Forest Regeneration in Abandoned Logging Roads in ...

BIOTROPICA 29(1): 15-28

1997

Forest Regeneration in Abandoned Logging Roads in Lowland Costa Rica’ Manuel R. Guariguata2 Center for International Forestry Research (CIFOR), Box 6596, JKPWB, Jakarta, Indonesia, and Unidad de Manejo de Bosques Naturales, CATIE, Turrialba, Costa Rica and

Juan M. Dupuy Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut 06269, U.S.A.

ABSTRACT We characterized plant regeneration in four old logging roads (700-1000 m long), 12-17 yr after abandonment, in selectively logged forests in lowland Costa Rica. Sets of 4-m2 plots were laid out at 20-m intervals in three distinct microhabitats: road track (topsoil eliminated), road edge (where removed topsoil accumulates on the sides after road construction), and adjacent logged forest. Density of stems 21 m tall and 5 5 cm DBH (included canopy tree, midstory tree, liana, palm, shrub, and tree fern species) was highest in the road edge plots than either the track or logged forest plots. This “edge effect” is presumably due to buried seed germination of light-demanding trees and shrubs after moderate soil disturbance, less compaction, and higher substrate fertility than in road tracks. Species richness was the lowest, but relative dominance the highest, in the track plots of all roads: 6-9 species comprised alone 50 percent of the Importance Value Index (M),in contrast to 11-15 and 16-22 species required to reach 50 percent M in edge and forest plots, respectively. We found evidence of soil compaction in tracks of three out of four roads which, in addition to low substrate fertility, and initial lack of on-site plant propagules, could explain slower recovery of stem density and species richness compared to edge and logged forest plots. For stems >5 cm and 5 2 0 cm DBH, density and basal area in the track plots averaged about one-fourth of edge and logged forest plot values. We estimated recovery of basal area in road tracks to take at least 80 yr to reach the status found in logged forest, and species richness over an even longer period. We suggest that abandoned logging roads serve as long corridors of relatively uniform and long-lasting floristic and structural characteristics that may confer particular ecological roles in selectively logged forests.

RESUMEN Caracterizamos la regeneraci6n vegetal en cuatm caminos de arrastre de troncos (700-1000 m de largo) que heron abande 4 m2 se colocaron donandos entre 12-17 aiios luego del madereo selectivo en bosqucs de bajura en Costa Ria. Par& borde (en a lo largo de 10s caminos en tres micrositios contrastantes: centm del camino (desprovisto de suelo OI#&O), donde se acumula el suelo orghico remaido luego de construir el camino), y en bsque perturbado adyacente. En general, la densidad de tallos 21 m alto y 5 5 an DAP (iicluldas especies de &boles del dosel y subdosel, lianas, palmas, arbustos y helechos arborexentes) h e IT& alta en las pardas del borde que en las del centm del camino o bosque perturbado adyacente. h e “&o de borde” se debe probablemente a la germinacibn de sunillas de &boles y arbustos demandantes de luz luego de la permrbacibn moderada del suelo, menor compactaci6n y mayor krtilidad del substrato con mpecto al centro del camino. En todos 10s &nos, la dquaa de especies h e m b baja y la dominancia relativa I& alta en las colocadas en el cenm, en las c d e s s610 6-9 especies acumularon el 50 por ciento del Indice de Valor de Importancia (M),en contraste con 11-15 y 16-22 espies requeridas para acumular 50 por ciento M en par& del borde del camino y bosque perturbado, respectimente. Enconuamos evidencia de c o m p c i 6 n en el centm de tres de 10s cuatm caminos gtudiados, lo cual surnado a una posible baja Lrtilidad del suelo y e s c a s ~de prop6gdos aut6ctonos pod& srplicar la baja densidad de tallos y riqueza de cspecies en las parcelas del centm del camino respecm a parcelas en el borde y bosque perturbado. La densidad y el &a basal de individuos >5 un y 5 2 0 un DAP en p”celas del centm de 10s caminos h e en promedio una cuarta parte de 10s valores en el bode y bosque perturbado. Estimamos que la racuperacibn de &a basal en el centro de 10s caminos mpecto al bosque perturbado podria tomar un mlnimo de 80 aiios y mucho I& tiempo para la riqueza de especies. Proponemos que 10s caminos de arrastre abandonados sirven como corredores de UM relativa uniformidad florlsdca y estructural, 10s cuales pueden jugar un papel ecol6gico particular en bosques perturbados por el madereo

+

seleCtiV0.

Key

word:

Costa Rica; forest regeneration; hgging roads; hgging impacts; hwlandjirest; sckctivc h&g; succession.

Received 27 February 1995; revision accepted 8 September 1995. Address for correspondence: Unidad de Manejo de Bosques Naturales, CATIE, Apartado 7170, Turrialba, Costa Rica. 15

