Girdled Trees Research Articles

Effects of girdling on fruit abscission, yield and shoot growth in macadamia

In Australian macadamia (Macadamia integrifolia Maiden and Betche, M. tetraphylla Johnson and hybrids) orchards, trees are generally side-hedged in early spring to maintain the inter-row for efficient orchard management. Hedging at this time increases fruit abscission and decreases yield due to competition for carbohydrates between fruit and post-pruning shoot growth, and to the loss of photosynthetic area. Girdling increases fruit set in many crops and the possibility that girdling might mitigate the effect of pruning on fruit abscission and yield was investigated in this study. Girdling was also investigated for its potential to control shoot growth and tree size. In the first experiment, in early spring around anthesis, trees were pruned (P), pruned and girdled (PG), or were left as unpruned and ungirdled control trees. Fruit per raceme over time, percent of racemes with fruit at 20 weeks post anthesis, fruit number per tree, nut weight, yield, and the shoot length and number of the post-pruning flush were measured. In a second experiment, trees were pruned (P) or pruned and girdled (PG) in autumn, and the shoot length and number of the post-pruning flush were measured. In a third experiment, trees were girdled at anthesis in 3 years over a 4-year period and shoot growth, tree height, yield, fruit number and nut weight were compared with ungirdled control trees. Girdling mitigated the effect of pruning on fruit abscission and yield but the mitigation was slight with PG trees producing 28% less yield than unpruned control trees. Girdling reduced shoot length and number but more so on unpruned branches (26% and 28%, respectively) than on pruned branches (10% and 14%, respectively). The tree height increment in girdled trees was around half that of ungirdled trees. In the 4-year study, girdling increased yield by around 10% in two out of four seasons, and decreased it in one season. Cumulative yields were similar for girdled and ungirdled trees. This study has shown that girdling was not useful in mitigating the effect of pruning on yield. However girdling was effective in controlling shoot growth and tree size, with no reduction in cumulative yield, and may be useful as a tree size control strategy. Further monitoring of long-term effects of repeat girdling is required to confirm this.

Soil-atmosphere fluxes of the greenhouse gases CO2, CH4 and N2O in a mountain spruce forest subjected to long-term N addition and to tree girdling

At Alptal, Switzerland, nitrogen (N) has been applied as NH4NO3 since 1995 in low doses during rain events to realistically mimic increased N deposition to a mature mountain spruce stand. Five years of measurements in a replicated plot design showed that N2O and CH4 emissions from the soil to the atmosphere increased due to the N addition. For CH4, this involved a shift from a net sink to a net source. CO2 emissions did not change significantly, although they averaged lower rates under simulated N deposition. The girdling of 40% of tree basal area, followed by subsequent felling of the girdled trees, increased emissions of N2O but reduced net emissions of CH4 from soils. CO2 and N2O emissions depended on soil temperature and water table depth. Soil temperature did not affect CH4 fluxes, whereas net CH4 production was higher when the water table was closer to the soil surface. Our data highlights the need that future investigations should focus more on the allocation of assimilates to tree roots in order to better quantify the ecosystem's C balance.

Late Mesolithic and early Neolithic forest disturbance: a high resolution palaeoecological test of human impact hypotheses

The transition in north-west Europe from the hunter–gatherer societies of the Late Mesolithic to the pioneer farming societies of the early Neolithic is not well understood, either culturally or palaeoecologically. In Britain the final transition was rapid but it is unclear whether novel Neolithic attributes were introduced by immigrants who supplanted the native hunter–gatherers, or whether the latest Mesolithic foragers gradually adopted elements of the Neolithic economic package. In this study, relatively coarse- (10 mm interval) and fine-resolution (2 mm), multi-proxy palaeoecological data including pollen, charcoal and NPPs including fungi, have been used to investigate two phases of vegetation disturbance of (a) distinctly Late Mesolithic and (b) early Neolithic age, at an upland site in northern England in a region with both a Neolithic and a Late Mesolithic archaeological presence. We identify and define the palaeoecological characteristics of these two disturbance phases, about a millennium apart, in order to investigate whether differing land-use techniques can be identified and categorised as of either foraging or early farming cultures. The Late Mesolithic phase is defined by the repetitive application of fire to the woodland to encourage a mosaic of productive vegetation regeneration patches, consistent with the promotion of Corylus and to aid hunting. In this phase, weed species including Plantago lanceolata, Rumex and Chenopodiaceae are frequent, taxa which are normally associated with the first farmers. The early Neolithic phase, including an Ulmus decline, has characteristics consistent with ‘forest farming’, possibly mainly for domestic livestock, with an inferred succession of tree girdling, fire-prepared cultivation, and coppice-woodland management. Such fine-resolution, potentially diagnostic land-use signatures may in future be used to recognise the cultural complexion of otherwise enigmatic woodland disturbance phases during the centuries of the Mesolithic–Neolithic transition.

