Structural & functional changes

Ecosystem services

2016-01-19T11:16:21+00:00

Authors:	Alejandro Valdecantos and Ramón Vallejo (CEAM) with input from study sites
Editor:	Jane Brandt
Source document:	Valdecantos & Vallejo. (2015) Report on structural and functional changes associated to regime shifts in Mediterranean dryland ecosystems. CASCADE Project Deliverable 5.1.

Landscapes of the Mediterranean Basin have been subjected to different human pressures since millennia in addition to the natural ones derived from climate features. These pressures have increased in number and/or intensity during the past century, with severe impacts on the wildland. Current ecosystems reflect this history of disturbances on plant community structure and composition, and environmental services provided. Pristine undisturbed ecosystems are difficult or impossible to find, instead different degraded ecosystems and landscapes can be identified along disturbance gradients.

Ecosystem services are the benefits societies get from the ecosystems. These are classified in four main groups:

supporting,
regulating,
cultural and
provisioning services,

with biodiversity as structural feature of ecosystems with direct influence in all other services. Following the Millennium Ecosystem Assessment, supporting services are those that are necessary for the production of all other ecosystem services (e.g. primary production, production of oxygen, soil formation, nutrient cycling) while regulating services are the benefits people obtain from the regulation of ecosystem processes (e.g. air quality, climate regulation, erosion control, regulation of diseases, water purification). There are also services that provide both regulating and supporting services such as water and soil conservation. Biodiversity has intrinsic value independent to any human concern.

In general terms, ecosystems have the ability to withstand some level of stress without showing signs of major changes, or to recover at the short- or medium term after disturbances by themselves. However, when pressures act for very long time and/or high intensity, ecosystem functions might overcome degradation thresholds (tipping points) and show abrupt changes in key ecological properties and ecosystem services (Scheffer et al. 2001, Daliakopoulos and Tsanis, 2013). Beyond these points, natural recovery is very unlikely to occur or very slow (Whisenant 1999) and degradation might also generate new ecosystems very dissimilar to the original reference one (Hobbs et al. 2006). Fire and grazing are the two major disturbances in CASCADE field sites. These two stresses differ significantly in the way they affect ecosystems and, as a consequence, in their short-, medium- and long term impacts. Wildfires represent discrete but very strong events of disturbance while grazing usually occurs in a continuous way with smoother effects on affected ecosystems. Therefore, the assessment of impacts and ecosystem services of sites impacted by grazing can be done at any time, but the same assessment in fire-affected ecosystems will largely depend on the time passed since the last fire because soil properties and plant communities change as secondary succession progresses (Baeza et al. 2007).

Restoring biodiversity and maximizing ecosystem services are priorities in the EU Biodiversity Strategy (Lammerant et al. 2014). Biodiversity can be assessed at different scales, from gene to ecosystems and it underlies all ecosystem processes (Mace et al. 2005). Water cycle regulation is a central ecosystem service for maintaining fresh water resources, controlling floods and, hence, protecting people living downstream (Vörösmarty et al. 2005). This ecosystem service is especially important in densely populated drylands due to the combination of high water demand, low availability and, in many places, low water quality derived from the absence of dilution potential. Transitions and movements of nutrients between and within components of the ecosystems is summarized by nutrient cycling which is regulated by a great variety of organisms and its alterations have deep impacts on ecosystem functioning, other ecosystem services and, finally, human well-being (Lavelle et al. 2005). Soil loss could be an irreversible process at the human and ecological scale. Soil retention provides very important ecosystem service to maintain primary productivity and prevent harmful effects because of soil erosion (de Groot et al. 2002). Ecosystems represent a sink for the removal and storage of carbon from the atmosphere in different biotic and abiotic components. In addition to the evident accumulation in plant aboveground biomass, soils of healthy systems can also store large amounts of C mainly in soil organic matter, roots of vegetation and microbial biomass. Furthermore, there are carbon credit markets where C sequestered in ecosystems can be sold (Jose 2009).

The main objective of this section of CASCADiS is to assess whether there are any losses of important environmental ecosystem services associated to the pressures acting in all six CASCADE study sites, and to quantify these losses if they occur. Knowing and understanding the structure, function and provision of services of degraded and reference (not necessarily pristine) ecosystems at present is a very useful tool to define restoration and conservation management practices.

Measurement of ecosystem properties and the potential for their restoration

2016-01-12T14:33:11+00:00

Authors:	Alejandro Valdecantos and Ramón Vallejo (CEAM) with input from study sites
Editor:	Jane Brandt
Source document:	Valdecantos & Vallejo. (2015) Report on structural and functional changes associated to regime shifts in Mediterranean dryland ecosystems. CASCADE Project Deliverable 5.1.

