Basal Area Gain Research Articles

Important role of a few large-diameter tree species in basal area and its increase in an old-growth deciduous broadleaf forest in Japan

Because of their large diameter and biomass, old-growth forests provide valuable wood and high levels of ecosystem services (e.g., carbon sinks). Most of the aboveground biomass or basal area (BA) in old-growth forests is provided by small numbers of large-diameter trees. If the diversity of these trees is lower in temperate forests than in tropical forests, then the BA of temperate forests should be dominated by small numbers of large-diameter species. To explore how and to what extent BA and increase in BA (ΔBA) are determined by species with large diameters in temperate old-growth forests, we examined changes in the size structure and demographic parameters of large-diameter tree species based on 11 years of diameter at breast height (DBH, ≥ 5 cm) records for a 6-ha plot in an old-growth deciduous broadleaf forest in Japan. To estimate the extent to which difference in the successional status affect future ΔBA, we compared demographic parameters between them. Individuals with DBH ≥ 50 cm represented only 4.2% of all trees; however, their relative BA (rBA, ratio of BA of individual trees to the BA of entire forest) and relative increase in BA (rΔBA, ratio of increase in BA of individual trees to increase in BA of entire forest) were 36.4% and 25.1%, respectively, indicating that both BA and ΔBA were dominated by a small number of large trees. The rBA and rΔBA of the four species with the highest maximum DBH (DBHmax) were 71.1% and 61.4%, respectively, indicating that BA and ΔBA were also dominated by a very small number of species with exceptionally high DBHmax. Even among individuals with DBH ≥ 50 cm, the top four species in terms of DBHmax represented 90.0% and 80.6% of the total BA and ΔBA, respectively, confirming that both BA and ΔBA are highly dependent on species with high DBHmax values irrespective of the successional status. Most of the top 10 species in terms of DBHmax also showed increasing diameter growth rates and survival rates with increases in DBH class. Although the species with the second-highest DBHmax value had relatively low BA and ΔBA, BA gain exceeded BA loss for 11 years, thereby increasing the overall BA of the forest. These findings suggest that small numbers of large-diameter tree species play an important role in the sustainable increase in biomass among temperate old-growth forests in Japan. However, late successional species have higher rates of gain in BA, lower mortality, and higher recruitment rates than mid successional and early succesional species, indicating that their populations are increasing strongly. It is expected that the late successional species will eventually become more dominant than the mid and early successional species, unless there occurs some large-scale disturbance.

Spatial and temporal structure of diversity and demographic dynamics along a successional gradient of tropical forests in southern Brazil.

Analysis of the structure, diversity, and demographic dynamics of tree assemblages in tropical forests is especially important in order to evaluate local and regional successional trajectories.We conducted a long‐term study to investigate how the structure, species richness, and diversity of secondary tropical forests change over time. Trees (DBH ≥ 5 cm) in the Atlantic Forest of southern Brazil were sampled twice during a 10‐year period (2007 and 2017) in six stands (1 ha each) that varied in age from their last disturbance (25, 60, 75, 90, and more than 100 years). We compared forest structure (abundance and basal area), species richness, alpha diversity, demographic rates (mortality, recruitment, and loss or gain in basal area), species composition, spatial beta diversity, and temporal beta diversity (based on turnover and nestedness indices) among stand ages and study years.Demographic rates recorded in a 10‐year interval indicate a rapid and dynamic process of species substitution and structural changes. Structural recovery occurred faster than beta diversity and species composition recovery. The successional gradient showed a pattern of species trade‐off over time, with less spatial dissimilarity and faster demographic rates in younger stands. As stands grow older, they show larger spatial turnover of species than younger stands, making them more stochastic in relation to species composition. Stands appear to split chronologically to some extent, but not across a straightforward linear axis, reflecting stochastic changes, providing evidence for the formation of a nonequilibrium community. Policy implications. These results reiterate the complexity and variability in forest succession and serve as a reference for the evaluation and monitoring of local management and conservation actions and for defining regional strategies that consider the diversity of local successional trajectories to evaluate the effectiveness of restoration measures in secondary forests of the Atlantic Forest biome.

