Introduction

In general, wildlife management requires habitat management. In agroforestry systems, there are several alternatives to manage habitat conditions, being “no habitat modification” one of the possible options. In order to adjust the management actions to the animals´ habitat requirements, it has to be considered that some groups of wildlife species, the so-called “edge effect species” (Shaw 1985), live better in ecotones with patch distribution of vegetational strata comprising trees, shrubs and grasslands (Guangzhi et al. 2003; Brazaitis et al. 2005). However, other groups of wildlife species are sensitive to changes in ecosystems and select more homogeneous ecosystems (Cox et al. 2003; Charles and Ang 2010; Toenies et al. 2018). There are also cases in which either this edge effect is not clear (Klein and Cameron 2012; Vetter et al. 2013; Lindemann et al. 2015) or has both positive and negative impacts on wildlife populations (Menzel et al. 1999; Brand and George 2001; Fischer and Lindemayer 2002). The Iberian lynx (Lynx pardinus) and Iberian eagle (Aquila adalberti) are examples of edge effect wildlife species in Mediterranean ecosystems (Palomares et al. 2000; González et al. 2008), while the goshawk (Accipiter gentilis) can be considered a species that is not favored by the edge effect (Abellán et al. 2011).

Red deer (Cervus elaphus) can be considered as an edge effect wildlife species, that is, its populations are higher where trees, shrubs and grasslands are close to each other, together or mixed. Besides, red deer is one of the main big game species not only in Spain, but in other countries (Fernández-Olalla et al. 2006; Schaefer et al. 2008; Herruzo and Martínez-Jáuregui 2013; Lande et al. 2014; Herruzo et al. 2016). Because red deer hunting can provide significant net revenues to hunting reserve managers and owners, one of their objectives is usually to maximize those net revenues (Herruzo et al. 2016). This work aims to compare the net revenues of two possible options to be considered by red deer managers in Mediterranean agroforestry systems: grasslands vs. shrublands (preserving tree canopy). In addition to assuming that deer are highly adaptable to these two options, the restriction of steady game harvesting is considered.

Materials and methods

As mentioned above, we propose two options (grasslands vs. shrublands) in which the tree canopy is preserved for various reasons. Firstly, if the tree canopy is dense and of natural origin (not from afforestation), it constitutes a vegetation unit of high value in terms of ecological succession (with more biomass, more protection for soil and usually more biodiversity).

However, if the tree canopy was established through afforestation, it can be converted into a good habitat (i.e., an area that can fulfill the vital requirements of the species, deer in our case) by means of adequate silvicultural treatments. Finally, if it is an open woodland like a Mediterranean dehesa (with Quercus spp. being the main tree species), such an ecosystem provides multiple benefits and services (Costa 2006; Campos et al. 2016, 2019), so it should be maintained. Therefore, the two options considered are grasslands or shrublands as understory of a Mediterranean tree canopy. One basic restriction is not to exceed a certain threshold for foraging capacity of the territory.

In this sense, following the guidelines of the Regional Government of Andalusia (Junta de Andalucía 2007), we will equal the food supply (from grasslands and shrublands, no extra feeding included) and the food demand by the animals (in kcal, referred to as Deer unit, DU) during the critical period (150 days in drought season).

We estimate 2100 kg/ha of dry matter (DM) per year as average grassland production, with a content of 1863 kcal of metabolic energy/kg DM (Díaz Gaona et al. 2014). For shrublands, we take 350 kg DM/ha as an average value for annual production with a content of 1377.50 kcal/kg DM (Junta de Andalucía 2007). Animal requirements are 5427 kcal/day for each DU (Junta de Andalucía 2007). When necessary, extra food will be supplied in summer at a rate of 3 kg DM/DU/day (Caballero 1985). For our study, corn will be supplied as food, since it is used for the supplementary feeding of red deer (Putman and Staines 2004; Katona et al. 2014).

Revenues and expenditures

Revenues

Deer game revenues are gained from selling both trophies and meat. With respect to revenues, we analyze two scenarios: (1) an optimistic scenario and (2) a pessimistic scenario (Table 1). Scenario 1 (optimistic) assumes an income of €1500/hunted deer (male of about 3 years old) and €3/kg for the sale of deer meat (males and females). Scenario 2 (pessimistic) assumes an income of €600/hunted deer (male of about 3 years old) and €1/kg for the sale of deer meat (males and females). Both scenarios for hunting rights prices are applicable to both publicly and private owned game reserves in Andalusia (www.ofertapublicacazandalucia.es). Although the current price of deer meat is slightly above €3/kg (www.asiccaza.org), a possible price range of €1-€3/kg in the medium to long term was considered.

