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An Acad Bras Cienc (2020) 92(suppl.1): e20180425 DOI 10.1590/0001-3765202020180425Anais da Academia Brasileira de Ciências | Annals of the Brazilian Academy of SciencesPrinted ISSN 0001-3765 I Online ISSN 1678-2690www.scielo.br/aabc | www.fb.com/aabcjournal

An Acad Bras Cienc (2020) 92(suppl.1)

AGRARIAN SCIENCES

Silvopastoral system with Eucalyptus as a strategy for mitigating the effects of climate change on Brazilian pasturelands

CRISTIAM BOSI, JOSÉ RICARDO M. PEZZOPANE & PAULO CESAR SENTELHAS

Abstract: The aim of the present study was to assess the effect of Eucalyptus trees in a silvopastoral system on the microclimate and the capacity of that to mitigate the effects of climate change on pasturelands. This study included an open pasture of Piatã palisadegrass and an adjacent pasture that contained both palisadegrass and East-to-West rows of Eucalyptus trees, with 15 m between rows, 2 m between trees within rows. The micrometeorological measurements were collected at several distances from the tree rows and in the open pasture. The silvopastoral system was associated with greater between-row shading when solar declination was high and greater near-tree shading when solar declination was around -22°. Both soil heat fl ux and temperature were infl uenced by solar radiation, wind speed, and the ability of tree canopies to reduce radiation losses. Wind speed was consistently lower in the silvopastoral system, owing to the windbreak effect of the Eucalyptus trees. The present study demonstrated that silvopastoral systems can be used to attenuate the effects of climate change, as trees can protect pastureland from intense solar radiation and wind, thereby reducing evapotranspiration and, consequently, improving soil water availability for the understory crop.

Key words: Agroforestry, microclimate, net radiation, shading, soil heat flux, windbreak.

INTRODUCTION

Agroforestry systems (AFSs) are characterized by the combined use of land for timber or fruit trees and crops and/or livestock, either simultaneously or sequentially (Lundgren and Raintree 1982), and silvopastoral systems, specifi cally, are characterized by the combined use of land for trees or shrubs and for pastureland and livestock (Nair 1993). In general, the main goal of AFSs is to optimize land use (Alao & Shuaibu 2013) by combining forest and food production systems (King 1979), improving soil conservation (Pattanayak & Mercer 1998), reducing the need to acquire new land area for agriculture (Schroeder 1994), and reducing

the need for external inputs (Filius 1982). However, the establishment of AFSs can cause microclimatic changes (Monteith et al. 1991) that can affect systems negatively if such systems are improperly planned.

The microclimates of AFSs depend on a variety of factors, including system design, arrangement, orientation, age, species composition, and architecture, all of which interact at macro- and meso-scales, and the main changes achieved through conversion to AFSs are caused by shade, which is provided by trees and reduces the solar radiation reaching sub-canopy crops (Pezzopane et al. 2015). Indeed, by reducing solar radiation, shade affects a variety of microclimatic variables,

CRISTIAM BOSI, JOSÉ RICARDO M. PEZZOPANE & PAULO CESAR SENTELHAS SILVOPASTORAL MITIGATES CLIMATE CHANGE EFFECTS

An Acad Bras Cienc (2020) 92(suppl.1) e20180425 2 | 15

including air and soil temperatures, relative humidity, soil moisture (Pezzopane et al. 2015), and evapotranspiration (Lin 2010), which affect crop growth (Bosi et al. 2014), and by reducing wind speed, tree plantings can also indirectly affect a variety of other microclimate variables (Pezzopane et al. 2015). According to Gomes et al. (2016), AFS can promote the microclimate stability of understory species by reducing soil water evaporation and run-off and by reducing air and soil temperatures, as reported by Amadi et al. (2016), who studied shelterbelts in Saskatchewan, Canada. Therefore, the ability of AFS establishment to modify microclimates and to improve the resilience of agricultural systems should be considered when comparing different strategies for adapting agriculture to climate change (Montagnini et al. 2013, Nguyen et al. 2013).

In this context, the aim of the present study was to assess the effect of Eucalyptus trees in a silvopastoral system on the microclimate and the capacity of that to mitigate the effects of climate change on pasturelands.

MATERIALS AND METHODSStudy siteThe study was conducted from August 2013 to June 2016 in São Carlos, São Paulo, Southern Brazil (22°01’ S, 47°53’ W, alt 860 m), where the climate is characterized as Cwa (Köppen), with a cool and dry season from April to September (mean air temperature of 19.9°C; and total rainfall of 250 mm), and a warm and wet season from October to March (mean air temperature of 23.0°C; and total rainfall of 1100 mm), according to Alvares et al. (2014). The study included a 6-ha open pasture of the palisadegrass Urochloa (syn. Brachiaria) brizantha (Hochst ex A. Rich.) Stapf ‘BRS Piatã’, which was a full-sun system, and a second 6-ha pasture, which contained

the same palisadegrass with rows of Eucalyptus urograndis (E. grandis × E. urophylla) ‘GG100’, which served as the silvopastoral system. The trees in the silvopastoral system were planted in April 2011 and were arranged in simple rows, with an East-to-West orientation, with 15 m between rows, 2 m between trees within rows, and density of 333 trees ha-1.

Weather and tree measurementsTo assess the effects of the Eucalyptus trees on the microclimatic conditions of the pastureland, sample sites were established at four different distances (SP1, 0.00 m; SP2, 3.75 m; SP3, 7.50 m; SP4, 11.25 m) from the Northernmost row of trees, which was responsible for causing shading during most of the year. A full-sun pasture (FS) was also established and considered as the control (Figure 1).

Three weather stations were installed in the study area: one in the open pasture, at 200 m from the silvopastoral system, and two into the silvopastoral system. Each weather station included linear quantum sensors (Apogee, Logan, UT, USA), a net radiometer (NR-Lite2; Kipp & Zonen, Delft, Netherlands), a heat flux plate (HFP01; Hukseflux, Delft, Netherlands), an ultrasonic anemometer (Windsonic; Gill Instruments, Lymington, UK), a thermo-hygrometer (HC2-S3; Rotronic, Bassersdorf, Switzerland), and a soil temperature probe (Thermistor 107; Campbell Scientific, Logan, UT, USA), which measured photosynthetically active radiation (PAR), net radiation (Rn), soil heat flux (SHF), wind speed, air temperature and relative humidity, and soil temperature, respectively.

