Disturbance dynamics and history of an old-growth subalpine fir (Abies fargesii) forest in central China

Disturbance history of an old-growth subalpine fir (Abies fargesii) forest in the Shennongjia Mountains of central China was reconstructed using dendroecological methods. Increment cores were extracted from 468 trees within six 100 m × 50 m permanent transects distributed across the old-growth subalpine fir forest of 300 ha. Growth patterns of 299 fir cores were examined for abrupt increases in radial growth to indicate formation of past canopy gaps and for rapid early radial growth to indicate establishment in past canopy gaps. The results showed that 70.8 % of the canopy fir trees experienced an average of 0.78 (ranging from 0 to 2) major release event for an average of 15.8 (ranging from 10 to 24) years, and an average of 1.94 (ranging from 0 to 3) moderate release events for an average of 25.6 (ranging from 10 to 36) years before they reached canopy. Recruitment pulse of trees coincided temporally with the peak of disturbance rate from the 1900s to the 1910s, suggesting occurrence of intense disturbance events during the time period. Radial growth analyses indicated that a history with small-scale disturbance events has resulted in the formation of the old-growth subalpine fir forest, and stand-replacing disturbances might not be necessary for the development of the forest. This study provides strong evidence that there are substantial variations in the disturbance severity and frequency over time. Most disturbance events might rather cause treefall gaps than clear large areas of forest at once. Thus, the old-growth subalpine fir forest experienced frequent gap-scale disturbances and few large-scale disturbances in its development history.     

Calibrating the radial-growth averaging method for detecting releases in old-growth forests of coastal British Columbia,Canada

Dendroecological methods that use growth releases to reconstruct the history of canopy disturbances are most useful when calibrated for specific species in specific forest types. In this study, we calibrate the radial-growth averaging method to detect growth releases of western redcedar (Thuja plicata Donn ex D. Don), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and Pacific silver fir (Abies amabilis Dougl. ex J. Forbes) following fine-scale canopy disturbances in old-growth forests of coastal British Columbia, Canada. Our goal is to establish a version of the method that will capture the full range of growth increases that occur for the study species following natural, fine-scale canopy gaps, yet will account for the effects of climatic variability on radial growth and growth increases. We used traditional dendroclimatological techniques and the radial-growth averaging method to examine how climatic and regional-scale factors contributed to radial growth and growth increases. In addition, we did a sensitivity analysis, using both ring widths and basal area increments, to explore how varying the values of three parameters of the radial-growth averaging method (threshold, moving average, and window) influenced the proportion of trees that showed a release pattern following the formation of canopy gaps of known timing of origin. Although radial growth of western redcedar and western hemlock was significantly associated with climate, percent-growth change derived from residual chronologies rarely exceeded 25%, which defined our minimum threshold for a release. For the sensitivity analysis, two general trends were common to all three species: (1) as threshold increased, the proportion of trees that showed a release pattern decreased, particularly for western redcedar and (2) a higher proportion of trees showed a release pattern using a 10-year versus a 5-year window, particularly for thresholds <100%. The greatest proportion of trees showed a release pattern using a 25% threshold, 5-year moving average, and 10-year window for both ring widths and basal area increments. Overall, a higher proportion of trees showed a release pattern using basal area increments as opposed to ring widths. Therefore, basal area increments are better suited to assess releases in these old-growth stands that have large inter- and intra-species variability in tree size. By establishing these empirically-based criteria, we have achieved the first step towards quantifying attributes of growth releases of trees in the study stands, allowing future studies to capture the variability of past disturbance events and predict changes in forest structure and composition over time.     

Disturbance history of an old-growth subalpine larch forest in the Qinling Mountains,north-central China

Knowledge on how historical disturbances shaped the long-term development of forests is essential for understanding the present forest structure and for predicting the future forest ecosystem dynamics. In this study, dendroecological methods were used to reconstruct the disturbance history of an old-growth subalpine larch (Larix chinensis) forest in the Qinling Mountains of north-central China. Growth patterns of 690 and 582 increment cores extracted respectively from two climatically and topographically different larch stands in the northern and southern slope of the Qinling Mountains were examined for abrupt increases in radial growth indicating formation of past canopy gaps and for rapid early growth rates indicating recruitment in former canopy gaps. The findings demonstrated that there were no large-scale, stand-replacing disturbances during the past more than two centuries. Low- and medium-severity disturbance events predominated, which were probably caused by windthrows due to strong winds. The stand was unevenly aged, and the recruitment pulses associated with disturbance peaks could be distinguished. There were considerable spatio-temporal differences in disturbance dynamics of the subalpine larch stand between the topographically and climatically different sites, manifesting that the larch stand in the northern slope experienced frequent moderate but rare major disturbance events, contrasting with frequent major and moderate disturbance events in the southern slope. This study provided strong evidences that there were substantial variations in the intensity and frequency of disturbance dynamics, leading to considerable differences in the size and age structures of the subalpine larch forest.     