Estrutura florestal e serapilheira acumulada predizem a velocidade da dinâmica demográfica em florestas secundárias da Mata Atlântica

O conhecimento dos fatores preditivos da dinâmica demográfica de florestas secundárias é útil para planejar estratégias de recuperação de áreas degradadas, estimar a produção de biomassa e para subsidiar o planejamento da utilização racional de recursos. O objetivo deste estudo foi investigar possíveis fatores bióticos e abióticos que predizem taxas de dinâmica demográfica da vegetação secundária da Mata Atlântica. Para isto, em seis florestas, que variaram em idade desde a última perturbação (25, 60, 75, 90 e mais de 100 anos), a ordenação por PCA das taxas demográficas (mortalidade, recrutamento, rotatividade em abundância, perda em área basal, ganho em área basal e rotatividade em área basal) foi utilizada como variável resposta em uma árvore de regressão. Como possíveis fatores preditivos foram utilizados: declividade, variáveis químicas do solo em diferentes profundidades, parâmetros da estrutura florestal, quantidade de serapilheira acumulada e padrões espaciais. A árvore de regressão revelou que variações locais nos padrões dinâmicos foram melhor preditas pela estrutura florestal e pela quantidade média de serapilheira acumulada. Locais com estrutura menos desenvolvida em relação ao diâmetro máximo, altura máxima e área basal ocorreram nas florestas mais jovens (25 anos) e em clareiras das florestas mais antigas (com 90 e 100 anos), onde foram observadas as maiores taxas de dinâmica demográfica. Áreas com estrutura mais desenvolvida foram frequentes em todas as florestas, independente da idade pós-perturbação. Nestas áreas, as mudanças foram mais lentas e a quantidade de serapilheira acumulada sobre o solo foi inversamente proporcional à rotatividade de árvores e de área basal.

IMPACTO DO ENCHIMENTO DO RESERVATÓRIO DE UMA UHE SOBRE A DINÂMICA DE UM FRAGMENTO DE FLORESTA OMBRÓFILA MISTA EM SANTA CATARINA

O presente estudo teve como objetivo investigar o impacto do enchimento do reservatório de uma usina hidrelétrica sobre as taxas de dinâmica do componente arbóreo em uma floresta adjacente. Para isso, foram alocadas 48 parcelas em três setores do fragmento: adjacente às margens do reservatório, meio da encosta e topo da encosta. Um ano após o enchimento do reservatório, todos os indivíduos arbóreos com circunferência a altura do peito (CAP) ≥ 15,7 cm foram avaliados (identificados e mensurados), e dois anos após o enchimento foi realizado o estudo de dinâmica, com as árvores sobreviventes remedidas, as mortas quantificadas e as recrutas incorporadas. Foi realizado o levantamento das variáveis ambientais edáficas, topográficas, de abertura do dossel e de impacto ambiental. Foram calculadas as taxas de dinâmica. Para ordenação das variáveis ambientais foi aplicada uma Análise de Componentes Principais (PCA) e a influência de gradientes ambientais sobre as taxas demográficas da comunidade foi verificada por meio de regressão logística. A dinâmica apresentou estabilidade no número de indivíduos, porém, com maior ganho (3,64%.ano-1) que perda (1,62%.ano-1) em área basal. Entre os setores houve distinções, sendo o setor 1 caracterizado pela maior taxa de perda em área basal (2,51%.ano-1). Houve pouca relação das taxas demográficas com as variáveis ambientais analisadas, indicando que a maior influência encontrada sobre o crescimento das árvores está associada a variáveis não mensuradas. O presente estudo indica que, dois anos após o enchimento do reservatório, foi possível perceber os primeiros efeitos da influência do lago da hidrelétrica na comunidade arbórea.

INTER-RELAÇÃO ENTRE PAISAGEM, ORGANIZAÇÃO FLORÍSTICO-ESTRUTURAL E DEMOGRAFIA DO COMPONENTE ARBÓREO EM FLORESTA COM ARAUCÁRIA