Measurements were taken continuously (Figure 1), and the sensors were connected to a data logger (CR3000; Campbell Scientific, Logan, UT, USA) that was configured to record measurements every 5 s and to calculate 15- and 60-min averages and/or totals. Daily averages,



maximums, and minimums were also calculated for air temperature, relative air humidity, and soil temperature, whereas only average and maximum values were calculated for wind speed. For PAR, Rn, and SHF, only daily total values were recorded. The sensors were installed at 1.7 m height, except for linear quantum sensors, which were installed at 0.6 m above the soil surface, and the heat fl ux plates and soil temperature probes, which were deployed 0.05 m depth in the soil. PAR was measured throughout the study period (August 2013 to June 2016), whereas wind speed, air temperature, relative humidity, and soil temperature were only measured from June 2014 to June 2016, and both Rn and SHF were only measured from December 2014 to June 2016 (Figure 2), and PAR was measured at all the sample sites, whereas the other variables were only measured at the FS, SP1, and SP3 sites. Finally, PAR transmission (PARt) was calculated by dividing the PAR measured at each position of the silvopastoral system by that measured at the open pasture.

The potential of the silvopastoral system to mitigate the effects of climate change was defi ned as the ability of the Eucalyptus trees to reduce PAR, Rn, wind speed, and air temperature and to increase relative humidity and was assessed by comparing the microclimatic conditions of the SP1 and SP3 sites with those of the FS site for each season of the year.

During the study period, the trees in the four rows close to the weather stations were also evaluated at least every 6 months (04/17/2013, 10/15/2013, 04/08/2014, 10/03/2014, 12/12/2014, 02/03/2015, 05/26/2015, 10/01/2015, 01/27/2016, and 06/02/2016), and each evaluation included the measurement of: each tree’s height and crown base height, using a clinometer; canopy width, using a metric tape; and diameter at breast height (DBH, ~1.3 m above the ground), using a diametric tape (Table I).

Statistical analysisThe study was performed using a completely randomized design with repeated measures, and the data were analyzed using the MIXED

Open pasture Silvopastoral System

FS SP4 SP3 SP2 SP1• • • • •

3.75 m

7.50 m

11.25 m

15 m

200 mFigure 1. Schematic representation of the study area indicating where the data were collected in the open pasture (left) and in the silvopastoral system (right). FS: full sun, SP1: 0.00 m, SP2: 3.75 m, SP3: 7.50 m, SP4: 11.25 m from North row. Gray strips illustrate the tree rows.



procedure of SAS (Littell et al. 2006). To analyze average and maximum wind speed and average, maximum, and minimum air temperature, relative humidity and soil temperature, the repeated factors were year (2 and 3; Figure 2) and season, being the comparison between seasons only within each study year, and each day of a season was considered a replicate, with 92 days or replicates per season. Rn and SHF were analyzed using the same procedure, except that seasons were used as the repeated factors and that only the last six seasons (summer and autumn of year 2 and all seasons of year 3), and PAR and PARt were analyzed by a similar process but using data from all three years and considering each 10-d period as a replicate (nine replicates per season), in order to reduce the

dataset’s variation and to improve the normality of its distribution. Means were compared using the Tukey test (P ≥ 0.05).

RESULTSSolar radiation dynamicsDuring the winter and autumn, PAR at the FS site was greater than at all the SP positions (SP1–4), except during the winter of year 1, when the PAR of the FS and SP4 sites were similar (Table II), whereas differences between the PAR of the SP positions were generally not significant (P<0.05). During the spring, PAR incidence was usually greater at the FS position than at the SP positions, except during the spring of year 1, when only the SP1 position received less PAR

Table I. Tree height, crown base height (CBH), canopy width, and diameter at breast height (DBH) of trees, in a silvopastoral system, measured in several dates of each study year.

Date Season/YearTree height CBH Canopy width DBH

m m m cm4/17/2013 - 10.8 - 4.3 10.210/15/2013 Spring/1 13.0 - 5.2 12.84/8/2014 Autumn/1 16.5 - 5.5 15.010/3/2014 Spring/2 17.7 - 5.0 16.112/12/2014 Spring/2 18.5 5.1 5.6 17.32/3/2015 Summer/2 20.0 5.3 5.5 17.75/26/2015 Autumn/2 20.1 5.5 4.5 19.110/1/2015 Spring/3 22.4 6.6 6.1 20.11/27/2016 Summer/3 23.7 6.7 7.0 20.86/2/2016 Autumn/3 26.4 9.3 6.1 21.7

Figure 2. Weather measurements during the three years of the study.



Table II. Photosynthetically active radiation (PAR) incidence at the full sun (FS) and at the four positions within the silvopastoral system (SP1: 0.00 m, SP2: 3.75 m, SP3: 7.50 m and SP4: 11.25 m from the North row), in each season of the three study years.

Year Position

PAR

MJ m-2 day-1

Winter Spring Summer Autumn Average

1

FS 8.08 Aab* 8.84 Aab 10.25 Aa 6.76 Ab 8.53SP1 3.86 BCa 1.60 Ba 1.97 Ba 2.90 Ba 2.43SP2 1.54 Cb 7.01 Aa 7.18 Aa 1.90 Bb 4.74SP3 5.16 BCab 7.39 Aa 8.38 Aa 2.16 Bb 5.86SP4 7.22 ABa 6.59 Aa 7.50 Aa 3.17 Bb 6.02

Average 5.17 6.28 7.06 3.38

2

FS 7.03 Aa 8.76 Aa 8.77 Aa 6.10 Aa 7.66SP1 3.55 Ba 3.03 Ca 2.46 Ba 1.99 Ba 2.78SP2 2.07 Bbc 5.07 BCab 5.32 ABa 1.67 Bc 3.58SP3 1.72 Bb 6.04 Ba 6.33 Aa 1.67 Bb 3.93SP4 3.06 Bbc 5.81 Ba 5.30 ABab 2.10 Bc 4.06

Average 3.49 5.74 5.64 2.70

3

FS 6.24 Aa 8.18 Aa 8.51 Aa 6.50 Aa 7.36SP1 2.16 Ba 2.86 Ba 2.27 Ba 1.93 Ba 2.31SP2 2.11 Ba 4.15 Ba 4.06 Ba 1.81 Ba 3.05SP3 1.86 Bb 5.12 Ba 4.70 Bab 1.75 Bb 3.40SP4 1.93 Bb 4.61 Ba 3.97 Bab 1.75 Bb 3.10

Average 2.86 4.98 4.70 2.75*Means followed by the same upper case letter are not different in column, and those followed by the same lower case letter are not different in line (P<0.05).

