Forest, water and more … – further infor­ma­tion

Biodi­ver­sity

• Ampoorter, E. et al. (2020): Tree diver­sity is key for promo­ting the diver­sity and abundance of forest-associated taxa in Europe. Oikos 129(2): 133–146. https://lirias.kuleuven.be/retrieve/86e3e71e-680e-4175-b0b3-694c3a90db74 Europe-wide multi-site study: Tree species diver­sity syste­ma­ti­cally promotes the diver­sity and abundance of associated species groups (birds, insects, soil organisms, among others) compared with species-poor stands. Status: last checked on 14/09/2026.
• Wirth, C., Bruel­heide, H., Farwig, N., Marx, J. M. & Settele, J. (eds.) (2024). Fakten­check Arten­viel­falt: Inven­tory and perspec­tives for the conser­va­tion of biolo­gical diver­sity in Germany. oekom Verlag, Munich. https://literatur.thuenen.de/digbib_extern/dn068840.pdf The work describes how native broad­leaved and mixed deciduous forests with well-decom­posed mull/mor horizons were exten­si­vely converted into conifer forests with thick raw humus layers – resul­ting in lower soil fauna abundance and diver­sity (with reference to Korbou­lewsky, Perez & Chauvat 2016; Vanbergen et al. 2007) as well as nutrient shifts and soil acidi­fi­ca­tion. Mixing broad­leaved trees into conifer monocul­tures shows the stron­gest positive effects on the diver­sity of soil fauna, fungi and bacteria. Status: last checked on 14/09/2026.

 