Delimitation and management of emerald ash borer (Coleoptera: Buprestidae): case study at an outlier infestation in southwestern New York State, United States of America

AbstractWe present a case study in which we developed an adaptive delimitation technique and implemented and evaluated management of emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), in the first infestation discovered in New York State, United States of America. Delimitation was accomplished using 106 girdled “sentinel” trees and management included girdling 18 clusters of trees as population “sinks” to attract EAB and concentrate larvae for removal. Weekly monitoring of traps hung in sentinel trees facilitated early detection of EAB on 12 trees and allowed deployment of additional sentinels and sinks. Sentinel trees were felled and debarked; 12 were positive for EAB larvae and the spatial extent of infestation estimated at ∼48 km2. Sinks nearest the infestation core had the highest numbers of larvae. Larval densities were significantly greater in girdled trees than in proximate ungirdled trees suggesting removal of girdled trees prior to the following year's emergence would lower local EAB densities. Sinks deployed in response to an EAB on a sentinel tree purple prism trap more than 0.6 km from the centre of the known infestation were negative for EAB indicating these would not be effective for managing an infestation of similar size and in similar habitats. This case study provides valuable information to land managers to facilitate delimitation and management of newly discovered EAB infestations.

Carbohydrate and Nutritional Responses to Stem Girdling and Drought Stress with Respect to Understanding Symptoms of Huanglongbing in Citrus

The most important worldwide problem in citrus production is the bacterial disease Huanglongbing (HLB; citrus greening) caused by a phloem-limited bacterium Candidatus Liberibacter asiaticus. The earliest visible symptoms of HLB on leaves are vein yellowing and an asymmetrical chlorosis referred to as “blotchy mottle,” thought to be the result of starch accumulation. We tested the hypothesis that such visible symptoms are not unique to HLB by stem girdling 2-year-old seedlings of two citrus rootstocks with and without drought stress in the greenhouse. After 31 days, girdling had little effect on shoot growth but girdling increased the relative growth rate of shoots in drought-stressed trees. Starch content in woody roots of non-girdled trees was three to 19 times higher than in girdled trees. In non-girdled trees, drought stress induced some starch accumulation in roots, but there were no effects of drought stress on root starch or sucrose in girdled trees. Girdling induced a 4-fold greater starch content in leaves on well-watered trees but leaf sucrose content was unaffected. Girdling reduced leaf transpiration in well-watered trees but net assimilation of CO2 was unaffected by girdling or leaf starch accumulation. Leaves on girdled trees clearly had visible blotchy mottle symptoms but no symptoms developed on non-girdled trees. The increase in leaf starch, up to 50% dry weight (DW), resulted in an increase in leaf DW per leaf area (LA) and an artificial reduction of many leaf nutrients on a DW basis. Most of these differences disappeared when expressed on a LA basis. Leaf boron (B), however, was inversely related to leaf starch when both were expressed on a LA basis. In the absence of HLB, girdling increased leaf starch, decreased root starch, and duplicated the asymmetric blotchy mottled visual leaf symptoms that have been associated with HLB-infected trees. This supports our contention that such symptoms generally attributed to HLB are not uniquely related to HLB infection, but rather are directly related to starch accumulation and secondarily to nutrient deficiencies in leaves.

