Abstract
Many studies highlight the role of mixed versus monospecific forests to provide numerous ecosystem services. Most reports of the positive effects of tree mixture on biodiversity focus on coniferous–deciduous combinations, but little is known about the effects of mixtures combining two coniferous tree species. We assessed the effects of mixed versus monospecific stands of Pinus sylvestris and P. pinaster on the understory richness and composition and its relationship with the soil status, based on research with six triplets in northern Spain. In ten square meter quadrats randomly located per plot, the cover of every understory vascular plant species was estimated visually and data were codified according to Raunkiær’s life-forms. One soil pit of 50 cm depth was dug in each plot to determine the soil water (water holding capacity) and fertility (carbon and exchangeable cations stocks) status. A water-stress gradient associated with the overstory composition indicated that P. pinaster tolerates lower soil water content than P. sylvestris. Mixed stands are under greater water stress than monospecific P. sylvestris stands but maintain the same level of understory richness. Also, a soil fertility gradient defined by organic carbon and exchangeable magnesium stocks was identified. Hemicryptophytes, whose abundance is greater in mixed stands, were the only understory life-form positively correlated to soil fertility. We conclude that the mixture of both Pinus species should continue to be favored in the study area because it helps to maintain understory richness under greater water-stress conditions and improves soil fertility.
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Acknowledgements
We would like to thank Luis Alfonso Ramos Calvo for his invaluable help with soil sampling, Carmen Blanco and Juan Carlos Arranz for their advice in the laboratory analyses, José Riofrío and Cristóbal Ordoñez for their assistance in location of plots in the field, and Juan Manuel Diez Clivillé, and María de la Fuente for their assistance with English. We also thank Pilar Zaldívar, Hans Pretzsch (Editor-in-Chief) and two anonymous reviewers for their valuable comments to improve the manuscript. This research was funded by a predoctoral grant to DLM (BES-2015-072852) and the Project FORMIXING (AGL2014-51964-C2-1-R) from the Ministry of Economy and Competitiveness of the Spanish Government.
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DLM carried out the field and laboratory work, ran the data analysis and discussed the results. DLM and CMR discussed data analysis and commented on the results and discussion. CMR supported DLM with the statistical analysis. MBT supported DLM with the laboratory analysis. DLM, CMR, MBT and FB edited the manuscript. FB coordinated the research project.
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Appendices
Appendix 1
Species classification according to the Raunkiaer’s life-forms (Raunkiaer 1934), following Aizpiru et al. (2007), their protection status in Spain according to Anthos project [(http://www.anthos.es/): CR critically endangered, EN endangered, VU vulnerable (UICN, 2012) and SI special interest] and Raunkiaer’s life-forms cover (%) of each stand type.
Life-forms | Species | Protection status | Raunkiaer’s life-forms cover (%) | |||||
