Canopy Thinning Research Articles

Seasonal controls on patterns of soil respiration and temperature sensitivity in a northern mixed deciduous forest following partial-harvesting

Disturbances can alter CO2 efflux from soils (FCO2) by altering the microclimate, structure, and biogeochemical properties of forest ecosystems. Results of prior studies are unclear if and how partial harvesting of northern deciduous forests affects FCO2. These mixed responses may be due to differences in harvesting levels, time since harvest, and the spatial and seasonal heterogeneity of treatment effects and soil properties. To account for this spatio-temporal dependence, we produced subject-level regression models from regular measurements of FCO2 and soil temperatures during the 2010–2012 growing seasons following tree-length (TL) and more intensive biomass (BIO) harvests. In this paper, we compare seasonal and inter-annual post-harvest recovery trends for measured and temperature-corrected soil respiration rates and the sensitivity of soil respiration to temperature (as Q10).FCO2 values from TL/BIO treatments exceeded unharvested controls, recurrently peaking in the autumn (average for TL/BIO: 28%/17%, p⩽0.05) and waning in the summer (14%/10%, not significant). A comparison of measured FCO2 vs. modelled respiration values corrected for temperature differences indicated that higher soil temperatures following canopy thinning accounted for 34–41% of these differences in 2010 but <15% by 2012. Initially lower in 2010, Q10 and summer respiration values for harvested treatments exceeded those of controls by 2012, and despite waning temperature differences, average annual effect sizes corrected for temperature differences did not decline. Autumn and basal respiration rates were correlated with post-harvest fine woody debris volumes in 2010 (r2=0.58/0.57, p=0.01), summer rates in all years decreased with harvested tree basal area (r2=0.43–0.58, p⩽0.05), and the post-harvest basal area of understorey vegetation predicted increasing Q10 effect sizes from 2010 to 2012 (r2=0.81, p⩽0.01). With consideration to studies demonstrating that the contribution of root respiration (RR) to FCO2 is highest in summer, we propose that partial harvesting initially restricts RR and peak summer respiration rates, but compensates for this decline by increasing basal respiration rates and FCO2 through elevated soil temperatures and decomposition rates from canopy thinning and harvest residue substrate inputs (i.e., woody debris and root necromass). During post-harvest recovery, forest understorey regrowth reduces soil temperatures but influences patterns of FCO2 by increasing summer respiration and Q10 values in harvested treatments, likely by increasing RR.

Microdochium paspali, a new species causing seashore paspalum disease in southern China

A new species of Microdochium was identified as the causal agent of leaf blight of seashore paspalum (Paspalum vaginatum), a turf grass widely used in tropical and subtropical golf courses. In 2010 foliar necrosis and canopy thinning were observed on 11 surveyed golf courses in Hainan province, China, especially on fairways and putting greens. The infected leaves initially appeared water-soaked and dark green, rapidly faded to yellow or became chlorotic and quickly died, resulting in a sparse appearance in infected areas, leading to the disease name “sparse leaf patch.” Isolates with rich and light pink to yellow mycelia and salmon-colored pionnotes were cultured from diseased turf foliage. Pathogenicity was demonstrated by inoculating these isolates onto “seaspray” seashore paspalum. Phylogenetic analysis based on the nuc rDNA internal transcribed spacer 1–5.8S–internal transcribed spacer 2 region (ITS), translation elongation factor 1-α (TEF1-α) and β-tubulin (BenA) indicated these isolates formed as a distinct clade within Microdochium (Xylariales). Further microscopic examination demonstrated that the species was morphologically distinct from three similar species of Microdochium. The name Microdochium paspali sp. nov. is proposed for this novel fungal pathogen.

