Patterns in the within-tree distribution of the emerald ash borer Agrilus planipennis (Fairmaire) in young, green-ash plantations of south-western Ontario, Canada

1 The emerald ash borer Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) is a serious exotic pest of ash trees (Fraxinus spp.) in North America, and is responsible for the deaths of millions of trees in Ontario and Michigan. One of the greatest challenges facing the successful management of the pest is the ability to accurately detect its presence in a tree. 2 Observations were made on A. planipennis larval feeding galleries found within 65 young, green‐ash trees cut from plantations in Essex County, Ontario, Canada. The within‐tree distributions of feeding galleries were described in relation to height‐above‐ground, stem diameter, bark thickness and stem aspect. 3 Galleries were not distributed randomly or evenly; minimum boundaries of stem diameter and bark thickness and a maximum boundary of height‐above‐ground were detected. Indications of maximum boundaries for stem diameter and bark thickness were also observed. Galleries were found most often on the south‐west side of the tree. 4 Using the technique of upper boundary regression, we were able to identify significant quadratic relationships between A. planipennis gallery density and stem diameter and bark thickness, as well as a significant negative linear relationship between gallery density and height‐above‐ground. 5 Agrilus planipennis gallery density in newly‐infested trees was lower than in previously‐infested trees, and was observed to peak at smaller stem diameters and bark thicknesses than in previously‐infested trees. 6 Survey teams would increase their probability of detecting new A. planipennis infestations by initiating searches for exit holes and feeding galleries in trunk sections and branches of approximately 7 cm in diameter.     

Allometric equations to predict the total aboveground biomass of tree species in a planted forest in Egypt

The aim of this study is to estimate the total above‐ground biomass (TAGB), stem height (H), diameter at breast height (dbh) and basal area of five tree species (ages 7‐8 years) irrigated by municipal sewage water in the Egyptian‐Chinese friendship forest, Sadat City, Egypt. From the biomass data that obtained through destructive sampling, models for predicting aboveground biomass were developed. The highest values for stem density and height were estimated for Eucalyptus citriodora, while the lowest value for density was obtained for Dalbergia sissoo and stem height for Khaya senegalensis. The highest values for basal area and dbh were obtained for Casuarina spp., while the lowest values were recorded for Dalbergia sissoo. Eucalyptus camaldulensis had the highest stand stem biomass and TAGB (55.5, 83.9 t DW ha^‐1, respectively). In addition, Casuarina spp. had the highest leafy branches biomass (32.5 t DW ha^‐1) while Dalbergia sissoo had the lowest values for all tree components. All the generated allometric equations had high correlation coefficients at high probability levels. Moreover, the results revealed that not only the dbh data can be used as independent variable for biomass determination, but also stem height and size index are recommended for biomass estimation (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Overwintering of Monilinia spp. on Mummified Stone Fruit

Mummies were evaluated over the course of four growing seasons to ensure they are source of primary inoculum. The percentage of mummies with presence of conidia and its viability were determined in tree and ground mummies. The number of conidia and its germination were also quantified. Fruit mummies with Monilinia spp. were consistently detected on tree mummies in all studied orchards and growing seasons. However, the percentage of viable mummies over the same sampling periods decreased, and in most cases, it was 0% by October. The percentage of ground mummies with Monilinia spp. was lower and less viable in comparison with tree mummies, tending to decrease faster. The number of overwintering conidia in tree mummies decreased smoothly from 1 × 10⁶ to 1 × 10⁴ conidia/mummy between April and September. On the other hand, the number of conidia in ground mummies rapidly decreased to 0 conidia/mummy at around May–July. The profiles for the percentage of conidia germinated were similar in all cases. The information obtained from this study is a step forward to understanding the epidemiology of Monilinia spp., a useful tool to manage disease development.     

