ORIGINAL ARTICLE

Space distribution of Pennisetum purpureum, according to projections for climate change in Cuba

Distribución espacial de Pennisetum purpureum, según las proyecciones de cambio climático para Cuba

A. Álvarez-Adán, G. Febles, J. M. Fernández

ABSTRACT

In order to determine the future space distribution of Pennisetum purpureum, according to projections of climate change for Cuba, with the purpose of contributing to take proper decisions regarding future management of this species and to establish efficient regulations for its adaptation to the influence of climate change, a general methodology of analysis was designed that combined the information of mean annual temperature and precipitation, type of soil, pH, and irrigation with the implementation of space analysis operations: filtration and map superposition to achieve space distribution. Therefore, daily outputs of the General Circulation Model Echan4 were used with forcing of emission scenarios A2 and B2, for the analysis of future climates. It was confirmed that, according to soil potential, only 34% of Cuban territory may be used for the cultivation of the studied species. In addition, there was a tendency to decrease the areas with potential of precipitation-temperature, favorable for the development and growth of this species. A2 scenario was the most critical. Negative anomalies increased up to 64 and 59% for A2 and B2, respectively. It is concluded that integration of physical, climate and soil factors allowed the identification of potentially usable areas for cultivation and development of this species.

Key words: future climates, Pennisetum purpureum, space distribution.

RESUMEN

Para determinar la distribución espacial futura de la especie Pennisetum purpureum, según las proyecciones del cambio climático para Cuba, con el propósito de que contribuya a tomar decisiones adecuadas en cuanto al manejo futuro de la especie y al establecimiento de medidas eficaces para su adaptación ante la influencia del cambio climático, se diseñó una metodología general de análisis, que combinó la información de temperatura y precipitación media anual, tipo de suelo, pH y drenaje con la ejecución de las operaciones de análisis espacial: filtrado y superposición de mapas para lograr la distribución espacial. Se utilizó para ello salidas diarias del Modelo de Circulación General Echan4 con forzamiento de los escenarios de emisiones A2 y B2, para el análisis de los climas futuros. Se comprobó que, según el potencial de suelo, solo  34 % del territorio cubano se puede utilizar para el cultivo de la especie estudiada. Además, se observó tendencia a la disminución de las áreas con potencial de precipitación – temperatura, favorables para el desarrollo y crecimiento de esta especie. El escenario A2 fue el más crítico. Las anomalías negativas crecieron hasta 64 y 59 % para el A2 y el B2, respectivamente. Se concluye que la integración de los factores físicos, clima y suelo, permitió la identificación de las áreas potencialmente utilizables para el cultivo y desarrollo de la especie.

Palabras clave: climas futuros, Pennisetum purpureum, distribución espacial.

INTRODUCTION

In the tropics, grasses are the main resource for cattle feeding. The lack of coarse feed for cattle during dry season leads to the increase of their production to raise livestock productivity. According to Suárez y Herrera (1986), the cultivation of these plants in Cuba shows its maximum productivity during rainy season (May-October), which basically decreases during dry period (November-April), in which only 30% of annual yield is reached (Herrera et al. 2014). In this season, temperature and solar radiation are low, and days are short compared to the months of rainy season. In addition, water scarcity is a climatic factor limiting production during this time.

Together with the above, climatic fluctuations recorded in various regions of Earth also affect Cuba and are the subject of study and concern by the national and international scientific community, because they affect food production. Added to this, nowadays, climate change scenarios are studied on the basis of assimilation and use of regional climate models integrated to the system of regional modeling PRECIS (Providing Regional Climates for Impacts Study) (Jones 2004).

Currently, the genus Pennisetum is found in the tropical and subtropical areas, represented by many species and varieties. This genre, and specifically P. purpureum, stands out as forage plant in Cuba (Herrera 2005, García et al. 2014)  and Latin America (Nava et al. 2013, Murillo et al. 2014) due to its energy value and high productive potential, in irrigation and drought.

Knowledge of the space distribution of pastures may be an effective tool for the management of the specific species and for the establishment of effective measures for adapting to future climate variations.

Given these conditions, the objective of this research was to determine the future space distribution of P. purpureum, according to projections of climate change for Cuba, so to take adequate decisions in the future management of this species and the establishment of effective adaptation measures in front of the influence of climate changes.