Stand management to reduce fire risk promotes understorey plant diversity and biomass in a semi‐aridPinus halepensisplantation

AbstractQuestionsHow do thinning and understorey management practices (ploughing, clearing) to reduce fire risk affect plant species composition, diversity and biomass within pine plantations on previous croplands? Do managed pine plantations promote changes in plant succession compared to unplanted areas (old fields) towards restoration goals including holm oak forest or other alternative land‐use types?LocationAltiplano del Conejo, Guadix‐Baza Basin,SEIberian Peninsula, Spain.MethodsWe evaluated plant species composition, diversity, cover and biomass in the understorey of a semi‐arid 10‐yr‐old afforestation area ofPinus halepensisthrough a manipulative experiment in which four different thinning regimes (T0 treatment: control plots; T100, T75, T60 and T48 treatments: 100%, 75%, 60%, and 48% of mean basal area removed, respectively), and two understorey vegetation treatments (clearing, ploughing) were applied, simulating stand practices to reduce fire risk. Sampling was performed annually for 5 yr (from 2006 to 2010). For comparison, four other land‐use types (rain‐fed cereal crops, old fields, alpha grass steppes and holm oak forests) were sampled to quantify understorey vegetation community composition and diversity.ResultsAfforestation plots were compositionally distinct from each other within 5 yr, mainly as a result of canopy thinning and to a lesser extent, vegetation treatments. Total species richness was highest in the low to medium densities of pines, where richness approached that found in native communities. However, afforestation plots were most similar in diversity, life‐form type and composition to abandoned agricultural fields, and large differences were found between afforestation plots, native forests and alpha grass steppes.ConclusionsThis study demonstrates that plant species composition in the understorey of pine plantations on former cropland can respond rapidly to common management practices intended to reduce fire risk. In particular, tree thinning increases both understorey plant diversity and biomass, but does not lead to recruitment of species that are typical of native forests. Rates of native forest succession appear to be slow in this semi‐arid Mediterranean ecosystem. Current pine plantation management practices, while useful for increasing understorey biomass and plant diversity will need to be coupled with additional restoration techniques (e.g. seeding and transplants) to recover species composition and structure of native forests.

Seagrass canopy photosynthetic response is a function of canopy density and light environment: a model for Amphibolis griffithii.

A three-dimensional computer model of canopies of the seagrass Amphibolis griffithii was used to investigate the consequences of variations in canopy structure and benthic light environment on leaf-level photosynthetic saturation state. The model was constructed using empirical data of plant morphometrics from a previously conducted shading experiment and validated well to in-situ data on light attenuation in canopies of different densities. Using published values of the leaf-level saturating irradiance for photosynthesis, results show that the interaction of canopy density and canopy-scale photosynthetic response is complex and non-linear, due to the combination of self-shading and the non-linearity of photosynthesis versus irradiance (P-I) curves near saturating irradiance. Therefore studies of light limitation in seagrasses should consider variation in canopy structure and density. Based on empirical work, we propose a number of possible measures for canopy scale photosynthetic response that can be plotted to yield isoclines in the space of canopy density and light environment. These plots can be used to interpret the significance of canopy changes induced as a response to decreases in the benthic light environment: in some cases canopy thinning can lead to an equivalent leaf level light environment, in others physiological changes may also be required but these alone may be inadequate for canopy survival. By providing insight to these processes the methods developed here could be a valuable management tool for seagrass conservation during dredging or other coastal developments.

Effects of two contrasting canopy manipulations on growth and water use of London plane (Platanus x acerifolia) trees

Two contrasting canopy manipulations were compared to unpruned controls on London plane trees, to determine the effects on canopy regrowth, soil and leaf water relations. ‘Canopy reduction’, was achieved by removing the outer 30 % length of all major branches and ‘canopy thinning’, by removing 30 % of lateral branches arising from major branches. Total canopy leaf areas recovered within two and three years of pruning for the canopy-thinned and reduced trees respectively. Canopy reduction increased mean leaf size, nitrogen concentration, canopy leaf area density and conserved soil moisture for up to 3 years, whereas canopy thinning had no effects. Another experiment compared more severe canopy reduction to unpruned trees. This produced a similar growth response to the previous experiment, but soil moisture was conserved nearer to the trunk. Analysis of 13C and 18O signals along with leaf water relations and soil moisture data suggested that lower boundary layer conductance within the canopy-reduced trees restricted tree water use, whereas for the canopy-thinned trees the opposite occurred. Only canopy reduction conserved soil moisture and this was due to a combination of reduced total canopy leaf area and structural changes in canopy architecture.

