Vegetation and climate changes in the forest of Campinas, São Paulo State, Brazil, during the last 25,000 cal yr BP

Abstract

A paleoenvironmental reconstruction was performed in a Riparian Forest near Campinas to improve knowledge of paleoclimate and paleoenvironment in the State of São Paulo, Brazil. A sediment core of 182 cm depth was collected in a swamp located within a Cerrado/Seasonal Semi-deciduous ecotone forest. The chronological frame is given by eight radiocarbon dating methods. Pollen and stable isotope analyses (δ ¹³C and δ ¹⁵N) were performed all along the core. Modern pollen rain is based on five surface samples collected along the Riparian Forest. Results show a sequence of changes in vegetation and climate between 25 and 13 cal kyr before present (BP), and from 4 cal kyr BP to the present time, with a hiatus between 11 and 4 kyr cal BP. Drier climatic conditions characterized the late Pleistocene and early Holocene, although they had moisture peaks able to maintain an open forest. The Riparian Forest became fully installed from 4 cal kyr BP onward. Our results are in agreement with other regional studies and contribute to build a regional frame for past climatic conditions at the latitude of São Paulo.

KEYWORDS:
Quaternary; palynology; riparian forest; late glacial; Holocene

INTRODUCTION

Palynology applications in paleoenvironmental reconstruction studies have allowed us to understand the main processes involved in the distribution of species during global climatic fluctuations in the Quaternary (Bennett 1997). Studies underwent a significant change from monoproxy to multiproxy in the last decades, in which pollen grains incorporate anthropological, sedimentological and isotopic data, allowing more realistic inferences, as well as environment and climate reconstructions (Flantua et al. 2015).

In Brazil, the Quaternary researches with emphasis on paleoenvironmental reconstructions in climate change are significantly important, considering the country has the world’s largest number of tropical species (IBGE 2004), consisted of diverse ecosystems that respond to climate changes. The forest studied here is part of this environment.

The oldest paleoclimatic record for Southeastern Brazil was identified at Colônia Crater (Ledru et al. 2015), in state of São Paulo. New studies are starting to be developed, and preliminary results indicate that sediments collected 14 meters deep present age approximately to 180 cal kyr before present (BP), which is an important record for Brazil and South America Quaternary (Ledru et al. 2015).

Cruz Jr. et al. (2006) studied relevant paleoclimatic records for Southeastern Brazil using isotopic data in speleothems (Santana/SP and Bouteverá/SC caves). Results show climatic variations of the last 110 cal kyr BP.

According to the paleoenvironmental records of Serra da Mantiqueira and Núcleo Curucutu in Serra do Mar (Pessenda et al. 2009), the climate conditions were cold and humid in Southeastern Brazil near the end of the Last Glacial Maximum (LGM). The records apply for Jacareí in Paraiba do Sul River Valley (Garcia 1994, Garcia et al. 2004) and São Paulo plateau (Bissa and Toledo 2015). From the Pleistocene end to the Holocene beginning, all of studies developed in the Paulista plateau (De Oliveira et al. 2014) showed evidence of temperature increase from 18,000 cal yr BP, with the stabilization of climatic conditions in the last 8,000 cal yr BP.

During the Holocene, the pollen record of Jacareí/SP showed cool and humid climatic conditions between 9,700 and 8,240 cal yr BP, followed by warmer episodes between 8,240 and 3,500 cal yr BP, and then back to cooler conditions between 3,500 and 1,950 cal yr BP (Garcia et al. 2004). The pollen analyses of a fluvial terrace of Mogi Guaçu River located in Jataí Ecological Station (JEE) of the Forestry Institute, State of São Paulo, show drier conditions at the beginning of Holocene characterized by open-field vegetation with fire incidence (Souza et al. 2013), followed by an expansion of the Riparian Forest of 2,183 cal yr. BP, as well as installation of humid climate similar to the current one (Souza et al. 2013).

Most palynological studies in Southeastern Brazil were concentrated in mountainous and coastal zones, specifically State of São Paulo, with the exception of JEE (Souza et al. 2013). Our research aims to provide new paleo-ecological data inland São Paulo related to Riparian Forest located within the Cerrado/Seasonal Semi-deciduous ecotone forest. Thus, the river course is a place of great importance, due to the main migrations of vegetal species that happen in periods of climate change at the Riparian Forests (Oliveira-Filho et al. 2015). The studied site is located on the margins of Quilombo Stream, Santa Elisa Farm, Campinas. The study allowed characterizing vegetation and climate evolution in the last 25 cal kyr BP.

STUDY AREA

Location

The analyzed core was collected inside the Riparian Forest according to Carvalho et al. (2013) and located at Santa Elisa Farm in São Paulo State (22°51’22.08”S, 47°05’35.50”W, 15 m a.s.l.). The forest covers an area of 6 ha along the Quilombo Stream (Fig. 1) and belongs to the Agronomic Institute of Campinas (IAC, acronym in Portuguese), in the city of Campinas (São Paulo).

Figure 1.
Map of the study area showing the core location at Santa Elisa Farm Study Site, Campinas, state of São Paulo.

Climate

The tropical rainfall system experiences a pronounced seasonal cycle in the region of Campinas (Garreaud et al. 2009). It presents a rainy season during the austral summer (from March to October) related to the South American Summer Monsoon activity over Southeastern Brazil, and a dry season during the austral winter (September to April). The mean of annual precipitation is 1,400 mm and of annual temperature varies between 23.1°C in January and 17.1°C in July.

