Effects of Recreational Activities on the Soil and Water Components Ofa Deciduous Forest Ecosystem in Turkey

International Journal ofEnvironmental Studies, Yol. 63, No. 3, June 2006, 273-282

; • l ," ! • ~. < t

j' Effects of recreational activities on the soil and water components ofa deciduous forest ecosystem in Turkey

YUSUF SERENGIL * AND SÜLEYMAN ÖZHAN

Department ofWatershed Faculty ofForestry, Istanbul University, I.U. Orman Fak:ultesi, Havza Anabilim Dali34450 Bahcekoy, Istanbul, Turkey

(Received 5 April 2006)

Impacts of recreational activities on some hydrological properties ofa deciduous forest ecosystem related to water production have been evaluated with an soil study, coupled with a two-year water quality monitoring program. Spatial variations of water quality parameters did not indicate a statistically significant deterioration caused by the activities in the stream water, but the effects of trampling on physical soil properties were clear. The bulk density of the soils increased with the intensity of recreation from 1.18 to 1.29 g cm 3, while percentage of clay fraction decreased, as an indicator of erosion. The soils of the stream banks in the recreation area had reason- able hydraulic conductivity values, and were affected sharply by the intensity of recreational use. The low inclination (0.5%) and the coarse texture ofthe soils were possibly the main factors diminishing or concealing the trampling effects not observed on the water quality of the stream passing through the recreation area.

Keywords: Recreational use; Soil compaction; Water quality monitoring

l. Introduction

Recreational use is one of the major functions of the forest ecosystems in highly populated regions. Although most recreation areas are rnanaged mainly for this purpose, other functions may have an equal priority in some cases. The multi-resource nature of modern forestry demands that rnanagers assess the potential of their decisions on a broad range of forest attributes related to biodiversity, production, carbon storage, recreation and other non-timber functions [1]. Numerous studies have been perfonned on the multiple use concepts to maximize the value of forest functions [2,3]. In one of them, Kochli et al. (2005) stated after implementing various strategies that no single strategy results in maxirnum values for all uses including recreation, water and air [4]. Nevertheless, it is unrealistic to expect a maximum value when non-timber forest products are in consideration. Ecological consequences of recreational human activities are the least perceptible in most cases, particularly

* Corresponcling author. Email: [email protected]; [email protected]

Inrernational Environmenrul Studies ISSN 0020-7233 print: ISSN 1029-0400 © 2006 Tay lor & Francis http://www.tandf.co.uk/joumals DOI: 10.1080/002072306007733 l 5 274 Ejfects ofrecreational activities on components ofa eco:,ystem around big cities like Istanbul [5], and this causes contlicts with other functions like water production and conservation of aquatic environrnent. The aim ofthis article is to highlight the conflicts between competing managernent objectives. Besides fauna; vegetation, soil and water are the major components generally affected by recreational activities in a forest ecosystem. Soil compaction associated with litter layer defonnation, erosion and sedimentation, of water bodies with nutrients, physical damage to the trees, seedlings, herbaceous and understorey species, riparian zone degradation and noise pollution, are of the seri o us impacts affecting the sustainability ofa forest ecosystem. These influences are subject to change according to the ecosystem attributes, size of the recreation area, ecological conditions (i.e. soils, climate, relief) and the type of recreation. The trampling effects during recreational activities are the most studied aspect of the issue [6]. Generally, compaction on the topsoil horizon is determined due to human [7,8]. The effect of this on the plant growth or other vegetation dynamics is not clear enough due to many other factors [9]. The stream bank might be considered the most susceptible part ofa fluvial system against degradation in a watershed [ 1O]. The erosion in this zone could cause quick: access of the sediments to the stream. The stream bank, either natural or is mostly subject to flooding frequently throughout the year, and it could also have gentle to steep inclination, which promotes abrasion [11]. Furthermore, around the reservoirs or streams that are used for recreational purposes, banks are generally among the most trampled zones due to visitors. Forest recreation sites are not generally accepted as pollution sources as agricultural or urban areas, and have rarely been subjected to water quality monitoring studies [12]. The Nesetsuyu Recreation Area in Belgrad Forest reflects the typical recreation habits of Turk:ish people. Hiking, running and picnicking are the rnost cornmon activities [5]. Around 800,000 people visit Belgrade Forest recreation areas each year, and around of them preferring the Nesetsuyu part of it [13]. Belgrad Forest is named after the village (in the Byzantine era, Petra) which once stood at its centre, and is so called because Suleyman the Magnificent rnany citizens of Belgrad here in 1521 after conquering the Serbian city of that name. The Belgrade people were brought to this place to the reservoirs and aqueducts that conveyed water to Constantinople. These reservoirs, are not major water supplies for Istanbul today, but still have historical value. The biggest one, Buyukbent, is located downstream of the Nesetsuyu Recreation Area, and owing to favourable ecological conditions it supports abundant aquatic biomass. In this study, the ecological consequences of the recreational activities in Nesetsuyu Picnic Area have been investigated with a two-year water quality monitoring program by assessing the reservoir condition, and soil properties.