A common methodology was applied in all six CASCADE field sites to assess Ecosystem Services in, at least, two ecosystems representative of a healthy reference and a degraded state. However, the protocol has been adapted locally to fit singularities, constraints and possibilities of the different field sites. The general framework includes the identification of representative Reference and Degraded ecosystems according to the pressure acting in each specific site.

Table: Summary of pressures, reference and degraded ecosystems in the six CASCADE field sites

Field Site	Pressure	Reference Ecosystem	Degraded Ecosystem
Várzea, PT	Fire	Pinus pinaster forest	4-times burned areas (2-years after last fire)
Albatera, SP	Multifactor (climate, historical use and mismanagement)	Semi-steppe dry shrubland	Dwarf shrubland
Ayora, SP	Fire	Unburned Pinus pinaster and P. halepensis forest	Shrubland. Areas burned in 1979
Castelsaraceno, IT	Grazing	Productive pastureland	1.Overgrazed lands 2. Undergrazed lands
Randi, CY	Grazing	Shrubland	Unpalatable community
Messara, GR	Grazing	Shrubland	Unpalatable community

Three spatially replicated plots were established for every level of pressure in every field site to conduct the assessment of different variables of ecosystem structure and functioning. Replicated plots shared most physiographic, climatic, and edaphic variables as well as land use history. From these variables, we calculated a balanced set of ecosystem services. The effects of degradation on the ecosystem structure and function as well as on ecosystem services were derived through a comparison of the Reference with the Degraded state.

The following were measured and calculated:

- determination of plant composition,
- quantification of stand plant biomass,
- quantification of litter and belowground biomass, and
- application of the methodology of Landscape and Function Analysis.

1. Plant composition

Three 33m linear transects (as straight as possible) were deployed following the maximum slope and the line intercept method was applied. A metal rod (<5 mm diameter) was placed vertically every 50 cm along the tape (66 points per transect) and the contacts of plant species recorded. The contact at the soil level was also described (bare soil, stone, rock outcrop, litter, biological crust). Several plants may touch the rod in a particular point and all of them were recorded as well as the height where the plant contacts the rod. Note that this allows plant cover percentages above 100% due to overlapping.

Transects were deployed avoiding ‘strange’ or artificial features of the plot such as pathways, stone accumulation points, gullies. In case that the size of the plot did not allow 33-m long transects, more shorter transects were established but always totalling 100 m per plot.

2. Plant biomass

Three 1-m² quadrats (subplots) were defined in every transect. The placement of the quadrats was predefined to avoid subjective selection of microsites. For instance and in the case of a 33 m transect, we placed the subplots at 10-11 m, 20-21 m and 30-31 m (one meter away from the tape). Within these subplots we evaluated biomass of shrubs by two alternative approaches:

By clipping, drying and weighing. When possible, we cut all the individuals whose stems were within the quadrat limits and took them separately (one bag per species and subplot) to the lab. We dried the plant samples at 60ºC for 48h in an oven and weighed them. Grasses were not separated by species.
By allometric relations. There are available allometric equations for many of the most common shrub species in the Mediterranean Basin. By knowing a morphological variable (basal diameter, total height or biovolume of the plant), we calculated the biomass of the individuals. Alternatively, as was the case of some shrub species in Messara and Randi field sites, we built up our own allometric equations by harvesting, drying and weighing a pool of individuals outside the plots covering the range of plant sizes present within the plot.

" data-placement="top" data-content=" Example of systematic placement of the 1m2 subplots for biomass assessment (red quadrats)" title="">

3. Litter and belowground biomass

After harvesting grasses and shrubs, we collected the litter layer in a 25 x 25 cm sub-subplot. We avoided taking mineral soil particles in the samples as they are much heavier than the litter fractions. Samples were taken to the lab to dry them at 60ºC for 48h. In the same sub-subplot once the organic layer was removed we took a soil core of the uppermost soil (0-10, 0-15 or 0-20 cm depending on the site). Once in the lab, roots were separated from the soil by sieving and washing gently with water before drying at 60ºC for 48h.

4. Landscape and Functional Analysis (LFA)

The following is a highly synthesised description of the method used for the assessment of ecosystem functioning.