Experimental release of a parasitoid, Doryctes yogoi Watanabe (Hymenoptera: Braconidae), onto Semanotus japonicus Lacordaire (Coleoptera: Cerambycidae) inoculated into live Japanese cedar trees (Cryptomeria japonica D.DON)

Release experiments of Doryctes yogoi Watanabe onto Semanotus japonicus Lacordaire larvae inoculated into Japanese cedar, Cryptomeria japonica D. Don, were conducted to clarify the role of the parasitoids in the mortality of S. japonicus and the efficiency of the parasitoid as a natural enemy of the beetle. S. japonicus larvae were inoculated into three types of samples: live trees, girdled trees, and logs, each of which was treated in three ways: D. yogoi was released into the sample, the sample was screened (excluding natural enemies), or the sample was used as a control. In live trees, more than 90% of the larvae were killed by resin flow, and the percentage of parasitism by D. yogoi was less than 6%. In girdled trees, most of the larvae were dead due to the resin in the trees, having survived inoculation as well as in live trees, but many larvae were parasitized by D. yogoi in dead trees like logs. The present study revealed three negative effects of resin flow on parasitism by D. yogoi in the live trees. First, most of the host larvae died before reaching a size suitable for parasitism. Second, parasitoid larvae were caught in the resin with their hosts and died. Third, the host-searching and oviposition of female D. yogoi were obstructed by resin flow on the surface of the trunk. The efficiency of D. yogoi as a natural enemy of S. japonicus is discussed.

Implications of Tanoak Decline in Forests Impacted ByPhytophthora ramorum: Girdling Decreases the Soil Hyphal Abundance of Ectomycorrhizal Fungi Associated WithNotholithocarpus densiflorus

Invasive plant pathogens are often recognized as serious threats to the maintenance of biodiversity affecting both structure and function of ecosystems. Here, we investigate the potential impact of the invasive pathogen Phytophthora ramorum Werres, de Cock & Man in't Veld by using physical girdling of tanoak, Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S. H. Oh (Fagaceae), as a surrogate for the disease and to test for changes on the hyphal abundance of ectomycorrhizal fungi. In this study, the flow of phloem to the roots of girdled trees was severed by cutting two narrow incisions (about 10 cm distant) through the inner bark around the circumference of the stem of each tree (fully-girdled), or by cutting two narrow incisions half of the circumference of the tree (half-girdled), to compare with untreated (non-girdled) trees. The hyphal abundance of two common and ecologically important ectomycorrhizal genera (Cenococcum and Tricholoma) was estimated from the roots and surrounding soil using real-time PCR quantification (TaqMan) assay. A significant decrease in the hyphal abundance from soil was observed in girdled tree plots. In contrast, no similar decrease in the root hyphal abundance was observed. Ectomycorrhizal fungi have a major impact on ecosystem function through their control over decomposition, nutrient acquisition, and mobilization and regulation of succession in plant communities. Given their important function, the decline in EM abundance of tanoak infected by P. ramorum will likely disrupt the function and structure of these forests.

