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Establishment and heteroblasty of Acacia koa in canopy gaps
... Although site preparation techniques have been developed to help control kikuyu grass for koa restoration plantings [7,56], this is still an emerging science [40], and few studies have examined the potential for nursery cultural treatments to promote koa seedling establishment in the absence of effective site preparation. Further, while some recent studies on koa reforestation and restoration have followed the basic premise of the TPC by tracking nursery treatments in the field [7,57], most trials have either reported results of nursery treatments in the absence of outplanting [58][59][60] or evaluated site preparation treatments without a nursery component [49,61,62]. Additionally, most koa reforestation studies, and those conducted under tropical conditions more broadly, have been limited in time frame to the first year or two after planting, with relatively few longer-term assessments. ...
... These different leaf types have varying ecophysiological attributes related to light capture and drought resistance [64][65][66][67][68][69]. Thus, cultural treatments that affect this rate of transition may have important implications on koa growth and development beyond the establishment phase [49,62]. ...
Anthropogenic activity has caused persistent and prominent losses of forest cover in dry tropical forests. Natural regeneration of forest trees in grazed areas often fails due to lack of seed sources and consumption by ungulates. To address this, the effective restoration of such sites often requires fencing and outplanting nursery-grown seedlings. In the degraded, dry forests of tropical Hawaii, USA, an additional challenge to restoration of native forest trees is the introduced kikuyu grass (Cenchrus clandestinus). This invasive, rapidly growing rhizomatous plant forms deep, dense mats. We studied the use of nursery cultural techniques to facilitate the establishment of koa (Acacia koa) seedlings outplanted amidst well-established kikuyu grass on a volcanic cinder cone on the dry, western side of Hawaii Island. Seedlings were grown four months in three container sizes (49, 164, 656 cm3) and with four rates (0, 4.8, 7.2, and 9.6 kg m−3) of 15–9–12 (NPK) controlled-release fertilizer incorporated into media prior to sowing. After 16 months in the field, seedling survival was > 80% for all treatments with two exceptions: the non-fertilized 49 cm3 (78%) and 164 cm3 (24%) containers. After 10 years, only these two treatments had significantly lower survival (35% and 10%, respectively) than the other treatments. One year following planting, none of the non-fertilized seedlings had transitioned to phyllodes from juvenile true leaves, regardless of container size. For the fertilized 656 cm3 container treatment, 78%–85% of seedlings had phyllodes, with mean values increasing by fertilizer rate. Phyllodes are known to confer greater drought resistance than true leaves in koa, which may help to explain the improved survival of fertilized trees on this relatively dry site. Overall, nursery fertilization was more influential on seedling height and diameter response than container size after outplanting. However, the largest container (656 cm3) with the addition of fertilizer, produced significantly larger trees than all other treatments during the early regeneration phase; early growth differences tended to fade at 10 years due to inter-tree canopy competition. Although koa is able to fix atmospheric nitrogen through rhizobium associations, our data confirm the importance of nursery fertilization in promoting regeneration establishment. Nursery cultural techniques may play an important role in forest restoration of dry tropical sites invaded by exotic vegetation.
... Although our study provides evidence that koa can exhibit fast growth under partial shade, we hypothesize that this can only occur under gap conditions. Rose et al. (2019b), a study in which koa was planted under a koa canopy, showed that overhead shading of the same average magnitude of our more closed canopy treatments negatively affected seedling survival and growth. The relationship between koa performance under varying canopy cover is likely dependent on stand structure and the presence of a canopy gap directly above the seedling. ...
... Finally, our methods facilitated the finding of a specific case in a novel restoration ecosystem in which heteroblasty was adaptive in partially shaded environments, likely contributing to the establishment of highperforming koa on a harsh, frost prone site. In contrast to another recent study on koa and canopy gaps (Rose et al., 2019b), growth increased with increased shade when seedlings were fertilized and increased performance was correlated with retention of true leaves, providing evidence for the adaptiveness of heteroblasty in canopy gaps for phyllodinous Acacia spp. Future work on frost-prone sites should include investigations into the role of anti-freeze proteins in tropical treeline species; and restoration efforts should integrate genetically improved planting material with silvicultural advances to further increase success rates (Friday et al., 2015;Löf et al., 2019). ...
Restoration of abandoned, high-elevation pastures is needed across many ecosystems. Diverse abiotic and biotic stressors often limit establishment of native trees species, however, justifying the need for novel approaches to alleviate such stressors. Freezing damage often negatively impacts survival of planted trees across temperate landscapes and on some high-elevation tropical restoration sites, such as for Acacia koa (koa) in Hawaii, USA. Koa performs poorly under forest canopies, a potential limitation to the use of nurse trees for establishment on frost-prone sites. Using a heterogeneous canopy of a non-native conifer, Cryptomeria japonica, we underplanted koa seedlings along a simulated range of canopy shelter levels in combination with field fertilization. We tested the effect of a canopy cover gradient and nutrient availability on frost avoidance and tolerance responses, as well as the potential to harness koa's developmental plasticity to optimize growth and survival. C. japonica canopy cover provided protection from frost damage, with increased sheltering under greater canopy closure. When combined with fertilization, increasing canopy closure reduced frost damage and increased koa growth. Although we observed limited frost damage in our study, leaf-level soluble sugars increased during the winter and in more open microsites, reflecting a potential mechanism for frost tolerance in this tropical species. We conclude that frost-tolerant conifers used as nurse trees represent a potential tool to help establish native tree species on high-elevation, frost-prone sites.
... Under drought, however, the L population had the lowest resistance to drought when light was co-limiting. This response might reflect koa's adaptation for gap regeneration in the denser forest canopies found at low elevations (Engelbrecht et al., 2007;Rose et al., 2019a). The low elevation population occurs naturally under conditions of high water and nutrient resource availability, and plants growing under such conditions tend to have large leaf area (Markesteijn and Poorter, 2009), which is accompanied by the increases in vulnerability to water deficit under high light. ...
Introduction
Plant species often exhibit significant variation in functional traits in populations along elevational gradients to cope with varying stress conditions. While plant development has been assumed to be most limited by a single resource, growing evidence suggests the potential for interactions of co-limiting resources to impact plant performance. Here, we aimed to determine how light, nitrogen, and water availability influence the growth and physiology of different populations of koa ( Acacia koa ), a tree species of concern that occurs across a large elevational gradient in tropical Hawaii, United States.
Methods
Populations from three seed sources [low (L), mid (M), and high (H) elevation] were grown in a controlled greenhouse experiment and exposed to co-limiting light, water, and nutrient (nitrogen) conditions. Light response, gas exchange, water status, resource use efficiency, nutrients and shoot non-structural carbohydrate concentrations, and growth and biomass allocation responses were quantified.
Results
We found that resource co-limitation sometimes interacted to determine responses of the measured parameters. In general, the low elevation (L) koa population was more sensitive to conditions where both moisture and nutrients were limiting, while the high elevation (H) koa population was more sensitive to conditions where either light and moisture or light and nitrogen were co-limiting. The M population performed well overall regardless of resource limitation.