Forest response to chronic hurricane disturbance in coastal New England

Question: Hurricanes and cyclones cause a wide range of damage to coastal forests worldwide. Most of these storms are not catastrophic in ecological terms, but forest responses to storms of moderate intensities are poorly understood. In regions with a high frequency of moderate hurricanes, how does variation in disturbance intensity affect the magnitude of ecological responses? Location: Naushon Island, Massachusetts, USA. Methods: We use historical records and dendroecological methods to characterize establishment and growth of Fagus grandifolia, Quercus alba, and Quercus velutina in response to seven non‐catastrophic hurricanes of varying intensity, and a major logging event, relative to baseline conditions, over the past 150 years. Our aim was to document variation in the magnitude of responses to known disturbance events of varying intensity, and to determine whether tree growth after moderate hurricanes differs from growth during periods of no disturbance. Results: Forest harvesting in 1824‐1827 had a strong impact on forest composition and growth. Since then, the study region has been characterized by little harvesting but frequent hurricanes. However, only one of the seven storms examined caused substantial increases in growth and new establishment for the dominant species; most moderate disturbances had minimal impact on growth and regeneration dynamics. We also document highly variable responses among species to individual storms, including substantial growth decreases that may not be detected by standard analytical approaches. Conclusions: Our results caution against the use of simple metrics such as wind speed to predict forest response to specific hurricanes, and highlight the importance of individual disturbance events in controlling long‐term forest dynamics, even in regions characterized by high disturbance frequency. In addition, we show that standard approaches to reconstructing disturbance history based on increases in radial growth and pulses of tree establishment are likely to underestimate the frequency of moderate disturbances.     

Nationally Representative Plot Network Reveals Contrasting Drivers of Net Biomass Change in Secondary and Old-Growth Forests

Uncertainty about the mechanisms driving biomass change at broad spatial scales limits our ability to predict the response of forest biomass storage to global change. Here we use a spatially representative network of 874 forest plots in New Zealand to examine whether commonly hypothesised drivers of forest biomass and biomass change (diversity, disturbance, nutrients and climate) differ between old-growth and secondary forests at a national scale. We calculate biomass stocks and net biomass change for live above-ground biomass, below-ground biomass, deadwood and litter pools. We combine these data with plot-level information on forest type, tree diversity, plant functional traits, climate and disturbance history, and use structural equation models to identify the major drivers of biomass change. Over the period 2002–2014, secondary forest biomass increased by 2.78 (1.68–3.89) Mg ha^?1 y^?1, whereas no significant change was detected in old-growth forests (+0.28; ?0.72 to 1.29 Mg ha^?1 y^?1). The drivers of biomass and biomass change differed between secondary and old-growth forests. Plot-level biomass change of old-growth forest was driven by recent disturbance (large tree mortality within the last decade), whereas biomass change of secondary forest was determined by current biomass and past anthropogenic disturbance. Climate indirectly affected biomass change through its relationship with past anthropogenic disturbance. Our results highlight the importance of disturbance and disturbance history in determining broad-scale patterns of forest biomass change and suggest that explicitly modelling processes driving biomass change within secondary and old-growth forests is essential for predicting future changes in global forest biomass.     

Plant functional types and disturbance dynamics – Introduction

Abstract. Plant functional traits and types are useful concepts in relation to disturbance responses of natural and managed ecosystems. To explore their applicability in greater depth, a set of 12 papers presents a broad range of issues from methodologies to the results of particular trait studies in the field, and modelling approaches. So far, empirical studies have only allowed us to identify a few functional traits that are consistently associated with disturbance. To determine the trait variations associated with climate, disturbance history and current disturbance regime as well as the interactions between these factors, global-scale comparisons of numerous individual studies are required. Significant advances toward this ambitious goal are presented in these papers, and include: (1) the articulation of experimental and analytical methodologies for individual studies that could usefully contribute to a global comparison; (2) the identification of core traits that can be used in the further search for disturbance-related traits common to a range of environments; (3) further information on vegetation response to disturbance in terms of trait representation, and the identification of attribute syndromes; (4) the identification of issues for modelling disturbance dynamics using functional types.     

