Multi-stemmed Trees Research Articles

Data quality in citizen science urban tree inventories

Citizen science has been gaining popularity in ecological research and resource management in general and in urban forestry specifically. As municipalities and nonprofits engage volunteers in tree data collection, it is critical to understand data quality. We investigated observation error by comparing street tree data collected by experts to data collected by less experienced field crews in Lombard, IL; Grand Rapids, MI; Philadelphia, PA; and Malmö, Sweden. Participants occasionally missed trees (1.2%) or counted extra trees (1.0%). Participants were approximately 90% consistent with experts for site type, land use, dieback, and genus identification. Within correct genera, participants recorded species consistent with experts for 84.8% of trees. Mortality status was highly consistent (99.8% of live trees correctly reported as such), however, there were few standing dead trees overall to evaluate this issue. Crown transparency and wood condition had the poorest performance and participants expressed concerns with these variables; we conclude that these variables should be dropped from future citizen science projects. In measuring diameter at breast height (DBH), participants had challenges with multi-stemmed trees. For single-stem trees, DBH measured by participants matched expert values exactly for 20.2% of trees, within 0.254cm for 54.4%, and within 2.54cm for 93.3%. Participants’ DBH values were slightly larger than expert DBH on average (+0.33cm), indicating systematic bias. Volunteer data collection may be a viable option for some urban forest management and research needs, particularly if genus-level identification and DBH at coarse precision are acceptable. To promote greater consistency among field crews, we suggest techniques to encourage consistent population counts, using simpler methods for multi-stemmed trees, providing more resources for species identification, and more photo examples for other variables. Citizen science urban forest inventory and monitoring projects should use data validation and quality assurance procedures to enhance and document data quality.

Adaptive strategy of tree communities on an environmental harshness hinterland inselberg in Minas Gerais, Brazil

Trees and other plants growing in stressful environments can display adaptive strategies such as sprouting, which is considered to be a functional trait for the persistence niche. For example, inselbergs are rocky outcrops that impose limitations on many plant forms through selective pressure to adapt to these environments. The present research tested the hypotheses that environmental harshness enhances sprouting, and that multi-stemmed trees have different persistence dynamics compared with single-stemmed trees. We sampled vegetation in 2006 and 2011 across a soil depth gradient in three areas: riparian forest, inselbergs and a corridor between the first two areas. Trees with a diameter at the breast height (dbh) ≥5 cm were sampled, and sprouts were counted. Results showed that the inselberg had more sprouted individuals and a larger amount of sprouts than the other areas. Thus, sprouting as a survival strategy was efficient in dealing with the environmental harshness and may be considered an adaptive strategy of trees to enable them to persist in such environments. The dynamic of multi-stemmed trees differed from single-stemmed ones, and the inselberg was distinct from the other areas. Over the 5 years of the present study, sprouting proved to be a strategy of persistence in this habitat, a finding that is in accordance with our hypothesis. Factors contributing to the environmental harshness, such as soil depth, may be the cause of sprouting in trees.

Why Be a Shrub? A Basic Model and Hypotheses for the Adaptive Values of a Common Growth Form.

Shrubs are multi-stemmed short woody plants, more widespread than trees, important in many ecosystems, neglected in ecology compared to herbs and trees, but currently in focus due to their global expansion. We present a novel model based on scaling relationships and four hypotheses to explain the adaptive significance of shrubs, including a review of the literature with a test of one hypothesis. Our model describes advantages for a small shrub compared to a small tree with the same above-ground woody volume, based on larger cross-sectional stem area, larger area of photosynthetic tissue in bark and stem, larger vascular cambium area, larger epidermis (bark) area, and larger area for sprouting, and faster production of twigs and canopy. These components form our Hypothesis 1 that predicts higher growth rate for a small shrub than a small tree. This prediction was supported by available relevant empirical studies (14 publications). Further, a shrub will produce seeds faster than a tree (Hypothesis 2), multiple stems in shrubs insure future survival and growth if one or more stems die (Hypothesis 3), and three structural traits of short shrub stems improve survival compared to tall tree stems (Hypothesis 4)—all hypotheses have some empirical support. Multi-stemmed trees may be distinguished from shrubs by more upright stems, reducing bending moment. Improved understanding of shrubs can clarify their recent expansion on savannas, grasslands, and alpine heaths. More experiments and other empirical studies, followed by more elaborate models, are needed to understand why the shrub growth form is successful in many habitats.