16

Guariguata and Dupuy

IN SELECTIVELY LOGGED TROPICAL FORESTS, extraction roads can disturb a considerable proportion of soil and canopy cover during timber harvesting (e.g., Nicholson 1958, Wyatt-Smith & Foenander 1962, Uhl & Vieira 1989; Cannon et al. 1994; but see Crome et al. 1992), creating distinct sites for plant establishment. Compared to logging gaps where regrowth occurs primarily from seeds and seedlings present at the time of tree felling (reviews in Brokaw 1985, Ganvood 1989), forest recovery in abandoned road tracks may be substantially retarded due to substrate compaction by machinery use (Malmer & Grip 1990, Jusoff & Majid 1992) and lack of on-site plant propagules after topsoil removal (e.g., Uhl et al. 1982). Forest recovery at the road edges may be faster than in road tracks because sidecast topsoil may retain regeneration sources (ie., buried seeds, resprouts; Jonkers 1987; Pinard et al. 1996) and soil compaction is of little importance. Although there exists abundant data on the physical characteristics of logging roads and their ecological impact on the residual forest (see Bruijnzeel 1990, Hendrison 1990), there is limited knowledge on vegetation recovery. Previous works have noted dense stocking of a few dominant, usually light-demanding tree species on logging road surfaces soon after timber harvesting (eg., Abdulhadi et al. 1981, Verissimo et al. 1992), but these observations were limited to early plant colonization (up to 3 yr after road creation), with little quantitative information provided on species composition and vegetation structure. In this paper, we examine the major patterns of forest regeneration and the floristic and structural recovery of the plant community in 12-17 yr-old, abandoned logging roads in lowland Costa R i a . In spite of the interest in implementing conservation of biodiversity as an integral component of natural forest management in the wet tropics (IUCN 1992, Johnson & Cabarle 1993), most of the available information on biotic recovery in logged forests focuses on vertebrates (e.g., Johns 1992; Thiollay 1992, Frumhoff 1995). Assessing natural regeneration in old logging roads may lead to a better understanding of logged forest tree dynamics and the autecology of woody plant species that either may benefit or adapt to this type of disturbance, and hold potential applications for restoration and enrichment planting guidelines. Here we refer to logging roads (known as "extraction roads" in Costa Rica) as those whose purpose is to provide access to the areas selected for timber harvesting and log yards. Based on previous observations in recently logged forests around the

study zone, we predicted that contrasting substrate conditions in road tracks and edges would influence plant community structure and species composition with respect to less disturbed, logged forest; in particular, we expected the slowest degree of floristic and structural recovery in abandoned road tracks.

METHODS STUDY sms.-The study was conducted in the Caribbean lowlands of Costa Rica, Heredia Province, Sarapiqui County. The natural vegetation is classified as Tropical Wet Forest (remu Holdridge 1967; Hartshorn & Peralta 1988). Annual rainfall and temperature records from La Selva Biological Station (10"26'N, 84"00'W, Organization for Tropical Studies, [OTS]), located within this life zone, average 4000 mm and 26" C, respectively (Sanford et al. 1994). Soils are derived from weathered volcanic deposits and alluvial processes, and include primarily Inceptisols and Ultisols. All study sites fall into the N o Cuarto topographic quadrangle (1:50,000; Instituto Geogr&fico Nacional, Costa Rica). We selected logging roads that had been abandoned for at least more than 10 yr prior to our study, and that were at least 500-600 m long under forest cover (Table 1). Based on these restrictions, four logging roads of similar age since abandonment were chosen and their vegetation characterized during mid-to-late 1994. It proved difficult to include more replicates because during the 1970s, the rapid expansion of the agricultural frontier in the area had caused the original forest in most sites to either disappear or suffer heavy fragmentation after logging due to conversion to pasture, exotic tree plantations, or cropland (Butterfield 1994). Throughout the Caribbean lowlands of Costa Rica, timber harvesting takes place in virtually all cases in individually owned farms; extensive forest concessions for long-term timber production are rare. The logging operations that took place in our study sites can be described as conventional. Bulldozers would open the logging roads with little or no planning and trees were felled when encountered by the logger, generating extensive soil disturbance during skidding because the machinery would be directed to the stump's base to remove the logs (Corder0 1989). Only recently have damage-controlled logging practices (such as road planning, directional felling, and long-distance log winching) been implemented around the study area (eg., Quir6s & Finegan 1994). Logging is usually car-

Forest Regeneration in Logging Roads

TABLE 1.

Characteristics of the abandoned lo@g road studied in the Caribbean lowland of Costa Rira.

Site

Mean ( ? l SE) road width (my

Number of sampling pointsb

Jaguar Sarapiqui Kelady La Martita

3.2 2 0.1 3.1 ? 0.2 3.0 2 0.2 3.5 ? 0.3

46 50 35 40

-

17

Estimated Minimum logging intensity road length (m) (stumps/ha)c 920 1000 700 800

3-4

3 4 8-9 9-10

Time since abandonment at start of study (yr) 15-17 15-17 12-14 12-15

Measured at the inner edge of sidecast material. Each sampling point corresponds to a set of three, 4-mZ quadrats placed in the road track and edge, and adjacent forest, spaced every 20 m (see Methods). c Estimated from a 20 m-wide belt transect located on both sides of the logging road extended along the total distance sampled for vegetation. a

b

ried out during the drier parts of the year (JanuaryMarch) to facilitate machinery access. Two logging roads (Jaguar and Sarapiqul; Table 1) are located within the grounds of La Selva Biological Station, where approximately 180 ha of forest were logged during the late 1970s (Pierce 1992). The age since abandonment of both roads is 15-17 yr (Gonzalo Cascantes, former caretaker of the property, pers. comm.). The third logging road is located in a private farm (Finca Kelady, Pueblo Nuevo, 10”29’N, 84“09’W) where logging occured 12-14 yr ago in about 70 ha of forest (Nuevos Recursos Forestales 1989). The fourth road is also located on private property, Finca La Martita, Chilamate (10”27‘N, 84”04’W). Here, the forest was logged approximately 12-15 yr ago (Don Elio, present caretaker of the property, pers. comm.). At both Kelady and La Martita sites, the residual forest looks very fragmented as old logging roads were found along pastures and tree plantations. Although the creation of logging roads encourages human traffic, especially for hunting, we found no obvious evidence of either recently cut vegetation nor heavy trampling at any site. From map information at two study sites (La Selva and Kelady; Centro Cientlfico Tropical 1982, Nuevos Recursos Forestales 1989), we estimated that the proportion of forested area disturbed by logging roads at the time of harvesting was about 4-5 percent, figures similar to more recent logging operations in nearby locations (4-7 percent; Koppelman 1990, Carrera 1992). In all sites, the topography varies from flat to moderately undulating. Signs of severe gully erosion were not evident in any of the studied logging roads. DATAc o L L E a I o N . T \ u r sampling differentiated three main microhabitats, hereafter called road