Transects set-up: Transects started at the downslope edge of a patch following the maximum slope and as taut as possible.
Patch and inter-patch identification: By definition, patch accumulates or diverts resources by restricting flow of water, topsoil and organic matter (e.g. perennial plants , stones > 10 cm). They act as a sink of resources. But not all patches behave the same and we discriminated when possible between different patches, e.g. resprouter shrub, seeder shrub, grasses, chamaephytes. Inter-patches represent areas where resources do not accumulate and even act as net export of resources (source areas). We measured three parameters along the transects: the number of patches (sinks), the width of every single patch (at the soil level, not the canopy and up to a maximum of 10 m), and the distance between patches (inter-patch length). However, in some field sites (e.g. Ayora) the continuity of vegetation hindered clear measurements of patch characteristics.
Soil Surface Assessment: This assessment was conducted per plot in five 50 x 50 cm areas per type of identified patch and inter-patch. These five replications were distributed throughout the plot. The soil surface assessment is rapidly made by the use of simple visual indicators. These indicators are:
•    Rainsplash protection: ephemeral grasses, foliage at heights above 50 cm and litter were excluded.
•    Perennial vegetation cover
•    Litter: amount, origin and degree of decomposition. It includes annual grasses and ephemeral herbage (both standing and detached) as well as detached leaves, stems, twigs, fruit, dung, etc. There are three properties of litter that were assessed in the following order: Cover (% and thickness of the litter layer), Origin (whether it is local or transported) and Degree of Decomposition/Incorporation.
•    Cryptogam cover
•    Crust brokenness
•    Soil erosion type and severity: Five major forms of erosion were assessed: Sheet erosion (progressive removal of very thin layers of soil across extensive areas, with few if any sharp discontinuities to demarcate them), Pedestal (is the result of removing soil by erosion of an area to a depth of at least several cm, leaving the butts of surviving plants on a column of soil above the new general level of the landscape), Terracette (abrupt walls from 1 to 10 cm or so high, aligned with the local contour), Rill (channels cut by the flowing water), and Scalding (is the result of massive loss of A-horizon material in texture-contrast soils which exposes the A2 or B horizon).
•    Deposited materials: presence of soil or litter materials transported from upslope.
•    Soil surface roughness: due to soil surface micro-topography or to high grass density.
•    Surface nature: resistance to disturbance.
•    Slake test: The test was performed by gently immersing air-dry soil fragments of about 1-cm cube size in distilled water and observing the response over a period of a minute or so. If the soil floats in water (high organic matter), then it is stable (Class 4), and if it cannot be picked (loose soils) was scored as not applicable.
•    Texture

" data-placement="top" data-content=" Measurement of patch-interpatch pattern along the transect and individual measures of the patch" title="">

Spreadsheets were prepared and were filled out with the collected information and Stability, Infiltration and Nutrient Cycling indices were automatically calculated. These indices varied between 0 and 100% depending on ecosystem functionality (100% represents fully functional systems).

Table: List of the soil functional indicators and their contribution to the indices of stability, infiltration and nutrient cycling (following Tongway and Hindley 2004). x means that the indicator is scored in the calculation of the index given above.

Indicator	Indices
Indicator	Stability	Infiltration	Nutrient Cycling
Rainsplash protection	x
Perennial vegetation cover		x	x
Litter cover	x	x
Litter origin and decomposition			x
Cryptogam cover	x		x
Crust brokenness	x
Soil erosion type and severity	x
Deposited materials	x
Soil surface roughness		x	x
Surface nature	x	x
Slake test	x	x

5. Data analysis

In every CASCADE field site we conducted t-test (sites with one Reference and one Degraded state of the ecosystem) or one-way ANOVA followed by post-hoc analysis (where three ecosystem states were identified) to assess if observed differences in all composition, functional, diversity and service variables were statistically significant. We conducted Principal Component Analysis (PCA) on specific plant cover data to assess general changes in vegetation composition and cover between Degraded and Reference sites.

Table: List of ecosystem services measured, variables from which their relative states were estimated through standardization,
and the methodology used to obtain the data of the variables.

Ecosystem Service	Variables	Methodology
Water Conservation	Infiltration Index Interpatch Cover Plant Cover	LFA + Point-intersect
Soil Conservation	Stability Index Interpatch Cover Plant Cover	LFA + Point-intersect
Nutrient Cycling	Nutrient Index Litter	LFA
Carbon Sequestration	Plant biomass Root biomass Litter	Allometries + direct quantification
Biodiversity	Richness Diversity Evenness	Point-intersect

Acquired data of structural and functional ecosystem properties were then grouped into related ecosystem services through standardization. We have selected regulating and supporting services as well as biodiversity, which underpins all services. Each variable was standardized using

ZPlot = (XPlot - AvgTot) / SDTot

where ZPlot is the standardized variable, XPlot the original variable, AvgTot the average of the variable of all plots within a field site and SDTot the standard deviation of all the plots within a field site. Variables were assigned to services as they were derived from validated methodologies selected on the basis of being appropriate indicators for this service. When several variables were combined into one service, each variable was weighted equally, as all of them are considered to be good indicators for the respective service and no available information points to a better performance of any of them. The five selected ecosystem services were also weighted equally and averaged for Degraded and Reference plots in each field site as a global result of ecosystem service losses. This way, the assessment provides a baseline integrated and global evaluation based on the simplest assumption. However, it is worth mentioning that stakeholders’ preferences regarding ecosystem services could be incorporated in the assessment in the form of different weights for each service, which could yield different global outcomes.