Current vegetation

Currently, vegetation in the area of Campinas shows high degree of human impact. Thus, fragments of native vegetation represent only 2.6% of the territory, which is almost entirely cultivated (Kronka et al. 2005). Vegetation at Santa Elisa Farm is a transition zone between Cerrado (Savanna) and Seasonal Semi-deciduous Forest (Penha 1998, Felfili et al. 2001, Rodrigues et al. 2004, Ferreira et al. 2007, Siqueira and Durigan 2007, Mendonça et al. 2008, Carvalho et al. 2013).

The environmental conditions that determine the distribution of Cerrado, Seasonal Semi-deciduous Sorest, and Riparian Forest are dry season length, winter temperatures, and soil drainage. Botanical surveys within the Riparian Forest described 35 families of angiosperms among 80 species, and the dominant families are: Fabaceae, Myrtaceae, Meliaceae, Lauraceae, and Rutaceae. They represent 41% of total species (Oliveira-Filho et al. 1990, Ferreira et al. 2007, Carvalho et al. 2013, Penha 1998, Rodrigues et al. 2004).

MATERIALS AND METHODS

Chronology

The chronology is based on eight radiocarbon ages (Tab. 1), three sediment samples were analyzed in the laboratory of ¹⁴C-AMS Beta Analytic (Miami, USA), and five samples of Humina extracted from the Laboratory of Paleo-Hydrogeology of the Institute of Geosciences from Universidade Estadual de Campinas - Unicamp (Campinas, Brazil) were analyzed in the laboratory of ¹⁴C AMS - University of Georgia (Athens, USA). ¹⁴C ages were calibrated using the CLAM 2.2 software (Blaauw 2010, version 2.2) with the SHCal13 calibration curve for the atmospheric southern hemisphere (Hogg et al. 2013). The result was based on a 95% probability of 2 sigma (Fig. 2).

Table 1.
Radiocarbon ages obtained from Santa Elisa Farm Core. ¹⁴C dates were calibrated using CLAM 2.2 (Blaauw 2010) and SHCal13 calibration curve for the Southern hemisphere (Hogg et al. 2013).

Sample/Depth (cm)	Age 14C (years BP)	Age 14C Cal. 2 δ (years BP)	13C/12C	Laboratory code
20	5,263 ± 27	5,910-6,022	-18.19‰	UGAMS-28843
42-44	2,890 ± 30	2,863-3,066	-19.9‰	BETA-314745
50	3,479 ± 27	3,607-3,734	-19.25‰	UGAMS-28844
60	11,065 ± 31	12,755-13,007	-15.76‰	UGAMS-28845
70	12,277 ± 32	15,026-15,315	-16.63‰	UGAMS-28846
80	7,330 ± 23	15,026-15,315	-18.37‰	UGAMS-28847
90-92	14,910 ± 60	8,023-8,170	-19.8‰	BETA-314746
174-176	20,850 ± 100	24,657-25,424	-16.9‰	BETA-314747

Figure 2.
Age-depth model of linear interpolation based on ¹⁴C BP ages with 95% confidence intervals ranging from 138 to 750 years (345 years on average). Ages at 80 and 20 cm were excluded; they are indicated with a red point considered as noise.

Stable nitrogen and carbon isotopes

Measures of δ¹³C and δ¹⁵N isotopic composition were performed at the Stable Isotope Laboratory of the Center for Nuclear Energy in Agriculture - CENA-USP (Piracicaba, Brazil). We used 1 g of sample for 27 levels (Tab. 2), which was distributed throughout the core (Fig. 3), as follows: in the upper 90 cm, the sampling interval is 10 cm; between 90 and 1.78 cm, it is 5 cm. Results of the isotopic ratio were expressed in δ unit (‰) and based on the Vienna-Pee-Dee-Belemnite (PDB) international standard, referring to two determinations with an accuracy of ±0,2‰ (Vidotto et al. 2007).

Table 2.
Results of stable isotopes analyses

Depth (cm)	TN (%)	15 N (‰)	C-total (%)	13 C (δ/pdb)
0	0.61	4.33	7	-24.42
10	0.36	6.13	4.28	-21.68
20	0.2	6.72	3.44	-18.19
30	0.16	7.53	2.64	-18.7
40	0.37	5.83	4.81	-22.1
50	0.24	5.55	4.03	19.25
60	0.17	5.55	4.28	-15.76
70	0.1	5.8	2.02	-16.63
80	0.1	5.58	1.67	-18.37
90	0.03	5.27	0.46	-19.69
100	0.02	7	0.36	-21.48
104	0.02	6.22	0.33	-21.53
110	0.02	8.14	0.32	-22.12
116	0.02	7.63	0.33	-22.11
120	0.02	9.36	0.32	-22.58
124	0.02	7.88	0.31	-22.64
130	0.07	4.59	1.32	-17.85
134	0.08	5.26	1.21	-18.3
140	0.02	9.21	0.31	-22.49
146	0.02	7.28	0.33	-22.26
150	0.02	7.49	0.32	-22.81
154	0.02	7.37	0.28	-21.77
160	0.02	5.49	0.25	-22.13
166	0.02	5.68	0.27	-21.03
170	0.01	7.21	0.23	-20.46
174	0.02	6.18	0.14	-17.44
178	0.02	6.15	0.31	-15.99

Figure 3.
Lithology ages of 14C BP and variations relative to depth of TN (%), 15N (‰), Carbon [C-total (%) and 13C (δ/pdb)] and C/N.

