Responses of ground vegetation species to clear-cutting in a boreal forest: aboveground biomass and nutrient contents during the first 7 years

Rapid growth of ground vegetation following clear-cutting is important to site productivity because vegetation retains nutrients in the ecosystem and can decrease nutrient leaching prior to stand re-establishment. Aboveground biomass, nutrient contents (N, P, K and Ca) and species composition of ground vegetation were determined 1 year before and for 7 years after clear-cutting of a mixed forest dominated by Norway spruce [Picea abies (L.) H. Karst.] in eastern Finland. The biomass of the feather mosses [Pleurozium schreberi Brid. and Hylocomium splendens (Hedw.) B. S.& G.] and the dwarf shrubs (Vaccinium myrtillus L. and V. vitis-idaea L.), which had dominated the ground vegetation in the mature forest, significantly decreased after clear-cutting. However, with the exception of H. splendens, these species had recovered within 3–5 years. The biomass of Deschampsia flexuosa (L.) Trin. considerably increased soon after clear-cutting, and Epilobium angustifolium L. appeared 3–5 years after cutting. These species contributed to the retention of nutrients not simply because of their biomass but also because of higher nutrient concentrations in their tissues. Total biomass and nutrient contents of the ground vegetation exceeded those of the pre-cutting levels. The proportion of ground vegetation biomass and nutrient contents represented by mosses decreased after cutting, while V. myrtillus, although reduced after cutting, remained a marked nutrient sink. The results suggest that H. splendens is the most sensitive species to cutting, but the biomass of P. schreberi, V. myrtillus and V. vitis-idaea return to initial levels soon after clear-cutting as do the nutrient contents of ground vegetation.     

Light capture efficiency decreases with increasing tree age and size in the southern hemisphere gymnosperm Agathis australis

We investigated leaf and shoot architecture in relation to growth irradiance (Q_int) in young and mature trees of a New Zealand native gymnosperm Agathis australis (D. Don) Lindl. to determine tree size-dependent and age-dependent controls on light interception efficiency. A binomial 3-D turbid medium model was constructed to distinguish between differences in shoot light interception efficiency due to variations in leaf area density, angular distribution and leaf aggregation. Because of the positive effect of light on leaf dry mass per area (M_A), nitrogen content per area (N_A) increased with increasing irradiance in both young and mature trees. At a common irradiance, N_A, M_A and the components of M_A, density and thickness, were larger in mature trees, indicating a greater accumulation of photosynthetic biomass per unit area, but also a larger fraction of support biomass in older trees. In both young and mature trees, shoot inclination angle relative to horizontal, and leaf number per unit stem length decreased, and silhouette to total leaf area ratio (S_S) increased with decreasing irradiance, demonstrating more efficient light harvesting in low light. The shoots of young trees were more horizontal and less densely leafed with a larger S_S than those of mature trees, signifying greater light interception efficiency in young plants. Superior light harvesting in young trees resulted from more planar leaf arrangement and less clumped foliage. These results suggest that the age-dependent and/or size-dependent decreases in stand productivity may partly result from reduced light interception efficiency in larger mature relative to smaller and younger plants.     

Effects of harvesting callianassid (ghost) shrimps on subtropical benthic communities

The effects of harvesting of callianassid shrimp (Trypaea australiensis) on the abundance and composition of macrobenthic assemblages in unvegetated sediments of a subtropical coastal embayment in Queensland, Australia were examined using a combination of sampling and manipulative experiments. First, the abundance and composition of the benthic infauna in an area regularly used for the collection of shrimp for bait by recreational anglers was compared with multiple reference areas. Second, a BACI design, with multiple reference areas, was used to examine the short-term effects of harvesting on the benthic assemblages from an intensive commercialised fishing competition. Third, a large-scale, controlled manipulative experiment, where shrimp were harvested from 10,000 m² plots at intensities commensurate with those from recreational and commercial operators, was done to determine the impacts on different components of the infaunal assemblage.

Only a few benthic taxa showed significant declines in abundance in response to the removal of ghost shrimp from the unvegetated sediments. There was evidence, however, of more subtle effects with changes in the degree of spatial variation (patchiness) of several taxa as a result of harvesting. Groups such as capitellid polychaetes, gammarid amphipods and some bivalves were significantly more patchy in their distribution in areas subjected to harvesting than reference areas, at a scale of tens of metres. This scale corresponds to the patterns of movement and activity of recreational harvesters working in these areas. In contrast, patchiness in the abundance of ghost shrimp decreased significantly under harvesting at scales of hundreds of metres, in response to harvesters focussing their efforts on areas with greater numbers of burrow entrances, leading to a more even distribution of the animals. Controlled experimental harvesting caused declines in the abundance of soldier crabs (Mictyris longicarpus), polychaetes and amphipods and an increase in the spatial patchiness of polychaetes. Populations of ghost shrimp were, however, resilient to harvesting over extended periods of time. In conclusion, harvesting of ghost shrimp for bait by recreational and commercial fishers causes significant but localised impacts on a limited range of benthic fauna in unvegetated sediments, including changes in the degree of spatial patchiness in their distribution.     