(difference of 7.24 MJ m-2 d-1). During the summer of year 3, PAR at the FS site was greater than that at all the SP positions, and during years 1 and 2, PAR at the FS position was only greater than that at the SP1. On average, PAR reduction at the SP1 and SP3 positions was 5.29 and 3.48 MJ m-2 d-1, respectively (Table III). PAR values of the SP1 position were always similar between seasons and comprised between 1.60 and 3.86 MJ m-2 d-1. At the other SP positions, PAR was generally greater during the spring and summer. The PARt during the winter and autumn were similar among all four SP positions, except for during the winter of year 1, when that of the SP4 position (86.6%) was significantly greater than that of the SP2 (22.1%; Figure 3 and Table IV). During the spring and summer, PARt was lower at the SP1 position than at the other positions, with few exceptions. The hourly dynamics of PAR varied

by year. During the first year, PAR incidence was greater at the FS, SP3, and SP4 positions than at the SP1 and SP2 positions, which indicated that the trees caused more shading at SP1 and SP2 (Figure 4). During subsequent years, PAR decreased at the SP3 and SP4 positions, which demonstrated shadow at these positions.

Net radiation was greater at the FS position than at the SP positions, except during the summer of year 2, when the Rn of the FS and SP3 positions (11.32 and 10.13 MJ m-2 d-1, respectively) were similar (Table V). The Rn of the SP1 position was either similar or greater than that of the SP3 position, and the mean Rn reductions observed at the SP1 and SP3 positions were 5.17 and 3.08 MJ m-2 d-1, respectively, with the greatest reductions observed during the spring and summer at the SP1 position and during the winter and autumn at the SP3 position (Table III).



Figure 3. Spatial and temporal photosynthetically active radiation transmission (PARt) between rows of a silvopastoral system, every ten-day period during the three years of the study, from July to June. (a) year 1 (starting from August 2013), (b) year 2, and (c) year 3. Interpolation made by the Natural Neighbor method.



Table III. Mean reductions of photosynthetically active radiation (PAR), net radiation (Rn), average wind speed (WSavg), maximum wind speed (WSmax), average air temperature (Tavg) and average relative air humidity (RHavg), every season, at 0.00 m (SP1) and 7.50 m (SP3) from the North row, in a silvopastoral system.

Variable PositionSeason


PAR(MJ m-2 day-1)

SP1 3.93 6.09 6.95 4.18 5.29

SP3 4.21 2.41 2.71 4.59 3.48

Rn(MJ m-2 day-1)

SP1 2.87 6.67 7.90 3.25 5.17

SP3 4.04 1.92 1.95 4.4 3.08

WSavg(m s-1)

SP1 0.91 1.01 0.80 0.64 0.84

SP3 0.93 1.00 0.81 0.66 0.85

WSmax(m s-1)

SP1 3.30 3.59 3.50 2.84 3.30

SP3 3.28 3.48 3.35 2.98 3.26

Tavg(°C)

SP1 0.03 -0.09 0.17 0.13 0.03

SP3 0.10 -0.22 -0.04 0.29 0.02

RHavg(%)

SP1 -0.46 -0.12 -2.23 0.41 -0.50

SP3 -0.84 0.00 -1.79 0.74 -0.36

Table IV. Photosynthetically active radiation (PAR) transmission at the four positions within the silvopastoral system (SP1: 0.00 m, SP2: 3.75 m, SP3: 7.50 m and SP4: 11.25 m from the North row), in each season of the three study years.

Year Position

PAR transmission

%


1

SP1 47.1 ABa* 20.5 Bb 20.3 Bb 43.8 Aa 31.3

SP2 22.1 Bb 75.8 Aa 68.3 Aa 30.6 Ab 52.4

SP3 62.2 ABab 80.3 Aa 80.4 Aa 32.3 Ab 64.2

SP4 86.6 Aa 71.8 Aa 72.1 Aa 44.4 Ab 66.9

Average 54.5 62.1 60.3 37.8

2

SP1 48.1 Aa 35.9 Ba 29.4 Ba 30.2 Aa 36.0

SP2 31.3 Aab 56.4 Aa 56.6 Aa 27.1 Ab 43.3

SP3 25.0 Ab 66.5 Aa 67.7 Aa 28.8 Ab 47.0

SP4 41.0 Aab 64.1 Aa 58.3 Aa 32.8 Ab 49.0

Average 36.3 55.7 53.0 29.7

3

SP1 32.7 Aa 35.3 Ba 27.7 Ba 28.8 Aa 31.2

SP2 34.0 Aab 49.6 Aa 45.1 ABab 27.4 Ab 39.2

SP3 31.5 Ab 60.1 Aa 52.2 Aab 27.5 Ab 43.3

SP4 30.1 Aab 54.6 Aa 45.3 ABab 27.8 Ab 39.8

Average 32.1 49.9 42.6 27.9*Means followed by the same upper case letter are not different in column, and those followed by the same lower case letter are not different in line (P<0.05).



The SHF of the FS position was generally similar to that of the SP1 and SP3 positions but was sometimes greater than that of either one or the other (Table V). Analysis of the hourly values of Rn and SHF revealed that the greatest night-time radiation and heat losses occurred at the FS position (Figure 5), as did the greatest day-time Rn and SHF occurred at the FS position, followed by the SP3 and SP1 positions, respectively.

