Abstract
Successional processes ultimately determine and define carbon accumulations in forested ecosystems. Although primary succession on wholly new substrate occurs across the globe, secondary ...succession, often following storm events or anthropogenic disturbance, is more common and is capable of globally significant accumulations of carbon (C) at a time when offsets to anthropogenic carbon dioxide (CO
2
) emissions are critically needed. In Hawai'i, prior studies have investigated ecosystem development during primary succession on lava flows, including estimates of C mass accumulation. Yet relatively little is known regarding secondary succession of Hawaii's native forests, particularly regarding C mass accumulation. Here we documented aboveground C mass accumulation by native‐ and nonnative‐dominated second‐growth forests following deforestation of mature native lowland rainforests in the Puna District of Hawai'i Island. We characterized species composition and stand structure of three distinct successional forest stand types: those dominated by the native tree,
Metrosideros polymorpha
(ʻŌhiʻa), and those dominated by invasive nonnative trees,
Falcataria moluccana
(albizia) and
Psidium cattleianum
(strawberry guava). We compared
M. polymorpha
‐dominated and
F. moluccana
‐dominated second‐growth forests to adjacent mature
M. polymorpha
‐dominated forests as well as young
M. polymorpha
‐dominated forests undergoing initial stages of primary succession on 36‐years‐old lava fields. Aboveground carbon density (ACD) values of mature primary forest stands (171 Mg/ha) were comparable to those of mature continental tropical forests.
M. polymorpha
‐dominated second‐growth stands attained nearly 50% of ACD values of mature primary forests after less than 30 years of post‐disturbance succession and exhibited aboveground carbon accumulation rates of ~3 Mg C·ha
−1
·year
−1
. Such rates were comparable to those of second‐growth forests in continental tropics. Rates of ACD accumulation by second‐growth forests dominated by nonnative
F. moluccana
stands were similar, or slightly greater than, those of
M. polymorpha
‐dominated stands. However,
M. polymorpha
individuals were virtually absent from stands dominated by either
P. cattleianum
or
F. moluccana
. Taken together, results demonstrated that re‐establishment and rapid accumulation of C mass by
M. polymorpha
stands during secondary succession is certainly possible, but only where populations of nonnative species have not already colonized areas during early stages of secondary succession.
Native forests of Hawaiʻi Island are experiencing an ecological crisis in the form of Rapid ʻŌhiʻa Death (ROD), a recently characterized disease caused by two fungal pathogens in the genus ...Ceratocystis. Since approximately 2010, this disease has caused extensive mortality of Hawaiʻi's keystone endemic tree, known as ʻōhiʻa (Metrosideros polymorpha). Visible symptoms of ROD include rapid browning of canopy leaves, followed by death of the tree within weeks. This quick progression leading to tree mortality makes early detection critical to understanding where the disease will move at a timescale feasible for controlling the disease. We used repeat laser‐guided imaging spectroscopy (LGIS) of forests on Hawaiʻi Island collected by the Global Airborne Observatory (GAO) in 2018 and 2019 to derive maps of foliar trait indices previously found to be important in distinguishing between ROD‐infected and healthy ʻōhiʻa canopies. Data from these maps were used to develop a prognostic indicator of tree stress prior to the visible onset of browning. We identified canopies that were green in 2018, but became brown in 2019 (defined as “to become brown”; TBB), and a corresponding set of canopies that remained green. The data mapped in 2018 showed separability of foliar trait indices between TBB and green ʻōhiʻa, indicating early detection of canopy stress prior to the onset of ROD. Overall, a combination of linear and non‐linear analyses revealed canopy water content (CWC), foliar tannins, leaf mass per area (LMA), phenols, cellulose, and non‐structural carbohydrates (NSC) are primary drivers of the prognostic spectral capability which collectively result in strong consistent changes in leaf spectral reflectance in the near‐infrared (700–1300 nm) and shortwave‐infrared regions (1300–2500 nm). Results provide insight into the underlying foliar traits that are indicative of physiological responses of M. polymorpha trees infected with Ceratocycstis and suggest that imaging spectroscopy is an effective tool for identifying trees likely to succumb to ROD prior to the onset of visible symptoms.
