RESEARCH WORK
Flora diversity in livestock production farms of Matanzas province
R. Machado1, Taymer Miranda1 y J.L. Álvarez2
1Estación Experimental de Pastos y Forrajes «Indio Hatuey» Central España Republicana CP 44280, Matanzas, Cuba.
E-mail: rmachado@indio.atenas.inf.cu
2Universidad de Matanzas «Camilo Cienfuegos», Matanzas, Cuba
ABSTRACT
The objective of this work was to determine and quantify the species that are part of the flora diversity in eight livestock production or integral farms, linked to the Local Agricultural Innovation Center of Matanzas. For that purpose, a systematic sampling design was used; the sample size was not lower than 0,5%. In general, there was high diversity for all farms. In three of the eight monitored farms 30 or more species were found; in other three this number fluctuated between 19 and 26; while in the other two 13 and 15 species were counted, respectively. This was in correspondence with the richness values, which were between 2,03 and 5,22. There was numeric superiority of grasses and legumes over the species from other families, which number oscillated between one and six species (four or less in 75% of the farms). The highest dispersion values were found in the grasses, higher than 60% and more than 80% for two farms. The performance of a casuistic analysis, in each farm, is suggested in order to determine the future strategies, including the partial eradication and improvement of the plant cover, or its eradication and total retransformation, variants that will be decided by the farmers supported by advice.
Key words: Biodiversity, natural pastureland
INTRODUCTION
In natural or established pasturelands, the diversity of higher plants in the plant cover or the botanical composition, as it is known in the livestock production environment, is generally represented by species belonging to one or more families. When this diversity is conveniently estimated using appropriate methods, highly important indicators in the evaluation of its structure and nature are obtained, as long as they allow to test the quantity, specificity and other important aspects related to the value of its components.
On the other hand, these indicators help to interpret the influence of the environment, including management, from the existing status. With that the decision-making for the design of partial or total retransformation alternatives for those areas, or the maintenance of the composition, is facilitated.
The monitoring of the floristic composition has been frequently used in agronomic trials or livestock production trials, in order to test the changes that occur in the plant cover due to the application of one or several treatments, and also for the development of population surveys in productive organizations, with the objective of establishing adjustment programs in the enhancement or recovery of pasturelands (MINAGRI, 1991; Anon., 2000).
The objective of this work was to monitor the floristic diversity in eight livestock production farms linked to the Local Agricultural Innovation Center (CLIA) of Matanzas province, in order to obtain information about the nature and quantity of the existing species, before making decisions for the retransformation of these areas.
MATERIALS AND METHODS
Characteristics of the farms and soils. The farms belong to leader farmers integrated to several Cooperatives of Credits and Services from Matanzas province. They have relatively small areas and, according to the purpose (integral or livestock production), the pasturelands are exploited without irrigation and include naturalized species; in some cases they are populated by cultivated grass species established in previous stages. None of these areas is fertilized and the animals depend mainly on pasture for milk or meat production and most of them receive limited quantities of supplement (table 1).
In order to determine the soil types, according to the currently used genetic classification (Hernández et al., 1999), trial pits more than one meter deep were dug in representative spots of the area, approximately coinciding with the center of each farm. In addition, between six and eight soil samples were taken around the trial pit and in disperse spots through diagonal transepts, at a depth of 15 cm. In the determination of the pH and OM content the potentiometric and Walkley Black methods were used, respectively; while the S value was calculated based on the addition of the main cations retained in the soil: Ca++; Mg++; K+ and Na+.
Six of the farms are located in soils of the Ferralitic group, which shows a moderately acid to neutral pH, low S values and moderately supplied with OM (3,7 to 5,2%). The other two are located on Brown and Fersialitic soils, more chemically fertile, but with some problems associated to drainage. Only in two of the farms on Ferralitic soil the existence of sufficient drainage due to the presence of gley horizons was observed (farms 1 and 2). According to these characteristics, the farms were distributed in three groups (table 2).
Experimental procedure
Sampling. In order to identify the species and their quantity, a systematic sampling system was conducted through diagonal and parallel transepts.
A sample size never lower than 0,5% was chosen, which is equivalent to counting the species in no less than 200 spots per hectare, when considering that in each spot all the existing species were determined in an area equivalent to 0,25 m2.
Analysis of the results
The interpretation of the results was made through a descriptive system for all the species and their taxonomic location by family for the grasses and legumes, unlike the others which were identified, in general, as species from other families.
Besides, the dispersion and richness values were determined. For the former the observations of all the species were added (value that was assumed as 100%) and by simple proportion the percentage of each particular species was determined; then all the percentages for each family were added. For the latter value the total sum of observations, the number of species and the number of times each one of them appeared were used. The data were processed through the program DIVERSI for Windows, which allows to obtain the richness value and other values of interest.
RESULTS AND DISCUSSION
The diversity of species, their abundance and the composition of the community in the agroecosystems, has been considered as a product of the interspecific biotic interactions (which basis lies on a strong competition and/or predation effect in the structure of the community, for example, the competition that is established with herbivores among plants), or as the effect produced by dispersion events and the limitations of local dispersion. It has been even considered a product of both effects (Tilman, 1997).
Considering this last approach the most appropriate, it is extremely important to reconsider, in the practical order, the quantity and nature of the species found in these agroecosystems and analyze the quality of the composition of the material, which will allow to reach a realistic vision for the proposal of change, maintenance or improvement strategies of that composition.
The results showed that there was high diversity in all the monitored farms (table 3). This way, the pasturelands in three of the farms were formed by 30 or more botanical species. This number fluctuated between 19 and 26 species in other three; while in the last two farms 13 and 15 species were counted, respectively. This was in correspondence with the richness values.
