Putting Density Back into the Habitat‐Quality Equation: Case Study of an Open‐Nesting Forest Bird

Abstract: Ecological traps and other cases of apparently maladaptive habitat selection cast doubt on the relevance of density as an indicator of habitat quality. Nevertheless, the prevalence of these phenomena remains poorly known, and density may still reflect habitat quality in most systems. We examined the relationship between density and two other parameters of habitat quality in an open‐nesting passerine species: the Ovenbird (Seiurus aurocapilla). We hypothesized that the average individual bird makes a good decision when selecting its breeding territory and that territory spacing reflects site productivity or predation risk. Therefore, we predicted that density would be positively correlated with productivity (number of young fledged per unit area). Because individual performance is sensitive to events partly determined by chance, such as nest predation, we further predicted density would be weakly correlated or uncorrelated with the proportion of territories fledging young. We collected data in 23 study sites (25 ha each), 16 of which were located in untreated mature northern hardwood forest and seven in stands partially harvested (treated) 1–7 years prior to the survey. Density explained most of the variability in productivity (R²= 0.73), and there was no apparent decoupling between density and productivity in treated plots. In contrast, there was no significant relationship between density and the proportion of territories fledging ≥1 young over the entire breeding season. These results suggest that density reflects habitat quality at the plot scale in this study system. To our knowledge this is one of the few studies testing the value of territory density as an indicator of habitat quality in an open‐nesting bird species on the basis of a relatively large number of sizeable study plots.     

Effects of Harvest of Nontimber Forest Products and Ecological Differences between Sites on the Demography of African Mahogany

Abstract: The demographic impacts of harvesting nontimber forest products (NTFP) have been increasingly studied because of reports of potentially unsustainable harvest. Nevertheless, our understanding of how plant demographic response to harvest is altered by variation in ecological conditions, which is critical for developing realistic sustainable‐use plans, is limited. We built matrix population models to test whether and how variation in ecological conditions affects population responses to harvest. In particular, we examined the effect of bark and foliage harvest on the demography of populations of African mahogany (Khaya senegalensis) in two contrasting ecological regions of Benin, West Africa. K. senegalensis bark and foliage harvest significantly reduced its stochastic population growth rates, but ecological differences between regions had a greater effect on population growth rates than did harvest. The effect of harvest on population growth rates (Δλ) was slightly stronger in the moist than in the drier region. Life‐table response experiments revealed that the mechanism by which harvesting reduced λ differed between ecological regions. Lowered stasis (persistence) of larger life stages lead to a reduction in λ in the drier region, whereas lowered growth of all life stages lowered λ in moist region. Potential strategies to increase population growth rates should include decreasing the proportion of individuals harvested, promoting harvester‐owned plantations of African mahogany, and increasing survival and growth by promoting no‐fire zones in gallery forests. Our results show how population responses to harvest of NTFP may be altered by ecological differences across sites and emphasize the importance of monitoring populations over the climatic range in which they occur to develop more realistic recommendations for conservation.     

Edge effects on trophic cascades in tropical rainforests

The cascading effects of biodiversity loss on ecosystem functioning of forests have become more apparent. However, how edge effects shape these processes has yet to be established. We assessed how edge effects alter arthropod populations and the strength of any resultant trophic cascades on herbivory rate in tropical forests of Brazil. We established 7 paired forest edge and interior sites. Each site had a vertebrate-exclosure, procedural (exclosure framework with open walls), and control plot (total 42 plots). Forest patches were surrounded by pasture. Understory arthropods and leaf damage were sampled every 4 weeks for 11 months. We used path analysis to determine the strength of trophic cascades in the interior and edge sites. In forest interior exclosures, abundance of predaceous and herbivorous arthropods increased by 326% and 180%, respectively, compared with control plots, and there were significant cascading effects on herbivory. Edge-dwelling invertebrates responded weakly to exclusion and there was no evidence of trophic cascade. Our results suggest that the vertebrate community at forest edges controls invertebrate densities to a lesser extent than it does in the interior. Edge areas can support vertebrate communities with a smaller contingent of insectivores. This allows arthropods to flourish and indirectly accounts for higher levels of plant damage at these sites. Increased herbivory rates may have important consequences for floristic community composition and primary productivity, as well as cascading effects on nutrient cycling. By interspersing natural forest patches with agroforests, instead of pasture, abiotic edge effects can be softened and prevented from penetrating deep into the forest. This would ensure a greater proportion of forest remains habitable for sensitive species and could help retain ecosystem functions in edge zones.     

