The ecological forecast horizon, and examples of its uses and determinants

Forecasts of ecological dynamics in changing environments are increasingly important, and are available for a plethora of variables, such as species abundance and distribution, community structure and ecosystem processes. There is, however, a general absence of knowledge about how far into the future, or other dimensions (space, temperature, phylogenetic distance), useful ecological forecasts can be made, and about how features of ecological systems relate to these distances. The ecological forecast horizon is the dimensional distance for which useful forecasts can be made. Five case studies illustrate the influence of various sources of uncertainty (e.g. parameter uncertainty, environmental variation, demographic stochasticity and evolution), level of ecological organisation (e.g. population or community), and organismal properties (e.g. body size or number of trophic links) on temporal, spatial and phylogenetic forecast horizons. Insights from these case studies demonstrate that the ecological forecast horizon is a flexible and powerful tool for researching and communicating ecological predictability. It also has potential for motivating and guiding agenda setting for ecological forecasting research and development

Conclusion: applying South East Asia Rainforest Research Programme science to land-use management policy and practice in a changing landscape and climate

The context and challenges relating to the remaining tropical rainforest are briefly reviewed and the roles which science can play in addressing questions are outlined. Key messages which articles in the special issue, mainly based on projects of the Royal Society South East Asia Rainforest Research Programme (SEARRP), have raised of relevance to policies on land use, land management and REDD+ are then considered. Results from the atmospheric science and hydrology papers, and some of the ecological ones, demonstrate the very high ecosystem service values of rainforest (compared with oil palm) in maintaining high biodiversity, good local air quality, reducing greenhouse emissions, and reducing landslide, flooding and sedimentation consequences of climate change—and hence provide science to underpin the protection of remaining forest, even if degraded and fragmented. Another group of articles test ways of restoring forest quality (in terms of biodiversity and carbon value) or maintaining as high biodiversity and ecological functioning levels as possible via intelligent design of forest zones and fragments within oil palm landscapes. Finally, factors that have helped to enhance the policy relevance of SEARRP projects and dissemination of their results to decision-makers are outlined

Effects of Dominance and Diversity on Productivity along Ellenberg's Experimental Water Table Gradients

Heinz Ellenberg's historically important work on changes in the abundances of a community of grass species growing along experimental gradients of water table depth has played an important role in helping to identify the hydrological niches of plant species in wet meadows. We present a previously unpublished complete version of Ellenberg's dataset from the 1950s together with the results of a series of modern statistical analyses testing for hypothesized overyielding of aboveground net primary production as a consequence of resource-based niche differentiation. Interactions of species with water table depth and soil type in the results of our analyses are qualitatively consistent with earlier interpretations of evidence for differences in the fundamental and realized niches of species. Arrhenatherum elatius tended to dominate communities and this effect was generally positively related to increasing water table depth. There was little overyielding of aboveground net primary production during the two repeats of the experiment conducted in successive single growing seasons. Examination of how the effects of biodiversity on ecosystem processes vary across environmental gradients is an underutilized approach--particularly where the gradient is thought to be an axis of niche differentiation as is the case with water availability. Furthermore, advances in ecology and statistics during the 60 years since Ellenberg's classic experiment was performed suggest that it may be worth repeating over a longer duration and with modern experimental design and methodologies

The complete dataset showing the yields of six different species in monoculture and mixture across the water table depth gradient on two soil types in two years.

<p>Note the absence of two species in 1953.</p

Results of the analysis of the effect of the water table depth on the strength and direction of the Selection Effect on sand and loam soils in 1952 and 1953.

<p> The curves are back-transformed slopes from the mixed-effects model with their 95% confidence intervals (shaded). The positive Selection Effect on loam in 1953 is driven by increasing dominance by <i>Arrhenatherum elatius</i> as depth to the water table increased.</p

Results of the analysis of the effect of the water table depth on relative overyielding (RYT) on sand and loam soils in 1952 and 1953.

<p>The curves are back-transformed slopes from the mixed-effects model with their 95% confidence intervals (shaded). The dotted lines show the zero sum null expectation where species perform the same in mixtures as in monoculture and increases in some species populations are exactly offset by declines in others. Complementarity effects produced similar results but the data are not so well behaved (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0043358#pone.0043358.s015" target="_blank">Figure S9</a>).</p

Results of the mixed-effects model analysis of the yields of individual species across the experimental water table depth gradient.

<p>Undetectable interactions with soil type have been removed from the model while the results are essentially averaged across the two years by including year as a random factor. The curves are slopes from the mixed-effects model with their 95% confidence intervals (shaded). Note that <i>F. pratensis</i> and <i>P. palustris</i> were present only in 1952.</p

Schematic diagram of Ellenberg's water table depth gradient experiment.

<p>The diagram shows the concrete tank from above (top) and the side (below) following Ellenberg (1953, 1954) and Schulze and Beck (2002). Note that the compost layer is on top of the sand, not underneath it as shown in Schulze and Beck (2002). The concrete tank was divided into two halves filled to varying depth with either loam or sand to generate increasing distance to the water table. Each half was divided into strips sown either as monocultures of individual species (4 in 1953, as shown here, 6 in 1952, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0043358#pone.0043358.s007" target="_blank">Figure S1</a>) or a mixtures of all species combined.</p

Results of the mixed-effects model analysis of the effect of the water table depth on total aboveground biomass production on sand and loam soils in 1952 and 1953.

<p>Note that there is little evidence for limitation of production by water: no drought was imposed. On the contrary, in 1953 there may have been some water logging on the loam since conditions were more productive as depth to the water table increased. The lines are slopes from the mixed-effects model with their 95% confidence intervals (shaded).</p