Research needs for restoring seasonal tropical forests in Thailand: accelerated natural regeneration

Accelerated natural regeneration (ANR) is a relatively cheap method of reforestation, which encourages natural establishment of indigenous trees and shrubs. It requires a low input of labour, but a high input of ecological information. In this paper, the knowledge required to predict and manipulate the natural regeneration of seasonal tropical forest is reviewed and areas in need of further research are identified. Regeneration will be influenced by five groups of potentially limiting factors; site resources (soil and microclimate); competition with weeds; site disturbance; occurrence of established woody plants or their propagules; seed dispersal by wild animals and birds. This paper considers each of these, their interactions with seasons, and each other. Collation of existing information on these topics, combined with the suggested further research, should facilitate the creation of tools that will enable practitioners to judge the regeneration potential of sites and to select the most appropriate ANR techniques.     

Survival and growth of upland oak and co-occurring competitor seedlings following single and repeated prescribed fires

Studies within and outside the U.S. indicate recurring oak (Quercus spp.) regeneration problems. In deciduous forests of the eastern U.S., a prevailing explanation for this trend is fire suppression leading to high competitor abundance and low understory light. In response, prescribed fire is increasingly used as a management tool to remedy these conditions and encourage future oak establishment and growth. Within eastern Kentucky, we implemented single and repeated (3×) prescribed fires over a 6-yr period (2002–2007). Pre- and post-burn, we quantified canopy cover and oak seedling survival and growth compared to other woody seedlings deemed potential competitors, primarily red maple (Acer rubrum L.) and sassafras (Sassafras albidum (Nutt.) Nees.). Burning temporarily decreased canopy cover 3–10%, but cover rebounded the subsequent growing season. Repeated burning ultimately produced canopy cover about 6% lower than sites unburned and burned once, suggesting a cumulative effect on understory light. Red maple exhibited low survival (∼40%) following single and repeated burns, but growth remained similar to unburned seedlings. Burning had little impact on sassafras survival and led to total height and basal diameters 2× greater than unburned seedlings. A single burn had no impact on red oak (Erythrobalanus spp.) survival and increased height and basal diameters 25–30%, but this positive growth response was driven by seedlings on several plots which experienced high burn temperatures and consequently high overstory mortality. White oaks (Leucobalanus spp.), however, exhibited twice as high mortality compared to those unburned, with no change in growth parameters. Repeated burning negatively impacted survival and growth of both oak groups compared to unburned seedlings. With both burn regimes, oaks with smaller pre-burn basal diameters exhibited the lowest post-burn survival. Thus, despite the ability of prescribed burns to temporarily increase understory light and reduce red maple survival, neither single or repeated burns placed oaks in an improved competitive position. These findings result from a combination of highly variable yet interdependent factors including the (1) life history traits of oaks compared to their co-occurring competitors, (2) pre-burn stature of pre-existing oak seedlings, and (3) variability in fire temperature and effects on understory light.     

Comparison between old-growth stands and secondary stands regenerating after clear-felling in warm-temperate forests of Yakushima, southern Japan

In order to infer successional changes in structure, species composition and diversity of warm-temperate forest, we compared secondary stands regenerating after clear-felling (41–64-years old) with old-growth stands at altitudes between 300 and 800 m on Yakushima Island, southern Japan. Stem density and maximum stem diameter differed between secondary and old-growth stands, but basal area and aboveground biomass did not. At lower altitudes, the dominant species in old-growth stands with a strong sprouting capacity (Castanopsis cuspidata) also dominated secondary stands, and species composition of secondary and old-growth stands was similar. At higher altitudes, by contrast, the dominant species in old-growth stands (Distylium racemosum) had little sprouting capacity and was poorly represented in diverse secondary stands, which were dominated by Castanopsis or other less abundant species. Secondary stands had greater species diversity (Shannon–Wiener index) than old-growth stands, particularly at higher altitudes. This was due to greater species richness resulting from higher stem density per area, but not to greater evenness. We grouped the component species that share ecologically similar traits into four guilds (fagaceous, primary evergreen, secondary evergreen and deciduous species). Secondary stands were characterized by greater numbers of deciduous and secondary evergreen species. We concluded that different sprouting capacities of dominant species and different regeneration traits among guilds are responsible for the change in species composition and diversity during succession.     