Global reforestation and biodiversity conservation

The loss of forest is a leading cause of species extinction, and reforestation is 1 of 2 established interventions for reversing this loss. However, the role of reforestation for biodiversity conservation remains debated, and lacking is an assessment of the potential contribution that reforestation could make to biodiversity conservation globally. We conducted a spatial analysis of overlap between 1,550 forest-obligate threatened species’ ranges and land that could be reforested after accounting for socioeconomic and ecological constraints. Reforestation on at least 43% (∼369 million ha) of reforestable area was predicted to potentially benefit threatened vertebrates. This is approximately 15% of the total area where threatened vertebrates occur. The greatest opportunities for conserving threatened vertebrate species are in the tropics, particularly Brazil and Indonesia. Although reforestation is not a substitute for forest conservation, and most of the area containing threatened vertebrates remains forested, our results highlight the need for global conservation strategies to recognize the potentially significant contribution that reforestation could make to biodiversity conservation. If implemented, reforestation of ∼369 million ha would also contribute substantially to climate-change mitigation, offering a way to achieve multiple sustainability commitments at once. Countries must now work to overcome key barriers (e.g., unclear revenue streams, high transaction costs) to investment in reforestation.     

Aluminium: The Need for a Re-Evaluation of Its Toxicity and Solubility in Mature Forest Stands

Aluminium (Al) is a key element in critical loadcalculations for forest. Here, we argue for re-evaluating theimportance of Al. Effects of two levels of enhanced Alconcentrations and lowered Ca:Al ratios in the soil solutionin a field manipulation experiment in a mature spruce stand(1996–1999) on tree vitality parameters were tested. Inaddition, Al solubility controls were tested. Various loads ofAl were added to forest plots by means of an irrigationsystem. Potentially toxic Al concentrations and criticalratios of Ca to inorganic Al were established. The ratio of Cato total Al was not a suitable indicator for unfavourableconditions for plant growth. No significant effects on crowncondition, tree growth and fine root production were observedafter three years of treatment. In 1999, foliar Mg content inthe highest Al addition treatment had declined significantly.This agreed with the known response to Al stress of seedlingsin nutrient solution experiments. No support was found forusing the chemical criterion Ca:Al ratio in soil solution,foliar and root tissue as an indicator for forest damage dueto acidification. Al solubility was considerably lower thanimplied by the assumption of equilibrium with gibbsite,particularly in the root zone. The gibbsite equilibrium iscommonly used in critical load models. Substitution of thegibbsite equilibrium with an Al-organic matter complexationmodel to describe Al solubility in soil water may have largeconsequences for calculation of critical loads. The resultsindicate that critical load maps for forests should bereconsidered.     

An Analysis of the Structure of the Simple Mass Balance Equation: Implications for Testing National Critical Loads Maps

The critical loads concept is used by the UN-ECEConvention on Long Range Transboundary Air Pollution(CLRTAP) for setting pollution reduction targets.Increasing numbers of countries are adopting the SimpleMass Balance equation (SMB) to calculate critical loads ofacidifying S and N for forest soils. The equation is madeup of a series of mass balances each of which is used tocalculate a leaching flux. The assumptions in the SMBequation were investigated by testing its ability topredict current sulphur load and by comparing each of thecalculated leaching fluxes to measured rates. It was notpossible to predict current sulphur load at our sites usingthe SMB equation. The leaching tests demonstrated that,primarily due to its steady state assumptions, the SMBequation generates critical loads that are theoretical longterm estimates of risk, and are untestable. Thesimplifying assumptions sometimes lead to illogicalresults. Some of these can be improved by adding a final,simple but dynamic, calculation step to determine theexpected time until effects are observed. Theacceptability of combining annual average data, which bestapproximates steady state, with a biological indicator isquestionable. It is not possible to test critical loadscalculated using the SMB equation when applied with all ofits assumptions but it is possible to test its fundamentalapproach using non steady state data.     

