tree species.

Species admixture can increase potential tree growth and reduce competition

Trees often show better growth in mixed as opposed to monospecific neighborhoods as consequence of competition reduction and facilitation between species. However, it can be challenging to discern the effect of these factors as they occur simultaneously, so often they are jointly refereed as complementarity. By using tree growth models based on potential tree growth reduced by a competition modifier and including species mixing effects on both components (potential tree growth and competition modifier), we aim to verify that tree potential growth is modified by admixture, which may provide further information on species interactions and complementarity.We used tree data from the Spanish National Forest Inventory, selecting plots located in two different mixtures, Scots pine – European beech and Scots pine – Oak mixtures, as well as in the corresponding monospecific stands of those species. To analyse whether the species mixture increases the potential basal area growth, we developed linear mixed quantile regressions to model the potential growth, while to analyse the competition reduction we developed linear mixed models. We include the Martonne aridity index as a measure of the site conditions in the models to explore whether climate conditions modify the effects of species mixture.Our results show a slight effect of the mixture on the potential basal area growth of pine while the potential growth of beech clearly benefited from the pine/beech mixtures. For the pine/oak mixtures the potential growth of both species was higher in mixtures than in monospecific stands. Moreover, we found a positive influence of humidity on potential growth for all the species and mixtures, although the magnitude of the effect was less important for beech and more notable in the case of the pine/oak mixtures. We also found that for the studied species, admixed species reduced competition, with lower inter-specific than intra-specific competition effects, and that these effects were mediated by climate conditions.We concluded that the potential tree basal area growth is influenced by the species admixture, which suggest that species mixing effects can be relevant also under low stand densities. Our results highlight the importance of integrating the effect of species interactions on both the potential growth of trees and the competition modifier when the aim of the research is to further our understanding of species interactions.

Neighborhood dissimilarity consistently attenuates competition stress on tree growth under altered water availability in a natural boreal forest

Tree growth regulates forest productivity and carbon sequestration. Although there has been evidence showing positive effects of neighborhood diversity on tree growth, few have experimentally demonstrated how tree growth may respond to neighborhood diversity in natural forests under altered water availability, which is anticipated to occur more frequently with ongoing global climate change. We examined three-year individual tree basal area growth under the water alteration treatments of reduced (-25% throughfall during the growing season), ambient and added (+25% throughfall during the growing season) rainfall in the broadleaf stands, conifer stands and their mixtures of a young natural boreal forest. We quantified neighborhood drought tolerance dissimilarity, phylogeny dissimilarity and neighborhood crowding based on individual tree sizes and the distance between them. We found that the tree growth on average did not change significantly with water alteration but decreased with neighborhood crowding, with the negative crowding effect being more pronounced in water reduction treatment than in ambient and water addition treatments. Higher neighborhood dissimilarity of drought tolerance and phylogeny promoted tree growth consistently across all water conditions. Moreover, the positive effects of neighborhood dissimilarity of drought tolerance and phylogeny became more pronounced with increasing neighborhood crowding. Our results suggest that promoting species mixtures in boreal forests may sustain higher boreal forest productivity under changing water availability.

Water Availability Determines Tree Growth and Physiological Response to Biotic and Abiotic Stress in a Temperate North American Urban Forest

Warmer temperatures and frequent drought directly affect urban tree health. Both abiotic conditions also affect tree health via increased density of some insect pests. Warming is predicted to benefit urban trees by increasing carbon sequestration and allocation to biomass. However, increased drought and pests are rarely considered despite often co-occurring with heat. To determine the combined effects of these abiotic and biotic factors, we manipulated water availability for established urban red maple trees across a gradient of warming and pest density and measured leaf-level processes and tree growth over two years. We find that water availability is a major determinant of tree growth, physiological processes, and resilience to urban stress factors. Maples performed better with more water, which also made them resistant to effects of temperature and pest density. However, when drought became too severe, leaf-level processes declined with warming. Tree basal area growth was unaffected after two years, but stem elongation increased with increasing water, temperature, and pest density. We discuss potential mechanisms driving these responses and the implications in the context of urban forest management. Urban forest designs that reduce drought and align species adaptations to local conditions are critical for designing more resilient and productive urban forests.

