Tree Diameter Distribution Research Articles

Ecosystem-Wide Impacts of Deforestation in Mangroves: The Urabá Gulf (Colombian Caribbean) Case Study

Mangroves are ecologically important and extensive in the Neotropics, but they are visibly threatened by selective logging and conversion to pastures in the Southern Caribbean. The objective of this paper was to summarize the impacts of both threats on forest structure, species composition, aboveground biomass and carbon reservoir, species introgressions, and benthic fauna populations by collating past and current data and by using an interdisciplinary approach in the Urabá Gulf (Colombia) as a case study. Mangroves in the Eastern Coast have been decimated and have produced unskewed tree-diameter (DBH) distributions due to the overexploitation of Rhizophora mangle for poles (DBH range: 7–17 cm) and of Avicennia germinans for planks and pilings (DBH >40 cm). Selective logging increased the importance value of the light-tolerant white mangrove Laguncularia racemosa, also increasing biomass and carbon storage in this species, thus offsetting reductions in other species. Introgressions (cryptic ecological degradation) by L. racemosa and Acrostichum aureum (mangrove fern) and low densities of otherwise dominant detritivore snails (Neritina virginea) were observed in periurban basin mangroves. Finally, basin mangroves were more threatened than fringing mangroves due to their proximity to expanding pastures, villages, and a coastal city.

Bamboo overabundance alters forest structure and dynamics in the Atlantic Forest hotspot

With fast growth rates and clonal reproduction, bamboos can rapidly invade forest areas, drastically changing their original structure. In the Brazilian Atlantic Forest, where recent mapping efforts have shown that woody bamboos dominate large areas, the present study assessed the differences in soil and vegetation between plots dominated (>90% of bamboo coverage) and not dominated (<10% of coverage) by the native Guadua tagoara. Surface soil was physically and chemically analyzed, and trees at three size classes (seedling, sapling, and adult) were counted, identified and measured. New inventories were conducted to assess recruitment, mortality, and damage rates. Bamboo plots had more fertile soils (higher bases saturation and lower potential acidity) due to the preferential occurrence of G. tagoara on more clayey soils. Bamboo-dominated plots had lower density of adult trees (diameter >5cm) and lower species density. In addition, overall tree diameter distribution was very different between environments, with bamboo plots having greater concentration of small-sized trees. Such differences are probably related to the general tendency of higher mortality, recruitment, and damage rates in bamboo plots. Greater physical (wind and bamboo-induced damages) and physiological stress (heat and light) in bamboo plots are probable causes of bamboo-dominated plots being more dynamic. Finally, we discuss the differences between Atlantic and Amazonian Guadua-dominated forests, causes, and possible consequences of bamboo overabundance to the Atlantic Forest conservation.

Estrutura do componente arbóreo de uma floresta estacional decidual ripária em Jaguari, RS

Este estudo analisou a estrutura do componente arbóreo de uma mata ciliar, no município de Jaguari, RS. A amostragem foi realizada em 15 parcelas de 10mx10m instaladas ao longo da mata ciliar de um afluente do rio Jaguari. Nessas parcelas, foram identificados e medidos os indivíduos com diâmetro à altura do peito (DAP) maior ou igual a 5cm. Podocarpus lambertii, Sebastiania commersoniana e Lithrea molleoides foram as espécies mais representativas da mata ciliar. A distribuição diamétrica do componente arbóreo e das espécies lenhosas de maior valor de importância (VI) seguiu o padrão comum a florestas inequiânias, com tendência à forma de "J" invertido, e revelou uma estrutura não balanceada, indicando que não há equilíbrio entre as taxas de mortalidade e recrutamento de indivíduos. A estrutura vertical e as espécies de maior VI apresentaram tendência à distribuição normal, com a maioria dos indivíduos posicionada nas classes intermediárias de altura.

