52a Reunião Anual da Sociedade Brasileira de
Zootecnia
Zootecnia: Otimizando Recursos e Potencialidades
Belo Horizonte – MG, 19 a 23 de Julho de 2015
Diversity of a natural pasture under rotational grazing
1
Liane Seibert2, Fernando Luiz Ferreira de Quadros3, Pedro Trindade Casanova4, Paula de Oliveira
Severo5, Régis Maximiliano Ross de Carvalho6, Liana Pereira de Pereira7, Carolina Goulart
Munhoz8
1
Parte da dissertação de mestrado da primeira autora,
Doutoranda do PPGZ– UFSM, Santa Maria-RS, Brasil, Bolsista da CAPES. e-mail: [email protected],
3
Prof. Associado do Departamento de Zootecnia, UFSM. Santa Maria-RS, Brasil e-mail: [email protected],
4
Mestrando do PPGZ – UFSM. Santa Maria-RS, Brasil Bolsista do CNPq/Capes. e-mail: [email protected],
5
Mestranda do PPGZ – UFSM. Santa Maria-RS, Brasil Bolsista do CNPq/Capes. e-mail: [email protected],
6
Doutorando do PPGZ – UFSM, Santa Maria-RS, Brasil, Bolsista da CAPES. e-mail: [email protected],
7
Professora de Instituto Federal Farroupilha-Campus Alegrete-RS Brasil. e-mail:[email protected],
8
Professora da Faculdade IDEAU-Campus Bagé-RS Brasil. e-mail: [email protected],
2
Abstract: The objective of this study was to evaluate the vegetation diversity index of a natural
grassland in the spring-summer period subjected to rotational grazing. Evaluations were made
along three years (2011, 2012 and 2013). The treatments were two intervals of rest under
rotational grazing, 375 and 750 degrees day, the experimental design was randomized blocks with
three replicates, with repeated measurements over time. The blocking factor was the proportion of
top, hillside and lowland relief on each repetition. Evaluations of the floristic composition were
performed by BOTANAL method and to assess the diversity the Shannon Index was used. Data
were analyzed as three-year joint assessments and submitted to ordination analysis and
randomization tests using MULTIV software. The Shannon diversity index showed neither
significant difference (P > 0.1) nor interaction for treatments (375 and 750degrees day) over the
three years of evaluation. The two different rest intervals (375 and 750degrees day) did not alter
the diversity of vegetation according to Shannon index along the evaluation period.
Keywords: grazing management, native species, Shannon index
Diversidade de uma pastagem natural submetida a pastoreio rotativo 1
Resumo: O objetivo deste trabalho foi avaliar o índice de diversidade específica de uma
pastagem natural no período de primavera-verão submetida a pastoreio rotativo. As avaliações
transcorreram ao longo de três anos (2011, 2012 e 2013). Os tratamentos foram dois intervalos de
descanso sob pastoreio rotativo, 375 e 750 graus-dias, o delineamento experimental utilizado foi
em blocos casualizados, com três repetições, com as medidas repetidas no tempo. O fator de
bloqueamento foi a proporção dos relevos topo, encosta e baixada em cada repetição. O
levantamento da composição florística foi realizado pelo método BOTANAL e para avaliar a
diversidade foi utilizado o Índice de Shannon. Os dados foram analisados como um conjunto de
três anos de avaliações e submetidos à análise de ordenação e testes de aleatorização utilizando
o software MULTIV. O índice de diversidade de Shannon não apresentou diferença significativa
(P>0,1), tampouco interação para os tratamentos (375 e 750graus-dia) ao longo dos três anos de
avaliação. Os dois diferentes intervalos de descanso (375 e 750graus-dia) não alteraram a
diversidade da vegetação segundo o índice de Shannon no período avaliado.
Palavras–chave: espécies nativas, índice de Shannon, manejo
Introduction
At Bioma Pampa on Rio Grande do Sul, there is a significant diversity of vascular plant
species, approximately 2,200 species, distributed in many families, where grasses and legumes
were the most relevant for forage (Boldrini, 2009). Livestock production is still considered the most
appropriate activity for the maintenance of this biome. However, complexity related to its
management may reduce economic profitability. In this context, evaluations of diversity can
contribute to the understanding of processes related to soil-plant-animal complex, providing
support for a more sustainable management of these pastures.