Discussion
Our findings lend support to the theory that multiple resources limit growth and physiology of populations rather than the traditional view of a single resource limiting performance. Therefore, the possibility that multiple resource limitations drive population differences should be considered when developing population-based guidelines for forest and tree species restoration.
Plant functional strategies change considerably as plants develop, driven by intraindividual variability in anatomical, morphological, physiological and architectural traits.
Developmental trait variation arises through the complex interplay among genetically regulated phase change (i.e. ontogeny), increases in plant age and size, and phenotypic plasticity to changing environmental conditions. Although spatial drivers of intraspecific trait variation have received extensive research attention, developmentally driven intraspecific trait variation is largely overlooked, despite widespread occurrence.
Ontogenetic trait variation is genetically regulated, leads to dramatic changes in plant phenotypes and evolves in response to predictable changes in environmental conditions as plants develop.
Evidence has accumulated to support a general shift from fast to slow relative growth rates and from shade to sun leaves as plants develop from the highly competitive but shady juvenile niche to the stressful adult niche in the systems studied to date.
Nonetheless, there are major gaps in our knowledge due to examination of only a few environmental factors selecting for the evolution of ontogenetic trajectories, variability in how ontogeny is assigned, biogeographic sampling biases on trees in temperate biomes, dependencies on a few broadly sampled leaf morphological traits and a lack of longitudinal studies that track ontogeny within individuals. Filling these gaps will enhance our understanding of plant functional ecology and provide a framework for predicting the effects of global change threats that target specific ontogenetic stages.
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Premise:
Chenopodium oahuense is a polymorphic Hawaiian endemic plant inhabiting several xeric habitats. Considerable variability in leaf morphology has made comprehensively describing its diversity difficult. Chenopodium oahuense subsp. ilioense is differentiated from C. oahuense subsp. oahuense by smaller, less-lobed, succulent leaves, smaller seeds, and prostrate to scandent habit. The lacking quantification of leaf shape, succulence, and previously unknown heteroblastic leaf transition in C. oahuense subsp. ilioense complicates the morphological boundaries separating subspecies.
Methods:
This study used landmark analyses, elliptical Fourier descriptors (EFDs), and traditional shape descriptors measured from 1585 greenhouse-grown plant leaves collected over 18 weeks. Principal component analyses visualized correlations in leaf shape, and linear discriminant analyses predicted classifications, either subspecific or heteroblastic.
Results:
Identity determination and heteroblastic change visualization were limited in landmark analyses. On the basis of EFDs and shape descriptors, C. oahuense subsp. ilioense was determined to be morphologically differentiated from C. oahuense subsp. oahuense with the Pu'u Ka Pele population as intermediate. The EFDs depicted heteroblastic change, predominantly in lobing. All analyses were restricted in correctly attributing a leaf to the week collected. Shape descriptors generally represented significant heteroblastic change over the growth period.
Conclusions:
These analyses support significant differentiation between the subspecies, particularly from shape descriptors. Furthermore, we quantified the morphological intermediacy of the Pu'u Ka Pele population. Results suggest this population could be the result of incomplete lineage sorting or a recent hybridization of the two subspecies. Hawaiian Chenopodium is a polymorphic lineage notable for future research in adaptive radiations, phenotypic plasticity, and heteroblasty.
Identifying and quantifying the importance of environmental variables in structuring population genetic variation can help inform management decisions for conservation, restoration, or reforestation purposes, in both current and future environmental conditions. Landscape genomics offers a powerful approach for understanding the environmental factors that currently associate with genetic variation, and given those associations, where populations may be most vulnerable under future environmental change. Here, we applied genotyping by sequencing to generate over 11,000 single nucleotide polymorphisms from 311 trees and then used nonlinear, multivariate environmental association methods to examine spatial genetic structure and its association with environmental variation in an ecologically and economically important tree species endemic to Hawaii, Acacia koa. Admixture and principal components analyses showed that trees from different islands are genetically distinct in general, with the exception of some genotypes that match other islands, likely as the result of recent translocations. Gradient forest and generalized dissimilarity models both revealed a strong association between genetic structure and mean annual rainfall. Utilizing a model for projected future climate on the island of Hawaii, we show that predicted changes in rainfall patterns may result in genetic offset, such that trees no longer may be genetically matched to their environment. These findings indicate that knowledge of current and future rainfall gradients can provide valuable information for the conservation of existing populations and also help refine seed transfer guidelines for reforestation or replanting of koa throughout the state.
Restoring degraded mesic-montane forests represents a major challenge in maintaining functioning ecosystems throughout the tropics. A key example of this lies in Hawai‘i, where restoring native koa (Acacia koa, A. Gray) forests are a top conservation and forestry priority because of the critical habitat and high-value timber products that they provide. Efforts to restore koa forests, however, are directly impeded by extensive, non-native kikuyu grass (Pennisetum clandestinum Hochst. ex Chiov.) swards occupying deforested montane landscapes. In this study, we implemented a combination of grass suppression and selection of koa seedling stocktypes to measure outplanting performance in a naturalized site on the island of Maui. Seedlings were grown in a nursery in two root container sizes (111 and 207 cm3) and subsequently outplanted into grass-dominated plots that were either untreated or suppressed with a high-rate herbicide combination of imazapyr and glyphosate (1.7 kg a.i. ha−1, respectively), 30 days prior to planting. Across all treatments, seedling survival was high (>95 %). Thirty months after planting, trees from the larger stocktype had significantly greater growth in height and root-collar diameter. Initial grass suppression resulted in trees that were 34 % taller with 66 % larger root-collar diameters after 30 months. Herbicide treated plots also had significantly higher leaf area indices (2.6 vs. 1.8 m2 m−2), indicative of higher photosynthetic capacity and canopy closure. Grass suppression increased soil temperature along with soil moisture in the first year followed by a dramatic drop in moisture corresponding to large growth responses by koa seedlings after the first year. These results demonstrate how the combination of fundamental silvicultural practices in the nursery and on the outplanting site can accelerate tree growth to meet restoration goals in shorter time intervals. This is a first report of koa (a leguminous species) tolerance to a high-rate, pre-plant application of the herbicide active ingredient imazapyr. © 2015, Springer Science+Business Media Dordrecht (outside the USA).
Hawai‘i has served as a model system for studies of nutrient cycling and conservation biology. The islands may also become a laboratory for exploring new approaches to forest restoration because of a common history of degradation and the growing number of restoration projects undertaken. Approximately half of the native ecosystems of Hawai‘i have been converted to non-native conditions. Many restoration projects have focused on intensively managed out plantings of native plants with emphasis on threatened and endangered species. While these projects have been effective in stabilizing plant populations, this model is often prohibitively expensive for restoration at the scale needed to protect watersheds and provide habitat for rare bird species. Here we suggest ways of rethinking ecological restoration that are applicable across the tropics, particularly on islands and fire-prone grasslands. First, we suggest making use of non-native, non-invasive species to help reclaim degraded or invaded sites or as long-term components of planned restoration outcomes. Second, we suggest incorporating remote sensing techniques to refine where restoration is carried out. Finally, we suggest borrowing technologies in plant production, weed control, and site preparation from industrial forestry to lower restoration costs. These suggestions would result in ecosystems that differ from native reference systems in some cases but which could be applied to much larger areas than most current restoration efforts while providing important ecosystem services. We also stress that community involvement is key to successful restoration, as a major goal of almost all restoration projects is to re-connect the community with the forest.
