DOI: 10.5061/dryad.vt4b8gv08
title: Data from: Positive effects of tree species diversity on productivity switch to negative after severe drought mortality in a temperate forest experiment

description: Synthesis of a large body of evidence from field experiments suggests more
 diverse plant communities are both more productive as well as more
 resistant to the effects of climatic extremes like drought. However, this
 view is strongly based on data from grasslands due to limited empirical
 evidence from tree diversity experiments. Here we report on the
 relationship between tree diversity and productivity over ten years in a
 field experiment established in 2005 that was then affected by the 2018
 megadrought in central Europe. Across a number of years, tree species
 diversity and productivity were significantly positively related, however,
 the slope switched to negative in the year of the drought. Net diversity
 effects increased through time, with complementarity making greater
 continuations to the net diversity effect than selection effects.
 Complementarity was clearly positive (95 % credible interval) in three and
 five species mixtures before the drought (2012-2016) but was found to
 decrease in the year of the drought. Selection effects were clearly
 positive in 2016, and remained positive in 2018, the drought year in two,
 three, and five species mixtures. Survival of the Norway spruce (Picea
 abies) plummeted during drought and a negative relationship between
 species diversity and spruce survival was found. Our findings suggest that
 tree diversity per se may not buffer communities against the impacts of
 extreme drought and that tree species composition and the drought
 tolerance of tree species (i.e., species identity) will be important
 determinants of community productivity as the prevalence of drought
 increases.
description: # Positive effects of tree species diversity on productivity switch to
 negative after severe drought mortality in a temperate forest experiment
 [https://doi.org/10.5061/dryad.vt4b8gv08](https://doi.org/10.5061/dryad.vt4b8gv08) The Kreinitz experiment site is located near the village of Kreinitz-Zeithain, Saxony, Germany (51°23’ 08” N, 13°15’41” E; 115 m a.s.l.). The local climate is characterized by a mean annual precipitation of 578 mm and mean annual temperature of 9.4 °C (30-year average 1981-2010, Oschatz station of German Weather Service DWD, ~15 km from the site). Maximum precipitation is normally observed during the growing season (Table S1), which usually starts in late March and ends in late October / early November (Scheuner, 2004). The soil is a humic cambisol on a bedrock of sand and gravel (93 % sand, 6 % silt, 1 % clay) with a pH of 5.5 (Schwarz et al., 2015).  Kreinitz was planted in a field that was cultivated until 1990. In summer 2005, the site was plowed and harrowed, and two experimental blocks were set up, each of them containing 49 plots of 5 m x 5 m area with distances of 2.5 m between plots and of c. 10 m between blocks. In November of 2005, two-year old tree saplings, obtained from a local nursery, were planted on each plot in five staggered rows with six individuals in each row (Fig. S1; 30 trees per plot). The distance between rows was 1.0 m, and trees within rows were separated by 0.8 m, resulting in a density of 1.2 individuals m-2 within a plot. To construct the gradient in tree diversity, six native tree species that are abundant in Central European forests were selected, including four broadleaved and two coniferous species: *Fagus sylvatica* L. (European beech), *Fraxinus excelsior* L. (common ash), *Quercus petraea* (Matt.) Liebl. (sessile oak), *Tilia cordata* Mill. (small‐leaved linden), *Picea babies* (L.) H. Karst. (Norway spruce), *Pinus sylvestris* L. (Scots pine). The 49 plots within each block were randomly assigned to six different diversity levels and to different species combinations within each diversity level: bare soil (not further considered in this paper), species monocultures (six “combinations”), two-species mixtures (15 combinations), three-species mixtures (20 combinations), five-species mixtures (six combinations), as well as the six-species mixture (one combination), resulting in 49 treatments (48 excluding the bare soil). The 30 planting positions within each plot were randomly, but in equal proportions, assigned to the respective species. For the first two years (2006, 2007), plots were regularly weeded to facilitate establishment of saplings, and dead saplings were replaced by individuals of the