Structure and dynamics of a <Emphasis Type="Italic">Castanopsis cuspidata</Emphasis> var. <Emphasis Type="Italic">sieboldii</Emphasis> population in an old-growth,evergreen, broad-leaved forest: The importance of sprout regeneration

The population structure and dynamics of Castanopsis cuspidata var. sieboldii were studied to evaluate vegetative and sapling regeneration in an old-growth, evergreen broad-leaved forest exposed to low-severity typhoon disturbances by annual typhoons on the Tsushima Islands in Japan. The density of individuals 5cm d.b.h. was 38.0ha^–1 in 1990; 7.9% were multiple-stemmed individuals. Over the 7-year study period (1990–1997), the number of individuals decreased, although the number of stems increased. Over 30% of apparently dead individuals were reconstituted by sprouting stems. Compared with sprout regeneration, sapling regeneration rarely occurred and was only observed in canopy gaps. Most individuals had at least one sprout shoot (H 30cm, d.b.h. <5cm), and the number and size of sprout shoots increased as the size of the individuals increased. During the study period, larger individuals with stem breakage tended to produce sprout stems. The density of saplings was 1074ha^–1 and they were more abundant in canopy gaps than under closed canopies, but large saplings were very rare even in canopy gaps. The population of C.cuspidata var. sieboldii consisted primarily of single-stemmed individuals with a few multiple-stemmed individuals providing a sprout bank. Larger individuals responded to the low severity typhoon disturbances and formed sprout stems. Although many saplings were observed, regeneration occurred more often by sprout formation than by growth of saplings. Thus, sprout regeneration is an important mode of regeneration, which allows this pioneer-like species to maintain its population in this forest.     

暖温带地区3种森林群落叶面积指数和林冠开阔度的季节动态

以辽东栎(Quercus liaotungensis)为主的落叶阔叶林、华北落叶松(Larix principis-rupprechtii)林和油松(Pinus tabulaeformis)林是暖温带林区具有代表性的森林群落类型。该研究应用国内外流行的半球图方法,通过对这3种森林群落叶面积指数和林冠开阔度的测定和综合比较,分析了叶面积指数和林冠开阔度的季节动态,揭示了暖温带地区不同类型森林群落叶面积指数和林冠开阔度的特征。研究结果表明,落叶阔叶林(优势种为辽东栎、棘皮桦(Betula dahurica)和五角枫(Acer mono))和华北落叶松林两种落叶森林群落的叶面积指数值均随生长季的到来而呈现增长的趋势,最大值出现在8月;林冠开阔度值随着生长季的到来而下降,最大值出现在11月。落叶阔叶林的叶面积指数和林冠开阔度的季节动态较之华北落叶松林明显。油松是常绿树种,其群落叶面积指数和林冠开阔度的变化程度均不明显,但林冠开阔度的变化趋势也是与叶面积指数的变化趋势相反。通过计算得出叶面积指数和林冠开阔度相关显著,并且呈现指数回归的关系。此研究结果为以遥感途径获取暖温带地区叶面积指数提供了地面校正依据,为研究该地区植被林冠的异质性及其造成的影响,以及进一步对该地区林分、景观和区域尺度上碳、水分和通量等方面的模拟提供了基础数据。     

Age‐related Crown Thinning in Tropical Forest Trees

Gap dynamics theory proposes that treefall gaps provide high light levels needed for regeneration in the understory, and by increasing heterogeneity in the light environment allow light‐demanding tree species to persist in the community. Recent studies have demonstrated age‐related declines in leaf area index of individual temperate trees, highlighting a mechanism for gradual changes in the forest canopy that may also be an important, but less obvious, driver of forest dynamics. We assessed the prevalence of age‐related crown thinning among 12 tropical canopy tree species sampled in lowland forests in Panama and Puerto Rico (total N = 881). Canopy gap fraction of individual canopy tree crowns was positively related to stem diameter at 1.3 m (diameter at breast height) in a pooled analysis, with 10 of 12 species showing a positive trend. Considered individually, a positive correlation between stem diameter and canopy gap fraction was statistically significant in 4 of 12 species, all of which were large‐statured canopy to emergent species: Beilschmiedia pendula, Ceiba pentandra, Jacaranda copaia, and Prioria copaifera. Pooled analyses also showed a negative relationship between liana abundance and canopy gap fraction, suggesting that lianas could be partially obscuring age‐related crown thinning. We conclude that age‐related crown thinning occurs in tropical forests, and could thus influence patterns of tree regeneration and tropical forest community dynamics.     

