Ecological impact of fire place use in urban forests and consequences for visitor management

Urban forests are popular recreation areas in Europe. At the same time, these
forests are important habitats for plants and animals and often harbour a high
biodiversity. Recreational activities, for example picnicking and grilling and in
particular the creation and usage of fire rings outside official picnic sites ("wild" fire
rings), can cause extensive damage to soil and vegetation. Firewood collection
depletes woody debris, leading to a loss of habitat for specialized organisms.
Economical consequences of forest recreation include maintenance costs of
recreational infrastructure and diminishing revenues due to visitor-related damage
to trees and subsequent reduction in timber quality.
In the present thesis I examined the effects of fire place use on the forest
soil, including soil microbial biomass and enzyme activity, ground vegetation,
shrubs, trees and amount of woody debris. In addition, the reduction in timber
value resulting from recreational damage to trees was estimated. In order to
develop and implement measures, it is important to find out why forest visitors
create and use "wild" fire rings instead of official picnic sites. Therefore, I
conducted a forest visitor survey focusing on visitor preferences concerning fire
places. An experiment was conducted with four new fire places designed to fulfil
forest visitors' requirements, and a follow-up survey documented visitors'
reactions. A survey aimed at forestry experts in the whole of Switzerland provided
valuable information on foresters' perceptions concerning the consequences of
picnicking and grilling and forest recreation in general.
At frequently used fire places we found reduced plant species densities in
the ground vegetation and shrub layer and changes in plant species composition.
Picnicking and grilling also reduced the height and changed the age structure of
shrubs and young trees. The amount of woody debris was lower in disturbed plots
than in control plots.
Soil microbial biomass (Cmic and Nmic) and dehydrogenase activity were
differently affected by short- and long-term trampling. In a short-term experiment,
these soil characteristics decreased at low and medium, but not at high trampling
frequencies. In contrast, the same soil characteristics decreased with increasing
trampling intensity in a long-term field survey at fire places that had been in use for
more than a decade. The activity of β-glucosidase was only affected by short-term
trampling. Phosphomonoesterase activity was most severely affected by long-term
trampling, most probably as a result of the loss of plants.
The reduction in timber value due to visitor-related damage to trees ranged
from 19 to 53 € per hectare and year in two suburban forests. Total recreationinduced
costs, i.e. additional expenses and reductions in timber value exceeded
10% of the total annual expenditures of the two forest enterprises examined.
The forest visitor survey revealed a preference for fire places near streams,
away from forest roads and close to open spaces. While some visitors highly
appreciated the well-equipped official sites, others preferred more natural
infrastructure with pieces of stones forming a fire ring rather than concrete rims,
and logs to sit on instead of benches. Experimental fire places consisting of a ring
of stones and logs fulfilled the needs concerning infrastructure of visitors who
normally use "wild" sites. However, the location of fire places was termed more
important than their infrastructure. Forestry experts' perceptions regarding reasons
for "wild" site creation differed largely from the results of the forest visitor survey.
According to experts, an insufficient number of barbecue pits, available firewood
and forest visitors seeking adventure and romanticism repeatedly lead to the
creation of "wild" fire rings.