山西省长治市过去150年森林的生长抑制和释放历史

森林生长与气候变化有着紧密的关系,在全球变暖情形下了解树木的干扰历史对准确预测森林生长的变化具有促进作用。本文选择山西黄土高原东南部长治地区保存较好的一个油松(Pinus tabuliformis)和两个白皮松(Pinus bungeana)森林为研究对象,利用树木年轮学方法分析了其干扰历史。结果表明:黎城县、平顺县和屯留县研究地点中年龄最老的树木分别有227、185、102a;通过计算树木径向生长的变化幅度,发现该地区在过去150年中发生了3次大的生长抑制事件(分别发生在1873—1877、1925—1930和1994—1997年期间)和5次大的生长释放事件(分别发生在1867—1871、1878—1884、1930—1935、1980—1985和1999—2004年期间)。树木径向生长与气象观测资料的相关分析显示,该地区森林生长在年际尺度上主要与6月份温度呈负相关而与4—5月份水分条件呈正相关,揭示了由降水减少或高温下水分蒸散所带来的极端干旱事件是导致森林抑制现象的主要原因。这些森林历史研究结果对区域林业管理具有实践意义,营林建设更宜选择在森林生长释放时期;经历多次干扰而存留下来的老龄树具有较强的抗干扰能力和丰富的历史信息,加强对老龄树的鉴定与针对性保护可有效维护区域森林生态服务功能。     

A comparison of algorithms for the identification of specimens using DNA barcodes: examples from gymnosperms

In order to use DNA sequences for specimen identification (e.g., barcoding, fingerprinting) an algorithm to compare query sequences with a reference database is needed. Precision and accuracy of query sequence identification was estimated for hierarchical clustering (parsimony and neighbor joining), similarity methods (BLAST, BLAT and megaBLAST), combined clustering/similarity methods (BLAST/parsimony and BLAST/neighbor joining), diagnostic methods (DNA–BAR and DOME ID), and a new method (ATIM). We offer two novel alignment‐free algorithmic solutions (DOME ID and ATIM) to identify query sequences for the purposes of DNA barcoding. Publicly available gymnosperm nrITS 2 and plastid matK sequences were used as test data sets. On the test data sets, almost all of the methods were able to accurately identify sequences to genus; however, no method was able to accurately identify query sequences to species at a frequency that would be considered useful for routine specimen identification (42–71% unambiguously correct). Clustering methods performed the worst (perhaps due to alignment issues). Similarity methods, ATIM, DNA–BAR, and DOME ID all performed at approximately the same level. Given the relative precision of the algorithms (median = 67% unambiguous), the low accuracy of species‐level identification observed could be ascribed to the lack of correspondence between patterns of allelic similarity and species delimitations. Application of DNA barcoding to sequences of CITES listed cycads (Cycadopsida) provides an example of the potential application of DNA barcoding to enforcement of conservation laws. © The Willi Hennig Society 2006.     

Refining the standardized growth change method for pointer year detection: Accounting for statistical bias and estimating the deflection period

Detecting pointer years in tree-ring data is a central aspect of dendroecology. Pointer years are usually represented by extraordinary secondary tree growth, which is often interpreted as a response to abnormal environmental conditions such as late-frosts or droughts. Objectively identifying pointer years in larger tree-ring networks and relating those to specific climatic conditions will allow for refining our understanding of how trees perform under extreme climate and consequently, under anticipated climate change. Recently, Buras et al. (2020) demonstrated that frequently used pointer-year detection methods were either too sensitive or insensitive for such large scale analyses. In their study, Buras et al. (2020) proposed a novel approach for detecting pointer years – the standardized growth change (SGC) method which outperformed other pointer-year detection methods in pseudopopulation trials. Yet, the authors concluded that SGC could be improved further to account for the inability to detect pointer years following successive growth decline. Under this framework, we here present a refined version of the SGC-method – the bias-adjusted standardized growth change method (BSGC). The methodological adjustment to the SGC approach comprises conflated probabilities derived from standardized growth changes with probabilities derived from a time-step specific global standardization of growth changes. In addition, BSGC allows for estimating the length of the deflection period, i.e. the period before extraordinary growth values have reached normal levels. Application of BSGC to simulated and measured tree-ring data indicated an improved performance in comparison to SGC which allows for the identification of pointer years following years of successive growth decline. Also, deflection period lengths were estimated well and revealed plausible results for an existing tree-ring data set. Based on these validations, BSGC can be considered a further refinement of pointer-year detection, allowing for a more accurate identification and consequently better understanding of the radial growth response of trees to extreme events.     