西天目山黄山松阔叶林的冠层干扰与动态推测

根据年龄结构和直径生长图分析研究了浙江省西天目山黄山松阔叶混交林的冠层干扰年表和发展动态。结果表明黄山松在该林地的定居发生在１８６１－１８８０年之间,黄山松定居３０－４０年后,其他阔叶树开妈在林下萌发生长,形成目前的黄山阔叶混交林,该林浆被阔叶叶树取代。     

Logging leaves a fingerprint on the number,size, spatial configuration and geometry of tropical forest canopy gaps

Recent advances in remote sensing such as airborne laser scanning have revolutionized our ability to accurately map forest canopy gaps, with huge implications for tracking forest dynamics at scale. However, few studies have explored how canopy gaps vary among forests at different successional stages following disturbances, such as those caused by logging. Moreover, most studies have focused exclusively on the size distribution of gaps, ignoring other key features such as their spatial distribution and shape. Here, we test a series of hypotheses about how the number, size, spatial configuration, and geometry of gaps vary across a logging disturbance gradient in Malaysian Borneo. As predicted, we found that recently logged forests had much higher gap fraction compared to old-growth forests, a result of having both a greater total number of gaps and a higher proportion of large gaps. Regrowing forests, on the other hand, fell at the opposite end of the spectrum, being characterized by both fewer and smaller gaps compared to nearby old-growth forests. Across all successional stages gaps were found to be spatially clustered. However, logging significantly diluted the degree of spatial aggregation and led to the formation of gaps with much more complex geometries. Our results showcase how logging and subsequent regrowth substantially alter not just the number and size of gaps in a forest, but also their spatial arrangement and shape. Linking these emergent patterns to their underlying processes is key to better understanding the impacts of human disturbance on the structure and function of tropical forests.     

2008特大冰冻灾害后大明山常绿阔叶林林冠结构动态

林冠结构是研究森林生态系统众多关键生态功能和过程的重要参数,常绿阔叶林是亚热带林区具有代表性的森林类型,对其林冠结构及动态特征的研究还很不深入。在广西大明山中山区选择了一个斜坡水平长200 m、宽160 m的典型坡面,在整个坡面建立了80个20 m×20 m的样地,将样地均匀分为5个坡段,每个坡段包含16个连续的样地,在2009—2012年的生长季测定了林冠高度(CH)、林冠体积(CV)、林冠覆盖度(CC)、林冠上/下冠盖比(HLr)和林冠叶面积指数(LAI),分析了各林冠结构指标的坡位及年际动态,揭示了亚热带常绿阔叶林的林冠结构特征及短期动态规律。研究结果表明,大明山常绿阔叶林林冠结构的一般特征是:平均CH(12.09±0.05)m,平均CV(2642.51±278.33)m~3(每400 m~2样地),平均CC(59.90±3.29)%,平均HLr2.48±0.23,平均LAI 2.00±0.06。大明山常绿阔叶林的林冠结构存在多层性,上层林冠覆盖度平均为42.20%,中层为30.35%,下层为18.05%。大明山常绿阔叶林的林冠结构存在坡面和年际差异,坡面变异系数为CV(29.84%—55.89%)HLr(32.90%—53.52%)LAI(22.48%—43.89%)CC(16.61%—25.74%)CH(8.26%—12.77%);年际变异系数为HLr(47.33%—57.00%)CV(39.70%—49.06%)LAI(21.58%—48.13%)CC(20.35%—24.15%)CH(9.19%—12.59%),表明CH有较强的稳定性。林冠LAI存在明显的坡面尺度效应,即向下顺坡每滑动100 m冠层LAI升高0.34。坡位对CH、HLr有显著(P=0.022)和极显著(P0.001)影响;年份对HLr有显著影响(P=0.013),对CV和CC有极显著影响(P0.001);坡位×年份对CV和LAI的交互作用显著(P=0.016,P=0.017)。回归分析发现树冠面积与林木胸径呈极显著的线性关系。此研究结果表明大明山常绿阔叶林冠层高度较低、林冠体积较小、林冠覆盖度不高、上/下冠盖比和叶面积指数偏小,这与研究区域的海拔较高(934—1223 m),土层浅薄(30—45 cm)以及经常受到冰冻灾害(特别是2008年的特大冰冻灾害)的影响有关,是山地常绿阔叶林树冠结构与山地环境条件长期适应的结果。     