Modelling irregular and multimodal tree diameter distributions by finite mixture models: an approach to stand structure characterisation

Tree structural diversity is assessed by modelling stand diameter at breast height (DBH) distribution. The aim of this study was to verify the suitability of a mixture of two- and three-component Weibull and gamma models for describing irregular and multimodal DBH distributions. Investigations were carried out in natural Abies alba Mill. and Fagus sylvatica L. stands, representing the growing-up stage, in the Świętokrzyski National Park (Central Poland) and in the Pieniny National Park (Southern Poland). Sample plots (0.25–0.5 ha in area) were selected from a database used for forest dynamics analysis. The parameters of the mixture model were estimated using maximum likelihood estimation (MLE) and a combination of an expectation–maximisation (EM) algorithm with a Newton-type (NT) method. The multistart method (MM) of choosing initial values was used. The DBH distributions in mixed Abies–Fagus forests of complex structure were accurately approximated by two- and three-component mixture models. The root mean square error (RMSE) values varied from 3.4515 to 7.6682 for the Weibull mixture and from 3.6457 to 7.1419 for the gamma mixture. The results indicated that the mixture Weibull and gamma models were, in general, equally suitable for modelling irregular and multimodal DBH distributions. Finite mixture models may be used to characterise tree structural diversity, especially in uneven-aged stands of complex structure.

Comparing normal, lognormal and Weibull distributions for fitting diameter data from Akashmoni plantations in the north-eastern region of Bangladesh

Statistical probability density functions are widely used to model tree diameter distributions and to describe stand structure. The objective of this study was to compare the performance of normal, logarithmic-normal and three-parameter Weibull distributions for fitting diameter data from Akashmoni (Acacia auriculiformis A. Cunn. ex Benth.) plantations grown in the north-eastern region of Bangladesh. Data from 96 plots, established in 24 plantations in north-eastern Bangladesh and ranging in age from 1 to 6 years, were used for this study. The parameters of the Weibull distribution were calculated using maximum likelihood estimation (MLE) and moment estimation (ME) methods. The goodness of fit of normal, lognormal, Weibull MLE and Weibull ME were tested using one-sample Kolmogorov-Smirnov (KS) tests. The KS test results showed that both lognormal and Weibull distributions were equally effective for describing the diameter distributions of these Akashmoni plantations grown in the north-eastern region of Bangladesh.

Stand and cohort structures of old‐growthPinus resinosa‐dominated forests of northernMinnesota,USA

AbstractQuestionsWhat is the natural range of variability in stand and age structure of old‐growthPinus resinosa‐dominated forests? Does the spatial pattern of tree ages provide insights into past disturbances that structured these forests?LocationOld‐growthP. resinosaforests at seven sites inMinnesota,USA.MethodsWe applied detailed dendrochronological methods to living and dead material to reconstruct stand and age structures prior toEuropean settlement of the region. We linked dendrochronological data to mapped stem locations to shed light on spatial patterns of past disturbance.ResultsData pooled across sites revealed a mean living tree basal area of 34.8 m2·ha−1, snag basal area of 6.9 m2·ha−1and down woody debris (DWD) volume of 100 m3·ha−1. Living tree diameter distributions varied between sites; however, at all sites, smaller diameter classes were dominated by non‐pines, many pre‐dating the onset of fire suppression in the 1920s. There were a variety ofP. resinosaage structures, including one‐cohort, two‐cohort (at times with additional sporadic recruitment) and three‐cohort stands. For multi‐cohort stands, the spatial pattern of cohorts shows considerable within‐stand patchiness.ConclusionsThe wide range of stand and age‐cohort structures in these old‐growthP. resinosastands depicts pre‐settlement forests more complex than those of the single‐cohort, post‐stand‐replacing‐fire model that has guided regional forest management. Within‐stand patchiness of cohort age structures implies disturbances operating at scales smaller than typically associated with this regional forest type. Presence of non‐pine ‘ingrowth' on all sites might suggest thatP. resinosastands supporting these species lie within the natural range of variability for this community type, representing situations in which surface fires did not occur for extended periods or were spatially patchy at the stand scale. The diversity of reference conditions documented here suggests targets that might guide ecological restoration prescriptions for these ecosystems, with the goal of reintroducing structural and compositional complexity reflecting natural disturbance and stand development.

