Dendrochronological potential of tropical species in the Peruvian Amazon: An analysis in flooded forests of the southeast

Abstract

Research on growth rings in tropical trees within flooded forests has unveiled the complexity of climate change in these ecosystems. However, there has been limited understanding regarding species and their potential for dendrochronology. This study assessed 20 species from 13 botanical families in a flooded forest in southeastern Peru. Wood samples were collected during the dry season using a non-destructive sampling with motorized drill, alongside botanical samples for identification. Growth ring features were described following the IAWA, at a macroscopic level. Thirteen species showed promise for dendrochronological studies, eight of which were previously undocumented. These findings are pivotal for prioritizing species in future dendrochronological investigations in the Peruvian Amazon.

Full Article

Dendrochronological Potential of Tropical Species in the Peruvian Amazon: An Analysis in Flooded Forests of the Southeast

Miguel A. Ranilla-Huamantuco ,^a,f Ingrid A. Cassana-Huáman ,^b,e John Canales-Ramirez ,^c Javier Navio-Chipa ,^d Kerly J. Macedo-Enriquez ,^d Robert F. Farfan-Huanca ,^d and Leif A. Portal-Cahuana ^b,e,*

Research on growth rings in tropical trees within flooded forests has unveiled the complexity of climate change in these ecosystems. However, there has been limited understanding regarding species and their potential for dendrochronology. This study assessed 20 species from 13 botanical families in a flooded forest in southeastern Peru. Wood samples were collected during the dry season using a non-destructive sampling with motorized drill, alongside botanical samples for identification. Growth ring features were described following the IAWA, at a macroscopic level. Thirteen species showed promise for dendrochronological studies, eight of which were previously undocumented. These findings are pivotal for prioritizing species in future dendrochronological investigations in the Peruvian Amazon.

DOI: 10.15376/biores.20.1.1482-1503

Keywords: Growth rings; Madre de Dios; Peruvian woods; Tropical dendrochronology; Tropical forest; Wood anatomy

Contact information: a: Laboratorio Desconcentrado de Peritaje sede Madre de Dios, Ministerio Público, Puerto Maldonado, Perú; b: Instituto de Investigación, Innovación y Desarrollo para el Sector Agrario y Agroindustrial (IIDAA), Facultad de Ingeniería y Ciencias Agrarias (FICA), Universidad Nacional Toribio Rodríguez de Mendoza de Amazonas (UNTRM), Calle Higos Urco 342 – Ciudad Universitaria, Chachapoyas, 01000, Perú; c: Empresa Agroforestal Orgánica R&H, Puerto Maldonado, Perú; d: Consultor independiente, Puerto Maldonado, Perú; e: Xiloteca Gocta, Escuela Profesional de Ingeniería Forestal, Universidad Nacional Toribio Rodríguez de Mendoza de Amazonas, Perú; f: Universidad Nacional San Antonio Abad del Cusco, Cusco, Perú;*Corresponding author: leif.portal@untrm.edu.pe

GRAPHICAL ABSTRACT

INTRODUCTION

Dendrochronology, an expanding field, has ventured into tropical forests, unveiling intriguing secrets and facing unique challenges. The presence of annual rings in over 20 tropical countries, as evidenced by Worbes (2002), highlights synchronized growth linked to extreme climatic events, such as brief droughts and prolonged floods. This technique has enabled an understanding of the influence of phenomena like El Niño on tree growth and the longevity of broadleaf trees in tropical lowlands. Rozendaal and Zuidema (2011) emphasize the relevance of understanding the growth and ecology of tropical trees to conserve and manage these ecosystems.

Despite the challenges posed by less pronounced changes in seasons, techniques, such as dendrometric measurement, cambial injuries, or carbon dating, have allowed us to comprehend the relationship between climate and tree growth in these regions. Meanwhile, Brienen et al. (2016) reveals that ring formation in the tropics is primarily linked to seasonal variations in rainfall or flooding rather than temperature. Despite the moderate sensitivity of tropical trees to climate, the ring studies offer valuable insights into the effects of climate change on these ecosystems.

Many studies have reinforced the importance of annual growth rings in understanding forest ecology and dynamics, as well as their application in projecting timber extraction and sustainable resource management (Schöngart et al. 2017; Marcelo-Peña et al. 2020). In the specific context of Peru, Portal-Cahuana et al. (2023a) highlight how the development of ring chronologies in tropical trees allows for the reconstruction of the neotropical environmental history. They identify sampling gaps and underscore Peru’s high tree diversity as a natural laboratory to better comprehend the growth and functioning of tropical species in interaction with the climate. This specific research provides a detailed insight into dendrochronology in the Peruvian context, contributing to guiding future dendrochronological studies in this region.