“track” and “edge”, and “forest”. Plots of 2 m X 2 m were laid out in each microhabitat at 20-rn intervals along the study roads. The forest plots were located 10 m into adjacent logged forest, aligned with the track and edge plots. The track and edge plots were separated by 0.5 m (in recently logged forests, we estimated the width of sidecast topsoil to vary between 1.0-1.5 m), and the location of the edge and forest plots was alternated at each distance interval to either side of the logging road. We did not attempt to distinguish old felling gaps from apparently undisturbed patches in our forest plots. The number of samples was adjusted among roads due to their different lengths (Table 1). The abandoned roads were always easy to follow since the old banks of pushed soil and the bulldozer tracks were still identifiable. In each plot location (track, edge, forest), we counted and identified all stems 21 m tall and 5 5 cm in diameter at breast height (1.3 m; DBH), and classified them as canopyhubcanopy tree species, midstory tree species, shrubs, tree ferns, lianas (only those free-standing stems rooted in the quadrat; not always identifiable), and palms. Life form dassification was based on our previous observations, and on herbarium information. Shrub species with multiple basal stems were counted as one individual. For each species, we calculated the Importance Value Index (M)as the sum of relative basal area, frequency, and density. We also sampled and measured tree and palm individuals >5 and 1 2 0 cm DBH. Although we did not distinguish resprouts from undamaged individuals, our impression was that at least in logging road tracks, the proportion of resprouted stems seemed fairly small. To estimate logging intensity, we counted all stumps located within a 20 rn-wide belt on both sides of each logging road, extended along its sampled

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length; we chose this width because most stumps were concentrated within this distance. Fresh specimens were identified in the field by the authors, with the assistance of the local expert, Orlando Vargas (OTS). In order to assess soil compaction between the track, edge, and forest plots, we took litter-free core samples (6 cm deep, 8 cm diameter) for dry bulk density determinations in the three plot locations, spaced 20-40 m along each study road ( N = 9 samples per location per site). Samples were oven dried at 70" C and weighed after 48 hr. STATISTICAL ANALYSES.-DifferenCeS in density of stems 2 1 m tall and 5 5 cm DBH across plot locations were tested in a paired fashion with the Wdcoxon Signed Ranks test. The Mann-Whitney U statistic was used to test for differences in species similarity index between plot locations (Jaccard's index; Greig-Smith 1983). To test for among-road differences in the number of stems of tree species across plot locations, we used Replicated Goodness of Fit G statistics ( S o u & Rohlf 1981). Effects of road location on the relative composition of plant life forms were tested with a Friedman two-way analysis of variance. We used ANOVA and Tkey's procedure to test for plot location effects on soil bulk density, and for mean basal area and density of stems >5 cm and 5 2 0 cm DBH. Analysis were performed with SYSTAT (1992), and statistical significance was h e d at P < 0.05.

TABLE 2. Mean ( 2 1 SE) bulk density (in g / c d ) of soil sampkd in tracks and edges of abandoned logging r o d and djacent .!aged forest. in the Caribbean lowlandr of Costa Rica (N = 9per plot location). Within sites, valuesfollowed dffmnt supcrscr+ts denote a statistical location effect at P < 0.01 (Tukey? test). Plot location Site

Jaguar SarapiquI Kelady La Martita All site mean

Track

Edge

0.90 (0.02)' 0.75 (0.02)b 0.73 (0.04)' 0.71 (0.03)" 0.95 (O.O1)a 0.76 (0.03)b 1.11 (0.04)' 0.76 (0.03)b 0.90 (0.02)' 0.73 (0.02)b

Forest

0.72 (0.03)b 0.63 (0.04)a 0.75 (0.02)b 0.75 (0.03)b 0.73 (O.O1)b

logging roads; two-tailed P c 0.001) than either the track or logged forest plots (which did not differ from each other; two-tailed P = 0.1). When differences in stem density were tested separately for each study road, however, only the Jaguar road showed no statistical location effect between the edge plots and either the track or forest plots (Fig. 1). The above microhabitat-related differences in stem density appeared independent of the type of plant colonist. All study roads varied in their relative composition of life forms across track, edge, and forest plots (Friedman two-way analysis of variance using roads as blocks; P c 0.01 in all cases). For example, the proportion of shrub species at Jaguar and Sarapiqui roads was higher in the RESULTS track and edge plots than at Kelady and La Martita. Logging intensity differed between the four logging In contrast, regeneration of canopy and midstory roads. An average of 3 4 stwnpdha were found in tree species at Kelady and La Martita comprised the Jaguar and Sarapiqui, while stump density was more than half of the total stem density (Fig. 1). twice as high at Kelady and La Martita roads (Table Compared to other life forms, lianas and palms 1). In three of the four roads, the effects of sub- were of low importance in road track and edge strate compaction were still evident more than a plots. decade after abandonment. Soil bulk density from Species richness was the lowest in the track plots the track plots was significantly higher than those of all roads (Fig. 2). Furthermore, species domifrom edge and logged forest plots (which did not nance-diversity patterns were very similar among differ from each other; Table 2). Across roads, soil roads but contrasted across plot locations. For exbulk density values differed in track plots only ample, 6-9 species comprised 50 percent of the M (ANOVA, P c 0.001), probably reflecting among- of all species in the track plots, while 11-15 and site differences in both the number of machinery 16-22 species were needed to accumulate 50 perpasses and logging intensity (see Hendrison 1990). cent M at the edge and forest plots, respectively. Overall, track plots were statistically more similar REGENERATION OF STEMS 2 1 M TALL AND 5 5 CM to edge (index range: 0.33-0.42) than to forest DBH.-Patterns of plant abundance, life form plots (index range: 0.05-0.25) in floristic compocomposition, and species richness varied between sition of the top 10 dominant species (Mannplot locations. Overall, stem density was highest in Whitney V, P < 0.01). Although the floristic comthe edge plots (Wilcoxon signed ranks test, N = position of the dominant species encountered in 171 quadrats in each plot category from all four the track plots differed among sites, strong domi-