Models Relating Individual Tree Basal Area Growth Rates to Tree Basal Areas in Even-Aged, Monoculture Forest Stands

As trees grow larger in even-aged, monoculture forests, stand density increases, taller trees shade smaller trees and a group of smaller, suppressed trees develops that may show little or no growth. Subsequent mortality is most common from this group. This work compares three models that may describe well the relationship between individual tree basal area growth rates and tree basal areas in a forest stand when a suppressed group of trees is present or not. The models are tested using a large collection of data from permanent sample plots in blackbutt (Eucalyptus pilularis Smith) forests in subtropical eastern Australia. An example is given for one stand showing how model parameter values may change as the stand ages; this illustrates how these models have potential for use in the first stage of model development to relate individual tree growth rates to tree sizes and stand characteristics. Such models may then be used widely across the forest population under consideration.

Tree-level differences in Norway spruce and Scots pine growth after extreme thinning treatments

ABSTRACT We studied tree-level dynamics (stem slenderness and growth) in spruce- and pine-dominated stands after intermediate commercial thinning of different type (low, crown normal, and crown strict) and intensity (standard and extreme), for two 5-years growth periods. Thinning treatments were included in modeling as numerical variables based on how they changed the stand- and tree-level conditions (in terms of mean diameter of remaining trees and basal area of larger trees removed). Stem slenderness significantly decreased with time for both species and all types only in the extreme intensity (excluding low thinning for pine). Regarding basal area growth, for both species it was slightly higher in low than crown thinning, and much higher in extreme intensity for all thinning types. Pine had a lower basal area growth in the second period after thinning compared with the first one. Height growth differences were not found across treatments. Concluding, extreme thinning increased individual tree basal area growth and decreased stem slenderness for both species compared with thinning carried out according to the standard guidelines. Across types, there were only small differences, hence crown thinning seems a viable option to the widely used low thinning in Fennoscandia.

Species stratification and weather conditions drive tree growth in Scots pine and Norway spruce mixed stands along Europe

Mixed forests are suggested as a strategic adaptation of forest management to climate change. Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) are tree species of high economic and ecological value for European forestry. Both species coexist naturally in a large part of their distributions but there is a lack of knowledge on the ecological functioning of mixtures of these species and how to manage such stands. This paper analyses these species’ intra- and inter-specific competition, including size-symmetric vs. size-asymmetric competition, and explore the effect of weather conditions on tree growth and competition. We studied basal area growth at tree level for Scots pine and Norway spruce in mixed versus pure stands in 22 triplets of fully-stocked plots along a broad range of ecological conditions across Europe. Stand inventory and increment cores provided insights into how species mixing modifies tree growth compared with neighbouring pure stands. Five different competition indices, weather variables and their interactions were included and checked in basal area growth models using a linear mixed model approach. Interspecific size-asymmetric competition strongly influenced growth for both tree species, and was modulated by weather conditions. However, species height stratification in mixed stands resulted in a greater tree basal area growth of Scots pine (10.5 cm2 year−1) than in pure stands (9.3 cm2 year−1), as this species occupies the upper canopy layer. Scots pine growth depended on temperature and drought, whereas Norway spruce growth was influenced only by drought. Interspecific site-asymmetric competition increased in cold winters for Scots pine, and decreased after a drought year for Norway spruce. Although mixtures of these species may reduce tree size for Norway spruce, our results suggest that this could be offset by faster growth in Scots pine. How inter-specific competition and weather conditions alter tree growth may have strong implications for the management of Scots pine-Norway spruce mixtures along the rotation period into the ongoing climate change scenario.

