THE CLIMATIC POTENTIAL AND THE KEY METEOROLOGICAL DRIVERS FOR THE DYNAMICS OF INVASIVE TERRESTRIAL PLANT SPECIES IN COMANA NATURAL PARK

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1 THE CLIMATIC POTENTIAL AND THE KEY METEOROLOGICAL DRIVERS FOR THE DYNAMICS OF INVASIVE TERRESTRIAL PLANT SPECIES IN COMANA NATURAL PARK Ines GRIGORESCU 1, Carmen-Sofia DRAGOTĂ 1, Monica DUMITRAŞCU 1, Mihaela NĂSTASE 2 1 Institute of Geography, Romanian Academy, 2 Protected Areas Department, Romanian Forest Administration, Bucharest Abstract. The paper is aiming to assess the key climatic and meteorological drivers responsible for the occurrence, development and spread of the Invasive Terrestrial Plant Specie (ITPS) in the Comana Natural Park. The authors used and processed annual, monthly and daily extreme climatic values (temperature, precipitations, wind, dangerous climatic phenomena) from Giurgiu meteorological station which, although located in the vicinity of the study area, was selected based on the resemblance of its environmental features to the ones displayed by Comana Natural Park in terms of: main climatic features, morphological conditions, elevation, and the presence of wetlands. Therefore, the complex climatic assessment was related to the environmental requirements of the most important ITPS in the study-area: Amorpha fruticosa (non-native) and Crataegus monogyna (native) in order to identify the main meteo-climatic drivers responsible to their distribution and spread. Taking into consideration the conservation value of this natural protected area, the paper would bring major contribution to developing and implementing management and control measures required by this protected area management plan. Keywords: Comana Natural Park, climatic potential, key meteorological drivers, Invasive Terrestrial Plant Species (ITPS), Romania. Introduction Climate-related issues (especially climate variability and change) become of greatly importance when arguing their role in ecosystem s dynamics and functioning. Therefore, the complexity of interaction between these two key global drivers climate change and biological invasions - has dramatically increased over the last period, thus enhancing the already visible impacts of invasive species (Burgiel and Muir, 2010) in terms of the environmental damages they produce: habitat degradation and loss, native flora extinction, changes in ecosystem functioning etc. (Shea and Chesson, 2002; Arim et al., 2006). Climate variability and change direct impacts, such as increased temperatures and CO 2 concentrations as well as changes of the precipitation patterns, are likely to increase ITPS opportunities to expand because of their high adaptability to a broader range of environmental conditions, thus causing significant disturbances to habitats (Bradley et al., 2010; Burgiel and Muir, 2010; Dragotă et al., 2011). Researches undertaken up to now, have put an emphasis on the complex linkages between the physical environment, resources and plant invasions (Shea and Chesson, 2002) or argued on the environmental drivers responsible for the spreading or shrinking the biological invasions (Shi et al., 2010). In some areas exposed to different disturbing events (e.g. extreme hydro-climatic phenomena) ecosystem s vulnerability might increase leading to the establishment and spread of invasive species (Burgiel and Muir, 2010) which, prove a higher environmental tolerance as compared to the native species (Shea and Chesson, 2002). The distribution and frequency of biological invasions bare the geographical pattern of their area of origin, as there are strongly influenced by latitude (lower latitudes determining more biological invasions), therefore linking biological invasions to climate types (Shi et al., 2010). 45

2 Consequently, changes in weather and climate trigger both individual and cumulative effects on ecosystems that can further facilitate the expansion and abundance of invasive plant species (Taush, 2008). Methods and data In assessing the climatic potential of Comana Natural Park in relation to the distribution and spread of invasive plant species the authors used and processed the meteorological data from Giurgiu meteorological station. Since there is no weather station inside the Park area, the authors selected it based on the resemblance of its environmental features to the ones displayed by Comana Natural Park in terms of: main climatic features, morphological conditions, elevation, and the presence of wetlands. Moreover, Giurgiu meteorological station is situated at about 30 km, which complies with the World Meteorological Organization requirements, in order to provide accurate data. Additionally, the current research relies on cross-reference bibliographical literature (geographical and biological) as well as on several field surveys. The study-area Comana Natural Park is located in the central-eastern part of the Romanian Plain (fig. 1), namely the southern part of Teleorman Plain, at the contact between the Burnas and Câlniştea Plains. It develops to its largest extent around the Comana Lake on the lower Neajlov River. Figure 1. Romanian natural protected areas network Due to its position at the biogeographic contact between mesophyllous deciduous forests and the sylvo-steppe, the study-area has favoured the development of different floristic 46