Testing the generality of above-ground biomass allometry across plant functional types at the continent scale.

Accurate ground-based estimation of the carbon stored in terrestrial ecosystems is critical to quantifying the global carbon budget. Allometric models provide cost-effective methods for biomass prediction. But do such models vary with ecoregion or plant functional type? We compiled 15054 measurements of individual tree or shrub biomass from across Australia to examine the generality of allometric models for above-ground biomass prediction. This provided a robust case study because Australia includes ecoregions ranging from arid shrublands to tropical rainforests, and has a rich history of biomass research, particularly in planted forests. Regardless of ecoregion, for five broad categories of plant functional type (shrubs; multistemmed trees; trees of the genus Eucalyptus and closely related genera; other trees of high wood density; and other trees of low wood density), relationships between biomass and stem diameter were generic. Simple power-law models explained 84-95% of the variation in biomass, with little improvement in model performance when other plant variables (height, bole wood density), or site characteristics (climate, age, management) were included. Predictions of stand-based biomass from allometric models of varying levels of generalization (species-specific, plant functional type) were validated using whole-plot harvest data from 17 contrasting stands (range: 9-356Mgha(-1) ). Losses in efficiency of prediction were <1% if generalized models were used in place of species-specific models. Furthermore, application of generalized multispecies models did not introduce significant bias in biomass prediction in 92% of the 53 species tested. Further, overall efficiency of stand-level biomass prediction was 99%, with a mean absolute prediction error of only 13%. Hence, for cost-effective prediction of biomass across a wide range of stands, we recommend use of generic allometric models based on plant functional types. Development of new species-specific models is only warranted when gains in accuracy of stand-based predictions are relatively high (e.g. high-value monocultures).

Long-term perennial weed control strategies: Economic analyses and yield effect in hazelnut (Corylus avellana)

Weeds limit hazelnut productivity through competition and interference. Field experiments were conducted from spring 2010 through 2013 to evaluate string trimming alone or combined with herbicides in hazelnut orchards to control mugwort (Artemisia vulgaris L.), purple nutsedge (Cyperus rotundus L.), and burning nettle (Urtica urens L.). Treatments were mowing with a string trimmer (ST) alone, or ST followed by glyphosate, glyphosate + diflufenican, and glyphosate + carfentrazone-ethyl. These combinations also were applied with pendimethalin and oxyfluorfen as pre-emergence applications. The experiments were conducted in Fatsa-Ordu, Turkey, on a sandy clay soil with multi-stemmed trees (ocak). The combination treatments improved weed control compared to ST alone. Glyphosate plus carfentrazone-ethyl application 15 days after ST was the most effective treatment for control of these weeds. This combination was more effective in reducing seed bank reserves of A. vulgaris, C. rotundus and U. urens than herbicides applied alone or in mixtures throughout all seasons. Hazelnut yield was not significantly affected by herbicide treatments in 2010 or 2011. Hazelnut yield increased during the latter half of the experimental period, in 2012 and 2013. In a mixed population of A. vulgaris, C. rotundus and U. urens, 89 plants per m2 caused 12.1% yield loss. When the density increased to 256 plants per m2, yield losses increased to 29.7%. Hazelnut treated with ST followed by glyphosate plus carfentrazone-ethyl had the highest financial return. Post-emergence weed management systems in hazelnut should include ST followed by glyphosate plus carfentrazone-ethyl applications for maximum returns.