Palynological analyses

For the palynological analysis of Santa Elisa core, we used intervals of 2 cm for the first 90 cm and 5 g of sediment. The samples were chemically processed following Faegri and Iversen (1989), where they were oven dried for 4 hours at ~60ºC. HF was added for the dissolution of silicates (leaving for 24 hours). In addition, warm HCl was included for colloidal silica removal, then it was washed with 10% KOH for the destruction of humic acids and amorphous organic matter. The samples were dehydrated with glacial acetic acid, and finally acetolysis. An average of 10 drops of glycerin was added to the final residue.

After preparing the material, non-permanent microscopy slides sealed with maximal limits of residues (LMR) of histopaque fast drying glue were prepared using a residual amount of 50 microliters to calculate the concentration following the mathematical method described by Cour (1974).

About 300 pollen grains were counted. Data were expressed as a percentage of each taxon in relation to the partial sum that includes the arboreal (PA), non-arboreal/herbaceous (NPA), and indeterminate pollen grains. The rate of aquatic plants and spore grains were excluded. Spores are generally removed from the sum, due to their large production and local significance. Percentages of spores and aquatic plants were calculated as to the total sum including AP, NPA, indeterminate pollens, aquatic plants and spores.

Modern pollen rain was collected following a type of random sampling at the study site, with the total of five surface sediment samples.

A reference collection with 24 pollen types (Tab. 3) was performed for Santa Elisa Farm site considering the botanical inventory proposed by Carvalho et al. (2013). Mature flowers were collected in the herbarium of Unicamp (UEC). It was made in permanent slides with Kisser Glycerinated Gelatin (Erdtman 1971) and sealed with preheated paraffin.

Table 3.
List of plant species of Santa Elisa Farm from Carvalho et al. (2013) incorporated in the pollen Reference Collection at the Institute of Geosciences, Universidade Estadual de Campinas (Unicamp).

Family	Species	Growth Habit	UEC Voucher
Acanthaceae	Ruellia brevifolia (Pohl) C. Ezcurra	Shrub	77977
Amaranthaceae	Chamissoa altissima (Jacq.) Kunth	Vine	26759
	Amaranthus retroflexus L.	Herb	40322
Annonaceae	Duguetia lanceolata A.St.-Hil.	Shrub	60172
	Xylopia aromatica (Lam.) Mart.	Shrub	33281
Apocynaceae	Forsteronia glabrescens Müll.Arg.	Vine	128083
Araliaceae	Dendropanax cuneatus (DC.) Decne. & Planch.	Tree	136977
Arecaceae	Syagrus romanzoffiana (Cham.) Glassman	Tree	128732
Asteraceae	Ageratum conyzoides L.	Herb	181832
	Erechtites valerianifolius Link ex Spreng.	Herb	120111
Bignoniaceae	Anemopaegma chamberlaynii (Sims) Burean. & K. Schum.	Vine	168626
	Handroanthus cf. heptaphyllus	Tree	829
	Jacaranda micrantha Cham.	Tree	136219
	Lundia obliqua Sond.	Vine	108782
	Mansoa difficilis (Cham.) Bureau & K.Schum.	Vine	151150
	Pyrostegia venusta (Ker Gawl.) Miers	Vine	132023
Boraginaceae	Cordia ecalyculata Vell	Tree	997
Burseraceae	Protium heptaphyllum (Aubl.) Marchand.	Tree	059437
Cactaceae	Pereskia aculeata Mill.	Vine	38379
Celastraceae	Maytenus aquifolium Mart.	Shrub	506771
Chlorantaceae	Hedyosmum brasiliense Mart. ex Miq.	Shrub	159981
Clusiaceae	Calophylum brasiliensis Cambess.	Tree	125495
Cucurbitaceae	Wilbrandia verticillata (Vell.) Cogn.	Vine	3971
Euphorbiaceae	Actinostemon klotzschii (Didr.) Pax.	Shrub	110913
	Croton floribundus Spreng.	Tree	105729
	Croton priscus Spreng.	Tree	173231
	Dalechampia pentaphylla Lam.	Vine	90366
	Dalechampia triphylla Lam.	Vine	168520
	Pachystroma longifolium (Nees) I.M.Johnst.	Tree	4945
	Sapium glandulosum (L.) Morong	Tree	124428
	Sebastiania brasiliensis Spreng.	Shrub	37556
	Tragia sellowiana (Baill.) Müll. Arg.	Vine	40668
Leguminosae	Anadenanthera colubrina (Vell.) Brenan	Tree	141859
	Chamaecrista flexuosa (L.) Greenes.	Shrub	119769
	Crotalaria paulina Schrank.	Shrub	123546
Malpighiaceae	Banisteriopsis stellaris (Griseb.) B.Gates	Vine	163362
	Byrsonima sp.	Tree	29474
Malvaceae	Abutilon fluviatile (Vell.) K.Schum.	Shrub	64231
Melastomataceae	Ceiba speciose (A. St.-Hil.) Ravenna	Tree	061815
	Miconia chamissois Naudin	Shrub	10718
Meliaceae	Cedrela fissilis Vell.	Tree	28836
	Trichilia catigua A. Juss.	Shrub	060488
	Trichilia claussenii C.DC.	Shrub	108412
	Trichilia elegans A. Juss.	Shrub	49464
Moraceae	Maclura tinctoria (L.) Don ex Steud.	Shrub	62326
	Sorocea bonplandii (Baill.) W.C. Burger, Lanjow & Wess. Boer.	Tree	53173
	Compomanesia guazumifolia (Cambess.) O.Berg.	Tree	151413
Myrtaceae	Calyptranthes concinna DC.	Shrub	108434
	Myrciaria floribunda (H.West ex Willd.) O.Berg.	Shrub	182667
Sapotaceae	Chrysophyllum gonocarpum (Mart. & Eichler) Engl.	Tree	2071
Urticaceae	Boehmeria caudata Sw.	Shrub	67612
Vochysiaceae	Vochysia tucanorum Mart.	Tree	24807