Objetivou-se verificar as interações entre a configuração espacial da paisagem, a organização florístico-estrutural e as taxas demográficas do componente arbóreo em um sistema de fragmentos e corredores de floresta com araucária em Lages, Santa Catarina. Para isso, foi elaborado um modelo conceitual das possíveis inter-relações, que foi avaliado pela técnica de Modelagem de Equações Estruturais. No ano de 2010, foram obtidos as métricas da paisagem (área, distância do vizinho mais próximo e relação borda e o interior da floresta) e os dados do primeiro inventário florestal. Neste caso, foram alocadas parcelas permanentes em cinco fragmentos e corredor florestal, onde todos os indivíduos arbóreos com CAP (circunferência a altura do peito, medida a 1,30 do solo) igual ou superior a 15,7 cm foram identificados e mensurados. Em 2014 foi realizado o segundo inventário, com a inclusão de indivíduos recrutas, contagem de mortos e sobreviventes, e foram calculadas as taxas demográficas. Os dados foram analisados por meio da Análise de Componentes Principais (PCA), Análise de Coordenadas Principais (PCoA), Modelagem de Equações Estruturais e Modelos Lineares Generalizados (GLM). Os resultados demonstraram que a estrutura da paisagem (PCA 1) exerceu influência apenas sobre a organização florístico-estrutural do componente arbóreo, indicada pela distribuição preferencial de espécies arbóreas em função da intensidade da fragmentação. Por sua vez, as taxas demográficas (taxas de ganho e perda em área basal e de mortalidade) foram influenciadas por aspectos estruturais da vegetação (abundância e área basal). Conclui-se que existem variações florístico-estruturais associadas à configuração espacial dos fragmentos na paisagem e que as taxas demográficas apresentam relação com o estágio sucessional da floresta, sintetizado pelas variáveis estruturais de área basal e abundância.

TREE COMPONENT DEMOGRAPHY IN AN UPPER MONTANE MIXED OMBROPHILOUS FOREST UNDER CHRONIC ANTHROPOGENIC DISTURBANCES

ABSTRACT The objective of this study was to understand the dynamics of an Upper Montane Mixed Ombrophilous Forest in the municipality of Painel, Santa Catarina, Brazil, where low-level but chronic disturbances, such as extensive cattle grazing and exploitation of non-timber products, are common practices. In 2008, permanent plots were allocated and all tree species with circumference at breast height (CBH) equal to or greater than 15.7 cm were measured. A second survey was conducted in 2014 by the same methodology. Mortality, recruitment, and basal area gain and loss rates were then determined. The tree species were classified into regeneration guilds and proportion tests were conducted to verify the associations between dynamics patterns and guilds. The community has shown a 2.3%.year-1 average mortality rate, a 2.2%.year-1 average recruitment rate, a 3.0%.year-1 average basal area gain rate and a 1.8%.year-1 average basal area loss rate. Species number has decreased from 55 to 48. Regeneration guilds have shown different dynamics patterns, where the pioneers have shown the greatest mortality (19.9%) and recruitment (15.6%) proportion and reduced representativeness in shade-tolerant climax species. Therefore, floristic impoverishment and higher representativeness reduction of late species have been observed. We have concluded that despite disturbances do not result in structural deterioration, they have the potential to slow the succession process and cause a floristic homogenization in the area under study.

DINÂMICA DE POPULAÇÕES DE ESPÉCIES ARBÓREAS EM UM FRAGMENTO DE FLORESTA OMBRÓFILA MISTA MONTANA EM LAGES, SANTA CATARINA

O presente estudo teve como principal objetivo avaliar a dinâmica de populações de espécies arbóreas, em um fragmento de Floresta Ombrófila Mista Montana, no Município de Lages, Santa Catarina - SC, ao longo de um período de quatro anos (2008-2012). Para isto, em todas as espécies amostradas em 50 parcelas permanentes de 10 x 20 m, foram determinadas as guildas de regeneração [Pioneiras (P), Climácicas Exigentes em Luz (CEL) e Climácicas Tolerantes ao Sombreamento (CTS)] e as taxas de dinâmica (mortalidade, recrutamento, ganho e perda em área basal, mudança líquida em abundância e área basal). A existência de associação significativa entre as guildas de regeneração e os padrões de dinâmica foi verificada por meio de testes de qui-quadrado, aplicados a tabelas de contingência. Mudanças das participações relativas das guildas de regeneração entre os anos foram analisadas por meio de testes de proporção. No ano 2008 foram verificadas 87 espécies (P: 9, CEL: 64, CTS: 11 e não classificadas: 3), 1.841 ind.ha-1 e 36,17m2.ha-1. Em 2012, verificaram-se 86 espécies (P: 9, CEL: 63, CTS: 11, não classificadas: 3), 1.882 ind.ha-1 e 39,17m2.ha-1. A maior parte das espécies apresentou ganho em abundância e área basal. Dentre as mais abundantes, as maiores taxas de recrutamento e ganho em área basal foram observadas para Banara tomentosa Clos, com, respectivamente, 5,43%.ano-1 e 6,08%.ano-1, e as maiores taxas de mortalidade e perda em área basal ocorreram para Zanthoxylum rhoifolium Lam., com, respectivamente, 7,75%.ano-1 e 4,74%.ano-1. Não foi verificada associação significativa entre os padrões de dinâmica observados e guildas de regeneração, cujas participações relativas na comunidade no período avaliado, permaneceram constantes. Desta forma, conclui-se que o fragmento florestal se encontra em fase de instabilidade estrutural, indicada pelo incremento no número de indivíduos e área basal, e estabilidade florística sucessional, em função da baixa substituição florística e manutenção da importância relativa das guildas de regeneração ao longo do tempo avaliado.