2. Material and methods

2.1. Site description The monitoring part of the study was conducted on two creeks that meet after draining similar sized small watersheds. The watersheds - named A and B - covered with deciduous forest ecosystems are located on the northwestern side of Thrace Region, in Turkey 1). Watershed A has an area of 150.3 ha with a mean elevation of 145.3 m. while B has an area and elevation of 134.5 ha and 122.3 m, respectively. The mean slopes of the watersheds are quite similar: 21.6% for watershed A and 18.9% for watershed B. Y. Serengil and S. Özhan 275

Figure 1. Location of the study area.

The Nesetsuyu recreation area (0.5 ha), operating since 1956 [14], is located downstream on a flat area (2% average slope ), where two creeks meet. The coordinates of the area are 41°11' 15'" North and 28°58'04'" East, and the elevation varies from 81 to 85 m. The climate of the region is described as 'humid, oceanic and some water shortage in summer' according to the Thornthwaite method and as B3B 1'sb4 ' [15]. The nearest meteorological station (5 km horizontally, 50 m vertically) receives an average of 1050 mm of rainfall annu- ally. Two different parent materials were detennined in the region, carboniferous ( clay greywacke-schist) and Neocene formations (upper Pliocene) [16]. Study watersheds are located on Neocene material that generated deep, acidic, coarse textured and gravelled soils. The region is included in the Castanetum-Fagetum vegetation zone [16]. Vegetation belts according to elevation are: .frainetto, Quercus cerris and Castanea ( < l 00 m); Tilia Castanea (100-180 m); and petrea, Tilia sp., and Castanea sp. ( 180-240 m) [17]. Many other tree and shrub species were also recorded in the region, either natural or planted.

2.2. Sampling and analyses The water quality monitoring period comprised two hydrologic years, starting from October 1999 until September 2001. Five sampling points (SPs) were established on the creeks 2) and grab samples were taken for 14-day intervals except for sorne extraordinary conditions. For instance, sampling was not done in case of zero flow in dry summer months but was made more frequently during heavy rainfall events. The total number of stream water samples was 51 on each sampling point. The analysed water quality parameters were pH, turbidity, electrical conductance (EC), dissolved oxygen concentration (DO) and saturation, water temperature, Mg2+, K+, Na+, N03-, NH/, and Total number of stream water sampling and analyses were 3570. To make a comparison, two and second SPs) of the sampling points were taken above the recreation area on each creek and water quality were compared with the ones below (third, fourth and As and second SPs were on two different creeks, their

/ 1 "" j / ,f - ~ GtiKit.~ i.i'l'fu17~ ) _..,,.,...,...,...,.,.,,. _..,,.

Figure 2. Schematic representation of th e soil and water sampling points. Numbered black circles are water sampling points.

where: ai: ith Electrical conductance (EC) value of SP 1, bi: ith EC value of SP2, ci: ith EC value of SP3, This equation is solved for the 51 EC measurements and 50 values have been computed for

t and k coefficients. Then, the mean values were calculated and symbolized as x1 and xk. EC was used to detennine the contribution ratios as it is thought to be the simplest and most reliable water quality pararneter. Thus, relative contribution coefficients of each creek in the conjunction point have been determined and in this way the water quality

