Students Avans university examine oak tree health in Loonse en Drunense Dunes

The Loonse and Drunense Dunes is a national park, famous as an inland dunes system in the province of North Brabant (The Netherlands). It originated when sand from the North Sea was transported by the wind after the last ice age. Daily dynamics of the dunes have been changed by an increased rate in vegetation succession, caused by nitrogen deposition. Pollutants like fertilizers full of nutrients, cause alternations of its fauna and flora, making it less diverse. The inland dunes environment hosts a very unique ecosystem which is in need of protection. 

Students Avans in Loonse and Drunense Dunes

For several years in a row, fourth-year Environmental Sciences students from Avans have monitored the effect of sheep grazing and topsoil removal on vegetation in an area of the Loonse and Drunense Dunes. The students conduct this research as part of the minor Environmental Geography. Each year this research has resulted in an updated map for the Atlas Natural Capital showing the areas of different habitats (see: Dutch dying desert at Atlas Natural Capital, and the latest map below). This year also the oak trees in the area were monitored. In a collaboration of four parties, the province of North Brabant, Natuurmonumenten, Holag and Atlas Natural Capital, three student teams from Avans university, were asked to investigate and monitor the Loonse and Drunense Dunes. One team was asked to determine the effectiveness of the restoration measures taken to improve nature quality in the area. This is done by soil and water analysis, as well as using drone images to classify vegetation types in the area. In a next article we will focus on their project. In this article we focus on the other two teams, who were asked to examine the health of oak trees in the Loonse and Drunense Dunes in more detail. 

Declining oak tree health

Oak trees on sandy soils throughout Europe have high mortality rates. Tree health seems to have declined especially fast in The Netherlands over the last few years. Several factors may play a role in this observed detoriation of oak tree health. Firstly, recent dry conditions and increased herbivory from caterpillars impose pressure on tree growth. Moreover, acidification of the soil due to nitrogen deposition, may deprive trees from essential micronutrients (such as potassium and calcium), as they are washed away in soils with a decreased pH. Lastly, mycorrhizal (fungal) communities may change due to lower soil pH, decreasing the ability of the root system to effectively take up nutrients even more. The exact reason for declining oak tree health however, is still unknown. Therefore there is a high need to assess tree health in an effective way.

Oak tree forest in the Loonse and Drunense Dunes

The Loonse and Drunense Dunes are located in the Dutch province North Brabant. They have been designated as a national park since the year 2002. The dunes cover an area of 3,500 hectares, mainly consisting of sandy dunes, heather- and coniferous forests. This area contains oak trees that are also deteriorating in health. Oak tree forests in the Loonse en Drunense Dunes are classified as a rare habitat as part of the Natura 2000 network. This classification means that measures should be taken to preserve oak forests in the dunes area. Nature managers need to know what the current oak health status is, and how they can monitor the area to assess the effect of the protection measures they take on the oaks.

Two projects, one goal

The general goal of the project of the Avans students is to get an insight in the oak’s health in the Dunes and to get to know how well remote sensing methods can measure this. To achieve this goal, the two teams have a different focus, but both groups are analyzing samples from the same trees.

Analyzing leaves

The first team, the so-called OaKKe-team, will focus on researching the health of oak trees by analyzing the leaves. The team consists of three fourth-year Environmental Science students (Riin Ōispuu, Gwen Harmelink and Niek Esselink) under supervision of Mart Verwijmeren, lecturer Environmental Science at Avans. They want to determine if remote sensing with an NDVI (Normalized Difference Vegetation Index)-sensor is an effective additional method to monitor the oak tree health during the project period of 13 weeks. To do so, the students will do fieldwork to perform aerial photography of the project area by using a drone. Furthermore, they collect leaf samples of ten oak trees and estimate the tree health based on visual observations such as leaf fall and the crown health. The team will also perform laboratory experiments to analyse the leaf samples and measure the main micronutrient present in the leaves. Last but not least, they will calculate an index for photosynthetic activity by using the NDVI remote sensing images. 

Analyzing soil consitions

The second team analyses the soil conditions like fungi. The team consists of three fourth-year Environmental Science students (Max Post, Léopoldine Tairou and Jiri Rous) under supervision of Ilse Rovers, lecturer Environmental Science at Avans. Their approach is to compare the soil surrounding healthy and unhealthy oak trees. Combining their results with the group studying the leaves, leads to an overview of a large range of characteristics of healthy and unhealthy trees. The team compares soil PH, the amount of selection of nutrients in the soil and trees’ mycorrhizal community. To do so, they will go to the field to take samples and aerial photographs. Next they will study the samples in the lab and do GIS work with the aerial photos. The research question that will be answered is: “How is the quantity and type of fungi related to oak health?” The hypothesis is that the more fungi are present, the healthier the oaks will be (assuming more beneficial than for pathogenic fungi).

Results

Curious about the outcome of the research? Follow the storymap Monitoring OAK tree health in the Loonse and Drunense Dunes, follow Oakke on Twitter, or take a look at the storymap Oaks health in the Loonse and Drunense Dunes of the second team. The final results will be presented on a poster to the clients at Avans in Breda. Also, the research will eventually lead to a final advise report, based on lab works results, field work results, GIS-work and a map in the Atlas Natural Capital.

Text: Students Avans university and Jeannine Brand, Atlas Natural Capital
Pictures: Students Avans university 
Map: Atlas Natural Capital