The study of potential species for tropical dendrochronology is crucial for understanding tree growth under diverse climatic conditions. Several researchers have addressed this pertinent area (Brienen et al. 2006; Beltrán and Valencia 2013; Groenendijk et al. 2014; Schöngart et al. 2017; Bauer et al. 2020; Marcelo-Peña et al. 2020). Traditionally, the analysis of growth rings was believed to be feasible only in biomes with marked seasonality, such as temperate forests. However, studies in Peru have revealed the presence of annual rings in various species across altitudinal gradients. These findings debunk the seasonal limitation in the tropics for dendrochronological studies (Marcelo-Peña et al. 2020).

The association between the phylogenetic relationship and the distinctiveness of growth rings, as discussed by Marcelo-Peña et al. (2019), suggests a diversity of responses among deciduous and evergreen species to environmental conditions. Bauer et al. (2020) complement this picture by observing the relationship between leaf phenological patterns and growth rings in subtropical forests, through identifying species with clear anatomical boundaries in their rings. Beltrán and Valencia (2013) delve into the challenges and findings of the anatomical characterization of growth rings in potential species for dendrochronological studies in the Central Selva of Peru. These studies highlight issues, such as difficulty in ring visualization, irregularities, and the presence of parenchyma in bands, emphasizing the importance of understanding variability in cell dimensions to infer the annual formation of rings.

Groenendijk et al. (2014) and other researchers have assessed the potential for applying growth ring analysis in tropical tree species under moist conditions. Despite the lack of seasonal variation in certain tropical forests, distinct boundaries in tree rings were identified, demonstrating the potential for obtaining precise growth data. Collectively, these studies underscore the significance of investigating and understanding potential species for tropical dendrochronology, particularly in the flooded forests of southeastern Peru. The complexity and unique conditions of these ecosystems, characterized by seasonal flooding, highlight the necessity of dendrochronological research in this region. This not only expands knowledge about growth ring formation in diverse tropical conditions but also provides valuable insights for sustainable forest management and understanding tree responses to climate change in these ecosystems. The upland forests exhibit greater species diversity compared to flooded forests (Myster 2015). These forests face annual flooding, raising water levels by over 10 m and submerging seedlings, and trees for up to seven months. This disrupts nutrients, oxygen, and toxins, creating optimal conditions for plant growth, and demanding adaptations (Parolin et al. 2004). Amid current climate changes, understanding the mechanisms of floods and water flows and their impact on the development and alterations of riparian forests becomes essential (Berthelot et al. 2015).

This is one of the first studies assessing the potential of tree species growing in a flooded forest in southeastern Peru. To achieve this, the authors distinguished and characterized the growth rings of 20 tree species. Specifically, the following questions were addressed: (i) How do the growth ring boundaries of 20 tree species growing in a flooded forest differ?; (ii) What are the anatomical characteristics of the growth ring boundaries of 20 tree species in a flooded forest?; (iii) Which tree species show greater potential for dendrochronological studies in this flooded forest? The authors approached these inquiries using 20 tree species from 13 different botanical families.

EXPERIMENTAL

Study Area

The study area focuses on the Low Terrace Forests (LTF) situated along the right bank of the Madre de Dios River in the Madre de Dios Department, Peru. These forests fall under the jurisdiction of the Amazon Producers Association of Camu Camu, known as APAYCNA-MDD, positioned at an altitude of approximately 120 m around coordinates 12°35’26.69″S – 69°18’25.52″W. The sampling sites are located 600 m away from the Madre de Dios River (Fig. 1).

Fig. 1. Location of the study site in the Madre de Dios region, southeastern Peru: A) Terrace Forest (blue circle). The color map illustrates the forest types. B) Red triangles indicate the position of sampled trees. C) The red arrow marked on the tree image indicates the maximum flood level in the area. D) Climate diagram for the period 1990 to 2019 is shown (Walter and Lieth 1960), where darker gray areas represent periods with over 100 mm of precipitation.

The Low Terrace Forests (Btb), also known as floodable forests, undergo annual flooding lasting between 3 to 8 months (Poma 2007). The diversity and floristic composition of tree species in these forests differ and are lower compared to upland forests (Normand et al. 2006; Féret and Asner 2014).

In climatic terms, this region is characterized by a warm, humid, and seasonal climate, with an average annual precipitation ranging between 2200 and 2400 mm, and an average annual temperature of 24.2 °C. Maximum temperatures reach 37.9 °C, while minimum temperatures drop to 11.3 °C (Terborgh and Andresen 1998; Román-Dañobeytia et al. 2015; Best et al. 2021).

