Remnant Trees in Enrichment Planted Gaps in Quintana Roo, Mexico: Reasons for Retention and Effects on Seedlings

Angélica Navarro-Martínez,Alfredo Álvarez-Ugalde,Francis Putz,Ana Iuit-Jiménez,Carolina Vargas-Godínez,Edward Ellis,Yavé Carrera-Quirino,Pascual Blanco-Reyes,Peter Ellis,Irving Hernández-Gómez,Sebastian Palmas,Samaria Armenta-Montero

doi:10.3390/f8080272

Abstract

Natural forest management in the tropics is often impeded by scarcity of advanced regeneration of commercial species. To supplement natural regeneration in a forest managed by a community in the Selva Maya of Mexico, nursery-grown Swietenia macrophylla seedlings were planted in multiple-tree felling gaps, known as bosquetes. Remnant trees are often left standing in gaps for cultural and economic reasons or due to their official protected status. We focus on these purposefully retained trees and their impacts on planted seedlings. Sampled bosquetes were 400–1800 m2, of which remnant trees covered a mean of 29%. Seedling height growth rates over the first 18 months after out-planting more than doubled with increased canopy openness from 0.09 m year−1 under medium cover to 0.22 m year−1 in full sun. Liana infestations and shoot tip damage were most frequent on seedlings in the open, but, contrary to our expectations, height growth rates were 0.14 m year−1 faster for liana-infested seedlings than non-infested and did not differ between damaged and undamaged seedlings. Apparently the more rapid height growth of well-illuminated seedlings more than compensated for the effects of lianas or shoot tip damage. Despite the abundance of remnant trees and their negative effects on seedling growth, enrichment planting in bosquetes has potential for community-based natural forest management in the tropics in supplementing natural regeneration of commercial species. One obvious recommendation is to leave fewer remnant trees, especially those of commercial species that are non-merchantable due to stem defects and trees retained for no apparent reason, which together constituted half of the remnant crown cover in the sampled bosquetes. Finally, given the rapid growth of lianas and understory palms in large canopy gaps, at least the most vigorous of the planted seedlings should be tended for at least two years.

Highlights

To sustain timber yields in selectively logged tropical forests, silvicultural treatments are often needed [1,2]
We explore the role and impacts on planted mahogany seedlings of the remnant trees that are allowed to remain standing in enrichment planting gaps
Given that communities are responsible for the management of an estimated 25% of the world’s remaining tropical forests [43], this finding is potentially of substantial importance

Summary

Introduction

To sustain timber yields in selectively logged tropical forests, silvicultural treatments are often needed [1,2]. For intensification of natural forest management by enrichment planting to succeed, the planted seedlings need to thrive, which depends largely on light conditions that are determined by canopy gap size and shape as well as by the heights of nearby trees [9,10]. The word “average” in this definition reflects an aspect of gap biology that seems to have attracted little attention from researchers—the presence of trees that remain standing within gaps. Many of these remnant trees suffered damage when the gaps were created, and some re-sprouted from broken stems, but they are present in many gaps.

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