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Species sequence

FIGURE 1. Density of stems 2 1 m tall and 5 5 cm DBH and total stem number (on top of each stacked bar) sampled in plots located in tracks and edges of abandoned logging roads, and also in adjacent logged forest, in the Caribbean lowlands of Costa Ria. Within sites, comparisons of stem density across plot locations followed: Edge > Track, Edge > Forest, and Forest = Track (Wilcoxon Signed Ranks test, two-sided P < 0.02),with the exception of Jaguar site where the only statistically significant &rence was:Track > Forest. Sampled area as in Table 1.

FIGURE 2. Species dominance-diversity patterns (expressed as cumulative percent of the total Importance Value Index) in stems 2 1 m tall and 5 5 cm DBH (life forms and total number of sampled stems as in Fig. 1) in plots located in tracks and edges of four abandoned logging roads, and in adjacent logged forest, in the Caribbean lowlands of costa R i a Sampled area as in Table 1.

again Pentacktbra, and the canopy tree fichysiafiruginea (Vochysiaceae). Among tree species only, patterns of stem density and species richness mirrored the overall trends described above. Tree saplings (individuals 2 1 m tall and 5 5 cm DBH) appeared to regenerate vigornance by only a few species was, nevertheless, a ously along road edges, while fewer individuals and consistent trend. The top three dominant species species were found in the tracks (Appendix). Overin the track plots at the Jaguar and Sarapiquf roads all, tree saplings were unevenly distributed across were the tree fern Cyatbea multijhra (Cyatheaceae), microhabitats (Gpoold = 43.65, df = 2, P < and the shrubs C l i h i a denrrflora (Melastomata- 0.001). Forty-four percent of all stems occurred at ceae), and Bes& columneoiihs (Gesneriaceae). In the edge, while 26 percent and 30 percent were contrast, the top three dominant species at Kelady found in the track and forest, respectively (N = road were the canopy tree Pentacktbra macroloba 688). This pattern was independent of road loca(Mimosoideae), and the midstory trees Piper colo- tion (Gheterogenciry = 6.22, df = 6 , P > 0.1). A few nense (Piperaceae), and Pvcbotria e&ta (Rubiaceae). species were present in all plot categories in all sites At La Martita, the top three dominant species were (Appendix). The most common were Pentachtbra, the shrub Miconia ncwosa (Melastomataceae), which comprised 19 percent of all stems, and Ca-

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TABLE 3. Abundance and basal area (B.A., in &/ha) offiee standing woody stems >5 cm DBH and 520 cm DBH (including palms) sampled in tracks and edges of abandoned logq'ng r o d and adiacent logged forest, in the Caribbean lowlandr of Costa Rica. Sampled area as in Table I . Plot location Track

Edge

Forest

Site

Stems/ha

B.A.

N

Stemslha

B.A.

N

Stemslha

B.A.

N

Jaguar Sarapiqui Kelady La Martita All site mean

434 350 142 62 263

6.2 1.7 0.9 0.3 2.3

8 7 2 1

978 1250 1000 1187 1104

10.0 13.7 10.6 11.0 11.3

18 25 14 19

923 1350 857 1125 1064

12.1 16.3 9.6 12.4 12.6

20 26 11 18

searia arborea (Flacourtiaceae) that ranked second in abundance (11 percent of all stems). Other common species that concentrated almost exclusively in the edge plots and that were rare in the forest included the light-demanding Apeiba membranacea (Tiliaceae), Laetia procera (Flacourtiaceae), and I/ochyzia. OF STEMS >5 CM AND 5 2 0 CM DBH.-Free-standing stems >5 cm DBH and 5 2 0 cm DBH were also unevenly distributed among plot categories (Gpooled = 46.2, df = 2, P < 0.001), independent of road location (Ghererogeneiry = 7.3, df = 6, P > 0.1). Road track plots were also species poor in this size class, ranging from 1-6 species in all four sites. In comparison, edge plots had 9-17 species and forest plots 11-19 species (Appendix). In track plots, basal area and stem density was about one-fourth (Tukey, P < 0.001) of that found at edge or adjacent forest plots (which did not differ from each other; Tukey, P > 0.5; Table 3). Abundant tree species in this size class (Appendix) were light demanding Goethahia meiantha (Tiliaceae),Lzetia, and Croton smithianur (Euphorbiaceae).