Ground­water recharge, water quality, erosion & flood protec­tion

• Federal Agency for Nature Conser­va­tion (BfN), Hölter­mann, A. & Jessel, B. (eds.) (2020): Forests in Climate Change: Incre­asing adapta­bi­lity and resili­ence through greater diver­sity and hetero­gen­eity. Position paper of the BfN, Bonn, 2nd revised version, April 2020, Ch. 2.3.1 „Improve the water balance and water reten­tion“, p. 12. https://www.bfn.de/publikationen/positionspapier/waelder-im-klimawandel-mehr-anpassungsfaehigkeit-durch-mehr-vielfalt The BfN assigns a key role to the water balance in adapting forests to incre­asing drought and heat events. Broad­leaved forests are seen as parti­cu­larly favourable, „which generally exhibit higher deep perco­la­tion and ground­water recharge than conife­rous forests (Ellison et al. 2017; Lasch et al. 2012)“. The paper also names, among other positive measures for the water balance, more deadwood, the preser­va­tion of old forests, low-impact forestry machi­nery, the closing of drainage ditches and the rewet­ting of forest bogs. Status: content checked on 13/10/2026 (PDF available).
• Federal Ministry of Food and Agricul­ture, Forest Report of the Federal Govern­ment 2021, https://www.uni-goettingen.de/de/document/download/82180a8cd55540f4ec20e9cef4a423cd.pdf/Waldbericht2021.pdf (p. 23): Shows the immense importance of forests for drinking water supply. Over 40 % of the area of all water protec­tion zones lies in forest. Water quality is parti­cu­larly good and falls below the nitrate limits appli­cable to drinking water at almost all sites. The share of forest area in Germany is 32 %. This means forests are of very great importance for ground­water quality. Status: last checked on 31/08/2026.
• Deutscher, Podlipný, Čech & Kupec (2025) – Diffe­rent behavior of pair spruce micro-waters­heds in low and high uplands in two hydro­lo­gi­cally contras­ting years­Ci­ta­tion: Deutscher, J., Podlipný, J., Čech, P. & Kupec, P. (2025). Rozdílné chování párových smrko­vých pahor­ka­tin­ných mikro­po­vodí ve dvou hydro­lo­gicky odlišných letech [Diffe­rent behavior of pair spruce micro-waters­heds in low and high uplands in two hydro­lo­gi­cally contras­ting years]. Zprávy lesnického výzkumu (ZLV), 70(4), 205–215. Mendel Univer­sity in Brno. https://www.vulhm.cz/files/uploads/2026/03/774b.pdf and summary under https://www.vulhm.cz/en/deciduous-forests-in-the-hills-are-more-effective-at-mitigating-floods-than-coniferous-forests/ The study compares two spruce-dominated small catch­ments at diffe­rent eleva­tions (Račín, high-altitude, spruce close to its ecolo­gical optimum; Křtiny, lower altitude, spruce outside its optimum) over two hydro­lo­gi­cally diffe­rent years (2023 normal, 2024 flood year). It also summa­rises exten­sive Czech/Central European prior litera­ture: Hemr et al. (2023), during heavy rainfall events, beech-dominated catch­ments dampen the flood peak twice as effec­tively, mixed catch­ments 1.5 times as effec­tively as spruce-dominated ones. Kantor et al. (2003) / Švihla et al. (2012): beech stands show higher annual runoff than spruce stands because of lower inter­cep­tion (e.g. +25.8 mm effec­tive stand preci­pi­ta­tion for beech compared with spruce in the Orlické hory Mountains). Status: last checked on 14/09/2026.
• Gutsch, M., Lasch, P., Suckow, F., Reyer, C. (2011): Forest conver­sion in Branden­burg: ground­water recharge under climate change. Poster, Potsdam Insti­tute for Climate Impact Research (PIK), Research Depart­ment II Climate Impacts & Vulnerabi­lity, Großräschen 2011. https://www.pik-potsdam.de/4c/web_4c/publications/poster_grossraeschen_2011.pdf Model study using the forest growth model 4C at 800 forest sites in Branden­burg (pure stands, age 55 years) for Scots pine, Douglas fir, beech and oak. Under the current climate (1977–2006), annual perco­la­tion — the measure for ground­water recharge — amounts to 195 mm under pine and 160 mm under Douglas fir, but 240 mm under beech and 284 mm under oak. The main reason is the lower inter­cep­tion losses of deciduous trees in winter. This advan­tage remains under all climate scena­rios up to 2060: in the +3 K scenario, perco­la­tion under pine falls by around 60 % (to 79 mm), under beech by only around 40 % (to 142 mm). The authors conclude that conver­ting conifer stands to suitable broad­leaved stands is a sensible adapt­a­tion measure to climate change that reduces impairm­ents of the landscape water balance. Status: content checked on 13/10/2026 (PDF available).
• Harsch, N., Branden­burg, M., Klemm, O. (2009): Large-scale lysimeter site St. Arnold, Germany: analysis of 40 years of preci­pi­ta­tion, leachate and evapo­tran­spi­ra­tion. Hydro­logy and Earth System Sciences 13: 305–317. https://hess.copernicus.org/articles/13/305/2009/Analysis of more than 40 years of measu­re­ment data (1965–2007) from the large lysimeter facility at St. Arnold (Münster­land, North Rhine-Westphalia) with one grass­land, one oak/beech and one pine lysimeter (Weymouth pine) each, of 20 × 20 m area and 3.5 m depth. Under deciduous forest, an average of 37 % of preci­pi­ta­tion perco­lates (295 mm/a), under conife­rous forest only 26 % (217 mm/a); conife­rous forest evapo­rates the largest share at 65 %. Reason: the evergreen needles inter­cept preci­pi­ta­tion year-round (leaf area index 8–13 compared with 1–3 in deciduous forest), while deciduous forest hardly evapo­rates in winter and then delivers almost the entire perco­la­tion water volume. Limita­tion: the authors empha­sise that the values apply to the young stands at this site (15–30 years) and cannot be trans­ferred without further ado to Central European forests. Status: content checked on 13/10/2026 (PDF available).
• Müller, J., 2005: 30 years of forest hydro­lo­gical research at the large lysimeter facility in Britz – objec­tives and results. In: Report on the 11th Gumpen­stein Lysimeter Confe­rence, „Lysimetry in the network of ecosystem dynamics“ on 5 and 6 April 2005, Higher Federal Teaching and Research Insti­tute for Agricul­ture, Irdning. Raumberg-Gumpen­stein: 29–32. Summary at https://www.afsv.de/images/download/literatur/waldoekologie-online/waldoekologie-online_heft-12–5.pdf: Describes the results of the lysimeter station in Britz, where conifer monocul­tures and deciduous forests are examined and compared with regard to their influence on the landscape water balance. Deciduous forests show clearly better deep perco­la­tion here, which leads to higher ground­water recharge. Status: last checked on 14/09/2026.
• Natkhin, M., Sanders, T., Holzhausen, M. (2022): The influence of forest and weather on deep perco­la­tion. Thünen Insti­tute, lysimeter data since 1972 (Britz experi­mental site near Ebers­walde). https://literatur.thuenen.de/digbib_extern/dn064527.pdf Direct, quanti­fied compa­rison: “On average over many years, deep perco­la­tion under beech is greater than under pine”, pine stands show hardly any measurable deep perco­la­tion. Status: last checked on 14/09/2026.
• Natkhin, M., Strer, M., Sanders, T. G. M., Schad, T., Schwärzel, K. (2026): Impact of extreme preci­pi­ta­tion events on summer deep seepage below tempe­rate forests in the Northe­as­tern Germany lowlands. Annals of Forest Science 83: 5. https://link.springer.com/article/10.1186/s13595-025–01318‑2 Reviewed follow-up study to Natkhin et al. (2022) using lysimeter data from the inten­sive monito­ring site Britz (Thünen Insti­tute; 100-m² large lysimeter under beech, young sessile oak, and pine on identical sandy soil). Water balance 2013–2023: Under pine, about 97 % of preci­pi­ta­tion is evapo­rated, while deep perco­la­tion remains very low; under beech, about 10 %, and under young oak, around one third of annual preci­pi­ta­tion flows into deep perco­la­tion and thus contri­butes to ground­water recharge. The authors conclude that tree species selec­tion and stand struc­ture influence ground­water recharge, and that forest manage­ment can substan­ti­ally contri­bute to both ground­water recharge and protec­tion against water scarcity. The site is considered typical for about two thirds of the forest sites in Branden­burg (restric­tion: no repeat sites). Last checked on 14.10.2026.
• Schume, H., Jost, G., Hager, H. (2004): Soil water deple­tion and recharge patterns in mixed and pure forest stands of European beech and Norway spruce. Journal of Hydro­logy 289: 258–274. https://doi.org/10.1016/j.jhydrol.2003.11.036 Field study by the Univer­sity of Natural Resources and Life Sciences, Vienna (BOKU) in Austria (pure and mixed beech-spruce stands): it directly compares how water extra­c­tion and reple­nish­ment in the soil differ under beech, spruce and their mixture – one of the few studies that quanti­fies the water balance so speci­fi­cally by species and mixture for Central Europe. Status: last checked on 14/09/2026.
• Umwelt­bun­desamt, https://www.umweltbundesamt.de/themen/neue-uba-daten-zur-grundwasserneubildung-in Summary: Summa­rises the results of the UBA study “Impact of climate change on water availa­bi­lity – adapt­a­tion to drought and drought in Germany (WADKlim): In many regions of Germany, water availa­bi­lity will decline due to climate change. Currently, 70 % of drinking water in Germany comes from ground­water resources. Status: last updated on 27/06/2025.