Woody vegetation dynamics in a floodplain campo de murundus in central Brazil

Campos de murundus (grasslands dotted with knolls that are covered with savanna-like woody vegetation) are a common landscape in central Brazil. In this study, we assessed for the first time the dynamics of the vegetation in a floodplain campo de murundus, describing changes in composition and structure of the woody vegetation. In 2005, we established 16 permanent 25 × 25 m plots, where we identified and mapped individuals with a trunk diameter at the base ≥ 2.86 cm, as well as measuring the height of those individuals. In 2008 (after two fire events), we resampled the plots. In 2005, we had registered 4.54 m² ha-1 of basal area, 430 individuals, 42 species, 36 genera and 24 families. In 2008, we found an increase in basal area (to 4.65 m² ha-1) and a decrease in numbers of individuals (to 399), species (to 41), genera (to 35) and families (to 23). Species diversity did not differ between the two surveys. Mortality exceeded recruitment (2.68% year-1 vs. 1.29% year-1). Nevertheless, the community showed a gain in basal area owing to the growth of surviving individuals and, particularly, to the rise in the number of basal sprouts. We argue that the small floristic turnover may be related to the great resilience of the woody vegetation, whereas the structural changes might reflect the effects of the burnings in the area.

Shifting dynamics of climate-functional groups in old-growth Amazonian forests

Background: Climate change is driving ecosystem shifts, which has implications for tropical forest system function and productivity. Aim: To investigate Amazon forest dynamics and test for compositional changes between 1985 and 2005 across different plant groups. Methods: Tree census data from 46 long-term RAINFOR forest plots in Amazonia for three climate-functional groups were used: dry-affiliate, climate-generalist and wet affiliate. Membership of each group was ascribed at genus level from the distribution of individuals across a wet–dry gradient in Amazonia, and then used to determine whether the proportions of these functional groups have changed over time, and the direction of any change. Results: In total, 91 genera, representing 59% of the stems and 18% of genera in the plots, were analysed. Wet-affiliates tended to move from a state of net basal area gain towards dynamic equilibrium, defined as where gain ≈ loss, governed by an increase in loss rather than a decrease in growth and mainly driven by plots in north-west Amazonia, the wettest part of the region. Dry-affiliates remained in a state of strong net basal area gain across western Amazonia and showed a strong increase in stem recruitment. Wet-affiliates and climate-generalists showed increases in stem mortality, and climate-generalists showed increased stem recruitment, resulting in overall equilibrium of stem numbers. Conclusions: While there were no significant shifts in most genera, the results suggest an overall shift in climate-functional forest composition in western Amazonia away from wet-affiliates, and potential for increased forest persistence under projected drier conditions in the future.