Variation in shade tolerance is a primary mechanism driving succession in northern deciduous forests. However, little is known about interspecific differences in the traits responsible for shade tolerance. Is shade tolerance due to the ability to grow or survive in deep shade, or both? How do plant morphology and photosynthesis relate to growth in shade? Is low light the sole critical stress determining differences in "shade tolerance" or do belowground resources interact with low light to affect growth and survival? In this study we address these questions for seedlings of Betula papyrifera Marsh., Betula alleghaniensis Britton, Ostrya virginiana (Mill.) K. Koch, Acer saccharum Marsh., and Quercus rubra L. grown for 2 yr in outdoor shade houses in a complete factorial of low light (2 and 8% open sky) and nitrogen (forest soil and forest soil plus 200 kg N·ha-1·yr$^{-1}$). For these seedlings we examined effects of light and nitrogen on the interrelationships among survival, growth, and shade tolerance and explored the physiological bases of shade tolerance by examining the relationship of plant morphology and photosynthesis to growth. Nitrogen amendments did not have a significant effect on any plant trait at either light level. In 8% light, growth and survival were highest for shade-intolerant Betula papyrifera and mid-tolerant Betula alleghaniensis, lower for shade-tolerant Ostry and Acer, and lowest for disturbance-adapted Quercus. In 2% light, species rankings reversed as Ostrya and Acer had higher growth and survival than the other species. Second-year survival was strongly related to 1st-yr growth($P
Premise of research. Heteroblastic species are those that show an abrupt change in shape and/or size among individual metamers during ontogeny. Gevuina avellana Mol. (Proteaceae) is a typical tree species in the temperate rain forests of Chile and Argentina. This tree shows drastic heteroblasty, changing from simple leaves at the seedling stage to pinnate leaves during development. It regenerates mostly in shady understories, but juveniles can be found growing under a wide range of light conditions (5%–50% canopy openness). Thus, considering that light has been proposed as a driver of the heteroblastic strategy, G. avellana is an interesting model to study the potential environmental modulation of its ontogenetically programmed heteroblasty. Therefore, the aim of this study was to determine the effect of light availability on G. avellana’s heteroblastic trajectory. We postulated that G. avellana’s ontogenetic changes in leaf complexity (i.e., heteroblasty) increase under high light availability.Methodology. Saplings along most of the light availability gradient were sampled. Plant height was used as a proxy for ontogeny. We measured several leaf traits (leaf area), shape (aspect ratio), pinnation (leaf dissection index), and complexity (fractal dimension index). First, we evaluated the change in each leaf trait with height by means of Pearson’s correlation. Then we tested for differences in leaf traits along the ontogeny between two light environments (higher and lower than 10% canopy openness) by the line-fitting standardized major axis method.Pivotal results. We found positive correlations between each leaf trait and plant height (P
Acacia sensu stricto is found predominantly in Australia; however, there are 18 phyllodinous taxa that occur naturally outside Australia, north from New Guinea to Indonesia, Taiwan, the Philippines, south-western Pacific (New Caledonia to Samoa), northern Pacific (Hawaii) and Indian Ocean (Mascarene Islands). Our aim was to determine the phylogenetic position of these species within Acacia, to infer their biogeographic history. To an existing molecular dataset of 109 taxa of Acacia, we added 51 new accessions sequenced for the ITS and ETS regions of nuclear rDNA, including samples from 15 extra-Australian taxa. Data were analysed using both maximum parsimony and Bayesian methods. The phylogenetic positions of the extra-Australian taxa sampled revealed four geographic connections. Connection A, i.e. northern Australia–South-east Asia–south-western Pacific, is shown by an early diverging clade in section Plurinerves, which relates A. confusa from Taiwan and the Philippines (possibly Fiji) to A. simplex from Fiji and Samoa. That clade is related to A. simsii from southern New Guinea and northern Australia and other northern Australian species. Two related clades in section Juliflorae show a repeated connection (B), i.e. northern Australia–southern New Guinea–south-western Pacific. One of these is the 'A. auriculiformis clade', which includes A. spirorbis subsp. spirorbis from New Caledonia and the Loyalty Islands as sister to the Queensland species A. auriculiformis; related taxa include A. mangium, A. leptocarpa and A. spirorbis subsp. solandri. The 'A. aulacocarpa clade' includes A. aulacocarpa, A. peregrinalis endemic to New Guinea, A. crassicarpa from New Guinea and Australia, and other Australian species. Acacia spirorbis (syn. A. solandri subsp. kajewskii) from Vanuatu (Melanesia) is related to these two clades but its exact position is equivocal. The third biogeographic connection (C) is Australia–Timor–Flores, represented independently by the widespread taxon A. oraria (section Plurinerves) found on Flores and Timor and in north-eastern Queensland, and the Wetar island endemic A. wetarensis (Juliflorae). The fourth biogeographic connection (D), i.e. Hawaii–Mascarene–eastern Australia, reveals an extreme disjunct distribution, consisting of the Hawaiian koa (A. koa, A. koaia and A. kaoaiensis), sister to the Mascarene (Réunion Island) species A. heterophylla; this clade is sister to the eastern Australian A. melanoxylon and A. implexa (all section Plurinerves), and sequence divergence between taxa is very low. Historical range expansion of acacias is inferred to have occurred several times from an Australian–southern New Guinean source. Dispersal would have been possible as the Australian land mass approached South-east Asia, and during times when sea levels were low, from the Late Miocene or Early Pliocene. The close genetic relationship of species separated by vast distances, from the Indian Ocean to the Pacific, is best explained by dispersal by Austronesians, early Homo sapiens migrants from Asia.
The forest reserves of Hawai‘i were established in the early 1900s in response to concerns about supplies of freshwater in the islands and the degraded condition of the native forests protecting the watersheds. Tree-planting was a coordinated effort involving both Harold Lyon and the Hawaiian Sugar Planters' Association and Territorial Forestry under the direction of R. S. Hosmer. The early foresters planted many types of trees on an experimental basis, but concluded that native species were of limited utility and turned largely to introduced species for large-scale reforestation efforts. The number of trees planted rose to many millions by the 1930s, when Depression-era labor was available for planting. Lyon envisioned the plantations as a buffer zone that would be established between the remaining native forests and the lower-elevation agricultural lands to protect the native forests and perform the functions (maintaining input of water to aquifers) that native forest no longer could. This large-scale attempt to engineer nature was probably the largest environmental project ever carried out in the islands. Forestry introductions have been a significant contributor to Hawaii's alien-species crisis, with many of these tree species now problem invasives.
Plantation silviculture of balckwood and the problem associated with its plantation are presented. Blackwood grows to 6-35 m in height and occurs naturally throughout the eastern seaboard of Queensland in areas with an annual rainfall greater than 600 mm. It is shown that the major problem for planting blackwood is its poor apical dominance which produces large number of branches and trees of poor stem form when grown in full light.
