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Modeling the effect of temperature changes on plant life-form distribution along a treeline ecotone in the tropical Andes

• A. Arzac
• E. Chacón-Moreno

L.D. Llambí

• R. Dulhoste

J.M. Olano

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Introduction

Human activities Livestok Agriculture Tropical Andes Biodiversity hotspot Ecosystem services Andean Treelines Dynamic Species richness Adaptative mechanisms Climate Impacts & vulnerability Water resources Climate-vegetation link

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Previous works have shown that temperature and incident radiation, determined by elevation and slope orientation gradients, can modulate the tropical treeline position.

Introduction

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In the northern Andes, the treeline ecotone corresponds to a complex and species rich transition boundary between continuous high mountain forests and grasslands “páramos”

Richness peaks

Trees and tall shrubs are replaced by tussock grasses, small sclerophyllous shrubs and caulescent rosettes with altitude

Arzac et al. (2011):

• Adaptation of Hedberg

system including: trees, bamboos and non-grass herbs.

• Leaf morphological

characteristics: pubescense in rosettes and size leaf in shrubs Introduction Life-form classification system Caulescent rosettes Acaulescent rosettes Tussock grasses Sclerophyllous shrubs Cushion plants Hedberg (1964):

• Classification of Afroalpine

vegetation into 5 categories according to morphological features:

Ø Dominant plant life-forms will respond differently to altitude and slope orientation, influencing treeline vegetation structure and the spatial distribution of vegetation belts Ø Plant life-forms will respond differently under temperature increase scenarios, modifying vegetation physiognomy across the treeline ecotone.

Study questions

Two main questions:

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Study area

Tomsk Venezuela

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Study area

3600 3520 3400 3200 3360 3280

Altitude (m)

Climate:

• Mean Temperature: 7.1 ºC
• Annual precipitation: 1811 mm
• Bimodal precipitation pattern

Study area:

• Altitudinal gradient (3300-3550 masl)
• Forest-páramo ecotone
• Mérida cable car system (Venezuela)

Morphology:

• Slope between 15 – 40º
• Slope orientation varied between

North, North-West and West

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Study area: Vegetation

Mountain forest at the bottom of gradietn Grassland-páramo at the top of gradient

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Sampling design

Transects: 6 Sampling units: 48 Sampling points: 4800

25 m ST1 ST2 ST3 ST4 ST5 ST6 3.300 m 3.550 m

Elevational gradient

Transects

2 m 10 m 20 cm

Sampling unit

Point quadrat method

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Data analysis enviromis 2016

Plant life-form along the gradient Multiple regression models were performed to analyze the response of cover for each plant life- form as a function of altitude and slope

• rientationndepende

nt variables) Distribution models Regression models were carried out to

• btain the predictive

models to be integrated into the geographical information system. Temperature change scenarios Projections based on climate change models used in the Fifth Assessment Report of the Intergovernmental Panel of Climate Change (AR5) Five plant life-forms were chosen for further analysis based on their relative abundance and structural importance (defining the major vegetation physiognomic types across the treeline ecotone).

Results: Plant life-form distribution along the gradient enviromis 2016

Distribution CPR and SS at the top (3489 & 3476 masl). TG and CNR in the middle (3455 & 3425 masl) Trees at the bottom (3390 masl)

Results: Distribution models (current climate conditions)

Caulescent pubescent rosettes Caulescent non-pubescent rosettes

4 8 12 16 20

4 8 12 16 20

20 40 60 80 10

20 40 60 80 100

Tussock grasses Tress

Study species

Temperature difference inrelation with period 1986-2005 (ºC) 2025-2055 (2040) 2045-2075 (2060) RCP 4.5 0.7 0.9 RCP 6.0 1.3 1.9 RCP 8.5 1.8 2.6

• Hierarchy of climate models: Coupled Model Intercomparison Project

Phase 5 (CMIP5) of the World Climate Research Program

• Four Representative Concentration Pathways (RCPs) scenarios were

used: RCP2.6, RCP4.5, RCP6.0 and RCP8.5.

• Predictions focused for years 2040 & 2060

Results: Distribution under climate change scenarios

Caulescent pubescent rosettes Caulescent non- pubescent rosettes

(A) (B) (C) (E) (D) (F)

RCP4.5 RCP8.5 RCP6.0 2040 2060

(G) (H) (I) (J) (K) (L)

RCP4.5 RCP8.5 RCP6.0 enviromis 2016

Results: Climate response and SPEI

Tussock grasses Trees

RCP8.5

(G) (H) (I) (J) (K) (L)

RCP4.5 RCP6.0 enviromis 2016 RCP8.5

(A) (B) (C) (E) (D) (F)

RCP4.5 RCP6.0 2040 2060

Conclusions

Ø The analysis

• f

plant life-forms distribution facilitates the characterization of changes in the vegetation composition in the tropical treeline, allowing the assessment of abundance of dominant elements of forest (such as trees) on the continuous treeline in relation to other plant life-forms. Ø Temperature increments seems to be a driver factor of life-forms upslope shift within the study area,

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Thank you very much for your attention!

This work has been funded by Inter-American Institute for Global Change Research (IAI) through LEAF CRNII 005 project. Special thanks to Mérida Cable Car System and Instituto Nacional de Parques (INPARQUES) for allowing the access to sampling sites. Thanks to A. Heredia for his help in vegetation sampling.