Population dynamics of four understorey shrub species during a 7‐yr period in a primary beech forest

Abstract. Shrubs persist in the understorey layer of forests throughout their lives, while tall trees remain there only during the juvenile stage and then grow into the canopy layer. Thus demographic parameters (recruitment‐, mortality‐, and growth‐rates) of shrub species are expected to differ from those of tall tree species. We investigated aspects of the demography of four dominant deciduous‐shrub species (Viburnum furcatum, Lindera umbellata var. membranacea, Magnolia salicifolia, and Hydrangea paniculata) in Fagus crenata forests at the beginning and at the end of a 7‐yr period in a 1‐ha permanent plot. For each species, the number of stems changed little (within ± 10%) during the study period, while total basal area increased markedly (11.7–33.8%), because (1) new stems continuously recruited by vegetative growth replaced the substantial number of dead stems, and (2) vegetative stems grew vigorously, probably due to nutrient support from parents. The results indicate that these four understorey shrub species have high ability to maintain their population size in the shaded forest understorey. While in each species more than half of the dead stems were standing dead, a substantial proportion of the dead stems (9.0–38.5%) showed signs of mechanical damage, such as stem breakage and suppression by fallen branches or trees. Snow pressure that resulted in decumbent stems was also an important mortality agent for V. furcatum (20.7%) and L. umbellata var. membranacea (5.6%). Probability of damage was constant across all DBH‐classes for all study species. In each species, newly recruited stems and dead stems were spatially aggregated, largely due to habits of vegetative growth and mechanical damage, respectively. This study revealed that several demographic traits, resulting from recruitment by vegetative growth and death by mechanical damage, were shrub‐species specific and markedly different from those of tall tree species.     

Variations in resistance to canopy disturbances and their interactions with the spatial structure of major species in a cool‐temperate forest

Question: How does typhoon‐related disturbance (more specifically, disturbance in the understorey due to tree‐fall and branch‐fall) affect different species mortality rates in a vertically well‐structured forest community? Location: Cool‐temperate, old‐growth forest in the Daisen Forest Reserve, Japan. Methods: We investigated the canopy dynamics and mortality rate trends of trees ≥5 cm diameter at breast height in a 4‐ha study plot, and analysed the effects of tree diameter and spatial structure on the mortality risks for major tree species in the understorey. Results: Significant differences were found in the mortality rates and proportions of injured dead stems between census periods, which were more pronounced in the understorey than in the canopy. Acer micranthum, which showed increased mortality during typhoon disturbance periods, had a clumped distribution. In contrast, Acer japonicum and Viburnum furcatum, which showed similar mortality rates between census periods, had a loosely clumped spatial distribution and a negative association with canopy trees, respectively. In the understorey stems of Acanthopanax sciadophylloides and Fagus crenata, whose spatial distribution patterns depended on canopy gaps, significant increases in mortality rates were observed only during severe typhoon‐related disturbance periods. Conclusions: The sensitivity of trees to typhoon‐related canopy disturbance is more pronounced in the lower layers of vertically structured forest communities. Differences in mortality patterns generated through the combined effects of spatial variation in disturbance regime and species‐specific spatial distribution patterns (spatial aggregation, association with canopy trees, and canopy gap dependency) contribute to the co‐existence of understorey species in forest communities that are subject to typhoon‐related disturbance.     

Hurricane disturbance in a temperate deciduous forest: patch dynamics, tree mortality, and coarse woody detritus

Patch dynamics, tree injury and mortality, and coarse woody detritus were quantified to examine the ecological impacts of Hurricane Fran on an oak-hickory-pine forest near Chapel Hill, NC. Data from long-term vegetation plots (1990–1997) and aerial photographs (1998) indicated that this 1996 storm caused patchy disturbance of intermediate severity (10–50% tree mortality; Woods, J Ecol 92:464–476, 2004). The area in large disturbance patches (>0.1 ha) increased from <1% to approximately 4% of the forested landscape. Of the forty-two 0.1-ha plots that were studied, 23 were damaged by the storm and lost 1–66% of their original live basal area. Although the remaining 19 plots gained basal area (1–15% increase), across all 42 stands basal area decreased by 17% because of storm impacts. Overall mortality of trees >10 cm dbh was 18%. The basal area of standing dead trees after the storm was 0.9 m²/ha, which was not substantially different from the original value of 0.7 m²/ha. In contrast, the volume and mass of fallen dead trees after the storm (129 m³/ha; 55 Mg/ha) were 6.1 and 7.9 times greater than the original levels (21 m³/ha; 7 Mg/ha), respectively. Uprooting was the most frequent type of damage, and it increased with tree size. However, two other forms of injury, severe canopy breakage and toppling by other trees, decreased with increasing tree size. Two dominant oak species of intermediate shade-tolerance suffered the largest losses in basal area (30–41% lost). Before the storm they comprised almost half of the total basal area in a forest of 13% shade-tolerant, 69% intermediate, and 18% shade-intolerant trees. Recovery is expected to differ with respect to vegetation (e.g., species composition and diversity) and ecosystem properties (e.g., biomass, detritus mass, and carbon balance). Vegetation may not revert to its former composition; however, reversion of biomass, detritus mass, and carbon balance to pre-storm conditions is projected to occur within a few decades. For example, the net change in ecosystem carbon balance may initially be negative from losses to decomposition, but it is expected to be positive within a decade after the storm. Repeated intermediate-disturbance events of this nature would likely have cumulative effects, particularly on vegetation properties.     

