Litter of an alien tree, <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis>, inhibits seed germination and initial growth of a native tree on the Ogasawara Islands (subtropical oceanic islands)

We investigated the effects of the accumulation of litter of an alien tree, Casuarina equisetifolia, on the initial establishment of Schima mertensiana, a tree native to the Ogasawara (Bonin) Islands, in the northwestern Pacific Ocean, in field and greenhouse experiments. The field experiment compared emergence of seedlings in forests dominated by C. equisetifolia with those in native forests, with and without litter removal. The greenhouse experiment compared seedling germination and biomass among 12 treatments that included two soil types (collected from the C. equisetifolia and native forests), two litter types (C. equisetifolia and native litter), and three amounts of litter (5, 15, or 45 g/pot). Significantly fewer S. mertensiana seedlings emerged at sites dominated by C. equisetifolia than at sites of native species in the field experiment. Litter removal tended to increase seedling emergence. Fewer and smaller S. mertensiana seedlings germinated with greater litter cover regardless of soil type or litter type in the greenhouse experiment. Our results demonstrate that C. equisetifolia litter suppresses germination and initial growth of S. mertensiana, and that the main cause of the suppression is the greater amount of litter accumulated under C. equisetifolia forest floor rather than factors such as the nature of the soil or litter between native and alien species.     

Vegetation status on Nishi-jima Island (Ogasawara) before eradication of alien herbivore mammals: rapid expansion of an invasive alien tree, <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis> (Casuarinaceae)

Insular ecosystems can be dramatically affected by alien species, and records of pre-eradication status are essential to evaluate the effects of eradicating alien species. Nishi-jima Island is a small island of the Ogasawara group on which the first program of complete eradication of alien herbivorous mammals (black rats and feral goats) will be conducted. After eradication, the government plans to conduct ecosystem restoration on the island. This paper reports the angiosperm flora and vegetation of Nishi-jima Island before eradication of the rats and goats, with the objective of aiding ecosystem management after the eradication. Our surveys indicate that vegetation cover by the alien tree, Casuarina equisetifolia has expanded compared with its distribution in a 1974 aerial photograph of the island. The predominant vegetation in 2006 was C. equisetifolia forests and Zoysia tenuifolia grasslands, with fragmented native tree vegetation. The flora of the island comprised 69 angiosperm species (50 indigenous species) of which 30% were endemic, far less than for the Ogasawara Islands as a whole (45%). However, several populations of endangered plants remain. To restore the native ecosystem on Nishi-jima, eradication of C. equisetifolia is important in addition to eradication of alien herbivorous mammals.     

Long-term ecological impacts of clear-fell logging on tree species diversity in a subtropical forest,southern Japan

Defining the spatial arrangement and length of the cutting cycle in a logged area is crucial for reconciling potential conflicts between timber yields and maintenance of ecosystem services in natural forests. In this study, we investigated long-term impacts of clear-fell logging on timber production and tree species diversity in a subtropical forest on the Ryukyu Islands, using an individual-based simulation model. We assumed six logging scenarios defined by combinations of forest type and regeneration processes, which acted as surrogates for spatial scales of clear-fell logging. These scenarios were simulated under cutting cycles ranging from 20 to 150 years. Short-cutting cycles resulted in dominance by the sprouting species Castanopsis sieboldii. The compositional shift was accelerated by the lack of seed dispersal from surrounding forest areas. The simulations demonstrated that a sustainable logging regime maintaining both yield and tree species diversity requires a cutting cycle longer than 50 years. The simulation results also suggest that the trade-off between the recovery of tree species diversity and timber production is favored more in stands surrounded by mature forest than in isolated stands or stands surrounded by immature forest. Ecological risk assessments based on model simulations provide an alternative to current forest management practices that rely on empirical knowledge.     

Removal of competitive native species combined with tree planting can accelerate the initial afforestation process:an experiment in an old field in Japan invaded by dwarf bamboo and kudzu

Restoring natural forests after field abandon-ment is a land management objective that fosters the re-covery of forest biodiversity. We performed seeding and transplanting of native tree species 40 yea...     

Photosynthesis, carbohydrate storage and survival of a native and an introduced tree species in relation to light and defoliation

Fraxinus uhdei (Wenz.) Lingelsh (tropical ash), a species introduced to Hawaii from Mexico, invades forests of the endemic tree Acacia koa A.Gray (koa). We examined physiological and morphological characteristics of koa and tropical ash to explore possible mechanisms that may facilitate invasion of koa forests by tropical ash. Seedlings of both species were grown in a greenhouse in three light treatments: 100% photosynthetic photon flux (PPF); 18% PPF; and 2% PPF inside the greenhouse. Light compensation point, maximum CO2 assimilation rate and dark respiration rate of seedlings differed significantly among light treatments, but were similar between species. A defoliation experiment indicated that tropical ash was better able to survive defoliation than koa, especially under high-light conditions. Tropical ash seedlings allocated more carbon (C) and nitrogen (N) to storage per unit PPF than koa seedlings. Total nonstructural carbohydrates were positively correlated with plant survival in both species. The patterns of C and N allocation associated with tropical ash seedlings favor their survival in high light, under intense herbivory and on sites where N availability is seasonal or highly variable. Variation in carbohydrate storage between koa and tropical ash greatly exceeded variation in photosynthetic performance at the leaf level.     