RESULTS

Core description

A core of 182 cm length named Santa Elisa was extracted using a manual probe on the swampy banks of Quilombo Stream. Changes in color, texture and presence of plant remains were observed in the sediment as follows (Fig. 3):

• 182 to 172 cm: dark gray color, composed of clay and presence of iron oxides dispersed in the matrix;

• 172 to 104 cm: light gray color and composed of clay;

• 104 to 90 cm: dark gray color, composed of clay and presence of iron oxides dispersed in the matrix;

• 90 to 0 cm: black color, composed of clay organic sediments that are not compacted, and abundant plant remains.

Chronology

The core basis shows age of 25,040 cal yr BP. Two chronological inversions were identified: one at 80 cm depth with age of 8,096 cal yr BP, possibly derived from bioturbation, and other at 20 cm depth, with age of 5,966 cal yr BP, which may be attributed to carbon enrichment of older ages. We observed a hiatus between 12,881 cal yr BP and 3,670 cal yr BP (Tab. 1, Fig. 2).

Total organic carbon, total nitrogen

Total organic carbon (TOC) concentration shows progressive enrichment along the core, due to interaction between organic matter replacement and decomposition (Pessenda et al. 1996). The minimum value of TOC (0.14%) in the 174 cm depth, and the maximum value of TOC (7%) was observed in the 0-2 cm depth, with an average of 1.53% (Tab. 3, Fig. 3). The concentration of total nitrogen (TN) percentage (Tab. 3, Fig. 3) shows a minimum value of 0.02% at various depths of the core, ranging from 178 (25 cal kyr BP) to 140 cm (22 cal kyr BP), and from 124 (20 cal kyr BP) to 100 cm (18 cal kyr BP) with a maximum value of 0.63% in the 0-2 cm interval and an average of 0.10%. The vegetal tissue deposition justifies the high N values on the core surface (Pessenda et al. 1996). Variations in nitrogen concentration follow those of carbon, as it is seen in the 30-60 cm (1,308-12,924 cal yr BP) and 125-40 cm (20,889-2534 cal yr BP) intervals with an increase of TOC % and TN % content. The relationship suggests significant organic matter deposition. Nevertheless, TOC and TN tend to decrease as depth increases.

δ¹³C of sedimentary organic matter

The carbon isotope approach was used to observe changes in the distribution of C₃ and C₄ plant communities (Pessenda et al. 2009).

High enriched values of δ¹³C are recorded for the core base, as -15.99‰, age of ¹⁴C 20,850 +- 100 yr BP ­(24,781-25,503 cal yr BP), characteristic of open vegetation dominated by Poaceae, as seen in Figure 3, Table 2. A progressive impoverishment of δ¹³C is observed from the core base to 140 cm (22,144 cal yr BP) depth associated with a mixture of C₃ and C₄ plants. At ­140-125 cm depth (22-20 cal kyr BP), an enrichment of δ¹³C was observed in the -18.3 to -17 interval. A depletion of δ¹³C with values of -22.64 to -21.48‰ is observed between 125 and 100 cm ­(20-18 cal kyr BP). Between 100 and 60 cm ­(18-12 cal kyr BP), the δ ¹³C ranges from -21.48‰ to -15.76‰ with average of -18.38‰. At this stage, there are four ¹⁴C ages at 90 cm of 14,910 ± 60 ¹⁴C yr BP ­(15,026-15,315 cal yr BP), 80 cm of 7,330 ± 23 ¹⁴C yr BP ­(8,044-8,144 cal yr BP), 70 cm of 12,277 ± 32 ¹⁴C yr BP ­(14,047-14,376 cal yr BP), and 60 cm of 11,065 ± 31 ¹⁴C yr BP ­(12,809-3,043 cal yr BP). In the 60-40 cm (13-3 cal kyr BP) interval, the δ¹³C values showed a trend of impoverishment with values ranging from -15.76 to -22.1‰.

In the 40-cm top (2,941-3,081 cal yr BP to the present time), the δ¹³C range from -22.1 to -24.42‰. At this stage, we found ¹⁴C age at 20 cm of 5,263 ± 27 ¹⁴C yr BP ­(5,937-6,031 cal yr BP) that is a chronological inversion associated with carbon enrichment of older ages.

Modern pollen rain

Twenty-five pollen types representing 20 families have been identified in the five surface sediment samples in the palynological diagram (Fig. 4).

• Point 1 (Riparian Forest, 22°51’21.15”S/47°5’37.11”W, 421 grains in total, including AP, NAP, indeterminate, and spores). The arboreal pollen grains contributed with 53% of total sum, belonging to Fabaceae [Crudia sp. (11%), Crotalaria sp. (1%) and Mimosa sp. (11%)]; Euphorbiaceae [Alchornea sp. (5%), and Euphorbia sp. (1%)]; Chloranthaceae [Hedyosmum sp. (6%)]; Melastomataceae/Combretaceae (4%); Myrtaceae (3%); Podocarpaceae [Podocarpus sp. (3%)], and Anacardiaceae [Lithraea sp. (2%)]. Other families showed 1% as Apocynaceae (1%); Malphigiaceae (1%) and Sapotaceae [Chrysophyllum sp. (1%)]. Families with less than 1% (+) were Euphorbiaceae [Sapium sp. (+), Sebastiania sp. (+)]; Arecaceae (+); Bignoniaceae (+); Malvaceae (+); Myrsinaceae (+), and Vochysiaceae (+). Non-arboreal pollen grains accounted for 41%, including Poaceae (31%); Asteraceae (9%); Lamiaceae [Aegiphila sp. (1%)], and Amaranthaceae [Gomphrena sp. (+)]. 6% were indeterminate pollen grains. Finally, among aquatic plants, Cyperaceae (12%), fern spores (15%), Athelia fungi spores (5%), and indeterminate fungi spores (9%);