Predicting individual tree growth of high-value timber species in mixed conifer-broadleaf forests in northern Japan using long-term forest measurement data

ABSTRACT Quantifying individual tree growth of economically high-value timber species is important for the simulation and development of forest management options. Long-term permanent plot data provides crucial information of forest stand dynamics that can be used to predict individual tree growth. In this study, we developed individual tree basal area growth models of three high-value timber species: monarch birch (Betula maximowicziana), castor aralia (Kalopanax septemlobus), and Japanese oak (Quercus crispula) in a cool temperate mixed forest in northern Japan using long-term measurement data (1968–2016) collected in permanent plots. Data included species, diameter at breast height, and survival status, and stand management history. We applied linear mixed-effects modelling to predict the individual tree basal area growth as a function of individual tree size, competition, and forest management. Model prediction followed by leave-one-out cross validation revealed a correlation between predicted and observed basal area increments with r values of 0.62, 0.73, and 0.70 and root mean square errors values of 10.44, 7.91, and 11.62 cm2/year for monarch birch, castor aralia, and Japanese oak, respectively. The individual tree growth models developed in this study will provide valuable information for species-specific forest management of economically high-value timber species.

Competition influences tree growth, but not mortality, across environmental gradients in Amazonia and tropical Africa.

Competition among trees is an important driver of community structure and dynamics in tropical forests. Neighboring trees may impact an individual tree’s growth rate and probability of mortality, but large‐scale geographic and environmental variation in these competitive effects has yet to be evaluated across the tropical forest biome. We quantified effects of competition on tree‐level basal area growth and mortality for trees ≥10‐cm diameter across 151 ~1‐ha plots in mature tropical forests in Amazonia and tropical Africa by developing nonlinear models that accounted for wood density, tree size, and neighborhood crowding. Using these models, we assessed how water availability (i.e., climatic water deficit) and soil fertility influenced the predicted plot‐level strength of competition (i.e., the extent to which growth is reduced, or mortality is increased, by competition across all individual trees). On both continents, tree basal area growth decreased with wood density and increased with tree size. Growth decreased with neighborhood crowding, which suggests that competition is important. Tree mortality decreased with wood density and generally increased with tree size, but was apparently unaffected by neighborhood crowding. Across plots, variation in the plot‐level strength of competition was most strongly related to plot basal area (i.e., the sum of the basal area of all trees in a plot), with greater reductions in growth occurring in forests with high basal area, but in Amazonia, the strength of competition also varied with plot‐level wood density. In Amazonia, the strength of competition increased with water availability because of the greater basal area of wetter forests, but was only weakly related to soil fertility. In Africa, competition was weakly related to soil fertility and invariant across the shorter water availability gradient. Overall, our results suggest that competition influences the structure and dynamics of tropical forests primarily through effects on individual tree growth rather than mortality and that the strength of competition largely depends on environment‐mediated variation in basal area.

Species Mixing Effects on Height–Diameter and Basal Area Increment Models for Scots Pine and Maritime Pine

Models that incorporate known species-mixing effects on tree growth are essential tools to properly design silvicultural guidelines for mixed-species stands. Here, we developed generalized height–diameter (h-d) and basal area growth models for mixed stands of two main forest species in Spain: Scots pine (Pinus sylvestris L.) and Maritime pine (Pinus pinaster Ait.). Mixed-effects models were fitted from plot measurement and tree rings data from 726 Scots pine and 693 Maritime pine trees from mixed and pure stands in the Northern Iberian Range in Spain, with the primary objective of representing interactions between the species where they are interspersed in mixtures of varying proportions. An independent dataset was used to test the performance of the h-d models against models previously fitted for monospecific stands of both species. Basal area increment models were evaluated using a 10-fold block cross-validation procedure. We found that species mixing had contrasting effects on the species in both models. In h-d models, the species-mixing proportion determined the effect of species interactions. Basal area growth models showed that interspecific competition was influential only for Maritime pine; however, these effects differed depending on the mode of competition. For Scots pine, tree growth was not restricted by interspecies competition. The combination of mixed-effect models and the inclusion of parameters expressing species-mixing enhanced estimates of tree height and basal area growth compared with the available models previously developed for pure stands. Although the species-mixing effects were successfully represented in the fitted models, additional model components for accurately simulating the stand dynamics of mixtures with Scots pine and Maritime pine and other species mixtures require similar model refinements. Upon the completion of analyses required for these model refinements, the degree of improvement in simulating growth in species mixtures, including the effects of different management options, can be evaluated.