General microclimatic conditionsAverage wind speed was greater at the FS position than at the SP positions, with a difference of 1.2 m s-1 between the SP1 and FS positions (Table VI), and the SP positions consistently yielded similar average wind speed values. A similar pattern was observed for maximum wind speed, with reductions of up to 3.85 m s-1 at the SP positions. The hourly wind speed dynamics indicated that the wind speed of the FS position was greater than that of the SP positions throughout the day, with the greatest differences observed

during the morning (Figure 6a, b). On average, there was a substantial reduction of wind speed at the SP positions during all seasons, especially for maximum wind speed, the average reduction of which was 3.28 m s-1 (Table III).

The average wind speed of the FS position was generally greatest during the spring, whereas that of the SP positions was more consistent. Meanwhile, maximum wind speed was greater during the spring, regardless of position, and decreased gradually from winter to autumn (Table VI).

Average, maximum, and minimum air temperature and relative humidity were statistically similar among the FS, SP1, and SP3 positions, regardless of season, with the exception of the minimum relative humidity of the summer of year 3, when it was more humid at the SP1 position than at the FS position (64.8 and 54.9%, respectively; Table VI). The hourly variation in air temperature and relative humidity were also similar among the positions.

Table V. Net radiation and soil heat flux, at full sun (FS) and at two positions within a silvopastoral system (SP1: 0.00 m and SP3: 7.50 m from the North row), in six seasons.

PositionSeason/Year

Summer/2 Autumn/2 Winter/3 Spring/3 Summer/3 Autumn/3 Average

Net Radiation

MJ m-2 day-1

FS 11.32 Aa* 6.25 Ab 5.43 Ab 10.43 Aa 10.60 Aa 6.03 Ab 8.34SP1 2.85 Ba 3.00 Ba 2.56 Ba 3.76 Ca 3.27 Ca 2.79 Ba 3.04SP3 10.13 Aa 1.74 Bc 1.39 Bc 8.51 Bab 7.90 Bb 1.74 Bc 5.27

Average 8.10 3.66 3.13 7.57 7.26 3.52Soil Heat Flux

MJ m-2 day-1

FS -0.01 Aa -0.11 Aab 0.13 Aa 0.02 ABa -0.24 Abc -0.42 Ac -0.11SP1 -0.13 ABa -0.37 Bc -0.15 Bab -0.07 Ba -0.12 Aa -0.34 Abc -0.19SP3 -0.28 Bc -0.27 ABc -0.08 Bb 0.20 Aa -0.07 Ab -0.35 Ac -0.14

Average -0.14 -0.25 -0.03 0.05 -0.14 -0.37*Means followed by the same upper case letter are not different in column, and those followed by the same lower case letter are not different in line (P<0.05).



The average, maximum, and minimum soil temperatures were generally greater than those of the SP1 and SP3 positions but were sometimes similar to either one or both of the SP positions and rarely even lower than those of either one or the other SP positions. In general, variation in average hourly soil temperature was greater during the day than during the night, with consistently greater values at the FS position (Figure 6c, d).

DISCUSSIONFactors influencing microclimateThe Eucalyptus rows promoted a shadow range projection in the silvopastoral area that was parallel to the tree rows. The East-to-West orientation of the trees resulted in little shadow movement throughout the day, and thus, the shadows were projected at the same distance from the tree rows during a great part of the day. On the other hand, the orientation promoted

Year 1FS SP1 SP2 SP3 SP4

5 5,45405 1,542259 2,258634 2,466395 2,2037596 87,03679 19,00725 28,20373 29,50145 27,138777 319,9635 109,8768 171,8642 154,9001 120,08518 627,033 181,8187 412,3456 464,8084 318,38359 896,6437 183,4103 552,0342 735,7987 628,6633

10 1085,567 287,2733 619,9324 882,431 962,089111 1201,409 397,1715 672,8984 959,8235 1057,45312 1174,189 343,6432 623,6746 958,1005 1039,94113 1077,506 422,3984 550,5481 817,5841 913,910114 895,2515 412,365 491,4159 662,4615 728,677715 676,238 290,9748 354,7607 461,8979 504,375316 402,0539 147,8772 207,4396 267,5673 240,464817 137,2488 38,82362 82,58028 93,89206 59,4616218 16,88262 5,438616 8,772584 8,703837 6,96897719 0,076442 0,02166 0,03263 0,034438 0,031073


5 5,190594 1,909452 1,910934 1,810488 1,8156476 71,59563 22,87896 23,85598 23,46682 23,03937 327,8467 121,4659 123,4217 105,8555 115,45468 671,4025 302,0251 366,8933 304,8117 244,75049 996,0933 404,9871 562,9504 582,461 456,032

10 1241,068 370,4132 651,7287 696,9002 738,321611 1410,453 479,8166 594,692 737,1735 814,423812 1422,118 495,0626 580,6772 722,4103 854,666213 1293,767 533,4614 573,8077 664,4455 752,107214 1045,199 420,8727 534,5101 570,52 614,618515 770,7574 265,1287 351,9091 395,983 392,12816 436,6847 116,2244 181,7376 200,0432 164,225617 158,9319 43,65232 67,68435 58,52529 54,0260418 22,89863 6,968899 8,319426 8,163773 7,94827819 -0,02899 0,036406 0,038739 0,031961 0,033886


5 4,07561 1,286879 1,41589 1,439893 1,3492136 66,08922 17,53985 20,43554 20,37607 18,96297 300,484 68,54365 94,99295 88,10315 83,948278 623,7852 211,6301 254,0521 220,6412 209,90849 934,6003 359,7157 445,2072 470,5821 338,1892

10 1195,613 317,9095 583,4731 675,0651 560,460211 1347,447 360,2419 539,4459 690,1738 648,126812 1348,536 449,6907 507,684 588,9579 642,696113 1242,309 477,1739 518,8489 579,4328 591,899414 1020,987 353,2366 451,9481 515,2117 469,311115 745,7464 203,9228 265,0937 301,0618 260,08916 444,4858 94,6009 148,8555 146,4911 120,275217 162,394 37,12696 54,80842 47,21814 42,3947518 20,19087 4,97599 6,366513 6,449459 5,88226319 0,045923 0,00729 0,037291 0,034248 0,035403

0200400600800

1000120014001600

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

PAR

(μm

ol m

-2s-1

)

Hour

FSSP1SP2SP3SP4

0200400600800

1000120014001600

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

PAR

(μm

ol m

-2s-1

)

Hour

FSSP1SP2SP3SP4

0200400600800

1000120014001600

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

PAR

(μm

ol m

-2s-1

)

Hour

FSSP1SP2SP3SP4

(a)

(b)

(c)

Figure 4. Average photosynthetically active radiation at full sun (FS) and at the four positions within a silvopastoral system (SP1: 0.00 m, SP2: 3.75 m, SP3: 7.50 m and SP4: 11.25 m from the North row), in three study years. a: year 1, b: year 2, c: year 3.



intense shadow variation throughout the year, due to changes in solar declination, with the North-to-South shadow length varying greatly, according to the period of the year (Figure 3, Tables II and III).

