Experimental and observational studies on seedling dynamics posit mechanisms that can influence forest diversity, structure and function. However, high mortality and slow growth of seedlings make it ...difficult to evaluate the importance of this life‐history filter to total tree life history. Quantifying the duration and transition of the seedling phase would help us understand this ‘black box’ in tree population biology.
We used a 16‐year dataset of comprehensive seedling‐to‐sapling demography from a subtropical rainforest to construct population models that capture temporal demographic fluctuations for eight major tree species. We used data‐driven demographic models and simulations to estimate the transition ratios from newly recruited seedlings to saplings of 2‐m height and the time taken to attain 2‐m height for a newly recruited seedling conditional on its survival.
Projections among species estimated that as few as 57 to more than 40,000 seedlings (with a median of 2,087) were required to make a single 2‐m high sapling. Furthermore, it would take 22–200 years (with a median of 47) for a newly recruited seedling to become a 2‐m high sapling. We found that temporal variation in demographic rates could greatly reduce the number of seedlings per established sapling, but not passage times (PTs). We also identified the importance of consistently fast growth rates for seedlings to escape the high mortality of early stages.
Synthesis. Our findings demonstrate that high mortality in the very early seedling stage severely limits the probability that a newly recruited seedling will transition to the sapling stage. Although the PTs vary, we found this to be true across species with a range of life‐history strategies. Only seedlings with consistently fast growth rates are expected to pass through this life‐history filter. Findings from seedling studies should consider how short‐term studies of seedling demography might capture the rare exceptional individuals and exceptional conditions that might define the dynamics of this seedling bottleneck.
摘要
許多小苗的動態監測與實驗研究均假定此階段的動態變化會影響森林的多樣性、結構與功能。然而，受限於小苗的高死亡率與低生長率，我們很難評估小苗階段的篩選對於樹木整體生活史動態的重要性。具體量化樹木個體在小苗階段的停留時間與轉換比例，可以幫助我們了解這個樹木族群動態中的「黑盒子」。
我們使用台灣福山亞熱帶雨林長達16年的小苗動態監測資料，來建構該森林中8種主要樹種的族群模式，此一模式可以忠實呈現樹木小苗生長率、死亡率隨時間變化之特性。我們透過此一族群模式進行數值模擬，估算樹木從剛萌發的新增苗成長到2 m高小樹之轉換比例，以及若小苗可以順利存活，其成長到2 m高所需的時間。
依據模式所推估的結果，有的樹種平均只需要57株新增苗就能有一株能長成2 m高的小樹，但也有樹種需要超過40,000株新增苗才能有一株小樹 (中位數為2,087株小苗)。而樹木個體在這個階段的停留時間，則介於22到200年 (中位數為47年)。當模式中納入小苗存活率與生長率之年間變化時，可以大幅地提高新增苗成長為小樹的成功率，但並不會影響在此階段的停留時間。我們也發現，樹木小苗持續性的快速生長是其能否突破小苗建立初期高死亡率的關鍵。
我們的研究顯示樹木小苗建立初期的高死亡率是新增苗能否成長為小樹的主要限制。儘管具有不同生活史策略的樹種從小苗成長為小樹時間有所差異，但其小苗同樣都受到這個限制的影響，只有能持續快速生長的小苗可以突破這層篩選。未來我們在詮釋小苗研究成果時，必須考慮小苗調查中能否涵蓋這些稀有但是能快速生長的個體，以及能讓小苗快速生長的條件，這兩者是決定樹木是否能突破「小苗瓶頸」的關鍵因子。
We used a demographic process model to quantify the seedling‐to‐sapling transition in a subtropical rainforest. Our results show that consistently fast growth is critical for tree seedlings to escape the high mortality of early stages, suggesting that the rare exceptional individuals (and exceptional conditions) might define the dynamics of this life‐history bottleneck.
Understanding processes and mechanisms of how species assemble in a metacommunity is crucial for illuminating the factors that contribute to the maintenance of biodiversity and developing management ...decisions. Ecologists have proposed a number of analytical methods for identifying the effects of various ecological processes, but there is no consensus on the best approach. Our study extends the existing framework which synthesizes multiple analytical methods and incorporates community data across space and time to understand the underlying ecological processes. We extended this framework by 1) including null‐model‐based analytical methods; 2) defining metacommunity archetypes that illustrate extreme cases of metacommunities, to observe how well they can be distinguished by different summary statistics, 3) applying the extended framework to real‐world vegetation data from a subtropical forest and interpreting the results, and 4) discussing the potential advantages, limitations, and future directions of applying this framework. We used a process‐based metacommunity simulation model to generate a simulated community dataset and applied random forest (RF) approach to estimate the strength of ecological processes in the process‐based model by considering the summary statistics calculated by the analytical methods as predictors. We also quantified the performance of the trained RF and applied it to estimate the strength of ecological processes in Fushan Forest Dynamics Plot. Our results demonstrate the framework's flexibility in incorporating different analytical methods and its generality to be applied to different community systems. We highlight its theoretical values in evaluating the performance of different statistics or indices in identifying ecological processes and its practical values in assessing the strength of ecological processes underlying real‐world metacommunities. Future improvements should focus on synthesizing statistics that capture specific signals of ecological processes and evaluating the robustness of estimation against dataset complexity and incompleteness.