Independence of stem and leaf hydraulic traits in six Euphorbiaceae tree species with contrasting leaf phenology

Hydraulic traits and hydraulic-related structural properties were examined in three deciduous (Hevea brasiliensis, Macaranga denticulate, and Bischofia javanica) and three evergreen (Drypetes indica, Aleurites moluccana, and Codiaeum variegatum) Euphorbiaceae tree species from a seasonally tropical forest in south-western China. Xylem water potential at 50% loss of stem hydraulic conductivity (P50_stem) was more negative in the evergreen tree, but leaf water potential at 50% loss of leaf hydraulic conductivity (P50_leaf) did not function as P50_stem did. Furthermore, P50_stem was more negative than P50_leaf in the evergreen tree; contrarily, this pattern was not observed in the deciduous tree. Leaf hydraulic conductivity overlapped considerably, but stem hydraulic conductivity diverged between the evergreen and deciduous tree. Correspondingly, structural properties of leaves overlapped substantially; however, structural properties of stem diverged markedly. Consequently, leaf and stem hydraulic traits were closely correlated with leaf and stem structural properties, respectively. Additionally, stem hydraulic efficiency was significantly correlated with stem hydraulic resistance to embolism; nevertheless, such a hydraulic pattern was not found in leaf hydraulics. Thus, these results suggest: (1) that the evergreen and deciduous tree mainly diverge in stem hydraulics, but not in leaf hydraulics, (2) that regardless of leaf or stem, their hydraulic traits result primarily from structural properties, and not from leaf phenology, (3) that leaves are more vulnerable to drought-induced embolism than stem in the evergreen tree, but not always in the deciduous tree and (4) that there exists a trade-off between hydraulic efficiency and safety for stem hydraulics, but not for leaf hydraulics.     

General allometric equations and biomass allocation of <Emphasis Type="Italic">Pinus massoniana</Emphasis> trees on a regional scale in southern China

Applying allometric equations in combination with forest inventory data is an effective approach to use when qualifying forest biomass and carbon storage on a regional scale. The objectives of this study were to (1) develop general allometric tree component biomass equations and (2) investigate tree biomass allocation patterns for Pinus massoniana, a principal tree species native to southern China, by applying 197 samples across 20 site locations. The additive allometric equations utilized to compute stem, branch, needle, root, aboveground, and total tree biomass were developed by nonlinear seemingly unrelated regression. Results show that the relative proportion of stem biomass to tree biomass increased while the contribution of canopy biomass to tree biomass decreased as trees continued to grow through time. Total root biomass was a large biomass pool in itself, and its relative proportion to tree biomass exhibited a slight increase with tree growth. Although equations employing stem diameter at breast height (dbh) alone as a predictor could accurately predict stem, aboveground, root, and total tree biomass, they were poorly fitted to predict the canopy biomass component. The inclusion of the tree height (H) variable either slightly improved or did not in any way increase model fitness. Validation results demonstrate that these equations are suitable to estimate stem, aboveground, and total tree biomass across a broad range of P. massoniana stands on a regional scale.     

Variation in litter under individual tree crowns: Implications for scattered tree ecosystems

In forest ecosystems litter is usually assessed in terms of the average amount produced by the canopy. In scattered tree ecosystems this approach is problematic because the canopy is discontinuous and the spatial arrangement of litter highly variable. We addressed this problem by quantifying the spatial variation in litter load and litter composition associated with individual trees in a Eucalyptus melliodora – Eucalyptus blakelyi woodland. Litter was sampled under crowns and in grassland adjacent to 10 E. blakelyi and 10 E. melliodora trees ranging in diameter at breast height (dbh) from 14 to 129 cm. A total of 302 L samples were collected from these trees, at distances ranging from 0 to 42 m from main stem. The sampled litter loads ranged from 0.02 to 109.3 t ha^?1 and were significantly higher under tree crowns than in grassland for litter and each component of litter (leaves, bark, fine twigs, coarse twigs). In particular, the mean litter load under tree crowns (12.5 t ha^?1) was an order of magnitude higher than the mean litter load in grassland (1.27 t ha^?1). There was a significant (P = 0.0103) positive relationship between mean litter load under the tree crown and dbh, indicating larger trees produced more litter per unit area of ground than smaller trees. Generalized Linear Modelling produced highly significant (P < 0.0001) models predicting the spatial variation in litter load and litter composition in terms of distance from main stem and dbh. Our models demonstrate gradients in litter load and composition under tree crowns. These gradients were most pronounced for the large trees in our study. The disproportionate input of litter and variety of litter components associated with large trees in our study supports their keystone role in scattered tree ecosystems and highlights the need to maintain these structures in agricultural landscapes.     