|---|---|---|---|---|---|---|---|---|
Status | Law | Red book | Region | PS | MM (mean ± SE) | PP | ||
Therophytes | Aira caryophyllea L. | 1.37 ± 1.02 | 1.37 ± 0.81 | 0.17 ± 0.11 | ||||
Geranium robertianum L. | ||||||||
Melampyrum pratense L. | ||||||||
Geophytes | Pteridium aquilinum (L.) Kuhn | VU | 7 | b | Murcia | 5.75 ± 2.37 | 2.08 ± 1.04 | 0.08 ± 0.08 |
Asphodelus albus Mill. | ||||||||
Simethis mattiazzii (Vand.) Sacc. | EN | 14 | e | Cataluña | ||||
Hemicryptophytes | Viola montcaunica Pau | SI | 5 | Castilla la Mancha | 8.87 ± 2.66 | 7.32 ± 2.69 | 4.92 ± 3.24 | |
Polygala vulgaris L. | VU | a | Baleares | |||||
Potentilla montana Brot. | ||||||||
Agrostis castellana Boiss. & Reut. | ||||||||
Galium saxatile L. | ||||||||
Juncus conglomeratus L. | ||||||||
Hypochaeris radicata L. | ||||||||
Lotus corniculatus L. | SI | 6 | Extremadura | |||||
Sanguisorba minor Scop. | ||||||||
Deschampsia flexuosa (L.) Trin. | ||||||||
Chamaephytes | Erica australis L. | 21.13 ± 8.21 | 26.08 ± 9.21 | 29.00 ± 7.32 | ||||
Erica arborea L. | EN | b | Murcia | |||||
Arenaria montana L. | ||||||||
Calluna vulgaris (L.) Hull | ||||||||
Arctostaphylos uva-ursi (L.) Spreng. | SI | 7 | b | Murcia | ||||
Vaccinium myrtillus L. | ||||||||
Phanerophytes | Quercus pyrenaica Willd. | CR | 5, 8, 10, 11 | d | Spain | 11.53 ± 3.10 | 5.83 ± 2.5 | 7.50 ± 2.22 |
Ilex aquifolium L. | VU | 1, 2, 3, 5, 6, 9, 11, 13 | d | Spain | ||||
Pinus sylvestris L. | ||||||||
Pinus pinaster Aiton | SI | 5, 10 | a, b | Baleares, Castilla la Mancha, Murcia | ||||
Quercus faginea Lam. | EN | 4, 7, 13 | b, c, d | Spain | ||||
Cistus laurifolius L. | ||||||||
Juniperus oxycedrus L. | EN | 7 | a | Murcia | ||||
Appendix 2
Data analyses of soil properties.
Water holding capacity
Water holding capacity of each horizon (WHCHi)
WHCHi = AWHi·bDHi·%EFHi THi | AWHi: available water of each horizon |
bDHi: bulk density of each horizon | |
%EFHi: % of earth fraction of each horizon | |
THi: thickness of each horizon |
Water holding capacity in the whole mineral soil profile (0–50 cm; WHC)
WHC = ∑ WHCHi |
Easily oxidizable carbon stock
Easily oxidizable carbon stock of each horizon (oxCstockHi)
oxCstockHi = oxCHi·bDHi·%EFHi THi | oxCHi: easily oxidizable carbon of each horizon |
bDHi: bulk density of each horizon | |
%EFHi: % of earth fraction of each horizon | |
THi: thickness of each horizon |
Easily oxidizable carbon stock in the whole mineral soil profile (0–50 cm; oxCstock)
oxCstock = ∑ oxCstockHi |
Total organic carbon stock
Total organic carbon stock of each horizon (CstockHi)
CstockHi = TOCHi·bDHi·%EFHi THi | TOCHi: total organic carbon of each horizon |
bDHi: bulk density of each horizon | |
%EFHi: % of earth fraction of each horizon | |
THi: thickness of each horizon |
Total organic carbon stock in the whole mineral soil profile (0–50 cm; Cstock)
Cstock = ∑ CstockHi |
Total nitrogen stock
Total nitrogen stock of each horizon (NstockHi)
NstockHi = TNHi·bDHi·%EFHi THi | TNHi: total nitrogen of each horizon |
bDHi: bulk density of each horizon | |
%EFHi: % of earth fraction of each horizon | |
THi: thickness of each horizon |
Total nitrogen stock in the whole mineral soil profile (0–50 cm; Nstock)
Nstock = ∑ NstockHi |
Available phosphorus stock