Agricultural activities and their complex effects on nature conservation, and the services that
ecosystems deliver to humans are controversial. We present an overview of land abandonment, its
driving forces and its consequences for landscape, biodiversity and humans. A descriptive meta-
analysis of independently published studies highlighted the fact that the abandonment of agri-
cultural land is a phenomenon mostly driven by socio-economic factors such as immigration into
areas where new economic opportunities are offered to rural people. Ecological drivers such as
elevation and land mismanagement leading to soil erosion are of secondary importance. We
identified the major problems related to abandonment of agricultural land and quantified their
relative importance. In order of decreasing importance, they were biodiversity loss, increase of
fire frequency and intensity, soil erosion and desertification, loss of cultural and/or aesthetic
values, reduction of landscape diversity and reduction of water provision. The impacts of these
problems were not equally relevant in all regions of the world. The abandonment of agricultural
land may also benefit humans. The benefits include passive revegetation and active reforestation,
water regulation, soil recovery, nutrient cycling and increased biodiversity and wilderness. In a
world that is becoming less natural and more intensively exploited by humans, we suggest that (1)
farmland must be viewed in a context of multi-functionality to take advantage of ecosystem goods
and services, (2) at the global scale, the abandonment of agricultural land is mostly positive for
humans and (3) there is a need for the implementation of policies based on the payments for
environmental services that encourage human societies to reconcile agricultural use, nature
conservation and ecological restoration.
One of the theories for the evolution of divaricating shrubs and juvenile forms of heteroblastic woody plants suggests that these forms were selected for resistance to water loss. We examined the water relations and carbon isotope ratios (δC) of excised shoots from juvenile and mature forms of one homoblastic species, seven heteroblastic species, and the divaricating shrub Coprosma rotundifolia. Shoots from the juvenile divaricate forms and C. rotundifolia showed responses (relatively high rates of water loss, high osmotic water contents, more negative δC, elastic cell walls and low water contents at turgor loss) characteristic of water spenders. Mature and juvenile forms of Pittosporum eugenioides and Pseudopanax crassifolius and mature Carpodetus serratus showed the opposite characteristics. The ordination of these characteristics suggested that juvenile forms of P. eugenioides, Streblus microphylllus, Sophora microphylla, and Carpodetus serratus were more water‐spending than their mature forms, whilst juvenile forms of Pseudopanax crassifolius, Hoheria angustifolia, and Plagianthus regius tended to be somewhat less water‐spending than their mature forms. Our results do not support the hypothesis that juvenile forms of heteroblastic trees are more resistant to water loss than their mature counterparts. We suggest that forms with a divaricating habit produce a micro‐environment within the shrub that favours small leaves, with relatively high leaf conductance, water loss, and CO2 assimilation rates, that also may be partially adapted to shade.
A high number of tree species, low density of adults of each species, and long distances between conspecific adults are characteristic of many low-land tropical forest habitats. I propose that these three traits, in large part, are the result of the action of predators on seeds and seedlings. A model is presented that allows detailed examination of the effect of different predators, dispersal agents, seed-crop sizes, etc. on these three traits. In short, any event that increases the efficiency of the predators at eating seeds and seedlings of a given tree species may lead to a reduction in population density of the adults of that species and/or to increased distance between new adults and their parents. Either event will lead to more space in the habitat for other species of trees, and therefore higher total number of tree species, provided seed sources are available over evolutionary time. As one moves from the wet lowland tropics to the dry tropics or temperate zones, the seed and seedling predators in a habitat are hypothesized to be progressively less efficient at keeping one or a few tree species from monopolizing the habitat through competitive superiority. This lowered efficiency of the predators is brought about by the increased severity and unpredictability of the physical environment, which in turn leads to regular or erratic escape of large seed or seedling cohorts from the predators.
For the past 25 years NIH Image and ImageJ software have been pioneers as open tools for the
analysis of scientific images. We discuss the origins, challenges and solutions of these two programs,
and how their history can serve to advise and inform other software projects.
Virtually all plants show a certain degree of variation among individual metamers during ontogeny. In some cases, however, there are abrupt and substantial changes in form and function (e. g. in leaf form, leaf size, phyllotaxy, internode length, anthocyanin pigmentation, rooting ability, or wood structure). These plants were called "heteroblastic" by Karl Goebel more than a century ago, but the functional significance of this type of ontogenetic change, the evolutionary trajectories in different plant groups, even their frequency in the plant kingdom are still unresolved issues. We argue that slow progress is partly due to an on-going terminological confusion and the lack of distinction between other developmental processes such as ontogenetic drift. This review develops a conceptual framework for future scientific work, proposes a quantitative index of heteroblasty, and discusses the evidence for developmental regulation, functional significance, and evolutionary implications of heteroblasty to provide a stimulating basis for further research with this fascinating group of plants.
CIMES is a multi-purpose, multi-platform, and free package of programs for the determination of solar radiation regimes and canopy structure attributes using hemispherical photographs. These command-line programs, like a toolbox, offer a unique set of features such as: a variety of approaches to invert gap fraction data, correction for slope (solar radiation and LAI), and different procedures to account for foliage clumping, spherical statistics for gap fraction distribution, photosynthetically active radiation (PAR) intercept ion under clear- and overcast sky conditions, and sun-fleck dynamics. We present the general overview of the programs, the solar radiation regime, and the canopy structure estimates as processed by CIMES software. The most important point of CIMES compared to other software would be to have statistics and estimates for each single photosite including all available theoretical and empirical algorithms, so that anyone working on methods rather than application will have more freedom compared to other software. For application, the batch processing does everything.
Background and aims:
Heteroblastic plant species, whose morphology or growth habit changes suddenly during development, offer unique opportunities to investigate the role of selection in canalizing development or increasing the adaptive importance of plasticity. Leaf forms of the Hawaiian tree Acacia koa (koa) change morphologically and physiologically during the first year of growth, providing time to study abiotic factors influencing transition rates relative to other Acacia species.
Methods:
The roles of light and water availability in triggering transition to the mature leaf form in contrasting (wet/dry) ecotypes of koa were investigated using a novel modelling technique to distinguish between chronological and ontogenetic controls in triggering transition. A light quality treatment was included to test interactions of heterophylly (the presence of multiple leaf forms) with heteroblastic processes on the resulting phenotype at transition.
Key results:
Increased light intensity increased transition rates, but reduced red to far-red light (R:FR) ratios did not affect transition rates, solidifying the current paradigm of heteroblasty. However, evidence was found for earlier transition ontogenetically under water stress, which is not part of the current paradigm and could differentiate the role of heteroblasty in some Acacia species versus other heteroblastic species. Ecotypic responses also indicate that plasticity of development could vary across koa's range and the adaptive significance of heteroblasty could be marginalized or amplified dependent on the disparate selective pressures present across koa's range.
Conclusions:
The use of novel survival functions and a species with an elongated transition time helped to elucidate abiotic modifiers of ontogenetic trajectories. Differences in ontogenetic trajectories between contrasting ecotypes suggest that ongoing climate and land use change will have non-uniform effects on koa regeneration and establishment dynamics across its range.