Dinâmica estrutural da comunidade lenhosa em Floresta Estacional Semidecidual na transição Cerrado-Floresta Amazônica, Mato Grosso, Brasil

O entendimento de processos ecológicos, especialmente das modificações estruturais e florísticas em ecossistemas naturais, é fundamental para embasar ações visando à sua conservação e/ou restauração. O objetivo do estudo foi avaliar mudanças ocorridas na estrutura da comunidade lenhosa na transição Cerrado-Floresta Amazônica, no período de 2003 a 2008. Foram estabelecidas 60 parcelas permanentes de 10 x 10 m onde foram amostrados todos os indivíduos com diâmetro à altura do peito > 5 cm. Em 2003 foram registrados 1.140 ind. ha-1 e área basal de 24,35 m² ha-1, enquanto em 2008 foram 1.071 ind. ha-1 e área basal de 22,04 m² ha-1. O recrutamento (2,76% ano-1) não compensou a mortalidade (3,95% ano-1) e o ganho em área basal (0,54% ano-1) não superou a perda (3,77% ano-1). Em função dessa diferença, a meia vida (17,3 anos) foi menor que o tempo de duplicação (29,9 anos), resultando em baixa estabilidade (12,6 anos) e reposição (23,6 anos) em relação a outras florestas estacionais. Os parâmetros de dinâmica da comunidade e das principais espécies sugerem que a floresta está passando por mudanças caracterizadas principalmente pela retração da densidade e biomassa dos indivíduos arbóreos, que podem estar relacionadas ao aumento das lianas, a uma fase de início de reconstrução do ciclo silvigenético da floresta ou ainda à forte seca que ocorreu na região no ano de 2005.

Low Thinning as a Forest Restoration Tool at Redwood National Park

Abstract A growing interest in the restoration of young second-growth forests by managers of reserves in the redwood region has led to a need to evaluate restoration-based silvicultural strategies. This case study assessed the effectiveness of low thinning as a forest restoration tool via analysis of stand structure at Redwood National Park's Whiskey Forty Forest Restoration Study. The second-growth stand had more than 5,500 trees ha−1 and 57.0 m2 ha−1 basal area and consisted chiefly of three species: Douglas-fir (the dominant species), redwood, and tanoak. Low thinning reduced stand density but also reduced species richness by eliminating scarce species. Seven years after thinning, growth was enhanced (33.6% gain in basal area), and mortality was minor (3% of all stems); however, Douglas-fir remained competitive in the upper canopy. Its average basal area increment was less than redwood's, but its radial growth was equal and its rate of basal area growth was greater in the years following thinning. We conclude that the thinning improved stand conditions but did not fully satisfy restoration goals and that other thinning methods, such as variable-density thinning, are likely to be more effective at promoting redwood dominance.

COMPOSICIÓN, ESTRUCTURA Y DINÁMICA DE DOS SITIOS DE BOSQUE SECO SECUNDARIO EN EL SUROESTE DE NICARAGUA: PAUTAS PARA EL DISEÑO E IMPLEMENTACIÓN DE ALTERNATIVAS DE MANEJO

En dos comarcas del municipio de Nandaime, Granada, se llevóa cabo un estudio de dinámica del bosque seco secundario, conel propósito de obtener pautas para la definición de actividadesde manejo forestal. Para monitorear y determinar el cambiodurante un año, se establecieron cinco parcelas permanentesde muestreo en sitios de edades de 11 y 16 años después dehaber sido abandonados para actividades agrícolas. En lasparcelas se levantó información relacionada a la composicióny estructura de los fustales, latizales y brinzales. Parámetrospoblacionales fueron calculados a partir de la aplicación deun modelo exponencial de cambios en tiempos continuos.La riqueza y diversidad florística fueron diferentes entrecomunidades, siendo el sitio de 11 años, el que presentó losmás altos valores. Las diferencias estructurales entre sitiosfueron determinadas por los valores en área basal y volumen.El sitio de 16 años contiene el doble de área basal y 30% másdel volumen que el bosque más joven. El número de individuospor hectárea disminuyó en los dos sitios en relación a la primeramedición. Los valores de mortalidad fueron iguales (2%) en losdos sitios. El reclutamiento fue mayor en el sitio de 16 años.La ganancia en área basal contribuyo al incremento de toda lamasa, solamente en el sitio de 11 años. Las especies de interéscomercial local presentan pocos o ningún individuos a nivel dela regeneración natural. Los sitios estudiados presentan desdeanejo a mediano plazo.Abreviaturas: Dap, diamétro a la altura del pecho; H, altura;ICA, incremento corriente anual.DOI: 10.5377/calera.v9i12.1

Canopy tree development and undergrowth bamboo dynamics in old-growth Abies– Betula forests in southwestern China: a 12-year study

