Publications

Several hypotheses have been advanced to explain why masting (i.e. episodic. synchronized seed production) occurs in coniferous trees, as well as aspects of its evolution and importance for reproductive success. However, the nutritional effects of the large number of seeds that simultaneously fall to the ground, die and decompose in the soil during mast years have not previously been considered. Norway spruce (Picea abies) has a typical masting behavior and may add 5-10 kg N ha -1 yr -1 through seed fall in mast years in the boreal zone of Northern Sweden. We performed a field experiment in a strongly nitrogen-limited forest in N Sweden where pre-killed Norway spruce seeds were added to plots at an amount comparable to 7 kg N ha -1 yr - '. Seeds were added to an understory vegetation dominated by ericaceous shrubs and two different bottom layer components, Pleurozium schreberi and Cladina spp. Seedlings of Scots pine (Pinus sylvestris) were then planted in the same plots to evaluate growth response to and availability of nutrients from the dead Norway spruce seeds that were added to the two plant communities. Seedlings of Scots pine grew larger and acquired more nitrogen when dead seeds were added in plots dominated by Cladina spp. However, in plots dominated by P. schreberi, uptake of nutrients from dead seeds by Scots pine was blocked by P. schreberi except in treatments where the P. schreberi moss carpet was experimentally disturbed. Analysis of nutrients in field- and bottom-layer vegetation showed that P. schreberi acquired a large proportion (80%) of N released from dead seeds while the ericaceous dwarf shrub Vaccinium vitis-idaea and the Cladina spp. macrolichens gained much less nitrogen. The rates of nutrient release and decomposition of dead Norway spruce seeds were compared with Norway spruce needle litter in a litter bag experiment. Dead Norway spruce seeds decomposed at much higher rates than needle litter, and 65-75% of the seed nitrogen content was lost during the first growing season. We hypothesize that, if germination conditions (type of bottom-layer vegetation) allow tree seedlings to emerge, their survival, growth and nutrition may be enhanced by the nutrient flush from dead seeds and germlings in seed mast years and that this may aid in establishment of a new seedling cohort. Nutrient pulses from dead seeds during mast years may help to explain the strongly pulsed natural tree regeneration patterns that have been found in mixed late successional coniferous forests.

This paper reports results of the first year of soil biochemical and microbiological monitoring programme carried out to establish "normal" ranges of values for these soil attributes. Study was conducted on 24 farm sites on yellow-brown loam soils around the Waikato area. Twelve dairy farms and a similar number of sheep-beef farms were selected on the basis of high productivity. Soil samples (0-75 mm depth) were collected at 3- monthly intervals and the following measurements were carried out: soil microbial- C, N, S and P, CO2 evolution, substrate-induced respiration, anaerobic mineralisable N, dehydrogenase activity, fluorescein diacetate (FDA) hydrolysis, amounts of soluble-C and N, extractable NO3 and NH4, soil pH, Olsen P, KH2PO4 extractable SO4-S and organic S, and hydraulic conductivity. Climatic data, records of fertiliser and other additives and productivity were also collected to interpret the variations in these properties. Variables measured from the Horotiu and Tirau silt loam soils showed considerable similarity, however, Otorohanga soils had significantly higher amounts of total and extractable soil C and N. As expected, being a higher input system, soil nutrient status (P, SO4, NO3 and NH4) on dairy farms was generally higher than the sheep-beef farms. The most significant difference was for the Olsen P values, which were about 60-70% higher under dairying. Soil pH on dairy farms was significantly higher than sheep- beef farms. However, total C and N values were significantly higher under sheep-beef than dairy farms. Similarly, the amounts of mineralisable N in all seasons were much higher for the sheep-beef than dairy farms. Apart from total microbial S, none of the other microbial biomass measurements showed any significant effect of season or difference among the soil types. This lack of seasonal effect on microbial biomass can be attributed to the unusual mild seasonal variation during the study. For the various microbial biomass measurements, sheep-beef farms generally had significantly higher values than dairy farms. Microbial C, N, SO4 and total S values were significantly higher for sheep-beef than dairying. The ratios between soil C, N to microbial C, N and microbial C:N showed no consistent pattern between the farm types. Keywords: C and N, enzyme activity, microbial biomass, seasonal variations, soil fertility