3 and faunistic associations of different geographical origin. Moreover, its location at the intersection of different floristic provinces points to the high biodiversity given by the large number of taxa, the great number of endemic species (Achillea getica, Dianthus trifasciculatus ssp. desertus, Viola jooi, Paeonia peregrina var. romanica) and species with different geographical origin (Ruscus aculeatus, Convalaria majalis, Crocus moesiacus etc.). Until the beginning of the 19 th century, the study-area was covered by Vlăsia Secular Forest, whose remnant patches appear as left-over of the one of the best-preserved forests in Europe (Călinescu et al., 1969; Grigorescu, 2010a, Grigorescu, 2010b). The study-area has granted the protected area status since 1954 by declaring Comana Forest (630.5 ha) as natural reserve. Recently, according to the IUCN categories and national regulations the entire protected area falls into the 5 th category Protected terrestrial ecosystems. Some internal small-size protected areas belong to the 4 th IUCN category Natural reserves: Oloaga-Grădinari Forest and Padina Tătarului Forest (Dumitraşcu et al., 2011a). Currently, Comana Natural Park is almost entirely overlapping the Natura 2000 Network (SPA Special Protection Areas and SCI - Site of Community Importance) aiming to protect wildlife and its habitats (fig. 2). Figure 2. Comana Natural Park (Grigorescu, 2010b) Over the last century, the natural ecosystem of this protected area was massively altered by human activity trough deforestation and replaced with secondary meadow and scrub associations, strongly affecting the floristic structure and composition. Therefore, considering its ecological connotation, the authors undertook a complex assessment of the key meteo-climatic drivers with impact on the main ITPS which are threatening the ecological balance of this protected area: Amorpha fruticosa (non-native invasive plant species) and Crataegus monogyna (native invasive species) (Dumitraşcu et al., 2011b) (fig. 3). 47

4 a b Figure 3. Amorpha fruticosa (a) and Crataegus monogyna (b) in the Comana Natural Park (Dumitraşcu et al, 2011b) The climatic potential and the key meteorological drivers for the dynamics of invasive terrestrial plant species This natural protected area displays a transitional temperate continental climate with excessive influences specific for the plain regions developed in southern Romania. The geomorphological features of the Comana Natural Park, resulting in the low altitude, high uniformity, large water and marsh-covered area, the absence of orographic barriers and the openness to all wind directions, lead to several major climatic features: the advection of air masses relatively simultaneous causing periodic and non-periodic variations but without significant amplitudes values, high values of the radiative balance, high degree of dryness and continental influences on high terraces, as well as a high humidity in the river floodplains etc. To these are added the climatic particularities imposed by the vegetal layer dominated by the azonal floodplain vegetation (hydrophilic and hygrophilic favoured by the presence of pond and Lake Comana and by the shallow water table) along with the nemoral forests. At the same time, the area is strongly influenced by the northern, north-western pond, meadow and lake topoclimates (developed on the joint lower courses of Neajlov, Argeş and Sabar Rivers) and by the forests in the north-west and east (fig.2). The major climate genetic factors - solar radiation, general atmospheric circulation and the underlying active surface imprints and therewith generates distinct characteristics for the variation and spatial-temporal distribution of all meteorological elements specific to the study-area, both at global and local scale. The solar radiation, as the primary energy source, correlated with astronomical and terrestrial genetic factors, both at lower atmosphere and in contact with the earth's surface is highlighted by a series of climatic parameters resulting from actinometric measurements. Total radiative balance values for all weather conditions (clear, cloudy, overcast) reached the highest average values of about 500 Wm -2 in July and the lowest at 12 pm in December, of around 90 Wm -2 (Sandu et al., 2010). Directly connected to the magnitude of the radiative flux, the global solar radiation at Giurgiu meteorological station reaches annual mean values of hours out of which hours during the warm semester of the year and hours during the cold semester (tab. 1). 48