Soil sampling was done both in the intensive (10,000-50,000 yr- 1) and fair recreation areas (500-10,000 visitor yr- 1) and in the non-recreational forested areas of the watersheds (figure 2). Two methodologies were applied to evaluate the effects of recreational activities on soil properties. First, double soil sampling was perfonned on transects perpendicular to the stream channel. Second, soil samples taken from stream banks were compared with the ones taken in (IR and FR areas) and outside the recreation area (forested). Stream banks are among the areas most vulnerable to human impact in a watershed hydrologic system. The soils of the stream bank are not generally protected by a litter layer from the dispersive effects of rain drops or detachment strength of surface runoff. The travelling distance to the fluvial system is also relatively short compared to the other parts of the watershed. Different indices can be applied to assess the affected soils according to Knoepp et al. [ 18]. Soil and site quality rankings vary with the indicator, showing that the soil or site of greatest quality may change depending on the use of the ecosystem under examination. The indicator properties for the soils in the study were selected as EC, pH, saturated hydraulic conductivity (SHC), bulk density, organic matter percentage (OM) and texture. Topsoil samples (0-1 O cm) were taken from 72 points in the watersheds (24 at each IR, FR and forested areas) with intensive systematic grid sampling pattern and from 40 points on the Y. Serengil ancl S. Özhan 277 stream bank. Ten cross-sections (CS) were detem1ined along the creek with 20 m intervals and 3 m transects on each side of the CSs were established for soil sampling 2). The locations of the CSs were chosen systematically with 15-day intervals so that the centre ones would be in the intensive recreation zone (IR). The CS was located outside the zone while the second one was located in the fair recreation area (FR). The SPs from to eight were in the IR and the ninth and tenth SPs were in the FR area. The intensity of trampling is given in 2. Four sampling points were taken on each transect, named according to their side and distance to the creek (al, a3, bl, b3). By implementing a transect survey along the channel we aimed to observe the changes in the soil properties passing through the centre of the recreation area.

2.3. Laboratory analytical methods Nitrate, K+, and Na+ were measured using Orion ISE multirneter (ion selective electrode technique). Mg2+ and NH/ were analysed with digital photometer [19]? chloride with titrimetric methods [20]? pH, temperature DO and electrical conductance (EC) with a digital pH meter in the field; turbidity with Hellige turbidimeter. OM percentage of the soil samples were determined with Walkley-Black method [21]. SHC (saturated hydraulic conductivity) according to Darcy Law [22] with procedure in [23] and texture with hydrome- ter method [21].

3. Results and discussion

3.1. Water quality 3.l.1. Reservoir condition. Büyükbent Reservoir is one of the historical water supply struc- tures of Istanbul. After 350 years of service, today observations around the lake point to a slow increase in the aquatic and riparian vegetation cover. Due to suitable ternperature and moisture conditions, the reservoir and the sunounding forest ecosystem is very fertile and activities in the region might be a factor in prornoting the slow natural process of eutrophication. The average annual temperature and EC of the reservoir were 11.75°C and 201 .60 µ S cm- 1, respectively, during the monitoring period. The mean monthly temperature, pH and DO concentration of the reservoir is presented in 3. The reservoir surface water temperature was very variable, changing between 5°C and 27°C. The highest temperature corresponded to July, but apparently DO concentration was still at its normal level during this month. It is slightly influenced by water temperature, increasing in winter months, with decreasing water temperature. The lowest concentrations were recorded in late autumn from September to November. No evidence, however, of drop down in DO concentration during the intensive recreation months of May to July was noticed. The pH of the reservoir was not an effective factor on DO (figure 3). Values ranged between 6.2 and 7.4 during the two years of the monitoring period. Although very acidic precipitation (pH < 4.0), particularly in winter falls in the region [24], no serious episodic acidification event was observed in the lake. Consequently, the pH of the reservoir water was favourable and fertile for the aquatic flora and riparian vegetation during the whole monitoring period. 278 Ejfects of recreational activities on components ofa eco:-,~vstem

J!Ji ==,,. ~ T

9'.5 :25 , tJO = 5 lt,O - ...... 2 Cr · B,5 a.o % 7,5 o. 7,0 tl,6

;tl,Ö tl~ fU.'.i

Figure 3. Monthly temperature, pH and DO concentration values of the reservoir.

3.1.2. Spatial variations. The spatial variation of all water quality the SPs are presented in table 1. The values are the average of 51 in two years of and the SPC was calculated as explained above. According to ANOV A test, no statistically significant difference was found among the SPs for the whole analysed water quality except for DO concentration. For DO concentration, ANOVA F value was 3.173 with a two-tailed significance of 0.026, and two homogenous groups were identi- fied according to the Duncan test. The differences found by both tests should be attributed to the low DO concentration of the Buyukbent reservoir. The DO concentration of the reservoir is naturally expected to be lower than the stream. The lowest average EC, turbidity K+, DO, and Na+ values were measured at the reservoir.