 

Table 1 Different scenarios considered
Full size table

Expenditures

For this study, we considered the expenditure of a supplementary food supply when the foraging capacity is exceeded. The cost of supplementary feeding was calculated based on monthly market corn prices for the province of Cordoba (Andalusia, SW Spain) from September 2015 to November 2019 (ASAJA Córdoba monthly bulletins 2015–2019). During this period, corn prices ranged from €0.16–€0.18/kg.

Therefore, €0.17/kg was taken as an average value, with an average increase of €0.04/kg to account for the transport of corn from the market to the game reserves (Table 1). We assume that the corn is supplied by the gamekeeper, that this employee is common in both options (shrubland and grassland) and there is no opportunity cost since the gamekeeper can do the work of vigilance while supplying the food. We also assume that grasslands provide the highest forage production in Mediterranean agroforestry systems, with a peak in production at the end of spring. The grassland forage supply then decreases throughout the summer due to drought conditions.

The different scenarios are shown in Table 1.

Steady foraging pressure

As mentioned in the Methods section, we assume a production of 2100 kg DM/ha/year and 1863 kcal/kg DM for grasslands, amounting to a total supply of 3.91 Mkcal/ha/year. Considering 5427 kcal/day as the energy requirement of an adult deer (male and female) and a production period of 215 days/year (365 days/year minus 150 drought season days with no grassland production), by equaling supply and demand, we obtain a steady foraging pressure of 3910,000/(5427 × 215) = 3.35 DU/ha. This 3.35 DU/ha foraging pressure could be sustained by the grasslands just before the summer. For the shrublands option, the supply in summer would be (see Methods section) 350 kg DM/ha × 1377.5 kcal/kg DM = 482,125 kcal/ha. By equaling supply and demand, we obtain the foraging pressure sustained by shrublands in the drought season (150 days): 482,125/(5427 × 150) = 0.59 DU/ha.

Results and discussion

Scenario 1

Revenues

As mentioned above, the revenue from the sale of hunting rights comes from three-year-old hunted male deer. To maintain a stable deer population, we made the following assumptions (Torres-Porras and Carranza 2017):

  • Fawn mortality rate 20%

  • Mortality rate for rest of deer individuals 5%

  • Fertility rate (in females aged > 2 years) 80% (1 cube/fertile female/year)

  • Sex ratio of newborn cubes 50%.

Therefore, to obtain a three-year-old male every hunting season, it is necessary to have 1 three-year-old male + 1/0.95 two-year-old males + 1/(0.95 × 0.95) one-year-old males + 1/(0.95 × 0.95 × 0.8) male fawns (i.e., 3.15 males + 1.38 male fawns). Since the sex ratio of newborn cubes is 50%, 1.38 + 1.38 = 2.76 fertile females are needed and given that the fertility rate in adult females is 80%, 2.76/0.8 = 3.45 adult females are needed. The number of young females (1–2 years old, not fertile) would be 1.38 x 0.8 = 1.1 individuals, which are assumed to be equivalent to 0.55 DU according to their metabolic weight.

Therefore, for each three-year-old male deer, we need to maintain

$$\begin{aligned} & 3.15{\mkern 1mu} + {\mkern 1mu} 3.45{\mkern 1mu} + {\mkern 1mu} 0.55{\mkern 1mu} \\ & = 7.15{\text{ DU }}\left( {{\text{fawns}}\;{\text{count}}\;{\text{as}}\;0\;{\text{DU}}} \right). \\ \end{aligned}$$

Each year, the revenue from the sale of meat will come from both the hunted males and the necessary culling of females to maintain the stability of the deer population structure.

Culling can be estimated as follows: once 3.45 DU adult females are obtained, 5% of them will die naturally the following year, that is, 0.05 × 3.45 = 0.17 DU. On the other hand, there will be new adult females that were young ones the previous year, 1.1 × 0.95 = 1.05 DU. Thus, we would obtain a surplus of adult females to be culled each year of 1.05 − 0.17 = 0.88 DU.