Mobility and Methylation of Mercury in Forest Soils Development of an In-Situ Stable Isotope Tracer Technique and Initial Results

A method for investigating in-situmethylation and mobility of mercury has beendeveloped and applied to forest soil. The methodis based on additions of stable ¹⁹⁹Hgisotopes to forest soil plots followed bysampling and analysis of isotope ratios of totalmercury and MeHg using ICP-MS. Initial resultsindicate that a fraction (30%) of the mercuryadded to the forest soils is immobilised over atime scale of 16 months. A small but significantfraction of the mercury is methylated during thesame time scale. Higher methylation rates werefound in wetland soil than in dry forest podzolsoil.     

我国森林资源产品流动及其变化特征分析

论文运用物流分析的基本思想,基于我国森林资源产品产量、贸易量统计资料,采用统一单位“原木当量”(m₃),估算了1981～2000年森林资源采伐和产品加工环节的资源流量,进而分析我国森林资源产品流动的变化特征。结果表明,我国从“六五”(1981～1985年)到“九五”(1996～2000年)期间,消耗森林资源量分别为10230×104、11678×104、13444×104和16962×104m₃/a,呈加速增长趋势。其中,来自国外的资源流量占总流量的比重呈增加趋势,“六五”期间占19.1%,到“九五”期间上升为48.3%。流入资源以原木、木浆、纸及纸板、胶合板为主,它们主要来自北美、东亚、东南亚地区,有来源多地区化的变化趋向。森林资源在“六五”期间主要流向原木锯材类产品加工,随着产品流向结构的逐步改善,更多的资源流向人造板类产品的生产消费;纸类产品生产消费的资源流量增加迅速,但主要来自国外。     

补贴对林业生产及森林生态效益影响的经济学分析:一个定量分析模型

不同的林业补贴产生不同的效果:可能提高社会福利,也可能降低社会福利。出现这种差别的原因是补贴使林业生产收益流发生了变化,从而使得林业生产收益最大净现值到来的时间相对于社会最优时间提前或延后。论文建立了一个以林木吸收碳来衡量森林生态效益的林业生产收益定量模型,并通过该模型对华东某市的一项林场补贴政策进行分析。分析结果是,在没有补贴的情况下,该林场最优砍伐时间为第19年,当存在补贴的情况下,林场的最优砍伐时间提前到第11年,而随着碳价格从0增加至1000元/t,社会最优砍伐时间从第19年增加到第31年,造成的社会净损失从7750元/hm²增加到17704元/hm²。鉴于此,合理的林业补贴要能够促使私人效益与社会效益相统一。     

采伐影响下森林景观服务功能变化研究

文章以大兴安岭呼中林业局亚里河林场为研究区,以遥感数据、林相图和采伐设计资料为信息源,选择水源涵养、固土保肥、固定CO2和释放O2四项服务功能,运用景观生态学原理,引用相应模型,估算了研究区1989年和2000年服务功能价值及其空间分布变化;建立历年采伐分布图,计算采伐造成的服务功能价值损失,揭示该损失值与木材生产的经济效益之间的关系,并分析了服务功能价值在各管理区域内的分布。结果表明,1989年服务功能价值为1.85×108元,2000年为1.37×108元,价值20×104元h/m₂以上的面积明显下降。生态服务功能的下降由采伐导致,1989至1999年采伐导致的生态损失价值为0.71×108元,是木材生产获利的1.9倍,采伐损失价值与年出材量呈现相同的变化趋势。最后证明了管理等级区划和限制采伐量,即“天保工程”,将有利于森林植被恢复,大幅度提高整个亚里河林场的生态服务功能。