Effects of overstory tree density, site preparation and ground vegetation on natural Scots pine seedling emergence and survival in northern boreal pine forests

Natural regeneration is commonly used forest regeneration method in Northern Finland. It is not known however, what would be the optimal overstory density and ground vegetation composition for seedling emergence and survival, and if site preparation is needed to accompany overstory density manipulation. We studied the effects of overstory density (unthinned control and thinning to 50, 150 and 250 trees ha-1) and ground vegetation removal (mechanical site preparation with disc trenching) on the number of naturally germinated pine seedlings and survival of individual seedlings during 8-11 years. Bare mineral soil was a superior seedbed compared to intact vegetation cover, even though also mortality rate was high on mineral soil. Greater cover of lingonberry, crowberry and slash had a negative effect on seedling number. Seedling mortality was initially high (60% died during the first two years) but decreased throughout the first five years. The mineral soil in the elevated part of disc trencher track showed twice the survival rate in the bottom part of the track. High coverage of small haired mosses was associated with poorer seedling survival. An overstory density of 50-150 trees ha-1 with site preparation seems to be an efficient treatment to promote regeneration under these circumstances.

Native bacteria and cyanobacteria consortia improve seedling emergence and establishment in dryland restoration

<p>Seed-based ecosystem restoration has huge potential to restore degraded lands but currently less than 10 % of directly sown seeds successfully establish in drylands. Soil microbial communities are important for improving plant establishment in degraded land. However, current methods such as soil translocation can potentially disturb the donor site. In this study, we investigated a novel non-destructive method for improving seedling growth of native plants used in restoration through seed-soil-microbial pelleting. We assessed seedling emergence and survival of <em>Triodia epactia</em> and <em>Acacia inaequilatera</em> seeds inoculated with whole soil bacteria and cyanobacteria consortia retrieved and isolated from a pristine ecosystem. A field experiment was set-up in a 35m x 40m purpose-built rain exclusion shelter that contained reconstructed soil profiles typically encountered in mine rehabilitation programs of Australia’s arid north-west. We hypothesized that inoculated seed-soil pellets would improve seedling emergence and survival of these species. After three weeks of planting, seedling emergence in microbially inoculated <em>Acacia</em> <em>inaequilatera</em> and <em>Triodia epactia</em> were 48% and 55% higher than non-inoculated seeds in bacteria and cyanobacteria, respectively. We also tested whether the use of cyanobacteria consortia as inocula promoted higher seedling emergence over whole soil bacteria. We found that there was no significant difference in seedling emergence between the microbial taxa. We show that, improving the diversity of soil microorganisms improves seedling emergence and the seed-soil pellet method used is viable to improve seed-based restoration outcomes.</p><p><strong>Key words</strong>: Seed-based restoration, microbial community, cyanobacteria, bacteria community, seedling emergence.</p>

Regeneration responses to water and temperature stress drive recruitment success in hemiepiphytic fig species

Mechanisms for surviving water and temperature stress in epiphytes are essential adaptations for successful regeneration in forest canopies. Hemiepiphytes start their life cycle as epiphytes, eventually establishing areal root connections to the ground. This strategy allows for greater light capture, while benefitting from minimized risk of fire, flooding, and damage by terrestrial herbivores, but exposes the vulnerable seedling stage to heat and drought stress. However, the response to temperature and water stress during early regeneration in hemiepiphytes is not known. In this study, we tested the effect of temperature (15/5°C, 25/15°C, 35/25°C; day/night diurnal variation) and water availability, as substrate moisture (0.00 MPa, −0.20 MPa, −0.35 MPa) and water vapor (18.5% to 99.5% relative humidity), on seed germination, seedling emergence, and survival in six hemiepiphytic and nine non-hemiepiphytic Ficus species. Under high temperature conditions (35/25°C), hemiepiphytes had higher gemination and seedling survival, achieved peak germination slower and extended germination. Greater water stress (−0.35 MPa) in the growth substrate resulted in higher germination of non-hemiepiphytes; hemiepiphytes, in contrast, took a shorter time to complete germination, but had higher seedling emergence and survival. Hemiepiphytes germinated at 99.5% relative humidity more readily compared to non-hemiepiphytes. These findings provide the first comprehensive evidence that hemiepiphytic Ficus species are better adapted to drier and warmer conditions during the critical transition from seed to seedling. Through greater flexibility in achieving peak germination and duration of regeneration activity, hemiepiphytes modulate their recruitment process to be more resilient under abiotic stressors. This may allow them to be more successful in regenerating in forest canopies under ambient conditions that are transient. These results support previous work showing greater drought tolerance of hemiepiphytic Ficus species in larger size classes, and extend this finding to show that physiological adaptations for drought and heat tolerance start from the early seedling emergence stage.

Seed-bank and seedling dynamics in Hyparrhenia hirta are influenced by herbicide application and mowing management

Hyparrhenia hirta (L.) Stapf (Coolatai grass) is a summer-active, C4 perennial tussock grass, native to southern Africa and the Mediterranean region, which has invaded areas of native flora in Australia in recent decades. Understanding its seed and seedling dynamics and how various management treatments (e.g. mowing, herbicide and no management) affect these may assist in identifying the conditions and management strategies required to limit its invasion. The population dynamics of H. hirta have not been comprehensively studied previously. A 2-year field experiment (December 2005–December 2007) was conducted to determine the seed-bank size, pattern of seedling emergence and survival of H. hirta seedlings at three sites in northern New South Wales, Australia, under three treatments: unmanaged (control), mowing and herbicide treatments. The density of H. hirta seeds in the soil at each experimental site under different treatments was measured in December 2005 at the start of the experiment, in December 2006 before the application of the second round of treatments and again at the end of the experiment in December 2007. Hyparrhenia hirta seedlings were assessed at monthly intervals in permanent quadrats (0.5 × 0.5 m) to determine seedling emergence and survival. Seedling emergence occurred on many occasions during the 2-year period of the experiment in each treatment and at all sites but the main seedling flushes were observed from mid summer to early autumn. In 2007, at all sites, seedling emergence declined by more than 90% on the mowing and herbicide treatments compared with the control treatment. Seedling survival was greater in the mowing and herbicide treatments than in the control treatment. The seedling cohorts emerging in winter had a lower survival. This study showed that H. hirta infestations have a large viable seed-bank (~3000 m–2), dependent on the level of infestation and climatic conditions, but that the seed-bank declines rapidly when seed addition is prevented. Some form of direct control of established H. hirta plants in combination with providing appropriate grazing management to encourage competition between grasses will assist in the control of H. hirta.