Population structure and spatial patterns for trees in a temperate old-growth evergreen broad-leaved forest in Japan

The population structure and spatial pattern of major tree species in a warm-temperate old-growth evergreen broad-leaved forest in the Tatera Forest Reserve of Japan were investigated. All stems 5 cm in diameter at breast height (DBH) were mapped on a 4 ha plot and analyses were made of population structure and the spatial distribution and spatial association of stems in different vertical layers for nine species. This was done in the context of scale dependency. The plot was located on a very gentle slope and 17.1% of its canopy layer was in gaps. It contained 45 woody plant species and 4570 living stems with a basal area of 63.9 m² ha^–1. Castanopsis cuspidata var. sieboldii, the most dominant species for the basal area, had the maximum DBH among the species present, fewer smaller stems and a lower coefficient of statistical skewness of the DBH distribution. The second most dominant species, Dystilium racemosum, had the highest stem density (410 ha^–1), more abundant smaller stems and a relatively higher coefficient of skewness. Most stems in different vertical layers showed a weakly aggregated distribution with loose colonies as basic units. Gap dependency for the occurrence of stems under the canopy layer was weak. Maximum slope degree of the plot also weakly affected the occurrence of stems. Spatial associations varied among intra- and interspecific cohorts in the different layers and spatial scales examined, and positive associations among cohorts were found more frequently as the scales examined became larger. This tendency suggests that key factors forming observed spatial associations might vary with the spatial scales.     

Population dynamics of four understorey shrub species in beech forest

Question: In the population dynamics of four understorey shrub species (Hp, Hydrangea paniculata Sieb, et Zucc.; Lu, Lindera umbellata Thunb. var. membranacea (Maxim.) Momiyama; Ms, Magnolia salicifolia (Sieb, et Zucc.) Maxim.; Vf, Viburnum furcatum Blume ex Maxim.), (1) What is the relative importance of seedling regeneration versus vegetative growth? (2) Can these shrubs persist stably for a long time in the understorey? (3) What kind of variation in demographic features is observed among these shrubs? Location: 780m a.s.l., north‐eastern Japan. Methods: Population dynamics were analyzed by using stage‐classified matrix models. Models were mainly constructed from five years stem‐census data, including current‐year seedlings and sprouts. Results: Current‐year sprouts emerged every year in every species. Current‐year seedlings emerged every year in Lu and Vf, but densities were very low. In every species, population growth rate (A) was close to the equilibrium value 1.0 and no statistical difference was found among species. The stable stage‐distribution predicted from the matrix model was similar to the observed distribution for Lu, Ms and Vf, but much different for Hp. Elasticity matrix was also similar among Lu, Ms and Vf, but was quite different for Hp. Conclusions: Lu, Ms and Vf were considered as climax shrubs that can regenerate and maintain their population stably in the understorey, even if canopy gaps form infrequently. Hp is a pioneer shrub that require more frequent formation of canopy gaps for long‐term persistence in the understorey.     

Seedling growth of climbing species from a southeast Brazilian tropical forest

Climbers are considered heliophytes. They are copious at the margins of forests and natural and man-made clearings. The objective of this paper was to study the initial growth of seedlings maintained under full sunlight and shaded conditions (under a vegetation canopy). The species studied were: Aristolochia galeata, Arrabidea triplinervia, Bidens brasiliensis, Canavalia parviflora, Chamissoa altissima, Cissus sicyoides, Dalechampia pentaphylla, Dicella bracteosa, Dioscorea sp., Gouania virgata, Mascagnia anisopetala, Mutisia coccinea, Oxypetalum molle, Pithecoctenium crucigerum, Rynchosia phaseoloides, Serjania multiflora and Solanum flaccidum. The initial growth of the seedlings was followed under two conditions: at the margin and under the canopy of a mesophyllous tropical forest (22° 4955S–47° 0633W). The climbers showed high rates of growth in sunlight when compared to those under canopy. Most of the species presented higher growth of the shoot than roots but in general no significative differences between root/shoot were found in both treatments. Bidens, Cissus, Mutisia and Pithecoctenium showed a very high mortality rate under canopy but, most of the studied species survived under deep shaded forest for approximately 100 days.     