Predicting the number of trees in small diameter classes using predictions from a two-parameter Weibull distribution

Summary Knowing the abundance of small trees is necessary for accurate calculation of gross production, total carbon and/or biomass of forest stands. The abundance of small trees can also be used to predict ingrowth into larger tree diameter classes. We present a method of predicting numbers of trees in small diameter classes using diameter distributions of larger trees in stands. A truncated two-parameter Weibull distribution was fit to large tree diameters (diameter at breast height (d.b.h.) ≥ 9.0 cm). These parameters were then used to predict the number of small trees in d.b.h. classes smaller than 9.0 cm. Three methods of predicting densities of small trees were used: (1) an extrapolation of the truncated Weibull to a full two-parameter Weibull distribution; (2) a modification of the Weibull using an empirical estimate and (3) a combined approach. While the full two-parameter Weibull distribution generally fitted the distribution of small trees, densities were typically under-predicted. The empirical method (i.e. method 2) produced the best predictions of small tree densities, with a root mean square error of 132 trees h 21 (28 per cent of mean small tree density). Overall, predicting the distribution of small trees using the distribution of large trees worked very well in this study.

Látex de amapá (Parahancornia fasciculata (Poir) Benoist, Apocynaceae): remédio e renda na floresta e na cidade

O estudo abordou a cadeia de produção e de comercialização e os aspectos do consumo do látex medicinal de amapá amargoso (Parahancornia fasciculata) em Belém e Ponta de Pedras, no Pará. Nosso objetivo foi investigar diversos aspectos do manejo e uso desse produto, revelando a sua importância na vida de seus produtores e consumidores. Foram utilizados a abordagem da 'cadeia de produção ao consumo' e métodos qualitativos e quantitativos de pesquisa, incluindo pesquisa de mercado, entrevistas com extrativistas, comerciantes e consumidores, oficinas, turnês guiadas e inventário florestal. Os oito mil litros de látex de amapá comercializados anualmente na região de Belém beneficiam, principalmente, consumidores de baixa renda, que têm tradição secular do uso desse látex. A renda obtida com esse produto representa 42% da renda total dos extrativistas com produtos florestais não madeireiros. A grande abundância da espécie e a distribuição diamétrica das árvores indicam possibilidade de regeneração natural. A melhoria na técnica de extração do látex realizada por alguns extrativistas revela que eles têm conhecimento da anatomia da árvore. A tradição de uso e manejo do látex e as características ecológicas da espécie sugerem grande potencial para programas de produção sustentável.

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

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

Spruce budworm, windthrow and partial cutting: Do different partial disturbances produce different forest structures?

Forest management that incorporates the emulation of natural disturbances is promoted as a coarse filter approach to maintaining natural ecosystem functions, yet the initial outcomes of different natural and anthropogenic disturbances of similar severity may be quite different. We question whether a variant of diameter-limit partial harvesting effectively generates structural and compositional patterns similar to those found after spruce budworm outbreaks or windthrow, and whether stands issued from these two partial natural disturbances are more similar to each other or to those resulting from the studied partial harvests. We conducted our study 20–25 years after these partial disturbances occurred to determine whether the patterns converged or diverged over time. Results showed that post-disturbance vegetation distribution and abundance were similar after all partial disturbance types. Tree diameter distribution followed a reverse- J pattern and mean densities of mature trees were similar, although a higher proportion of deciduous species was observed in the partial harvest sites. Snag densities converged among the three partial disturbance types, despite initial differences that likely occurred in snag abundance and differences in the type of mortality (selective tree removal in partial cuts, uprooting/snapping in windthrow and standing mortality after insect outbreaks). The density of moderately decomposed coarse woody debris was significantly lower after partial harvesting relative to after windthrow and spruce budworm disturbances. Although a higher total number of canopy gaps was observed in the sites disturbed by spruce budworm, the percentage of canopy openness was similar among the three partial disturbances. Our results suggest that convergence of structural and compositional components occurred over the 25 year period since the disturbance. Thus after one entry, the studied partial harvests may be reasonable analogs to both of the studied natural disturbances in terms of medium-term post-disturbance species composition and structural complexity.