Successional processes ultimately determine and define carbon accumulations in forested ecosystems. Although primary succession on wholly new substrate occurs across the globe, secondary succession, ...often following storm events or anthropogenic disturbance, is more common and is capable of globally significant accumulations of carbon (C) at a time when offsets to anthropogenic carbon dioxide (CO2) emissions are critically needed. In Hawai'i, prior studies have investigated ecosystem development during primary succession on lava flows, including estimates of C mass accumulation. Yet relatively little is known regarding secondary succession of Hawaii's native forests, particularly regarding C mass accumulation. Here we documented aboveground C mass accumulation by native‐ and nonnative‐dominated second‐growth forests following deforestation of mature native lowland rainforests in the Puna District of Hawai'i Island. We characterized species composition and stand structure of three distinct successional forest stand types: those dominated by the native tree, Metrosideros polymorpha (ʻŌhiʻa), and those dominated by invasive nonnative trees, Falcataria moluccana (albizia) and Psidium cattleianum (strawberry guava). We compared M. polymorpha‐dominated and F. moluccana‐dominated second‐growth forests to adjacent mature M. polymorpha‐dominated forests as well as young M. polymorpha‐dominated forests undergoing initial stages of primary succession on 36‐years‐old lava fields. Aboveground carbon density (ACD) values of mature primary forest stands (171 Mg/ha) were comparable to those of mature continental tropical forests. M. polymorpha‐dominated second‐growth stands attained nearly 50% of ACD values of mature primary forests after less than 30 years of post‐disturbance succession and exhibited aboveground carbon accumulation rates of ~3 Mg C·ha−1·year−1. Such rates were comparable to those of second‐growth forests in continental tropics. Rates of ACD accumulation by second‐growth forests dominated by nonnative F. moluccana stands were similar, or slightly greater than, those of M. polymorpha‐dominated stands. However, M. polymorpha individuals were virtually absent from stands dominated by either P. cattleianum or F. moluccana. Taken together, results demonstrated that re‐establishment and rapid accumulation of C mass by M. polymorpha stands during secondary succession is certainly possible, but only where populations of nonnative species have not already colonized areas during early stages of secondary succession.
A substantial amount of organismal complexity is thought to be encoded by enhancers which specify the location, timing, and levels of gene expression. In mammals there are more enhancers than ...promoters which are distributed both between and within genes. Here we show that activated, intragenic enhancers frequently act as alternative tissue-specific promoters producing a class of abundant, spliced, multiexonic poly(A)+ RNAs (meRNAs) which reflect the host gene's structure. meRNAs make a substantial and unanticipated contribution to the complexity of the transcriptome, appearing as alternative isoforms of the host gene. The low protein-coding potential of meRNAs suggests that many meRNAs may be byproducts of enhancer activation or underlie as-yet-unidentified RNA-encoded functions. Distinguishing between meRNAs and mRNAs will transform our interpretation of dynamic changes in transcription both at the level of individual genes and of the genome as a whole.
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► Intragenic enhancers act as unidirectional, cell-specific, alternative promoters ► Activated intragenic enhancers produce a class of multiexonic poly(A)+ RNAs, meRNAs ► meRNAs appear as isoforms of the host gene ► meRNAs add significantly to transcriptome complexity
Genotype‐by‐environment interaction (G × E), that is, genetic variation in phenotypic plasticity, is a central concept in ecology and evolutionary biology. G×E has wide‐ranging implications for trait ...development and for understanding how organisms will respond to environmental change. Although G × E has been extensively documented, its presence and magnitude vary dramatically across populations and traits. Despite this, we still know little about why G × E is so evident in some traits and populations, but minimal or absent in others. To encourage synthetic research in this area, we review diverse hypotheses for the underlying biological causes of variation in G × E. We extract common themes from these hypotheses to develop a more synthetic understanding of variation in G × E and suggest some important next steps.
Genotype‐by‐environment interaction (G × E) been extensively documented, and its presence and magnitude vary dramatically across populations and traits. Despite this, we still know little about why G × E is so evident in some traits and populations, but minimal or absent in others. Here, we review diverse hypotheses for the underlying biological causes of variation in G × E, extract common themes from these hypotheses to develop a more synthetic understanding of variation in G × E and suggest some important next steps.