Variability in allometric relationships for temperate woodland Eucalyptus trees

Essential to effective vegetation management and habitat conservation is an understanding of tree and stand structure. However, such data for Australian Eucalyptus woodlands come mostly from forestry research and tend to be restricted to production forest types, and merchantable stems and species. We aimed to improve understanding of allometric relationships and stand dynamics for temperate Eucalyptus from critically endangered temperate woodlands. We explored relationships among tree height, diameter at breast height (DBH), crown width, crown senescence, and vegetation density. We measured 3748 naturally-occurring trees on 105 one-hectare sites in remnant vegetation in an agricultural landscape in semi-arid eastern Australia. Four species accounted for 94% of trees measured: Eucalyptus camaldulensis Dehnh. (river red gum), E. melliodora A.Cunn. ex Schauer (yellow box), E. microcarpa Maiden (grey box) and E. populnea F.Muell. subsp. bimbil L.A.S.Johnson & K.D.Hill (poplar box). Six Eucalyptus species were present in relatively low numbers. At about 15cm DBH, growth changed from being directed primarily at height gain to increasing relative crown width. Trees with DBH⩾15cm showed large and increasing variation in shape with increasing DBH, and tree dimensions varied among species. For a given DBH, yellow box were taller with relatively narrow crowns than poplar box, and river red gum and grey box intermediate to these two species. Human manipulation of the agricultural landscapes has impacted on these allometric relationships. Past attempts by people to kill trees has resulted in frequent coppicing, with up to 13 trunks. Up to 50% of trees of each species (mean 29%) had multiple stems and multi-stemmed trees had relatively broader crowns than single-stemmed trees. Similarly, decreasing vegetation density by tree removal generally resulted in shorter trees with wider canopies for any DBH. Progression through crown development and senescence was similar among species except that it occurred at different trunk sizes for different species. The variability of allometric relationships within temperate Eucalyptus species, combined with their variable growth rates, makes it difficult to accurately predict outcomes of current land management decisions in terms of vegetation structure and biological habitat attributes.

Disturbance and density-dependent processes (competition and facilitation) influence the fine-scale genetic structure of a tree species' population.

Disturbances, dispersal and biotic interactions are three major drivers of the spatial distribution of genotypes within populations, the last of which has been less studied than the other two. This study aimed to determine the role of competition and facilitation in the degree of conspecific genetic relatedness of nearby individuals of tree populations. It was expected that competition among conspecifics will lead to low relatedness, while facilitation will lead to high relatedness (selection for high relatedness within clusters). The stand structure and spatial genetic structure (SGS) of trees were examined within old-growth and second-growth forests (including multi-stemmed trees at the edge of forests) of Nothofagus pumilio following large-scale fires in Patagonia, Chile. Genetic spatial autocorrelations were computed on a spatially explicit sampling of the forests using five microsatellite loci. As biotic plant interactions occur among immediate neighbours, mean nearest neighbour distance (MNND) among trees was computed as a threshold for distinguishing the effects of disturbances and biotic interactions. All forests exhibited a significant SGS for distances greater than the MNND. The old-growth forest genetic and stand structure indicated gap recolonization from nearby trees (significantly related trees at distances between 4 and 10 m). At distances smaller than the MNND, trees of the second-growth interior forest showed significantly lower relatedness, suggesting a fading of the recolonization structure by competition, whereas the second-growth edge forest showed a positive and highly significant relatedness among trees (higher among stems of a cluster than among stems of different clusters), resulting from facilitation. Biotic interactions are shown to influence the genetic composition of a tree population. However, facilitation can only persist if individuals are related. Thus, the genetic composition in turn influences what type of biotic interactions will take place among immediate neighbours in post-disturbance forests.

Timber production and ecological characteristics of trees in coppice forest in the Voskop nature reserve in Český kras - a case study

Anew approach to forestry that increasingly values non-timber forest functions brings new interest and value also to coppice forests. A case study in the Voskop nature reserve located in the Česk&amp;yacute; kras Protected Landscape Area was focused on a comparison of the timber production of individually growing trees and in multistemmed trees resprouting after cutting (stools). We recorded tree ecological characteristics of trees such as existence of stem cavities, whether the tree grows individually or from a stool and whether or not the tree is broken, dead or has a dying crown. In total 2,670 trees were sampled on a 1,875 ha sample plot. The main tree species forming coppice stands are Quercus petraea and Carpinus betulus. The total stock volume of only 136 m&lt;sup&gt;3&lt;/sup&gt;&amp;middot;ha&lt;sup&gt;&amp;ndash;1&lt;/sup&gt; is very low at 84 years of age. The stock volume of individually growing trees is 84 m&lt;sup&gt;3&lt;/sup&gt;&amp;middot;ha&lt;sup&gt;&amp;ndash;1&lt;/sup&gt; and the stock volume of trees in stools is only 52 m&lt;sup&gt;3&lt;/sup&gt;&amp;middot;ha&lt;sup&gt;&amp;ndash;1&lt;/sup&gt; although the number of individually growing trees is lower. &amp;nbsp;

Dendrochronological Studies of Alder (Alnus Glutinosa) on Scottish Crannogs

On most Scottish crannogs that have been investigated alder is the species most extensively used for construction and therefore has the potential to provide fine chronological resolution for these sites. Dendrochronological studies of alder have now been undertaken on three crannogs, with mixed results. At Buiston the construction of a single comprehensive alder chronology has contributed significantly to the overall chronology of the crannog, whereas at Oakbank and Cults Loch 3 it was only possible to construct numerous small chronologies which have limited value for chronological resolution on the sites. Comparison between the datasets suggest that factors such as the structure of the parent tree, i.e. whether it comes from multi-stemmed coppice or single maiden trees, and the presence of multiple sources are likely to be significant factors in the successful dendro-dating of the species.

