The seed germination of berry-producing ericaceous shrubs in relation to dispersal by hare

Hare pellets contribute greatly to the seed dispersal of a berry-producing shrub, Gaultheria miqueliana Takeda (Ericaceae), on Mount Koma, northern Japan. Numerous seeds of G. miqueliana germinated from the hare pellets (122.2 ± 7.3/pellet, mean ± SE), confirming that the pellets potentially had a role in the seed dispersal. Lab-experiments confirmed that the seeds of G. miqueliana needed light for full germination without cold stratification. Besides, hare pellets were collected from a post-mined peatland in Sarobetsu Mire, northern Japan, where G. miqueliana was not distributed but two berry-producing ericaceous species were distributed. No seeds germinated on the pellets collected from the Mire. These results suggested that the tight relationships between hare and berry-producing shrubs were species-specific

Seed survival for three decades under thick tephra

Seed longevity in situ is a prerequisite for understanding the life histories and community dynamics of species, although long-term longevity under thick tephra has not been documented because of a lack of opportunity and/or awareness. The seed bank for this study was estimated by both germination and flotation tests. Seeds of 17 species have survived with high density, having been buried under thick tephra for 30 years, since the 1977-1978 eruptions on Mount Usu, Hokkaido Island, northern Japan. The total seed density was > 1000/m2. Rumex obtusifolius was the most common seed-bank species for 30 years, but decreased in density between 20 and 30 years. More seeds of Hypericum erectum occurred in deeper soil. The total seed density decreased gradually for 30 years, but H. erectum and Juncus effusus did not decline. Native seeds tended to be viable longer than exotic seeds. These results suggest that small, native seeds tend to survive longer with deep burial, while the more numerous weedy, exotic seeds located at the soil surface declined faster. The seed bank provides long-term monitoring of seed survival under natural conditions, and could be used to detect genetic changes

Remote sensing of forest diversities : the effect of image resolution and spectral plot extent

Detecting field diversities via remote sensing is becoming important to monitor vegetation dynamics at large scale. The characteristics of the remotely sensed image, depending on the study organism and habitat, affect the efficiency of measuring alpha-and beta-diversities. Therefore, we examined the impact of image resolutions and spectral plot extents on the accuracy of estimating forest alpha-diversities and compositional variances on the active volcano Mount Usu, northern Japan. Low- (3.2 m) and high-resolution (0.8 m) IKONOS multispectral images were used to create spectral indicators from pixels covering the field plots (narrow extent) and from pixels including neighbouring area (wide extent). Six forest diversity indices were obtained for canopy and for canopy-herb layer (total diversity): species richness (S), Shannon (H'), evenness (J'), Gini-Simpson (D), and true diversity of order 1 (N (1) = expH') and order 2 (N (2) = 1/D). Changes in species composition were assessed by dissimilarity matrices. The spectral diversity indicators were calculated from the combination of image resolutions and spectral plot extents, and then compared with field diversities. The low-resolution-narrow extent based spectral indicators showed the highest correlations with canopy and total diversities. The best spectral indicators were derived from the scores of the first axis of principal component analysis and from the near infrared band, reaching high correlations with both canopy and total field diversity indices. Of the six field diversities, J' showed the highest correlations with single spectral indicators, and N (1, 2) showed the highest correlations with pairs of spectral indicators. The correlations between spectral and field dissimilarities were lower than the correlations between alpha-diversities and spectral indicators, and were unaffected by the resolution and extent. In conclusion, the best spectral indicators were obtained from the low-resolution-narrow extent combination, and the indicators estimated canopy and total field diversity indices of temperate forests equally

Plant responses to nitrogen fertilization differ between post-mined and original peatlands

