Edge influence on the microclimate and vegetation of fragments of a north Amazonian forest

https://doi.org/10.1016/j.foreco.2021.119546Get rights and content

Highlights

  • Edge type and distance of edge have an influence on the diversity, composition and forest structure.

  • The edge effect leads to the loss of abundance and richness of ferns in less humid areas.

  • Palm distribution pattern is not associated to edge type but with the floodplains.

  • In forests near pastures temperature is higher and humidity is lower favoring grass species.

  • The rubber plantation (Hevea brasiliensis) has a strong effect on maintaining humidity.

Abstract

There are multiple pressures on Amazon forests due to, anthropic activities such as extensive cattle ranching, logging, and legal and illegal crops. These pressures generate highly fragmented landscapes that leads to an increase in forest edges. Thus, forest vegetation exposed to the surrounding open environment generates a series of direct effects that extend into the interior of the forest. Changes in the microclimate are among the most notable effects, and these can impact the composition and structure of the vegetation and affect the alteration of multiple ecological processes and ecosystem services. To better understand these consequences, we evaluated the distance of the edge influence on the microclimate, the composition of the vegetation, and the forest structure in the northern Amazon. We considered two types of edges according to adjacent cover: grasslands dedicated to extensive cattle ranching and rubber plantations (Hevea brasiliensis (Willd. ex A.Juss.) Müll.Arg.). We recorded significant differences in the composition and abundance of plants of all size categories. We found less richness and dominance of generalist species, that are characteristic of disturbed environments, in the forest sector adjacent to pastures. These edges had also lower humidity and higher temperatures than rubber plantations ones. The distance from the edge to the interior also affected the structure of the vegetation, with a higher density of individuals in the interior of the forest and significant differences in the diameter and height of individuals. We argue that the rubber plantations could be used as a forest management strategy of drought adaptation since it forms a less abrupt border and has a buffer function, keeping higher humidity values and lower temperatures than forest edges adjacent to pastures.

Introduction

Besides the global loss of forests, there is a generalized trend towards more fragmented forests, in which the interior area is reduced. The loss of this interior area can be at least twice as much as the net loss of forests due to deforestation (Riitters et al., 2015). Globally, most of the remaining forest fragments have an area of less than 10 ha and 20% of the interior areas are less than 100 m from the edge, a fact that can reduce biodiversity by up to 75% and alters key ecosystemic functions (Haddad et al., 2015). For this reason, due to combined effects of the forest fragmentation and increased edges, less than a fourth of the current forest cover might be capable of fully satisfying the demands of ecosystem services (Ferraz et al., 2014). Indeed, the loss of ecosystem services has been associated to the extension of edge effects towards the forest interior (Broadbent et al., 2008). These effects generate long-term changes in the structure and function of the interior forest areas (Lindenmayer and Fischer, 2006, Broadbent et al., 2008) and alter ecological processes (Riutta et al., 2012, Finegan et al., 2015). This inward incidence of edge effects is due to the property of the edges that facilitates or inhibits ecological flows and interactions in the landscape (Ries and Sisk, 2010). The variability of ecological responses will depend on the type of edge, understood often as the contrast to adjacent land cover type (López-Barrera, 2004).

The influence of edge effects includes physical effects that are related to disturbances that occur in the soil and vegetation (Harper et al. 2005) and abiotic effects related to microclimatic variations (Sih et al., 2000). Within the microclimatic variations, the most common is a reduction in humidity and an increase in temperature due to greater wind exposure and solar radiation at edges (Sih et al., 2000). These edge derived changes in humidity and air temperature in the forest have a direct impact on ecological processes such as litter decomposition and its regulatory factors (Romero-Torres and Ramírez, 2011), altering, for example, the nutrient cycle (Redding et al., 2003). Alterations in the microclimate also have a direct impact on the distribution of species. Although it is possible that all organisms are affected by small variations in humidity and temperature, some species are more sensitive than others (Baker et al., 2014). Thus, the changes associated with humidity can be indicators of patterns of distribution of biodiversity (Lopez, 2009). In the specific case of vegetation, variations in humidity and temperature significantly influence the composition of species, their distribution (Godefroid et al., 2007, Riutta et al., 2012), and their functional responses (Susan-Tepetlan et al., 2015). In turn, these changes in vegetation alter local environmental conditions, affecting the interaction of species and ecological processes, such as seed dispersal, pollination, growth patterns, survival, and the migration of species (Granados et al., 2014).