Seedling dynamics are critical for determining community composition and future forest structure. Two mechanisms are crucial drivers of seedling vital rates: biotic interactions and environmental ...filtering. Biotic interactions at the neighbourhood scale, such as the Janzen–Connell effect, are considered among the main mechanisms maintaining species coexistence. These effects can show considerable temporal variation because of changes in neighbourhood density (i.e. seedling recruitment following masting years) and weather conditions. However, there is limited evidence of whether interannual variation in these conditions modulates biotic interactions and its potential cascading effects on seedling vital rates.
We used seedling data collected over 17 years in a subtropical rainforest in northern Taiwan. We modelled interannual variation in first‐year survival and growth of 12,830 seedlings of 36 species and 47 cohorts using (generalized) linear mixed‐effects models with several crowding indices and abiotic conditions (edaphic and topographic factors) as predictors.
The first‐year seedling survival and growth depended on both weather conditions and neighbourhood density. Seedling survival was greater when recruitment was more abundant and in years with greater rainfall, and this was mostly mediated by the interaction with conspecific and heterospecific seedlings. Seedling growth decreased with the increasing abundance of new recruits and increased with annual rainfall. Growth was negatively affected by the basal area of conspecific and heterospecific trees and by the density of conspecific seedlings when the number of new recruits was greater. The abiotic factors had a limited effect on seedling survival and growth compared to biotic factors.
Synthesis. Our results show that variation in recruitment abundance due to masting and annual rainfall significantly affects seedling vital rates by changing biotic interactions. These findings are in accordance with the economy of scale hypothesis, which predicts higher per‐capita reproductive success in years of higher seed production. Furthermore, the results support the hypothesis that fluctuations in rainfall can alter biotic interactions in forests. Efforts to predict forest community responses to climate changes should consider the temporal variations in biotic interactions.
Using data from 12,830 seedlings collected over 17 years in a subtropical rainforest, our study supports predictions of the Economy of Scale hypothesis, providing support for the expectations that higher seed production is reflected in higher recruitment success over the first year. We also found significant influence of rainfall fluctuations on biotic interactions. Climate changes might significantly affect future forest dynamics and composition through altering biotic interactions.
Summary
The relative importance of tree mortality risk factors remains unknown, especially in diverse tropical forests where species may vary widely in their responses to particular conditions.
We ...present a new framework for quantifying the importance of mortality risk factors and apply it to compare 19 risks on 31 203 trees (1977 species) in 14 one‐year periods in six tropical forests. We defined a condition as a risk factor for a species if it was associated with at least a doubling of mortality rate in univariate analyses. For each risk, we estimated prevalence (frequency), lethality (difference in mortality between trees with and without the risk) and impact (‘excess mortality’ associated with the risk, relative to stand‐level mortality).
The most impactful risk factors were light limitation and crown/trunk loss; the most prevalent were light limitation and small size; the most lethal were leaf damage and wounds. Modes of death (standing, broken and uprooted) had limited links with previous conditions and mortality risk factors.
We provide the first ranking of importance of tree‐level mortality risk factors in tropical forests. Future research should focus on the links between these risks, their climatic drivers and the physiological processes to enable mechanistic predictions of future tree mortality.
Plants have evolved mechanisms to track seasonal variation in environmental resources, enabling them to time key life‐history events to appropriate seasons. While the proximate cues for flowering ...initiation are well documented in the temperate region, it is still unclear what the flowering cues are in the tropics, especially in the subtropics. Our study compared first flowering dates (FFDs) predicted by eight hypothesized proximate cues concerning photoperiod, mean and directional changes in solar irradiance and warm/cool temperature, and rainfall with flowering dates observed over 19 years of weekly monitoring for 16 species in a subtropical rain forest. We observed considerable interannual variation in the median FFDs for the study species, ranging from 21 to 101 days. The early‐spring flowering species tended to have greater interannual variation in FFDs than the summer flowering species. For 13 study species, temperature cues best explained interannual variation in FFDs. Cool temperatures in the previous fall/winter and warm temperatures in the current spring (or previous summer) might trigger the onset of flowering in these 13 species. Cues associated with photoperiod and irradiance also predicted interannual variation in FFDs with small root mean square error (<1.5 census intervals) for 12 species but generally had higher prediction errors than temperature‐related cues. Cues associated with seasonal variation in rainfall failed to predict flowering times in any species. Our results suggest that future changes in temperature may alter flowering times for most species in subtropical forests, leading to changes in ecosystem processes and biosphere feedback to the climate system.
in Chinese is available with online material.