Small mammals exhibit limited spatiotemporal structure in Sierra Nevada forests

Forests in the Sierra Nevada, similar to those across the continent, have been substantially altered by logging, fire exclusion, and other human activities. Current forest management emphasizes maintenance or restoration of resiliency in the face of contemporary disturbance factors that include wildfire, climate change, continued urbanization, and invasive species. We evaluated responses of small mammals to forest management by monitoring a series of 12 replicate trapping grids in compositionally homogeneous forest over 8 years, and implemented 2 levels of canopy thinning. Livetrapping efforts (119,712 trap-nights) yielded 15,613 captures of 2,305 individuals of 13 species, and although forest structure was significantly influenced by canopy treatments, small mammal numbers and assemblage composition were not. To better understand this we assessed habitat associations of small mammals at 599 census points on 75 transects established in a stratified random manner throughout Plumas National Forest. We analyzed these data with 2 complementary forms of constrained ordination (canonical correspondence and canonical correlation) that extract major gradients in 1 data set (e.g., distribution of small mammal captures) and explain these in terms of measured variables from a 2nd data set (e.g., habitat and environmental measurements). Over 3 years and 57,504 trap-nights of effort we captured 1,367 individuals of 11 species. Both forms of ordination exposed significant associations between small mammals and underlying habitat metrics, but they explained remarkably little variation in these data, suggesting that small mammals are responding only modestly to habitat variation as expressed by the available environmental variables measured at each plot. We followed this with stepwise multiple Poisson regression to build models of habitat associations of these species. We applied model-averaging and employed Akaike's information criterion corrected for small sample size (AICC) to evaluate candidate models. Reflecting ordination results, competitive models (e.g., those with Akaike differences [ΔAICC] < 2.0) cumulatively explained little variation (12–36%) and regression coefficients were very low. Hence, both ordination and Poisson multiple regression suggest that the limited response by small mammals to canopy thinning primarily reflects the generalist habits of the common species in this forest. We propose that anthropogenic influences have led to structural homogenization of these forests, even across > 800 m of elevation, such that habitat specialists (e.g., old-forest-dependent species such as Myodes [Clethrionomys] californicus and Glaucomys sabrinus) have become less common due to the lack of suitable habitat. Further efforts should target nonforested habitats (meadows and riparian corridors), but results presented here suggest that managers should strive to increase heterogeneity at large spatial scales and especially to promote the development of mature forest structure.

The impact of mast years on seedling recruitment following canopy thinning and deer fencing in contrasting northeastern U.S. coastal forests1

This five-year study (2007–2011) investigated the impacts of canopy thinning, deer fencing, acorn production, and deer density on tree seedling recruitment in contrasting Quercus-Carya forests to explore the fate of mast and non-mast seedlings in different understory environments. It was conducted at the Mashomack Preserve on Shelter Island near the eastern end of Long Island, NY where tree regeneration in mature forests is very sparse due to extremely high deer (Odocoilus virginianus) populations. Forest thinning increased seedling density (mainly Q. alba L., C. glabra (Mill.) Sweet, Acer rubrum L. and Ostrya virginiana (Mill.) K. Koch) in both fenced and unfenced plots for the duration of the study. Fenced plots had higher total seedling density and taller white Q. alba seedlings than the unfenced plots. Four Quercus plus one Carya species had at least one mast year between 2007 and 2010 and generally during different years with variable impacts on seedling establishment. Acorn/nut production for all species was lowest in the fall of 2011 following nearly two years of drought. Quercus alba seedling density increased dramatically following a 2007 mast year, but had no further increase after a 2010 mast year. Deer density estimates ranged from 82–129 per km2 in 2007 to 2010, but dropped to 29 per km2 in 2011 associated with very low mast production. There was 100% removal of 260 exposed Q. velutina Lam acorns placed in both deer fenced and unfenced areas throughout the preserve, suggesting an important role of small mammals or birds. The results of this study suggest that mast year, canopy thinning and deer fencing, either individually or in concert, played a positive but variable role by increasing Quercus and Carya seedling establishment and sustainability.