환상박피 처리에 의한 일본잎갈나무의 착과유도 효과와 질소 화합물 함량의 증가

낙엽송(Larix kaempferi) 채종원의 종자생산을 증진하기 위하여 접목 32년생의 채종목에 환상박피 처리를 하였다. 환상박피처리에 의하여 무처리보다 4배에 이르는 착과량 증가 효과가 있어 환상박피 처리의 효과가 뚜렷하게 나타났다. 환상박피 처리에 의한 낙엽송 주간 수피조직내의 대사물질의 변화를 IR-MS, GC-MS 및 HPLC로 분석하여 무처리와 비교한 결과 전질소 함량, sucrose 함량 및 전체 유리 아미노산의 함량이 무처리에 비해 유의적(p<0.05)으로 증가되었다. 또한 유리아미노산의 경우 화아원기가 형성되는 8월의 aspartic acid, glutamic acd, glycine, serine, cysteine, threonine 및 alanine이 환상박피 처리에서 무처리에 비해 유의적으로 높게 함유된 것으로 나타났다. 대사물질과 착과량간에 상관관계를 분석한 결과 착과량과 수피조직내의 전질소 함량(r=0.765, p<0.01)과 전체 유리 아미노산 함량(r=0.802, p<0.01)간에 고도의 정의 상관관계가 있었다. 특히, 화아원기 형성기인 7월 및 8월의 수피조직내의 aspartic acid, glutamic acd, glycine, serine 및 cysteine이 착과량과 정의 상관관계(p<0.05)가 있어, 아미노산의 질소화합물 인자가 낙엽송 화아원기 유도에 직, 간접적으로 관련이 있을 것으로 추정되었다. Japanese larch (Larix leptolepis) has been extensively planted in Korea as a reforestation species but their supply has been a major bottleneck due to sporadic natural seed production. In this study, stem girdling was applied to 32-year-old grafted Japanese larches, resulting in significantly enhanced seed production compared to the controls. Stem girdling induced about 4 times higher cone production than that of controls in the Japanese larch seed orchard. Time-dependent metabolic alterations after girdling were investigated by stable isotope ratio mass spectrometer, HPLC, and GC-MS analysis. In girdled trees, the contents of total nitrogen, sucrose, and total free amino acids were significantly higher than the non-girdled trees at the flowering differentiation season (from July to August). Moreover, the numbers of female strobilus per tree were positively correlated with the contents of both total nitrogen (r=0.765, p<0.01) and total amino acids (r=0.802, p<0.01) in the bark being collected at the flowering differentiation time (August 20). Interestingly, the levels of various individual amino acids at the flowering differentiation times, such as aspartic acid, glutamic acid, glycine, serine, and cysteine, were also significantly correlated (p<0.05) with the numbers of strobilus, suggesting that those amino acids might be involved in the induction of female strobilus formation of Japanese larches.

Seasonal variation in functional properties of microbial communities in beech forest soil

Substrate quality and the availability of nutrients are major factors controlling microbial decomposition processes in soils. Seasonal alteration in resource availability, which is driven by plants via belowground C allocation, nutrient uptake and litter fall, also exerts effects on soil microbial community composition. Here we investigate if seasonal and experimentally induced changes in microbial community composition lead to alterations in functional properties of microbial communities and thus microbial processes. Beech forest soils characterized by three distinct microbial communities (winter and summer community, and summer community from a tree girdling plot, in which belowground carbon allocation was interrupted) were incubated with different 13C-labeled substrates with or without inorganic N supply and analyzed for substrate use and various microbial processes. Our results clearly demonstrate that the three investigated microbial communities differed in their functional response to addition of various substrates. The winter communities revealed a higher capacity for degradation of complex C substrates (cellulose, plant cell walls) than the summer communities, indicated by enhanced cellulase activities and reduced mineralization of soil organic matter. In contrast, utilization of labile C sources (glucose) was lower in winter than in summer, demonstrating that summer and winter community were adapted to the availability of different substrates. The saprotrophic community established in girdled plots exhibited a significantly higher utilization of complex C substrates than the more plant root associated community in control plots if additional nitrogen was provided. In this study we were able to demonstrate experimentally that variation in resource availability as well as seasonality in temperate forest soils cause a seasonal variation in functional properties of soil microorganisms, which is due to shifts in community structure and physiological adaptations of microbial communities to altered resource supply.

Mortality of girdled trees and survival of seedlings in canopy gaps after logging in a terra firme forest in Brazilian Amazon

Post harvest silvicultural practices in managed forests are seldom applied in the Amazon region. To tackle this problem an experiment was established in 700 ha of terra firme dense forest of the Brazilian Amazon aiming to test the main silvicultural treatments applied elsewhere in the tropics in order to select the most promising ones and recommend their application as part of forest management practices in the region. The experimental area is located in the Rio Capim Forest Management Unit, municipality of Paragominas (2o25’-4o09’S, 46o25’-48o54’W), State of Para, Brazil, where some post-harvest silviculture activities are performed such as tree girdling, planting in gaps and assistance of natural regeneration in gaps, which were discussed in the present paper. Large sized trees had higher mortality rates corroborating with some studies carried out in Amazonia and elsewhere. In general survival of planted seedlings was considerable high (over 75%). Prospects of success of this approach as post harvest silviculture are very promising. Survival of seedlings from natural regeneration of commercial species, mainly light-demanding, was high in the gaps created by logging, suggesting that natural regeneration can establish stands of commercial value.