Transpiration and canopy conductance in a pristine broad-leaved forest of Nothofagus: an analysis of xylem sap flow and eddy correlation measurements

Summary Tree transpiration was determined by xylem sap flow and eddy correlation measurements in a temperate broad-leaved forest of Nothofagus in New Zealand (tree height: up to 36 m, one-sided leaf area index: 7). Measurements were carried out on a plot which had similar stem circumference and basal area per ground area as the stand. Plot sap flux density agreed with tree canopy transpiration rate determined by the difference between above-canopy eddy correlation and forest floor lysimeter evaporation measurements. Daily sap flux varied by an order of magnitude among trees (2 to 87 kg day^–1 tree^–1). Over 50% of plot sap flux density originated from 3 of 14 trees which emerged 2 to 5 m above the canopy. Maximum tree transpiration rate was significantly correlated with tree height, stem sapwood area, and stem circumference. Use of water stored in the trees was minimal. It is estimated that during growth and crown development, Nothofagus allocates about 0.06 m of circumference of main tree trunk or 0.01 m² of sapwood per kg of water transpired over one hour.Maximum total conductance for water vapour transfer (including canopy and aerodynamic conductance) of emergent trees, calculated from sap flux density and humidity measurements, was 9.5 mm s^–1 that is equivalent to 112 mmol m^–2 s^–1 at the scale of the leaf. Artificially illuminated shoots measured in the stand with gas exchange chambers had maximum stomatal conductances of 280 mmol m^–2 s^–1 at the top and 150 mmol m^–2 s^–1 at the bottom of the canopy. The difference between canopy and leaf-level measurements is discussed with respect to effects of transpiration on humidity within the canopy. Maximum total conductance was significantly correlated with leaf nitrogen content. Mean carbon isotope ratio was –27.76±0.27 (average ±s.e.) indicating a moist environment. The effects of interactions between the canopy and the atmosphere on forest water use dynamics are shown by a fourfold variation in coupling of the tree canopy air saturation deficit to that of the overhead atmosphere on a typical fine day due to changes in stomatal conductance.This paper is dedicated to Prof. Dr. O.L. Lange on the occasion of his 65th birthday     

Midday stomatal conductance is more related to stem rather than leaf water status in subtropical deciduous and evergreen broadleaf trees

Midday depressions in stomatal conductance (g_s) and photosynthesis are common in plants. The aim of this study was to understand the hydraulic determinants of midday g_s, the coordination between leaf and stem hydraulics and whether regulation of midday g_s differed between deciduous and evergreen broadleaf tree species in a subtropical cloud forest of Southwest (SW) China. We investigated leaf and stem hydraulics, midday leaf and stem water potentials, as well as midday g_s of co‐occurring deciduous and evergreen tree species. Midday g_s was correlated positively with midday stem water potential across both groups of species, but not with midday leaf water potential. Species with higher stem hydraulic conductivity and greater daily reliance on stem hydraulic capacitance were able to maintain higher stem water potential and higher g_s at midday. Deciduous species exhibited significantly higher stem hydraulic conductivity, greater reliance on stem capacitance, higher stem water potential and g_s at midday than evergreen species. Our results suggest that midday g_s is more associated with midday stem than with leaf water status, and that the functional significance of stomatal regulation in these broadleaf tree species is probably for preventing stem xylem dysfunction.     

