Floristic and structural variation of weeds in eucalyptus plantations as influenced by relief and time of year

Variação florística e estrutural de plantas daninhas em cultivos de eucaliptos em função do relevo e da época do ano

Abstracts

The objective of this work was to analyze the floristic variation and phytosociological structure of weeds as influenced by relief and time of year in eucalyptus plantations in Santana do Paraíso and Guanhães - MG. The total area sampled for each locality was approximately 10 ± 3 hectares, comprising three types of relief: lowland, slope, and upper area. In each type of relief, 10 plots of 1 m² were sampled, corresponding to 30 plots per locality, where they were randomly allocated in a zigzag. The taxonomic identification was performed in four assessments, corresponding to the months of November and March, comprising two ratings each season, always at the same points, and geo-referenced using the Global Positioning System (GPS). A total of 3,893 individuals, 18 families and 61 species, were identified in Santana do Paraiso and a total of 1,166 individuals, 13 families and 58 species, in Guanhães. In both localities, the most representative families in terms of wealth were: Poaceae, Asteraceae, and Fabaceae. Galinsoga parviflora was the most abundant species. The Vernonia polyantes was identified only in the lowlands, while Arrabida florida was identified in the slope and upper area. On the other hand, Emilia coccinea, Sida rhombifolia, S. paniculatum and Spermacoce latifolia were common to all three environments. Commelina benghalensis was present only in the month of March, while G. parviflora was present only in the month of November. It was concluded that the floristic and phytosociological variation of weeds in eucalyptus plantations is influenced by the type of relief and time of year, which should guide the management practices used in the culture.

Eucalyptus; dynamics; phytosociology; ecological adaptation

Objetivou-se analisar a variação florística e a estrutura fitossociológica de plantas daninhas em função do relevo e da época do ano em cultivos de eucalipto nos municípios de Santana do Paraíso e Guanhães-MG. A área total amostrada para cada localidade foi de aproximadamente 10 ± 3 hectares, compreendidos em três tipos de relevo: baixada, encosta e parte alta. Em cada tipo de relevo, foram amostradas 10 parcelas de 1 m², correspondendo a 30 parcelas por município, onde foram distribuídas aleatoriamente em zigue-zague. A identificação taxonômica foi efetuada em quatro avaliações, correspondentes aos meses de novembro dos anos de 2009 e 2010 e março de 2010 e 2011, sempre nos mesmos pontos, os quais foram georreferenciados por meio do Sistema de Posicionamento Global (GPS). Foi identificado, no município de Santana do Paraíso, um total de 3.893 indivíduos, distribuídos em 18 famílias e 61 espécies; já em Ganhães identificaram-se 1.166 indivíduos, sendo 13 famílias e 58 espécies. Em ambos os municípios, as famílias mais representativas, em termos de riqueza, foram Poaceae, Asteraceae e Fabaceae. Galinsoga parviflora foi a espécie mais abundante. Vernonia polyantes ocorreu apenas na baixada, e Arrabida florida, na encosta e parte alta. Já Emilia coccinea, Sida rhombifolia, S. paniculatum e Spermacoce latifolia foram comuns aos três ambientes. Commelina benghalensis esteve presente apenas no período correspondente a março, assim como G. parviflora no mês de novembro. Diante do estudo, conclui-se que a variação florística e fitossociológica de plantas daninhas em cultivos de eucalipto é influenciada pelo tipo de relevo e pela época do ano, o que deve nortear práticas de manejo na cultura.

Eucalyptus; dinâmica; fitossociologia; adaptação ecológica

ARTICLES

Floristic and structural variation of weeds in eucalyptus plantations as influenced by relief and time of year

Variação florística e estrutural de plantas daninhas em cultivos de eucaliptos em função do relevo e da época do ano

Tuffi Santos, L.D.^I; Cardoso Filho, O.^II; Santos Júnior, A.^III; Sant'Anna-Santos, B.F.^IV; Felix, R.C.^IV; Leite, F.P.^IV

^IProfessor do Instituto de Ciências Agrárias, Universidade Federal de Minas Gerais – ICA/UFMG, Campus Montes Claros-MG, <[e-mail]>, <[e-mail]>

