МОНИТОРИНГ СХЕМЫ мелкомасштабных АЛЬФА И БЕТА разнообразия в открытой песчаной степи Венгрии в период 1996-2011 гг.

Monitoring patterns of fine-scale alpha and beta diversity in open sand steppe in Hungary between 1996 and 2011

 

Сандор Барта1, Андраш Хорват1, Сандор Чете2, Зита Зиммерман3, Жилард Жентес3, Джудит Хази3, Зольт Мольнар1

S?ndor Bartha1, Andr?s Horv?th1, S?ndor Csete2, Zita Zimmermann3, Szil?rd Szentes3, Judit H?zi3, Zsolt Moln?r1

1Институт экологии и ботаники ВАН, Центр экологических исследований,
(Алкотмани 2-4, H-2163, г.Вакратот, Венгрия)
1Institute of Ecology and Botany, Centre for Ecological Research,
Hungarian Academy of Sciences
(MTA OK OBI, Alkotmany ut 2-4. Vacratot, Hungary, H-2163)
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2Печский университет, научный факультет Института биологии, г.Печ, Венгрия
2University of Pecs, Faculty of Science, Institute of Biology
(Ifjusag u. 6, Pecs, Hungary, H-7624)
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3Отдел охраны природы и ландшафтной экологии Университета Святого Иштвана, г.Геделле, Венгрия
3Department of Nature Conservation and Landscape Ecology, Szent Istvan University
(Pater Karoly u. 1., Godollo, Hungary, H-2100)
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На протяжении 16 лет методом трансект проводился мониторинг за травянистыми псаммофитными сообществами лесостепных и степных ландшафтов Венгрии. Метод секущихся трансект – основной точный и объективный метод долгосрочного мониторинга растительности. Был использован подход, при котором регистрировались виды растений на протяжении 52 м ленточной трансекты из 1040 прилегающих друг к другу площадок 5х5 см. Мониторинговые исследования позволили выявить смену доминирующих видов трав в каждой точке на протяжении 16 лет. Однако в целом альфа и бета разнообразие остались неизменными. Влияние отсутствия выпаса (сопровождающееся накоплением подстилки) уравновешивалось воздействием засушливых периодов. Следов деградации на исследованных охраняемых участках обнаружено не было, поэтому специальных мероприятий по локальному управлению или восстановлению, направленных на сохранение этих травянистых сообществ не требуется. Тем не менее, такие факторы как распространение инвазивных видов, разрушение местообитаний и снижение уровня грунтовых вод представляют собой потенциальную угрозу на уровне ландшафта.

Sand grassland communities were monitored by transect method over 16 years in contrasting forest steppe and steppe landscapes in Hungary. Line-intercept sampling is a standard, precise and objective method for long-term vegetation monitoring. We used a modified design where presence of plant species are recorded along 52 m long circular belt transects of 1040 units of 5 cm x 5 cm contiguous microquadrats. Monitoring revealed an exchange of dominant grasses in each stands over 16 years. However, overall alpha and beta diversity remained unchanging. The effects of grazing abandonment (e.g. litter accumulation) were counterbalanced by the effects of recurrent droughts. We found no signs for degradation in the studied protected areas. Therefore no specific local management or restoration efforts are required to maintain these grasslands. However, at landscape scale, the spread of invasive species, habitat destruction and the drop of groundwater table appear as potential threatening factors.


Introduction. The open sand steppe, an endemic community is component of the remnant natural forest-steppe vegetation of the Hungarian Plain [6]. Dominant species are drought-tolerant tussock grasses (Festuca vaginata, Stipa borysthenica). Other characteristic and constant species are: Koeleria glauca, Bothriochloa ischaemum, Bromus tectorum, B. squarrosus, Carex liparicarpos, Festuca wagneri, Poa bulbosa, Secale sylvestre, Stipa capillata, Achillea ochroleuca, Alkanna tinctoria, Alyssum tortuosum, A. montanum subsp. gmelini, Arenaria serpyllifolia, Artemisia campestris, Centaurea arenaria, Colchicum arenarium, Corispermum nitidum, C. canescens, Dianthus serotinus, D. diutinus, Ephedra distachya, Euphorbia seguierana, Fumana procumbens, Gypsophila fastigiata subsp. arenaria, Iris humilis, Kochia laniflora, Linum hirsutum subsp. glabrescens, Medicago minima, Onosma arenaria, Polygonum arenarium, Potentilla arenaria, Salsola kali, Silene borysthenica, S. conica, Syrenia cana(Erysimum canum), Teucrium chamaedrys [10, 12]. Contrary to their specific and rather uniform species pool, the local stands of these communities vary greatly in composition, relative abundances and diversity [3, 6]. Coarse-scale spatiotemporal differentiation in open sand steppe is well documented [4, 5, 12], however, little is know about the fine-scale coexistence relations and dynamics.