Note: The selection of the key common indicators and assessment methods has been based on the work developed by the EU-funded PRACTICE project on ground-based assessment indicators. They represent few essential indicators that could characterize ecosystem function for a majority of drylands worldwide, mostly focusing on water and soil conservation, nutrient cycling, carbon sequestration, and biological diversity. Most provisioning and cultural services are considered to be very much context dependent. Furthermore, half of the sites included in CASCADE are natural areas that are not expected to directly deliver goods. Therefore, our across-site comparative assessment of ecosystem services provision has been only based on supporting-regulating services, which together with biodiversity, are considered to be baseline services and properties that underpin other types of services.

References

For ease of reading, references to other scientific work have been removed from this page. See the full report for details of all the citations

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Results highlights from all study sites

2016-01-12T15:40:29+00:00

Authors:	Alejandro Valdecantos and Ramón Vallejo (CEAM) with input from study sites
Editor:	Jane Brandt
Source document:	Valdecantos & Vallejo. (2015) Report on structural and functional changes associated to regime shifts in Mediterranean dryland ecosystems. CASCADE Project Deliverable 5.1.

{tipLocations of the six CASCADE field sites} {/tip}

There is a clear climatic gradient across the study sites. Two of the sites fall within the humid climate, three belong to the dry sub-humid climate, and one is classified as semiarid. The average annual rainfall ranges from 267 mm yr-¹ in Albatera to 1289 mm yr-¹ in Castelsaraceno. There are also large differences in temperatures along the field sites. Castelsaraceno is again the coldest station with average annual mean temperature below 10ºC, while the hottest field site is Randi forest in Cyprus with mean annual temperatures close to 20ºC. The two Spanish sites show the lowest aridity indices (0.16 and 0.26 in Albatera and Ayora, respectively) while Castelsaraceno and, in a lesser extent, Várzea showed the highest aridity indices (1.05 and 0.84, respectively). Therefore, in addition to types and levels of degradation pressures, the CASCADE project includes a great variety of climates, soils, land uses and histories (Table 2) that may eventually condition the loss of ecosystem services.

Table: Climatic characteristics of the six CASCADE field sites

	Várzea	Albatera	Ayora	Castelsaraceno	Messara	Randi
Climate	Humid	Semi-arid	Dry sub-humid	Humid	Dry sub-humid	Dry sub-humid
Average annual rainfall (mm)	1170	267	385	1289	503	489
Average mean temperature (ºC)	13.0	18.0	14.6	9.1	17.9	19.5
Aridity Index (mm/mm)	0.84	0.16	0.26	1.05	0.31	0.29
PET (monthly)	118.6	136.0	123.4	102.5	136.0	141.5

Table: Summary of main properties of the six CASCADE field sites

	Varzea	Albatera	Ayora	Castelsaraceno	Messara	Randi
Elevation	450-600 m	225-310 m	830-1030 m	972-1284 m	100-230 m	90-230 m
Bedrock	Schists	Dolomites, conglomerates and sandstones	Marl and limestone colluvium, limestones	Limestones and dolomites	Limestones and marls	Marls
Soils	Cambisols	Calcisols, Cambisols and Fluvisols	Regosols, Cambisols and Leptosols	Regosols	Cambisols and Luvisols	Calcaric regosols
Land use	Forests and shrublands (and agriculture in lesser extent)	Agriculture (52%) and shrublands (24%)	Forests and shrublands	Cropland, pasturelands and forests	Croplands and shrublands	Croplands and shrublands
History	Recurrent fires (1978, 1985, 2005, 2012)	Abandonment of rainfed croplands, alpha grass harvesting and wood gathering, afforestations	Fire (1979) and abandonment of wood harvesting	Land abandonment (especially after 1990s)	Overgrazing and overexploitation of water resources	Agriculture and grazing

Fire-Driven Landscapes

Two contrasting situations are assessed on a very similar ecosystem (Pinus pinaster forest): changes of ecosystem services at the very short term on a repeatedly burned site (Várzea) and at the long term on a community without significant recovery of the overstory layer (Ayora).

Várzea

In the Várzea study site, focus is on comparing the land degradation impacts of a recent wildfire (which occurred in early September 2012) for plots that had experienced three previous wildfires since 1975 and plots that had been long unburned (for at least 37 years) (Annex 1). During the last two decades, the predominant land-cover types have been forests, shrublands and, to a lesser extent, heterogeneous agricultural areas. These agricultural areas revealed little to no changes between 1990 and 2006, whereas this same period exhibited noticeable transitions between forest and shrubland. These transitions corresponded to a change from shrublands to forests between 1990 and 2000, and to a change from forest to shrublands between 2000 and 2006. Wildfires, in 1985 and again in 2005 (with burnt areas of roughly 10 and 1 km², respectively) are probably the reason behind these transitions.