Growth, recruitment and attrition of Eucalyptus tree species in semi-arid temperate woodland

Conservation planning for many fauna relies on an ability to predict length of time lags to production of habitat requirements in restoration plantings or with natural regeneration. One key consideration is the growth rate of dominant trees, as tree age and size are linked to characteristics that provide fauna habitat, such as canopy cover, tree hollows and coarse woody debris. In this study we examined growth rate and mortality of Eucalyptus species for all individuals with diameter at breast height (DBH)⩾15cm on forty one-ha sites in temperate semi-arid woodland in eastern Australia. Over five years (2008–2013) encompassing drought and flood, mean growth was <2.5cm in DBH. Mixed effects models indicated that growth rate differed among species, and decreased with increasing senescence and greater initial foliage projective cover on the site. There was no link between initial tree DBH and growth rate for most species. Growth in DBH was similarly variable in large and small trees. Consequently increases in cross-sectional area, and hence biomass accumulation, are likely to be faster in larger trees. Growth of E. microcarpa, E. camaldulensis, E. blakelyi and E. conica did not significantly differ but was faster than that of E. populnea and E. melliodora. The random factors site and tree identity (for multi-stemmed trees) explained around 10% and 30% of the overall variability in growth rate respectively. Twelve trees (∼1%) died and 4 live trees were cut down and removed. Five (6.5%) of the 75 standing dead trees present in 2008 collapsed, and a further eight (10.5%) were cut down and removed by people. Forty saplings of four species with DBH<15cm in 2008 grew to DBH⩾15cm by 2013, equating to a recruitment rate of <4%, but this occurred on only nine of the 40 sites. Our study suggests mortality rate is being met by recruitment rate at the regional scale, but recruitment was extremely patchy and may result in site scale extinctions. The growth rates measured indicate that trees planted to create fauna habitat may take centuries to reach sizes that would contain large nesting or roosting hollows for fauna.

Treeline advances along the Urals mountain range - driven by improved winter conditions?

High-altitude treelines are temperature-limited vegetation boundaries, but little quantitative evidence exists about the impact of climate change on treelines in untouched areas of Russia. Here, we estimated how forest-tundra ecotones have changed during the last century along the Ural mountains. In the South, North, Sub-Polar, and Polar Urals, we compared 450 historical and recent photographs and determined the ages of 11,100 trees along 16 altitudinal gradients. In these four regions, boundaries of open and closed forests (crown covers above 20% and 40%) expanded upwards by 4 to 8 m in altitude per decade. Results strongly suggest that snow was an important driver for these forest advances: (i) Winter precipitation has increased substantially throughout the Urals (~7 mm decade(-1) ), which corresponds to almost a doubling in the Polar Urals, while summer temperatures have only changed slightly (~0.05°C decade(-1) ). (ii) There was a positive correlation between canopy cover, snow height and soil temperatures, suggesting that an increasing canopy cover promotes snow accumulation and, hence, a more favorable microclimate. (iii) Tree age analysis showed that forest expansion mainly began around the year 1900 on concave wind-sheltered slopes with thick snow covers, while it started in the 1950s and 1970s on slopes with shallower snow covers. (iv) During the 20th century, dominant growth forms of trees have changed from multistemmed trees, resulting from harsh winter conditions, to single-stemmed trees. While 87%, 31%, and 93% of stems appearing before 1950 were from multistemmed trees in the South, North and Polar Urals, more than 95% of the younger trees had a single stem. Currently, there is a high density of seedlings and saplings in the forest-tundra ecotone, indicating that forest expansion is ongoing and that alpine tundra vegetation will disappear from most mountains of the South and North Urals where treeline is already close to the highest peaks.