Response of Federally ThreatenedScutellaria montana(Large-Flowered Skullcap) to Pre-Transplantation Burning and Canopy Thinning

Abstract Federally threatened Scutellaria montana (Large-flowered Skullcap) is a perennial herbaceous species endemic to southeastern Tennessee and northwestern Georgia. A large population of S. montana is located at the 648-ha Tennessee Army National Guard Volunteer Training Site (VTS) in Catoosa County, GA. Due to necessary operational activities that include vegetation clearing along site boundaries to maintain security and prescribed burning and overstory clearing to reduce fuel loads as a wildfire-prevention measure, S. montana individuals and groups at the VTS may be disturbed unavoidably at times. Our objectives were to provide recommendations for land managers at the VTS and elsewhere regarding the response of S. montana to transplantation when plant rescue is necessary and to guide site selection for transplantation by elucidating the effects of pre-transplantation burning and canopy thinning on transplant survival and subsequent success. We relocated 100 S. montana individuals in spring 2010 fro...

Effects of experimental forest management on a terrestrial, woodland salamander in Missouri

Successful multi-use planning for forested landscapes requires an understanding of timber management effects on wildlife species. Lungless, woodland salamanders depend on forested habitats and are sensitive to changes in temperature and moisture associated with many forestry practices. Additionally, woodland salamanders are territorial and have relatively low vagility, making it unlikely that they can successfully migrate to more favorable habitat when the surrounding forest is harvested. Therefore, we examined the abundance of the Western Slimy Salamander, Plethodon albagula, in an experimentally manipulated forest in central Missouri. We used artificial cover object searches to compare salamander abundance in three replicate treatments that were clear-cut then burned to reduce maple regeneration, clear-cut and not burned, partially harvested, and un-manipulated control forest. We captured a total of 300 Western Slimy Salamanders between April 2007 and September 2011. We found significantly fewer salamanders in the burn and clear-cut treatments compared with the partial and control treatments. We also found a lower proportion of juveniles and had fewer recaptures in the burn and clear-cut than in the partial and control treatments. Consistent with other studies of woodland salamanders, our results suggest that for at least the first 7years post-harvest, clear-cutting is detrimental to woodland salamander populations. This initial reduction in abundance combined with the further reduced proportion of juveniles may have longer lasting effects even as the forest regenerates. Finally, it appears that timber harvest resulting in limited canopy thinning may be compatible with maintaining populations of Western Slimy Salamanders in Missouri.

Silvicultural treatments for converting loblolly pine to longleaf pine dominance: Effects on resource availability and their relationships with planted longleaf pine seedlings

Throughout the southeastern United States, land managers are currently interested in converting loblolly pine (Pinus taeda L.) plantations to species rich longleaf pine (Pinus palustris Mill.) ecosystems. In a 3-year study on moderately well- to well-drained soils of the Lower Coastal Plain in North Carolina, we examined the effects of four canopy and three cultural treatments on plant resources and quantified relationships between plant resources and longleaf pine seedling survival and growth. Canopy treatments consisted of four levels of timber harvest applied to loblolly pine stands: Control (uncut, mean basal area of 16.2m2/ha), MedBA (single-tree selection to a mean residual basal area of 9.0m2/ha), LowBA (single-tree selection to a mean residual basal area of 6.4m2/ha), and Clearcut (complete canopy removal). Within each canopy treatment, we applied three cultural treatments designed to benefit the early growth of planted seedlings: no treatment (NT), herbicide (H), and herbicide plus fertilization (H+F). Gap light index (GLI) significantly differed among canopy treatments and nonlinearly increased with decreasing basal area. The H treatment resulted in higher temperatures at 10cm in the soil. Canopy thinning increased foliar calcium (Ca) concentration. The annual root collar diameter (RCD) increment of planted longleaf pine seedlings was positively correlated with GLI, and foliar phosphorus (P) and Ca concentrations but was negatively correlated with soil moisture. Our results confirm that light is an important factor controlling the growth of longleaf pine seedlings.

