Role of fire in the distribution of vegetation in a Mediterranean type-ecosystem (MTE)

Transcription

1 Role of fire in the distribution of vegetation in a Mediterranean type-ecosystem (MTE) Nyasha Magadzire Supervisors: Dr Helen de Klerk Prof. Karen Esler Dr Jasper Slingsby

2 Climate change projections: - Rise in temperatures - More hot days, fewer cold days - Less winter rainfall in the south-west areas - More rainfall inland and towards the east Drastic shifts in fire activity Legend Cape Floristic Region (CFR) Fynbos

3 Changes in climate and fire regime pose a double risk to plant diversity HOW MUCH OF THE DISTRIBUTION OF FYNBOS IS EXPLAINED BY FIRE? Fynbos is a fire dependent ecosystem CAPE FLORISTIC REGION biodiversity hotspot How will vegetation respond to changes in climate and fire?

4 Aim: Investigate the effect of fire on the distribution of fynbos vegetation Significance of study: Gain a better understanding of potential vegetation responses to future climate AND FIRE REGIME (projections for later analysis)

5 Distribution model Multinomial Logistic Regression (MLR) Observed ~ = Soil Climate Fire Predicted MLR allows us to model multiple vegetation types at one go. Accounts for the fact that more than one vegetation type can exist under the same location and set of conditions. Measures the likelihood of each vegetation type occurring at a given point on a scale of 0 1 (i.e. low to high probability).

6 Vegetation data 30 vegetation subtypes were extracted from the Vegetation Map of South Africa (Mucina & Rutherford 2006) using the following criteria: Fynbos vegetation type 100 pixels per vegetation subtype

7 Environmental data

8 Model accuracy Overall model accuracy: Cohen Kappa=0.77, Area Under Curve (AUC) = 0.88 Proportion of vegetation subtype correctly predicted ranged between 0% and 97 % 8 out of the 30 veg subtypes had <50% of their pixels correctly predicted Veg Subtype No. of pixels Percent correct Veg Subtype No. of pixels Percent correct Bokkeveld Sandstone Fynbos % North Kammanassie Sandstone Fynbos % Canca Limestone Fynbos % North Langeberg Sandstone Fynbos % Cederberg Sandstone Fynbos % North Outeniqua Sandstone Fynbos % De Hoop Limestone Fynbos % North Rooiberg Sandstone Fynbos 100 0% Graafwater Sandstone Fynbos % North Sonderend Sandstone Fynbos % Grootrivier Quartzite Fynbos % North Swartberg Sandstone Fynbos % Hawequas Sandstone Fynbos % Olifants Sandstone Fynbos % Hopefield Sand Fynbos % Overberg Sandstone Fynbos % Kango Conglomerate Fynbos % South Langeberg Sandstone Fynbos % Kogelberg Sandstone Fynbos % South Outeniqua Sandstone Fynbos % Kouga Grassy Sandstone Fynbos % South Rooiberg Sandstone Fynbos % Kouga Sandstone Fynbos % South Swartberg Sandstone Fynbos % Leipoldtville Sand Fynbos % Swartruggens Quartzite Fynbos % Matjiesfontein Quartzite Fynbos % Tsitsikamma Sandstone Fynbos % North Hex Sandstone Fynbos % Winterhoek Sandstone Fynbos %

9 Variable importance Akaike Information Criterion (AIC) was used to assess the importance of the environmental variables. AIC measures the quality of a model relative to other models model fire map mmp rainfall seasonality soil tmax tmin AIC

10 Thank you

11 Hopefield Sandstone fynbos

12 North Langeberg Sandstone Fynbos

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14 Insights Fire return interval contributes substantially to explaining/describing the distribution of fynbs vegetation. Fire regime is a function of fuel load and fire weather which are both closely linked to climate (rainfall seasonality and annual precipitation) - resulting in shared explanatory ability between fire and climate. Having observed that fire is indeed important I will now proceed to model vegetation response to future climate and fire regime 14

15 Mediterranean Type Ecosystems (MTEs) Mild wet winters and warm and dry summers. High levels of plant diversity and endemism = biodiversity hotspots. Fire-adapted and fire-dependent ecosystems. Plant diversity vulnerable to changes in climate and fire regime. (Source: gimcw.org/climate/map-world.cfm)

16 How will vegetation respond to changes in climate and fire? Distribution models provide valuable insights into species-environment relationships and potential climate change impacts on diversity. Most models do not consider the role of natural disturbance regimes such as fire in determining vegetation distributions, or how changes in disturbance regime may alter future projections.