Composition and structure of natural mixed-oak stands in northern and central Portugal

Stand composition and structure of natural mixed-oak stands of common-oak ( Quercus robur L.) and pyrenean-oak ( Quercus pyrenaica Willd.) were studied. Diverse compositional and structural elements in early and late successional stand stages were analysed. The study was conducted in north and central Portugal where different natural mixed oak forests types are located. The following mixed-oak forest types involving common-oak and pyrenean-oak were studied: common-oak & other hardwoods; common-oak & cork-oak ( Quercus suber L.); ash ( Fraxinus angustifolia Vahl) & pyrenean-oak; and pyrenean-oak & madrone ( Arbutus unedo L.). Measurements were made in early and late successional stand stages on the different mixed oak forest types. Different stand characteristics and indices were used to describe and compare stand structure and composition. The study showed changes in species diversity and stand structure. Most tree species in mature stands are present in early stages but with higher abundance. Shannon diversity index may change between 0.798 and 1.915. Significant differences on species diversity and abundance were found depending on the forest type and successional stage. Mature mixed-oak forests have high species diversity with an abundance of small to medium tree size species. Species distribution and diameter differentiation indices range from 0.30 to 0.70 and 0.52 to 0.82, respectively, revealing significant structural complexity. The average number of standing and downed dead trees was 265 and 83 trees ha −1 for early and late stage, respectively, with 6.9 and 65.4 m 3 ha −1. Higher values of stand diversity index were 41 and 53 in more complex and developed forests. Later stand stages have complex structure, with a wider range of tree diameter distribution and higher degree of irregularity.

The Quest for a Suitable Host: Size Distributions of Host Trees and Secondary Hemiepiphytes Search Strategy

ABSTRACTAs climbing plants lack the capacity to hold themselves upright, they need to encounter a suitable host. Vines, lianas, and secondary hemiepiphytes need, therefore, an effective searching strategy. Various hypotheses have been put forward on searching strategies, including ‘skototropism’—growth toward darkness—and random searching. We studied host searching strategies of three secondary hemiepiphyte species belonging to the genus Heteropsis. We recorded information on the diameter distribution of host and evaluated whether these hosts were ‘suitable’, i.e., sufficiently tall for Heteropsis individuals to reach reproductive size. The diameter distribution of host trees bearing Heteropsis seedlings was similar to that of the trees in our study plots. Also, we found that 72–81 percent of the Heteropsis seedlings were present on unsuitable hosts (seedlings, saplings, herbs). These results suggest that Heteropsis seedlings search hosts in a random manner and not by skototropism. We found quite a distinct pattern for adult Heteropsis individuals, which predominantly occur on host trees bigger than 10 cm dbh. Host diameter distribution for Heteropsis adults differed significantly from that of the entire tree community. This difference suggests that Heteropsis individuals may change hosts if they are initially present on nonsuitable hosts. We observed that Heteropsis seedlings and juveniles on unsuitable hosts often produced vegetative shoots that searched for another host. In many cases, such shoots did not find a suitable host. For Heteropsis, our results suggest that host tree searching is a long‐term trial and error process that is governed by a random searching strategy.Abstract in Spanish is available in the online version of this article.

Natural development and regeneration of a Central European montane spruce forest

Montane Norway spruce forests of Central Europe have a very long tradition of use for timber production; however, recently there has been increasing concern for their role in maintaining biological diversity. This concern, coupled with recent severe windstorms that led to wide-spread bark beetle outbreaks, has brought the management of montane spruce forests to the forefront of public policy discussions in Central Europe. In order to shed light on the natural development and current structure of mature montane spruce forests, we established four 0.25 ha research plots in a semi-natural montane spruce forest in the Šumava Mountains (The Bohemian Forest), Czech Republic. We mapped all trees, extracted increment cores for age and growth-pattern analyses, and inventoried all current tree regeneration, including the substrates on which it was found. Stands were characterized by uni-modal tree diameter distributions and high basal areas (56.6 m 2 ha −1 on average), indicating a natural transition from the stem exclusion phase towards the understory reinitiation phase. The stands showed largely single-cohort recruitment age structures, however, with recruitment spanning seven decades. Our analyses suggest that this cohort existed as advance regeneration prior to major disturbances in the late 1800s, which included post-bark beetle salvage logging. Spatial pattern analyses of living and dead stems combined, showed an increase in uniformity of living trees, pointing to the role of natural density-dependent mortality. However, past growth patterns and historical documentation suggest that low intensity canopy disturbances (wind and snow) also caused mortality and diversified canopy structure. Because the stands developed naturally over the past 120+ years and thus escaped thinning operations, high volumes of coarse woody debris (94 m 3 ha −1) and snag densities (546 stems ha −1) have accrued. Advance spruce regeneration was quite abundant and existed primarily on deadwood substrates, even though these occupied only a small percent of stand area. Because of salvage logging in the late 1880s, these stands do not qualify, according to the traditional paradigm, as natural spruce forests. As a result, they are recently subject to active management practices including salvage logging that remove dead and dying trees. Given the importance of deadwood for forest regeneration and recovery from disturbance, as demonstrated in this study, we argue that dead wood removal may limit future natural regeneration in these stands. Thus, the purported benefits of removing dead and dying trees from semi-natural forests must be carefully weighed against the potential detrimental impacts on natural spruce forest regeneration and biodiversity.

