European beech controls biodiversity in mixed forests – Mixed versus pure forests of beech and conifers

Date:
2018/06/15

Time:
10:30

Room:
A1 Wilhelm

European beech controls biodiversity in mixed forests – Mixed versus pure forests of beech and conifers

(Oral)

Steffi Heinrichs
sheinri@gwdg.de

Silviculture and Forest Ecology of the Temperate Zones University of Göttingen Büsgenweg 1 D-37077 Göttingen, Germany
,
Martin. M. Gossner
Research Unit Forest Dynamics Swiss Federal Research Institute WSL Zürcherstrasse 111 CH-8903 Birmensdorf, Switzerland
,
Peter Schall
Silviculture and Forest Ecology of the Temperate Zones University of Göttingen Büsgenweg 1 D-37077 Göttingen, Germany

DOI: 10.17011/conference/eccb2018/107267

SEE PEER REVIEW

Monocultures of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) have been promoted in Central Europe since the early 19th century due to economical, ecological and management constraints on sites naturally dominated by broadleaved species. Catastrophic damages and the call for multifunctional forest ecosystems with a high degree of naturalness initiated a large-scale conversion of these monocultures into mixed forests often with the naturally dominant European beech (Fagus sylvatica). Beside an increased stability, mixed forests are assumed to facilitate forest biodiversity conservation due to an increased habitat heterogeneity compared to the respective monocultures. Scientific evidence for this assumption is, however, scarce [1]. Here we investigated data on 15 organismic groups from plants to bacteria sampled in two regions of Germany to reveal the effect of mixed versus pure forests of beech and conifers on biodiversity.
Although species composition of mixed stands was intermediate between beech and conifer stands for most organismic groups, they never exceeded gamma-diversity of either pure stand. To identify a landscape composition of pure and mixed stands that maximizes biodiversity, we generated virtual forest landscapes by resampling plots of pure and mixed stands in a way that all compositional combinations were represented in steps of 10 % with 1000 replications. Landscapes were created containing beech and pine stands and its mixtures for 15 taxonomic groups and containing beech and spruce stands and its mixtures for three groups. Most groups as well as multidiversity benefited from mixing different pure stands at the landscape scale and not from local within-stand mixtures. Except deadwood fungi that prefer a high percentage of pure beech stands, most species groups need a share of at least 30 % of conifer stands for a maximum biodiversity. For a landscape with beech, pine and its mixtures, 97 % of multidiversity was achieved with a combination of 70 % pure pine and 30 % pure beech stands. Within-stand mixtures supported only 77 % of multidiversity as the competitive beech determined resource availability. Thus, the habitat heterogeneity provided by different pure stands at the landscape scale is more effective for biodiversity than the heterogeneity by mixing species at the stand scale.
Our findings indicate that the ongoing large-scale conversion of pure conifer into mixed stands with beech will lead to biodiversity loss. An optimized forest landscape for regional biodiversity contains pure beech and pure conifer stands that show complementarity in species composition. We can, however, not yet say if pure forest stands should be larger than the here investigated 1 ha to be effective.

[1] Cavard X et al. (2011) Importance of mixedwoods for biodiversity conservation: Evidence for understory plants, songbirds, soil fauna, and ectomycorrhizae in northern forests. Environ Rev 19: 142-161