" data-placement="top" data-content=" Várzea reference plot. Mature Pinus pinaster forest unburned for 30 years at least" title="">

" data-placement="top" data-content=" Várzea degraded plot: area burned four times in the last 37 years. Last fire in 2012 (picture taken soon after the fire)" title="">

The experimental setup in Várzea was highly conditioned by land availability of the four times burned sites. Three spatially replicated plots of ca. 1000 m² were established in the Reference ecosystem (mature Pinus pinaster forest, > 40 years old) while one single block with three smaller plots was identified in the 4-times burned area (last fire in 2012). As a consequence, the length of transects and the number of subplots to assess plant biomass and litter were reduced (33 m transects and 3 subplots per plot). Biomass data of the overstory layer in the Reference plots are not yet available. As this is a key variable in determining the C sequestration service, we used available published information for a proxy of this ecosystem service in Várzea.

Results highlights

Fire produced a temporal reduction of total plant cover but higher understory plant cover only 2-years after fire
Fire opened the space for the recovery of pre-existing (both resprouters and obligate seeders) species but changed sp composition and abundance
Recurrent fires reduced habitat heterogeneity
Recurrent fires eradicated sensitive species to short fire interval (e.g. Pinus pinaster)
Ecosystem functioning, e.g. stability, infiltration and especially nutrient cycling, was severely reduced by fire
Degradation produced by recurrent fires produced significant losses for all ecosystem services considered

Ayora

Wildfires represent the degradation driver in the Ayora field site with strong effects on the landscape configuration. In the period 1975-2000 several wildfires took place in the area. Of these, the 1979 wildfire was the biggest and most devastating one. As a consequence, within the study site we may find different fire recurrences in such a small period of time. These forest fires have altered the composition of the forest surface, which previous to 1979 was dominated by Pinus halepensis and P. pinaster with scattered Quercus ilex individuals or small patches. Therefore, the landscape is a mosaic of pine forests and shrublands that differ in their composition and structure. The little economic activity taking place in the area is mostly associated with sheep and goat grazing. Before the 1979 wildfire, animals grazed the rangeland. As forest gave way to dense shrublands after the fire, sheep were mostly confined to croplands that were easier to go across. In limited cases, administrative subsidies promoted grazing in fuelbreaks in order to assist in their maintenance. On the other hand, goats are able to feed in shrublands but the number of animals is much lower than that of sheep (ca 3,000 vs 12,000). Furthermore, beekeeping is an important economic activity in the region. The big 1979 wildfire also resulted in a reduction of the logging exploitation of the forest from 24,000 to 2,000 m³ of wood per year. Rural tourism is an emergent activity in the area. Land tenure status has changed significantly, especially after the 1979 fire.

" data-placement="top" data-content=" Ayora reference plot. Mature Pinus pinaster forest" title="">

" data-placement="top" data-content=" Ayora degraded plot: shrubland" title="">

Three spatially replicated plots were established under the two states of the ecosystem: more than 50 year old Pinus pinaster forest and a secondary successional shrubland recovered after the 1979 wildfire. These two situations represent large parts of the territory of inland areas in the region of Valencia.

Results highlights

Thirty-four years after the fire plant cover in the burned sites is still lower than in the pine forest
Grasses and resprouter shrubs characterize the mature shrubland while trees are the key species in the Reference
Secondary shrubland accumulates large proportion of dead fraction in its biomass conferring a very high fire risk to the ecosystem
Patches of vegetation at the ground level are more abundant and larger in the burned sites than in the forest with lower habitat heterogeneity and diversity
Ecosystem functioning was very similar in both ecosystem states
Biodiversity and C sequestration, and their contributing variables, are the services that present the highest losses

Grazing-driven Landscapes

Grazing is the major degradation pressure in three out of six CASCADE field sites. From those, Messara and Randi share many landscape characteristics, physical features and land use histories while Castelsaraceno shows clear specificities. The three sites represent a good example of the most important environmental and socio-economic features of their respective regions.

Castelsaraceno

The vegetation cover in Castelsaraceno shows that broad-leaved forest is the most representative unit and only a small part of the surface is devoted to agriculture. After 2000, and due to rural exodus, a large part of the territory is, instead of traditional agricultural practices, covered by natural grassland and broad-leaved forest. Land cover under transition is noteworthy and there has been a progressive encroachment of pastures towards woods and shrublands. The target Reference ecosystem is a pastureland characterized by low presence and reduced quality of dominant species together with the disappearance of shrubs because livestock farming is widespread. Since 1991, the land was unevenly grazed resulting in over- and undergrazed zones.

" data-placement="top" data-content=" Castelsaraceno reference plot: productive pastureland" title="">

" data-placement="top" data-content=" Castelsaraceno degraded by overgrazing plot" title="">

" data-placement="top" data-content=" Castelsaraceno degraded by undergrazing plot" title="">

The experimental setup in Castelsaraceno included three spatially replicated blocks, Monte Alpi, Favino and Piano del Campi. We have identified Reference, Overgrazed and Undergrazed ecosystems in all of them and three replicated plots were established for each block x pressure combination (9 plots).