During the winter and autumn, neither the PAR or PARt of the SP positions varied significantly because the solar declination during these seasons was high, thereby projecting shadows at all the SP positions. However, this pattern was not observed when tree height was low (~12 m; Table I) or when the solar declination was insufficient to project significant shadows at SP4 (Table II and Table IV). In fact, during the spring and summer of year 1, significant shadows were only observed at the SP1 position, owing to insufficient tree height, but as the trees grew, the

shadow height increased significantly, especially during the third year, when tree height reached ~25 m (Table I). This PAR dynamics, caused by tree growth, can be observed in the hourly PAR values of each study year (Figure 4).

Prasad et al. (2010) reported a PARt of 40% at 0.5 m from rows of 4-year-old Eucalyptus trees (11-m spacing), and Oliveira et al. (2007) reported that PAR was greater between rows of 4.5-year-old Eucalyptus trees (15-m spacing) than below the tree canopies (difference of 762 μmol m-2 s-1). In addition, Siles et al. (2010), who evaluated microclimate in a coffee-based AFS in Costa Rica that was shaded by Inga densiflora Benth., reported a PARt of ~40% during the dry season and of 25% during the wet season.

Rn SHFFS SP1 SP3 FS SP1 SP3

0 -36,8003 -12,5844 -18,1284 0 -18,1489 -13,5253 -14,50021 -36,6505 -12,5488 -18,2523 1 -18,3025 -13,7706 -14,7692 -36,312 -12,4623 -17,9543 2 -18,284 -13,9012 -14,98283 -36,3047 -12,4382 -17,836 3 -18,2573 -13,881 -15,06624 -36,4775 -12,5167 -17,8634 4 -18,2983 -13,8309 -15,12615 -35,092 -12,0544 -17,2453 5 -18,2712 -13,8206 -15,20536 -11,1888 -5,56922 -9,13513 6 -16,9522 -12,86 -14,15457 62,50401 25,20052 16,50739 7 -11,2826 -8,23267 -9,273228 176,333 93,4495 67,55647 8 -0,58642 2,902437 1,729929 289,2922 142,3839 187,2049 9 12,97359 11,58281 16,69901

10 374,8532 138,7908 262,8786 10 27,43641 21,28088 27,8869511 428,1257 102,6739 276,8036 11 39,15476 22,20138 33,5331912 429,164 138,6064 260,6281 12 45,03065 23,39777 33,5658513 390,7177 128,7161 258,5214 13 43,55169 24,41637 27,7400414 312,4014 118,9219 206,2337 14 36,17343 23,28933 22,386715 218,0291 78,59376 129,6663 15 24,98491 14,77934 15,6779316 100,1725 26,66155 57,44838 16 11,79846 6,522446 6,79036117 8,80206 -0,5054 5,396623 17 -0,91758 -0,44885 -2,0122218 -30,9526 -10,344 -15,0763 18 -12,02 -7,01791 -9,177319 -37,3492 -12,3611 -18,2624 19 -16,2632 -10,3262 -11,805920 -37,5538 -12,3954 -18,4686 20 -17,3486 -11,5618 -12,730221 -37,3135 -12,3688 -18,4278 21 -17,6541 -12,2845 -13,344922 -37,2777 -12,4107 -18,3115 22 -17,9088 -12,8783 -13,847423 -36,9957 -12,4995 -18,1202 23 -18,1301 -13,3473 -14,2965

-500

50100150200250300350400450500

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Net

radi

atio

n (W

m-2

)

Hour

FSSP1SP3

-20

-10

0

10

20

30

40

50

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Soil

heat

flux

(W m

-2)

Hour

FSSP1SP3

(a)

(b)

Figure 5. Average net radiation (a) and soil heat flux (b) at full sun (FS) and at two different positions within a silvopastoral system (SP1: 0.00 m and SP3: 7.50 m from the North row).



In the present study, Rn was strongly influenced by solar radiation incidence and, thus, by tree height and solar declination. During the winter and autumn, Rn was greater at the FS position, owing to the relatively high solar declination and low solar radiation incidence of the silvopastoral system. During the spring and summer, the differences were attributed to the strong shading of the SP1 position and weak shading of the SP3 position.

Soil heat flux was affected by solar radiation incidence, wind speed, and the effects of tree canopies on radiation losses, including the reflection and re-emission of long-wave radiation to the soil. The importance of each factor varied, depending on position and season, although solar radiation incidence was the most determinant factor.

Wind speed was consistently lower in the silvopastoral system, owing to the arrangement of the trees in rows, the short spacing between trees in each row (2 m), the high crown base height (Table I), and, likely, the prevailing wind direction, which was transverse to the tree rows. The wind speed reduction mainly occurred during the day, especially during the morning, when solar radiation-mediated changes in air temperature caused air movement. Tamang et al. (2010) reported that the average wind speed reduction at the leeside of 8-m-tall cadaghi (Corymbia torelliana syn. Eucalyptus torelliana (F. Muell.) KD Hill & LAS Johnson) windbreaks was up to 50%, especially when the wind direction was perpendicular to the windbreak. Böhm et al. (2014) also reported that the wind speed of alley cropping systems, with black locust, was reduced to 80% of open areas.

