Implications of Wood Collecting Activities on Invertebrates Diversity of Conservation Areas

Biomass, in the form of deadwood can be described as the end product of series of physiological processes that lead to the deterioration of a piece of wood or the entire tree (Kaarik, 1974; Franklin et al., 1987). The rate at which this occurs depend on the exposure of the tree to various physical and physiological stresses (Savory, 1954; Bader et al, 1987; Jansson & Jansson, 1995). Once dead, the tree or part thereof can be harvested and used as a source of energy, mostly for cooking or heating in the household. While these are common uses of deadwood, what is also apparent is that deadwood supports ecological systems that are crucial for the maintenance of various components of biodiversity (Graham, 1925; Gosz et al., 1972; Ausmus, 1977; Harmon et al., 1993). As a result natural processes and systems of deadwood production which are often well preserved and maintained within the conserved environment (Graham, 1925; Raphael & Morrison, 1987; Harmon et al., 1993) requires that deadwood be regarded as critical part of biodiversity management (Harmon et al., 1993; Bergeron, 2000; Andrzej, 2002; Hagar, 2007). In the past years, the management of deadwood within conservation areas has solely been based on observations that 1) deadwood provides habitat for different species of birds, bats and mammals (Brandlmaier et al., 2004), 2) deadwood serves as a source of food for various organisms (Raphael & White, 1984; Harmon et al., 1993) including the less visible invertebrates, fungi and lichens and that 3) deadwood has a potential of supplementing soil organic nutrient (Hart, 1999) and thus promoting soil fertility. As with the case of standing dead trees (Andrzej, 2002), which are used by different vertebrates, such as birds for nesting sites (Johnston & Odum, 1956; Du Plessis, 1995), fallen dead trees are used by small mammals (Rhoades, 1986), reptiles and various species of invertebrates as mating sites, shelter or sources of food (Hirth, 1959; Harmon 1982). All these observations, combined have increased the value of deadwood as playing a key role in sustaining the efficiency and productivity of the ecological systems within conservation areas. Unfortunately in most parts of the world deadwood still remain the main source of energy and is in great demand for domestic fuel. This is the main cause for concern among conservation agencies (Anderson & Fishwick, 1984; Wall & Reid, 1993; Abbot & Mace, 1999) as it poses a threat to biodiversity that is housed within deadwood (Kavin, 2001). Of considerable importance is that among certain societies dead wood is not only used for energy alone but has some cultural link (Furness, 1979). An example is the Xhosa, Vhenda


Introduction
Biomass, in the form of deadwood can be described as the end product of series of physiological processes that lead to the deterioration of a piece of wood or the entire tree (Käärik, 1974;Franklin et al., 1987). The rate at which this occurs depend on the exposure of the tree to various physical and physiological stresses (Savory, 1954;Bader et al, 1987;Jansson & Jansson, 1995). Once dead, the tree or part thereof can be harvested and used as a source of energy, mostly for cooking or heating in the household. While these are common uses of deadwood, what is also apparent is that deadwood supports ecological systems that are crucial for the maintenance of various components of biodiversity Gosz et al., 1972;Ausmus, 1977;Harmon et al., 1993). As a result natural processes and systems of deadwood production which are often well preserved and maintained within the conserved environment Raphael & Morrison, 1987;Harmon et al., 1993) requires that deadwood be regarded as critical part of biodiversity management (Harmon et al., 1993;Bergeron, 2000;Andrzej, 2002;Hagar, 2007). In the past years, the management of deadwood within conservation areas has solely been based on observations that 1) deadwood provides habitat for different species of birds, bats and mammals (Brandlmaier et al., 2004), 2) deadwood serves as a source of food for various organisms (Raphael & White, 1984;Harmon et al., 1993) including the less visible invertebrates, fungi and lichens and that 3) deadwood has a