Fire disturbance and forest structure in an old‐growth Pinus ponderosa forest,southern Cascades,USA

Questions: Did fire regimes in old‐growth Pinus ponderosa forest change with Euro‐American settlement compared to the pre‐settlement period? Do tree age structures exhibit a pattern of continuous regeneration or is regeneration episodic and related to fire disturbance or fire‐free periods? Are the forests compositionally stable? Do trees have a clumped spatial pattern and are clumps even‐ or mixed‐age? How might information from this old‐growth forest inform current restoration and management practices? Location: A 235‐ha old‐growth forest in the Ishi Wilderness, southern Cascade Mountains, California. Methods: Age, size, and spatial pattern of trees were quantified in seven stands. Fire history was reconstructed using fire scar dendrochronology. The influence of fire on stand structure was assessed by comparing fire history with age, size, and spatial structure of trees and identifying and measuring trees killed by two recent fires. Results: Species composition in plots was similar but density and basal area of tree populations varied. Age structure for P. ponderosa and Quercus kelloggii showed periods of episodic recruitment that varied among plots. Fire disturbance was frequent before 1905, with a median period between fires of 12 years. Fire frequency declined after 1905 but two recent fires (1990, 1994) killed 36% and 41% of mostly smaller diameter P. ponderosa and Q. kelloggii. Clusters of similar age trees occurred at scales of 28‐1018 m² but patches were not even‐aged. Interactions between tree regeneration and fire promoted development of uneven age groups of trees. Conclusions: Fire disturbance strongly influenced density, basal area, and spatial structure of tree populations. Fire exclusion over the last 100 years has caused compositional and structural changes. Two recent fires, however, thinned stands and created gaps favorable for Q. kelloggii and P. ponderosa regeneration. The effects of infrequent 20th century fire indicate that a low fire frequency can restore and sustain structural characteristics resembling those of the pre‐fire suppression period forest.     

Genet dynamics of a regenerating dwarf bamboo population across heterogeneous light environments in a temperate forest understorey

Despite the advantage of plant clonality in patchy environments, studies focusing on genet demography in relation to spatially heterogeneous environments remain scarce. Regeneration of bamboos in forest understoreys after synchronous die‐off provides an opportunity for assessing how they come to proliferate across heterogeneous light environments. In a Japanese forest, we examined genet demography of a population of Sasa kurilensis over a 7‐year period starting 10 years after die‐off, shortly after which some genets began spreading horizontally by rhizomes. The aboveground biomass was estimated, and genets were discriminated in 9‐m² plots placed under both canopy gaps and closed canopies. Overall, the results suggest that the survival and spread of more productive genets and the spatial expansion of genets into closed canopies underlie the proliferation of S. kurilensis. Compared to canopy gaps, the recovery rate of biomass was much slower under closed canopies for the first 10 years after the die‐off, but became accelerated during the next 7 years. Genet survival was greater for more productive genets (with greater initial number of culms), and the spaces occupied by genets that died were often colonized afterward by clonal growth of surviving genets. The number of genets decreased under canopy gaps due to greater mortality, but increased under closed canopies where greater number of genets colonized clonally from outside the plots than genets died. The colonizing genets were more productive (having larger culms) than those originally germinated within the plots, and the contribution of colonizing genets to the biomass was greater under closed canopies. Our study emphasizes the importance of investigating genet dynamics over relevant spatiotemporal scales to reveal processes underlying the success of clonal plants in heterogeneous habitats.     

Beta-diversity of lepidopteran larval communities in a Japanese temperate forest: effects of phenology and tree species

The specialization of herbivores among tree species is poorly understood despite its fundamental importance as a factor regulating diversity. To examine the effect of tree species on larval community structure, the larval communities in 10 temperate deciduous tree species that differed in leaf emergence pattern (flush- vs. intermediate-type) were seasonally surveyed. The newly developed soft, nitrogen-rich leaves of all species became tough and nitrogen-poor as the season progressed. Following the changes in leaf quality, two distinct seasonal lepidopteran larval communities emerged, with a marked turnover in early July. The beta diversity, or dissimilarity, of species composition in the larval communities among tree species was higher in summer than in spring. These results imply that the lepidopteran larval communities as a whole were supported by alpha diversity in spring and by beta diversity in summer, demonstrating that the plant diversity of this forest could support a caterpillar community. We examined the importance of spatio-temporal variations in leaf quality within and among tree species in promoting herbivore diversity, although other factors, such as tree species phylogeny and predators, may also have a large effect on lepidopteran larval communities.     