Considering an average body weight of 120 kg for a three-year-old adult male, 90 kg for adult females (Sáenz de Buruaga and Carranza 2009), a meat yield from body weight of 60% (González Redondo 2010) and €3/kg for deer meat, we obtain an annual revenue from the sale of meat as follows:

One three−year−old male : 120 × 0.6 × 3 = €216

0.88 adult females: 0.88 × 90 × 0.6 × 3 = €142.56

Total revenue from the sale of meat = €358.56

Total revenues (hunting rights + sale of meat) = 1500 + 358.56 = €1858.56/year for 7.15 DU, that is, €259.94/DU per year. Hence, each extra DU amounts to an additional income of €259.94/year.

Expenditures

To estimate the expenditure of supplemental feeding, we considered that each individual deer (except for fawns) eats 3 kg of DM per day (Caballero 1985), that is, 3.53 kg of corn/day with a corn moisture percentage of 85%. As mentioned above, the critical period was 150 days in the summer and the price for corn set in the field was €0.21/kg.

Based on these assumptions, the expenditure for maintaining each DU during the critical period is 3.53 × 150 × 0.21 = €111.20/DU.

Since the expenditure of supplementary feeding (€111.20/DU) is clearly lower than the revenue (€259.94/DU), in Scenario 1 it is profitable to have grasslands and supply the deer with extra food (corn) in the summer (150-day period).

As regards the area unit, since the carrying capacity for grasslands was estimated at 3.35 DU/ha, the revenue is €259.94/DU × 3.35 DU/ha = €870.80/ha. The expenditures would amount to €111.20/DU × 3.35 DU/ha = €372.52/ha with a net revenue of €498.28/ha. Although this is not the real economic margin of the exploitation since fixed and indirect costs have not been taken into account, this value is appropriate to compare the management options studied here. In this regard, €498.28/ha can be considered a marginal net revenue for each additional hectare managed as grasslands. If shrublands are the chosen option, the revenue would be €259.94/DU × 0.59 DU/ha = €153.36/ha.

In this case, there would be no extra feeding expenditures, so the net revenue would also be €153.36/ha. The difference between both options is €498.28 − €153.36 = €344.92/ha. Therefore, grasslands are a more profitable option than shrublands.

We can estimate a critical price for the corn such that if the price increases above that amount, the grasslands option would be economically worse than maintaining shrublands. This can be expressed as:

Revenues minus Expenditures in the grasslands option: €870.80/ha – E (E is expenditures)

Revenues in the shrublands option: €153.36/ha.

E (€/ha) can be expressed as 3.35 × 150 × 3.53 × p, where 3.35 is the grasslands carrying capacity (DU/ha), 150 is the critical period (days in drought season) in which extra feeding is necessary, 3.53 is the daily kg of corn eaten per DU, and p is the price of corn set in the field.

Thus, equaling 870.80 − E = 153.36 would mean that the grasslands option is not better than the shrublands option. Hence, 870.80 − (3.53 × 150 × p × 3.35) = 153.36

We obtain p = €0.4/kg of corn.

According to this result, if the price of corn is equal to or higher than €0.4/kg, it would be more profitable to maintain the shrublands than change the land use to grasslands under the conditions of Scenario 1.

Scenario 2

In this scenario, extra feeding expenditures are the same as in Scenario 1 (€111.20/DU) but the revenues would now be €600/hunted male deer and €1/kg of meat (Table 1). Therefore, the revenues per each DU and year are:

Sale of hunting rights: €600/hunted male deer

Sale of meat:

1 three-year-old male with 120 kg body weight: 120 × 0.6 × 1 = €72

0.88 females with 90 kg body weight: 0.88 × 90 × 0.6 × 1 = €47.52. The total revenue

from the sale of meat is therefore €119.52.

