Spiny Forest Heterogeneity: Implications for Regeneration and its Detection Catherine Reuter Advisor: Jules Ramangalahy Academic Director: Jim Hansen Spring 2009 1 Acknowledgements I would like to thank Barry Ferguson for helping me originate the idea for this project and for innumerable resources from compasses to aerial maps. I would also like to thank Christian, translator and invaluable field assistant, without whose innovative thinking and possibly photographic memory this project would not of succeeded. 2 Table of Contents Section Page 88 Acknowledgements ________________________________________________ 2 Abstract __________________________________________________________ 4 Introduction _______________________________________________________ 5 Methods __________________________________________________________ 7 Results ___________________________________________________________ 12 Discussion ________________________________________________________ 17 Conclusion ________________________________________________________ 26 Appendix 1: Comprehensive Species List ________________________________ 27 Appendix 2: FTM 1954 Map of Forest Cover _____________________________ 30 Sources Cited _______________________________________________________ 31 3 ABSTRACT This study sought to verify claims made in a recently published paper by Thomas Elmqvist that certain portions of Madagascar’s spiny forest are rapidly regenerating. The study took place in the forest around the village of Manavy located in Central Antandroy, where historical and current images of the land cover do not collaborate Elmqvist’s conclusions. Using maps derived from remote sensed images of the area, quadrats were established within Elmqvist’s ‘regenerating’ area. Within these sites detailed vegetative analyses of species composition and regenerative process were performed as well as qualitative assessment of disturbance level. The results of this study indicate that density of plots as ascertained from remote sensed images did not correspond level of perturbation. The vegetative surveys showed extreme heterogeneity in the forest due to both natural and human causes, however, attributing this heterogeneity to any specific factor proved difficult. In light of these findings, many of Elmqvist’s methods appear inappropriate and his finally interpretation of the landscape as undergoing extensive regeneration unlikely. Future study that sought to untangle the web of human and natural forces informing forest quality is necessary before a statement about the regenerative capacity of the forest can be made. 4 INTRODUCTION Scientists and conservationists have identified Madagascar as one of the world’s priority Biodiversity hotspots (8). This categorization has its basis in the combined threatened nature of Madagascar’s natural resources and their extreme diversity and uniqueness. Madagascar boasts an extreme diversity of “ecological communities and associated flora” (4), remarkable in its variety considering the size of the island (8). Estimates of species endemism reach as high as 83% for plants and in many cases still higher for animals (8). No where is this diversity more apparent than in the southern spiny forests of Madagascar’s Tandroy region, home to some of the jewels of Madagascar’s unparalleled evolutionary history. 95% of the plants species of the southern dry forests are endemic and 48% of the genera (2). Its animal diversity though less varied presents equally fascinating endemics with the notable Verreaux’s sifaka and the radiated tortoise. Despite its special nature, government authorities have historically neglected the region such that as of 1995 less than 3.2% of the spiny forest is formally protected (3). Luckily, local traditions have preserved many segments of forest, limiting resource use in areas of spiritual significance (2). However, this local protection can not combat the human pressures on forest resources, which consist primarily of the collection of firewood, charcoal, and construction materials for urban areas (5). Though deforestation rates remain contested, it is generally believed that dry forest cover has been in decline since the 1970s (2). Sadly, the prognosis for recovery appears equally bleak, with many experts believing the spiny forest, like many arid ecosystems, has little potential for large-scale natural regeneration due to the region’s harsh climate and related slow growth rate of many of its endemic plants. However, a recent paper presented in PLOS by the Swedish researcher Thomas Elmqvist and a team of Malagasy scientists has placed this common belief in question, asserting that the spiny forest is 5 indeed capable of rapid natural regeneration (2). In their 2007 paper, Elmqvist investigated changes in forest