Spatial genet dynamics of a dwarf bamboo: Clonal expansion into shaded forest understory contributes to regeneration after an episodic die-off

The ability of clonal plants to spread horizontally and to share resources within genets has long been considered advantageous in spatially heterogeneous environments, yet our understanding of how such traits relate to its widespread success and dominance is still limited. Using a dwarf bamboo, Sasa kurilensis, that often dominates cool-temperate forest understorys, we investigated how population recovery over 20 years after an episodic die-off may be augmented by clonal expansion via rhizomes. Previous analyses on genet demography using 9-m² plots showed that more productive genets were more likely to survive, spread laterally, and replace less productive ones. In this study, we examined whether the recovery of biomass in lower light microsites, where biomass recovery was initially slower, was supported by the spread of productive genets at larger scales, from surrounding higher-light microsites. We found that the biomass recovery in lower-light plots was more supported by genets that spread clonally into the plots. Such genets that spread from outside plots produced larger culms than those that had originally germinated there. Whereas genets that contributed much to the biomass of the low-light plots spread extensively from higher-light microsites, the spatial extent of genets that originally germinated in these plots was quite limited, so that the patterns of clonal expansion appeared to be unidirectional along the light gradient. Our findings suggest that clonal expansion of productive genets from higher-light into shaded microsites may be important for S. kurilensis to proliferate across heterogeneous light environments.     

Contrasting traits,contrasting environments,and considerations on population dynamics under a changing climate: an ecophysiological field study of two co‐dominant tree species

The increase in light availability resulting from canopy changes or opening is not always beneficial and can inhibit photosynthesis of tree seedlings already under other environmental stress. Tree seedlings' responses to compounded abiotic stress depend on their life‐history traits, and understanding the variations of such responses is important for understanding population dynamics under a changing climate. In this study we investigate how the photosynthesis of juveniles of two canopy tree species with different life‐history traits, Abies sachalinensis and Betula ermanii, differs in two contrasting sites at a sub‐boreal forest in northern Japan—one under a deciduous canopy (Closed site) and the other at a wide canopy opening (Open site). Seedlings at the Open site had low F_v/F_m (quantum yield of photosystem II) for a longer period than those at the Closed site. Abies sachalinensis at the Closed site showed lower F_v/F_m in spring than those at the Open site, but recovered after the canopy's new leaves flushed, indicating its acclimation to the shaded condition. Mean P_max (light‐saturated photosynthetic rate at ambient CO₂ levels) of A. sachalinensis seedlings was affected by site and air temperature, while B. ermanii seedlings were also affected by precipitation. Only B. ermanii's seedlings presented growth in the period studied, in spite of observed mid‐day drops to F_v/F_m attributed to water‐deficit‐related photoprotection. Results suggest that the climate change predicted for the Hokkaido area may increase the competitive advantage of broad‐leaved deciduous species, such as B. ermanii, in relation to evergreen conifers like A. sachalinensis.     