REGENERATION

DISCUSSION Forest recovery in abandoned logging roads appears to be influenced by microhabitat effects in our study. Plots located in old road tracks showed about two-thirds to one-half the number of woody plant species than those located at the road edge and adjacent logged forest, respectively. Stem density of individuals 2 1 m tall and 5 5 cm DBH was, overall, higher in the road edge plots compared to track and forest plots, and these differences between plot categories were even more pronounced for larger individuals. It is uncertain how long it will take for these roads to approach logged

forest diversity and structure since we lack longterm data for the region; forested areas where mechanized logging took place more than 20 yr ago are rare to find. Yet, our results indicate that recovery of plant species richness and diversity, particularly in road tracks, can be a slow process. Lower species richness in track versus edge and forest plots is likely a combination of depauperate on-site regeneration mechanisms and substrate conditions. At least during the first years after abandonment, natural regeneration in road tracks may depend much more on dispersed- than soilstored seeds, due to topsoil removal (e.g.. Uhl et a/. 1982). In addition, plant propagules landing on compacted logging roads are at risk of being rapidly washed off before they can root (Pinard et al. 1996). In two nearby, recently logged forests (=3 yr-old at the time of our study), we observed no woody seedlings along 300 m of sampled road tracks, while at the edges, shrubs and light-demanding tree saplings had already established. We found in three of our study roads evidence of soil compaction in the road tracks several years after abandonment (see also Hendrison 1990). Soil compaction may also retard root growth and restrict plant nutrient availability (Greacen & Sands 1980). Logging road tracks may also be unfavorable sites for plant growth due to reduced organic matter and nutrient content (Gillman et al. 1985). O n the other hand, the higher stem density found in road edge plots, with respect to track and forest plots, is probably the result of accumulated sidecast topsoil, presumably with little elimination of a germinable seed bank. Moderate soil disturbance at the road edges and improved light conditions after road construction (M. Guariguata, pers. obs.), offers favorable substrate conditions for plant recruitment. Upturned topsoil may facilitate establishment of small-seeded, light demanding tree species (Pun 1983), and shrubs (Ellison et al.


1993). For example, we found Cecropia established almost exclusively along the road edge plots, and none in logged forest. Germination of dormant Cecropia seeds is triggered by soil mechanical disturbance (Williams-Linera 1990) and large temperature fluctuations (Vkquez-Yanes & OrozcoSegovia 1985), events that are likely to occur during and immediately after logging road construction. Other small-seeded, light-demanding tree species such as Laetia and Goetbahia were also more abundant in road edge plots than elsewhere. Both species are capable of recruiting from the seed bank (Foresta & Prevost 1986, Young 1985). Across roads, the track plots differed in floristic composition of the dominant plant species, with marked dominance of only a few colonists. These dominant species vary widely in their propagule types: Cyatbea tree ferns regenerate via spores (Page 1979), and the shrubs Best%&, Clidnnia, Miconia, and Pipn; produce fruits with small seeds that are primarily bird-dispersed ( k e y 1988, Loiselle & Blake 1990). The two most common tree species, Pentachbra and bcbysia, produce seeds that are dispersed by gravity (Hartshorn 1983), and wind (Standley 1937), respectively. The fact that the track plots in all the study roads were dominated by ecologically distinct species, suggests that local and historical effects such as timing of propagule release, composition of surrounding vegetation, and substrate fertility, may control plant regeneration in road tracks, perhaps to a larger extent than propagule attributes per re (but see Pinard et af. 1996). Density and basal area of stems >5 cm and 5 2 0 cm DBH was considerably lower in track plots than elsewhere. Although slow plant colonization may partially account for this result, it appears that conditions for plant growth may also be limited in the road tracks. We did not measure overhead canopy openness along our study roads, but our observations point out that, in addition to potential substrate limitations such as soil compaction and low fertility, established vegetation in road tracks may also suffer from light limitation by tree crown encroachment from adjacent forest. Assuming that basal area accumulation continues at the present rate in road tracks (using 2.3 m2/ha as the road track average and 15 yr as the base time period: -0.15 m2 ha-' yr-l), an estimated minimum of 80 yr would be required for road tracks to resemble logged forest values in this size class. Although basal area and stem density did not differ between edge and forest plots, this does not necessarily imply more vigorous tree growth along edges because

21

we were not able to distinguish those individuals that might have survived road construction. We speculate that recovery of species richness in road tracks may even take a longer time period than structural recovery. Although dispersal limitation from adjacent forest seems unimportant because our study roads are relatively narrow (not wider than 4 m), new plant colonists may face unfavorable site conditions in old road tracks such as soil compaction and competitive effects from a few but very abundant invaders. In particular, common light-demanding tree species found in both road tracks and edges in our study are, perhaps with the exception of Cecropia, usually long-lived (e.g.,Apeiba, Casearia, Goetbahia,Jkcarad, Luetia, Strypbnodendmn, bcbysia; see Appendix), and therefore may dominate the overstory for several decades as observed in secondary forest stands within the study area (Finegan 1992; Werner 1984; M. Guariguata, pers. obs.). In Malaysia, reports of single-tree species dominance in very old logging roads are not uncommon (e.g.,Meijer 1970). Furthermore, tree ferns, which dominated the track plots in two of the four study roads, are generally tolerant of low fertility substrates (they colonize landslide scars; Guariguata 1990), cast a deep shade, and are also thought to be long-lived (e.g., Waker & Aplet 1994). Finally, the dominance of shrub species observed in two study roads could also interfere with tree seedling establishment (e.g., P u a & Canham 1992, Hill et al. 1995). In our case, guidelines to restore abandoned logging roads could be targeted at first, in reducing above and belowground competition of road track dominants in order to enhance the establishment and survival of other plant species. To condude, we hypothesize that old logging roads serve as long and narrow corridors with relatively uniform and long-lasting floristic and structural characteristics that may confer them particular ecological roles in selectively logged forests. For example, the high density of bird-dispersed shrub species found along road tracks could influence the population dynamics of forest birds. Changes in diversity of the avian community were still apparent 10 yr after logging with respect to unlogged forest patches in French Guiana. There, increased abundance of generalist, frugivore-insectivore bird species along logging roads and large felling gaps seemed to occur at the expense of mature-forest specialists (Thiollay 1992). In addition, the high perimeter-to-area ratios of these roads may broaden the seed shadows of those light-demanding tree and shrub species established along tracks and edges, much more than as scattered, tree-fall gap invaders.