 

Humus build-up / soil ferti­lity

• Augusto, L., Ranger, J., Binkley, D., Rothe, A. (2002): Impact of several common tree species of European tempe­rate forests on soil ferti­lity. Annals of Forest Science 59: 233–253. https://www.afs-journal.org/articles/forest/abs/2002/03/01/01.html Speci­fi­cally shows that spruce (Picea abies), compared with many deciduous tree species, has negative nutrient balances (e.g. calcium, magne­sium) and contri­butes to soil acidi­fi­ca­tion – parti­cu­larly proble­matic on nutrient-poor sites with acidic deposi­tion. Status: last checked on 14.09.2026.
• Reich, P.B., Oleksyn, J., Modrzynski, J., Mrozinski, P., Hobbie, S.E., Eissenstat, D.M., Chorover, J., Chadwick, O.A., Hale, C.M., Tjoelker, M.G. (2005): Linking litter calcium, earthworms and soil proper­ties: a common garden test with 14 tree species. Ecology Letters 8: 811–818. https://doi.org/10.1111/j.1461–0248.2005.00779.x Common-garden experi­ment in Poland (14 tree species, inclu­ding several conifers and broad­leaves) directly on the topic: the calcium content of leaf/needle litter largely deter­mines earthworm abundance and, through this, important soil proper­ties. Calcium-poor, acidic conifer litter (typical of spruce/pine) supports far less soil life than calcium-richer deciduous litter – a central mecha­nism why humus build-up and soil biology under conifers are often poorer. Status: last checked on 14.09.2026.