^IIMestre em Ciências Agrárias/Agroecologia pelo ICA/UFMG, Campus Montes Claros-MG, <[e-mail]>

^IIIEngº-Agrº., pelo ICA/UFMG, Mestrando em Fitotecnia, DFT/UFV, <[e-mail]>

^IVPesquisador na Celulose Nipo-Brasileira, CENIBRA, Minas Gerais, <[e-mail]>, <[e-mail]>

ABSTRACT

The objective of this work was to analyze the floristic variation and phytosociological structure of weeds as influenced by relief and time of year in eucalyptus plantations in Santana do Paraíso and Guanhães - MG. The total area sampled for each locality was approximately 10 ± 3 hectares, comprising three types of relief: lowland, slope, and upper area. In each type of relief, 10 plots of 1 m² were sampled, corresponding to 30 plots per locality, where they were randomly allocated in a zigzag. The taxonomic identification was performed in four assessments, corresponding to the months of November and March, comprising two ratings each season, always at the same points, and geo-referenced using the Global Positioning System (GPS). A total of 3,893 individuals, 18 families and 61 species, were identified in Santana do Paraiso and a total of 1,166 individuals, 13 families and 58 species, in Guanhães. In both localities, the most representative families in terms of wealth were: Poaceae, Asteraceae, and Fabaceae. Galinsoga parviflora was the most abundant species. The Vernonia polyantes was identified only in the lowlands, while Arrabida florida was identified in the slope and upper area. On the other hand, Emilia coccinea, Sida rhombifolia, S. paniculatum and Spermacoce latifolia were common to all three environments. Commelina benghalensis was present only in the month of March, while G. parviflora was present only in the month of November. It was concluded that the floristic and phytosociological variation of weeds in eucalyptus plantations is influenced by the type of relief and time of year, which should guide the management practices used in the culture.

Keywords:Eucalyptus, dynamics, phytosociology, ecological adaptation.

RESUMO

Objetivou-se analisar a variação florística e a estrutura fitossociológica de plantas daninhas em função do relevo e da época do ano em cultivos de eucalipto nos municípios de Santana do Paraíso e Guanhães-MG. A área total amostrada para cada localidade foi de aproximadamente 10 ± 3 hectares, compreendidos em três tipos de relevo: baixada, encosta e parte alta. Em cada tipo de relevo, foram amostradas 10 parcelas de 1 m², correspondendo a 30 parcelas por município, onde foram distribuídas aleatoriamente em zigue-zague. A identificação taxonômica foi efetuada em quatro avaliações, correspondentes aos meses de novembro dos anos de 2009 e 2010 e março de 2010 e 2011, sempre nos mesmos pontos, os quais foram georreferenciados por meio do Sistema de Posicionamento Global (GPS). Foi identificado, no município de Santana do Paraíso, um total de 3.893 indivíduos, distribuídos em 18 famílias e 61 espécies; já em Ganhães identificaram-se 1.166 indivíduos, sendo 13 famílias e 58 espécies. Em ambos os municípios, as famílias mais representativas, em termos de riqueza, foram Poaceae, Asteraceae e Fabaceae. Galinsoga parviflora foi a espécie mais abundante. Vernonia polyantes ocorreu apenas na baixada, e Arrabida florida, na encosta e parte alta. Já Emilia coccinea, Sida rhombifolia, S. paniculatum e Spermacoce latifolia foram comuns aos três ambientes. Commelina benghalensis esteve presente apenas no período correspondente a março, assim como G. parviflora no mês de novembro. Diante do estudo, conclui-se que a variação florística e fitossociológica de plantas daninhas em cultivos de eucalipto é influenciada pelo tipo de relevo e pela época do ano, o que deve nortear práticas de manejo na cultura.

Palavras-chave:Eucalyptus, dinâmica, fitossociologia, adaptação ecológica.