Tsoil Year 2FS SP1 SP3 Wind speed FS SP1 SP30 20,9474 20,54068 20,57196 0 1,890089 1,11056 1,1046371 20,74328 20,37296 20,41258 1 1,869867 1,083997 1,0818362 20,54836 20,19558 20,2555 2 1,843981 1,044598 1,0343143 20,37617 20,05282 20,11641 3 1,811761 1,017661 1,0041784 20,21939 19,92666 19,98703 4 1,798703 0,996945 0,9806175 20,06642 19,7942 19,86111 5 1,807289 1,009732 0,9927316 19,96678 19,72171 19,77047 6 1,847061 0,976066 0,9568587 20,07195 19,85655 19,84295 7 2,048914 1,026227 1,0033728 20,56083 20,52355 20,3352 8 2,324856 1,083862 1,054759 21,47514 21,46934 21,30633 9 2,450202 1,093034 1,062236

10 22,72343 22,42889 22,32667 10 2,454876 1,060034 1,03989411 24,00785 23,13607 23,12328 11 2,377384 1,010365 1,00365212 25,06287 23,80715 23,67758 12 2,297356 0,973908 0,981213 25,73519 24,21634 23,79109 13 2,231384 0,955339 0,97504214 25,97401 24,65426 23,85781 14 2,194956 0,923654 0,96271115 25,76837 24,50599 23,81049 15 2,172312 0,937586 0,9751816 25,22362 23,97057 23,39902 16 2,035928 0,877189 0,914817 24,41631 23,33861 22,85023 17 1,747868 0,850977 0,86808618 23,47787 22,62077 22,27764 18 1,640643 0,926049 0,92240819 22,71233 22,03261 21,81191 19 1,691025 1,010673 1,00569220 22,1885 21,62452 21,48045 20 1,803753 1,085115 1,08143321 21,80428 21,31615 21,21699 21 1,923236 1,138379 1,13505622 21,48697 21,0252 20,99176 22 1,966178 1,183232 1,16948923 21,20611 20,77398 20,78167 23 1,947922 1,145874 1,137164

Tsoil Year 3FS SP1 SP3 Wind speed FS SP1 SP30 20,78387 20,8376 20,74587 0 1,63339 1,177223 1,162141 20,6349 20,709 20,60365 1 1,630096 1,178153 1,1577992 20,51132 20,60198 20,48445 2 1,633918 1,160914 1,138543 20,39652 20,50081 20,36884 3 1,629756 1,124613 1,0996474 20,30324 20,41994 20,26676 4 1,621563 1,082925 1,0726535 20,20324 20,33656 20,16047 5 1,597299 1,065034 1,0498786 20,13302 20,26774 20,08346 6 1,63394 1,080631 1,0566087 20,20827 20,27412 20,11504 7 1,776786 1,088699 1,0526358 20,52954 20,44086 20,36416 8 2,024546 1,145469 1,0970639 21,14612 20,77956 20,86076 9 2,192216 1,186868 1,139727

10 21,99582 21,22481 21,57524 10 2,224609 1,162508 1,10838411 22,83027 21,61863 22,26975 11 2,230205 1,132527 1,09320612 23,47 21,91779 22,72403 12 2,174525 1,087525 1,06128913 23,79243 22,17445 22,91798 13 2,147432 1,053388 1,04034914 23,8253 22,40973 22,92402 14 2,097284 1,027344 1,0223315 23,62434 22,43033 22,82914 15 2,054478 1,00279 1,01496916 23,28708 22,32378 22,60494 16 1,904383 0,953945 0,9702517 22,85689 22,15719 22,30735 17 1,579475 0,899802 0,91549718 22,31672 21,90265 21,95485 18 1,468298 0,996039 1,00381519 21,86614 21,6429 21,64124 19 1,538485 1,110713 1,12686820 21,54153 21,42887 21,40499 20 1,639277 1,193061 1,21042321 21,29693 21,25006 21,20452 21 1,650041 1,224978 1,22697222 21,09479 21,08496 21,0321 22 1,655033 1,228432 1,21649623 20,92285 20,94544 20,87622 23 1,666515 1,213786 1,199389

0

0.5

1

1.5

2

2.5

3

0 2 4 6 8 10 12 14 16 18 20 22

Win

d sp

eed

(m s-1

)

Hour

FSSP1SP3

(a)

0

0.5

1

1.5

2

2.5

3

0 2 4 6 8 10 12 14 16 18 20 22

Win

d sp

eed

(m s-1

)

Hour

FSSP1SP3

16

18

20

22

24

26

28

0 2 4 6 8 10 12 14 16 18 20 22

Soil

tem

pera

ture

(ºC

)

Hour

FSSP1SP3

16

18

20

22

24

26

28

0 2 4 6 8 10 12 14 16 18 20 22

Soil

tem

pera

ture

(ºC

)

Hour

FSSP1SP3

(d)(c)

(b)

Figure 6. Average wind speed (a, b) and soil temperature (c, d) in the study years 2 (a, c) and 3 (b, d) at different positions: full sun (FS), below row (SP1), and 7.50 m from the North row (SP3).



Tabl

e VI

. Mea

n av

erag

e (W

Savg

) and

max

imum

(WSm

ax) w

ind

spee

d; a

vera

ge (T

avg)

, max

imum

(Tm

ax) a

nd m

inim

um (T

min

) air

tem

pera

ture

; ave

rage

(R

Havg

), m

axim

um (R

Hmax

) and

min

imum

(RHm

in) r

elat

ive

hum

idity

; and

ave

rage

(TSa

vg),

max

imum

(TSm

ax) a

nd m

inim

um (T

Smin

) soi

l tem

pera

ture

at

full

sun

(FS)

and

at t

wo

posi

tions

with

in a

silv

opas

tora

l sys

tem

(SP1

: 0.0

0 m

and

SP3

: 7.5

0 m

from

the

Nort

h ro

w),

in e

ach

seas

on o

f tw

o st

udy

year

s.

Year

Seas

onPo

sitio

nVa

riabl

eW

Savg

WSm

axTa

vgTm

axTm

inRH

avg

RHm

axRH

min

TSav

gTS

max

TSm

inm

s-1

m s

-1°C

°C°C

%%

%°C

°C°C

2

Win

ter

FS2.