potential of supplementing soil organic nutrient (Hart, 1999) and thus promoting soil fertility. As with the case of standing dead trees (Andrzej, 2002), which are used by different vertebrates, such as birds for nesting sites (Johnston & Odum, 1956;Du Plessis, 1995), fallen dead trees are used by small mammals (Rhoades, 1986), reptiles and various species of invertebrates as mating sites, shelter or sources of food (Hirth, 1959;Harmon 1982). All these observations, combined have increased the value of deadwood as playing a key role in sustaining the efficiency and productivity of the ecological systems within conservation areas. Unfortunately in most parts of the world deadwood still remain the main source of energy and is in great demand for domestic fuel. This is the main cause for concern among conservation agencies (Anderson & Fishwick, 1984;Wall & Reid, 1993;Abbot & Mace, 1999) as it poses a threat to biodiversity that is housed within deadwood (Kavin, 2001). Of considerable importance is that among certain societies dead wood is not only used for energy alone but has some cultural link (Furness, 1979). An example is the Xhosa, Vhenda and Zulu communities of South Africa where deadwood is specifically collected and used during traditional functions such as weddings, funerals and circumcision ceremonies (Furness, 1979). The combined effect of this has resulted in the decline of the availability of deadwood outside conservation areas (Shackleton, 1993a;Wall & Reid, 1993;Maruzane & Cutler, 2002). This has placed pressure on conservation areas to make this resource available to communities (Anderson & Fishwick, 1984;Bembridge, 1990). With the possible negative effects associated with deadwood harvesting, it is clear that the collection of deadwood from conserved areas might disturb and fragment some ecosystem processes and this could increase species loss and extinction. The debate on deadwood availability outside conservation areas has largely been limited to its shortage as caused by over-harvesting and demand (Arnold, 1978;Anderson & Fishwick, 1984;Bembridge & Tarlton, 1990;Shackleton, 1993b) with its exploitation being reported as leading to habitat destruction for wood-inhabiting organisms and deforestation (Mainguet, 1991). Little attention has been given to the ecological effects of deadwood harvesting or the role of deadwood in maintaining ecological integrity and biodiversity (Banerjee, 1967;Bilby, 1981;Bilby & Likens, 1980) outside conservation areas. This oversight is despite the well-recognized fact that the presence of wood-inhabiting organisms in deadwood attracts other organisms that are either predators of these organisms or their larvae (Fager, 1968;Harmon et al., 1993). This relationship has long been recognized and appreciated by entomologists and has generated some interest in research and management of biodiversity associated with deadwood Fager, 1968;Käärik, 1974;Deyrup, 1981;Araya, 1993;Bennett et al., 1994;Lachat et al., 2006). Such plant-animal interactions has been identified as one of the dominant biotic interactions Farrell et al., 1992) that sustains much of the terrestrial faunal diversity (Samways, 1993) through the support of ecological interactions that exist among terrestrial living organisms. Thus, activities such as collection of deadwood for energy from conservation areas may indirectly affect the maintenance of these interactions, and hence the conservation of the diversity of organisms that are associated with deadwood (Gandar, 1984;Anderson & Fishwick, 1984). To highlight some of these threats and their possible effects on biodiversity, invertebrate diversity associated with deadwood was determined through an experimental study that was conducted in Vaalbos National Park (VNP, South Africa). The investigation addressed the hypothesis that the collection of deadwood for energy from conservation areas does not only endanger trees but also other elements of biodiversity. These may include those invertebrates whose existence is largely dependent on the presence of deadwood. In investigating this, it was hypothesized that the invertebrate diversity associated with deadwood correlate with the increasing wood size, and hence the value of the material as both fuelwood and in supporting biodiversity.