cover and their institutional context in the dry forests of southern Madagascar. Using remote sensed images spanning two decades, they tracked the presence or absence of forest looking at three patterns: 1) loss of forest cover, 2) increase in forest cover, 3) and stable forest cover. As part of his conclusions from this study, Elmqvist emphasized the capacity of the spiny forest for “large-scale spontaneous regeneration dominated by native endemic species” and identified specific regions where such regeneration had occurred (Figure 1, 2). He presents a scenario in which extensive forest cover, noted on aerial maps of the region predating his images, was completely clear cut and has since regenerated. This assessment of regeneration potential resulted in a flurry of positive media which asserted that the spiny forest was recovering from human degradation (5, 6) Unfortunately, “inferring historical patterns of forest cover is always likely to be subject to a high degree of error” (9) and recent Google Earth images showing patterns of heavy vegetative cover similar to those in the 1950s makes Elmqvist regenerative scenario seem improbable (Appendix 2). Furthermore, questions surround the appropriateness of the methods Elmqvist used to establish this scenario, satellite remote sensing of forest regeneration assessment being uncommon (9). This study therefore sought to verify Elmqvist’s claims and determine the true state of the forests of Central Androy between the towns Antanimora, Ambohimalaza, and Ifotaka. By exploring the authenticity and process of forest composition and structure, this study investigated the present state of the forests of Central Tandroy, their potential for regeneration, and how Elmqvist may have reached his conclusions of increasing forest cover. 6 Figure 1. “Time-series analysis of changes in forest cover based on satellite images (dry season synoptic views from 25 June 1984 (Landsat 5 TM), 15 April 1993 (Landsat TM) and 28 May 2000 (Landsat 7 ETM+) from Androy, southern Madagascar. Three patterns of forest cover change between 1984 and 2000 is presented: 1) red-reddish areas-loss of forest, 2) blue-bluish areas–increase offorest cover and 3) green areas–stable forest. doi:10.1371/journal.pone.0000402.g005”; (Figure 5, Elmqvist et al. 2007) METHODS Study Area This study took place in the forests surrounding the fokotany of Manavy, a small community of several small scattered villages. It is located just east of Route Nationale 13 between the town of Antanimora to the north and the urban center of Ambovombe to the south. This site lies within reach of several patches of forest denominated as regenerating by Elmqvist (Figure 2). As is the subject of this paper, the landscape is a mosaic of fields and forests in a several stages of degradation and regrowth. Naturally, the area supports heterogeneous forest characterized by assorted endemic species in the Didieraceae family and of Euphorbia. The canopy typically ranges between 4-5m with protruding Dideraceae reaching 15m in some instances. The remaining vegetation consists of plants well adapted to the region’s harsh semi-arid climate, displaying assorted water-saving modifications 7 such as minimized leaves, conversion of leaves to spine and photosynthetic stems as well as the ability to store water in trunks and roots (8). Such modifications are necessary in an area that receives on average less than 500 mm of rain per year and where drought is a constant threat (2). In these forests the emblematic inhabitants of the south, radiated tortoises and lemurs such as Verreaux’s sifaka and ring-tailed maki, abound. Figure 2. This map segment is taken from Elmqvist map of changing forest cover (see Figure 1). The rectangle delineates the study area in relation to Elmqvist’s The same semi-arid conditions that have shaped the natural environment play an important role in the lives of the local human population. Villagers engage primarily in agriculture, cultivating corn, manioc, and sweet potatoes as well as raising livestock. The expansion of agricultural fields necessitates the slash and burn of forest cover and animals are grazed directly in the forest. In times of famine, the population heavily supplements their livelihoods via commercial harvest of forest resources, an option facilitated by the fokotany’s proximity to the national route and nearby urban areas. The villagers of Manavy exploit principally two endemic tree species: ‘katrafay’ (Cedrelopsis greveii) the preferred firewood and ‘fantiolotse’ (Alluaudia procera) used in the construction of boards. In the past few months, Manavy underwent a “transfer de gestion” facilitated by ONG Sokake in the early 2000s. This process placed responsibility for the management of local forests directly into