Species Mixing Effects on Forest Productivity: A Case Study at Stand-, Species- and Tree-Level in the Netherlands

Many monoculture forests have been converted to mixed-species forests in Europe over the last decades. The main reasons for this conversion were probably to increase productivity, including timber production, and enhance other ecosystem services, such as conservation of biodiversity and other nature values. This study was done by synthesizing results from studies carried out in Dutch mixed forests compared with monoculture stands and evaluating them in the perspective of the current theory. Then we explored possible mechanisms of higher productivity in mixed stands, in relation to the combination of species, stand age and soil fertility, and discussed possible consequences of forest management. The study covered five two-species mixtures and their corresponding monoculture stands from using long-term permanent forest plots over multiple decades as well as two inventories (around 2003 and 2013) across the entire Netherlands. These forest plot data were used together with empirical models at total stand level, species level and tree level. Overyielding in Douglas-fir–beech and pine–oak mixtures was maintained over time, probably owing to the intensive thinning and was achieved on the poorer soils. However, this overyielding was not always driven by fast-growing light-demanding species. On individual tree level, intra-specific competition was not necessarily stronger than inter-specific competition and this competitive reduction was less seen at lower soil fertility and dependent on species mixtures. Moreover, size-asymmetric competition for light was more associated with tree basal area growth than size-symmetric competition for soil resources. Overall, this study suggests a substantial potential of species mixing for increasing productivity and implies developing forest management strategies to convert monospecific forests to mixed-species forests that consider the complementarity in resource acquisition of tree species.

Contrasting effects of flooding on tree growth and stand density determine aboveground production, in baldcypress forests

Stand production, a common indicator of site productivity, is often low in flooded wetland forests. However, it remains unclear whether the low production reflects flood stress limiting tree growth, flood disturbance limiting tree density, or both. Here, we investigate how tree growth and stand density vary in baldcypress forests, across gradients of flooding by both fresh and saline waters. We used three investigations to conduct this analysis: (a) a meta-analysis of previously reported tree- and stand-production measurements; (b) an analysis of tree cores from 204 baldcypress trees in 16 sites; and (c) intensive stand surveys and growth measurements across two freshwater flooding gradients in southern Louisiana. The meta-analysis (a) showed that stand production generally varies linearly with stand density, and that detrimental effects of flooding on tree-level growth are only consistently evident in saline systems. The tree-core investigation (b) showed that tree basal area growth was largely a function of tree sapwood area, but basal area growth per sapwood area (i.e. sapwood efficiency, a measure of how efficiently trees grow per growing space occupied) was higher in the more flooded sites of freshwater gradients and lower in the more saline sites of salinity gradients. The intensively studied sites (c) showed that deeper flooding was associated with sparse stands with lower production; however, trees in those sparser sites had higher sapwood efficiency, implying that the benefits of reduced competition were greater than any potential physiological limitations caused by that deeper flooding. Our findings generally show that sparser stands with saline flooding contained poorly growing trees, but sparser stands with freshwater flooding generally did not. These dichotomous effects of freshwater flooding on tree growth versus stand density demonstrate the need to conceptualize production as a dual function of disturbance effects on stand structure and environmental limitations on individual trees, each with potentially different limiting factors.

Distance-independent tree basal area growth models for Norway spruce, Douglas-fir and Japanese larch in Southern Belgium