Elements of disturbance that affect epiphyte vitality in a temperate rainforest: an experimental approach

Aims Epiphytes are an abundant and diverse component of many wet temperate forests and have significant roles in ecosystem processes. Little is known about the processes and rates of their death and decomposition when they fall from the canopy, which limits our understanding of their role in forest carbon sequestration and nutrient cycling. In the temperate rainforest of the Quinault River Valley, Washington State, our aim was to test hypotheses regarding four elements of disturbance that might contribute to their decline.     

Legacy effects of canopy gaps on liana abundance 25 years later in a seasonal tropical evergreen forest in northeastern Thailand

Lianas require host trees to reach and stay in the forest canopy, but as seedlings and juveniles, they benefit from canopy gaps created by treefalls. Here, we evaluated the relative importance of these two aspects, that is, the availability of potential hosts vs. the legacy effect of past treefall gaps, on the local abundance of liana stems in a seasonal tropical evergreen forest in the Sakaerat Biosphere Reserve in northeastern Thailand. Within a 2.5-ha plot for forest dynamics monitoring, canopy height was measured in 1993 and 2018 at 5-m intervals to distinguish areas of mature (canopy height ≥ 20 m), building (10–20 m), and gap phases (< 10 m). In 2017–2018, we surveyed all liana stems ≥ 1 cm in diameter at breast height within 50 subplots (10 m × 10 m each) and recorded their diameter and the diameter of the host tree. Of a total of 445 liana individuals, 242 could be identified at least to the family level, while the others had clear morphological traits of climbing mechanisms. The number of liana stems was higher in areas that had been at the building/gap phase than those at the mature phase in 1993. When this 25-year-old legacy of past gap locations was considered, there was a positive association of local abundance between lianas and trees in areas at the mature phase in 2018. In conclusion, liana abundance reflected a long-term legacy of past treefall gaps more than 25 years earlier in this seasonal evergreen forest.     

黄土高原苹果园蒸腾导度大气驱动规律比较

植物蒸腾导度是表征土壤-植物-大气连续体（SPAC）中植物-大气间水汽传导过程、反映植物水分调控能力的一类重要变量,常见有冠层导度（G_c）、冠层气孔导度（G_s）与叶片气孔导度（g_s）,明确三者在反映冠层蒸腾过程时的异同或关联性对于理解植物水分利用机制具有重要意义。本研究基于对黄土高原果园苹果树生长季内树干液流（J_s）及环境因子的连续观测,计算了G_c、G_s及脱耦联系数（Ω）等变量,并与短期连续观测的叶片气孔导度（g_s）比较,分析了G_c、G_s和g_s在反映冠层蒸腾特征方面的异同及其关系。结果表明,日变化过程中G_s、g_s呈"单峰"型曲线,而G_c则呈"先增后减,午后抬升"的"双峰"型曲线。g_s与G_s存在较紧密的线性关系（R²=0.80）,但与G_c的线性关系较弱（R²=0.02）。G_c、G_s均随大气水汽压亏缺（VPD）的变化呈现确定的规律,其中,上边界函数呈递减的对数函数关系,平均值则符合先增后减的Log-Normal函数关系（R²>0.95）,拐点对应的VPD值分别为1.33和1.16 kPa。在一日内,G_s对VPD变化的响应过程与g_s对VPDL （基于叶片温度计算的水汽压亏缺）变化的响应过程总体一致,其一致性高于G_c对VPD变化的响应。整个生长季（4-10月）中果树的Ω平均值为0.12,随着Ω递减,G_c与G_s的线性相关性愈趋紧密,其斜率呈递增趋势,G_c越来越趋近于G_s。研究结果表明,在北方地区,基于树干液流的监测能较准确的推导整株并估算林分的冠层蒸腾导度。与实测g_s的变化过程比较,G_s比G_c具有更高的一致性,G_s可以作为描述苹果树水分利用过程响应大气驱动的更为恰当的变量。     

Three-dimensional soil heterogeneity modulates responses of grassland mesocosms to an experimentally imposed drought extreme

