For our second contribution for National Tree Week, we hear from authors Zilong Ma and Han Chen, whose recently published paper was included in the special National Tree Week Virtual Issue.

Zilong Ma is a PhD student at Lakehead University in Canada, supervised by Han Y.H. Chen who is also an Associate Editor for Journal of Ecology. Research in Dr Chen’s lab focuses on causes of biological diversity, ecosystem functioning, and nutrient dynamics. Much of his work is designed to provide scientific underpinning for ecological sustainability of forest ecosystems in a changing environment. Zilong Ma’s dissertation research examines the relationship between diversity and below-ground function with a special emphasis on fine root productivity in natural forests. Part of Zilong’s work was recently published in Journal of Ecology titled ‘Effects of species diversity on fine root productivity increase with stand development and associated mechanisms in a boreal forest’ and is included in the BES cross-journal National Tree Week 2016 virtual issue.

There is a growing interest for understanding the relationship between diversity and below-ground productivity due to the critical contribution of below-ground systems to overall terrestrial productivity. Yet, the temporal (seasonal and developmental) changes in diversity effects on below-ground productivity and their underlying mechanisms remain unclear.

In our Journal of Ecology paper,  we hypothesized that (i) diversity effects on fine root productivity increase with stand development, and (ii) increased diversity effects associated with stand development result from augmented horizontal soil space utilization, increased forest floor depth for rooting, enhanced effects in nutrient-poor soil layers and/or foraging towards high nutrient availability.

To test these hypothesises, we sampled 18 stands dominated by single species and their mixtures in post-fire boreal forests of two stand ages (8 and 34 years following stand-replacing fire). We found that the annual fine root production was higher in mixtures than the mean of single-species-dominated stands in both stand ages, with a significantly higher magnitude of effects in the 34-year-old than 8-year-old stands. Mixtures had higher horizontal soil volume filling than single-species-dominated stands with a more pronounced increase in the 34-year-old than 8-year-old stands. Moreover, compared with the eight-year-old stands, the 34-year-old stands had greater depth of forest floor and greater overyielding with soil depth, and their fine root productivity was more responsive to the vertical variation in soil phosphorus concentrations among soil layers.

Our results provide evidence for increasing positive diversity effects on fine root productivity with stand development in heterogeneous natural forests. Moreover, our results indicate that the increased positive diversity effects on stand development was the result of multiple mechanisms, including higher horizontal soil volume filling, a thicker forest floor layer for rooting, a higher magnitude of complementarity in nutrient-poor deep soil layers and stronger nutrient foraging towards soil layers with high nutrient concentrations in older than younger stands.

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Zilong Ma and Han Chen, Lakehead University, Canada

Find out more about National Tree Week on the Tree Council Website, including an article on this year’s activities, an interactive map of events near you, and a free downloadable poster. You can also keep track on what’s going on throughout the festival using the hashtags #NationalTreeWeek, #ChangingViews and #TreeCharter.