same age and same seed source. Leaf litter (c. 600 g m-2) was also added to each plot to facilitate tree establishment from planting until 2009, with litter identity and amount representing the planted tree species composition. ## Description of the data and file structure ### biodiversity\_effects.xlsx | variable | description | values | | :---------------------- | :------------------------------- | :-------------------------------------------------------------------------------------------------------------------------- | | Block | block | | | Plot | plot id | | | diversity | species richness | | | combination | species composition | Bu = Fagus sylvatica Es = Fraxinus excelsior Fi = Picea abies Ki = Pinus sylvestris Ei = Quercus petraea Li = Tilia cordata | | Year | calendar year | | | complementarity effect | complementarity effect in Mg/ha | | | selection effect | selection effect in Mg/ha | | | net biodiversity effect | net biodiversity effect in Mg/ha | | ### biomass\_increment\_tree\_survival.xlsx | variable | description | values | | :--------------------- | :-------------------------------------------------------------------------------------------------------------- | :----------------------------------------------------------------------------------------------------------------------------------------- | | Block | two blocks of the tree diversity experiment | | | Plot | plot id | | | Diversity | Number of tree species planted at the beginning of the experiment | | | Combination | Species composition | Bu = Fagus sylvatica Es = Fraxinus excelsior Fi = Picea abies Ki = Pinus sylvestris Ei = Quercus petraea Li = Tilia cordata | | Species | Common name of tree species | ash = Fraxinus excelsior beech = Fagus sylvatica linden = Tilia cordata oak = Quercus petraea pine = Pinus sylvestris spruce = Picea abies | | Year | calender year  | | | total\_biomass\_Mg\_ha | plot level total biomass of live trees in Mg/ha | | | increment\_Mg\_ha\_y | plot level biomass increment per year in Mg/ha/year | | | sur\_pre | total number of trees per species survived in the previous inventory | | | sur\_current | total number of trees per species survived in the current inventory | | | alive\_2017 | total number of trees per species present in the 2017 inventory | | | incidence\_2018 | total number of trees per species infested by bark beetles in the 2018 inventory (out of those present in 2017) | | | incidence\_2019 | total number of trees per species infested by bark beetles in the 2019 inventory (out of those present in 2017) | | ### all\_year\_data\_ht\_basal\_diameter Missing data are indicated in the dataset as "NA". Instances of "NA" signify that the variable was not measured during the inventory due to either its small size, or because the individual tree was deceased. **Sheets** * 2008-2013: Height and basal diameter of tree individuals from 2008 to 2013. Multiple observations for a given tree individual refer to multiple stems of that individual. * 2016-2018: Height, basal diameter and diameter at breast height (DBH) of tree individuals in 2016 and 2018. Multiple observations for a given tree individual refer to multiple stems of that individual. In 2016, both basal diameter and DBH were measured for each stem. In 2018, DBH was measured for each stem, and basal diameter only for smaller stems. | variable | description1 | description2 | | :-------------- | :---------------------------------------------------------------------------------------------------------------------- | :-------------------------------------------------------------------------------------------------------------------------- | | Year | Calender year at the end of which tree size was measured | 2008, 2009, 2010, 2011, 2012, 2013, 2016, 2018 | | Block | Block id of the tree diversity experiment | A, B | | Plot | Plot serial number within each block | 1 to 49 | | Plot\_ID | Unique plot id | A1 to A 49, B1 to B49 | | Tree\_ID | Tree serial number within each plot | 1 to 30 | | Species | Abbreviation of tree species name | Bu = Fagus sylvatica Es = Fraxinus excelsior Fi = Picea abies Ki = Pinus sylvestris Ei = Quercus petraea Li = Tilia cordata | | Height | Height of an individual tree in cm. In case of multi-stemmed individuals, height of each stem is given. | | | Basal\_diameter | Basal diameter of an individual tree in cm. In case of multi-stemmed individuals, basal diameter of each stem is given. | | | DBH | Diameter at breast height of an individual tree in cm. In case of multi-stemmed individuals, DBH of each stem is given. | |