3.2. Effects on soil properties

3.2.1. Stream bank soil properties. The spatialchange in the physical properties ofthe stream bank soils indicated a compaction at the topsoil (0- 1O cm) increasing with the intensity of recreational activities (figure 4). Bulk density increased at the heavily trampled parts inversely proportional with soil organic matter. It was 1.03 g cm- 3 at the first cross-section, and increased gradually to reach 1.4 g cm·-3 in the middle transects and decreased to 1.22 g at the tenth

Table 1. Mean values of water quality parameters for whole

SPs EC pH T Tur. PO4- SO42- NO 3- Na+ K+ Mg2+ NH 4+

µ S oc NTU mgL- 1 SPl 193 .73 6.85 1 1.16 6.68 31 .85 3.03 5.34 7.60 2.89 10.65 2.98 3.13 0.23 SP2 252.38 6.86 10.64 5.94 44.62 3.43 6.10 7.47 2.90 10.84 2.64 3.71 0.22 SPc 220.12 6.86 10.92 6.34 37.59 3.21 5.68 7.54 2.90 10.73 2.83 3.39 0. 22 SP3 218.48 6.97 11.01 6.65 42.23 3.21 5.28 9.33 2.41 10.30 2.59 4.04 0.24 SP4 230.38 6.90 10.86 6.13 42.83 3.23 5.42 8.90 2.66 10.77 2.52 3.56 0.29 SP5 201.60 6.89 11.75 5.65* 31.15 3.17 4.74 9.00 2.94 9.74 2.53 4.35 0.32

*Statistically (p < 0.05). Y. Serengil and S. Özhan 279

~ · U ' u T.J U}

{}_ ij;

Figure 4. The change in the soil organic and bulk density values passing the recreation area. The values are the average of four points on transect (eight samples with replicates).

one. The organic matter contents of the stream bank soils throughout the creek longitudinal profile changed between 3.5-5.5% and did not follow a significant trend, unlike bulk density. The OM contents of the soils at the seventh and tenth cross-sections were higher than the first one. Apparently, OM should not be considered as a reliable indicator of compaction. SHC decreased passing through the heavily trampled part of the recreation area while pH, EC, and the texture composition did not show a defineci trend. On the other hand, the distance to the channel also influenced some of the soil properties. As explained above, soil sampling was done at two distance rows, on the transects 2). The average values for some soil properties are computed according to the distance to the channel (figure 5). As can be seen from figure 5, clay and organic matter content of the soil decreased, while electrical conductance, pH and saturated hydraulic conductivity increased, approaching the channel. A non-parametric Kruskal Wallis test was applied to compare means (as the number of data in each group was 10) and no difference was found among the sampling rows (al, a3, b3, bl) on the transects.

3.2.2. Comparison of soil samples taken from recreation and non-recreation areas. Some soil properties are given in table 2, to make a comparison between the creek banks, heavy and fair recreation areas and the non-recreation forested areas. OM percentages of soil

Figure 5. The soil properties on the transversal cro ss section of the stream. 280 E.ffects ofrecreational activities on components ofa eco:.y stem

Table 2. Cornparison of sorne soil properti es.

Electrical SHC Bulk density Clay fraction Sami fraction pH conductance Organic matter

cm hr- 1 g cm- 3 % % µScrn- 1 % Bank lR 15.00 1.28" 10.92" 77.66" 6.34 111.25a 4.35a Bank FR 61.17 1.18" 12.24a 73 .58" 6.03. 110.50a 4_54• IR 6.45 1.29a 13 .53a 75_ 15• 5.90a 80.25 4.91 a FR 26.17" 1 .18° 12.61 a 72.193 5_92• 94_33• 5.643 Forested 26.90a 1. 12• 16.00 73.50" 5.45 96.37° 11.36

