Study area

Three areas were selected: one in the indigenous community of San Martín de Amacayacu and the other two in Macedonia. The first area (at 3°46'38"S, 70°18'12"W, on the riverside of the Amacayacu River) has denudation soils, as well as the second one (at 03°53'00"S, 70°11'17"W, on the Amazon River). The third area (at 3°51'21"S, 70°13'19"W), known as Mocagua Island, has alluvial soils (Figure 1).

Figure 1 Location of the indigenous communities in the study area 

Data analysis

The ATLAS.ti 7.0 software served for coding and analyzing the qualitative information from the interviews, and ArcGIS 10.6.1 for the geographic data. First, the sampling points and the observation routes were digitized, and then the area of influence to determine the abundance of the cat's claw species was calculated. This area totaled 25.34 hectares, including the buffer established on the observation routes with a margin of 5 m on each side of the road.

The level of local knowledge of U. tomentosa and U. guianensis botanical aspects was estimated by the percentage frequency. Species distribution and frequency on the different types of landscapes were also determined. A Kruskal-Wallis non-parametric variance test was performed to establish significant differences with a 5% probability for each soil type, for soils in the study areas and soils associated with the species.

Local identification of Uncaria species

Cat's claw commonly names both Uncaria species in these communities, but "garabato" is also used, albeit less commonly. Indigenous populations in the Peruvian Amazon use it also (López, 2006). However, these communities have specific names to identify each species: U. tomentosa, for example, is known as white cat's claw (u«a de gato blanca in

Spanish and michipatü choü in Tikuna language). The local experts described it as a plant with a green vine and a white inner bark, green, ovate leaves, and a slightly curved spine. U. guianensis is locally called red cat's claw (uña de gato roja, michipatü dauü) and it is identified by its reddish inner bark, reddish leaves on the underside, and fully curled spines (Figure 2). Another classification of these species claims that U. guianensis is the "male" and U. tomentosa is the "female".

Figure 2 Morphological identification of leaf, bark, and spine of Uncaria species. A) Uncaria tomentosa; B) Uncaria guianensis 

Three samples from Macedonia identified as a cat's claw belong to another species. Two uña de gato roja samples from Mocagua Island belong to the Machaerium sp. genus (Fabaceae), and an uña de gato blanca belonged to Macfadyena unguis-cati (Bignoniaceae). Although some species reported as cat's claws did not belong to the Uncaria genus, it was evident that the experts are very knowledgeable of the morphological characteristics of the species as 90% of the samples were correctly identified as U. tomentosa and 89% as U. guianensis, which demonstrate locals' expertise in establishing the species location and distribution.

Uncaria species distribution by landscapes

Indigenous communities identified six landscape types where cat's claw species could occur (Table 1). This categorization is based on spatial location, temporal aspects of land use, flooding periods, soil types, vegetation cover, and predominant fauna. According to the degree of intervention and the type of vegetation, cultivated land (chagra - naane in Tikuna language), stubble (rastrojo - íchikü), and primary forest (naimacatüxü) were identified.

The Tikuna also distinguish two divisions in the physical space: the highland areas (dauchitáààné) and the annual flooded areas (tatüànè). Depending on the type of flooding, this second space can be divided into floodplains during the rainy months (várzea, tatúmüànè) and flooded areas during days of prolonged rains (bajial, nibaiü) (^{Montes, 2002}). Field observations showed that U. guianensis distribution and abundance are higher than U. tomentosa, especially in flooded areas. There were 1.62 cat's claws individuals per hectare and 1.06 U. guianensis individuals in high altitudes and floodplains (Figure 3). In contrast, U. tomentosa abundance was 0.43 individuals per hectare, restricted to secondary forests in highlands (Figure 4). This was the only one observed in mature forests with low intervention.

Figure 3 Distribution rate of Uncaria guianensis by landscape type 

Figure 4 Distribution rate of Uncaria tomentosa by landscape 

The highest number of U. guianensis plants was found in San Martín de Amacayacu, i.e., 82% of the individuals of this species (Figure 5). U. tomentosa was more frequent in Macedonia (60%), all in the stubble on highlands (Figure 6). None of these species were found on the Mocagua Island.

