Legacies of past land use challenge grassland recovery - Our new paper in Nature Conservation

Our new paper, with the shared first authorship of Balázs Deák and Orsolya Valkó has been recently published in Nature Conservation.

The paper is freely available on the Journal's homepage (please click here to download).

The citation of the paper is:

Deák, B. & Valkó, O., Tóth, C.A., Botos, Á., Novák, T. (2020): Legacies of past land use challenge grassland recovery – An example from dry grasslands on ancient burial mounds. Nature Conservation 39: 113-132. doi: 10.3897/natureconservation.39.52798 [IF2018: 1.220]

In cooperation with Csaba Tóth (University of Debrecen, Department of Physical Geography and Geoinformatics), Tibor Novák and Ágnes Botos (University of Debrecen, Department of Landscape Protection and Environmental Geography) we studied the changes in the soil parameters and vegetation during the spontaneous recovery of severely degraded habitats.

We studied kurgans - ancient burial mounds built by nomadic steppic tribes - as widespread small natural features and iconic landscape elements of the Eurasian steppes which often hold the last remnants of grassland habitats in the otherwise intensively used agricultural landscapes (please see our former post for further details about kurgans). There are approximately half million mounds in Eurasia, but unfortunately many of them have been partly or completely destroyed by human activities. In our Eurasian-scale review paper (Deák et al. 2016 Biodiversity and Conservation) we emphasised that plouging and the encroachment of woody species represent the two major threats for the mounds and the grassland habitats on them. The objective of our current study was to evaluate the effects of land use change (cessation of crop production or clear-cut) on the soil parameters and vegetation composition of formerly ploughed or afforested mounds.

The figure below shows the soil and vegetation changes typical on ancient burial mounds in the past 6000 years. In the last 250 years the human-induced degradation by ploughing and establishment of plantations became typical. The last panel shows the potential successional pathways after clear-cut or the cessation of crop production.

We found that four years after the land use change (i.e. clear-cut or cessation of arable farming), the vegetation is still dominated by weeds. Segetal weeds and high level of soil phosphorous content was typical on former croplands, while ruderal weeds and high level of soil nitrogen was typical in the former black locust plantations. Our results suggest that the legacy of a former intensive land use (i.e. cropland and plantation) is more complex than the effect of excess soil nutrients. The long-lasting various disturbance regimes (fertilization, herbicide application, tillage) typical for croplands, shading and altered microclimate typical for plantations and the deep cultivation typical for both, are the most likely legacies that hamper or slow down the grassland recovery in the studied habitats.

We found that, without proper management measures, recovery of grassland vegetation is slow on mounds formerly used as cropland or black locust plantation. Our results suggest that arable use transformed the habitat conditions in a more moderate way than the establishment of plantations. Thus, restoration efforts, focused on the restoration of mounds formerly covered by arable lands, can be more effective compared to the restoration of mounds formerly covered by forest plantations. In isolated and severely degraded habitats, the introduction of target grassland species would be inevitable for speeding up the recovery of grassland habitats.

Ploughing is a major threat factor for the structure and the wildlife of the mounds. On the picture, the ploughed Black-mound (Fekete-halom) can be seen.

Black locust (Robinia pseudoacacia) is the most problematic woody species on Hungarian kurgans. Due to its shading and its effect on soil nutrient content and water table, it leads to the severe degradation of the grassland vegetation. The mound on the picture is called Murderer mound (Gyilkos-halom).

The original vegetation of the mounds is usually dry grassland. On this picture, the so-called Big Grassy mound (Nagy Füves-halom) can be seen, which is an iconic landmark in the landscape.

Abstract

Due to large-scale agricultural intensification, grasslands are often restricted to habitat islands in human-transformed landscapes. There are approximately half a million ancient burial mounds built by nomadic steppic tribes in the Eurasian steppe and forest steppe zones, which act as habitat islands for dry grassland vegetation. Land use intensification, such as arable farming and afforestation by non-native woody species are amongst the major threats for Eurasian dry grasslands, including grasslands on mounds. After the launch of the Good Agricultural and Environmental Condition framework of the European Union, in Hungary there is a tendency for ceasing crop production and cutting non-native woody plantations, in order to conserve these unique landmarks and restore the historical grassland vegetation on the mounds. In this study, restoration prospects of dry grassland habitats were studied on kurgans formerly covered by croplands and Robinia pseudoacacia plantations. Soil and vegetation characteristics were studied in the spontaneously recovering grasslands. The following questions were addressed: 1) How does site history affect the spontaneous grassland recovery? 2) Do residual soil nutrients play a role in grassland recovery? In former croplands, excess phosphorus, while in former Robinia plantations, excess nitrogen was present in the soil even four years after the land use change and grassland vegetation was in an early or mid-successional stage both on the mounds. The results showed that, without proper management measures, recovery of grassland vegetation is slow on mounds formerly used as cropland or black locust plantation. However, restoration efforts, focused on the restoration of mounds formerly covered by croplands, can be more effective compared to the restoration of mounds formerly covered by forest plantations.