Drivers of species richness and community integrity of small forest patches in an agricultural landscape

Krista Takkis, Tiiu Kull, Tiit Hallikma, Piia Jaksi, Karin Kaljund, Karin Kauer, Thea Kull, Olavi Kurina, Mart Külvik, Kaire Lanno, Malle Leht, Jaan Liira, Indrek Melts, Hannes Pehlak, Janar Raet, Kaarel Sammet, Kalev Sepp, Ülo Väli & Lauri Laanisto

Studied forest patches within the agricultural landscape in northeast Estonia. Most of the uncultivated areas in the region are affected by karst formations. Figure from the original paper.

Small forest patches (up to a few hectares in size) are a common feature in European agricultural landscapes. These patches can be valuable harbours for biodiversity within the generally species-poor agricultural systems with strong human impact. Different natural species and communities can find refuge in these forest patches. Therefore, it is important to understand what determines species richness and composition of small forest patches in agricultural systems. Equally important is to identify what influences forest community integrity in these patches – the general condition and capability of a community to support its normal composition and functioning.

We studied these two questions based on 27 small forest patches in an agricultural system in Estonia in North-East Europe. The patches were dispersed in an old-established agricultural landscape, which had contained mainly karst-related uncultivated formations since early modern agricultural history. We identified the vascular plants growing in each patch and divided the species into four habitat preference groups – forest specialists, forest generalists, grassland specialists and synanthropic species (those mainly found in anthropogenic habitats). We also calculated three indices to study community integrity – the index of Favourable Conservation Status (FSCi; Helm et al. 2015) and two related indices. These indices characterize community condition and the impact of external influences and non-characteristic species on forest communities and enable studying factors that influence community integrity. In our modelling approach, we combined the island biogeographic theory (patch area and isolation effect) with the properties of the surrounding landscape and local environmental conditions within a patch to study comprehensively the different drivers affecting species richness and community integrity.

Our analyses confirmed the necessity of studying separately species with different habitat preferences, and of incorporating various landscape and environmental factors in a study. Total plant species richness was determined only by patch area, whereas individual habitat preference groups were influenced by different factors, including patch area, landscape composition and environmental factors. Most important factors for different species groups, as well as for forest community integrity, were patch area, the amount of light above the forest understory and soil reaction. Higher-integrity forest patches were identified by larger patch area, lower light conditions and slightly more acidic soils.

Effects of patch size, landscape composition and local environment on species richness and community integrity indices. Numbers on the arrows and arrow thickness indicate the importance of predictors (averaged Akaike weights). Figure from the original paper.

Our study highlights the role of small forest patches as refugia for different species and valuable communities, as well as providers of ecosystem services in the generally impoverished agricultural landscapes. Additionally, it illustrates the necessity to use comprehensive models and take into account patch configuration, surrounding landscape composition and local environmental conditions within a patch to fully understand the drivers behind observed patterns. Better understanding of processes and drivers of species richness and community integrity can help us to protect and promote the favourable conditions in small forest patches and thereby improve the conditions for numerous species and the provision of ecosystem services in agricultural systems.

Reference:

  • Helm, A., Zobel, M., Moles, A. T., Szava-Kovats, R., & Pärtel, M. (2015). Characteristic and derived diversity: implementing the species pool concept to quantify conservation condition of habitats. Diversity and Distributions, 21, 711–721. https://doi.org/10.1111/ddi.12285

This is a plain language summary for the paper of Krista Takkis et al. published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.12689)