Assessing the impact of post-fire forest management using beetles and ants as bioindicators

(Poster)

Josep M. Bas
josep.bas@udg.edu

Department of Environmental Sciences, University of Girona, 17003 Girona, Catalonia, Spain, Spain
,
Carles Tobella
Department of Environmental Sciences, University of Girona, 17003 Girona, Catalonia, Spain, Spain
,
Amador Viñolas
Museum of Natural Sciences of Barcelona. Laboratory of Nature. Passeig Picasso, s / n., 08003 Barcelona, Catalonia, Spain, Spain
,
Esther Lucha
Department of Environmental Sciences, University of Girona, 17003 Girona, Catalonia, Spain, Spain
,
Carla Miarons
Department of Environmental Sciences, University of Girona, 17003 Girona, Catalonia, Spain, Spain
,
Pere Pons
Department of Environmental Sciences, University of Girona, 17003 Girona, Catalonia, Spain, Spain

DOI: 10.17011/conference/eccb2018/107762

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Fire is one of the most frequent disturbances in forests ecosystems. Burnt forests in southern Europe are usually harvested with heavy machinery leaving very little woody biomass on-site. This second disturbance can alter the forests physical structure, ecological key processes, and the species dynamics and interactions. However, postfire logging practices using light machinery and leaving coarse woody debris on-site, would be a more sustainable alternative. This work analyzes the impact of forest fire and salvage logging in a Mediterranean pine-oak forest burnt in July 2016. Four plots of around 1 ha were logged in April 2017 (sustainable logging; SL) with light machinery, leaving the canopies on-site as piles of branches and preserving standing living trees. Three plots of similar size were unlogged (non-intervention, NI). The impact of the two treatments (NI and SL) on beetle and ant communities, has been studied in spring-summer 2017, soon after the logging. Ants and beetles have important ecological roles and are considered good bioindicators of forest disturbances. To capture flying beetles, 14 flight traps were placed at 3-4 meters from the ground in NI and SI treatments (7 per treatment) for 6 weeks. We then analyzed their abundance, species richness, diversity and feeding guild (DE defoliator, D detritivore, S sap feeding, G granivore, F fungal feeding, P predator, PD predator-detritivore, V vegetation feeding and X xylophagous). We captured 4533 individuals belonging to 123 beetle species from 23 families. There were no significant differences in species richness between the two treatments, although abundance and diversity were significantly higher in SL. A FAMD (Factor Analysis of Mixed Data) separates a group of non-saproxylic (G, DE, D, P and V) from a group of saproxylic (F, X, PD) species, more abundant at SL. On the other hand, 125 pitfall traps were set up in 5 microhabitats (25 traps/microhabitat): open ground and below sprouted shrubs in the NI treatment; and ground, below sprouted shrubs and under branch piles at SL. We captured 687 individuals belonging to 13 species of ants. There were no significant differences in species richness between treatments (NI vs. SL) and between microhabitats. However, ant abundance was highest below shrubs and under branch piles and diversity was highest in the open ground of SL. The higher temperature of this microhabitat likely favours the activity of different species. These provisional results will be completed with new plots managed by conventional salvage logging, with longer sampling until 2020 and with the parallel monitoring of vegetation, spiders, birds and mammals. Together, we hope to provide diversity indicators to be used in decisions regarding the management of burnt forests.

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INTRO:
The study examines the effects of post-fire salvage logging on beetle and ant assemblages. Logging has been done in a sustainable manner, retaining dead wood and living trees. Beetles and ants have been sampled in four logged and three unlogged burned stands. In comparison to the unlogged stands, the species richness of ants and beetles is not affected by sustainable logging, while abundance and diversity are higher in logged stands.
MERITS:
The topic of the study is interesting and has a high practical relevance as well; the authors specifically mention that they hope to provide information to be used in the management of burned forests. Both the study question and design are clearly presented and appear to be appropriate.
CRITIQUE:
Composition of beetle and ant communities has not been studied, although it could be important since the community composition might differ among treatments even when species richness or abundance do not. From a conservation point of view it would also be interesting to examine the effects of logging on red-listed species or species of other conservation concern: do these respond to the treatments the same way as more common species?