SEE PEER REVIEW

INTRO:
Although species composition of mixed stands was intermediate between beech and conifer stands for most organismic groups, they never exceeded gamma-diversity of either pure stand. For most taxa biodiversity was highest in conifer forests, making a high percentage of pure pine stands best for a maximum in biodiversity. Within mixed stands of pine and beech the authors found a large difference between arthropods that are considered specialist of beech and pine in vertical layers of the stand. The higher occurrence of beech specialists in lower layers shows the strong impact of beech on near-ground resources, which restricts species specialized on pine to canopy habitats. The authors state therefore the concern that a conversion of pure stands to mixed stands, as it is happening recently as a conservation measure, might be negative for biodiversity.
MERITS:
With this study, the authors stress a very important topic of recent conservation measures. Due to an ongoing climate change, foresters are starting to look for new ways to increase the stability of the forests. This is often combined with a call to integrate conservation measures into forestry practice. However, these measures, such as the changes in tree mixture, need to be scientifically evaluated before they are implemented. The authors did not only look at the gamma diversity of different landscapes designs to develop detailed recommendations for managers, but also evaluated the occurrence of specialized species in mixed forests to make detailed assumptions on what happens to biodiversity with an increase in tree mixtures compared to pure stands.
CRITIQUE:
Although the authors gave clear recommendations on the proportion of stands in the landscape, however, they did not mention how large the single stands should be, making the recommendations again less valuable for managers. Also they did very detailed analysis on a landscape containing beech and pine but not on a landscape containing beech and spruce or all three tree species together.
DISCUSSION:
This study is a highly useful contribution to conservation science concerning a very relevant topic in Germany. The extension of this question to additional tree species such as oak or elder would be highly recommendable. Additionally, it would be interesting to see how other conservation measures such as deadwood enrichment might be compatible with the recommended type of landscape design.

- - -
INTRO:
In this manuscript, the authors have used an empirical approach to assess the influence of mixed vs. pure forests on a wide range of taxa at the stand and landscape scales. Authors found that (i) gamma diversity of mixed forest stands was never greater than gamma diversity of pure stands; (ii) overall pure coniferous stands supported higher biodiversity; (iii) maintaining a mosaic of different types of pure stands at the landscape level was more beneficial for promoting biodiversity in forests than mixing deciduous and coniferous trees at the local scale.
MERITS:
By looking at the responses of 15 different taxa (plants, animals, fungi and bacteria) to forest composition, the manuscript provides a clear understanding of how forest composition influences forest biodiversity at different spatial scales.
CRITIQUE:
None.
DISCUSSION:
This research has strong management implications at both stand and landscape scales. To prevent a loss of biodiversity that may happen due to the conversion of pure coniferous stands to mixed ones, the authors highlight the importance of maintaining/creating in the landscape a mosaic of pure deciduous and pure coniferous stands.

- - -
INTRO:
The paper by Heinrichs et al. reports results of studies carried in the lanscape scale and aimed on assessment of the role, which mixed stands play in maintenance of biodiversity. Pure stands of pine and beech, versus their various mixtures were taken into account. The Authors found that monocultures, if mixed in the landscape at proper proportions, are more beneficial to the biodiversity, than mixed stands.
MERITS:
The study was well designed and addressed wide range of organisms dwelling in forest ecosystems. The conclusions are interesting, pointing out, that maintenance of some monocultures in the landscape scale is benefitial do biodiversity.
CRITIQUE:
The last paragraph, concentrating on 'control' of biodiversity by beech is in my opinion doubtful. The observed pattern: beech specialists in the lower canopy layer vs. pine specialists in the highest canopy layer could be simply effect of ecological characteristics of the tree species in question. Beech, as one of the most shadow tolerant species, may thrive under canopy of pines, but the opposite situation is impossible, because pine is one of the most light demanding european tree species and could not survive under beech canopy for a longer period. Therefore, the statement from the title 'European beech controls biodiversity' is overestimated. The same for the conclusions given in the last paragraph.
DISCUSSION:
The research reported in the paper has high importance for forest management and nature conservation. It's implications can be very far reaching as it may change recent paradigm of mixed stands as biodiversity hotspots.

European beech controls biodiversity in mixed forests – Mixed versus pure forests of beech and conifers

Date:2018/06/15

Time:10:30

Room:A1 Wilhelm

European beech controls biodiversity in mixed forests – Mixed versus pure forests of beech and conifers

(Oral)

SEE PEER REVIEW

SEE PEER REVIEW

Date:
2018/06/15

Time:
10:30

Room:
A1 Wilhelm