Sequences of nuclear ribosomal DNA internal (ITS) and external (ETS) transcribed spacers were used to generate a phylogeny of Acacia Mill. s.str. (synonyms: Acacia subg. Phyllodineae (DC.) Seringe; Racosperma Mart.). This study included 109 exemplar taxa from all seven sections recognised in previous classifications, and represents the largest sampling of diversity for molecular phylogenetics of Acacia s.str. undertaken so far. Four main clades were identified from the combined dataset of ITS and ETS using parsimony and Bayesian analyses. Two of these clades consist mostly of uninerved phyllodinous taxa assigned to sect. Phyllodineae. One clade includes taxa related to A. victoriae and A. pyrifolia, and the second comprises taxa in the A. murrayana species group. These taxa occur predominantly in semi‐arid and arid regions. Relationships also resolve the previously identified Pulchelloidea clade, which includes members of sects. Pulchellae, Alatae, Phyllodineae and Lycopodiifoliae. A large clade with limited phylogenetic resolution was also identified (the "p.u.b. clade"). This is an assemblage of plurinerved and uninerved phyllodinous taxa and also bi‐pinnate taxa from sect. Botrycephalae. Clades are discussed with reference to morphological characters, and while some morphological states are correlated with clades, including seedling ontogeny, inflorescence and phyllode nerves, clear synapomorphies remain to be identified. Traditional classifications of Acacia s.str. are artificial and a preliminary informal classification based on phylogenetic relationships within Acacia s.str. is proposed.
We quantified the differences in growth responses between Cryptomeria japonica and Chamaecyparis obtusa trees in approximately 0.1-ha group selection openings in southern Japan. We measured the position, height (H), and diameter at ground level (D) of 6- and 13-year-old C. japonica and C. obtusa trees that were planted in two respective openings. The annual H and D growth of C. japonica increased until trees were 10 and 8 m, respectively, distant from the nearest edge of the opening. For C. obtusa, the annual H and D growth increased slightly until the trees were 6 m distant from the nearest edge, but they did not significantly differ between 6 and 18 m distant from the nearest edge. While the shortest distance from the edge explained 63% and 50% of the variationsal H and D growth, respectively, of C. obtusa. Our result demonstrates that C. obtusa is less sensitive to edge effects than C. japonica. We conclude that C. obtusa is likely to be more suitable than C. japonica for planting within 0.1-ha...
Field fertilization can promote early growth and survival of planted trees on degraded pastures and agricultural lands where low soil fertility and high herbaceous competition inhibit regeneration success. Controlled-release fertilizers (CRF) may improve the effectiveness of fertilization relative to that of immediately available fertilizers (IAF) because CRF gradually release nutrients directly to the root zone, thereby limiting nutrient losses. Despite past research in boreal and temperate landscapes, few studies have tested the efficacy of similar applications in tropical systems where year-round high temperatures can increase release rates of CRF and intensity of competing vegetation. On two contrasting sites on the Island of Hawaii, USA, we evaluated early growth and survival responses of koa (Acacia koa Gray), a fast-growing legume, using ten treatments: a control, four IAF formulations, and five rates of polymer-coated CRF (15N-9P-12K; 15–75 g). At Pahala, a productive site, we detected no significant growth, survival, or foliar nitrogen (N) or phosphorous (P) responses to the fertilizer treatments. At Volcano, a rockier and cooler site on younger soil, height increased by 36–49% for the highest performing CRF and IAF relative to the control; diameter likewise increased by 55–92%. Growth responses appeared to be a result of P fertilization rather than N. The highest performing IAF had a reduced survival rate relative to the lowest CRF (46% vs. 83%). Although total nutrient application rates were much lower for CRF, our results suggest that on tropical restoration sites, CRF may promote seedling performance at least equally to that of IAF. There is a need to more carefully evaluate the effects of site-specific interactions that may determine field fertilizer responses, across a range of genera and functional groups.
The survival, morphological, and growth responses of European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) seedlings to different light intensities, from full sunlight to heavy shade, were studied over two growing seasons in a shadehouse experiment. Although shade treatments significantly affected seedling growth, they did not influence seedling survival. Both growth and biomass increased as light intensity increased. Diameter growth of oak seedlings was higher than that of beech. Beech and oak seedlings showed typical acclimation to shade, including greater specific leaf area and height to diameter ratios, and lower leaf thickness and root:shoot ratios with increasing shade. Beech seedlings exhibited greater specific leaf area, and lower leaf thickness and root:shoot ratios than oak seedlings. In spite of the greater growth at full sunlight, the results from this study suggest that beech and oak seedlings would have high survival rates and would acclimate well if underplanted below overstories that reduce the available light to as low as 28% of full light.
Discusses silvicultural control of Arceuthobium americanum in various types of Pinus contorta stands where fiber production is the primary goal, and also in forests used mainly for recreation. -from Authors
Tested the hypotheses that seed dispersal enhances seedling survival by 1) escape of distance-dependent or density-dependent mortality or both, and 2) colonization of light-gaps. Spatial patterns of seedling survival for 1 yr in shade and in light-gaps and causes of seedling mortality for the first 2 mo were determined for 1 tree of each of 9 species that use wind dispersal on Barro Colorado Island, Panama. The colonization hypothesis was supported by all 9 trees. At some time interval during the 1st yr, the escape hypothesis was supported by 8 of the 9 trees; dispersal away from the parent to shaded conditions lowered the probability of seedling mortality. However, the trees differed greatly in 1) when the dispersal advantage became apparent, 2) whether the advantage persisted through time, 3) the distance at which survival was most enhanced, and 4) the strength of the advantage. Pathogens caused the largest proportion of deaths among shaded seedlings in 6 of the 9 trees. For the 2 trees with the strongest support for the escape hypothesis, pathogens caused distance-and/or density-dependent mortality; those trees had high seedling densities near the parent. Only the four trees with moderate to strong support for the escape hypothesis had large numbers of seedlings survive to 1 yr in the shade. -from Author
We give suggestions for the presentation of research results from frequentist, information-theoretic, and Bayesian analysis paradigms, followed by several general suggestions. The information-theoretic and Bayesian methods offer alternative approaches to data analysis and inference compared to traditionally used methods. Guidance is lacking on the presentation of results under these alternative procedures and on nontesting aspects of classical frequentist methods of statistical analysis. Null hypothesis testing has come under intense criticism. We recommend less reporting of the results of statistical tests of null hypotheses in cases where the null is surely false anyway, or where the null hypothesis is of little interest to science or management.
Advance conifer regeneration readily survives release from overs tory competition in the Inland West, but foresters are concerned about the ability of released trees to attain normal growth rates. There are also concerns about forest health issues associated with managing advance regeneration. The best pre-release predictors of post-release growth response are pre-release vigor and crown ratio at release. The fastest growing trees before release grow the fastest following release. A general recommendation is that at least a 0.50 crown ratio at release is necessary for good response to release. A 0.50 crown ratio means that trees will have the necessary photosyn-thetic capability to respond to changes in stand conditions. The best time to release advance regeneration is after budset in the fall but before budburst in the spring. Release during this time period means needles that develop the first summer after release will be adapted to full sunlight. A conceptual framework of physiological response to release is presented.