 

Climate resili­ence / adapta­bi­lity

• Ammer, C. (2019): Diver­sity and forest produc­ti­vity in a changing climate. New Phyto­lo­gist 221: 50–66. https://doi.org/10.1111/nph.15263 Review by the Freiburg/Göttingen forest scien­tist Chris­tian Ammer: mixed stands have an advan­tage over monocul­tures (inclu­ding pure conifer stands) under climate change because diffe­rent tree species respond differ­ently to drought, storms and pests, thereby sprea­ding risks across several species. Status: last checked on 14.09.2026.
• Federal Agency for Nature Conser­va­tion (BfN), Hölter­mann, A. & Jessel, B. (eds.) (2020): Forests in climate change: incre­asing adapta­bi­lity and resili­ence through more diver­sity and hetero­gen­eity. BfN position paper, Bonn, 2nd corrected version, April 2020. ): https://www.bfn.de/publikationen/positionspapier/waelder-im-klimawandel-mehr-anpassungsfaehigkeit-durch-mehr-vielfalt „Struc­tu­rally diverse mixed forests … are … attri­buted a higher resili­ence and adapta­bi­lity to climate-change-induced distur­bances than conifer monocul­tures (Jenssen 2007; Pretzsch et al. 2012; Schel­haas et al. 2003). Broad­leaf forests are further­more considered … to be less suscep­tible to windthrow than conifer forests … They make a higher contri­bu­tion to ground­water recharge … and, due to their moister forest interior climate, reduce the risk of forest fires, whereas in conifers … fire danger increases with drought.“ The BfN expli­citly recom­mends that conifers in future should „generally no longer be grown in monocul­ture.“ Status: last checked on 14.09.2026.
• Marx, A., Blauhut, V., Boeing, F. et al. (PIK) (2023): https://publications.pik-potsdam.de/rest/items/item_29892_5/component/file_29893/content Droughts and forest fires under climate change. Confirmed separa­tely: pine forests with a litter layer promote wildfire spread, while broad­leaf-rich mixed forests reduce fire risk through a denser, moister canopy; recom­mends „forest conver­sion to multi-layered mixed forests“. Status: last checked on 14.09.2026.

 

Carbon sink / pest resili­ence / stable timber produc­tion

• Kowalski, K., Viana-Soto, A., Brandt, M., Ciais, P., De Keers­mae­cker, W., Fensholt, R., Pugh, T.A.M., Xu, Y., Senf, C. (2026): Accele­ra­ting biomass loss from forest distur­bances across Europe. Nature Geosci­ence, published 5 August 2026. https://www.nature.com/articles/s41561-026–02032‑y — Lead author at the Technical Univer­sity of Munich (School of Life Sciences, Earth Obser­va­tion for Ecosystem Manage­ment, Freising). The study speci­fi­cally confirms and quanti­fies that high-biomass Norway spruce stands (the classic conifer produc­tion forest of Central Europe) carry by far the greatest and accele­ra­ting loss risk from bark beetles — a key argument for conver­ting forests away from spruce monocul­tures. For carbon sink/stable timber produc­tion, the study is also highly relevant, as it shows that precisely the stands with the largest biomass stock (previously counted as a climate protec­tion benefit) are now becoming the greatest loss risk — which calls into question the relia­bi­lity of pure conifer stands as a stable carbon sink. Status: last checked on 14/09/2026.
• Liang, J. et al. (2016): Positive biodi­ver­sity-produc­ti­vity relati­onship predo­mi­nant in global forests. Science 354(6309): aaf8957. https://eprints.whiterose.ac.uk/114846/14/LiangEtAl2016_biodiversityVsProductivityGlobalForests_Science_pre_proof.pdf Large global meta-study (almost 1 million forest plots): Higher tree species diver­sity corre­lates world­wide with higher and more stable timber produc­ti­vity — a key argument for mixed forests over monocul­tures in carbon sequestra­tion and yield. Status: last checked on 14/09/2026.
• Miglia­v­acca, M., Grassi, G., Bastos, A. et al. (2025): Securing the forest carbon sink for the European Union’s climate ambition. Nature 643. https://publications.jrc.ec.europa.eu/repository/handle/JRC139211 The article does not directly compare mixed deciduous forest vs. conifer monocul­ture, but instead generally shows the decli­ning carbon sink perfor­mance of EU forests and cites that tree species diver­sity increases stand resis­tance to distur­bance („tree diver­sity drives forest stand resis­tance to natural distur­bances“). Status: last checked on 14/09/2026.
• Pretzsch, H., Block, J., Dieler, J. et al. (2010): Compa­rison between the produc­ti­vity of pure and mixed stands of Norway spruce and European beech along an ecolo­gical gradient. Annals of Forest Science 67: 712. https://doi.org/10.1051/forest/2010037 Assess­ment of 23 long-term plots: mixed stands of spruce and beech clearly outper­form the respec­tive pure stands on nutrient-poor sites in terms of incre­ment (up to +138 %) – concrete evidence for more stable timber produc­tion in mixed stands rather than softwood monocul­ture. Status: last checked on 14.09.2026.

