Elsevier

Acta Oecologica

Volume 112, October 2021, 103773
Acta Oecologica

The influence of growth types on soil properties along an elevation gradient in a semi-arid oak forest

https://doi.org/10.1016/j.actao.2021.103773Get rights and content

Highlights

  • Soil properties improved with increasing canopy cover.

  • Soil fertility decreased with soil depth but did not vary significantly according to elevation.

  • Patches of woody vegetation create ‘islands of fertility’.

  • Conservation of these patches is essential in semi-arid areas.

Abstract

In semi-arid environments like Zagros (western Iran), soil properties are influenced by vegetation cover particularly tree species. This research addressed the effect of three oak (Quercus brantii Lindl.) growth types (seed-origin trees, old and young coppice forms areas) on soil physio-chemical and biological properties along an elevation gradient. Soil sampling was carried out at two soil depths (0–5 and 5–25 cm) and three elevations (low, middle and high) in the three types of growth and in treeless area. We found lower values in soil nutrients, carbon sequestration, soil moisture and microbial activities in the open area than beneath the vegetation cover at all elevations. There was a significant influence of the type of growth: values of most of the biological and chemical properties were lower in the young coppice type than in the old coppice type and seed-origin trees. We also found negative correlations between carbon sequestration and microbial biomass nitrogen and basal respiration in all types of growth. These results thus emphasize the role of patches of woody vegetation in creating ‘islands fertility’. The type of growth significantly influence soil properties through the whole elevation gradient and the old seed-origin type was the most favorable for soil fertility.

Introduction

Semi-arid regions cover about 15 percentage of the land surface around the world (Huang et al., 2016). In these areas, the forests play a vital role on people's livelihoods in providing wood and non-wood products (Conti and Díaz 2013; Martin et al., 2015). These ecosystem services largely rely on the soil component, which also plays a key role in mitigating the impacts of climate change by carbon sequestration (Lal 2010; Yücesan et al., 2019). However, vegetation of semi-arid regions were largely modified by anthropogenic disturbances including land-use changes. For instance, many forest areas were transformed into simpler formations such as pastures, croplands and rainfed areas. Such huge changes have deeply affected not only the composition and the diversity of the vegetation but also the soil fertility (Rotenberg and Yakir 2010). In present forest areas, it has been shown that soil properties were influenced by the past and present forest activities and anthropogenic disturbances through the modification of the vegetation composition and structure (e.g. Jandl et al., 2007; Liu et al., 2013; Valipour et al., 2014; Clay et al., 2019). However, the frequent patchy structure of the woody vegetation in semi-arid regions have induced a great variability in soil properties. In fact, woody species can create nutrient-rich areas under their canopy, an effect known as ‘fertility islands’ which play a marked ecological role in arid and semiarid regions (Camargo-Ricalde and Dhillion 2003; Heydari et al., 2017b; Li et al., 2008). The presence and distribution of these islands cause spatial heterogeneity in soil properties and are likely to affect species distribution, establishment of biodiversity and plant production (Maestre et al., 2003; Heydari et al., 2017 a). Although the effects of tree species on creating fertility islands have been studied in different regions (Rong et al., 2016; Avendaño-Yáñez et al., 2018; Salazar et al., 2019), our knowledge on how different growth types can affect the soil properties of these islands is still limited particularly in semi-arid areas. Besides, we largely ignore how the variation in the environmental factors (e.g. along an elevation gradient) can modulate the effects of the fertility islands (Su et al., 2004; Yao et al., 2017). This ‘island’ effect also largely depends on the forest management system as silvicultural operations largely control the nature and the importance of the forest cover. For instance, the conversion of high forests into coppices, or the reverse operation, can modify the cover of the overstory and understory and therefore influence soil properties although only few studies have documented this process. For example, Darenova et al. (2016) stated that CO2 emission and soil moisture varied according to the forest structure in temperate oak forests (high forest, high forest converted from coppice, coppice). Studying the conversion of oak coppice into high forest in Turkey, Yücesan et al. (2019) found that the decrease in canopy cover percentage during this process could lead to soil erosion and C sequestration and Martin et al. (2015) also showed that the Ca, K, N, soil organic matter contents and C/N ratios were influenced by the intensity of management in the coppice systems. In addition, in oak forests of western Iran, the conversion of high forests into coppices resulted in reduced soil fertility and soil moisture content (Heydari et al., 2017 b). However, these studies were achieved in similar site conditions and have not investigated how the influence of the forest structure on soil properties can be changed along an elevation gradient. Answering this question can be helpful to select adapted restoration management methods such as selecting the most favorable forest structure to promote seed or seedling installation. In addition, the intensity with which soil properties are modified beneath vegetation in these islands is likely to vary with soil depth (Li et al., 2008; Rong et al., 2016). It is well known that soil characteristics such as soil texture, nutrient elements content, bulk density, temperature, and moisture change with soil depth. For example, content in organic matter and nitrogen under woody species, were more concentrated in the top soil (de Boever et al., 2015) and microbial contents sharply decreased with soil depth in oak forests of southern Spain (Aponte et al., 2010). However, this process has received little attention in the semi-arid oak forests particularly after the conversion of high forests to simple coppice systems.