5 Table 1. The annual mean values of global solar radiation registered at Giurgiu weather station ( ) Months I II III IV V VI VII VIII IX X XI XII Source: National Meteorological Administration database The general dynamics of the atmosphere, common throughout the south-eastern sector of the Romanian Plain, is dominated by the advection of air masses of polar-maritime and continental-polar origin, (with an annual frequency of approximately 60%), and followed by maritime-tropical and tropical-continental air masses. Under this radiative and synoptic context, the entire complex where climatic elements develop displays distinct features, specific for the analyzed area. Thus, the mean annual air temperature generally ranges between 10 and 12 ºC and mean annual amplitudes of this parameter reach C. The degree of continentalism specific for the plain areas of the southern Romania is underlined by the seasonal thermal variations. Thus, during summer, hot weather prevails favoured by clear and dry conditions, as a result of continentalisation of the air masses of tropical African origin or continental air masses from Eastern Europe. The thermal features are enhanced by lower amounts of precipitation and the presence of dry and hot wind, more frequent from the east, south east, specific for the plain areas situated in the south of the country. Winters are generally dominated by cold continental air advections coming from the east or north (Arctic) that cause extreme negative values determining air and soil temperature shrink, most often determined by the lack of a solid and stable snow layer (Dragotă and Grigorescu, 2010). Transitional seasons are characterised by warm and early springs (sometimes in February) and dry, warm autumns until mid-october. These general climate features are moderated by local conditions imposed by the compact vegetal formations (forests) and wetlands topoclimates. Mean monthly temperatures reveal the thermal contrasts between both extreme seasons and between the months of the analyzed years. The average air temperature in the extreme months (January and July) ranges between - 1 C - 2 C and 23 C - 24 C, respectively, and in the transitional seasons, between 11 C - 12 C both in April and in October (fig. 4) C I II III IV V VI VII VIII IX X XI XII -10 Mean temperature Mean maximum temperature Mean minimum temperature Figure 4. Mean monthly temperatures and average daily extremes registered at Giurgiu weather station ( ) 49

6 Non-periodic variations due to fluctuations in general atmospheric circulation highlight very cold (1942, 1947, 1963) or very warm (1936, 1948, 2000, 2007) years. The same thermal differences at all time scales occur at the local level between the elementary topoclimates of Comana Natural Park (forests, fields, valley corridors with terraces, wetlands etc.). In the distribution of thermal parameters the mean values of extremes temperatures are noteworthy, reaching maximum annual values of 17.4 C and minimum values of 6.3 C. The monthly average values in January vary between 1 C - 2 C and C and in July between 29 C -30 C and 15 C -16 C. Annual maximum temperatures exceeded 40 C in the air (43.5 C on 5.VII.2000), but also dropped below -24 ºC (-24.8 C on 26.I.1963) becoming even more reduced at ground level. In regard to the frost phenomenon, especially the annual interval without frost which has major implications for the development of vegetal phenophases, Comana Natural Park has as a main feature the multi-annual average of days per year where the minimum temperatures go beyond the 0 C threshold. Soil temperature, considered as the ratio between the absorption processes and the radiative reflection generating heat which converts the soil surface into the main source of heat for the troposphere, is also significant, thus having a strong impact on the vegetative cycle. The variation of soil temperature parameters in the studied area registers an annual average of nearly 13 C, with higher amplitudes in January of -1.9 ºC in the presence of predominantly negative temperatures and the persistence of snow layer when the baric field favours cold advection of air masses. The maximum annual average of 27.6 ºC is favoured by the highest values of solar radiation, dark soils formed under steppe and forest steppe conditions, the high degree of vegetal coverage, low altitude, etc. The extreme values reached maximum soil temperatures of 67.4 ºC ( ) and minimum soil temperatures of ºC ( ). Table 2. The mean monthly number of days with different characteristic temperatures for the cold semester of the year at Giurgiu weather station ( ) Months VIII IX X XI XII I II III IV V VI VII Winter days (T max. 0 0 C) Frosty days (T min. 0 0 C) Frosty nights (T min C) Source: National Meteorological Administration database The average date where the first frost at soil level occurs frames between 11 and 21 of October and the last frost - between 11 and 21 of April, resulting a mean annual period without ground-level frost of days. The high frequency of days with extreme temperatures highlights the temperate continental climate features with arid (excessive) climatic influences specific for southern Romanian Plain. The monthly values of these parameters register records which exceed the specific thermal thresholds with climatic significance for the temperate latitudes Comana Natural Park is framing into (tab. 2 and 3). 50