采伐和火烧对森林氮动态的影响

森林是重要的陆地生态系统类型,它通过特有的养分循环机制维持其结构和功能.其中氮素对林木生长和发育十分重要,而且常是森林生产力的限制因素.另一方面,森林氮动态又常受到人类活动干扰的影响.根据国内外研究结果综述了采伐和火烧对森林氮动态的影响.结果表明采伐后环境因素的变化将影响森林N动态,其中最为关注的是采伐后一系列因素引起的N损失,如:N淋溶增加、伴随生物量的N迁移以及因径流或侵蚀增加造成的枯枝落叶层和土壤层N流失.这些N损失又将影响更新林分的生长和生产力.此外,采伐后N吸收速率一般下降,但随着植被快速生长N吸收速率将不断增加.采伐后氨化和硝化过程增强,但因短期内同化作用较弱,生态系统中大部分N将发生损失.火烧对森林N动态的短期影响主要包括:第一,火烧时N直接挥发损失;第二,火烧后N有效性增加,这主要由灰分沉积、根和微生物死亡及有机质N矿化增强等综合造成.随着时间延长,N有效性逐渐降低,这可能与火烧引起的有机质损失、植物N吸收增加、淋溶或侵蚀损失有关.然而,目前关于火烧造成的长期生态影响,如火烧后地上植被恢复与地下生物地球化学过程变化有何联系仍不太清楚.未来研究应着重于探讨氮素对森林采伐和火烧作出的短期响应将如何长期影响森林的结构和功能.此外,建议在实施营林方案时需考虑采伐和火烧对生态系统氮的影响.     

Ecological and evolutionary consequences of size‐selective harvesting: how much do we know?

Size-selective harvesting, where the large individuals of a particular species are preferentially taken, is common in both marine and terrestrial habitats. Preferential removal of larger individuals of a species has been shown to have a negative effect on its demography, life history and ecology, and empirical studies are increasingly documenting such impacts. But determining whether the observed changes represent evolutionary response or phenotypic plasticity remains a challenge. In addition, the problem is not recognized in most management plans for fish and marine invertebrates that still mandate a minimum size restriction. We use examples from both aquatic and terrestrial habitats to illustrate some of the biological consequences of size-selective harvesting and discuss possible future directions of research as well as changes in management policy needed to mitigate its negative biological impacts.     

The nature of fisheries- and farming-induced evolution

Humans have a penchant for unintentionally selecting against that which they desire most. In fishes, unprecedented reductions in abundance have been associated with unprecedented changes in harvesting and aquaculture technologies. Fishing, the predominant cause of fish-population collapses, is increasingly believed to generate evolutionary changes to characters of import to individual fitness, population persistence and levels of sustainable yield. Human-induced genetic change to wild populations can also result from interactions with their domesticated counterparts. Our examination of fisheries- and farming-induced evolution includes factors that may influence the magnitude, rate and reversibility of genetic responses, the potential for shifts in reaction norms and reduced plasticity, loss of genetic variability, outbreeding depression and their demographic consequences to wild fishes. We also suggest management initiatives to mitigate the effects of fisheries- and farming-induced evolution. Ultimately, the question of whether fishing or fish farming can cause evolutionary change is moot. The key issue is whether such change is likely to have negative conservation- or socio-economic consequences. Although the study of human-induced evolution on fishes should continue to include estimates of the magnitude and rate of selection, there is a critical need for research that addresses short- and long-term demographic consequences to population persistence, plasticity, recovery and productivity.     

黄土高原集水农业研究进展

回顾了黄土高原集水农业理论与技术体系的研究成果．分析评价了集水农业的研究进展。随着黄土高原集水农业研究方法的改进、研究内容的深入、研究领域的扩充．提出了广义性集水农业研究范畴。在黄土高原集水农业理论研究的基础上．应加强微集雨微灌溉应用技术、现代集雨技术、计算机控制技术与集雨网络等高新技术手段的技术集成．以提高雨水汇集与利用效率。同时．黄土高原集水农业的研究已经从微生境条件下的农业生态系统延伸至区域生态环境保育。利用汇集雨水合理调配生态用水．进行小流域综合治理。农林牧综合发展。生态环境重建的集水型生态农业是黄土高原集水农业的发展趋势。     