Saproxylic beetles in disturbed boreal forests: Temporal dynamics, habitat associations, and community structure

Early postfire habitats harbour numerous saproxylic species. Some are opportunistic feeders, while others are closely associated with burned forests. This distinction is important for developing sound postfire forest management aimed at conserving biodiversity, as concerns should be mostly directed towards burn-associated saproxylic beetles rather than opportunistic species. Here, we examine species—habitat associations, temporal dynamics, and community structure of saproxylic beetles in black spruce and jack pine stands disturbed by wildfire and by a “non-fire” disturbance generated by girdling trees to mimic the small-scale gap dynamics characterizing old-growth boreal forests in Canada. We used flight-interception traps and reared logs to compare abundance, species richness, and species composition of saproxylic beetles among treatments. We found that over 30% of saproxylic beetles had an affinity with jack pine or black spruce affected by either fire or girdling. Assemblages consistently differed between disturbance types over the 3 y of the study. We found that successional changes in species composition were more pronounced in burned sites than those with the girdling treatment, which indicates that the contribution of fire-generated habitats to regional diversity increases over time. While postfire forests are notable for their early-colonizing saproxylic species, our results show that they can also have substantial value for supporting mid-successional species such as Acmaeops pratensis, which is already on European red lists. This forewarns us about long-term negative consequences that postfire salvage logging could have for certain species.

The relative contributions of seed bank, seed rain, and understory vegetation dynamics to the reorganization of Tsuga canadensis forests after loss due to logging or simulated attack by Adelges tsugae

Profound changes are occurring in forests as native insects, nonnative insects, or pathogens irrupt on foundation tree species; comprehensive models of vegetation responses are needed to predict future forest composition. We experimentally simulated hemlock woolly adelgid ( Adelges tsugae Annand) infestation (by girdling trees) and preemptive logging of eastern hemlock ( Tsuga canadensis (L.) Carrière) and compared vegetation dynamics in replicate 90 m × 90 m treatment plots and intact hemlock stands from 2004 to 2010. Using Chao–Sørensen abundance-based similarity indices, we assessed compositional similarities of trees, shrubs, forbs, and graminoids among the seed bank, seed rain, and standing vegetation over time and among treatments. Post-treatment seed rain, similar among treatments, closely reflected canopy tree composition. Species richness of the seed bank was similar in 2004 and 2010. Standing vegetation in the hemlock controls remained dissimilar from the seed bank, reflecting suppressed germination. Recruits from the seed rain and seed bank dominated standing vegetation in the logged treatment, whereas regeneration of vegetation from the seed bank and seed rain was slowed due to shading by dying hemlocks in the girdled treatment. Our approach uniquely integrates multiple regeneration components through time and provides a method for predicting forest dynamics following loss of foundation tree species.

Snag Benchmarks and Treatment Options for Mixed‐Pine Forest Restoration in Eastern Upper Michigan

AbstractSnags (dead‐standing trees) are biological legacies that remain after disturbances in forests. We enhanced the ecological underpinnings of snag management within the context of mixed‐pine forest restoration in the northern Lake States by quantifying characteristics of live trees and snags within eighty-five 500‐m2 plots at Seney National Wildlife Refuge (NWR) in eastern Upper Michigan. Study plots represented reference conditions (i.e. no past harvesting, relatively unaltered fire regime) and altered (i.e. harvested, altered fire regime) conditions. We also compared three treatments for creating snags from live trees. Snags were found in 87% of the reference plots and 85% of the altered plots. The only snag variables that differed between plot types were mean snag basal area, which was greater in altered plots (Student's t‐test, p = 0.04), and mean percent total basal area of snags (greater in reference plots, p = 0.06). The composition of snags differed only in the 10‐ and 25‐cm diameter classes (Multi‐Response Permutation Procedure, p &lt; 0.10). The percentage of snags that developed into the most advanced decay class (DC) differed among treatments after 4 years (χ2 = 16.49, p &lt; 0.01), with 26% of girdled trees, 3% of prescribed fire trees, and zero topped trees reaching DC5. Logistic regression illustrated that the influence of predictor variables on DC development varied by species and treatment. The findings from this study, past studies, and ongoing projects at Seney NWR are directly applicable to innovative management of snags in mixed‐pine forests.