The total revenues (hunting rights + meat) = €719.52/year for 7.15 DU (see Scenario 1 for explanation). That is, for each extra DU, an additional revenue of €100.63/DU is obtained. Given that this amount (€100.63/DU) is lower than the expenditure of supplementary feeding (€111.20/DU), having grasslands with an extra food supply in summer is not profitable in this scenario unless the price of corn is equal to or less than a certain value p such that revenues and expenditures are the same, that is, 3.53 × 150 × p = 100.63; p = €0.19/kg of corn set in the field and €0.15/kg in the market. In the period analyzed (2015–2019), the price of corn was never equal to or lower than €0.15/kg. Moreover, the shrublands option would yield €100.63/DU × 0.59 DU/ha = €59.37/ha as net marginal revenue. Hence, the best option in this scenario would be to maintain shrublands rather than changing the land use to grasslands. Nevertheless, to determine the price of corn for which grasslands would be the best option in this scenario, we equal the marginal net revenue of grasslands and shrublands (€/ha):

€100.63/DU × 3.35 DU/ha − E (extra feeding cost per ha, €/ha) = €100.63/DU × 0 59 DU/ha.

Therefore, the expenditure would be E = €277.74/ha.

Since E (see Scenario 1 for explanation) = 3.53 × 150 × p × 3.35, then by equaling to E = €277.74, we obtain p = 0.15 €/kg corn set in the field and €0.11/kg in the market. In the period analyzed (2015–2019), the price of corn was always higher than €0.11/kg, so it can be affirmed that the best option in this scenario would be to maintain the shrublands. We should take into account that the price of foraging products (including corn) increases in drought years and the critical period may exceed 150 days. Therefore, changing shrublands for grasslands for purposes of habitat management will probably not be a good option under conditions similar to those considered in this scenario. The economic implications of both scenarios are shown in Table 2.

Table 2 Economic balance according to different options and scenarios
Full size table

Grassland option may require the removal of shrubs periodically to prevent them from re-occupying the land. Assuming an extra expenditure for this removal of €150/ha every five years, i.e., €30/ha each year, after solving the previous equations we obtain now as critical prices 0.387/kg and €0.1/kg, values that are very close to those included in Table 2 (€0.4/kg and €0.11/kg, respectively).

Conclusions

Although the tendency for managing Mediterranean ecosystems in SW Spain is to maintain open dehesa woodlands with a Quercus spp. canopy and an understory of grasslands with little or no presence of shrublands as the most productive option both economically and, in some cases, also in terms of biodiversity, this may not be true even solely in economic terms.

In the case of deer management, our study shows that price fluctuations in both revenues (selling of hunting rights and meat) and expenditures (supplementary feeding products like corn and, eventually, periodical shrub removal) will make grasslands or shrublands the more profitable option. When the economic balance is similar, we think it is better to preserve shrublands since they usually support more biodiversity and make ecosystems more resilient to perturbations like global warming or steady drought periods, though these last aspects have not been analyzed in this study.

Management recommendations

Shrublands should not be substituted for grasslands when the grasslands produce less than values around 2000 kg DM/ha/year. Moreover, Mediterranean shrubland species of high ecological value, such as Phillyrea spp., Arbutus unedo or Myrtus communis, should always be maintained, although species such as Cistus spp. could be removed periodically to permit the development of the grasslands and prevent forest fires propagation.

From an economic perspective, the substitution of shrublands for grasslands is not efficient if deer hunting rights count for about €600/hunted individual and the price of deer meat is around €1/kg. In this situation, only when the price of corn is less than € 0.1/kg should such a substitution be considered. If the price of both hunting rights and meat is relatively high (€1500/hunted individual and €3/kg for meat), grasslands are the best, economically, option, unless the price of corn for supplementary feeding exceeds €0.4/kg.

Nevertheless, substituting shrublands for grasslands requires a management routine consisting in continuous food supplementation that may have effects on the populations´distribution as well as negative impacts in the physiological conditions of deer individuals (Pérez-González et al. 2010; Torres-Porras and Carranza 2017). It also has to be taken into account that regulations in some natural or protected areas prohibit or limit the removal of shrublands.

As a general conclusion, it is important to note that other scenarios could be analyzed using different values for the price of hunting rights, meat or corn. For example, it would be of interest to study variables such as the average age of the hunted males with relation to the revenue obtained from the selling of their hunting rights. In this study we have fixed some values we believe to be rather common in the area studied to provide a clearer account of the main economic implications of the habitat management of red deer in Mediterranean agroforestry systems.

Finally, it must be said that, as some authors point out (Pasalodos-Tato et al. 2015; Campos et al. 2019) there are other economical activities and environmental services, besides commercial hunting, linked to Quercus spp. woodlands (cork, mushroom, water supply, carbon caption, firewood, recreation, and livestock…) for which grasslands vs. shrublands options could be analyzed.