INTRODUCTION

In Brazil, eucalyptus has gained prominence in the forestry sector, occupying about 4.9 million hectares in 2011 (ABRAF, 2012). The reason for the farmers' preferred choice of this kind of plantation is its fast growth, high forest productivity and the widespread use of timber, in addition to the availability of cultivation technologies easily employed in properties.

In eucalyptus plantation, one of the greatest difficulties in achieving high cultivation yield is related to the availability of growth factors, almost often scarce in the production environments. This fact is exacerbated by the presence of weeds that are well adapted to unfavorable edaphoclimatic conditions, aggressive in terms of colonization of new areas and with large numbers of propagules with high dispersal ability and longevity (Lorenzi, 1990). Although some species of the genus Eucalyptus have characteristics that favor its establishment in the land, this fact does not prevent them from the interference of weeds, especially in the early stages of development. Thus, these plants require intense management during the first years of the culture, which, in case of re-infestation, may extend to almost the entire cycle for operational and productivity reasons (Bentivenha et al., 2006).

Weed management in planted forests can be done mechanically or chemically. Chemical control may cause changes in the environment such as alterations in the diversity of vegetal species; in the microbiological activity in soil, including beneficial microorganisms such as mycorrhizae, nitrogen fixing bacteria and phosphate solubilizing bacteria; and impacts on the physical and chemical characteristics of soil (Dodd & Jeffries, 1989; Paula Junior, 1995). In addition, the culture itself may be poisoned by the herbicide used (Tuffi Santos et al., 2011) and cause damages to the trees production. The management practices used, the land topography, the edaphoclimatic conditions (Oliveira & Freitas, 2008) and the phenological stage of eucalyptus trees may interfere with the weed dynamics in the fields.

Studies on the composition and floristic and structural variation of weeds in planted lands are important to understand the populations and biology of the existing species, to provide information on the diversity and to understand the dynamics of these plants – an important contribution for the recommendation of management practices.

This study aimed to analyze the floristic and phytosociological structure of weeds in eucalyptus cultures as influenced by the topography of planted areas and time of year.

MATERIAL AND METHODS

Floristic and phytosociological surveys were conducted in Eucalyptus spp. stands in the areas of Forestry Projects of Japanese-Brazilian Pulp (CENIBRA), in Santana do Paraíso and Guanhães - Minas Gerais.

Santana do Paraíso is located at km 232 of highway MG 381, at the geographic coordinates of 19º 21' 49'' south latitude and 42º 34' 07'' W longitude. Altitude is 240 m, and the regional climate is humid tropical, corresponding to the category Aw of Köppen climate classification, with reduced rainfall in the winter. Guanhães is located at km 381 of highway MG 434, at the geographic coordinates of 18º 46' 30'' south latitude and longitude of -42º 55' 57'' W. The altitude is 1,012 m, and the regional climate is humid tropical (Aw).

Total trial area of each locality was approximately 10 ± 3 hectares, comprising three types of relief: lowland, slope and upper area. In each type of relief 10 plots of 1 m² were sampled, determined by a wooden frame, corresponding to 30 plots per locality, which were systematically and randomly distributed in the areas in zigzag design (Oliveira & Freitas, 2008). The samples were geo-referenced using the Global Positioning System (GPS), with the center points of each plot recorded by software of geographic data, and delimited with stakes, ensuring the reliability of sampling in the same plot in different times of the survey.

The selected areas were previously cultivated with eucalyptus in homogeneous planting, with clear-cut logging of the entire plot. For planting, the plot was cleared via desiccation with application of glyphosate herbicide over the entire area 30 days prior to planting for control of weeds and remaining eucalyptus shoots. Then, 700, 1,000 and 1,500 kg ha^-1 of lime was applied in the lowland, slope and upper land, respectively, according to recommendations.

After liming, the area was subsoiled and furrows were plowed, and the equivalent to 700 kg ha^-1 of natural phosphate was distributed onto the furrows. Planting took place in January 2010 using clonal seedlings with spacing of 3 x 2.5 m. Six months after planting, fertilization was incremented with the addition of 100 kg ha^-1 hectare of NPK (6‑30-6) to the three types of relief. Subsequent to planting, two chemical weedings were performed with application of 2.5 L ha^-1 of glyphosate during the period of study, as determined by the need of management of weed competition. The assessment times regarding the application of glyphosate and the age of the eucalyptus plantation studied are presented in Table 1. Taxonomic identification was performed in four evaluations, corresponding to the months of November, 2009 and 2010 and March, 2010 and 2011 (Table 1).