Local-scale drivers of multi-stemmed tree formation in Acer, in a temperate forest of Northeast China

Acer is an important genus in temperate forests in Northeast China. Individual Acer trees can re-sprout from the root collar and can occur in clonal units, either as a single-stemmed or multi-stemmed tree. However, the factors that induce multiple-stems in Acer remain only partly understood. In this study, we determined the relative importance of abiotic and biotic variables in driving the production of multiple-stems in this genus, within a 25-hm2 experimental forest dynamics plot in Changbaishan (CBS) temperate forest. We used generalized linear mixed models to perform analyses at two levels (community- and species-level). We found seven Acer species in total within the plot, where they form a key part of the forest community. Our results show that abiotic factors play a more important role in producing multi-stemmed trees at the community level in CBS. At the species level, the relative importance of different factors varied among species. Shrub species tended to have a higher frequency of multi-stemmed trees under stressful conditions, whereas tree species tended to have more multi-stemmed trees in more suitable habitat. Our results indicate that the relative importance of different factors influencing the frequency of multi-stemmed individuals in Acer differs at the community and species level in the temperate forest.

Effects of the pruning intensity and tree size on multi-stemmed Prosopis flexuosa trees in the Central Monte, Argentina

Forestry use in Prosopis flexuosa woodlands in the Central Monte is limited by low wood productivity and by most of the trees being multi-stemmed. Desert inhabitants have turned pruning into a common practice to get some forest products, increase wood production and improve tree shape. In this study we tested pruning practices used by locals on trees of different diameter classes and different pruning intensities in the aeolian plains of the Central Monte Desert. Two trials were conducted: (a) we tested the effects of pruning on three types of trees: adult multi-stemmed trees (7.5–15cm basal diameter; n=12 for pruned trees and 10 for control), young trees (3–7.5cm basal diameter; n=20 for pruned trees and 18 for control), and saplings (<3cm basal diameter; n=15 for pruned trees and 18 for control); (b) we compared the effects of different pruning intensities: heavy pruning (50% of crown removed and n=10), intermediate pruning (25% of crown removed; n=10), and unpruned individuals (n=10). Basal diameters of all stems, total tree height, largest and smallest crown diameters were measured yearly. We estimated the equivalent basal diameter (EBD) and crown volume. Linear mixed models (LMM), in continuous variables, and general linear mixed models (GLMM), in discrete variables, were used for evaluating the effects of the treatments on the different variables. The response observed in pruned trees was an increased length of branches, which in both trials translated into increased crown diameter and volume. No initial response was recorded in basal diameter growth of the remaining stem. In adult trees, an increase in basal diameter was detected five years after pruning. A greater response of crown growth was found in individuals subjected to heavy pruning vs. individuals under intermediate pruning. Results suggested that pruning could improve the shape of Prosopis in the short run, and increase stem diameter growth in the long run, as observed for other tree species of Prosopis that received pruning throughout the world. This suggests that this practice could be potentially used to obtain poles and firewood without a decrease in wood productivity but with an increase in branch growth, and, in consequence, it could be included in silvicultural management of woodlands dominated by multi-stemmed trees and in models of sustainable management at local scale.

Multi-stemmed trees of Nothofagus pumilio second-growth forest in Patagonia are formed by highly related individuals

Multi-stemmed trees (tree clusters) in Nothofagus pumilio, a dominant tree species in Patagonia, are very uncommon and are restricted to the edge of second-growth forests following human-provoked fires. No vegetative reproduction has been reported so far. The genetic structure of multi-stemmed trees of this species was investigated and it was hypothesized that genets within a cluster were more closely related than average in the population. Fifteen clusters (composed of at least three purported stems) and 15 single trees were sampled at the edge of a second-growth forest and genotyped using two amplified fragment length polymorphism (AFLP) primer pairs. We obtained 119 polymorphic markers that allowed clonality to be determined, together with sibship structure and relatedness among samples. Clonality was detected in seven clusters but all clusters had at least two different genotypes. Full sibs were found exclusively within clusters and in all clusters. Within a cluster, stems that were not identified as full sibs were often half sibs. Relatedness values for the full sibs and half sibs were higher than the theoretical values of 0·5 and 0·25 but the relatedness between clusters was very low. Tree clusters that are merged at the edge of the second-growth forest of N. pumilio are composed of stems of the same genotype and of other genotypes that are highly related (but not always). It is suggested that this peculiar genetic structure results from a combination of several causes, including selection for merging of related individuals.