Results highlights

In general, Undergrazed areas show more dissimilarities to both Reference and Overgrazed sites associated to changes in plant composition and biomass
Different directions of the grazing pressure (under- and over-grazing) changed in opposite ways the spatial distribution and size of vegetation and interpatches
Ecosystem functioning was very similar in all three ecosystem states
C sequestration, biodiversity and nutrient cycling are the ecosystems services that showed higher losses due to Overgrazing
Undergrazed resulted in gains of C sequestration and biodiversity (shrub encroachment) and in losses in the soil conservation service

Messara

The natural landscape in Messara is dominated by the evergreen maquis/phrygana. Many marginal areas under natural vegetation were cleared and planted with olives. Widespread olive production in steep hilly areas in combination with grazing has triggered desertification processes. In addition further land abandonment led to less productive lands susceptible to degradation and at the same time grazing pressure significantly increased (more than 200% increases in sheeps and goats between 1980 and 1990).

" data-placement="top" data-content=" Messara reference plot: shrubland" title="">

" data-placement="top" data-content=" Messara: degraded plot" title="">

In addition to the Reference and Degraded ecosystems, we selected an intermediate state of pressure defined as Semi-Degraded. Three replicated plots were established in all three states but one of the Semi-Degraded plots was completely affected by a fire in summer 2013 therefore we conducted the evaluation of this pressure level in two plots.

Results highlights

Grazing pressure changed species composition and cover but Reference and Degraded sites showed more common species than with the Semi-Degraded
Intermediate grazing pressure produced higher ground biomass while high pressure increased plant biomass mostly associated to annuals
The most important losses related to grazing were observed in Biodiversity with lower values as pressure increased
Soil and water conservation and nutrient cycling were also severely impacted by high grazing pressure

Randi

The study sites are open areas with shrubs and sparse carob and olive trees. The land is not suitable for agriculture anymore and it is used for grazing, in particular goats and sheep. The major land use change occurred in the 1930s, when Randi was still a forest. Currently, the natural landscape is dominated by scrublands, the typical Mediterranean maquis, garrigue and phrygana. This landscape has been formed by man-made activities such as forest destruction with subsequent periodic burning and overgrazing, followed by soil erosion.

" data-placement="top" data-content=" Randi reference plot: shrubland" title="">

" data-placement="top" data-content=" Randi degraded plot" title="">

Results highlights

Plant cover and composition was significantly affected by grazing with shrubs and grasses characterizing the Reference and Degraded sites, respectively
Grazing generated smaller patches of vegetation and more open sites
Ecosystem functioning is severely decreased by grazing, producing losses in all ecosystem services assessed
All variables but grass biomass are reduced in the Grazed areas, interpatch related properties being the most sensitive to pressure
Degradation threshold might be highly exceeded

Multifactor Driven Landscapes

Albatera

The natural climate-driven vegetation communities in Albatera site are thermo-Mediterranean shrublands, dominated by deep-rooting tall shrub species that are particularly adapted to water scarcity and extreme summer drought conditions. Intense land exploitation has led to changes in vegetation towards ecosystems dominated by subshrubs and tussock grass species. Before the 1950s, the mountain range area supported some marginal activities such as alpha-grass harvesting for fiber production and wood gathering for firewood while grazing was moderately important. In Albatera, agriculture abandonment during the second half of the 20th century mostly affected rainfed crops and agricultural terraces located on (or near to) the mountain range. Most activities also ceased on the mountain range.

" data-placement="top" data-content=" Albatera reference plot: open shrubland with tall shrubs. Photo by M. Boeschoten" title="">

" data-placement="top" data-content=" Albatera degraded plot. Photo by M. Boeschoten" title="">

Results highlights

Significant plant species substitution and dominance was observed between the Degraded and References decreasing plant cover and diversity indices
Higher connectivity between source areas is found in the Degraded and, hence, higher risk to loss of resources
Infiltration and nutrient cycling were sharply altered by stress but stability was not
Sink-source pattern distribution is the most sensitive ecosystem property to degradation
All ecosystem services showed significant losses to the long-term multifactorial degradation pressures

Comparisons of changes in ecosystem properties between study sites

2016-01-19T10:17:53+00:00

Authors:	Alejandro Valdecantos and Ramón Vallejo (CEAM) with input from study sites
Editor:	Jane Brandt
Source document:	Valdecantos & Vallejo. (2015) Report on structural and functional changes associated to regime shifts in Mediterranean dryland ecosystems. CASCADE Project Deliverable 5.1.