Species, Processing, and Analysis of Growth Rings

Twenty tree species from a low terrace forest, belonging to 18 genera and 13 different botanical families, representative of the study area, were selected; detailed information regarding the wood samples is provided in Table 1. Botanical samples were collected, and photographs of leaves, flowers, fruits, trunk, roots, and outer and inner bark were recorded. Subsequently, the samples were preserved and sent to the Forest Herbarium (MOL) at the National Agrarian University La Molina (UNALM) in Lima, Peru, for proper classification and deposition.

Wood samples were collected during the dry season (May to August) using a non-destructive method employing the Stihil BT45 gasoline-powered motorized drill with hollow bits (Fig. 3), measuring 2.5 cm in diameter and adjustable in length to fit the tree diameter, ranging from 60 to 110 cm, collected at 1.30 m in a 90° angle from the tree axis (Marcelo-Peña et al. 2019; Aragão et al. 2022). The wound created on the tree trunk was covered with a protective and wound-healing paste and subsequently sealed with a liquid silicone gun to prevent the entry of insects and pathogens (Portal-Cahuana et al. 2023c).

Fig. 2. In the field: A) Non-destructive collection; B) Sample extraction; C) Fungicide paste; and D) Sealed with silicone

The samples were placed on coded wooden mounts and secured with twine. They were then left at room temperature to air dry at the Xiloteca Gocta (specialized environment) of the National University Toribio Rodríguez de Mendoza de Amazonas. Subsequently, they were affixed to the wooden mounts with the cross-section facing upward and sanded and polished using an 80 to 600 grain/cm² sandpaper sequence (Portal et al. 2021; Roquette et al. 2023b) to aid in the precise visualization of ring growth boundaries (Roquette et al. 2023a). The samples were digitized at 1200 dpi using a scanner with a scale and examined under a stereoscopic microscope at various magnifications (Aragão et al. 2019; Menezes et al. 2022).

Finally, the growth rings of the twenty wood samples (Fig. 3) were described following the IAWA guidelines of (IAWA 1989); including their general and macroscopic descriptions. Additionally, the qualitative information was systematized, and a Principal Component Analysis (PCA) was conducted to distinguish and describe the growth ring boundaries using the PAST software (Hammer, Øyvind, version 1.0, Tromsø, Norway) (Hammer 2001).

RESULTS AND DISCUSSION

General and Macroscopic Description of Woods

A comprehensive study was conducted to provide a general and macroscopic description of 20 types of wood from a flooded Forest of Southeast Peru, as detailed in the accompanying Table 1.

Through meticulous observation and analysis, the distinctive and anatomical features of each wood species have been recorded. Additionally, macrophotographs of the transverse cuts of each species are presented for better visual understanding. Furthermore, a PCA analysis was performed, which provides a visual representation of the similarity between forest species, along with clustering to facilitate the identification and characterization of groups of species with similar anatomical characteristics (Appendix, Supplementary Material).

The findings of the study support the importance of investigating wood anatomy as a crucial tool to address the issue of illegal logging in the Peruvian Amazon, by providing a means to accurately identify tree species and their origins, which can help trace and prevent illegal harvesting practices (Portal-Cahuana et al. 2023c). A detailed understanding of the anatomical characteristics of different wood species allows for better identification and classification of wood, playing a fundamental role in combating the trade of illegally extracted timber.

Furthermore, the implementation of precise and reliable wood identification systems, such as the convolutional neural networks mentioned in the article (Ferreira et al. 2020), facilitates the distinction between legal and illegal timber, thereby strengthening efforts to promote sustainable logging practices and protect valuable forest resources. It is necessary to emphasize the importance of monitoring, incentivizing, and monetizing legal and sustainable wood value chains in the Peruvian Amazon, thus highlighting the ongoing need for studies on wood anatomy to address environmental and socio-economic challenges in the region (Da Cunha Soares 2017).

Table 1. General and Macroscopic Description of 20 Wood Species from Flooded Forests in Southeast Peru

Note: MCR: Manual cutting resistance; VIS: Visibility; APO: Apotracheal; DIA: Diffuse in aggregate; PAR: Paratracheal; VAS: Vasicentric; SCA: Scalariform

Distinguishing the Boundaries of the Growth Ring

The distinction of growth ring boundaries is a relevant aspect of wood anatomy, which aids in the identification of tree species. Among the 20 studied species, varied growth ring patterns were observed: three species (15%) displayed highly distinct growth rings, ten species (50%) showed moderately distinct growth rings, seven species (30%) presented growth rings with low distinctiveness, and in one species (5%), the growth rings were indistinct or absent (Table 2).

Table 2. Characterization of Growth Rings of Twenty Trees from the Madre de Dios Region