植物演化出許多不同的機制來追蹤環境資源的季節變化，讓關鍵的生活史事件發生在適當的季節。誘發植物開花的氣候因子在溫帶地區已有許多研究，但在熱帶，特別是亞熱帶地區，這類研究仍然相當缺乏。我們的研究使用了在亞熱帶雨林中進行19年的長期物候監測資料，分析16種植物的首次開花日期(first flowering date, FFD)的年間變化，以及光週期、太陽輻射、積溫、低溫以及雨量對於開花時間的影響。我們發現各植物的FFDs年間變化相當大，範圍從21到101天不等，早春開花的物種傾向於比夏季開花的物種具有更大的FFDs年間變異。溫度的年間變化可以準確預測13種植物的FFDs，前一年秋季/冬季的低溫和當年春季(或去年夏季)的高溫可能會誘發這13種植物的花芽發育。光周期和日照輻射也能夠預測12種植物的FFDs的年際變化，但通常比與溫度相關的物候模式具有較高的預測誤差。降雨量的年間變化並無法預測本研究16種植物的開花時間。由我們的研究結果推論，未來的氣溫變化可能會改變亞熱帶森林中大多數植物的開花時間，從而改變生態系與生物圈對氣候系統的反饋.
Plants in subtropical rain forests time their flowering using various cues. Our 19‐year study reveals temperature as the key factor influencing 13 out of 16 species. Changing temperatures may impact flowering times, reshaping subtropical ecosystems.
Accurate estimates of forest biomass stocks and fluxes are needed to quantify global carbon budgets and assess the response of forests to climate change. However, most forest inventories consider ...tree mortality as the only aboveground biomass (AGB) loss without accounting for losses via damage to living trees: branchfall, trunk breakage, and wood decay. Here, we use ~151,000 annual records of tree survival and structural completeness to compare AGB loss via damage to living trees to total AGB loss (mortality + damage) in seven tropical forests widely distributed across environmental conditions. We find that 42% (3.62 Mg ha−1 year−1; 95% confidence interval CI 2.36–5.25) of total AGB loss (8.72 Mg ha−1 year−1; CI 5.57–12.86) is due to damage to living trees. Total AGB loss was highly variable among forests, but these differences were mainly caused by site variability in damage‐related AGB losses rather than by mortality‐related AGB losses. We show that conventional forest inventories overestimate stand‐level AGB stocks by 4% (1%–17% range across forests) because assume structurally complete trees, underestimate total AGB loss by 29% (6%–57% range across forests) due to overlooked damage‐related AGB losses, and overestimate AGB loss via mortality by 22% (7%–80% range across forests) because of the assumption that trees are undamaged before dying. Our results indicate that forest carbon fluxes are higher than previously thought. Damage on living trees is an underappreciated component of the forest carbon cycle that is likely to become even more important as the frequency and severity of forest disturbances increase.
Tree mortality is typically considered the only source of biomass loss in forest systems. A pervasive but commonly neglected biomass loss is the damage to living trees (i.e., branchfall, trunk breakage, wood decay). We show that 42% of total aboveground biomass loss is due to damage to living trees across seven tropical forests. Our results contrast with the typically low forest biomass losses estimated only from tree mortality and suggest that forest carbon turnover may be higher than previously thought. Since forest disturbance rates are expected to increase under climate change, biomass loss to damage is likely to become more important
Questions
Quantifying tree species persistence through recurrent disturbances is of crucial importance for understanding forest dynamics in typhoon‐prone regions. We ask the following: (a) What are ...the major determinants of dominant tree survival in frequently typhoon‐disturbed forests? (b) Are survival determinants different between small and large trees?
Location
A subtropical old‐growth forest located in Fushan, Taiwan (24°45′34″N, 121°33′58″E), with frequent typhoon disturbances.
Methods
Data were from three consecutive censuses of a 25‐ha permanent forest plot that censused trees ≥1 cm in diameter every five years. The survival of three dominant tree species was modeled using generalized additive model and boosted trees with abiotic and biotic predictors. We evaluated model performance using validation data obtained from the two available census intervals.
Results
Model validations showed that multi‐stemming and tree size enhanced the survival of large and small trees, respectively. For the most dominant species, multi‐stemming had a consistently positive effect on survival irrespective of diameter classes. Abiotic factors and conspecific density had little effect on tree survival. Furthermore, evaluating model performance based on the data used in the model construction (i.e., training data) overestimated the predictive ability of survival models.
