Exotic vascular plant invasiveness and forest invasibility in urban boreal forest types

The riverine forests of the northern city of Edmonton, Alberta, Canada display strong resilience to disturbance and are similar in species composition to southern boreal mixedwood forest types. This study addressed questions such as, how easily do exotic species become established in urban boreal forests (species invasiveness) and do urban boreal forest structural characteristics such as, native species richness, abundance, and vertical vegetation layers, confer resistance to exotic species establishment and spread (community invasibility)? Eighty-four forest stands were sampled and species composition and mean percent cover analyzed using ordination methods. Results showed that exotic tree/shrub types were of the most concern for invasion to urban boreal forests and that exotic species type, native habitat and propagule supply may be good indicators of invasive potential. Native forest structure appeared to confer a level of resistance to exotic species and medium to high disturbance intensity was associated with exotic species growth and spread without a corresponding loss in native species richness. Results provided large-scale evidence that diverse communities are less vulnerable to exotic species invasion, and that intermediate disturbance intensity supports species coexistence. From a management perspective, the retention of native species and native forest structure in urban forests is favored to minimize the impact of exotic species introductions, protect natural succession patterns, and minimize the spread of exotic species.     

Extent of industrial plantations on Southeast Asian peatlands in 2010 with analysis of historical expansion and future projections

Tropical peatlands cover over 25 Mha in Southeast Asia and are estimated to contain around 70 Gt of carbon. Peat swamp forest ecosystems are an important part of the region's natural resources supporting unique flora and fauna endemic to Southeast Asia. Over recent years, industrial plantation development on peatland, especially for oil palm cultivation, has created intense debate due to its potentially adverse social and environmental effects. The lack of objective up‐to‐date information on the extent of industrial plantations has complicated quantification of their regional and global environmental consequences, both in terms of loss of forest and biodiversity as well as increases in carbon emissions. Based on visual interpretation of high‐resolution (30 m) satellite images, we find that industrial plantations covered over 3.1 Mha (20%) of the peatlands of Peninsular Malaysia, Sumatra and Borneo in 2010, surpassing the area of Belgium and causing an annual carbon emission from peat decomposition of 230–310 Mt CO_2e. The majority (62%) of the plantations were located on the island of Sumatra, and over two‐thirds (69%) of all industrial plantations were developed for oil palm cultivation, with the remainder mostly being Acacia plantations for paper pulp production. Historical analysis shows strong acceleration of plantation development in recent years: 70% of all industrial plantations have been established since 2000 and only 4% of the current plantation area existed in 1990. ‘Business‐as‐usual’ projections of future conversion rates, based on historical rates over the past two decades, indicate that 6–9 Mha of peatland in insular Southeast Asia may be converted to plantations by the year 2020, unless land use planning policies or markets for products change. This would increase the annual carbon emission to somewhere between 380 and 920 Mt CO_2e by 2020 depending on water management practices and the extent of plantations.     

Population dynamics in changing environments: the case of an eruptive forest pest species

In recent decades we have seen rapid and co‐occurring changes in landscape structure, species distributions and even climate as consequences of human activity. Such changes affect the dynamics of the interaction between major forest pest species, such as bark beetles (Coleoptera: Curculionidae, Scolytinae), and their host trees. Normally breeding mostly in broken or severely stressed spruce; at high population densities some bark beetle species can colonise and kill healthy trees on scales ranging from single trees in a stand to multi‐annual landscape‐wide outbreaks. In Eurasia, the largest outbreaks are caused by the spruce bark beetle, Ips typographus (Linnaeus), which is common and shares a wide distribution with its main host, Norway spruce (Picea abies Karst.). A large literature is now available, from which this review aims to synthesize research relevant for the population dynamics of I. typographus and co‐occurring species under changing conditions. We find that spruce bark beetle population dynamics tend to be metastable, but that mixed‐species and age‐heterogeneous forests with good site‐matching tend to be less susceptible to large‐scale outbreaks. While large accumulations of logs should be removed and/or debarked before the next swarming period, intensive removal of all coarse dead wood may be counterproductive, as it reduces the diversity of predators that in some areas may play a role in keeping I. typographus populations below the outbreak threshold, and sanitary logging frequently causes edge effects and root damage, reducing the resistance of remaining trees. It is very hard to predict the outcome of interspecific interactions due to invading beetle species or I. typographus establishing outside its current range, as they can be of varying sign and strength and may fluctuate depending on environmental factors and population phase. Most research indicates that beetle outbreaks will increase in frequency and magnitude as temperature, wind speed and precipitation variability increases, and that mitigating forestry practices should be adopted as soon as possible considering the time lags involved.     