CASCADE field sites include different Mediterranean ecosystems in a wide range of climates and degradation pressures and, as a consequence, the range of values of ecosystem properties obtained is also very large. Although comparisons between such different sites is not straightforward, Albatera, which holds the lowest aridity index, and, in a lesser extent, Randi represent the ecosystems with lower quality and functioning. Albatera presents the worst values of plant and interpatch cover, patch size (both Reference and Degraded states), diversity and infiltration (Degraded) and stability indices (Reference) of all six sites. On the contrary, Ayora offered the highest values of the Degraded states of all sites in plant spatial distribution and LFA indices. Biodiversity indices were highest in Castelsaraceno both for the Reference and the Degraded (Undergrazed) states and lowest in Várzea (Reference) and Albatera (Degraded). Várzea showed the two extreme values for aboveground biomass: the lowest in the Degraded (just two years after the last fire) and the highest in the Reference. In general, climate conditions frame degradation vulnerability through their effect on plant productivity and, probably, in plant community resilience to disturbances.

{tip
Direct comparison of ecosystem properties between the Reference and the Degraded states in the six CASCADE study sites.} {/tip}

" data-placement="top" data-content=" Summary of the loss of standardized ecosystem services due to the local degradation pressure in all CASCADE field sites. Bars represent an average of all five environmental services evaluated. Várzea* refers to the C sequestration service including estimated biomass of the overstory with bibliographic data." title="">

Areas under pressure from grazing

In general, the plant communities in the Degraded situations are very different from the respective healthy References both in composition and abundance. Pressure resulted in more homogeneous communities than in undisturbed states, except in Randi, where high heterogeneity is observed within both Reference and Degraded ecosystems, and Castelsaraceno, with little variations within degradation levels. Intense grazing may represent a stronger effect than soil texture in determining vegetation pattern distribution (Fuhlendorf and Smeins 1998). However, Adler et al. (2001) suggested that grazing might lead either to higher or lower heterogeneity depending on both the pre-grazing spatial pattern of vegetation and grazing.

Our field sites affected by grazing showed a generalized decrease in diversity with grazing pressure and, hence, can be described as overgrazed (Perevolotski and Seligman 1998). Papanastasis et al. (2015) applied the same methodology to assess the change in ecosystem services due to grazing in rangelands in Greece. They obtained very similar results to those we observed in CASCADE grazing sites, with a significant loss of biodiversity, stability, infiltration and nutrient cycling indices, plant cover and size and cover of vegetated patches in heavily grazed areas. But they also reported increases in some properties and ecosystem services when grazing pressure is moderate. Some authors have observed an increase in plant species diversity when disturbed by grazing (Belsky 1992), partly because of the change of competitive relationships between plant species (Crawley 1983). In addition to these change in diversity, we observed a profound change in species composition in all grazed sites, more modest in Castelsaraceno, as demonstrated in the PCA analysis and figures. Holocheck et al. (1989) reported a shift in species composition due to heavy grazing, partly due to an increase in the competitive ability of unpalatable species. But many dominant species of grazed rangelands present morphological and biochemical mechanisms to withstand grazing providing a relatively high resilience to the system (Perevolotsky 1995). Aboveground biomass was reduced in two out of three grazed sites (Castelsaraceno overgrazed and Randi) but increased in Messara. The reduction in leaf area associated to grazing severely affects to primary production in herbaceous pastures such as Castelsaraceno but the same does not happen in areas where shrubs are more abundant such as Randi. Shrubs have longer annual growth cycles and allocate photosynthates to woody parts and roots, often showing compensation growth responses (Tsiouvaras et al. 1986; Perevolotski and Seligman 1998). However, in sites that present a long history of grazing, higher levels of pressure may not significantly affect productivity. Plant pattern in the grazed states is markedly different than in the ungrazed ones, with higher interpatch cover and lower length and width of the plant patches in the grazed plots. These changes reduce the resource sink capacity as observed in other areas subjected to grazing (Papanastasis et al. 2015). Similarly, LFA derived indices are lower in all Degraded sites than in their respective References suggesting a reduction of soil surface conditions and, hence, soil, water and nutrient conservation in the system (Papanastasis et al. 2015). Ecosystem services have shown important losses due to grazing in the order Randi>Messara>Castelsaraceno following a decreasing order of aridity. Wang et al. (2014) established 0.32 as the threshold value of the aridity index that determines net N losses or accumulations. Castelsaraceno and Randi are well above and below this value of aridity, respectively, while Messara is just in that supposed threshold. On the other hand, grazing, especially when intense, represents an important tool to reduce fire risk in areas like the Mediterranean basin with prolonged drought periods by reducing the amount of fuel susceptible to burn during them. In these cases, grazing systems provides another service to people as it is the reduction of fire hazard.