Canopy structure in a temperate old-growth evergreen forest analyzed by using aerial photographs

We used aerial photographs to create a digital elevation model of the canopy surface of a 10-ha study area in a temperate old-growth evergreen forest. A topographic map of the ground surface in a 4-ha permanent plot within the study area was also drawn from ground measurements. The difference between the two elevation values (i.e., canopy surface – ground surface) at each point in a 5-m grid was considered to be the canopy height, and a canopy height profile was constructed from these data. The canopy structure in the 4-ha plot that was estimated in this way was compared with that obtained by two ground observation methods, i.e., the canopy (vegetation) height profile method and the canopy coverage census method. Large gaps were adequately detected by the aerial photograph method, but small gaps were less often detected. Gap size distribution obtained by the aerial photograph method was similar to that observed on the ground, and was a function of gap depth. This study indicates that if a detailed topographic map can be made, the canopy height profile derived from aerial photography can be effective in analyzing the canopy structure of evergreen forests, such as tropical rain forests, over large areas.     

Fire disturbance and forest structure in old‐growth mixed conifer forests in the northern Sierra Nevada,California

Question: This study evaluates how fire regimes influence stand structure and dynamics in old‐growth mixed conifer forests across a range of environmental settings. Location: A 2000‐ha area of mixed conifer forest on the west shore of Lake Tahoe in the northern Sierra Nevada, California. Methods: We quantified the age, size, and spatial structure of trees in 12 mixed conifer stands distributed across major topographic gradients. Fire history was reconstructed in each stand using fire scar dendrochronology. The influence of fire on stand structure was assessed by comparing the fire history with the age, size, and spatial structure of trees in a stand. Results: There was significant variation in species composition among stands, but not in the size, age and spatial patterning of trees. Stands had multiple size and age classes with clusters of similar aged trees occurring at scales of 113 ‐ 254 m². The frequency and severity of fires was also similar, and stands burned with low to moderate severity in the dormant season on average every 9–17 years. Most fires were not synchronized among stands except in very dry years. No fires have burned since ca. 1880. Conclusions: Fire and forest structure interact to perpetuate similar stand characteristics across a range of environmental settings. Fire occurrence is controlled primarily by spatial variation in fuel mosaics (e.g. patterns of abundance, fuel moisture, forest structure), but regional drought synchronizes fire in some years. Fire exclusion over the last 120 years has caused compositional and structural shifts in these mixed conifer forests.     

Colonization of subtidal macroalgae in a fucalean-dominated algal assemblage,southwestern Australia

The influence of fucalean canopy species and dominant understory macroalgae on algal colonization was investigated to evaluate whether layering contributes to patterns in algal diversity. Patterns in recruitment were compared among total-clearing, understory-removal, canopy-removal, and undisturbed plots (plot area = 0.25 m²), using a randomized block design in depths <10 m and 10–20 m at Woody Island, Western Australia. To evaluate if propagules were available in the water column above the canopy layer, settlement plates (plate area = 0.04 m²) were deployed in depths <10 m, 10–20 m, and >20 m. A total of 198 macroalgal species was recorded. Biomass of the understory species Osmundaria prolifera Lamouroux and Botryocladia sonderi Silva was similar between canopy-removal and undisturbed plots. Diversity of macroalgae was similar in the presence and absence of a canopy layer. Taxa found in the canopy showed different patterns in recruitment. Cystoseiraceae recruited predominantly in total-clearings in both depth strata. Sargassaceae recruited most abundantly in depths <10 m. Density of canopy taxa on settlement plates was similar with depth (20–30 juveniles per plate), and juveniles were mainly Cystoseiraceae. In contrast to kelp beds or forests, patterns in algal colonization appeared to be maintained by environmental factors or processes other than the direct effects of layering in the subtidal fucoid-dominated assemblages at Woody Island. Handling editor: K. Martens     

