Forests, Water, and Land Use Change across the Central American Isthmus: Mapping the Evidence Base for Terrestrial Holocene Palaeoenvironmental Proxies

Abstract

An ever-increasing demand for agriculture while conserving biodiversity, maintaining livelihoods, and providing critical ecosystem services is one of the largest challenges for tropical land management across the Central American Isthmus today. Climatic and anthropogenic drivers threaten to cause changes in the forest cover and composition for this region, and therefore, understanding the dynamics of these systems and their variability across space and through time is important for discerning current and future responses. Such information is of value especially for risk mitigation, planning, and conservation purposes. The understanding of the forests, water, and land use for this region through time is currently limited, yet it is essential for understanding current patterns of change, particularly with reference to: (i) forest fragmentation; (ii) water availability; and (iii) land management. Through the examination of biotic (e.g., pollen, diatoms, and Sporormiella) and abiotic (e.g., δ 18O, CaCO3, and magnetic susceptibility) proxies, extracted from environmental archives, evidence for longer-term environmental changes can be inferred and linked to drivers of change including climate, burning, and human activities. Proxy environmental data from terrestrial depositional archives across the Central American Isthmus were identified and mapped following best practice for systematic evidence synthesis. Results from the evidence base were summarised to show the spatial and temporal extent of the published datasets. A total of 12,474 articles were identified by a comprehensive search in three major bibliographic databases. From these, 425 articles were assessed for relevance at full-text, and 149 fully met inclusion criteria for the review. These articles yielded 648 proxy records in 167 study sites that were mapped on an interactive map with filters to allow full exploration of the evidence base. Just under half of the studies were published in the last decade. Most studies extracted their data from lake sediments, with a focus on moist tropical forests in lowland sites in Guatemala, Belize, and Mexico. The largest data gaps in the evidence base are Honduras, Nicaragua, Panama, and El Salvador. There are also significant evidence gaps for dry tropical forests, coniferous forests, mangroves, and grasslands. Most of the studies assessed had methodological or presentational limitations that make future meta-analysis difficult and significantly affect the ability to draw conclusions that are helpful for future decision-making. A degree of standardisation, transparency, and repeatability in reporting would be beneficial to harness the findings of the existing evidence base and to shape future research in this geographical area. The systematic map of the evidence base highlights six key review topic areas that could be targeted, if the raw data could be obtained, including: (i) dating uncertainty and standardising reporting; (ii) land use change across space and time; (iii) dispersal pathways of agriculture; (iv) the role and impacts of fire and burning; (v) changes in hydro-climate, water availability, and the risk of tropical storms; and (vi) forest resilience and recovery.

Biophysical and Biocultural Upheavals in Mesoamerica, a Conservation Perspective: Mountains, Maize-Milpa, and Globalization

“…Many plants, including maize, squash, and beans, were poly-cultivated, as revealed by palaeoecological studies in Joya de Cerén, Salvador (Slotten et al, 2020). Still, more studies and multiple approaches are needed to provide accurate quantitative assessments of such impacts in Mesoamerica (Harvey et al, 2021a) and to understand the complex biocultural interactions that caused the rise and decline of pre-Columbian human settlements (Castanet et al, 2022).…”

The Value of Systematic Evidence Synthesis in Forestry, Land Use and Development to Improve Research, Decision-Making and Practice

“…Harvey et al [14] introduce the first use of a systematic evidence synthesis in forest palaeo-environmental studies. The map records published palaeo-ecological proxies for regional environmental variables such as charcoal, diatoms, and phytoliths.…”

Four millennia of geomorphic change and human settlement in the lower Usumacinta–Grijalva River Basin, Mexico

“…Understanding long-term water resource challenges and ancient societal interactions provides a range of ways societies responded to hydrological changes. These past responses can also help us understand how current societies can respond and mitigate future events such as a recent study of Holocene environmental change of the Central American Isthmus (Harvey et al, 2021). In this sense, we study here how long-term water resource challenges affected the ancient Maya in the Usumacinta River Delta.…”