 

Cooling effects

• Arx, G., Graf Panna­tier, E., Thimo­nier, A., Rebetez, M. (2013): Micro­cli­mate in forests with varying leaf area index and soil moisture: poten­tial impli­ca­tions for seedling estab­lish­ment in a changing climate. Journal of Ecology 101(5): 1201–1213. https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/1365–2745.12121 Study by the Swiss research insti­tute WSL at Swiss forest sites (i.e. Western Europe) exami­ning the micro­cli­mate in forests with diffe­rent leaf area index (LAI) and diffe­rent soil moisture. As conife­rous forests have a high, closed leaf area index all year round, while mixed deciduous forests vary seaso­nally (much more open in winter), the study provides a direct basis for diffe­rences in cooling and moisture effects between forest types – relevant to the question of how well young trees and ground vegeta­tion are protected from heat stress under the respec­tive canopy. Status: last checked on 14.09.2026.
• Schwaab, J., Davin, E. L., Bebi, P. et al. (2020). Scien­tific Reports, 10, Art. 14153. https://usys.ethz.ch/en/news-events/news/archive/2020/08/lokaler-kuehlungseffekt-durch-laubbaeume-in-europa.html#:~:text=broad%2Dleaved%20trees,forests. Satel­lite-data-based analysis of European forests. Key finding: the land surface tempe­ra­ture of deciduous forests is, depen­ding on the region, 0.5–1.8 °C lower than that of conife­rous forests. Two main mecha­nisms: (1) higher albedo of deciduous trees (more reflec­tion of sunlight instead of conver­sion into heat), (2) stronger evapo­tran­spi­ra­tion during the growing season (more evapo­ra­tive cooling). The authors conclude from this that incre­asing the propor­tion of deciduous trees – especi­ally in spruce monocul­tures – could mitigate local tempe­ra­ture extremes in climate change, but point out that forest conver­sion decis­ions must also take biodi­ver­sity and protec­tion from natural hazards into account. As of: last checked on 14.09.2026.
• Thater, N., Natkhin, M. Holzhausen, M. Spaet­helf (2024): The tempe­ra­ture-equali­sing effect of forest stands using the example of the Britz inten­sive monito­ring plot. Project brief. Thünen Insti­tute of Forest Ecosys­tems. https://britz.thuenen.de/fileadmin/britz/PB_Britz_tiefenversickerung.pdf Summary: Compared with pine forest, beech stands have a greater cooling effect. This effect is parti­cu­larly strong on hot days. Status: last checked on 14.09.2026.
• Yao, Y., Sieber, P., Hauser, M., Schwaab, J. et al. (2025). Nature Commu­ni­ca­tions, 16. https://www.nature.com/articles/s41467-025–64580‑y#:~:text=Converting%20all%20existing,large%20part%20of%20Europe. Model­ling study (follow-up work with partly the same authors as Schwaab 2020) simula­ting what a large-scale conver­sion from conife­rous to deciduous forest would mean for the European summer climate. Result: such a conver­sion would lower the mean July maximum tempe­ra­ture in conti­nental Europe by 0.6 °C, and in Northern Europe by up to 1.0 °C – an effect on the scale of defore­sta­tion, but while retai­ning the forest’s carbon storage function. Mecha­nism: higher evapo­ra­tion from deciduous trees increases latent heat flux and reduces sensible heat flux. Status: last checked on 14.09.2026.