MATERIALS AND METHODS

To determine the potential of temperature-precipitation for the development of P. purpureum, data of temperature and average monthly precipitation was used, from 61 meteorological stations distributed throughout the country, belonging to the Meteorological Institute of Cuba (INSMET, initials in Spanish). A record of 30 years, from 1961 to 1990 period, was considered, and it was used as baseline. In order to know the potential of the soil, information about soil type, pH and irrigation soil map of Cuba, at a scale of 1: 250 000, was used and it was correlated to the New Genetic Classification of Soils from Cuba (Hernández et al. 2015).

With soil type information, three groups were formed: good, regular and poor, according to studies conducted by Paretas (1990) for this species (table 2), covering 20 soil types described in the New Genetic Classification of Soils of Cuba (Hernandez et al. 2015).

Temporary periods 2040, 2070 and 2099 were considered as limits of the three periods established for the analysis of future climates. Daily outputs of temperature and mean precipitations of General Circulation Models (GCM) Echan4 were used, with space resolution of 25 km and A2 and B2  emission scenarios (SRES) were used, proposed by Houghton and IPCC (2001). Both scenarios propose a situation in which the world does not follow a globalizing pattern. Nevertheless, A2 indicates that local identities are preserved and population will grow at a medium rhythm. Economic and technological development will be fragmented and slower than in other scenarios. Therefore, a less favorable scenario will be considered, regarding greenhouse effect gases emissions. In scenario B2, local solutions for social, economic and environmental problems will be very important. Technological evolution will be less fast but more diverse than in the rest of scenarios. It will be oriented to environment protection and social equality, at local or regional level. A more favorable scenario will be considered.  

This selection of scenarios was confirmed by Bárcena (2010) and Bárcena et al. (2014), because it is considered that conditions of Latin America and the Caribbean will be determined by economic development, with new clean technologies, mainly at regional or local level. In addition, this model, according to criteria of Jones (2004) and Campbell et al. (2011), is one of the available models and represent, properly, the general circulation of the atmosphere in the Caribbean.

It is important to point out that the function of climate is well documented as a soil forming factor so there is a relationship among temperature, precipitation and physical properties of soil. However, there are no current studies on the effects of climate change on soil properties. Hernández et al. (2008), for example, refer that combination of temperature and humidity conditions determine the rate of creation and decomposition of organic matter, as well as the speed and character of weathering processes. Likewise, changes of precipitations and temperatures create different conditions of the type of formation of clay minerals in the soil, which contribute to important changes in their physical and chemical properties. Among other effects, the increase of global temperature may also accelerate carbon losses of soils, which increases the concentration of carbon dioxide in the atmosphere. Equally, changes of rain patterns may contribute to the increase of erosion in vulnerable soils that usually experience a low content of organic matter, as in the case of those occupying grasses in Cuba.

Nevertheless, in Cuba, some precise studies on soil use changes and erosion have been conducted. In this last case, there is a very specific study of Febles et al. (2014), stating that red ferrallitic soils from Mayabeque and Artemisa provinces will experiment losses of 50 % towards 2050, due to the erosions provoked by the increase of the frequency of hurricanes of high intensity in the area.

RESULTS AND DISCUSSION

For conducting any predictive study, it is important to know the available potentialities, in this case, climatic ones. They may be known from temperature, mean monthly precipitations and soil indicators, from the type of soil, pH and drainage to cover the needs of crops under analysis that will be used in the space
distribution.  

- Not advisable: areas with precipitations lower than 800 mm and temperature inferior to 18 ºC or superior to 30 ºC.

- Acceptable: areas with mean annual temperatures between 18 and 24 ºC or superior (26-30 ºC) and acceptable precipitations between 800 and 1000 mm.

- Moderately good: areas with incidence of proper temperatures (24- 26 ºC) and acceptable precipitations or with another combination of high temperatures with proper precipitations, superior to 1,000 mm.

- Good: areas with values of precipitation superior to 1000 mm and temperatures range between 24 and
26 ºC.