Revising the language might be useful, as a few sentences are difficult to interpret - for example, I am not certain whether it is the non-saproxylic or saproxylic beetle group that is more abundant in SL.
DISCUSSION:
Developing more sustainable methods for the management of burned forests has high practical importance. Based on the results presented here it would seem that sustainable logging does not have negative impacts on beetle and ant fauna; instead, species abundance and diversity increases in comparison to unlogged stands. Inventories in conventionally logged stands, which the authors are planning to add later on, will complete the results by telling whether sustainable logging is actually an improvement in comparison to the current practices.

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INTRO:
This presentation reports the short term effects from an experiment assessing differences in community composition of beetles and ants between plots exposed to post fire salvage logging and unlogged plots. The imposed salvage logging is a low intensive logging that supposedly should have lower impact on biodiversity than conventional salvage logging.
MERITS:
Well formulated research question concerning an important conservation issue. Quantifications of the effects of salvage logging, and more importantly quantifications of the potential mitigating effects that partial retention of trees might have on biodiversity are needed as the empirical support for the usefulness of this type of environmental concern is limited. In this context this study is highly relevant.
CRITIQUE:
The experimental design has some weaknesses. The most important weakness is that the experimental design lack a treatment that mimic conventional salvage logging. This complicate interpretation of the results and makes it difficult, or even impossible, to evaluate whether the supposedly low impact type of salvage logging result in less effect on community composition of ants and beetles than expected by conventional logging. A non-significant difference from untreated controls is simply not enough to say that the low intensive logging is any better than conventional logging. Towards the end, the authors mention that this study will be followed by a long-term study assessing the effect of conventional salvage logging. Maybe it is possible to relate results of that study to this one, but my gut feeling is that this will be complicated. Hopefully the authors will be able to address this during the presentation.
DISCUSSION:
Some of the results are very intriguing, but not discussed (maybe due to limited space). For example I found it very interesting that saproxylic species was less common in plots with higher resource availability (amount of dead wood). I am really interested in hearing potential explanations to this in my mind very surprising results.

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INTRO:
This study assesses the impact of post-fire logging on beetle and ant communities by comparing the species richness, abundance and diversity between plots where sustainable logging with light machinery was performed and plots without any intervention. Significant differences between both treatments were found for abundance and diversity for both taxonomic groups. Plots with sustainable logging showed higher abundance and diversity.
MERITS:
The authors have addressed an important research topic with high practical relevance, especially in the Mediterranean region. The studied taxonomic groups are wide spread and are considered good indicators of disturbances. The analysis also matches the aim of the study.
CRITIQUE:
Research question should be written clearer.

The authors compare species richness and abundance in non-intervention and sustainable logging treatment. It is not clear why it was not possible to include a third treatment where conventional salvage logging with heavy machinery was performed? The inclusion of conventional treatment would help to cover the whole spectrum of management activities.

Was it possible to increase the number of studied 1 ha plots or you were limited for some reason? Do you think that lack of differences in species richness between the treatments reflects the reality or it might result of small sample size?

Information about the study area (country and region) is missing.

Currently, the authors describe the methods and then provide the results for the beetles and then do the same for the ants. However, methods and results should not be mixed but logically follow one after another. I suggest joining methods and results for both groups together.

In the following sentence it is not clear to me which group was more abundant:

"A FAMD (Factor Analysis of Mixed Data) separates a group of non-saproxylic (G, DE, D, P and V) from a group of saproxylic (F, X, PD) species, more abundant at SL."

The result and inference section require clarification of the differences between dead-wood dependent and open-land species.

The authors used a mixture of British or America English. I suggest a spell and grammar check to be performed.
DISCUSSION:
Obviously, the study is still ongoing and the authors plan to include the third treatment in the future. However, the current title conveys the impression that the study covered the whole spectrum of post-fire management. Therefore, I would suggest to change the title in a way that it best reflects the results included in the abstract.

Having in mind the treatments, I would expect that in SL plots the dead-wood dependent species would be the "losers", because of the reduced deadwood quantity, and open-land species would be the "winners", because of the increased microhabitat diversity. I guess that from management prospective it is most important to answer the question which type of treatment benefits the "losers", namely the dead-wood dependent species. Therefore, I would suggest to rephrase the research question as a short hypothesis explaining which species were expected to benefit from the tested treatments. Then provide the results the support or reject the hypothesis and discuss them in the inference section. After that the future plans for inclusion of further treatments could be stated. These changes will improve the abstract's readability and will also provide clear practical message to decision-makers and managers.

The abstract should be acceptable for publication after making these changes.