This paper presents new harmonized distance-independent individual tree basal area growth models for Norway spruce, Douglas-fir and Japanese larch in pure even-aged stands in Southern Belgium. The selected model was originally developed for Norway spruce and Douglas-fir in neighboring France. New formulations are proposed for some of the model components in order to lower the number of fitted parameters and facilitate the fitting procedure. The resulting models integrate the most recent corresponding top-height growth models and use four simple and usually collected explanatory variables: stand age, top-height, total basal area and tree girth at breast height. The modified formulations maintain similar fitting performances and make it easier to interpret the influence of the explanatory variables on tree growth. Parameters estimates were fitted on thousands of growth measurements gathered from several monitoring plots, forest management inventories and silvicultural field experiments that represent the wide range of site conditions and of forest management scenarios applied to coniferous stands in Southern Belgium. Cross-validation of the models revealed no bias and highlighted their consistent behavior over the entire range of girth at breast height, age, top-height, site index and density represented in our dataset. Combining utility and robust performances, these models represent useful forest management tools, purposely ideal for forest simulation software development. Moreover, the flexibility and generic capabilities of the model formulation should make it easily adjustable for other species in even-aged stands.

Modelos de crecimiento de árbol individual: Aplicación del Simulador BWINPro7

Se describe el simulador de crecimiento y producción de rodales forestales BWINPro7 versión El Salto, Durango. Es una herramienta de sencillo manejo para ser utilizada por gestores y propietarios forestales como apoyo a la toma de decisiones en el manejo forestal. El programa incorpora modelos de crecimiento de árbol individual, desarrollados en los últimos años para las principales especies de pino y encino de los bosques mixtos e irregulares del noroeste de México. Específicamente, fueron incorporados al simulador de crecimiento BWINPro7: 1) modelos para estimar el diámetro de copa y la altura de fuste limpio, 2) modelos para la estimación del crecimiento en altura y área basal de árboles individuales y, 3) un modelo para la cuantificación de la mortalidad natural. Adicionalmente, el simulador puede ser usado con parcelas permanentes de inventario para describir la estructura espacial y prescribir cortas de aclareo y aprovechamientos forestales a escala industrial.

Species shade tolerance affects tree basal area growth behaviour in two eucalypt species in thinned and unthinned even-aged monoculture

ABSTRACTIndividual tree and stand basal area growth were studied in a thinning experiment established over two sites in subtropical eastern Australia. The experiment compared the less shade tolerant species Eucalyptus dunnii with the more shade tolerant Corymbia citriodora var. variegata, both grown in plantation monoculture. Growth was compared over a 2½−3 year period that immediately followed thinning at 5½−7½ years of age. Towards the end of the growth period, tree crown depths and leaf mass per unit area were measured at one site. Crown depth and leaf mass per area of C. citriodora were greater than of E. dunnii, characteristics consistent with a more shade tolerant species. Gross stand basal area growth of E. dunnii was faster than that of C. citriodora. Individual-tree basal area growth behaviour was consistent with inter-tree competition involving asymmetric competition for light. Opening the stand by thinning reduced inter-tree competition to near zero. In unthinned control stands, smaller, more shaded trees of C. citriodora were better able to retain their basal area growth rates than those of E. dunnii in the face of competition. In consequence, the more shade tolerant C. citriodora developed a more evenly spread frequency distribution of tree diameters than less shade tolerant E. dunnii. This would have consequences for the assortment of log sizes that would be available ultimately from monocultures of the two species.

Individual tree basal area growth models for Chir pine (Pinus roxberghii Sarg.) in western Nepal

The individual tree growth models are important decision-making tools in forestry. Age dependent and age independent individual tree basal area growth models were developed for Chir pine ( Pinus roxberghii Sarg.) in one of the western districts, Rukum district, in Nepal. Data from thirty-five destructively sampled trees, which were representative of all possible stand densities, site productivities, age classes, and size classes of Chir pine forests in the district, were used. Sample trees were felled and diameters and ages were measured on the cut surface of the stump (at 30 cm above the ground). Since measurements from the same stump of a tree were strongly correlated, the autoregressive error structure modelling approach was applied while specifying the model in order to reduce bias. All parameter estimates of the models were significant ( P 0.86). Residual graphs showed no serious systematic bias for all observed age classes and diameter classes. The age independent growth model showed relatively better fit statistics ( R 2 = 0.8751, RMSE = 4.8494) than

Climate modifies tree interactions in terms of basal area growth and mortality in monospecific and mixed Fagus sylvatica and Pinus sylvestris forests

