Anthropogenic disturbances strengthened tree community-environment relationships at the temperate-boreal interface

Context

Knowledge of how environmental gradients generate changes in community composition across forest landscapes (β-diversity) represents a critical issue in the era of global change, which exerts especially powerful impacts by shifting disturbance regimes.

Objectives

We analyzed the response of tree communities to increased disturbance rates that were linked to European settlement at the temperate-boreal interface of eastern Canada. We tested whether disturbance has led to spatial homogenization or heterogenization, and to decoupling or strengthening of community-environment relationships.

Methods

We used a reconstruction of pre-industrial tree communities based on historical land survey records (1854–1935), together with modern data, to assess changes in tree β-diversity patterns. Then, β-diversity was partitioned into fractions explained by spatial (dbMEM) and environmental variables (latitude, elevation, slope, drainage and surface deposits) in order to assess changes in spatial structures and community-environment relationships.

Results

In pre-industrial times, environmental variables explained only a small proportion of β-diversity since dominant taxa were present across the range of environmental gradients, whereas habitat specialists were very rare. Between pre-industrial and modern times, our analysis highlights an increase in β-diversity and the proportion of β-diversity that was explained by environmental variables. Increased disturbance rates have favored early-successional habitat specialist taxa and reduced the habitat breadth of pre-industrial generalists, thereby increasing the strength of community-environment relationships.

Conclusions

Our results support that disturbance can alter the strength of community-environment relationships and also suggest that functional traits of species within the regional pool could predict whether or not disturbance alters such relationships.

     

Suggested guidelines for immunohistochemical techniques in veterinary diagnostic laboratories

This document is the consensus of the American Association of Veterinary Laboratory Diagnosticians (AAVLD) Subcommittee on Standardization of Immunohistochemistry on a set of guidelines for immunohistochemistry (IHC) testing in veterinary laboratories. Immunohistochemistry is a powerful ancillary methodology frequently used in many veterinary laboratories for both diagnostic and research purposes. However, neither standardization nor validation of IHC tests has been completely achieved in veterinary medicine. This document addresses both issues. Topics covered include antibody selection, fixation, antigen retrieval, antibody incubation, antibody dilutions, tissue and reagent controls, buffers, and detection systems. The validation of an IHC test is addressed for both infectious diseases and neoplastic processes. In addition, storage and handling of IHC reagents, interpretation, quality control and assurance, and troubleshooting are also discussed. Proper standardization and validation of IHC will improve the quality of diagnostics in veterinary laboratories.     

Long-term safety, efficacy and palatability of oral meloxicam at 0.01-0.03 mg/kg for treatment of osteoarthritic pain in cats

Osteoarthritis is a chronic, painful condition that is now recognised as affecting a large proportion of cats. Non-steroidal anti-inflammatory drugs (NSAIDs) have proven efficacy in dogs and humans but there are limited published data on the use of NSAIDs in the long-term management of this condition in cats. This prospective study aimed to assess the long-term safety and palatability of oral meloxicam and its efficacy in treating osteoarthritic pain in cats when given at a dose of 0.01-0.03 mg/kg once daily. Forty cats diagnosed with osteoarthritis completed the trial with a mean treatment duration of 5.8 months. Gastrointestinal upset in 2/46 (4%) cats was the only adverse effect noted. No deleterious effect on renal function was detected in cats studied. Owners subjectively assessed treatment efficacy as good or excellent in 34/40 (85%) of cases. The results of this study showed oral meloxicam to be safe and palatable long-term treatment for osteoarthritis in cats when given with food at a dose of 0.01-0.03 mg/kg.     

Automatic adjustment of harrowing intensity in cereals using digital image analysis

Precision farming technologies were implemented into a commercial harrow to increase selectivity of weed harrowing in spring cereals. Digital cameras were mounted before and after the harrow measuring crop cover. Crop soil cover (CSC) was computed out of these two images. Eight field experiments were carried out in spring cereals. Mode of harrowing intensity was changed in four experiments by speed, number of passes and tine angle. Each mode was varied in five intensities. In four experiments, only intensity of harrowing was changed. Weed control efficacy (WCE) and CSC were measured immediately after harrowing. Crop recovery was assessed 14 days after harrowing. Modes of intensity were not significantly different. However, intensity had significant effects on WCE and CSC. Cereals recovered from 10% CSC, and selectivity was in the constant range at 10% CSC. Therefore, 10% CSC was the threshold for the decision algorithm. If the actual CSC was below 10% CSC, intensity was increased. If the actual CSC was higher than 10%, intensity was decreased. Image analysis, decision support system and automatic control of harrowing intensity by hydraulic adjustment of tine angle were installed on a controller mounted on the harrow. The new system was tested in an additional field study. Threshold values for CSC were set at 10%, 30% and 60%. Automatic tine angle adjustment precisely realised the three different CSC values with variations of 1.5% to 3%. This development contributes to selective weed control and supports farmers during harrowing.     