Conclusions
We showed that the survival determinants for the three most dominant species at Fushan changed from tree size for small trees to multi‐stemming for large trees. The results suggest that the dominant species in this frequently typhoon‐disturbed forest have the stature and architectural traits to persist, and thereby maintain their dominance and shape the forest physiognomy. Our approach illustrates how datasets from different census periods can be used in model validation to better assess model performance.
In a frequently typhoon‐impacted forest in Taiwan, yet with low mortality, we found that the survival determinants for the dominant species changed from tree size for small trees to multi‐stemming for large trees. The results suggested that the dominant species in this forest had the stature and architectural traits to persist, and thereby maintain their dominance and shape the forest physiognomy. (Photography by Hui‐Yi Yu.)
DNA barcodes of the native ray‐finned fishes in Taiwan Chang, Chia‐Hao; Shao, Kwang‐Tsao; Lin, Han‐Yang ...
Molecular ecology resources,
July 2017, 2017-Jul, 2017-07-00, 20170701, Volume:
17, Issue:
4
Journal Article
Peer reviewed
Species identification based on the DNA sequence of a fragment of the cytochrome c oxidase subunit I gene in the mitochondrial genome, DNA barcoding, is widely applied to assist in sustainable ...exploitation of fish resources and the protection of fish biodiversity. The aim of this study was to establish a reliable barcoding reference database of the native ray‐finned fishes in Taiwan. A total of 2993 individuals, belonging to 1245 species within 637 genera, 184 families and 29 orders of ray‐finned fishes and representing approximately 40% of the recorded ray‐finned fishes in Taiwan, were PCR amplified at the barcode region and bidirectionally sequenced. The mean length of the 2993 barcodes is 549 bp. Mean congeneric K2P distance (15.24%) is approximately 10‐fold higher than the mean conspecific one (1.51%), but approximately 1.4‐fold less than the mean genetic distance between families (20.80%). The Barcode Index Number (BIN) discordance report shows that 2993 specimens represent 1275 BINs and, among them, 86 BINs are singletons, 570 BINs are taxonomically concordant, and the other 619 BINs are taxonomically discordant. Barcode gap analysis also revealed that more than 90% of the collected fishes in this study can be discriminated by DNA barcoding. Overall, the barcoding reference database established by this study reveals the need for taxonomic revisions and voucher specimen rechecks, in addition to assisting in the management of Taiwan's fish resources and diversity.
Our aim was to analyze the clinical and survival differences among patients who underwent the two main treatment modalities, endoscopic ablation and radical nephroureterectomy. This study examined ...all patients who had undergone endoscopic management and RNU between Jul. 1988 and Mar. 2019 from the Taiwan UTUC registry. The inclusion criteria were low stage UTUC in RNU and all cases in endoscopic managed UTUC with a curative intent. The demographic and clinical characteristics were included for analysis. In total, 84 cases in the endoscopic group and 272 cases in the RNU group were enrolled for final analysis. The median follow-up period were 33.5 and 42.0 months in endoscopic and RNU group, respectively (p = 0.082). Comparison of Kaplan-Meier estimated survival curves between groups, the endoscopic group was associated with similar overall survival (OS), cancer specific survival (CSS), and intravesical recurrence free survival (IVRS) but demonstrated inferior disease free survival (DFS) (p = 0.188 for OS, p = 0.493 for CSS and p < 0.001 for DFS). Endoscopic management of UTUC was as safe as RNU in UTUC endemic region.
We previously presented the YM500 database, which contains >8000 small RNA sequencing (smRNA-seq) data sets and integrated analysis results for various cancer miRNome studies. In the updated YM500v3 ...database (http://ngs.ym.edu.tw/ym500/) presented herein, we not only focus on miRNAs but also on other functional small non-coding RNAs (sncRNAs), such as PIWI-interacting RNAs (piRNAs), tRNA-derived fragments (tRFs), small nuclear RNAs (snRNAs) and small nucleolar RNAs (snoRNAs). There is growing knowledge of the role of sncRNAs in gene regulation and tumorigenesis. We have also incorporated >10 000 cancer-related RNA-seq and >3000 more smRNA-seq data sets into the YM500v3 database. Furthermore, there are two main new sections, 'Survival' and 'Cancer', in this updated version. The 'Survival' section provides the survival analysis results in all cancer types or in a user-defined group of samples for a specific sncRNA. The 'Cancer' section provides the results of differential expression analyses, miRNA-gene interactions and cancer miRNA-related pathways. In the 'Expression' section, sncRNA expression profiles across cancer and sample types are newly provided. Cancer-related sncRNAs hold potential for both biotech applications and basic research.
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