Two decades ago the first Earth Summit raised the question of how biological diversity loss alters ecosystem functioning and affects humanity; this Review looks at the progress made towards answering this question. The 1992 Earth Summit in Rio de Janeiro, Brazil, stimulated an explosion of research into how biodiversity loss influences the processes that underpin the goods and services that ecosystems provide to humanity. That research has established that biodiversity is crucial for ecosystem function, but just how the relationship works has been a source of controversy. This Review considers recent advances that are beginning to explain how biological diversity influences the functioning of ecosystems, and the provision of specific ecosystem services. The authors conclude that, together with management strategies such as payment for ecosystem services, the next generation of biodiversity science has the potential to bring the modern era of biodiversity loss to an end and to maintain a satisfactory level of ecosystem services. The most unique feature of Earth is the existence of life, and the most extraordinary feature of life is its diversity. Approximately 9 million types of plants, animals, protists and fungi inhabit the Earth. So, too, do 7 billion people. Two decades ago, at the first Earth Summit, the vast majority of the world’s nations declared that human actions were dismantling the Earth’s ecosystems, eliminating genes, species and biological traits at an alarming rate. This observation led to the question of how such loss of biological diversity will alter the functioning of ecosystems and their ability to provide society with the goods and services needed to prosper.

Predicted changes in soil water availability regimes with climate and land-use change will impact the community of functionally important soil organisms, s

No abstract is provided for this article.

Summary Angiosperm trees often dominate forests growing in resource‐rich habitats, whereas conifers are generally restricted to less productive habitats. It has been suggested that conifers may be displaced by angiosperms except where competition is less intense, because conifer seedlings are inherently slow growing, and are outpaced by faster‐growing angiosperm species. Here we investigate whether competition with ferns and deeply shading trees also contributes to a failure of conifers to regenerate in resource‐rich habitats. We examined how changes in soil nutrient availability and drainage affected vegetation along the retrogressive stages of a soil chronosequence in southern New Zealand. Vegetation composition shifted from angiosperm‐tree dominance on ‘recent’ alluvial terraces (< 24 ky), via coniferous‐tree dominance on older marine terraces (79–121 ky), to coniferous‐shrub dominance on the oldest marine terraces (291 ky). Soil drainage deteriorated along the sequence, and N : P leaves and N : P soil indicate increasing P‐limitation. Conifer species appear to be adapted to persistence on infertile and poorly drained soils. The floor of the relatively fertile alluvial forests was deeply shaded (∼1% light transmission) by dense groves of tree‐ferns and ground‐ferns, and by large‐leaved subcanopy trees. Few seedlings of any type were found on the forest floor, even in tree‐fall gaps, and establishment was restricted to rotting logs and tree‐fern trunks. Angiosperms were particularly successful at colonizing these raised surfaces. Less shade was cast by the conifer‐dominated forests on infertile marine terraces (∼5% light transmission), which lacked tall ferns. There were many opportunities for conifer establishment, with high seedling densities recorded on the forest floor and on logs. By contrast, angiosperm seedlings were mainly restricted to logs. Our results suggest that several mechanisms act in concert to reduce regeneration opportunities for conifers in productive habitats. In particular, we suggest that tall ferns and deep shade are responsible for a restriction of regeneration opportunities in relatively productive forests in New Zealand, diminishing the opportunities for conifers to escape the competitive effects of fast‐growing angiosperms. Thus ‘crocodiles’ may alter the outcome of the race between ‘hares’ and ‘tortoises’.