• Point 2 (Riparian Forest, 22°51’25.82”S/47°5’29.66”W, 587 grains in total, including AP, NAP, indeterminate, and spores). The arboreal pollen grains contribute with 58% of total sum, belonging to Fabaceae [Crudia sp. (9%), Crotalaria sp. (1%), Mimosa sp. (10%)]; Euphorbiaceae [Alchornea sp. (4%), Euphorbia sp. (1%), Sapium sp. (1%), and Sebastiania sp. (1%)]; Myrtaceae (7%); Anacardiaceae [Lithraea sp. (7%)]; Melastomataceae/Combretaceae (5%); Chloranthaceae [Hedyosmum sp. (4%)]; Arecaceae (3%); Podocarpaceae [Podocarpus sp. (2%)], and Apocynaceae (2%). Other families showed 1% representation as Malphigiaceae (1%); Myrsinaceae (1%); Vochysiaceae (1%); Sapotaceae [Chrysophyllum sp. (1%)], and Bignoniaceae (1%). Malvaceae (+) was the family with less than 1%. The non-arboreal pollen grains accounted for 31%, with Poaceae (23%); Asteraceae (6%), and Amaranthaceae [Gomphrena sp. (2%)]. Lamiaceae [Aegiphila sp. (+)] was the family with lower than 1%. Indeterminate pollen grains accounted for 11%. Finally, among aquatic plants, Cyperaceae (8%), fern spores (8%), Athelia fungi spores (1%), and indeterminate fungi spores (10%);

• Point 3 (Riparian Forest, 22º51’25.74”S/47º5’28.68”W, 238 grains in total, including AP, NAP, indeterminate pollen, and spores). At this point, a few palynomorphs were found with an increase of non-arboreal pollen to 81%, dominated by Poaceae (72%); Lamiaceae [Aegiphila sp. (7%)], and Asteraceae (2%). The AP grains decreased to 19% of the total sum, dominated by Fabaceae [Mimosa sp. (8%)]; Apocynaceae (5%); Melastomataceae/Combretaceae (3%); Malphigiaceae (2%), and Myrtaceae (1%). Among aquatic plants, Cyperaceae family was dominant with 19%, fern spores, 17%; Athelia fungi spores, 11%; and indeterminate fungi spores, 18%;

• Point 4 (Riparian Forest, 22°51’27.21”S/47°5’27.76”W, 371 grains in total, including AP, NAP, indeterminate pollen, and spores). The arboreal pollen grains contribute with 50% of total sum, belonging to Fabaceae [Crudia sp. (7%), Crotalaria sp. (1%), and Mimosa sp. (10%)]; Euphorbiaceae [Alchornea sp. (7%)]; Myrtaceae (15%); Melastomataceae/Combretaceae (3%); Podocarpaceae [Podocarpus (4%)]; Apocynaceae (1%), and Anacardiaceae [Lithraea sp. (1%)]. Families with less than 1% (+) were Euphorbiaceae [Euphorbia sp. (+), Sebastiania sp. (+), and Sapium sp. (+)]; Malpighiaceae (+); Malvaceae (+); Vochysiaceae (+), and Sapotaceae [Chrysophyllum sp. (+)]. Non-arboreal pollen grains accounted for 46%, with Poaceae (29%), Asteraceae (10%), Lamiaceae [Aegiphila sp. (2%)], and Amaranthaceae [Gomphrena sp. (2%)], indeterminate pollen grains (5%). Among aquatic plants, Cyperaceae (12%), fern spores (8%), Athelia fungi spores (5%), and indeterminate fungi spores (12%);

• Point 5 (Riparian Forest, 22°51’27.21”S/47°5’27.76”W, 421 grains in total, including AP, NAP, indeterminate, and spores). AP grains contribute with 39% of total sum, belonging to Fabaceae [Crudia sp. (4%), and Mimosa sp. (7%)]; Euphorbiaceae [Alchornea sp. (7%), and Euphorbia sp. (1%)]; Myrtaceae (8%); Anacardiaceae [Lithraea sp. (4%)]; Melastomataceae/Combretaceae (3%); Chloranthaceae [Hedyosmum sp. (2%)]; Podocarpaceae [Podocarpus sp. (2%)]. Families with less than 1% (+) were Myrsinaceae (+); Fabaceae [Crotalaria sp. (+)]; Euphorbiaceae [Sebastiania sp. (+)]; Apocynaceae (+); Arecaceae (+); Bignoniaceae (+); Malvaceae (+); Malphigiaceae (+), and Sapotaceae [Chrysophyllum sp. (+)]. NAP grains accounted for 56%, with Poaceae (41%); Asteraceae (10%); Lamiaceae [Aegiphila sp. (2%)], and Amaranthaceae [Gomphrena sp. (2%)]; indeterminate pollen grains (5%). Among aquatic plants, Cyperaceae with 15%, fern spores (8%), Athelia fungi spores (5%), and indeterminate fungi spores (14%).