Available phosphorus stock of each horizon (PavstockHi)
PavstockHi = TNHi·bDHi·%EFHi THi | PavHi: total nitrogen of each horizon |
bDHi: bulk density of each horizon | |
%EFHi: % of earth fraction of each horizon | |
THi: thickness of each horizon |
Available phosphorus stock in the whole mineral soil profile (0–50 cm; Pavstock)
Pavstock = ∑ PavstockHi |
Exchangeable sodium stock
Exchangeable sodium stock of each horizon (Na+stockHi)
Na+stockHi = TNHi·bDHi·%EFHi THi | Na +Hi : exchangeable sodium of each horizon |
bDHi: bulk density of each horizon | |
%EFHi: % of earth fraction of each horizon | |
THi: thickness of each horizon |
Exchangeable sodium stock in the whole mineral soil profile (0–50 cm; Na+stock)
Na+stock = ∑ Na+stockHi |
Exchangeable potassium stock
Exchangeable potassium stock of each horizon (K+stockHi)
K+stockHi = TNHi·bDHi·%EFHi THi | K +Hi : exchangeable potassium of each horizon |
bDHi: bulk density of each horizon | |
%EFHi: % of earth fraction of each horizon | |
THi: thickness of each horizon |
Exchangeable potassium stock in the whole mineral soil profile (0–50 cm; K+stock)
K+stock = ∑ K+stockHi |
Exchangeable calcium stock
Exchangeable calcium stock of each horizon (Ca2+stockHi)
Ca2+stockHi = TNHi·bDHi·%EFHi THi | Ca +2Hi : exchangeable calcium of each horizon |
bDHi: bulk density of each horizon | |
%EFHi: % of earth fraction of each horizon | |
THi: thickness of each horizon |
Exchangeable calcium stock in the whole mineral soil profile (0–50 cm; Ca2+stock)
Ca2+stock = ∑ Ca+2stockHi |
Exchangeable magnesium stock
Exchangeable magnesium stock of each horizon (Mg2+stockHi)
Mg2+stockHi = TNHi·bDHi·%EFHi THi | Mg 2+Hi : exchangeable magnesium of each horizon |
bDHi: bulk density of each horizon | |
%EFHi: % of earth fraction of each horizon | |
THi: thickness of each horizon |
Exchangeable magnesium stock in the whole mineral soil profile (0–50 cm; Mg2+stock)
Mg2+stock = ∑ Mg2+stockHi |
Appendix 3
Soil properties (mean ± SE), in each stand type, fitted as vectors onto the RDA ordination (Fig. 3). PS Pinus sylvestris monospecific plots, PP Pinus pinaster monospecific plots, MM mixed plots of both Pinus species.
PS | MM | PP | R 2 | p value | |
|---|---|---|---|---|---|
WHC (gwater cm−2) | 8.65 ± 0.93 | 6.61 ± 1.54 | 5.36 ± 1.57 | 0.39 | 0.03 |
oxCstock (Mg ha−1) | 85.42 ± 12.48 | 94.40 ± 21.18 | 71.83 ± 13.40 | 0.08 | 0.53 |
Cstock (Mg ha−1) | 88.07 ± 11.42 | 97.84 ± 13.53 | 75.35 ± 10.33 | 0.32 | 0.07 |
Nstock (Mg ha−1) | 3.83 ± 0.56 | 3.59 ± 0.48 | 3.97 ± 1.60 | 0.03 | 0.81 |
Pavstock (Mg ha−1) | 18.98 ± 1.66 | 17.07 ± 2.52 | 15.03 ± 2.14 | 0.24 | 0.14 |
Na+stock (Mg ha−1) | 0.91 ± 0.07 | 0.93 ± 0.08 | 0.82 ± 0.11 | 0.16 | 0.29 |
K+stock (Mg ha−1) | 0.33 ± 0.08 | 0.28 ± 0.05 | 0.21 ± 0.03 | 0.30 | 0.10 |
Ca+2stock (Mg ha−1) | 1.98 ± 0.13 | 2.00 ± 0.38 | 1.67 ± 0.33 | 0.27 | 0.12 |
Mg+2stock (Mg ha−1) | 0.33 ± 0.04 | 0.35 ± 0.08 | 0.30 ± 0.06 | 0.31 | 0.08 |
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López-Marcos, D., Turrión, MB., Bravo, F. et al. Understory response to overstory and soil gradients in mixed versus monospecific Mediterranean pine forests. Eur J Forest Res 138, 939–955 (2019). https://doi.org/10.1007/s10342-019-01215-0
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DOI: https://doi.org/10.1007/s10342-019-01215-0