Nitrogen addition experiments were conducted in three plant communities in a post-mined peatland and on the surrounding original Sphagnum bog in northern Japan to compare the effects of nitrogenous fertilization among the plant communities. Gradients of added nitrogen were prepared by adding nitrogen to 1 m x 1 m plots at rates of 0-36 g/m(2)/yr. These different levels of nitrogen addition were applied to four sites representing a vegetation development chronosequence: bare ground (BG), a Rhynchospora alba sedgeland (RA), a Moliniopsis japonica grassland (MJ) and the original Sphagnum bog (SS). Vegetation was monitored in each plot for three years, and the groundwater level and nitrogen concentration in peat-pore water were monitored in each plot. The nitrogen concentration in peat-pore water increased with increasing nitrogen addition on BG, but was constantly low at the vegetated sites, suggesting the occurrence of nutrient uptake by plants. Species richness decreased as a result of nitrogen addition at the SS site, where plant cover was high. The aboveground biomass of the two common grasses M. japonica and Phragmites communis was not influenced by nitrogen addition in the post-mined peatland. Grasses and sedges, which produce large underground organs, showed increased biomass as a result of nitrogen addition in the SS plot whereas Sphagnum declined. Additionally, forbs declined in the SS plot with increasing nitrogen, most likely due to competition with the increased populations of grasses. Therefore, nitrogen enrichment can promote the dominance grasses, leading to a decrease in mosses and forbs

Hares promote seed dispersal and seedling establishment after volcanic eruptions

Although seed dispersal through animal guts (endozoochory) is a process that determines plant establishment, the behaviour of carriers mean that the seeds are not always dispersed to suitable habitats for germination. The germinable seeds of Gaultheria miqueliana were stored in the pellets of a hare (Lepus timidus ainu) on Mount Koma in northern Japan. To clarify the roles of hares in seed dispersal and germination, field censuses and laboratory experiments were conducted. The field observations were conducted on pellets and seeds in four habitats (bare ground, G. miqueliana shrub patch, Salix reinii patch, and Larix kaempferi understory), and the laboratory experiments were conducted on seed germination with different light, water potential and cold stratification treatments. The laboratory experiments confirmed that seed germination began a few weeks after the sowing of seeds, independent of cold stratification, when light was sufficient and the water potential was low. The seeds did not germinate at high water potential. The pellets were gradually degraded in situ. More seeds germinated from crushed than from intact pellets. Therefore, over the long term, seeds germinated when exposed to light due to the degradation of pellets. The pellets were proportionally dispersed among the four studied habitats. More seeds sown in the field germinated more in shaded habitats, such as in the Gaultheria patch and the Larix understory, and seeds did not germinate on bare ground, where drought often occurred. Thus, the hares had two roles in the dispersal and germination of seeds: (1) the expansion of G. miqueliana populations through seed dispersal to various habitats and (2) the facilitation of delayed seed germination to avoid risks of hazards such as drought. The relationships between small mammals represented by the hare and the shrubs that produce berries are likely to be more mutually evolved than was previously thought

Occurrence patterns of facilitation by shade along a water gradient are mediated by species traits

In disturbed habitats, shade often has facilitative effects on plants by ameliorating water and thermal stresses. Facilitation by shade tends to increase as water availability decreases. At the same time, several studies have suggested that facilitation by shade is not affected by water status or collapses under extremely dry conditions. We hypothesized that traits of beneficiary plants, specifically, the flexibility in the allocation of biomass between shoots and roots, would mediate variation in the relationship between facilitation by shade and water status. To test this hypothesis, we examined the responses of two bog species to shade under various water conditions in a post-mined peatland. The seeds of Rhynchospora alba and Moliniopsis japonica were sown under three water levels (dry: 53% peat water content, wet: 77%, and control: 71%) x two shading levels (50% shaded and unshaded). The survival, biomass, and biomass allocation between the shoots and roots of the two species were monitored for two years. Shade increased the survival and biomass of both species. However, the facilitation of R. alba by shade was independent of water level, whereas the strength of the facilitative effects on M. japonica increased as water content decreased. R. alba preferentially allocated biomass to roots under dry conditions and was highly drought tolerant. M. japonica did not alter the allocation of its biomass in response to either shade or water level and was drought intolerant. Our results suggest that flexibility in biomass allocation of beneficiary plants mediates occurrence patterns of facilitation by shade along a water gradient. The facilitation of species with inflexible biomass allocation by shade through the amelioration of water stress increases as water availability decreases, whereas the facilitation of species with flexible biomass allocation is independent of water status. Such species-specific facilitation would promote the coexistence of diverse species in a community. (C) 2014 Elsevier Masson SAS. All rights reserved