According to data of table 3, it can be stated that Cuban climate, at baseline, shows high potential for the development of this species. It means that 100% of national territory has climatic conditions for fulfilling the requirements of this species. An amount of 93.2 % of its areas is included into the categories of moderately acceptable and good. This condition indicates that the space distribution has homogeneous conditions, which means high vulnerability of the territory to future variations of regional climate.

After a joint analysis of the requirements of P. purpureum, in order to determine the soil potential from the criteria stated in tables 1 and 2, it was confirmed that only 35,603.62 km² (34 %) of national territory (distributed into the categories of acceptable and good) can be used for cultivating this species. The first category included the areas where the type of soil was qualified as regular, with acceptable conditions of pH and drainage. Second category corresponded to areas where the type of soil was considered as good, with proper drainage and accepted values of pH for P. purpureum (figure 2). This means that the reported percentage corresponds to areas with acceptable conditions of type of soil, pH and drainage for the development of this crop. However, this does not indicate that this species is exclusive for these areas. Nowadays, it may be found in several ecosystems from Cuban territory, although, as it happens with the cultivar Cuba CT-115, it does not reach all its productive potential, even though it is used for animal feeding during dry period, as its technology recommends (Martínez and Herrera 2015).

It is important to state that space distribution of P. purpureum at the baseline presented the same categories and percentages that showed the space distribution of soil potential.

Projected scenarios. Mean superficial temperature of air, projected up to 2099 for Cuba, should present a tendency to increase with high variability between years (figure 3) and possibilities to reach maximum values of 30.1 ºC for scenario A2, and 29.3 ºC for B2 in the temporary period 2071-2099. These values depend on increases between 2.7 and 5.0 ºC of scenario A2 versus 2.7 and 4.2 ºC of B2. Regarding tendency, it is highlighted that, up to 2070, there will be a marked differentiation between scenarios.

Del Pozo (2002) states that one of the structural mechanisms for grasses to reduce stress effects due to high temperatures is the increase of cell wall content, mainly in lignin, which reduces their digestibility and quality. In addition, it is known that, during rainy season, when temperatures are high and transpiration reaches superior values, quality of grasses is negatively altered, which mostly may be measured with leaf percentage.

Unlike the adequate coherence among the future estimations of air temperature, results of precipitations showed higher dispersion and variability of values in both scenarios (figure 4a). It is important to highlight that the three temporary periods to be analyzed (2011-2040, 2041-2070 and 2071-2099) should show negative anomalies, which supposes increase of water deficiencies for this crop (figure 4b).

In a general sense, performance of water deficit indicates a slight recovery towards period 2041-2070 and a later decrease. Simulation of scenario B2 reveals a tendency to recovery, despite that, in 2099, there will be no superior values to those of the first temporary period and it will not reach values of precipitation reported for the baseline. It means that values of anomalies will range between -15 and -13 %. Scenario A2 will show the highest water deficit, with a tendency to intensification for the last period of analysis and its values of anomalies will vary from -10 a -21 %.

Stress due to droughts, common in tropical regions, intensified from projections of precipitations established for Cuba, may affect the physiological and morphological performance of the plant, depending on intensity, and growth and development state of the plants. Among the most sensitive effects, there is a reduction of cell expansion, motivated by decrease of turgency, stoma closure, transpiration and photosynthesis. In addition, water deficit modifies the relationship of biomass between the aerial and radicular part of the plant (Coraza and Quintero 1991, Hernández et al. 2008).

These results agree with reports of Centella et al. (2001), Solano et al. (2005) and Planos et al. (2013), which indicate an increase of temperature that, in the most adverse scenario (A2), could increase up to 4 °C for 2100. The uncertain performance of precipitations, with dispersion of values in magnitude and in sign, may decrease in 20%, as well as the increase of evaporation due to increase of temperature that will favor aridity of Cuban territory.

In order to talk about expected impacts on future space distribution of P. purpureum, it is necessary to perform an integral analysis of the projections of each factor: temperature, mean annual precipitation, type of soil, pH and drainage. In addition, relations among cited factors should be established in order to have an idea, close as possible, of the wanted result.