Seasonal soil‐surface carbon fluxes from the root systems of young Pinus radiata trees growing at ambient and elevated CO2 concentration

Elevated atmospheric CO₂ concentration may result in increased below‐ground carbon allocation by trees, thereby altering soil carbon cycling. Seasonal estimates of soil surface carbon flux were made to determine whether carbon losses from Pinus radiata trees growing at elevated CO₂ concentration were higher than those at ambient CO₂ concentration, and whether this was related to increased fine root growth. Monthly soil surface carbon flux density (f) measurements were made on plots with trees growing at ambient (350) and elevated (650 μmol mol^?1) CO₂ concentration in large open‐top chambers. Prior to planting the soil carbon concentration (0.1%) and f (0.28 μmol m^?2 s^?1 at 15 °C) were low. A function describing the radial pattern of f with distance from tree stems was used to estimate the annual carbon flux from tree plots. Seasonal estimates of fine root production were made from minirhizotrons and the radial distribution of roots compared with radial measurements of f. A one‐dimensional gas diffusion model was used to estimate f from soil CO₂ concentrations at four depths. For the second year of growth, the annual carbon flux from the plots was 1671 g y^?1 and 1895 g y^?1 at ambient and elevated CO₂ concentrations, respectively, although this was not a significant difference. Higher f at elevated CO₂ concentration was largely explained by increased fine root biomass. Fine root biomass and stem production were both positively related to f. Both root length density and f declined exponentially with distance from the stem, and had similar length scales. Diurnal changes in f were largely explained by changes in soil temperature at a depth of 0.05 m. Ignoring the change of f with increasing distance from tree stems when scaling to a unit ground area basis from measurements with individual trees could result in under‐ or overestimates of soil‐surface carbon fluxes, especially in young stands when fine roots are unevenly distributed.     

Density and distance-to-adult effects of a canker disease of trees in a moist tropical forest

We compared the spatial distribution of stem cankers on the canopy tree Ocotea whitei (Lauraceae) in a 20-ha plot on Barro Colorado Island, Panama, with spatial and temporal patterns of mortality in this host over the previous decade. The cankers occur both on adult and juvenile individuals, aothough juveniles are much more likely the adults to show symptoms. Disease incidence is host-density dependent, and both the presence of the disease and host mortality are more likely close to than far from a conspecific adult, which resulted in a net spatial shift of the juvenile population away from conspecific adults through time. Disease incidence is lower than expected among juveniles of O. whitei growing near to adults of the non-susceptible canopy tree Beilschmiedia pendula. The coincidence of spatial patterns of canker incidence and host mortality suggest a role for the disease in regulating host spatial distribution, in agreement with predictions of the Janzen-Connell hypothesis.     

Liana cover in the canopies of rainforest trees is not predicted by local ground‐based measures

Lianas (woody climbers) are structural parasites of trees that compete with them for light and below‐ground resources. Most studies of liana–tree interactions are based on ground‐level observations of liana stem density and size, with these assessments generally assumed to reflect the amount of liana canopy cover and overall burden to the tree. We tested this assumption in a 1‐ha plot of lowland rainforest in tropical Australia. We recorded 1072 liana stems (≥1 cm diameter at breast height {dbh}) ha^?1 across all trees (≥10 cm dbh) on the plot and selected 58 trees for detailed study. We estimated liana canopy cover on selected trees that hosted 0–15 liana individuals, using a 47‐m‐tall canopy crane. Notably, we found no significant correlations between liana canopy cover and three commonly used ground‐based measurements of liana abundance as follows: liana stem counts per tree, liana above‐ground biomass per tree and liana basal area per tree. We also explored the role of tree size and liana infestation and found that larger trees (≥20 cm dbh) were more likely to support lianas and to host more liana stems than smaller trees (≤20 cm dbh). This pattern of liana stem density, however, did not correlate with greater liana coverage in the canopy. Tree family was also found to have a significant effect on likelihood of hosting lianas, with trees in some families 3–4 times more likely to host a liana than other families. We suggest that local ground‐based measures of liana–tree infestation may not accurately reflect liana canopy cover for individual trees because they were frequently observed spreading through neighbouring trees at our site. We believe that future liana research will benefit from new technologies such as high‐quality aerial photography taken from drones when the aim is to detect the relative burden of lianas on individual trees.     