22


Such a potential augmentation of soil seed densities could shift hture floristic composition and ultimately modif) forest tree dynamics after another logging operation.

ACKNOWLEDGMENTS We thank M. Molina, R. Ostertag, R. Rheingans, and 0. Vargas for help in the field, and M. V. Castro for

map information. Access to Finca Kelady was granted by the Centro Cientlfico Tropical, Costa Rica. Logistics at La Selva Biological Station were provided by the Organization for Tropical Studies. Financial support was provided by NSF grant DEB-9208031 and by CIFOR. S. Brown, D. B. Clark, B. Finegan, M. Pinard, J. Putz, S. Stanley, and an anonymous reviewer, made useful suggestions for improvement on earlier drafts of the manuscript.

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23

JONKERS, W. B. J. 1987. Vegetation structure, logging damage and silviculture in a tropical rain forest in Suriname. Agricultural University, Wageningen, The Netherlands. JUSOFF,K., AND N. M. MAJID.1992. An analysis of soil disturbance from logging operation in a hill forest of Peninsular Malaysia. For. Ecol. Manage. 47: 323-333. KOPPELMAN, R. 1990. Damage caused by selective logging in a neotropical rain forest. Thesis, Wageningen Agricultural University, The Netherlands. LEVEY, D. J. 1988. Spatial and temporal variation in Costa Rican fruit and fruit-eating bird abundance. Ecol. Monogr. 58: 251-269. LOISELLE, B. A., AND J. G. BLAKE.1990. Diets of understory fruit-eating birds in Costa Ria. Studies in Avian Biology 13: 91-103. MALMER, A., AND H. GRIP. 1990. Soil disturbance and loss of infiltrability caused by mechanized and manual extraction of tropical rainforest in Sabah, Malaysia. For. Ecol. Manage. 38: 1-12. W. 1970. Regeneration of tropical lowland forest in Sabah, Malaysia, forty years after logging. Malays. For. MEIJER, 33: 204-229. NICHOLSON, D. I. 1958. An analysis of logging damage in tropical rain forest in North Borneo. Malays. For. 21: 235-245. NUEVOSRECURSOSFORESTALES. 1989. Forest Management Plan. Kelady Farm, Pueblo Nuevo, Sarapiqui. San Jose, Costa Rica. PAGE,C. N. 1979. Experimental aspects of fern ecology. In A. F. Dyer (Ed.). The experimental biology of ferns, pp. 552-589. Academic Press, Orlando, Florida. PIERCE, S. M. 1992. La Selva Biological Station history: colonization/land useldeforestation of Sarapiqui, Costa Ria. Thesis, Colorado State University, Fort Collins, Colorado. PINARD, M., B. HOWLETT, AND D. DAVIDSON. 1996. Site conditions limit pioneer tree recruitment after logging of Dipterocarp forests in Sabah. Biotropica 28: 2-12. PUTZ,F. E. 1983. Treefall pits and mounds, buried seeds, and the importance of soil disturbance to pioneer tree species on Barro Colorado Island, Panaml. Ecology 64: 1069-1074. , AND C. D. CANHAM.1992. Mechanisms of arrested succession in shrublands: root and shoot competition between shrubs and tree seedlings. For. Ecol. Manage. 49: 267-275. QUIR~S, D., AND B. FINEGAN. 1994. Manejo sustentable de un bosque natural tropical en Costa Rica. Informe Tkcnico No. 225. Colecci6n Silvicultura y Manejo de Bosques Naturales. CATIE, Turrialba, Costa Rica. R. L. JR., l? PAABY, J. C. LUVALL, AND E. PHILLIPS. 1994. Climate, geomorphology, and aquatic systems. In SANFORD, L. A. McDade, K. S. Bawa, H. A. Hespenheide, and G. S. Hartshorn (Eds.). La Selva. Ecology and natural history of a neotropical rain forest, pp. 19-33. University of Chicago Press, Chicago, Illinois. SOKAL, R R., AND F. J. ROHLF.1981. Biometry. W. H. Freeman, New York. STANDLEY, l? C. 1937. Flora of Costa Rica. Field Museum of Natural History, Botanical Series. Publication No. 392, Chicago, Illinois. SYSTAT. 1992. Statistics, version 5.2 edition. Evanston, Illinois. THIOLIAY, J-M. 1992. Influence of selective logging on bird species diversity in a Guianan rain forest. Conservation Biology 6: 47-63. UHL,C., AND I. C. G. VIEIRA.1989. Ecological impacts of selective logging in the Brazilian Amazon: a case study from the Paragominas region of the state of Pad. Biotropica 21: 98-106. , C. JORDAN, K. CLARK,H. CLARK,AND R. HERRERA.1982. Ecosystem recovery in Amazon caatinga forest after cutting, cutting and burning, and bulldozer clearing treatments. Oikos 38: 313-320. 1985. Posibles efectos del microclima de 10s claros de la selva sobre VAZQUEZ-YANES, C., AND A. OROZCO-SEGOVIA. la germinaci6n de tres especies de irboles pioneros: Cecropia obtwi$lia, Heliocarpw hnnell-smithii, y Piper aurimm. In A. Gbma-Pompa and S. Del Am0 R. (Eds.). Investigaciones sobre la regeneracibn de selvas altas en Veracruz, Mtxico, pp. 241-253. Editorial Alhambra, Mtxico. VERISSIMO, A., I? BARRETO, M. MATTOS, R. TARIFA, AND C. UHL. 1992. Logging impacts and prospects for sustainable forest management in an old Amazonian frontier: the case of Paragominas. For. Ecol. Manage. 55: 169-199. WALKER, L. R., AND G. H. APLET. 1994. Growth and fertilization responses of Hawaiian tree ferns. Biotropica 26: 378-383. WERNER, l? 1984. La reconstitution de la f6ret tropicale humide au Costa Rica: analyse de croissance et dynamique de la vtgttation. Dissertation, Universid de Lausanne, Switzerland. WILLIAMS-LINERA, G. 1990. Origin and early development of forest edge vegetation in Panaml. Biotropica 22: 235241. WYATT-SMITH, J., AND E. C. FOENANDER. 1962. Damage to regeneration as a result of logging. Malays. For. 25: 40-44. YOUNG,K. R. 1985. Deeply buried seeds in a tropical wet forest in Costa Rica. Biotropica 17: 336-338.