The present trend towards transformation of forests is the result of public dissatisfaction with the appearance and perceived unnaturalness of plantations. Many foresters are reacting to this political pressure by pursuing a complete shift from plantations to single-tree selection forestry. Many other options exist that can provide the structural variability desired while using simpler management strategies and our existing knowledge of even-aged stands. These include systems to produce two- or three-aged stands, or enhancing the variability of existing even-aged stands. (C) 2001 Elsevier Science BN. All rights reserved.
Active forest restoration in Hawaii’s Hakalau Forest National Wildlife Refuge has produced a network of Acacia koa tree corridors and islands in deforested grasslands. Passive restoration by root suckering has potential to expand tree cover and close gaps between planted stands. This study documents rates of encroachment into grassland, clonal stand structure, and tree architecture. Data were collected from random replicate strip transects that started inside 23-year-old koa plantations and ended either in open grassland or in adjacent planted stands. For the former, sucker densities increased from near zero inside planted stands to a maximum of 5–38 stems m−2 5–14 m away from the edge of the plantation canopy, and then decreased to zero–a typical pattern for trees invading grassland. No suckers occurred more than 28 m from the canopy edge on east-facing slopes, or more than 18 m on south-facing slopes. Rates of expansion into grassland ranged from 0.8 to 1.5 m yr−1; suckers had already filled gaps between closely spaced plantation stands located on north-facing slopes. Continued suckering should result in the eventual re-establishment of tree cover on deforested areas between planted tree islands and corridors, and without additional active restoration.
Reforesting degraded landscapes with native, high-value timber trees may contribute to biodiversity protection while also increasing the economic value of the land. Ideally, reforested areas should have the habitat characteristics to support viable populations of native fauna. We investigated habitat use by Akiapolaau (Hemignathus munroi), an endangered Hawaiian honeycreeper, in three habitat types: a relatively intact old-growth forest, an old-growth forest with a long history of grazing, and a native Acacia koa plantation. We quantified habitat characteristics, calculated foraging preferences, mapped home ranges, measured territoriality, and determined reproductive success at all sites. We found that Akiapolaau were highly selective foragers, foraging primarily on A. koa despite its relative scarcity in the environment, and then secondarily on several subcanopy species. Home range size was significantly smaller at the intact old-growth site and the A. koa plantation, the two sites with the greater cover of A. koa and of the subcanopy species preferred by Akiapolaau. Birds at these sites were also less territorial, supporting behavioral theory that predicts a nonlinear relationship between food availability and territoriality. Overall, our results show that the A. koa plantation, the site with the highest percentage of A. koa, the smallest Akiapolaau home ranges, and the least territoriality, supported the highest density of birds with no apparent reproductive cost. Because A. koa is an extremely high-value hardwood and thus can be selectively harvested, there is tremendous potential for conservation advocates to work with landowners to grow A. koa for economic benefit while also enhancing biodiversity.
For the first time, trends of five climate change indices related to extreme precipitation events in the Hawaiian Islands are investigated using daily observational records from the 1950s to 2007. Four indices [simple daily intensity index (SDII), total number of day with precipitation ≥25.4 mm (R25), annual maximum consecutive 5-day precipitation amount (R5d), and the fraction of annual total precipitation from events exceeding the 1961–90 95th percentile (R95p)] describe the intensity (SDII), frequency (R25), and magnitude (R5d and R95p) of precipitation extremes, and the fifth index [consecutive dry days (CDD)] describes drought conditions. The annual probability density functions (PDFs) of precipitation indices for two epochs (i.e., 1950–79 and 1980–2007) are analyzed. Since the 1980s, there has been a change in the types of precipitation intensity, resulting in more frequent light precipitation and less frequent moderate and heavy precipitation intensity. The other three precipitation-related indices (R25, R5d, and R95p) demonstrate a shift toward the left of the distribution over time, suggesting shorter annual number of days with intense precipitation and smaller consecutive 5-day precipitation amounts and smaller fraction of annual precipitation due to events exceeding the 1961–90 95th percentile in the recent epoch relative to the first epoch. The changes of PDF distribution for SDII, R25, R5d, and CDD are significant at the 5% level according to a two-sample Kolmogorov–Smirnov test.
A nonparametric trend analysis is then performed for four periods, with different starting years (e.g., the 1950s, the 1960s) but the same ending year (2007). Long-term downward trends are evident for four precipitation-related indices, and long-term upward trends are observed for CDD. Geographically, Kauai and Oahu are dominated by long-term decreasing trends for four precipitation-related indices, while increasing trends play the major role over the island of Hawaii. The upward trends of drought conditions in the long run are predominant on all the major Hawaiian Islands.
To investigate whether the trends are stable throughout the time, the derivatives of trends for each of the 30-yr running series are calculated (e.g., 1950–79, 1951–80, … , 1978–2007) for four precipitation-related indices at each station. For Kauai and Oahu, positive derivatives prevail for all indices in the presence of long-term negative trends, suggestive of a phase change in precipitation extremes and such extremes showing an upswing recently. For the island of Hawaii, there is also an indication of phase reversal over the last 60 yr, with negative derivatives occurring in the presence of the background positive trends.
A positive relationship is found between the precipitation indices and the Southern Oscillation index (SOI), implying more precipitation extremes during La Niña years and vice versa for El Niño years. Spatial patterns of standardized anomalies of indices are presented for the La Niña/−PDO minus El Niño/+PDO composites.
Field measurements of gas exchange parameters, water relations, carbon isotope discrimination (Delta(13)C), and nitrogen content were used to test the hypothesis that juvenile leaves and phyllodes of Acacia koa possess characteristics that promote establishment (rapid growth) and persistence (stress tolerance), respectively. Juvenile leaves had higher conductance, higher photosynthetic rate by mass, lower water-use efficiency, higher photosynthetic nitrogen-use efficiency, higher nitrogen content, a lower ratio of carbon content to nitrogen content, lower average water potential, and higher Delta(13)C than phyllodes. As conductance and photosynthesis rates increased for both leaf types, rates in phyllodes were more limited than rates in juvenile leaves. Differences in leaf morphology, including the ratio of leaf mass to leaf area, inclination, and minimal leaf dimension, account for differences in leaf performance.
Small volumes of timber are now being produced from Acacia mangium plantations in Indonesia. These trees require pruning and thinning to increase the strength and appearance of the wood. However, cut surfaces from pruning are potential infection courts for the entry of decay-causing fungi like heart rot. This study investigated the effects of pruning on stem form and the incidence of heart rot in an 18-month-old plantation of Acacia mangium in South Sumatra. The objectives were to assess whether pruning is associated with an increase in the incidence of heart rot and whether form pruning compared to lift pruning reduced the incidence of heart rot and improved stem form. Form pruning removed 25% of leaf area by removing large branches and those subtending a narrow angle with the stem up to 3m height, and lift pruning removed 25% of crown length from below. Trees in these treatments were singled before pruning. The third treatment, a control, was not singled and was used to assess base levels of heart rot.No significant difference in diameter increment between the two pruning treatments was found. There was strong evidence that form pruning was associated with better form 18 months after treatment. Trees in this treatment had a reduced number of branches >30mm diameter and improved stem straightness (reduced kink). Lift pruning reduced average branch size but did not improve stem straightness. No heart rot was detected in any treatment.The results showed that form pruning is likely to have positive benefits on stem straightness and is likely to be effective to any selected pruning height. However a subsequent lift pruning is still considered a requirement. While wounds created from pruning and singling are assumed to have a large impact on the incidence of heart rot, this may not be an issue unless there is a sufficient source of fungi present in the environment to invade the wounds.