24 A

ab*

8.03

Ab

19.9

Ab

26.8

Ab

14.3

Ad

56.6

Ac

78.8

Ac

33.7

Ac19

.9 A

c24

.9 A

c16

.7 AB

d

SP1

1.13

Ba4.

64 B

b19

.8 A

b26

.8 A

b14

.4 Ad

56.3

Ac

77.5

Ac

33.6

Ab

20.4

Ab25

.8 A

a17

.2 A

d

SP3

1.12

Bab

4.64

Bb

19.7

Ab26

.7 Ab

14.4

Ad57

.9 A

c79

.4 Ac

34.6

Ab

17.6

Bc

20.6

Bc

15.8

Bd

Sprin

g

FS2.4

6 Aa

8.82

Aa

22.3

Aa

29.5

Aa

17.1

Ab68

.1 Ab

88.3

Ab

41.0

Abc

24.3

Aa

29.6

Aa

21.0

Ab

SP1

1.22

Ba4.

97 B

a22

.4 Aa

29.6

Aa

17.4

Ab67

.1 Ab

86.3

Ab

41.2

Ab

22.6

Ba

26.7

Ba19

.9 B

b

SP3

1.23

Ba5.0

7 Ba

22.6

Aa

30.1

Aa17

.4 Ab

68.1

Ab87

.9 A

b40

.8 A

b24

.5 A

a30

.1 Aa

21.3

Ab

Sum

mer

FS1.6

2 Ac

7.39

Ac22

.9 A

a29

.6 A

a18

.7 Aa

77.7

Aa95

.3 A

a49

.8 A

ab24

.3 A

a26

.9 A

b22

.6 A

Ba

SP1

0.76

Bb

3.84

Bc

22.9

Aa

28.7

Aa19

.0 A

a79

.3 A

a94

.5 A

a53

.9 A

a23

.5 A

a26

.0 A

a21

.8 B

a

SP3

0.77

Bc

4.05

Bc

23.0

Aa

29.7

Aa19

.0 A

a79

.2 A

a95

.3 A

a51

.5 A

a24

.5 A

a26

.6 A

b22

.9 A

a

Autu

mn

FS1.6

9 Ab

c6.

49 A

d19

.9 A

b26

.0 A

b15

.6 A

c77

.8 A

a94

.5 A

ab51

.7 Aa

21.0

Ab

24.0

Ac

19.1

Ac

SP1

0.98

Bab

3.65

Bd19

.7 Ab

25.0

Ab

16.1

Ac80

.3 A

a95

.7 Aa

56.3

Aa

20.2

ABb

22.1

Bb18

.9 A

c

SP3

0.96

Bbc

3.62

Bd19

.8 A

b25

.1 Ab

16.1

Ac78

.4 Aa

93.1

Aab

55.5

Aa

19.7

Bb21

.3 B

c18

.6 A

c

3

Win

ter

FS1.9

3 Aa

7.52

Ab19

.7 Ab

26.1

Ab14

.7 Ab

62.9

Ac

82.1

Ac39

.6 A

b19

.2 A

b22

.9 A

b16

.8 A

d

SP1

1.21

Ba4.

30 B

b19

.7 Ab

25.6

Ab

15.2

Ab

64.3

Ac

82.4

Ac42

.1 Ac

18.5

ABc

20.2

Bb

17.3

Ac

SP3

1.18

Ba4.

35 B

b19

.7 Ab

25.7

Ab15

.2 A

b63

.5 A

c81

.1 Ac

41.5

Ab

18.1

Bb19

.5 B

c17

.0 A

b

Sprin

g

FS1.9

5 Aa

8.26

Aa

23.1

Aa30

.1 Aa

18.3

Aa

73.9

Aab

93.4

Aab

46.1

Aab

23.3

ABa

25.8

Ba

21.6

Ab

SP1

1.18

Ba4.

93 B

a23

.2 A

a29

.4 Aa

18.6

Aa

75.1

Ab93

.0 A

ab52

.8 A

b23

.1 Ba

24.8

Ba

21.7

Aa

SP3

1.18

Ba5.0

5 Ba

23.3

Aa

30.0

Aa

18.7

Aa73

.9 A

b91

.9 A

ab47

.7 Ab

24.2

Aa

27.6

Aa

22.1

Aa

Sum

mer

FS1.7

7 Aa

b7.3

8 Ac

22.8

Aa

29.2

Aa

18.9

Aa

81.9

Aa

97.8

Aa

54.9

Ba

24.0

Aa

25.6

Aa

22.7

Aa

SP1

1.01

Ba3.9

3 Bc

22.5

Aa

28.1

Aa18

.9 A

a84

.7 Aa

97.5

Aa

64.8

Aa

23.3

Aa

24.6

Aa

22.3

Aa

SP3

1.00

Ba4.

02 B

c22

.8 A

a28

.8 A

a19

.2 A

a84

.2 A

a97

.5 A

a58

.7 AB

a24

.0 A

a25

.8 A

b22

.7 Aa

Autu

mn

FS1.5

8 Ab

6.62

Ad

20.1

Ab26

.6 A

b15

.5 A

b73

.7 Ab

89.4

Ab51

.7 Aa

20.2

Ab

22.1

Ab18

.8 A

Bc

SP1

1.01

Ba3.

78 B

d20

.0 A

b25

.6 A

b15

.7 Ab

70.5

Abc

87.2

Abc

52.5

Ab

20.0

ABb

21.1

ABb

19.1

Ab

SP3

1.00

Ba3.

51 B

d19

.7 Ab

25.0

Ab

15.6

Ab

71.1

Abc

87.3

Ab

48.1

Ab19

.0 B

b20

.4 Bc

18.0

Bb

*Mea

ns fo

llow

ed b

y th

e sa

me

uppe

r cas

e le

tter

are

not

diff

eren

t (P<

0.05

), co

mpa

ring

posi

tions

with

in e

ach

seas

on; a

nd th

ose

follo

wed

by

the

sam

e lo

wer

cas

e le

tter

are

not

di

ffere

nt (P

<0.0

5) in

the

com

paris

on a

mon

g se

ason

s.