Figure 4.
Diagram presenting the results of surface pollen samples collected along the riparian forest, Quilombo stream, watershed, near water course, in Campinas, São Paulo state, Brazil. (+) represents the taxa with less than 1% representation.

Fossil pollen

We observed four pollen zones based on changes in pollen frequency and δ ¹³C isotopic results, numbered from I (older) to IV (younger), as seen in Figure 5. Forty-three pollen types belonging to 32 families were identified in four pollen zones:

• Zone I: 15 samples, 90 and 60 cm depth, between -17,770 and 12,924 cal yr BP. It is characterized by the absence of palynomorphs in 13 samples and low concentration in the sample at the 78-76 cm depth interval. The total number of pollen grains is 86, which represents 230 pollen grains per grams of sediment. 55% of arboreal pollen, 30% of non-arboreal pollen, and 15% of indeterminate pollen. Spores accounted for 47 to 32%, and fungi from 21 to 26%. Arboreal pollen grains identified in the zone belong to Malpighiaceae [Byrsonima sp. (18 to 4%)]; Myrtaceae (13 to 8%); Sapotaceae [Chrysophyllum sp. (11 to 8%)]; Melastomataceae/Combretaceae (9 to 8%); Euphorbiaceae [Euphorbia sp. (4 to 2%), and Croton sp. (1 to 2%)]; Vochysiaceae [Vochysia sp. (2%)]; Arecaceae (4%); Chloranthaceae [Hedyosmum sp. (2%)]; Meliaceae (2%) and Sapindaceae (2 to 3%). The family that represented with less than 1% was Dilleniaceae (+). Poaceae (9 to 63%) and Asteraceae (21 to 7%) are among non-arboreal pollen grains. Cyperaceae represented the aquatic plants with 42 to 26%. The δ¹³C values ranged from -16.63‰ to -18.37‰, which determine a predominance of C₄ plants;

• Zone II: 13 samples, 60 to 40 cm depth. 60 cm with age of 12,924 cal yr BP, 50 cm with age of 3,831 cal yr BP, 40 cm between 2,534 cal yr BP; between 60 cm and 50 cm, there is a hiatus. The concentration of pollen grains was 65.7 to 487.9 with an average of 312.4 grains of pollen per gram of sediment. Arboreal pollen grains account for 42%; non-arboreal pollen, 50%; indeterminate pollen, 8%; aquatic plants, 26%. Spores accounted for 3%, and fungi, 29 to 15% of total pollen. Arboreal pollen grains identified in the zone are mainly represented by Apocynaceae (20 to 6%); Dillenaceae [Tetracera sp. (1 to 11%), Curatella americana (1%)]; Arecaceae (7 to 4%); Melastomataceae/Combretaceae (7%); Myrtaceae (2 to 7%); Sapotaceae [Chrysophyllum sp. (1 to 3%)]; Aquifoliaceae [Ilex sp. (1 to 2%)]; Podocarpaceae [Podocarpus sp. (1%)]; Fabaceae [Copaifera sp. (1%), Crudia sp. (1%) and Mimosa sp. (1%)]; Malvaceae [Pseudobombax sp. (1%)]; Caryocaraceae [Caryocar brasiliense (1%)]; Malphigiaceae [Byrsonima sp. (1%)]; Urticaceae [Cecropia sp. (1%)]; Vochysiaceae [Vochysia sp. (1%)]; Bignoniaceae (1%); Euphorbiaceae [Euphorbia sp. (1 a 3%), Croton sp.(1%), Sapium sp. (1%) and Sebastiania sp.(1%)], and Meliaceae (1%). The family represented with less than 1% was Anacardiaceae [Lithraea sp. (+)]. Among non-arboreal pollen grains appear Poaceae (36 to 30%); Asteraceae (3 to 13%); Lamiaceae [Aegiphila sp. (3%)]; Amaranthaceae [Gomphrena sp. (1%)], and Caryophyllaceae (1%). Cyperaceae (24 to 19%) represents the aquatic taxa. The δ¹³C results showed a ¹³C enrichment of -22.1‰ to -18.19‰, as a mixture of C₃ and C₄ plants with predominance of C₄ plants;

• Zone III: 10 samples, 40 to 20 cm depth, between 2,364 and 718 yr. The concentration of pollen grains ranged from 488 to 856, with an average of 442 grains of pollen per gram of sediment. Arboreal pollen grains corresponded to 43%; non-arboreal pollen, 51%; indeterminate pollen, 6%; and aquatic taxa, 24%. Spores accounted for 8 to 7% and fungi from 36 to 25%. Arboreal pollen grains identified in the zone are represented by Arecaceae (21 to 7%); Apocynaceae (12 to 5%); Fabaceae [Mimosa sp. (10 to 2%), Crudia sp. (2 to 1%), and Crotalaria sp. (1%)]; Anacardiaceae [Lithraea sp. (15 to 1%) and Tapirira sp. (1%)]; Euphorbiaceae [Euphorbia sp. (8 to 1%), Alchornea sp. (2 to 1 %), Sapium sp. (3 to 1%), Croton sp. (1%), and Sebastiania sp. (2 to 1%)]; Aquifoliaceae [Ilex sp. (2 to 1%)]; Chloranthaceae [Hedyosmum sp. (1%)]; Melastomatacea/Combretaceae (16 to 4%); Myrtaceae (4 to 1%); Urticaceae [Cecropia sp. (3%)]; Podocarpaceae [Podocarpus sp. (2 to 1%)]; Sapotaceae [Chrysophyllum sp. (2 to 1%)]; Bignoniaceae (1%); Dilleniaceae [Tetracera sp. (6 to 1%)]; Verbenaceae [Lantana sp. (1%)], and Malpighiaceae (4 to 1%). Non-arboreal pollen grains are represented by Poaceae (20 to 57%); Asteraceae (23 a 4%); Amaranthaceae [Gomphrena sp (3 to 1%)]; Caryophyllaceae (2 to 1%), and Xyridaceae [Xyris sp. (3 to 1%)]. Aquatic taxa Cyperaceae shows 36 to 24%. The δ¹³C isotopic results showed ¹³C enrichment of -22.1‰ to -18.19‰, as a mixture of C₃ and C₄ plants with predominance of C₄ plants;