The Bivariate Gompertz Diffusion Model for Tree Diameter and Height Distribution

Abstract With this research we present a new method for describing the bivariate diameter and height distribution of trees growing in a pure, uneven-aged forest. We use a stochastic differential equation framework to derive a bivariate age-dependent probability density function of tree diameter and height when the tree diameter and height follow a bivariate stochastic Gompertz shape growth process. We also adopt the two-dimensional transition probability function methodology for growth modeling of forest stands. The bivariate stochastic Gompertz model is fit to diameter and height observations for 1,575 pine trees in the Dubrava district of Lithuania. A considerable advantage of the bivariate stochastic Gompertz growth model is that the model parameters are easily interpretable. All results are implemented in the symbolic algebra system MAPLE.

Trivariate Distribution Modeling of Tree Diameter, Height, and Volume

Abstract Trivariate distribution models were constructed for tree diameter (D), height (H), and volume (V) using a normal copula (a mathematical function that joins or links marginal distribution functions to form multivariate distribution functions). The model parameters were estimated by a two-stage semiparametric method as follows: univariate distribution models were fitted separately for each tree variable, and then the copula dependency (correlation) parameters were independently estimated using empirical distribution functions to approximate the marginal models. Our results indicated that, for the available trivariate data in this study, the log-logistic (a limiting form of the logit-logistic distribution) best described both D and V distributions, whereas the logit-logistic, Johnson's SB, and Weibull marginal models provided roughly the same fitting for the H distribution. The trivariate distribution models produced satisfactory estimates of trivariate frequencies for the three variables, as well as the volume predictions from the resulting median regression models, which were comparable with commonly used volume regression models. The advantage of the normal copula method is that one can use any marginal models suitable for modeling tree diameter, height, and volume distributions separately, rather than being restricted to the SB marginal model in Johnson's SBBB system.

Anomalous diameter distribution shifts estimated from FIA inventories through time

Summary In the past decade, the United States Department of Agriculture Forest Service's Forest Inventory and Analysis Program (FIA) has replaced regionally autonomous, periodic, state-wide forest inventories using various probability proportional to tree size sampling designs with a nationally consistent annual forest inventory design utilizing systematically spaced clusters of fixed- area plots. This has resulted in significant changes in the spatial-temporal distribution of observations on the nation's forest resource. This paper discusses the resulting changes in the observation of the distribution of tree diameters measured at 1.37 m above ground level. We show that in three of the four FIA regions, a significant portion of the upper end of the diameter distribution has thus far gone unobserved by the new inventory design. We conclude that the reason is not that the larger diameter trees have become less common but rather that there is a low enough probability of observing these trees that they are not being observed. This postulate is supported by the observation that large-diameter trees are not missing from the data acquired by the fourth FIA region (the Pacific Northwest), which uses an additional sampling mechanism for large-diameter trees. We explore the implications of this effect in addition to potential solutions.

QUANTIFYING TREE DIAMETER DISTRIBUTIONS WITH ONE-DIMENSIONAL DIFFUSION PROCESSES

This study presents diffusion processes methodology on tree diameter distribution problem. We use stochastic differential equation methodology to derive a univariate age-dependent probability density function of a tree diameter distribution. The purpose of this paper is to investigate the relationship between the stochastic linear and logistic shape diameter growth models and diameter distribution laws. We establish the probabilistic characteristics of stochastic growth models, such as the univariate transition probability density of tree diameter, the mean and variance of tree diameter. We carry out comparison of proposed continuous time stochastic models on the basis of Hong-Li, Gini, Shapiro-Wilk goodness-of-fit statistics and normal probability plot. Parameter estimations are based on discrete observations over age of trees. To model the tree diameter distribution, as an illustrative experience, a real data set from repeated measurements on a permanent sample plot of pine (Pinus sylvestris) stand in the Kazlu Ruda district at Lithuania is used. The results are implemented in the symbolic computational language MAPLE.