Stand dynamics of a yellow-poplar (Liriodendron tulipifera L.) forest in the Appalachian Mountains, Virginia, USA

Yellow-poplar (Liriodendron tulipifera L.) is a large, rapidly growing, shade-intolerant tree species common after disturbances on moist sites in the Appalachian Mountains. The species is typically scattered throughout old-growth mesophytic forests, where periodic gap formation creates conditions favorable for yellow-poplar establishment and growth. On abandoned agricultural fields, however, it is common for nearly monospecific forests of yellow-poplar to develop.This study examines stand dynamics of a yellow-poplar forest in western Virginia, USA that was established on agricultural fields abandoned in the late 1940s. Increment cores were collected from yellow-poplar trees growing on exposed ridgetops and in a more sheltered hollow. Tree-ring data show that the forest is even-aged. Tree establishment began about 5 years earlier on the ridgetops than in the hollow. Major ice storms disturbed the forest in 1978 and 1994, with two separate events in 1994. Ice storms disturb forests by depositing heavy loads of freezing rain on trees, breaking or uprooting them. The dendroecological data collected for this study provide little support for the hypothesis that ice storm disturbance promotes the establishment of new yellow-poplar cohorts. However, the data show that radial growth of some trees increased after ice storm disturbance, a pattern that reflects the increased availability of light following disturbance. Radial growth declined in some other trees as a consequence of severe injury during the storms.Radial growth responses following the 1978 ice storm were stronger on the ridgetops than in the hollow, suggesting that tree damage was more severe on the higher, more exposed sites. Growth responses were relatively mild following the storms of 1994, and did not exhibit pronounced topographic variations.     

Lack of intermediate-scale disturbance data prevents robust extrapolation of plot-level tree mortality rates for old-growth tropical forests

Lloyd et al. (2009) question the methods, concepts and conclusions of Fisher et al. (2008) . We address these assertions, and place our work into a broader context. We demonstrate the veracity of Fisher et al. , and further show that lack of data for intermediate-scale tree mortality disturbance events for old-growth tropical forests might prevent robust extrapolation of forest plot biomass accumulation data, and accurate estimates of distribution parameters such as power-law exponents ( α ).     

An automated program to find animals and crop photographs for individual recognition

Detailed data on individual animals are critical to ecological and evolutionary studies, but attaching identifying marks can alter individual fates and behavior leading to biases in parameter estimates and ethical issues. Individual-recognition software has been developed to assist in identifying many species from non-invasive photographic data. These programs utilize algorithms to find unique individual characteristics and compare images to a catalogue of known individuals. Currently, all applications for individual identification require manual processing to crop images so only the area of interest remains, or the area of interest must be manually delineated in each image. Thus, one of the main bottlenecks in processing data from photographic capture-recapture surveys is in cropping to an area of interest so that matching algorithms can identify the individual. Here, we describe the development and testing of an automated cropping program. The methods and techniques we describe are broadly applicable to any system where raw photos must be cropped down to a specific area of interest before pattern recognition software can be used for individual identification. We developed and tested the program for use with identification photos of wild giraffes.     

浙江古田山次生与老龄常绿阔叶林群落特征的比较

常绿阔叶林为东亚亚热带地区的地带性植被, 对该地区的生物多样性维持和社会发展具有重要的意义。由于长期人类活动的影响, 目前我国分布的常绿阔叶林绝大部分为次生常绿阔叶林。探究次生与老龄常绿阔叶林群落特征的差异, 有利于了解人类干扰对亚热带常绿阔叶林的影响, 为其保护和恢复提供依据。本研究在古田山老龄与次生常绿阔叶林内共设置了29个0.04 ha样地, 比较两者在优势种组成、物种和功能多样性以及生物量等方面的差异。结果表明: (1)次生林与老龄林优势种组成相似, 二者均以甜槠(Castanopsis eyrei)、木荷(Schima superba)等典型常绿阔叶林优势种为主, 但这些树种在次生和老龄常绿阔叶林中的优势度次序不同。(2)整体而言, 次生林的Shannon-Wiener指数和功能离散度高于老龄林; 次生林与老龄林的物种Bray-Curtis指数和功能Sørensen指数均无显著差别。(3)就垂直层次而言, 次生林与老龄林在Shannon-Wiener指数和Bray-Curtis指数的差异主要体现在乔木层和灌木层。(4)就群落结构而言, 次生林的植株密度高于老龄林, 但群落水平和个体水平的生物量均显著小于老龄林。上述结果表明, 人类干扰改变了古田山常绿阔叶林群落的多个重要特征, 不同群落特征的恢复过程并不同步。因此, 对常绿阔叶林生物多样性和生态系统功能的保护和恢复需要从多个角度着手。     