• Zone IV: 10 samples, 20 to 0 cm depth, the last 718 years. Characterized by the highest pollen concentration of Santa Elisa core, between 856 and 1,787 pollen grains per gram of sediment, and an average of 1,082 pollen grains per gram of sediment, with arboreal pollen (46%), non-arboreal pollen (50%), indeterminate pollen (4%), aquatic taxa (17%), spores (6 to 5%), and fungi (36 to 25%). Arboreal pollen grains identified in the zone are represented by Arecaceae (21 to 7%); Fabaceae [Copaifera sp. (3 to 1%), Crudia sp. (8 to 1%), Crotalaria sp. (2 to 1%), Mimosa sp. (7 to 2%) and Myroxylon sp. (1%)]; Anacardiaceae [Tapirira sp. (1%) and Lithraea sp. (15 to 7%)]; Chloranthaceae [Hedyosmum sp. (4 to 1%)]; Euphorbiaceae [Alchornea sp. (4 to 1 %), Euphorbia sp. (2 to 1%), Sapium sp. (1%) and Sebastiania sp. (2 to 1%)]; Apocynaceae (3 to 1%); Melastomatacea/Combretaceae (5 to 2%); Myrtaceae (6 to 1%); Sapotaceae [Chrysophyllum sp. (8 to 1%)]; Podocarpaceae [Podocarpus sp. (3 to 1%)]; Aquifoliaceae [Ilex sp. (1%)]; Malvaceae (Pseudobombax sp. 1%); Malpighiaceae [Byrsonima sp. (1%)]; Myrsinaceae [Cybianthus sp. (1%)]; Urticaceae [Cecropia sp. (1%)]; Vochysiaceae [Vochysia sp. (1%)]; Bignoniaceae (1 a 3 %); Dilleniaceae [Tetracera sp. (3 a 1%)], and Meliaceae (1%). The family with less than 1% is Euphorbiaceae [Croton sp (+)]. Non-arboreal pollen include Poaceae (30 to 47%); Asteraceae (10 to 4%); Amaranthaceae [Gomphrena sp (2 to 1%)]; Xyridaceae [Xyris sp. (1%)], and Lamiaceae [Aegiphila sp. (3 to 1%)], and aquatic Cyperaceae (21 to 11%). The δ¹³C isotopic results (-18, 19‰ at -24, 42‰) indicate an impoverishment of δ¹³C with predominance of C₃ plants.

Figure 5.
Fossil pollen diagram of Santa Elisa Farm core. Selected pollen and ferns taxa are expressed as percentages of the total sum (except aquatics and ferns) along a depth scale with δ13C, total concentration, AP/NAP and four pollen zones. 14C dates are reported along the depth scale.

DISCUSSION

Modern pollen rain

Considering the studied taxa at our site, only Podocarpaceae (Podocarpus sp.) represents gymnosperms. Podocarpus sp., a wind pollinated taxa, was not observed in the area of Santa Elisa (Carvalho et al. 2013). Its presence in surface sediment samples may be explained as being transported from nearby cities as it is widely used as an ornamental plant.

The pollen grains identified in the modern pollen rain were derived mostly from angiosperms, mainly Fabaceae, Myrtaceae, Asteraceae, Poaceae, and Cyperaceae, with a good correspondence between pollen results and botanical surveys (Carvalho et al. 2013). The pollen taxa with restricted occurrence were Vochysiaceae, Myrsinaceae, Euphorbiaceae (Sapium sp. and Sebastiania sp.), and Arecaceae.

Most of the identified pollen grains represent a broad range of habitats and belong to the physiognomies of Riparian, Cerrado, and Seasonal Semi-deciduous forests (Oliveira-Filho et al. 1990, Flora do Brasil 2012, Carvalho et al. 2013) with 25 taxa (arboreal and non-arboreal) belonging to 20 families. Of these, only 5% have exclusive species to the Riparian Forest physiognomy (Apocynaceae, Arecaceae, Bignoniaceae Myrtaceae, and Malvaceae) observed in surface sediments and in quaternary (core) samples. An exception of Malvaceae was not found in core samples. However, Chloranthaceae (Hedyosmum sp.) associated with Seasonal Semi-deciduous Forest was found in surface, sediment, and core samples.

The remaining 95% represent taxa inhabit either in Riparian, Cerrado or in seasonal semi-deciduous forests (Podocarpaceae, Anacardiaceae, Amaranthaceae, Bignoniaceae, Euphorbiaceae, Sapotaceae, Fabaceae, Asteraceae, Lamiaceae), and are in surface and quaternary sediments.

Not surprisingly, as all the samples are located within the forest, the pollen content of surface samples (1, 2, 4 and 5) shows little changes with dominance of arboreal pollen (50%), as seen in Figure 4. Sample 3 demonstrates higher herbaceous taxa frequency (81%), due to its proximity to the limit between forest and open field, corresponding to a transition zone or ecotone.