7 Table 3. The average monthly number of days with different characteristic temperatures for the warm semester of the year at Giurgiu weather station ( ) Months I II III IV V VI VII VIII IX X XI XII Summer days (T max C) Tropical days (T max C) Tropical nights (T min C) Source: National Meteorological Administration database On mean annual regime the characteristic temperatures fall within normal limits for the southern plain area, prevailing the winter days for the cold semester of the year and the summer days for the warm semester of the year - each covering one third of the year (fig. 5). frosty nights tropical nights winter days tropical days frosty days summer days no. days no. days Figure 5. The annual average of days with different characteristic temperatures during the cold and warm semester of the year, respectively at Giurgiu weather station ( ) The amount of vapours in the atmosphere, mainly depending on to the physical characteristics of air masses dynamics, temperature and the characteristics of the active surface (large water and vegetation-covered surfaces), increase the level of air humidity, while being permanent sources of evaporation and evapotranspiration. The air saturation with water vapours, namely the relative air humidity, displays in the Comana Natural Park mean annual values of over 75%, higher during winter, usually over 90% in December, and lower in April-May (71-77%) (tab. 4). Table 4. Annual mean relative air humidity registered at Giurgiu weather station ( ) I II III IV V VI VII VIII IX X XI XII Annual In the studied area, the average annual frequency of "dry days" (where air moisture falls below 30%, indicating a high degree of dryness) varies around 10 to 11 cases, most of them during the warm semester of the year. The number of "humid days, when the relative humidity is equal or higher than 80% at 1 PM displays a maximum frequency during the cold semester of the year of up to 19 cases and a minimum frequency in the warm semester of the year of about 2 cases (fig. 6). 51

8 Figure 6. Mean monthly and annual frequency of days with characteristic relative humidity (RH) 30% and 80% (recorded at 1 pm) at Giurgiu weather station ( ) The total amount of precipitation registered in the Comana Natural Park area ranges between 500 and 600 mm, registering substantial monthly, seasonal and semestrial differences showing the active influence of humid air masses from the west and south-west on the studyarea. Table 5. Mean monthly and annual precipitation amounts registered at Giurgiu weather station ( ) Monthly Annual I II III IV V VI VII VIII IX X XI XII The largest share of seasonal precipitation amounts is registered during summer, when the values can reach mm, June being the richest month and February and October the poorest (tab. 5 and fig. 7). Spring Summer 43% Autumn 57% Winter mm cold semester warm semester Figure 7. Mean seasonal amounts and the semestrial precipitation share registered at Giurgiu weather station ( ) The warn semester of the year registers about 55 65% of the annual average, totalizing over 300 mm, while in the cold semester the values rise up to mm. An important role in assessing excess precipitation fallen in short periods of time is the mean maximum quantities of precipitation fallen in 24 hours (between 40 and 50 mm), 48 and 72 hours (between 50 and 60 mm). These may affect the optimal development of the vegetative cycle and may influence the dissemination of invasive plant species in the Comana Natural Park. 52