According to the proposal made by Christensen (1995), this diversity responds, firstly, to the maturity reached by these agroecosystems, because they are pasturelands with many years of existence; secondly, to the almost permanent presence of the animals (mainly cattle), which play an important role in species diversity, because of the direct and indirect effects they have on the plant cover, according to the review made by Machado and Olivera (2003); and finally, to the effect which can be caused by climate and other factors on the richness of species (Jones et al., 1995).
On the other hand, the number of species, besides being high, was also considerably variable. This indicates that the species composition in numerical terms can be different among agroecosystems of natural pastures and even more in commercial pasturelands. Machado (2002) detected 39 species in a pastureland established with one cultivated variety five years before monitoring and indistinctly managed with the contribution of nitrogen fertilization during the rainy season (three years) or without fertilization (two years); while Jones et al. (1991) found 57 different species that grew, from the seed reserves, on the soil in associated pastures or fertilized grasses in an experimental period of 11 years, which confirms such criterion.
The number of species is an important indicator, like the nature of the species that compose the plant cover, which obeys the higher or lower presence of plants with a certain value for animal production. In this sense, it is valid to emphasize the lower quantity of the species from other families, which in general showed a lower value and are less consumed than grasses and legumes, with some exceptions. The number of these species fluctuated between one and six (four or less in 75% of the farms).
The higher presence of grasses and legumes, with a higher value, is explained by several known morphostructural and physiological features, such as: a higher number of growing spots; enough reserves to develop their regrowth potential after defoliation or damage produced by stress; stolons or rhizomes (or both), which provide them with high colonization capacity in most cases and high seed production, ensuring their rapid propagation in the area; in such aspects they exceed the species from other families, which were always found in lower number.
The richness values were indistinctly observed with high or low values. Thus, in farms 4 and 6 (group 1) they were 3,93 and 2,13 (from moderate to low); these are the soils with higher fertility and water retention, on which a wide range of plant species is normally adapted. The values of the farms from group 2 (3, 5, 7 and 8) fluctuated between 4,1 and 5,1 for three of them (acceptable), although the soils have moderate fertility, and they were only 2,03 in farm 5; while in the farms of group 3, with prevalence of soils with low fertility and limiting physical conditions for the development of diverse plant species (farms 1 and 2), were 5,2 (high) and 2,9 (low), respectively. This indicates that the richness value does not seem to have much relation, in these cases, with the type, quality and productive capacity of the soils, but it can obey aspects related to the capacity and adaptation of species to colonize a certain agroecosystem, independently from fertility, which confirms the report made by Tilman (1997).
Although legume species were found in these agroecosystems (tables 2 and 3; annex 1), independently from the fertility degree of the soils and their physical properties, the lowest number was found in the farms located on the soils from group 3, that is, those with the lowest fertility, low water retention and regular to deficient drainage, although with good depth. In four of the farms located on soils from groups 1 and 2, where the edaphic conditions are better, the number of legumes was higher than grasses, in another it was equal and in only one of them (farm 7) it was lower. These species, much less efficient than grasses from the physiological point of view and in general more limited to adapt to aggressive environments, tend to increase in number and area when conditions are more favorable or propitious for their development, because they can survive and achieve a certain growth rate on moderate to high fertility soils (Thornley et al., 1995), and they also show preference to proliferate on well-drained soils (Álvarez, 2002), especially when no inorganic fertilizers and other agrotoxicals are not used (Abdala et al., 2000).
The highest values in terms of dispersion for all farms, except one, were detected in grasses (table 4), with values higher than 60%, and higher than 80% for two of them. In the farm where legumes exceeded grasses in dispersion (farm 5), the percentage was higher in only three units, which rather shows a balance status than absolute superiority.
Nevertheless, the dispersion values of legumes are considered adequate, particularly in farms 3, 6 and 8, in addition to 5, and they were below 15% only in farm 2, in correspondence with its characteristics (table 2). The combination of legumes with grasses of different habits in the pasturelands is ascribed to the high compatibility degree that characterizes many of their species, mainly when they are found in adequate environments for their development and proliferation. The presence of these species, with high dispersion degree in the systems, was described in detail by Jardines (2006) when studying the prevailing flora in natural pastures subject or not to grazing.
It is important to state that practically all the naturalized grasses in these pasturelands, and even many legumes, have remarkable aggressiveness and wide adaptation margin in those places, where their seed banks have been created, and in turn have contributed to the maintenance of a certain production level in the livestock that grazes in them. This warns about the need to carry out transformations in these farms, including among them herbaceous or tree types with possibilities of adaptation, but which in turn facilitate the increase of the production potential of the animals based on higher quality and higher intake.
The dispersion rates in the species from other families were low. They do not are dangerous of becoming invading plants in large compact areas, because they are normally distributed individually or create small populations of individuals, which can be observed in most natural pasturelands.
The results are considered valuable, because they allow to obtain a real vision of the flora composition in farms in which transformations are intended to be made. This presupposes making a casuistic analysis, in each one, to determine the future strategies to be applied, which could include: partial eradication and improvement of those areas (in the case of farms 3, 5, 6 and 8) or total eradication and transformation of the areas (farms 1, 2 and 7), in which very low quality grasses and few legume species with low dispersion prevail; even in farm 4, in which there is a higher number of legumes, they do not reach an acceptable dispersion degree with regards to grasses. However, it is suggested that any of the alternatives to be applied is based on the decision made by farmers, supported by technical advice.