Materials and methods
Invertebrates in deadwood were harvested using the following procedure. Deadwood from a range of unidentified plant species of the park was randomly collected from three selected sites in the park, simulating the method of h a r v e s t i n g d e a d w o o d b y c o m m u n i t i e s a n d transported to a research station where the invertebrates were extracted from the deadwood. As wood collectors prefer wood size that can be easily transported by hand (Bembridge & Tarlton, 1990), three deadwood sizes (i.e. Finger size (FS) (<2 cm in diameter), Arm-size (AS) (2 -5 cm diameter), and Leg-size (LS) (> 5 cm diameter but less than 10 cm) were identified www.intechopen.com and chosen for the study. These were also regarded as representing wood pieces that break and burn easily (Bembridge & Tarlton, 1990). Collected deadwood was cut into 30 cm long pieces, weighed and loaded into 18 modified 100-litre drums that were divided into replicates of each wood size. The drums were modified such that the bottom one third of the drum was separated from the upper portion by a 38-mm mesh grid supported by iron bars. The lower separated portion was used as pitfall trap in which emerging invertebrates were collected. Each pitfall trap was filled with 5 litres of water that prevented invertebrates from leaving the trap. Twelve of the drums served as an "illuminated" insect harvest, with each wood size class having four replicates. Drums were illuminated by 60 watt white light bulbs that were suspended 60 cm above the wood layer. This encouraged the mobility of the invertebrates to make them leave the wood. The lights were connected to a photo-sensor switch, which followed a reserve diurnal cycle to ensure 24-hour lighting so as to maintain light throughout the period of the experiment. The six remaining drums (two replicates for each wood size class) were left without light and represented the uncontrolled condition without apparently induced invertebrate mobility. The top of each drum was covered with black cloth that ensured that sunlight did not interfere with the harvest process and that insects did not escape from or enter the drums from the outside. All drums were placed in the shade to reduce temperature variations during the experiment. The invertebrate harvest was conducted over two time periods, both during the summer months and both running for a period of nine months. These periods were selected because the activity of invertebrates is recognizably high during this period of the year (Davies, 1994). Invertebrates were collected from the bases of the drums once a week, preserved in 70% alcohol and identified to family level (Davies, 1994). The families were categorized into the following functional guilds: obligate wood dwellers (OWD), semi-obligate wood dwellers (SOWD) and associates of deadwood (AODW), depending on their level of association with deadwood. After the experiment was completed, the deadwood was broken down with a chisel and hammer to determine whether any invertebrates remained within the wood. Invertebrates collected through this method were added to the sample of emerged invertebrates.

Statistical analysis
Data collected from the two seasons in which the experiment was conducted and from illuminated and non-illuminated drums were first tested for statistical differences. Where there was no statistical differences, data were pooled and analyzed together. Where there was a statistical difference, data were analyzed separately (e.g. numbers of invertebrates collected from illuminated drums with LS wood). The differences between numbers of invertebrates collected from illuminated and non-illuminated drums were compared statistically using one-way Kruskal-Wallis Analysis of Variance (Zar, 1984). Differences in a numbers of invertebrates and the larvae collected from three wood classes were also compared statistically using a one-way Kruskal-Wallis Analysis of Variance (Zar, 1984).

Results
In analysing and interpreting the results, it was considered that environmental factors, such as humidity, temperature and weather might have played a role in influencing the www.intechopen.com emergence of invertebrates from the wood. However, the fact that the drums were housed in the same conditions negated this concern. While attempts were made to identify all collected invertebrates into families some such as Pseudoscorpionida and Lepidoptera were identified to Order level only, this was due to a limited ability available to identify these invertebrates further. The sequence of emergence of invertebrates from deadwood was such that the buprestids and cyrambecids were the first to emerge, while groups such as clerids and halictids (Table  1) emerged at the later stages of the experiments. One thousand seven hundred and fifty invertebrates were collected (Table 2). For two of the wood size classes (FS (H = 3.71, df = 5, p>0.05) and AS (H = 4.56, df = 5, p > 0.05) there was no statistically significant difference between the invertebrates collected from illuminated and non-illuminated drums ( Table 2). For the leg size wood class, the illuminated drums yielded a significantly higher (H = 23.24, df = 5, p < 0.001) number of invertebrates than drums without light (Table 2). An average of 1.5 ± 2.3 (Average ± SD) invertebrates per kilogram of FS wood, 2.5 ± 3.1 per kilogram of AS wood and 4.5 ± 5.6 per kilogram of LS wood ( Figure 1) were harvested from each size class of wood. This was interpreted as indicating that a head-load of deadwood (Bembridge & Tarlton, 1990, Shackleton, 1993b with an approximate mass of 20 kg of finger-size wood could contain an average of 30 ± 1.4 invertebrates, a head-load of arm-size wood could contain an average of 50 ± 2.7 invertebrates and a head-load of leg-size wood 90 ± 1.5 invertebrates of a variety of guilds, families and species.