Recovery of native forest after removal of an invasive tree, Falcataria moluccana, in American Samoa

Invasive species are among the greatest threats to global biodiversity. Unfortunately, meaningful control of invasive species is often difficult. Here, we present results concerning the effects of invasion by a non-native, N2-fixing tree, Falcataria moluccana, on native-dominated forests of American Samoa and the response of invaded forests to its removal. We sampled species richness, seedling and stem densities, biomass, and soil inorganic N status in native-dominated forests, and in forests invaded by F. moluccana where it was subsequently removed. While total biomass of intact native forests and those invaded by F. moluccana did not differ significantly, greater than 60% of the biomass of invaded forest plots was accounted for by F. moluccana, and biomass of native species was significantly greater in intact native forests. Biomass of native Samoan tree species following removal of F. moluccana accumulated rapidly from 128 Mg ha−1 immediately after tree girdling treatment to 185 Mg ha−1 following 8 years of post-removal recovery, at which point biomass of F. moluccana-removal plots did not differ significantly from native-dominated forest plots. Native trees exhibiting early successional traits accounted for a large portion of aboveground biomass in these forests where frequent large-scale disturbance events (i.e., tropical cyclones) are a salient feature. We suspect that this is the single most important reason why F. moluccana removal is a successful management strategy; once F. moluccana is removed, native tree species grow rapidly, exploiting the legacy of increased available soil N and available sunlight. Seedling densities of F. moluccana were high in invaded forest stands but effectively absent following only 3 years of forest recovery; a result likely due to the shade cast by reestablishing native trees. Although F. moluccana is a daunting invasive species, it exhibits characteristics that make it vulnerable to successful control: it is easily killed by girdling or herbicides, and its seeds and seedlings do not tolerate shade. These characteristics, combined with the important capacity for rapid growth exhibited by many of Samoa’s native trees, provide conditions and opportunities for successful, long-term control of F. moluccana across lowland forests of American Samoa. Caution should be exercised, however, in anticipating comparable management success in the control of F. moluccana elsewhere, as post-removal responses of invaded forest communities may differ dramatically from what has been documented in American Samoa.

Tree girdling affects the soil microbial community by modifying resource availability in two subtropical plantations

We used tree girdling and phospholipid fatty acid (PLFA) analysis to evaluate the effect of nutrient availability and rhizodeposition on soil microbial community composition in two plantations (Acacia crassicarpa and Eucalyptus urophylla) in subtropical China. The magnitude of the girdling effect was also evaluated as a function of tree species and time after girdling (2 months vs. 9 months). In both plantations, tree girdling reduced the concentration of fungal PLFAs and increased the concentration of bacterial PLFAs with a consequent decrease in the fungi/bacteria ratio, but did not affect the concentration of total PLFAs. Tree girdling affected the concentration of gram-negative PLFAs and the ratio of gram-positive bacteria to gram-negative bacteria at 9 months but not at 2 months after girdling. The ratio of cy17:0 to 16:1ω7c was increased by girdling of A. crassicarpa, indicating a stressful and nutrient-deficient habitat for soil microorganisms, but was inconsistent for girdling of E. urophylla. In the A. crassicarpa plantation, responses to girdling for most microbial groups were associated with changes in dissolved organic carbon (DOC), dissolved organic nitrogen (DON), the ratio of carbon to nitrogen, and soil pH. In the E. urophylla plantation, responses to girdling were associated with changes in DON, DOC, and NO3−-N. These results confirm that (i) recent photosynthates allocated belowground affect soil C and N availability and therefore greatly affect microbial community composition in subtropical plantations; (ii) the magnitude of the tree girdling effect increases with time after girdling and differs between plant species; and (iii) soil microbial communities are closely linked to vegetation types and plant C allocation.