Assessing the above‐ground biomass of a complex tropical rainforest using a canopy crane

Abstract Current estimates of the total biomass in tropical rainforests vary considerably; this is due in large part to the different approaches that are used to calculate biomass. In this study we have used a canopy crane to measure the tree architectures in a 1 ha plot of complex mesophyll vine forest at Cape Tribulation, Australia. Methods were developed to measure and calculate the crown and stem biomass of six major species of tree and palm (Alstonia scholaris (Apocynaceae), Cleistanthus myrianthus (Euphorbiaceae), Endiandra microneura (Lauraceae), Myristica insipida (Myristicaceae), Acmena graveolens (Myrtaceae), Normanbya normanbyi (Arecaceae)) using the unique access provided by the crane. This has allowed the first non‐destructive biomass estimate to be carried out for a forest of this type. Allometric equations which relate tree biomass to the measured variable ‘diameter at breast height’ were developed for the six species, and a general equation was also developed for trees on the plot. The general equation was similar in form to equations developed for tropical rainforests in Brazil and New Guinea. The species equations were applied at the level of families, the generalized equation was applied to the remaining species which allowed the biomass of a total of 680 trees to be calculated. This has provided a current estimate of 270 t ha⁻¹ above‐ground biomass at the Australian Canopy Crane site; a value comparable to lowland rainforests in Panama and French Guiana. Using the same tree database seven alternative allometric equations (literature equations for tropical rainforests) were used to calculate the site biomass, the range was large (252–446 t ha⁻¹) with only three equations providing estimates within 34 t ha⁻¹ (12.5%) of the site value. Our use of multiple species‐specific allometric equations has provided a site estimate only slightly larger (1%) than that obtained using allometric equations developed specifically for tropical wet rainforests. We have demonstrated that it is possible to non‐destructively measure the biomass in a complex forest using an on‐site canopy crane. In conjunction the development of crown maps and a detailed tree architecture database allows changes in forest structure to be followed quantitatively.     

Changes in the factor of safety within the superstructure of a dicot tree

The objective of this study was to determine whether the factor of safety for mechanical stability varied among stems differing in size and age within the superstructure of a large dicot tree. Two factors of safety were selected for study: the quotient of the critical buckling height and the actual length of stems, Hcrit/L, and the quotient of the modulus of rupture (the force per unit area required to break a stem) and the working stress (the force per unit area resulting from the biomass measured distal to a stem), M_R/σ_w. These two dimensionless safety factors were determined for a total of 420 shoot segments comprising much of the aboveground biomass of a Robinia pseudoacacia (Fabaceae) tree measuring 18.7 m in height and 1347 kg in mass, and 0.46 m in diameter (40 yr old) at 1.2 m from the ground. An S-shaped trend was observed when each of the two factors of safety was plotted as a function of stem age. Each factor decreased from a local maximum for the most distal (peripheral) stems in the canopy to a local minimum value for stems ∼10 yr old; each factor increased again to another local maximum for stems 11–18 yr old, and then decreased steadily toward the base of the trunk. This trend was the result of the allometric relationships among stem diameter, length, biomass, and material properties (stiffness and strength) with respect to stem age. Although they were disproportionately more slender than their older counterparts, peripheral stems were sufficiently stiff and strong to sustain the stresses resulting from their weight and that of foliage without deflecting under these loads, yet they were sufficiently flexible to easily bend and thereby presumably provide a mechanism to reduce the drag forces acting on the entire tree. In contrast, the internally imposed mechanical forces acting on progressively older stems increased at a greater rate than the observed rate of increase in stem stiffness, strength, or diameter. The probability of mechanical failure, which must be considered from a demographic perspective (i.e., an age-dependent phenomenon), thus increased from older branches to the base of the trunk. Reports of similar allometric trends based on interspecific comparisons among diverse dicot species comply with the allometry observed for the R. pseudoacacia tree and suggest that the S-shaped trend for the factor of safety holds for stems differing in age drawn from individual trees and for the trunks of conspecifics differing in age drawn from a dense population.     