IR: Jntensive recreation; FR: Fa.ir recreation. • in the same group in mean comparison with Tukey test (p < 0.05). in the fecfeation afea, even intensive Of faif, wefe half of the fofested part of the watefshed. The absence of littef layef and a healthy decomposition mechanism are cleafly the main factofs of the significantly low OM content of the soils, in the fecfeation area. Additionally, the intensity of recfeation was not a significant driving variable to affect soil OM content. Recreational activities, intensive Of faifly rnoderate, influenced the soil organic rnatter by interrupting the forma ti on and decomposition of littef la yer. The stream banks had the highest EC value among all sites. The statistically low EC value ofIR area may have many causes and it is not possible to identify one particu- lar cause. Additionally, the difference was statistically but not noticeable in prac- tical tem1s, as the highest EC value was even far below the water quality standards. The soil pH in the region was acidic, mainly caused by parent material, while recreation area soil pH was highef than forest soils due to the fewer immobilization possibilities of lower clay and organic content. The highest pH values were measured on stream bank soils as the water pH was over 6.5 during the whole monitoring period. Usually, more wash up is expected to cause H+ accumulation. Textural composition of the soils was also affected from compaction in the recreation area. The percentage of thinner fractions decreased, but not parallel, with the intensity of trampling. Statistical difference was found just for clay percentage after arc sinus transformation. Bulk density values did not differ statistically, while SHC was quite variable. As expected, the highest bulk density and lowest SHC was at the IR area. The SHC of FR area was very similar to forest areas while stream banks had reasonably high values. The SHC was not found to be a general problem in the recreation area, except IR

4. Conclusions

Soil and water components of a deciduous forest ecosystem have been investigated to discover the effects of intensive recreational activities in the Nesetsuyu Recreation Area. The results showed that the hydraulic properties of soils were adversely affected by human activities, while a detectable influence on the stream and reservoir water quality was lacking. There are several possible reasons:

(1) The recreation area might be not large enough to cause a detectable deterioration in water quality. This explanation is also supported by Leung and Marion's [25] which suggest that concentrating heavy use on a limited number of impacted sites will result in Y. Serengil and S. Özhan 281

less aggregate impact than spreading use among a Iarger number of low to moderate use sites. (2) Micro-topographical conditions were not favourable for surface runoff as the slope was very gentle and infiltration capacities of the stream banks were very high. (3) Although there were gaps at the canopy especially at the intensive recreation parts, the stream temperature was still lower than that of the reservoir in summer months and, in

general average TsP2, T5p3, T5p4

On the stream bank, bulk density values increased at the intensive recreation areas while saturated hydraulic conductivity (r = -0. 71) and organic matter changed, inversely proportional with bulk density (r = -0.57). Yet the dimension of the effect was not large enough to cause a problem, as the soil hydraulic properties under observation were better than even the non-recreation areas probably because of the high sand content of the soil on the stream banks. There was also no statistically significant difference between the bulk density values, whereas more than 0.5 g difference between trampled and surrounding undisturbed areas was recorded in previous studies [26]. Organic matter content was low but this was not even effective to decrease SHC. According to soil properties on the 1 m soil zone, there is flooding and wash away of clay and organic matter particles that also possibly caused an increase in pH. Multiple use management of forest recreation sites requires knowledge about the compatibility of uses and the points of possible conflict [27). Thus, research on the compatibility of recreation and other forest ecosystem functions should be encouraged, especially giving priority to the biotic influences which are generally ignored in the planning phase.

Acknowledgement

This work was supported by the Research Fund of the University ofistanbul, project 1272/050599.

References

[!] Seely, B., Nelson, J., Wells, R., Peter, B., Meitner. M., Anderson, A., Harshaw, H., Sheppard, S., Bunnel, F.L., H. and Harrison, D., 2004. The application ofa hierarchical decision support to evaluate multi objective forest strategies: a case study in the Northeastem British Canada. Forest Ecology and Management, 199, 283-305. [2] Strange, N., Tarp, P., Helles, F. and Brodie, J.D., 1999, A four stage approach to evaluate management alterna- tives in forestry. Forest Ecology and Management, 124, 79- 91. [3] Ohman, K. and Lamas, T., 2003, Clustering of harvest activities in planning. Forest Ecology 116, 161-171. [4] Kochli, D.A. and Brang, P., 2005, Simulating effects of forest management and selected public forest goods and services: a case study. Forest Ecology 209, 57-68. [5] Destan, S., 2001, Management and cbaracteristics and assessment of forest ecosystcms in forest activities. Doctoral thesis, Graduale School, Softa University. [6] Cole, D.N., 1995, Recreational trampling experiments: effocts oftrampler weight and shoe type. USDA Forest Service lntermountain Research Station, Researcb Note INT-RN-425. [7] Sutherland, R.A., Bussen, J.O., Plondke, D.L, Evans, B.M. Ziegler, A.D., 2001. Hydrophysical degradation associated witb hiking-trail use: a case study of Hawai 'iloa ridge trail, O 'ahu, Hawai' i '. Land Degradation and Developmenl, 12, 71-86. / -· 282 Ejfects ofrecreationa/ activities on ofa forest ecosystem