Factors controlling deadwood availability and branch decay in two Prosopis woodlands in the Central Monte, Argentina

Deadwood is an important resource commonly used by inhabitants in arid lands. However, the low wood productivity and the presence of multi-stemmed trees restrict the use. Prosopis flexuosa woodlands are protected and inhabited by pastoralists who have land rights to use natural resources. As in other forests in the world, dead branches are the most commonly used. The factors causing the death of branches these trees are unknown. As P. flexuosa is a highly heliophilous species, branch mortality may depend on the growth habit and orientation of dry branches under the tree crown. With the participation of inhabitants, we assessed the present availability of deadwood in two Prosopis woodlands of different structure (semi-closed and open woodland), and evaluated the formation of deadwood in terms of shape and cardinal location of dry branches under the crown. We developed and compared regression models to estimate the amount of deadwood for erect, semi-erect and decumbent trees, and for the north and south areas under the crown ( n = 120 trees). In addition, to determine the period of growth decline and the factors determining branch mortality, we compared annual radial increment between live and dead branches ( n = 30 trees; 10 for each tree shape). The total amount of deadwood in adult Prosopis trees is higher in the semi-closed than in the open woodland (8.6 and 4.4 Tn ha −1, respectively). Only tree size determined the amount of deadwood present in each Prosopis tree, since we found no evidence related to the shape of the tree or the position of dry branches in the canopy. Branch decay was a large process of 18–20 years, and branch death appears to be the result of the action of climatic factors (dry period). The results suggest that the use of deadwood by the desert inhabitants is a tool that can potentially be used; however, the use of this resource taking into account the generation rates of deadwood has not been developed in arid lands. These practices at appropriate sites can contribute to a sustainable management of these woodlands, including the removal of deadwood in a model of local management on a site where potential productivity is relatively low.

Merged trees in second-growth, fire-origin forests in Patagonia, Chile: positive spatial association patterns and their ecological implications

• Negative density-dependent processes have been thought to be the primary cause of shifting spatial patterns of tree populations through time. The existence of adult tree clusters might challenge this classical prediction. Here, we document the prevalence of merged stems (clustering of mature trees leading to stem fusion) in second-growth forests of Nothofagus pumilio and hypothesize that it is nonrandom but predictable in space. • We stem-mapped nine sites in second-growth edge and interior forests of fire origin and in mature forests of N. pumilio (>3500 trees) in central Patagonia, Chile. The spatial structure of stand-level and individual-level features was estimated with spatial analyses (pair-correlation function and nearest-neighbor distances). • Multistemmed trees were merged clusters of separate individuals. Merged trees were predominantly found at the edge of the second-growth forests. We found strong clustering (≤5 m) at forest edge sites and none at interior sites. Nearest-neighbor distance distributions were unimodal for unmerged trees and monotonically decreasing for merged trees; interstem distances were much smaller at the edge sites than at the interior sites. • The occurrence of merged trees at the forest edge, and the resulting high spatial aggregation of stems, is consistent with the hypothesis that establishment was probably aggregated. The spatial pattern found at the forest edge changes the standard spatial pattern sequence through time in temperate forests, altering traditional forest-stand-dynamics models.

Merged trees in second‐growth, fire‐origin forests in Patagonia, Chile: positive spatial association patterns and their ecological implications

•Premise of the Study: Negative density‐dependent processes have been thought to be the primary cause of shifting spatial patterns of tree populations through time. The existence of adult tree clusters might challenge this classical prediction. Here, we document the prevalence of merged stems (clustering of mature trees leading to stem fusion) in second‐growth forests of Nothofagus pumilio and hypothesize that it is nonrandom but predictable in space.•Methods: We stem‐mapped nine sites in second‐growth edge and interior forests of fire origin and in mature forests of N. pumilio (&gt;3500 trees) in central Patagonia, Chile. The spatial structure of stand‐level and individual‐level features was estimated with spatial analyses (pair‐correlation function and nearest‐neighbor distances).•Key Results: Multistemmed trees were merged clusters of separate individuals. Merged trees were predominantly found at the edge of the second‐growth forests. We found strong clustering (≤5 m) at forest edge sites and none at interior sites. Nearest‐neighbor distance distributions were unimodal for unmerged trees and monotonically decreasing for merged trees; interstem distances were much smaller at the edge sites than at the interior sites.•Conclusions: The occurrence of merged trees at the forest edge, and the resulting high spatial aggregation of stems, is consistent with the hypothesis that establishment was probably aggregated. The spatial pattern found at the forest edge changes the standard spatial pattern sequence through time in temperate forests, altering traditional forest‐stand‐dynamics models.