Biodiversity and ecosystem functions in drylands have been observed to depend on the relative cover of woody species, with linear relationships in dry-subhumid sites and hump-shaped curves peaking at relative woody covers of 40-60% in semiarid (Soliveres et al. 2014). Isbell et al. (2015) suggested that the reduction in biodiversity generates an 'ecosystem service debt’ and defined it as 'a gradual loss of biodiversity-dependent benefits that people obtain from remaining fragments of natural ecosystems'. These authors highlighted the relevance not only of the extension of ecosystems but also the necessity of preserving and enhancing their quality in order to guarantee a sustainable provision of ecosystem services.

Areas under pressure from fire

The sites with fire pressure offer two complementary pictures of secondary succession after wildfires: a very initial stage of vegetation recovery in Várzea and a mature continuous shrubland without tree-canopy recovery in Ayora. In the short term, the ecosystem shows important reduction in species richness, biomass, vegetation patches, stability, infiltration and nutrient cycling. All these things result in an overall significant loss of ecosystem services. But this maritime pine forest system has the ability to recover with time most of them, if not all. Thirty-five years after the fire, the Ayora burned areas recovered ecosystem functionality to values of the Reference pine forest, and showed a spatial arrangement of vegetation that better conserves the resources, and accumulated similar amounts of understory and belowground biomass and litter. Pine regeneration after fire depends on many factors such as fire-interval, pre-fire basal area, slope aspect, land use history or competition with grasses at the seedling stage (Pausas et al. 2003, 2004; Baeza et al. 2007). The scarce presence of pines in the Degraded states of Ayora field site resulted in a significant reduction of the C sequestration service and could be improved by appropriate post-fire management.

The observed shift from forest to non-forest (shrubland) vegetation observed in Ayora is not uncommon especially in drylands. The very high fire recurrence of the Degraded plots in Várzea and the short interval between the two latest fires (2005 and 2012) may cause the change from forest to non-forest vegetation in this area as the time for the first flowering in Pinus pinaster may take between 4 and 10 years (Tapias et al. 2004). This imbalance between fire regime and dominant plant species’ life histories or unfavorable post-fire conditions may result in a failure to recover pre-fire carbon stocks and hence C sequestration service (Rocca et al. 2014). Stephens et al. (2013) suggested that this shift might not be catastrophic but would affect most ecosystem services. All ecosystem services showed significant short-term losses after the fire (Várzea) but only biodiversity and C sequestration losses lasted in the long term (Ayora). However, the particular conditions in Várzea, especially the higher water availability (0.84 and 0.26 aridity indices in Várzea and Ayora, respectively) suggest that the recovery of these assessed ecosystem services will be faster.

Area under multiple, diffuse pressures

Albatera showed the highest relative losses of all individual ecosystem services and the combined value of all CASCADE field sites. It is the most stressed site as reflected by the very low aridity index (0.16 classified as semi-arid) and multiple diffuse pressures are and have been acting in the place for long. The main ecosystem properties affected by degradation were those related to the spatial distribution of vegetation and open areas (sink/source spatial pattern). The Degraded landscape showed a reduction of vegetation cover, with less and smaller patches of vegetation at longer distances from each other, and higher proportion of bare soil, which in turn reduces capacity of water infiltration and nutrient cycling, and decreases water conservation and soil conservation, and, finally, reduces productivity (Boeschoten 2013). The loss of water conservation is said to be the most essential function in semi-arid ecosystems (Whitford, 2002). Biodiversity was also highly reduced in the Degraded areas probably related to the absence of tall shrubs that act as keystone species in these semiarid shrublands (Maestre and Cortina 2004). Rey Benayas et al. (2009) observed a positive relationship between biodiversity and ecosystem services and suggested that restoration efforts should be directed to increase biodiversity. Stability is the index that showed the lowest loss in the Degraded as compared to the Reference state. Previous works in semiarid Mediterranean areas have showed that the Stability index is less sensitive than the other LFA indices to detect differences between land uses and/or degradation levels (Mayor and Bautista, 2012). However, it could also be that current erosion in the degraded state is actually low due to accumulated effects of past erosion. Thus, higher surface stone cover due to past soil loss may be protecting the soil from further severe erosion. Similarly, higher surface compaction due to accumulated disturbance and the loss of the top soil layers, richer in organic matter, may result in higher runoff but lower soil loss (Mayor et al. 2009). López et al. (2013) found lower values of the LFA stability index as degradation increased associated to lower vegetation cover and patch density, length and width, but a further increase of the index with more intense degradation as the exposed rock surface is higher and the sediments susceptible to be transported is lower. These results could therefore suggest that the system might have overcome a threshold of irreversibility (Scheffer and Carpenter 2003).

Summary

In summary, degradation pressures severely impacted ecosystem properties and services of the selected ecosystems along the Mediterranean Basin in a wide range of ecological, biogeographical and historical characteristics. The higher the aridity, the higher the loss of ecosystem services. Some observed changes from the Reference towards the Degraded states suggest that certain degradation thresholds might have been passed.

References

See the full report for details of all the other work cited on this page

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