Figure 5 Sampling points and observation routes in San Martín de Amacayacu 

Figure 6 Sampling points and observation routes in Macedonia 

Regarding the most frequent species in Uncaria habitats, in flooded areas, Scleria secans (Cyperaceae) and Calathea lutea (Maranthaceae) were found with U. guianensis, and in the highlands, Vismia sp. (Hypericaceae) and Cecropia sp. (Urticaceae). In non-flooded areas habitats, Apeiba membranacea (Malvaceae) and Ormosia sp. (Fabaceae) were frequent next to U. tomentosa (Figure 7).

Figure 7 Percentage frequency of most abundant plant species in Uncaria species’ landscapes. A) Uncaria guianensis; B) Uncaria tomentosa 

Local identification of soils

Local experts identified four common names for three soil classes in which they believe cat's claw species grow (Table 2): Oxisols and Entisols (according to the USDA nomenclature system). "Black color layer" (capa de color negro - wamüànèü) and "compost soil" (suelo abonoso - jomüane) refer to the same kind of soil found in cultivated areas and in dryland stubble. Commonly, soil types receive different names depending on the characteristics they are associated with. The first name is related to the color and the second to the texture. Their properties are described according to their fertility and location in high and flooded areas during the rainy months (várzeas) or those flooded on days of prolonged rain (bajiales).

Table 2 Soil types where Uncaria species grow 

Uncaria species distribution by soils

Uncaria guianensis grows in the two soil types evaluated (Table 3): 68% of the U. guianensis individuals were found in alluvial Entisols and 32% in Oxisols on highlands. U. tomentosa was found only in Oxisols on the highlands. According to the soil physicochemical composition in the study areas, the Uncaria species grow in soils with diverse textural classes (Table 4) categorized as highly (pH less than 4.5) or strongly acidic (maximum pH of 5.5), with low to medium available phosphorus ranging from 5.08 to 15.63 mg/kg and medium to high cation exchange capacity (CEC) from 21.65 to 29.71 cmol(+)/kg.

Table 3 Number of Uncaria individuals by area and soil type 

Table 4 Physicochemical composition of soils identified in Tikuna communities in the study area 

Variables are expressed in mean and standard deviation (SD) in parentheses according to the number of soils collected for each soil type. Texture: F = loam; Ar = clay; FL = silt loam; FAr = clay loam; FArA = sandy clayloam; FArL = silty clay loam; FArL = silty clay loam. pH (1:1 in water); A.I = Exchangeable acidity with KCl in cmol(+) kg-1; S.A.I% = Percentage saturation exchangeable acidity with KCl; C.T% = Percentage total carbón with complete oxidation; P = Phosphorus available by Bray II in mg/kg; C. I.C = Cation exchange capacity with neutral ammonium acetate in cmol(+) kg-1; Ca = Calcium by DTPA in cmol(+) kg-1; Mg = Magnesium by DTPA in cmol(+) kg-1; K = Potassium by DTPA in cmol(+) kg-1; B.T. = Total bases; S.B.% = Percent saturation of bases with neutral ammonium acetate

The statistical results showed a homogeneous physicochemical composition in the corresponding soil types (Table 5). Differences were found in the physicochemical composition of Oxisols and Entisols. The concentration of phosphorus (22.94 mg/kg) and sodium (0.14 cmol(+)/kg) were higher in Entisols. On average, the pH levels in soils where U. guianensis grows were lower than in U. tomentosa.

Table 5 Non-parametric test for physicochemical soil composition 

The variability in soil chemical properties is reflected in the significant differences in pH, sodium and calcium levels, the percentage of aluminum saturation, the base saturation, and the cation exchange concentration. U. tomentosa was found only in Oxisols on drylands with a pH between 3.78 and 5.53, exchangeable aluminum variations ranging from 0.15 to 12.62 cmol(+)/kg, and aluminum saturation percentages from 3.04 to 85.42%. U. guianensis grows especially in acidic soils with a pH ranging from 3.43 to 4.62, exchangeable aluminum levels from 4.66 to 12.36 cmol(+)/kg, and aluminum saturation percentages from 29.44 - 95.18%.