Impact of long-term, saline flooding on condition and reproduction of the clonal wetland tree, Melaleuca ericifolia (Myrtaceae)

Although water regime modification and salinity are recognised as significant threats to wetland ecosystems worldwide, the effects of long-term saline flooding (decades) on woody tree persistence are poorly quantified. We compared the condition, growth, structure and reproduction (sexual and asexual) of mature individuals of the clonal tree, Melaleucaericifolia (Myrtaceae), that experienced continual (>30 years) flooding with trees that were only intermittently (approximately every 5 years) flooded. An index developed to assess the condition of multi-stemmed trees found that continually flooded trees were in significantly poorer condition than intermittently flooded trees, having lower crown cover, foliar cover and foliar density, and a higher incidence of dead stags and dieback. Annual stem growth correlated strongly with condition scores. Evidence for a trade-off between sexual and asexual reproductions was found; flooded trees were constrained in their vegetative lateral spread (<12 m dia.) and flowered more than intermittently flooded trees, which were not restricted in lateral spread (~30 m dia.). Flooded trees used intensively by the colonially roosting Australian Sacred Ibis (Threskiornis molucca) were in especially poor condition. These trees flowered infrequently and produced the lowest number of infructescences, but produced many new vegetative stems (ramets) within their centre. Although chronic flooding appeared to compromise the condition of M. ericifolia trees in Dowd Morass, their existence upon woody hummocks (~40 cm high) upon which they are able to produce new stems is likely to be a key mechanism in their persistence. It is unknown, however, how long this process can maintain the existing population. Production and maintenance of a large aerial seed bank by living mature trees under flooded conditions may allow M. ericifolia to regenerate sexually upon drawdown and may be important for population persistence in the longer term.

The Mesquite Economy in the Mexican-American Borderlands

Scrubby mesquite trees infest large regions of the Mexican-American borderland. In this same area, demand for mesquite wood and charcoal places pressure on mature trees. This paper examines consumption of this biomass fuel on both sides of the Sonora-Arizona border and the demands that consumption places on the environment in Northern Sonora. In Sonora multi-stemmed trees provide wood for heating homes and cooking stoves upon which coffee pots bubble and large, flat tortillas cook to perfection. At the opposite extreme, large, mature trees fall to the chainsaw and charcoal pits to provide North American restaurants and backyard cooks with a chic and flavorful grilling fuel. This research in northern Sonora reveals details of this hidden industry. This study provides important information and discussion about biomass use in a dry region. Studies like this, which consider direct use of biomass resources, are important, especially in light of present and future industrial, population, and urban growth along the border, which all place additional pressure on natural resources.

The need for full inventories of tree modes of disturbance to improve forest dynamics comprehension: An example from a semideciduous forest in Brazil

Abstract A study was carried out to characterize the general pattern of tree mortality and damage in an old-growth semideciduous seasonal forest in the Caetetus Ecological Station, southeastern Brazil, and to assess species-specific patterns of mode and frequency of disturbances. We counted all disturbance events promoted by trees or parts of them larger than 20 cm in diameter within a 10.24 ha plot and recorded their mode of disturbance, basal diameter, age class, presence of re-sprouts and, whenever possible, their species. A total of 743 disturbance events were recorded inside the studied plot. Of these events, 650 were occasioned by entire trees (33% uprooted, 28% dead-standing, 26.5% snapped, 10.5% inclined and 2% complex events) while 93 were due to parts of trees (60.2% branch-falls and 39.8% stem-fall from multi-stemmed trees). Dead-standing trees were predominant in the recent age class, while uprooted trees predominated in the oldest age class. Probably, a large fraction of the trees in this forest die standing and then fall, exposing their roots. We found that considering all modes of disturbance is quite important, otherwise forest disturbance rates might be underestimated by approximately 25%. Even when usually neglected modes of disturbance were excluded from the estimates, this forest revealed a high disturbance rate compared to other forests. Some species showed damage and death rates greater than expected by chance, while others species showed significantly lower rates. A high proportion of re-sprouting was observed in this forest and the species presenting the greatest re-sprouting proportion were also the most abundant in the study area, corroborating the idea that this ability can be important to increase their competitive potential, especially in forest with high disturbance rates.