Interpretation of palynological and isotopic results

Results of pollen and isotopic analyses of TOC, N-Total, and δ¹³C allow establishing a sequence of changes in vegetation and climate between 25 and 13 kyr BP, and from 4 kyr BP to the present, with a sedimentation gap between 13 and 4 kyr BP.

From 25 to 13 kyr BP

This core basal interval presented clayey sediment and was characterized with evidence of oxidation. Isotopic data indicated low content of TOC and TN with enriched values of δ¹³C -15.99‰, suggesting that around 25 kyr BP had a more open vegetation associated with drier climatic conditions than current ones. Dry conditions were not constant recording small cold humidity variations in the area.

Between 25 and 15 kyr BP, δ¹³C shows a progressive impoverishment from -15.99‰ to -22.49‰. The values reflect impoverishment associated with a mixture of C₃ and C₄ vegetation (Pessenda et al. 2009), suggesting the forest expansion, which is likely related to in water table changes.

Between 15 and 13 kyr, BP, the δ¹³C shows a predominance of C₄ plants with values from -19.69‰ to -15.76‰, low TOC content, and low concentration of pollen grains. The dates showed a chronological inversion of 8 kyr BP associated with a regression of the forest vegetation cover, which is likely associated with return to dry climatic conditions.

Ledru (1993) reported similar climatic conditions to this time interval from 15 to 13 kyr BP pollen record for another environment known as Salitre, in Minas Gerais State, around 500 km North in the city of Campinas. In Salitre, between 15 and 12 cal kyr BP, the presence of Araucaria sp. and other mixed ombrophilous forest taxa (e.g., Ilex sp., Symplocos sp., and Drymis sp.) have been attributed to cool temperature.

At Santa Elisa, we infer water body fluctuations to explain the moisture variability between 25 and 13 kyr BP. Pessenda et al. (2009) reinforces occurrences of groundwater level fluctuations in the countryside of São Paulo as a consequence of relative sea level variations. It indicates drier climatic conditions than today. The result is in agreement with other studies (e.g., Ledru et al. 1998, Behling 2002), which observed the predominance of dry climate in the South and Southeast Brazil at the late Pleistocene.

Between 13 and 4 kyr BP

The hiatus (Figs. 2 and 5) at 13 and 4 kyr BP found at Santa Elisa was also observed in the Northwest of São Paulo State at JEE, on a river terrace of Mogi Guaçu River (Souza et al. 2013). For the JEE record, the gap ranges from 10,192 to 2,183¹⁴C yr BP, and it is interpreted as an absence of sedimentation or removal of sediments previously deposited by erosion.

At Santa Elisa, absence of sediment deposition may correspond to erosion, due to the fluvial system, a temporal functioning of Quilombo Stream or even drier climatic conditions (Ledru et al. 1998).

From 4 cal yr BP to the present

Impoverishment of δ¹³C found here may represent forest expansion with a mixture of C₃ and C₄ plants, and predominance of C₃ plants (Pessenda et al. 2009). The TOC concentration shows a progressive enrichment due to the interaction between organic matter replacement and decomposition (Pessenda et al. 1996). The vegetal tissue deposition justifies high N values on core surface (Pessenda et al. 1996).

From 3,700 cal yr BP, a record of Cecropia sp. appear at Santa Elisa, which is pioneer taxa in secondary forests (Marchant et al. 2002). The episode likely happens due to the expansion of Riparian Forest, under warmer and moister climatic conditions. It is in agreement with other pollen records of São Paulo State, in which an increase in moisture rates was observed at 2,189 yr BP for JEE (Souza et al. 2013), and at 3,500-1,950 yr BP for Paraíba do Sul River Valley (Garcia et al. 2004).

The increase of moisture rates after three kyr BP was also observed in other Brazilian regions, such as Lagoa La Gaiba, North of Pantanal and Eastern Bolivia, where a marked expansion of tropical moist forest after three kyr BP was followed by a dry early-mid Holocene (Whitney et al. 2011, Mayle et al. 2000).

CONCLUSIONS

Our research provides new paleo data in a poorly studied region. River dynamics and their associated Riparian Forests are very sensitive to water table and climate changes. Pleistocene climatic changes showed differentiated impacts on the ecosystems in São Paulo State, due to their high landscape heterogeneity. The paleo-ecological record of Santa Elisa farm showed drier climatic conditions than current ones and variations in moisture content between 25 and 15 kyr BP. Erosive conditions likely due to drier climatic conditions characterize the late Pleistocene and early Holocene between 13 and 4 kyr BP. The wetter conditions only returned after 4 kyr BP, a general trend for São Paulo State, when climatic conditions relatively like the current ones became fully established.

ACKNOWLEDGEMENTS

The authors thank the anonymous reviewers whose comments greatly improved our paper. This work was possible thanks to Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) funding (Process 10/16507-9 - “Water in soil morphology associated with the physiognomic gradient Riparian Forest - Cerrado in Campinas, SP”), Ms. Marina B. Carvalho, and Dr. Ricardo M. Coelho for providing the core studied here, and field support collecting the modern pollen rain. In the same way, the National Council for Scientific and Technological Development (CNPq) for the master scholarships, research fellowship awarded, and research grant (PQ), as well as UEC for the flowers provided to build the reference collection of Santa Elisa Farm. In addition, we would like to thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).

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ARTICLE INFORMATION

• 1
  Manuscript ID: 20190040.

Publication Dates

• Publication in this collection
  10 Oct 2019
• Date of issue
  2019

History

• Received
  25 Sept 2018
• Accepted
  22 July 2019