To tackle these issues, we have investigated the effects of different forest structures on soil properties (taking into account soil depth) along an elevation gradient. The study was conducted in the semi-arid Zagros oak forests in western Iran. These formations are of major importance in providing ecosystem services such as climate regulation, carbon sequestration, soil conservation, water resource, biodiversity and all people who live in this region (Talebi et al., 2013; Niknejad et al., 2014; Heydari et al., 2017 c). Originally, the region was largely covered by naturally regenerated forests which were then submitted to drastic land-use changes (e.g. deforestation and conversion into agricultural lands). At the same time, the forests were intensively exploited to respond to the fuel wood demand and largely converted into coppice systems (Talebi et al., 2013; Heydari et al., 2016). The too frequent biomass harvesting in these systems have probably altered soil fertility on the long term as documented in other regions (García-Orenes et al., 2017; Lucas-Borja et al., 2019). While, coppices were commonly found in European forests, they have been largely converted into high forests as a more adapted system mostly for economic reasons but also, to a lesser extent, for ecological reasons (Ciancio et al., 2006; Kupec et al., 2015). In semi-arid areas like Zagros, such transformations may lead to similar benefits in particular in improving soil fertility (Heydari et al., 2017 a). However, this question is still underexplored particularly in changing site conditions. In this context, we seek to answer the following questions:

  • (1)

    Does the transformation of high forest into coppice stand reduce soil fertility, soil carbon sequestration, and microbial activities? We hypothesize that the reduced canopy cover in the coppice system could alter most of the soil physico-chemical properties compared to the high forests.

  • (2)

    Does the intense management of the coppice system affect negatively soil biological attributes? We expect the effect is all the more negative as the management is intense.

  • (3)

    Do soil properties vary with the elevation gradient and soil depth? Our assumption is that the modification of the climatic factors along the elevation gradient could influence the interaction between the soil and the types of tree growth. We also expect strong variation of soil properties with soil depth.

Section snippets

Study area

The study area (387 ha) is located in the middle of the Zagros zone in the Ilam province (western Iran) and is known as Gachan oak forest (33° 39′–33° 40′ N and 46° 28′–46° 30′ E) (Fig. 1). The Zagros zone is covered with oak forests (Quercus brantii Lindl.) in form of patches of variable size intersperse with treeless areas. These forests are composed of coppice systems (thereafter named ‘sprout clump’ tree growth type) and of naturally regenerated stands from self-sown seeds for a small part

Influence of elevation, oak growth types and soil depth on soil properties

All soil chemical (Pava, Kava, CEC, Ntot, OM and CS), physical (BD and SP) and biological (BR, MBC and MBN) properties were significantly influenced by elevation gradient (all P-values <0.0001), types of tree growth (all P-values <0.0001) and soil depths (except for Pava and Kava) (Table 2). The highest and lowest soil chemical, physical and biological values were observed in SO and OA, respectively (Fig. 2) while, the highest values of BD were found in OA. In addition, values for OCO and YCO

Soil chemical properties

The comparison of contents in available P, K and Ntot among the different types of tree growth showed that, whatever the elevation, values were the highest under SO followed by OCO and then decreased significantly under YCO and OA. This finding, as well as the results recorded on soil biological properties (see below), confirms our first hypothesis about the influence of types of tree growth on soil properties. It illustrates the high capacity of trees and shrubs to increase the content in

Conclusion

Soils types and properties in the Mediterranean landscapes are the result of a complex interplay of factors including site conditions, vegetation patterns and a long history of human disturbances. In this study, we have investigated the influence of elevation and different types of tree growth on soil properties at two soil depths in a semi-arid oak ecosystem. A main result is that tree cover plays a prominent role in shaping soil properties along the whole elevation gradient. This ‘canopy

Author contribution statement

Conceptualization, MB and MH; writing—original draft preparation, MB, MH, RO; writing—review and editing, MB, MH, PB; visualization, MB, MH; Data analysis, MH and RO; supervision MB, MH; All authors have read and agreed to the published version of the manuscript.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We are grateful to the Ilam University for financial support of the research and extend our appreciation to the natural resource office for the technical support.