Effects of the ecological restoration practices of prescribed burning and mechanical thinning on soil microbial enzyme activities and leaf litter decomposition

The effects of ecological restoration on belowground processes such as decomposition are generally unknown. To assess the immediate effects of prescribed fire and mechanical thinning on belowground processes, we measured the activities of five extracellular enzymes (phosphatase, β-glucosidase, β-N-acetylglucosaminidase, phenol oxidase, and lignin-peroxidase) in soils and on decomposing Quercus falcata leaf litter in unburned, burned, and burned and thinned plots in a mesic forest in northern Mississippi. Decomposition rates of Q. falcata leaf litter were also assessed at each plot. Soil phosphatase activity decreased after a prescribed burn and was related to an increase in soil organic matter in plots that had been burned. Soil β-N-acetylglucosaminidase activity increased after a burn, and was related to a decrease in leaf litter. Leaf litter enzyme activity showed no consistent patterns amongst treatments, or between individual enzymes, while decomposition rates of leaf litter were slightly accelerated in the treatment plots, but not significantly so. Decomposition rates were related to cumulative enzyme activity, with phenol oxidase and lignin-peroxidase having the highest apparent efficiencies in degrading the leaf material. Overall, the microbial degradation of Q. falcata leaf litter was more efficient in plots that were burned and thinned than in the other plots. Increases in the efficiency of litter decomposition coupled with reductions in litter inputs due to canopy thinning likely allows for increased solar penetration to the soil, and could promote the restoration of the shade-intolerant species that once dominated the understory. Post-burn increases in β-N-acetylglucosaminidase activity and decreases in phosphatase activity also suggest a potential shift in the soil community from phosphorus limitation to nitrogen limitation following a fire.

CO2 dilution in the lower atmosphere from temperature and wind speed profiles

Temperature and wind speed profiles obtained from 3 years of radio acoustic sounding system sodar measurements at a rural site in the northern Spanish plateau were fitted to polynomial functions. Depending on the extrema of these fits, several groups of profiles were considered. Daily evolution of temperature profiles corresponded to the lower boundary layer evolution. However, wind speed profiles revealed a frequent low-level jet during the whole day. CO2 surface concentrations were analysed, and surface CO2 dilution was also considered by selection of thin canopies with variable depth, resulting in dilution rates of 7 and 18 ppm when the layer increased 100 m for the 95th percentile and temperature and wind speed profiles, respectively.

Response of anIsotria medeoloidesPopulation to Canopy Thinning

Isotria medeoloides (Small Whorled Pogonia) is a globally rare woodland orchid. Observed population declines in this species may be related to decreased light availability resulting from forest maturation. In East Alton, NH, a population of Small Whorled Pogonia was partitioned into two groups, with one left as a control and the other subjected to canopy-reduction management. The removal of all shrubs and 25% of the tree basal area approximately doubled light transmission to the managed group. The number of stems and seed capsules significantly increased in this group relative to the control group. While this was not a replicated experiment, our observations suggest that canopy thinning may help promote the long-term conservation of this federally threatened species.

Identification of a New Waitea circinata Variety Causing Basal Leaf Blight of Seashore Paspalum.

Seashore paspalum (Paspalum vaginatum) is a saline-tolerant, warm-season turfgrass species popular for golf course use in tropical and subtropical climates. A new variety of Waitea circinata (proposed as W. circinata var. prodigus) is described as the causal agent of basal leaf blight, a novel disease of seashore paspalum. Foliar necrosis and canopy thinning of seashore paspalum were observed on three different golf course fairways in Florida over an 18-month period. Five isolates with profuse, pink to yellow mycelia and small, salmon-colored or yellow to light-brown sclerotia were cultured from diseased turf foliage. Isolates grew rapidly over a temperature range of 25 to 35°C and were initially identified as an uncharacterized variety of W. circinata. Internal transcribed spacer sequences of rDNA from the isolates were compared with sequences from previously described W. circinata varieties. The paspalum isolates formed a phylogenetic clade that was distinct from the other W. circinata varieties. Pathogenicity was confirmed on 'SeaDwarf' and 'SeaIsle Supreme' seashore paspalum, 'Penncross' creeping bentgrass (Agrostis stolonifera), 'Senesta' bermudagrass (Cynodon dactylon), and 'Dark Horse' roughstalk bluegrass (Poa trivialis). The geographical distribution and potential impact of basal leaf blight is unknown. However, the range of potential turfgrass hosts and environmental conditions conducive for disease development suggest that the pathogen may infect other species in addition to seashore paspalum.