Variation at regulatory elements, identified through hypersensitivity to digestion by DNase I, is believed to contribute to variation in complex traits, but the extent and consequences of this ...variation are poorly characterized. Analysis of terminally differentiated erythroblasts in eight inbred strains of mice identified reproducible variation at approximately 6% of DNase I hypersensitive sites (DHS). Only 30% of such variable DHS contain a sequence variant predictive of site variation. Nevertheless, sequence variants within variable DHS are more likely to be associated with complex traits than those in non-variant DHS, and variants associated with complex traits preferentially occur in variable DHS. Changes at a small proportion (less than 10%) of variable DHS are associated with changes in nearby transcriptional activity. Our results show that whilst DNA sequence variation is not the major determinant of variation in open chromatin, where such variants exist they are likely to be causal for complex traits.
Land-use change in forested regions of the tropics is currently one of the largest anthropogenic perturbations on earth; it is a force capable of altering biogeochemical cycles at local, regional, ...and global scales. However, significant uncertainties exist concerning the impact of land-use change on biomass and elemental pools of tropical forests. To evaluate the response of biomass and elemental pools to deforestation and land-use in the Los Tuxtlas Region, Mexico, total aboveground biomass (TAGB), C, N, S, and P pools were quantified along a land-use gradient that included primary forests, pastures, cornfields, and secondary forests. TAGB of primary forests averaged 403 Mg/ha; pastures and cornfields averaged 24 and 23 Mg/ha, respectively. Conversion of primary forests to pastures or cornfields resulted in declines of $\approx$94% of aboveground C pools, $\approx$92% of aboveground N, $\approx$83% of aboveground P, and between 89% and 95% of aboveground S. Soil pools of C, N, and S did not differ significantly between primary forests, pastures, and cornfields. Soil C to a 1 m depth ranged from 166-210 Mg/ha; N and S ranged from $\approx$16,000-20,000 kg/ha and $\approx$3400-3800 kg/ha, respectively. In secondary forests, TAGB increased with increasing forest age; accumulations ranged from 4.8 Mg/ha in a 6-month-old site to 287 Mg/ha in a 50-year-old site. Results indicate that secondary forests will attain the equivalent of primary forest TAGB in 73 years. However, rates of TAGB accumulation were constrained by land-use history; rates decreased with increasing duration of land use prior to abandonment. Soil pools of secondary forests were not correlated to forest age or prior land-use history and did not differ significantly from soil pools of primary forests, pastures, or cornfields. As a group, soils of primary and old secondary forest sites had significantly larger pools of available N and higher rates of nitrification and N mineralization than the combined group of pastures, cornfields, and recently abandoned sites. Currently, the Los Tuxtlas Region functions as a net source of greenhouse gases. Regenerating secondary forests have the capacity to counterbalance emissions resulting from deforestation, but presently constitute only a small percentage of the regional landscape.
Variation at regulatory elements, identified through hypersensitivity to digestion by DNase I, is believed to contribute to variation in complex traits, but the extent and consequences of this ...variation are poorly characterized. Analysis of terminally differentiated erythroblasts in eight inbred strains of mice identified reproducible variation at approximately 6% of DNase I hypersensitive sites (DHS). Only 30% of such variable DHS contain a sequence variant predictive of site variation. Nevertheless, sequence variants within variable DHS are more likely to be associated with complex traits than those in non-variant DHS, and variants associated with complex traits preferentially occur in variable DHS. Changes at a small proportion (less than 10%) of variable DHS are associated with changes in nearby transcriptional activity. Our results show that whilst DNA sequence variation is not the major determinant of variation in open chromatin, where such variants exist they are likely to be causal for complex traits.
Pacific Rim Forestry Brandeis, Thomas; Kuegler, Olaf; Pattison, Robert ...
Journal of forestry,
12/2011, Letnik:
109, Številka:
8
Journal Article
Recenzirano
Odprti dostop
Abstract 68Stakeholders' questions about subtropical and tropical forests can be as diverse and unique as the forests themselves. Obtaining the information needed to begin answering these questions ...requires innovation and adaptation of existing forest mensuration and inventory techniques that were developed primarily for use in temperate and boreal forests with a strong forest industry presence. Five cycles of forest inventory and monitoring in Puerto Rico and two cycles in the US Virgin Islands under the Forest Inventory and Analysis (FIA) program highlight the commonalities and differences between working in these subtropical forests and the temperate forests of the continental United States. Additionally, the Caribbean implementation of the FIA program has often taken a different approach from that used in the Pacific Islands territories. We can improve on delivery of forest resource information to island stakeholders by studying these experiences. By sharing the lessons learned with other Pacific Rim countries engaging in forest inventory and monitoring, we can learn from each other.
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