Tree girdling effect on bacterial substrate utilization pattern depending on stand age and soil microclimate in Eucalyptus plantations

It has been increasingly recognized that soil microorganisms and plants are tightly linked, however, the effects of belowground plant-carbon allocation on soil microbial communities has not been fully understood, particularly in subtropical and tropical forest ecosystems. In the present study, we conducted a tree-girdling experiment to explore the relationships between plant belowground carbon allocation and the functional diversity of soil microbial communities in two subtropical Eucalyptus plantations (2-year-old and 24-year-old). The functional diversity of soil culturable bacterial communities was characterized with community level physiological profile (CLPP) 1 year after tree girdling. We found that carbon substrate utilization patterns of soil culturable bacterial communities were significantly affected by both tree girdling and sampling season; but microbial metabolic activity and functional diversity were only affected by sampling season. Microbial metabolic activity and substrate utilization pattern, as well as soil moisture and temperature, did not show any apparent variations among stand ages. Pearson's correlation analysis indicated that both microbial metabolic activity of all 95 carbon sources (r=0.869; P<0.01) and the specific substrate metabolic activities (amides and amines: r=0.838, P<0.01; polymers: r=0.884, P<0.01; miscellaneous: r=0.895, P<0.01; carboxylic acids: r=0.910, P<0.01; amino acids: r=0.806, P<0.01; carbohydrates: r=0.808, P<0.01) were positively correlated with soil temperature. Metabolic diversity (r=0.806, P<0.01) and metabolic evenness (r=0.819, P<0.01) was positively correlated with soil temperature but metabolic richness (r=−0.517, P<0.05) was negatively correlated with soil moisture. Metabolic evenness was positively correlated with soil temperature (r=0.416, P<0.05). Seasonal changes in soil bacterial community were greater than those induced by girdling and stand age, and were tightly linked to seasonal soil microclimatic differences, such as soil moisture and temperature. The girdling treatment exerted a greater effect on soil bacterial communities during the dry season than in the rainy season. Our study illustrated that the response of bacterial substrate utilization profiles to changes in plant belowground carbon supply is seasonally dependent in subtropical Eucalyptus plantations.

Effects of stem girdling on cone yield and endogenous phytohormones and metabolites in developing long shoots of Douglas-fir (Pseudotsuga menziesii)

Stem-girdling treatments were applied in early spring to stimulate cone formation in two genotypes of interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco). After girdling treatments, male cone yield increased significantly in the next growing season. The increase was 14-fold in genotype 9137. In genotype 9550, more than 8,700 male cones were induced from each tree whereas no male cones were found in controls. Female cone yield was zero in controls and low for girdled trees in both genotypes. Multiple phytohormone-related compounds, including gibberellins (GAs), cytokinins, indole-3-acetic acid (IAA), abscisic acid (ABA) and their selected metabolites, were analyzed in developing long shoots after girdling treatments by high performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC–ESI–MS/MS) in multiple reaction monitoring mode. Concentrations of GA4 were slightly higher at week 2 following girdling treatment, whereas at week 8 lower GA4 concentrations were found in girdled samples. Stem girdling did not affect concentrations of IAA and major cytokinins, such as zeatin riboside and isopentenyl adenosine. Concentrations of ABA differed two-fold between the genotypes. Although girdling treatment did not cause differences in ABA concentrations, it generally resulted in higher concentrations of ABA glucose ester. Concentration increase of 7′-hydroxy ABA by girdling was only found in genotype 9550 at week 8. Girdling caused little change in concentrations of phaseic acid in both genotypes.

The autotrophic contribution to soil respiration in a northern temperate deciduous forest and its response to stand disturbance