Monitoring of tube‐nesting bees and wasps with bamboo tube nest traps of different types in two types of forests in temperate Japan

AbstractTube‐nesting bees and wasps were collected with bamboo tube nest traps in a cherry blossom forest and an old secondary forest in Tama Forest Science Garden in the western suburbs of Tokyo. Curtain type traps, in which bamboo tubes were vertically arranged, attracted more bees and wasps to nests than bundle type traps, in which bamboo tubes were bundled haphazardly. The attractiveness of small tubes was similar between small tube traps, which were only composed of small tubes (about 4 mm in diameter), and size mixture traps, which set small tubes together with larger tubes, indicating that the presence of the larger species did not affect the nesting of small species. In the cherry forest, which was characterized by the sparse distribution of deciduous cherry trees with a thin canopy layer and rich growth of weeds, Megachilidae, Colletidae, Sphecidae and Eumenidae were common. In the shady secondary forest, where evergreen trees (Abies firma Sieb. et Zucc., Quercus glauca Thunb.) and shrubs (Aucuba japonica Thunb., Eurya japonica Thunb., Camellia japonica L.) were prevalent, Pompilidae was abundant. Among five species of Crabronidae recorded in this study, four were collected mostly in the cherry forest, whereas the most abundant, Trypoxylon malaisei Gussakovskij, was also common in the secondary forest. Likewise, Auplopus carbonarius (Scopoli) (Pompilidae) was common in the secondary forest and not rare in the cherry forest. These results suggest that the tube‐nesting bees and wasps can be a good bioindicator for monitoring environment.

Ecological Research and the Management of Young Successional Forests: A Case Study on the Reintroduction of Native Tree Species on a Terra Firme Site in Northeastern Peru

Despite the increased expansion into areas away from floodplains and the resulting increase in experimental timber tree management by small landholders, basic ecological knowledge about managing native tree species in secondary forests on terra firme sites in the Amazon basin is sparse. I examine the use of stand thinning as a technique for aiding the active reintroduction of a diverse assemblage of native tree species in a young successional forest on a terra firme plateau in northeastern Peru. I monitored the growth and survivorship of 17 native tree species across an experimental canopy gradient that I created by implementing seven 144 m2 replicates of each of four levels of stand thinning treatments (no trees removed, 60% of the stand basal area removed, 80% of the stand basal area removed, and 100% of the stand basal area removed). Seedlings were established from seeds in four seedling beds within each treatment replicate. The plants were monitered monthly for 13 months and then at 6 and 10 years following establishment. Results suggest that the potential for tree management is substantial. By 10 years of age, individuals of 11 of the study species had grown to at least a 15-m height. Stand thinning was critical for 14 of the 17 species, indicating that management strategies that do not include canopy thinning will likely fail. The optimal levels of canopy openness varied among species, however, which suggests that the implementation of stand thinning in ways that create spatially heterogeneous forest canopy structure is needed to promote the reintroduction and management of diverse assemblages of tree species. Complex ecosystem management schemes developed by professional researchers rarely succeed in Amazonia. Instead of promoting an explicit model of forest management, therefore, small landholders in the study area have been encouraged to understand the value of stand thinning simply by observing the results of this study. I have observed that they have subsequently combined this information with their general knowledge of tree management (e.g., species selection, collection of germ plasm, seedling propagation, herbivore removal, etc.), and appear to be developing effective strategies for managing native timber species on terra firme sites. If indeed successful, they may soon realize the ecological and socioeconomic benefits that the management of native timber species can potentially provide. Further studies on cost and benefit of nutrient input and herbivory control, as well as applicability in other forest types, are needed to increase the likelihood that the results of this study will be widely adapted.