片断化生境中滇桐传粉生物学和繁育系统

通过野外观察和人工授粉试验方法,对云南省文山州西畴县法斗分布区片断化生境中濒危植物滇桐(Craigia yunnanensis)的传粉生物学特征和繁育系统进行研究.结果表明:滇桐每个聚伞花序有2～9朵两性花,单花花期为3～4d,单花雌雄蕊在时空上有一定的隔离;杂交指数(OCI) ＞4,花粉-胚珠比(P/O)为1381±53;有效传粉昆虫为大头丽蝇(Chrysomyia megacephala);同株异花授粉结实率低;滇桐的繁育系统属于异交为主,部分自交亲和,传粉过程需要传粉者;自然状态下滇桐的座果率(56.67％±3.85％)和结籽率(6.26％±0.75％)均较低,而异株异花授粉均可显著提高座果率及结籽率(P＜0.01),这与当前片断化生境中传粉昆虫少、效率低下等有关,表明生境片断化正在影响滇桐植株的早期生殖成功.     

Do Eucalyptus plantations host an insect community similar to remnant Eucalyptus forest?

Abstract We examined the potential of forest plantations to support communities of forest‐using insects when planted into an area with greatly reduced native forest cover. We surveyed the insect fauna of Eucalyptus globulus (Myrtaceae) plantations and native Eucalyptus marginata dominated remnant woodland in south‐western Australia, comparing edge to interior habitats, and plantations surrounded by a pastoral matrix to plantations adjacent to native remnants. We also surveyed insects in open pasture. Analyses focused on three major insect orders: Coleoptera, Lepidoptera and Hymenoptera. Plantations were found to support many forest‐using insect species, but the fauna had an overall composition that was distinct from the remnant forest. The pasture fauna had more in common with plantations than forest remnants. Insect communities of plantations were different from native forest both because fewer insect species were present, and because they had a few more abundant insect species. Some of the dominant species in plantations were known forestry pests. One pest species (Gonipterus scutellatus) was also very abundant in remnant forest, although it was only recently first recorded in Western Australia. It may be that plantation forestry provided an ecological bridge that facilitated invasion of the native forest by this nonendemic pest species. Plantation communities had more leaf‐feeding moths and beetles than remnant forests. Plantations also had fewer ants, bees, evanioid wasps and predatory canopy beetles than remnants, but predatory beetles were more common in the understory of plantations than remnants. Use of broad spectrum insecticides in plantations might limit the ability of these natural enemies to regulate herbivore populations. There were only weak indications of differences in composition of the fauna at habitat edges and no consistent differences between the fauna of plantations adjacent to remnant vegetation and those surrounded by agriculture, suggesting that there is little scope for managing biodiversity outcomes by choosing different edge to interior ratios or by locating plantations near or far from remnants.     

Peatland restoration: A brief assessment with special reference to Sphagnum bogs

Recent literature on peatland restorationindicates as a general goal repairing orrebuilding ecosystems by restoringecosystem structure, trophic organization,biodiversity, and functions to thosecharacteristic of the type of peatland towhich the damaged ecosystem belonged, or atleast to an earlier successional stage.Attainment requires provision of anappropriate hydrological regime,manipulating surface topography, improvingmicroclimate, adding appropriate diaspores,manipulating base status where necessary,fertilizing in some cases, excludinginappropriate invaders, adaptively managingthrough at least one flood/drought cycle toensure sustainability, and monitoring on ascale of decades. Several matchingconditions favoring or opposing restorationare suggested.In the restoration of peatlands, successeshave generally been those of short-termrepair. Periods of restoration have beenmuch too short to ensure progression to, oreven well toward, a fully functionalpeatland reasonably compatible with thepristine state of similar peatlandselsewhere, although with altered surfacepatterns.Long-term monitoring ofpeatland-restoration projects is essentialfor a better understanding of how to carryout such restoration successfully.Paleoecology is suggested as anunderutilized tool in peatlandrestoration.     