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52a Reunião Anual da Sociedade Brasileira de
Zootecnia
Zootecnia: Otimizando Recursos e Potencialidades
Belo Horizonte – MG, 19 a 23 de Julho de 2015
Material e Methods
The trial was conducted in an experimental area of natural pasture, with grassland
physiognomy characterized by “campos mistos” at Central Depression State of Rio Grande
do Sul. The evaluations were held along spring-summer seasons over three years (2011,
2012 and 2013). We evaluated two rotational grazing intervals (375 and 750 degrees day)
where the criteria used were accumulated thermal sums equivalent to the average length of
leaf expansion of representative grasses of the functional groups A and B (375 degreedays(DD)) and C and D (750 DD) proposed by Quadros et al. (2009). The thermal sum was
obtained by the equation: ST = Σ Tmd. Where: ΣTmd is the sum of daily average
temperatures for the period. Six experimental paddocks of 0.5 ha were selected, three
representing each grazing interval.
Transects with 40 m length were set at each plot. On these transects 0,25m2 quadrats
were laid each 2 m, totaling 20 sampling units in each transect per paddock. The floristic
composition estimated the contribution of the main components on total available forage
mass and relative frequency of other components following the procedures of method
BOTANAL (Tothill et al., 1992).
Diversity of species in the area was evaluated using the diversity index of ShannonWeaver. This index allows analyzing how the species are distributed along the ecosystem.
Data from the floristic composition and diversity were analyzed through a principal
coordinates ordination analysis, standardizing data by its range, and analysis of variance
used randomization tests performed by MULTIV software (Pillar, 2004 ).
Results and Discussion
In Figure 1, the average values of Shannon indices for 375 and 750 DD treatments for the
three evaluation periods (2011, 2012, 2013) are presented.
Figure 1. Mean values of the Shannon-Weaver Diversity Index for 375 DD e750 DD
treatments along spring / summer of 2011, 2012 and 2013.
There was no difference (P> 0.1) and also no interaction treatment-period. Thus,
vegetation presented a "steady-state" condition for Shannon diversity index in both
treatments along the three years of evaluation, with values ranging from H '1.9 to H' 2.4.
Rossi (2009) performed evaluations, in the same experimental area, comparing grazing,
grazing exclusion and burning and recorded Shannon index of H'2,59 for grazed areas and
H '2.11 for grazing excluded areas, the values found by the author greatly resemble those
found in our work indicating a "similar" vegetation diversity.
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52a Reunião Anual da Sociedade Brasileira de
Zootecnia
Zootecnia: Otimizando Recursos e Potencialidades
Belo Horizonte – MG, 19 a 23 de Julho de 2015
The variation of species production in space and time is related to edaphoclimatic
factors that determine changes in botanical composition, in addition to management practices
(Nabinger, 2006).
This process coupled with the herbivory effect, induced by man’s imposed
management results in different pressures (selectivity and preference) on the vegetation,
determines the frequency of its different floristic components. However, research at Rio
Grande do Sul natural grasslands are still recent, considering the objective of understanding
the ecosystem function of these pastoral ecosystems, showing that productivity and
conservation practices are not mutually exclusive and it is possible to optimize animal
production and plant in moderate grazing intensities (Nabinger, 2006).
Nabinger et al. (2006), assumes that the environmental conditions and the soil are
determining the floristic composition. This process coupled with the herbivory effect, which from
the management imposed by man results in different pressures (selectivity and preference) on the
vegetation, interacting with the grazing method, determines the frequency of its different floristic
components. However, are still somewhat recent, research in Rio Grande do Sul, about the
objective of understanding the functioning and potential of these pastoral ecosystems, showing
that productivity and conservation practices are not mutually exclusive and it is possible to
optimize animal production and plant in moderate grazing intensities.
Conclusions
The diferente grazing intervals (375 and 750 DD) didn’t change grassland Shannon index
diversity along three evaluation years.
Acknowledgements
We are acknowledging CNPq, CAPES and FAPERGS for grants that allows this research.
References
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