Kinetics of leaf temperature fluctuation affect isoprene emission from red oak (Quercus rubra) leaves

Because the rate of isoprene (2-methyl-1,3-butadiene) emission from plants is highly temperature-dependent, we investigated natural fluctuations in leaf temperature and effects of rapid temperature change on isoprene emission of red oak (Quercus rubra L.) leaves at the top of the canopy at Harvard Forest. Throughout the day, leaves often reached temperatures as much as 15 degrees C above air temperature. The highest temperatures were reached for only a few seconds at a time. We compared isoprene emission rates measured when leaf temperature was changed rapidly with those measured when temperature was changed slowly. In all cases, isoprene emission rate increased with increasing leaf temperature up to about 32 degrees C and then decreased with higher temperatures. The temperature at which isoprene emission rates began to decrease depended on how quickly measurements were made. Isoprene emission rates peaked at 32.5 degrees C when measured hourly, whereas rates peaked at 39 degrees C when measurements were made every four minutes. This behavior reflected the rapid increase in isoprene emission rate that occurred immediately after an increase in leaf temperature, and the subsequent decrease in isoprene emission rate when leaf temperature was held steady for longer than 20 minutes. We concluded that the observed temperature response of isoprene emission rate is a function of measurement protocol. Omitting this parameter from isoprene emission models will not affect simulated isoprene emission rates at mild temperatures, but can increase isoprene emission rates at high temperatures.     

Movement of three stream‐resident balitoroid loaches and a goby in a Hong Kong hillstream

We undertook a mark–recapture study of three pool‐dwelling balitoroid loaches and a nonmigratory goby in a Hong Kong hillstream, which extended over a 35‐week period. The target species were Pseudogastromyzon myersi and Liniparhomaloptera disparis (Balitoridae), Schistura fasciolata (Nemacheilidae) and Rhinogobius duospilus (Gobiidae). Recapture rates of tagged individuals were high (58% overall), especially for the abundant R. duospilus (70% of 412 tagged) and P. myersi (57% of 762 tagged). At the end of the study, most recaptured individuals (78% of gobies, 62% of P. myersi, 42% of L. disparis and 67% of S. fasciolata) were within the pools where they had been released. Of those that had moved elsewhere, maximum displacements ranged from 46 m (R. duospilus) to 101 m (P. myersi), giving rise to a strongly leptokurtic distribution of movement distances. Mean displacements after 35 weeks ranged from only 2.9 m (R. duospilus) to 10.0 m (L. disparis). The sedentary behaviour of these species was more marked than most other small benthic fishes, although our study excluded the breeding period and wet season when high flows might have stimulated movement. Among the mobile P. myersi individuals, most travelled upstream, whereas mobile gobies tended to move downstream. Juveniles of P. myersi and R. duospilus, as well as large adult P. myersi, were especially sedentary, while mobile adult P. myersi that travelled further showed smaller growth increments. The highly sedentary habits of all four fishes suggest that they may exert persistent local top‐down control of benthic communities within pools in Hong Kong streams.     

Effects of Co‐stocking Smallmouth Buffalo,Ictiobus bubalus,with Channel Catfish,Ictalurus punctatus

Proliferative gill disease (PGD) in catfish is caused by the myxozoan Henneguya ictaluri. The complex life cycle requires Dero digitata as the oligochaete host. Efforts to control PGD by eradicating D. digitata have been unsuccessful. Smallmouth buffalo, Ictiobus bubalus, (SMB) are opportunistic bottom feeders and a putative option for controlling D. digitata. In 2011, 15 ponds (0.4 ha) were stocked with 5000 channel catfish, Ictalurus punctatus; 7 of these 15 ponds were also stocked with 300 SMB fingerlings. There were no differences in benthic invertebrate numbers or water quality variables between ponds with or without SMB. At harvest, there were no differences in percent survival, total weight, or catfish feed conversion ratio. In the second year, 18 ponds (0.4 ha) were stocked with 6000 channel catfish. Half the ponds were also stocked with 300 SMB. Sentinel fish were used to estimate disease severity, and pond water was collected for molecular estimation of H. ictaluri actinospore concentrations. Similar to the first year, there were no differences between treatments in any variable tested, including PGD severity in sentinel fish and parasite concentrations in pond water. Under these study conditions, presence of SMB did not have a measureable effect on PGD incidence, parasite density, or overall catfish production.     