Do restoration measures rehabilitate fauna diversity in raised bogs? A comparative study on aquatic macroinvertebrates

To assess whether raised bog restorationmeasures contribute to the conservation andrestoration of the fauna diversity,macroinvertebrate species assemblages werecompared between water bodies created byrewetting measures and water bodies whichhave not been subject to restorationmeasures, but are remnants offormer peat cuttings and trenches used forbuckwheat culture in the past.The restoration sites were inhabited bycharacteristic raised bog species and rarespecies, but their numbers were higher atthe remnant sites not affected byrestoration management. A considerablenumber of characteristic and rare faunaspecies were only found at the remnantsites. The remnant sites includedconsiderably more variation inmacroinvertebrate species assemblages andhad a higher cumulative species richness.The number of characteristicmacroinvertebrate species was not clearlyrelated to the presence of a characteristicraised bog vegetation. In restoration sitesnumbers of rare and characteristic speciesper site tended to increase with the timeelapsed after rewetting. However,restoration measures will not automaticallyresult in restoration of a more or lesscomplete macroinvertebrate speciesspectrum, as restoration measures have sofar resulted in habitats for only a limitednumber of the characteristic species.When planning restoration measures, it isrecommended to protect the populations ofrare and characteristic species present inthe area, as these populations may becomethe sources for colonization of rewettedsites. Safeguarding habitat diversityduring the restoration process andrestoration of different elements of thehabitat diversity of complete raised bogsystems will result in the characteristicfauna diversity being conserved andrestored more successfully.     

Use of Shallow Basins to Restore Cutover Peatlands: Hydrology

Basins 20‐, 10‐, and 4‐m wide were excavated 15 to 20 cm into cutover peat fields near Lac Saint Jean, Québec, Canada to facilitate the establishment of Sphagnum mosses. Sphagnum diaspores (fragments) and straw mulch were spread over the excavated surfaces, a control peat field, and a mulch‐protected site without basins. Mean water tables in the 20‐, 10‐, and 4‐m wide basins and the mulch‐protected site were 27.2, 8.3, 11.4, and 9.7 cm higher, respectively, than in the control peat field in May to August 1996. Similar improvements were observed in 1997 (a drier summer). The higher water table was due to lowering of the peat surface with respect to the local water table, retention of meltwater and stormwater by the peripheral ridges formed during excavation, retention of water during drier periods by the groundwater mound beneath the ridges, and mulch. Soil moisture was always higher in the experimental basins than in the control peat field or in the mulch‐protected site, demonstrating the superior soil wetness characteristic of sites with basins and straw mulch. Water tension data signaled the absence of the capillary fringe (i.e., capillary drainage) near the surface for some finite period, thus possibly limiting water for best Sphagnum growth. At the experimental basins and mulch‐protected site, 100% of these periods lasted four or fewer days. In the control peat field, 20% of the periods when capillary drainage had occurred lasted more than four days, with one period of 17 days. The mulch protection alone provided considerable improvement in hydrological conditions compared with the control peat field, but the additional water retained in the experimental basins protected against Sphagnum desiccation and loss during more extreme dry periods.     

Catastrophic disturbance, logging and the ecology of mahogany (Swietenia macrophylla King): grounds for listing a major tropical timber species in CITES

Recent debate on whether or not mahogany ( Swietenia macrophylla King) is threatened by the international timber trade has focused on the breadth of its range and estimates of the remaining stock of mahogany trees. These data are inadequate to reveal the status of mahogany populations, both because they are incomplete in areal extent and because they do not reveal population parameters such as the existence or density of young trees smaller than commercial size. However, there is sufficient information on the regeneration ecology of mahogany to indicate that under natural conditions this species regenerates in essentially even-aged stands after catastrophic disturbances destroy many or most trees, and, in the case of fires and flooding, saplings and seedlings as well. Adult mahoganies tend to survive these events, and regenerate by shedding seed onto the resulting gaps or clearings. This ecological strategy makes mahogany vulnerable to logging, first because juvenile mahoganies are not found in the understorey, and secondly because logging operations shortcircuit mahogany regeneration processes by selectively removing almost all mahogany seed sources while leaving standing competing vegetation of other species. Listing of mahogany in CITES Appendix II could provide both a mechanism to fill in gaps in information and an incentive to change current practices in favour of silvicultural management to provide for regeneration of this valuable timber species in forests subjected to logging.