Interactions between forest canopy characteristics and plants in the forest understory are important determinants of forest community structure and dynamics. In the highlands of southwestern, China the dwarf bamboo Bashania fangiana Yi is an understory dominant beneath a mixed canopy of the evergreen Abies faxoniana (Rheder & Wilson) and the deciduous Betula utilis (D. Don). The goal of this study was to better understand the role of bamboo dominance, canopy characteristics, and periodic bamboo dieback on forest development. To achieve this goal, we measured tree seedling, tree saplings, and trees, forest canopy characteristics, and bamboo cover in permanent forest ( n = 4) and gap plots ( n = 31) in a mixed A. faxoniana and B. utilis forest in Sichuan, China. Dwarf bamboos died off in 1983 in the gap plots, and in three of the four forest plots. Forest development was assessed for the period 1984–1996. The seedling bank in forest and gap plots increased after bamboo die-off. A. faxoniana seedlings increased more than B. utilis in forest plots; the opposite pattern characterized gap plots. The proportion of seedlings on raised micro-sites on the forest floor also changed and new seedling were more abundant on the forest floor. By 1996, bamboo seedling cover and biomass had recovered to ca. 45% or their pre-flowering values. Rates of bamboo seedling recovery were faster beneath canopy gaps and deciduous trees than beneath forest or evergreen trees. Tree mortality exceeded recruitment in plots with dense bamboo; the opposite pattern was found in the plot with little bamboo. The mortality rate for B. utilis trees (2.4% year −1) was higher than that for A. faxoniana (0.8% year −1) and forests with dense bamboos became more open over the census period. Tree mortality was size-dependent and intermediate sized trees had the lowest rates of mortality. Stand basal area increased mainly due to greater basal area gain than loss for A. faxoniana. Interactions between tree species life history, canopy type, and bamboo life-cycles create heterogeneous conditions that influence tree and bamboo regeneration and contribute to the coexistence of A. faxoniana and B. utilis in old-growth forests in southwestern China.

Effects of flooding regime and woody bamboos on tree community dynamics in a section of tropical semideciduous forest in South-Eastern Brazil

The influence of a population of the understorey woody bamboo Merostachys riedeliana and different flooding regimes on tree community dynamics in a section of tropical semideciduous forest in South-Eastern Brazil was examined. A forest section with an area of 1.6 ha composed of 71 adjacent plots was located on a slope ending at the river margin. The section was divided into five topographical sectors according to the mean duration of river floods. In 1991 and 1998 all trees with a diameter at the base of the trunk ≥ 5 cm were measured, identified and tagged, and all live bamboo culms were counted. Annualised estimates of the rates of tree mortality and recruitment, gain and loss of tree basal area, and change in bamboo density were calculated for each of the 71 plots and five topographical sectors as well as for diameter classes and tree species. To segregate patterns arising from spatially autocorrelated events, geostatistical analyses were used prior to statistical comparisons and correlations. In general, mortality rates were not compensated by recruitment rates but there was a net increase in basal area in all sectors, suggesting that the tree community as a whole was in a building phase. Tree community dynamics of the point bar forest (Depression and Levee sectors) differed from that of the upland forest (Ridgetop, Middle Slope and Lower Slope sectors) in the extremely high rates of gain in basal area. The predominant and specialised species, Inga vera and Salix humboldtiana, are probably favoured by relaxed competition in an environment stressed by long-lasting floods. In the upland forest, mortality rates were highest at the Middle Slope, particularly for smaller trees, while recruitment rates were lowest. As bamboo clumps were concentrated in this sector, the locally higher instability in the tree community probably resulted from the direct interference of bamboos. The density of bamboo culms in the upland forest was negatively correlated with the rates of tree recruitment and gain in basal area, and positively correlated with tree mortality rates. Bamboos therefore seemed to restrict the recruitment, growth and survival of trees.