Invertebrate guilds associated with deadwoods
The collected invertebrate fell into three broad functional guilds i.e. obligate wood dwellers (OWD), semi obligate wood dwellers (SOWD) and associate of dead woods (AODW) ( Table  2). This classification was based on taxonomic categorization; feeding behavior and the maximum time an invertebrate was found to spend in deadwood (Scholtz & Holm, 1996). Nine of the identified families i.e. 26 % of the total numbers of families collected were identified as obligate wood dwellers (OWD) (Appendix). These invertebrates spend their entire lifecycle in deadwood. They inhabit the tree while it is still alive, with certain stages of their development (larval stage) being completed in dead wood (Harman et al., 1993). This group has a considerable pathological effect on trees and influence tree mortality (Harmon et al., 1993). The Halictidae (46.5 % of the total number of OWD collected), Buprestidae (25.1 %) and Cerambycidae (22.9 %) dominated this group. The Pseudoscorpionidae (Order) and 14 (40 % of the total number of families collected) other identified families (Appendix) were classified as a group that depends on deadwood for only certain of their lives (Table 1). This group was referred to as semi-obligate wood dwellers (SOWD) and spends a portion of their lives in deadwood. They are either predators of OWD invertebrates (e.g. Histeridae), colonize holes excavated by the larvae of OWD group (e.g Carabidae) or are parasitoids (e.g. Chalcididae and Gasteruptidae) of these larvae. The dominant families that represented this group were Formicidae (20.4 %) of the total number of SOWD collected), Histeridae (15.6 %) and Lepismatidae (14.7 %). Lepidoptera (Order) and 13 other families (33 % of the total number of families collected) were identified as those invertebrates that use deadwood either for hunting, hiding or feeding on fungi that grow on the deadwood. This group was referred to as associates of deadwood (AODW) (Scholtz & Holm, 1996) (Appendix). These invertebrates can survive and complete their life cycle in the absence of deadwood (Scholtz & Holm, 1996) www.intechopen.com (Appendix). Megachilidae (21.2 %), Galleridae (11.9 %) and Tenebrionidae (11.0 %) represented this category.   Table 2. Numbers (per kg) of invertebrates collected from the studied wood sizes. (FS = finger size; AS = arm size; LS = leg size; OWD = Obligate wood dwellers, SOWD = Semiobligate wood dwellers, AODW = Associate of deadwood).

Deadwood diameter and invertebrate assemblage
Wood with larger diameter (AS and LS classes) were found to have a significantly higher number (H = 34.3, df = 2, p < 0.001) of invertebrates than those with a smaller diameter (finger size (<2cm) (Figure 1, Table 2). This was understood to be due to the size of the niche provided by this wood class. Both arm-(AS) and leg-size (LS) wood classes had the higher numbers of the size-specific invertebrates (invertebrates limited to wood of specific diameter) (Table 2), with some invertebrates only occurring in wood of the largest diameter (LS) ( Table 2). The diversity of invertebrates (i.e. number of families per wood size) calculated as occurring in a kilogram of each wood size did not differ significantly (H = 0.00, df = 36, p > 0.05) between the three studied wood sizes (Figure 3).  In addition to adult invertebrates, an average of 13.2 ± 1.5 larvae per kg and 7.4 ± 0.6 larvae per kg (through breaking wood) were collected. Collected larvae were identified as belonging to four taxa (Table 3). Three of the families were those of OWD (Buprestidae, Cerambycidae and Cleridae) and one for the AODW (Lepidoptera (Order)( Table 3). Larvae for buprestids (74.5% of total collected larvae) and Cerambycids (12.8 % of total collected larvae) were significantly (H = 6.12, df = 4, p < 0.01) more abundant than those of Cleridae (10.6%) and Lepidoptera (2.1%).  Table 3. Total numbers and average (±SD) mass of larvae collected from three different sizes of deadwood (FS = finger size, AS = arm size and LS = leg size).