u.

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C

C

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Canopy/subcanopy tree saplings Plot location Track

Edge

Forest

5 cm < DBH 5 2 0 cm Plot location

Number ofcanopylsubcanopy tree saplings (items = I m tall and 55 em DBH) and o f f i e standing woody stems (>5 em DBH and 520 em DBH; includingpalms), and tbeir presence (mngefiom one to four sites; in parentheses) sampled in plots located in track and edges offour abandoned logging r o d and aajacent loggedforest in tbe Caribbean lowland o f Costa Rica. Commercial status (C)f;.m Finegan (1992). Quirds and Finegan (1994) and unpublished informationfiom CXTIE, Costa Rica. Rejkence vouchers fin bmcketsJ at tbe Costa Ruan National Herbarium correqond to col&aiOns around tbe study area.

Palmae E u t q e macrospadk Oersted [M. Grayum & G. Herrera 78131 Iriartea <oa&a Ruiz & Pav6n 0. Morales et al. 11151 Soeratea mbo& (Mart.). H. Wendl. Morales et al. 11161 We&a georgi? H. Wend. ex Burret Morales 15011 Anacardiaceae Tapirira guianmis Aublet [Hammel 173221 Annonaceae Anaxagorea cruss@ta& Hemsley [R Rueda et al. 13901 Cuatteria amrginosa Standey [G. Schatz & M. Grayum 6501 C.dioswo&s Baillon [A. Gentry & R Ortiz 785401 Rollinia pim'm' SafTord [M. Grayum 29411 Xylpia serimpbyfkz Stand. & Williams [B. Hammel & J. Trainer 127641 Apocynaceae Apihspmna spruceanurn Benth. ex Muell. Arg. [B. Hammel et al. 178931 LanneUrapanammis (Woods.) Mark. [B. Hammel & R Robles 167171 Aquifoliaceae I h skutcbii Edwin [B. Hammel & M. Grayum 141241 Araliaceae Dendropanax arboreus (L.) Dec. & Planch. [M. Grayum & B. Hammel 55491 Bignoniaceae jacaranda copaia (Aublet) D. Don [w. D. Stevens 238221 Boraginaceae Cordia bicolor A. DC. [G. Hartshorn 14821 C.dqeri Nowicke Morales et aL 10821 Burseraceae Protium costaricme (Rose)End. [M. Grayum & B. Hammel 155461 P panamme (Rose) I. M. Johnston [B. Jacobs 21481 P pim'm. D. Porter [O. Vargas 3311 Ztragus~panammis(Engl.) Kunm [B. Hammel & G. de Nevers 153341

&pen&.

P

5 n

%

c

(0

5.

c

0

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Continued.

Clusiaceae Culophyffumbrusifiense Cambess. [O. Vargas 1891 Symphoniu globufijra L. F. [A. Chacbn 6201 Vismiapanamensis Duchass. & Walp. [B. Hammel 87991

Combretaceae Tminalia ammonia 0. E Gmelin) Exell [B. Boyle 13571 Elaeocarpaceae Sloanea genicuhta D. Smith [R. Aguilar 1681 Euphorbiaceae Alchornea corturicensis Pax & H o f h . [RWilbur 374741 Conceveibupfeiortemonu J. D. Sm. [B. Hammel 94261 Croton biflbqunur Muell. Arg. [O. Vargas 1611 C. rchiedeunur Schldl. [M. Grayum et uf. 61661 C. smithiunw Croizat [F. Quesada 5401 Rich& dress& Webster [B. Hammel 86891 Flacourtiaceae Cuseariu arbonu (Rich.) Urban [R. Rueda et uf. 13801 C. corymbosa H. B. K. [B. Hammel 105811 Luetiu procera (Poepp.) Eichl. [B. Hammel & J. Trainer 128541

Clethraceae Clrthru hnutu Martens & Galeotti [B. Jacobs 23211

Cecropiaceae Cecropia insignis Liebm. [G. Rivera 13871 Pouroumu bicolor Martius [B. Boyle 14101 I? minor Benoist [A. Gentry & R. Ortiz 786261 Chlorantaceae Hedyormum scubertimum Standl. [R. Wilbur 374601 Chrysobalanaceae Licunk hypoleuca Benth. [C. Alvarado 601 Muranther punamensis (Standl.) Prance & White [D. Acevedo 1131

Appendix.