Use of Lorenz curves and Gini coefficients to assess yield inequality within paddocks

The opportunity for site-specific management of crops depends on both the magnitude and spatial structure of yield variation. This study explored the applicability of Lorenz curves and Gini coefficients (G) to characterise the magnitude of the variation in grain yield. Maize crops were grown in farmers fields in a semi-arid region of central Argentina. Major sources of yield variation between and within paddocks included season, soil type and topography, rate of nitrogen fertiliser (nil to 132 kg N ha⁻¹), and the interactions among these factors. Nitrogen treatments were applied in a complete block strip trial (strip size700 m×9.8 m) with three replicates. Data were collected with an AgLeader™ yield monitor, and GIS software was used to create 9.8 m×9.8 m grids over the observations. Average yield in 0.7–2.8 ha field sections ranged from 1.6 to 7.0 t ha⁻¹. Gini coefficient ranged from 0.027 to 0.191 whereas its theoretical limits are 0 for a perfectly uniform population, and 1 for a theoretical population of infinite size where all units but one yield 0. Conditions conducive to high yield, e.g. adequate availability of nitrogen and water, reduced crop yield inequality, as quantified with G. The agronomic relevance of G was summarised in an inverse relationship with yield. Lorenz curves seemed particularly apt to present crop heterogeneity in terms of inequality, and to highlight the relative contribution of low- and high-yielding sections of the field to total paddock yield. Lorenz curves and Gini coefficients provide a potentially useful extension tool, a complement to yield maps and other statistical indices of yield variation, and further contact points between site-specific management, economics and ecology.     

树冠喷药毒杀光肩星天牛成虫效果及农药残留分析

利用杀虫剂防治害虫是一种见效快、效果好的方法 ;但是 ,杀虫剂的使用也带来环境污染问题 ,因此杀虫剂的合理使用已成为目前关注的焦点。光肩星天牛 [Anoplophoraglabripennis (Motsch .) ]是杨树的重要蛀干害虫 ,幼虫期在树干内钻蛀危害 ,而且个体分散 ,加之树木高大 ,防治起来十分困难。成虫期以树的小枝、叶柄和叶片作补充营养 ,是进行化学防治的有利时期。以前用化学方法防治该害虫 ,往往仅注意杀虫剂的防治效果 (张仲信 ,1 964 ;康青 ,1 981 ;孙长春 ,1 987;梁成杰等 ,1 997a ;1 997b ;高瑞桐等 ,2 0 0 1 ;萧刚柔 ,1 992 ) ,缺乏杀虫…     

Growth CO2 concentration modifies the transpiration response of Populus deltoides to drought and vapor pressure deficit

Cottonwood (Populus deltoides Bartr. ex Marsh.) trees grown for 9 months in elevated carbon dioxide concentration ([CO2]) showed significant increases in height, leaf area and basal diameter relative to trees in a near-ambient [CO2] control treatment. Sample trees in the CO2 treatments were subjected to high and low atmospheric vapor pressure deficits (VPD) over a 5-week period at both high and low soil water contents (SWC). During these periods, transpiration rates at both the leaf and canopy levels were calculated based on sap flow measurements and leaf-to-sapwood area ratios. Leaf-level transpiration rates were approximately equivalent across [CO2] treatments when soil water was not limiting. In contrast, during drought stress, canopy-level transpiration rates were approximately equivalent across [CO2] treatments, indicating that leaf-level fluxes during drought stress were reduced in elevated [CO2] by a factor equal to the leaf area ratio of the two canopies. The shift from equivalent leaf-level transpiration to equivalent canopy-level transpiration with increasing drought stress suggests maximum water use rates were controlled primarily by atmospheric demand at high SWC and by soil water availability at low SWC. Changes in VPD had less effect on transpiration than changes in SWC for trees in both CO2 treatments. Transpiration rates of trees in both CO2 treatments reached maximum values at a VPD of about 2.0 kPa at high SWC, but leveled off and decreased slightly in both canopies as VPD increased above this value. At low SWC, increasing VPD from approximately 1.4 to 2.5 kPa caused transpiration rates to decline slightly in the canopies of trees in both treatments, with significant (P = 0.004) decreases occurring in trees in the near-ambient [CO2] treatment. The transpiration responses at high VPD in the presence of high SWC and throughout the low SWC treatment suggest some hydraulic limitations to water use occurred. Comparisons of midday leaf water potentials of trees in both CO2 treatments support this conclusion.