Heterogeneity is an intrinsic characteristic of soils, which regulates plant diversity and ecosystem functioning. However, whether soil heterogeneity also modulates responses of plant communities to climate change, including climate extremes, remains largely an open question. Here, we explore responses of plant communities to drought extremes across four levels of spatial soil heterogeneity, with cell sizes varying from very small to very large, i.e. 0, 12, 24 and 48 cm. These were created in mesocosms by alternating nutrient-rich and nutrient-poor substrate in three dimensions. A seed mixture of 24 grassland species was evenly sown on each mesocosm in spring. In late summer, a three-week drought was imposed with a rainout shelter. During the drought, soil water content at the mesocosm scale decreased more at intermediate (12 and 24 cm) than at small or large (0 and 48 cm) cell sizes, which was reflected in increased senescence and drought-induced heat stress. These responses could be traced to greater plant biomass coupled with higher water demand at those intermediate cell sizes, likely related to between-cell access to nutrients and effects of diversity and community composition. Our results indicate that soil heterogeneity can modulate the impact of drought extremes on plant communities, though more research is needed on the transition between intermediate and extreme cell sizes, where heterogeneity effects seem to change most. We propose that soil heterogeneity be considered more explicitly in studies of changing precipitation regimes.     

Linking canopy leaf area and light environments with tree size distributions to explain Amazon forest demography

Forest biophysical structure – the arrangement and frequency of leaves and stems – emerges from growth, mortality and space filling dynamics, and may also influence those dynamics by structuring light environments. To investigate this interaction, we developed models that could use LiDAR remote sensing to link leaf area profiles with tree size distributions, comparing models which did not (metabolic scaling theory) and did allow light to influence this link. We found that a light environment‐to‐structure link was necessary to accurately simulate tree size distributions and canopy structure in two contrasting Amazon forests. Partitioning leaf area profiles into size‐class components, we found that demographic rates were related to variation in light absorption, with mortality increasing relative to growth in higher light, consistent with a light environment feedback to size distributions. Combining LiDAR with models linking forest structure and demography offers a high‐throughput approach to advance theory and investigate climate‐relevant tropical forest change.     

Short‐term Dynamics and the Effects of Biotic and Abiotic Factors on Plant Physiognomic Groups in a Hurricane‐impacted Lower Montane Tropical Forest

We assessed the short‐term effects of biotic (density, plant size) and abiotic factors (light), on the dynamics of physiognomically different plant groups (palms, tree ferns, lianas, and trees) in a hurricane‐impacted tropical wet montane forest, John Crow Mountains, Jamaica. All plants ≥2 cm (dbh) found within 45, 25 × 25 m permanent sample plots (2.8125 ha), established according to a randomized block design along an elevation gradient, were tagged and measured (dbh) in 2006 and re‐assessed in 2012 after Hurricane Dean (2007). Hemispheric light was measured in 2007 and 2008. Tree and liana size class distributions changed due to high mortality in the smallest size classes and their densities declined; however, palm and tree fern density remained unchanged. The dynamics of trees were only related to tree fern and liana dynamics (e.g., tree mortality was negatively related to liana recruitment etc.). Although pre‐ and posthurricane light was related to palm density and the density of the other plant groups, respectively, there were no significant changes in light. Tree survivorship increased with increasing dbh while posthurricane light and overall density influenced the growth and survivorship of tree species. Species importance value did not change, suggesting that direct regeneration may be the model of forest recovery following this small‐scale disturbance. Over the short term, tree species showed life history trade‐offs that aid species coexistence after this moderate/low disturbance event. Our study highlights that hurricanes with low impacts can have differential short‐ and possibly long‐term effects on different plant groups.     

Predicting Liana Crown Location from Stem Diameter in Three Panamanian Lowland Forests1

In three forests that differed in annual rainfall and seasonality, the probability of a liana with a stem ≥2.0 cm stem diameter reaching the canopy was >50 percent. Lianas reached the canopy at significantly smaller size‐classes (1.5 cm) in the wet aseasonal forest, suggesting that this estimate changes with forest type. Nevertheless, as a general rule, we suggest that 2.0 cm is the minium stem diameter to examine the abundance and diversity of canopy lianas or canopy competition between lianas and trees.