In the 1960s, Soviet planners covered the hills around Tbilisi with vast monocultures of Pinus nigra, the Black Pine, to provide tree cover and forest products for a rapidly growing city. Now, in 2021, large portions of that legacy forest are dead or dying due to the ongoing effects of Dioryctria zimmermani, the Zimmerman Pine Moth.

Ruderal was approached last December to develop a framework for replacing part of this forest on Mtatsminda, the mountain overlooking central Tbilisi. Supplied with GIS analyses of soil conditions and a list of recommended species from the Georgian Institute of Botany, we designed a palette of seven different ‘forest patches’ to replace the dying Pinus nigra canopy.

Senescent pines, flowering steppe, and the many thousands of holes prepared for planting this autumn. Photo courtesy of Christian Moore.

Utilizing the landscape ecology principles of patch, edge, and forest mosaic as well as visual references from the Swedish University of Agricultural Sciences’ ‘Landscape Lab’ at Alnarp, we developed each forest patch to fill a unique ecological niche and provide visual and spatial variety across the territory.

Designed forest patch from SLU Alnarp’s Landscape Lab: note the rich textural variety and multiple vegetation strata. Photo courtesy of Sarah Cowles.

Some patches such as the ‘Fruit Grove’ and ‘Almond Grove’ will produce bright displays of flowers in the spring followed by an abundance of fruit for foraging animals (and people!) to taste in the summer and fall. Others, like the ‘Ravine Forest’ and ‘Acer Scrub’ will exploit specific moisture gradients and create important ecotones—ecological transition zones—between the different forest patches and areas of open steppe. Each patch is richly layered with different forest strata and varying species to provide four seasons of visual interest.

Autumn rendering of the ‘Acer Scrub’ patch. This patch balances species diversity with visual coherence and forest legibility.

The patches are designed with two overlapping frames: a 3m x 3m grid for canopy trees and a 2m x 2m grid for understory trees and shrubs. For the pilot site on the south slope of Mtatsminda, we anticipate a sapling survival rate of 60 - 70%, hence the density of the planting. As the patches mature, they should meld together, filling in vacancies left by the pines and creating a much more biodiverse and resilient urban forest.

Planting diagram of the ‘Savanna Edge’ patch. We used a Grasshopper script to iterate species composition and growth over time.

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