Track

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Edge

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Continued.

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Mimosoideae Ingu cocleenris Pittier Meave & A. Howe 14201 I. comcunr Kunth ex Willd. [N. Zamora et al. 17851 I. figzfiliu (L.) Willd. ex Benth. [B. Hammel 116621 I. tuiziunu G. Don [G. E. Schaa & B. Bockbrader 10421 I. thibuudiunu DC [R. Rueda et al. 13791 Ingu sp. PenMCkthru murrolobu (Willd.) Kuntze [A. Fernanda 781 Pithecellobiurn e&guns Ducke [N. Zamora 3951 Shyphnodendmn rnirrostuchyurn Poepp. & End. [G. S. Harsthorn 13311 Papilionoideae Andiru inmnis (W. Wright) DC. Folsom 100471 Dusriu rnurropmphylhtu D. Smith) Harms [K. Thomsen 4781 Lonchocutpus penruplzylllur (Poiret) DC. [R Robles 18301 ptrrOratpuc huyerii (Hemsley) [G. S . Hartshorn 17481 Swurtziu simplex (Sw.) Spreng. [R. Rueda 13951

Lecythidaceae Erchwei&ru corturicenris S . Mori [M. Grayum et ul. 61641

Humiriaceae Sucoglottis trikhogynu Cuatr. [D. Acevedo 1151 Lauraceae Licuriu rurupiquenrir Hammel [D. Smith & G. Schaa 12101 Licuriu sp. Nectundru cisrzslfloru Nees [B. Hammel 111681 N . hypolpuca Hammel [B. Hammel 185231 N . kunthiunu (Nees) Kost. [B. Hammel 112263 Ocoteu bubosu C. K. Allen [B. Hammel 115301 0. c m u a (Nees) M a . [O. Vargas 2951 0. hurtrhorniunu Hammel [B. Hammel 106301 0. rneziunu C. K. Allen [w. Burger & K. Swagel 124161

Hernandiaceae Hernundiu didymanthu Donn. Sm. [B. Hammel 116561 H. rtenuru Standl. [B. Hammel 116551

Appendix.

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C C C

C

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Canopylsubcanopy tree saplings Plot location Track

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e

l 5

P

m

h)

Continued.

Mynaceae Eugenia sp. Ochnaceae Cerpehria macrophylIa Seem. [G. S . Hartshorn 22451 Olacaceae Minquartih guianenris Aublet [A. Chac6n 7171

u.

Meliaceae Carapa nicaraguenris C. DC. [G. Herrera 10911 Guurea guidonia (L.) Sleumer [D. Smith 3501 Trichlia reptmtrionalis C. DC. Folsom 99271 Monimiaceae Siparuna guianenris Aublet [D. Acevedo 1691 Moraceae Brosimum guianemir (Aublet) Huber [B. Hammel & J. Trainer 130711 B. lactcscnrr (Moore) Berg [B. Jacobs 20961 Ficus ghucercenr (Liebm.) Miq. [R Aguilar 10031 Naucleopris naga Pittier [O. Vargas 1481 Trophis racemora (L.) Urban [B. Hammel 166901 Myristicaceae Viroh korchnyi Warb. [M. Ballestero 721 K re&a Aublet [G. E. Schaa & B. Bockbrader 10371

u.

Malphigiaceae Byrronima rrirpa A. Juss. [A. Fernanda 891 Malvaceae Hampea a p p d i r u h t a D. Smith) Standl. [O. Vargas 1961 Melastomataceae Conortegia Lviopodn Benth. [B. Hammel 123261 Miconia afinis DC. [N. Zamora 171I] M. multirpicata Naudin [B. Hammel 121901 M. rteumriana Almeda [B. Hammel 111661 Orraea macrophylIa (Benth.) Cogn. [B. Hammel 86191

Appendix.

C

C

C C

C

C

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Continued.

Vochysiaceae Q u a h sp. VorhysiuferrugineuMartius [B. Jacobs 27671 Total number of stems Total number of species

Ulmaceae Ampelorera rnurrorurpu Forero & Gentry [B. Boyle 14381 Violaceae Rinoreu &@zfiru Bartlett [A. Gentry ct al. 784991

Sapindaceae Vouarunuguiunemis Aublet [B. Hammel 185061 Sapotaceae Pouteriu rumpechiunu (Kunth.) Baehni [G. S. Hartshorn 11371 I? reticukztu (Engler) Eyma [K. Thomsen 11401 Pouteriu sp. Simaroubaceae Simuroubu amura Aublet [G. E. Schaa and H. J. Young 9691 Tiliaceae Apeibu rnernbrunureu Spruce ex Benth. [R. L. Wilbur & B. Jacobs 349041 Goetbalriu rneiantbu 0. D. Sm.) Burret [B. Jacobs 29391

Rubiaceae Borojou punamensis Dwyer [O. Vargas 3351 Coussureu hon&mis (Standl.) Taylor & Burger [N.Zamora 17301 C. tukzmunruna Stand. [Q.Jimena 14501 Furumeu purvibructeu Steyerm. [B. Hammel 80521 E stenura Standl. [B. Boyle 13791 Ferdinundusupanurnensis Stand. & Williams [R. Rueda et ul. 13711 Posoqueriu grandzfiru Stand. [B. Hammel 177451 Pyrhotriu ekztu (Sw.) Taylor & Burger [T. McDowel 7131 Wursznuirziu rocrineu (Vahl) Klotzsch [R. Aguilar 1631

Appendix.

42

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59

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58

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Canopylsubcanopy tree saplings Plot location

12

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35

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47

Forest


N

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% i

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fn

F

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