Drivers of inter-year variability of plant production and decomposers across contrasting island ecosystems

Despite the likely importance of inter-year dynamics of plant production and consumer biota for driving community- and ecosystem-level processes, very few studies have explored how and why these dynamics vary across contrasting ecosystems. We utilized a well characterized system of 30 lake islands in the boreal forest zone of northern Sweden across which soil fertility and productivity vary considerably, with larger islands being more fertile and productive than smaller ones. In this system we assessed the inter-year dynamics of several measures of plant production and the soil microbial community (primary consumers in the decomposer food web) for each of 9 years, and soil microfaunal groups (secondary and tertiary consumers) for each of 6 of those years. We found that for measures of plant production and each of the three consumer trophic levels, inter-year dynamics were strongly affected by island size. Further, many variables were strongly affected by island size (and thus bottom-up regulation by soil fertility and resources) for some years but none in others, most likely due to inter-year variation in climatic conditions. For each of the plant and microbial variables for which we had 9 years of data, we also determined the inter-year coefficient of variation (CV), an inverse measure of stability. We found that CVs of some measures of plant productivity were greater on large islands while those of other measures were greater on smaller islands; CVs of microbial variables were unresponsive to island7 size. We also found that the effects of island size on the temporal dynamics of some variables were related to inter-year variability of macroclimatic variables. As such, our results show that the inter year dynamics of both plant productivity and decomposer biota across each of three trophic levels, as well as the inter-year stability of plant productivity, differs greatly across contrasting ecosystems, with potentially important but largely overlooked implications for community and ecosystem processes

Utvalgte år i en årringkurve fra Suldal, Rogaland, korrelert med historiske klimadata.

A comparison was made between climate information obtained from tree rings of Pinus sylvestris L. from Suldal, SW Norway, and historical documents. In six occasions during the time span of AD 1700-1900 indices showed remarkable high deviations from the mean. In 1709-10, 1740-42, 1784 and 1863-1865, the tree rings were very narrow indicating poor growth conditions and in 1729-32 and 1797-99 they were wide, indicating good growth conditions. The correlation of the tree ring data with historical climate proxy data exhibited that when the collected historical data were subjected to thorough source criticism and then evaluated, they were in good accordance with the results from the tree ring curve. A control test on the periods 1771-1773 and 1812 confirmed this result, this indicating the usefulness of the correlation process

Drivers of inter-year variability of plant production and decomposers across contrasting island ecosystems

Despite the likely importance of inter-year dynamics of plant production and consumer biota for driving community- and ecosystem-level processes, very few studies have explored how and why these dynamics vary across contrasting ecosystems. We utilized a well-characterized system of 30 lake islands in the boreal forest zone of northern Sweden across which soil fertility and productivity vary considerably, with larger islands being more fertile and productive than smaller ones. In this system we assessed the inter-year dynamics of several measures of plant production and the soil microbial community (primary consumers in the decomposer food web) for each of nine years, and soil microfaunal groups (secondary and tertiary consumers) for each of six of those years. We found that, for measures of plant production and each of the three consumer trophic levels, inter-year dynamics were strongly affected by island size. Further, many variables were strongly affected by island size (and thus bottom-up regulation by soil fertility and resources) in some years, but not in other years, most likely due to inter-year variation in climatic conditions. For each of the plant and microbial variables for which we had nine years of data, we also determined the inter-year coefficient of variation (CV), an inverse measure of stability. We found that CVs of some measures of plant productivity were greater on large islands, whereas those of other measures were greater on smaller islands; CVs of microbial variables were unresponsive to island size. We also found that the effects of island size on the temporal dynamics of some variables were related to inter-year variability of macroclimatic variables. As such, our results show that the inter-year dynamics of both plant productivity and decomposer biota across each of three trophic levels, as well as the inter-year stability of plant productivity, differ greatly across contrasting ecosystems, with potentially important but largely overlooked implications for community and ecosystem processes

Appendix E. Soil microfaunal density data measured over six years in relation to island size.

Soil microfaunal density data measured over six years in relation to island size

Appendix F. Strength of relationship between island size and plant variables as affected by climatic variables.

Strength of relationship between island size and plant variables as affected by climatic variables

Appendix C. Soil microbial variables measured over nine years in relation to island size.

Soil microbial variables measured over nine years in relation to island size

Appendix B. Understory shrub biomass and production data measured over nine years in relation to island size.

Understory shrub biomass and production data measured over nine years in relation to island size

Appendix A. Tree litterfall in litter trays and tree radial growth data over nine years in relation to island size.

Tree litterfall in litter trays and tree radial growth data over nine years in relation to island size