Effects of using certain tree species in forest regeneration on volume growth,timber yield,and carbon stock of boreal forests in Finland under different CMIP5 projections

We studied how the use of certain tree species in forest regeneration affected the volume growth, timber yield, and carbon stock of boreal forests in Finland under the current climate (1981–2010) and recent-generation global climate model (GCM) predictions (i.e., multi-model means and individual GCMs of CMIP5), using the representative concentration pathways RCP4.5 and RCP8.5 over the period 2010–2099. Forest ecosystem model simulations were conducted on upland national forest inventory plots throughout Finland. In a baseline management regime, forest regeneration was performed by planting the same tree species that was dominant before the final cut. In alternative management regimes, either Scots pine, Norway spruce, or silver birch were planted on medium-fertility sites. Other management actions over rotation were done as in a baseline management. Compared to baseline management, an increased planting of birch resulted in relative sense highest increase in the volume growth, timber yield, and carbon stock in forests in the south, especially under severe climate projections (e.g., multi-model mean RCP8.5, and GCMs such as HadGEM2-ES RCP8.5 and GFDL-CM3 RCP8.5). This situation was opposite for Norway spruce. In the north, the volume growth, timber yield, and carbon stock of forests increased the most under severe climate projections (e.g., multi-model mean RCP8.5 and CNRM-CM5 RCP8.5), regardless of tree species preference. The magnitude of the climate change impacts depended largely on the geographical region and the severity of the climate projection. Increasing the cultivation of birch and Scots pine, as opposed to Norway spruce, could be recommended for the south. In the north, all three species could be cultivated, regardless of the severity of climate change.     

A thirteen‐year study on the impact of a severe canker disease of Corymbia calophylla,a keystone tree in Mediterranean‐type forests

Worldwide, forests and woodlands have shown progressive declines in health as a result of global environmental changes in combination with local anthropogenic drivers. This study examined the incidence and progression of a canker disease of marri (Corymbia calophylla) caused by the endemic fungal pathogen Quambalaria coyrecup at three paired forest and anthropogenically disturbed sites in the southwest of Western Australia over 13 years. At the time of plot establishment in 2001, cankers were present on trees at all six sites with 22.7% of the assessed trees cankered. By 2014, cankers had led to the death of 6.7% of the trees, and an additional 10.0% of the trees developed cankers during this time. A further 2.3% of trees died due to causes other than canker, resulting in a final figure of 65.0% of trees remaining alive and free of cankers for the duration of the survey period. Canker incidence was significantly greater on trees present at anthropogenically disturbed sites (along roadsides and in paddocks) than forest trees (35.3% increasing to 50.7%, 10.0% increasing to 14.7%, respectively). Trunk diameter at breast height, tree height and crown ratings were not correlated with canker presence. This long‐term study provides evidence of the increasing severity of this canker pathogen and the impact it is having on the survival of marri.     

Biomass production and potential ethanol yields of shrub willow hybrids and native willow accessions after a single 3-year harvest cycle on marginal lands in central Minnesota,USA

Short rotation woody crops are being developed as a sustainable source of biomass for the production of bioenergy, biofuels, and bioproducts. With the potential increase in demand of biomass for energy in the future, there is a need to diversify and expand its source. In the present study, we evaluated the growth performance, biomass production, energy content, and potential ethanol yields of shrub willow hybrids and native willow accessions. Shrub willow hybrids cuttings were obtained from the State University of New York through its controlled breeding program while cuttings used for native willow accessions were collected naturally. At the end of one rotation, consisting of three growing seasons, we found that shrub willow hybrids outperformed native willow accession species (P = 0.0004), with an average survival rate of 80 and 39 %, respectively. Biomass production of shrub willow hybrids and native willow accessions ranged from 7.42 to 16.0 and from 0.69 to 1.83 Mg ha^?1 oven dry weight, respectively. The chemical composition (mass fraction % on dry basis) of willow hybrids and native willow accessions generally contained 39 % cellulose, 19 % hemicellulose, 25 % lignin, 1.4 % ash content, 17,500–18,500 kJ kg wood^?1, and 385 L Mg^?1 of theoretical ethanol yield. Energy content and potential ethanol yields on a dry weight basis did not vary between shrub willow hybrids and native willow accessions; however, the amount of biomass produced per unit land area is known to influence potential ethanol yields. Thus, we suggest that shrub willow hybrids offer promising potential as an alternative source of biomass. The results of our study suggest that four of the shrub willow hybrids evaluated have a greater potential for use as biomass energy crops on marginal lands in central Minnesota than the native willow accessions; hence, there is a need to test their potential at a larger scale.