Eucalyptus spp. are propagated extensively as non-natives in plantations in many parts of the tropics and sub-tropics. A number of diseases result in serious losses to this economically important forest resource. Eucalyptus rust, caused by Puccinia psidii, is one such example. The economic losses due to this disease the result of infections of seedlings, young trees, and coppice. R psidii occurs predominately in Central and South America, but reports of a similar rust are known from other areas. Eucalyptus rust is a remarkable disease in that the pathogen is not known on eucalypts in their centers of origin. It has apparently originated on native Myrtaceae in South America and is highly infective on some Eucalyptus spp. planted there. R psidii causes one of the most serious forestry diseases in Brazil and is considered to he the most serious threat to eucalypt plantations worldwide. Advances in eucalyptus rust research are reviewed here, with a focus on topics such as distribution, host range, pathogen specialization, symptomatology, etiology, epidemiology, and control.
Koa (Acacia koa Gray) seedlings were grown under full sunlight (HH treatment) and under 27% of full sunlight (LL treatment). Some of these seedlings were moved to the opposite light intensity to form two additional treatments--HL and LH. Phyllodes developed only on seedlings in the HH treatment. If seedlings with phyllodes were placed under shade, leaves instead of phyllodes developed at the terminal. Leaflets of leaves in the HH treatment were smaller but thicker and had lower specific leaf areas than those in the LL treatment. Koa leaves in the HH and LL treatments had similar photosynthetic characteristics. Leaves in the HH treatment had higher ribulose 1,5-bisphosphate carboxylase levels and lower chlorophyll levels than leaves in the LL treatment. When seedlings were moved to the opposite light intensity, leaves and phyllodes adapted both morphologically and physiologically to the altered photosynthetic photon flux density (PPFD). Leaves and phyllodes that were only partially developed when the PPFD changed showed greater adaptive potential than those that were fully developed. Generally, leaves and phyllodes adapted by developing morphological and physiological characteristics of those grown continuously in the new PPFD. There were no detectable deleterious affects to exposing leaves or phyllodes to increased or decreased PPFDs For. Sci. 36(4):1050-1060
Advance conifer regeneration readily survives release from overstory competition in the Inland West, but foresters are concerned about the ability of released trees to attain normal growth rates. There are also concerns about forest health issues associated with managing advance regeneration. The best pre-release predictors of post-release growth response are pre-release vigor and crown ratio at release. The fastest growing trees before release grow the fastest following release. A general recommendation is that at least a 0.50 crown ratio at release is necessary for good response to release. A 0.50 crown ratio means that trees will have the necessary photosynthetic capability to respond to changes in stand conditions. The best time to release advance regeneration is after budset in the fall but before budbust in the spring. Release during this time period means needles that develop the first summer after release will be adapted to full sunlight. A conceptual framework of physiological response to release is presented.
Reforestacion de terrenas degredados en los tropicos es una meta mas importante de restoracion ecologia. Restoracion de montane bosque humedo esta en processo a Hakalau Bosque Nacional Refugio, Hawaii, usando plantaciones de Acacia koa (koa), un arbol de dosel de montane bosque humedo. Usamos escarabajos longicornos (Plagithmysus claviger y P. varians) a espieces indicadores para amillarar restoracion. Los escarabajos se alimentan por ataladrar agujeros en los ramas muertos de koa, y son comida por el pajaro indegeno del bosque Hemignathus munroi. Cuantificamos la densidad de escarabajos en ramas de koa de tres categorias de edad: plantaciones jovenes (3–8 anos; 222 ramas), plantaciones mas viejos (12–15 anos; 212 ramas) y arboles de dosel de bosques indegenos (167 ramas). Probamos por rompiendo ramas muertos a pedazos cortos y contamos los escarabajos dentro. La cantidad de escarabajos eran mas en arboles nativos del dosel (4.89 escarabajos/rama) que en arboles plantados, y fue mas alto en plantaciones viejos (3.24 escarabojos/rama) que en plantaciones jovenes (0.90 escarabajos/rama). Escarabajos se agrupaban entre los ramas (el coeficiente de la dispersión = 5.17). El diametro medio de ramas en arboles nativos (32.6 mm) fue mas que los de arboles plantadas, y fue mas en plantaciones viejos, (29.3 mm) que en los mas joven (19.0 mm). En ambos plantaciones, ramas que albergaban escarabajos eran mas grande que los ramas no los tenian, pero en arboles nativos no habia differencia. El diámetro de las ramas tiene un impacto positivo en la cantidad de escarabajos de cada rama para todas las categorías de edad. Plantaciones de koa promovia la recupracion de la diversidad de plantes y animals en habitaciones degredados occupado en tiempos pasados por bosques humedos de los montanas.
Aims To highlight the increasing importance of pests and pathogens to Australian Acacia species, where they are planted as non-natives in commercial plantations and in their native environment.
Location Africa, Asia, Australia, South America.
Methods Existing literature and results of unpublished surveys on pests and pathogens of Australian acacias are reviewed. These are discussed within the context of a growing importance of invasive alien insects and pathogens including novel encounters and host jumps.
Results Australian acacias planted as non-natives in various parts of the world are increasingly threatened by pests and pathogens. These include those that are accidentally being introduced into the new environments as well as ‘new encounter’ pests and pathogens that are undergoing host shifts to infect non-native acacias. Furthermore, insects and pathogens for biological control of invasive Australian acacias present substantial challenges for plantation forestry.
Main conclusions Pests and pathogens will seriously challenge plantation forestry based on non-native Australian acacias. In the longer term, new encounter pests and pathogens will also threaten these trees in their native environments.
Hawaiian forests are subject to the effects of periodic hurricane conditions. Hurricane Iniki struck the island of Kauai, Hawaii on September 11, 1992 with winds exceeding 200 km/h and caused defoliation, felling of trees by snapping and uprooting, and standing tree mortality due excessive limb and leaf loss. The purpose of this study was to evaluate if measured wood mechanical characteristics could be correlated with stem failure of trees under windstorm conditions. A field survey indicated that post-hurricane stem condition (snapped, uprooted, or standing) differed among five common canopy species and was significantly correlated with stem apparent elastic modulus (relative flexibility). Species that tended to snap had significantly higher apparent elastic moduli than those that remained standing or were uprooted. Wood density and stem diameter were not significantly related to stem failure mode. Native trees had a higher percentage per species of standing individuals but also had increased uprooting. Nonnative tree species were more often snapped and fewer were standing after the hurricane. The higher incidence of stem failure for introduced canopy trees may increase the spread of alien understory species following wind disturbance events. These relationships provide a simple means to predict relative differences in stem failure due to high wind conditions and should be considered in planning reforestation efforts on the Hawaiian Islands.