Diversity of patch structure in Central European forests: are tree diameter distributions in near‐natural multilayered Abies–Fagus stands heterogeneous?

AbstractNear‐natural multilayered Abiesalba Mill.–Fagus sylvatica L. forests form structural mosaics and consist of patches in different developmental stages and phases. Knowledge of the diversity of patch structure and adequate methods to describe the diameter structure is essential for modeling forest dynamics. The hypotheses tested in the study are that near‐natural multilayered stands are structurally heterogeneous (i.e., tree diameter (DBH) distributions of these stands are heterogeneous) and, that in these forests the finite‐mixture models are suitable for modeling the empirical DBH distributions. Diversity of patch structure was studied based on data collected from 33 sample plots. In multilayered stands, four groups of empirical DBH distributions were distinguished using hierarchical cluster analysis (HCA) and correspondence analysis (CA). Stands investigated are structurally heterogeneous; 27% multilayered stands showed the slightly rotated sigmoid (SRS) type of empirical DBH distribution, 34% the distinctly rotated sigmoid (DRS) type, 18% the bimodal M‐shaped (BMS) type, and 21% the unimodal highly skewed (UHS) type. The gamma distribution, the two‐component mixture gamma model, and the two‐component mixture Weibull model were more flexible for the SRS type of DBH distributions. The average p‐values (Chi‐square test) for these theoretical distributions were 0.4712, 0.4718, and 0.4660, respectively. The two‐component mixture gamma model and the two‐component mixture Weibull model were a good choice for modeling the DRS, BMS, and UHS types of DBH distributions. The average p‐values (Chi‐square test) for these models ranged from 0.2684 to 0.4854. In near‐natural multilayered Abies–Fagus forest patches of different DBH distributions occur together. The empirical DBH distributions in these stands are characterized by irregular and complicated shapes and therefore are best approximated by finite‐mixture models.

Diameter distribution of trees in natural stands managed on polycyclic cutting system

Diameter frequency distribution in a specific stand provides basic information for forest resources management. In this study, four probability models were applied to analyze diameter distribution of natural forests after selective cutting with different intensities (low intensity of 13.0% in volume, medium intensity of 29.1%, high intensity of 45.8%, and extra-high intensity of 67.1%). The results show that the skewness and kurtosis of the four models are positive except that of low intensity selective cutting, which suggest that the number of small-size trees dominate the stand. The more intensity of selective cutting, the wider range of diameter distributions. The diameter structure of selective cutting with low intensity met Weibull and Beta distributions; that of medium intensity met Weibull, negative exponential as well as Gamma distributions; that of high intensity cutting met Weibull and negative exponential distributions, but that of extra-high intensity could not meet any above model. Weibull distribution model fits better than others regarding the structure of diameter distribution in natural forests managed on polycyclic cutting system. The results will provide basic information for sustainable management for mixed natural stands managed on a polycyclic cutting system.

Using Florida Keys Reference Sites As a Standard for Restoration of Forest Structure in Everglades Tree Islands

In south Florida, tropical hardwood forests (hammocks) occur in Everglades tree islands and as more extensive forests in coastal settings in the nearby Florida Keys. Keys hammocks have been less disturbed by humans, and many qualify as “old-growth,” while Everglades hammocks have received much heavier use. With improvement of tree island condition an important element in Everglades restoration efforts, we examined stand structure in 23 Keys hammocks and 69 Everglades tree islands. Based on Stand Density Index and tree diameter distributions, many Everglades hammocks were characterized by low stocking and under-representation in the smaller size classes. In contrast, most Keys forests had the dense canopies and open understories usually associated with old-growth hardwood hammocks. Subject to the same caveats that apply to off-site references elsewhere, structural information from mature Keys hammocks can be helpful in planning and implementing forest restoration in Everglades tree islands. In many of these islands, such restoration might involve supplementing tree stocking by planting native trees to produce more complete site utilization and a more open understory.