From the temporary point of view, there was a tendency to decrease the areas with potential for precipitation and temperature, favorable for biomass production of this species. Scenario A2 was the most critical. Negative anomalies will increase, from the first to the last temporary period, from 5.7 to 64.1 % for A2 and from 6 up to 58.5 % in B2, according to table 4. In addition, for both scenarios, the areas within the not advisable category will increase during the last thirty years of the century. It is also observed the disappearance of areas with the combination of temperatures between 24 and 26 °C and precipitations superior to 1,000 mm, considered as good, from 2041 to 2070.

The previous result is spatially confirmed (figure 5) and it is foreseen that this species will occupy almost all the territory during the first two periods (2011 – 2070), up to 36 and 42 % in scenarios A2 and B2, respectively.

A first interpretation of this analysis may be that these projected scenarios of increase of mean annual temperature will be notably determining the space pattern of potentialities of precipitation-temperature for the development of this species. A second interpretation will be that, up to 2070, there will be a homogenization of distribution towards all the country of moderately good category, which will substitute the good category existing at the baseline of occidental region and some areas of central region. From 2071, climate will be potentially favorable only for some regions of the country. The most affected areas will be those from the central region.

The analysis of space distribution (figure 6) shows that, despite projections of potentially usable areas are low, they are represented by one category or another all over the country. It will only be affected in the last studied temporary period, in which three well defined regions are observed. One of great extension will include some areas of Pinar del Río province, as well as Artemisa, La Habana, Mayabeque and the North part of Matanzas province. The second is smaller, and includes limiting areas of Villa Clara and Sancti Spiritus provinces. The third is more disperse, with small cores within Santiago de Cuba, Guantánamo and Holguín provinces.

This performance of the decrease of future potentially usable areas of P. purpureum agrees with studies carried out for other species of commercial interest like oaks (Querscus spp.) (Mascot et al. 2015), plum (Spondias spp.) (Arce et al. 2015 ) and others (Monterroso et al. 2015) developed in Mexico, and with those of potato (Veneros et al. 2015) conducted in Peru. It also coincides with results of researches by Gavazov et al.(2013), who studied dynamics of forage production in mountain areas in Switzerland, according to projections of climate change. In addition, there are reports on the increase of areas for wheat in Yunnan province, in China (Lu et al. 2013).

It is important to state that, although there are only representations of good and moderately good categories in this space distribution, as potentially usable areas, they could have important problems of floodings during intense rains and huricanes. It means that, despite these categories include soils of good drainage, P. purpureum is very sensitive to prolonged floodings (Febles and Herrera 2015) for more than two days, mainly provoked by these meteorological phenomena. Although it may be a local fact , it has adverse effects on development and growth of this plant and may cause its death due to lack of oxigen within the roots (Taiz and Zeiger 2006).

Results of this study are very important from a practical point of view, taking into consideration that the Ministry of Agriculture of Cuba recommends the generalization of this technology of biomass banks as an alternative for grazing during dry period in tropical areas with one of the varieties of this species (Cuba CT-115), because it presents better potentialities for this purpose, according to reports of Martínez and Herrera (2015). In addition, other varieties are included on the strategy such as OM-22 and CT-169, as well as varieties of sugar cane with similar requirements to those of Pennisetum.

CONCLUSIONS

The potential precipitation- temperature for the development of P. purpureum in Cuba will be highly affected and will contribute to reduction of potential areas from 2071, between 59 (scenario B2) and 64 % (scenario A2). The most affected areas will be those from central region. On the other hand, soil potential will determine 34 % of usable area.

Integration of physical factors (climate and soil) allowed to identify potentially usable areas (space distribution) for cultivating and developing this species, which will follow the model stated by the potential of precipitation-temperature. In this case, reduction of potential areas, according to edaphoclimatic requirements of this species, will be between 20 (B2) and 22 % (A2) for the temporary period 2071-2099.

This research may be used as pattern for planning an in situ and ex situ conservation strategy of genetic resources of P. purpureum, because the most suitable places for the establishment of in vivo germplasm banks of this phytogenetic resource may be predicted. It can be also used as a strategy for management of areas established with this species, as to allow to minimize the effects of climate change and reach a better adaptation to different productive systems.

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Received: 15/7/2015
Accepted: 30/5/2016

A. Álvarez-Adán, Instituto de Ciencia Animal, Apartado Postal 24, San José de las Lajas, La Habana, Cuba. Email: adanalvarez@ica.co.cu