Larvae were more abundant in larger diameter wood than in smaller diameter wood (H = 3.8, df = 2, p < 0.05). Notably, larvae that occurred in all three sizes of deadwood differed in body size (H = 5.7, df = 3, p < 0.01) (Table 3), with larvae from deadwood of larger diameter (AS and LS) having higher average mass than those from deadwood with smaller diameter (finger-size) ( Table 3). www.intechopen.com

Discussion
This study shows that deadwood supports a broad diversity of invertebrates. These belong to a variety of guilds (Deyrup, 1976) and types  and differ in numbers (Deyrup, 1981;Harcombe & Marks, 1983) within the different sizes of deadwood (Fager, 1968;Harmon, 1982;Marshall, Setälä & Trofymow, 1998). Of notable significance is that, while Deyrup (1981) recorded more than 300 species of invertebrates from single species of Douglas-fir, this study recorded 1 757 individuals of invertebrates, identified as belonging to thirty-six families (Table 2). With such a high number of invertebrates species recorded and the wide variety of taxa found to be associated with deadwood, it is obvious that different tree species, although in different stages of their developments serve as a host to a diversity of invertebrate species (Saniga & Schütz, 2001). The fact that each stage of the tree is associated with a particular community of invertebrates (Araya, 1993;Bennett et al., 1994), indicates that a thorough investigation of the role and contribution of deadwood to the conservation of biodiversity needs to be investigated further to determine the other cryptic implications of collecting deadwood on biodiversity of conservation areas. What this chapter highlights which is of critical importance in respect to wood inhabiting invertebrates and the conservation of invertebrate diversity through maintenance of deadwood in conservation areas, is that some invertebrates are distinctly characterized of and limited to the habitat that is only provided by deadwood (Brues, 1920;Deyrup, 1976). This is obvious for the OWD and SOWD guilds (Käärik, 1974;Ausmus, 1977) whose life history is confined within deadwood such that these invertebrates cannot survive in the absence of deadwood (Brues, 1920;Brumwell, Craig & Scudder, 1998) (Table 1). This indicates that the removal of deadwood from conservation areas could have direct negative effects on those organisms that rely on the presence of deadwood for survival (Blanchet & Shaw, 1978;Baker, 1979). As each part (Deyrup, 1981) and size of wood is distinctly associated with different groups of invertebrates (Baumbeger, 1919;Deyrup, 1981) that colonize trees at different levels of decay (Christensen, 1984;Gashwiler, 1970), it is obvious that the removal of trees from conserved systems may interrupt the processes of ecological succession that takes place in dying or dead trees (Saunders, Hobbs & Margules, 1991;Harmon et al., 1993;Sánchez-Azofeifa et al., 1999). As these processes are associated with chemical changes that take place in a senescing tree, this would thus impede the progression of invertebrate from one group (e.g. truly wood eating (xylophagous) invertebrates (OWD) to those that are able to digest wood into fine powder (e.g. Lyctidae) (Deyrup, 1981). This progression is critical for the maintenance of the natural production of deadwood in a protected ecosystem. For example, true wood-eating invertebrates (xylophagous), with their ability to digest and assimilate food material from fresh wood tissues Hickins, 1963;Käärik, 1974), trigger the death of the tree. Without this group, potential food material in wood can be locked up and the development of the succeeding stages of wood decay would be impeded such that the entire process of deadwood production would be retarded. This would normally lead to a scarcity of deadwood and would, in turn, trigger the destructive harvesting of wood through the cutting of live trees (Anderson & Fishwick, 1984;Gandar, 1984). This process would then normally lead to vegetation clearing which is prevalent in unprotected areas. The evidence provided by this study suggest that it will be necessary to give serious consideration to all the effects associated with the removal of deadwood from conservation areas. Such effects may have long-term negative implications that would directly affect the biodiversity associated with deadwood.