As the most abundant animals on earth, nematodes are a dominant component of the soil community. They play critical roles in regulating biogeochemical cycles and vegetation dynamics within and across landscapes and are an indicator of soil biological activity. Here, we present a comprehensive global dataset of soil nematode abundance and functional group composition. This dataset includes 6,825 georeferenced soil samples from all continents and biomes. For geospatial mapping purposes these samples are aggregated into 1,933 unique 1-km pixels, each of which is linked to 73 global environmental covariate data layers. Altogether, this dataset can help to gain insight into the spatial distribution patterns of soil nematode abundance and community composition, and the environmental drivers shaping these patterns.

This paper studies the survivability of peatland-related programs in Indonesia. Despite an increase in the global and national programs for peatland restoration, many of these programs fail to survive in the long-term. To understand this low survivability, this paper examines how peatland-related programs re-arrange the relationship between the local community and peatland across time and how the new actor-network contributes to the survivability of peatland programs. We develop a multi-level actor-network framework that combines the multi-level perspective from transition studies to capture the stability of actors' relationships and power from actor-network theory to investigate how activities mobilise human and non-human actors to comply with a specific program. Our research shows that non-human actors such as peat, paddy, Acacia, and fire shape peatland-related programs by resisting non-suitable crops, by re-shaping the program, by mobilizing human actors, and by creating pressure to the existing regime. We highlight that the survivability of peatland restoration programs is strongly influenced by how they are adjusted to the materiality of these non-human actors. Given the importance of peatland restoration programs, our study provides an approach in which human and non-human come together to generate plural voices to ensure the survival of peatland restoration programs.

• Recent studies have revealed that nitrogen fixation by cyanobacteria living in association with feather mosses is a major input of nitrogen to boreal forests. We characterized the community composition and diversity of cyanobacterial nifH phylotypes associated with each of two feather moss species (Pleurozium schreberi and Hylocomium splendens) on each of 30 lake islands varying in ecosystem properties in northern Sweden. • Nitrogen fixation was measured using acetylene reduction, and nifH sequences were amplified using general and cyanobacterial selective primers, separated and analyzed using density gradient gel electrophoresis (DGGE) or cloning, and further sequenced for phylogenetic analyses. • Analyses of DGGE fingerprinting patterns revealed two host-specific clusters (one for each moss species), and sequence analysis showed five clusters of nifH phylotypes originating from heterocystous cyanobacteria. For H. splendens only, N2 fixation was related to both nifH composition and diversity among islands. • We demonstrated that the cyanobacterial communities associated with feather mosses show a high degree of host specificity. However, phylotype composition and diversity, and nitrogen fixation, did not differ among groups of islands that varied greatly in their availability of resources. These results suggest that moss species identity, but not extrinsic environmental conditions, serves as the primary determinant of nitrogen-fixing cyanobacterial communities that inhabit mosses.

Boreal forests store 30% of the world's terrestrial carbon (C). Consequently, climate change mediated alterations in the boreal forest fire regime can have a significant impact on the global C budget. Here we synthesize the effects of forest fires on the stocks and recovery rates of C in boreal forests using 368 plots from 16 long‐term (≥100 year) fire chronosequences distributed throughout the boreal zone. Forest fires led to a decrease in total C stocks (excluding mineral soil) by an average of 60% (range from <10% to >80%), which was primarily a result of C stock declines in the living trees and soil organic layer. Total C stocks increased with time since fire largely following a sigmoidal shape Gompertz function, with an average asymptote of 8.1 kg C m −2 . Total C stocks accumulated at a rate of 2–60 g m −2 yr −1 during the first 100 years. Potential evapotranspiration (PET) was identified as a significant driver of C stocks and their post‐fire recovery, likely because it integrates temperature, radiation, and the length of the growing season. If the fire return interval shortens to ≤100 years in the future, our findings indicate that many boreal forests will be prevented from reaching their full C storage potential. However, our results also suggest that climate warming‐induced increases in PET may speed up the post‐fire recovery of C stocks.