9 The pluvial characteristic of the time span, as compared to the previous one (before 1961), shows annual fluctuations in precipitation amounts materialized as deficits (1961, 1983, 1986, 1990, 1993, 1994, 2000, 2007) and excess rainfall (1969, 1970, 1975, 1991, 1992, 1997, 2005). These situations display negative deviations from the secular media, due partly to the reduced amounts accumulated in the period June-December in southern and eastern Romania. Coupled with warmer periods, as compared to the annual average (the second half of winter and spring), this pluvial deficit triggers negative impacts on the growing season of humidity-loving species, including the invasive Amorpha fruticosa. Regarding the precipitation frequency (pp 01 mm) in various types, one might notice the prevalence of liquid precipitation over the solid, as well as the high frequency during the summer of consecutive days without precipitation (45-50 days). An extremely important process for carrying out the phenophases of the main invasive species in the Comana Natural Park, generally defined by the loss of soil moisture through the direct evaporation processes together with plant transpiration, is the Thornthwaite potential evapotranspiration. Mean annual values of potential evapotranspiration, strongly related to changes in air temperature exceed 700 mm, with a monthly maximum of 160 mm in July and a monthly minimum of about 35 mm in October. The correlation between rainfall and evapotranspiration highlights the Climatic Water Deficit, according to which, under poor precipitation amounts and strong evaporation, this aridity index frames the Comana Natural Park into an area with values ranging between mm, specific to a climate of transition between sub-humid and semi-arid (Sandu et al. 2010). The wind, a climatic phenomena acting as a vector for the spread of invasive plant species, contributes through its presence and dynamics to the mixing of air masses with different thermal and hydric properties. Furthermore, atmospheric calm can cause the stagnation of air masses of diverse duration. Depending on the speed and frequency, wind plays a major role in spreading plant reproductive material (seeds, spores etc.), contributing to the widening of areas with invasive species by means of anemochoria. In the Comana Natural Park, the dominant wind directions are north-east and east (with a higher frequency during the cold semester of the year), then southwest and west (in August and September). The average annual frequency of the atmospheric calm is estimated between 20 and 40 % of the year and the average speed no matter the direction ranges between 2 and 3 m/sec, being generally higher in winter when it can reach 3 m/sec, and lower in summer and early autumn, ranging between 2 and 3 m/sec (tab. 6). Table 6. Mean monthly and annual wind speed regardless of the direction registered at Giurgiu weather station ( ) Months Annual I II III IV V VI VII VIII IX X XI XII Source: National Meteorological Administration database Maximum speeds do not have special representation in the area of study, generally ranging between 20 and 30 m/sec, their directions belonging to the north-eastern and southwestern sectors. These are also the potential direction of expansion for the areas hosting invasive plant species due to the climatic wind factor. Dangerous climatic phenomena specific to both the warm and cold semesters of the year, contribute differently to providing favourable/unfavourable conditions for the development of phenonophases of invasive plant species. Among the most representative phenomena within Comana Natural Park are frost, heavy rainfall and strong winds, whose annual rate is of more than 11% days (tab. 7). 53

10 Table 7. Mean monthly and annual frequency of days with extreme climatic events registered at Giurgiu weather station ( ) Extreme climatic events I II III IV V VI VII VIII IX X XI XII Annual Hoarfrost Hail Heavy rainfall Strong winds Blizzard Source: National Meteorological Administration database The presence of hydrometeors in steady weather conditions contribute to an increase in soil and air humidity thus having a favourable effect, while climatic hazards in terms of high intensity and frequency or through the mechanical effects enacted on plans have a negative contribution to the development of invasive plants species (Dragotă and Grigorescu, 2010). Thus early or late frosts and hoarfrosts, aridity and drought, heavy rainfalls, hail storms, strong winds, blizzards, etc. through their physiological and mechanical effects distort, break or cause temporary imbalances in the natural evolution of vegetation. Conclusions The climatic parameters of meteorological elements, overlapping local environmental features (slope, soil, water etc.), as defining factors in the diagnosis and prognosis of the current situation and future development and expansion of invasive plant species, indicate the achievement of optimum thermal, hydric and aeolian conditions for their development in Comana Natural Park (in terms of specific bioclimatic requirements) (Dragotă et al., 2011). Climatic stress elements correlated with the plants requirements during the growing season sum up to: - recording maximum air temperatures ( 35 ºC) between May and August with high intensities and throughout more consecutive days, but also of minimum temperatures ( 10 C and 15 C) in the same period, underlining critical situations during extremely hot years; - the high frequency of consecutive days with RH 30% especially in the afternoon hours, between April and October and especially during summer, indicating a high degree of vulnerability to the hygric stress; - the total and effective monthly precipitation amounts exceeding/not reaching the optimal thresholds for physiological development, describing the frequency and intensity of rainfall anomalies, or the succession of rainy/dry days, months and years; - the frequency and intensity of drought phenomena (extreme, strong and moderate) overlapping optimal periods of plants physiological development, marked by high values of evapotranspiration and hence by the values of the monthly and annual water deficit; - the monthly and annual variation in the number of days with strong wind, blizzard, late autumn and early spring hoarfrost and frost, heavy rains, hail and other dangerous meteorological phenomena that mark individual or combined mechanical, thermal and hydric stress elements. All these general and local climatic features provide the favourable framework for the optimal development of invasive plant species growing in the Comana Natural Park, concurrently indicating the expansion/reduction probability of areas occupied by Amorpha fruticosa and Crataegus monogyna, thus defining the climatic stress elements specific for the area under analysis. 54