Leaf dynamics of seedlings of rain forest species in relation to canopy gaps

Summary Leaf dynamics of eight tropical rain forest species seedlings was studied in three environments: the shaded forest understorey, a small gap of ±50 m², and a large gap of ±500 m². Leaf production rate and leaf loss rate were enhanced in gaps, and a large gap resulted in larger increases than a small gap. For most species net leaf gain rate was larger in gaps, although this rate was not always largest in the large gap. Leaf loss decreased, and leaf survival percentages increased with increasing shade tolerance of species, indicating a slower leaf turnover for more shade tolerant species. Leaf area growth rate was only partly determined by net leaf gain rate. Ontogenetic effects on leaf size were also important, especially in the large gap. Species which possessed leaves with high specific leaf weight (SLW) showed lower leaf loss rates and higher leaf survival percentages than species with low SLW leaves. Leaf life span seemed to be related to leafcost per unit area. The relation of specific patterns in leaf production and leaf loss to the regeneration mode of the species is briefly discussed.     

南方冰灾干扰后车八岭山地常绿阔叶林地被植物动态变化

按生长型划分广东省车八岭国家级自然保护区山地常绿阔叶林地被植物,研究自然干扰后连续3a(2008—2010年)不同生长型地被植物的动态变化。结果表明:(1)自然干扰后地被植物优势种的变化不大;草本植物约占优势种的60%,藤本植物约占20%—30%,灌木约占10%—20%。(2)2008年各生长型地被植物的在样方中个体数分布较其它年份都更为分散且更多;2009和2010年各生长型地被植物的个体数分布模式更为相似,尤其是灌木。2008—2010年草本植物丰富度逐年增加;藤本植物逐年减少;灌木2009年最多,2008年次之,2010年最少。(3)多响应置换过程的结果显示各生长型地被植物3a间的组成和分布有极显著差异(P0.0001);从各年度的两两比较看,各生长型地被植物组成和分布的年际差异显著程度逐渐降低:其中以草本植物的年间差异最大、年间变化的指示种最多;藤本植物居中;灌木的年间差异最小、年间变化指示种也最少。指示种分析与指示种在不同组分年份中的变化情况结合起来能筛选出指示作用更强的指示种。     

Tree diversity,composition, forest structure and aboveground biomass dynamics after single and repeated fire in a Bornean rain forest

Forest fires remain a devastating phenomenon in the tropics that not only affect forest structure and biodiversity, but also contribute significantly to atmospheric CO2. Fire used to be extremely rare in tropical forests, leaving ample time for forests to regenerate to pre-fire conditions. In recent decades, however, tropical forest fires occur more frequently and at larger spatial scales than they used to. We studied forest structure, tree species diversity, tree species composition, and aboveground biomass during the first 7 years since fire in unburned, once burned and twice burned forest of eastern Borneo to determine the rate of recovery of these forests. We paid special attention to changes in the tree species composition during burned forest regeneration because we expect the long-term recovery of aboveground biomass and ecosystem functions in burned forests to largely depend on the successful regeneration of the pre-fire, heavy-wood, species composition. We found that forest structure (canopy openness, leaf area index, herb cover, and stem density) is strongly affected by fire but shows quick recovery. However, species composition shows no or limited recovery and aboveground biomass, which is greatly reduced by fire, continues to be low or decline up to 7 years after fire. Consequently, large amounts of the C released to the atmosphere by fire will not be recaptured by the burned forest ecosystem in the near future. We also observed that repeated fire, with an inter-fire interval of 15 years, does not necessarily lead to a huge deterioration in the regeneration potential of tropical forest. We conclude that burned forests are valuable and should be conserved and that long-term monitoring programs in secondary forests are necessary to determine their recovery rates, especially in relation to aboveground biomass accumulation.     

Structure and dynamics in seasonal dry evergreen forest in northeastern Thailand

Abstract. Studies of tropical forest dynamics have often been based on one large-scale permanent plot, representative of a given forest type. Broad classifications of tropical forest types are expected to include a wide range of stand structures, dynamics patterns and species compositions – a range which cannot be represented in a single plot. To demonstrate this problem two 1-ha permanent plots, dominated by Hopea ferrea and Shorea henryana (both Dipterocarpaceae), respectively, were established in 1987 in seasonal dry evergreen forest at the Sakaerat Environmental Research Station in northeastern Thailand. In 1997 the plots were remeasured as to patterns of recruitment, mortality and growth. The Hopea plot was relatively static with low mortality, recruitment and growth. The Shorea plot was very dynamic with high rates of growth, mortality and recruitment. If the current trends continue, the plots are likely to further diverge. Even if the study of a large forest plot provides a good insight into tropical forest dynamics, it is necessary to consider the entire local pattern of variation.