Air temperature and relative humidity were not different among the assessed positions, since the system design and tree species allowed high canopy porosity and, consequently, enough air movement to suppress such differences. In contrast, Karki & Goodman (2015) reported that the air temperature of a silvopastoral system with mature loblolly pine was 2.3°C lower than that of open pasture, and Pezzopane et al. (2015), who evaluated a silvopastoral system with North-to-South rows of native trees in Brazil, reported that the air temperature was higher and the relative humidity was lower near the tree rows than those either between rows or in the full sun. Therefore, microclimatic changes in silvopastoral systems are affected by their design and the specific structure of the tree species used.

In the present study, soil temperature was affected by solar radiation incidence, wind speed, and the effects of tree canopies on long-wave radiation balance. These results contradict those of Karky & Goodman (2015). Indeed, these authors reported that the soil temperature of a silvopastoral system was consistently lower than that of open pasture, regardless of season, whereas the present study found that such differences were only observed in certain seasons (Table VI). However, Amadi et al. (2016) reported that soil temperature was greater in cropped fields in Saskatchewan, Canada, than in shelterbelts, but only during certain seasons. For example, during late summer and early autumn, when the crop fields cooled more quickly, the soil temperature of the crop fields was actually lower than that of the shelterbelts.

In this context, it is possible to conclude that a silvopastoral system with East-to-West oriented rows causes shadow movement throughout the year, which promotes greater shading between rows when solar declination is high and greater shading near trees when solar declination is

close to the local latitude (22o S). Net radiation is strongly influenced by incoming solar radiation and also depends on the factors that affect the shading. Soil heat flux and temperature are also affected by incoming solar radiation, but wind speed and the effects of canopies on radiation losses may be more important. In the present study, wind speed was consistently lower in the silvopastoral system, especially during the day, owing to the arrangement of trees in rows and the short spacing between plants within rows, which formed an effective windbreak. Air temperature and relative humidity did not differ between the open area and silvopastoral system, likely owing to the high canopy porosity, which allowed enough air movement between the areas.

Use of silvopastoral systems for mitigating climate change effects According to the IPCC (2013), temperature increase and rainfall reduction will be significant in many regions of the world. Thus, protection from solar radiation, such as that provided by the silvopastoral system, may be very important for mitigating climate change effects in locations where evapotranspiration increases as a function of higher temperature, lower rainfall, and lower cloudiness. The silvopastoral system design assessed in the present study significantly reduced solar radiation incidence, mainly at positions that were closer to the tree rows, and these changes were more evident during the spring and summer, when solar radiation incidence was greater and when high solar radiation, especially close to noon, can affect plants and animals negatively.

Excessively high leaf temperatures can cause plant stress and, consequently, reduce photosynthesis (Boyer 1971), as well as plant growth and productivity. Siles et al. (2010) reported that the leaf temperature of coffee plants grown in full-sun was greater than the air temperature,



(CNPq) for financial support (grant 478067/2013-5), and to Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA Agrossilvipastoril) for cession of the weather stations.

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BALISCEI MA, BARBOSA OR, SOUZA W, COSTA MAT, KRUTZMANN A & QUEIROZ EO. 2013. Microclimate without shade and silvopastoral system during summer and winter. Acta Sci Anim Sci 35: 49-56.

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whereas that of shaded coffee was consistently lower. In animals, body temperature determines thermal comfort (Baliscei et al. 2012), as well as productivity and reproductive efficiency (Garcia et al. 2010). Baliscei et al. (2013) measured black globe temperature, which is strongly correlated with animal body temperature, and reported lower values in a silvopastoral system than in an open area. The Rn and wind speed reductions in the silvopastoral systems could contribute to the reduction of pasture evapotranspiration.

Meanwhile, the wind speed reductions observed in the present study confirm the great capacity of silvopastoral systems to reduce excessive wind speeds or strong gusts, which are likely to increase with climate change (IPCC 2013) and which have been associated with both physical damages to plants (Tamang et al. 2010) and stress in animals (Mader et al. 1997). However, in the present study, the Eucalyptus planting failed to significantly affect either air temperature or relative humidity. Therefore, other system designs should be investigated, in order to protect plants and animals from changes in these variables.

Analyzing the potential of silvopastoral systems to attenuate the effects of climate change has revealed that protection from solar radiation can be very important for locations where rainfall and cloudiness are reduced, and reductions in net radiation and wind speed, as observed in the present study, may be important for reducing the evapotranspiration of understory plants of silvopastoral systems, for ensuring more soil water availability for them, and for protecting plants from excessive winds and strong gusts.

AcknowledgmentsWe are grateful to the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for a scholarship (grant 2014/11931-8) granted to the first author, Conselho Nacional de Desenvolvimento Científico e Tecnológico



Assessment Report of the Intergovernmental Panel on Climate Change, 1st ed., Cambridge: Cambridge University Press.

KARKI U & GOODMAN MS. 2015. Microclimatic differences between mature loblolly-pine silvopasture and open-pasture. Agrofor Syst 89: 319-325.

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How to citeBOSI C, PEZZOPANE JRM & SENTELHAS PC. 2020. Silvopastoral system with Eucalyptus as a strategy for mitigating the effects of climate change on Brazilian pasturelands. An Acad Bras Cienc 92: e20180425. DOI 10.1590/0001-3765202020180425.

Manuscript received on March 30, 2018; accepted for publication on December 4, 2018

CRISTIAM BOSI1

https://orcid.org/0000-0001-8318-6477

JOSÉ RICARDO M. PEZZOPANE2

https://orcid.org/0000-0001-5462-6090

PAULO CESAR SENTELHAS1

https://orcid.org/0000-0002-9277-6871

1Universidade de São Paulo/ESALQ, Av. Pádua Dias, 11, 13418-900 Piracicaba, SP, Brazil2Embrapa Pecuária Sudeste, Rodovia Washington Luiz, Km 234, Caixa Postal 339, 13563-776 São Carlos, SP, Brazil

Correspondence to: Cristiam BosiE-mail: [email protected]

Author contributionsCristiam Bosi performed the literature review, data collection, data analysis and wrote the paper. José Ricardo Macedo Pezzopane helped in the design of methodology, data collection, data analysis and article writing. Paulo Cesar Sentelhas helped in the design of methodology, data analysis and article writing.

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