11 Acknowledgements The current study was conducted in the framework of the FP7 Project Building Capacity for Black Sea Catchment Observation and Assessment System supporting Sustainable Development (EnviroGRIDS); Refernces Arim M., Abades S. R., Neill P. E., Lima M., Marquet P.A., (2006), Spread dynamics of invasive species, PNAS, vol. 103, no. 2, , doi_ _pnas Bradley B.A., Wilcove D.S., Oppenheimer M., (2010), Climate change increases risk of plant invasion in the Eastern United States, Biol Invasions, 12: , DOI /s y. Burgiel, S.W. and A.A. Muir, (2010) Invasive Species, Climate Change and Ecosystem- Based Adaptation: Addressing Multiple Drivers of Global Change, Global Invasive Species Programme (GISP), Washington, DC, US, and Nairobi, Kenya. Călinescu, R. Antonescu C., Bănărescu P., (1969), Biogeografia României, Edit. Ştiinţifică, Bucureşti. Dragotă Carmen-Sofia and Grigorescu Ines (2010), Climatic hazards in the Bucharest Metropolitan Area. The assessment of the main extreme climatic phenomena in the Bucharest municipality and its surroundings, LAP Lambert Academic Publishing, ISBN , paperback, 108. Dragotă, Carmen-Sofia, Grigorescu, Ines, Dumitraşcu, Monica, Doroftei, M., Mierlă, M., Năstase, Mihaela (2011), Climatic potential and key meteorological drivers for the dynamics of invasive terrestrial plant species in Romanian protected areas, 3 rd Proceedings of the International Symposium on Weeds and Invasive Plants, October 2-7, 2011, Ascona, Switzerland. Dumitraşcu, Monica, Grigorescu, Ines, Kucsicsa, Ghe., Dragotă, Carmen-Sofia, Năstase, Mihaela (2011a), Assessing the potential distribution of the invasive plant species related to the key environmental driving forces in Comana Natural Park, Proceedings of the 12th International Conference on Environmental Science and Technology (CEST 2011), Rhodes, Greece. Dumitraşcu Monica, Grigorescu Ines, Kucsicsa Ghe., Dragotă Carmen-Sofia, Năstase Mihaela, (2011b), Non-native and native invasive terrestrial plant species in Comana Natural Park. Case-studies: Amorpha fruticosa and Crategus monogyna, Romanian Journal of Geography, vol. 55 (2), p , Editura Academiei Române, Bucureşti. Grigorescu Ines (2010a), Modificările mediului în Aria Metropolitană a Municipiului Bucureşti, Editura Academiei Române, Bucureşti, 228 pg, ISBN Grigorescu Ines (2010b), Parcul Natural Comana, Terra, anul XL-XLI (LX-LXI), Editura CD Press, Bucureşti, Sandu I., Pescaru V., Poiană I., Geicu A. Cândea I. and Ţâştea D. (eds.) (2008), Clima României, Editura Academiei Române, Bucureşti, 365. Shea K, Chesson P (2002), Community ecology theory as a framework for biological invasion. Trends in Ecology and Evolution, 17, no.4, Shi J., Luo Y-Q, Zhou F., He P. (2010), The relationship between invasive alien species and main climatic zones, Biodiversity Conservation,19: , DOI /s Taush R.J. (2008), Invasive Plants and Climate Change, U.S. Department of Agriculture, Forest Service, Climate Change Resource Center. 55