The goal of this study was to evaluate the contribution of oak trees (Quercus spp.) and their associated mycorrhizal fungi to total community soil respiration in a deciduous forest (Black Rock Forest) and to explore the partitioning of autotrophic and heterotrophic respiration. Trees on twelve 75 × 75-m plots were girdled according to four treatments: girdling all the oaks on the plot (OG), girdling half of the oak trees on a plot (O50), girdling all non-oaks on a plot (NO), and a control (C). In addition, one circular plot (diameter 50 m) was created where all trees were girdled (ALL). Soil respiration was measured before and after tree girdling. A conservative estimate of the total autotrophic contribution is approximately 50%, as indicated by results on the ALL and OG plots. Rapid declines in carbon dioxide (CO(2)) flux from both the ALL and OG plots, 37 and 33%, respectively, were observed within 2 weeks following the treatment, demonstrating a fast turnover of recently fixed carbon. Responses from the NO and O50 treatments were statistically similar to the control. A non-proportional decline in respiration rates along the gradient of change in live aboveground biomass complicated partitioning of the overall rate of soil respiration and indicates that belowground carbon flux is not linearly related to aboveground disturbance. Our findings suggest that in this system there is a threshold disturbance level between 35 and 74% of live aboveground biomass loss, beyond which belowground dynamics change dramatically.

Forest dynamics following eastern hemlock mortality in the southern Appalachians

Understanding changes in community composition caused by invasive species is critical for predicting effects on ecosystem function, particularly when the invasive threatens a foundation species. Here we focus on dynamics of forest structure, composition and microclimate, and how these interact in southern Appalachian riparian forests following invasion by hemlock woolly adelgid, HWA, Adelges tsugae. We measured and quantified changes in microclimate; canopy mortality; canopy and shrub growth; understory species composition; and the cover and diversity in riparian forests dominated by eastern hemlock Tsuga canadensis over a period of seven years. Treatments manipulated hemlock mortality either through invasion (HWA infested stands) or girdling (GDL) hemlock trees.Mortality was rapid, with 50% hemlock tree mortality occurring after six years of invasion, in contrast to more than 50% mortality in two years following girdling. Although 50% of hemlock trees were still alive five years after infestation, leaf area lost was similar to that of girdled trees. As such, overall responses over time (changes in light transmittance, growth, soil moisture) were identical to girdled stands with 100% mortality. Our results showed different growth responses of the canopy species, shrubs and ground layer, with the latter being substantially influenced by presence of the evergreen shrub, rhododendron Rhododendron maximum. Although ground layer richness in the infested and girdled stands increased by threefold, they did not approach levels recorded in hardwood forests without rhododendron. Increased growth of co‐occurring canopy trees occurred in the first few years following hemlock decline, with similar responses in both treatments. In contrast, growth of rhododendron continued to increase over time. By the end of the study it had a 2.6‐fold higher growth rate than expected, likely taking advantage of increased light available during leaf‐off periods of the deciduous species. Increased growth and dominance of rhododendron may be a major determinant of future responses in southern Appalachian ecosystems; however, our results suggest hemlock will be replaced by a mix of Acer, Betula, Fagus and Quercus canopy genera where establishment is not limited by rhododendron.

Influence of Host Tree Condition on the Performance ofTetropium fuscum(Coleoptera: Cerambycidae)

Tetropium fuscum (F.) attacks weakened Norway spruce, Picea abies (L.) Karst., in its native Europe and may colonize healthy spruce in Nova Scotia, Canada. We used manipulative field experiments to evaluate: 1) the development of T. fuscum on apparently healthy red spruce (Picea rubens Sarg.) in Nova Scotia; 2) the influence of red spruce physiological condition (healthy, girdled or cut) on T. fuscum performance; and 3) the impact of natural enemies and competitors on T. fuscum performance when developing on trees of varying condition. Tetropium fuscum successfully developed on healthy red spruce. Survival was higher on healthy than on girdled or cut trees when larvae were exposed to natural enemies and competitors. The benefits of reduced competition and parasitism on healthy trees appeared to compensate for any reductions in nutritional quality, increase in host resistance, or both. In contrast, when T. fuscum were protected from natural enemies, apparent survival was highest on girdled trees. Tetropium fuscum development took longer on healthy than on cut or girdled trees, and emerged adults were largest on healthy trees. The disparities in adult sizes among the three treatments may mean that healthy trees are more nutritious. Alternatively, the differences may indicate that a greater amount of time was spent feeding in healthy than in girdled or cut trees. Tree condition appears to have a direct impact on the success of T. fuscum, influencing survival, development time, and adult size, and may mediate the impact of natural enemies and competitors, further affecting T. fuscum performance.