 

Pest/disturbance resis­tance (partial aspect of climate resili­ence)

• BMUKN, FAQ on forest damage 2018–2022 (2024): https://www.bundesumweltministerium.de/faq/zu-welchen-waldschaeden-haben-die-extremen-trocken-und-hitzeperioden-zwischen-2018-und-2022-gefuehrt Official minis­te­rial source with specific figures: 233 million m³ of damaged conife­rous timber compared with only 22 million m³ of deciduous timber in the same period; spruce identi­fied as parti­cu­larly vulnerable due to its shallow root system. Status: last checked on 14.09.2026.
• Jactel, H. & Brocker­hoff, E.G. (2007): Tree diver­sity reduces herbi­vory by forest insects. Ecology Letters 10: 835–848. https://doi.org/10.1111/j.1461–0248.2007.01073.x
  Meta-analysis of numerous studies: tree species mixtures signi­fi­cantly reduce attack by specia­list pest insects (e.g. bark beetle-like pests) compared with monocul­tures – a key argument against pure spruce or pine stands. Status: last checked on 14.09.2026.
• Jactel, H., Pluchard, E., Schillé, L. et al. (2025): Experi­mental evidence of reduced Ips typogra­phus damage in mixed spruce planta­tions. Journal of Pest Science https://www.researchsquare.com/article/rs-6370382/v1 Very strong experi­mental evidence with figures: in pure spruce stands, 29.2 % of trees died due to bark beetle infesta­tion, whereas in mixed stands only 2.6 % did. Mecha­nisms: „resource dilution“ (beetles find host trees less easily) and „reduced apparency“ (neigh­bou­ring trees visually/chemically conceal spruces). Status: last checked on 14.09.2026.
• Hochschule für nachhal­tige Entwick­lung Ebers­walde (HNEE) & Thünen-Institut für Waldöko­sys­teme (TI-WO) (2024): Final report on the project WINMOL – Recor­ding and predic­tion options for storm damage in forestry (funding reference 2220NR024A/B; duration 01.07.2020–31.12.2023; funded by BMEL/FNR). Project page: https://winmol.thuenen.de/ (pp. 14–15): Various studies showed that „conifer species, especi­ally spruce, pine and Douglas fir, are more suscep­tible to storm damage than broad­leaved species“. The report cites the reason often given that conifers are also foliated in winter, when most strong storms occur. At that time, the broad­leaved trees have already shed their leaves and there­fore provide less surface area for the wind. The report refers to, among others, Albrecht et al. 2012, Jung et al. 2016, Peltola et al. 1999, Pukkala et al. 2016 and Seidl et al. 2011. Restric­tion: The report’s scenario analysis considers only even-aged pure stands; mixed stands were not examined, and a direct species compa­rison is „hardly possible“ without knowledge of the site condi­tions (pp. 33–34). In the model, unmanaged beech and oak stands were more vulnerable than unmanaged spruce and Douglas fir stands (p. 34). Status: Content reviewed on 14.10.2026 (PDF available).

 

Water consump­tion in Germany

• Federal Environ­ment Agency (UBA) „Water use by private house­holds“: https://www.umweltbundesamt.de/daten/private-haushalte-konsum/wohnen/wassernutzung-privater-haushalte#direkte-und-indirekte-wassernutzung As of: last updated on 10.09.2024 Summary: In 2022, direct drinking water consump­tion averaged 126 litres per person per day (personal hygiene 36 %, toilet flushing 27 %, laundry 12 %, cleaning 6 %, food/drink 4 %, small businesses 9 %). Histo­ri­cally: 144 l (1991) → 123 l (2016) → 128 l (2019) → 126 l (2022). The indirect or „virtual“ water consump­tion for the produc­tion of food, clothing and consumer goods is signi­fi­cantly higher (especi­ally agricul­tural irriga­tion): direct and indirect consump­tion together amounts to around 7,200 litres per person per day. As of: last checked on 14.09.2026.

 

You can find the summed-up advan­tages of mixed deciduous forests over monocul­ture conifer forests here here.