This study investigated the feasibility of silvicultural intervention in Acacia melanoxylon (R. Br.) plantations grown with Pinus radiata (D. Don) nurse crops, to improve stem form and growth rate. The objective of the study was to evaluate silvicultural options for managing a nurse-crop to avoid suppression but improve stem form of A. melanoxylon. Using a 5-year-old A. melanoxylon–P. radiata plantation, various levels of form pruning of the A. melanoxylon were tested by removing prescribed proportions of leaf area from treatment trees. In addition, a range of thinning treatments was imposed on the nurse-crop. The effects of these treatments on A. melanoxylon growth rate, stem form, rate of crown development, and canopy light environment were assessed.Altering the canopy structure of the plantations by thinning the P. radiata nurse-crop had a positive effect on A. melanoxylon diameter growth. However, less desirable changes were also evident following thinning of the P. radiata, such as reduced height increment, loss of dominance and a greater incidence of large branches in A. melanoxylon trees. Appreciable changes in the light environment of the A. melanoxylon crowns occurred only after more than 50% of P. radiata trees were removed. Crowns of A. melanoxylon trees pruned of 50% of their foliage area took 12 months to recover to pre-pruning foliage area levels. Form pruning A. melanoxylon significantly reduced growth when 50% of foliage area was removed.Improvements in form by pruning were transient in nature, highlighting the need for on-going, low-intensity form pruning treatment to establish good stem form. The rapid deterioration in form after heavy thinning of the nurse-crop indicated the need to establish form before reducing nurse-crop competition.
Questions: Is the introduced timber species Fraxinus uhdei invasive in Hawai'i? Has logging disturbance facilitated the spread of Fraxinus and other alien species?
Location: Windward Mauna Kea, island of Hawai'i.
Methods: We surveyed 29 plots which were established before selective logging of the native tree Acacia koa in 1971 to determine if Fraxinus spread beyond the borders of an existing plantation and if other alien species increased. We created gaps in the canopy of the Fraxinus plantation and measured seed rain and regeneration, and we sampled foliar and soil nutrients inside and around the plantation.
Results: Basal area of Fraxinus increased from 0.7 m ² .ha ‐1 in 1971 to 10.8 m ² .ha ‐1 in 2000. Fraxinus was not found in plots that were located more than 500 m from those where it occurred in 1971 except along a road. Basal area of Acacia koa decreased after logging but subsequently recovered. Occurrence of the alien vine Passiflora tarminiana and alien grass Ehrharta stipoides decreased. Seedling regeneration of Fraxinus was prolific in gaps but did not occur under the canopy. Basal area of Fraxinus did not correlate with soil nutrient concentrations.
Conclusions: Fraxinus was able to regenerate following logging more rapidly than native tree species. Basal area growth of Fraxinus was great enough to offset a decline in native trees and cause an increase in forest productivity. If the Fraxinus plantation is harvested, managers should plan ways of favoring regeneration of the native Acacia which is more valuable both for timber and for conservation.
Restoring natural capital is essential for biodiversity and ecosystem services that support human well-being. Although ecological pathways for restoration are a major area of study, little is known about the economic pathways to which these efforts must be linked. This linkage, however, is important for maximizing return-on-investment (ROI) from restoration projects. We developed a general ROI framework to guide investments in restoration. We applied this framework to reforestation of montane pastureland in Hawaii, focusing on two specific conservation targets: native forest birds and understory plants. We found that restoring partial tree cover on pastureland is most attractive for birds, while understory plants require investment in full forest restoration. Nonlinearities in restoration pathways present in Hawaii, and likely elsewhere, generate these substantially different ROI profiles across potential projects. This information can guide the design of policies supporting cost-effective practices to help ensure that limited resources achieve the greatest impact.
Blackwood (Acacia melanoxylon R. Br.) is a species with poor apical dominance, and in plantations, silvicultural interventions are required to improve stem form. Planting blackwood with a nurse crop and pruning to remove large branches and multiple leaders are common methods used in blackwood plantations. An experiment was established to determine whether applications of nitrogen (N), phosphorus (P) or magnesium (Mg) could also be used to improve stem growth and form. Other aims of the experiment were to compare responses of the blackwood and the Pinus radiata D. Don nurse crop to fertiliser application, and to identify changes in blackwood physiology resulting from fertilising.Application of P had a more marked positive effect on blackwood stem growth than application of N or the combination of N and P. Mg had no effect on stem growth. The response to P may have been related to a substantial increase in root nodulation and a 35% increase in coarse root dry mass. Foliar nutrient analysis suggested that these responses led to an improvement in plant nutrition. In contrast N application reduced root nodulation by 60%. P application improved stem form in the short term by increasing biomass partitioning to stems at the expense of branches. However this response was no longer apparent 24 months after fertilising, suggesting that frequent applications of P may be necessary for long-term improvements in stem form. While light-saturated CO2 assimilation was increased by applications of N, this was not translated into greater biomass production, probably because of shading of many of the blackwood crowns by the nurse crop. The P. radiata nurse crop responded to fertilising differently to the blackwood, with greatest growth increases following application of either the combination of N and P or Mg alone. This highlights the need to understand responses to fertilising of both blackwood and the nurse crop. The most favourable nurse crop:blackwood height ratio was observed following P application, meaning that this treatment is the least likely to result in suppression of the blackwood by the nurse crop.
Endoraecium digitatum was described on Acacia notabilis from South Australia but has been reported on more than 20 Acacia spp. throughout the Australian and the Pacific regions. Results are presented on the micro-morphology and taxonomy of E. digitatum from different Acacia species and geographic provenience. E. digitatum revealed a highly non-uniform morphology and is considered a species complex comprising at least six morphologically distinct
rust fungi. The name E. digitatum could not be applied to any of the distinguished species by a comparison with available type specimens or the original description
as types were depleted and the diagnosis not detailed enough. An epitype is therefore proposed to supplement the lectotype
of E. digitatum selected here and to allow delimitation of the new species E. parvum, E. violae-faustae and E. walkerianum from Australia, and E. kauaianum from Hawaii. Endoraecium phyllodiorum is shown to be different from E. digitatum and is proposed as a new combination for Uromyces phyllodiorum. Specimens from Hawaii formerly considered to be E. digitatum represent two species, E. kauaianum and another one preliminarily assigned to E. phyllodiorum. The investigated species show differences between and plasticity within their life cycles. E. parvum, E. violae-faustae and E. kauaianum are macrocyclic. In E. walkerianum, only demicyclic specimens were found, while demi- and macrocyclic specimens occurred in E. digitatum. E. phyllodiorum revealed variable combinations of spore states as well and comprised macro-, demi- and microcyclic life cycle variants. Life
cycle variants were considered to express specific variability and were not used to create new taxa. The present results indicate
that members of the E. digitatum complex in Australia are not narrowly host specific. Keys are presented for the Australian and Hawaiian species. Taxonomical
novelties: Endoraecium kauaianum R. Berndt, Endoraecium parvum R. Berndt, Endoraecium phyllodiorum (McAlp.) R. Berndt, Endoraecium violae-faustae R. Berndt and Endoraecium walkerianum R. Berndt.
Keywords
Acacia
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Racospermyces
–Life cycle–Epitype–Species complex