Local landscape identification

The common names for the Uncaria species are associated with the external characteristics of stems, leaves, and spines. For indigenous experts, the most outstanding feature is the shape of the spine, which resembles the anatomical structure of the claw (patü) of some animals: michipatü [michi - cat (Felis catus)], bauepatü [baue - charapa turtle (Podocnemis expansa)] or daupatü [dau - sparrowhawk (Buteo sp.)]. Although there is no clear explanation for the gender differentiation between these species, some local experts make this distinction based on their healing. U. tomentosa is the "female" and U. guianensis is the "male". They consider that "males" have more medicinal uses and effectiveness in healing. The non- Uncaria species identified here have been reported before in other studies in the Amazon region (^{Obregón, 1995}; ^{Domínguez, 1997}). The Machaerium genus, especially Machaerium nyctitans, is more commonly associated with the name "cockspur" (espuela de gallo (^{Bisby et al., 1994})). Macfadyena unguis-cati had previously been reported in Colombia with the name cat's claw and in Perú with bat's claw (^{Gallegos, 2017}).

In the study communities, Uncaria species are well distinguished, but many species are associated with the name cat's claw in the Amazon region. ^{Domínguez (1997}) reported 22 species called cat's claw in Perú belonging to the Bignoniaceae, Caesalpinaceae, Liliaceae, Mimosaseae, Rosaseae, Rutaceae, Sterculeaceae, and Fabaceae families. ^{Beutelspacher & Farrera-Sarmiento (2015}) reported 31 species in México where other families (Cactaceae, Cannabaceae, Loginiaceae, Martyniaceae, Nyctaginaceae, Solanaceae, and Verbenaceae) have been found. The number of botanical families related to this common name is evidence of the confusion in identifying their botanical characteristics. The name is used by local peoples in the Amazon region for plants with similar anatomical structures, especially the presence of the spine (Beutelspacher & Farrera-Sarmiento, 2015). The correct determination of cat's claws is crucial for their medicinal use. ^{Obregón (1995}) points out that misidentification can lead to social and health problems, as some species may be toxic or may not have the pharmacological properties against specific diseases.

Uncaria species distribution by landscapes

San Martín de Amacayacu has more streams than Macedonia, so there may be more floodable areas that favor U. guianensis development and growth in this territory. Although Uncaria species are not cultivated directly in the chagras, usually remnant plants are left as they are considered medicinal. People sometimes preserve the seedlings that have grown spontaneously in the stubble when prepared for new chagras. Likewise, when these cultivation areas are abandoned to let the soil rest, the plant can grow and continue its propagation, as these species have no cultural relevance for the Tikuna people and are considered invasive.

Uncaria species distribution and abundance patterns are similar to ^{Miranda et al. (2003}) reports in the State of Acre, in the Brazilian Amazon, with a higher number of U. guianensis individuals per hectare than U. tomentosa in areas of 200 m.a.s.l. on average. However, U. guianensis abundance in the study area was higher (24.02 individuals per hectare), especially in flooded areas, and its distribution in the southern Colombian Amazon is related to its ability to grow in low areas between 100 and 800 m.a.s.l., near big rivers or second and third order streams. Due to crop rotation in indigenous communities, U. guianensis is commonly found in stubble fields because it usually colonizes the area after planting ceases. Its presence in chagras and stubble fields responds to its ephemeral heliophyte life form. U. guianensis is more susceptible to luminosity levels; as sun rays in open areas reach the soil with medium effectiveness, they promote its development (^{Zevallos-Pollito et al., 2000}).

As for U. tomentosa, some nearby species support for its entanglement and growth in disturbed areas of primary and secondary forests, and its heliophyte life form requires less light consumption to regenerate (^{Zevallos-Pollito et al., 2000}). The abundance of U. tomentosa in the study areas was low compared to those registered by ^{Quinteros (2001}) and Canales-Springett et al. (2003) Ucayali and Huánuco forest reserve areas in the Peruvian Amazon. They found 51 individuals per hectare in undisturbed forests and 900 individuals per hectare in mature disturbed forests.