Role of Salix reinii patches in spatio-temporal patterns of cohabitants on a Japanese volcano

Shrub patches often support the colonizers particularly under stressful and/or disturbed environments. The intensities of stresses and disturbances on mountains are often related to an elevation gradient and are decreased by shrub patches (canopy and litter). We aim to clarify these relationships by using shrub patches at different elevations on a volcano. We monitored all shoots in plots established inside and outside of patches of Salix reinii (Salicaceae) and their related environments, such as temperature, light, moisture and chemistry, at three elevations on Mount Koma (1131 m a.s.l.), northern Japan, from early spring in 2005 to summer in 2006. The patch structures were evaluated by area, branch density and litter thickness. The structures of shrub patches did not differ among the elevations. The patches increased the diversity of rare species, by an overall increase in plant species richness. The moisture, nitrogen and phosphate contents in the patches were higher than outside of patches. The effects of shrub patches on the cohabitants were overall positive, although the effects were negative on seedling abundance, shoot survival and flowering. These results suggest that the growth patterns of shrub patches determine the plant community structures and facilitate plant diversity

Effects of Water Level via Controlling Water Chemistry on Revegetation Patterns After Peat Mining

The recovery of plant communities is related to various environmental factors, in particular, waterlevel and chemistry, after peat mining. The changes over time after peat-mining were annually monitored from 2002 to 2007 in Sarobetsu peatland mined during 1970 and 2003, northern Japan, by using permanent plots setting up in various ages after mining. Rhynchospora alba was the earliest colonizer in the post-mined peatland, and three grasses followed. The recovery was slow when waterlevel was low, while Sphagnum papillosum, being predominant in pre-mined peatland, established well in post-mined sites with high waterlevel of which values were equivalent to post-mined site. Water chemistry was variable according to the effect of waterlevel in the post-mined peatland, while they were relatively stable in pre-mined peatland. Therefore, with large scale, merged with post-and pre-mined peatlands, water chemistry became the first determinants manipulated by waterlevel. In conclusion, high waterlevel that decreases nutrients in groundwater is a prerequisite to promote Sphagnum recovery in a post-mined peatland. Also, low pH was related to nutrient uptake by vascular plants and dilution by groundwater, and was advantageous for Sphagnum establishment. Re-establishment of vascular plants may promote the stabilization of water chemistries and facilitate revegetation towards the original Sphagnum peatland.Published online: 18 Ocober 201

Habitat Differentiation Between Drosera anglica and D. rotundifolia in a Post-Mined Peatland, Northern Japan

The preservation of endangered species requires clarifying habitat preferences through survival, growth and competitive ability. The determinants of habitat differentiation between the endangered species, Drosera anglica, and a widespread congener, D. rotundifolia, were compared. The effects of water level, Sphagnum mats and overstory vascular plants on Drosera distribution, recruitment and survival were monitored at a previously mined Sphagnum peatland. Seedling transplant experiments were conducted using different water levels. Seed-sowing experiments were conducted using different light intensities in three habitat-types: bare ground, Sphagnum mat and waterlogged surface. Distributions of D. anglica and D. rotundifolia were determined using survival at the seedling stage. D. anglica seedling recruitment and survival occurred more at lower water levels and/or lower plant cover, while D. rotundifolia seedlings established independent of these factors. In the greenhouse the seedlings of both species survived better at lower water levels but grew more slowly. D. anglica seedlings reduced their growth under shade more than D. rotundifolia. D. anglica showed low competitive light and nutrient ability on Sphagnum mats. Therefore, D. anglica was pushed to areas of high water levels where few competitors could establish. The habitat differentiation between D. anglica and D. rotundifolia originated from the interactions with Sphagnum mats