At stand scale, sand steppe communities often appear as a dynamic mosaic of patches formed by different combinations of tussock grasses and patches of annuals, mosses, and lickens. As patches have various sizes, shapes and transitions, quantifying vegetation states and transformations in this dynamic landscape is a major methodological. According to our experiences, detecting presence of species in small contagious quadrates (a version of line-intercept sampling) used in this study provides a relatively simple and effective method for monitoring various aspects of vegetation patterns at multiple scales [9, 15].

Previous studies [10, 11] found significant differences in alpha diversity, species composition and plant cover between open sand steppe stands from different localities of the Hungarian Plain. Here, we explore the temporal dimension of diversity and extend the study from alpha to beta diversity. Our main question is weather fine-scale within-stand coexistence relations of species are changing due to recent landscape and climate changes.

Material and Methods. Representative stands from protected areas were selected for monitoring in 1995. They were sampled 4 times between 1996 and 2004, and yearly since 2004. Results from two stands will be reported here: one stand at Csevharaszt (47?17’N, 19?24’E) within a forest steppe landscape and the other at Fulophaza (46?53’N, 19?23’E) within a steppe landscape (where woody components were removed in the past). The climate is temperate. Annual precipitation ranges between 450 mm and 600 mm and the mean annual temperature varies between 10-11 ?C [7]. There are strong seasonal and daily fluctuations in temperature and air humidity and uneven temporal distribution in precipitation. The vegetation appears on loose, humus-poor sand and it can be considered as edaphic semi desert [10, 11].

Presences of plant species were recorded along 52 m long circular belt transect of 1040 units of 5 cm x 5 cm contiguous microquadrats. The sampling was performed in late spring, during the phenological optimum of the vegetation. Alpha and beta diversity measures were estimated across a range of scales from 5 cm x 5 cm to 5 cm x 25 m by subsequent computerised samplings from the baseline transect data sets [3, 14, 15]. Alpha diversity was calculated as the average number of species in sampling units. Beta diversity was represented by Compositional diversity (diversity of species combinations) detected as a function of increasing sampling unit sizes [9]. Diversity indices were calculated by the PRIMPRO [2] and the INFOTHEM [8] softwares.

Results and Discussion.

Population level patterns.

There were considerable changes in the abundance of dominant grasses in the monitored 16-year-period. The transect sampled in the forest-steppe landscape showed a switch from Stipa dominated stand to Festuca dominated stand, while an opposite change was detected in the steppe landscape (Fig. 1.A-B.). These results are consistent with the coarse-scale patch dynamics detected by repeated vegetation mapping [11].

The two sites experienced similar weather pattern with a relatively dry period between 1999 and 2002, an extreme drought in 2003, and normal and relatively wet years since 2004 [13]. While the direction of transformations between patches varied, the time of the switch of dominants was synchronous, and appeared in the year of the major drought in 2003.

Community level patterns.

Fine-scale alpha diversity (the average number of species detected in 5 cm x 100 cm sampling units) showed no trend, and varied slightly over the study period. Alpha diversity was consistently lower in the steppe landscape (Fig. 2). Patch-scale alpha diversity was also lower in the steppe landscape between 1996 and 2002. However, later on (from 2002) this measure became similar at the two sites (Fig. 2).

The higher fine-scale alpha diversity in the forest steppe landscape suggests the existence of some facilitative effects of trees and shrubs on the species density of grassland patches. Trees might moderate micro-climate and tree litter provides extra nutrients to grassland patches.

Beta diversity was also higher in the forest-steppe landscape, i.e. in the grassland patch surrounded by trees and shrubs (Fig. 3.B.). When estimated in a particular year of monitoring, beta diversity reflects the actual within-stand spatial heterogeneity of species combinations [3], i.e. it describes the spatial variability of local assembly of species. Diversity of species combinations usually follows a unimodal curve (Fig. 3.A) as a function of sampling resolution (increasing plot sizes) and its maximum is considered as an important coenostate variable (a variable describing the state of the plant community) [2]. The maximum of this function was projected over time together with the spatial scale where the maximum beta diversity appeared (called characteristic maximum scale [9] (Fig. 3.B.). Maximum beta diversity was found at fine-scales between 5 cm and 80 cm. This characteristic spatial scale was close to the size of the tussocks of dominant grass individuals (ca. 10-20 cm), and varied little in the stand recorded in the forest-steppe landscape. Although the relative abundance of grasses changed considerable, the overall spatial pattern of dominant grass matrix was stationary, providing predictable microhabitats for subordinate species, and consequently it stabilized the fine-scale dynamics in this community. The other site in the steppe landscape showed larger fluctuations of beta diversity reflecting less predictable microhabitats, and larger variability of local coexistence relations.

Conclusions. Monitoring revealed fluctuating pattern of alpha and beta diversity without trends of degradation over the 16 years studied. The effects of land use change (grazing abandonment and litter accumulation) was compensated by the mass dieback and decay of dominant grasses due to weather fluctuation (recurrent serious droughts).


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The study was supported by the Hungarian National Science Foundation (OTKA K 72561).


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