Assessment and management of old-growth forests in south eastern Australia

Abstract

Old-growth forests in south eastern Australia are important for biodiversity conservation, recreation, carbon storage, social values and, to a declining extent, for timber production. Developing a comprehensive definition of old-growth forest that can apply across all Australian vegetation types has been challenging. Old growth can be viewed from ecological and social perspectives. For policy and management purposes old growth has been defined as a growth stage in forest development, incorporating ecological maturity and lack of evidence of past disturbance. Classification and assessment of old growth has largely been restricted to those areas covered by regional forest agreements (RFAs) between different states and the Federal Government. Old growth can be impacted by wildfire, timber harvesting, insect pests, diseases and other disturbances. Climate change will also present challenges for the future management of old-growth forests. There is increasing scientific understanding of the relationships between species, forest growth stage and old-growth forest attributes. To meet biodiversity conservation objectives, the management focus is shifting from assessing and protecting old-growth forests, to providing for forests across the landscape with old-growth attributes. This approach may be at odds with other conceptions of old growth based on notions of undisturbed systems free of human influence.     

Does the disturbance hypothesis explain the biomass increase in basin‐wide Amazon forest plot data?

Positive aboveground biomass trends have been reported from old-growth forests across the Amazon basin and hypothesized to reflect a large-scale response to exterior forcing. The result could, however, be an artefact due to a sampling bias induced by the nature of forest growth dynamics. Here, we characterize statistically the disturbance process in Amazon old-growth forests as recorded in 135 forest plots of the RAINFOR network up to 2006, and other independent research programmes, and explore the consequences of sampling artefacts using a data-based stochastic simulator. Over the observed range of annual aboveground biomass losses, standard statistical tests show that the distribution of biomass losses through mortality follow an exponential or near-identical Weibull probability distribution and not a power law as assumed by others. The simulator was parameterized using both an exponential disturbance probability distribution as well as a mixed exponential–power law distribution to account for potential large-scale blowdown events. In both cases, sampling biases turn out to be too small to explain the gains detected by the extended RAINFOR plot network. This result lends further support to the notion that currently observed biomass gains for intact forests across the Amazon are actually occurring over large scales at the current time, presumably as a response to climate change.     

Tree mortality and effects of release from competition in an old‐growth Fagus‐Abies‐Picea stand

Abstract. In a montane mixed Fagus‐Abies‐Picea forest in Babia Gora National Park (southern Poland), the dynamics of an old‐growth stand were studied by combining an 8‐yr annual census of trees in a 1‐ha permanent sample plot with radial increments of Abies and Picea growing in the central part of the plot. The mortality among the canopy trees was relatively high (10% in 8 yr), but the basal area increment of surviving trees slightly exceeded the losses caused by tree death. DBH increment was positively correlated with initial diameter in Abies and Picea, but not in Fagus. For individual trees smaller than the median height, basal area increment was positively related to the basal area of old snags and the basal area of recently deceased trees in their neighbourhood, but negatively related to the basal area of live trees. Dendrochronological analysis of the past growth patterns revealed numerous periods of release and suppression, which were usually not synchronized among the trees within a 0.3 ha plot. The almost normal distribution of canopy tree DBH and the small number of young individuals in the plot indicated that stand dynamics were synchronized over a relatively large area and, hence, were consistent with the developmental phase concept. On the other hand, the lack of synchronization among periods of growth acceleration in individual mature Abies and Picea trees conforms more closely to the gap‐dynamics paradigm.     