Forest canopy and community dynamics in a temperate old‐growth evergreen broad‐leaved forest, south‐western Japan: a 7‐year study of a 4‐ha plot

Summary Forest canopy gap and community dynamics were studied in a 4‐ha permanent plot of an old‐growth evergreen broad‐leaved forest dominated by Castanopsis cuspidata var. sieboldii and Distylium racemosum in the Tatera Forest Reserve, Tsushima Islands, south‐western Japan. The forest was affected by a powerful typhoon in 1987 and was monitored from 1990 to 1997. In 1990, all woody stems ≥ 5 cm diameter at breast height (d.b.h.) in the plot were identified, mapped and marked, and the state of 1600 5 m × 5 m contiguous quadrats used to locate canopy gaps. Gaps occupied 17.1% of the plot, which contained 4494 tree and shrub stems (total basal area 63.48 m2 ha−1). Gaps were re‐censused in 1997 and both marked and newly recruited (≥ 5 cm d.b.h.) stems were recorded in 1992 and 1997. Over 7 years the rates of canopy gap formation and closure were 0.72% year−1 and 1.61% year−1, respectively, mortality and recruitment rates were 0.97% year−1 and 0.99% year−1, and the rates of loss and gain in basal area were 0.95% year−1 and 0.83% year−1. The mortality of stems was size‐dependent, with those in middle size classes having the lowest rates. Mortality of stems was lower in canopy and higher in the understorey, while the proportion of stems killed by disturbances increased with height. Stems that died during the 7 years were predominantly located in newly created gaps, whereas stems were recruited into both established and new gaps. Deciduous broad‐leaved species were largely restricted to gaps that remained open throughout the study. Both composition and structure of the forest changed in response to disturbance‐related effects on canopy dynamics.

Growth response of loblolly pine, sweetgum, and water oak in a pine-hardwood density study

A study was established with loblolly pine (Pinus taeda L.) planted at 1683 trees/ha competing with sweetgum (Liquidambar styraciflua L.), water oak (Quercus nigra L.), or loblolly pine at densities of 0, 1794, 2692, and 5382 trees/ha. The study is a split-split plot with three blocks. Main plots are the three competitor species; subplots are with or without 2 years of herbaceous vegetation control (HVC); and sub-subplots are competitor densities. The study was measured at 6 years after establishment. Pines in pure plots responded to HVC with a mean basal area gain of 1.8 m2/ha (13%). With HVC, basal area increased 2.7 m2/ha (70%) for sweetgum and 2.3 m2/ha (58%) for water oak. Pines in mixed plots did not respond, or responded negatively, to HVC. Pine height, basal area, volume index, and canopy projection were only slightly affected by sweetgum density above zero. Pine characteristics decreased as water oak density increased. Adding sweetgum or water oak to pine reduced total (pine + hardwood) volume index and basal area.

Long‐term growth dynamics of natural forests in Hokkaido, northern Japan

Abstract. The long‐term growth dynamics of natural forest stands on the island of Hokkaido were described on the basis of an analysis of data from 38 permanent plots spanning 15–22 yr. Stand structure was characterized by basal area, stem density and tree size variability. To detect trends in stand structure, regression models for recruitment rate (per ha per yr), mortality rate and the rate of change in stem density and tree size variability were developed by a stepwise method using initial basal area, stem density, tree size variability, species composition summarized by LNMDS ordination, altitude, annual mean temperature, annual precipitation, type of understorey vegetation, topography and slope aspect as candidates for predictor variables. The same analyses were conducted for basal area increment (net growth) and its components: survivor growth = basal area gain by growth of surviving individuals and mortality = basal area loss by death of individuals.Stem density remained generally unchanged; recruitment was relatively low even in very sparse stands. Stand basal area generally increased as survivor growth was approximately double the mortality.Recruitment rate was strongly affected by the presence of dwarf bamboo (Sasa spp.) vegetation on the forest floor which inhibited tree regeneration. Mortality rate was density‐dependent; dense stands had higher mortality than sparse stands. Density change rate (recruitment rate ‐ mortality rate) was, therefore, determined by both the type of understorey vegetation and stem density. Survivor growth was high in stands with high stem density and basal area. Mortality was dependent on basal area and altitude. Net basal area increment (net growth) was dependent only on stem density with other factors that influenced survivor growth and mortality omitted. Tree size variability decreased in stands with high tree size variability whereas it increased in stands with low size variability. Based on the obtained models for density change rate and net basal area increment, trajectories of stands were illustrated on a log‐log diagram of stem density and basal area. The predicted differences in trajectories as affected by the understorey vegetation type indicated the importance of dwarf bamboo vegetation for forest dynamics on Hokkaido.