Multiple-year Protection of Ash Trees from Emerald Ash Borer with a Single Trunk Injection of Emamectin Benzoate, and Single-year Protection with an Imidacloprid Basal Drench

Green ash (Fraxinus pennsylvanica Marsh.) street trees ranging in size from 25 to 45 cm dbh were trunk injected with emamectin benzoate at rates of 0.10–0.60 g ai/2.54 cm dbh at three Michigan, U.S., locations in 2005 or 2006. Tree health was monitored by annual canopy thinning and dieback ratings for up to four years after a single treatment. Branch samples were collected in the autumn and the bark removed to count emerald ash borer larvae for most treatments over the same period of time. A single trunk injection treatment of emamectin benzoate at the 0.1, 0.2, or 0.4 g ai rate gave 100% control of emerald ash borer larvae in 98 of 99 treated trees for 2–3 years. Canopy ratings for treated trees remained similar for 2–4 years following trunk injection, while &gt;50% of the control trees died during the same period of time. Ash trees that received a combination of an imidacloprid trunk injection and an imidacloprid basal drench or an annual imidacloprid basal drench had similar canopy ratings, but more larvae were found in branches from trees receiving the annual basal drench.

Survival, growth and reproduction by big-leaf mahogany (Swietenia macrophylla) in open clearing vs. forested conditions in Brazil

Big-leaf mahogany (Swietenia macrophylla) trees are often retained in agricultural fields and pastures for seed and timber production after selective logging and forest clearing in the Brazilian Amazon. At a forest management site in southeast Para, we censused trees growing scattered across a large open clearing after forest removal and in heavily disturbed forest after selective logging and canopy thinning for survival, stem diameter growth, fruit production, and date of dry season flowering initiation annually during 1997–2003. Trees in the open clearing died at faster rates, grew more slowly, produced fewer fruit, and initiated flowering earlier, on average, than trees in logged and thinned forest during this period. The principal cause of mortality and stem damage in both environments was dry season groundfires. Mahogany trees in logged and thinned forest at the study site grew faster than mahogany trees at a selectively logged but otherwise undisturbed closed-canopy forest site in this region during the same period. This was likely due to vine elimination by groundfires, increased crown exposure after canopy thinning, and soil nutrient inputs due to groundfires. Without effective regulation and control of anthropogenic fires, attempts to manage remnant mahogany trees for future timber yields or to restore commercially viable populations in this region may prove futile.

Protection of Individual Ash Trees From Emerald Ash Borer (Coleoptera: Buprestidae) With Basal Soil Applications of Imidacloprid

We conducted field trials at five different locations over a period of 6 yr to investigate the efficacy of imidacloprid applied each spring as a basal soil drench for protection against emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). Canopy thinning and emerald ash borer larval density were used to evaluate efficacy for 3-4 yr at each location while treatments continued. Test sites included small urban trees (5-15 cm diameter at breast height [dbh]), medium to large (15-65 cm dbh) trees at golf courses, and medium to large street trees. Annual basal drenches with imidacloprid gave complete protection of small ash trees for three years. At three sites where the size of trees ranged from 23 to 37 cm dbh, we successfully protected all ash trees beginning the test with <60% canopy thinning. Regression analysis of data from two sites reveals that tree size explains 46% of the variation in efficacy of imidacloprid drenches. The smallest trees (<30 cm dbh) remained in excellent condition for 3 yr, whereas most of the largest trees (>38 cm dbh) declined to a weakened state and undesirable appearance. The five-fold increase in trunk and branch surface area of ash trees as the tree dbh doubles may account for reduced efficacy on larger trees, and suggests a need to increase treatment rates for larger trees.

Growth and mortality patterns in a thinning canopy of post-hurricane regenerating rain forest in eastern Nicaragua (1990-2005)

One of the strongest hypothesis about the maintenance of tree species diversity in tropical areas is disturbance. In order to assess this, the effect of intensive natural disturbances on forest growth and mortality in a thinning canopy was studied after the landfall of hurricane Joan in 1988. We evaluated the growth and mortality rates of the 26 most common tree species of that forest in eastern Nicaragua. Permanent plots were established at two study sites within the damaged area. Growth and mortality rates of all individual trees > or = 3.18cm diameter at breast height were assessed annually from 1990 to 2005. During this period the forest underwent two phases: the building phase (marked by increased number of individuals of tree species present after the hurricane) and the canopy thinning phase (marked by increased competition and mortality). Our results from the thinning phase show that tree survival was independent of species identity and was positively related to the increase in growth rates. The analysis of mortality presented here aims to test the null hypothesis that individual trees die independently of their species identity. These findings were influenced by the mortality observed during the late thinning phase (2003-2005) and provide evidence in favor of a non-niche hypothesis at the thinning phase of forest regeneration.