Clinical and molecular features and therapeutic perspectives of spinal muscular atrophy with respiratory distress type 1

Spinal muscular atrophy with respiratory distress (SMARD1) is an autosomal recessive neuromuscular disease caused by mutations in the IGHMBP2 gene, encoding the immunoglobulin μ‐binding protein 2, leading to motor neuron degeneration. It is a rare and fatal disease with an early onset in infancy in the majority of the cases. The main clinical features are muscular atrophy and diaphragmatic palsy, which requires prompt and permanent supportive ventilation. The human disease is recapitulated in the neuromuscular degeneration (nmd) mouse. No effective treatment is available yet, but novel therapeutical approaches tested on the nmd mouse, such as the use of neurotrophic factors and stem cell therapy, have shown positive effects. Gene therapy demonstrated effectiveness in SMA, being now at the stage of clinical trial in patients and therefore representing a possible treatment for SMARD1 as well. The significant advancement in understanding of both SMARD1 clinical spectrum and molecular mechanisms makes ground for a rapid translation of pre‐clinical therapeutic strategies in humans.     

Effect of pruning and ground treatments on the populations of Hylobitelus xiaoi Zhang, a new debarking weevil in slash pine plantations

1 Adults of Hylobilus xiaoi Zhang spend the daylight hours in bark crevices of lower stem or shallow cracks in the soil near the base of the host. Adults are both thermophobic and photophobic. 2 Pruning the lower whorls of slash pine branches and removing duff and scraping soil around the tree base modified the adult habitat. 3 Both adult and larval abundance was inversely related to intensity of treatment, suggesting that the greater exposure to light or heat, or both, at the tree base, the less favourable was the habitat to the insect. 4 It was concluded that branch pruning together with duff removal and ground scarification was the best silvicultural approoach to reduce weevil abundance.     

Relationship between size hierarchy and density of trees in a tropical dry deciduous forest of western India

Questions: Density dependence is thought to restrict exponential growth as well as give rise to size structure in populations. Size hierarchy in trees from tropical dry deciduous forests is studied to ask (1) whether nature of competition is symmetric or asymmetric and (2) what is the self thinning trajectory under a natural gradient of tree density. Location: Western India. Methods: Density was measured as the number of trees in 10‐m radius circular plots (n= 96) and size was measured at DBH. Size variation was evaluated by the Gini coefficient (n= 1239 trees). Results: Size inequality between neighbours decreased with density but in a non‐linear manner. In the backdrop of existing theory this indirectly suggests that competitive interactions may be symmetric over a ‘depletive’ resource such as below‐ground water (rather than a ‘pre‐emptive’ resource such as light), which is very plausible in a semi‐arid environment. The self thinning coefficient derived from the relationship between stem diameter and density (γ～?1/4), is higher than expected from existing models of allometric plant growth (γ=?1/3) which are based on above‐ground interactions alone. Seen in conjunction, these results suggest that above‐ground structures, such as stem size, do not adequately represent the outcome of competitive interactions when below‐ground resources, such as water, may be more important under semi‐arid conditions. Conclusions: The non‐linear relationship between size inequality and density indicates that there exists a density threshold beyond which investment in above‐ground biomass becomes sluggish in semi‐arid, deciduous forests. Since current allometric models do not incorporate below‐ground biomass for trees, these data suggest that a more comprehensive allometric growth model may have higher predictive power and wider applicability.     

Resprouting of Quercus suber in NE Spain after fire

Abstract. Many Mediterranean species have evolved strategies that allow them to survive periodic wildfires. Quercus suber trees resprout after fire, some from stem buds and others from basal buds only. In the former case the canopy recovers quickly. In the latter case the stem dies but the tree survives and regrows from basal sprouts. The probability of stem death and the degree of height recovery were studied after a fire in a Q. suber forest in NE Spain using logistic regression analysis. The results suggest that most trees survive after fire; the probability of stem death is negatively related to tree diameter; and recovery is positively related to tree diameter and to bark thickness. Implication for management and conservation of cork-oak forests are discussed.     