[8] Yilmaz, M., 1994, Rekreasyonel kullanimin topraklarin hidrofiziksel ozellikleri uzerine etkisi. MSc thesis, Institute of Science, Istanbul University. [9] Cole, D.N., 1993, Trampling effects on mountain vegetation in Washington, Colorado, New Hampshire and North Carolina. USDA Forest Service lntennountain Research Station. Research Paper TNT-464. [10] Volny, S., 1984, Riparian stands, in: in and Managed-Forest Ecology Elsevier Science), pp. 423-453. [ 11 J Mitsch, W.J. and Gosselink, S.G., 1993, Wetlands (New York: Van Nostrand Reinhold). [12] Serengil, Y. and Ozyuvaci, N., 2002, Water quality management in Balabandere Creek lnterna- tional of Water, 2(2/3), 220-228. [13] Caglayan, A.Y., 1999, Belgrad onnaninda rekreasyonel talep ozelliklerinin saptanmasi. MSc Thesis, I.U. Insti- tute of Science. [14] Pehlivanoglu, T., 1987, Belgrad Onnaninin rekreasyonel potansiyeli ve planlama tespiti . Doctoral thesis, I.U. Institute of Science. [ 15] Serengil, Y. and Ozhan, S., 2001, and spatial variations of nitrogen and phosphorus concentrations ona suburban creek near lstanbul in Turkey. Silva Balcanica, 1, 63-70. [16] Ozhan, S., 1977, Belgrad omrnni ortadere yagis havzasinda olu ortunun hidrolojik bakimdan onemli ozelliklerinin bazi yoresel etkenlere gore degisimi. I.U.Orman Fakultesi Yayinlari, l.U.Yayin No: 2330, No: 235, Istanbul. [I 7] Kantarci, D. and Tolunay, D., 1996, I.U.Orman Fakültesi egitim ve arastirma ormaninda toprak ve yetisme ortami belirlenmesi. I.U.Research Fund Project Report, lstanbul. [18] K.noepp, J.D., Coleman, D., Crossley, D.A. and Clark, J.S. , 2000, Biological indices of soil quality: an ecosystem study of their use. Forest Ecology and 138, 357-368. [ 19] Ewing, G.W., 1975, Methods (New York: McGraw Hill). [20] APHA-AWWA-WPCF, 1975, Standard Methodsfor examination of'water wastewater, 14th edition (New York: APHA-AWWA-WPCF). [21] Irmak, A., 1956, Topragin arastirilmasi l.U.Yayin No: 599, O.F. Yayin No: 27, Istanbul. [22] Wanielista, M., Kersten, R. and Eaglin, R., 1997, Hydrology, Water and Control (New York: Wiley). [23] Ozyuvaci, N., 1976, Amavutkoy Deresi yagis havzasinda hidrolojik durumu etkileyen bazi bitki-toprak-su iliskileri, I.U.Om1an Fakultesi Yayinlari, l.U.Yayin No: 2082, O.F. Yayin No: 221, lstanbul. [24] Serengil, Y., 2002, Acid rains in Belgrad Forest, Istanbul, IUFRO 7.04.00 Conference, Long Tenn Air Pollu- tion Effect on Forest Ecosystems, 20th lntemational Meeting Specialists in Air Pollution Effect on Forest Ecosystems, Zvolen, Slovak Republic, pp. 74-76. [25] Leung, Y.F. and Marion, J.L., 1999, Characterizing camping impacts in Great Mountains National Park, USA. of Environmental 57, 193-203. [26] Liddle, M.J., 1975, A selective review of the ecological effects of on natura! ecosystems. Biological 7, 17-36. [27] Home, P., Boxal, P.C. and Adamowicz, W.C., 2005, Multiple use management of forest recreation sites: a spatially explicit choice experiment. Forest Ecology and 207, 189-- 199.