References (70)

  • R. Jandl et al.

    How strongly can forest management influence soil carbon sequestration?

    Geoderma

    (2007)
  • P.X. Li et al.

    Fertile islands under Artemisia ordosica in inland dunes of northern China: effects of habitats and plant developmental stages

    J. Arid Environ.

    (2008)
  • M.E. Lucas-Borja et al.

    The impact of straw mulching and salvage logging on post-fire runoff and soil erosion generation under Mediterranean climate conditions

    Sci. Total Environ.

    (2019)
  • E. Marchi et al.

    Impact of silvicultural treatment and forest operation on soil and regeneration in Mediterranean Turkey oak (Quercus cerris L.) coppice with standards

    Ecol. Eng.

    (2016)
  • A.C. Treydte et al.

    Trees enhance grass layer quality in African savannas of distinct rainfall and soil fertility

    Perspect Plant Ecol

    (2007)
  • A. Valipour et al.

    Traditional silvopastoral management and its effects on forest stand structure in northern Zagros, Iran

    For. Ecol. Manag.

    (2014)
  • L. Zhou et al.

    Soil respiration after six years of continuous drought stress in the tropical rainforest in Southwest China

    Soil Biol. Biochem.

    (2019)
  • K. Alef et al.

    Methods in Applied Soil Microbiology and Biochemistry

    (1995)
  • M. Allegrezza et al.

    Microclimate buffering and fertility island formation during Juniperus communis ontogenesis modulate competition–facilitation balance

    J. Veg. Sci.

    (2016)
  • C. Aponte et al.

    Microbial C, N and P in soils of Mediterranean oak forests: influence of season, canopy cover and soil depth

    Biochemistry

    (2010)
  • M.D. Avendaño-Yáñez et al.

    Leguminous trees from tropical dry forest generate fertility islands in pastures

    Arid Land Res. Manag.

    (2018)
  • D. Binkley et al.

    Ecology and Management of Forest Soils

    (2013)
  • G.R. Blake et al.

    Bulk Density. Methods of Soil Analysis: Part 1 Physical and Mineralogical Methods

    (1986)
  • G.J. Bouyoucos

    Hydrometer method improved for making particle size analyses of soils

    Agron. J.

    (1962)
  • J.M. Bremner et al.

    Methods of Kjeldahl Digestion. Methods of Soil Analysis: Part, 2

    (1982)
  • S.L. Camargo-Ricalde et al.

    Endemic Mimosaspecies can serve as mycorrhizal ‘‘resource islands’’within semiarid communities of the Tehuaca ́n-Cuicatla ́n Valley, Mexico

    Mycorrhiza

    (2003)
  • L. Clay et al.

    An analysis of common forest management practices for carbon sequestration in South Carolina

    Forests

    (2019)
  • G. Conti et al.

    Plant functional diversity and carbon storage–an empirical test in semi-arid forest ecosystems

    J. Ecol.

    (2013)
  • R.A. Dahlgren et al.

    Oak tree and grazing impacts on soil properties and nutrients in a California oak woodland

    Biogeochemistry

    (1997)
  • E. Darenova et al.

    Different structure of sessile oak stands affects soil moisture and soil CO2 efflux

    J. For. Sci.

    (2018)
  • J. Fox

    Applied Regression Analysis and Generalized Linear Models

    (2015)
  • W.E. Frost et al.

    Effects of tree canopies on soil characteristics of annual rangeland

    Rangel. Ecol. Manag.

    (1991)
  • F.A. García-Morote et al.

    Effects of woodland maturity, vegetation cover and season on enzymatic and microbial activity in thermophilic Spanish Juniper woodlands (Juniperus thurifera L.) of southern Spain

    Eur. J. Soil Sci.

    (2012)
  • C.J. Harman et al.

    Spatial patterns of vegetation, soils, and microtopography from terrestrial laser scanning on two semiarid hillslopes of contrasting lithology

    J. Geophys. Res.: Biogeosciences

    (2014)
  • M. Heydari et al.

    Influence of soil properties and burial depth on Persian oak (Quercus brantii Lindl.) establishment in different microhabitats resulting from traditional forest practices

    Eur. J. For. Res.

    (2017)
  • Cited by (0)

    View full text