A methodology to evaluate disease severity: a case study of chestnut blight in El Bierzo region (northwestern Spain)

Correct knowledge of the incidence and severity of disease is essential for implementation of timely and effective management control strategies. In this article, multiple correspondence analysis (MCA) is applied to evaluate the severity of chestnut blight incited by the ascomyceteous fungus Cryphonectria parasitica. This economically important bark disease leads to the loss of an important part of the chestnut production and the progressive death of the tree. A total of 7240 living European chestnut (Castanea sativa) trees across 452 plots were surveyed in El Bierzo, NW Spain. For each tree, the main stem and canopy were visually assessed for signs of the pathogen and/or symptoms of the disease and the extent of the disease was classified on a qualitative ordinal scale consisting of six levels. The statistical procedure is useful because it quickly analyses measurable, discrete observations from assessed individuals to provide a disease severity measure related to tree features and disease extension inside the tree. The results indicated that the penetration of the pathogen is located in the lower part of the crown and spreads to the tips of the branches in the upper part of the crown. Thus, our results suggest that man‐made wounds, when the tree was grafted or pruned, are the main channel of pathogen penetration in El Bierzo region. Disease severity estimates and incidence data for C. parasitica across the region were compared. From the perspective of the management and control of the disease, a disease severity value provides a more accurate indication of the scenario of the disease in a region than presence or absence data alone.     

Responses of root‐crown bearing shrubs to differences in fire regimes in Pinus palustris (longleaf pine) savannas: Exploring old‐growth questions in second‐growth systems

Question: What are the effects of fire season and intensity on resprouting of different root‐crown bearing shrub species in second‐growth Pinus palustris (longleaf pine) savannas? Location: northern Florida and eastern Louisiana, USA. Methods: In Florida, quadrats were burned biennially either during the dormant season or the growing season. In Louisiana, we applied intensity treatments to quadrats by manipulating ground‐cover fuels, just prior to biennial growing season fires. Maximum fire temperatures were measured, and stem densities were censused before and after fires in both regions. Results: After dormant season fires in Florida, stem densities were seven times greater than initial levels for Hypericum spp. In contrast, growing season fires reduced densities of H. brachyphyllum by 65%, but did not change densities of H. microsepalum. Only resprouting of H. microsepalum decreased with increased fire intensity. In Louisiana, fire intensity influenced Ilex vomitoria, but not Quercus spp. Following fires, stem densities oil. vomitoria were five times greater in fuel removal than fuel addition areas. Conclusions: Past use of dormant season fires likely contributed to increased abundances of some species of root‐crown bearing shrubs observed today in old‐growth savannas. Reintroduction of growing season fires will be effective in maintaining or decreasing stem densities, depending on species and fuel type. Genet mortality and stem density reductions appear most likely in areas at localized scales where tree falls and needle coverage create hotspots in Pinus palustris savannas.     

Modeling above‐ground litterfall in eastern Mediterranean conifer forests using fractional tree cover,and remotely sensed and ground data

Question: How can we model above‐ground litterfall in Mediterranean conifer forests using remotely sensed and ground data, and geographic information systems (GIS)? Location: Eastern Mediterranean conifer forest of Turkey. Methods: Above‐ground litterfall from Mediterranean forest stands of Pinus nigra, Cedrus libani, Pinus brutia and Juniperus excelsa and mixed Abies cilicica, C. libani and P. nigra was modeled as a function of fractional tree cover using a regression tree algorithm, based on IKONOS and Landsat TM/ETM+data. Landsat TM/ETM+images for the study area were used to map actual stand patterns, based on a land‐cover map of species stands using a supervised classification. Results: Total amount of annual above‐ground litterfall for the entire study area (12 260 km²) was estimated at 417.2 Mg ha^?1 for P. brutia, 291.1 Mg ha^?1 for the mixed stand, 115.5 Mg ha^?1 for P. nigra, 54.6 Mg ha^?1 for J. excelsa and 45.9 Mg ha^?1 for C. libani. The maps generated indicate the distribution of the seasonal amount of total above‐ground litterfall for different species and the distribution of species stands in the study area. There was an increase in the amount of above‐ground litterfall for P. brutia stand in summer, for J. excelsa in autumn and for C. libani, P. nigra and the mixed stand of A. cilicica, P. nigra and C. libani in winter. Conclusion: Application of this model helps to improve the accuracy of estimated litterfall input to soil organic carbon pools in the Mediterranean conifer forests.