The Macedonia and San Martín de Amacayacu indigenous communities in the Colombian Amazon have high population densities, which puts additional pressure on the abundance and distribution of the natural populations of Uncaria species. Self-consumption agricultural production plots may have implied high levels of intervention in the territory, especially in secondary forests where many wild species are removed, including cat's claws. This anthropic intervention would explain the differences between this and ^{Quinteros' study (2001}), which was conducted in areas of undisturbed forest.

Local identification of soils

The four soils identified in the communities are Oxisols and Entisols (USDA classification). Although local experts mentioned that muddy soil (alluvial Entisols) favors plant growth, none of the Uncaria species were found in this soil. These soils correspond to the first layer, i.e., the A horizon, at approximately 15 cm. The Tikuna relate these soils directly to the layer that provides the necessary nutrition for plants to grow because the microbial activity is restricted to the first 20 cm of these soils (^{Peña-Venegas et al., 2007}), which is essential for the species to absorb phosphorus and other nutrients for their growth and development.

Uncaria species distribution by soils

Uncaria tomentosa was identified in loam-textured and clay loam soils. According to ^{Quinteros (2001}), the texture does not have a significant effect on the abundance of this species, while ^{Mechán et al. (2007}) have reported that U. tomentosa grows better in clay loam soils in the Aguaytía river basin (Ucayali, Perú), as those soils have greater aeration capacity and water availability, which facilitates the absorption of nutrients. Here, this species was the only one observed in primary and secondary forests, but no relevant differences were observed in the composition of the soil samples.

^{Peña-Venegas & Cardona (2010}) reported a close relationship between highlands successional forests biogeochemical cycles in the southern Colombian Amazon. They found that they tend to be more acidic than those of the Ucayali region studied by ^{Domínguez & Castillo (2007}). In the acidity measurements, aluminum saturation percentages were above 60% in the Colombian Amazon, which can affect the species' growth by decreasing its capacity to absorb water and nutrients.

The abundance of U. tomentosa (0.40 individuals per hectare) is low compared to the values reported by ^{Quinteros (2001}) in the Ucayali region (51 individuals per hectare in undisturbed forests). The author points out that the available phosphorus content (estimated at 3.62 mg/kg) is directly related to the abundance of the species. However, in our study, there was no significant difference in this edaphic variable (5.34 mg kg^-1), so other factors must be responsible. U. guianensis is the cat's claw species that grows in the most acidic soils, with higher exchangeable aluminum levels and saturation percentages ranging from 29.44 to 95.18%. These results support the data reported by ^{Zavala & Zevallos (1996}) in the Peruvian Amazon, where they concluded that U. guianensis grows in more acid soils than U. tomentosa. This species has a greater capacity to adapt to the variability of physicochemical conditions in soils of secondary forests and is less demanding in nutritional terms than U. tomentosa (^{Domínguez, 1997}).

Although the alluvial Entisols in the study areas tend to be less acidic, there were no significant differences concerning the Oxisols. It cannot be said that pH is conditioning Uncaria growth, and other edaphological characteristics should be considered to explain the changes in these species growth, for example, drainage conditions; when these are good, aeration and organic matter mineralization processes are favored, which facilitates the nutrition of various plant species (^{Monsalve et al., 2017}). Oxisols are highly evolved, deep, and well drained soils, while alluvial Entisols are not so well-evolved and tend to have low depth and poor drainage (^{IGAC, 2015}). The distribution of Uncaria species in these soil types coincides with the report of ^{Zevallos-Pollito et al. (2000}) that found U. tomentosa individuals only in well-drained soils, which commonly favor its growth, while U. guianensis was more abundant in poorly drained soils (^{Quevedo, 1995}). More detailed research on the physical, chemical, and biological characteristics of soil types is required to clarify the behavior of Uncaria population distribution.

On the other hand, the physicochemical composition of the soil on Mocagua Island is not a limiting factor for the cat's claw growth. ^{Quevedo (1995}) has documented that the dispersal range of these plants is wide as the wind disperses their filiform seeds. The indigenous communities' establishment of plots for agricultural production reinforces the idea that anthropogenic intervention has influenced the population density of Uncaria species in the study areas.