Drought-induced mortality affects understory vegetation: release after death

In recent decades, severe droughts have become an important cause of canopy disturbance in forests, and have shown potential to cause rapid and pronounced vegetation shifts. Under dead canopy, undamaged understory could influence the nature of resource limitation for seedling growth and survival, limiting forest regeneration. We assessed the release response of understory vegetation after a severe drought event in temperate forests of northern Patagonia. Growth trends of dominant tree saplings, and changes in vegetation biodiversity and cover were compared between drought-dead and unaffected canopy. Nothofagus dombeyi undergo growth release after the climatic event in affected forests, and the response was evidenced immediately after the disturbance. For Austrocedrus chilensis, the growth release response was less evident, due mainly to a difference in age structure. In the understory the release response was barely discernable for some components. There was a tendency towards higher cover of the shrub layer in the understory of drought-affected forests, and an important presence of the exotic shrub Rosa rubiginosa. However, the clearest biotic response following drought mortality was the release in growth of understory dominant tree component. Those results strongly suggest that the environment under drought-dead canopy, and the die-off in woody sapling cohorts in a self-thinning process, could favor crown expansion and growth release of understory species that could help predict future forest trajectories in the context of the influence of climatic extreme events.     

Land snails as experimental animals: a study of the variability and distribution of individual weights in Helix aspersa snails born from the same clutch

A study was carried out to examine the distribution of individual weights in Helix aspersa snails, the aims being to establish the best estimate of the ponderal growth and also to obtain a model growth curve. Four groups of 20 snails from the same clutch were analysed and kept under experimental conditions from birth up to 6 months. The variability of their individual weights within groups was studied by calculating the coefficients of variation every 15 days. At the same time, the assumed normal distribution of those weights was being tested. The coefficients of variation increased with age and the assumed normal distribution of individual weights had to be rejected. By means of a log transformation of the original data, a model growth curve was constructed, and was used to assess the possibility of estimating age from weight. We finally reached the conclusion that median weight, rather than the mean, would be a better measure of central tendency to use until it is possible to obtain selected populations. The difficulty of estimating age from weight is emphasized.     

Anthropogenic disturbance and the formation of oak savanna in central Kentucky, USA

Aim To deepen understanding of the factors that influenced the formation of oak savanna in central Kentucky, USA. Particular attention was focused on the link between historical disturbance and the formation of savanna ecosystem structure. Location Central Kentucky, USA. Methods We used dendrochronological analysis of tree‐ring samples to understand the historical growth environment of remnant savanna stems. We used release detection and branch‐establishment dates to evaluate changes in tree growth and the establishment of savanna physiognomy. We contrasted our growth chronology with reference chronologies for regional tree growth, climate and human population dynamics. Results Trees growing in Kentucky Inner Bluegrass Region (IBR) savanna remnants exhibited a period of suppression, extending from the establishment date of the tree to release events that occurred c. 1800. This release resulted in a tripling of the annual radial growth rate from levels typical of oaks suppressed under a forest canopy (< 1 mm year^?1) to levels typical of open‐grown stems (3 mm year^?1). The growth releases in savanna trees coincided with low branch establishment. Over the release period, climatic conditions remained relatively constant and growth in regional forest trees was even; however, the growth increase in savanna stems was strongly correlated with a marked increase in Euro‐American population density in the region. Main conclusions Our data suggest that trees growing in savanna remnants originated in the understorey of a closed canopy forest. We hypothesize that Euro‐American land clearing to create pasturelands released these trees from light competition and resulted in the savanna physiognomy that is apparent in remnant stands in the IBR. Although our data suggest that savanna trees originated in a forest understorey, this system structure itself may have been a result of an unprecedented lack of Native American activity in the region due to population loss associated with pandemics brought to North America by Euro‐Americans. We present a hypothetical model that links human population dynamics, land‐use activities and ecosystem structure. Our model focuses on the following three land‐use eras: Native American habitation/utilization; land abandonment; and Euro‐American land clearance. Ecological understanding of historical dynamics in other ecosystems of eastern North America may be enhanced through recognition of these eras.     

Analysis of the pathway structure of metabolic networks.

Metabolic networks comprise a multitude of enzymatic reactions carrying out various functions related to cell growth and product formation. Although such reactions are occasionally organized into biochemical pathways, a formal procedure is desired to identify the independent pathways in a bioreaction network and the degree of engagement of each individual reaction in these pathways. We present a procedure for the identification of the independent pathways of bioreaction networks of any size and complexity. The method makes use of the steady-state internal metabolite stoichiometry matrix and defines the independent pathways through the reaction membership of its kernel matrix. Examples from the aromatic amino acid biosynthetic pathway and central carbon metabolism of cells in culture are provided to illustrate the method. Applications to the analysis of the control structure of bioreaction networks are also discussed.