This study has identified a group of wood-dwelling invertebrates that would be potentially vulnerable to habitat loss and population decline in the event of wood collection from conservation areas if deadwood harvesting is considered. It is therefore recommended that studies be undertaken to measure the impact of various proportions of wood being removed, and that the consequences of wood removal on this element of biodiversity and the processes provided by these species be monitored. As the replacement of deadwood takes a long time, it is also obvious that the impacts associated with the removal of deadwood from conservation areas would have a long term affects and may have extended effects on those organisms that depend on the presence of deadwood for survival Holmes & Sturges, 1975;du Plessis, 1995). These include woodpeckers, snakes and different species of reptile that colonize deadwood killed by wood inhabiting invertebrates (Elton, 1966;Fager, 1968;Losey & Vaughan, 2006). In addition, as the presence of wood-inhabiting invertebrates attracts other organisms to wood, either as predators, parasitoids or through symbiotic relationships Johnston & Odum, 1956;Conner, Miller & Adkisson, 1976;Mannan, Meslow & Weight, 1980;Bader, Jansson & Jansson, 1995), the removal of wood from conservation areas would limit this diversity of organisms (Hirth, 1959;Hamilton, 1978;Manna, Meslow & Weight, 1980;Farrell, Milter & Futuyma, 1992). Thus, maintaining the presence of deadwood as part of the ecosystem of conservation areas seem to enhance the success of conservation areas in conserving biodiversity (Brumwell, Craig & Scudder, 1998).
In conclusion, it could be mentioned that in the absence of firm evidence of the amount of wood that can be collected from conservation areas without incurring negative effects on the web of biodiversity associated with deadwood, it is difficult to commend wood harvesting from conservation areas as being sustainable. This calls for increased efforts towards developing an understanding of the importance of deadwood in mantaining biodiversity within protected ecosystems. This should include the development of methods of harvesting deadwood from conservation areas with little effects on biodiversity.
What is emerging is that deadwood (especially in Europe) is gaining much recognition as the indicator of ecosystem health such that in various parts of Europe researchers and government authorities have started to survey the role of deadwood in natural forests (Sippola et al., 1998;Brandlmaier et al., 2004). The aim of these studies is to determine how much deadwood should be mantained in natural forest so as to manage healthy forest ecosystem. Initiatives like these need to be extended to other areas sush as Africa where the use and demand for deadwood far exceeds production.

Appendix
Families of invertebrates collected from deadwood and the reasons for their association with deadwood. Reasons were extracted from Scholtz & Holm (1996). Biodiversity is strongly affected by the rapid and accelerating changes in the global climate, which largely stem from human activity. Anthropogenic activities are causing highly influential impacts on species persistence. The sustained environmental change wildlife is experiencing may surpass the capacity of developmental, genetic, and demographic mechanisms that populations have developed to deal with these alterations. How biodiversity is perceived and maintained affects ecosystem functioning as well as how the goods and services that ecosystems provide to humans can be used. Recognizing biodiversity is essential to preserve wildlife. Furthermore, the measure, management and protection of ecosystem biodiversity requires different and innovative approaches. For all these reasons, the aim of the present book is to give an up-to-date overview of the studies on biodiversity at all levels, in order to better understand the dynamics and the mechanisms at the basis of the richness of life forms both in terrestrial (including agro-ecosystems) and marine environments.