If the consequences of microclimatic changes on the diversity and structure of small forest fragments are to be predicted reliably, it is necessary to determine the area of the forest edge that is exposed to these changes and the magnitude of the microclimatic difference in relation to the interior of the unaffected forest (Hofmeister et al., 2019). That is why, although the changes in the forest due to the edges are site-specific, to identify the changes that occur in the microclimate, diversity, density, and abundance of species along the gradient of the edge to the interior of the forest wooded area, is essential for the management of forest ecosystems.

In the case of the tropics, despite recent changes in livestock activity such as intensive production or the establishment of silvopastoral systems, pastures for grazing is still the predominant land use after deforestation (Silva et al., 2021). With the expansion of pastures and to reduce the distance from producing areas, a specific fragmented and homogeneous pattern is often formed (Peng et al., 2016), with forests remnants associated only with the water courses, as in the case of the northeast of the Amazon (Meza-Elizalde and Armenteras, 2018).

In the case of NW Amazonia is common crops such as cocoa (Theobroma cacao L) and rubber (Hevea brasiliensis Mull. Arg.). These species have been promoted as an economically productive strategy for reducing deforestation and environmental degradation (Rice and Greenberg, 2000, Wei et al., 2021), and as an alternative for the substitution of illicit crops (Meza-Elizalde and Armenteras, 2018). This research evaluates the influence of the border on the microclimate and vegetation in Amazonian forest fragments located on the deforestation arc in the Colombian Amazon. We consider two types of adjacent covers that correspond to grasslands and rubber plantations. Our hypothesis is that the influence of the edge effects cause decreases in the humidity content inside the fragment, generating changes in species composition, natural regeneration and the effect is lesser when the forest is adjacent to rubber plantations.

Section snippets

Study site

The study area was located in the deforestation arc of the northern Colombian Amazon, specifically in the municipalities of El Retorno and San Jose del Guaviare in the department of Guaviare (Fig. 1). Historically the area has been affected by changes in land use. A detailed time series for the Guaviare, shows that coca crops were the first use of the land leading to forest fragmentation and the establishment of pastures (Armenteras et al., 2006). Between 2005 and 2010, the main deforestation

Edge influence on the humidityhumidity and temperature

A total of 10,752 temperature and humidity data were recorded (Fig. 2a and b). The temperature model with an AIC of 36,067 shows that there were significant differences in temperature according to distance from the edge to the interior of the forest (p = 0.0277), the time of day (p = <0.0001), the interaction between the type of edge and the time of day (p = 0.0048), and the interaction between the type of edge, the distance from the edge, and the time of day (p = 0.0004). The highest

Edge influence on the variables of humidity and temperature

The edges influence can show positive, negative or mutual responses (López-Barrera, 2004). We found that from the two adjacent covers, the temperature followed the pattern of a soft ecotone effect, with higher values at the edge that decrease towards the interior of the forest. But, the response of humidity differed according to the adjacent cover, with a marked positive ecotone with higher values at the edge when the adjacent cover was rubber; and a matrix effect with an abrupt edge when the

CRediT authorship contribution statement

María Meza Elizalde: Conceptualization, Investigation, Methodology, Data curation, Formal analysis, Writing – original draft, Writing - review & editing, Visualization, Funding acquisition. Dolors Armenteras Pascual: Conceptualization, Investigation, Methodology, Writing - review & editing, Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We thank the Rincón family and ASOPROCAUCHO for allowing us to carry out this research on their premises and open the doors of their homes to us. We also thank to forestry engineers Alejandra Reyes and José Luis Acosta, Katherine Lezama and Dairo Gutiérrez Rincón, for their support in field activities and also Josep Maria Espelta and Fernando Casanoves for their useful guidance and revision of the analysis performed. Thanks to Professor Gilberto Emilio Mahecha and Forest Engineer Jorge Eduardo

Funding

Freezailah Scholarship. Period 2017 - I of the International Tropical Timber Organization (ITTO) for the completion of the International Diploma in Biostatistics at the Tropical Agronomic Research and Teaching Center (CATIE).

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