Model for fluorescence quenching in light harvesting complex II in different aggregation states

Low-temperature (77 K) steady-state fluorescence emission spectroscopy and dynamic light scattering were applied to the main chlorophyll a/b protein light harvesting complex of photosystem II (LHC II) in different aggregation states to elucidate the mechanism of fluorescence quenching within LHC II oligomers. Evidences presented that LHC II oligomers are heterogeneous and consist of large and small particles with different fluorescence yield. At intermediate detergent concentrations the mean size of the small particles is similar to that of trimers, while the size of large particles is comparable to that of aggregated trimers without added detergent. It is suggested that in small particles and trimers the emitter is monomeric chlorophyll, whereas in large aggregates there is also another emitter, which is a poorly fluorescing chlorophyll associate. A model, describing populations of antenna chlorophyll molecules in small and large aggregates in their ground and first singlet excited states, is considered. The model enables us to obtain the ratio of the singlet excited-state lifetimes in small and large particles, the relative amount of chlorophyll molecules in large particles, and the amount of quenchers as a function of the degree of aggregation. These dependencies reveal that the quenching of the chl a fluorescence upon aggregation is due to the formation of large aggregates and the increasing of the amount of chlorophyll molecules forming these aggregates. As a consequence, the amount of quenchers, located in large aggregates, is increased, and their singlet excited-state lifetimes steeply decrease.     

野化培训大熊猫采食和人为砍伐对拐棍竹无性系种群更新的影响

亚高山竹类占据着野生大熊猫(Ailuropoda melanoleuca)食物组分的99%,竹子的生命周期与大熊猫的生活史密切相关,竹子的更新和生长直接影响着大熊猫的生存与保护.为了弄清大熊猫的采食利用和人为砍伐是否促进或制约竹子的繁殖更新,应用样方法、定位观察法,连续研究了卧龙自然保护区大熊猫栖息地内野化培训大熊猫采食、人为砍伐和对照样方中拐棍竹无性系种群的更新动态.结果表明,在相同种群数量和环境条件的基础上(p>0.05),被大熊猫采食竹子的比例为67.07%,致死率29.07%;人为砍伐竹子的比例为65.67%,致死率46.68%,可见与大熊猫采食相比,砍伐更为影响拐棍竹种群的生存.从出笋数量来看,不同处理方式有利于拐棍竹无性系种群的更新(p<0.05),尤其是人为砍伐措施大大提高了竹子的出笋率,但人为砍伐样方的竹笋质量(地径和株高生长)却远低于大熊猫采食和对照样方,未能达到大熊猫觅食的选择利用标准.不同年份之间,各种处理方式下的拐棍竹出笋数量波动较大(p=0.006～0.035),并随着恢复时间的延长,逐渐趋于相似(2007,p=0 825).不同处理方式之间,拐棍竹无性系种群的年补充率,各年份均具有显著性差异(p<0.05,除2007年外),年死亡率仅2003年和2004年有明显的差异(p<0.05),2005～2007年均不显著(p>0.05).拐棍竹无性系种群的年补充率与年死亡率之间表现出年补充率﹥年死亡率的格局(p<0.05),唯有大熊猫采食样方的2004年和2005年、人为砍伐和对照样方的2005年的年死亡率略高于年补充率(p>0.05),这表明拐棍竹无性系种群对大熊猫采食和人为砍伐具有无性系整合的补偿效应.     

Change in CO2 balance under a series of forestry activities in a cool-temperate mixed forest with dense undergrowth

To evaluate the effects on CO₂ exchange of clearcutting a mixed forest and replacing it with a plantation, 4.5 years of continuous eddy covariance measurements of CO₂ fluxes and soil respiration measurements were conducted in a conifer-broadleaf mixed forest in Hokkaido, Japan. The mixed forest was a weak carbon sink (net ecosystem exchange, −44 g C m⁻² yr⁻¹), and it became a large carbon source (569 g C m⁻² yr⁻¹) after clearcutting. However, the large emission in the harvest year rapidly decreased in the following 2 years (495 and 153 g C m⁻² yr⁻¹, respectively) as the gross primary production (GPP) increased, while the total ecosystem respiration (RE) remained relatively stable. The rapid increase in GPP was attributed to an increase in biomass and photosynthetic activity of Sasa dwarf bamboo, an understory species. Soil respiration increased in the 3 years following clearcutting, in the first year mainly owing to the change in the gap ratio of the forest, and in the following years because of increased root respiration by the bamboo. The ratio of soil respiration to RE increased from 44% in the forest to nearly 100% after clearcutting, and aboveground parts of the vegetation contributed little to the RE although the respiration chamber measurements showed heterogeneous soil condition after clearcutting.