Net interactions between trees vary depending on environmental conditions and other factors such as stand density, age, or between-species complementarity and/or facilitation. According to the stress gradient hypothesis, positive or facilitative interactions are more frequent in high-stress environments whereas negative or competitive interactions occur in benign environments, although recent studies highlight the influence of species composition, type of stress, ontogeny, etc. on the interaction–stress gradient pattern. The aim of this paper is to analyze whether site climatic variables are a key factor in tree interactions in mixed stands of beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.). To test how site climatic conditions modify the effect of inter-specific competition on tree basal area growth and tree mortality, growth and mortality models were fitted using monospecific and mixed sample plots located in matching site conditions selected from the Spanish National Forest Inventory in the Navarra Province. Tree competition status was broken down into four terms according to size-symmetry (size-symmetric vs. size-asymmetric) and species identity (intra-specific vs. inter-specific). The results showed that the size-symmetric inter-specific component was non-significant on beech basal area growth and had a negative effect on pine growth. The effect of size-asymmetric inter-specific competition was always non-significant, resulting in a higher basal area growth when the admixed species are of a larger size. The interaction between annual precipitation and this inter-specific competition effect was much more pronounced on beech than on pine. Inter-specific competition had a negative effect on pine growth under better climatic conditions and a positive effect at dryer sites, while beech always benefited from the presence of pine, although the benefit was greater where climatic site conditions were better. In tree mortality models, pine mortality increased with the proportion of beech, while beech mortality was lower as the proportion of pine increased. Precipitation modified the inter-specific competition effect on tree mortality although the site influence was less relevant than on tree growth. For pine mortality, the negative effect of beech admixture was stronger at lower mean annual precipitation, while in the case of beech the positive effect of pine increased at higher levels of precipitation. The influence of climate on the effect of competition, the variation in their strength depending on the mode of competition (size-symmetric or size-asymmetric), along with the inter-specific competition component, highlight the importance of considering the effect of site conditions on between-species interactions when modeling tree growth and mortality. The species-specific patterns of variation in tree interactions along climatic gradients and the differences in tree growth and mortality corroborate the need to consider the nature of stress-limiting factors and species composition and the importance of analyzing both dynamic processes simultaneously.

Compatibility of whole-stand and individual-tree models using composite estimators and disaggregation

This study presents a new approach in linking models with different levels of resolution. Data from 50 permanent sample plots installed in even-aged birch (Betula alba) dominated stands were used to develop both, a whole-stand growth model and an individual-tree model. In a first step, six disaggregation approaches to link number of trees per hectare with tree survival were combined with four disaggregation approaches to link stand basal area with tree basal area growth predictions. To analyze the effect of stand variable predictions on disaggregation estimates, two different methods to obtain these predictions were evaluated: (a) 1-fold cross-validation of the stand growth model and (b) a method involving composite estimators. Therefore, altogether 48 different approaches in linking models were analyzed in this first step. In a second step, two common methods based on the use of a threshold to translate the survival tree probabilities into a discrete event, i.e. dead or alive, were combined with the four disaggregation approaches to link stand basal area with tree basal area growth predictions and the two methods to obtain stand variable predictions. Therefore, altogether 16 different approaches in linking models were analyzed in this second step. Finally, the best combinations obtained in each step were compared. Regarding the disaggregation of predicted stand density, the approach based on considering the intercept of the logit function for tree survival as a specific parameter of each sample plot and optimizing its value produced the best results. Regarding the disaggregation of stand basal area among trees, the constrained least squares method was selected, since it showed the best results among four alternative approaches. The use of composite estimators instead of the 1-fold cross validation predictions improved the accuracy of both, tree survival and tree basal area estimates, although the differences were not significant. Finally, disaggregation approaches performed better than the methods based on the use of a threshold. The results show that the combination between composite estimators and disaggregation provided compatible and reliable predictions of stand density, tree survival, stand basal area and tree basal area. The main limitation of this new approach is the dependency of accurate stand growth predictions, therefore, it should be tested in future studies with more complicated stand structures, such as mixed and un-even aged forests, or to include the effect of silvicultural treatments.