The future of interurban forest structures ?!

Abstract

This graduation project proposes a new critical approach towards the design of drought adaptive interurban forest structures. The increasing drought during the summer is currently neglected in the design (and management) of green structures in the Netherlands. Several studies underpin the importance of taking drought stress in consideration for the future well-being of trees and forests. Gerrits (2010) provides insight into the cause of drought stress following the hydrological cycle of trees. De Vries et al. (2000) gives an overview of the indirect factors that can contribute to the level of drought stress that trees perceive. The research of Brunner (2010) reveals the response mechanism of trees. Zadworny et al. (2014) and Pretzsch et al. (2012) showed that changing the current forestry practice can result in more drought adaptive forest. However, these studies do not look into the spatial implications of the drought-stress. Since, they do not consider forests as part of a spatial structure which is embedded in a landscape that is defined by its palimpsest, scale-continuum. The Utrechtse Heuvelrug serves as a case to map the spatial implications of transforming the current forest structure into an expanding drought adaptive interurban forest structure. The desk analysis of the Utrechtse Heuvelrug provided more insights in about everyday functioning of indirect factors. The soil conditions, water cycle appears, and human interference seems to make existing vegetation less capable of dealing with increasing extreme climate conditions. Furthermore analyses the forest structure shows that it contains four tree constellations: lanes, estates, forest plantations and nature reserves. A new framework is proposed that include these neglected spatial aspects. The framework combines the drought stress cycle with scales of urban forestry. The framework is applied to develop a vision Utrechtse Heuvelrug which is elaborated in regional design for the area between Austerlitz and Woudenberg. The vision proposed a new forest structure which will be realized in two stages. The first stage is the transformation of the structure, which consists of the addition of seasonal buffers in between the forestry, agricultural and urban cores. The second stage consists of the expansion of the forest in patches between the forestry, agricultural and urban cores. The regional design proposes a new green and blue system that adapts the current grid to make it drought adaptive. Moreover, the adapted grid will facilitate further expansion of the forest. The central element is regional water bodies. They buffer excesses of rainwater and diminish the amount of water that drained into the river Eem and river Rhine through the local canal ‘Valleikanaal’. Two different subsystems are connected to these regional water bodies. The purpose is to retain water and distribute it later. Lastly, the different corresponding constellations which are needed to transform and expand the current grid are described. This includes seven different constellations. Changing a new forest structure consists of four types of tree constellation. The catchment valleys and network of ditches are two primary constellations that will be constructed to prevent exciting forest of further deteriorating from drought stress. The sprengbeek and the zigzag are constellations mainly let circulates the retained water. The sprengbeek is responsible for disposal whereas the zigzag take care of the (emergency) supply of water. The constellation of expansion contains four types of tree constellation. These tree-constellations are the backbone of both developing agriculture and urban patches. The food clearing consists of wooded banks and swamp forests. The living clearings is the last constellation which is part of dense forest patchwork which will develop in between food clearings. This graduation project resulted in the design of seven tree-constellations. They illustrate spatial implications which are necessary to designing drought adaptive interurban forest structure in the Utrechtse Heuvelrug.