The weed species in each plot were identified through consultation with herbariums, experts specialists, specialized literature (Lorenzi & Souza, 2001; Lorenzi, 2008; Lorenzi & Matos, 2008), and catalog of the weeds found in the company's reforestation areas.

The phytosociological parameters calculated were density and relative frequency (Mueller-Dombois & Ellenberg, 1974). With the number of individuals per species of weeds found in each area, the most abundant species in eucalyptus plantations were determined as a function of the type of relief and sampling time. The predominant families in number of species were also determined. In addition, Venn diagram was used to determine the species distributed at or exclusive to each type of relief and respective occurrence times.

RESULTS AND DISCUSSION

In the surveys conducted in eucalyptus plantations, in Santana do Paraíso a total of 3,893 individuals were found, distributed in 18 families and 61 species. In Guanhães, 1,166 individuals were identified, comprising 13 families and 58 species. In both localities, the most representative families in terms of richness were Poaceae, Asteraceae e Fabaceae (Figure 1).

Poaceae and Asteraceae were reported as the most representative families in previous phytosociological studies (Caporal & Boldrini, 2007; Oliveira & Freitas, 2008). According to Holm et al. (1991), species of the family Poaceae produce large quantities of seeds, which favor its dissemination and colonization in the most varied environments. These characteristics, combined with the competitive ability and edaphoclimatic adaptation may explain the high incidence of these species. Thus, these families have been predominant in floristic surveys of cultivated areas (Rodrigues et al., 2010).

The highest incidence of the family Poaceae was found in the first and third assessments (Table 2), both in November, a time corresponding to the spring season. In accordance with this, Welker & Longhi-Wagner (2007) report that annual tropical species of this family usually stay dormant or with dormant seeds in winter and grow in the spring.

In Santana do Paraíso, in the surveys performed in March, Commelina benghalensis and Pteridum aquilinum were the most important species in terms of density and relative frequency (Table 2), C. benghalensis having density and frequency relatively expressive in the lowland, and P. aquilinum in the lowland and sloped areas. In the investigations conducted in November, Galinsoga parviflora was the species with the highest phytosociological ratings (Table 2). This might have occurred because of climatic factors with regard to the adaptive conditions of each species, considering that March is part of the summer season, and November, spring. However, they show differences relating to environmental factors, such as, for example, rainfall, solar radiation, among others. This has possibly caused the occurrence of vegetal species. For Carvalho & Nakagawa (2000), most of these plants have seeds or structures that lie dormant in periods that are unfavorable to germination and growth, leaving their establishment to a favorable time. In Guanhães, as well as in Santana do Paraíso, Spermacoce latifolia was very representative (Tables 2 and 3), but not showing specificity depending on the topography, which can be attributed to its ability to adapt to different environments. According to Lorenzi (2008), it is a plant found in almost the entire Brazilian territory.

The occurrence of species that are difficult to control with glycophosate and mechanical methods, such as Commelina benghalensis, Spermacoce latifolia, Digitaria insularis, Mikania cordifolia, Vernonia polyanthes, Tibouchina moricandiana and Arrabidaea florida, must be monitored. The repeated and frequent application of this herbicide, commonly used in eucalyptus plantations (Tuffi Santos et al., 2011), may favor species that are tolerant to glyphosate, in contrast to other weeds that are controlled with this herbicide, exacerbating the problem of difficult control and the frequency and density of the problem-species.

Arrabidea florida, belonging to the family Bignoniaceae, was present in all assessments, presenting high density and frequency values, especially at the sloped and upper areas, in all periods studied (Table 3). The high occurrence may be due to its climbing-habit form of development, allowing coverage of large areas. Vernonia polyanthes is another species that is prominent in view of its high density and frequency values in the lowland in the first survey (Table 3), as well as regarding its stay in the same area, though with lower values. Probably, the high density and frequency of this species are established based on its affinity for the soil composition in the area of occurrence. V. polyanthes multiplies easily in soils of high fertility (Alzugaray & Alzugaray, 1984).