The implications of various silvicultural funding arrangements for privately managed public forest land in Canada

When devising policies for financing private silvicultural operations on public forest land, government agencies should consider carefully the benefits and costs of alternative arrangements and how they arc likely to affect tenure holders' behavior. Three general methods of achieving silvicultural objectives arc discussed — the creation of incentives for private voluntary expenditures, reimbursement by governments of expenditures on approved or required silvicultural operations, and required silvicultural operations at the tenure holder's expense.Private firms will only invest voluntarily in silviculture on public lands if they have adequate security of tenure and hold sufficient equity in the timber values resulting from their activities. If firms' silvicultural costs arc reimbursed, their behavior will depend on the extent of reimbursement and whether they have a financial interest in the outcomes of their reimbursed activities. Generally, reimbursement of expenditures must be supported by minimum performance standards and costly monitoring and enforcement procedures. If silvicultural operations are required at the tenure holder's expense, firms will only undertake silviculture to avoid penalties and have a strong incentive to achieve required standards at minimum cost. More stringent monitoring and enforcement procedures may be necessary than if costs arc reimbursed.The impact of policy alternatives is illustrated by means of a survey of silvicultural expenditures on two forest tenure types in British Columbia.     

Antimicrobial resistance and recovery of Salmonella,Campylobacter, and Escherichia coli from chicken egg layer flocks in Canadian sentinel surveillance sites using 2 types of sample matrices

Eggs are important to the diet of Canadians. This product is one of the supply-managed commodities in Canada, but unlike other commodities, where food safety risks are extensively explored and reported, information on the prevalence of enteric organisms (e.g., Salmonella, Campylobacter) and antimicrobial resistance (AMR) in layers in Canada are limited. This study was conducted to determine the prevalence of select bacteria and the associated AMR patterns in layer flocks using 2 sample matrices. Farms were located within FoodNet Canada and the Canadian Integrated Program for Antimicrobial Resistance Surveillance sentinel sites (SS). Fecal samples (Ontario: ON_SS1a, ON_SS1b) and environmental sponge swabs (British Columbia: BC_SS2a) were collected. Salmonella prevalence was 29% and 8% in ON_SS1a and ON_SS1b, respectively, and 7% in BC_SS2a. S. Kentucky and S. Livingstone were the most frequently isolated serovars and no S. Enteritidis was detected. Campylobacter was not detected in the BC sponge swabs but was isolated from 89% and 53% of Ontario fecal samples (ON_SS1a and ON_SS1b, respectively). Seven C. jejuni from Ontario were ciprofloxacin-resistant. Escherichia coli prevalence was high in both sample types (98%). Overall, tetracycline resistance among E. coli ranged from 26% to 69%. Resistance to ceftiofur (n = 2 isolates) and gentamicin (n = 2) was relatively low. There were diverse resistance patterns (excludes susceptible isolates) observed among E. coli in Ontario (10 patterns) and British Columbia (14 patterns). This study revealed that fecal samples are more informative for farm-level monitoring of pathogen and AMR prevalence. Without further validation, sponge swabs are limited in their utility for Campylobacter detection and thus, for public health surveillance.     

不同施肥处理下小麦季潮土氨挥发损失及其影响因素研究

氨挥发是肥料氮素损失的重要途径之一,由于土壤类型、气候条件、肥料种类、用量和施用时间等因素不同而存在很大差异。试验采用间歇式密闭室通气法,对华北平原不同施肥处理(新鲜牛粪与尿素配施、堆腐牛粪与尿素配施和NPK单施)下,冬小麦生长季粘质潮土氨挥发及其影响因素进行了研究。结果表明:冬小麦季土壤氨挥发总量占肥料氮用量的1.23%~1.97%,主要来源于追肥,占整个小麦生长季氨挥发总量的80%左右。不同施肥处理强烈影响氨挥发强度,新鲜牛粪与尿素配施处理氨挥发损失量最高,氮素损失率为1.97%,显著高于堆腐牛粪与尿素配施和NPK单施。基肥期氨挥发速率与气温密切相关,追肥期土壤含水量和NH~+_4-N浓度是影响氨挥发的主控因子。