Throughout the study period, G. parviflora was the most abundant species in eucalyptus plantations in the areas under study, particularly in the lowland (Figure 2).

In each kind of relief, exclusive species were found in addition to those that were common to all areas. During the surveys, it was possible to identify the occurrence of alterations in the number of species common to each area of study (Figure 3).

Such changes may have been due to the management of the culture or even influenced by the culture growth. According to Mulugueta & Stoltenberg (1997), the different forms of management condition the seeds to the soil microenvironments, as a function of alterations in the properties and superficial composition of this substrate.

In Santana do Paraíso, in the first survey, the three areas had six species in common (Figure 3): Desmodium barbatum, Digitaria insularis, Galinsoga parviflora, Glycine wightii, Panicum maximum and Richardia brasiliensis. In the second, they were three (Figure 3): Brachiaria brizantha, Digitaria insularis and Momordica charantia. In the third, only one (Figure 3): Panicum maximum. In the fourth and last survey, three species in common were identified (Figure 3): Acanthospermum hispidium, Bidens subalternans and Spermacoce latifolia. But in the study areas in Guanhães, it was observed a difference in regard to the common species. In the first study (November, 2009), there were no species in common. In March 2010, two species were found (Figure 4): Sida rhombifolia e Solanum asperolanatum. In November 2010, they were five (Figure 4): Brachiaria sp., Emilia coccinea, S. rhombifolia, S. paniculatum and Spermacoce latifolia. In the last assessment, conducted in March 2011, in the three types of relief, five species in common were found (Figure 4): Bambusa sp., Brachiaria mutica, S. rhombifolia, S. paniculatum and S. latifolia. It can be seen that there was a change in the species that are common to all areas. It can be inferred that this is a result of the local environmental conditions provided by the eucalyptus growth.

The families Poaceae and Asteraceae showed several common species to all areas under study, with emphasis on R. brasiliensis, B. subalternans, D. insularis and Panicum maximum. Glicyne wightii, Pothomorphe umbellata and Scoparia dulcis were exclusive in Santana do Paraíso, while Conyza bonariensis, Diatenopterix sorbifolia, Melampodium paniculatum and Rhynchospora corymbosa were only found in Guanhães.

Some weeds have the ability to adapt and multiply in environments with contrasting characteristics, a good indicator of the species plasticity.

Changes in the eucalyptus cultivation environment are in part determined by growth and alterations in the architecture of the trees canopy as well as the required resources of each phenological stage. Thus, studies on the weeds dynamics as discussed herein should be extended to the whole cycle of the eucalyptus culture.

Floristic and phytosociologic variation of weeds in eucalyptus forestry is influenced by the topography and time of year, as a result of the ecological conditions to which they are submitted in each situation. The largest number of individuals is found in the lowlands, and the lowest one in the upper area. Some species have affinity for a given type of topography, and some occur preferably at a certain time of the year. In contrast, there are some weeds that are present in all kinds of topography. However, the occurrence of weeds in eucalyptus plantation has no patterns regarding the topography and time of year, requiring a specific evaluation to decide on the management practices to be adopted. The species Commelina benghalensis, Spermacoce latifolia, Digitaria insularis, Mikania cordifolia, Vernonia polyanthes, Tibouchina moricandiana and Arrabidaea florida are considered of difficult management in forested areas and have importance in the eucalyptus plantations investigated.

ACKNOWLEDGEMENTS

The authors wish to thank the Japanese-Brazilian Pulp and its field technicians for the support and research funding. To FAPEMIG for the financial aid and to CNPq for the scholarship awarded to the first and fifth authors.

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Recebido para publicação em 2.10.2012 e aprovado em 20.4.2013.

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Publication Dates

• Publication in this collection
  31 July 2013
• Date of issue
  Sept 2013

History

• Received
  02 Oct 2012
• Accepted
  20 Apr 2013